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A systematic approach for product modelling and function integration to support adaptive redesign of product variants

A systematic approach for product modelling and function integration to support adaptive redesign... Res Eng Design https://doi.org/10.1007/s00163-022-00401-3 ORIGINAL PAPER A systematic approach for product modelling and function integration to support adaptive redesign of product variants 1 1 Foo Shing Wong  · David C. Wynn   Received: 10 December 2021 / Revised: 30 September 2022 / Accepted: 3 October 2022 © The Author(s) 2022 Abstract When a product variant offers functionality that and tested through reverse engineering studies of consumer is high in demand, firms may decide to leverage that design products, confirming its applicability. to enhance other variants in their product line. This can be achieved by extracting functions and their realisations Keywords Product variant design · Function integration · from one product variant and integrating them into another Product modelling · Reverse engineering · Mechanical variant, resulting in a third product variant that has a new assemblies · Design Structure Matrix · CAD · Detailed combination of functions and physical features. This article Design Model · Adaptive Redesign Method introduces a systematic approach called the Adaptive Rede- sign Method (ARM) to support this function integration pro- cess. The ARM is based on a new product model called the 1 Introduction Detailed Design Model (DDM). In comparison to existing approaches, the DDM allows the architecture of an existing This article introduces a method that provides detailed guid- product to be modelled on a sufficiently detailed level to ance for function integration in engineering design. Function identify geometric features and parts that realise particular integration involves extracting particular functions and their operating functions of a product. This detailed information physical realisations from existing products and integrating provides a basis for systematic determination of the redesign them into other product variants to form a new variant with activities needed to derive a new variant design, down to the a unique combination of features and operating functions. detailed level of adding, removing and integrating specific One situation in which function integration occurs is when a parts and features. The main benet fi is to assist with planning product variant has functions or technology that are high in the redesign process while ensuring nothing is overlooked, demand. In such cases, companies may want to implement which might be especially useful if the task is to be divided that new technology into their other existing product variants among several designers or if designers are not fully familiar (Li et al. 2009; Zhang et al. 2011; Liu et al. 2014). with the designs at hand. A secondary benefit is to show how Function integration is a form of redesign in which an this type of redesign process can be decomposed into sys- existing product variant is adapted. In general, product rede- tematic steps, which could potentially reveal opportunities sign can be grouped into two major categories: parametric for computer support. The new approach has been developed and adaptive redesign (Otto and Wood 1998). Parametric redesign is concerned with improving a product’s architec- ture or its performance by adjusting parameters of an exist- Supplementary Information The online version contains ing design. Adaptive redesign, which is the focus of this supplementary material available at https:// doi. org/ 10. 1007/ s00163- article, is concerned with modifying the functionality of an 022- 00401-3. existing product to derive a new product. In research litera- * Foo Shing Wong ture, studies of adaptive redesign often involve the reverse fwon360@aucklanduni.ac.nz engineering of existing products (Otto and Wood 1998). The 1 purpose of reverse engineering in this context is to support Department of Mechanical and Mechatronics Engineering, University of Auckland, Auckland, New Zealand the reuse of existing elements of the design, with a particular Vol.:(0123456789) 1 3 Res Eng Design emphasis on appreciating how those elements influence each redesign activities, requiring later correction (Tang et al. other and how they must be considered in combination when 2010b). This may be especially useful if the redesign work introducing changes. The changes may involve a combina- needs to be coordinated between several team members, or tion of adding, removing, redesigning, and reusing parts to if a designer is not fully familiar with the designs at hand. achieve desired functions (Lee and Park 2014). Finally, decomposing the redesign process into well-defined One of the important issues to consider in redesign is smaller steps may suggest opportunities for computer sup- the product architecture. The architecture of a product to be port of that process. redesigned can be described in terms of functions and physi- cal parts. Three types of interactions are possible on this 1.2 Research method level of description: interactions between functions, interac- tions between parts, and interactions between functions and To address the research questions a representative redesign parts. Each function or part can interact with several oth- task based on a simple product (redesigning a ballpoint pen) ers, exhibiting complex many-to-many relationships (Ulrich was generated as a test case. Existing approaches from the and Seering 1988). On a more granular level, physical part literature were assessed in light of this test case. From this, interactions are realised at the interfaces between specific limitations of the existing product models and function inte- part surfaces. In a CAD model, these surfaces are typi- gration methods were appreciated. This led to the generation cally defined by geometric features of the respective parts. of a new approach for product modelling, and based on it, a Overall, the complex patterns of connections that comprise new systematic approach for function integration. The new product architectures need to be considered when integrating approaches were then applied to a series of more complex existing design elements into an existing product to develop consumer products to test and further improve them. Overall, a new product variant. the development was highly iterative. Literature review also proceeded concurrently with the activities described above. 1.1 Research questions 1.3 Article outline To provide systematic support for function integration between product variants, this article addresses three The rest of this article proceeds as follows. In Section  2, research questions: literature is reviewed and the research gap is pinpointed. Section 3 introduces the basis of our solution, which is to – RQ1: How can product variants be systematically mod- model existing variants using a new product model called elled at an appropriate level of detail to support function the Detailed Design Model (DDM). Section 4 then explains integration at a part and feature level? the Adaptive Redesign Method (ARM) itself. Section 5 dis- – RQ2: How can the resulting models of product variants cusses some application cases and insights drawn from them. be systematically analysed to identify redesign activities Section 6 discusses advantages, limitations and some sug- required for function integration? gestions for further work. Concluding remarks are offered – RQ3: Is the resulting systematic approach useful and in Section 7. what future research opportunities does it reveal? In this context, a systematic approach is expected to provide 2 Literature review several benefits. First, a systematic approach is helpful to model existing designs in a structured way and better appre- As established in Sect.  1, function integration requires ciate how the design solutions work (Otto and Wood 1998; extracting existing design solutions from a product and inte- Tang et al. 2010a). A systematic approach is particularly grating it into another product to derive a new variant. It was useful when modelling products having moving parts that determined that a method to support this should satisfy four are each involved in multiple functions, such that function method requirements (MRs), for the reasons outlined below: realisation is complex. Second, a systematic process for modelling design information supports the sharing and reuse – MR1: Determine low-level and high-level functions of a of that information (Gietka et al. 2002; Tang et al. 2010b). design and link them to the parts and physical features. Reusing existing design information should support the This information is needed to identify the aspects of a development of reliable products, since it facilitates adop- design that realise each function that is to be integrated. tion of proven principles and solutions (Smith et al. 2012). – MR2: Determine the physical interactions between fea- Third, a systematic approach allows for detailed planning tures of a design. This information is needed to identify of the (re)design process and may reduce design rework, supporting features that help primary features realise since designers will be less likely to initially overlook some desired functions that are to be integrated. 1 3 Res Eng Design – MR3: Ensure that product data obtained for different domain to capture the coupling between user requirements/ product variants is consistently represented, using similar interface and product architecture elements. The coupling function terminology. This is needed so that the variant between these domains was used to determine whether the designs can be directly compared for function integra- user interface of the product needs to be redesigned when tion. there are changes to user requirements. However, this model – MR4: Systematically process the obtained product data uses mathematical equations to link elements between these to determine how parts and specific features of parts can four design domains, which may be difficult to formulate be carried over, removed and modified from existing from a product decomposition and are not necessary to meet variants to generate a new variant design that provides a MR1-MR4. unique desired combination of existing functions and fea- The second type of hierarchical product model to be dis- tures. The benefits of such function integration, as well cussed is the Function-Behaviour-State diagram (Umeda as the reasons for a systematic approach, were outlined et al. 1990). In this approach, the behaviour domain of a in Sect. 1. design exists between the function and structure domains. Including this domain enables consideration of the perfor- In the next subsections, product models and function inte- mance attributes of a product during redesign. However, gration methods from literature are reviewed against these this extra domain also increases modelling effort and is not method requirements. This confirms the gap addressed by required for MR1-MR4. Furthermore, the extra domain will this article. unnecessarily increase the complexity of tracing between function and structure domains, as required by MR1. Deng 2.1 Product models for function integration et  al. (1999) extended this approach to form the FEBS model, additionally capturing the interaction between the Most product modelling approaches in literature are based product and its operating environment. Tor et al. (2002) in on hierarchical decomposition of a design (typically involv- turn extended FEBS to form B-FES, a model to support ing tree diagramming), on block diagramming, and/or on product variant concept generation. B-FES can be used to matrix-based modelling. Some models of these types are extract and reuse certain physical attributes from existing discussed in the next subsections. products when given a set of requirements. However, B-FES does not meet MR2 because it does not consider the support- 2.1.1 Product models based on hierarchical decomposition ing features required by the primary parts that realise desired and tree diagramming functions (requirements). The third type of hierarchical product model builds on the This subsection discusses decomposition-based product Chromosome Model (Andreasen 1992), which is based on modelling approaches based on (1) Axiomatic Design, (2) Domain Theory (Andreasen 1980). This model represents Function-Behaviour-State modelling, (3) The Chromosome product information in three domains: activities, organs, model and (4) Function-Means Tree approaches. and parts, in addition to the process of using the product Firstly, tree-based product models building on axiomatic (Andreasen et al. 2014). It captures the connections between design (Suh 1995) essentially consist of two tree diagrams, elements within and across these domains, and hence could to model the functions and parts domains of a product be used to extract features that realise high level functions respectively. In a reverse engineering context, the trees can (MR1) and to determine necessary supporting features be formed progressively while disassembling a product by (MR2). However, in common with other approaches this considering how the functions relate to each assembly, sub- does not directly address the need for consistent modelling assembly, and so on. While convenient for decomposition, of different products, required to support their comparison this type of model does not emphasise the relationships and integration (MR3). between parts, features or between functions at a particu- The final type of hierarchical model to be discussed is lar level of the tree. Hence, it is not ideal to identify sup- the function-means tree. This model represents a product by porting features (as required by MR2). This limitation was decomposing top-level functions into the subsystems realis- partially addressed by the transdisciplinary product devel- ing them, then decomposing those subsystems into constitu- opment life-cycle model (TDPL) of Gumus et al (2008). ent subsystems and so on until individual parts (potentially TPDL captures the interaction between parts and according features) are reached. Malmqvist (1997) extended the func- to Gumus et al. (2008), it can help to verify whether the tion-means tree by including information such as functions parts can realise the functional requirements of a product. relevant to different product life-cycle phases, alternative However, it does not capture low-level functions (as required design solutions, parametric constraints and design objec- by MR1). Lo and Helander (2007) also adopted axiomatic tives. The relationship between these elements are also design concepts, introducing a goal domain and user actions captured. Borgue et al. (2019) built on this work to model 1 3 Res Eng Design connections between product functions, design solutions Hirtz et al. 2002; Caldwell and Mocko 2012; Mohammed and additive manufacturing constraints. Müller et al. (2020) and Shammari 2021). Gietka et al (2002) also found that linked the function-means tree to an automation approach, model variation can also be reduced if designers describe drawing connections between the function domain and the each function based on its input and output flows rather than physical domain to enable CAD models of design concepts identifying them based on a higher-level function. to be generated from different combinations of design solu- Other block diagram models of product structure are tions. Advantages of all function-means tree based models based on standardised modelling notations. For instance, are that they are well-suited to systematic product decompo- SysML has been used for this purpose, as has Object-Pro- sition, and that they directly show the relationship between cess Methodology (Dori 2011). functions and the parts that realise them. However, they do not capture the relationships between parts involved in func- 2.1.3 Models based on matrices tion realisation. Such approaches are therefore not ideal to identify supporting features, as required by MR2. The final group of product architecture models to be dis- Overall, hierarchical models support product modelling cussed are based on matrices. In one well-known approach, in a reverse engineering context by structuring analysis and Pimmler and Eppinger (1994) used the Design Structure description of a product at progressively increasing levels Matrix (DSM) to represent the interactions between parts of of detail. A general disadvantage is that they are not well a product. The DSM consists of a square matrix with identi- suited to represent connections across branches of the tree. cal row and column headings, used to represent the product Although several tree-based approaches allow such connec- elements, while the content of the matrix cells indicates con- tions to be made, e.g. by adding diagonal lines that cut across nections between pairs of elements. For instance, Pimmler the tree diagram, the diagrams are likely to become difficult and Eppinger (1994) used letters in the cells to differentiate to visually manipulate and trace as the modelled product spatial, signal, material, and energy interactions between increases in complexity. These limitations could perhaps be parts. Tilstra et al. (2012) developed systematic steps for addressed by appropriate software support. However, such modelling a product structure using DSMs, adopting a hier- modelling software is not readily available at present. archical approach in which a product is decomposed and subsystems are modelled separately, prior to combination of 2.1.2 Models based on block diagramming those models. They demonstrated the importance of prede- fining the types of interactions to ensure that consistency is Other models used to represent product information are maintained when a product is modelled by different people. based on block diagrams. For instance, the operation of a They also emphasised the importance of producing consist- product can be modelled using concepts from the Theory of ent DSMs to allow for product architecture comparisons, Technical Systems (Hubka and Eder 1988). Here, the main which is required for function integration (this supports function of a design to realise a transformation process is MR3). DSMs have also been used to represent and evaluate represented as a black box, with input arrows to represent multiple design alternatives by Wyatt et al. (2008). How- the human, knowledge and management systems needed to ever, while providing a concise overview, the DSM does not operate the design to perform the function. Arrows are also directly capture the detailed logic of interactions, which can used to indicate the operands being transformed while using be problematic for applications in which logic is important a design. Hubka and Eder (2002) integrated this model with (Karniel and Reich 2009). For further information on DSMs the Chromosome model to provide a more comprehensive the reader is referred to the reviews by Yassine and Braha block diagram-based product model. A related and very (2003) and Browning (2015). well-established approach is function-flow modelling ( Pahl Researchers have also used more elaborate matrices to and Beitz 1996). This depicts how sub-functions operate show connections across product information domains. For together to realise the overall function of a product. Func- example, the Domain Mapping Matrix (DMM) is a non- tion-flow models could be useful for assessing functional square mapping matrix that can be used to map the function changes during redesign, but do not relate these functions elements of a product to its physical elements (Danilovic to physical parts and features as needed for MR1. Another and Browning 2007). Lindemann and Maurer (2007) inte- drawback is that function-flow models are constructed at grated DSMs and DMMs covering multiple domains to form a high level of abstraction and can be very different when a multi-domain matrix (MDM) to more comprehensively constructed by different people, which means this approach model product architectures and product families, among is not ideal to meet MR3. To reduce this variation, some other applications. Tang et al. (2010b) applied MDMs in a researchers have developed sets of vocabulary, grammar and database-based approach to trace how elements of an exist- topology rules to improve the consistency of function struc- ing product will be impacted when there are changes to func- ture models (Szykman et al 1999; Stone and Wood 2000; tions. Eisenbart et al (2017) adopted the MDM concept to 1 3 Res Eng Design form the Integrated Function Model (IFM) to show how low- which occur when a newly added function reduces the per- level functions and parts relate to a particular high-level user formance of other functions. In this scenario, the researchers function. This model combines block diagrams and matrices. suggested using the Theory of Inventive Problem Solving (TRIZ) to resolve the performance conflicts. Alternatively, 2.2 Methods to support function integration in product the Advanced Systematic Inventive Thinking (ASIT) redesign approach can be used to generate ideas for deriving the new combination design (Moon et al. 2012). Finally, Smith et al. Having discussed a number of product modelling (2012) proposed a method to combine more than two exist- approaches, this subsection moves on to discuss how such ing products to derive a new product. Instead of selecting a approaches have been used as the basis of methods to sup- single product as a foundation for the new variant design, port function integration. Our review revealed that there they selected parts from different products based on custom- are relatively few methods of this type in literature. In one ers’ needs and combined them to form a new design. Their publication, Kalyanasundaram and Lewis (2014) proposed method is similar to a morphological analysis. A drawback a product integration method to support the derivation of is that it does not model the architectures of the products. re-configurable products and multi-functional products from Therefore, it can only determine parts to carry over to the two existing products. Their method combines the function- new variant design based on the user’s needs. It does not ality of two existing products to form a new design, using a compare product parts functionally to determine the physical matrix model to compare low-level functions between parts modifications required for a part to fulfil the desired func- (as required by MR3) and interactions between physical tions, as is required by MR4. parts (partially addressing MR2). However, this approach does not model products at the feature level and there- 2.3 Critique and the need for a new approach fore cannot identify physical features of a product variant involved in function integration (MR1). Since it does not To recap, a relatively small number of function integration capture parts at a features level, the method also does not methods have been proposed in literature, based on analysis provide detailed guidelines for part modification (MR4). A of products using hierarchical models, flowchart-based mod- similar method was developed by Kang and Tang (2013) els and matrix models. Hierarchical models offer systematic for developing multi-functional products. This method also procedures for identifying detailed functions and parts of uses matrices to model existing products, resulting in similar products. However, they do not clearly (or sometimes at all) advantages and drawbacks. However, it does consider sup- represent the relationship between detailed functions and porting parts for primary parts that realise the functions, parts as required by MR1 and MR2. Block diagram mod- which better addresses MR2 in comparison to the afore- els capture flow information and allow function elements mentioned method. Lu et al. (2017) also combined existing to be placed in their sequence of operation to depict how products to produce multi-functional products using matrix a product operates. However, they typically do not capture models. However, they used a different approach to model the parts and features that realise the functions, and are not the function of existing products. Instead of modelling prod- graphically well-suited to this due to the dense structures ucts using the functional decomposition approach by Pahl of dependency involved. Hence, block diagramming-based and Beitz (1996), they derive their function structures from models are not ideal to meet MR1, MR2 and MR3. Overall, detailed flows and parts. This increases the consistency of neither tree- nor block diagramming-based approaches are the product model which should make product comparison ideally suited to reflect the complexity of function-form rela- more effective (MR3). Liu et al. (2014) proposed a method tionships in a product. In comparison, matrices are very well for integrating products with interrelated functions. They suited to graphically represent the dense structures of rela- compared the functions of existing parts using a table, list- tionships between functions and parts/features, which allows ing the functions of products as the row headings and the existing design solutions to be comprehensively represented, products being compared as the column headings. The cor- extracted, compared and traced without specialised software. responding parts of each product that realise the function are These characteristics make a matrix-based product model recorded in the cell of the table. An advantage of this com- the most suitable basis for a function integration method. parison table format is that it enables more than one vari- Regarding the  methods themselves, the majority of ant to be compared. However, it cannot represent multiple function integration methods in literature simply merge all functions for a given part. As a result, the approach cannot high-level functions of existing products by comparing the accurately compare the function realisations across product corresponding low-level functions of existing products to variants, which is needed to determine the redesign activi- determine which parts to carry over into the new design. ties required for a new variant design (MR4). The method They do not capture design information at the features level does, however, consider conflicts between product functions which prevents them from identifying redesign activities at 1 3 Res Eng Design 1 3 Table 1 Assessment of function integration methods in literature with respect to requirements MR1-MR4 MR1: Determine low-level and MR2: Determine the physical interac- MR3: Ensure that product data is con- MR4: Systematically process the high-level functions of a design and tions between features of a design. sistently represented across variants, obtained product data to determine how link them to the parts and physical This information is needed to identify using similar function terminology. parts and specific features of parts can features. This is needed to identify the supporting features that help primary This is needed so that variant designs be carried over, removed and modi- aspects of a design that realise each features to realise a desired function can be directly compared for function fied from existing variants to generate high-level function. integration. a new variant design that provides a new desired combination of existing functions. Kang and Tang (2013) Partially met: Modelled low-level Partially met: Modelled interactions Partially met: Modelled the function Partially met: Systematically determined: functions and their relationship with between primary and supporting parts of a product from flows and function Parts to carry over. Briefly mentioned: parts. Grouped low-level into primary, decomposition. to merge to remove, to modify param- secondary and auxiliary chunks based eters on flow Kalyanasundaram and Partially met: Modelled low-level Partially met: Modelled the interaction Partially met: Modelled the function Partially met: Systematically determined: Lewis (2014) functions and their relationship with between primary parts only of a product from flows and function Parts to carry over. Briefly mentioned: parts. Grouped the low-level functions decomposition Parts to merge into basic, application and accessory functions Liu et al. (2014) Partially met: Modelled low-level func- Partially met: Modelled the interaction Partially met: Modelled the function Partially met: Systematically determined: tions and their relationship with the between primary parts only of a product from flows and function Parts to carry over. Briefly mentioned: parts decomposition to merge Lu et al. (2017) Partially met: Modelled low-level func- Partially met: Modelled the interaction Partially met: Modelled the function Partially met: Systematically determined: tions and their relationship with the between primary parts only of a product from flows and function Parts to carry over. Briefly mentioned: parts decomposition to merge, to remove Smith et al (2012) Not met: Modelled user requirements Partially met: Modelled the interaction Not met: Modelled the importance of Partially met: Systematically determined: and their relationship with parts between key primary parts considered user requirements using customer Parts to carry over. Briefly mentioned: only survey to elicit important parts. to modularise, to modify parameters Res Eng Design the level of specific modifications to parts. Overall, none of 3.1 Elements of the DDM product model the existing approaches fully address the requirements set out at the start of Sect. 2. This gap, addressed by the current The DDM is a matrix-based product model that represents a article, is summarised in Table 1. design in both functional and physical domains, in terms of functions, flows, parts, features, states and state transitions, as well the interactions among these elements. It provides 3 Detailed Design Model (DDM) enough detail to capture how all these elements and their interactions contribute to the design’s functionality in use. This section introduces a new product model called the The following product elements are included in the DDM: Detailed Design Model (DDM) which was developed to capture design information of existing product variants. Sec- – Function: In the DDM the concept of function focuses tion 4 will then detail how the information captured in this on what a product does as a physical artefact. Under this new model is used to support function integration. definition, functions enable the use of a product but do To demonstrate the DDM and the reverse engineering not describe the multitude of ways in which it could be procedure used to construct such a model, a BiC ballpoint used, which additionally depend on the user, the task to pen is used as an example. This product is complicated be performed, the use environment, and so on. Two types enough to illustrate all aspects of the model, while also of functions are distinguished in the DDM: being simple enough to explain in full detail. It is referred to here as the retracting pen. Variations of it are available – Operating function: A transformation in the state of from several manufacturers. The design allows the user to a product, that is associated with operation (use) of extend the ballpoint tip by pressing a button at the opposite the product. end of the barrel. The tip can then be retracted into the barrel – Technical function: A transformation process occur- by pressing a latch on the side of the barrel. An exploded ring when a flow (defined below) interacts with view depicting parts and features of the retracting pen is feature(s) of a design (also defined below). provided in Fig. 1. Before moving on to describe the DDM in detail using the – Flow: The input or output of a technical function. The retracting pen as an example, the next sub-section introduces model distinguishes three types of flow: key concepts and terminology used in the model. Clicker.Shaft Clicker.Plunger hammer Clicker.Latch Plunger.Plunger tip Plunger.Ink chamber connector Upper barrel.Tip Spring.Coil Upper barrel.Latch hole Ink Chamber.Chamber body Upper barrel.Merger Upper barrel.Upper clip Plastic nib.Ink chamber connector Plastic nib.Ink stopper Upper barrel.Lower clip Plastic nib.Ballpoint tip connector Ballpoint tip.Plastic nib connector Upper barrel.Body Ballpoint tip.Ball socket Ballpoint tip ball.Ball Lower barrel.Slot Lower barrel.Upper barrel grip Lower barrel.Lower grip Lower barrel.Ballpoint funnel Fig. 1 Parts and features of the retracting pen used in the running example 1 3 Res Eng Design – Material flow: Motion of matter. Can involve solid, – State: A set of partially-constrained connections (and liquid, or gas. related flows) that can change configuration (i.e. rela- – Energy flow: Doing mechanical work, or transferring tive motion can occur between the features and flow pro- the potential to do work. Energy flow can take many cesses can occur) when a product is operated. Two types forms such as potential, mechanical, electrical and of states are distinguished in the DDM: thermal. – Signal flow: Information, typically regarding the – Static state: A stable physical configuration. actual or desired status of a system, that is transmit- – Transition state: A temporary configuration involv - ted or received to and from another system. ing flow processes and relative motion of features, while a product variant is in process of changing – Product variant: A product that provides a unique com- from one static state to another. bination of features and operating functions. – Part: A discrete physical component used for pre-pro- All these elements of the DDM are required for the Adaptive duction of a product variant, that cannot be disassembled Redesign Method (ARM), that is to be described in Sect. 4. without physically damaging it. – Feature: A geometric segment of a part. 3.2 Procedure for modelling a product with the DDM – Connection between two features: A DDM representation of a product variant is developed in – Fully constrained connection (C): There are zero six steps, described below. degrees of freedom for relative motion between the two features. 3.2.1 Step 1. Model the product in CAD (or obtain – Partially constrained connection (P): At least one an existing CAD model) degree of motion is possible between the two fea- tures. The features may be in constant contact The first step is to model the existing variant using CAD or (allowing sliding, rolling, flexing etc.) or may only to obtain an existing model. Basing the analysis on a CAD be in contact when the product is in certain states model ensures that no physical elements of the product are (see below for definition). overlooked. It also provides a basis and nomenclature to reference specific features of each part, which is necessary for the Adaptive Redesign Method (ARM). The parts must Fig. 2 CAD model of the retracting pen upper barrel. The model tree contains the CAD features which form the physical features of the upper barrel as shown by the red arrows—these will be the basis of describing the part in the Detailed Design Model (DDM) 1 3 Res Eng Design be modelled with appropriate detail to capture the geometric 3.2.2 Step 2. Form the feature interaction matrix features. For instance, Fig. 2 shows how the Upper Barrel part of the retracting pen is decomposed into six features in A DDM of a product is represented as a matrix called the DDM matrix. An overview schematic of the DDM matrix the CAD model. Only geometric features of a part that physically realise is shown in Fig. 3. The CAD features that form the parts are used as the row and column headings for the top-left an operating function need to be modelled. This is because the aim of the ARM method (to be discussed in Sect. 4) is field of the DDM matrix, as shown for the retracting pen in Fig. 6. Features that physically interact with another feature to derive product variants by adapting existing features from two product variants to realise a desired new combination are indicated by the letter C or P in the corresponding cell: of operating functions. The method only currently considers product use functionality. For instance, it does not consider manufacturing and assembly processes required for the new design. Therefore, minor features such as rounds do not need to be modelled, except where important to realising an oper- ating function. In general, only 3D CAD features that are derived from a 2D sketch need be considered, because these CAD fea- tures generate the spatial geometry of a part. CAD features that only modify the spatial geometry of an existing CAD feature need not be modelled. This is to prevent repetitive referencing of the same physical feature in the DDM. For instance, considering Fig. 2, the Upper Barrel.Tip should be recognised as a feature in the DDM because this dome- shaped geometric feature is formed by connecting the sur- faces between two differently-sized 2D circles. Whereas the Upper Barrel.Tip Hole is not regarded as a feature for this Fig. 4 Fully constrained connection between the features Upper Bar- analysis because the hole feature only modifies the existing rel.Body (blue) and Lower Barrel.Slot (green) of the retracting pen. feature Upper Barrel.Tip. These features do not move relative to one another once the product is assembled Fig. 3 Overview of the fields in a DDM matrix, mapped to the corresponding steps in the DDM modelling procedure 1 3 Res Eng Design – C indicates feature connections that are fully-constrained. – Flows applied to a feature. For example, a flow of human For example, the connection between the Upper Barrel. energy and a human finger are applied to the Clicker.Tip Body and Lower Barrel.Slot of the retracting pen is fully- of the retracting pen to extend its ball point tip. Note that constrained because, as shown in Fig. 4, these two fea- only flows that are involved in operating the product need tures do not move relative to each other in the assembled be included. product. Therefore C is placed in cell S9 and, symmetri- – Flows caused by a feature. For instance, a flow of elastic cally, cell I19 of Fig. 6. energy released from the Spring.Coil is used to retract the – P indicates connections between features that are par- ballpoint tip of the retracting pen. Note that only flows tially constrained. An example of a partially constrained that involve modelled features need be included. connection occurs between the features Upper Barrel. – Flows occurring between features. For example, ink flows Tip and Clicker.Shaft. This connection is partially con- from the ink chamber, through the plastic nib, ballpoint strained because the Clicker.Shaft can slide through the socket and ball when the retracting pen is being operated hole of the Upper Barrel.Tip as shown in Fig. 5. Hence, for writing. the letter P is placed in the cells D20 and T4 of Fig. 6. Flows that only describe physical connections between fea- This differentiation between partially-constrained and fully- tures (e.g. “flow of force”) are not modelled, because they constrained connections is necessary to distinguish features are already captured in the feature-feature interactions sec- and interactions that are directly involved in realising a func- tion of the DDM matrix. tion (P) from those that provide support structures (C). Flows are listed in the DDM matrix headings immediately The modeller should physically operate each mechanism after the feature headings, as shown in Fig. 3. As indicated of the variant to identify all the possible feature-feature in the bullet points above, every flow interacts with at least interactions. This is recommended to avoid overlooking any one feature. In the DDM, each interaction between a flow feature-feature interactions which are not explicitly captured and a feature is described using a technical function descrip- in the CAD model. For example, when modelling the retract- tor to support consistent modelling. The technical function ing pen, it should be retracted and extended to observe which descriptors used for the ballpoint pen example are defined features interact with each other in each stable configuration, in Table 2. This is a subset of the list provided by Hirtz et al. and in the transition between configurations. All must be (2002).  For brevity we show only the terms necessary for included in the DDM matrix. modelling the pens and internet protocol (IP) cameras dis- cussed in this article. 3.2.3 Step 3. Identify flows and flow‑feature interactions Numbers are placed in the top-rightmost field and the middle-leftmost field of the DDM matrix to indicate the The next step of the DDM modelling procedure is to identify features responsible for each flow, and the type of technical and model flows and their interactions with the features. In function involved. For example, in Fig. 6, the numbers 11 the DDM, flows can be in the form of material, energy or and 33 both appear in cell AB8 to indicate that the feature signal as set out in Sect.  3.1. Three situations should be Ink Chamber. Chamber Body (in row 8) Guides (technical considered: function type 11) and also Contains (technical function type 33) the Material.Ink flow (in column AB). Note that unlike feature-feature connections, this relationship is directional— the feature or flow in the matrix row is the producer of the technical function while the feature or flow in the column is the receiver. 3.2.4 Step 4. Identify motions, states and operating functions Operating functions describe how a design can be mechani- cally operated. In the DDM, an operating function is defined in terms of an initial (static) state, an intermediate (transi- tion) state, and a subsequent (static) state. (The ARM will subsequently determine whether there are any operating functions that are dependent on other operating functions. Fig. 5 Partially constrained connection between the Upper barrel.Tip This will be explained in Sect. 4.2.1). The total number of and Clicker.Shaft of the retracting pen. The Clicker.Shaft can slide operating functions in a variant is determined by the physical through the hole of the Upper Barrel.Tip 1 3 Res Eng Design configurations it can be used in, which is in turn dependent the DDM matrix. Representing operating functions in terms on the arrangements of connections within the design. of three states has proven helpful for the reverse engineer- To identify operating functions of a variant, the possi- ing of complex motions to identify the parts, features and ble independent motions are identified by, firstly, physically flows involved when a product is operated. The three-states moving each partially-constrained connection one-at-a-time. approach has proved sufficient for all products modelled to Once the motions are identified, the state transitions gener - date and also, has the benefit of being possible to visualise in ated by each motion can be established. Two situations are a simple table format. However, it is recognised that a more common: (1) motions that occur when the user changes the elaborate representation might be necessary to efficiently product configuration from one static state into another, and describe some situations. (2) motions that are essentially continuous while operating Note how the modelling procedure outlined in this step the product. differs from a top-down identification of product functions In the running example, an example of the former type starting from considerations of how the product would be of motion occurs when the pen user pushes the clicker to used. The advantage of the bottom-up approach is that, extend the tip of the pen (see Fig. 5). Here, the transition while the possible functions of a device are subject to inter- state (the state of the pen during the motion) involves energy pretation, the motions and states possible within it can be input from the user and a certain set of partially-constrained unambiguously identified. Hence, following the procedure connections whose features are in relative motion. This tran- outlined in this section leads to a more objective model of sition state can be described as Ballpoint tip extending. It product functions than a top-down analysis. can only occur from an initial (static) state of Ballpoint tip retracted. When the transition is completed, the pen is left 3.2.5 Step 5. Link operating functions to feature in the subsequent (static) state of Ballpoint tip extended. In connections and flows the DDM, each combination of initial-transition-subsequent state is listed to define an operating function. The features The penultimate step of the DDM modelling procedure is and flows involved in each state are also identified. This to link the states of each operating function to the feature- is necessary because different features may be involved in feature and feature-flow interactions that are active in each operating functions that are complementary to each other. state. This is required by the ARM method to be described in For instance, although both the operating functions of the the next section, so that the features responsible for specific retracting pen To extend ballpoint tip and To retract ballpoint operating functions can be identified. tip contain the same static states: Ballpoint tip retracted and For each transition state, the modeller must identify the Ballpoint tip extended, it does not imply that their respective active flow processes and the active connections involved transition states Ballpoint tip extending and Ballpoint tip in the motion. An active connection is one in which relative retracting involve identical features. In this case, extending motion is occurring between the two features, or in which the ballpoint tip of the retracting pen involves applying force force transmission between the two features is necessary to to the Tip of the Clicker whereas retracting the ballpoint tip enable the motion. These flows and interactions are repre - of the pen involves applying force on the Latch which is sented in the rows of the transition states in the DDM matrix located on the side of the pen body. This example demon- by referencing the coordinates. Only the numerical coor- strates that the features involved in a transition state are not dinates (rows) are recorded. The alphabetical coordinates always identical to its reverse state. Each of these operating (columns) do not need to be recorded because the numerical functions and its three states are shown at the bottom of the coordinate is placed in the corresponding column. For exam- DDM matrix in Fig. 6. ple, in the Ballpoint tip extending state, a “human energy” An example of the continuous motion type is rolling the flow is being applied to the Clicker.Tip of the retracting pen ballpoint ball in its socket. In the DDM, this is viewed as a as shown in cell E25 of Fig. 6. Therefore 25 appears in col- transition state Ball rolling. It is only possible from a certain umn E of the Ballpoint tip extending row. initial (static) state Ballpoint tip extended and, when the Next, it is necessary to identify the unique connections motion finishes, leads to a subsequent (static) state which that occur in the initial and subsequent states. Unique con- is the same as the initial state. In this case, the three-state nections are those in which the two features are in direct combination defines the operating function To deposit ink. physical contact in that state, but not in the complement To summarise, the procedure for identifying operating state. For example, in the Ballpoint tip extended state of the functions is to first identify motions in the design, then to retracting pen, the Clicker.Latch is engaged with the Upper identify the initial, transition and subsequent states for each Barrel.Latch hole. This contact only occurs when the pen motion, and finally to denote this combination of product is extended and is not present when the pen is retracted or states as an operating function. The operating functions and in the transition state. Thus, in Fig. 6 the coordinates G21 their corresponding states are shown in the bottom part of 1 3 Res Eng Design 1 3 Res Eng Design ◂Fig. 6 DDM matrix of the retracting pen showing the relationship 4.1 ARM Phase I: Develop DDM for each variant between the features, flows and operating functions. The operating functions are composed of states. The features and flow interactions As input to the ARM, a DDM matrix must be formed for that occur in each state are referenced to the co-ordinates to model the each of the two product variants to be combined. Although relationship between the features, flows and operating functions this is quite time-consuming, each DDM matrix is a reuse- able resource that could be drawn upon in future each time a and U7 appear respectively in columns G and U in the row new variant is required. As additional variants are modelled, defining the state. a data library would be built up, broadening the possibili- ties for forming new variants without additional modelling 3.2.6 Step 6. Verify the product model effort. The DDM for the first pen variant to be used in the run- The final step of the DDM modelling procedure is to check ning example was already discussed and is shown in Fig. 6. that the DDM matrix has been correctly completed. The fol- Fig. 8 shows the DDM matrix for the second variant, namely lowing checks may be helpful to reveal errors: the basic pen. Note how the basic pen has a different set of operating functions than the retracting design—the only 1. Check that the feature-feature portion of the DDM common operating function between the two pens is To matrix is diagonally symmetrical. deposit ink. It is important that technical function descrip- 2. Check that each feature and flow listed in the DDM is tors are used consistently when modelling the different shown to interact with at least one other feature or flow. product variants, so that the variants can be compared. For Features with empty rows or columns should be revisited example, noting that the number 6 is used to describe import to check that no interactions were missed, and if not, to functions in the retracting pen DDM, the same number is reconsider whether the feature is necessary to include in used to describe this type of interaction in the basic pen the model. DDM. 3. Review any CAD features that were not included at the beginning of the modelling process, and confirm they 4.2 ARM Phase II: Identify adaptive redesign steps are not involved in any identified operating function. In the method, the variant to be adapted/redesigned is described as the base variant. The variant from which addi- 4 Adaptive Redesign Method (ARM) tional operating functions are to be drawn is described as the source variant. Parts and features from the source variant Having completed description of the Detailed Design Model that realise a desirable operating function are to be inte- and modelling procedure, we now move on to the Adaptive grated into the base variant. For the running example, the Redesign Method (ARM) itself. To support description of basic pen is chosen as the base variant while the retracting the ARM, we return to the ballpoint pen example and con- pen (offering the desired retraction and extension functional- sider the situation in which the To retract and To extend ity) is chosen as the source variant. operating functions of the retracting pen are to be carried The second phase of the method involves systematic anal- across into another pen design, referred to here as the basic ysis of the DDM matrices for these two variants to identify pen. As shown in Fig. 8, the basic pen has a hexagonal bar- the features of the base variant that will need to be removed, rel which mimics the shape of a pencil and a cap which those that will need to be carried across from the source covers the ballpoint tip. More detail is provided in the Sup- variant, and which parts need to be redesigned to generate plementary Materials. The objective of the running example the new variant design. The phase comprises eight steps, is to combine these two variants to produce a unique new described in the next subsections. design, i.e. a retractable pen with hexagonal barrel. This case is deliberately simple to allow the new method to be 4.2.1 Step 1: Categorise operating functions in the base explained in full depth within the space constraints of this variant and source variant article. In Sect. 5, application of the method to more com- plex products is discussed to demonstrate that it is scaleable The set of desirable operating functions for a new product and to indicate the effort involved. variant depends on market needs, product strategy and other The ARM comprises of three phases, which are depicted factors. Identifying that set is beyond the scope of this arti- in Fig. 7 and detailed in the next subsections. cle. For the worked example, the desired operating functions of the new variant are: To extend ballpoint tip; To retract ballpoint tip; and To deposit ink. 1 3 Res Eng Design Table 2 Descriptors used retracting pen, it would therefore require To deposit ink to Code Technical for technical functions when be categorised in this way as well. function modelling the ballpoint pens type The modeller should also check for redundancy or other and IP cameras conflicts among the functions that are intended for the new 6 Import variant design. In the running example, considering that the 7 Export To retract function of the source variant is desired in the new 8 Transfer variant, the modeller can observe that two operating func- 10 Transmit tions of the base variant, namely To cover ballpoint tip and 11 Guide To uncover ballpoint tip (that are realised by the cap of the 12 Translate pen), will no longer be necessary and therefore are labelled 13 Rotate as Uo (Undesired operating function) in the base variant 15 Couple DDM matrix as shown in Fig. 8. 33 Contain 44 Secure 4.2.2 Step 2 Identify undesired features of the base variant (to be removed) This step proceeds as follows: 1. Identify features of the base variant that are involved in the previously-identified undesired operating functions. These can be readily identified by tracing the DDM matrix dependencies from all three states involved in that operating function. 2. Examine the DDM matrix columns for each of these undesired features to determine whether they are also involved in any of the previously-identified desired oper - ating functions. If not, the feature should be classified as undesired. To illustrate, since the To clip operating function is to be removed from the basic pen, the Cap.Lower clip inner face must be removed because it is not involved in any other Fig. 7 The Adaptive Redesign Method (ARM) comprises three desired operating functions, as can be identified by reading phases down column L of the operating functions section of the DDM matrix in Fig. 8. On the other hand, the Barrel.Body In this step of the ARM, operating functions are classi- feature cannot be removed because column G of Fig. 8 con- fied as follows: tains entries relating the Barrel.Body to the desired function To deposit ink. – Desired operating functions. These are needed in the new The base variant DDM matrix is annotated by adding variant. They are labelled as Do in the bottom sections Uf (Undesired feature) next to the row and column of each of the source and base variant DDM matrices of Figs. 6 undesired feature, to indicate that their interactions are to be and 8. ignored later in the analysis. In Fig. 8 these are highlighted – Undesired operating functions. These are not required in dark pink. To provide another example, these are also in the new variant. These are labelled Uo in the DDM identified in Fig.  6 (although identifying undesired features matrices of Figs. 6 and 8. for the source variant is not strictly required for the method). For each desired operating function, the modeller must 4.2.3 Step 3. Identify undesired supporting features identify whether it requires any prerequisite operating func- of the base variant’s undesired features (to be tion, and if so, classify it as also being desired. For exam- removed) ple, the To deposit ink operating function of the retracting pen requires the pen to be extended, which means that the Features of the base variant whose only purpose is to sup- operating function To extend must be executed beforehand. port undesired features are to be classified as undesired If To deposit ink was a desired operating function of the supporting features. Such features are identified from their 1 3 Res Eng Design connections to the features to be removed, as shown in the other features that interact with the Spring.Coil, but these base variant DDM matrix. These supporting features may be need not be classified as supporting features because they from the same part or from another part as the features to be were already classified as desired features (as labelled Df removed. Continuing the previous example, the Cap.Lower and highlighted in blue). Supporting features for the desired clip inner face was identified as an undesired feature of the operating functions are marked with Dsf and highlighted in base variant to be removed. Column L of the DDM matrix light blue in the DDM matrix of the source variant. These in Fig. 8 shows that the feature has two supporting features: are to be carried over into the base variant. the Barrel.Body and Cap.Lower clip outer face. The Bar- rel.Body cannot be removed, since it is involved in desired 4.2.6 Step 6. Determine the functional similarity functions. However, the Cap.Lower clip outer face can and between each desired/desired supporting feature should be removed, because tracing its dependencies in the of the source variant and each desired/desired DDM indicates that it is not supporting any features required supporting feature of the base variant for any desired operating function. For each undesired supporting feature that is identified for The next step is to complete a pairwise comparison of the removal, the matrix should be checked again to ensure that features across the two variants and compute their similar- no additional features have become redundant, in which case ity. This is required so that, in Step 7, it will be possible to those are to be removed as well (this check is repeated until determine which features need to be drawn from each of the no more features are candidates for removal). two existing variants to create the new variant. Once identified, all undesired supporting features are Each part of the source variant that contains at least one annotated with Usf in the base variant DDM matrix. In Fig. 8 desired feature or desired supporting feature (as identified these are highlighted in light pink. To provide another exam- in the previous step) is compared to each of the desired fea- ple, such features are also identie fi d in Fig.  6 (although iden- tures and desired supporting features of the base variant. A tifying undesired supporting features for the source variant comparison matrix is formed with these base variant fea- is not strictly required for the method) tures in the column headings and the source variant features in the row headings, as shown in Fig. 10. Empty columns 4.2.4 Step 4. Identify desired features of the two variants represent base variant features that were identified as unde- sired or undesired supporting features (Uf or Usf) in Steps The next step is to identify desired features of the source 2 and 3. Similarly, empty rows represent source variant fea- variant, which are features that contribute to realising any of tures that are not desired. For each of the non-empty cells the desired operating functions. As before, this is achieved in the matrix, the flow interactions and partially-constrained by tracing the numbers in the rows of the desired operating connections of the corresponding pair of features are next functions located in the bottom field of the source variant compared (by analysing the two DDM matrices) to compute DDM matrix. Recall from Sect.  3.2.5 that these numbers the degree of functional similarity between that pair of fea- indicate the features required for the function. tures. Fully-constrained connections between features are To distinguish desired features in the source variant DDM not included in this comparison since they provide structural matrix they are annotated Df. The flow of dependencies from support but are not directly involved in realising operating the desired operating functions through to the desired fea- functions. Functional similarity is defined here as the total tures is highlighted in blue in Fig. 6. number of interactions that meet the above criteria and are common to both features, divided by the total number of 4.2.5 Step 5. Identify desired supporting features interactions that meet the criteria. The result is interpreted of the two variants’ desired features as follows: Supporting features that are necessary to the working of – 100% indicates that the two features are functionally carried-across features also need to be carried over to the identical. new variant design. They can be identified by reading down – 0% indicates that the two features are functionally dis- the columns of the desired features in the source variant joint. DDM matrix. For example, reading down column R of – Greater than 0% and less than 100% indicates that the Fig. 6 shows that the Lower barrel. Slot (in row 9) of the existing feature in the base variant realises some, but not retracting pen is a supporting feature for the desired fea- all of the functions of the source variant feature. The two ture Spring.Coil. This can be explained by considering features are functionally similar. Fig. 9, which shows how the Lower barrel.Slot keeps one end of the Spring.Coil in place during the retract/extend To illustrate, consider the comparison between the Ink cham- state. The source variant DDM matrix also reveals several ber.Chamber body features of the two variants. Comparing 1 3 Res Eng Design 1 3 Res Eng Design ◂Fig. 8 DDM matrix of the basic pen (the base variant in the running the base variant, the entire part of the source variant is example). The dark pink backgrounds indicate features and functions to be carried over into the new variant. For example, the that are undesired in the new variant (as described in Sect. 4.2.2); the part Clicker of the retracting pen will be used in the new light pink backgrounds indicate features whose only purpose is to variant design because no parts of the base variant (basic support those features (as described in Sect.  4.2.3). The blue high- lights indicate features and functions that are desired. The light blue pen) have features with any functional similarity to it. highlights represent features and functions that support the desired This is identified by noting that in Fig.  10 all the entries features and functions in the new variant design are 0% for every row describing features of the Clicker. The same is true for the Plunger and Spring. the DDMs of Figs. 6 and 8 reveals that these features par- – If the desired feature of the source variant has 100% in ticipate in two identical technical functions with respect to one or more of the cells, when reading across its row, the same flows, namely To store (33) Ink and To channel then the base variant feature already offers the desired (11) Ink. Figure 8 shows that the feature of the basic pen has functionality. This means that those base variant features no partially-constrained connections to other features of that are to be retained when creating the new variant design. design, while Fig. 6 shows that the feature of the retracting An example of this can be found between the Ballpoint pen has one partially-constrained connection, namely to the tip ball.Ball and Ballpoint tip.Socket features of the two Spring.Coil. pens. In this case the feature of the source variant (retracting – If the desired feature of the source variant is function- pen) has three interactions in total. Two of them also appear ally disjoint from all features of the base variant, i.e. all in the feature of the base variant being compared, i.e. the two entries across the row are 0%, then that source variant flow interactions, while one does not. This leads to a similar - feature must be carried over into the base variant. This ity score of 2∕3 = 67% , so the two features are classified as is done by modifying the part of the base variant that is functionally similar. Note the importance of comparing tech- functionally most similar to the part of the source vari- nical functions in the flows part of the DDM, which allows ant that contains the desired feature being carried across. the more accurate discernment of functional similarity of Functional similarity between two parts is calculated as the two features from different variants. The required accu- the average of the functional similarity of all pairwise racy would not be possible if only the physical connections comparisons of their features. For example, the Upper to other parts of the respective variants were considered. barrel. Tip and Upper barrel. Latch hole features of the The technical functions and flows modelled in the DDM retracting pen will be carried over by adding them to the matrices allow features performing similar functions, even Barrel of the basic pen because the Upper barrel of the across variants that have slightly different architectures to retracting design (from which the features are drawn) be compared. is the most functionally similar part to the Barrel of the For functionally similar feature pairs, if the base variant basic pen design. feature contributes to all the desired technical functions of – If the source variant feature is functionally similar to the source variant feature, a ‘ ’ sign is placed alongside one or more base variant features, and is not function- the similarity score. On the other hand, if the base variant ally identical to any feature, its row contains at least one feature does not meet all the desired technical functions of entry > 0% and no entries = 100%. In this case, it is nec- the source variant feature, the matrix cell is denoted with ‘+’ essary to visually/geometrically compare the feature of to indicate that additional technical functions would need the source variant against each of the functionally most to be met by the base variant feature if it were to realise the similar features of the base variant to determine what technical functions of that source variant feature. changes to the base variant feature(s) might be needed to produce the desired functionality of the source variant 4.2.7 Step 7. Determine which features to carry feature. This comparison requires design judgement. For across from the source variant into the new variant example, the Ink chamber. Chamber body of the basic pen needs to be geometrically compared to the Ink cham- Recall that the base variant is the baseline design to be ber. Chamber body of the retracting pen (source variant). changed when creating the new variant. To determine which This is because the ‘+’ sign in front of the 67% (calcu- parts/features and supporting features of the source variant lated in Step 6) indicates that the basic pen needs fulfil a are to be carried across to the new variant design, the rows desired interaction to realise the operating function. This of the comparison matrix are next worked through system- desired interaction happens to be with the Spring.Coil atically. Each part is considered one-at-a-time as follows: which can be traced by comparing the DDM of the two pens as discussed in Step 6. In this example, the exist- – If all desired/desired supporting features of the source ing geometry of the basic Ink chamber.Chamber body variant part are functionally disjoint from all features of is identical to that of the retracting pen Ink chamber. 1 3 Res Eng Design Fig. 9 An example of a sup- porting feature for the extend- ing and retracting ballpoint tip operating function of the retracting pen Fig. 10 The comparison matrix between the basic pen (base variant) and the retracting pen (source variant) is used to identify the reusable fea- tures of the base variant, which features of the source variant to add to the new variant and which features of the base variant to redesign Chamber body and is therefore capable of accommodat- – If the desired feature of the source variant has < 0% in ing the Spring.Coil. Hence, no changes are required and one or more cells when reading across its row, then it also this base variant feature can be retained. However, if the indicates that the base variant feature already provides existing feature of the base variant cannot geometrically the desired functionality of the source variant feature. In fulfil this interaction then it will need to be geometrically this case, the base variant feature is also retained. Note modified. the percentage shown in the matrix cell may not neces- 1 3 Res Eng Design sarily be 100% if the features being compared have dif- variant, redesign of existing parts of the base variant are ferent connections to other features in their respective required. An example of two steps from the basic pen’s bar- variants. rel being redesigned is provided in Fig. 12. Features of the base variant which do not require feature modification can be 4.2.8 Step 8: Compile list of redesign activities to create reused in the new variant design, although some adjustment the new variant design to dimensions may be required. Figure 13 shows the completed design of the new pencil- Finally, the results of the previous steps are compiled to form shaped pen with the retractable function, that was gener- a list of redesign activities that will be needed to form the ated by following the redesign steps laid out in the redesign new variant design as shown in Fig. 11. activities table. The list shows what redesign activities are needed in terms of operations on features and parts. It does not show the geometric and dimensional details, such as where on a 5 Application cases part a feature should be added and what dimensional adjust- ments will be necessary. These details are usually quite obvi- As previously mentioned, the ballpoint pens example was ous when viewing the two parts for each step, as illustrated chosen to illustrate the DDM and ARM because it is sim- in the next subsection. ple enough to present the approaches in full detail. To also illustrate that the new approaches can support modelling and 4.3 ARM phase III: execute adaptive redesign steps redesign of more complex products, this section discusses to generate the new variant design their application to a pair of Foscam IP cameras (security cameras). The final phase of the method is for the human designer/ The cameras to be discussed are from a product range in method user to execute the identified redesign activities to which different variants offer different functions. Depending form the new variant design on CAD. Firstly, undesired fea- on the variant, these functions include motorised panning, tures of the base variant are removed by removing CAD motorised tilting, recording, motion detection, voice detec- features from the CAD model. Before a CAD feature is tion, audio output, and single press calling. In this section, removed, it is important to check that there are no depend- the motorised panning function is integrated into a simple ent sketches and features built upon it in the model tree that IP camera (here called the fixed camera) that is capable of are desired to be retained. Secondly, features from the source being manually tilting upwards and downwards. The motor- variant that realise the desired operating function are added ised panning function was sourced from a motorised IP to the base variant. To integrate these features to the base Fig. 11 The generated list of redesign activities needed to derive the new variant design 1 3 Res Eng Design Fig. 12 A series of steps showing how retracting pen Upper barrel.Tip feature, Upper barrel.Latch hole feature and Clicker part are added to the barrel of the basic pen by executing Task 23 and Task 24, respectively, from Fig. 11 5.1 Application of the DDM modelling procedure to the two IP cameras The detailed design modelling procedure was applied to generate DDM matrices for the two product variants, as shown in Fig.  15. More detail is provided in the Supple- mentary Materials. In overview, the DDM of the PT camera comprises 37 parts, 157 features with 155 interactions, 59 technical functions, and 7 operating functions. Of the seven Fig. 13 CAD model of the new pen design which is pencil-shaped with functions to extend and retract the  ballpoint tip. More detail is operating functions, the automatic panning function will be provided in the Supplementary Materials carried across from the PT camera into the fixed camera. The DDM revealed that this operating function requires 25 camera that can be panned and tilted using software control features to realise it. The equivalent information for the fixed (here called the PT camera). position IP camera is provided in Fig. 15. In comparison to The PT camera (the more complex variant) contains 37 the ballpoint pens case study, there are energy and signal parts, and as can be seen in Fig. 14, its mechanical assem- flows in both camera variants. bly is representative of many moderately-complex consumer The IP cameras contain various electronic components products. More detail for both cameras is provided in the that were not modelled in detail. This is because this article Supplementary Material. focuses on mechanical considerations. Geometric features relating only to part manufacturing processes were also not 1 3 Res Eng Design generate the design activities table in about 1.5 h. An addi- tional 5 h were then required to follow the steps by complet- ing the new variant design in CAD—but this would be nec- essary whether or not the new method was used. The effort would have been substantially less if the straightforward matrix tracing steps and calculations were automated. This indicates that the method, if implemented in special-purpose software, could potentially help to identify redesign activi- ties for even quite complex products fairly rapidly, provided that existing CAD models were available. Reflecting on the ballpoint pens example and the more complex IP cameras analysis, the latter added insight by confirming that the ARM could be used to compare parts having substantially different geometric features across the two designs, and still identify redesign activities at the parts level for the new design. It was also observed that the effort required for the first phase of the approach (DDM genera- tion) and the n fi al phase (executing redesign steps) increased signic fi antly with the complexity of the product. At the same time, the majority of this effort (and about 75% of the total effort according to the estimates above) was devoted to CAD activities that would need to be done to generate the variants, regardless of whether the method was used in support of the redesign process. Put another way, the overhead of using the method (without any specialised software) appears to be approximately 33%. Overall the cameras analysis provided a measure of confidence in the DDM and ARM, although more studies will be required to substantiate the benefits set out in Sect. 1.1. Fig. 14 Exploded view of the motorised PT Camera to  indicate its level of mechanical complexity. More detail is provided in the Sup- plementary Materials 5.3 Initial assessment of the useability of the DDM and ARM modelled in detail because, to recap, this article focuses on operating functions associated with product use. Noting that the DDM and ARM approaches are quite intri- Overall, this application confirmed that the DDM mod- cate, we sought to assess whether they could be applied by elling procedure can be applied to products that are more a person other than the authors. In an initial assessment, an complex than the ballpoint pens discussed earlier. The matri- undergraduate mechanical engineering student was tasked to ces generated for the IP cameras are rather large, but also apply the emerging method to two cases. In the first case, the extremely sparse. The majority of interactions are fully-con- student applied the method to implement a sheet-fed scan- strained connections between features of the same part (i.e. ning function into a budget inkjet printer having a single- within the clusters shown in Fig. 15). In total, generating sheet scanner. In the second case study, the student applied the DDMs for the two camera variants required about 8 h of the method to implement an automatic juicing function into effort. Additionally, about 24 h was required for the CAD a simple hand-operated juicer. While not a comprehensive modelling of the two variants, but this would not be needed evaluation, these cases along with the pen and camera cases for an application in an industrial context where CAD mod- provided additional confidence that the method can work els would already be available. with a variety of products and also, that it is useable. The application cases also highlighted that the method 5.2 Application of the Adaptive Redesign Method relies on the user to detect whether there are conflicts for function integration between the two IP between operating functions across variants being integrated cameras (this was subsequently included in the method description, see Sect. 4.2.1). A conflict occurs when more than one oper - Once the DDM matrices were completed, by following the ating function of the new variant design addresses the same steps of the Adaptive Redesign Method, it was possible to task from a user’s perspective. For example, the ARM does 1 3 Res Eng Design Fig. 15 Overview of the matrices generated when applying the Detailed Design Model and Adaptive Redesign Method for function integration in the IP cameras study. Detail is provided in the Supplementary Materials not directly identify that the cap of the basic pen, which is 2. The information captured by the model is at an appropri- used to protect the ballpoint tip, is not needed when the ball- ate level of detail to support the adaptive redesign activi- point tip of the basic pen is made retractable in the new vari- ties needed for function integration—namely adding, ant. The underpinning reason is that the DDM deliberately removing, redesigning and carrying over features and only captures what the operating functions are, not what they parts to achieve a desired new combination of existing are used for, to reduce subjectivity in product modelling. operating functions. If a conflict is detected by the method user while perform- 3. The method can be applied to different types of products ing a function integration, then the features (and potentially and those with moderate levels of mechanical complex- parts) related to the redundant operating function should ity. be removed from the base variant. If not identified early 4. The systematic steps of the method are possible to per- on, these conflicts become obvious towards the end of the form by different users (not only the researchers). redesign phase while the physical form of the new design is being manipulated in CAD. In such cases, it is possible to return to steps 2 and 3 of the ARM to identify the features 6 Discussion and parts that should be removed. Several iterations among steps of the method may be necessary to finalise the design.6.1 Recap of contributions 5.4 Summary To summarise, this article offers the following contributions. Firstly, the DDM and ARM provide means to systemati- While a comprehensive evaluation of the method with prac- cally extract selected operating functions and their physi- titioners has not yet been attempted, applications by differ - cal realisations from existing product designs and integrate ent researchers to four different types of product (pens, IP them into other existing product variants. This is achieved cameras, printers and juicers) build confidence that: by modelling the parts of the products at the geometric level using CAD features and capturing their interactions with 1. The DDM provides a basis for systematically identifying other features, flows, states and state transitions to realise and modelling functions, flows, parts, features, states operating functions. Function integration is not compre- and interactions in existing product designs. hensively supported by prior methods, that are discussed in 1 3 Res Eng Design Sect. 2.2, because as summarised in Table 1 none analyse redundant functionality in the new variant design. A second a product down to the features, states and state transition limitation of the DDM and ARM in the functional domain levels. is that they do not consider the relationships between the Secondly, the Adaptive Redesign Method (ARM) sup- technical functions involved in each operating function. In ports identification of redesign activities required to derive a particular, the sequence of operation for the technical func- desired new variant design. In particular, it helps to identify tions is not represented and, if it is important, it will need to the redesign activities for removing unnecessary operating be considered separately by a designer using the approach. functions and their physical realisations, as well as the rede- Other limitations concern the physical domain. Firstly, sign activities required for modifying an existing part. This the features listed in the DDM matrix depend on how each is achieved by analysing and comparing data at the features physical part is modelled with CAD and since parts can be level of the DDM for the two product variants under con- modelled in different ways, this list may vary. However, sideration. This level of detail is not offered by previous because the ARM outputs a redesign activities list in terms function integration methods discussed in Sect. 2.2. of the features of the input CAD models, the utility of the Thirdly, the two approaches consider not only the primary method is not greatly dependent on CAD modelling choices. features but also the supporting features for each operat- Secondly, the DDM does not consider the spatial relation- ing function. This is achieved by distinguishing partially- ships and interface constraints between features and between constrained interactions (involving primary features) from parts. As a result, the geometry of features from the source fully constrained interactions (involving supporting fea- variant that are being integrated into a base variant part tures). Considering the latter allows identification of sup- may need to be scaled to ensure physical fit with other parts porting features and supporting parts that might need to of the base variant. These parametric adjustments are not also be modified when primary features are carried over or accounted for in this article. Another constraint-related limi- removed. Existing function integration methods do not com- tation is that the ARM assumes that all existing parts of a prehensively consider supporting features. product are possible to redesign. However, in practice some Finally, the DDM provides a more objective approach to parts of a product cannot be easily modified, e.g. because modelling the high-level functions of existing products by they are purchased from a supplier or form part of a product forming operating function descriptions based on the possi- platform. Future work could incorporate such constraints in ble physical configurations of a product. In other words, the the method. modelling procedure is based on describing what a product Regarding the relationships between functional and can do instead of what a product can be used for. Low-level physical domains, the case studies reported in this article technical functions are then identified based on the interac- confirmed that these relationships are captured by the DDM tion between features and flows based on a set of vocabu- in sufficient detail for the function integration task. However, lary by Hirtz et al (2002). As previously stated in literature, future applications may reveal opportunities for improve- identifying function descriptors based on flows is beneficial ment in this area as well. to reduce subjectivity of functional modelling (Gietka et al 2002). 6.3 Additional areas for future work 6.2 Limitations By considering the limitations above and also by considering the PSI analysis approach developed by Reich and Subrah- In this section, some limitations will be discussed with manian (2022), three additional areas of future work have respect to functional and physical domains of the DDM and been identified. ARM. Firstly, we hope to undertake empirical studies in compa- Some limitations concern mainly the functional domain. nies with product families to explore how function integra- Firstly, the DDM does not consider what the user uses the tion is done in practice. Additional application studies are product for, i.e. use case functions. This was a deliberate also needed to test the practicality of the method and to test choice to reduce subjectivity in the modelling and analysis. it against the expected benefits set out in Sect 1.1. However as a result, the ARM is unable to identify repeat- Secondly, the method could be extended to account for ing use cases between different operating functions for the different contexts of use. For instance, in the context of prod- new variant design. Recall from Sect. 5.2, that for the ball- uct families there are multiple variants with different operat- point pens redesign, the ARM did not detect that the cap ing functions and architectures available for integration. In of the basic pen was not needed once that pen was made a product family context, the scope of the method could be retractable. Therefore, future work is needed to model the expanded to determine which variant to source each desired relationship between the use case functions and operating operating function from, and to determine the best sequence functions of existing products to more systematically avoid of implementing multiple functions to avoid redesigning the 1 3 Res Eng Design sharing their reflections on the methods reported here. We appreci - same parts multiple times. Also noting that a design is influ- ate the constructive comments provided by the anonymous reviewers enced by many considerations beyond the use of a product, and the editor, Yoram Reich. All CAD models and drawings are par- and hence that multiple reference frames are possible for tial approximations of products by BiC (the ballpoint pens) and Fos- design analysis, the methods reported in this article could cam (the cameras) drawn for the purpose of illustrating the approaches presented in this article. potentially be expanded to support product modelling and integration from the viewpoints of other lifecycle phases Funding Open Access funding enabled and organized by CAUL and apart from product use, such as assembly, inspection and its Member Institutions. repair, etc. To achieve this would require expanding the DDM to map design elements onto considerations in differ - Open Access This article is licensed under a Creative Commons ent lifecycle phases. Attribution 4.0 International License, which permits use, sharing, adap- tation, distribution and reproduction in any medium or format, as long Finally, future work could investigate opportunities to as you give appropriate credit to the original author(s) and the source, reduce the data requirements and effort-intensiveness of provide a link to the Creative Commons licence, and indicate if changes the DDM and ARM. Data requirements might be reduced were made. The images or other third party material in this article are by developing an initial assessment approach to determine included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the parts of a product that need to be modelled down to the article’s Creative Commons licence and your intended use is not the feature level and those that only need to be modelled at permitted by statutory regulation or exceeds the permitted use, you will the parts level for instance, because they are not involved need to obtain permission directly from the copyright holder. To view a in any function expected to change, or because they can- copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . not be changed—for instance because they are off-the-shelf parts. Effort-intensiveness could be reduced by automating some of the steps in the DDM modelling method and the References ARM to reduce the overall analysis time. Automatable steps Andreasen MM (1980) Machine design methods based on a systematic include (1) extracting features and their interactions from the approach–contribution to a design theory (in Danish). 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A systematic approach for product modelling and function integration to support adaptive redesign of product variants

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Abstract

Res Eng Design https://doi.org/10.1007/s00163-022-00401-3 ORIGINAL PAPER A systematic approach for product modelling and function integration to support adaptive redesign of product variants 1 1 Foo Shing Wong  · David C. Wynn   Received: 10 December 2021 / Revised: 30 September 2022 / Accepted: 3 October 2022 © The Author(s) 2022 Abstract When a product variant offers functionality that and tested through reverse engineering studies of consumer is high in demand, firms may decide to leverage that design products, confirming its applicability. to enhance other variants in their product line. This can be achieved by extracting functions and their realisations Keywords Product variant design · Function integration · from one product variant and integrating them into another Product modelling · Reverse engineering · Mechanical variant, resulting in a third product variant that has a new assemblies · Design Structure Matrix · CAD · Detailed combination of functions and physical features. This article Design Model · Adaptive Redesign Method introduces a systematic approach called the Adaptive Rede- sign Method (ARM) to support this function integration pro- cess. The ARM is based on a new product model called the 1 Introduction Detailed Design Model (DDM). In comparison to existing approaches, the DDM allows the architecture of an existing This article introduces a method that provides detailed guid- product to be modelled on a sufficiently detailed level to ance for function integration in engineering design. Function identify geometric features and parts that realise particular integration involves extracting particular functions and their operating functions of a product. This detailed information physical realisations from existing products and integrating provides a basis for systematic determination of the redesign them into other product variants to form a new variant with activities needed to derive a new variant design, down to the a unique combination of features and operating functions. detailed level of adding, removing and integrating specific One situation in which function integration occurs is when a parts and features. The main benet fi is to assist with planning product variant has functions or technology that are high in the redesign process while ensuring nothing is overlooked, demand. In such cases, companies may want to implement which might be especially useful if the task is to be divided that new technology into their other existing product variants among several designers or if designers are not fully familiar (Li et al. 2009; Zhang et al. 2011; Liu et al. 2014). with the designs at hand. A secondary benefit is to show how Function integration is a form of redesign in which an this type of redesign process can be decomposed into sys- existing product variant is adapted. In general, product rede- tematic steps, which could potentially reveal opportunities sign can be grouped into two major categories: parametric for computer support. The new approach has been developed and adaptive redesign (Otto and Wood 1998). Parametric redesign is concerned with improving a product’s architec- ture or its performance by adjusting parameters of an exist- Supplementary Information The online version contains ing design. Adaptive redesign, which is the focus of this supplementary material available at https:// doi. org/ 10. 1007/ s00163- article, is concerned with modifying the functionality of an 022- 00401-3. existing product to derive a new product. In research litera- * Foo Shing Wong ture, studies of adaptive redesign often involve the reverse fwon360@aucklanduni.ac.nz engineering of existing products (Otto and Wood 1998). The 1 purpose of reverse engineering in this context is to support Department of Mechanical and Mechatronics Engineering, University of Auckland, Auckland, New Zealand the reuse of existing elements of the design, with a particular Vol.:(0123456789) 1 3 Res Eng Design emphasis on appreciating how those elements influence each redesign activities, requiring later correction (Tang et al. other and how they must be considered in combination when 2010b). This may be especially useful if the redesign work introducing changes. The changes may involve a combina- needs to be coordinated between several team members, or tion of adding, removing, redesigning, and reusing parts to if a designer is not fully familiar with the designs at hand. achieve desired functions (Lee and Park 2014). Finally, decomposing the redesign process into well-defined One of the important issues to consider in redesign is smaller steps may suggest opportunities for computer sup- the product architecture. The architecture of a product to be port of that process. redesigned can be described in terms of functions and physi- cal parts. Three types of interactions are possible on this 1.2 Research method level of description: interactions between functions, interac- tions between parts, and interactions between functions and To address the research questions a representative redesign parts. Each function or part can interact with several oth- task based on a simple product (redesigning a ballpoint pen) ers, exhibiting complex many-to-many relationships (Ulrich was generated as a test case. Existing approaches from the and Seering 1988). On a more granular level, physical part literature were assessed in light of this test case. From this, interactions are realised at the interfaces between specific limitations of the existing product models and function inte- part surfaces. In a CAD model, these surfaces are typi- gration methods were appreciated. This led to the generation cally defined by geometric features of the respective parts. of a new approach for product modelling, and based on it, a Overall, the complex patterns of connections that comprise new systematic approach for function integration. The new product architectures need to be considered when integrating approaches were then applied to a series of more complex existing design elements into an existing product to develop consumer products to test and further improve them. Overall, a new product variant. the development was highly iterative. Literature review also proceeded concurrently with the activities described above. 1.1 Research questions 1.3 Article outline To provide systematic support for function integration between product variants, this article addresses three The rest of this article proceeds as follows. In Section  2, research questions: literature is reviewed and the research gap is pinpointed. Section 3 introduces the basis of our solution, which is to – RQ1: How can product variants be systematically mod- model existing variants using a new product model called elled at an appropriate level of detail to support function the Detailed Design Model (DDM). Section 4 then explains integration at a part and feature level? the Adaptive Redesign Method (ARM) itself. Section 5 dis- – RQ2: How can the resulting models of product variants cusses some application cases and insights drawn from them. be systematically analysed to identify redesign activities Section 6 discusses advantages, limitations and some sug- required for function integration? gestions for further work. Concluding remarks are offered – RQ3: Is the resulting systematic approach useful and in Section 7. what future research opportunities does it reveal? In this context, a systematic approach is expected to provide 2 Literature review several benefits. First, a systematic approach is helpful to model existing designs in a structured way and better appre- As established in Sect.  1, function integration requires ciate how the design solutions work (Otto and Wood 1998; extracting existing design solutions from a product and inte- Tang et al. 2010a). A systematic approach is particularly grating it into another product to derive a new variant. It was useful when modelling products having moving parts that determined that a method to support this should satisfy four are each involved in multiple functions, such that function method requirements (MRs), for the reasons outlined below: realisation is complex. Second, a systematic process for modelling design information supports the sharing and reuse – MR1: Determine low-level and high-level functions of a of that information (Gietka et al. 2002; Tang et al. 2010b). design and link them to the parts and physical features. Reusing existing design information should support the This information is needed to identify the aspects of a development of reliable products, since it facilitates adop- design that realise each function that is to be integrated. tion of proven principles and solutions (Smith et al. 2012). – MR2: Determine the physical interactions between fea- Third, a systematic approach allows for detailed planning tures of a design. This information is needed to identify of the (re)design process and may reduce design rework, supporting features that help primary features realise since designers will be less likely to initially overlook some desired functions that are to be integrated. 1 3 Res Eng Design – MR3: Ensure that product data obtained for different domain to capture the coupling between user requirements/ product variants is consistently represented, using similar interface and product architecture elements. The coupling function terminology. This is needed so that the variant between these domains was used to determine whether the designs can be directly compared for function integra- user interface of the product needs to be redesigned when tion. there are changes to user requirements. However, this model – MR4: Systematically process the obtained product data uses mathematical equations to link elements between these to determine how parts and specific features of parts can four design domains, which may be difficult to formulate be carried over, removed and modified from existing from a product decomposition and are not necessary to meet variants to generate a new variant design that provides a MR1-MR4. unique desired combination of existing functions and fea- The second type of hierarchical product model to be dis- tures. The benefits of such function integration, as well cussed is the Function-Behaviour-State diagram (Umeda as the reasons for a systematic approach, were outlined et al. 1990). In this approach, the behaviour domain of a in Sect. 1. design exists between the function and structure domains. Including this domain enables consideration of the perfor- In the next subsections, product models and function inte- mance attributes of a product during redesign. However, gration methods from literature are reviewed against these this extra domain also increases modelling effort and is not method requirements. This confirms the gap addressed by required for MR1-MR4. Furthermore, the extra domain will this article. unnecessarily increase the complexity of tracing between function and structure domains, as required by MR1. Deng 2.1 Product models for function integration et  al. (1999) extended this approach to form the FEBS model, additionally capturing the interaction between the Most product modelling approaches in literature are based product and its operating environment. Tor et al. (2002) in on hierarchical decomposition of a design (typically involv- turn extended FEBS to form B-FES, a model to support ing tree diagramming), on block diagramming, and/or on product variant concept generation. B-FES can be used to matrix-based modelling. Some models of these types are extract and reuse certain physical attributes from existing discussed in the next subsections. products when given a set of requirements. However, B-FES does not meet MR2 because it does not consider the support- 2.1.1 Product models based on hierarchical decomposition ing features required by the primary parts that realise desired and tree diagramming functions (requirements). The third type of hierarchical product model builds on the This subsection discusses decomposition-based product Chromosome Model (Andreasen 1992), which is based on modelling approaches based on (1) Axiomatic Design, (2) Domain Theory (Andreasen 1980). This model represents Function-Behaviour-State modelling, (3) The Chromosome product information in three domains: activities, organs, model and (4) Function-Means Tree approaches. and parts, in addition to the process of using the product Firstly, tree-based product models building on axiomatic (Andreasen et al. 2014). It captures the connections between design (Suh 1995) essentially consist of two tree diagrams, elements within and across these domains, and hence could to model the functions and parts domains of a product be used to extract features that realise high level functions respectively. In a reverse engineering context, the trees can (MR1) and to determine necessary supporting features be formed progressively while disassembling a product by (MR2). However, in common with other approaches this considering how the functions relate to each assembly, sub- does not directly address the need for consistent modelling assembly, and so on. While convenient for decomposition, of different products, required to support their comparison this type of model does not emphasise the relationships and integration (MR3). between parts, features or between functions at a particu- The final type of hierarchical model to be discussed is lar level of the tree. Hence, it is not ideal to identify sup- the function-means tree. This model represents a product by porting features (as required by MR2). This limitation was decomposing top-level functions into the subsystems realis- partially addressed by the transdisciplinary product devel- ing them, then decomposing those subsystems into constitu- opment life-cycle model (TDPL) of Gumus et al (2008). ent subsystems and so on until individual parts (potentially TPDL captures the interaction between parts and according features) are reached. Malmqvist (1997) extended the func- to Gumus et al. (2008), it can help to verify whether the tion-means tree by including information such as functions parts can realise the functional requirements of a product. relevant to different product life-cycle phases, alternative However, it does not capture low-level functions (as required design solutions, parametric constraints and design objec- by MR1). Lo and Helander (2007) also adopted axiomatic tives. The relationship between these elements are also design concepts, introducing a goal domain and user actions captured. Borgue et al. (2019) built on this work to model 1 3 Res Eng Design connections between product functions, design solutions Hirtz et al. 2002; Caldwell and Mocko 2012; Mohammed and additive manufacturing constraints. Müller et al. (2020) and Shammari 2021). Gietka et al (2002) also found that linked the function-means tree to an automation approach, model variation can also be reduced if designers describe drawing connections between the function domain and the each function based on its input and output flows rather than physical domain to enable CAD models of design concepts identifying them based on a higher-level function. to be generated from different combinations of design solu- Other block diagram models of product structure are tions. Advantages of all function-means tree based models based on standardised modelling notations. For instance, are that they are well-suited to systematic product decompo- SysML has been used for this purpose, as has Object-Pro- sition, and that they directly show the relationship between cess Methodology (Dori 2011). functions and the parts that realise them. However, they do not capture the relationships between parts involved in func- 2.1.3 Models based on matrices tion realisation. Such approaches are therefore not ideal to identify supporting features, as required by MR2. The final group of product architecture models to be dis- Overall, hierarchical models support product modelling cussed are based on matrices. In one well-known approach, in a reverse engineering context by structuring analysis and Pimmler and Eppinger (1994) used the Design Structure description of a product at progressively increasing levels Matrix (DSM) to represent the interactions between parts of of detail. A general disadvantage is that they are not well a product. The DSM consists of a square matrix with identi- suited to represent connections across branches of the tree. cal row and column headings, used to represent the product Although several tree-based approaches allow such connec- elements, while the content of the matrix cells indicates con- tions to be made, e.g. by adding diagonal lines that cut across nections between pairs of elements. For instance, Pimmler the tree diagram, the diagrams are likely to become difficult and Eppinger (1994) used letters in the cells to differentiate to visually manipulate and trace as the modelled product spatial, signal, material, and energy interactions between increases in complexity. These limitations could perhaps be parts. Tilstra et al. (2012) developed systematic steps for addressed by appropriate software support. However, such modelling a product structure using DSMs, adopting a hier- modelling software is not readily available at present. archical approach in which a product is decomposed and subsystems are modelled separately, prior to combination of 2.1.2 Models based on block diagramming those models. They demonstrated the importance of prede- fining the types of interactions to ensure that consistency is Other models used to represent product information are maintained when a product is modelled by different people. based on block diagrams. For instance, the operation of a They also emphasised the importance of producing consist- product can be modelled using concepts from the Theory of ent DSMs to allow for product architecture comparisons, Technical Systems (Hubka and Eder 1988). Here, the main which is required for function integration (this supports function of a design to realise a transformation process is MR3). DSMs have also been used to represent and evaluate represented as a black box, with input arrows to represent multiple design alternatives by Wyatt et al. (2008). How- the human, knowledge and management systems needed to ever, while providing a concise overview, the DSM does not operate the design to perform the function. Arrows are also directly capture the detailed logic of interactions, which can used to indicate the operands being transformed while using be problematic for applications in which logic is important a design. Hubka and Eder (2002) integrated this model with (Karniel and Reich 2009). For further information on DSMs the Chromosome model to provide a more comprehensive the reader is referred to the reviews by Yassine and Braha block diagram-based product model. A related and very (2003) and Browning (2015). well-established approach is function-flow modelling ( Pahl Researchers have also used more elaborate matrices to and Beitz 1996). This depicts how sub-functions operate show connections across product information domains. For together to realise the overall function of a product. Func- example, the Domain Mapping Matrix (DMM) is a non- tion-flow models could be useful for assessing functional square mapping matrix that can be used to map the function changes during redesign, but do not relate these functions elements of a product to its physical elements (Danilovic to physical parts and features as needed for MR1. Another and Browning 2007). Lindemann and Maurer (2007) inte- drawback is that function-flow models are constructed at grated DSMs and DMMs covering multiple domains to form a high level of abstraction and can be very different when a multi-domain matrix (MDM) to more comprehensively constructed by different people, which means this approach model product architectures and product families, among is not ideal to meet MR3. To reduce this variation, some other applications. Tang et al. (2010b) applied MDMs in a researchers have developed sets of vocabulary, grammar and database-based approach to trace how elements of an exist- topology rules to improve the consistency of function struc- ing product will be impacted when there are changes to func- ture models (Szykman et al 1999; Stone and Wood 2000; tions. Eisenbart et al (2017) adopted the MDM concept to 1 3 Res Eng Design form the Integrated Function Model (IFM) to show how low- which occur when a newly added function reduces the per- level functions and parts relate to a particular high-level user formance of other functions. In this scenario, the researchers function. This model combines block diagrams and matrices. suggested using the Theory of Inventive Problem Solving (TRIZ) to resolve the performance conflicts. Alternatively, 2.2 Methods to support function integration in product the Advanced Systematic Inventive Thinking (ASIT) redesign approach can be used to generate ideas for deriving the new combination design (Moon et al. 2012). Finally, Smith et al. Having discussed a number of product modelling (2012) proposed a method to combine more than two exist- approaches, this subsection moves on to discuss how such ing products to derive a new product. Instead of selecting a approaches have been used as the basis of methods to sup- single product as a foundation for the new variant design, port function integration. Our review revealed that there they selected parts from different products based on custom- are relatively few methods of this type in literature. In one ers’ needs and combined them to form a new design. Their publication, Kalyanasundaram and Lewis (2014) proposed method is similar to a morphological analysis. A drawback a product integration method to support the derivation of is that it does not model the architectures of the products. re-configurable products and multi-functional products from Therefore, it can only determine parts to carry over to the two existing products. Their method combines the function- new variant design based on the user’s needs. It does not ality of two existing products to form a new design, using a compare product parts functionally to determine the physical matrix model to compare low-level functions between parts modifications required for a part to fulfil the desired func- (as required by MR3) and interactions between physical tions, as is required by MR4. parts (partially addressing MR2). However, this approach does not model products at the feature level and there- 2.3 Critique and the need for a new approach fore cannot identify physical features of a product variant involved in function integration (MR1). Since it does not To recap, a relatively small number of function integration capture parts at a features level, the method also does not methods have been proposed in literature, based on analysis provide detailed guidelines for part modification (MR4). A of products using hierarchical models, flowchart-based mod- similar method was developed by Kang and Tang (2013) els and matrix models. Hierarchical models offer systematic for developing multi-functional products. This method also procedures for identifying detailed functions and parts of uses matrices to model existing products, resulting in similar products. However, they do not clearly (or sometimes at all) advantages and drawbacks. However, it does consider sup- represent the relationship between detailed functions and porting parts for primary parts that realise the functions, parts as required by MR1 and MR2. Block diagram mod- which better addresses MR2 in comparison to the afore- els capture flow information and allow function elements mentioned method. Lu et al. (2017) also combined existing to be placed in their sequence of operation to depict how products to produce multi-functional products using matrix a product operates. However, they typically do not capture models. However, they used a different approach to model the parts and features that realise the functions, and are not the function of existing products. Instead of modelling prod- graphically well-suited to this due to the dense structures ucts using the functional decomposition approach by Pahl of dependency involved. Hence, block diagramming-based and Beitz (1996), they derive their function structures from models are not ideal to meet MR1, MR2 and MR3. Overall, detailed flows and parts. This increases the consistency of neither tree- nor block diagramming-based approaches are the product model which should make product comparison ideally suited to reflect the complexity of function-form rela- more effective (MR3). Liu et al. (2014) proposed a method tionships in a product. In comparison, matrices are very well for integrating products with interrelated functions. They suited to graphically represent the dense structures of rela- compared the functions of existing parts using a table, list- tionships between functions and parts/features, which allows ing the functions of products as the row headings and the existing design solutions to be comprehensively represented, products being compared as the column headings. The cor- extracted, compared and traced without specialised software. responding parts of each product that realise the function are These characteristics make a matrix-based product model recorded in the cell of the table. An advantage of this com- the most suitable basis for a function integration method. parison table format is that it enables more than one vari- Regarding the  methods themselves, the majority of ant to be compared. However, it cannot represent multiple function integration methods in literature simply merge all functions for a given part. As a result, the approach cannot high-level functions of existing products by comparing the accurately compare the function realisations across product corresponding low-level functions of existing products to variants, which is needed to determine the redesign activi- determine which parts to carry over into the new design. ties required for a new variant design (MR4). The method They do not capture design information at the features level does, however, consider conflicts between product functions which prevents them from identifying redesign activities at 1 3 Res Eng Design 1 3 Table 1 Assessment of function integration methods in literature with respect to requirements MR1-MR4 MR1: Determine low-level and MR2: Determine the physical interac- MR3: Ensure that product data is con- MR4: Systematically process the high-level functions of a design and tions between features of a design. sistently represented across variants, obtained product data to determine how link them to the parts and physical This information is needed to identify using similar function terminology. parts and specific features of parts can features. This is needed to identify the supporting features that help primary This is needed so that variant designs be carried over, removed and modi- aspects of a design that realise each features to realise a desired function can be directly compared for function fied from existing variants to generate high-level function. integration. a new variant design that provides a new desired combination of existing functions. Kang and Tang (2013) Partially met: Modelled low-level Partially met: Modelled interactions Partially met: Modelled the function Partially met: Systematically determined: functions and their relationship with between primary and supporting parts of a product from flows and function Parts to carry over. Briefly mentioned: parts. Grouped low-level into primary, decomposition. to merge to remove, to modify param- secondary and auxiliary chunks based eters on flow Kalyanasundaram and Partially met: Modelled low-level Partially met: Modelled the interaction Partially met: Modelled the function Partially met: Systematically determined: Lewis (2014) functions and their relationship with between primary parts only of a product from flows and function Parts to carry over. Briefly mentioned: parts. Grouped the low-level functions decomposition Parts to merge into basic, application and accessory functions Liu et al. (2014) Partially met: Modelled low-level func- Partially met: Modelled the interaction Partially met: Modelled the function Partially met: Systematically determined: tions and their relationship with the between primary parts only of a product from flows and function Parts to carry over. Briefly mentioned: parts decomposition to merge Lu et al. (2017) Partially met: Modelled low-level func- Partially met: Modelled the interaction Partially met: Modelled the function Partially met: Systematically determined: tions and their relationship with the between primary parts only of a product from flows and function Parts to carry over. Briefly mentioned: parts decomposition to merge, to remove Smith et al (2012) Not met: Modelled user requirements Partially met: Modelled the interaction Not met: Modelled the importance of Partially met: Systematically determined: and their relationship with parts between key primary parts considered user requirements using customer Parts to carry over. Briefly mentioned: only survey to elicit important parts. to modularise, to modify parameters Res Eng Design the level of specific modifications to parts. Overall, none of 3.1 Elements of the DDM product model the existing approaches fully address the requirements set out at the start of Sect. 2. This gap, addressed by the current The DDM is a matrix-based product model that represents a article, is summarised in Table 1. design in both functional and physical domains, in terms of functions, flows, parts, features, states and state transitions, as well the interactions among these elements. It provides 3 Detailed Design Model (DDM) enough detail to capture how all these elements and their interactions contribute to the design’s functionality in use. This section introduces a new product model called the The following product elements are included in the DDM: Detailed Design Model (DDM) which was developed to capture design information of existing product variants. Sec- – Function: In the DDM the concept of function focuses tion 4 will then detail how the information captured in this on what a product does as a physical artefact. Under this new model is used to support function integration. definition, functions enable the use of a product but do To demonstrate the DDM and the reverse engineering not describe the multitude of ways in which it could be procedure used to construct such a model, a BiC ballpoint used, which additionally depend on the user, the task to pen is used as an example. This product is complicated be performed, the use environment, and so on. Two types enough to illustrate all aspects of the model, while also of functions are distinguished in the DDM: being simple enough to explain in full detail. It is referred to here as the retracting pen. Variations of it are available – Operating function: A transformation in the state of from several manufacturers. The design allows the user to a product, that is associated with operation (use) of extend the ballpoint tip by pressing a button at the opposite the product. end of the barrel. The tip can then be retracted into the barrel – Technical function: A transformation process occur- by pressing a latch on the side of the barrel. An exploded ring when a flow (defined below) interacts with view depicting parts and features of the retracting pen is feature(s) of a design (also defined below). provided in Fig. 1. Before moving on to describe the DDM in detail using the – Flow: The input or output of a technical function. The retracting pen as an example, the next sub-section introduces model distinguishes three types of flow: key concepts and terminology used in the model. Clicker.Shaft Clicker.Plunger hammer Clicker.Latch Plunger.Plunger tip Plunger.Ink chamber connector Upper barrel.Tip Spring.Coil Upper barrel.Latch hole Ink Chamber.Chamber body Upper barrel.Merger Upper barrel.Upper clip Plastic nib.Ink chamber connector Plastic nib.Ink stopper Upper barrel.Lower clip Plastic nib.Ballpoint tip connector Ballpoint tip.Plastic nib connector Upper barrel.Body Ballpoint tip.Ball socket Ballpoint tip ball.Ball Lower barrel.Slot Lower barrel.Upper barrel grip Lower barrel.Lower grip Lower barrel.Ballpoint funnel Fig. 1 Parts and features of the retracting pen used in the running example 1 3 Res Eng Design – Material flow: Motion of matter. Can involve solid, – State: A set of partially-constrained connections (and liquid, or gas. related flows) that can change configuration (i.e. rela- – Energy flow: Doing mechanical work, or transferring tive motion can occur between the features and flow pro- the potential to do work. Energy flow can take many cesses can occur) when a product is operated. Two types forms such as potential, mechanical, electrical and of states are distinguished in the DDM: thermal. – Signal flow: Information, typically regarding the – Static state: A stable physical configuration. actual or desired status of a system, that is transmit- – Transition state: A temporary configuration involv - ted or received to and from another system. ing flow processes and relative motion of features, while a product variant is in process of changing – Product variant: A product that provides a unique com- from one static state to another. bination of features and operating functions. – Part: A discrete physical component used for pre-pro- All these elements of the DDM are required for the Adaptive duction of a product variant, that cannot be disassembled Redesign Method (ARM), that is to be described in Sect. 4. without physically damaging it. – Feature: A geometric segment of a part. 3.2 Procedure for modelling a product with the DDM – Connection between two features: A DDM representation of a product variant is developed in – Fully constrained connection (C): There are zero six steps, described below. degrees of freedom for relative motion between the two features. 3.2.1 Step 1. Model the product in CAD (or obtain – Partially constrained connection (P): At least one an existing CAD model) degree of motion is possible between the two fea- tures. The features may be in constant contact The first step is to model the existing variant using CAD or (allowing sliding, rolling, flexing etc.) or may only to obtain an existing model. Basing the analysis on a CAD be in contact when the product is in certain states model ensures that no physical elements of the product are (see below for definition). overlooked. It also provides a basis and nomenclature to reference specific features of each part, which is necessary for the Adaptive Redesign Method (ARM). The parts must Fig. 2 CAD model of the retracting pen upper barrel. The model tree contains the CAD features which form the physical features of the upper barrel as shown by the red arrows—these will be the basis of describing the part in the Detailed Design Model (DDM) 1 3 Res Eng Design be modelled with appropriate detail to capture the geometric 3.2.2 Step 2. Form the feature interaction matrix features. For instance, Fig. 2 shows how the Upper Barrel part of the retracting pen is decomposed into six features in A DDM of a product is represented as a matrix called the DDM matrix. An overview schematic of the DDM matrix the CAD model. Only geometric features of a part that physically realise is shown in Fig. 3. The CAD features that form the parts are used as the row and column headings for the top-left an operating function need to be modelled. This is because the aim of the ARM method (to be discussed in Sect. 4) is field of the DDM matrix, as shown for the retracting pen in Fig. 6. Features that physically interact with another feature to derive product variants by adapting existing features from two product variants to realise a desired new combination are indicated by the letter C or P in the corresponding cell: of operating functions. The method only currently considers product use functionality. For instance, it does not consider manufacturing and assembly processes required for the new design. Therefore, minor features such as rounds do not need to be modelled, except where important to realising an oper- ating function. In general, only 3D CAD features that are derived from a 2D sketch need be considered, because these CAD fea- tures generate the spatial geometry of a part. CAD features that only modify the spatial geometry of an existing CAD feature need not be modelled. This is to prevent repetitive referencing of the same physical feature in the DDM. For instance, considering Fig. 2, the Upper Barrel.Tip should be recognised as a feature in the DDM because this dome- shaped geometric feature is formed by connecting the sur- faces between two differently-sized 2D circles. Whereas the Upper Barrel.Tip Hole is not regarded as a feature for this Fig. 4 Fully constrained connection between the features Upper Bar- analysis because the hole feature only modifies the existing rel.Body (blue) and Lower Barrel.Slot (green) of the retracting pen. feature Upper Barrel.Tip. These features do not move relative to one another once the product is assembled Fig. 3 Overview of the fields in a DDM matrix, mapped to the corresponding steps in the DDM modelling procedure 1 3 Res Eng Design – C indicates feature connections that are fully-constrained. – Flows applied to a feature. For example, a flow of human For example, the connection between the Upper Barrel. energy and a human finger are applied to the Clicker.Tip Body and Lower Barrel.Slot of the retracting pen is fully- of the retracting pen to extend its ball point tip. Note that constrained because, as shown in Fig. 4, these two fea- only flows that are involved in operating the product need tures do not move relative to each other in the assembled be included. product. Therefore C is placed in cell S9 and, symmetri- – Flows caused by a feature. For instance, a flow of elastic cally, cell I19 of Fig. 6. energy released from the Spring.Coil is used to retract the – P indicates connections between features that are par- ballpoint tip of the retracting pen. Note that only flows tially constrained. An example of a partially constrained that involve modelled features need be included. connection occurs between the features Upper Barrel. – Flows occurring between features. For example, ink flows Tip and Clicker.Shaft. This connection is partially con- from the ink chamber, through the plastic nib, ballpoint strained because the Clicker.Shaft can slide through the socket and ball when the retracting pen is being operated hole of the Upper Barrel.Tip as shown in Fig. 5. Hence, for writing. the letter P is placed in the cells D20 and T4 of Fig. 6. Flows that only describe physical connections between fea- This differentiation between partially-constrained and fully- tures (e.g. “flow of force”) are not modelled, because they constrained connections is necessary to distinguish features are already captured in the feature-feature interactions sec- and interactions that are directly involved in realising a func- tion of the DDM matrix. tion (P) from those that provide support structures (C). Flows are listed in the DDM matrix headings immediately The modeller should physically operate each mechanism after the feature headings, as shown in Fig. 3. As indicated of the variant to identify all the possible feature-feature in the bullet points above, every flow interacts with at least interactions. This is recommended to avoid overlooking any one feature. In the DDM, each interaction between a flow feature-feature interactions which are not explicitly captured and a feature is described using a technical function descrip- in the CAD model. For example, when modelling the retract- tor to support consistent modelling. The technical function ing pen, it should be retracted and extended to observe which descriptors used for the ballpoint pen example are defined features interact with each other in each stable configuration, in Table 2. This is a subset of the list provided by Hirtz et al. and in the transition between configurations. All must be (2002).  For brevity we show only the terms necessary for included in the DDM matrix. modelling the pens and internet protocol (IP) cameras dis- cussed in this article. 3.2.3 Step 3. Identify flows and flow‑feature interactions Numbers are placed in the top-rightmost field and the middle-leftmost field of the DDM matrix to indicate the The next step of the DDM modelling procedure is to identify features responsible for each flow, and the type of technical and model flows and their interactions with the features. In function involved. For example, in Fig. 6, the numbers 11 the DDM, flows can be in the form of material, energy or and 33 both appear in cell AB8 to indicate that the feature signal as set out in Sect.  3.1. Three situations should be Ink Chamber. Chamber Body (in row 8) Guides (technical considered: function type 11) and also Contains (technical function type 33) the Material.Ink flow (in column AB). Note that unlike feature-feature connections, this relationship is directional— the feature or flow in the matrix row is the producer of the technical function while the feature or flow in the column is the receiver. 3.2.4 Step 4. Identify motions, states and operating functions Operating functions describe how a design can be mechani- cally operated. In the DDM, an operating function is defined in terms of an initial (static) state, an intermediate (transi- tion) state, and a subsequent (static) state. (The ARM will subsequently determine whether there are any operating functions that are dependent on other operating functions. Fig. 5 Partially constrained connection between the Upper barrel.Tip This will be explained in Sect. 4.2.1). The total number of and Clicker.Shaft of the retracting pen. The Clicker.Shaft can slide operating functions in a variant is determined by the physical through the hole of the Upper Barrel.Tip 1 3 Res Eng Design configurations it can be used in, which is in turn dependent the DDM matrix. Representing operating functions in terms on the arrangements of connections within the design. of three states has proven helpful for the reverse engineer- To identify operating functions of a variant, the possi- ing of complex motions to identify the parts, features and ble independent motions are identified by, firstly, physically flows involved when a product is operated. The three-states moving each partially-constrained connection one-at-a-time. approach has proved sufficient for all products modelled to Once the motions are identified, the state transitions gener - date and also, has the benefit of being possible to visualise in ated by each motion can be established. Two situations are a simple table format. However, it is recognised that a more common: (1) motions that occur when the user changes the elaborate representation might be necessary to efficiently product configuration from one static state into another, and describe some situations. (2) motions that are essentially continuous while operating Note how the modelling procedure outlined in this step the product. differs from a top-down identification of product functions In the running example, an example of the former type starting from considerations of how the product would be of motion occurs when the pen user pushes the clicker to used. The advantage of the bottom-up approach is that, extend the tip of the pen (see Fig. 5). Here, the transition while the possible functions of a device are subject to inter- state (the state of the pen during the motion) involves energy pretation, the motions and states possible within it can be input from the user and a certain set of partially-constrained unambiguously identified. Hence, following the procedure connections whose features are in relative motion. This tran- outlined in this section leads to a more objective model of sition state can be described as Ballpoint tip extending. It product functions than a top-down analysis. can only occur from an initial (static) state of Ballpoint tip retracted. When the transition is completed, the pen is left 3.2.5 Step 5. Link operating functions to feature in the subsequent (static) state of Ballpoint tip extended. In connections and flows the DDM, each combination of initial-transition-subsequent state is listed to define an operating function. The features The penultimate step of the DDM modelling procedure is and flows involved in each state are also identified. This to link the states of each operating function to the feature- is necessary because different features may be involved in feature and feature-flow interactions that are active in each operating functions that are complementary to each other. state. This is required by the ARM method to be described in For instance, although both the operating functions of the the next section, so that the features responsible for specific retracting pen To extend ballpoint tip and To retract ballpoint operating functions can be identified. tip contain the same static states: Ballpoint tip retracted and For each transition state, the modeller must identify the Ballpoint tip extended, it does not imply that their respective active flow processes and the active connections involved transition states Ballpoint tip extending and Ballpoint tip in the motion. An active connection is one in which relative retracting involve identical features. In this case, extending motion is occurring between the two features, or in which the ballpoint tip of the retracting pen involves applying force force transmission between the two features is necessary to to the Tip of the Clicker whereas retracting the ballpoint tip enable the motion. These flows and interactions are repre - of the pen involves applying force on the Latch which is sented in the rows of the transition states in the DDM matrix located on the side of the pen body. This example demon- by referencing the coordinates. Only the numerical coor- strates that the features involved in a transition state are not dinates (rows) are recorded. The alphabetical coordinates always identical to its reverse state. Each of these operating (columns) do not need to be recorded because the numerical functions and its three states are shown at the bottom of the coordinate is placed in the corresponding column. For exam- DDM matrix in Fig. 6. ple, in the Ballpoint tip extending state, a “human energy” An example of the continuous motion type is rolling the flow is being applied to the Clicker.Tip of the retracting pen ballpoint ball in its socket. In the DDM, this is viewed as a as shown in cell E25 of Fig. 6. Therefore 25 appears in col- transition state Ball rolling. It is only possible from a certain umn E of the Ballpoint tip extending row. initial (static) state Ballpoint tip extended and, when the Next, it is necessary to identify the unique connections motion finishes, leads to a subsequent (static) state which that occur in the initial and subsequent states. Unique con- is the same as the initial state. In this case, the three-state nections are those in which the two features are in direct combination defines the operating function To deposit ink. physical contact in that state, but not in the complement To summarise, the procedure for identifying operating state. For example, in the Ballpoint tip extended state of the functions is to first identify motions in the design, then to retracting pen, the Clicker.Latch is engaged with the Upper identify the initial, transition and subsequent states for each Barrel.Latch hole. This contact only occurs when the pen motion, and finally to denote this combination of product is extended and is not present when the pen is retracted or states as an operating function. The operating functions and in the transition state. Thus, in Fig. 6 the coordinates G21 their corresponding states are shown in the bottom part of 1 3 Res Eng Design 1 3 Res Eng Design ◂Fig. 6 DDM matrix of the retracting pen showing the relationship 4.1 ARM Phase I: Develop DDM for each variant between the features, flows and operating functions. The operating functions are composed of states. The features and flow interactions As input to the ARM, a DDM matrix must be formed for that occur in each state are referenced to the co-ordinates to model the each of the two product variants to be combined. Although relationship between the features, flows and operating functions this is quite time-consuming, each DDM matrix is a reuse- able resource that could be drawn upon in future each time a and U7 appear respectively in columns G and U in the row new variant is required. As additional variants are modelled, defining the state. a data library would be built up, broadening the possibili- ties for forming new variants without additional modelling 3.2.6 Step 6. Verify the product model effort. The DDM for the first pen variant to be used in the run- The final step of the DDM modelling procedure is to check ning example was already discussed and is shown in Fig. 6. that the DDM matrix has been correctly completed. The fol- Fig. 8 shows the DDM matrix for the second variant, namely lowing checks may be helpful to reveal errors: the basic pen. Note how the basic pen has a different set of operating functions than the retracting design—the only 1. Check that the feature-feature portion of the DDM common operating function between the two pens is To matrix is diagonally symmetrical. deposit ink. It is important that technical function descrip- 2. Check that each feature and flow listed in the DDM is tors are used consistently when modelling the different shown to interact with at least one other feature or flow. product variants, so that the variants can be compared. For Features with empty rows or columns should be revisited example, noting that the number 6 is used to describe import to check that no interactions were missed, and if not, to functions in the retracting pen DDM, the same number is reconsider whether the feature is necessary to include in used to describe this type of interaction in the basic pen the model. DDM. 3. Review any CAD features that were not included at the beginning of the modelling process, and confirm they 4.2 ARM Phase II: Identify adaptive redesign steps are not involved in any identified operating function. In the method, the variant to be adapted/redesigned is described as the base variant. The variant from which addi- 4 Adaptive Redesign Method (ARM) tional operating functions are to be drawn is described as the source variant. Parts and features from the source variant Having completed description of the Detailed Design Model that realise a desirable operating function are to be inte- and modelling procedure, we now move on to the Adaptive grated into the base variant. For the running example, the Redesign Method (ARM) itself. To support description of basic pen is chosen as the base variant while the retracting the ARM, we return to the ballpoint pen example and con- pen (offering the desired retraction and extension functional- sider the situation in which the To retract and To extend ity) is chosen as the source variant. operating functions of the retracting pen are to be carried The second phase of the method involves systematic anal- across into another pen design, referred to here as the basic ysis of the DDM matrices for these two variants to identify pen. As shown in Fig. 8, the basic pen has a hexagonal bar- the features of the base variant that will need to be removed, rel which mimics the shape of a pencil and a cap which those that will need to be carried across from the source covers the ballpoint tip. More detail is provided in the Sup- variant, and which parts need to be redesigned to generate plementary Materials. The objective of the running example the new variant design. The phase comprises eight steps, is to combine these two variants to produce a unique new described in the next subsections. design, i.e. a retractable pen with hexagonal barrel. This case is deliberately simple to allow the new method to be 4.2.1 Step 1: Categorise operating functions in the base explained in full depth within the space constraints of this variant and source variant article. In Sect. 5, application of the method to more com- plex products is discussed to demonstrate that it is scaleable The set of desirable operating functions for a new product and to indicate the effort involved. variant depends on market needs, product strategy and other The ARM comprises of three phases, which are depicted factors. Identifying that set is beyond the scope of this arti- in Fig. 7 and detailed in the next subsections. cle. For the worked example, the desired operating functions of the new variant are: To extend ballpoint tip; To retract ballpoint tip; and To deposit ink. 1 3 Res Eng Design Table 2 Descriptors used retracting pen, it would therefore require To deposit ink to Code Technical for technical functions when be categorised in this way as well. function modelling the ballpoint pens type The modeller should also check for redundancy or other and IP cameras conflicts among the functions that are intended for the new 6 Import variant design. In the running example, considering that the 7 Export To retract function of the source variant is desired in the new 8 Transfer variant, the modeller can observe that two operating func- 10 Transmit tions of the base variant, namely To cover ballpoint tip and 11 Guide To uncover ballpoint tip (that are realised by the cap of the 12 Translate pen), will no longer be necessary and therefore are labelled 13 Rotate as Uo (Undesired operating function) in the base variant 15 Couple DDM matrix as shown in Fig. 8. 33 Contain 44 Secure 4.2.2 Step 2 Identify undesired features of the base variant (to be removed) This step proceeds as follows: 1. Identify features of the base variant that are involved in the previously-identified undesired operating functions. These can be readily identified by tracing the DDM matrix dependencies from all three states involved in that operating function. 2. Examine the DDM matrix columns for each of these undesired features to determine whether they are also involved in any of the previously-identified desired oper - ating functions. If not, the feature should be classified as undesired. To illustrate, since the To clip operating function is to be removed from the basic pen, the Cap.Lower clip inner face must be removed because it is not involved in any other Fig. 7 The Adaptive Redesign Method (ARM) comprises three desired operating functions, as can be identified by reading phases down column L of the operating functions section of the DDM matrix in Fig. 8. On the other hand, the Barrel.Body In this step of the ARM, operating functions are classi- feature cannot be removed because column G of Fig. 8 con- fied as follows: tains entries relating the Barrel.Body to the desired function To deposit ink. – Desired operating functions. These are needed in the new The base variant DDM matrix is annotated by adding variant. They are labelled as Do in the bottom sections Uf (Undesired feature) next to the row and column of each of the source and base variant DDM matrices of Figs. 6 undesired feature, to indicate that their interactions are to be and 8. ignored later in the analysis. In Fig. 8 these are highlighted – Undesired operating functions. These are not required in dark pink. To provide another example, these are also in the new variant. These are labelled Uo in the DDM identified in Fig.  6 (although identifying undesired features matrices of Figs. 6 and 8. for the source variant is not strictly required for the method). For each desired operating function, the modeller must 4.2.3 Step 3. Identify undesired supporting features identify whether it requires any prerequisite operating func- of the base variant’s undesired features (to be tion, and if so, classify it as also being desired. For exam- removed) ple, the To deposit ink operating function of the retracting pen requires the pen to be extended, which means that the Features of the base variant whose only purpose is to sup- operating function To extend must be executed beforehand. port undesired features are to be classified as undesired If To deposit ink was a desired operating function of the supporting features. Such features are identified from their 1 3 Res Eng Design connections to the features to be removed, as shown in the other features that interact with the Spring.Coil, but these base variant DDM matrix. These supporting features may be need not be classified as supporting features because they from the same part or from another part as the features to be were already classified as desired features (as labelled Df removed. Continuing the previous example, the Cap.Lower and highlighted in blue). Supporting features for the desired clip inner face was identified as an undesired feature of the operating functions are marked with Dsf and highlighted in base variant to be removed. Column L of the DDM matrix light blue in the DDM matrix of the source variant. These in Fig. 8 shows that the feature has two supporting features: are to be carried over into the base variant. the Barrel.Body and Cap.Lower clip outer face. The Bar- rel.Body cannot be removed, since it is involved in desired 4.2.6 Step 6. Determine the functional similarity functions. However, the Cap.Lower clip outer face can and between each desired/desired supporting feature should be removed, because tracing its dependencies in the of the source variant and each desired/desired DDM indicates that it is not supporting any features required supporting feature of the base variant for any desired operating function. For each undesired supporting feature that is identified for The next step is to complete a pairwise comparison of the removal, the matrix should be checked again to ensure that features across the two variants and compute their similar- no additional features have become redundant, in which case ity. This is required so that, in Step 7, it will be possible to those are to be removed as well (this check is repeated until determine which features need to be drawn from each of the no more features are candidates for removal). two existing variants to create the new variant. Once identified, all undesired supporting features are Each part of the source variant that contains at least one annotated with Usf in the base variant DDM matrix. In Fig. 8 desired feature or desired supporting feature (as identified these are highlighted in light pink. To provide another exam- in the previous step) is compared to each of the desired fea- ple, such features are also identie fi d in Fig.  6 (although iden- tures and desired supporting features of the base variant. A tifying undesired supporting features for the source variant comparison matrix is formed with these base variant fea- is not strictly required for the method) tures in the column headings and the source variant features in the row headings, as shown in Fig. 10. Empty columns 4.2.4 Step 4. Identify desired features of the two variants represent base variant features that were identified as unde- sired or undesired supporting features (Uf or Usf) in Steps The next step is to identify desired features of the source 2 and 3. Similarly, empty rows represent source variant fea- variant, which are features that contribute to realising any of tures that are not desired. For each of the non-empty cells the desired operating functions. As before, this is achieved in the matrix, the flow interactions and partially-constrained by tracing the numbers in the rows of the desired operating connections of the corresponding pair of features are next functions located in the bottom field of the source variant compared (by analysing the two DDM matrices) to compute DDM matrix. Recall from Sect.  3.2.5 that these numbers the degree of functional similarity between that pair of fea- indicate the features required for the function. tures. Fully-constrained connections between features are To distinguish desired features in the source variant DDM not included in this comparison since they provide structural matrix they are annotated Df. The flow of dependencies from support but are not directly involved in realising operating the desired operating functions through to the desired fea- functions. Functional similarity is defined here as the total tures is highlighted in blue in Fig. 6. number of interactions that meet the above criteria and are common to both features, divided by the total number of 4.2.5 Step 5. Identify desired supporting features interactions that meet the criteria. The result is interpreted of the two variants’ desired features as follows: Supporting features that are necessary to the working of – 100% indicates that the two features are functionally carried-across features also need to be carried over to the identical. new variant design. They can be identified by reading down – 0% indicates that the two features are functionally dis- the columns of the desired features in the source variant joint. DDM matrix. For example, reading down column R of – Greater than 0% and less than 100% indicates that the Fig. 6 shows that the Lower barrel. Slot (in row 9) of the existing feature in the base variant realises some, but not retracting pen is a supporting feature for the desired fea- all of the functions of the source variant feature. The two ture Spring.Coil. This can be explained by considering features are functionally similar. Fig. 9, which shows how the Lower barrel.Slot keeps one end of the Spring.Coil in place during the retract/extend To illustrate, consider the comparison between the Ink cham- state. The source variant DDM matrix also reveals several ber.Chamber body features of the two variants. Comparing 1 3 Res Eng Design 1 3 Res Eng Design ◂Fig. 8 DDM matrix of the basic pen (the base variant in the running the base variant, the entire part of the source variant is example). The dark pink backgrounds indicate features and functions to be carried over into the new variant. For example, the that are undesired in the new variant (as described in Sect. 4.2.2); the part Clicker of the retracting pen will be used in the new light pink backgrounds indicate features whose only purpose is to variant design because no parts of the base variant (basic support those features (as described in Sect.  4.2.3). The blue high- lights indicate features and functions that are desired. The light blue pen) have features with any functional similarity to it. highlights represent features and functions that support the desired This is identified by noting that in Fig.  10 all the entries features and functions in the new variant design are 0% for every row describing features of the Clicker. The same is true for the Plunger and Spring. the DDMs of Figs. 6 and 8 reveals that these features par- – If the desired feature of the source variant has 100% in ticipate in two identical technical functions with respect to one or more of the cells, when reading across its row, the same flows, namely To store (33) Ink and To channel then the base variant feature already offers the desired (11) Ink. Figure 8 shows that the feature of the basic pen has functionality. This means that those base variant features no partially-constrained connections to other features of that are to be retained when creating the new variant design. design, while Fig. 6 shows that the feature of the retracting An example of this can be found between the Ballpoint pen has one partially-constrained connection, namely to the tip ball.Ball and Ballpoint tip.Socket features of the two Spring.Coil. pens. In this case the feature of the source variant (retracting – If the desired feature of the source variant is function- pen) has three interactions in total. Two of them also appear ally disjoint from all features of the base variant, i.e. all in the feature of the base variant being compared, i.e. the two entries across the row are 0%, then that source variant flow interactions, while one does not. This leads to a similar - feature must be carried over into the base variant. This ity score of 2∕3 = 67% , so the two features are classified as is done by modifying the part of the base variant that is functionally similar. Note the importance of comparing tech- functionally most similar to the part of the source vari- nical functions in the flows part of the DDM, which allows ant that contains the desired feature being carried across. the more accurate discernment of functional similarity of Functional similarity between two parts is calculated as the two features from different variants. The required accu- the average of the functional similarity of all pairwise racy would not be possible if only the physical connections comparisons of their features. For example, the Upper to other parts of the respective variants were considered. barrel. Tip and Upper barrel. Latch hole features of the The technical functions and flows modelled in the DDM retracting pen will be carried over by adding them to the matrices allow features performing similar functions, even Barrel of the basic pen because the Upper barrel of the across variants that have slightly different architectures to retracting design (from which the features are drawn) be compared. is the most functionally similar part to the Barrel of the For functionally similar feature pairs, if the base variant basic pen design. feature contributes to all the desired technical functions of – If the source variant feature is functionally similar to the source variant feature, a ‘ ’ sign is placed alongside one or more base variant features, and is not function- the similarity score. On the other hand, if the base variant ally identical to any feature, its row contains at least one feature does not meet all the desired technical functions of entry > 0% and no entries = 100%. In this case, it is nec- the source variant feature, the matrix cell is denoted with ‘+’ essary to visually/geometrically compare the feature of to indicate that additional technical functions would need the source variant against each of the functionally most to be met by the base variant feature if it were to realise the similar features of the base variant to determine what technical functions of that source variant feature. changes to the base variant feature(s) might be needed to produce the desired functionality of the source variant 4.2.7 Step 7. Determine which features to carry feature. This comparison requires design judgement. For across from the source variant into the new variant example, the Ink chamber. Chamber body of the basic pen needs to be geometrically compared to the Ink cham- Recall that the base variant is the baseline design to be ber. Chamber body of the retracting pen (source variant). changed when creating the new variant. To determine which This is because the ‘+’ sign in front of the 67% (calcu- parts/features and supporting features of the source variant lated in Step 6) indicates that the basic pen needs fulfil a are to be carried across to the new variant design, the rows desired interaction to realise the operating function. This of the comparison matrix are next worked through system- desired interaction happens to be with the Spring.Coil atically. Each part is considered one-at-a-time as follows: which can be traced by comparing the DDM of the two pens as discussed in Step 6. In this example, the exist- – If all desired/desired supporting features of the source ing geometry of the basic Ink chamber.Chamber body variant part are functionally disjoint from all features of is identical to that of the retracting pen Ink chamber. 1 3 Res Eng Design Fig. 9 An example of a sup- porting feature for the extend- ing and retracting ballpoint tip operating function of the retracting pen Fig. 10 The comparison matrix between the basic pen (base variant) and the retracting pen (source variant) is used to identify the reusable fea- tures of the base variant, which features of the source variant to add to the new variant and which features of the base variant to redesign Chamber body and is therefore capable of accommodat- – If the desired feature of the source variant has < 0% in ing the Spring.Coil. Hence, no changes are required and one or more cells when reading across its row, then it also this base variant feature can be retained. However, if the indicates that the base variant feature already provides existing feature of the base variant cannot geometrically the desired functionality of the source variant feature. In fulfil this interaction then it will need to be geometrically this case, the base variant feature is also retained. Note modified. the percentage shown in the matrix cell may not neces- 1 3 Res Eng Design sarily be 100% if the features being compared have dif- variant, redesign of existing parts of the base variant are ferent connections to other features in their respective required. An example of two steps from the basic pen’s bar- variants. rel being redesigned is provided in Fig. 12. Features of the base variant which do not require feature modification can be 4.2.8 Step 8: Compile list of redesign activities to create reused in the new variant design, although some adjustment the new variant design to dimensions may be required. Figure 13 shows the completed design of the new pencil- Finally, the results of the previous steps are compiled to form shaped pen with the retractable function, that was gener- a list of redesign activities that will be needed to form the ated by following the redesign steps laid out in the redesign new variant design as shown in Fig. 11. activities table. The list shows what redesign activities are needed in terms of operations on features and parts. It does not show the geometric and dimensional details, such as where on a 5 Application cases part a feature should be added and what dimensional adjust- ments will be necessary. These details are usually quite obvi- As previously mentioned, the ballpoint pens example was ous when viewing the two parts for each step, as illustrated chosen to illustrate the DDM and ARM because it is sim- in the next subsection. ple enough to present the approaches in full detail. To also illustrate that the new approaches can support modelling and 4.3 ARM phase III: execute adaptive redesign steps redesign of more complex products, this section discusses to generate the new variant design their application to a pair of Foscam IP cameras (security cameras). The final phase of the method is for the human designer/ The cameras to be discussed are from a product range in method user to execute the identified redesign activities to which different variants offer different functions. Depending form the new variant design on CAD. Firstly, undesired fea- on the variant, these functions include motorised panning, tures of the base variant are removed by removing CAD motorised tilting, recording, motion detection, voice detec- features from the CAD model. Before a CAD feature is tion, audio output, and single press calling. In this section, removed, it is important to check that there are no depend- the motorised panning function is integrated into a simple ent sketches and features built upon it in the model tree that IP camera (here called the fixed camera) that is capable of are desired to be retained. Secondly, features from the source being manually tilting upwards and downwards. The motor- variant that realise the desired operating function are added ised panning function was sourced from a motorised IP to the base variant. To integrate these features to the base Fig. 11 The generated list of redesign activities needed to derive the new variant design 1 3 Res Eng Design Fig. 12 A series of steps showing how retracting pen Upper barrel.Tip feature, Upper barrel.Latch hole feature and Clicker part are added to the barrel of the basic pen by executing Task 23 and Task 24, respectively, from Fig. 11 5.1 Application of the DDM modelling procedure to the two IP cameras The detailed design modelling procedure was applied to generate DDM matrices for the two product variants, as shown in Fig.  15. More detail is provided in the Supple- mentary Materials. In overview, the DDM of the PT camera comprises 37 parts, 157 features with 155 interactions, 59 technical functions, and 7 operating functions. Of the seven Fig. 13 CAD model of the new pen design which is pencil-shaped with functions to extend and retract the  ballpoint tip. More detail is operating functions, the automatic panning function will be provided in the Supplementary Materials carried across from the PT camera into the fixed camera. The DDM revealed that this operating function requires 25 camera that can be panned and tilted using software control features to realise it. The equivalent information for the fixed (here called the PT camera). position IP camera is provided in Fig. 15. In comparison to The PT camera (the more complex variant) contains 37 the ballpoint pens case study, there are energy and signal parts, and as can be seen in Fig. 14, its mechanical assem- flows in both camera variants. bly is representative of many moderately-complex consumer The IP cameras contain various electronic components products. More detail for both cameras is provided in the that were not modelled in detail. This is because this article Supplementary Material. focuses on mechanical considerations. Geometric features relating only to part manufacturing processes were also not 1 3 Res Eng Design generate the design activities table in about 1.5 h. An addi- tional 5 h were then required to follow the steps by complet- ing the new variant design in CAD—but this would be nec- essary whether or not the new method was used. The effort would have been substantially less if the straightforward matrix tracing steps and calculations were automated. This indicates that the method, if implemented in special-purpose software, could potentially help to identify redesign activi- ties for even quite complex products fairly rapidly, provided that existing CAD models were available. Reflecting on the ballpoint pens example and the more complex IP cameras analysis, the latter added insight by confirming that the ARM could be used to compare parts having substantially different geometric features across the two designs, and still identify redesign activities at the parts level for the new design. It was also observed that the effort required for the first phase of the approach (DDM genera- tion) and the n fi al phase (executing redesign steps) increased signic fi antly with the complexity of the product. At the same time, the majority of this effort (and about 75% of the total effort according to the estimates above) was devoted to CAD activities that would need to be done to generate the variants, regardless of whether the method was used in support of the redesign process. Put another way, the overhead of using the method (without any specialised software) appears to be approximately 33%. Overall the cameras analysis provided a measure of confidence in the DDM and ARM, although more studies will be required to substantiate the benefits set out in Sect. 1.1. Fig. 14 Exploded view of the motorised PT Camera to  indicate its level of mechanical complexity. More detail is provided in the Sup- plementary Materials 5.3 Initial assessment of the useability of the DDM and ARM modelled in detail because, to recap, this article focuses on operating functions associated with product use. Noting that the DDM and ARM approaches are quite intri- Overall, this application confirmed that the DDM mod- cate, we sought to assess whether they could be applied by elling procedure can be applied to products that are more a person other than the authors. In an initial assessment, an complex than the ballpoint pens discussed earlier. The matri- undergraduate mechanical engineering student was tasked to ces generated for the IP cameras are rather large, but also apply the emerging method to two cases. In the first case, the extremely sparse. The majority of interactions are fully-con- student applied the method to implement a sheet-fed scan- strained connections between features of the same part (i.e. ning function into a budget inkjet printer having a single- within the clusters shown in Fig. 15). In total, generating sheet scanner. In the second case study, the student applied the DDMs for the two camera variants required about 8 h of the method to implement an automatic juicing function into effort. Additionally, about 24 h was required for the CAD a simple hand-operated juicer. While not a comprehensive modelling of the two variants, but this would not be needed evaluation, these cases along with the pen and camera cases for an application in an industrial context where CAD mod- provided additional confidence that the method can work els would already be available. with a variety of products and also, that it is useable. The application cases also highlighted that the method 5.2 Application of the Adaptive Redesign Method relies on the user to detect whether there are conflicts for function integration between the two IP between operating functions across variants being integrated cameras (this was subsequently included in the method description, see Sect. 4.2.1). A conflict occurs when more than one oper - Once the DDM matrices were completed, by following the ating function of the new variant design addresses the same steps of the Adaptive Redesign Method, it was possible to task from a user’s perspective. For example, the ARM does 1 3 Res Eng Design Fig. 15 Overview of the matrices generated when applying the Detailed Design Model and Adaptive Redesign Method for function integration in the IP cameras study. Detail is provided in the Supplementary Materials not directly identify that the cap of the basic pen, which is 2. The information captured by the model is at an appropri- used to protect the ballpoint tip, is not needed when the ball- ate level of detail to support the adaptive redesign activi- point tip of the basic pen is made retractable in the new vari- ties needed for function integration—namely adding, ant. The underpinning reason is that the DDM deliberately removing, redesigning and carrying over features and only captures what the operating functions are, not what they parts to achieve a desired new combination of existing are used for, to reduce subjectivity in product modelling. operating functions. If a conflict is detected by the method user while perform- 3. The method can be applied to different types of products ing a function integration, then the features (and potentially and those with moderate levels of mechanical complex- parts) related to the redundant operating function should ity. be removed from the base variant. If not identified early 4. The systematic steps of the method are possible to per- on, these conflicts become obvious towards the end of the form by different users (not only the researchers). redesign phase while the physical form of the new design is being manipulated in CAD. In such cases, it is possible to return to steps 2 and 3 of the ARM to identify the features 6 Discussion and parts that should be removed. Several iterations among steps of the method may be necessary to finalise the design.6.1 Recap of contributions 5.4 Summary To summarise, this article offers the following contributions. Firstly, the DDM and ARM provide means to systemati- While a comprehensive evaluation of the method with prac- cally extract selected operating functions and their physi- titioners has not yet been attempted, applications by differ - cal realisations from existing product designs and integrate ent researchers to four different types of product (pens, IP them into other existing product variants. This is achieved cameras, printers and juicers) build confidence that: by modelling the parts of the products at the geometric level using CAD features and capturing their interactions with 1. The DDM provides a basis for systematically identifying other features, flows, states and state transitions to realise and modelling functions, flows, parts, features, states operating functions. Function integration is not compre- and interactions in existing product designs. hensively supported by prior methods, that are discussed in 1 3 Res Eng Design Sect. 2.2, because as summarised in Table 1 none analyse redundant functionality in the new variant design. A second a product down to the features, states and state transition limitation of the DDM and ARM in the functional domain levels. is that they do not consider the relationships between the Secondly, the Adaptive Redesign Method (ARM) sup- technical functions involved in each operating function. In ports identification of redesign activities required to derive a particular, the sequence of operation for the technical func- desired new variant design. In particular, it helps to identify tions is not represented and, if it is important, it will need to the redesign activities for removing unnecessary operating be considered separately by a designer using the approach. functions and their physical realisations, as well as the rede- Other limitations concern the physical domain. Firstly, sign activities required for modifying an existing part. This the features listed in the DDM matrix depend on how each is achieved by analysing and comparing data at the features physical part is modelled with CAD and since parts can be level of the DDM for the two product variants under con- modelled in different ways, this list may vary. However, sideration. This level of detail is not offered by previous because the ARM outputs a redesign activities list in terms function integration methods discussed in Sect. 2.2. of the features of the input CAD models, the utility of the Thirdly, the two approaches consider not only the primary method is not greatly dependent on CAD modelling choices. features but also the supporting features for each operat- Secondly, the DDM does not consider the spatial relation- ing function. This is achieved by distinguishing partially- ships and interface constraints between features and between constrained interactions (involving primary features) from parts. As a result, the geometry of features from the source fully constrained interactions (involving supporting fea- variant that are being integrated into a base variant part tures). Considering the latter allows identification of sup- may need to be scaled to ensure physical fit with other parts porting features and supporting parts that might need to of the base variant. These parametric adjustments are not also be modified when primary features are carried over or accounted for in this article. Another constraint-related limi- removed. Existing function integration methods do not com- tation is that the ARM assumes that all existing parts of a prehensively consider supporting features. product are possible to redesign. However, in practice some Finally, the DDM provides a more objective approach to parts of a product cannot be easily modified, e.g. because modelling the high-level functions of existing products by they are purchased from a supplier or form part of a product forming operating function descriptions based on the possi- platform. Future work could incorporate such constraints in ble physical configurations of a product. In other words, the the method. modelling procedure is based on describing what a product Regarding the relationships between functional and can do instead of what a product can be used for. Low-level physical domains, the case studies reported in this article technical functions are then identified based on the interac- confirmed that these relationships are captured by the DDM tion between features and flows based on a set of vocabu- in sufficient detail for the function integration task. However, lary by Hirtz et al (2002). As previously stated in literature, future applications may reveal opportunities for improve- identifying function descriptors based on flows is beneficial ment in this area as well. to reduce subjectivity of functional modelling (Gietka et al 2002). 6.3 Additional areas for future work 6.2 Limitations By considering the limitations above and also by considering the PSI analysis approach developed by Reich and Subrah- In this section, some limitations will be discussed with manian (2022), three additional areas of future work have respect to functional and physical domains of the DDM and been identified. ARM. Firstly, we hope to undertake empirical studies in compa- Some limitations concern mainly the functional domain. nies with product families to explore how function integra- Firstly, the DDM does not consider what the user uses the tion is done in practice. Additional application studies are product for, i.e. use case functions. This was a deliberate also needed to test the practicality of the method and to test choice to reduce subjectivity in the modelling and analysis. it against the expected benefits set out in Sect 1.1. However as a result, the ARM is unable to identify repeat- Secondly, the method could be extended to account for ing use cases between different operating functions for the different contexts of use. For instance, in the context of prod- new variant design. Recall from Sect. 5.2, that for the ball- uct families there are multiple variants with different operat- point pens redesign, the ARM did not detect that the cap ing functions and architectures available for integration. In of the basic pen was not needed once that pen was made a product family context, the scope of the method could be retractable. Therefore, future work is needed to model the expanded to determine which variant to source each desired relationship between the use case functions and operating operating function from, and to determine the best sequence functions of existing products to more systematically avoid of implementing multiple functions to avoid redesigning the 1 3 Res Eng Design sharing their reflections on the methods reported here. We appreci - same parts multiple times. Also noting that a design is influ- ate the constructive comments provided by the anonymous reviewers enced by many considerations beyond the use of a product, and the editor, Yoram Reich. All CAD models and drawings are par- and hence that multiple reference frames are possible for tial approximations of products by BiC (the ballpoint pens) and Fos- design analysis, the methods reported in this article could cam (the cameras) drawn for the purpose of illustrating the approaches presented in this article. potentially be expanded to support product modelling and integration from the viewpoints of other lifecycle phases Funding Open Access funding enabled and organized by CAUL and apart from product use, such as assembly, inspection and its Member Institutions. repair, etc. To achieve this would require expanding the DDM to map design elements onto considerations in differ - Open Access This article is licensed under a Creative Commons ent lifecycle phases. Attribution 4.0 International License, which permits use, sharing, adap- tation, distribution and reproduction in any medium or format, as long Finally, future work could investigate opportunities to as you give appropriate credit to the original author(s) and the source, reduce the data requirements and effort-intensiveness of provide a link to the Creative Commons licence, and indicate if changes the DDM and ARM. Data requirements might be reduced were made. The images or other third party material in this article are by developing an initial assessment approach to determine included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the parts of a product that need to be modelled down to the article’s Creative Commons licence and your intended use is not the feature level and those that only need to be modelled at permitted by statutory regulation or exceeds the permitted use, you will the parts level for instance, because they are not involved need to obtain permission directly from the copyright holder. To view a in any function expected to change, or because they can- copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . not be changed—for instance because they are off-the-shelf parts. Effort-intensiveness could be reduced by automating some of the steps in the DDM modelling method and the References ARM to reduce the overall analysis time. Automatable steps Andreasen MM (1980) Machine design methods based on a systematic include (1) extracting features and their interactions from the approach–contribution to a design theory (in Danish). 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Journal

Research in Engineering DesignSpringer Journals

Published: Apr 1, 2023

Keywords: Product variant design; Function integration; Product modelling; Reverse engineering; Mechanical assemblies; Design Structure Matrix; CAD; Detailed Design Model; Adaptive Redesign Method

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