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Simulation study on evolutionary cycle to cycle time control of exposure controlled projection lithography

Simulation study on evolutionary cycle to cycle time control of exposure controlled projection... PurposeExposure controlled projection lithography (ECPL) is an additive manufacturing process based on controlled UV photopolymerization. This paper aims to explore an advanced closed-loop control methodology to ECPL.Design/methodology/approachThis paper proposes an evolutionary cycle to cycle (EC2C) control method, and started with a reduced order EC2C time control to control only the exposure time for given DMD bitmaps, which correspond to target 3D part cross-sections. A preliminary EC2C time control scheme was developed and followed by two types of EC2C time controllers based on two different parameter estimation methods, recursive least squares and L1 norm minimization (L1Min). Both algorithms were in an exponential weighted form, resulting in EWRLS and EWL1Min, to weight more on recent data to reflect the current process dynamics.FindingsEWRLS was found to outperform EWL1Min in terms of computation speed and stability. The simulation study demonstrated that the proposed EC2C time control method was capable of adaptively tracking the ECPL process dynamics and updating online the model parameters with real-time measurements. It could control perfectly the exposure time for each bitmap, achieving the desired height for each layer and resulting in a total cured height conforming to the target 3D part height.Research limitations/implicationsThe accuracy of EC2C time control method relies heavily on fast and accurate measurement, and this research assumes availability of an adequate real-time metrology. Measurement errors are not considered in this paper and will be explored in future. Only simulation study was performed without physical experiments to verify the EC2C controller.Practical implicationsFor implementation, a real-time measurement system needs to be developed and the EC2C control software needs to be programmed and interfaced with the physical system.Originality/valueIt concludes that EC2C control method is very promising for a physical implementation, and could be extended for the development of a more comprehensive closed-loop controller for both exposure time and intensity to improve the ECPL process precision and robustness. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Rapid Prototyping Journal Emerald Publishing

Simulation study on evolutionary cycle to cycle time control of exposure controlled projection lithography

Rapid Prototyping Journal , Volume 22 (3): 9 – Apr 18, 2016

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References (13)

Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
1355-2546
DOI
10.1108/RPJ-01-2015-0008
Publisher site
See Article on Publisher Site

Abstract

PurposeExposure controlled projection lithography (ECPL) is an additive manufacturing process based on controlled UV photopolymerization. This paper aims to explore an advanced closed-loop control methodology to ECPL.Design/methodology/approachThis paper proposes an evolutionary cycle to cycle (EC2C) control method, and started with a reduced order EC2C time control to control only the exposure time for given DMD bitmaps, which correspond to target 3D part cross-sections. A preliminary EC2C time control scheme was developed and followed by two types of EC2C time controllers based on two different parameter estimation methods, recursive least squares and L1 norm minimization (L1Min). Both algorithms were in an exponential weighted form, resulting in EWRLS and EWL1Min, to weight more on recent data to reflect the current process dynamics.FindingsEWRLS was found to outperform EWL1Min in terms of computation speed and stability. The simulation study demonstrated that the proposed EC2C time control method was capable of adaptively tracking the ECPL process dynamics and updating online the model parameters with real-time measurements. It could control perfectly the exposure time for each bitmap, achieving the desired height for each layer and resulting in a total cured height conforming to the target 3D part height.Research limitations/implicationsThe accuracy of EC2C time control method relies heavily on fast and accurate measurement, and this research assumes availability of an adequate real-time metrology. Measurement errors are not considered in this paper and will be explored in future. Only simulation study was performed without physical experiments to verify the EC2C controller.Practical implicationsFor implementation, a real-time measurement system needs to be developed and the EC2C control software needs to be programmed and interfaced with the physical system.Originality/valueIt concludes that EC2C control method is very promising for a physical implementation, and could be extended for the development of a more comprehensive closed-loop controller for both exposure time and intensity to improve the ECPL process precision and robustness.

Journal

Rapid Prototyping JournalEmerald Publishing

Published: Apr 18, 2016

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