Research article
Improving the capability of a redundant robotic
cell for cast parts finishing
Laurent Sabourin, Vincent Robin, Grigore Gogu and Jean-Michel Fauconnier
Laboratory of Mechanics and Engineering, Clermont Universite
´
, Clermont-Ferrand, France
Abstract
Purpose – Precision aluminium moulding makes possible the production of large-size, complex and high-technology cast parts. However, industrial
requirements linked to economic and safety reasons call into question the manual performance of finishing operations. The purpose of this paper is to
enhance industrial robot applications by using vision and redundancy optimization to improve their capability.
Design/methodology/approach – After having presented the concepts associated with machine and kinematics capability, the paper first describes
the finishing constraints related to the process and the study of inaccuracy factors. Adjusting the trajectory by vision minimizes some inaccuracy factors
but does not take into account the structure loading. Therefore, the authors present the optimization, kinematics and precision criteria as well as the
multi-objective method developed by integrating the loading aspect. This method has been verified by simulation and the results validated on industrial
parts.
Findings – The paper presents an improvement in machine capacities based on redundancy and an optical 3D measurement system. It develops the
strategies, sensors and cell architecture to perform finishing operations.
Research limitations/implications – The finishing of high-technology structural cast parts requires the completion of the machining and polishing
processes adapted to each part. The choice was made to develop a robotic cell dedicated to integrating specific features, in contrast to machine tools.
Practical implications – This study was carried out within the framework of the Eureka SANDCAST project in cooperation with the Alcan group,
specialized in high-technology moulded aluminum parts.
Originality/value – The paper presents an approach to robotic cell capability improvement. The robotic cell is dedicated to finishing operations, by
machining and polishing large cast aluminum parts; the objectives are to improve machine capability and kinematics capacity with vision and
redundancy management.
Keywords Industrial robot, Foundry engineering, Metals, Polishing, Kinematics, Machining, Optical 3D measurement system,
Kinematics redundancy, Foundry parts
Paper type Research paper
Introduction
The production of high-technology structural parts (thin
walls, veins, boxes, etc.) in aluminum foundry requires highly
specialized knowledge, which positions the SFU Company,
part of Alcan group, among only five manufacturers in the
world making such parts. The applications relate mainly to
aeronautical, energy and transport activities. Technically, cast
parts finishing is a delicate operation due to dimensional
variability related to the process and the difficulties in
accessing some surfaces. This operation is currently carried
out manually. Its automation, mainly for economic and safety
reasons, requires the definition of a robotized finishing cell
performing machining and polishing operations.
The constraints of the foundry process require machining
and polishing trajectories to be adjusted to the
particular workpiece. A measurement system is therefore
integrated to adjust the trajectory, which also offsets some
inaccuracy factors. However, this correction is not sufficient
to take into account all the constraints applied to the
structure. For this, we present an approach to optimize
kinematic redundancy.
We first present the inaccuracy factors impacting machine
capability whose improvement requires an in-depth study of
the constraints related to the machining and polishing process
and the rigidity of the structure. The second part presents the
optical measuring system which compensates for the influence
of inaccuracy factors. The third part relates to the definition
of criteria to optimize kinematic redundancy in order to
improve accuracy requirements and kinematic capability. The
final section is dedicated to optimization; the results were
validated on industrial parts.
Context and application
This type of part requires complex moulds, with multiple cores,
coolers and a 3D feeding system, and whose volume can be
significantly greater than the part (Figure 1). In this
manufacturing process, obtaining the finished part requires a
major de-burring operation, including on the one hand the
The current issue and full text archive of this journal is available at
www.emeraldinsight.com/0143-991X.htm
Industrial Robot: An International Journal
39/4 (2012) 381–391
q Emerald Group Publishing Limited [ISSN 0143-991X]
[DOI 10.1108/01439911211227962]
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