Stiffness evaluation of a hexapod machine tool with integrated force sensors
 
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TU Dresden, Institute of Mechatronic Engineering, Chair of Machine Tools Development and Adaptive Controls, Dresden, Germany
Submission date: 2019-11-13
Acceptance date: 2020-01-16
Online publication date: 2020-02-26
Publication date: 2020-03-06
 
Journal of Machine Engineering 2020;20(1):58–69
 
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ABSTRACT
Today, in-process force measurement is required by many manufacturing applications, such as process monitoring, quality assurance, or adaptive process control. A very promising force measurement approach bases on sensor-integration into the machine structure and is particularly suitable for hexapod structures and kinematics, where it allows a measurement in 6 degrees of freedom. On the other hand, a sensor integration also affects the machine. Especially for strain-gauge-based force sensors, a stiffness reduction is predicted, as their measuring principle requires a deformation. The practical consequences of these influences are investigated in this contribution. In particular, this work presents extensive experimental studies of the stiffness change caused by sensor integration for a single hexapod strut as well as for the complete hexapod machine tool. The results are evaluated in comparison to compliances of other components, such as the kinematic joints, and to stiffness changes resulting from sensor-integration into the end-effector or the application of a commercial force/torque sensor at the end-effector. In conclusion, the studies support the approach of structure-integrated force measurement for parallel kinematics, as the stiffness loss is rather small in many cases.
ACKNOWLEDGEMENTS
The authors are grateful to the German Research Foundation (DFG) who supported this work with the projects "Fundamentals for structure-integrated measurement and control-integrated processing of spatial forces and torques in machine tools" (DFG No 202081830) and “Fundamentals for the use of eccentric joints in parallel kinematic machine tools” (DFG No 53530748). Further, the authors want to thank the editors and reviewers for their helpful comments and constructive suggestions with regard to the revision of this paper.
 
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