University of Twente Student Theses


A Linearized Parameter Study Of A Friction Isolator System : Towards A Frequency Domain Design Guideline

Fix, J.A. (2023) A Linearized Parameter Study Of A Friction Isolator System : Towards A Frequency Domain Design Guideline.

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Abstract:Nonlinear friction effects in linear guides can limit the positioning performance in high-precision systems. Stick-slip is one of these effects, through which a bearing makes a sudden transition from standstill to movement due to a nonlinear drop in friction force. Stick-slip in combination with an integral action in a typical PID controller can lead to hunting or friction induced limit cycles, which negatively affect the positioning performance of a servo system. In this study, a friction isolator that mitigates hunting through the addition of a compliant joint between the linear guide and the actuator is analyzed, designed, and tested. By combining the low linear stiffness of the compliant joint in series with the higher nonlinear pre-motion friction stiffness of the linear guide, the friction forces are linearized. Through simulations of a friction isolator with a LuGre friction model, the main system parameters are identified and design guidelines for a friction isolator are determined. From the parameter study, it was found that a friction isolator can be helpful in a system with limited control bandwidth and a significant gap between static and dynamic friction. Regarding the design of the friction isolator, it was found that the drive stiffness of the compliant joint should be as low as possible whilst the parasitic frequencies of the joint should be large enough not to limit the desired controller bandwidth. The stroke of the joint can be significantly smaller than the amplitude of the hunting cycles. The test setup build for this research, with an equivalent moving mass of 2.5 kg and static friction forces in the range from 1 to 2.5 N, saw hunting mitigation through the friction isolator with a control bandwidth of 5 Hz or larger. Which is significantly lower compared to the nonisolated system, which required a 15 Hz bandwidth. A stroke of 0.3 mm for the compliant joint is found to be sufficiently large for a satisfying performance of the friction isolator in this case. The experiments performed on the test setup agreed with the results of the parameter study.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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