Abstract

Motion stages are widely used for precision positioning in manufacturing and metrology applications. However, they suffer from nonlinear pre-motion (i.e., “static”) friction which adversely affects their precision and motion speed. Existing friction compensation methods are not robust enough to handle the highly nonlinear and variable dynamic behavior of pre-motion friction. Therefore, the first two authors have proposed the concept of a friction isolator as a simple and robust solution to mitigate the undesirable effects of pre-motion friction in precision motion stages. They experimentally demonstrated that a motion stage with friction isolator can achieve significantly improved precision, speed and robustness to variations in pre-motion friction. However, a theoretical study was not carried out to fundamentally understand the dynamic phenomena associated with using a friction isolator on a motion stage. This introductory paper investigates the dynamics of a PD-controlled motion stage with friction isolator. The influence of the friction isolator on the response and stability of the system is examined through theoretical and numerical analysis. It is shown, using a case study, that the addition of a friction isolator shrinks the range of P and D gains that can stabilize the motion stage. Several other case studies that include the effects of external excitation and integral controller are carried out to motivate deeper dynamic analyses of the friction isolator for precision motion control.

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