Rate-dependent inverse hysteresis feedforward controller for microsurgical tool

This paper presents the development and initial results of a controller based on a novel rate-dependent hysteresis model. The controller has been developed for "Micron," a microsurgical instrument designed to sense and actively cancel tremor and other undesired motion during vitreoretinal intervention. To accomplish this, Micron uses a three-degree-of-freedom parallel manipulator with piezoelectric actuation. In order to achieve high accuracy it is necessary to deal with the hysteresis of the piezoelectric actuators. Most hysteresis models are based on elementary rate-independent operators and are not suitable for modeling actuator behavior across a wide frequency band. This work proposes a rate-dependent controller, based on a modification of the rate-independent Prandtl-Ishlinskii (PI) model, to counteract hysteresis during open-loop control of piezoelectric actuators tracking multi-frequency motion profiles. In experiments tracking real tremor, it consistently outperforms its rate-independent counterpart.