Stability and Precision Positioning of Piezoelectric Stepper Systems

Abstract

This research addresses a fundamental problem using stick-slip devices, including steppers, in which the output velocity has oscillations induced by the stepping behavior. Stepper systems allow smaller actuators to achieve large ranges by making multiple steps with each step generating small motions. The main contribution of this research is to develop a new large-range high-precision stepper system capable of constant velocities (i.e., suppressed oscillations). Towards this, a full analysis of a single actuator stepper system is presented with stability shown using a Poincar´e map approach with extension to a discontinuous equation of motion. Further, experimental results show agreement with model predictions, however, it is also shown that the oscillations cannot be suppressed with a single actuator stepper. Thus, a new dual-actuator stepper system is needed. The new stepper system uses two piezoelectric actuators to drive a motion stage. By creating a phase shift phi between the motion of the actuators, the new stepper system is capable of suppressing the oscillations found in the single actuator stepper system. The new stepper system also allows the capability to be driven in a single actuator mode (setting the phase shift phi = 0). From experimental results, driving the actuators in dual mode (out-of phase,phi not equal 0) trajectories show ~62% suppression in oscillation size can be achieved when compared to the single (in-phase, phi = 0) mode.