Stiffness Controlled Piezoelectric Stick-Slip Actuator for Rapid Positioning Applications

Abstract

Rotary screw-type stick-slip actuators driven by smart materials offer the attractive characteristics of large stroke, fine resolution, high power-off holding force, and relative simplicity to manufacture. However, the actuation speed of current rotary stick-slip actuators limits their applications. The research presented in this study focuses on rapid positioning applications and involves the development of two mechanism designs. Both designs utilize piezoelectric stacks driven by sawtooth waves to provide stick-slip contact between two partially threaded jaws and a 1/4-80 screw. The first mechanism design utilizes two piezoelectric stacks in a push-pull configuration. The motion of the two stacks is coupled through a lever amplification mechanism. The second design uses a single stack to directly drive the jaws without amplification. However, a second stack is oriented perpendicular to the first stack and driven with a triggered square wave. This stack varies the normal and thus frictional force between the jaws and screw, permitting more efficient slipping and sticking of the actuator. This allows for potential increases in both output speed and force. Existing actuators were modeled using both theoretical and finite element analysis techniques. These results were compared with experimental data to validate the models.