Piezoelectric Tweezer-Type End Effector With Force- and Displacement-Sensing Capability

This paper presents the design and development of robotic tweezers with a force- and displacement-sensing capability driven by piezoelectric stack actuators. In order to satisfy sufficient stroke and tip force for future medical operations, a rhombus strain amplification mechanism is adopted. One of the serially connected piezoelectric stack actuators nested in the end effector is used as a force sensor. The force-displacement characteristics at the outermost layer with respect to the forces of the innermost PZT actuators (i.e., forward model) is obtained from a lumped parameter model of the rhombus strain amplification mechanism and a Bernoulli-Euler beam model of the tweezer-style end effector. The end-effector tip force and displacement are measured using an inverse model of the nested multilayer structure relating these quantities to an induced voltage across the innermost PZT actuator. The prototype end effector has the size of 69 mm (length) × 14 mm (height) × 13 mm (width). The performance test shows that the prototype has 1.0-N force and 8.8-mm displacement at the tip. The sensing accuracy was also evaluated through experiments. The experimental results show that the prototype has mean error of 0.086 N for force and 0.39 mm for displacement, which are equivalent to 11% of their maximum measurable values.