Piezoelectric Tweezer-type End-effector with Force- and Displacement-Sensing Capability
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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 outer-most layer with respect to the forces of the inner-most 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 tweezerstyle end-effector. The end-effector tip force and displacement is measured using an inverse model of the nested multi-layer structure relating these quantities to an induced voltage across the inner-most PZT actuator. The prototype end-effector has the size of 69 (length) × 14 (height) × 13 (width) [mm]. 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.