100g-100N finger joint with load-sensitive continuously variable transmission

Abstract

This paper presents a 99 g finger joint that can exert a very strong fingertip force of more than 100 N. We have shown that a simple five-bar linkage can be used as a load-sensitive continuously variable transmission (CVT) for a finger joint. The maximum fingertip force of our previous finger was limited by the mechanical strength of its links and bearings, not by the power of its DC motor. If the machine strength can be improved, a much greater fingertip force can be expected. To design a lightweight CVT with sufficient mechanical strength, we analyze the internal force of the CVT and select light plain bearings. We also analyze the stress by using the finite element method and select the materials of its links. Experimental results verify that the maximum fingertip force is more than 100 N near the singular configuration of the CVT and the maximum angular velocity is more than 550 deg/s. These motions are impossible without the CVT. We also developed a very light shape memory alloy brake of 0.56 g. The CVT with the brake can hold a fingertip force of more than 100 N not only near the singular configuration. The electric energy consumed by the brake is much less than that by the DC motor