A Novel Compact Underactuated Tendon-Driven Mechanism with Shape Memory Alloys

Abstract

An underactuated mechanism, which has less input than the active degree of freedom, is often used for grippers such as robot hands. The use of this mechanism can contribute to the reduction of actuators, that is, the reduction in size and weight. However, many of the conventional underactuated mechanisms are equipped with ordinary springs at the joints and are driven by a motor and they tend to be bigger and bulkier. Therefore, we have developed a compact underactuated tendon-driven mechanism using a lightweight shape memory alloy (SMA) actuator and a superelastic SMA sheet with an elastic range that cannot be achieved by conventional metal leaf springs. It has a range of motion of over 140 deg and can lift a weight of 60 g by energizing the SMA actuator. Using the shape memory effect and the superelastic effect of SMA, it is possible to exert a large force while keeping the mechanism compact and lightweight with a length of 13 mm and a weight of 0.14 g.