The Effect of Constraint Conditions on the Bending Operating Characteristics of a Weft Yarn-type Shape Memory Alloy Actuator

Abstract

For the purpose of developing an actuator for wearable-assistive devices, we have devised and produced a weft yarn-type shape memory alloy (SMA) actuator using the resistance feedback control method. This actuator consists of a polyethylene terephthalate (PET) plate and SMA wire woven into the weft pattern. Since the PET plate and SMA wire are constrained in the lateral direction, this actuator can do the bending operation by the actuation of the SMA wire. In this research, the effects of constraint conditions of the PET plate and SMA wire (i.e. the distance between PET plate and SMA wire (D)), and the number of constraining points (N) were investigated with respect to the bending operating characteristics (bending deflection and operating velocity) of the weft yarn-type SMA actuator. The bending deflection of the actuator was seen to increases with the increase of N. However, the bending deflection of the actuator was seen to decreases with the increase of N beyond the maximum value. The variation of deflection is caused by the variation of frictional force due to the variation of N. Furthermore, the bending deflection of the actuator and operating velocity decrease as D increases. This tendency is caused by the increase of the curvature radius of actuator with the increase of D.