Segmented binary control of shape memory alloy actuator systems using the Peltier effect

A new approach to the design and control of shape memory alloy (SMA) actuators is presented. SMA wires are divided into many segments and their thermal states are controlled individually in a binary manner. The Peltier effect is used for heating and cooling individual segments of the SMA. Unlike the traditional way of controlling the wire length by driving a current to the entire SMA wire, the new method controls the binary state (hot or cold) state of each segment. The total displacement is then proportional to the number of the segments having the heated state, i.e. austenite phase. This architecture has three salient features, which would overcome fundamental difficulties of SMA. 1) Although the inherent property of SMA is highly nonlinear and uncertain with a prominent hysteresis, the binary state/phase control does not depend on the complexity of SMA state transition. 2) With use of the Peltier effect thermoelectric devices the response of SMA becomes more controllable, stable, and more accurate compared to the traditional air cooling and electric wire heating. 3) By operating at the heated state, SMA shows considerable load disturbance rejection compared to traditional methods. First, the basic principle and architecture of the segmented SMA actuator system are described. Initial implementation and feasibility tests are then presented, followed by discussion of the experimental results.