Relationship between bias spring parameters and output performances of SMA actuators

The parameters of the bias spring have great impacts on the output performances of the shape memory alloy (SMA) actuator. To investigate the rules of influences, the output stroke and response rate of a SMA actuator with different bias spring stiffness and precompression load were studied. The output degradation due to cyclic actuation was also investigated. Experimental results show that the strokes and response rates decrease with the increase of preloads or stiffness. The performance of the actuator degrades significantly in the first few cycles and stabilizes eventually with the increase of the number of cycles. The test results also indicate that less cycling is needed to stabilize the actuator when the preload is increased, and the stiffness seems to affect the cyclic performance of the actuator slightly.