A Gripper Actuated by a Pair of Differential SMA Springs

This article presents a gripper actuated by a pair of differential shape memory alloy (SMA) springs. The mechanical structure of the gripper includes a pair of fingers, a coupler, a tension rod, a slider, and a frame. An experimental setup of the SMA gripper is established. The SMA actuator is heated by the electric current and cooled by fans. Thermal resistance sensors are used to measure the temperature of the SMA springs and a slide rheostat is used to sense the output displacement of the actuator. In order to evaluate the potential of the SMA actuator for application to the proposed gripper, three types of tests are performed as follows: influence of the cooling methods, heating current, and action frequency on the characteristics of the SMA actuator and the gripper. The experimental results show that the output displacement amplitude can increase by increasing the heating current and decreasing the action frequency. A good cooling method can increase the cyclic output displacement amplitude and the bandwidth of the SMA actuator. A proportional-integral (PI) controller is presented to control the output position of the gripper, and a two-phase control method is developed to reduce the overshooting of the system. Position control experiments for the SMA gripper are performed, and the experimental results demonstrate that a good position control performance of the gripper is obtained by using the proposed controller.