Design of a precise tracking shape memory alloy wire actuated gripper

Abstract

Shape memory alloy (SMA) actuators’ unique features like compact design and high force to weight ratio attracts numerous position control applications. Due to the nonlinear behaviour and control difficulties SMA actuators are not widely employed in position control applications. In this work, a simple and easy to construct closing mode SMA wire actuated gripper is presented. The mechanical structure of the gripper includes a pair of jaws - one movable and other fixed, an SMA wire employed to close the jaw upon actuation and a torsion spring bias for the strain recovery in SMA wire. An experimental setup of the SMA gripper is established to perform the study. The SMA actuator is heated by an electric current. A non-contact laser displacement sensor is engaged to measure the position of the movable jaw. In order to control the position of the devised gripper, a model of the gripper is estimated from open loop experimental data using system identification technique. Experimental evaluation of manually tuned PI controller for SMA actuated closing mode gripper is compiled to track various stationary and variable (dynamic) trajectories to suit applications that can manipulate objects of varied dimensions. Control results demonstrate that the gripper is able to track the position rapidly and precisely.