Control of Shape Memory Alloy Actuated Gripper using Pulse-Width Modulation

End effectors like grippers find wide applications in robotic systems. Direct drive actuators like Shape Memory Alloys (SMAs) produce seemingly large linear or rotational movements of a modular actuator upon electrical heating. Mechanical work thus generated by SMAs can be harnessed to develop gripping systems with minimal moving parts. This article presents a simplest gripper actuated by SMA wire. The mechanical structure of the gripper is comprised of a pair of jaws (one movable) and an actuation means (a SMA wire and a counteracting torsion spring) for the movable jaw. Open loop and closed loop performance of the gripper are experimentally evaluated to manipulate objects of various sizes. In order to control the position of the devised gripper, a model is estimated from open loop data using system identification technique. Accurate and precise position tracking control is achieved using Pulse Width Modulation (PWM) technique.