New Shape Memory Alloy Actuator: Design and Application in the Prosthetic Hand

This paper describes a new SMA actuator design and its application in the prosthetic hand replacing conventional servo motors which are bulky and noisy in nature. Two one-way memory SMA wires are used in the development of the actuator. The proposed actuator consists of two 0.3 mm in diameter SMA wires inserted from both ends of a stainless outer tube which functions as a guide and simultaneously a heat sink for the dissipation of heat from the SMA. These wires meet at the centre of the stainless tube where an electrode is placed. There are 2 other electrodes, each located at the end of the outer tube. These electrodes are the points where current is passed through each of the SMA wire asynchronously. In order to actuate a degree of freedom (DOF) of a robotic finger, 2 actuators are used each for the flexion and extension actions respectively. A high voltage PWM signal of very short intervals is used in actuation to avoid excessive heat build-up in the SMA due to long unnecessary heating