Forced Air Cooling of Shape-Memory Alloy Actuators for a Prosthetic Hand

Abstract

This research paper presents the development of nonconventional actuation technology for use in a prosthetic hand. Shape-memory alloy (SMA) is used for the actuation. SMA is a material which contracts when heated and relaxes when cooled and has a work density 25 times greater than traditional electric motor actuators. A compact SMA actuator array, position sensors, and power electronics are developed. A proportional-integral-derivative (PID) controller is used to control the contraction of the actuators. Forced air cooling is implemented to improve actuation frequency. The performance of an actuator is demonstrated in dynamic and static position experiments. The static position control of the actuator is found to remain within 0.7% (70 μm) of the setpoint during initial oscillation and then within 0.15% (15 μm) after oscillations subside. The dynamic position control experiment finds that the forced air cooling reduces actuation frequency from 9.5 s to 3.5 s. This results in an actuation frequency comparable to current commercial prosthetics. When compared with the most advanced commercial devices, this actuator array provides improvements in terms of cost, noise, and weight. All of which are important acceptance criteria for prosthetic hand users.