Hybrid actuator combining shape memory alloy with DC motor for prosthetic fingers

Direct Current (DC) motors are widely used in prosthetic hands. Since the power to weight ratio of DC motors is relatively low, the driving systems are usually bulky and heavy to meet the requirements for the grasping speed and force. However, high grasping speed is a basic requirement for the grasping reflex to prevent the grasped object from slipping. With increasing force, the possibility that grasped objects will slip off is significantly reduced. This study proposes a hybrid actuator combining shape memory alloy (SMA) with a micro DC motor for a prosthetic finger. The SMA is used to improve reflex speed. Rapid response can be achieved when SMA is subjected to high voltage. Experimental results show that in the grasping reflex, the rate of force is increased four times, and the sliding displacement of the grasped object subjected to unexpected disturbances is reduced from 10 mm to 5.7 mm.