A Study On Hybrid Actuation In Prosthetic Hands Using Shape Memory Alloy And Dc Motors

Abstract:Due to using less actuators, being light, being easy to control and possessing self-adaptive grasping function, recently, underactuated prosthetic hands possessing the characteristic of motion-coupling are developed. With the number of actuators reducing, the grasping speed of underactuated prosthetic hands is rapidly decreased. And the grasping reflex speed is crucial for preventing objects falling down when suffering external disturbance. Taking into account that, hybrid actuators combining shape memory alloy (SMA) with Dc motors are presented for underactuated artificial hands to improve grasping reflex speed.According to the design principles for hybrid actuators-complementary principle and compatibility principle, a hybrid actuator integrating SMA with Dc motors is proposed. The design of the hybrid actuator consists of three parts:design of the Dc motor actuator stage, design of the SMA actuator stage and combination of the two actuators.Some theoretical analysis are conducted, the mathematical model of shape memory alloy is built. Then, unknown parameters of the SMA model are detected by experimentation. For example, the elastic Modulus and yield limit of austenite. Finally, a comparison of simulation and experiment of the SMA-spring system is conducted to verify the accuracy of the model.The model of the designed TDUPF driven by the hybrid actuator is built. The feasibility of the system is proved by simulation. According to the simulation results, the force loading rate when the TDUPH is driven by the hybrid actuator is3.6times faster than when driven by the Dc motor. The impact on the maximum driving force and force loading speed made by the changes in objects stiffness, the length of SMA and driving voltage is studied.A hybrid actuation experimental platform is set up, and sliding grasping reflex experiments are conducted. A comparison between hybrid actuation and Dc motor actuation is carried out. According to the experimental results, the force loading rate is about3times faster when the prosthetic finger is driven by the hybrid actuator than when driven by Dc motor, and the sliding displacement is reduced from10mm to5.7mm.