Design, drive and control of a novel SMA-actuated humanoid flexible gripper

Abstract

An elemental SMA actuator, consisting of an elastic rod with two embedded SMA wires, is presented. The recovering wire w1, with remembered ‘U’ shape, is located along the rod’s axis. The restoring wire w2, with memorized straight shape, is located in parallel with the rod’ axis with an offset distance d1. Two strain gauges, arranged in complemental configuration and sticking to the rod, are used to implement accurate displacement control. Upon the elicitation of the structure of a human being’s hands, a finger with multi-units is proposed. The finger has two flexible rods with embedded SMA wires and one shorter rod as a connecting part. The number and position of fingers are investigated by making use of a nonlinear plan process with an index W, a function of grasp matrix G. The hardware of the drive and control system of the gripper has been completed on the base of a DSP chip. After the track plan is realized in the joint space through B spline interpolation method, the software of the position control system is fulfilled through two-staged slide control strategy. The simulations and experiments of step response of the SMA actuator are carried out. It is shown in the experiments that the maximum angle between ends’ tangents of each finger is 68.5, 79 and 79 degrees, respectively, and the tip of each finger could reach its final position by using approximately the same time period.