Current-Sensor-Based Contact Stiffness Detection for Prosthetic Hands

Abstract

When a prosthetic hand grasps an object, a proper grasping force should be exerted according to the stiffness properties of the grasped object so that damage caused by excessive force or slide caused by insufficient force is prevented. To implement stiffness detection and simultaneously to prevent errors and defects caused by the use of force sensors and the difficulties in the direct measurement of the deformation of the grasped object, a force sensor-less method of contact stiffness detection is proposed for a single degree of freedom prosthetic hand with a self-locking mechanism. In this method, force sensor signals are replaced with motor current signals. An analytic solution of contact stiffness is obtained based on a linearized grasping model near the initial contact position between the prosthetic finger and the grasped object. Contact stiffness is thus calculated by using the current of the driving motor and the angular displacement of the prosthetic hand rather than directly through the ratio of the force to the deformation. Simulation and experiment results demonstrate the effectiveness and feasibility of the proposed method.