Design and Evaluation of a Low-Cost Force Feedback System for Myoelectric Prosthetic Hands

Abstract

Myoelectrically powered prosthetic hands lack sensory feedback relating to the force exerted by the artificial hand on a grasped object. The degree of control is imprecise, and often much more force than necessary is applied. The aim of this study was to develop and evaluate a force feedback system considering design constraints, providing the user with closed-loop control. Different methods and design criteria for providing myoelectric prosthetic hands with force feedback were analyzed, with stimulation by vibration being preferred. A new feedback system was designed, consisting of a miniature vibration motor, a piezoresistive force sensor, and control electronics. Grasping forces with and without feedback were recorded and compared from five habitual myoelectric hand users when grasping a hand dynamometer with different weights attached to it. All five patients rapidly improved their ability to regulate the grasping force without the help of vision when feedback was applied. An average force reduction of 37% was found when vibration was applied indirectly to the hand, and a decrease of 54% was found when feedback was applied directly to the skin of the residual limb. Constraints for a prosthetic force feedback system such as low power consumption, compactness, and being imperceptible to others are included in the design. General acceptance of vibration as a feedback signal was good, especially when applied indirectly. The results indicate that the new system is of potential value for myoelectric prosthetic hand users. More precise control is possible, and redundant grasping force can be diminished with a feedback system.