Enhanced visual feedback for slip prevention with a prosthetic hand

Background: Upper limb amputees have no direct sense of the grip force applied by a prosthetic hand; thus, precise control of the applied grip force is difficult for amputees. Since there is little object deformation when rigid objects are grasped, it is difficult for amputees to visually gauge the applied grip force in this situation. Objectives: To determine if the applied grip force from a prosthetic hand can be visually displayed and used to more efficaciously grasp objects. Study Design: Experimental controlled trial. Methods: Force feedback is used in the control algorithm for the prosthetic hand and supplied visually to the user through a bicolor LED experimentally mounted to the thumb. Several experiments are performed by able-bodied test subjects to rate the usefulness of the additional visual feedback when manipulating a clearly visible, brittle object that can break if grasped too firmly. A hybrid force-velocity sliding mode controller is used with and without additional visual force feedback supplied to the operators. Results: Subjective evaluations and success rates from the test subjects indicate a statistically significant reduction in breaking the grasped object when using the prosthesis with the extra visual feedback. Conclusions: The additional visual force feedback can effectively facilitate the manipulation of brittle objects. Clinical relevance The novel approach of this research is the implementation of a noninvasive, effective and economic technique to visually indicate the grip force applied by a prosthetic hand to upper limb amputees. This technique provides a statistically significant improvement when handling brittle objects.