An Above-Elbow Prosthesis Employing Programmed Linkages

The use of EMG signals from residual muscles to control an above-elbow prosthesis has been tried, but presents many problems, not the least being that the prosthesis is under open-loop control. A more satisfactory control technique is extended physiological proprioception where the inherent proprioceptive feedback present within an intact joint is used to provide closed-loop control. We have developed a prototype of a self-contained above-elbow prosthesis which has electric-powered wrist and elbow joints controlled by an Intel 8751 microcomputer. Our technique is to control the positioning of this above-elbow prosthesis using the motion of the intact shoulder. Grasp, which does not involve positioning in space, is separately controlled using EMG signals from biceps and triceps muscles. The relationship between output (wrist and elbow positions) and input (shoulder position) can be set according to a program or linkage stored in the microcomputer memory. A choice from a range of linkages can enable the user to perform different tasks in different situations. We have verified experimentally that after an amputee has learned to associate the position of the wrist and elbow joints of the prosthesis with his shoulder position, the prosthesis will become a very useful aid. Also, because of the repeatability of operation and the inherent closed-loop nature of the prosthesis, the amputee will be motivated to wear it every day.