Development of Electrohydraulic Controlled Above-Knee Prostheses

In this study, a four-bar linkage above-knee (AK) prosthesis with an electrohydraulic controller was developed. A microcomputer was employed to regulate the puppet valve of the hydraulic control system. To obtain a reliable design, a test rig was also designed for evaluation of the knee controller performance. The rig had a variablespeed alternate-current servomotor for simulating the angular displacement of the hip joint at different walking speeds. A proportional+derivative (PD) controller was employed to regulate the knee torque of the above-knee prosthesis. Experimental results revealed that the controller can produce a knee joint trajectory close to that of a normal person or a designed one. Use of the electrohydraulic controller can be expected to improve the amputee swing phase gait.