Active ankle prosthesis powered by electrohydrostatic actuation technology: Design and implementation

Currently, the majority of published ankle prostheses employ electrical drives or hydraulic drives. In this paper, an active ankle prosthesis powered by electrohydrostatic actuation (EHA) is proposed. EHA is a new actuator that integrates the actuation system energy source and the output actuator. It has been successfully applied to aircrafts such as the A380, A400M, B787 and F35. The use of EHA in the prosthesis provided high power density, and the ability to switch quickly and smoothly between passive and active modes. The prototype consists of more than ten components, such as the motor, double-plunger pump, valves, double-outlet hydraulic cylinder, pressure sensors, accumulators, carbon fiber foot plate, etc. After rigorous verification via simulation and evaluation, this study proved that its structure was reliable and durable. A simulation model was then developed to analyze the performance of EHA, results showed that this hydraulic system could provide enough torque to satisfy energy needs of human bodies. The innovation of this study was reflected in the creative use of combining the hydraulic cylinder and the plunger pump to be a closed hydraulic circuit, thereby forming proactive assistance prosthesis. Moreover, another novelty is that micro-accumulators also used for energy storage, released when in necessity. With laboratory experiments, the overall control of the prosthesis and structural improvement are also in progress at present.