Design, fabrication and testing of a hydropneumatic actuator for use in below knee prosthesis

Currently there is no passive prosthesis that can simulate human walking from low to medium walking speeds. In this study a passive mechanism that simulates the human ankle joint in low walking speeds is proposed. The mechanism has the ability to adjust the ankle stiffness/damping from low to medium walking speeds. In the proposed mechanism, the desired stiffness is adjusted through trapped gas in a cylinder, and damping is controlled by hydraulic valve. A model of the system is derived and simulated to show the behavior of ankle function. Finally, to validate the simulation response a prototype of the mechanism is made and tested experimentally. The results show that the proposed mechanism can be used as an ankle joint prosthesis similar to human walking.