Implementation and Testing of Ankle-Foot Prosthesis With a New Compensated Controller

Abstract

In this study, a powered ankle-foot prosthesis driven by a nonlinear parallel elastic actuator (PEA) is developed and tested. A finite state impedance controller is utilized to identify the state of the prosthesis and then generate the reference for the control of the actuator. Note that the finite state machine used in the impedance controller is improved. Specifically, the transition between controlled dorsiflexion and the push-off phase is triggered not by a fixed condition but by the motion of users, which enables the maximum flexion angle of the prosthesis to be changed according to the gait of users. A PD controller with a compensation part (steady-state output) is used to regulate the motor current. Besides, a drive circuit with two working modes is proposed for the motor used in the prosthesis to enable the prosthesis to work properly in both powered and passive (powered-off) modes. Clinical trials indicate that the developed prosthesis can reproduce the desired function when working in both powered and passive modes. The powered prosthesis can deliver a net positive work of 11 J in each cycle to the subjects for facilitating forward propulsion, which is helpful for improving the symmetry of ground reaction forces of the sound and prosthetic sides. Consequently, the peak impact force on the sound side is reduced. In addition, the powered prosthesis can decrease the subjects’ metabolic cost by 15%, compared with the subjects’ original passive prostheses.