One of the most difficult issues in the design of power ankle-foot prosthetics is to create a control
system that can simulate biological ankle-foot behavior in various operating conditions. The
powered semi-active ankle-foot prosthetic is a complex nonlinear system with high coupling. This
work presents the dynamic model of powered ankle prosthetics. For powered ankle prostheses, a
fuzzy logic- proportional-integral (FL-PI) controller is presented. In the initial stage of control,
two proportional-integral (PI) controllers are designed to regulate motor speed and current,
respectively. In the next stage of control, two FL-PI controllers are designed. The Fuzzy logic
controller is designed to tune online the gains of the PI controller. During a normal walking gait
cycle, FL-PI controllers are used to regulate the specified model under these external disturbances.
The performance of PI controllers and FL-PI controllers are compared during the walking gait
cycle. The results reveal that a powered semi-active ankle-foot prosthetic with a fuzzy logic-PI
controller method outperforms a PI controller alone.