In this paper after reviewing some previous studies, in order to improve our previous modeling of above knee prosthesis comprises SEP controlling parameter, moving ankle assumption is considered. SEP controlling parameter makes the prosthesis able to act as a multi behavior system when the amputee is opposing to different environments. This active prosthesis with the new controlling parameter can simplify the control of prosthesis and reduce the rate of energy consumption in comparison to recently presented similar prosthesis “Agonist-antagonist active knee prosthesis”. In this paper three models are generated; a simple passive, an active, and an optimized active prosthesis. The optimization procedure is genetic algorithm. The SEP controlling prosthesis model with moving ankle during the swing phase represents acceptable results in comparison to natural behavior of shank and the fixed ankle model. Reported results in this paper represent 3.2 degrees as the maximum deviation of optimized model shank angle from the natural pattern. The natural gait pattern belongs to walking at the speed of 81 m/min.

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