Providing powered joint actuation has been the latest trend in transfemoral prosthesis research. The capability of actively powering the joints enables the prosthesis to meet the energetic requirements of locomotion, and thus provides higher performance in restoring the lost lower limb functions in comparison with traditional passive prostheses. In this paper, a powered transfemoral prosthesis is presented, in which the knee and ankle are powered with pneumatic artificial muscle actuators, leveraging the multiple advantages of this unique actuator (such as large force output and high power density). To address the issue of uneven force capacity, a new variable-radius pulley-based mechanism is utilized, which enables the adjustment of the available actuation torque curve to better match the desired torque curve as dictated by the locomotive requirements. The design details of the prosthesis are presented, and the prosthesis is expected to provide sufficient torque for an 85 kg user in various locomotion modes, including level walking at slow/normal cadence and stair ascent/descent.

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