Design of powered ankle-foot prosthesis driven by parallel elastic actuator

To improve the energy efficiency and downsize the powered ankle-foot prostheses (PAFP) but still provide sufficient instantaneous power output, elastic actuators (EAs) are widely used. Generally, there are two kinds of EAs: series elastic actuator (SEA), and parallel elastic actuator (PEA). Both of them can reduce the energy requirement and peak power of the motor in the PAFP by using elastic elements to store and release energy during walking cycles. Researchers working on prostheses fields have been focusing on the design of PAFP driven by SEAs. As a result, several PAFP driven by SEAs were proposed. Compared with the PAFP driven by SEAs, the PAFP driven by PEAs could have more benefits, such as lower copper loss and higher force bandwidth due to the smaller motor output torque requirement. In this paper, we aim at designing a PAFP driven by a PEA. Based on the energy requirement analysis, an energy-efficient PAFP is proposed. The designed PAFP can mimic human intact ankle with the minimum energy consumption that equals to the human ankle net positive work. Besides, with the motor output torque being decreased, the motor peak power of the PAFP is reduced by 64%.