The above-knee prosthesis, as a supplement of the lost biological leg, is supposed to provide equivalent or enhanced shock absorption capability and reduce the shock waves on the amputee body when walking and running. Prosthesis knee joint with a shock absorber is a feasible solution that efficiently absorbs the impact loads during each heel-strike. Conventional shock absorbers consist of springs and dampers with constant coefficients produce excessive rigid reactions when encountering impact forces, while unreasonable weak responses for gentle loads. This study proposes an innovative viscous damper design for the prosthesis knee joint which automatically and smoothly tunes the damping coefficient without any electronic components according to the input force velocities. High order differential system of the shock absorber is constructed and simulates the system dynamics during cyclic loads. The fluid-structure interactive finite element model for key components in the absorber is established in this study. Design parameters of the damper system under certain absorbing performance requirements are determined in this paper.

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