A compliant add-on mechanism for polycentric prosthetic knees was designed to provide two additional features beyond those already provided by the knee, the additional features being a stable equilibrium position when the knee is bent for the sitting posture and a moment-rotation profile that helps prevent excessive heel rise. The mechanism, dubbed the Bistable Compliant Extension Aid (BCEA), was developed and analyzed using finite-element-analysis (FEA) software. The BCEA was shown to satisfy the design requirements, prevention of excessive heel rise and providing a stable sitting position, based on its reaction moments for knee flexions ranging between 0 and 90 degrees.
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