Bi-behavioral prosthetic knee enabled by a metamorphic compliant mechanism

Abstract

Metamorphic mechanisms with two distinct behaviors were designed using compliant mechanism theory with a potential application as a prosthetic knee. The mechanism has discrete "locking" points to restrict rotation when under a compressive load. The designs use cross-axis flexural pivots, either in inversion or isolation, with engaging teeth to carry loads at distinct angles. Inverted compliant mechanisms function by inverting the mechanism so the compliant members are in tension when a compressive load is applied. Compliant mechanisms in isolation provide an alternative loading pattern which redirects the load to a passive rest. The mechanism incorporates teeth which engage during weight-bearing in flexion at up to 60° of flexion to lock the mechanism. When tension is applied to the device, the teeth are disengaged and the mechanism is allowed to rotate freely. The purpose of this design is to hold compressive loads both when un-flexed and flexed. The concept is applied in the preliminary design of a prosthetic knee joint. Proof-of-concept prototypes successfully demonstrate the metamorphic behavior. © Springer-Verlag 2012.