Preliminary Design Concepts for Compliant Mechanism Prosthetic Knee Joints

Abstract

Compliant mechanisms present several design advantages that may be exploited in prosthetic joint design — low friction and wear, low part count, light weight, high reliability, efficient manufacturing and assembly, etc. However, they also come with their share of challenges. For example, in the past compliant mechanisms have not been viable alternatives to rigid-body joints in high compression applications. Two principles, isolation and inversion, can be successfully applied to many compliant joints to increase their ability to withstand high compressive loads and make them viable design alternatives to some current prosthetic joint designs. This paper presents preliminary design concepts for a compliant prosthetic knee. The inverted cross-axis flexural pivot design is selected and a proof of concept prototype is constructed and tested. The prototype exceeds the functional specification of 550 lbs, and satisfies a maximum deflection of 140°, an infinite life for a deflection of 110°, and a weight under 2 lbs.