A BENCH-TOP PROTOTYPE OF A VARIABLE STIFFNESS PROSTHESIS

Abstract

A prototype of a variable stiffness prosthetic joint has been constructed and tested. The joint is based on two actuator subsystems arranged in an antagonistic configuration. Each actuator subsystem is composed of a small, high-speed electric motor, a single stage, worm-gear based transmission and a nonlinear stiffness element. Each nonlinear stiffness element is composed of a set of short sections of elastic tube that was chosen based on its stiffness characteristics. The system is powered by batteries and can be controlled in a number of ways. The paper will present the basis used for selecting the nonlinear stiffness elements, the details of the design as constructed and a comparison of the actual performance of the prototype to predictions based on design calculations and simulations. The prototype has performance that is comparable to commercially available prostheses and showed good correspondence between simulation and prototype. The prototype was able to lift a 2 kg load through 135 degrees in 1.42 seconds and to vary its stiffness from 14 to 24 Nm/rad.