Conception and evaluation of a novel variable torsion stiffness for biomechanical applications

This paper proposes a novel variable torsion stiffness (VTS) aiming on biomechanical applications like prosthetic knee joints. By varying the effective length of a torsional elastic element via a relocatable counter bearing, the stiffness of a rotational joint is adjusted. This functional concept is described in detail by the authors as well as the design of such VTS joints. Additionally, analytical models for the transfer behaviour of drivetrain and stiffness control are derived. These are used for a simulative evaluation of a pendulum driven by a VTS unit. Based on the results of this simulation, the power requirements of VTS are analysed. Furthermore, an analysis of its structural strength is presented. For practical comprehensibility, the example of the design of a prosthetic knee joint is taken up for several times in this paper. Finally, the concept, modeling and design of VTS as well as the simulation results are concluded and discussed in a final assessment and in comparison to other contemporary concepts.