Dimensioning and evaluation of the elastic element in a Variable Torsion Stiffness actuator

Variable stiffness joints are essential for robots or biomechanical applications to generate torque with sufficient compliance to ensure safety simultaneously. This paper presents the dimensioning of the elastic element for an actuator with Variable Torsion Stiffness (VTS). Analytical and finite element calculations are compared to experimental evaluation of a splined shaft profile realized in a prototype implementation. Based on simplifications and effects in the real test-rig the results show similar behaviour. Furthermore, an analytical and finite element investigation of four cross-sections with torsional load illustrate optimal utilization of cylindrical geometries considering the torsional stress. In contrast, the low stressed edges of uncylindrical cross-sections are adequate areas to bear additional stresses.