Mechanical Design and Torque Estimation Model of a Variable Stiffness Joint with Hysteresis Characteristics

This paper presents the design of a variable stiffness joint utilizing a lever mechanism for changing the stiffness and its real-time computational model to estimate applied joint torque taking into account the nonlinear hysteresis characteristics. Typical stiffness model considering hysteresis is difficult to be applied on real-time estimation because it depends on the deformation velocity value of which its accurate value couldn't be achieved in general digital measurement meters. However, the proposed computation model employs deformation value being measured easily, thus can be used to estimate the applied force based on the defined pivot position of lever mechanism on a realtime basis. By comparing the experimental and the simulation results, it was shown that the proposed computation model can estimate the torque only with the deformation measurement. Furthermore, by this computation model, it was verified experimentally whether the torque generated in the joint axis by the external force can be estimated correctly in real-time.