Optimal design of a variable stiffness joint using permanent magnets

Safety and performance are often required for robots interacting with humans. A variable stiffness joint (VSJ) is a useful device to reduce the shock against a human being by decreasing the joint stiffness quickly. In this study, a novel concept of VSJ using permanent magnets is suggested. It can have stronger stiffness compared with previous systems to satisfy payload conditions. However, this system requires a positioning mechanism to move the rotor to the axial direction for the variable stiffness. This study focuses on the optimal design of a permanent-magnet-type VSJ. The analysis is based on the finite-element simulation. The virtual work method is used to calculate the force and torque of VSJ. The modification of the initial concept model is preceded and a prototype is implemented and tested to compare analysis results. Also, the Halbach array concept is added to increase the torque of VSJ. The parameter optimization scheme is applied based on the design of experiments and a final design is suggested.