Minimizing Input Torques of a High-Speed Five-Bar Mechanism by Using Variable Stiffness Springs

Recently, variable stiffness actuators (VSAs) have been introduced for reducing the input efforts of pick-and-place robots. However, the serial arrangement of springs and motors in the VSAs decreases the accuracy at high-speeds due to uncontrolled robot deflections. To ensure accuracy while reducing the input efforts, this paper proposes the use of variable stiffness springs (VSS) in parallel configuration with the motors. The parallel arrangement of VSS and motors is combined with a shooting method to adjust the stiffness of the system in order to enforce its limit cycle to converge to a desired trajectory, and, thus, to decrease the input torques. Numerical simulations of the suggested approach on a five-bar mechanism show the reduction of the robot input efforts.