Switchable compliant actuator with fast stiffness modulation and energy efficient power transmission

Abstract

This article presents the design of a switchable compliant actuator (Swi-CA), capable of fast stiffness modulation over a wide range and energy-efficient equilibrium position control. Compliant actuators are designed to have a variable stiffness to generate a restoring force upon displacement. In previous studies, such actuators provided compliance by changing both output stiffness and equilibrium position using a clutch to switch between two modes. We implemented a bifurcation-based switching mechanism to shift between stiffness modulation and equilibrium position control modes via mechanical integration of a variable stiffness spring with a parallel elastic unit without the use of an additional clutch. The distinctive features of the proposed Swi-CA are threefold. First, the central bending of a leaf spring widens the range of modulated stiffness and increases the average stiffness modulation speed. Second, the developed slider-crank mechanism has high power transmission efficiency and fast stiffness modulation. Lastly, an optimized elliptical cam generated negative stiffness during output and enabled switching between the two modes without the use of a controllable clutch. Analytical models and experimental validation of the proposed design clearly demonstrated its advantages for applications requiring fast stiffness modulation and energy-efficient operation, such as some robotics applications.