A Novel Variable Stiffness Actuator Based on Cable-Pulley-Driven Mechanisms for Robotics

Variable stiffness actuator (VSA) is an effective actuation approach to increase safety in physical human-robot interaction. This acticle proposes a novel compact variable stiffness actuator (CVSA) that can regulate stiffness by changing the preload of springs using a series of cable-pulley-driven mechanisms. By changing the number of variable stiffness units, the stiffness regulation range of VSA can be customized and reconfigured. To reduce internal friction, the pulleys and steel balls are adopted in the driving system. The driving cable passed through the central-hole of the VSA allows the stiffness-adjusting motor to be placed in a remote location. The stiffness model of the VSA is established, and its design parameters related to stiffness are analyzed. An improved active disturbance rejection controller for the VSA is developed to achieve robust position tracking in the presence of disturbances. An adaptive term is introduced into the controller for online parameter adjustment. The stiffness identification, collision test, and trajectory tracking experiments under different conditions prove the feasibility of the actuator and verify the proposed algorithm.