A joint Electromagnetic Torsional Actuator for low-frequency chatter suppression in robotic milling

Abstract

The demand for robotic milling with higher efficiency has grown significantly across industries. However, the low-frequency chatter caused by the insufficient dynamic stiffness of the robot body structure remains a critical challenge. Existing vibration suppression devices mounted on the robot’s end effector are prone to kinematic interference, affecting the robot’s flexibility. The delays between motor command and execution limit the bandwidth of the vibration suppression method based on joint motor control. This paper introduces a joint-mounted Electromagnetic Torsional Actuator (ETA) designed to actively apply torque on robotic joints, effectively improving the dynamic stiffness of the robot body structure. First, the performance requirements that the ETA should meet were analyzed, followed by the design of the ETA’s structure based on these demands. Next, an input current-to-output torque mapping model was established using alternating current winding theory and the principle of virtual work. Output torque performance tests were subsequently conducted, demonstrating that the actuator’s bandwidth approaches 100Hz along with the desired torque amplitude. Finally, three ETAs were installed on the joints of an ESTUN ER70B robot, and a proportional controller was designed for verification through modal hammer tests. Results demonstrate that the joint-mounted ETA enhances the dynamic stiffness of the robot body structure, achieving an average reduction of 40% in modal dynamic compliance across various directions, with reductions ranging from 22% to 61%, showing significant potential for suppressing low-frequency chatter and improving robotic milling efficiency.