ABSTRACT
Low-stiffness-induced vibration in industrial robots is problematic especially for robotic machining processes. In robotic milling, the spindle may experience chatter with varying characteristics under different working conditions, leading to unsatisfactory surface finishes. Active vibration control using robust controllers may therefore be an ideal solution for chatter suppression. This paper demonstrates that with two inertia actuators and one accelerometer attached near the spindle, on the robot, chatter suppression may be achieved using simple yet powerful H ∞ controllers with feedback of measured accelerations. The implementation of the controller follows a procedure, including characterisation and model identification of the robot system dynamics, selection of weighting functions, H ∞ synthesis and controller verification. Robotic milling tests of an aluminium block using a KUKA KR120R2500 PRO robot were performed to show that the designed H ∞ controller targets a low chatter frequency around 26 Hz and reduces vibration by up to 80%. The surface finishes with and without active chatter suppression are compared, confirming an improvement of over 60% in the surface roughness. The proposed active chatter suppression could benefit large volume manufacturing, where the system dynamics change during the operation.
