Simultaneous tracking and drive-based vibration suppression of CNC machine tool feed systems

Computer numerical controlled (CNC) machine tools requires higher performances due the continuous development of high-precision and high-speed capabilities. Objective in the control of the feed drive systems is to accurately track the specified reference trajectory for the position of the workpiece. However, cutting force disturbances or structural vibrations during the machining process may cause unacceptable tracking errors. Therefore, it is crucial to design a control system which ensures accurate tracking on reference trajectories and simultaneously suppressing undesirable vibrations. Escalating requirements on high acceleration and high speed leading to the larger sized and lightweight feed drive systems, also pose elevated risks about excitation of vibrations during the operation. Hence, machining performance depends on the dynamic properties and characteristics of the feed drive system as they constitute an important part of CNC machine tools. Transformation from rotary to linear motion using ball-screw feed drives are widely applied in machine tool industry for the time being due to their high mechanical efficiency and lower cost. However, during the high-speed machining process, the probable vibrations of the elastic ball-screw drive system dynamics will have an adverse affect on the machining accuracy of the machine tool and also on the stability of the control system. We establish an expedient lumped parameter model of the ball-screw feed drive system considering several axial and rotational degrees of freedom. Incorporating this model with the electrical drive and the position/vibration control system we build a complete simulation model. We show that our position/vibration controller with feedforward and feedback control can grant high positioning accuracy with simultaneous suppression of possible vibrations during machining.