Disturbance Elimination Filter for Machine Tools

In this paper, a frequency-domain disturbance observer (DOB)-based filter is designed to reduce the disturbances in the low and medium frequency bands below 120 Hz generated by the feed shaft of a machine tool. The filter consists of an inverse model of the nominal plant and a Q-filter in the low-pass filter form. The disturbances in the low and medium frequency bands are estimated by inputting the motor speed of the feed shaft into the filter and then compensated to the q-axis reference voltage of the feed drive controller to suppress the noise and vibration caused by the disturbances. The designed disturbance elimination filter is simple in structure and does not require the use of external sensors except for an encoder for speed feedback. Furthermore, although the designed filter effectively suppresses disturbances, it can be implemented using only software without additional external devices. The performance is evaluated by MATLAB/Simulink-based simulations and real experiments using a one-axis feed drive control system. The experimental results show that the resonant frequency component of the feed drive system obtained from acceleration is reduced by 25.95 % in the simulations and by 11.47 % in real experiments.