Precision Improvement in the Continuous Path Control of Direct Drive Rotary Table Systems for Machine Tools by Identifying the Vibration Modes with Higher Resonance Frequencies than the Control Cycle's Defined Nyquist Frequency

Abstract

Direct drive (DD) motors realize precise position control but are easily affected by torque ripple vibrations. Higher gain leads to suppression of the vibrations but it brings excitations of other mechanical resonances at higher frequencies than the Nyquist frequency. We propose a new measurement method of exact frequency response to the Nyquist and beyond to identify such mechanical resonances. The performance has been evaluated in an actual machine tool with a DD motor. The precision of continuous path control is improved with higher gain assisted by the proposed method.