In high-precision machining, knowing the precise diameter and length of the cutting tools and the correct setting of the coordinate system are very important. In general, the relative distance between the cutting edge and workpiece has to be measured using two measuring instruments in numerically controlled machine tools such as machining centers (MCs). The machining accuracy is affected by indirect errors in the measuring instrument and the error in the relative distance between the cutting edge and the workpiece. In order to eliminate this problem, this paper proposes an on-machine measurement system. This system uses an acoustic emission (AE) technique to precisely detect the cutting edge position when the cutting tool is in contact with the workpiece in real cutting conditions. This measurement system is installed into MCs and evaluated with different feed speeds and approach directions of the cutting tool with respect to the workpiece. Through this system, we successfully minimized the contact depth of the cutting edge and the workpiece, which also facilitated detection of the cutting edge position. The responsiveness of AE signals and measurement system were investigated and found to be suitable with few limitations.

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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.

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This study presents the method of active vibration damping in cutting using relative acceleration, which is intended for full-closed controlled ball-screw-driven stage. Disturbance against rigid body motion is canceled out by using multi-encoder-based disturbance observer. Disturbance/internal disturbance against relative motion is canceled out by using relative acceleration instead of relative velocity or displacement. The use of acceleration signal recovers phase lag and leads to suppress vibration in higher frequencies. In addition, it enhances low-frequency cutoff characteristics in extracting relative motion, which enables band-limited vibration control separating the rigid body and the relative motion. By introducing suitable phase lead filter which makes phase shift zero between load force and current response, vibration of the table can be effectively suppressed without significantly changing the resonance frequency. The results of end milling tests show that the vibration near the resonance frequency is suppressed by relative acceleration feedback.

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