マシニングセンタの円弧補間運動における二山象限突起の補正

概要

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Quadrant glitches are one of the causes of deteriorating the machining accuracy in NC machine tools because those leave streaky marks on the machined surfaces. The quadrant glitch is caused by friction of the ball screw and linear guides of feed drive systems. In this study, when the circular trajectories are precisely investigated by conducting the circular motions under various conditions, it is found that the preload in the ball screw affects the height and shape quadrant glitches at low feed speed. It is caused by the difference of contact points between balls and grooves of ball screws. It is also found that the quadrant glitch becomes one peak in case of oversize preload in ball screw, and two peaks in case of offset preload. In this study, a method for compensating two peaks observed in quadrant glitches due to the change of contact points between balls and grooves of a ball screw is proposed. A proposed compensating method can cancel the friction torque changes generated in the ball screws with a new mathematical model. It is confirmed that the proposed method can decrease the quadrant glitches in a wide feed speed range through simulation and experiment, and the proposed method can correct two peaks of the quadrant glitches in high accuracy. In addition, from circular motions with mass, it is confirmed that the proposed method can correct the quadrant glitches without deteriorating effect of mass.