Development of a Linear-Motor-Driven Table Supported by Hydrostatic Water Bearings: Effect of Air Volume Contained in Water-Supply Tube on Pitching Motion of Table Slider

A linear-motor-driven table supported by hydrostatic-water bearings had been developed. The table slider is supported by a single-sided recess type bearing system and preloaded by attractive force using a linear-motor magnet. Since eccentric excitation force is applied to the table slider due to the change of attractive force according to the magnet track position of the linear-motor, pitching motion of the table occurs. This paper investigates the effect of air volume contained in a water-supply tube on the pitching motion. Larger air volume results in lower natural pitching frequency of the table slider, lower logarithmic decrement of the pitching motion and larger pitching angle. When the natural pitching frequency corresponds to the frequency of the eccentric excitation force during table feed, pitching angle grows by resonation.