Development of a Linear-Motor-Driven Table with Hydrostatic Water Bearings (Influence of Air Bubble Contained in Hydraulic Fluid on Dynamic Behavior of the Table)

Abstract

A linear-motor-driven table sustained by constant-flow hydrostatic water bearings has been developed. The table, which is supported by single-sided recess type bearings, is preloaded by its weight and the attractive force arising from permanent magnets of the linear-motor. Due to periodic change of the magnet polarity, the amplitude of the attractive force changes according to the table position. As a result, pitching motion of the table is generated during the table-feed motion. This paper investigates the influence of air bubble contained in hydraulic fluid on static stiffness and dynamic behavior of the table. Damping ratio and natural frequency of the table become smaller under larger volume of containing air. When natural frequency of the table pitching motion coincides with the frequency of the attractive-force change, the largest pitching motion is observed.