STATIC PRESSURE BEARING DEVICE

摘要

PURPOSE:To prevent self-excited vibration by constituting a periodic fluctuation component of a phase delay of 90 deg. with respect to a decrease in clearance dimension among static fluctuation components in such a manner as to be positive at frequency equal to natural frequency of a vibrating system including a moving table at the time of a periodic change of the bearing clearance. CONSTITUTION:Natural frequency of a positioning stage of a vibrating system including a bearing housing 2, a porous pad 3 and other members integrally connected to the housing 2 and the pad 3 which are all mounted on a moving table 1 is calculated to be 200Hz, at which resonance is realized. The moving table 1 is vibrated at predetermined frequency, a variation DELTAp of gaseous static pressure of a bearing clearance by reducing a bearing clearance dimension (h) from an equilibrium state value hg by DELTAh is measured, and a vibration component DELTAp1 of the same phase as a periodical decrease DELTAh of the bearing clearance dimension and a periodical fluctuation component DELTAp2 having a phase delay of 90 deg. are detected, thus obtaining a frequency characteristic of the porous pad 3. The component DELTAp2 becomes the positive maximum value in the vicinity of frequency of 200Hz. Consequently, vibration can be alleviated in a short time even if the vibration is generated in the positioning stage.