Development of active squeeze air bearing using oscillation of piezoelectric actuators (3rd report) - Theoretical analysis and experimental verifications for motion guide

The aim of this research is to achieve a real time motion error correction of an object guided by squeeze air films. They are generated through sinusoidal relative perpendicular motions between the object and the driving pads excited by piezoelectric actuators. The non-contact motion error correction can be realized by controlling piezo expansion according to the measured motion error of the object while keeping piezo oscillations. In this paper, theoretical considerations and experimental verifications for squeeze air film characteristics are presented. Lees' difference approximation method is applied to solve the Reynolds equations governing pressure distribution for the upper and lower side air film and the equation of object motion simultaneously. The experimental equipment has an object of which the radial motion is constrained by an aerostatic guide to make a free vertical motion. It was experimentally confirmed that the squeeze air film could suspend the object with the mass of 1.39kg. The influence of step between surfaces of the driving pad and a pressure sensor embedded in the pad was considered by numerical analysis. When the depth of sensor surface was less than 20μm, the drop of a time mean pressure at the center of the driving pad was 2% or less for the flat surface. The experimental results of the time mean air film pressure and the floating height of the object agreed well with the numerical ones within 5% error when only the lower exciter was driven. Furthermore, as the lower and upper exciters were driven, it was demonstrated that the proposed technique could expect the characteristics of squeeze air films.