Active Air Rotary Bearing

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The aim of the research project was to establish the mechatronic air bearing which has following features : (1) Measurement and control of five degrees of freedom of the axis error motion, (2) Active improvement of the bearing stiffness and damping capability, and (3) Measurement and control of the absolute error motion of the axis.First, a measurement method of the absolute rotation accuracy of an axis and its profile error i. e. the roundness error was established. The method was proved using the active air journal bearing (AAJB) which could radially position the axis by piezoelectric actuators. The accuracy of both of measurements were 15nm.Secondly, in order to realize the absolute accuracy of the rotation motion, a control method was discussed of the position of the axis which had a profile error. The method was examined using the AAJB and the rotation accuracy less than 20nm at 750rpm was accomplished.Lastly, the active air rotary bearing (AARB) which could control five degrees of freedom of the axis error motion was designed and constructed. The bearing comprises of two AAJBs to control four degrees of freedom of the axis motion and an active air thrust bearing to control the thrust motion. The performance of the AARB was :(1) Control band width : 30OHz, Positioning resolution ; 15nm(2) Rotation accuracy at 45rpm ; radial motion, 15nm and inclination, 0.015arcsec(3) Static stiffness ; infinite