An Active Air Bearing : Control of Radial Axis Motion and Stiffness

The aim of this paper is the development of bearings with the following features : ( 1 ) ultrahigh precision, ( 2 ) infinite static stiffness, ( 3 ) high vibration damping capability, ( 4 ) new functions (axis positioning and dynamic stiffness control). For this purpose, an active air journal bearing (AAJB) is proposed. The AAJB is a new type of mechatronics bearing composed of noncontact sensors to detect the radial position of its axis, noncontact actuators (movable air pads driven by PZT actuators) to support and drive the axis, and a controller to regulate the whole system. An experimental AAJB is constructed and experiments prove that the AAJB has the following advantages : ( 1 ) an almost infinite static stiffness and an improved damping capability, ( 2 ) axis positioning over 8μm with a resolution better than l0nm, ( 3 ) an axis rotational accuracy better than 25nm at 1000rpm with an unbalanced load, ( 4 )quick and precise axis positioning at 1OOOrpm by a rectangular reference input.