Design and control of an air-bearing supported three degree-of-freedom fine positioner

The authors discuss design considerations and control issues of a fine-motion device which provides very high performance, precision, and speed (12-g acceleration, 0.2 μm resolution). Coupled with a standard industrial robot and external sensing, improvements in precision up to two orders of magnitude can be achieved. Software enables it to be operated from a serial port of an IBM PC or PS/2. The moving element of the positioning head can be commanded to move over a ±1 mm range in x and y, and rotated up to ±1.75° in θ about the z axis. The device provides variable compliance with compliance set by loop gain in a digital controller. It incorporates a novel three-degree-of-freedom motor, a pair of internal position sensors to enable controlled motion in the plane, and an air bearing to support the moving elements