A SURFACE MOTOR-DRIVEN PRECISE POSITIONING SYSTEM

A novel precise positioning system incorporating a surface motor (SFM) drive, called the SFM positioning system, has been developed and its performance experimentally evaluated. The positioning stage is guided along a base plate by three air-bearing pads and driven in 3-degrees of freedom (x, y, theta(z)) by coupled forces produced by three brushless-type linear DC motors. The positioning and guidance of the stage's planar motion is accomplished via the simultaneous operation of three identical force-controlled servo systems with a laser-interferometer position feedback loop. The system's advantageous design features and its fundamental configuration and operating principles are described. In addition, we discuss the design of the servo control system, being based on proportional-integral-derivative and decoupling compensations and providing dynamic accuracy as well as rapid response capabilities, including the control system configuration, which incorporates a high-performance parallel processor. Evaluations of experimental positioning tests indicate that a resultant positioning resolution of 10-20 nm, maximum speed of 150 mm/s, and frequency response bandwidth of 105 Hz are successfully achieved.