Design and continuous gain scheduling control of high precision XY-Theta stage

Abstract

Recently, many kinds of systems are invented to meet the purpose of long stroke and ultra precision positioning resolution. There are two categories for these purposes: dual servo system and one servo system. Dual servo system consists of coarse servo and fine servo. Dual servo mechanism has more actuator than the degree of freedom to be controlled. As another approaches for high precision stage, there is one servo system that can move long range and fine range with one actuator. With one actuator, the whole system structure is simpler than the dual servo system. And these systems also provide good performance in travel length and position resolution. The simple, easy, VCM(Voice Coil Motor) type, one servo system is proposed in this study as a comparatively smart design approach for the precision positioning system. It has fast response and fairly good position accuracy. It consists of three actuators. Each actuator is the same and is positioned 120 degrees radially to make the three degrees of freedom motion(XYθ). The whole system is designed conceptually to have the symmetry, simple and compact servo, and inherently infinite position resolution to meet the principles for precision system design. When the system is working, there are disturbances and unwanted vibration around the system. System must have enough force to reject disturbances and to have fast working rate. Therefore, in this study, acceleration is chosen as cost function of optimal design. There has been no trial of optimal design in the point of designing precision positioning stage. New Continuous Gain Scheduling Control (CGSC) is proposed. Controllers should be adapted according to the task. In fine positioning regions, the controller gain should be large enough to reject the disturbance and to maintain high precision positioning. In coarse positioning regions, since the reference input is large, the controller gain should be small in order to avoid the controller saturation. The simple con...