Evaluation of positioning performance of a fine-coarse mechanism by AC servomotors

A new positioning system has been developed to realize both the fine motion and the coarse motion independently and/or simultaneously to reduce the positioning time under the limitation of guaranteeing the positioning accuracy. To cope with this problem, the conventional reducer unit driven by AC servomotor is utilized. The fine-coarse motion of the developed mechanism is realized by only mechanical parts consisted of two servomotors and a harmonic drive speed reducer aligned in an axis. The main characteristic is that there are no stroke limitations in the fine and coarse motions with respect to the conventional fine-coarse motion stage by usage of the PZT device. The basic performances of angular positioning are evaluated by the feedback positioning system. The paper reports the fine and coarse positioning performances of the developed system.