Control of a long range high-precision positioning system

Among a variety of actuators, Lorentz actuators are often used as fine actuators in DSA systems under an environment where disturbances are expected at fine actuators’ base. Their advantage is that they show an almost ideal zero stiffness characteristics, which is that disturbances from bases do not transmit to the moving parts [1]. Such zero-stiffness DSA systems have been applied to wafer scanners for lithography [2]. However, since movable parts need to float, these setups tend to be heavy and bulky with granite plates and air feet for pneumatic levitation or require relatively complicated sensing and control for magnetic levitation with multiple Lorentz actuators [3]. In addition, heavy moving parts are under constraint of the mass dilemma of precision positioning systems, which is that the mass of a moving part is determined by a compromise between the achievable acceleration and the sensitivity for disturbance [1]. Thus the dilemma restricts the performance of the dual stage system, limiting either its operational speed or accuracy.