Design and control for an electromagnetically driven X-Y-θ stage

In this paper, the design and control of a novel precision motion stage is presented. It combines a flexural stage, electromagnetic actuation, capacitance position measurement, and nonlinear digital feedback control. This system has high open loop stiffness, and such a spring-dominated regime design provides a sufficient phase margin for applying phase lag-based control to reduce environmental effects such as base vibration and high frequency noises. In addition, the incorporation of the rotational motion not only increases the degree of freedom, but also provides capability for correcting possible undesired coupling between major axes. As a result, there would be fewer requirements in degree of precision for stage machining and assembly. With nonlinear control, the performance of this stage would be more consistent than those with controller based on linearizing system dynamics. Experiments show that the system has a bandwidth of 85 Hz with a minimum resolution of 50 nm, which is dominated by the quantization of data acquisition devices. This implies that the present design can be readily modified to achieve higher performance. However, it is also found that a major difficulty in the present design is the insufficient damping of the rotational mode, which limits the applicable control gain and achievable performance and should be corrected by proper mechanical redesign in the future. Nevertheless, this design still shows its potential advantages. Finally, the stage is integrated with a stylus to demonstrate the possible application in surface morphology measurement. Possible applications also include the fine motion control and scientific instrumentation. (C) 2002 Elsevier Science Inc. All rights reserved.