Katsumi Asada

Modeling of Three-Degree-of-Freedom Fine Motion Mechanism and Improvement of Control Performance.

As miniaturization of exposure patterns progresses, high positioning accuracy of submicron order is necessary for the semiconductor components. Moreover, in order to transcribe the circuit pattern to multiple positions on an IC wafer, a positioning mechanism with long stroke also must be developed. This paper focuses on the former. By driving the piezo actuators mounted under the flat plate, this mechanism has a positioning function with 3 degrees of freedom. This paper first describes a mathematical model of a fine motion mechanism with 3 d. o. f., and we confirm the adequacy of the control model by comparison with the measured frequency response. Secondly, both static and dynamic decoupling conditions for the controlled object itself are derived, and we show that this conditions are equivalent to that of the center of percussion. In the case of control for the positioning mechanism with multi-d. o. f., the matrix inversions are generally inserted into the control loop to cancel the interference based on the space assignment of both the position sensors and actuators. However, if the controlled object can be kinematically decoupled by the mechanical design, it is unnecessary to construct the complex control loop. Finally, we propose acceleration feedback in order to improve the control performance, and its superior performance is illustrated by the numerical simulation.