The next-generation fine stage of the wafer scanner needs a suitable actuator to meet the requirements of high speed, high acceleration, and high precision. The voice coil actuator is no longer the best choice because of its large size and the heat dissipation is difficult to solve. The reluctance actuator can provide a big force based on a unique property of small volume and low current, making it a very suitable candidate. But the strong nonlinearity such as the hysteresis between the current and force limits the reluctance actuator applications in nanometer positioning. This paper proposes a nonlinear current control configuration with hysteresis compensation using the adaptive multilayer neural network. Simulation results show that the hysteresis compensator is effective in overcoming the hysteresis and is promising in precision control applications. 1. Introduction In high-precision applications such as semiconductor lithography systems, the force density and accuracy of wafer scanner increase rapidly in recent years [1]. For wafer scanner, it needs accurate positioning to meet the requirement of high-precision actuation. It is realized by a fine stage mounted on a coarse stage. The fine stage has a millimeter range with an accuracy of nanometers and the coarse stage has a range of meters with the accuracy of submicrometers. In conventional design of fine stage actuators, the relatively low variation of the force is the main reason to choose for voice coil actuator. But in the development of new short-stroke actuator, the production speed and the positioning accuracy gain more importance [2]. A higher throughput is achieved by increasing the acceleration of the fine actuator. If voice coil actuator is still used to achieve greater force, its size will become very large and the heat dissipation problem will be very difficult to solve [3]. Therefore, the voice coil actuator is no longer the best choice as the main driving actuator of fine stage. Because the reluctance actuator, whose force is proportional to the square of the excitation current, can produce greater force with a small volume and low current than the voice coil motor, it provides a solution to meet the driving requirements of the next-generation fine stage. The mentioned advantage of the reluctance actuator comes at a sacrifice of parasitic effects such as the eddy current and hysteresis, which deteriorate the force predictability and add additional nonlinearity to the actuator. These effects can be reduced by using magnetic cores made of thin laminations of soft ferromagnetic
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