| As a representative in high-technology industry, IC manufacturing has been given more and more attention by various countries around the world. Its key indexes are lithography’s pitch and productivity. At present, with the improvement of these two indexes, the ultra-precision positioning technology is advancing towards high precision, high acceleration and long stroke. The voice coil motor(VCM) is a linear motor, and its design is based on Lorentz force principle. VCM has been widely used in ultra-precision positioning systems because of its advantages, such as simple structure, small size, high acceleration and fast response. In order to realize ultra-precision positioning motion of VCM, the research of this paper is mainly focused on the following aspects, the mathematical model of VCM, high-precision power converters and ultra-precision positioning motion control strategy.In order to establish accurate mathematical model of VCM in high frequency motion, the impacts of air damping force, eddy current damping force and elastic stiffness force on positioning precision must be considered. The causes and influencing factors of hysteresis characteristic of VCM in high frequency motion are analyzed and verified. The sweep experiment verified that the hysteresis characteristic is closely associated with motion frequency and motion stroke. At the same time, the causes and influencing factors of eddy current damping force are analyzed. With two kinds of stators made of different materials, the free vibration experiment is conducted to identify the eddy current damping coefficient and air damping coefficient accurately. In addition, the mechanical resonant frequency of VCM is tested; the notch filter is designed to eliminate the mechanical resonance peak.In the lithography motion control system which has extremely high requirements for response time, positioning precision and efficiency, the power converter of VCM should possess high power, high precision and high bandwidth simultaneously. In order to solve the contradiction of high power and high precision, a switch-linear series hybrid power amplifier(SLSHPA) is proposed in this paper. The switch-mode amplifier adopts the asymmetric cascade H-bridge(ACHB) seven-level topology structure. The multi-frequency carrier-based PWM(MFPWM) modulation method is adopted, which can prevent current flow-backwards effectively. At the same time, the current ripple and voltage harmonic expressions of ACHB power converter are derived. The LCCR low-pass filter is designed to filter out voltage harmonics and current ripple. The closed-loop voltage control based on linear power amplifier is regulated to compensate for the small voltage error. To compensate voltage error quickly and accurately, the double cascaded PI controller is realized in the way of analog circuit. Finally, the validity of the SLSHPA is verified by the DC and AC experiments, the performance indexes of SLSHPA are tested, power: 750 W, peak current: 10 A, current ripple: 1.2m A, the voltage THD: 2.4%(250Hz). The experimental results show that the SLSHPA has the advantages of high power, high precision and low distortion.The motion conditions of VCM in lithography mainly include high-precision trajectory tracking motion(HPTTM) and high-precision point-to-point positioning motion(HPPTP). Different control strategies are used to meet different motion conditions and requirements. In HPTTM control, the 5 order S-shade curve is used as the position reference; the active disturbance rejection control(ADRC) strategy is used as positioning control. As the simulation results show, ADRC has both strong robustness and high tracking accuracy compared with the traditional PID. In HPPTP control, an improved composite nonlinear feedback(CNF) control is proposed, the extended state observer and integrator are put into the original CNF. The simulation results show that the improved strategy maintains the merits of high dynamic and low overshoot, meanwhile, improves the steady-state accuracy and anti-disturbance.The VCM ultra-precision positioning experiment platform is established to verify the performance of HPTTM and HPPTP motion. The experiment test is carried out in the case of single-axis with unloaded and muti-axis with load, the positioning precision is 1μm in the range of ±2mm under single-axis with unloaded exprement condition. The positioning precision is 0.4μm in the range of 500μm under muti-axis with unloaded exprement condition. In HPTTM experiment, the sinusoidal signal and 5-order S-type signal is used as position reference, the positon loop bandwidth is 10 Hz by experiment test. |
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