| With the advances in precision machining and precision measurements and the development of aerospace technology, the demands for the dynamic stability of mechanical structures and vibration resistance are continuously increasing. Lithography equipment, ultra-precision optical test instruments, and ultra-fine processing equipment for micro-vibration technology and scientific experiments require very stringent environmental requirements. Gravity compensator, as an important component of micro lithography machines, its anti-vibration performance will directly affect the vibration exposure precision of the silicon wafer. Vibration disturbance can affect the structural stability and the precision of the system, especially some low frequency interference, passive vibration isolation is easy to implement, but its low-frequency vibration control effect is not sufficient and it has a poor ability to cope with environmental mutation. Therefore, this paper introduces an active virtual mass micro-vibration isolation control method based on two-parameter acceleration feedback. Using acceleration feedback systems can increase the virtual mass, thereby reducing the natural frequency and improving the vibration isolation performance of the system, but this is accomplished at the cost of excessive output from the motor, so this paper proposes a new two-parameter acceleration feedback control method, which not only has the advantages of traditional acceleration feedback, like micro-vibration isolation, increasing the virtual mass and reducing the natural frequency of the system, but also prevents excessive motor output. At the same time, this paper also uses the feedforward control to improve the response speed to vibration disturbance of the system. The main tasks of this paper are as follows:This paper first analyzes the structure and function of gravity compensator, and establishes the model of single degree of freedom. Gravity compensator is obtained by theoretical derivation and calculation, vertical movement part of each parameter, finally obtaining the mechanical transfer function. The parameters of vertical movement part of gravity compensator can be obtained by theoretical derivation and calculation, so the system transfer function can be got.Secondly, establishes the single degree of freedom model of active vibration isolation system and selects the acceleration feedback control method. Mainly through the acceleration feedback to increase system virtual mass and reduces the natural frequencies of the system, improving the system performance of vibration isolation. At the same time, uses feedforward control to the response speed to vibration disturbance of the system. Using SIMULINK software to analyses various control methods to get the simulation results of their inhibitory effect on vibrating disturbance, the size of the motor output, and the impact on the natural frequency. These results verify the feasibility and effectiveness of the control methods in theory.Finally, using the gravity compensator builds the single degree of freedom system for experimental analysis. We test the voice coil motor on gravity compensator at first to see if it meets the design requirements. On system natural frequency test experiments, the experimental results show that using two-parameter acceleration feedback of active vibration isolation control method can reduce the natural frequencies of the system from 1.0 Hz down to 0.5 Hz,which was reduced by 50%.The effect was very obvious. Feedforward and feedback control method can not only reduce the natural frequency of the system, but also can reduce the resonance peak in the transmission rate. The vibration speed of the system after the closed loop was smaller than the open loop, which was reduced by 50%.And the system became not sensitive to the vibration disturbance of base stations. Relative acceleration feedback can reduce the natural frequency of system down to 0.2Hz, but the resonance peaks became larger too. |
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