Research On Active Vibration Isolation System Based On Modal Decoupling

With the rapid development of semiconductor industry in recent years,the demand of chip keep increasing in quite a few industries.In order to overcome the technical difficulties and increase yield,each step of the production process needs to be done well.The environmental vibration is an unavoidable factor for all instruments and equipments.How to isolate vibration and provide a stable working environment for instruments and equipment,which has become a hard problem.In addition,in order to improve the performance,such as the precision measurement field represented by gravitational wave detection,ultra-precision machining field represented by micro and nano fabrication,they are also faced with the problem of vibration isolation.Vibration isolation not only needs to suppress the vibration produced when the equipment works,but also needs to reduce the influence of ground vibration on the equipment.Because vibration isolation equipment needs to simultaneously suppress vibration of multiple degrees of freedom,it is a typical multi-input and multi-output motion control problem.It is difficult to design the controller for this system.In this paper,the vibration mode theory is introduced.The vibration isolation platform is decoupled by modal theory,and each modal is used as the controlled object in modal decoupling.According to PID control theory,an independent controller is designed for each modal.The main research work is as follows:Firstly,the mechanical model of the vibration isolation platform has be given,and the dynamic model of the vibration isolation platform is established.And this paper analys the disadvantages of passive vibration isolation.It is necessary to introduce active control strategy.Independent PID controller is designed in modal space,which is based on the analysis of active control strategy and control principle of multi-degree-of-freedom platform.Secondly,this paper selects appropriate reference points to establish different coordinate systems and establishs the relationship between each position and state of the system.A series of decoupl tasks,such as position decoupl,force decoupl and modal decoupl have be analysed.The mechanical model of the system is established in the Adams environment to verify the feasibility of each decoupling method,and the single-point excitation method is used to measure the natural frequency.And the theoretical calculation value is compared to correct the theoretical calculation error.Third,the PID controller is designed and simulated.This paper takes the single-degree-of-freedom vibration isolation system as an example to analyze the limitations of different feedback variables introduced by the controller.Finally,the vibration isolation system introduces relative displacement as feedback.The modal PID controller is designed.In order to improve the measurement accuracy of the sensor,this paper introduces a kalman filter to reduce the noise of the sensor.Experiments shows that relative displacement sensor can reach 1um measurement resolution and the use of the kalman filter will cause a delay of 0.27 ms.Finally,the combined simulation model of Adams and Simulink is established to test the performance index of active vibration isolation experimental platform based on modal decoupling.A control system block diagram is built,the Adams mechanical model is described in linear space,the mathematical control model is established.The results show: The stability time of step response in X?Y direction is less than 20 ms,The stability time of step response in X?Y direction is less than 50 ms.The sensitivity of the X?Y?Z direction system is less than 0 d B in the whole frequency band.The X and Y of sensitivity resonance peak decreases from 10 d B to-22 d B d B,the Z sensitivity resonance peak from 20 d B to-34 d B.The resonant peak of X and Y of transmissibility decreases from 25 d B to 1 d B,the Z of transmissibility decreases from 20 d B to-8 d B.To sum up,the modal decoupling control method can effectively improve the vibration isolation performance of the vibra tion isolation system.