Research On Low Frequency Micro Vibration Isolation System Of Large Precision Instrument

In recent years,the acceleration of infrastructure construction in major regional central cities,a large number of low-frequency pulse vibrations are generated during the start-up and braking of vehicles and propagate in the form of ground pulsation,which has a great impact on the use of precision instruments.The electron microscope as an example,as the most important research instrument of nano biotechnology,it is extremely sensitive to environmental vibration,and the environmental vibration required to work should reach VC-G level.In order to meet the vibration environment requirements of precision instruments,a reliable low-frequency micro vibration isolation system is usually designed for large precision instruments.At present,there is a lack of research on the design method and isolator of low-frequency micro vibration isolation system for large precision instruments in China.In this dissertation,the dynamic characteristics of air spring with additional chamber and the dynamic characteristics and design method of floating foundation vibration isolation system are studied theoretically and experimentally.The main contents and conclusions of this dissertation are as follows:(1)Based on the ideal gas state equation,the mechanical models of the main chamber and additional chamber of the air spring are derived.Assuming that the gas in the throttling orifice is a reciprocating mass,the mechanical model of the throttling orifice is deduced through Bernoulli equation,and the nonlinear constitutive model of the air spring with additional chamber is obtained.The small deviation linearization method is used to linearize the mechanical models of the main chamber,additional chamber and throttling orifice at the equilibrium position.The frequency dependent low-frequency micro vibration stiffness of air spring with additional chamber is obtained by Laplace transform of the linearized model.The derived formula is verified by the designed micro vibration stiffness experiment.(2)Based on the obtained nonlinear constitutive model of air spring,a single degree of freedom floating foundation vibration isolation system with system damping is established,and the numerical solution and calculation program are given.Based on the low-frequency micro vibration stiffness model,the equivalent mechanical model of air spring with additional chamber is obtained,the transfer function of floating foundation isolation system is deduced,and the characteristics of transfer function are discussed.Based on the energy method,the mass,stiffness and damping matrix of rigid body supported by elastic axial spring are derived,and the equation of motion and eigen-analysis equation are given.Finally,the derived equation is applied to the actual vibration isolation system,and the calculation results of analytical model and finite element model are compared.The results show that the calculation of the first six modes of the floating foundation is consistent between the analytical model and the finite element model,and the relative calculation error of the first six modes is less than 5%.(3)The mechanical experiment of viscous damper is designed by using the loading mode of sine wave displacement control.It is loaded horizontally and vertically under different temperature and frequency.Based on the variation of the number of viscous dampers,the damping optimization of the floating foundation vibration isolation system is studied,and the vibration isolation effect of the floating foundation vibration isolation system is tested.Combined with the deduced nonlinear constitutive model of air spring,the finite element model of floating foundation vibration isolation system is established in SAP2000 finite element software.The laboratory ground vibration measured in the experiment is input into the finite element model,and the finite element simulation results are compared with the vibration response measured on the floating foundation vibration isolation system.The finite element simulation results are in good agreement with the experimental data,especially in the lowfrequency micro vibration region less than 6Hz,which shows that the model performs well in the low-frequency micro vibration region.(4)Combined with the working characteristics of Convolution Neural Network(CNN)and Long Short Term Memory(LSTM)networks,Recurrent Convolution Neural Network(RCNN)is proposed,and a deep neural network logical constitutive model of air spring restoring force based on physical information is established.The numerical model results verify the effectiveness of the air spring restoring force prediction model based on logical constitutive model,which is excited by artificial wave,El Centro wave and white noise.The dynamic model of floating foundation vibration isolation system based on air spring restoring force is established,and 11 natural seismic waves and 11 artificial seismic waves are used as excitation inputs.The dynamic response of floating foundation vibration isolation system with air spring force calculated by numerical constitutive calculation and logical constitutive model as input is compared and analyzed,and the reliability of the model is verified.In the micro vibration analysis of floating foundation vibration isolation system of large precision instrument in National Synchrotron Radiation New Light Source Laboratory,a data-driven logical constitutive model of floating foundation damping system is established.The RCNN,CNN and LSTM logical constitutive models are compared and analyzed.The results show that the RCNN logical constitutive model based on physical information has the highest accuracy.(5)In this dissertation,the design method of floating foundation vibration isolation system for large precision instrument is proposed by referring to relevant specifications and design guidelines and summarizing the design experience of engineers.Finally,the design method of floating foundation vibration isolation system of large precision instrument is explained by using the design of micro vibration isolation system of large precision equipment in a nanotechnology research center.