Research On Stiffness Regulation Technology For Large-Scale Precision Air-Floating Micro-Vibration Isolation

With the large-scale ultra-precision machining equipment,measuring instruments,and large-scale cutting-edge scientific experimental systems stepping into nanometer and sub-nanometer precision,low-frequency micro-vibration in the environment have become one of the crucial factors limiting the further improvement of ultra-precision machining and measurement accuracy,imaging resolution,and other core indexes.Therefore,large-scale precision micro-vibration isolation technology has become the core technology to guarantee the accuracy of large-scale ultra-precision machining equipment,measuring instruments,and cutting-edge scientific experimental systems.Air-floating micro-vibration technology has the advantages of large loading capacity,natural frequency basically does not fluctuate with the mass of loading capacity and is suitable for multi-degree-of-freedom vibration isolation.Therefore,it is applied to large-scale ultra-precision machining,measurement,and cutting-edge scientific experiments.The following vital problems still exist in the field of large-scale air-floating micro-vibration isolation.(1)As the core equipment of air-floating micro-vibration isolation technology,the current vertical stiffness models of large-scale air-floating micro-vibration isolators fail to comprehensively characterize the influence of elastic membrane deformation on its vertical stiffness.(2)Current permanent magnetic or electromagnetic stiffness regulation technologies are limited by parallel magnetized permanent magnets or electromagnets arranged by an equal gap,which makes it difficult to generate high negative stiffness that solves the mutual constraints between the large loading capacity and low stiffness vibration isolation characteristics of largescale air-floating micro-vibration isolators.(3)The micro-vibration amplitude of large-scale precision air-floating micro-vibration systems is too weak to implement accurate sensing and feedback control.This paper addresses the above problems and the main work accomplished is as follows.Firstly,an analytical model for the effect of elastic membrane deformation on the vertical stiffness of large-scale air-floating micro-vibration isolators is investigated,to address the problem that current vertical stiffness models fail to comprehensively characterize the influence of elastic membrane deformation on the vertical stiffness of large-scale air-floating micro-vibration isolators.The law of the changes of arc length and chamber volume caused by the deformation of elastic membrane,which in turn affects the change rate of bearing area and chamber volume,is analyzed and modeled,so that the mechanism of elastic membrane deformation on the vertical stiffness of large-scale air-floating micro-vibration isolators can be analyzed.The difference between the stiffness calculated by the model and the measured stiffness is less than 9.7%,which is better than that of current models.This model allows the introduction of material parameters,structural parameters,inflation pressure,loading capacity,and the accurate analysis of their influence on the vertical stiffness of large-scale air-floating micro-vibration isolators,laying a theoretical foundation for the optimization of large loading capacity and low stiffness air-floating micro-vibration isolators.Secondly,a passive stiffness regulation method based on spatial magnetic ring array is studied to address the problem that current permanent magnetic or electromagnetic stiffness regulation technologies are limited by parallel magnetized permanent magnets or electromagnets arranged by an equal gap,which has low magnetic flux density and is difficult to produce high negative stiffness.The mechanism of the current stiffness regulation technologie is analyzed in depth,and the basic reasons that limiting the generation of high negative stiffness are investigated.The high negative stiffness characteristics is achieved in the axial direction by arranging multi-layer magnetic rings axially,magnetizing adjacent layers perpendicularly,and nesting them coaxially to form a high magnetic density spatial magnetic ring array.Compared with the current coaxial magnetic ring negative stiffness structures,the negative stiffness can be increased up to 155 times at the same size.In parallel with a large-scale air-floating micro-vibration isolator,it is possible to create localized low dynamic stiffness characteristics under large loading capacity,thus effectively solving the mutual constraints between the large loading capacity and low stiffness vibration isolation of large-scale air-floating micro-vibration isolators.Thirdly,an active stiffness regulation method based on the composite feedback of acceleration and velocity is studied to address the problem that the micro-vibration amplitude of large-scale precision air-floating micro-vibration systems is too weak to implement accurate sensing and feedback control.By adjusting the virtual mass through load acceleration feedback,the equivalent adjustment of air floating stiffness is realized,and the composite load absolute velocity feedback is used to suppress the peak vibration transmissibility.Simulation analysis of the regulation effect of the active stiffness regulation method on the frequency domain index of the air-floating micro-vibration isolation system,as well its effect on the vibration attenuation performance are carried out.The proposed active stiffness regulation method reduces the peak vibration transmissibility of the large-scale precision air-floating microvibration isolation system and its corresponding frequency,and achieves excellent vibration suppression performance at low frequency.Finally,experimental setups are built respectively to verify the passive stiffness regulation method based on spatial magnetic ring array,the active stiffness regulation method based on the composite feedback of acceleration and velocity.Experimental results indicate that the passive stiffness regualation method can reduce the stiffness of the air-floating micro-vibration isolation system by 28.40%,attenuate the peak vibration transmissibility by 74.76%,and reduce the frequency corresponding to the peak vibration transmissibility from 1.625 Hz to 1.375 Hz.The active stiffness regulation method can reduce the stiffness of the air-floating micro-vibration isolation system by 71.01%,attenuate the peak vibration transmissibility by 57.59%,reduce the frequency corresponding to the peak vibration transmissibility from 1.625 Hz to0.875 Hz,and upgrade the vibration isolation level from VC-F to VC-G.