Research On The Dynamic Characteristics Of High-speed Aerostatic Bearing-rotor System

The molding processing of ultra-precision optical components with complex curved surfaces generally uses precision grinding electric spindles.Aerostatic bearings have become the mainstream support method for precision grinding electric spindles due to their inherent advantages such as near-zero friction,no wear,high rotation speed and ultra-high precision.Under ultra-high-speed rotating conditions,the complex dynamic behavior of the high-speed aerostatic bearing-rotor system directly affects the motion accuracy of the electric spindle,which further directly affects the grinding accuracy of complex curved optical components,so it is particularly important to study the dynamic behavior of the high-speed aerostatic bearing-rotor system.There is an urgent need to conduct relevant research on the dynamic behavior of high-speed aerostatic bearing-rotor system and its mechanism,so as to guide the development of high-speed gas bearing electric spindle with better performance and higher precision.In this dissertation,the high-speed aerostatic bearing-rotor system is taken as the research object to study the static and dynamic characteristics and stability enhancement of the system,and at the same time,a physical prototype of the system is developed.Theoretical and experimental studies provide guidance for system design and performance improvement.The main research work is:(1)Aiming at the problem of ignoring the spatial position of the rotor,which is dominated by the structural parameters in the research of the static flow field characteristics of the aerostatic bearing-rotor system.The gas film thickness equation including all spatial positions of the rotor is established.By coupling the gas film thickness equation,the steady-state flow balance equation and the steady-state gas film flow field control equation,the mathematical representation of the static flow field of the bearing is achieved.The influences of the rotor eccentricity,attitude angle,angular pendulums and rotational speed on the gas film thickness,pressure distribution and bearing capacity are investigated,and the influence of the rotor position on the gas film flow field is pointed out,which provided theoretical basis and guidance for the actual operation of the bearing and the subsequent bi-directional fluid-solid coupling modeling as well as dynamics research.(2)Aiming at the problem that the dynamic modeling of the aerostatic bearing-rotor system is dominated by the small perturbation method,which ignores the effect of rotor motion on the gas film flow field.The transient flow balance equation,transient gas film flow field control equation and rotor motion equation are derived through gas lubrication theory and kinetic theory.By directly coupling these three types of equations,a bidirectional fluid-structure coupling mathematical model of the bearing system is established,which can consider the interaction between the bearing flow field and the rotor motion in real time.Based on the steady-state values calculated above,various numerical methods such as alternating direction implicit format method,Thomas method,finite difference method and Newmark method are used to solve the coupling model and obtain the response of the bearing system.(3)Aiming at the problem of unclear evolution process of dynamic properties of high-speed aerostatic bearing-rotor system under different parameters.Based on the results calculated by the aforementioned bi-directional fluid-solid coupling mathematical model,the axial trajectory,the axial swing trajectory,the rotor center trajectory,the Poincare map,the rotor moving and swing displacements,the spectrum diagram,the mass flow rate of the bearing,the gas film force,and the bifurcation diagram are used to study the evolution of the dynamic characteristics of the bearing system under different parameters.The transition process of the system from stability to instability is given,and the instability phenomenon of pneumatic hammer at high speed is captured for the first time,while reasonable operating,mass and structural parameters of the system are given.(4)Traditional methods to improve the stability of high-speed aerostatic bearingrotor system mainly focus on limiting system parameters and modifying the system structure.In view of the problem that these methods are difficult and require a lot of repeated experiments,a method of using neon as a lubricating medium to improve system stability is proposed.Considering the rarity of the neon,it is mixed with air,and the physical properties such as density,viscosity,and adiabatic index of the mixed gas under different volume ratios are calculated.Based on the calculation results,the bifurcation of the system under different volume ratios is investigated.It provides a simple and easy new idea for improving the stability and adjustment of the bearing system.(5)Based on the above theoretical analysis conclusions and the proposed optimization design method,a physical prototype of high-speed aerostatic bearing-rotor systems is developed,and the related experimental test platform for dynamic characteristics is designed and constructed.Experimental research is conducted under different rotation speeds and air supply pressures,and the experimental results are consistent with the theoretical prediction trends,proving the correctness of the theoretical research.