可变节流高度气浮支承结构设计及动态性能分析

为了使气浮支承的承载力动态可调，设计了一种可变节流高度气浮支承. 通过建立气浮支承计算流体动力学(Computational Fluid Dynamics，CFD)模型，利用CFD动网格技术来模拟小孔节流器的运动，研究小孔节流器的结构参数、运动参数及气浮支承的工作参数对可变节流高度气浮支承动态性能的影响. 结果表明:通过调节小孔节流器的节流高度可以明显改变气浮支承的承载力；在只考虑单一变量的前提下，气浮支承承载力的波动量随着小孔节流器的运动幅值、运动频率、节流高度、直径和气浮支承供气压强的增加而增加，但随着气膜厚度的增大而减小；当小孔节流器直径较小时，随着小孔节流器运动频率的增加，气浮支承动刚度的增幅很小，但当小孔节流器直径增大时，随着小孔节流器运动频率的增加，气浮支承动刚度的增幅会明显变大. 

Structure Design and Dynamic Performance Analysis of Aerostatic Bearing with Variable Height Restrictor

Aerostatic bearing widely used in precision manufacturing equipment because of the characteristics of no friction, no wear, no pollution and high stability. But with the ultra-precision machinery to the requirement of increasing the machining precision, loading capacity and stability of the aerostatic bearing greatly affect the machining precision of ultra-precision machine tools. The traditional surface throttling method is mainly to improve the static performance of the aerostatic bearing. Therefore, a piezoelectric active aerostatic bearing with variable height restrictor was designed to improve the loading capacity and reduce the micro vibration of the aerostatic bearing. The aerostatic bearing worked by controlling the output force of piezoelectric actuator to change throttling height of the orifice restrictor. The quarter gas domain model of the aerostatic bearing was established. The quarter gas domain model was meshed and boundary conditions were set. In the CFD (Computational Fluid Dynamics) software, the dynamic grid technology was used to simulate the movement of the orifice restrictor. The realizable k-ε turbulence model was used to simulate the dynamic characteristics of the aerostatic bearing with variable height restrictor. The influences of the structure parameters, movement parameters of the orifice restrictor and the working parameters of the aerostatic bearing on the dynamic performance of aerostatic bearing with variable height restrictor were analyzed by orthogonal analysis method. The adaptability of the computational model and the accuracy of the dynamic grid technology were verified by comparing with the simulation data of references. The results of transient simulation showed that the loading capacity of the aerostatic bearing can be obviously changed by adjusting the throttling height of the orifice restrictor by controlling the expansion of the center part of the flexure hinge. The motion state of the orifice restrictor had great influence on the dynamic characteristics of the aerostatic bearing with variable height restrictor. Under the premise of considering only a single variable, the fluctuation of the loading capacity of the aerostatic bearing with the orifice restrictor increased with the increase of the moving amplitude, moving frequency, throttling height, diameter and the supply pressure of the aerostatic bearing, but decreased with the increase of the gas film clearance. When the diameter of the orifice restrictor was small, the increase of the dynamic stiffness of aerostatic bearing with variable height restrictor was small with the increase of the moving frequency of the orifice restrictor. When the diameter of orifice restrictor was large, the increase of the dynamic stiffness of the aerostatic bearing with variable height restrictor was obviously large with the increase of the moving frequency of the orifice restrictor. The dynamic characteristics of the aerostatic bearing with variable height restrictor can be improved effectively by adopting appropriate control strategy.