Research On Dynamic Stiffness Enhancement Methods Of Ultra-Precision Aerostatic Bearings

As a non-contact suspension support/guide component,the aerostatic bearings are the key components of the motion system in equipment such as ultra-precision manufacturing and measurement,and zero-gravity simulation.The dynamic stiffness of the aerostatic bearing is a decisive factor for the motion system to resist disturbance and ensure motion accuracy and stability.The increasingly demanding requirements for the dynamic stiffness of the aerostatic bearing stand out.For example,in the zero gravity simulation,the aerostatic bearing is required to support spacecraft weighing several tons.When it comes to ultra-precision manufacturing,the aerostatic bearing needs to maintain stability under the acceleration impact of the workbench.With the above-mentioned remarkable static/dynamic loads,the influence of the static and dynamic deformation of the aerostatic bearing structure on the support characteristics cannot be ignored.How to estimate the fluid-solid interaction effect on the aerostatic bearing and how to enhance the dynamic stiffness of the aerostatic bearing are difficult and hot issues in the design of the aerostatic bearing.For the needs of major national projects,this research considered fluid-solid interaction effect in the aerostatic bearing,proposed the dynamic stiffness modeling of the aerostatic bearing and the analysis of the pneumatic hammer vibration,and explored the design method of the vertical dynamic stiffness and the tilt dynamic stiffness of the aerostatic bearing,which provided a basis for the design of aerostatic bearings.Aiming at the problem that the deformation of the air bearing structure affects the support performance under heavy loads,especially high dynamic loads,we first clarified the static/dynamic stiffness generation mechanism of the supporting air film,and established the fluid-solid interaction model of the air bearing structure considering the structural deformation.The mesh update algorithm combined with the accelerated iterative operator was proposed to realize the high-accuracy and fast iterative solution of the coupled dynamics equations.The fractional derivative model was further introduced to characterize the dynamic characteristics of the air bearing,which significantly improved the accuracy of the dynamic stiffness of the air bearing,and provided a theoretical basis for the stiffness enhancement design of aerostatic bearings.Since pneumatic hammer can not be predicted accurately,this paper introduced the concepts of air capacity,air inductanced,and air resistance,to establish a mathematical model of pneumatic hammer vibration,and characterizes the pneumatic hammer vibration through numerical simulation.Through the analysis of the influence of structural parameters and working conditions on the vibration of the pneumatic hammer,our study identified the core factors that dominate the pneumatic hammer.Based on this model,the instability of the aerostatic bearing caused by the stiffness enhancement design could be avoided.To improve insufficient vertical dynamic stiffness of the air film in ultra-precision milling and other processing equipment,this paper proposed a piezoelectric-based air shape compensation method,which improves the vertical dynamic stiffness by adding active structures.The dynamic and static simulation and experimental results showed that the load capacity and dynamic stiffness of the aerostatic bearing have been improved significantly.To prompt insufficient tilt dynamic stiffness of the aerostatic bearing in ultra-precision measurement and microgravity simulation equipment,we deduced the steady-state and unsteady gas film lubrication models of the aerostatic bearing under tilt motion.The effect of working conditions and structural parameters on dynamic tilt stiffness was analyzed.The tilt dynamic stiffness was then improved through structure optimization.The accuracy of the theoretical model of the tilt vibration of the aerostatic bearing was verified experimently.