The Static And Dynamic Characteristics Analysis Of The New Type Hybrid Rotary Table

Rotary table is the key component of large-scale NC processing equipment and it's performance has remarkable influence on the processing quality and running accuracy.The thrust bearing is the critical component of rotary table as it's structure has a great influence on the performance of rotary table.It is not only hard to manufacture but also cost too much to apply ball thrust bearing in the large-scale rotary table.Currently,hydrostatic thrust bearings are widely used in equipment manufacturing industry.The hybrid bearing is a kind of new oil film bearing which is based on the development of hydrostatic and hydrodynamic bearings.It has the advantages of small starting torque,high stiffness,high carrying capacity and reliable performance.The large dynamic carrying capacity can be produced because of the dynamic effect,which can decrease the supply pressure on the running conditions.This paper established the mathematical modeling of rotary table's pressure distribution and studied the static and dynamic characteristics.The main research content are as follows:Firstly,the structure of the rotary table was introduced and the film thickness equation in the area of spiral wedge was established.Considering Reynolds equation and flow continuity equation,the mathematical modeling of rotary table's pressure distribution was established.The calculation results were compared with the results of the foreign literature,verifying the correctness of MATLAB procedure which is composited by FEM.Solving Reynolds equation and flow continuity equation simultaneously,the static characteristics were calculated including carrying capacity,friction moment and flow.Secondly,the impact of rotating speed and supply pressure on the static characteristics was analyzed under a certain of fixed load.The impact of structure parameters on the static characteristics was also studied and based on the influence results,a proper selection range of each parameter was advised considering both carrying capacity and dynamic ratio.It is discovered that the flow rate of oil recess is smaller than that of spiral oil wedge when the film thickness is small.In order to solve the problem the structure of oil recess is improved.The results showed that the problem can be solved under a certain condition and the carrying capacity can be improved greatly.Then,considering the squeeze effect,the steady-state Reynolds equation and flow continuity equation were modified.The dynamic characteristics including stiffness coefficient and damping coefficient were calculated by difference method.The impact of working condition and structure parameters on the dynamic characteristics was studied,which can provide references for the structure optimization.Lastly,the composition of testing system and the arrangement of sensors were introduced.The actual initial installation clearance of eddy-current sensor was calibrated.The experimental data was processed by the ideal low-pass filter and compared with the calculation results.It is showed that the error between the experimental data and calculation results is acceptable and the calculation method is reliable.The mathematical modeling of pressure distribution was established and the static and dynamic characteristics were analyzed in this paper,which laid a theoretical foundation for structure optimization and the study of motion stability.