The Analysis On Mechanical Properties And Parameter Identification Of Quantitative Type Hydrostatic Rotary Table

While developing of science and technology, market competivion is becoming more and more fierec, and the development of equipment manulfaeturing industry has also been highly valued by many industries. Precision and ultra-precis ion machining technolog, plays an importanl rule in pillar industries such as aerospace, energy cxpluitation, engineering machinery and so on, CNC machine tools are one of the important cquipment for precision machining For example,to obtain a complex optical surface,high precision mould free-form surface and large ultra precision optical parts,each axis of NC machine tool should be controlled precisely so that the accuracy of position of the tool and workpicce and attitude between them can be ensured while the tool and the workpiece move along the trajectory predetermincd. The accuracy not only depends on the control accuracy of each axis, but also is afTected by the guideway accuracy of each axis. Hydrostatic bearing is widely used on precision NC machine tools because of the advantages that hydrostatic bearing has. But the perfarmance of precision machine is directly affected by the sensitivity of hydustatic bearing oil film to laad. In order to improve the oil film stiffness of hydrostatic bearing----the ability that oil film of hydrostatic bearing reistes the load changing, hydostacie rotary table driven directly with the quantiative oil supply system was taken as the research subject, the mathematical model of its mechanical characteristics was established, the relationship beteen its performance and design parameters was studiedd based on the mechanical properties model of hydrostatic rotary table established in this thesis, The result of the simulation experiments was verified by the experiments. To achieve the research purposes above, main work has been done as followFirstly, according to the workinig characteristics of hydrostatic rotary table, the simulation about the influence of centrifugal fonrce on the pressure of the oil pad sector was done based-on the analysis of flow field characteristics of oil pad, and then the mathematical model for oil pressure in a fan-shaped ped oil pad was established The correctness of the model above was proved by comparing the results of theory simulation of the flow field of the oil pad in a single oil cavity with the numerical simulation of that under CFX On the basis of the model gotten.the effects of hydraulic oil density, rotating speed, inlet flow rate and oil chamber structure on the load carrying capacity of hydostatic rotary table were analyzed. Research has shown that the bearing characteristics of hydostatic rotary table increases with the raise of inlet flow but decreases with the increase of rotate speed and the oil density because of the centrifugal force.It was found from the result that the bearing capacity and stiffness of hydrostatic rotary table with double-layer oil cavity was improved while the oil supply system is the same, comparing with that with single-layer oil cavity.Secondly, in order to study the dynamic properties of hydrostatic rotary table with the quantitative oil supply system, its transfer function and mathematical expressions of dynamic performance were deduced based-on the force balance equation and flow continuity equation.Then, how oil film thickness designed, oil temperature, oil pressure of the main chamber and the oil pad structure to effect the dynamic properties of hydrostatic rotary table was analyzed in the time domain and frequency domain. It was shown from the result that the better rapidity of hydrostatic rotary table can be got and its dynamic stiffness and vibration were improved when the temperature of the oil is higher, but the anti-vibration is not affected. The vibration and dynamic stiffness of hydrostatic rotary table were increased while the pressure of oil cavity raising. The higher the initial thickness of the oil film was, the better the fast speed was but the worse the vibration, the anti-vibration and the dynamic stiffness were. At the same time, it was verified that the speed of hydrostatic rotary table would be improved if double-layer oil cavity structur of hydrostatic rotary table was used through the response that hydrostatic rotary tables with the different oil pad structure under step signal.Moreover, the static characteristic and dynamic characteristic of hydrostatic rotary table with different structures were experimented. The curves for the bearing capacity and dynamic stiffness of hydrostatic rotary table were obtained and the damping coefficient of it was identified from experimental results. It was indicated from the experiment that the bearing capacity, dynamic stiffness and vibration of hydrostatic rotary table with double-layer oil cavity structure were better than that of it with single-layer oil cavity structure.The research results will provide a theoretical reference for the structural design and performance optimization of hydrostatic rotary table.