| The precision&ultra-precision machine becomes vital processing equipment for ultra-precision parts in national defense industry, aerospace, industrial and civil optical industry, also strategic equipment for national defense security. Machine spindle is the core part of ultra-precision machine, and the rotational accuracy of hydrostatic spindle plays a determinative influence on the machine’s processing precision. Currently, there is successful application for ultra-precision hydrostatic spindle. However, specialized research on the mechanism of rotary accuracy is still lacking, the physical origin of rotation error caused by the spindle rotation is not effectively revealed, the transitional process of rotary accuracy is not quantitatively explained, and systematically guidance and prediction cannot be provided for engineering design.Focused on the dynamic development process, the dynamic model of the fluid-structure interaction for hydrostatic spindle rotary accuracy is constructed in this paper, and its new solution based on CFD dynamic mesh model is proposed. The trajectory of the axis of spindle during spindle forming rotary accuracy is quantitatively simulated, meanwhile the physical origin of rotary error caused by the spindle rotation is revealed. On such basis, the effect of working parameter, structure parameter and manufacturing error of hydrostatic spindle friction pair on the rotary accuracy is systematically studied in this paper, and the hydrostatic spindle rotary accuracy test platform is constructed, the spindle error trajectory and rotary accuracy obtained by the theoretically calculated and experimentally tested are comparatively studied, which confirms the correctness and validity of the research. The research work and key result of this paper is listed as follows:(1) The dynamic model of the fluid-structure interaction for hydrostatic spindle rotary accuracy based on Navier-stokes equation and spindle dynamics equation is constructed, and its new solution based on CFD moving mesh model is proposed. This solution inserts the spindle rotational and translational equation into CFD software and solves the N-S equation, calculates the transient oil film pressure, the spindle mesh rotational boundary is transformed into static boundary, the influence of speed disturbance and displacement disturbance on the oil film force is compared, which determined the numerical range of spindle speed effect. The theoretical calculation and experimental test on hydrostatic spindle’s stiffness is compared and analysed, which ensures the validity and feasibility of the hydrostatic spindle rotary accuracy model and solving method.(2) The trajectory of the axis of spindle is quantitatively simulated, and the physical mechanism of hydrostatic spindle forming rotary accuracy is revealed. Three types of method, which is full moving mesh, equilibrium position and moving mesh, and equilibrium position and simplified formula, are applied to calculate and simulate the trajectory of spindle from concentric position to form rotary error. While the hydrostatic spindle forming rotary centre and rotary error, the dynamic development of total force, flow and spindle position are comparatively analysed. Through comparatively studying the influence of these three calculation methods on the rotary centre position and rotary error of hydrostatic spindle, the physical reason of the difference of output among the three methods is found, which shows that combining the moving mesh method and simplified formula to calculate the rotary accuracy of hydrostatic spindle is feasible and valid.(3) The effect of the spindle structure parameters and working parameters on the spindle rotary accuracy is revealed. The operating parameter (including operating rotation speed and oil supply pressure) and the structure parameter (including length to diameter ratio, orifice diameter and bearing clearance) on the rotary centre and oil film dynamic characteristics are quantitatively calculated, and the mechanical reasons of attitude angle, eccentricity, stiffness and damping is analysed, and then the working parameter and structure parameter’s influence on the spindle rotational precision under the condition of the dynamic imbalance excitation is revealed. The result show that when increasing the oil supply pressure and the length to diameter ratio, the rotary accuracy will increase. When increasing the orifice diameter, rotational speed and bearing clearance, the rotary accuracy will decrease.(4) The effect of the shape errors of the bearing on the spindle rotary accuracy is revealed. The influence of the roundness error and the cylindrical error on the rotary centre and oil stiffness&damping were quantitatively calculated. After compared and analysed mechanical root of the structure difference between the error bearing and smooth bearing, the reason of the rotary centre and oil stiffness&damping influenced by the shape errors of the bearing is shown. The effect of the roundness error and the cylindrical error on rotary accuracy of hydrostatic was discussed, the result shows that the shape error of the bearing doesn’t form rotation error, but it affects rotational accuracy through the central position of spindle and the stiffness and damping of oil film. (5) The effect of the shape errors of the journal on the spindle rotary accuracy is revealed. The influence of the roundness error and the cylindrical error on the equilibrium position and oil stiffness&damping were quantitatively calculated. The change of equilibrium position affected by switching between peak and valley of the roundness error was emphatically analysed. Through comparatively analysis the rotary centre position and rotary accuracy affected by the error journal and smoothing journal, the averaging effect of the hydrostatic bearing on the shape error of the journal was discovered finally. The result shows that, the roundness error of the journal forms the rotation error, and the accuracy has relation with the roundness error’s amplitude and frequency. The cylindrical error of the journal doesn’t forms rotation error, but affects rotational accuracy through the central position of spindle and the stiffness and damping of oil film.(6) The trajectory and rotary accuracy of the spindle received by the theoretical calculation and experiments were comparatively studied. A hydrostatic spindle rotary accuracy experiment apparatus was developed, and three dimensional motion of the hydrostatic spindle was experimentally studied. For simplification inclination motion of grinder spindle as cylindrical motion, the scientific basis was found. The spindle trajectory and rotary accuracy obtained by theoretical calculation and experimental test were compared. The result shows that the trajectory of spindle of theoretical calculation and experimental test were ellipse, the theoretical calculated major axis of the ellipse is around78.8%of experimental result. The theoretical calculated rotary accuracy is around75.6%of the experimental result, with a high degree of consistency of theory and experiment.The dynamic model of fluid-structure interaction for hydrostatic spindle rotary accuracy and its new moving mesh method is proposed in this thesis, develops the theoretically analytical methods of rotary accuracy of hydrostatic spindle is developed, the mechanical mechanism of hydrostatic spindle forming rotational error is revealed, the average effect of hydrostatic bearing on the shape error of the journal is theoretical interpreted, the analyze theory of hydrostatic spindle rotation accuracy preliminarily is established and developed, theoretical guidance and technical support for the development of ultra-precision hydrostatic spindle is provided. |
