Abstract
The rotation accuracy of the aerostatic spindle can easily be affected by shaft shape errors due to the small gas film clearance. Thus, the main shaft shape errors with the largest scale—that is, the roundness and cylindricity errors—are studied in this paper, and a dynamic mathematical model is established with the consideration of the roundness, cylindricity errors, and spindle speed. In order to construct the shaft model, the discrete coefficient index of the shaft radius based on roundness measurement data are proposed. Then, the simulation calculations are conducted based on the measured cylindricity data and the constructed shaft model. The calculation results are compared with the spindle rotation accuracy measured using the spindle error analyzer. The results show that the shaft with a low discrete coefficient is subjected to less unbalanced force and smaller rotation errors, as obtained by the experiment.
Highlights
In contrast with traditional spindles, an aerostatic spindle uses compressed gas to form a gas film, which has the characteristics of high precision, high speed, and low noise
The influence of shaft shape errors on spindle rotation accuracy is verified by comparing the simulation results with experimental results
Because of the errors of roundness and cylindricity in the shaft, the film thickness inside the spindle will be different at different places, resulting in an uneven distribution of film pressure
Summary
In contrast with traditional spindles, an aerostatic spindle uses compressed gas to form a gas film, which has the characteristics of high precision, high speed, and low noise. The roundness and cylindricity are the largest errors among the shaft shape errors, usually between 1 and 4 micrometers These errors have the most obvious impact on the aerostatic spindle’s rotation accuracy. It is necessary to study the dynamic rotation accuracy of the aerostatic spindle under the effects of roundness and cylindricity errors. A dynamic mathematical model considering roundness, cylindricity errors and spindle speed is established by using the finite difference method based on the Reynolds equation in this paper. Through the comparison of the simulation and the experiment, it is proved that the shaft roundness and cylindricity errors will produce an unbalanced gas film force on the shaft and affect the spindle’s rotation accuracy. The research shows that this discrete coefficient is a more effective index to predict the spindle’s rotation accuracy compared with the roundness and cylindricity
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