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The ultra-precision spindle is the key component of ultra-precision machine tool, which largely influences the machining accuracy. Its frequency characteristics mainly affect the frequency domain error of the machined surface. In this article, the error measurement setup for the ultra-precision aerostatic spindle in a flycutting machine tool is established. The dynamic and multi-direction errors of the spindle are real-time measured under different rotation speeds. Then, frequency domain analysis is carried out to obtain its regularity characteristics based on the measurement result. Through the analysis, the main synchronous and asynchronous errors with relatively large amplitude of the spindle errors are found, and the amplitude change law of these main spindle errors is obtained. Besides, the cause of the main synchronous and asynchronous errors is also analyzed and indicated. This study deepens the understanding of ultra-precision spindle dynamic characteristics and plays the important role in the spindle frequency domain errors' control, machining process planning, frequency characteristics analysis and oriented control of the machined surface errors.

The pressure distribution in an aerostatic bearing has an important effect on the performance of the associated mechanical equipment. To more accurately predict performance, a new dynamic modeling method has been developed that takes into account the pressure distribution in the bearing by integrating the principle of flow equilibrium and finite element theory. The direct corresponding relationship between the fluid film characteristics and spindle dynamic performance is established using this method. The simulation and experimental results show that the new dynamic modeling method for the aerostatic bearing is more efficient and reliable than traditional modeling methods.

The frequency domain error of the machined surface in the ultra-precision machining attracts more attention for its strong relationship with the functional requirements of the workpieces. As the key component of ultra-precision machine tool, the spindle error largely influences the machined surface errors. However, little attention has been paid to the influence of spindle error on the surface error formation mechanism in the frequency domain for ultra-precision flycutting. This paper deeply studies the influence of spindle error on the frequency domain error formation of machined surface in ultra-precision flycutting. The influence analysis of the spindle error is theoretically and experimentally carried out according to two different evaluation directions of the machined surface by flycutting, i.e., cutting direction and feed direction. The KDP crystal flycutting experiment is designed and conducted for the theoretical verification. The theoretical analysis has been found to agree well with the experimental results. This study is quite meaningful for deeply understanding the influence law of spindle error from the viewpoint of frequency domain. The research results are quite useful for the spindle error control, machined surface error prediction, machining process planning, and also show the potential use for the spindle (machine tool) design.