Abstract: Hydrostatic spindles are crucial core components for the precision and ultra-precision machine tools, which have direct and significant influence on the processing efficiency, machining accuracy and machined surface quality. The rotation accuracy is the key performance of hydrostatic spindle systems. At present, there is a lack of unified cognition of the intrinsic relationship with various evaluation indexes of rotation accuracy in academic and engineering communities, besides, the mechanism and formation law of rotation accuracy still need in-depth investigations. The intrinsic relationships between various measuring methods and evaluation indexes of rotation accuracy are systematically analyzed. The formation causes of different error components are clarified. Finally, aiming at the limitation of the existing evaluation methods of rotation accuracy, a comprehensive evaluation method of "minimum peak-to-peak value + synchronous error + asynchronous error" is proposed. On the basis of systematically coMParing the influence of different throttling methods on the hydrostatic journal bearing stiffness, the method of adopting controllable restrictor to achieve higher rotation accuracy is put forward. The flow-structure-thermal coupling model of the hydrostatic spindle is established to achieve the accurate quantitative simulation of the transient process of the axial motion trajectory, which further revealed the laws of oil supply pressure, fluctuation of oil supply pressure, the dynamic unbalance and the journal roundness error on the rotation accuracy. Ultimately, the attainable extreme limit of rotating accuracy for hydrostatic spindle system is predicted.

Key words: the ultra-precision, hydrostatic bearing, machine tool spindle, rotation accuracy, accuracy limitation