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Purpose This paper aims to present a simplified method to predict the pressure of the recess, no matter whether the tilt center coincides with the geometric center of the hydrostatic journal bearings. Design/methodology/approach To validate the effectiveness of the presented model, computational fluid dynamics (CFD) method and experimental method are performed in this study. Findings By comparing the CFD results and the experimental results, the pressure of the recess is related to the tilt direction, the tilt center, the width of the land and the circumferential angle of the land. Originality/value The mathematic model requires equivalent resistance of land edge – tilt position, tilt direction, tilt angle and the thickness of oil film instead of any digital iteration. Furthermore, a novel experimental apparatus including a circular hydrostatic bearing called ball bearing is designed to study the tilt effect produced by manufacturing error and offset load force on the pressure of the recess.

Hydrostatic guideways are used as an alternative to contact bearings due to high stiffness and high damping in heavy machine tools. To improve the dynamic characteristic of bearing structure, the dynamic modeling of the hydrostatic guidway should be accurately known. This paper presents a "mass-spring-Maxwell" model considering the effects of inertia, squeeze, compressibility and static bearing. To determine the dynamic model coefficients, numerical simulation of different cases between displacement and dynamic force of oil film are performed with fluent code. Simulation results show that hydrostatic guidway can be taken as a linear system when it is subjected to a small oscillation amplitude. Based on a dynamic model and numerical simulation, every dynamic model's parameters are calculated by the LevenbergMarquardt algorithm. Identification results show that "mass-spring-damper" model is the most appropriate dynamic model of the hydrostatic guidway. This paper provides a reference and preparation for the analysis of the dynamic model of the similar hydrostatic bearings.

This paper presents experimental and theoretical studies used to assess the dynamic performance of open-type constant flow hydrostatic bearings. A nonlinear dynamic model accounting for the compressibility effect, the squeeze effect, and the hydrostatic effect of hydrostatic fluid for the analytical perdition of the step response is proposed. Moreover, an innovative point-to-point contact step excitation setup is designed. In addition, a test rig is developed to measure the step response of the hydrostatic bearings by removing the imposed displacement within 0.0002 second. The experimental results are in good agreement with the theoretical results. The results show that the maximum dynamic displacement is twice the imposed displacement. Furthermore, the settling time of the step response is related to the inlet flow rate, irrespective of the imposed displacement. | INTRODUCTIONHydrostatic bearings are widely used in ultraprecision machine tools. Compared with traditional bearings, their main advantages are their low friction coefficient, high stiffness, and high damping. As is widely known, the dynamic characteristics of hydrostatic bearings affect the stability of machine tool worktables and the quality of the workpieces. To assess the dynamic performance of hydrostatic bearings, dynamic model solutions are investigated. The problem of determining how to establish an accurate equation based on the experimental results has attracted much research interest.Many researchers evaluate the dynamic performance of hydrostatic bearings starting with their stiffness and damping. Essentially, the time-dependent Reynolds equation and the flow equation must be solved by applying the finite difference method or the finite element method to obtain the dynamic pressure and the dynamic force. Additionally, the stiffness and damping coefficients of the hydrostatic bearing are obtained by expanding the Taylor series of the oil film force of the bearing in the steady-state equilibrium position. 1-5 However, the influence of fluid compressibility on stiffness and damping is not taken into account in these papers.In practical applications, air ingestion into the oil film through the oil pipe and oil recess is a common phenomenon that affects the dynamic performance of the hydrostatic bearing. An equivalent spring-damper model accounting

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