Theoretical Analysis and Numerical Simulation of Dynamic Characteristics of Hydrostatic Guides for Heavy NC Machine Tool
Based on analysis of hydrostatic bearing with circular pocket, equations of static pressure, volvme pressure and squeezing pressure which influence dynamic characteristics of hydrostatic guides with rectangle pocket have been deduced. The function and their influencing factors of the three kinds pressure mentioned above are clarified. The amplitude-phase-frequency characteristics of the hydrostatic guides system have been analyzed qualitatively and quantitatively, it is indicated that the sensitive oil volume has greater effect on the stability of the guide, the volume should be reduced as small as possible while the hydrostatic guides meet the needs of the field working situation. To increasing the oil visosity properly is also helpful to improve the dynamic performance of hydrostatic guides.
Effects of fluid compressibility on the dynamic response of hydrostatic journal bearings
Abstract A theoretical analysis for the dynamic performance characteristics of laminar flow, capillary and/or orifice compensated hydrostatic journal bearings is presented. The analysis considers in detail the effect of fluid compressibility in the bearing recesses. At high frequency excitations beyond a break frequency the bearing hydrostatic stiffness increases sharply and is accompanied by a rapid decrease in direct damping. Also, the potential of pneumatic hammer instability (negative damping) at low frequencies is likely to occur in hydrostatic bearing applications handling highly compressible fluids. Useful design criteria for avoiding undesirable dynamic operating conditions at low and high frequencies are determined. The effect of fluid recess compressibility is brought into perspective, and found to be of utmost importance to the entire frequency spectrum response and stability characteristics of hydrostatic and hybrid journal bearings.
Dynamic and Static Properties of Recessed Hydrostatic Journal Bearings by Small Displacement Analysis
Coefficients are presented for hydrostatic stiffness, hydrodynamic stiffness and squeeze damping for capillary, orifice and constant flow control. Due to the linear behaviour of such bearings these coefficients may be used for conservative design and with reasonable accuracy where the displacements are less than half the clearance. The dynamic coefficients may also be employed to predict the onset of whirl. The results are illustrated by application to rotating and non-rotating load situations. It is demonstrated that the squeeze damping constant for the concentric condition may be obtained from a steady loading test for hydrodynamic stiffness since Csq = λhd /(πN). It is argued that this relationship may be generalised for all types of bearings capable of exhibiting half-speed whirl operating at any speed.