Research on error averaging effect of hydrostatic guideways

Hydrostatic guideways can obtain high motion accuracy due to their error averaging ability. In order to optimize the structural and accuracy design of hydrostatic guideways, the mechanism and affecting factors of the error averaging effect are investigated in detail in this paper. A new method is proposed to quantitatively analyze the motion errors of a typical closed hydrostatic guideway with four pads, and the restrictor is also taken into consideration. A hydrostatic guideway in an ultra-precision grinding machine LGF750 is analyzed with the method. The results show that the wavelength of each profile error component is a main affecting factor on the error averaging effect. Fluid films usually show obvious error averaging effect on each profile error component when the wavelength λ is shorter than twice of the pad length 2l_u. However, for each component with the wavelength λ over 2l_u, the error averaging effect becomes obvious only when the ratio of the pad length to the evaluation length of motion straightness l_u/l_e is greater than 0.5. Furthermore, the instability of the oil supply system is taken into consideration, and possible influences on the error averaging effect due to the supply pressure fluctuation are investigated preliminarily.     

The combined effects of the centripetal inertia and the surface roughness on the hydrostatic thrust spherical bearings performance

This paper deals with the surface roughness and the predominant centripetal inertia terms due to the shaft rotation of the externally pressurized thrust spherical bearings. The solutions are presented for the fitted type of bearings, un-recessed and recessed hemispherical and partial hemispherical seats, with capillary tube and orifice restrictors. On the basis of the stochastic theory, Reynolds equation is developed. The bearing surfaces are assumed to have randomly distributed roughness. Expressions for the pressure distribution, load carrying capacity, volume flow rate, frictional torque, friction factor, power factor, power losses and stiffness factor are obtained. The paper shows the combined effects of the centripetal inertia and the surface roughness on the bearing performance. An optimum design based on the minimum power losses, minimum flow rate and optimal restrictor dimensions is theoretically examined.     

电极几何尺寸误差对纳米时栅位移传感器测量精度的影响及其抑制方法

在纳米时栅传感器的制造过程中,由加工工艺引入的制造误差主要表现为电极几何尺寸误差。通过运用分段面积积分方法进行数学建模,详细地分析了电极几何尺寸误差对测量精度的影响,并揭示了采用多个感应电极进行信号拾取会具有一种平均效应,能够有效地匀化由电极几何尺寸误差随机变化所引入的测量误差。采用制造精度在1μm级的微纳加工工艺和制造精度在10μm级的印制电路板(PCB)工艺分别制作了两套量程为200 mm的传感器样机,并进行了精度对比实验。实验结果表明,由于平均效应的作用,PCB工艺制作的样机经过简单的线性补偿后,在满量程内取得了±250 nm的测量精度,接近微纳加工工艺制作的样机的测量精度。实验结果验证了多个感应电极平均效应的有效性。     

Performance analysis of four-pad hydrostatic squeeze film dampers loaded between pads under laminar and turbulent flow conditions

This paper presents a theoretical study of the effects of Poiseuille Reynolds number and eccentricity ratio on the performance of four-pad hydrostatic squeeze film dampers. The finite difference method has been used to solve Reynolds equation based on Constantinescu’s turbulent lubrication theory. The numerical results obtained are analysed and compared between three and four-lobe hybrid journal bearings. The computed results indicate that the performance of a hydrostatic squeeze film damper loaded between pads is significantly influenced by the flow regimes. The results presented in this work can be useful to the bearing designers.