Papers by Keyword: Hydrostatic Bearing

Abstract: In general, high-precision machines, such as machine tools and measuring equipment, have employed moving tables with hydrostatic bearings. Hydrostatic bearings for these high-precision applications require high bearing stiffness and response speed. Various flow-control restrictors inserted in oil passages were proposed to improve bearing characteristics. However, the active control of conventional flow-control restrictors has some shortcomings because most flow-control restrictors employ voice coil motors (VCMs), which generally consume a large amount of electricity and raise the oil temperature. The increased oil temperature decreases the oil viscosity, which reduces bearing stiffness and damping. Although piezo actuators can solve the above problems and are suitable candidate alternatives to VCMs, their small range of travel has prevented their use in flow-control restrictors. In this paper, a novel flow-control restrictor using a bending beam in stroke expansion is proposed for the purpose of employing piezo actuators. In addition, the bearing characteristics of the hydrostatic bearing with the proposed flow-control restrictor were investigated numerically. In this investigation, the Rayleigh-Ritz method for solving the deformation equations of the bending beam and the divergence formulation method to obtain the pressure distribution in the hydrostatic bearing were adopted in the numerical calculations. The results showed that the hydrostatic thrust bearing with the proposed restrictor has higher stiffness compared with conventional hydrostatic bearings using a capillary restrictor.

Abstract: A hydrostatic bearing using ionic liquid (IL) has been developed to float semiconductor wafers in a high vacuum chamber. In semiconductor manufacturing, it is important to suppress overheating of wafers and maintain a constant temperature distribution. This method aims to achieve uniform temperature distribution by supplying IL from the backside of the wafer to float it, thereby without mechanical contact. However, since there are no examples of wafers levitated by hydrostatic bearings using IL in a high-vacuum environment, the effect of circulating IL to the vacuum conditions such as vacuum pressure and outgassing were investigated in this study. Experimental results showed that the developed prototype machine was capable of maintaining a stable ultrahigh-vacuum of 10^-5 Pa and supplying sufficient pressure to levitate wafers even when 100 ml of IL was circulated.

Abstract: In this paper, a hydrostatic bearing controlled by servo-valve for precise closed-loop oil-film gap control is developed. Due to the increasing demands of larger dimension, heavier load and higher precision for current and future machine tools, the development of hydrostatic bearing has become a more and more important issue over the past decades. Nowadays, the most commonly used active pressure feedback restrictor for hydrostatic bearing is membrane type, in which a thin and flexible metal sheet serves as the key component to meter the hydraulic oil flow precisely. However, the membrane type pressure feedback restrictor is not quite suitable for extremely heavy load. Therefore, an alternative to design the active restrictor for hydrostatic bearing using servo-valve is presented in this paper. Different controllers are also designed and compared in this paper. There are two significant features regarding the proposed design. The first one is the introduced orifice restrictor inside the servo-valve which avoids the influence of possible oil temperature variation. The second feature is the introduced closed-loop oil-film gap control scheme that widens the application range effectively. Finally, a test rig of servo-valve controlled hydrostatic bearing is implemented and the experimental results prove the validity of the hydrostatic bearing with the proposed servo-valve and the closed-loop gap control scheme.

Abstract: Thermal deformation of large size hydrostatic bearing rotary workbench is the most direct factor that affects the machining accuracy of work-piece. The thesis puts forward the method of adding reinforcing plate structure to restrain the workbench thermal deformation, establishes three-dimensional supporting workbench model, with finite element method and sequence of fluid-solid coupling technology have carried on the thermal deformation calculation workbench, and reveals the influence law of different installation position of rib plate on the workbench thermal deformation. The results of the study shows that the method of adding reinforcing plate structure to reduce the thermal deformation of hydrostatic bearing worktable is feasible, and determine the optimal position of reinforcing plate by comparing different results.

Abstract: Recently, it is essential to enhance the value of the products to make them more competitive. Therefore, the technical level of the high-precision products is required. Thermal deformation error, which accounts for a significant effect of processing accuracy of machine tools. In order to reduce thermal deformation error such studies the thermal characteristics of the Hydrostatic spindle is required. In this study, we could confirm the reliability of the analysis by assessing the thermal characteristics through measurement of the grinding machine temperature and thermal structural analysis. The temperature of the front bearing 10 °C or more higher than the temperature of the rear bearing, thermal deformation of the spindle, was found to be dependent on the temperature of the hydrostatic bearing. And could identify the thermal characteristics of the hydrostatic spindle.

Abstract: Large size hydrostatic bearing is the core component of heavy CNC equipment. The influence of pressure, heating and running time can reduce film thickness during operation. This will directly affect machining accuracy and operation reliability of the entire machine. Aiming at the problem of influence of rotational velocity on carrying capacity of heavy hydrostatic bearing, use finite volume method (FVM) to simulate gap film pressure field of heavy hydrostatic bearing with Constant Flow and study pressure field distribution law on the conditions of the different rotational velocity and same cavity depth, oil cavity area, then optimize oil cavity structure. Results show that, pressure field distribution law of the different rotational velocity is basically identical, but its carrying capacity is different. From the relation curve of the pressure and rotational velocity can be seen, because of the dynamic pressure of existence, along with the increase of rotational velocity, carrying capacity gradually. The study is of vital theoretical significance for the improvement of machining accuracy of numerical control machine and the entire CNC equipment and provides valuable theoretical basis for the design of hydrostatic guide rail in engineering practice.

Abstract: In order to solve deformation problem of large size hydrostatic thrust bearing under different load. Simulation model of fan cavity hydrostatic thrust bearing, three-dimensional mathematical model in guide rail is set up. Using CFD principle, FIUENT and ANSYS Workbench software, temperature field, pressure field and deformation field of hydrostatic bearing is simulated. Hydrostatic bearing deformation under different load conditions can be simulated and the lubrication characteristic is forecast in advance through this method. It provides valuable theoretical basis for hydrostatic bearing structure parameter optimization of oil cavity and worktable.

Abstract: This essay briefly introduces a structure scheme design of a high diameter-length ratio rotary plate. This structure scheme is unique from any well-known schemes. In this scheme, there is only one flat act as the working flat for both main thrust bearing and aux thrust bearing. It minimizes the faces which need lapping. At the same time, this scheme minimizes the number of assembling parts. So, it will be easier for this scheme to achieve high accuracy. This essay includes the process of design: calculation for bearings and schemes compare.

Abstract: This paper describes a hydrostatic bearing to maintain the oil film thickness, which integrates the hydraulic servo control technology. This study has designed the different intelligent nonlinear controllers by using a non-contact displacement sensor to feedback the oil film thickness of the bearing. This study proposes a fuzzy controller, a self-tuning fuzzy controller and a self-tuning fuzzy sliding mode mechanism to modify the output scaling factor and adds a dead zone compensator to achieve a constant oil film thickness. Finally, the experimental results are used to verify the feasibility and practical implementation success of this study.

Abstract: A self-compensated hydrostatic rotary bearing is designed and manufactured. The bearing is modeled by fluid flow network method, and simulations are performed to predict the load carrying capacity. A hydrostatic bearing prototype has been tested and results show that it can achieve a stiffness of 120N/μm in radial direction and 220N/μm in axial direction under a supply pressure of 1 MPa, and its motion accuracy is 0.3μm. The designed bearing is suitable to be used in precision machines.