A review of the design and optimization of large-scale hydrostatic bearing systems

http://manuscript.elsevier.com/S0301679X21004011/pdf/S0301679X21004011.pdf

Experimental research on a hydrodynamic thrust bearing with hydrostatic lift pockets: Influence of lubrication modes on bearing performance

Research in the field of tribo-mechatronics has been gaining popularity in recent decades. The objective of the current research is to improve static/dynamics characteristics of hydrostatic bearings. Hydrostatic bearings always work in harsh environmental conditions that effect their performance, and which may even result in their failure. The current research proposes a mathematical model-based system for hydrostatic bearings that helps to improve its static/dynamic characteristics under varying conditions of performance-influencing variables such as temperature, spindle speed, external load, and clearance gap. To achieve these objectives, the capillary restrictors are replaced with servo valves, and a mathematical model is developed along with robust control design systems. The control system consists of feedforward and feedback control techniques that have not been applied before for hydrostatic bearings in the published literature. The feedforward control tries to remove a disturbance before it enters the system while feedback control achieves the objective of disturbance rejection and improves steady-state characteristics. The feedforward control is a trajectory-based controller and the feedback controller is a sliding mode controller with a PID sliding surface. The particle swarm optimization algorithm is used to tune the 6-dimensional vector of the tuning parameters with multi-objective performance criteria. Numerical investigations have been carried out to check the performance of the proposed system under varying conditions of viscosity, clearance gap, external load and the spindle speed. The comparison of our results with the published literature shows the effectiveness of the proposed system.

https://www.mdpi.com/2227-7390/9/4/388/pdf

Model-Based Design Approach to Improve Performance Characteristics of Hydrostatic Bearing Using Multivariable Optimization

Investigation of the deformation characteristics of adaptive hydrostatic thrust bearings has been performed under extreme conditions, considering the relationship between viscosity and temperature of lubricating oil. A 3D model is generated, including the oil pad, the oil film and friction pairs. The oil film temperature field and the oil cavity pressure field have been calculated based on CFD. According to the lubrication theory and tribology principle, the force deformation, the thermal deformation, the force and thermal coupling deformation have been studied by using workbench simulation software, and the best working condition of adaptive hydrostatic thrust bearing is obtained. The results show that the load causes the table and the base to undergo inward elastic deformation, and the temperature causes them to undergo outward thermal deformation. The two deformations have opposite directions, and the deformations compensate each other. When the load is between 28 and 32t, the possibility of dry friction generated by the friction pair is low. The research results provide a theoretical basis for the stability of adaptive hydrostatic thrust bearings under extreme working conditions.

Deformation characteristics of adaptive hydrostatic thrust bearing under extreme working conditions

Purpose




Hydrostatic thrust bearing is a key component of the vertical CNC machining equipment, and often results in friction failure under the working condition of high speed and heavy load. The lubricating oil film becomes thin or breaks because of high speed and heavy load and it affects the high precision and stable operation of the vertical CNC machining equipment; hence, it is an effective way of avoiding friction failure for achieving the oil film shape prediction




Design/methodology/approach




For the hydrostatic thrust bearing with double rectangular cavities, researchers solve the deformation of the friction pairs in hydrostatic bearing by using the computation of hydrodynamics, elasticity theory, finite element method and fluid-thermal-mechanical coupled method. The deformation includes heat deformation and elasticity deformation, the shape of gap oil film is got according to the deformation of the friction pairs in hydrostatic bearing, and gets the shape of gap oil film, and determines the influencing factors and laws of the oil film shape, and achieves the prediction of oil film shape, and ascertains the mechanism of friction failure. An experimental verification is carried out.




Findings




Results show that the deformation of the rotational workbench is upturned along its radial direction under the working condition of high speed and heavy load. However, the deformation of the base is downturned along its radial direction and the deformation law of the gap oil film along the radius direction is estimated; the outer diameter is close but the inner diameter is divergent wedge.




Originality/value




The conclusion can provide a theoretical basis for the oil film control of hydrostatic thrust bearing and improve the stability of vertical CNC machining equipment.

Oil film shape prediction of hydrostatic thrust bearing under the condition of high speed and heavy load

This paper aims to describe a theoretical and experimental research concerning influence of recess shape on comprehensive lubrication performance of high speed and heavy load hydrostatic thrust bearing with a constant flow.,The lubrication performance of a hydrostatic thrust bearing with different recess shape under the working conditions of high speed and heavy load has been simulated by using computational fluid dynamics and finite volume method.,It is found that the comprehensive lubrication performance of a hydrostatic thrust bearing with circular recess is optimal. The results demonstrate that recess shape has a great influence on the lubrication performance of the hydrostatic thrust bearing.,The simulation results indicate that to get an improved performance from a hydrostatic thrust bearing with constant flow, a proper selection of the recess shape is essential.

Influence of recess shape on comprehensive lubrication performance of high speed and heavy load hydrostatic thrust bearing

The invention discloses a method for researching thermal characteristics of a static pressure rotating worktable under extreme conditions. A relationship among flow, bearing capacity and oil film thickness of a dual rectangular cavity oil pad structure is subjected to theoretical derivation. The heat emission coefficients of the worktable under different extreme conditions are calculated out by applying a heat conduction theory; and the calculation of a convective heat transfer coefficient of the rotating worktable can be divided into the calculation of an upper surface and a side surface, namely, the calculation of a convective heat transfer coefficient of the upper surface can be likened to that a fluid flows through a horizontal plate, and the calculation of a convective heat transfer coefficient of the side surface can be likened to that the fluid transversely skims over a vertical plane wall. An area trisection method is proposed; the convective heat transfer coefficient of each part of the upper surface of the rotating worktable is calculated; and finally a mean value is calculated to serve as the convective heat transfer coefficient of the rotating worktable. A base is divided into two parts, namely natural convective heat transfer of the surface of the vertical plane wall and natural convective heat transfer coefficient of the horizontal plate with a downward hot surface, and the convective heat transfer coefficients are calculated. Finally the overall deformation of the worktable and the base is solved by taking a temperature field and a pressure field of an oil film as body loads.

Method for researching thermal characteristics of static pressure rotating worktable under extreme conditions

The invention discloses an oil film thickness calculation method for a double-rectangular-cavity hydrostatic thrust bearing with a tilting-type oil pad. The problem of oil film thickness calculation of the oil pad tilting type double-rectangular-cavity static pressure thrust bearing can be effectively solved. The method comprises: respectively calculating the axial inclination, the radial inclination and the elastic deformation of the oil pad tilting type double-rectangular-cavity static pressure thrust bearing by adopting a step-by-step superposition calculation method; then superposing the three numerical values to obtain an oil film thickness value of each point. The method is characterized in that the oil film thickness is calculated in a step-by-step superposition calculation mode. The oil film thickness range of the oil pad tilting type double-rectangular-cavity static pressure thrust bearing is obtained through theoretical calculation. Under the condition that a small number ofdisplacement sensors are used, the accurate thickness value of the hydrostatic bearing pressure oil film is obtained, the number of sensors needing to be arranged can be reduced, the problem that sensors at individual positions are difficult to install is solved, and hardware and time cost is effectively saved.

Oil film thickness calculation method for double-rectangular-cavity hydrostatic thrust bearing with tilting-type oil pad

The invention relates to a method for calculating the convective heat transfer coefficient of a hydrostatic rotary table. The method comprises the steps of calculating convective heat transfer coefficients of the rotary table and a base, wherein the calculation of the convective heat transfer coefficient of the rotary table can be divided into two parts: the calculation of the upper surface and the calculation of side faces, that is, the calculation of the convective heat transfer coefficient of the upper surface can be compared to fluid flowing through a horizontal plate and the calculation of the convective heat transfer coefficient of the side faces can be compared to the fluid horizontally flitting through vertical planar walls; the convective heat transfer coefficient of each part ofthe upper surface of the rotary table is calculated by using an area trisectioning method, that is, the rotary table has a large radius and the heat emission coefficients at different positions at thesame rotation speed have large differences, so that the upper surface of the rotary table is divided into three parts and the average value is calculated through averaging to serve as the convectiveheat transfer coefficient of the rotary table; and the convective heat transfer of the base is divided into two parts: the natural convective heat transfer of the vertical planar wall surface and thenatural convective heat transfer of the horizontal plates, hot faces of which are downwards arranged, to calculate the convective heat transfer coefficient of the base.

Zheng Xuhang

Papers

Oil film shape prediction of hydrostatic thrust bearing under the condition of high speed and heavy load

Influence of recess shape on comprehensive lubrication performance of high speed and heavy load hydrostatic thrust bearing

Method for researching thermal characteristics of static pressure rotating worktable under extreme conditions

Oil film thickness calculation method for double-rectangular-cavity hydrostatic thrust bearing with tilting-type oil pad

Method for calculating convective heat transfer coefficient of hydrostatic rotary table