Hydrostatic Guideway Research Articles

Research on the online evaluation of the straightness error of hydrostatic guideways based on deep learning

Research on the online evaluation of the straightness error of hydrostatic guideways based on deep learning

Investigation of the error averaging effect on design and assembly of external slider closed hydrostatic guideways

Hydrostatic guideways are widely used in ultra-precision machine tools. However, in most cases, assemblers must rely on their experience to adjust the manufacturing errors of the guide rail and slider, which indirectly controls the error motion. To ensure assembly accuracy and improve efficiency, an error motion calculation model is established based on the external slider closed hydrostatic guideway. The accuracy of the model is verified through experiments, and the main factors that affect the error motion are analysed. Finally, a traversal algorithm is used to calculate the distribution of the error averaging coefficient. Once the error motion index is clarified, the design and assembly process of the guideway can be constrained by the error averaging coefficient.

Influence of multisource errors of oil film contact surface on motion accuracy of hydrostatic guideway

PurposeThis study aims to explore the impact of multisource deformation errors on the oil film contact surface, which arise from manufacturing, assembly, oil pressure and thermal influences, on the motion accuracy of hydrostatic guideway.Design/methodology/approachUsing thermal-structural coupling simulations, this research investigates the effects of assembly, oil pressure and thermal factors on deformation errors of the oil film contact surface. By integrating these with manufacturing errors, a profile error model for the oil film contact surface is developed, characterizing the cumulative effect of these errors. Using kinematic theory and progressive Mengen flow controller characteristics, the motion error at any position of the hydrostatic guideway is quantified, examining how surface error traits impact motion accuracy.FindingsThe error averaging effect is affected by the profile error of oil film contact surface. Meanwhile, the motion accuracy of hydrostatic guideway is highly sensitive to the oil film contact surface error amplitude.Originality/valueThis approach allows for precise prediction and analysis of motion accuracy in hydrostatic guideways during the design and manufacturing stages. It also provides guidance for planning process tolerances.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2024-0063/

Static and dynamic characteristics of large-span six-slider closed hydrostatic guideway considering pitch moment and yaw moment

Purpose The purpose of this study is to design a closed hydrostatic guideway has the ability to resist large-side load, pitch moments and yaw moments, has good stiffness and damping characteristics, and provides certain beneficial guidance for the design of large-span closed hydrostatic guideway on the basis of providing a large vertical load bearing capacity. Design/methodology/approach The Reynolds’ equation and flow continuity equation are solved simultaneously by the finite difference method, and the perturbation method and the finite disturbance method is used for calculating the dynamic characteristics. The static and dynamic characteristics, including recess pressure, flow of lubricating oil, carrying capacity, pitch moment, yaw moment, dynamic stiffness and damping, are comprehensively analyzed. Findings The designed closed hydrostatic guideway has the ability to resist large lateral load, pitch moment and yaw moment and has good stiffness and damping characteristics, on the basis of being able to provide large vertical carrying capacity, which can meet the application requirements of heavy two-plate injection molding machine (TPIMM). Originality/value This paper researches static and dynamic characteristics of a large-span six-slider closed hydrostatic guideway used in heavy TPIMM, emphatically considering pitch moment and yaw moment. Some useful guidance is given for the design of large-span closed hydrostatic guideway.

Splicing Measurement and Compensation of Straightness Errors for Ultra-Precision Guideways.

The straightness error of guideways is one of the key indicators of an ultra-precision machine, which plays an important role in the machining accuracy of a workpiece. In order to measure the straightness error of a long-distance ultra-precision guideway accurately, a splicing measurement for the straightness error of a guideway using a high-precision flat mirror and displacement sensor was proposed in this paper, and the data splicing processing algorithm based on coordinate transformation was studied. Then, comparative experiments on a splicing measurement and direct measurement of the straightness error were carried out on a hydrostatic guideway grinder. The maximum difference between the two measurements was 0.3 μm, which was far less than the straightness error of 5.8 μm. The experiment demonstrated the correctness of the proposed splicing measurement method and data processing algorithm. To suppress the influence of the straightness error on machining accuracy, a straightness error compensation algorithm based on error rotation transformation and vertical axis position correction was proposed, and the grinding experiment of a plane optics with a size of 1400 mm × 500 mm was carried out. Without error compensation grinding, the flatness error of the element was 7.54 μm. After error compensation grinding, the flatness error was significantly reduced to 2.98 μm, which was less than the straightness errors of the guideways. These results demonstrated that the straightness error of the grinding machine had been well suppressed.

Modeling and analysis on motion accuracy of hydrostatic guideways incorporating the manual lapping effect

As one of the crucial functional units in ultra-precision machines, the hydrostatic guideways have been commonly adopted due to their own superiority. Although the existed analysis approaches can enable researchers to understand the influence of various design parameters on motion accuracy of hydrostatic guideways, the corresponding imperfections remain to be captured easily. In this paper, targeted at avoiding those defectiveness as much as possible, the kinematic theory based quasi-static analysis model with less simplification is developed directly, wherein the profile pattern difference between main and vice guide rails induced by the manual lapping technology is taken into consideration, and the general structure of hydrostatic guideways extracted from Z axis of the ultra-precision grinding machine UPG80 is determined as the research object. Three CASE studies are proposed orderly to verify the correctness and effectiveness of the established analytical model, and the results demonstrate that the variation trends of the theoretically calculated vertical straightness errors are in good accordance with those of the experimentally measured. Furthermore, the fluctuation amplitude deviation between the predicted and the measured motion accuracy does occur in CASE 3, which should be attributed to the accumulated thermal effect revealed via an experimental platform of hydrostatic guideways with similar structure type to the research object. It also is figured out that, the variation of three components of guide rails’ profile errors caused by the thermal accumulation leads to the fluctuation amplitude deviation reflected in CASE 3, and the level of influence can be known as Amplitude component ( E) > Phase component ( φ) Upside wavelength component ( λup) > Downside wavelength component ( λdown). This study can serve as a valuable foundation for improving the motion accuracy of hydrostatic guideways and is also confirmed to be valuable to the peer designers.

Influence of Pressure-Equalizing Groove on Static Load Performance of Aerostatic Guideway

The load capacity and static stiffness of the existing air hydrostatic guideways are relatively low, and the static performance of the air film is degraded when external forces are increased during the process. Therefore, this study considered an aerostatic guideway of an ultra-precision micromachine tool as the research object. Single- and double-row orifice structures were designed on the guideway, and linear, extended, and X-shaped pressure-equalizing groove (PEG) structures with rectangular cross-sections were designed on the working surface of the guideway. By establishing a computational fluid dynamics model of the guideway air film, the pressure contour was obtained through simulation, and finally, the advantages of the double-row orifice structure were determined. Then, the influences of the structure, width, and depth of PEG and the diameter and number of orifices on the load capacity, stiffness, and air consumption were studied, which provided a theoretical basis for improving the load performance of the aerostatic guideway. The results showed that the design of the PEG effectively improved the load performance but increased the air consumption. The extended PEG exhibited the best load performance. When the eccentricity was large, the width of the PEG moderately increased, improving the load capacity and stiffness. While increasing the depth only improved the stiffness, it had little effect on the load capacity and air consumption. When the eccentricity was small, the diameter and number of orifices moderately increased. The experimental data were consistent with the simulation results, demonstrating the accuracy of the simulation method.

Application of direct coupling method to design problems of hydrostatic guideways accounting for fluid-structure interactions

The deformation of slide carriages caused by oil pressure produces a substantial effect on the performance of hydrostatic guideways. This paper is aimed to propose a practical fluid-structure interaction (FSI) model adopting the direct coupling method to predict the performance more efficiently. To this end, the full-size model containing elastic deformation and thin film pressure fields is solved simultaneously, and the specific boundary conditions caused by the orifice are considered and enforced via the root iterative method. The model is confirmed to be mesh-independent by meshing with three different densities. Furthermore, the vertical stiffness, deformation, and flow rate of the hydrostatic guideway are evaluated and tested with various oil supply pressures. Compared with the theoretical values without considering deformation, the simulation results take the structural deformation into account and thereby exhibit good agreement with those of the experiment. Based on the proposed FSI model, the orthogonal design method is also employed to analyze the influence of structure geometry, and the carriage slide thickness is introduced as the key influential factor of stiffness.

Modeling on Motion Error of Vertical Hydrostatic Cylindrical Guideways

Modeling on Motion Error of Vertical Hydrostatic Cylindrical Guideways

COMPENSATIONOF WORKTABLEMOTIONERROR BYANACTIVELY CONTROLLEDHYDROSTATIC GUIDEWAY

The accuracy of machine tools is limited by many factors,such as geometric and thermal errors. Current error reduction approaches include e.g. volumetric compensation. However, if a machine tool has only linear axes, angular errors cannot be compensated since there is no controllable axis that could change the tool or workpiece inclination. Therefore, an actively controlled hydrostatic guideway was developed to compensate for angular and other geometric errors. This paper aims to experimentally verify the hybrid use of constant resistance and the pilot stage of an industrial proportional pressure relief valve for regulation of oil flow through hydrostatic pockets and control of these pockets as well as active compensation of machine tool geometric errors. The error reduction of the tested linear axis is presented.

THERMO-MECHANICAL ANALYSIS OF A MACHINE TOOL WITH HYDROSTATIC BEARINGS

Thermal behaviour is a key factor affecting the operatingstatus of high performance hydrostatic (HS) bearings of rotational axes of machine tools (MT). This paper introduces a novel model developed for transient thermo mechanical analysis of hydrostatic guideways with a surrounding MT structure. In contrast to common approaches to HS bearing design, which only consider the static load carrying capacity, the new model enables detailed prediction of the bearing thermal stability under various operating conditions. An analytical description of the HS bearing heat generation coupled with a MT finite element (FE) model enables calculation of heat transfer, conduction and especially thermal deformations of the entire MT structure affecting the working accuracy of the machine tool.

In-Situ Measurement and Slow-Tool-Servo Compensation Method of Roundness Error of a Precision Mandrel.

This paper describes a method for measuring and compensating the roundness error of a larger mandrel manufactured by an ultra-precision diamond-turning lathe aimed to obtain a calibration cylinder with a roundness of less than 0.1 μm. The diamond-turning machine has a cross-stacked hydrostatic guideway, produces a cutting depth and feed movement direction, and a dual-spindle system that is firmly connected to the bed. Due to the good repeatability of aerostatic spindles, only in situ rather than online real-time measurements are required. To this end, three high-precision capacitance displacement sensors were utilized to detect the cross-section of the workpiece and the time domain via the three-point error separation technique to separate the roundness error from the rotation motion error. The slow tool servo (STS) cutting technique was employed to compensate for the roundness error, which did not require extra axes, only the excellent dynamic response of the feed axis; hence, the servo control parameters could be suitably adjusted. The experimental results reveal that the low-order harmonic error, often caused by aerostatic spindles, is almost removed completely. For this particular lathe, the experiments indicate that about 60% of the rotational error motion is compensated, and the roundness error is reduced to less than 0.1 μm, which is evaluated by the least-squares circle method.

Combined effect of recess shape and fluid film thickness on the performance characteristics of hydrostatic guideways

Hydrostatic guideways, meant for linear motion are used in high-precision machine tools, to reduce vibration and improve the damping characteristics. The hydrostatic pad in the guideway is provided with a recess, to facilitate the formation of fluid film for supporting the load acting on it. The objective of this work is to study the influence of recess shape in the hydrostatic pad, on the load-bearing capacity and static pressure inside the recess. A numerical model of the hydrostatic pad with recess is analyzed to obtain the pressure distribution of fluid in the recess under operating conditions. Among the various recess shapes analyzed, the newly proposed full rounded rectangular recess is observed to have better load carrying capacity and recess pressure. A comparative analysis has been performed on various recess shapes, having a constant ratio of recess area to fluid film area. Further, the influence of constant flow resistance restrictors using a capillary compensator is included, to study the bearing capability. The static pressure developed in the recess for supporting the externally applied load is determined by making the inlet pressure to the restrictor and the fluid film thickness as constant. The other performance characteristics including variation in mass flow rate and stiffness of the fluid are also studied. Later, the influence of fluid film thickness on the performance characteristic is investigated. The recess shape having better performance characteristics in terms of load bearing capacity, static pressure, mass flow rate, and stiffness is proposed.

Research on the Control Method of Force Servo System of Liquid Hydrostatic Guide Oil Film Thickness Test Bench for Machine Tools

The test bench was designed to solve the problem of measuring the oil film thickness of the liquid hydrostatic guideway of machine tools. And based on the fast overshoot of the classical PID control, introducing the self-antidisturbance control algorithm, this study established a mathematical model of the test bench electro-hydraulic servo control system. At the same time, this paper also designed a specific structure of the self-turbulence controller, which adopts optimal quadratic control, pole configuration, PID control, and self-turbulence control to study the control methods of the test bench electro-hydraulic servo system, respectively, and uses the SIMULINK module to establish the system simulation model of the above-mentioned four control methods of the test bench. Simulation results of the test bench control system show that the response speed of the self-turbulence control is 0.4 seconds, 0.2 seconds, and 4.4 seconds faster than PID control, pole configuration, and optimal quadratic control, respectively, and the overshoot is significantly reduced. Finally, the test bench was built to complete the experiments, and the experimental results showed that the followability of the loading force and thickness detection accuracy of the test bench were better after adding the self-turbulence control algorithm and the stability of the oil film thickness was significantly improved by the test bench electro-hydraulic servo control system.

Thermal Characteristics of a Vertical Hydrostatic Guideway System for Precision Milling Machine Applications

This paper investigates the thermal characteristics of a vertical guideway system for precision milling machine applications by considering three heat sources, namely motor heat, viscous shearing heat of hydrostatic bearings, and friction heat from a ballscrew nut. A finite element (FE) model using ANSYS/Fluent was used to simulate the thermal characteristics of the system by considering the oil film friction of the hydrostatic bearings in the operational feed speed and heat generation in the ballscrew nut. Eight K-type thermocouples were installed in the vertical hydrostatic guideway system to measure the temperature rise in the key components. Nine thermal experiments of the vertical hydrostatic guideway system under three operational feed rates, namely 1.25, 2.5 and 5 m/min were conducted to measure the temperature of seven thermocouples in practical running conditions. The experimental temperature data then was used to adjust the FE model setting to guarantee the accurate prediction of the thermal deformation in real operational conditions. The FE model of the vertical hydrostatic guideway system built in this study can be used to predict the thermal deformation of worktable at center point at any running conditions. At a sliding feed rate of 1 m/s, the thermal positioning error of worktable at center point was 0.1539 µm in the X direction, 0.0009 µm in the Y direction and 2.0246 µm in Z direction.

Origin of the lateral return error in a five-axis ultraprecision machine tool and its influence on ball-end milling surface roughness

Precision ball-end milling is widely used in the manufacture of complex microstructures. The purpose of this paper is to explore the origin of the lateral return error in an ultraprecision five-axis machine tool and its influence on a precision ball-end milling surface. First, the origin of the lateral return error of the linear axis is analyzed. Theoretical analysis and experimental results show that the root of the lateral return error is the gap variation between the slider and the guide, which is decided by the eccentric force moment acting on the hydrostatic guideway. The eccentric force moment relies on the external force and motor eccentricity. In general, the larger the eccentric force moment, the more the gap variation, and resultantly the greater the lateral return error. In addition, the lateral return error is inversely proportional to the oil supply pressure. Because the cutting forces are small enough, the cutting parameters, such as feed speed, cutting depth and cutting stepover, have little effect on the error. Secondly, the lateral return error has an important impact on the yield surface roughness, which will significantly increase the surface roughness and reduce the surface quality. Finally, the lateral return error of the hydrostatic guideway can be suppressed by compensating the machining program. The experimental results show that the surface quality of the compensated surface is significantly improved.

The prediction of large-scale hydrostatic bearing pad misalignment error and its compensation using compliant support

Hydrostatic bearings offer numerous advantages in large-scale moving mechanisms and structures. Nonetheless, the limits of manufacturing, transportation, and assembly in such scales are often encountered. The manufacturing and assembly errors significantly influence the hydrostatic bearing's overall performance. Therefore, it is desirable to compensate the resulting errors and pad misalignment of the hydrostatic multi-pad bearing. Previous research dealt with accuracy improvement and error prediction of small hydrostatic guideways. A little attention was aimed at the use of compliant materials for pads, but this area did not develop any further. The present study offers a methodology on how to estimate allowed assembly errors based on the analysis of the influence of manufacturing errors on the bearing's performance. Additionally, this article describes effects of the compliant support on assembly errors of hydrostatic multi-pad bearings. The proposed prediction is compared with experimental measurements on a hydrostatic bearing experimental rig. The effects of compliant support for a hydrostatic bearing can significantly increase the allowed error as compared to the usual rigid support. Furthermore, the experimental results indicate that the prediction of performance influence based on a known manufacturing error could be used for the hydrostatic bearing's performance improvement. The obtained results might help to enhance the design process of a hydrostatic bearing and improve its performance and extend the lifetime.

Damping in ram based vertical lathes and portal machines

Chatter vibrations originated by the machine structure are a major limitation for the productivity of ram based machines performing heavy duty operations. Consequently, the damping of the machine structure has a capital importance. It is known that interfaces and guideways are the main origin of damping. Recently, the use of active dampers has been introduced in industry. In this work, the damping of hydrostatic and rolling guideways with and without active damping has been experimentally identified and compared using receptance coupling. The results show that hydrostatic guidance can introduce 3–4 times more damping than a roller based system. However, the introduction of active damping is a game changer enhancing damping more than 30 times.

Simulation, Modeling and Experimental Research on the Thermal Effect of the Motion Error of Hydrostatic Guideways.

Hydrostatic guideways are widely applied in ultra-precision machine tools, and motion errors undermine the machining accuracy. Among all the influence factors, the thermal effect distributes most to motion errors. Based on the kinematic theory and the finite element method, a 3-degrees-of-freedom quasi-static kinematics model for motion errors containing the thermal effect was established. In this model, the initial state of the closed rail as a “black box” is regarded, and a self-consistent setting method for the initial state of the guide rails is proposed. Experiments were carried out to verify the thermal motion errors simulated by the finite element method and our kinematics model. The deviation of the measured thermal vertical straightness error from the theoretical value is less than 1 μm, which ensured the effectiveness of the model we developed.

INCREASING PERFORMANCE AND ENERGY EFFICENCY OF A MACHINE TOOL THROUGH HYDROSTATIC LINEAR GUIDEWAYS WITH SINGLE DIGIT MICROMETRE FLUID FILM THICKNESS

Ever increasing requirements to machine tool performance lead to a shift from regular roller bearing towards hydrostatic guideways. These have many advantageous properties, such as non-existent stick and slip, nearly no wear, while increasing dampening and stiffness. Compared to traditional guideways, hydrostatic have a constant energy demand, resulting from pump losses. The pump losses are composed out of the pressure and the flow rate of the fluid. The flowrate can be influenced with the third power via the fluid film thickness. For this, a novel micro gap design is proposed and tested. The static and dynamic stiffness and the power consumption are analysed and compared.