• 연구논문집
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• 통권34호
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• pp.101-112
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• 2004

In order to analyze the motion errors of the aerostatic stage, it is necessary to consider the influence of the moment variation occurredinside the pads. In this paper, a motion error anaysis method utilizing the transfer functions on the reaction force and moment is proposed, and general characteristics of the transfer functions are discussed. Calculated motion errors by the proposed method show good agreement with the ones calculated by Multi Pad Method, which is considered the entire table as an analysis object. Also, by the introduction of the transfer function of motion errors, which represent the relationship between the spatial frequency components of the rail form error and motion errors, motional characteristics of the porous aerostatic stage can be generalized. In detail, the influence of the spatial frequencies is analyzed quantatively, and the patterns of the insensitive frequencies which almost do not affect the linear motion error or angular motion error according to the rail length ratio and the number of the pad are verified. The relationship between the moment variation occurred inside the pads and the motion errors is also verified together.

• 한국정밀공학회지
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• 제21권7호
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• pp.185-194
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• 2004

In order to analyze the motion errors of the aerostatic stage, it is necessary to consider the influence of the moment variation occurred inside the pads. In this paper, a motion error analysis method utilizing the transfer functions on the reaction force and moment is proposed, and general characteristics of the transfer functions are discussed. Calculated motion errors by the proposed method show good agreement with the ones calculated by Multi fad Method, which is considered the entire table as an analysis object. Also, by the introduction of the transfer function of motion errors, which represent the relationship between the spatial frequency components of the rail form error and motion errors, motional characteristics of the porous aerostatic stage can be generalized. In detail, the influence of the spatial frequencies is analyzed qualitatively, and the patterns of the insensitive frequencies which almost do not affect the linear motion error or angular motion error according to the rail length ratio and the number of the pad are verified. The relationship between the moment variation occurred inside the pads and the motion errors is also verified together.

• 한국정밀공학회지
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• 제19권5호
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• pp.56-63
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• 2002

A new model utilizing a transfer function is introduced in the present paper for analizing motion errors of hydrostatic tables. Relationship between film reaction force in a single hydrostatic pad and form error of a guide rail is derived at various spacial frequencies by finite element analysis, and it is expressed as a transfer function. This transfer function clarifies so called averaging effect of the oil film quantitively. For example, it is found that the amplitide of the film reaction farce is reduced as the spacial frequency increases or relative width of the pocket is reduced. Motion errors of a multiple pad table is estimated from transfer function, geomatric relationship between each pads and form errors of a guide rail, which is named as Transfer Function Method(TFM). Calculated motion errors by TFM show good agreement with motion errors calculated by Multi Pad Method, which is considered entire table as an analysis object. From the results, it is confirmed that the proposed TFM is very effective to analyze the motion errors of hydrostatic tables.

• International Journal of Precision Engineering and Manufacturing
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• 제4권2호
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• pp.64-70
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• 2003

A new method using a transfer function is introduced in the present paper for analyzing the motion errors of hydrostatic bearing tables. The relationship between film reaction force in a single-side hydrostatic pad and the form error of guide rail is derived at various spatial frequencies by finite element analysis, and it is expressed as a transfer function. This transfer function clarifies so called 'the averaging effect of an oil film' quantitively. It is found that the amplitude of film force is reduced as the spatial frequency increases or the relative width of the pocket is reduced. The motion errors of a multi pad type table are estimated using a transfer function, the form errors of a guide rail and the geometric relationship between the pads. The method is named as the Transfer Function Method (TFM). The motion errors calculated by the TFM show good agreement with the motion errors calculated by the Multi Pad Method considering the entire table as an analysis object. From the results, it is confirmed that the proposed TFM is very effective to analyze the motion errors of hydrostatic tables.

• 대한기계학회논문집A
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• 제21권10호
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• pp.1718-1729
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• 1997

This paper describes motion errors due to acceleration and deceleration types of servo motors in NC machine tools. Motion errors are composed of two components : one is due to transient response of a servomechanism and the other comes from gain mismatching of positioning servo motors. It deals with circular interpolation to identify motion errors by using Interface card. Also in order to minimize motion errors, this study presents an effective method to optimize parameters which are connected with motion errors. The proposed method is based upon a second order polynomial regression model and it includes an orthogonal array method to make the effective results of experiments. The validity and reliability of the study were verified on a vertical machining center equipped with FANUC 0MC through a series of experiments and analysis.

• 한국정밀공학회지
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• 제10권2호
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• pp.126-137
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• 1993

This paper presents an efficient method for the identification of motion error sources in NC machine tools by making use of the circular interpolation test, which is often used in estimating the motion accuracy of NC machine tools. Mathematical formulae are described for motion errors due to various kinds of error sources. Two identification formulae are proposed: one is based on the frequency analysis and the other is formulated with the weithted residual method. Motion error signal is classified into two patterns, mean errors(mean of CW and CCW test signals from mean errors). The sources of the mean errors are identified by using the frequency analysis technique and the sources of the deviation errors by the weighted residual formulaltion. A menu driven, user oriented, computer program is written to realize the full steps of the proposed identificationprocedure. Then, the identification method is applied to two NC machine tools.

• 한국정밀공학회지
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• 제28권3호
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• pp.275-284
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• 2011

The accuracy simulation technology of linear motion system is introduced in this paper. Motion errors and positioning errors are simulated using informations on the design parameters of elements of linear motion system. 5 Degree-of-freedom motion error analysis algorithm utilizing the transfer function method and positioning error analysis algorithm which are main frame of accuracy simulation are introduced. Simulated motion errors are compared with experimental results for verifying the effectiveness. Then, using the proposed algorithms, simulation is performed to investigate the effects of ballscrew and linear motor on the motion errors. Finally, the influence of feedback sensor position on the positioning error is also discussed.

• 한국정밀공학회지
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• 제26권2호
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• pp.109-117
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• 2009

This paper presents a linear air bearing stage with compensated motion errors by active control of preloads generated by magnetic actuators with combination of permanent and electromagnets. A 1-axis linear stage motorized with a linear motor with 240mm of travel range is built for verifying this design concept and tested its performances. The three motions of the table are controlled with four magnetic actuators driven by current amplifiers and a DSP based digital controller. Three motion errors were measured combined method with laser interferometer and two-probe method with $0.085{\mu}m$ of repeatability for straightness error. The measured motion errors were modeled as functions of the stage position, and compensation were carried out with feedforward control because the characteristics of the motion control with magnetic actuators are linear and independent for each degree-of-freedoms. As the results, the errors were reduced from $1.09{\mu}m$ to $0.11{\mu}m$ for the vertical motion, from 9.42 sec to 0.18 sec for the pitch motion and from 2.42 sec to 0.18 sec for roll motion.

• International Journal of Precision Engineering and Manufacturing
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• 제5권2호
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• pp.60-67
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• 2004

For improving the motion accuracy of hydrostatic tables, a corrective machining algorithm is proposed in this paper. The algorithm consists of three main processes. The reverse analysis is performed firstly to estimate the rail profile from the measured linear and angular motion error, in the algorithm. For the next step, the corrective machining information is obtained based upon the estimated rail pronto. Finally, the motion errors on the correctively machined rail are analyzed by using the motion error analysis method. These processes are iterated until the analyzed motion errors are satisfactory within the target accuracy. In order to verify the validity of the algorithm theoretically, the motion errors calculated by the estimated rail after the corrective machining process, are compared with those by the true rail which is previously assumed as the initially measured value. The motion errors calculated using the estimated rail show good agreement with the assumed values, and it is shown that the algorithm is effective in acquiring the corrective machining information to improve the accuracy of hydrostatic tables.

• 대한기계학회논문집
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• 제19권1호
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• pp.38-44
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• 1995

We made a counter to measure the output of motor encoders for the motion error analysis of a CNC machining center, and have measured the dynamic characteristics and the position errors experimentally. Especially, we measured the radius errors for different feedrates and different radii when the CNC machining center performed a circular interpolation. We have also used an iterative learning method to reduce the radius errors and stick motion errors generated by the CNC machining center performing a circular interpolation. The results show that the proposed learning scheme can reduce the radius error and stick motion error significantly. The reduction of errors becomes more pronounced for higher feedrate and smaller radius.