KR100269776B1 - Active capillary apparatus for a hydraulic bearing and displacement error compensating method by using the same - Google Patents

Abstract

PURPOSE: A variable capillary tube apparatus and a method for compensating motion errors by using the same are provided to compensate relative displacement corresponding to the motion error amount of each position of a principal axis or a feed table with using resistance change of a compensation element by changing a capillary tube compensation element. CONSTITUTION: A variable capillary tube apparatus(400) includes a circular base plate(410), a hollow first cylinder member(420) coupled with the upper surface of the base plate, a hollow second cylinder member(440) coupled with the upper part of the first cylinder member and having the same outer diameter as the outer diameter of the first cylinder member with opening the bottom part to guide the flow of fluid supplied from a fluid supply source at predetermined pressure, a circular leaf spring(430) installed between the first and second cylinder members and regulating the amount of fluid to be flew into the first cylinder member by changing the shape, and a piezo-electric element(450) installed within the first cylinder member contact with the bottom surface of the leaf spring to change the shape of the leaf spring.

Description

Variable capillary device for hydrostatic bearings and motion error correction method using the same

The present invention relates to a hydrostatic bearing, and more particularly, a capillary device for a hydrostatic bearing capable of correcting motion errors occurring during operation of various ultra-precision measuring equipment and ultra-precision machine tools by adjusting the pocket pressure of the hydrostatic bearing; It relates to a motion error correction method using the same.

Hydrostatic bearings are non-contact bearings that retain a load capacity by guiding fluids such as air, lubricating oil, and the like and restricting the discharge of the fluids. The hydrostatic bearing reduces the error component of the low frequency transmitted along the main shaft or the guide rail by the averaging effect of the fluid film formed between the facing object and the high attenuation characteristic. It is suitable for spindles for precision machine tools and feed tables by damping vibrations of the machine tool, and is mainly used for spindles and guide surfaces for various precision grinding machines and guide surfaces for ultra precision machine tools. 1 shows the principle and equivalent electrical circuit of hydrostatic bearing 100. The table on which the bearing 100 is installed moves linearly along the guide surface 120. The table maintains a predetermined distance from the guide surface 120 by a thin fluid film of a high pressure state ejected from the pocket 130 formed on the upper surface. A plurality of pockets may be formed in the transfer table of the machine tool, and the inflow of the fluid into the plurality of pockets is regulated so as to apply appropriate pressure to the guide surface according to the load applied to the table. As the load of the workpiece is applied to the table, the bearing gap on the side to which the force is applied decreases, and the bearing gap on the opposite side increases. In the case of the cross-sectional pad type, the bearing gap h is the total pressure P formed between the guide surface and the table by the hydrostatic lubrication as the sum of the loads (including the weight of the table) W applied to the table, as in Equation 1 It is calculated from the principle that it is equal to the value integrated over the area A. In other words,

(Where, Is the dimensionless area and the dimensionless flow coefficient by the ratio of the pocket area to the bearing area, P _s Is the supply pressure of the lubricating fluid supply device, P _r Is the pocket pressure, k _c Is the capillary coefficient of the capillary tube used to give the bearing rigidity.)

The value increases as the ratio of the pocket area increases.

On the other hand, the hydrostatic bearing has the advantage of low friction and high accuracy by the averaging effect, but has the disadvantage of low stiffness (stiffness). In order to increase the rigidity of the hydrostatic bearing, it is effective to minimize the bearing gap. In addition, in order to optimally design a bearing to satisfy the minimum bearing gap, it is necessary to limit the amount of fluid flowing into the bearing according to the bearing gap.

However, in order to reduce the bearing gap, the machining precision of the bearing must be increased. Therefore, there is a limit to improving the stiffness of the bearing in such a way as to reduce the bearing gap. To overcome this limitation, various variable restricting mechanisms have been proposed.

As an example of such a mechanism, diaphragm type variable limit bearings 200 and 250 are shown in FIGS. 2 and 3. 2 and 3, the bearing surfaces 210 and 260 are made of an elastically deformable diaphragm. The shape of the bearing surfaces 210 and 260 is deformed according to the pressure change acting on the bearing surfaces 210 and 260 according to the load change applied to the bearings 200 and 250. Therefore, high rigidity is achieved. In particular, in the mechanism shown in FIG. 3, the inner circumferential surface of the diaphragm 260 is elastically supported by the O-ring 270. The pressure at the back of the diaphragm 260 varies with the pressure acting on the bearing surface 260 through a small hole 290 formed in the center of the housing. Therefore, the shape of the diaphragm is sensitively changed as the load changes.

High bearing stiffness can be obtained when the diaphragm variable limiting mechanism described above is used in proper bearing conditions. However, the diaphragm variable limiting mechanism described above has the following disadvantages. (1) The application is limited because the bearing surface must be deformed. (2) A pocket is formed when the diaphragm is greatly deformed. Therefore, the diaphragm may self-oscillate according to the compression of air. (3) It is not easy to process the diaphragm. The bearing characteristics change depending on the machining accuracy, which affects the life of the diaphragm.

On the other hand, for the manufacture of a spindle or table using hydrostatic bearings, in the case of the spindle, the machining accuracy, such as the roundness and the cylindricalness of the shaft, and in the case of the transfer table, the straightness, the top view, the right angle to at least two guide rails It is not easy to achieve the motion precision of the submicron order even if the averaging effect of the oil film is expected because the processing accuracy such as the degree and the parallelism and the squareness of the two rails must be obtained. In addition, since the motion error due to such processing error depends on the geometric shape, it is difficult to correct the motion error even if the peripheral device is high precision.

Conventionally, three types of correction have been proposed. First, there is a fixed correction where the capillary or orifice is used as a fixed value resistor. Second, the variable correction uses diaphragms and valves to create a flow inversely proportional to the pocket resistance, thereby achieving a pressure differential that is greater than the pressure differential that can be formed in the fixed correction device. However, both of the above correction schemes require each device to fit the bearing gap.

Smaller bearing gaps are required to improve the performance of the bearings, and manufacturing errors occur because the correction devices require manual tuning, making the use of the two correction schemes even more difficult. In addition, the machine tool with three axes requires approximately 36 bearing pockets, thus consuming a great deal of labor.

The third correction scheme is so-called self-compensation, which uses a change in the bearing gap to allow for a change in fluid flow into the pocket itself. In the self-calibration method, a linear groove is formed on a bearing surface and is mainly applied to a spindle. However, the self-calibration method did not show an excellent effect in terms of its economy, which made it difficult to quantitatively analyze the flow pattern and, in particular, it was difficult to judge the flow near the linear groove end, resulting in inadequate resistance design. As a result, manual tuning of the correction device is required. In addition, the self-correction unit employing the above-described linear groove has a disadvantage in that it can not be actually used in a structure in which the groove cannot be formed properly.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above problems, and a first object of the present invention is to provide a variable capillary device capable of varying a capillary compensation element installed to give rigidity to a hydrostatic bearing.

In addition, the motion error correction method using a variable capillary device that can correct the relative displacement corresponding to the amount of motion error at each position of the main shaft or the transfer table using the variable capillary device using the resistance change of the compensation element There is a second purpose in providing it.

In order to achieve the first object the present invention is:

Base plate;

A hollow first cylinder member coupled to an upper surface of the base plate;

First means coupled to an upper portion of the first cylinder member and guiding a flow of fluid;

Second means for adjusting an amount of the fluid introduced into the first means by being installed between the first cylinder member and the first means and changing its shape; And

It provides a variable capillary device characterized in that it comprises a third means for changing the shape of the second means.

According to a preferred embodiment of the present invention, the first means includes a hollow second cylinder member having an outer diameter that is the same as the outer diameter of the first cylinder member and whose bottom surface is opened, and an upper portion of the second cylinder member. A first opening for introducing the fluid therein is formed, and an annular guide having an inner diameter approximately equal to the size of the first opening is integrally formed with the second cylinder member downwardly from the first opening. An extension extends the fluid flowing through the first opening to the lower portion of the second cylinder member, and a second opening is formed at one side of the second cylinder member to discharge the introduced fluid to the outside.

On the other hand, the first and second openings are internally screwed on the inner circumferential surface thereof and engaged with the male threads of the first pipe connected with the fluid supply source and the second pipe connected with the hydrostatic bearing, respectively, so that the fluid supply source and the hydrostatic bearing Connected.

According to a preferred embodiment of the present invention, the second means is a circular leaf spring, the size of which is equal to the outer diameter of the first and second cylinder members, and is press-installed between the first and second cylinder members. The degree of bending in the upward direction is changed by the force applied from the bottom surface, so that the gap of the capillary tube formed between the upper edge and the lower end of the annular guide is changed so that the fluid flows into the second cylinder member. Allow the amount to be adjusted.

According to a preferred embodiment of the present invention, the third means is a piezoelectric element which is installed in the first cylinder member such that its upper end is in contact with the bottom surface of the leaf spring, the upper end of the piezoelectric element according to the voltage applied thereto The displacement in the upward direction changes to change the gap of the capillary.

As the voltage applied to the piezoelectric element increases, the upper end of the piezoelectric element moves upwards, thereby decreasing the amount of the fluid flowing into the second cylinder member by decreasing the gap of the capillary tube, and conversely, the piezoelectric element As the applied voltage decreases, the upper end of the piezoelectric element moves downward, and accordingly, the gap of the capillary tube increases, thereby increasing the amount of the fluid flowing into the second cylinder member.

According to a preferred embodiment of the present invention, an adjustment screw is installed on the bottom wall of the first cylinder member to adjust the overall position of the piezoelectric element by adjusting its position to set the initial gap of the capillary tube.

Further, in order to achieve the second object, first and second variable capillary devices, each outlet of the first and second fixed capillary tubes, each of which is connected to a fluid source, according to the present invention communicate with respective pockets thereof. Movable first and second guide rails juxtaposed in parallel with each other and the first and second guide rails extending in a first direction using the first, second, third and fourth hydrostatic bearings In the method of compensating the motion error for a table combined with

(1) installing the first hydrostatic bearing on a first side of a first surface facing the vertical surface of the first guide rail of the table bottom surface;

(2) installing the second hydrostatic bearing on a second side spaced apart from the first side of the first surface of the table bottom by a predetermined distance in the first direction;

(3) On a third side of the second surface facing the vertical surface of the second guide rail of the table bottom surface, the first side of the first surface and the third side in a second direction perpendicular to the first direction. Installing the third hydrostatic bearing;

(4) installing the fourth hydrostatic bearing on a second side of the first side of the table, parallel to the second side of the first side and in the second direction;

(5) measuring a displacement in the second direction of the table in each step by applying a stepwise increasing voltage to the first and second variable capillary devices;

(6) evaluating a relationship between the voltage applied to the first and second variable capillary devices and thus the displacement of the table in the second direction, thereby first and second of the first and second variable capillary devices; Determining a second gain;

(7) the table and the first and second guides in the second direction of the table while transferring the table in the first direction without applying voltage to the first and second variable capillary devices; Measuring an error displacement resulting from an error in the straightness and parallelism of the rail; And

(8) the first and second capillary devices according to the first and second gains obtained from the step (6) so as to cancel the error displacement while the table is transported in the first direction. Applying a varying correction voltage corresponding to the varying error displacement.

According to a preferred embodiment of the present invention, in step (5), the displacement of the table in the second direction is a first position parallel to the first side and the second direction of the first surface of the table. And a second position parallel to the second side of the first side of the table in the second direction and a third position centrally located between the first and second positions.

In step (5), the increasing voltage is applied to the first and second piezoelectric elements installed in the first and second variable capillary devices to form the first and second variable capillary devices to form the first and second variable capillary devices. By varying the pocket pressure of the first and second hydrostatic bearings by adjusting the gap between the first and second capillaries for adjusting the amount of fluid discharged to the second variable capillary device outlet, the second direction of the table Will change its position.

On the other hand, in step (6), the first and second gains are obtained by roughly linearizing the relationship between the voltage and the displacement for each of the first and second variable capillary devices.

In step (7), the error displacement has repeatability, so that, when transferring the table in the first direction, the voltage to be applied to the first and second capillary devices is specified.

According to an exemplary embodiment of the present invention, the first and second variable capillary devices may be provided with first and second piezoelectric elements each having a maximum displacement amount capable of canceling the error displacement.

The error displacement is a straightness error of the table and the first and second guide rails in the first direction, and a rotational error with respect to the vertical direction perpendicular to the first and second directions. error, wherein the straightness and rotational errors are varied by varying the voltage applied to the first and second variable capillary devices according to the obtained first and second gains of the first and second variable capillary devices. It is corrected at the same time.

The variable capillary device for hydrostatic bearings according to the present invention and the method of compensating motion error using the same correspond to the amount of motion error at each position of the spindle or feed table by varying the capillary compensation element installed to give rigidity to the hydrostatic bearing. The relative displacement can be corrected by using the resistance change of the compensating element.

1 is a schematic diagram showing an operating principle and an equivalent electric circuit of a general sectional pad type hydrostatic bearing device.

2 and 3 is a cross-sectional view showing a diaphragm hydrostatic bearing device according to the prior art.

Figure 4 is a perspective view of a variable capillary device according to an embodiment of the present invention.

Figure 5 is a schematic diagram for explaining the principle of motion error correction of the oil pressure table using a variable capillary device according to an embodiment of the present invention.

Figure 6 is a graph showing the displacement and the pocket pressure when the step voltage is input to the variable capillary device according to an embodiment of the present invention.

Figure 7 is a schematic diagram showing an experimental device for simultaneously correcting the straightness (straightness) and angular (angular) error of the oil pressure table using a variable capillary device according to an embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating a structure of a hydrostatic pressure table illustrated in FIG. 7.

FIG. 9 is a graph showing correction results of straightness and angular motion errors of the hydrostatic pressure table using the experimental apparatus shown in FIG. 7.

** Explanation of symbols for main parts of drawings **

402 and 404: first and second variable capillary devices

402a, 404a: first and second piezoelectric elements

402c and 404c: first and second capillary tubes

810 Hydrostatic Table

702, 704: first and second fixed capillaries

h: bearing gap

P _r Pocket pressure

Hereinafter, the operating principle of the variable capillary device 400 and the variable capillary device 400 for the hydrostatic bearing 500 according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

4 and 5 illustrate a variable capillary device 400 and a working principle thereof for a hydrostatic bearing according to a preferred embodiment of the present invention. 4 and 5, the variable capillary device 400 includes a circular base plate 410, a hollow first cylinder member 420 coupled to an upper surface of the base plate 410, and a first cylinder member 420. In order to guide the flow of the fluid which is coupled to the top of the fluid and supplied at a predetermined pressure from the fluid source Ps, according to a preferred embodiment of the present invention, the bottom surface has the same outer diameter as that of the first cylinder member 420 The amount of the fluid flowing into the first means is provided between the open second cylindrical cylinder member 440, the first cylinder member 420 and the second cylinder member 440, and its shape is changed. A circular leaf spring 430 for adjustment and a piezoelectric element installed in contact with the bottom surface of the leaf spring 430 in the first cylinder member 420 so as to change the shape of the leaf spring 430. An element 450 is provided.

The first opening 470 for introducing the fluid into the upper portion of the second cylinder member 440 is formed. In order to guide the fluid flowing through the first opening 470 to the lower portion of the second cylinder member 440, the annular guide 480 having an inner diameter approximately equal to the size of the first opening 470 is provided in the second. It extends downward from the first opening 470 integrally with the cylinder member 440. According to a preferred embodiment of the present invention, the lower end of the annular guide 480 forms a capillary tube 432 having a fine gap h and the upper surface of the leaf spring 430. According to one preferred embodiment of the present invention, the fine gap h has a size of several tens of microns.

According to the voltage applied to the piezoelectric element 450 installed in the first cylinder member 420, the displacement of the upper end of the piezoelectric element 450 in the upward direction is changed to change the gap h of the capillary tube 432. The size of the leaf spring 430 is equal to the outer diameter of the first and second cylinder members 420 and 440, and is press-fitted between the first and second cylinder members 420 and 440, and is applied to the force applied from the bottom surface thereof. As a result, the degree of bending in the upward direction is changed, so that the gap h of the capillary tube 432 formed between the upper surface and the lower end of the annular guide 480 is changed so that the fluid flowing into the second cylinder member 440 Allow the amount to be adjusted.

That is, when the voltage applied to the piezoelectric element 450 is increased, the upper end of the piezoelectric element 450 is moved upward, and accordingly, the gap h of the capillary tube 432 is reduced, thereby flowing into the second cylinder member 440. When the amount of fluid decreases and, on the contrary, when the voltage applied to the piezoelectric element 450 decreases, the upper end of the piezoelectric element 450 moves downward, thereby increasing the gap of the capillary tube 432 so that the second cylinder member 440 is increased. The amount of the fluid entering the) increases.

Meanwhile, according to an exemplary embodiment of the present invention, a screw for preload 460 is installed on the bottom wall of the first cylinder member 420. By adjusting the adjusting screw 460 to adjust the overall vertical position of the piezoelectric element 450, the initial gap hi of the capillary tube 432 is set.

One side of the second cylinder member 440 is formed with a second opening 490 for discharging the introduced fluid to the outside.

On the other hand, the first and second openings 470 and 490 of the second pipe 492 connected to the first pipe 472 and the hydrostatic bearing 500 whose inner circumferential surfaces are female threaded and connected to the fluid source Ps, respectively. Engagement with the male threaded portion is in communication with the fluid source Ps and the hydrostatic bearing 500.

On the other hand, Figure 5 shows an example of the principle of correcting the movement error of the transfer table using the variable capillary device 400.

Referring to FIG. 5, a variable capillary device 400 is connected to an upper pad 510 of a hydrostatic bearing 500, and a general fixed capillary 700 is connected to a lower pad 520. in this condition Δ When it is necessary to displace the hydrostatic bearing 500 by h, when a predetermined voltage is applied to the piezoelectric element 450, the gap h of the capillary tube 432 is reduced, thereby increasing the resistance and thus the upper pad 510. The pocket pressure in the interior is reduced instantaneously. At this time, since the forces formed by the integration of the pressure distribution applied by the upper and lower pads 510 and 520 to the conveying rail 600 should be the same, for this purpose, the upper pad 510 to increase the pocket pressure of the upper pad 510. Is Δ It is displaced downward by h. Using this principle, if the applied voltage applied to the piezoelectric element 450 and the displacement of the table (not shown) are obtained in advance, the movement error of the table generated within the maximum displacement of the piezoelectric element 450 can be corrected.

Fig. 6 (a) shows the 1V / step input of the D / A converter 800 (shown in Fig. 7) on the table surface of the pad 510 side to which the variable capillary device 400 is connected at a supply pressure of 100 N / cm ² . The response displacement of the table is properly tracked to the input value, and the response gain for the D / A converter is 0.55. μ It shows that it is m / V. FIG. 6 (b) is a response displacement measured on the opposite side of the pad 520 to which the fixed capillary 700 is connected, and shows a positive displacement as shown in FIG. 10 (a). You can see that none. 10 (c) and 10 (d) measure the change in the pocket pressure of the pads 510 and 520 at that time, and it can be seen that the pocket pressure closely follows the change in the gap h of the capillary tube 432. This confirms that the table is moving to a new equilibrium position of both pocket pressures.

Hereinafter, a method of correcting a motion error of a hydrostatic pressure table using the variable capillary device 400 according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

7 and 8 illustrate the structures of the experimental apparatus 900 and the experimental hydrostatic pressure table 810 for correcting the movement error of the hydrostatic pressure table 810. 7 and 8, the hydrostatic pressure table 810 is a double-sided pad type, and the first and second variable capillary devices 402 and 404, the first and second fixed capillaries, each of which is connected to the fluid source Ps at its inlet. The first and second guide rails 910, juxtaposed parallel to each other, using the first, second, third and fourth hydrostatic bearings in which each outlet of 702 and 704 and their respective pockets are in communication. 912 and the first and second guide rails 910 and 912 are movably coupled in an extended first direction X.

The hydrostatic pressure table 810 is installed as follows. (1) The first hydrostatic pressure on the first side 812a of the first surface 812 facing the vertical surface of the first guide rail 910 of the bottom portion of the table 810. Install the bearing 840. (2) A second hydrostatic bearing (not shown) is installed on the first side 812a of the first surface 812 of the bottom portion of the table 810 and the second side 812b spaced apart from each other in the first direction X by a predetermined distance. do. (3) Orthogonal to the first side 812a and the first direction X of the first surface 812 of the second surface 814 facing the vertical surface of the second guide rail 912 of the bottom portion of the table 810. The third hydrostatic bearing 850 is installed on the third side 814a at a position parallel to the second direction Y. As shown in FIG. (4) A fourth hydrostatic bearing (4) on the fourth side 814b of the second surface 814 of the bottom surface of the table 810 in parallel with the second side 812b of the first surface 812 in the second direction Y ( Not shown).

The table 810 is driven by a ball screw 920, an AC servo motor 998, and a digital signal processor (DSP) motion controller 996.

In order to give linear and angular displacements to the table 810 using two variable capillary devices 402 and 404, the gain value of each variable capillary device 402 and 404, i.e., the D / A converter input voltage / table displacement It needs to be obtained in advance experimentally. To this end, (5) a stepwise increasing voltage is applied to the first and second variable capillary devices 402 and 404 to measure the displacement of the table 810 in the second direction Y in each step. (6) The first and second variable capillary devices by evaluating the relationship between the voltages applied to the first and second variable capillary devices 402, 404 and thus the displacement in the second direction Y of the table 810. Determining the first and second gains of (402, 404).

In this case, according to an exemplary embodiment of the present invention, as shown in FIG. 7, the displacement of the table 810 in the second direction Y may correspond to the first side 812a of the first surface 812 of the table 810. A first position parallel to the second direction Y and a second position 812b of the first surface 812 of the table 810 and a second position parallel to the second direction Y and at the center of the first and second positions Each is measured at the third position.

The incremental voltage is applied to the first and second piezoelectric elements 402a and 404a installed in the first and second variable capillary devices 402 and 404, so that the first and second variable capillary devices 402 and 404 First and second hydrostatic bearings by adjusting the gap between the first and second capillary tubes 404a and 404c to adjust the amount of fluid formed and discharged to the first and second variable capillary device outlets 402b and 404b. By changing the pocket pressure of each, the position of the table 810 in the second direction Y is changed. The first and second gains of the first and second variable capillary devices 402, 404 are obtained by roughly linearizing the relationship between the voltage and displacement for each of the first and second variable capillary devices 402, 404. do.

In this case, the horizontal displacement of the table 810 is measured using a capacitive sensor 988.

Thereafter, (7) the table 810 is moved in the first direction X while the voltage is not applied to the first and second variable capillary devices 402 and 404, and in the second direction Y of the table 810, Error displacements due to errors in the straightness and parallelism of the table 810 and the first and second guide rails 910 and 912 are measured. (8) First and second variable capillary devices in accordance with the first and second gains obtained from step (6) so that the error displacement can be canceled while the table 810 is conveyed in the first direction X. A changing correction voltage corresponding to the changing error displacement is applied to (402, 404).

In step (7), the error displacement has repeatability such that the voltage to be applied to the first and second variable capillary devices 402, 404 is specified upon transfer of the table 810 in the first direction X.

According to a preferred embodiment of the present invention, the first and second variable capillary devices 402 and 404 respectively include first and second piezoelectric elements 402a and 404a having a maximum displacement amount that can cancel the error displacement. It can be provided.

The error displacement is perpendicular to the straightness error of the table 810 in the first direction X and the first and second guide rails 910 and 912, and perpendicular to the first and second directions X and Y. A yaw error with respect to the direction, wherein the straightness and the rotational error are determined according to the first and second gains of the obtained first and second variable capillary devices 402, 404. It is simultaneously corrected by varying the voltage applied to the variable capillary devices 402, 404.

FIG. 9 (a) shows the horizontal linear motion error and the angular motion error of the hydrostatic table 810 five times. Straightness 2.21 for travel distance 200mm μ m, the degree of angular motion is 1.4 arcsec, while FIG. 9 (b) shows the degree of motion when the variable capillary device is used. As a result of simultaneously correcting linear motion error and angular motion error by applying the motion error correction method using the variable capillary device, the linear motion error is 0.25 which is about 1/10 of the uncorrected state. μ As m, the angular motion error is improved to 0.4 arcsec, which is about one third of the uncorrected state, and thus it can be confirmed that the angular motion error is very effective for the error correction of the oil pressure table 810.

The variable capillary device for hydrostatic bearings according to the present invention and the method of compensating motion error using the same correspond to the amount of motion error at each position of the spindle or feed table by varying the capillary compensation element installed to give rigidity to the hydrostatic bearing. The relative displacement can be corrected by using the resistance change of the compensating element.

Although the present invention has been described above according to an embodiment of the present invention, it will be apparent to those skilled in the art that various modifications may be made without departing from the spirit of the present invention.

Claims (14)

Base plate; A hollow first cylinder member coupled to an upper surface of the base plate; First means coupled to an upper portion of the first cylinder member and guiding a flow of fluid; Second means for adjusting an amount of the fluid introduced into the first means by being installed between the first cylinder member and the first means and changing its shape; And And a third means for changing the shape of the second means. The method of claim 1, wherein the first means comprises a hollow second cylinder member having an outer diameter equal to the outer diameter of the first cylinder member, the bottom of which is open, the upper portion of the second cylinder member A first opening for introducing into the inside is formed, and an annular guide having an inner diameter approximately equal to the size of the first opening is extended downwardly from the first opening in an integral manner with the second cylinder member. A variable capillary tube guides the fluid introduced through one opening to a lower portion of the second cylinder member, and a second opening is formed at one side of the second cylinder member to discharge the introduced fluid to the outside. Device. According to claim 2, wherein the first and the second opening portion of the fluid supply and the inner peripheral surface of the first pipe connected to the fluid supply source and the male threaded portion of the second pipe connected to the hydrostatic bearing, respectively, so that the fluid supply and the Variable capillary device, characterized in that in communication with the hydrostatic bearing. 3. The method of claim 2, wherein the second means is a circular leaf spring, the size of which is equal to the outer diameter of the first and second cylinder members, is press-fitted between the first and second cylinder members, and from the bottom surface thereof. The degree of bending in the upward direction is changed by the applied force, so that the gap of the capillary tube formed between the upper edge and the lower end of the annular guide is changed so that the amount of the fluid flowing into the second cylinder member is controlled. Variable capillary device, characterized in that. The piezoelectric element of claim 4, wherein the third means is installed in the first cylinder member such that an upper end thereof is in contact with the bottom surface of the leaf spring. A displacement capillary device, characterized in that the displacement is changed to change the gap of the capillary. The method of claim 5, wherein when the voltage applied to the piezoelectric element is increased, the upper end of the piezoelectric element is moved upwards, thereby reducing the amount of the fluid flowing into the second cylinder member by reducing the gap of the capillary tube On the contrary, when the voltage applied to the piezoelectric element decreases, the upper end of the piezoelectric element moves downward, thereby increasing the amount of the fluid flowing into the second cylinder member by increasing the gap of the capillary tube. Variable capillary device. 6. The variable capillary device according to claim 5, wherein an adjustment screw is provided on the bottom wall of the first cylinder member to adjust the overall vertical position of the piezoelectric element by adjusting the adjustment screw to set the initial gap of the capillary tube. First and second variable capillary devices having their respective inlets connected to the fluid source, first, second, third and fourth hydrostatic bearings having their respective pockets in communication with each outlet of the first and second fixed capillaries; A method of correcting a motion error of a table movably coupled in a first direction in which the first and second guide rails are extended to first and second guide rails juxtaposed in parallel to each other using: (1) installing the first hydrostatic bearing on a first side of a first surface facing the vertical surface of the first guide rail of the table bottom surface; (2) installing the second hydrostatic bearing on a second side spaced apart from the first side of the first surface of the table bottom by a predetermined distance in the first direction; (3) On a third side of the second surface facing the vertical surface of the second guide rail of the table bottom surface, the first side of the first surface and the third side in a second direction perpendicular to the first direction. Installing the third hydrostatic bearing; (4) installing the fourth hydrostatic bearing on the second side of the table bottom surface, on the fourth side parallel to the second side of the first side in the second direction; (5) measuring a displacement in the second direction of the table in each step by applying a stepwise increasing voltage to the first and second variable capillary devices; (6) evaluating a relationship between the voltage applied to the first and second variable capillary devices and thus the displacement of the table in the second direction, thereby first and second of the first and second variable capillary devices; Determining a second gain; (7) the table and the first and second guides in the second direction of the table while transferring the table in the first direction without applying voltage to the first and second variable capillary devices; Measuring an error displacement resulting from an error in the straightness and parallelism of the rail; And (8) the first and second variable capillary devices according to the first and second gains obtained from the step (6) so as to cancel the error displacement while the table is being transported in the first direction. And applying a varying correction voltage corresponding to the varying error displacement. 9. The method of claim 8, wherein in step (5), the displacement of the table in the second direction is a first position parallel to the first side of the first surface of the table in the second direction, of the table. Motion error correction using a variable capillary device, characterized in that measured in the second position parallel to the second side and the second direction of the first surface and the third position located in the center of the first and second position, respectively Way. 9. The method of claim 8, wherein in step (5), the incremental voltage is applied to first and second piezoelectric elements installed in the first and second variable capillary devices, thereby providing the first and second variable capillary devices. By varying the pocket pressure of the first and second hydrostatic bearings by adjusting the gaps of the first and second capillaries for controlling the amount of fluid that is formed and discharged to the outlet of the first and second variable capillary devices. A motion error correction method using a variable capillary device, characterized in that for changing the position of the table in the second direction. 9. The variable capillary tube according to claim 8, wherein in step (6), the first and second gains are obtained by roughly linearizing the relationship between the voltage and the displacement for each of the first and second variable capillary devices. Motion error correction method using the device. 9. The method of claim 8, wherein in step (7), the error displacement has repeatability such that, during transfer of the table in the first direction, a voltage to be applied to the first and second variable capillary devices is specified. Motion error correction method using a variable capillary device, characterized in that. 9. The method of claim 8, wherein in step (7), the first and second variable capillary devices are each provided with first and second piezoelectric elements having a maximum amount of displacement capable of canceling the error displacement. Motion error correction method using a variable capillary device. 9. The method of claim 8, wherein in step (8), the error displacement is a straightness error of the table and the first and second guide rails in the first direction, and the first and second A yaw error in a vertical direction orthogonal to the direction, wherein the straightness and the rotation error are in accordance with the first and second gains of the obtained first and second variable capillary devices. And correcting at the same time by varying a voltage applied to the second variable capillary device.