JPH05215133A - Static pressure fluid bearing and positioning control device thereof - Google Patents

Abstract

PURPOSE:To provide a static pressure air bearing which prevents change of a bearing gap due to fluctuation of assembling precision or mechanical precision of the bearing or positional change caused by movement of the bearing. CONSTITUTION:A bearing comprises static pressure pads 5a, 5b for jetting fluid to an opposite surface to keep a gap between those and the opposite surface by static pressure, bias magnets 12a, 12b which work in the directions to reduce the gap, and coils 13a, 13b for modulating magnetic fields of the bias magnets.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a static pressure air bearing used as a guide for a positioning device of a semiconductor exposure apparatus (stepper or the like), and more particularly to a permanent magnet for generating an attractive force for balancing the levitation force. The present invention relates to a static pressure air bearing in which a magnetic field modulation coil is provided in a portion. Furthermore, the present invention relates to a positioning device using this static pressure air bearing, and more particularly to a positioning control device configuration for controlling the posture change of a moving body.

[0002]

2. Description of the Related Art A guide surface is one of the important factors that control the motion accuracy of precision equipment. In recent years, hydrostatic bearings have been widely used from the viewpoint of ensuring straight running accuracy. For example, in a positioning stage that requires high accuracy, static pressure bearings are usually used for guides and supporting parts to improve motion accuracy.

The advantage of this hydrostatic air bearing is that high straightness can be obtained due to the averaging effect of the air film and friction, wear and dust are reduced due to non-contact support, and as a result the driving force can be reduced and the cleaning can be improved. This means that it can be used in an environmental environment.

On the other hand, the disadvantage of the hydrostatic air bearing is that it is supported by air of low viscosity, so that it is difficult to improve rigidity and load capacity, and self-excited vibration easily occurs due to the compressibility of air. is there.

Next, an example of a positioning device using a hydrostatic air bearing will be described. FIG. 5 is an example of a uniaxial positioning device that guides the moving body 1 using the static pressure air bearing 2. Here, 3 is a drive ball screw, which is a drive mechanism for positioning the moving body 1 in the linear movement direction via the coupling 4. The hydrostatic air bearing 2 used as a guide has high movement resolution because there is no stick slip or backlash due to solid friction, and the hydrostatic pressure pad shape error is averaged in the working fluid film. Therefore, the guide accuracy is improved, and since there is no friction, it is possible to perform a permanent high-precision feed.

FIG. 6 is an enlarged sectional view of the static pressure air bearing mounting portion. The principle of this bearing will be described with reference to FIG. This figure depicts a state in which the moving body 1 floats in a non-contact manner from the surface plate 7 through the gaps 6a and 6b by the action of the static pressure pads 5a and 5b. The supply tube 8 is attached to each of the static pressure pads 5a and 5b attached to the static pressure pad holders 9a and 9b.
Compressed air is supplied from a and 8b, so that the levitation force with respect to the surface plate 7 is obtained. Also, the magnet holders 10a, 1
The moving body 1 is attracted to the surface plate 7 side by the action of the permanent magnets 11a and 11b attached to 0b. Therefore, the clearances 6a and 6b are stable in a state where the upward floating force of the static pressure pads 5a and 5b to which the compressed air is guided and the downward attractive force of the permanent magnets are balanced, and the clearances 6a and 6b are not in contact with the surface plate 7. The state is obtained.

In the figure, the moving body 1 has a static pressure pad 5a,
5B is a diagram showing a case where the movable body 1 is supported in a non-contact manner in the direction opposite to gravity by 5b, but the principle is the same when the movable body 1 is supported in a non-contact manner in the horizontal direction. However, in this case, the permanent magnet also has a role of preventing the moving body 1 from being laterally deformed by the repulsive force of the air bearing.

[0008]

In the above-mentioned prior art, as described above, the static pressure air bearing provides the movable body with a certain clearance due to the balance between the attractive force of the permanent magnet and the pressure of the working fluid. Support non-contact. In this case, the gap becomes an important parameter related to the device performance. That is, the clearance determines the mechanical rigidity of the device, and this mechanical rigidity greatly affects the performance of the positioning device that constitutes the control loop and uses the hydrostatic air bearing. The conventional static pressure air bearing has a problem that the clearance cannot be managed sufficiently.

That is, the magnetizing force determines the attractive force of the permanent magnet, but it was difficult to make the size of the permanent magnet accurately and without variation. Also, the pads themselves had variations in production. Therefore, the balance between the levitation force and the magnetic attraction force obtained when the working fluid is supplied to the static pressure pad also varies, and thus the gap cannot be set as the target value. In this case, the absolute value of rigidity cannot be managed as desired, so that the positioning performance when the control system is configured could not be managed.

The above-mentioned problems are related to the absolute value of the rigidity which limits the performance of the control system of the positioning device, but in the prior art, it is caused by the spatial arrangement of the hydrostatic air bearings. There was a problem of the posture change of the positioning device. This will be described below.

Generally, when the static pressure pad and the permanent magnet are one unit constituting a static pressure air bearing, this unit is used at many places in the positioning device to support the moving body. Therefore, the balance between the levitation force of the static pressure pad and the attraction force of the permanent magnet differs from unit to unit, and naturally the gaps between them also differ. Conventionally, since the attraction force of a given permanent magnet cannot be adjusted after being incorporated, the pressure of the working fluid has been adjusted so that the gaps of all units are close to the target value. However, the gap between the units is slightly different, and each time the moving body supported by the unit is positionally driven, a change in posture occurs due to the difference in the gap.

That is, the clearance of the stationary air bearing is equivalent to the bearing rigidity, but the relationship between the resonance frequency of the moving body and the bearing rigidity is given by the following equation as is well known.

[0013]

## EQU1 ## f = (k / m) 1/2 / 2.pi., Where m is stage mass and k is rigidity.

In the above equation, the rigidity k of the static pressure air bearing changes depending on the bearing clearance. However, the bearing gap also changes at the position where the moving body moves. Therefore, if the rigidity changes in each part of the bearing, the posture of the moving body changes. Therefore, the positioning time varies depending on the position of movement due to a change in posture, and even if a good positioning time is achieved in one place, in another place, in an extreme case, an oscillation phenomenon may be caused. Sometimes. Furthermore, changes in the bearing clearance, along with changes in machine dimensions over time and material deformation during machine assembly, sometimes lead to mechanical contact accidents.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is a static pressure air bearing in which variations in bearing assembly accuracy and mechanical accuracy or changes in bearing clearance due to locational changes due to movement of the bearing are prevented. For the purpose of providing.

[0016]

In order to achieve the above object, the present invention provides a hydrostatic air bearing that can be operated by a current that applies a bias attraction force by a permanent magnet to a magnetic field modulation coil. With this configuration, the bearing gap can be adjusted, and thus the rigidity can be adjusted.

Further, in order to suppress the posture change such as pitching and yawing of the moving body in the positioning device, there is provided a device configuration for controlling the current to the magnetic field modulation coil so as to correct the posture change. In this case, the rigidity of each part of the static pressure air bearing is not made uniform, but the rigidity value of each part of the static pressure air bearing is changed so as to suppress the change in position, and the position of the moving body is corrected.

[0018]

1 is an enlarged sectional view of a static pressure air bearing mounting portion provided with a magnetic field modulation coil according to an embodiment of the present invention. In the figure, 12a and 12b are permanent magnets for bias, and 1
3a and 13b are magnetic field modulation coils, and 14a and 14b are yokes.

In the conventional static pressure air bearing shown in FIG. 6 described above, since the static pressure pads 5a and 5b have variations, even if the same compressed air is guided to the supply tubes 8a and 8b, the levitation force is different. Further, the permanent magnets 11a and 11b that generate the attraction force to the surface plate 7 also have variations in the attraction force due to uneven magnetization. Therefore, the gaps 6a and 6b in the vicinity of the static pressure pad 5a and in the vicinity of the static pressure pad 5b are not the same. In this state, when the moving body 1 is driven to position in the horizontal direction at high speed, a posture change called pitching occurs,
As a result, the settling of positioning was significantly hindered. In the worst case, a contact accident with the surface plate 7 may occur. On the other hand, when the hydrostatic bearing is arranged so as to support the moving body 1 in the horizontal direction in a non-contact manner, when the moving body 1 is positioned at a high speed, a change in posture called yawing occurs.

However, in the static pressure air bearing having the magnetic field modulation coil according to the embodiment of the present invention shown in FIG. 1, the permanent magnets 12a and 12b as well as the magnetic field modulation coil 13a,
13b is prepared, and it is possible to adjust the attraction force by the electric current supplied to this. Therefore, the gaps 6a and 6b of the moving body 1 with respect to the surface plate 7 can be adjusted to the respective target values. That is, when a current is applied in the direction of strengthening the magnetic field, the attraction force is increased, so that the gaps 6a and 6b are narrowed. On the contrary, when current is applied in the direction of weakening the magnetic field, the attraction force is also weakened and the gaps 6a and 6b are expanded. The adjustment of the gaps 6a and 6b is equivalent to the adjustment of the rigidity, and the horizontal positioning of the moving body 1 having the bearings having the uniform characteristics can cause the pitching motion if the surface plate 7 has good flatness. Since it does not exist, the positioning characteristics are stable regardless of the moving location. Of course, since the rigidity value can be set to a target value, the resonance frequency itself can be increased within a feasible range, and thus the positioning performance can be maximized.

In the embodiment of FIG. 1, static pressure pads 5 are provided at two places.
a and 5b are arranged, and the magnetic field modulation coil 1 is placed at two locations at the same time.
It was equipped with 3a and 13b. Instead of such a configuration,
As shown in FIG. 2, a static pressure air bearing including a static pressure pad 5a and a permanent magnet 11a, and a static pressure air bearing including a static pressure pad 5b and a bias permanent magnet 12b provided with a magnetic field modulation coil 13b are arranged. You may. In this case, at the portion of the static pressure air bearing composed of the static pressure pad 5a and the permanent magnet 11a, the gap 6a is passively determined by the balance between the supply amount of compressed air and the attraction force of the permanent magnet. The adjustable part is the gap 6 of the part of the static pressure pad 5b provided with the magnetic field modulation coil 13b.
b.

In both the embodiment shown in FIG. 1 and the embodiment shown in FIG. 2, the flatness of the surface plate 7 is good, and the gap 6
The values a and 6b are adjusted by the current supplied to the magnetic field modulation coil. However, according to the present invention, high-speed and high-accuracy positioning operation can be realized even when the flatness of the surface plate 7 is not good. The configuration of the positioning control device when the flatness of the surface plate 7 is not shown will be described below.

Generally, a high flatness is required for a surface plate which serves as a guide surface, but surface undulation exists on this surface.
Due to the averaging effect of the static pressure air bearing, the short pitch surface waviness reduces the influence on the posture change of the moving body. However, when there is a long pitch swell, it has a great influence on the posture change of the moving body.

FIG. 3 shows the configuration of a positioning control device for suppressing the pitching motion when the movable body 1 is horizontally positioned along the guide surface in which the central portion of the surface plate 7 is raised. In order to position the moving body 1 along the surface plate 7 having such a shape at high speed and with high accuracy, it is not enough to adjust the gap 6a6b only at a specific place. That is, the gaps 6a and 6b need to be adjusted for each moving place in order to suppress the pitching movement of the moving body 1.

In the figure, 15 is a mirror, 16 is a laser beam, 17 is an interferometer head, and 18 is a position detector, which serve as position detecting means. Further, 19 is a distributor, 20a and 20b are power amplifiers, and 21 is a compensator. In this device configuration, the horizontal position of the moving body 1 is detected by the position detector 18 by irradiating the mirror 15 mounted on the moving body 1 with the laser beam 16 and receiving the reflected light by the interferometer head 17. Now, consider the case where no current is supplied to the magnetic field modulation coils 13a and 13b. In this case, the gaps 6a and 6b are determined by the balance between the attraction force generated by the permanent magnets 12a and 12b and the levitation force of the static pressure pads 5a and 5b. However, in this state, when the moving body 1 is positioned along the guide surface having a convex central portion, since the flatness of the surface plate 7 of the guide surface is insufficient, a pitching motion is generated to improve the positioning performance. It significantly inhibits.
However, the pitching amount of the moving body 1 can be known in advance for each moving place. For example, the pitching amount is known by measurement with an autocollimator. Alternatively, the state of the pitching motion of the moving body 1 can be indirectly grasped by measuring the frequency characteristic for each moving place and observing the change in the frequency response of the pitching motion. Therefore, the correction amount of the gap 6 for suppressing the pitching is known for each position of the moving body 1. In the configuration of FIG. 3, the absolute position of the moving body 1 is measured by the position detector 18, and this signal is sent to the distributor 1
It is led to 9. The distributor 19 has a table in which the distribution ratios of the currents to be supplied to the magnetic field modulation coils 13a and 13b are stored, and the power amplifiers 20a and 20b are excited in accordance with the absolute position of the moving body 1 to generate magnetic fields. A current is passed through the modulation coil 13 to adjust the gaps 6a and 6b. By doing so, the movable body 1 can be stably positioned and driven without causing a pitching motion. However, in the figure, reference numeral 21 is a compensator for the positioning control system of the moving body 1, which operates with a deviation signal between the target signal applied from the terminal R and the output of the position detector 18. Although not shown, this output is led to an actuator for positioning and driving the moving body 1. Although FIG. 3 shows the configuration of the positioning control device for suppressing the pitching motion of the moving body 1, when the moving body 1 moves in the direction perpendicular to the drawing, the position detection output in that direction is used. It goes without saying that it becomes a positioning control device for suppressing rolling motion.

Further, FIG. 4 is a top view of the moving body 1 of the positioning device in which static pressure air bearings are arranged on both side surfaces, and shows a positioning device structure for suppressing the yawing motion. As shown in the figure, the movable body 1 that moves in the Y direction includes the movable body 22 of the positioning device that is movable in the horizontal X direction.
Is also installed. In such a positioning device, the center of gravity of the moving body 1 changes as the moving body 22 moves. Therefore, the yawing motion is generated due to the difference between the driving point of the moving body 1 and its center of gravity.
Of course, the yawing motion is caused even when there is surface waviness on the yaw guides 23a and 23b or the parallelism between the two yaw guides is poor. However, the yawing motion can be controlled by configuring the positioning control device as shown. That is, in the figure, of the absolute positions of the moving body 1 in the horizontal two-axis directions, the interferometer head 17 is used in the X direction.
x, laser beam 16x, mirror 15x, position detector 18
The Y-direction is detected by the position detecting means including x, and the position detecting means including the interferometer head 17y, the laser beam 16y, the mirror 15y, and the position detector 18y. The outputs of the position detectors 18x and 18y are guided to the distributor 24.

In the distributor 24, the moving body 1 and the moving body 22 are
Magnetic field modulation coils 13a, 13b, 13 depending on the position of
It has a table in which the distribution ratios of the currents to be supplied to c and 13d are stored. Therefore, the moving body 1 and the moving body 2
Power amplifiers 20a, 20b, 20 according to the absolute position of 2
c and 20d are excited to generate magnetic field modulation coils 13a and 13d.
As a result of the current flowing to b, 13c, and 13d, the clearances of the static pressure air bearing portions at the four places of each portion are adjusted. Therefore,
The yawing motion of the moving body 1 can be suppressed, and high-speed and high-precision positioning can be realized. Of course, the outputs of the position detectors 18x and 18y are input to the distributor 24, and the moving body 2 is also provided in the same manner as the configuration of FIG.
2 and a compensator for driving the moving body 1 (not shown).

[0028]

As described above, according to the present invention,
Since the attractive force of the permanent magnet can be varied by the current flowing through the magnetic field modulation coil, the gap of the static pressure air bearing can be adjusted. Therefore, the rigidity can be adjusted. The rigidity value is a parameter that defines the positioning performance of the positioning device, but since the rigidity value can always be set as the target value, the reliability of positioning is improved and it is possible to always maintain the desired optimum position.

Further, according to the present invention, it is possible to reduce or eliminate the posture change at the time of positioning the moving body. Conventionally, in a moving mechanism using a static pressure air bearing for each part of a positioning device, the air bearing gap is slightly different depending on the moving place, which causes the resonance characteristics to fluctuate and the posture to change. Further, this makes the control system parameter adjustment troublesome, and, for example, performs gain scheduling by changing the gain of the control system for each moving location.
However, according to the present invention, since the gap that changes depending on the moving position of the moving body can be adjusted by the value of the electric current supplied to the magnetic field modulation coil, the resonance characteristic is kept constant over the entire moving range of the moving body, and the posture change is achieved. Can be eliminated. Therefore, the control system parameters can be easily adjusted. Further, there is an effect that the positioning time and the positioning accuracy are constant regardless of the moving place.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of a static pressure air bearing mounting portion including a magnetic field modulation coil according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a static pressure bearing mounting portion including a magnetic field modulation coil according to another embodiment of the present invention.

FIG. 3 is a structural explanatory view of a positioning control device for suppressing pitching movement.

FIG. 4 is a configuration explanatory view of a positioning control device for suppressing yawing motion.

FIG. 5 is a perspective view of a uniaxial positioning device using a hydrostatic air bearing.

FIG. 6 is an enlarged sectional view of a conventional static pressure air bearing mounting portion.

[Explanation of symbols]

1; moving body, 2; static pressure air bearing, 3; drive ball screw, 4; coupling, 5a, 5b; static pressure pad, 6
a, 6b; gap, 7; surface plate, 8a, 8b; supply tube, 9a, 9b; static pressure pad holder, 10a, 10b;
Magnet holder, 11a, 11b; Permanent magnet, 12a, 12
b; permanent magnets, 13a, 13b, 13c, 13d; magnetic field modulation coils, 14a, 14b; yokes, 15, 15
x, 15y; mirror, 16, 16x, 16y; laser beam, 17, 17x, 17y; interferometer head, 18, 18
x, 18y; position detector, 19; distributor, 20a, 20
b, 20c, 20d; power amplifier, 21; compensator, 2
2; moving body, 23a, 23b; yaw guide, 24; distributor.

Claims (4)

[Claims] 1. A static pressure pad for ejecting a fluid to an opposing surface to maintain a gap between the fluid and the opposing surface by the static pressure, a bias magnet acting to reduce the gap, and a biasing member. A hydrostatic bearing comprising a magnetic field modulation coil of a magnet. 2. The static pressure pad and the bias magnet are provided on the moving body side, and the moving body is movably supported in a non-contact state on a stationary guide surface facing the moving body.
Hydrostatic bearing. 3. A position measuring means of the moving body, a distributor having a table storing the amount of the gap to be corrected according to the output of the position measuring means, and the distributor according to the output of the distributor. The positioning control device using the hydrostatic bearing according to claim 2, further comprising a power amplifier that generates a current that flows through the magnetic field modulation coil. 4. The positioning control device according to claim 3, wherein bearing units each including the static pressure pad and the bias magnet are provided at a plurality of positions of the moving body.