JP2006132642A - Static pressure gas bearing pad - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bearing pad structure capable of achieving both of high rigidity and high vibration damping characteristics in an orifice restriction type static pressure gas bearing. <P>SOLUTION: In the bearing pad 20 having a jetting outlet arranged in the physically non-equivalent position, a first jetting outlet 1 is arranged in a center of the bearing pad 20, and a first ventilation groove 3 communicating with it is linearly formed. A second jetting outlet 2A and a third jetting outlet 2B are arranged in two portions of both peripheral ends, and second and third ventilation grooves 4A and 4B communicating with them are formed in a shape of U. The second jetting outlet 2A and the third jetting outlet 2B are in the physically equivalent position, and the second jetting outlet 2A and the third jetting outlet 2B are in the physically non-equivalent position with respect to the first jetting outlet 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a static pressure gas bearing pad used in a precision positioning device of a moving stage for positioning a workpiece or a master at high speed and high accuracy in a static pressure gas bearing, particularly a precision processing machine and an inspection / measurement device. In the present specification, for the sake of convenience, the “static pressure gas bearing pad” may be simply referred to as “bearing pad” or “pad”.

  Static pressure gas bearings are widely used for linear guide bearings or rotary bearings in measuring instruments, precision machine tools, LSI manufacturing apparatuses, etc. because they are low friction, do not vibrate, and are clean.

  The static pressure gas bearing is basically composed of a bearing pad for ejecting gas and a member arranged to face the bearing pad, and the bearing pad is gas from the gas ejection port or the vent groove connected thereto. A rigid static pressure gas film is formed between the bearing pad and the facing member, and the jet gas is discharged from the outer periphery of the bearing pad to the atmosphere (generally the atmosphere). Yes.

  FIG. 6 shows an example in which this static pressure gas bearing is applied to high-accuracy linear guide (moving stage). As shown in the figure, the bearing A is composed of a guide a and a slider b, and a plurality of bearing pads are usually provided on the surface of the slider b opposite to the guide a, and gas flows from the bearing pad toward the guide a. It is configured to eject and form a static pressure gas film that supports the guide a between the guide a and the slider b.

  This static pressure gas bearing is classified into orifice supply, thin supply, porous restriction, slot restriction, and surface restriction according to the form of supply, that is, gas injection, and further, for the restriction of the supply type using the orifice, A self-contained throttle that produces a throttling effect formed by the hole circumference and the bearing gap by making a hole in the bearing pad surface, and a pocket that provides a recess (pocket) on the bearing pad surface and supplies air through a small throttle hole in the bottom There are orifice restriction, and capillary restriction that produces a restriction effect due to the viscous resistance of the capillary due to a smaller diameter hole.

  Among them, as a method for obtaining a stable characteristic with uniform pressure distribution of static pressure gas as a bearing, a gas outlet or a gas outlet using an orifice restrictor and a self-contained restrictor in combination is used. There is an orifice throttling system having a connected ventilation groove.

  FIG. 7 and FIG. 8 show an outline of the bearing pad c to which the orifice throttle system having the ventilation groove is applied as seen from the bearing pad surface.

  As shown in the figure, the bearing pad c is usually provided with a plurality of gas outlets d and ventilation grooves e connected to the gas outlets d, and each of the gas outlets d and the ventilation grooves e is provided on the bearing pad surface. In FIG. In the example shown in FIG. 7 and FIG. 8, the gas outlet d is arranged at a physically equivalent position as a rectangular bearing pad.

  The diameters of the respective gas outlets d are usually the same, and are arranged at “physically equivalent positions” at which the gas ejection flow rates from the respective gas outlets d are substantially the same. The “physically equivalent position” of the arrangement of the gas outlets d or the gas outlets d provided with the ventilation grooves e is a gas in which the gas pressures ejected from any of the gas outlets d are substantially the same. In other words, it can be referred to as the position of the jet outlet.

  And the performance of such a static pressure gas bearing is represented by various characteristics, such as the rigidity of the jet gas by a bearing pad, a load capacity, and a gas flow rate. Non-Patent Document 1 discloses a method for calculating the bearing performance based on the pressure distribution in the bearing gap based on these characteristics using the continuous conditions of the gas flow in the bearing gap. .

  In this case, the gas ejection ports are substantially physically equivalent positions, and the gas ejection pressures from the respective gas ejection ports are calculated and evaluated as the same. However, a bearing in which a plurality of gas jets arranged on the assumption that the gas pressures from the individual gas jets are made uniform is arranged in a physically equivalent position is well balanced, but has a damping property, rigidity, etc. There is a problem in terms of characteristics.

  In Non-Patent Document 2, in a static pressure gas bearing pad having a gas jet port with a two-row circumferential groove developed for improving rigidity, a small number of gas jet ports are connected to both ends near the pad. Although a static pressure gas bearing aiming at low flow rate with high efficiency, high rigidity by reducing the number of gas jets by providing a circumferential groove has been disclosed, Various problems due to the arrangement of the gas outlet cannot be solved.

  On the other hand, when this static pressure gas bearing is used for high-accuracy linear guide, vibration damping performance by the static pressure gas is an important factor in order to obtain a high-accuracy stop position together with the rigidity of the static pressure gas. However, in the case of a gas bearing, the compressibility and viscosity coefficient of the gas are small, so the damping performance is poor compared to a bearing using incompressible oil, etc., and it is difficult to stop in high accuracy and in a short time. It is. In addition, there is a trade-off relationship between the rigidity and the damping property due to the static pressure gas, and it is difficult to make a bearing that achieves both a high level of rigidity and damping property.

  In particular, when the gas flow rate and load capacity are limited by design, the rigidity is generally inevitably low. In such a case, it is desirable to increase the damping ratio as much as possible. As means for solving this problem, Patent Document 2 discloses that helium gas is injected from pores having a diameter of 0.04 to 0.4 mm. This means that the pressure on the bearing surface is greater than that of air, so that the vibration damping characteristics are improved in a specific pressure range, but there is a problem that the bearing becomes expensive.

  Further, Patent Document 3 discloses that the vibration damping capability due to static gas pressure is improved by adjusting the space between the bearings and the groove depth. However, in order to effectively improve the vibration damping capability with this method, the bearing clearance needs to be 5 μm or less, and in order to realize this, a considerably high machining accuracy is required and machining technology is required. In addition, there is a problem that the processing cost becomes high.

Furthermore, in Patent Document 4, in the static pressure air bearing spindle, by arranging a plurality of gas jets in a circumferential direction at one or more rows in the middle position of the gas jets arranged at physically equivalent positions, It is disclosed to improve the vibration damping characteristics of static pressure. However, there is a problem that it cannot be applied to a hydrostatic gas bearing other than the spindle, particularly a flat bearing, due to its structure, together with a restriction that the pressure in the intermediate portion must be higher than that at both ends.
JP 58-134226 A JP 2002-54634 A JP 2004-144188 A JP-A-10-96423 "Gas Bearing Handbook" (Juri: 2002) Chapter 5 “Two-row circumferential grooved air supply type static pressure gas thrust bearing (1st report, characteristics in low supply air pressure region)” (Ono et al .: Transactions of the Japan Society of Mechanical Engineers (C) 51: 468: 1985)

  An object of the present invention is to provide a bearing pad structure that can have both high rigidity and high damping performance in an orifice throttle type static pressure gas bearing.

  The required characteristics required for a high-accuracy linear guide mechanism are improvement of motion accuracy (vertical and horizontal straightness, rolling, etc.) and shortening of the settling time for positioning. It is necessary to increase rigidity and damping.

  The present invention requires effective use of gas viscosity in order to increase the damping by the gas thin film in the static pressure gas bearing. For this purpose, the gas pressure in the bearing surface is increased. It was completed based on the idea that the structure should be such that the change in the gas flow in the bearing surface due to gap fluctuation (vibration) increases.

  However, when the gas outlet is arranged at an equivalent position, the pressure in the bearing surface is increased by increasing the diameter of the gas outlet or simply increasing the pressure in order to increase the attenuation of the gas thin film. Ascending uniformly, the change in the gas flow due to the gap fluctuation is small, the effect of increasing the change in the gas flow in the bearing surface is small, and the rigidity that is the basic required characteristic of the hydrostatic gas bearing There is a problem that it is easy to cause a decrease and oscillation.

  The present invention achieves the above object by arranging at least one gas jet port at a physically non-equivalent position with respect to other gas jet ports among the plurality of gas jet ports arranged on the bearing pad surface. Settled.

  The term “physical non-equivalent position” as used herein refers to the term “physically equivalent position” described in the background art, and “physically equivalent position”. Means the arrangement position of the gas ejection port where the gas ejection flow rate from each gas ejection port is substantially the same, whereas the "physically non-equivalent position" is formed on the bearing pad surface The gas jet flow rate from a specific gas jet port is substantially different among the gas jet ports that are made, and the gas pressure at the same diameter gas jet port is different from the gas pressure from other gas jet ports. This means that even when the gas pressure is the same, the gas ejection flow rate is different even when the arrangement is not substantially the same, or when the jet nozzle diameter is different.

  As one of the specific modes of disposing a plurality of gas jets at the physically non-equivalent positions, the gas jets of the same diameter arranged on the bearing pad surface are geometrically non-equivalent. It is possible to adopt a means of changing the gas flow rate from each gas jet port by arranging the gas jet port at a position or changing the diameter of the gas jet port at a geometrically equivalent position.

  As a result, the degree of change in pressure of the gas from the gas outlet at each position of the bearing surface, i.e., the bearing pad surface, is different, i.e., the change in the flow rate of the ejected gas is different. The change in the gas flow in the bearing surface is increased due to the fluctuation of the gap, and it is possible to increase the damping effect due to the viscosity.

  The gas jet port applied to the present invention basically means an orifice throttle type, and includes a gas jet port itself and a structure provided with a ventilation groove connected to this jet port, The plurality of gas orifices of the orifice orifice type on the bearing pad surface can at least partially form a ventilation groove connected to the gas orifice.

  The ventilation groove connected to the gas outlet is intended to increase the rigidity of the gas thin film formed by the gas originally ejected from the gas outlet. Further, there is a problem that the damping effect due to the gas viscosity is reduced, and in some cases, oscillation due to compressibility is induced.

  For this reason, in the present invention, in order to improve the damping property, instead of extending, deepening, and further widening the ventilation groove, a gas outlet is arranged at a non-equivalent position, and the bearing surface The damping effect of the gas thin film is increased by increasing the pressure and controlling the gas flow.

  Furthermore, the gas outlet and the ventilation groove provided on the bearing pad surface of the bearing pad of the present invention can be provided at an arbitrary place, but as a premise, the symmetry that the gap between the bearing pad and the member facing it is uniform. Is to hold.

  Specifically, when a plurality of bearing pads are incorporated in a linear guide slider, it is also possible to design asymmetrical combination of asymmetric bearing pads so that the floating of the slider with the guide is uniform. .

  Further, the gas flow rate from at least one gas jet port arranged at the non-equivalent position is different from the flow rate of the gas jet port arranged at the physically equivalent position by 10% or more. As a result, the rigidity and damping of the bearing can be aligned at a high level. If it is less than 10%, the change in the gas flow due to the gap fluctuation is insufficient, and it is difficult to obtain a sufficient damping effect.

  And to make the gas flow rate different in this way can be obtained by making the position of the gas ejection port or the ventilation groove, the shape of the ventilation groove, etc. different between the equivalent position and the non-equivalent position, More preferably, the diameters of the gas outlets arranged at physically equivalent positions and the gas outlets arranged at physically non-equivalent positions are different. In other words, it is difficult to cause a decrease in rigidity, and the change in pressure of the gas outlet due to gap fluctuation, that is, generation of vibration, is further different from that in the case where the diameter of the outlet is the same. Become bigger.

  In addition, a preferable form in the case where the uniform clearance is maintained by one bearing pad is a square or circular shape in which the outer shape of the bearing pad surface has a two-fold rotational symmetry, and a two-fold rotational symmetry is provided at the center of the bearing pad surface. The first ventilation groove having the two and the third and the third of the patterns having line symmetry are arranged by aligning two orthogonal line symmetry axes thereof with the two orthogonal line symmetry axes of the outer shape of the bearing pad surface. The ventilation groove is arranged independently on both sides of the first ventilation groove, with its line symmetry axis coinciding with one of the two orthogonal axis of symmetry of the first ventilation groove and all independent ventilation It is the form which provided the gas jet nozzle for every groove | channel. Here, having two-fold rotational symmetry is equivalent to having two orthogonal axes of line symmetry.

  As a specific arrangement form of the first to third ventilation grooves, a first ventilation groove having a two-fold rotational symmetry such as a straight line and an H-shape is arranged at the center portion of the bearing pad surface, and further, a straight line, The second and third ventilation grooves made of a set of axisymmetrical patterns such as arcs, squares, U-shapes, etc., or a combination of arbitrary patterns, are symmetrically arranged on both sides of the first ventilation groove. It can arrange | position and can be set as the form which provided one or more gas jet nozzles for every independent ventilation groove | channel.

  Thereby, in the gas ejected from the gas ejection port, the change in the gas flow accompanying the fluctuation in the gap is increased, so that the gas viscosity effect can be effectively enhanced and higher attenuation can be derived.

  Ventilation groove pattern or combination, depth and width of each ventilation groove, and diameter of gas outlet are required characteristics related to outer shape and size of bearing pad, gas flow rate, load capacity, rigidity, damping ratio, slider, etc. An appropriate form can be selected in consideration of restrictions on the position of the gas ejection port depending on the shape and the like. Assuming that the sliders and the like are evenly levitated, if the total number of gas outlets is two, they must be arranged at equivalent positions, so at least one gas outlet at an unequal position The total number of gas jets is 3 or more.

  The bearing pad of the present invention can achieve both a rigidity and a damping ratio at a much higher level as compared with the conventional bearing pad in which the gas ejection ports are disposed at physically equivalent positions.

  Further, by using the bearing pad of the present invention having high rigidity and good damping property, the moving stage for positioning the workpiece or the master at high speed with high accuracy in the precision processing machine and the inspection / measurement apparatus has higher accuracy and settling time. It can be a short stage.

  The embodiment will be described below with reference to an example in which the present invention is applied to the hydrostatic gas bearing support high-precision linear guide shown in FIG.

Example 1
FIG. 1 is a view of a first example of a bearing pad 10 according to the present invention as viewed from the gas ejection surface side.

  In the bearing pad 10, the first jet port 1 is arranged at the center of the bearing pad surface 5, and the first ventilation groove 3 that communicates with the first jet port 1 is formed in an “H” shape. The first ventilation groove 3 has two-fold rotational symmetry. Furthermore, two orthogonal line symmetry axes of the first ventilation groove 3 coincide with two orthogonal line symmetry axes of the outer shape of the bearing pad surface.

  Moreover, the 2nd jet nozzle 2A and the 3rd jet nozzle 2B are arrange | positioned in two places, and the 2nd vent groove 4A and 3rd ventilation | gas_flowing which lead to this in each of the 2nd jet nozzle 2A and the 3rd jet nozzle 2B The groove 4B is formed linearly. The second ventilation groove 4A and the third ventilation groove 4B have line symmetry, and each line symmetry axis coincides with one of two orthogonal line symmetry axes of the first ventilation groove 3, and It is independently arranged on both sides of the first ventilation groove 3.

  Each of the second jet outlet 2A and the third jet outlet 2B has the same shape (width, length, and depth) of the second vent groove 4A and the third vent groove 4B, and the same jet nozzle diameter. Time is in a physically equivalent position, and the first ejection port 1 is in a physically non-equivalent position because the shape of the ventilation groove is different.

  The depth of the first ventilation groove 3 is 100 μm, and the groove width is a horizontal line portion of “H” of 0.6 mm and a vertical line portion of “H” of 0.3 mm. On the other hand, the depth of the second and third ventilation grooves 4A and 4B is 100 μm, and the groove width is 0.3 mm. Moreover, the distance to the bearing pad outer periphery of 2nd, 3rd jet nozzle 2A, 2B is 4 mm.

  In the bearing pad 10 shown in FIG. 1, the rigidity and damping ratio (at a frequency of 1150 Hz) were measured for the examples and comparative examples shown in Table 1 in which the sizes of the respective jet outlets 1, 2A, and 2B were changed. .

First, the non-equivalence referred to in the present invention is measured by measuring the jet flow rate ratio of the jet flow rate of the second jet port 2A or the third jet port 2B shown in FIG. Difference in flow rate (1-jet flow rate ratio) x 100%
Sought by.
For example, in the case of Example No. 1 in the table, the jet flow rate ratio is 0.24, so the difference in jet flow rate is 76%.

The rigidity was measured by the following method.
A bearing pad that was allowed to be vacuum-pressed was placed on a surface plate having a flatness of a submicron level so that the surface plate surface would be the opposite surface.
Various weights were placed on the vacuum pressure and the bearing pad, and air with a predetermined pressure was jetted and supplied to the surface of the platen. At this time, the height fluctuation of the upper part of the bearing pad was measured using a displacement sensor of an electric micrometer.
Rigidity was calculated from the relationship between the height of the upper portion of the bearing pad with respect to the vacuum pressurization and the load of the total weight of the weight and the bearing pad, that is, the relationship of the floating gap based on the following formula.
Rigidity at (levation gap 1 + levitation gap 2) / 2 =
− (Load 1−Load 2) / (Floating gap 1−Floating gap 2)

The unit rigidity was calculated by dividing the rigidity by the area of the bearing surface.
Unit rigidity = Rigidity / Bearing area The attenuation ratio was measured based on the following method.

  As in the case of the measurement of rigidity, a bearing pad having a predetermined structure was manufactured, and this was placed on a surface plate having a flatness of submicron so that the surface plate surface would be the opposing surface.

  After installing a displacement sensor to measure the height fluctuation on the top of the bearing pad, place a weight with a weight corresponding to a specific resonance frequency on the bearing pad, supply air of a predetermined pressure to the surface plate surface, The vacuum pressure was adjusted so that there was a gap.

  The upper part of the weight was vibrated by an impact hammer having a load cell for exciting force measurement at the tip, and the vibration waveform output from the displacement sensor was analyzed by an FFT device to obtain a resonance frequency and a damping ratio.

  The jet flow rate ratio was measured by separately supplying the supply pipe side to the gas jet outlet and providing a flow meter in the middle of the pipe.

Table 1 shows the rigidity and damping ratio obtained.

In the case of the examples of the present invention indicated by numbers 1, 3 to 6, 8, and 9 shown in the same table, it was possible to obtain the rigidity and damping ratio per unit area that were difficult to achieve in the past. For example, the embodiment shown in number 1 of Table 1 has a rigidity exceeding ^2.5 N / μm / cm ² and an attenuation ratio of about 0.05.

  On the other hand, in the comparative example of No. 2, the second gas outlet 2A and the third gas outlet 2B in FIG. 1 are basically omitted, and the gas nozzle is basically disposed at the “physically equivalent position”. Is the case. The rigidity per unit area in the simulation performed using the difference method approximation based on the fluid dynamics described in the well-known Non-Patent Document 1 is a high numerical value, but self-excited and cannot be used as a bearing. .

  In Table 1, as shown in Examples 3 to 6, the gas jets provided on the bearing pad surface are arranged at “physically non-equivalent positions” based on the present invention, and The characteristic that each jet port diameter is two or more types is rigid and damped as compared with the gas thin film formed by the gas jet port arranged in a substantially “physically equivalent position” in the case of the comparative example. It can be seen that the ratios are effectively balanced.

  Similarly, in Table 1, the comparative example indicated by reference numeral 7 shows an example of being arranged at the “physically equivalent position” shown in the conventional example of FIG. 7, and is inferior in rigidity and damping ratio.

Examples of Nos. 8 and 9 are examples in which the distance from the center of the second and third jet nozzles 2A and 2B to the outer periphery of the bearing pad in FIG. 1 is changed to 2 mm and 3 mm, respectively. It has been shown that rigidity exceeding 3 N / μm / cm ² can be obtained.

Example 2
In the examples of Nos. 10, 11 and 14 shown in Table 2, the groove depths of the first, second and third ventilation grooves 3, 4A and 4B in FIG. In the example shown in Table 1, the flow rate (consumption amount) is 2.2 to 5.0 Nl / min, whereas it is decreased to 1.4 to 1.7 Nl / min.

  The comparative example of Nos. 12 and 13 shows an example in which the second and third jet nozzles 2A and 2B are not provided in FIG.

As shown in the table, even when the gas flow rate (consumption) is decreased, 10, 11 and 14 according to the example of the present invention have a higher attenuation ratio than the comparative examples of 12 and 13. It shows that a high bearing can be obtained.

  FIG. 2 is a diagram showing a damping effect by gas by a simulation performed using a difference method approximation based on fluid dynamics.

  FIG. 2 shows the damping pressure at each position as a relative value with respect to the average value of the damping pressure on the line crossing the first ejection port 1 and the second and third ejection ports 2A, 2B in FIG. It can be said that the greater the damping pressure, the better the damping.

  In the figure, the solid line indicates the case of the embodiment indicated by reference numeral 11, and the dotted line indicates the case of the comparative example indicated by reference numeral 13.

  In the graph of the comparative example, it can be seen that the damping pressure is low in the ventilation groove portion and the outer edge portion, and once it increases in the vicinity of the ventilation groove portion and in the vicinity of the outer edge portion, then gradually decreases as it is further away from the ventilation groove and the outer edge portion.

  In the example graph, the second and third vents 2A and 2B shown in FIG. 1 are additionally provided with the second and third ventilation grooves 4A and 4B that adversely affect the attenuation of the gas thin film. It can be seen that the damping pressure is increased.

  From this result, in the structure shown in FIG. 1, the requirement of the present invention is that “at least one or more of the gas outlets are disposed at non-equivalent positions and that the diameters of the outlets are two or more”. In the embodiment shown by No. 11, the second and third jet outlets 2A and 2B are made smaller in diameter than the first jet outlet 1, so that the rigidity of the gas thin film is not lowered and the damping property is improved. It can be seen that is effectively achieved. Moreover, in the Example of No. 14, although rigidity is low, it turns out that damping property is improved 3 to 4 times compared with the comparative example of No. 12 and 13.

  This is because the structure of the bearing pad 10 shown in FIG. 1 is such that the first ventilation groove 3 with the letter “H” at the center bears the development of bearing rigidity, and the linear second and third ventilation on both sides. It can be said that the grooves 4A and 4B have the effect of increasing the attenuation.

  Specifically, in the embodiment of No. 9, the pressure (0.37 MPa when the gap is 5 μm) of the second jet outlet 2A or 2B in the center of the linear second and third ventilation grooves 4A and 4B is “H "" Is higher than the pressure of the first jet port 1 in the center of the first ventilation groove 3 (gap 5 μm, 0.26 MPa), and the pressure difference when the gap is 5 μm and 6 μm is linear The center of the first vent groove 3 having the letter “H” is about 0.03 MPa at the second outlet 2A or 2B in the middle of the linear second and third vent grooves 4A and 4B. 1 is about 0.04 MPa, and it is considered that a change in the gas flow in the bearing surface occurs due to the gap variation, and draws out the attenuation due to the gas viscosity effect.

Example 3
FIG. 3 shows another example of the bearing pad in which the gas ejection ports are disposed at physically non-equivalent positions. Table 3 shows an example using this bearing pad 20 as No. 15 and a comparative example as No. 16 Shown in

  As shown in the figure, the first jet nozzle 1 is disposed at the center of the bearing pad 20, and the first ventilation groove 3 communicating with the first jet nozzle 1 is formed linearly. The 2nd jet nozzle 2A and the 3rd jet nozzle 2B are arrange | positioned in two places of both peripheral edges, and the 2nd and 3rd ventilation grooves 4A and 4B leading to this are formed in the shape of a "U". The second outlet 2A and the third outlet 2B are in physically equivalent positions, and the second outlet 2A and the third outlet 2B are physically non-equivalent to the first outlet 1. It is in. These ventilation grooves 3, 4A, 4B have a depth of 60 μm and a groove width of 0.3 mm.

Table 3 shows the rigidity, damping ratio, and ejection flow rate ratio when the bearing clearance is 7 μm.

In Table 3, the unit No. 15 has a unit rigidity of ^2.5 N / μm / cm ² and a damping ratio of 0.03.

  On the other hand, the comparative example of number 16 shows the case where there is no 1st jet nozzle 1 in FIG. In this comparative example, the unit rigidity by simulation was the same as that of the example, but the damping ratio was less than 0.01 and the damping property was poor.

Example 4
The bearing pad 30 shown in FIG. 4 shows an example in which at least one of the gas ejection ports is disposed at a non-equivalent position different from other gas ejection ports with an ejection flow rate of 10% or less.

  The bearing pad 30 has a rectangular bearing surface (bearing pad surface 5), the first outlet 10A and the second outlet 10B are on the short side, and the third outlet 20A and the fourth outlet 20B are on the long side. The 1st ventilation groove | channel 3 which is arrange | positioned and connects to each jet nozzle is formed in the shape of a "mouth".

  In the same figure, the first jet port 10A and the second jet port 10B are in a physically equivalent position, and the third jet port 20A and the fourth jet port 20B are also in a physically equivalent position. The third jet outlet 20A and the fourth jet outlet 20B are physically non-equivalent to the outlet 10A and the second jet outlet 10B. The first ventilation groove 3 has a depth of 20 μm and a groove width of 1 mm.

Table 4 shows the rigidity, damping ratio, and jet flow rate ratio when the bearing gap of the jet gas by the bearing pad shown in FIG. 4 is 5 μm.

  In the same table, in the example shown by the number 18, a fifth jet port having a diameter of 60 μm is added to the central portion of FIG. 4 and the diameters of the first to fourth jet ports 10A, 10B, 20A, 20B are made small. Thus, the unit rigidity is substantially matched with the comparative example shown in No. 17, and the damping ratio is easily compared. The ejection flow ratio of the fifth ejection port to the first and second ejection ports 10A, 10B is 0.42. Yes, it can be seen that the damping ratio is significantly improved compared to the comparative example indicated by numeral 17.

On the other hand, in the comparative example shown by No. 17, the ratio of the ejection flow rate of the third and fourth ejection ports 20A and 20B to the first and second ejection ports 10A and 10B is 0.98, and therefore the difference in the ejection flow rate. Is 2%, the unit rigidity is 2.6 N / μm / cm ² , and the damping ratio is only 0.02.

  Even in the case of a jet outlet arranged at a non-equivalent position as in the comparative example, when the difference in jet flow rate is as small as 2%, the effect of improving the damping ratio is relatively small.

  From this example, it can be seen that it is desirable that at least one of the gas outlets is disposed at a “non-equivalent position” where the jet flow rate is 10% or more different from other gas outlets.

Example 5
An embodiment 19 of a bearing pad that does not oscillate even at a supply pressure much higher than the normal supply pressure and can be used as a highly rigid bearing will be described below. FIG. 5 and Table 5 show the structure and characteristics of Example 19.

  In the nineteenth embodiment, as shown in FIG. 5, the H-shaped first ventilation groove 3 and the “D” -shaped second and third ventilation grooves 4 </ b> A and 4 </ b> B are formed at the center of the bearing pad surface 5. Are arranged symmetrically with the central straight portion of the H-shaped first ventilation groove as a symmetric line, and each of these three ventilation grooves is provided with one jet outlet, The diameters of the second and third jet outlets 2A and 2B provided in the ventilation grooves 4A and 4B are smaller than the jet diameter of the first jet outlet 1 provided in the first ventilation groove 3. Each of the ventilation grooves 3, 4A, 4B has a groove depth of 40 μm and a groove width of 0.3 mm.

The characteristics shown in Table 5 are when the bearing clearance is 5 μm. A typical supply pressure of 0.4 MPa shows a very high attenuation ratio of 0.15, and even if the supply pressure is 1.0 MPa, a relatively high attenuation ratio of 0.04 (which naturally does not oscillate) is very high. A high unit rigidity of 6.0 N / μm / cm ² is exhibited.

  When the bearing gap is small, the gas flow from the first outlet 1 provided in the first ventilation groove 3 is the second and third ventilation grooves 4A and 4B and the second and third outlets 2A provided therein. 2B mainly prevents the flow to the region of the second and third ventilation grooves 4A and 4B, and the flow to both sides of the H-shape is dominant. When the bearing gap is wide, the pressure of the gas film formed mainly by the second and third ventilation grooves 4A and 4B and the second and third jet outlets 2A and 2B provided on the second and third ventilation grooves 4A and 4B decreases. Part of the gas from the first jet port 1 provided in the ventilation groove 3 flows to the area of the second and third ventilation grooves 4A and 4B (in the vertical direction of the H shape), and the second and third It flows out to the outer edge part through the ventilation grooves 4A and 4B. That is, it is considered that a large change occurs in the gas flow in the bearing surface due to the gap variation, and the damping due to the gas viscosity is effectively extracted.

  According to the present invention, a remarkably high supply air pressure can be used, and a static pressure gas bearing having a very high rigidity and a good damping property that has not been considered in the past with a gas bearing can be realized.

   It is apparent from the gist of the present invention that the bearing surface (bearing pad surface) of the bearing pad of the present invention may be a spherical or cylindrical curved surface. Further, the bearing pad of the present invention may be formed as a single bearing and used by being assembled to the slider portion of the moving stage, or the bearing pad of the present invention may be directly configured on the slider.

  In the above description of the present invention, the bearing pad according to the present invention has been mainly described based on an example in which the bearing pad according to the present invention is applied to a high precision linear guide supported by a static pressure gas bearing. Utilizing the characteristics, it is also suitable for thrust bearings and radial bearings of rotary spindles.

It is the figure which looked at the 1st example of the bearing pad concerning the present invention from the gas ejection side. The attenuation | damping pressure of the gas thin film formed with the bearing pad which concerns on this invention is shown by contrast with a comparative example. The other example of the bearing pad which concerns on this invention is shown. The further another example of the bearing pad which concerns on this invention is shown. The further another example of the bearing pad which concerns on this invention is shown. A highly accurate linear guide using a static pressure gas bearing is shown. It is the figure which looked at the conventional bearing pad from the plane. The other example of the conventional bearing pad is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10A 1st jet 2A, 10B 2nd jet 2B, 20A 3rd jet 20B 4th jet 3 3 1st ventilation groove 4A 2nd ventilation groove 4B 3rd ventilation groove 5 Bearing pad surface 10, 20, 30, 40 Bearing pad of the present invention

Claims (8)

  A hydrostatic gas bearing pad having a gas jet port disposed at a position physically equivalent to the bearing pad surface and at least one gas jet port disposed at a position not physically equivalent to the gas jet port.   The gas jet flow rate from at least one gas jet port arranged at a physically non-equivalent position is different from the gas jet flow rate from the gas jet port arranged at a physically equivalent position by 10% or more. The hydrostatic gas bearing pad described. The outer shape of the bearing pad surface is a square or circular shape with rotational symmetry twice,
A first ventilation groove having two-fold rotational symmetry at the center of the bearing pad surface, with the two orthogonal axis of symmetry aligned with the two orthogonal axis of symmetry of the outer shape of the bearing pad surface;
The second and third vent grooves of the pattern having line symmetry are aligned with one of two orthogonal axis of axis symmetry of the first vent groove, and the first vent groove Placed independently on both sides,
The hydrostatic gas bearing pad according to claim 1, wherein a gas outlet is provided for every independent ventilation groove.   The hydrostatic gas bearing pad according to any one of claims 1 to 3, wherein a diameter of a gas jet port arranged at a physically equivalent position is different from a diameter of a gas jet port arranged at a physically non-equivalent position. . The first V-shaped first ventilation groove in the center of the bearing pad surface and the linear second and third ventilation grooves are symmetrical with respect to the central straight line portion of the first ventilation groove. Place it in a direction parallel to the straight part of the center of the ventilation groove,
A gas outlet is provided at the center of each of the first to third ventilation grooves,
The hydrostatic gas bearing pad according to claim 3, wherein the diameter of the gas outlet provided in the second and third ventilation grooves is equal to or smaller than the diameter of the gas outlet provided in the first ventilation groove. .   A straight first ventilation groove in the center of the bearing pad surface, and a U-shaped second and third ventilation groove, and a first ventilation groove on both sides of the first ventilation groove. These are arranged symmetrically with respect to the line of symmetry, and each one of these three ventilation grooves is provided with one gas outlet, and the diameters of the gas outlets arranged in the first ventilation groove are second and third. The hydrostatic gas bearing pad according to claim 3, wherein the hydrostatic gas bearing pad is formed to be equal to or smaller than a diameter of a gas jet port provided in the ventilation groove.   The H-shaped first ventilation groove and the D-shaped second and third ventilation grooves are arranged symmetrically with the straight line portion at the center of the first ventilation groove as the symmetry line in the center of the bearing pad surface. And each of these three ventilation grooves is provided with one gas outlet, and the diameter of the gas outlet provided in the second and third ventilation grooves is equal to or less than the diameter of the gas outlet provided in the first ventilation groove. The hydrostatic gas bearing pad according to claim 3, which is formed to be.   The hydrostatic gas bearing pad according to any one of claims 1 to 7, wherein a planar outer shape of the bearing pad surface is a square or a rectangle.

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