Pneumatic static pressure bearing

Abstract

A pneumatic static pressure bearing (1) includes: an air supply device (30) that supplies air (A) to a bearing part (11); and a control device (40) that controls the air supply device (30). The air supply device (30) includes a plurality of air supply systems (31, 32). Each of the air supply systems (31, 32) can be switched to an air supply state or a stop state. The control device (40) reduces the number of air supply systems that are in the air supply state when a bearing gap has decreased.

Description

Air static pressure bearing

[0001] The present invention relates to an air static pressure bearing.

[0002] As a bearing mechanism, an air static pressure bearing is used. The air static pressure bearing is used not only to support the radial load or thrust load of the rotating shaft, but also to support the load of linear moving parts such as linear guides. In an air static pressure bearing, in order to obtain a desired bearing rigidity, it is necessary to appropriately design conditions such as the throttle hole diameter, the number of holes, and the bearing clearance of the air supply. Among these design conditions, the bearing clearance changes due to thermal deformation and centrifugal force during operation, and as a result, the desired rigidity cannot be obtained. For such changes in the bearing clearance due to thermal deformation and centrifugal force, in a hydrodynamic bearing, a variable throttle mechanism is used for countermeasures (Patent Document 1).

[0003] Japanese Patent Laid-Open No. 53-88440

[0004] When the above-described variable throttle mechanism is applied to an air static pressure bearing to cope with changes in the bearing clearance due to thermal deformation and centrifugal force, there are the following problems. In an air static pressure bearing, since compressible air is used, when the bearing clearance is narrowed so as to form a surface throttle, when a large pocket is provided, or when the bearing effective area is increased compared to the flow rate, self-excited vibration (pneumatic hammer phenomenon) may occur, and the bearing accuracy may not be maintained. In order to prevent such a pneumatic hammer phenomenon, it is necessary to suppress the air volume in the middle, and for that purpose, it is necessary to approach the bearing clearance and the variable throttle mechanism. However, the installation space obtained around the bearing is limited, and it has been difficult to install the variable throttle mechanism while preventing the pneumatic hammer phenomenon. Regarding such a variable throttle mechanism, attempts have been made to form a small variable throttle using a piezoelectric element and to use a variable throttle mechanism with a minute structure, but problems such as the complexity of the structure and the manufacturing cost cannot be avoided.

[0005] An object of the present invention is to provide an air static pressure bearing having a simple structure and capable of ensuring a desired bearing rigidity even when the bearing clearance changes.

[0006] The air hydrostatic bearing of the present invention is an air hydrostatic bearing having an air supply device that supplies air to the bearing portion and a control device that controls the air supply device, wherein the air supply device has a plurality of air supply systems, each of the air supply systems can be switched between an air supply state and a stopped state, and the control device reduces the number of air supply systems in the air supply state when the bearing clearance decreases.

[0007] In the present invention, the multiple air supply systems can be piping or conduits that can supply air from an air supply source to the bearing section at a predetermined flow rate and can be switched between an air supply state and a stopped state (closed state) using a solenoid valve or the like. Each of the multiple air supply systems has an air supply port that opens to the bearing surface or a static pressure pocket facing the bearing section, and it is preferable that the air supply ports of each system are evenly distributed on the bearing surface. It is preferable that the groups of air supply ports of the multiple air supply systems are arranged superimposed on the same bearing surface, and that the amount of air supplied to the bearing section increases substantially uniformly across the entire bearing surface by increasing the number of air supply systems that are in an air supply state.

[0008] In this invention, by keeping some of the multiple air supply systems in an air supply state while others are stopped, a predetermined flow rate of air suitable for the bearing gap is supplied to the bearing from the air supply systems in the air supply state, thereby ensuring the desired bearing rigidity. That is, when the bearing gap decreases in the bearing due to thermal deformation or centrifugal force, the control device switches some of the air supply systems in the air supply state to a stopped state, reducing the number of air supply systems in the air supply state. As a result, the flow rate of air supplied to the bearing decreases, and the desired bearing rigidity is maintained in the bearing. On the other hand, when the bearing gap increases in the bearing, the control device switches the air supply systems that were stopped to an air supply state, increasing the amount of air supplied to the bearing and maintaining the desired bearing rigidity in the bearing. In this way, the air hydrostatic bearing of the present invention can ensure the desired bearing rigidity even when the bearing gap changes. In other words, by using multiple air supply systems and intermittently switching some of them, the range of bearing rigidity provided by each system can be connected and expanded. Furthermore, as described above, by ensuring bearing rigidity against changes in bearing clearance, it becomes unnecessary to use a variable throttling mechanism in multiple air supply systems, thereby preventing structural complexity caused by the variable throttling mechanism and preventing the pneumatic hammer phenomenon associated with the complexity or size of the variable throttling mechanism. Thus, the present invention provides an air hydrostatic bearing that has a simple structure and can ensure the desired bearing rigidity even when the bearing clearance changes.

[0009] In the air hydrostatic bearing of the present invention, it is preferable that the control device has a gap sensor for detecting the value of the bearing gap. In this invention, the control device can use the value of the bearing gap obtained by the gap sensor to control the switching of multiple air supply systems. As a result, the control by the control device can be made appropriate according to the actual bearing gap of the bearing.

[0010] In the air hydrostatic bearing of the present invention, it is preferable that the air supply system has a valve device that switches between the air supply state and the stopped state by intermittently interrupting the flow of air under the control of the control device. In this invention, the switching control of the air supply system can be easily performed by the control device using a valve device such as a solenoid valve.

[0011] In the air hydrostatic bearing of the present invention, the control device may reduce the number of air supply systems in the air supply state by switching one of the air supply systems from the air supply state to the stopped state when the value of the bearing clearance falls below a predetermined reference clearance value. In this invention, by using a predetermined reference clearance, the control device can easily and reliably control the switching of multiple air supply systems.

[0012] In the air hydrostatic bearing of the present invention, the control device preferably has a reference gap set for each of the air supply systems, and the value of the reference gap is such that the bearing gap stiffness characteristic when the air supply system is in the stopped state and the bearing gap stiffness characteristic when the air supply system is in the supply state are the same. In this present invention, the control device can easily set a reference gap that serves as the basis for operation in switching control of multiple air supply systems. In particular, the reference gap can be set efficiently by obtaining the bearing gap stiffness characteristics of each of the multiple air supply systems, that is, the relationship between bearing gap and bearing stiffness, by measurement or calculation, and setting a reference gap for switching operations of the air supply systems from the obtained characteristic data.

[0013] In the air hydrostatic bearing of the present invention, it is preferable that the control device performs control to predict the value of the bearing gap from the operating conditions of the bearing. In this invention, the control device can predict the value of the bearing gap based on data indicating the operating conditions of the bearing (the operating state of the machine in which the bearing is installed), and use this value to control the switching of multiple air supply systems. For example, if the air supply pressure and the number of supply systems are constant, the gap will be determined once the air flow rate is determined. Therefore, if the relationship between the flow rate and the gap is measured in advance, the gap can be estimated from the flow rate. Alternatively, the relationship between the rotational speed, the temperature of each part of the main shaft, and the gap may be measured multiple times in advance, and the gap may be calculated from the rotational speed and temperature using an AI (artificial intelligence) system that has been trained on this data. By using the predicted value of the bearing gap when controlling the switching of the air supply system by the control device, gap sensors and other devices required to obtain actual measured values ​​can be omitted, and the switching of multiple air supply systems can be performed prior to actual fluctuations in the bearing gap. As a control method for predicting the value of the bearing gap, a method of obtaining the value of the bearing gap for each operating condition of the air hydrostatic bearing by actual measurement or calculation, and then creating a database or training the database can be used as appropriate.

[0014] According to the present invention, it is possible to provide an air hydrostatic bearing that has a simple structure and can ensure the desired bearing rigidity even when the bearing clearance changes.

[0015] A partially broken perspective view showing a first embodiment of the present invention. A schematic diagram showing the planar arrangement of the bearing portion and the air supply system of the first embodiment. A graph showing the switching control of the air supply system of the first embodiment. A graph showing the switching control of a modified example of the first embodiment. A schematic diagram showing the planar arrangement of the bearing portion and the air supply system of a second embodiment of the present invention. A schematic diagram showing the vertical arrangement of the bearing portion and the air supply system of the second embodiment.

[0016] [First Embodiment] Figures 1 and 2 show an air hydrostatic bearing 1 according to the first embodiment of the present invention. In Figure 1, the air hydrostatic bearing 1 has a shaft member 10 arranged along a rotation axis C and a bearing member 20 that rotatably supports the shaft member 10. An air hydrostatic bearing portion 11 is formed between the inner circumferential surface of the bearing member 20 and the outer circumferential surface of the shaft member 10, having a predetermined bearing clearance. In the bearing portion 11, the inner circumferential surface of the bearing member 20 serves as the bearing surface, and the shaft member 10 is supported non-contact by supplying pressurized air to this bearing surface.

[0017] To supply pressurized air to the bearing section 11, the bearing member 20 has a plurality of ventilation pipes 21 that extend radially with respect to the rotation axis C. The inner ends of the ventilation pipes 21 are air inlets 22 that open to the inner circumferential surface of the bearing member 20. Multiple air inlets 22 are arranged in the circumferential direction around the rotation axis C on the inner circumferential surface of the bearing member 20. In the middle of the ventilation pipes 21, near the air inlets 22, there are fixed throttling sections 23 that are necessary for the bearing to function as an air-static pressure bearing. Providing separate air inlets 22 and throttling sections 23 is done in the case of orifice throttling or capillary throttling, but in the case of self-forming throttling, the function of the throttling section 23 is integrally formed in the air inlet 22. An air supply device 30 is connected to the outside of the ventilation pipes 21 to supply pressurized air A to the bearing section 11.

[0018] In Figure 2, the air supply device 30 has an air supply source 39 that supplies pressurized air A, and a plurality of air supply systems 31 and 32 that supply pressurized air A from the air supply source 39 to the bearing section 11. The first air supply system 31 has a distribution pipe passage 311 on the outside of the bearing member 20. The second air supply system 32 has a distribution pipe passage 321 on the outside of the bearing member 20. The ventilation pipe passages 21 formed in the bearing member 20 are connected to either the distribution pipe passages 311 or 321.

[0019] The air inlet 22 of the ventilation pipe 21 connected to the distribution pipe 311 is designated as the air inlet 221 of the first air supply system 31. The air inlet 22 of the ventilation pipe 21 connected to the distribution pipe 321 is designated as the air inlet 222 of the second air supply system 32. In this embodiment, one-third of the multiple air inlets 22 are designated as the first air supply system 31, and two-thirds are designated as the second air supply system 32. On the inner circumferential surface of the bearing member 20 facing the bearing portion 11, a repeating arrangement of air inlets 221, air inlets 222, air inlets 222 is formed in the circumferential direction.

[0020] In the first air supply system 31, pressurized air A from the air supply source 39 is constantly supplied to the air inlet 221. In the second air supply system 32, an open / close solenoid valve 322 is installed in the middle, allowing the pressurized air A supplied to the air inlet 222 from the air supply source 39 to be intermittently supplied. The air supply device 30 has a control device 40 for controlling the switching of the solenoid valve 322, and a gap sensor 41 for detecting the bearing gap of the bearing section 11.

[0021] The control device 40 is configured using an embedded microcomputer system and switches the solenoid valve 322 on and off according to the comparison result between the bearing gap value detected by the gap sensor 41 and a predetermined reference gap described later. The control device 40 may have other configurations; for example, it may utilize part of the control system of the device in which the air hydrostatic bearing 1 is installed.

[0022] The predetermined reference gap in the control device 40 described above is set by the following procedure. When setting the reference gap, first the air hydrostatic bearing 1 is activated and the correlation between the bearing gap and bearing stiffness between the shaft member 10 and the bearing member 20 is measured. In Figure 3, when the solenoid valve 322 is closed and pressurized air A is supplied to the bearing section 11 only by the first air supply system 31, the bearing gap and bearing stiffness between the shaft member 10 and the bearing member 20 are as shown in data series R2 (◇). When the solenoid valve 322 is open and pressurized air A is supplied to the bearing section 11 by the first air supply system 31 and the second air supply system 32, the bearing gap and bearing stiffness between the shaft member 10 and the bearing member 20 are as shown in data series R1 (□).

[0023] As shown in Figure 3, when pressurized air A is supplied to the bearing section 11 by the first air supply system 31 and the second air supply system 32, a larger amount of pressurized air A is supplied to the bearing section 11 than when supplied by the first air supply system 31 alone, and high bearing rigidity is obtained even in regions where the bearing gap is relatively small. On the other hand, when pressurized air A is supplied to the bearing section 11 by the first air supply system 31 and the second air supply system 32, the bearing rigidity becomes lower in regions where the bearing gap is relatively large than when supplied by the first air supply system 31 alone, and the data series R1 and R2 intersect at the value Cr where the bearing gap is. This value Cr is set as the reference gap in the control device 40. In setting the reference gap as described above, it is ideal to measure the correlation by detecting the change in bearing rigidity when the bearing gap between the shaft member 10 and the bearing member 20 changes. However, in radial bearings, the bearing gap is radial, so it is difficult to change the gap with the same shaft member 10 and bearing member 20. Therefore, by preparing multiple shaft members 10 with different diameters and sequentially measuring the bearing clearance and bearing stiffness of each, the correlation between the bearing clearance and bearing stiffness can be measured.

[0024] When the bearing gap detected by the gap sensor 41 is less than the reference gap Cr, the control device 40 closes the solenoid valve 322 and supplies pressurized air A to the bearing section 11 only through the first air supply system 31. As a result, the bearing section 11 obtains the bearing rigidity shown in data sequence R2 in Figure 3. On the other hand, when the bearing gap detected by the gap sensor 41 is greater than or equal to the reference gap Cr, the solenoid valve 322 opens and supplies pressurized air A to the bearing section 11 through both the first air supply system 31 and the second air supply system 32. As a result, the bearing section 11 obtains the bearing rigidity shown in data sequence R1 in Figure 3. In this way, by switching the air supply state based on the reference gap Cr, the control device 40 obtains the bearing rigidity characteristic Rm (shown as a solid line in Figure 3) which is a combination of data sequences R1 and R2.

[0025] This embodiment provides the following advantages. In this embodiment, by keeping the first air supply system 31 (part of multiple air supply systems) in an air supply state while keeping the second air supply system 32 (another part) in a stopped state, a predetermined flow rate of pressurized air A is supplied to the bearing section 11, and the desired bearing gap is formed in the bearing section 11. When the bearing gap decreases in the bearing section 11 due to thermal deformation or centrifugal force, the control device 40 refers to the detection signal of the gap sensor 41 and switches the air supply system 32 that is in an air supply state to a stopped state, thereby reducing the number of air supply systems. In other words, the state is switched from supplying air through two systems, the first air supply system 31 and the second air supply system 32, to supplying air through only one system, the first air supply system 31. As a result, the flow rate of pressurized air A supplied to the bearing section 11 is reduced, and the desired bearing rigidity can be maintained in the bearing section 11. On the other hand, when the bearing clearance in the bearing section 11 decreases, the control device 40 refers to the detection signal from the clearance sensor 41 and switches the air supply system 32, which was in a stopped state, to an air supply state, thereby increasing the amount of pressurized air A supplied to the bearing section 11 and maintaining the desired bearing rigidity in the bearing section 11.

[0026] Thus, in the air hydrostatic bearing 1 of this embodiment, the desired bearing rigidity can be ensured even if the bearing clearance changes. In other words, by using multiple air supply systems 31 and 32 and intermittently supplying a portion of them, the range of bearing rigidity provided by each air supply system 31 and 32 can be connected and extended. Furthermore, as described above, since bearing rigidity is ensured against changes in the bearing clearance, it becomes unnecessary to use a variable throttling mechanism in the multiple air supply systems 31 and 32, thereby preventing structural complexity caused by the variable throttling mechanism and preventing the pneumatic hammer phenomenon associated with the complexity or size of the variable throttling mechanism. As described above, according to this embodiment, an air hydrostatic bearing 1 can be provided that has a simple structure and can ensure the desired bearing rigidity even if the bearing clearance changes.

[0027] In this embodiment, the control device 40 can use the bearing gap value obtained by the gap sensor 41 to control the switching of multiple air supply systems 31 and 32. As a result, the control by the control device 40 can be made appropriate according to the actual bearing gap of the bearing section.

[0028] In this embodiment, the second air supply system 32 used a solenoid valve 322 that intermittently interrupted the flow of air using an electrical signal to switch between an air supply state and a stopped state by the control device 40. This allowed for a simplified control system configuration and facilitated switching control of the air supply system by the control device 40.

[0029] In this embodiment, the control device 40 reduces the number of air supply systems 31 and 32 in the air supply state by switching the second air supply system 32 (one of the air supply systems) from the air supply state to the stopped state when the bearing clearance value falls below a predetermined reference clearance Cr value. In this way, by using a predetermined reference clearance Cr, the control device 40 can easily and reliably control the switching of multiple air supply systems 31 and 32.

[0030] In this embodiment, the control device 40 has a reference gap Cr set for the second air supply system 32, and the value of the reference gap Cr is set to the gap value at which the bearing gap stiffness characteristics (data series R1) when the second air supply system 32 is in an air supply state and the bearing gap stiffness characteristics (data series R2) when the second air supply system 32 is in a stopped state are the same. By doing this, the reference gap Cr, which serves as the basis for operation when the control device 40 controls the switching of multiple air supply systems, can be easily set. In particular, the reference gap can be set efficiently by obtaining the bearing gap stiffness characteristics of each of the multiple air supply systems, that is, the relationship between bearing gap and bearing stiffness, by measurement or calculation, and setting the reference gap for switching operations of the air supply systems from the obtained characteristic data.

[0031] [Modification of the First Embodiment] In the first embodiment described above, a first air supply system 31 that continuously supplies air and a second air supply system 32 that can be switched between a stopped state and an air supply state by a solenoid valve 322 are provided as multiple air supply systems, and a reference gap Cr is used for switching the second air supply system 32. In contrast to this first embodiment, three or more air supply systems may be used, and the amount of air supplied may be increased by sequentially increasing the number of air supply systems in the air supply state from one.

[0032] In Figure 4, for example, in an air supply device having four air supply systems, the bearing clearance and bearing stiffness when each system is sequentially switched to the air supply state are given by data series R1 to R4. That is, data series R4 is the case when only the first system is in the air supply state and the other systems are stopped. Data series R3 is the case when the first and second systems are in the air supply state and the third and fourth systems are stopped. Data series R4 is the case when the first to third systems are in the air supply state and the fourth system is stopped. Data series R1 is the case when all systems from the first to the fourth are in the air supply state. In such an air supply device, the intersection of each data series can be obtained using the same procedure as in the first embodiment, and the value of the bearing clearance at each point can be used as the reference clearance. That is, the reference clearance Cr4 is calculated from the value of the bearing clearance at the intersection of data series R4 and data series R3, and this reference clearance Cr4 can be used as the switching criterion when switching from the air supply state of only the first system to the air supply state of the first and second systems. Similarly, a reference gap Cr3 can be obtained from the intersection of data sequences R2 and R3, and a reference gap Cr2 can be obtained from the intersection of data sequences R1 and R2, which can be used as references when sequentially switching the third and fourth systems to the supply air state, respectively.

[0033] [Second Embodiment] Figures 5 and 6 show an air hydrostatic bearing 2 according to a second embodiment of the present invention. The air hydrostatic bearing 1 of the first embodiment described above was a radial bearing. That is, a bearing portion 11 was formed between the surface of the shaft member 10 and the inner circumference of the bearing member 20, and air intake ports 22 for supplying air to the bearing portion 11 were arranged circumferentially on the inner surface of the bearing member 20. In contrast, the air hydrostatic bearing 2 of this embodiment is a thrust bearing, and a disc portion 12 is formed on the shaft member 10A, and a bearing portion 13 is formed between the disc portion 12 and the surface of the bearing member 20A facing it. On the surface of the bearing member 20A facing the bearing portion 13, a plurality of air intake ports 22 for supplying air to the bearing portion 13 are arranged in an annular shape around the rotation axis C of the shaft member 10A.

[0034] The bearing member 20A has a ventilation pipe 21 that communicates with a plurality of air intake ports 22. A fixed throttling section 23 is formed in the ventilation pipe 21 near the air intake ports 22. These air intake ports 22, ventilation pipe 21, and throttling section 23 are the same as in the first embodiment described above, although their arrangements differ. An air supply device 30A for supplying pressurized air A to the bearing section 13 is connected to the end of the ventilation pipe 21 opposite to the air intake ports 22.

[0035] The air supply device 30A has an air supply source 39 that supplies pressurized air A, and also has a plurality of air supply systems 31, 32, and 33 that supply pressurized air A from the air supply source 39 to the bearing section 13. That is, in the first embodiment described above, two air supply systems 31 and 32 were used, but in this embodiment, three air supply systems 31 to 33 are used. The first to third air supply systems 31, 32, and 33 each have distribution pipes 311, 321, and 331 near the bearing member 20A. The ventilation pipe 21 formed in the bearing member 20A is connected to one of the distribution pipes 311, 321, or 331.

[0036] The air inlet 22 of the vent pipe 21 connected to the distribution pipe 311 is designated as the air inlet 221 of the first air supply system 31. The air inlet 22 of the vent pipe 21 connected to the distribution pipe 321 is designated as the air inlet 222 of the second air supply system 32. The air inlet 22 of the vent pipe 21 connected to the distribution pipe 331 is designated as the air inlet 223 of the third air supply system 33. In this embodiment, the multiple air inlets 22 are distributed equally among the air supply systems 31 to 33, with each receiving 1 / 3 of the inlets. On the surface of the bearing member 20A facing the bearing portion 13, a repeating arrangement of air inlets 221, 222, and 223 is formed in the circumferential direction.

[0037] The air supply device 30A is equipped with solenoid valves 312, 322, and 332 in each of the first to third air supply systems 31, 32, and 33, respectively, and can intermittently supply pressurized air A from the air supply source 39 to each air supply system 31, 32, and 33. These solenoid valves 312, 322, and 332 are switched and controlled by the control device 40A.

[0038] The control device 40A may determine the measured gap from the gap sensor 41 based on the reference gap Cr as described in the first embodiment above when controlling the switching of the first to third air supply systems 31, 32, and 33. Alternatively, the control device 40A may predict the bearing gap value based on data indicating the operating status of the bearing unit 13 (the operating status of the machine device in which the bearing unit 13 is installed), and use this value to control the switching of the first to third air supply systems 31 to 33. As a control method for predicting the bearing gap value in this way, a method of acquiring the bearing gap value for each operating status of the air hydrostatic bearing by actual measurement or calculation, and storing it in a database or training it can be used as appropriate.

[0039] According to this embodiment, in addition to the same effects as the first embodiment described above, the following effects can be obtained. In this embodiment, the thrust bearing can bear a load in the direction of the rotation axis C. Thus, the air hydrostatic bearing of the present invention can be configured as a radial bearing like the air hydrostatic bearing 1 of the first embodiment, and as a thrust bearing like the air hydrostatic bearing 2 of this embodiment.

[0040] In this embodiment, by using a predicted value of the bearing gap when controlling the switching of the first to third air supply systems 31, 32, and 33 by the control device 40A, a gap sensor 41 and other devices for obtaining measured values ​​can be omitted, and the switching control of the first to third air supply systems 31, 32, and 33 can be performed prior to actual fluctuations in the bearing gap.

[0041] In this embodiment, solenoid valves 312, 322, and 332 are provided in each of the first to third air supply systems 31, 32, and 33, respectively, so that continuous air supply or minimal air supply can be performed by any of the air supply systems 31, 32, and 33. That is, in the first embodiment described above, continuous air supply was fixed to the first air supply system 31, but in this embodiment, continuous air supply may be set to any of the first to third air supply systems 31, 32, and 33.

[0042] [Other Embodiments] The first and second air supply systems 31, 32 in the first embodiment, or the first to third air supply systems 31, 32, 33 in the second embodiment, are not limited to supplying pressurized air A at the same flow rate. For example, the first and second air supply systems 31, 32 may be set to have different flow rates. In the above embodiments, solenoid valves 312, 322, and 332 were used as switching valves for each air supply system, but other types of valve devices may be used as long as switching between each system is possible.

[0043] This invention can be used in air-hydrostatic bearings.

[0044] 1, 2... Air hydrostatic bearing, 10, 10A... Shaft member, 11, 13... Bearing section, 12... Disc section, 20, 20A... Bearing member, 21... Ventilation pipe, 22, 221, 222, 223... Air inlet, 23... Constriction section, 30, 30A... Air supply device, 31... First air supply system, 311, 321, 331... Distribution pipe, 312, 322, 332... Solenoid valve, 32... Second air supply system, 33... Third air supply system, 39... Air supply source, 40, 40A... Control device, 41... Gap sensor, A... Pressurized air, C... Rotating shaft, Cr, Cr2, Cr3, Cr4... Reference gap, R1, R2, R3, R4... Data series, Rm... Bearing stiffness characteristics.

Claims

1. An air hydrostatic bearing comprising an air supply device for supplying air to a bearing portion and a control device for controlling the air supply device, wherein the air supply device has a plurality of air supply systems, each of the air supply systems can be switched between an air supply state and a stopped state, and the control device reduces the number of air supply systems in the air supply state when the bearing clearance decreases.

2. An air hydrostatic bearing according to claim 1, wherein the control device is an air hydrostatic bearing having a gap sensor for detecting the value of the bearing gap.

3. An air hydrostatic bearing according to claim 1, wherein the air supply system has a valve device that switches between the air supply state and the stopped state by intermittently controlling the flow of air under the control of the control device.

4. An air hydrostatic bearing according to any one of claims 1 to 3, wherein the control device reduces the number of air supply systems in the air supply state by switching one of the air supply systems from the air supply state to the stopped state when the value of the bearing clearance falls below a predetermined reference clearance value.

5. An air hydrostatic bearing according to claim 4, wherein the control device is configured such that the reference gap is set for each of the air supply systems, and the value of the reference gap is such that the bearing gap stiffness characteristic when the air supply system is in the stopped state and the bearing gap stiffness characteristic when the air supply system is in the air supply state are the same bearing stiffness.

6. An air hydrostatic bearing according to claim 1, wherein the control device performs control to predict the value of the bearing clearance from the operating conditions of the bearing portion.

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