Air bearing spindle and method for controlling air bearing pressure of air bearing spindle

Abstract

To realize a processing of high accuracy by compensating gyro effect acting on a spindle main shaft in a case when the spindle main shaft is inclined during high-speed rotation.SOLUTION: In an air bearing spindle including a spindle main shaft and air bearing means rotatably supporting the spindle main shaft via an air layer, and its bearing pressure control method, the air bearing means is disposed on a housing and includes a plurality of radial air bearings and thrust air bearings. The radial air bearings include a plurality of distance sensors for measuring a distance to the spindle main shaft, and an air pad divided into a plurality of sections for keeping an interval of clearances by supplying the air to the clearance of the air layer to the spindle main shaft. The distance sensor increases and decreases a pressure supplied to the air pad by pressure control means according to the distance to the spindle main shaft and changes a pressure of the air pad at a position shifted by 90 degrees in a circumferential direction from the air pad corresponding to the distance sensor.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an air bearing spindle that uses an air bearing, and more particularly to a pressure control method for a radial air bearing used in an air bearing spindle. [Background technology]

[0002] Hard, brittle, and difficult-to-cut materials such as silicon (Si) and ceramics are often used as materials for semiconductor wafers, jigs, and other components. As demand for semiconductors increases, machine tool manufacturers are being asked to improve productivity and precision when machining hard, brittle materials such as Si, SiC (silicon carbide), and GaN (gallium nitride). Ultrasonic vibration cutting using an ultrasonic spindle equipped with an ultrasonic vibrator in the spindle is effective for machining hard-to-cut materials (microgroove machining, chamfering, etc.), and Figure 24 shows the structure of such an ultrasonic spindle.

[0003] Fig. 24 is a schematic diagram of an ultrasonic spindle that uses rolling bearings. The ultrasonic spindle 100 shown in Fig. 24 has piezoelectric ceramics (lead zirconate titanate) 102 built into the spindle main shaft 103, and is structured so that the entire spindle main shaft 103 resonates at a predetermined frequency (for example, 40 kHz). The spindle main shaft 103 is supported by rolling bearings (ball bearings) 101 at two locations and rotates. Tool 105 (mounted grinding wheel) is attached to spindle main shaft 103 by a shrink-fit chuck 104, and rotation of spindle main shaft 103 is imparted by motor 107 attached to the rear end thereof. Ultrasonic oscillator 106 and motor 107 are each driven by power supplied from an external dedicated power source. Note that the housing that houses spindle main shaft 103 is omitted from Figure 24.

[0004] Ultrasonic vibration cutting is effective for the above-mentioned hard and brittle materials, but it also has the following problems. To improve machining accuracy, ultrasonic vibration machining must be performed at even higher rotation speeds, but there is a limit to the rotation of the balls or rollers used in the currently used ball bearing 101, and there are also problems with durability.

[0005] That is, the current ultrasonic spindle 100 is limited to a few tens of thousands of revolutions per minute because it uses ball bearings 101, and it is difficult to exceed 100,000 revolutions per minute, which is expected to improve precision. Furthermore, due to the influence of vibrations, the ball bearings 101 wear out quickly, making it unsuitable for the long-term continuous machining required for mold machining or machining of hard-to-cut materials, and the high costs of bearing maintenance, etc., hinder its widespread use.

[0006] To solve this problem, the ball bearing 101 of the ultrasonic spindle can be replaced with an air bearing, which allows for high speed rotation and also improves durability. An invention has already been proposed in which ball bearings are replaced with air bearings, as shown in Patent Document 1. The invention in Patent Document 1 is an aerostatic bearing spindle device and a machine tool using the same. This spindle device increases the pressure of the air supplied to the spindle device, controls the temperature of the air using a temperature adjustment device, and supplies air to a pressure regulator. By controlling the pressure and temperature of the supplied air, this aerostatic bearing spindle device can stably achieve high-precision machining. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-104449 A [Patent Document 2] Japanese Patent Application Publication No. 58-81217 Summary of the Invention [Problem to be solved by the invention]

[0008] However, if the spindle spindle tilts due to load or other factors while rotating at high speed, a new force acts on the rotation axis in a direction 90 degrees off from the tilt direction due to the gyro effect, making it necessary to control the air pressure in the bearings at points other than the direction the spindle rotation axis is tilted.For this reason, if the spindle spindle tilts quickly, the rotation axis will shift, making accurate machining difficult.

[0009] An invention disclosed in Patent Document 2 is an example of a document that aims to stabilize the spindle by suppressing the gyroscopic effect. The invention in Patent Document 2 relates to the control of a magnetic bearing, and is not an invention of an air bearing. Furthermore, magnetic bearings are controlled by electrically generating magnetic force, which means that magnetic bearings, unlike air bearings, have a complex structure and are expensive. [Means for solving the problem]

[0010] The present invention solves the above problems by replacing the ball bearings in the spindle with air bearings, enabling high-speed rotation and improved durability. It also achieves the same rigidity and size as conventional ball bearings. Furthermore, it provides a high-precision air bearing that suppresses the effects of gyroscopic moment and is not affected by machining torque.

[0011] That is, the present invention provides an air bearing spindle comprising a spindle main shaft, a housing for accommodating the spindle main shaft, air bearing means for rotatably supporting the spindle main shaft via an air layer, air supply means for supplying air to the air bearing means via a pressurizing device, a pressure regulator and pressure control means, and rotation drive means for rotating the spindle main shaft, wherein the air bearing means is attached to the housing and comprises a plurality of radial air bearings for supporting a load in a direction perpendicular to the spindle main shaft and a thrust air bearing for supporting a load in the direction of the spindle main shaft, the radial air bearings comprise a plurality of distance sensors for measuring the distance from the spindle main shaft and a plurality of divided air pads for supplying air to a gap in the air layer between the spindle main shaft and the radial air bearing to maintain the gap, and the distance sensors increase or decrease the pressure supplied to the air pads by pressure control means in accordance with the distance from the spindle main shaft, At the same position in the circumferential direction This air bearing spindle is characterized in that instead of an air pad, the pressure of air pads at positions shifted in the circumferential direction is changed.

[0012] With this configuration, the spindle main shaft can be rotated at high speed by the radial air bearing without coming into contact with the housing.

[0013] The air pad of the radial air bearing of the present invention is characterized in that the radial air bearing has a three-dimensional shape that is annularly divided into multiple sections along the circumferential direction, and each of the divided air pads has multiple air nozzles and air supply holes that supply air to the air nozzles on the surface facing the spindle main shaft, and the air pad to which air whose pressure is controlled by pressure control means connected to a distance sensor is supplied is shifted 90 degrees circumferentially from the distance sensor. With this configuration, even if the spindle main shaft is tilted and tilts in a different direction due to the gyro effect, the tilt can be suppressed.

[0014] The pressure control means is characterized by being a diaphragm type pilot valve. With this configuration, the gap distance of the distance sensor can be converted into pressure to be supplied to the air pad.

[0015] Furthermore, the distance sensor is a nozzle flapper that is configured with a nozzle having a pressure detection port and the circumferential side surface of the spindle main shaft as a flapper, and is a sensor that controls the air pressure supplied to the air pad by a pilot valve connected to the nozzle, and when the distance between the nozzle tip and the spindle main shaft becomes narrow, the pressure control means Shifted 90 degrees circumferentially from the distance sensor Pressure supplied to the air pads of the radial air bearing Low power When the distance between the nozzle tip and the spindle shaft becomes wider, the pressure control means Shifted 90 degrees circumferentially from the distance sensor Pressure supplied to the air pads of the radial air bearing Power is higher It is characterized by rising. Furthermore, when the distance between the nozzle tip and the spindle main shaft becomes narrower, the pressure supplied to the air pad of the radial air bearing shifted 90 degrees circumferentially from the distance sensor increases due to pressure control means having characteristics opposite to those of the above pressure control means, and when the distance between the nozzle tip and the spindle main shaft becomes wider, the pressure supplied to the air pad of the radial air bearing shifted 90 degrees circumferentially from the distance sensor decreases due to pressure control means having characteristics opposite to those of the above pressure control means. With this configuration, tilting of the spindle main shaft can be suppressed by controlling the pressure using the distance sensor.

[0016] The air pads of the thrust air bearing of the present invention are characterized in that they are shaped so that both sides of a thick, disk-shaped flange that is integrally machined with the spindle main shaft face each other across an air layer gap, and the surface facing the flange is equipped with a plurality of air nozzles and air supply holes that supply air to the air nozzles. With this configuration, the spindle main shaft can be stabilized even if a load is applied in the vertical direction of the spindle main shaft.

[0017] The present invention is also characterized in that an ultrasonic oscillator is added to the air bearing spindle to form an air bearing ultrasonic spindle. By configuring in this way, an ultrasonic vibration function can be added to the air bearing spindle, making it possible to perform high-precision spindle machining.

[0018] Furthermore, the air pressure of the distance sensor is measured to monitor the load state of the tool attached to the tip of the spindle main shaft. By configuring in this way, it is possible to grasp the wear state of the tool.

[0019] The present invention also provides an air bearing pressure control method for an air bearing spindle comprising a spindle, a housing for accommodating the spindle, air bearing means for rotatably supporting the spindle via an air layer, air supply means for supplying air to the air bearing means via pressure control means, and rotation drive means for rotating the spindle, wherein the air bearing means is attached to the housing and comprises a plurality of radial air bearings for supporting a load in a direction perpendicular to the spindle, and a thrust air bearing for supporting a load in the direction of the spindle axis, the radial air bearings comprise a plurality of distance sensors for measuring the distance from the spindle, and a plurality of divided air pads for supplying air to a gap in the air layer between the spindle and the radial air bearing to maintain the gap, and the distance sensors increase or decrease the pressure supplied to the air pads by pressure control means in accordance with the distance from the spindle, At the same position in the circumferential direction This is an air bearing pressure control method for an air bearing spindle, characterized in that the pressure of the air pads at positions shifted in the circumferential direction is changed instead of the air pad.

[0020] By controlling the pressure of the air bearing of the spindle in this way, tilt of the spindle main shaft due to the gyroscopic effect can be suppressed. [Effects of the Invention]

[0021] As described above, according to the present invention, by replacing the ball bearings in a spindle with air bearings, it is possible to achieve rigidity and size equal to or greater than those of ball bearings, and to improve durability. Furthermore, it is possible to suppress the gyroscopic moment and realize a high-precision spindle that is not affected by the load caused by machining. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an outline view of an air bearing spindle according to an embodiment of the present invention; [Figure 2] FIG. 2 is a right side view of the air bearing spindle shown in FIG. [Figure 3] FIG. 2 is a left side view of the air bearing spindle shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view of the air bearing spindle taken along the AA section shown in FIG. 3. [Figure 5] FIG. 4 is a cross-sectional view of the air bearing spindle taken along the BB section shown in FIG. 3. [Figure 6] 6 is a cross-sectional view of the radial air bearing taken along the YY cross section shown in FIG. 5. [Figure 7] FIG. 5 is an enlarged view of the nozzle flapper in the circular area in the upper left of the cross-sectional view shown in FIG. 4. [Figure 8] FIG. 6 is an enlarged view of a radial air bearing and a thrust air bearing in the circularly enclosed area shown in FIG. 5. [Figure 9] FIG. 5 is a diagram showing the connection of a pneumatic circuit including a pilot valve to the cross-sectional view of the spindle shown in FIG. 4. [Figure 10] FIG. 7 is a diagram showing the connection of a pneumatic circuit including a pilot valve to the radial air bearing cross section shown in FIG. 6. [Figure 11]FIG. 2 is a schematic diagram showing the arrangement of air bearings and nozzle flappers that constitute the air bearing spindle, as well as a pneumatic circuit including a pilot valve. [Figure 12] 10A and 10B are diagrams illustrating pressure changes when the distance between the nozzle and the flapper is increased. [Figure 13] 10A and 10B are diagrams illustrating changes in pressure when the distance between the nozzle and the nozzle cap is narrowed. [Figure 14] 1 is a schematic structural diagram of a nozzle flapper and a pilot valve, and a pneumatic circuit diagram. FIG. [Figure 15] 10A and 10B are diagrams illustrating a decrease in air bearing pressure when the distance between the nozzle and the flapper becomes narrower. [Figure 16] 10A and 10B are diagrams illustrating an increase in air bearing pressure when the distance between the nozzle and the flapper is increased. [Figure 17] 1A and 1B are diagrams illustrating the operation of a thrust air bearing in response to a load in the vertical direction. [Figure 18] FIG. 10 is a diagram showing pressure values ​​for holding a vertical load relative to the air pad diameter of a thrust air bearing. [Figure 19] 1A and 1B are diagrams illustrating the operation of a radial air bearing. [Figure 20] FIG. 10 is a diagram showing the pressure difference for maintaining a radial load relative to the spindle diameter. [Figure 21] 10A and 10B are diagrams illustrating an operation for compensating for a gyroscopic effect. [Figure 22] 10A and 10B are diagrams illustrating the operation of compensating for the gyroscopic effect using another pilot valve. [Figure 23] 1 is a flow chart showing the operation of an air bearing that compensates for the gyroscopic effect. [Figure 24] FIG. 1 is a schematic diagram of an ultrasonic spindle using rolling bearings. DETAILED DESCRIPTION OF THE INVENTION

[0023] An air bearing spindle according to an embodiment of the present invention will be described with reference to FIGS. Fig. 1 is an outline view of an air bearing spindle 1 according to an embodiment of the present invention, Fig. 2 is a right side view of the air bearing spindle 1 shown in Fig. 1. Fig. 3 is a left side view of the air bearing spindle 1 shown in Fig. 1. Fig. 4 is a cross-sectional view of the air bearing spindle 1 taken along the A-A cross section shown in Fig. 3, and Fig. 5 is a cross-sectional view of the air bearing spindle 1 taken along the B-B cross section shown in Fig. 3.

[0024] Figure 6 is a cross-sectional view of radial air bearing 27 taken along the YY cross section shown in the cross-sectional view of Figure 5. Figure 7 is an enlarged view of nozzle flapper 57 shown in the circled area at the upper left of the cross-sectional view of Figure 4, and Figure 8 is an enlarged view of radial air bearing 27 and thrust air bearing 29 shown in the circled area at the right of the cross-sectional view of Figure 5.

[0025] The air bearing spindle 1 shown in Figure 1 is composed of multiple, roughly cylindrical housings 15(1) to 15(9) divided into sections. Two radial air bearings 27 and one thrust air bearing 29 are attached to the inside of the housing 15 of this spindle 1. One radial air bearing 27 is combined with four nozzle flappers 57, so the two radial air bearings 27 have a total of eight nozzle flappers 57.

[0026] The housing 15 is opened with the following: a pilot valve control pressure supply port 10 for connecting the nozzle flapper 57 used to control the air pressure of the radial air bearing 27 to the pilot valve 50; a nozzle flapper air supply port 11 for supplying air to the nozzle flapper 57; a radial air bearing air supply port 12 for supplying pressure-controlled air from the pilot valve 50 to the radial air bearing 27; two thrust air bearing air supply ports 13 for supplying air to the thrust air bearing 29; and an air exhaust port 14 for exhausting the air supplied to the nozzle flapper 57, the radial air bearing 27, and the thrust air bearing 29.

[0027] The radial air bearing 27 supports a load perpendicular to the spindle main shaft 33, and the thrust air bearing supports a load in the axial direction of the spindle main shaft 33. These air bearings support the spindle main shaft 33 via the air layers of the air bearings. In this invention, the radial air bearing 27 and the thrust air bearing 28 correspond to the air bearing means. In this embodiment, one radial air bearing 27 is provided with a total of eight radial air bearing air supply ports 12. Here, the air layer refers to the gap between the spindle main shaft 33 and the radial air bearing 27 or the thrust air bearing 29, and is a space into which air can be supplied. Furthermore, when referring to air in this invention, it does not refer to the atmosphere but to compressed air having a relative pressure (gauge pressure). Furthermore, an ultrasonic oscillator can be appropriately attached to form an air bearing ultrasonic spindle.

[0028] In the right side view shown in FIG. 2, there are provided a wiring outlet 20 for supplying power to a built-in motor 30 that rotates a spindle main shaft 33 (described later), and a connection port 23 for connecting each housing 15 with a bolt or the like. In the left side view of FIG. 3, connecting ports 23 that connect the housings 15 and plugs 24 that prevent air leakage from the air supply holes 37 of the four nozzle flappers 57 are formed. The central opening is a tool attachment port 31.

[0029] FIG. 4 is a cross-sectional view of air bearing spindle 1 taken along the line AA shown in FIG. The housings 15(1) to (9) are connected and fixed with bolts or the like, and the spindle main shaft 33 is inserted inside them. The housing 15(1) is a disk-shaped thick plate, and has a hole in the center for the wiring outlet 20. The housing 15(2) is cylindrical, and is attached to the spindle main shaft 33 with a wide gap between them. The housing 15(3) is provided with a nozzle flapper 57 for controlling the air pressure of the radial air bearing 27, and an air supply hole 26 is provided which detects the gap distance between the nozzle flapper 57 and the air bearing and transmits an air pressure signal to the pilot valve 50.

[0030] Radial air bearing 27 is fixed inside housing 15(4). Housing 15(4) is formed with an inverted L-shaped cross section, with housing 15(5) placed in the recess and housing 15(6) having a thin cylindrical shape placed inside it. Also, air supply holes 35 (shown in FIG. 5) are formed in housing 15(4) to supply air to air pads 27a of radial air bearing 27, as will be described later. A stator 30a of a built-in motor 30 is fixed inside the housing 15(5) via a housing 15(6), and inside that, a rotor 30b of the built-in motor is fixed to a spindle main shaft 33. The built-in motor 30 corresponds to the rotation drive means of the present invention. When the housing 15(5) and the housing 15(6) are stacked together, multiple grooves can be formed on the outer periphery of the housing 15(6), and cooling water can be passed through these grooves to cool the heat of the built-in motor 30.

[0031] A thrust air bearing 29 is attached to one side of a flange 28 of the spindle main shaft 33 in the housing 15(6), and a thrust air bearing 29 is fixed to the other side of the flange 28 in the housing 15(8). The housing 15(7) is disposed on the outer periphery of the flange 28 so as to face it while allowing the flange 28 to rotate. Furthermore, a radial air bearing 27 is disposed inside the housing 15(8) in continuation with the thrust air bearing 29. Furthermore, the housing 15(8) is formed with an air supply hole 36 for supplying air to the thrust air bearing 29, and with an air supply hole 35 (shown in FIG. 5) for supplying controlled air pressure to the radial air bearing 27, which will be described later with reference to FIG. 5.

[0032] Similar to the housing 15(3), the housing 15(9) is provided with a nozzle flapper 57 for controlling the air pressure of the radial air bearing 27, and an air supply hole 26 for detecting the gap between the bearing and the nozzle flapper 57 and transmitting an air pressure signal to the pilot valve 50. A tool attachment port 31 for attaching a tool is formed at the left end (which faces downward when in use) of the spindle main shaft 33. The wear state of the tool can be determined as the load state of the tool by measuring the air pressure of the distance sensor.

[0033] Figure 5 is a cross-sectional view of the same spindle as Figure 4, but there is an angle difference of 22.5 degrees from the cross-section of Figure 4. Here, the cross-section BB has an angle difference of 67.5 degrees from the cross-section AA, but since the cross-section of Figure 4 is the same cross-section even when rotated 90 degrees, the angle difference is the same as 22.5 degrees. FIG. 5 differs from the cross-sectional view of FIG. 4 in that the nozzle flappers are not shown on the housings 15(3) and 15(9), and that the air supply holes 35 that supply pressure-controlled air to the radial air bearings 27 are formed on the housings 15(4) and 15(8). Also, there is no description of the air supply holes 36 to the thrust air bearing 29 of the housing 15(8). Other than that, the cross section is the same as in FIG. 4, so the explanation will be omitted.

[0034] Figure 6 is a cross-sectional view of radial air bearing 27 taken along the YY cut plane of Figure 5. Eight radial air bearing air supply ports 12 and air supply holes 35 are arranged circumferentially, and the air supply holes 35 are connected to eight air nozzles 32 formed on air pads 27a of radial air bearing 27.

[0035] The cross-sectional view of Figure 6 shows, from the outside to the center, housing 15(5), housing 15(6), housing 15(4), air pad 27a of radial air bearing 27, and spindle main shaft 33, with radial air bearing 27 and spindle main shaft 33 rotatably held by the bearing with a gap between them. Air supply hole 35 is drilled to pass through the three housings 15(5), 15(6), and 15(4) and is connected to air nozzle 32. In addition, connecting holes 25 are formed to pass through bolts or the like that assemble multiple housings 15. The connection between the air pad 27a and the control pressure air of the pilot valve 50 will be described later with reference to FIG.

[0036] Figure 7 is an enlarged view of air supply holes 37 and 26, which transmit air pressure signals to nozzle flapper 57 and pilot valve 50. Their function will be described later. Air is supplied from nozzle flapper air supply port 11, and changes in the gap between the tip of nozzle 57a of nozzle flapper 57 and spindle 33 are converted into an air pressure signal, which is then connected to pilot valve 50 via air supply holes 37 and 26 and pilot valve control pressure supply port 10. Air whose pressure is controlled by pilot valve 50 is supplied to air nozzle 32 of air pad 27a (shown in Figure 6) of radial air bearing 27 (not shown in Figure 7). The nozzle flapper 57 is embedded in the housing 15(9), the air supply holes 37 and 26 are drilled in the housing 15(9), and plugs 24 are inserted into the openings that are not connected.

[0037] Figure 8 is an enlarged view of the circled portion in the cross-sectional view of Figure 5, and is an enlarged view of the radial air bearing 27 and the thrust air bearing 29. The thrust air bearings 29 are attached to the housings 15(6) and 15(8) so as to surround the flange 28 of the spindle main shaft 33 on the left and right sides as shown in the figure, allowing the spindle main shaft 33 to rotate. The housing 15(7) is fixed to the outer circumferential side of the flange 28 so as not to contact the flange 28, but to contact the left and right air pads 29a of the thrust air bearing 29. Air supply holes 36 that supply air to thrust air bearing 29 are not visible due to the angle of the cross section, but air is supplied from two thrust air bearing air supply ports 13 shown in FIG. Radial air bearing 27 is disposed continuous with thrust air bearing 29 shown in FIG. 8, and the configuration of radial air bearing 27 is the same as the cross-sectional view of radial air bearing 27 shown in FIG.

[0038] Here, air pad 27a of radial air bearing 27 has a shape obtained by dividing an annular Baumkuchen-shaped three-dimensional shape into multiple sections that surrounds spindle main shaft 33. In the following, the air pad is described as having a three-dimensional shape, for example, an annular sector divided into four or two sections. A plurality of air nozzles 32 are arranged on the surface of each divided air pad of the radial air bearing 27 shown in Figure 6 that faces the spindle main shaft 33, and air is supplied through the radial air bearing air supply port 12 and air supply holes 35.

[0039] In addition, multiple air nozzles 32 are configured on the surface of each air pad of the radial air bearing 27 shown in Figure 8 that faces the spindle main shaft 33, and pressure-controlled air is supplied from a pilot valve 50 via air supply holes 35. In this way, air is supplied to the gap between each air pad 27a of the radial air bearing 27 and the spindle main shaft 33, and the spindle main shaft 33 is held by the air with controlled pressure.

[0040] The thrust air bearing 29 shown in FIG. 8 is composed of two air pads 29a that face both sides of a disk-shaped flange 28 that is integrally molded with a spindle main shaft 33, and a plurality of air nozzles 32 are formed on the surface facing the flange 28, through which air at a constant pressure is supplied from air supply holes 36. Although the air pad of thrust air bearing 29 has an annular three-dimensional shape, it is not divided like radial air bearing 27, so the pressure distribution of air pad 29a and flange 28 is almost the same. In this embodiment, the plurality of air nozzles 32 of the radial air bearing 27 and the thrust air bearing 29 are each constituted by a known automatic throttle valve.

[0041] Fig. 9 is a diagram illustrating the air pressure circuit between the air pressure supply source 64 and the pilot valves 50 in the cross-sectional view shown in Fig. 5. The pilot valves 50 are configured with a total of eight pilot valves 50 for two radial air bearings 27, but four pilot valves 50 are omitted. Air is supplied from an air pressure supply source 64 to a nozzle flapper 57 shown in the cross-sectional view, a thrust air bearing 29, and four pilot valves. Pilot valve 50 receives a pressure signal from nozzle flapper 57 shown in the cross-sectional view and supplies pressure-controlled air to the radial air bearing 27.

[0042] 10 shows the pneumatic circuit of the nozzle flapper 57 (not shown in the cross-sectional view, but the mounting position is indicated by a square frame), the pilot valve 50, and the eight air supply holes 35 of the radial air bearing 27 in the cross-sectional view shown in FIG. Air is supplied to each pilot valve 50 from an air pressure supply source 64, and the pilot valve 50 receives a pressure signal from the nozzle flapper 57 and supplies pressure-controlled air to two air supply holes 35 that are offset from the position of the nozzle flapper 57. The angle from the position of the nozzle flapper 57 to the centers of the two air supply holes 35 is offset by 90 degrees clockwise.

[0043] The number of air supply holes 35 to which pressure-controlled air is supplied from the pilot valve 50 may be one, but in this embodiment, there are two. The angle difference between the two air supply holes 35 is 45 degrees. In other words, the eight air supply holes 35 are arranged at equal intervals of 45 degrees. In this way, when a load is applied to the spindle main shaft 33 and it displaces, the present invention suppresses the gyroscopic effect by changing the pressure of the air pad 27a of the radial air bearing 27 that is shifted by 90 degrees from the direction of displacement. This controls the air pressure of the air pad 27a in the direction shifted by 90 degrees from the direction of displacement.

[0044] Next, the relationship between the radial air bearing 27 and the nozzle flapper 57 of the present invention will be described. FIG. 11 is a schematic diagram showing the arrangement of the radial air bearings 27 and nozzle flappers 57 that constitute the air bearing spindle 1, as well as the air pressure circuit including the pilot valve 50. Unlike FIG. 10, FIG. 11 does not show the air supply holes 35 for the pressure-controlled air of the pilot valve 50, and the number of the air supply holes 35 is also different from that of the present embodiment.

[0045] Air pads 27a of radial air bearing 27 are described below as being divided into two or four sections, but in this embodiment, radial air bearing 27 is not divided into multiple sections. Here, the phrase "divided into a plurality of parts" refers to a state in which the radial air bearing 27 is virtually divided into a plurality of air pads 27a in accordance with the number of nozzle flappers 57 or pilot valves 50. In other words, the pressure-controlled air pressure supplied to the divided air pads 27a differs for each air pad 27a, and is the air pressure controlled by the pilot valve 50 corresponding to that air pad 27a. In addition, the pressure-controlled air supplied from the pilot valve 50 may be supplied to a single air supply hole 35, but in this embodiment it can also be supplied to two air supply holes 35 or to multiple air supply holes 35.

[0046] The diagram shown in the lower part of Fig. 11 is a schematic side view of the arrangement of the two radial air bearings 27 and the thrust air bearing 29 of the air bearing spindle 1, and the diagram shown in the upper part of Fig. 11 is a schematic top view of the arrangement of the radial air bearing 27. Fig. 11 also shows that the pilot valve 50 is connected to the air pad 27a of the radial air bearing 27 and the nozzle 57a of the nozzle flapper 57, and their positional relationship.

[0047] In FIG. 11, one radial air bearing 27 is divided into four air pads 27a, and a nozzle 57a corresponding to each air pad 27a measures the gap between the air pad and the spindle main shaft 33, and the air pressure of the air pad 27a is controlled by the pressure corresponding to that gap.

[0048] As shown in Figure 6, this air pad 27a is equipped with air supply holes (air reservoir chambers) 35 for storing air, and air with pressure controlled by a pilot valve 50 is supplied to the air supply holes 35. On the side facing the spindle main shaft 33, air pad 27a is equipped with multiple air nozzles (automatic throttle valves) 32 suitable for holding the spindle main shaft 33, so that the air supply path, which is narrowed in the vicinity of the gap between the bearing and the main shaft, and the bearing gap form a bearing that obtains a throttling effect on an imaginary cylindrical surface made up of multiple air pads.

[0049] A pneumatic circuit is connected from the nozzle 57a to the pilot valve 50, and the pilot valve 50 Nozzle 57aThe air pad 27a is connected to an air pad 27a that is shifted by 90 degrees in the circumferential direction, rather than being in the same position as the air pad 27a. By supplying pressure-controlled air to the air pad 27a that is shifted by 90 degrees, the gyro effect is suppressed and the operation of the spindle main shaft 33 is stabilized. In addition, the thrust air bearing 29 is a bearing in which a thick disk-shaped flange 28 is formed on the spindle main shaft 33, and the entire circumferential portion of the flange 28 formed on the spindle main shaft 33 is supported from both the top and bottom by air layers, and a plurality of air nozzles (self-acting throttle valves) 32 are provided on the surface of the air pad 29a facing the flange, similar to the radial air bearing 27. An air layer is formed between the air nozzle 32 and the flange 28 to hold the spindle main shaft 33.

[0050] Next, pressure control by the nozzle flapper 57 will be described. FIG. 12 is a diagram illustrating a change in pressure when the distance (gap) between the nozzle 57a and the flapper 57b of the nozzle flapper 57 is widened. A flapper 57b faces the tip of the nozzle 57a with a gap between them. Air at a constant pressure (supply pressure Ps) is supplied to the nozzle 57a, and the amount of air (Ge) discharged from the tip of the nozzle 57a varies depending on the distance from the flapper 57b. The pressure inside the nozzle 57a (output pressure Pc) varies depending on the distance between the nozzle 57a and the flapper 57b. This output pressure is connected to the pilot valve 50 via a pressure detection port.

[0051] When the distance between the nozzle 57a and the flapper 57b in the upper diagram of Fig. 12 becomes wider, the outflow rate from the tip of the nozzle 57a increases, and the output pressure Pc decreases as shown in the lower diagram of Fig. 12. This output pressure is transmitted to the pilot valve 50, which will be described later, and the air pressure is controlled by the pilot valve 50.

[0052] FIG. 13 is a diagram illustrating the change in pressure when the distance between the nozzle and the flapper is narrowed. 13 is similar to FIG. 12, and therefore, explanation of the overlapping parts will be omitted. When the distance between the nozzle 57a and the flapper 57b becomes narrower, the flow rate of air flowing out from the tip of the nozzle 57a decreases, and the output pressure inside the nozzle 57a increases. In the present invention, the flapper 57b corresponds to the circumferential side surface of the spindle main shaft 33, and the nozzle flapper 57 has the function of converting the distance (gap) from the circumferential side surface of the spindle main shaft 33 into a pressure change.

[0053] Next, the air pressure control of the air bearing by the pilot valve in accordance with the distance between the nozzle and flapper of the nozzle flapper 57 will be described. Fig. 14 is a structural schematic diagram and pneumatic circuit diagram of the nozzle flapper 57 and pilot valve 50. Fig. 15 is a diagram explaining that the pressure in the air reservoir chamber (air bearing) 63 decreases when the distance between the nozzle and the flapper decreases, and Fig. 16 is a diagram explaining that the pressure in the air reservoir chamber 63 increases when the distance between the nozzle and the flapper increases. The air bearing (air reservoir chamber) 63 corresponds to the air supply hole (radial air bearing) 35.

[0054] The pilot valve 50 shown in Figure 14 is composed of first to fourth pressure chambers 59 to 62. As shown in Figure 14, the second pressure chamber 60 of the pilot valve 50 is connected to the nozzle flapper 57, and the third pressure chamber 61 of the pilot valve 50 is connected to an air reservoir chamber 63 of the air bearing. The other three pressure chambers 59, 60, and 62 of the pilot valve 50 are connected to an air pressure supply source 64, and air at a pressure higher than atmospheric pressure is supplied. The air pressure supply source 64 is air supply means composed of a compressor (pressurizing device) that compresses air and a pressure regulator, and is controlled to a constant pressure. The pilot valve 50 also serves as pressure control means of the present invention. Since air flows out from the air bearing and is also discharged into the atmosphere from the pilot valve 50, the supply pressure of the air pressure supply source is kept constant by a pressure regulator.

[0055] The first pressure chamber 59 and the second pressure chamber 60 of the pilot valve 50 are separated by a diaphragm 51. A cylindrical exhaust valve 52 is fixed to the center of the diaphragm 51, and the exhaust valve 52 moves integrally with the diaphragm 51 (up and down in FIG. 14) in response to changes in pressure on the diaphragm 51. The exhaust valve 52 is assembled so that it can slide between the first pressure chamber 59 and the second pressure chamber 60 and so that air does not leak from these pressure chambers.

[0056] One end of the cylindrical exhaust valve 52 is open (discharged) to the atmosphere, and the other end is in contact with an exhaust valve portion 54 of the main valve 53. The exhaust valve portion 54 is a substantially spherical valve body formed on one side of the main valve 53, and when in contact with the exhaust valve 52, air is blocked between the exhaust valve 52 and the exhaust valve portion 54.

[0057] A hemispherical intake valve portion 55 is formed on the other side of main valve 53, and a spring coil 56 is fixed to the hemispherical flat surface side of intake valve portion 55. The other end of spring coil 56 is fixed to the partition of fourth pressure chamber 62. The air intake valve portion 55 is biased upward in the drawing by the spring coil 56, and is in contact with the through-hole in the center of the partition between the third pressure chamber 61 and the fourth pressure chamber 62. When the air intake valve portion 55 is in contact with the partition between the third pressure chamber 61 and the fourth pressure chamber 62, the flow of air is blocked.

[0058] 15 and 16, a description will be given of a change in pressure in the air chamber 63 when the distance between the nozzle and the flapper of the nozzle flapper 57 changes. FIG. 15 is a diagram illustrating the pressure drop in the air reservoir chamber 63 when the distance between the nozzle 57a of the nozzle flapper (called an air distance sensor in this invention) 57 and the flapper (circumferential side surface of the spindle main shaft 33) 57b becomes narrow.

[0059] In other words, when the distance between the nozzle 57a and the flapper 57b becomes narrower, the spindle main shaft 33 tilts toward the nozzle 57a, i.e., a load is applied, and it is necessary to reduce the pressure of the air pad to return the spindle main shaft 33 to its original position (details will be described later). To reduce the pressure, the following steps are taken: (A) When the distance between the nozzle 57a and the flapper 57b of the nozzle flapper 57 becomes narrower, the distance between the nozzle 57a and the flapper 57b, i.e., the spindle main shaft 33, becomes shorter, blocking the release of air from the nozzle 57a and causing the pressure inside the nozzle 57a to rise. (B) When the pressure inside the nozzle 57a increases, the pressure in the second pressure chamber 60 of the pilot valve 50 also increases. The diaphragm 51 located in the center of the second pressure chamber 60 and the first pressure chamber 59 of the pilot valve 50 bends upward as shown in FIG. 15 due to the pressure difference between the two pressure chambers 59 and 60.

[0060] (C) When diaphragm 51 bends upward, exhaust valve 52 fixedly attached to diaphragm 51 moves upward. An approximately spherical exhaust valve portion 54 formed on the upper part of main valve 53 at the lower tip of exhaust valve 52 is biased upward by pulling coil 56 at air intake valve portion 55 at the lower part of main valve 53, but main valve 53 cannot move upward because air intake valve portion 55 at the lower part of main valve 53 is in contact with the air circulation holes of pressure chamber 61 and pressure chamber 62.

[0061] (D) Since the intake valve portion 55 of the main valve 53 cannot move upward, the substantially spherical exhaust valve portion 54 formed on the upper portion of the main valve 53 cannot move upward either. As the diaphragm 51 bends upward, the exhaust valve 52 moves upward as it is. The exhaust valve 52 and the exhaust valve portion 54 move apart, and air flows out from between the lower part of the exhaust valve 52 and the exhaust valve portion 54 into the atmosphere. (E) The third pressure chamber 61 is connected to the air reservoir chamber 63 of the air bearing, and the air in the third pressure chamber 61 flows out into the atmosphere, and the air in the air reservoir chamber 63 is exhausted to the atmosphere through the pressure chamber 61, causing the pressure in the air reservoir chamber 63 to decrease. As a result, when the distance between the nozzle 57a and the spindle main shaft 33 becomes narrower, the pressure in the pressure chamber of the air reservoir chamber 63 decreases.

[0062] Here, if the gap between the nozzle 57a and the flapper 57b narrows, it would be desirable to increase the pressure in the air reservoir chamber 63 (here, the air pad 27a corresponding to the spindle main shaft 33) in an attempt to push back the flapper, i.e., the spindle main shaft 33. However, since the present invention takes the gyro moment into consideration, control is exercised to reduce the pressure of the air pad, which is in a direction rotated 90 degrees from the nozzle flapper 57.

[0063] FIG. 16 is a diagram for explaining the operation of the bearing pressure rise when the distance between the nozzle 57a of the nozzle flapper 57 and the spindle main shaft 33 becomes wider. The explanation is almost the same as that of FIG. 15, but the directions in which the exhaust valve 52 and the main valve 53 move are reversed.

[0064] (A) When the distance (gap) between the nozzle 57a of the nozzle flapper 57 and the spindle main shaft 33 becomes wider, the distance between the nozzle 57a and the spindle main shaft 33 becomes wider, so air is released from the nozzle 57a and the pressure inside the nozzle 57a decreases. (B) When the pressure inside the nozzle 57a decreases, the pressure in the second pressure chamber 60 of the pilot valve 50 decreases. The diaphragm 51 located at the center between the second pressure chamber 60 and the first pressure chamber 59 of the pilot valve 50 bends downward due to the pressure difference between the first pressure chamber 59 and the second pressure chamber 60. (C) When the diaphragm 51 bends downward, the exhaust valve 52, which is integrated with the diaphragm 51, also moves downward. Because the spherical exhaust valve portion 54 formed on the upper part of the main valve 53 is in contact with the lower tip of the exhaust valve 52, the main valve 53 also moves downward.

[0065] Here, a spring coil 56 is connected to the lower air intake valve section 55 of the main valve 53 on the flat side below the air intake valve section 55, and the main valve 53 is biased upward by the spring coil 56, so that the upper tip of the air intake valve section 55 and the air circulation holes of the pressure chamber 61 and the pressure chamber 62 are normally sealed, blocking the circulation of air. (D) When the main valve 53 moves downward due to the movement of the diaphragm 51, the hemispherical air intake valve portion 55 formed at the bottom of the main valve 53 also moves downward against the spring force of the spring coil 56.

[0066] The air flow hole between the third pressure chamber 61 and the fourth pressure chamber 62 was sealed by the air intake valve portion 55, blocking the air, but as the air intake valve portion 55 moves downward, the air flow hole is opened. (E) Since the fourth pressure chamber 62 is supplied with air from the air pressure supply source 64, the supply valve portion 55 of the fourth pressure chamber 62 is opened, and the compressed air is supplied to the air reservoir chamber 63 through the third pressure chamber 61. As a result, when the distance between the nozzle 57a and the flapper 57b increases, the pressure in the air reservoir chamber 63 increases.

[0067] Through the operation described above, the air pressure is controlled by the pilot valve 50 in accordance with the distance between the nozzle 57a and the flapper 57b of the nozzle flapper 57, and the air pressure is supplied to the air reservoir chamber 63 (air bearing, i.e., air pad 27a), changing the pressure of the air bearing.

[0068] FIG. 17 is a diagram illustrating the thrust air bearing 29 in the axial direction of the spindle main shaft 33 (usually, the spindle main shaft 33 is attached in the up-down direction, that is, in the vertical direction). 17 is a side view of spindle main shaft 33 and thrust air bearing 29, and the upper view is a top view of thrust air bearing 29. This is a diagram for explaining a state in which a load is applied upward to spindle main shaft 33.

[0069] When a load is applied vertically upward, the flange 28 formed integrally with the spindle main shaft 33 also moves upward. Because the air pads 29a of the thrust air bearing 29 are installed above and below the flange, when the flange 28 moves upward, the gap between the flange 28 and the upper air pad 29a narrows, and the pressure in the gap between the air pad 29a and the flange 28 increases. As the pressure in the gap increases, a force is generated that pushes back the flange 28. In other words, when a load is applied in an upward direction, a force is generated that pushes back the load, returning it to its original position.

[0070] In this way, even if an upward load is applied to the spindle main shaft 33, the thrust air bearing 29 acts to prevent the spindle main shaft 33 from moving upward. Furthermore, even when a load is applied vertically downward, the air pads 29a of the thrust air bearing 29 are also provided below the flange 28, and an upward pushing force is generated, causing the load to return to its original position.

[0071] Here, how much pressure should be applied to the diameter Da of the thrust air bearing 29 of the spindle main shaft 33 will be considered. The calculation conditions are that the diameter Ds of the spindle main shaft 33 is 20 mm and the pressure satisfies a thrust load of 735 kPa (7.5 kgf).

[0072] The hatched area shown in the upper part of Figure 17 is the area S obtained by subtracting the spindle diameter Ds from the thrust air bearing diameter Da. Since it is sufficient that pressure ΔP × area S ≥ 735 kPa, The thrust air bearing diameter Da = 30 mm, and the spindle diameter Ds = 20 mm, so the area S = 3.93 cm 2 Therefore, the pressure ΔP is 187 kPa or more. Also, if the thrust air bearing Da = 25 mm, the area S = 1.77 cm 2 and the pressure ΔP is 415 kPa or more. Similarly, for thrust air bearing Da=35 mm, the pressure ΔP is 113 kPa or more. Figure 18 is a diagram created based on the above calculation values, showing the pressure required to maintain a vertical load versus the air pad diameter. The horizontal axis represents the thrust air bearing diameter (air pad diameter) and the vertical axis represents the required pressure value.

[0073] From Figure 18, if the thrust air bearing diameter is 30 mm and the pressure is about 200 kPa, the thrust load condition is met. Typically, the air pressure used in industrial machinery is several hundred kPa, and as can be seen from Figure 18, an air bearing functions at a pressure within the normal operating range or lower. Here, as can be seen from Figure 18, it is preferable to maintain the supply pressure of thrust air bearing 29 at 0.5 MPa, but taking into account the manufacturing conditions of air bearing spindle 1, it may be higher, at 1.0 MPa.

[0074] 19 is a diagram illustrating the operation of radial air bearing 27 that supports the load in the direction perpendicular to spindle main shaft 33. Since spindle main shaft 33 is usually attached in the up-down direction (vertical direction), the direction perpendicular to spindle main shaft 33 is the horizontal direction. The diagram shown at the bottom of Figure 19 is a view of the spindle viewed from the horizontal (side) direction, showing the air pad 27a of the radial air bearing 27 attached below the spindle main shaft 33, and indicating that the load is applied from the horizontal direction.

[0075] The diagram at the top of Figure 19 shows radial air bearing 27 as seen from above, with two air pads 27a shown. Note that radial air bearing 27 shown in Figure 19 illustrates the operation of a typical radial air bearing when pilot valve 50 or the like is not used and the gyroscopic effect is not taken into consideration. When a load is applied in the horizontal direction, the pressure of the air layer increases in the air pad 27a facing the load, and decreases in the air pad 27a facing the spindle main shaft 33. The pressure difference between the air pads pushes back the spindle main shaft 33, and even if a load is applied, a force acts to return it to its original state, offsetting the load.

[0076] Here, the required pressure value is calculated from the spindle diameter Ds. From Figure 19, if the length of the spindle spindle 33 to the tool tip is L, the tool length is L2, the air pad height is h, the air pad width is W, and the spindle spindle diameter is Ds, then the length to the center of the air pad 27a is L-(L2+h / 2). If the air pad left bearing pressure is P1, the air pad right bearing pressure is P2, and a load F is applied to the tool tip from the right in the figure, then (P1-P2)×h×W×(L-(L2+h / 2))≧F×L If the above equation holds, spindle main shaft 33 can be held. In other words, when load F is applied from the right to the tool (distance L) at the tip of spindle main shaft 33, the pressure difference at the center of the air pad of radial air bearing 27 (distance (L-(L2+h / 2))) should be balanced.

[0077] Calculations are based on an air pad height of h = 40 mm. Radial load F = 441 kPa (4.5 kgf), L = 150 mm, L2 = 25 mm, spindle main shaft diameter Ds = 20 mm, and air pad width W is approximated as Ds / √2, resulting in (P1 - P2) ≥ 111 kPa. Furthermore, when the spindle diameter Ds is 30 mm, (P1-P2) is 74 kPa or more. Similarly, when Ds is 40 mm, (P1-P2) is 56 kPa or more. FIG. 20 is a diagram illustrating the above results. Furthermore, if the air pad height h is, for example, 20 mm, the area of ​​the air pad will be halved, and the pressure difference shown in FIG. 20 will be doubled.

[0078] Figure 20 is a diagram showing the pressure difference to support the radial load relative to the spindle shaft diameter. The air pad height is, for example, 40 mm for the radial pad, and the spindle diameter is plotted on the horizontal axis, with the pressure value (P1-P2) required per air pad on the vertical axis. As the spindle diameter increases, the opposing area between the air pad and spindle shaft 33 increases, and so the required pressure per air pad decreases. The air pressure used in industrial machinery is usually several hundred kPa, and as can be seen from Figure 20, the normal range of use is lower than this and the air bearing functions. Here, the supply pressure of the radial air bearing 27 may be the same as that of the thrust air bearing 29, but the supply pressure of the air pressure supply source 64 may be a plurality of different supply pressures. For example, the radial air bearing 27 and the thrust air bearing 29 may be different.

[0079] When a force is applied to a rotating object, the object will move in a direction that is offset by 90 degrees to the right or left of the direction of the force, depending on the direction of rotation of the spindle main shaft 33. This is known as the gyroscopic effect. Since the air bearing spindle of this embodiment has a maximum rotation speed of 150,000 revolutions per minute, this gyroscopic effect must be taken into consideration.

[0080] A method for compensating for the gyroscopic effect is outlined in FIG. FIG. 21 is a diagram illustrating the operation of compensating for the gyroscopic effect (gyroscopic moment) of the air bearing spindle 27 used in the present invention.

[0081] In Figure 21, a load F is applied from the right side of the bottom of the figure, causing the spindle main shaft 33 to tilt to the left. When load F is applied from the right side as shown in the bottom of Figure 21, if the rotation axis of spindle main shaft 33 is the Z axis and the direction of load F is the Y axis, a gyro moment is generated in the X axis direction according to the right-handed coordinate system. In Figure 21, a gyro moment is generated on the front side.

[0082] In Figure 21, two air pads 27a are shown to show the positional relationship between the nozzles 57a, pilot valves 50, and air pads 27a, but the explanation will be given with two more nozzles 57a, pilot valves 50, and air pads 27a added to the upper diagram. When a gyroscopic moment occurs on the front side of Figure 21, the gap between the nozzle 57a on the right side (not shown) of the upper part of the figure and the spindle main shaft 33 widens from the direction of the load F, and the corresponding pressure in the pilot valve 50 rises (as described above with reference to Figure 16). The rising, controlled air is supplied to the air pad 27a (not shown) located below the circle at the top of the figure.

[0083] When a load F is applied and a gyro moment is generated on the front side, the pressure in the gap of the air pad 27a increases due to that force, pushing back the spindle main shaft 33, suppressing the tilt of the spindle main shaft 33 due to the load F, and the spindle main shaft 33 remains in a normal state. Meanwhile, the gap of nozzle 57a (not shown) on the left side of the upper part of the figure narrows, and the pressure of pilot valve 50 corresponding to nozzle 57a drops. The controlled air is supplied to air pad 27a (not shown) on the upper side of the circle in the upper part of the figure, and acts to pull back spindle main shaft 33. Even if the rotation direction of the spindle main shaft 33 is reversed and the gyro moment acts on the other side of the bottom of the figure, the explanation is the same except that the positional relationship between the pilot valve 50 and the air pad 27a changes, so it will be omitted.

[0084] In this way, the deviation X of the spindle main shaft 33 caused by the load F is detected by the nozzle flapper (pneumatic distance sensor) 57. The pressure inside the nozzle 57a changes depending on the distance from the flapper (in this invention, the circumferential side surface of the spindle main shaft) 57b, and the resulting pressure change is controlled by the pilot valve 50 to change the pressure on the air pad 27a. The gyro effect is compensated for by positioning the nozzle flapper 57 and the air pad 27a offset by 90 degrees.

[0085] FIG. 22 is a diagram illustrating the operation of compensating for the gyroscopic effect by another pilot valve. Figure 22 is a diagram similar to Figure 21, but unlike pilot valve 50, pilot valve 80 is structured so that when the output pressure of nozzle flapper 57 increases (the gap narrows), the output pressure of pilot valve 80 increases. In other words, it has the opposite characteristics to the pilot valve 50 described above. Therefore, the position of air pad 27a, the pressure of which is controlled by pilot valve 80, is different from that in Figure 21. The explanation of the operation of Figure 22 is similar to that of Figure 21, so details will be omitted.

[0086] In such a pilot valve 80, the connection between the nozzle flapper 57 and the pressure chamber 60 shown in FIG. 14 may be changed to the connection between the nozzle flapper 57 and the pressure chamber 59, for example. Various combinations can be selected for the relationship between the gap between the nozzle 57a and the spindle main shaft 33 and the increase or decrease in air pressure output from the pilot valve 50, the positional relationship between the nozzle 57a and the air pad 27a, and the like.

[0087] Figure 23 shows the operational flow of an air bearing that compensates for the gyroscopic effect. A load F is applied to the spindle main shaft 33, and the nozzle flapper detects the amount of misalignment X between the spindle main shaft 33 and the nozzle 57a. The air pressure is controlled by the pilot valve 50 or pilot valve 80, which serves as the pressure control means, and this pressure is output to the corresponding air pad 27a. The pressure changes, acting as a support force for the bearing to push back the load and offset it. In other words, the support force is fed back, and the amount of misalignment returns to normal.

[0088] By using the nozzle flapper 57 and the pilot valve 50, the spindle main shaft 33 can be supported without using any electrical control even when a load is generated and the spindle main shaft 33 tilts. This means that while magnetic bearings require large-scale equipment to control magnetism using electric current, radial and thrust air bearings can be controlled using only air pressure without using electricity. [Explanation of symbols]

[0089] 1 Spindle, 10 Pilot valve controlled pressure air supply port, 11 Nozzle flapper air supply port, 12 Radial air bearing air supply port, 13 Thrust air bearing air supply port, 14 Air exhaust port, 15, 15(1)~15(9) Housing, 20 Wiring outlet, 23 Connection hole, 24 Stopcock, 25 Connection hole, 26 Air supply hole (pilot valve), 27 Radial air bearing, 27a Air pad, 28 Flange, 29 Thrust air bearing, 29a Air pad, 30 Built-in motor, 30a Stator, 30b Rotor, 31 Tool mounting port, 32 Air nozzle, 33 Spindle main shaft, 35 Air supply Supply hole (radial air bearing), 36... air supply hole (thrust air bearing), 37... air supply hole (nozzle flapper), 50, 80... pilot valve, 51... diaphragm, 52... exhaust valve, 53... main valve, 54... exhaust valve section, 55... air supply valve section, 56... spring coil, 57... nozzle flapper, 57a... nozzle, 57b... Flapper, 59-62 First to fourth pressure chambers, 63 Air chamber (air bearing), 64 Air pressure supply source, 100 Spindle, 101 Rolling bearing (ball bearing), 102 Piezoelectric ceramics, 103 Spindle main shaft, 104 Shrink-fit chuck, 105 Cutting tool, 106 Ultrasonic oscillator, 107 Motor.

Claims

1. An air bearing spindle comprising: a spindle main shaft; a housing for accommodating the spindle main shaft; air bearing means for rotatably supporting the spindle main shaft via an air layer; air supply means for supplying air to the air bearing means via a pressurizing device, a pressure regulator, and a pressure control means; and rotation drive means for rotating the spindle main shaft, the air bearing means is attached to the housing and includes a plurality of radial air bearings for supporting a load in a direction perpendicular to the spindle main shaft and a thrust air bearing for supporting a load in the direction of the spindle main shaft; The radial air bearing comprises a plurality of distance sensors that measure the distance from the spindle main shaft, and a plurality of divided air pads that supply air to the gap between the spindle main shaft and the air layer to maintain the gap, and the distance sensor increases or decreases the pressure supplied to the air pads using the pressure control means depending on the distance from the spindle main shaft, and changes the pressure of the air pads at positions shifted circumferentially rather than the air pads at the same circumferential position as the distance sensors.

2. 2. The air bearing spindle according to claim 1, wherein the air pads of the radial air bearing have a three-dimensional shape that forms an annular sector divided into a plurality of sections along the circumferential direction, each of the divided air pads having a plurality of air nozzles and air supply holes that supply air to the air nozzles on the surface facing the spindle main shaft, and the air pad to which air whose pressure is controlled by the pressure control means connected to the distance sensor is supplied is the air pad that is shifted 90 degrees circumferentially from the distance sensor.

3. 3. An air bearing spindle according to claim 2, wherein said pressure control means is a diaphragm type pilot valve.

4. 4. The air bearing spindle according to claim 3, wherein the distance sensor is a nozzle flapper configured with a nozzle having a pressure detection port and the circumferential side surface of the spindle main shaft as a flapper, and the sensor controls the air pressure supplied to the air pad by the pilot valve connected to the nozzle, so that when the distance between the nozzle tip and the spindle main shaft becomes narrower, the pressure supplied to the air pad of the radial air bearing shifted 90 degrees in the circumferential direction from the distance sensor by the pressure control means decreases, and when the distance between the nozzle tip and the spindle main shaft becomes wider, the pressure supplied to the air pad of the radial air bearing shifted 90 degrees in the circumferential direction from the distance sensor by the pressure control means increases.

5. 5. An air bearing spindle as described in claim 4, wherein the air pads of the thrust air bearing are shaped to face both sides of a thick, disk-shaped flange machined integrally with the spindle main shaft, with an air layer gap between them, and the surface facing the flange is configured with a plurality of air nozzles and air supply holes for supplying air to the air nozzles.

6. 6. An air bearing spindle according to claim 1, wherein an ultrasonic oscillator is added to said air bearing spindle to form an air bearing ultrasonic spindle.

7. 7. An air bearing spindle according to claim 6, wherein the load state of a tool attached to the tip of the spindle main shaft is monitored by measuring the air pressure of said distance sensor.

8. An air bearing pressure control method for an air bearing spindle comprising a spindle main shaft, a housing for accommodating the spindle main shaft, air bearing means for rotatably supporting the spindle main shaft via an air layer, air supply means for supplying air to the air bearing means via a pressurizing device, a pressure regulator and pressure control means, and rotation drive means for rotating the spindle main shaft, comprising: the air bearing means is attached to the housing and includes a plurality of radial air bearings for supporting a load in a direction perpendicular to the spindle main shaft and a thrust air bearing for supporting a load in the direction of the spindle main shaft; a radial air bearing comprising a plurality of distance sensors that measure the distance from the spindle main shaft, and a plurality of divided air pads that supply air to gaps between the radial air bearing and the spindle main shaft to maintain the gap, and wherein the distance sensors increase or decrease the pressure supplied to the air pads by the pressure control means in accordance with the distance from the spindle main shaft, and change the pressure of the air pads at positions shifted circumferentially from the distance sensors rather than the air pads at the same circumferential position as the distance sensors.

9. 9. The air bearing pressure control method for an air bearing spindle according to claim 8, wherein the air pads of the radial air bearing have a three-dimensional shape that is annular sectorially divided into a plurality of sections along the circumferential direction, each of the divided air pads having a plurality of air nozzles and air supply holes for supplying the air to the air nozzles on the surface facing the spindle main shaft, and the air pad to which air whose pressure is controlled by the pressure control means connected to the distance sensor is supplied is the air pad that is shifted 90 degrees in the circumferential direction from the distance sensor.

10. 10. The air bearing pressure control method for an air bearing spindle according to claim 9, wherein said pressure control means is a diaphragm type pilot valve.

11. 11. The air bearing pressure control method for an air bearing spindle according to claim 10, wherein the distance sensor is a nozzle flapper configured with a nozzle having a pressure detection port and the circumferential side surface of the spindle main shaft as a flapper, and the sensor controls the air pressure supplied to the air pad by the pilot valve connected to the nozzle, so that when the distance between the nozzle tip and the spindle main shaft narrows, the pressure supplied to the air pad of the radial air bearing shifted 90 degrees circumferentially from the distance sensor by the pressure control means decreases, and when the distance between the nozzle tip and the spindle main shaft widens, the pressure supplied to the air pad of the radial air bearing shifted 90 degrees circumferentially from the distance sensor by the pressure control means increases.

12. 12. The air bearing pressure control method for an air bearing spindle according to claim 11, wherein the air pads of the thrust air bearing are shaped to face both sides of a thick, disk-shaped flange that is integrally machined with the spindle main shaft, with an air layer gap between them, and the surface facing the flange is configured with a plurality of air nozzles and air supply holes that supply air to the air nozzles.

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