Bearing device

Abstract

To provide a bearing device that does not dispose a measurement unit near a rotating member when supporting the rotating member by a rolling bearing and more accurately measure displacement of a radial direction or displacement of an axial direction of the rotating member.SOLUTION: A bearing device includes a displacement measurement unit that supports a rotating member by a fixing member via a rolling bearing, and measures displacement in a radial direction or displacement in an axial direction of the rotating member by supplying a compressed gas to a measured gap between the rotating member and the fixing member around the rolling bearing. The displacement measurement unit includes: a displacement detection unit having a compressed gas discharge nozzle discharging a compressed gas to the measured gap; a pressure loss measurement unit measuring pressure loss of a compressed gas supplied to the displacement detection unit; and a restriction member (differential pressure adjustment unit) provided near the rotating member and between the pressure loss measurement unit and the displacement detection unit. A supply source of the compressed gas is connected to a pipeline for connecting a high-pressure side of the pressure loss measurement unit and the restriction member, and a low-pressure side of the pressure loss measurement unit is connected to a pipeline for connecting the displacement detection unit and the restriction member.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a bearing device, and more particularly to a bearing device capable of detecting displacement of a rotating shaft supported by a rolling bearing and measuring an axial load.

Background Art

[0002] In the spindle of a machine tool, there is an increasing movement to control the cutting load and achieve higher machining speed, higher precision, and longer bearing life. As one of the measures, the need to measure the axial load during the operation of the machine tool is increasing. For example, Patent Document 1 discloses a technique for calculating an axial load by measuring an axial displacement amount with a non-contact sensor and multiplying it by a rigidity value of a bearing or the like, rather than directly measuring the axial load.

[0003] Patent Document 2 also discloses a technique for measuring and calculating the displacement and axial load of a shaft of a machine tool by using a differential pressure sensor arranged at a position separated from the machine tool.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technique described in Patent Document 1, when measuring the displacement of a rotating shaft using a non-contact sensor, it is necessary to arrange the non-contact sensor near the measurement part, and the circuits and wirings attached thereto also need to be arranged near the measurement part. In addition, appropriate measurement may not be possible due to the complexity of the internal structure of the machine tool, damage caused by adhesion of chips and cutting fluid during machining, and the like.

[0006] In the technology described in Patent Document 2, the differential pressure and axial load may not be accurately calculated depending on the installation position of the differential pressure sensor. The present invention aims to solve the above-mentioned problems by providing a bearing device that, when a rotating member is supported by a rolling bearing, does not require a measuring unit to be placed near the rotating member, and can more accurately measure the radial displacement (or axial displacement) of the rotating member. [Means for solving the problem]

[0007] To achieve the above objective, a bearing device according to one aspect of the present invention supports a rotating member on a stationary member via a rolling bearing, and includes a displacement measuring unit that measures the radial or axial displacement of the rotating member by supplying compressed gas to a gap to be measured between the rotating member and the stationary member around the rolling bearing, wherein the displacement measuring unit includes a displacement detection unit having a compressed gas discharge nozzle that discharges compressed gas into the gap to be measured, a pressure loss measuring unit that measures the pressure loss of the compressed gas supplied to the displacement detection unit, and a throttling member (differential pressure adjustment unit) provided near the rotating member and between the pressure loss measuring unit and the displacement detection unit. The compressed gas supply source is connected to a pipeline connecting the high-pressure side of the pressure loss measuring unit and the throttling member, and the low-pressure side of the pressure loss measuring unit is connected to a pipeline connecting the displacement detection unit and the throttling member.

[0008] Preferably, the pressure loss of the compressed gas is the differential pressure between the pressure of the compressed gas between the displacement detection unit and the throttling member and the pressure of the compressed gas output from the compressed gas supply source. Preferably, the installation position of the throttling member (relative position to the displacement detection unit) is fixed, and the installation position of the pressure loss measuring unit (relative position to the displacement detection unit) is movable. Preferably, the flow velocity of the compressed gas is zero from the point where the compressed gas supply source is connected to the pipeline connecting the high-pressure side of the pressure loss measurement unit and the throttling member, up to the high-pressure side of the pressure loss measurement unit. Also preferably, the flow velocity of the compressed gas is zero from the point where the low-pressure side of the pressure loss measurement unit is connected to the pipeline connecting the displacement detection unit and the throttling member, up to the low-pressure side of the pressure loss measurement unit.

[0009] The displacement detection unit may further include gas recovery grooves on one or both sides in the axial direction of the compressed gas discharge nozzle for recovering the compressed gas discharged from the compressed gas discharge nozzle into the gap to be measured. The displacement detection unit may further include a compressed gas discharge unit for discharging the compressed gas recovered in the gas recovery groove to the outside. The bearing device may further include a calculation processing unit that calculates the amount of load applied to the rotating member based on the differential pressure detected by the pressure loss measuring unit. According to another aspect of the present invention, a spindle device for a machine tool is provided, which includes the bearing device, the bearing device rotatably supports the spindle as the rotating member, and measures the load applied to the spindle. [Effects of the Invention]

[0010] According to the bearing device of the present invention, when a rotating member is supported by a rolling bearing, the radial or axial displacement of the rotating member can be measured using compressed gas, and the radial or axial displacement of the rotating member can be accurately measured regardless of the installation position of the differential pressure sensor. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing a first embodiment of a bearing device for a machine tool according to the present invention. [Figure 2] (a) is an enlarged axial cross-sectional view of the bearing device in Figure 1, and (b) is an enlarged cross-sectional view perpendicular to the axis of the bearing device in Figure 1. [Figure 3]It is a diagram showing the positional relationship between the rotating shaft, the throttle, and the differential pressure sensor in the first embodiment. [Figure 4] It is a diagram for explaining the case where the distance between the rotating shaft and the differential pressure sensor is large in the first embodiment. [Figure 5] It is a diagram showing the positional relationship between the rotating shaft, the throttle, and the differential pressure sensor in the comparative example. [Figure 6] It is a diagram for explaining the case where the distance between the rotating shaft and the differential pressure sensor is large in the comparative example. [Figure 7] It is a graph showing the relationship between the differential pressure and the supply air pressure obtained in the experiment using the configuration of the first embodiment. [Figure 8] It is a graph showing the relationship between the differential pressure and the supply air pressure obtained in the experiment using the configuration of the comparative example. [Figure 9] It is a schematic diagram showing the case where the spindle is supported by the bearing device of FIG. 1. [Figure 10] It is a diagram showing the bearing device of the second embodiment of the present invention, where (a) is an enlarged cross-sectional view in the axial direction and (b) is an enlarged cross-sectional view in the direction perpendicular to the axis. [Figure 11] It is an enlarged cross-sectional view in the axial direction showing the bearing device of the third embodiment of the present invention. [Figure 12] It is a cross-sectional view showing the rotating table of a machine tool to which the bearing device according to the present invention is applied. [Figure 13] It is a cross-sectional view showing the bearing device of the fourth embodiment of the present invention. [Figure 14] (a) is an enlarged cross-sectional view in the axial direction of the bearing device of FIG. 13, and (b) is an enlarged cross-sectional view in the direction perpendicular to the axis of the bearing device of FIG. 13. [Figure 15] It is a diagram showing a modified example of the fourth embodiment, where (a) is an enlarged cross-section when the compressed gas discharge nozzle is in an upward state, (b) is an enlarged cross-section when the compressed gas discharge nozzle is in a downward state, and (c) is an enlarged cross-section when the compressed gas discharge nozzle is in a right-handed rotation state on the radial line. [Figure 16] It is a cross-sectional view showing the bearing device of the fifth embodiment of the present invention, where (a) is an enlarged cross-sectional view in the axial direction and (b) is an enlarged cross-sectional view in the direction perpendicular to the axis. [Figure 17] It is an enlarged cross-sectional view showing a bearing device according to a sixth embodiment of the present invention.

Mode for Carrying Out the Invention

[0012] Embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thicknesses of each layer, etc. may be different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Also, there are portions where the dimensional relationships and ratios are different between the drawings. The embodiments shown below exemplify devices and methods for embodying the technical idea of the present invention, and do not specify the materials, shapes, structures, arrangements, etc. of the component parts of the device of the present invention as the following. The technical idea of the present invention can be subjected to various modifications, changes, and substitutions within the technical scope defined by the claims described in the claims.

[0013] First Embodiment A first embodiment of a bearing device (main shaft device) of a machine tool according to the present invention will be described with reference to FIGS. 1 and 2. The bearing device (main shaft device) 10 of the machine tool is of a motor built-in type, and a hollow rotating shaft (for example, a spindle) 21, which is a rotating member, is rotatably supported by a front rolling bearing 31 and a rear rolling bearing 41 in a housing (stationary member) 11. The rotating shaft 21 is rotationally driven by a drive motor 51 disposed between the front rolling bearing 31 and the rear rolling bearing 41.

[0014] The housing 11 is composed of a front cylindrical portion 12 and a rear cylindrical portion 13 that are divided into two parts between the front rolling bearing 31 and the drive motor 51. The front cylindrical portion 12 is composed of a small outer diameter portion 12a at the front, which has a smaller outer diameter, and a large outer diameter portion 12b at the rear, which has a larger outer diameter compared to the small outer diameter portion 12a. The inner circumferential surfaces of these small outer diameter portion 12a and large outer diameter portion 12b are formed to have the same inner diameter, but a bearing housing step portion 12c for housing the front rolling bearing 31 is formed from the front end to the rear end of the small outer diameter portion 12a. Conversely, the rear cylindrical portion 13 is formed by a large inner diameter portion 13a and a small inner diameter portion 13b with an inner diameter smaller than that of the large inner diameter portion 13a.

[0015] The front rolling bearing 31 consists of a pair of angular contact ball bearings 31a and 31b of substantially the same dimensions, arranged in a back-to-back configuration. These angular contact ball bearings 31a and 31b each include an outer ring 33 which is a stationary raceway, an inner ring 34 which is a rotating raceway, and a plurality of balls 35 which are rolling elements arranged at a contact angle between the outer ring raceway groove (stationary raceway) and the inner ring raceway groove (rotating raceway). In other words, each bearing 31a, 31b has an inner ring 34, an outer ring 33, and balls (rolling elements) 35 which are rotatably arranged between the inner ring 34 and the outer ring 33. Each bearing 31a, 31b may also be provided with a cage to hold the rolling elements. Each angular contact ball bearing 31a and 31b has its outer ring 33 fitted into a bearing housing step portion 12c formed in the front cylindrical portion 12 of the housing 11 via an outer ring spacer 36, and is fixed by a front bearing outer ring retainer 37 that is bolted to the front cylindrical portion 12 of the housing 11. Furthermore, the inner rings 34 of each angular contact ball bearing 31a and 31b are fitted onto the rotating shaft 21 via inner ring spacers 38 and fixed to the rotating shaft 21 by nuts 39 fastened to the rotating shaft 21. A fixed position preload is applied to the angular contact ball bearings 31a and 31b by the nuts 39. Therefore, the axial position of the rotating shaft 21 is positioned by the front rolling bearing 31.

[0016] The rear rolling bearing 41 is a cylindrical roller bearing and has an outer ring 42, an inner ring 43, and a plurality of cylindrical rollers 44 as rolling elements. The outer ring 42 of the rear rolling bearing 41 is fitted into the small inner diameter portion 13b of the rear cylindrical portion 13 of the housing 11 and is fixed to the small inner diameter portion 13b via an outer ring side spacer 46 by a rear bearing retainer 45 bolted to the small inner diameter portion 13b. The inner ring 43 of the rear rolling bearing 41 is fixed to the rotating shaft 21 via an inner ring side spacer 48 by a nut 47 fastened to the rotating shaft 21. The drive motor 51 consists of a stator 52 fitted inside the large inner diameter portion 13a of the rear cylindrical portion 13 of the housing 11, and a rotor 53 fitted outside the rotating shaft 21 which faces the inner circumference of the stator 52 with a gap in between.

[0017] The bearing device 10 of the machine tool having the above configuration is provided with a displacement measuring unit (load measuring unit) 60 for measuring the load applied to the rotating shaft 21. The displacement measuring unit 60 consists of a displacement detection unit 61 that uses compressed gas to detect the radial displacement of the rotating shaft 21, a pressure loss measuring unit 71 that measures the pressure loss of the compressed gas according to the gap between the outer ring spacer 36 and the inner ring spacer 38, and a differential pressure adjustment unit 70 that is connected to the compressed gas supply unit 80 and provided between the displacement detection unit 61 and the pressure loss measuring unit 71. In this embodiment, multiple sets of the displacement detection unit 61, differential pressure adjustment unit 70, and pressure loss measuring unit 71 are provided in the circumferential direction (two sets in Figure 1). The displacement measuring unit 60 also includes a calculation processing unit PU that calculates the load applied to the rotating shaft 21 based on the measurement results of each pressure loss measuring unit 71. The displacement measuring unit 60 can be positioned at any position in the axial direction of the rotating shaft 21. More preferably, the displacement measuring unit is positioned near the rear of the front row bearing, where the amount of axial displacement in response to the load is large and the effect of the extension of the axial length due to the installation of the displacement measuring unit is small. Compressed gas is supplied from one compressed gas supply unit 80 to each pair of differential pressure adjustment unit 70 and pressure loss measuring unit 71. Compressed gas is also supplied to the displacement detection unit 61 via the differential pressure adjustment unit 70. The compressed gas supply unit 80 is the source of compressed gas.

[0018] As shown in Figures 2(a) and 2(b), the displacement detection units 61 are formed at two locations in the small outer diameter portion 12a of the front cylindrical portion 12 of the housing 11, at least at a distance of, for example, 120° in the circumferential direction, so as not to face each other via the central axis. Figure 2(b) is a cross-sectional view taken along the BB arrow in Figure 2(a). Each of the displacement detection units 61 is configured to include an outer ring spacer 36 and an inner ring spacer 38 of the front rolling bearing 31. Specifically, the outer ring spacer 36 comprises an outer circumferential ring portion 36a that contacts the opposing axial end faces of the outer rings 33 of the angular contact ball bearings 31a and 31b, and an inner ring portion 36b that is narrower than the outer circumferential ring portion 36a.

[0019] The outer ring portion 36a has a recess 36c formed in the axial center that is recessed from the outside to the inside. The inner ring portion 36b is positioned so that its inner surface faces the outer surface of the inner ring spacer 38, forming a predetermined gap g to be measured. Then, a funnel-shaped compressed gas discharge nozzle 62 is formed that extends radially from the bottom of the recess 36c of the outer ring portion 36a to the inner circumferential surface, and compressed gas is discharged from the compressed gas discharge nozzle 62 into the gap g to be measured between the outer ring spacer 36 and the inner ring spacer 38. The rotating shaft of a machine tool (for example, a spindle) is often hollow in size because a drawbar is provided in the inner diameter of the shaft as a mechanism for gripping the tool, and it is also designed to rotate at high speeds to improve machining efficiency. For this reason, especially when used at high speeds, the rotating members such as the rotating shaft 21 and the inner ring spacer 38 expand by several to several tens of micrometers due to centrifugal force. Furthermore, a temperature difference occurs between the housing 11 and the rotating shaft 21 while the spindle is rotating, and in most cases the rotating shaft 21 becomes hotter, so the gap between the housing 11 and the rotating shaft 21 becomes smaller by several to several tens of micrometers.

[0020] Furthermore, in machine tool spindles, the gaps formed between the housing 11 and the rotating shaft 21, such as between the outer ring spacer 36 and the inner ring spacer 38, are set to a maximum of a few tenths of a millimeter to prevent foreign matter from entering the spindle interior and the rolling bearing 31. Therefore, the measured gap g between the outer ring spacer 36 and the inner ring spacer 38 is set to 0.05 mm to 0.5 mm when the rotating shaft 21 is stationary. However, since the change in pressure loss with respect to the radial displacement of the rotating shaft 21 increases as the gap size decreases, it is preferable to set the measured gap g to 0.05 mm to 0.2 mm.

[0021] In order to accurately measure the gap g between the outer ring spacer 36 and the inner ring spacer 38 during operation, it is desirable that the inner ring spacer 38 provided in the displacement detection unit 61 be as coaxial as possible with the rotation axis 21. For this reason, it is desirable that the inner ring spacer 38 be fitted to the axis by an intermediate fit or interference fit. A circular opening 63 is formed in the small outer diameter portion 12a of the housing 11, coaxially with the compressed gas discharge nozzle 62, extending from the outer circumferential surface to the recess 36c of the outer ring side spacer 36, and its inner diameter is reduced in two stages. As shown in Figure 1, one end of a compressed gas supply passage 64 formed in the front cylindrical portion 12 is open to the rear side wall of the opening 63. The other end of the compressed gas supply passage 64 communicates with a compressed gas supply passage 65 formed in the rear cylindrical portion 13, which opens to the rear end and extends forward in the axial direction, as shown in Figure 1.

[0022] As shown in Figures 2(a) and 2(b), a gas connection section 66 is installed inside the opening 63 as a gas direction changing unit that changes the direction of the compressed gas supplied from the compressed gas supply passage 64 from axial to radial before supplying it to the compressed gas discharge nozzle 62. The gas connection section 66 has a shape that can be fitted inside the opening 63, for example, an outer circumference shape that is the same as the inner circumference shape of the opening 63, and has a gas passage 66a that communicates with the opening 63 and a gas passage 66b that communicates with the gas passage 66a at one end and with the other end that communicates with the compressed gas discharge nozzle 62. O-rings 67, 67 are placed between the side wall of the gas connection section 66 and the inner wall of the opening 63, and an O-ring 68 is also placed between the bottom surface of the gas connection section 66 and the bottom surface of the recess 36c, and the O-rings 67, 67 and 68 prevent leakage of compressed air.

[0023] As shown in Figures 2(a) and 2(b), the gas connection portion 66 is positioned radially by the stepped portion on its outer circumferential surface contacting the stepped portion on the inner circumferential surface of the opening 63. Furthermore, the radially outer end face of the gas connection portion 66 contacts a retaining piece 69 that is screwed to the outer circumferential surface of the small outer diameter portion 12a, preventing it from coming out of the opening 63. It should be noted that the gas connection portion 66 is not limited to the method of fixing the gas connection portion 66 to the housing 11 using the retaining piece 69; a flange portion can also be formed on the outer circumferential surface side of the gas connection portion 66 and this flange portion can be screwed in. Furthermore, the displacement detection unit 61 is not limited to being installed at two locations in the circumferential direction of the housing 11, but may be installed at three or more locations in the circumferential direction, straddling the central axis and not facing each other. Also, since the compressed gas is discharged from the compressed gas discharge nozzle 62 into the gap between the outer ring side spacer 36 and the inner ring side spacer 38, it is preferable to arrange the displacement detection unit 61 at three or more locations at equal angular intervals in order to cancel the load on the rotating shaft 21 generated by the compressed gas.

[0024] As shown in Figure 1, compressed gas is supplied from a compressed gas supply unit 80 to the lubrication system (not shown) that supplies lubricating oil to the front rolling bearing 31 and the rear rolling bearing 41, using oil-air lubrication or oil mist lubrication. The compressed gas supply unit 80 includes a compressor 81 that discharges compressed gas, a regulator 82 for the lubrication system that regulates the pressure of the compressed gas discharged from the compressor 81, and a regulator 83 for measuring pressure loss, connected in parallel with the regulator 82. Reference numeral 80a indicates the connection point where the piping connecting the compressor 81 and the regulator 83 is connected to the piping from the regulator 82. Note that the supply of lubricating oil to the front rolling bearing 31 and the rear rolling bearing 41 is not limited to oil-air lubrication or oil mist lubrication. For example, grease lubrication may be used. Lubricating oil and grease are examples of lubricants. The lubrication system is a lubricant supply unit that supplies lubricant to the bearings 31 and 41.

[0025] The differential pressure adjustment unit 70 is connected to the compressed gas supply passage 65 of the housing 11 by a compressed gas supply passage (piping) 74. The differential pressure adjustment unit 70 has a throttle (throttling member) 72 inserted into the compressed gas supply passage 74, a first branch pipe 76a branching off from the first branching point 74a of the supply passage 74, and a second branch pipe 76b branching off from the second branching point 74b of the supply passage 74. The first branch pipe 76a extending from the first branch point 74a is connected to the low-pressure side of the differential pressure sensor 73, and the second branch pipe 76b extending from the second branch point 74b is connected to the high-pressure side of the differential pressure sensor 73. The first branch point 74a is the downstream branch point of the aperture 72, and the second branch point 74b is the upstream branch point of the aperture 72.

[0026] The pressure loss measurement unit 71 is connected to the differential pressure adjustment unit 70 by the first branch pipe 76a and the second branch pipe 76b. The differential pressure sensor 73 included in the pressure loss measurement unit 71 detects the difference (differential pressure) between the pressure on the upstream side and the pressure on the downstream side of the throttle 72. In other words, the differential pressure sensor 73 detects the differential pressure between the pressure of the compressed gas between the displacement detection unit 61 and the throttle 72 and the pressure of the compressed gas output from the compressed gas supply unit 80 as the pressure loss of the compressed gas. The compressed gas supply path 74 extends downward from the second branching point 74b and connects to the compressed gas supply unit 80 via the path merging point 74c. Therefore, the source pressure of the compressed gas supply unit 80 is input to the upstream side of the throttle 72. In such a compressed gas path (piping and branching), no flow velocity of compressed gas occurs between the first branching point 74a and the low-pressure side of the differential pressure sensor 73 (i.e., within the first branch pipeline 76a). Also, no flow velocity of compressed gas occurs between the second branching point 74b and the high-pressure side of the differential pressure sensor 73 (i.e., within the second branch pipeline 76b).

[0027] As shown in Figure 1, the throttle 72 is interposed in a pipe 74 that connects the regulator 83 and the opening of the compressed gas supply passage 65 formed in the housing 11. The amount of throttle 72 is set so that the differential pressure detected by the differential pressure sensor 73 when the radial displacement of the rotating shaft 21 is "0" during the rotation of the rotating shaft 21 becomes a preset value. As a result, the pressure downstream of the throttle 72 represents a pressure loss corresponding only to the radial displacement of the rotating shaft 21, taking into account the flow resistance due to the length and diameter of the pipe from the throttle 72 to the displacement detection unit 61.

[0028] The low-pressure side of the differential pressure sensor 73 is connected to the downstream pipe 74 of the restrictor 72 (connected to the first branch point 74a) via the first branch pipe 76a, and the high-pressure side of the differential pressure sensor 73 is connected to the upstream pipe 74 of the restrictor 72 via the second branch pipe 76b. The second branch point 74b, which is the junction of the second branch pipe 76b and the pipe (compressed gas supply path) 74, is connected to the regulator 83 via pipe 74. The differential pressure sensor 73 detects the differential pressure between the compressed air pressure supplied from the regulator 83 (pressure at the second branch point 74b) and the downstream pressure of the restrictor 72 connected to the displacement detection unit 61 (pressure at the first branch point 74a), that is, the pressure loss corresponding to the displacement of the rotating shaft 21 at the displacement detection unit 61, and outputs the detected differential pressure value as an analog or digital value. The arithmetic processing unit (PU) is composed of an arithmetic processing unit such as a microcomputer, and receives differential pressure detection values ​​output from the differential pressure sensors 73 of each pressure loss measurement unit 71. Based on these differential pressure detection values, it calculates the radial displacement of the rotating shaft 21. The arithmetic processing unit (PU) also calculates the load applied to the rotating shaft 21 by multiplying the calculated radial displacement of the rotating shaft 21 by a pre-calculated axial stiffness value at the axial position of the compressed gas discharge nozzle 62, and outputs the calculation result to the display unit DP for display. The axial stiffness value is calculated based on the load point, the bearing position of the front rolling bearing 31, the bearing stiffness, the axial stiffness, and the axial position of the compressed gas discharge nozzle 62 of the displacement detection unit 61.

[0029] Furthermore, the load applied to the rotating shaft 21 does not necessarily have to be calculated by the above-described calculation. For example, by repeatedly applying a known load to the rotating shaft 21 and measuring the differential pressure detected value output from the differential pressure sensor 73 of the pressure loss measurement unit 71 at that time, a load calculation map representing the relationship between the load and the differential pressure detected value is created and stored in the memory of the calculation processing unit PU. In this case, the load amount can be directly calculated (obtained) from the differential pressure detected value by referring to the load calculation map based on the differential pressure detected value detected by the differential pressure sensor 73 during cutting. In this way, there is no need to convert the differential pressure detected value of the differential pressure sensor 73 into a displacement amount, and the load amount can be easily calculated. At this time, instead of using the load calculation map, it is also possible to calculate the load amount by finding the equation of the characteristic line of the load calculation map and substituting the differential pressure detected value of the differential pressure sensor 73 into the obtained equation. Furthermore, as mentioned above, two or more sets of the displacement detection unit 61, differential pressure adjustment unit 70, and pressure loss measurement unit 71 are provided. Therefore, the combination of the differential pressure adjustment unit 70 and the pressure loss measurement unit 71 is connected in parallel to the regulator 83, as shown in Figure 1.

[0030] Next, the operation of the bearing device 10 of the first embodiment will be described. First, compressed gas is supplied from the compressed gas supply unit 80 to the differential pressure adjustment unit 70 and the pressure loss measurement unit 71. With the rotating shaft 21 of the machine tool bearing device 10 rotating, and the radial displacement of the rotating shaft 21 being "0", the amount of throttling of the throttle 72 of the differential pressure adjustment unit 70 is adjusted so that the differential pressure detected by the differential pressure sensor 73 becomes a preset value. Then, with the rotating shaft 21 of the bearing device 10 stopped, the compressor 81 is started to regulate the pressure of the compressed gas with the regulator 82, and the compressed gas at the set pressure is supplied to the lubrication oil supply system for the front rolling bearing 31 and the rear rolling bearing 41 (not shown), thereby starting the supply of lubricant to the front rolling bearing 31 and the rear rolling bearing 41.

[0031] Simultaneously, or before or after, the compressed gas discharged from the compressor 81 is regulated by the regulator 83 and supplied to the differential pressure adjustment unit 70 and the pressure loss measurement unit 71. The compressed gas supplied to the differential pressure adjustment unit 70 is introduced into the compressed gas supply passage 65 of the housing 11 via the throttle 72. The compressed gas introduced into the compressed gas supply passage 65 is redirected 90 degrees radially from the axial direction at the gas connection unit 66 from the compressed gas supply passage 64 and supplied to the compressed gas discharge nozzle 62. The compressed gas supplied to the compressed gas discharge nozzle 62 is supplied to the gap g to be measured between the outer ring spacer 36 and the inner ring spacer 38. When the gap g to be measured, i.e., the radial displacement of the rotating shaft 21, increases from a state of "0", the gap g to be measured decreases, and the pressure loss decreases accordingly. Conversely, when the radial displacement decreases, the gap g to be measured increases, and the pressure loss increases accordingly. As described above, when the rotating shaft 21 of the hollow shaft rotates at high speed, the rotating members such as the rotating shaft 21 and the inner ring spacer 38 increase due to centrifugal force, and the gap g to be measured decreases when the rotating shaft 21 becomes hotter relative to the housing 11.

[0032] Therefore, in an unloaded state where the radial displacement of the rotating shaft 21 is "0", the differential pressure detected by the differential pressure sensor 73 becomes a preset value, and the differential pressure detected value indicating that the radial displacement of the rotating shaft 21 is "0" is output to the arithmetic processing unit PU. Therefore, the processing unit (PU) converts the differential pressure detected by the differential pressure sensor (73) into a radial displacement of the rotating shaft (21), and calculates the load applied to the rotating shaft (21) by multiplying the converted radial displacement by a preset shaft stiffness value. The calculated load is output and displayed on the display unit (DP). In this case, since the radial displacement is "0", the load displayed on the display unit (DP) will be "0".

[0033] From this state, if cutting is started, for example, a cutting load will be applied to the rotating shaft 21, and a radial displacement corresponding to the cutting load will occur in the rotating shaft 21. The radial displacement depends on the direction of the cutting load applied to the rotating shaft 21. Therefore, in accordance with the radial displacement of the rotating shaft 21, a pressure loss occurs in the compressed gas discharged from the compressed gas discharge nozzles 62 of the multiple displacement detection units 61, corresponding to the radial displacement. This pressure loss is detected as a differential pressure value by the differential pressure sensor 73 of the pressure loss measurement unit 71. The detected differential pressure value is supplied to the arithmetic processing unit (PU). The PU converts the differential pressure value into a radial displacement of the rotating shaft 21, and multiplies the converted radial displacement by a preset shaft stiffness value to calculate the load applied to the rotating shaft 21. The calculated load is output to the display unit (DP) and displayed.

[0034] As described above, according to the bearing device 10 of the first embodiment, compressed gas is supplied to the displacement detection unit 61, which is composed of the outer ring spacer 36 and the inner ring spacer 38 of the front rolling bearing 31. As a result, compressed gas is discharged from the compressed gas discharge nozzle 62 into the gap g to be measured between the outer ring spacer 36 and the inner ring spacer 38. Therefore, a pressure loss of compressed gas occurs in accordance with the gap g to be measured, i.e., the radial displacement of the rotating shaft 21. The pressure loss is detected by the differential pressure sensor 73 of the pressure loss measurement unit 71 provided on the outside of the housing 11, and the detected differential pressure value is supplied to the calculation processing unit PU, thereby allowing the load applied to the rotating shaft 21 to be calculated.

[0035] Therefore, the displacement detection unit 61 can generate pressure loss corresponding to the radial displacement of the rotating shaft 21 with a simple configuration that only requires the provision of an outer ring side spacer 36 and an inner ring side spacer 38 facing each other via a predetermined gap g, a compressed gas supply passage 64, a gas connection part 66, and a compressed gas discharge nozzle 62. For this reason, the displacement detection unit 61 does not require any electrically operated parts, so there is no need to consider wiring or electrical insulation. Furthermore, the differential pressure adjustment unit 70 supplies compressed gas to the displacement detection unit 61 via the throttle 72, and the pressure loss measurement unit 71 detects the differential pressure between the pressure downstream of the throttle 72, i.e., the displacement detection unit 61 side, and the original pressure of the compressed gas supplied to the pressure loss measurement unit 71 (differential pressure adjustment unit 70), thereby measuring the pressure loss at the displacement detection unit 61.The detected differential pressure value can then be converted into the radial displacement of the rotating shaft 21 to calculate the load applied to the rotating shaft 21, or the load applied to the rotating shaft 21 can be calculated directly from the differential pressure.

[0036] Therefore, when the rotating shaft 21 is rotatably supported by rolling bearings, it is possible to calculate the radial displacement of the rotating shaft 21 or the load applied to the rotating shaft 21 using compressed gas with a simple configuration. Figure 3 is a simplified diagram of the configuration in Figure 1. In Figure 3, only one set of the displacement detection unit 61, differential pressure adjustment unit 70, and pressure loss measurement unit 71 is shown. The compressed gas supply unit 80 is also omitted. In this embodiment, in order to suppress the effect of the distance from the rotating shaft 21 to the pressure loss measurement unit 71 (effect in differential pressure measurement), the differential pressure adjustment unit 70 (throttle 72) and the pressure loss measurement unit 71 (differential pressure sensor 73) are separated, the differential pressure adjustment unit 70 is placed between the rotating shaft 21 and the pressure loss measurement unit 71, and the differential pressure adjustment unit 70 is provided within a predetermined distance from the rotating shaft 21, and compressed gas is supplied to the differential pressure adjustment unit 70. The differential pressure adjustment unit 70 and the pressure loss measurement unit 71 are connected by branch pipes 76a and 76b. Figure 9 shows the case where the rotating shaft 21 in Figure 3 is a spindle. In the configuration shown in Figure 9 (spindle device), the spindle, which is the rotating shaft member (spindle), is supported by bearings, and the load acting on the spindle can be measured.

[0037] As shown in Figure 3, a differential pressure adjustment unit 70 is provided at a distance L1 from the rotating shaft 21. Distance L1 is the distance at which the measurement accuracy required for the differential pressure sensor 73 can be ensured. A pressure loss measurement unit 71 is provided at a distance L2 from the differential pressure adjustment unit 70. Compressed gas supplied from the compressed gas supply unit 80 (Figure 1) flows through the piping 74 toward the second branching point 74b as indicated by arrow A1, flows to the left from the second branching point 74b (arrow A2), then passes through the throttle 72 and the first branching point 74a, and is supplied to the rotating shaft 21 (displacement detection unit 61) as indicated by arrow A3. The compressed gas is then supplied to the gap to be measured g (Figure 1), and a pressure change occurs in the gap to be measured g regardless of whether the rotating shaft 21 is rotating or not (the pressure decreases). The value of the decreased pressure is input to the low-pressure side of the differential pressure sensor 73 via the first branch pipe 76a. As described above, no compressed gas flow velocity is generated in the first branch pipe 76a from the first branch point 74a to the differential pressure sensor 73, so the pressure at the first branch point 74a becomes the low-pressure value of the differential pressure sensor 73. Similarly, no compressed gas flow velocity is generated in the second branch pipe 76b from the second branch point 74b to the differential pressure sensor 73, so the pressure at the second branch point 74b becomes the high-pressure value of the differential pressure sensor 73.

[0038] Here, we will explain the effect of pipe resistance in pipe 74 on pressure measurement values. Since the flow velocity of compressed gas is not zero in pipe 74, the compressed gas experiences resistance from pipe 74 as it flows through pipe 74. In this embodiment, this resistance is referred to as pipe resistance. As pipe resistance increases, the pressure value of the compressed gas in pipe 74 decreases. Therefore, if the length of pipe 74 is too long, the pressure value of the compressed gas in the gap g under measurement and the pressure value of the compressed gas measured by the differential pressure sensor 73 will diverge. In that case, the differential pressure sensor 73 cannot measure the pressure value in the gap g under measurement with high accuracy. Therefore, in this embodiment, the differential pressure adjustment unit 70 is installed near the rotating shaft 21 (at a distance L1), so that the pressure value input to the low-pressure side of the differential pressure sensor 73 becomes the pressure value at the first branching point 74a, and the pressure value input to the high-pressure side of the differential pressure sensor 73 becomes the pressure value at the second branching point 74b. In the pipeline 76a extending from the first branching point 74a to the low-pressure side of the differential pressure sensor 73, the flow velocity of the compressed gas is zero, so the pressure value at the first branching point 74a is directly input to the low-pressure side of the differential pressure sensor 73. The compressed gas is subjected to pipeline resistance in the pipeline 74 from the rotating shaft 21 to the first branching point 74a, but the differential pressure adjustment unit 70 is located near the rotating shaft 21, and in this embodiment, the pipeline length (distance L1) subjected to pipeline resistance is set to a distance that allows the pressure loss in the gap g under measurement to be input to the differential pressure sensor 73 with high accuracy. The pressure value input to the high-pressure side of the differential pressure sensor 73 is the pressure value at the second branching point 74b, and since the flow velocity of the compressed gas is zero in the pipeline 76b, the pressure value of the compressed gas supplied from the compressed gas supply unit 80 is input to the high-pressure side of the differential pressure sensor 73 with high accuracy.

[0039] The bearing device 10 of this embodiment is a device that converts a change in clearance g into a change in pressure loss due to that change and measures it as a differential pressure with the supply pressure. In other words, the bearing device 10 is a device for determining the change in clearance g from the measured differential pressure. The reference gap g for measurement is the gap g under no load and no rotation, and the reference differential pressure for measurement is the differential pressure under no load and no rotation. The variation in gap g includes three types of displacement: (a) axial displacement due to load, (b) centrifugal expansion and contraction due to rotation, and (c) thermal displacement. In other words, the variation in gap g is the sum of (a) + (b) + (c). (a) depends on external load fluctuations, (b) depends on rotational speed changes, and (c) depends on temperature changes. In order to measure each displacement, it is preferable to keep the other two parameters constant. In order to generate pressure loss in the gap g, it is necessary to ensure sufficient flow in the pipe 74. However, if the pipe 74 is made longer, the flow will be obstructed by pipe resistance, and the pressure loss due to the gap g will decrease. If the pipe 74 is too long, the flow velocity in the pipe 74 will eventually become zero, making differential pressure measurement impossible. In the pipeline where flow velocity is generated (mainly L1), pipeline resistance exists. If this resistance is too great, the flow is obstructed, reducing the change in pressure loss due to changes in gap g, and ultimately preventing differential pressure from being generated (gas stops flowing in pipeline 74). In this embodiment, the distance L1 is determined so that the pipeline resistance generated at distance L1 does not affect the accuracy of pressure measurement. Furthermore, the greater the change in pressure loss due to the change in gap g, the higher the measurement accuracy of the change in gap g. Therefore, a shorter distance L1 is preferable. However, when actually installing the pressure adjustment section 70 (throttle 72), a certain amount of piping (mainly L1) may be necessary. Since the calibration value of the gap (calibration value of the differential pressure) changes when the piping 74 changes, it is preferable to fix the piping (L1).

[0040] Figure 4 shows the case where the distance between the differential pressure adjustment unit 70 and the pressure loss measurement unit 71 is increased. Specifically, it shows the case where the distance between the differential pressure adjustment unit 70 and the pressure loss measurement unit 71 is increased by an extension distance L3 compared to Figure 3. Depending on the type, application, size, and installation location of the machine tool within the factory, the installation location of the pressure loss measurement unit 71 may be quite far from the rotating shaft 21 (for example, several tens of meters). Also, if the rotating shaft 21 is a spindle, the spindle itself may move, so the pipeline (path) between the rotating shaft 21 and the pressure loss measurement unit 71 must be changed as appropriate. Even when the pressure loss measurement unit 71 is installed far from the rotating shaft 21 as shown in Figure 4, in this embodiment, only the first branch pipeline 76a and the second branch pipeline 76b are extended. Since the flow velocity of compressed gas in the first branch pipe 76a and the second branch pipe 76b is zero, the pressure value input to the differential pressure sensor 73 is not affected by the length of the first branch pipe 76a or the second branch pipe 76b. Therefore, the measurement accuracy of the differential pressure sensor 73 does not decrease depending on the installation position of the pressure loss measurement unit 71 (relative position to the displacement detection unit 61). In other words, it is possible to freely change the distance between the rotating shaft 21 and the pressure loss measurement unit 71.

[0041] Figures 5 and 6 show comparative examples to illustrate the effects of this embodiment. Figure 5 corresponds to Figure 3, and Figure 6 corresponds to Figure 4. In the comparative example, the throttle 72 and the differential pressure sensor 73 are housed in the same housing (the throttle 72 is located inside the pressure loss measuring unit 71), and the position of the throttle 72 and the position of the differential pressure sensor 73 are substantially the same. Reference numeral 74e indicates the connection point where the piping downstream of the throttle 72 is connected to the piping on the low-pressure side of the differential pressure sensor 73. Reference numeral 74f indicates the connection point where the piping connecting the upstream side of the throttle 72 and the high-pressure side of the differential pressure sensor 73 is connected to piping from a compressed gas supply source (not shown). In the comparative example, when the distance from the rotating shaft 21 to the pressure loss measurement unit 71 is short (for example, when the distance is only L1), the effect of the pipe resistance of the pipe 74 on the pressure measurement value is almost negligible. In other words, when the pipe resistance is small, as shown in Figure 5, the accuracy of the pressure measurement value is almost the same between the comparative example and the embodiment of the present invention (Figure 3). However, as shown in Figure 6, when the distance from the rotating shaft 21 to the pressure loss measurement unit 71 becomes longer (for example, L1 + L2 + L3), the pipe length increases, which increases the pipe resistance and reduces the accuracy of the pressure measurement value at the differential pressure sensor 73. In the case of Figure 6, the flow velocity of the compressed gas is generated between the throttle 72 and the rotating shaft 21, so the distance over which the compressed gas experiences flow velocity resistance is long. As a result, the pressure measurement value on the low-pressure side of the differential pressure sensor 73 decreases. Depending on the installation position of the pressure loss measurement unit 71, it is conceivable that the pipe resistance may become excessive, preventing the compressed gas that should flow through the pipe 74 from flowing, making it impossible to measure the differential pressure at the differential pressure sensor 73.

[0042] Next, experimental results regarding the effects of the configuration of the embodiment of the present invention (Figures 3 and 4) and the configuration of the comparative example (Figures 5 and 6) will be explained using Figures 7 and 8. In this experiment, the gap g was fixed, and the pressure of the supplied compressed gas was varied to measure the differential pressure. Although it would also be possible to fix the pressure of the supplied compressed gas and vary the gap g to measure the differential pressure, the only requirement is to understand the effect of pipe resistance due to the distance L3, so the gap g was fixed and the pressure of the compressed gas was varied to measure the differential pressure. The graph in Figure 7 shows the experimental results when using the configuration of this embodiment, and the graph in Figure 8 shows the experimental results when using the configuration of the comparative example. In the graphs of Figures 7 and 8, the horizontal axis represents the pressure of the compressed gas supplied by the compressed gas supply unit 80 (supply air pressure), and the vertical axis represents the differential pressure measured by the differential pressure sensor 73. In the graph of Figure 7, □ represents the differential pressure value when the distance from the rotating shaft 21 to the differential pressure sensor 73 is short (arrangement in Figure 3), and △ represents the differential pressure value when the distance from the rotating shaft 21 to the differential pressure sensor 73 is long (arrangement in Figure 4). Similarly, in the graph of Figure 8, □ represents the pressure value when the distance from the rotating shaft 21 to the differential pressure sensor 73 is short (arrangement in Figure 5), and △ represents the pressure value when the distance from the rotating shaft 21 to the differential pressure sensor 73 is long (arrangement in Figure 6).

[0043] As can be seen from Figure 7, in the configuration of this embodiment, the square and triangle overlap. In other words, even if the distance from the rotating shaft 21 to the differential pressure sensor 73 increases, the differential pressure measurement value at the differential pressure sensor 73 does not change. On the other hand, as can be seen from Figure 8, in the configuration of the comparative example, the square and triangle do not overlap (the triangle is below the square). In other words, as the distance from the rotating shaft 21 to the differential pressure sensor 73 increases, the differential pressure measurement value at the differential pressure sensor 73 changes from square to triangle due to the effect of pipe resistance. Therefore, in the configuration of the comparative example, as the distance from the rotating shaft 21 to the differential pressure sensor 73 increases, the accuracy of the output value of the differential pressure sensor 73 decreases. Thus, in the configuration of the comparative example (Figure 6), the pipe resistance increases due to the addition of distance L3, which hinders the flow of compressed gas in the pipe 74 and reduces the pressure loss due to the gap g. As a result, the differential pressure becomes smaller (the accuracy of the output value of the differential pressure sensor 73 decreases). In the configuration of this embodiment, the accuracy of the output value of the differential pressure sensor 73 does not decrease. In this embodiment, the position of the differential pressure adjustment unit 70 (throttle 72) as viewed from the rotating shaft 21 is fixed within a range up to a distance L1. In other words, the installation position of the throttle 72 (relative position to the displacement detection unit 61) is fixed within a range up to a distance L1. This is because if the differential pressure adjustment unit 70 (throttle 72) is installed at a position beyond the distance L1, the accuracy of pressure measurement cannot be ensured. On the other hand, the position of the pressure loss measurement unit 71 as viewed from the rotating shaft 21 is movable. This is because the position of the pressure loss measurement unit 71 does not affect the accuracy of pressure measurement. As described above, these test results show that the pipe resistance of pipe 74 makes it difficult for pressure loss due to gap g to occur. When pressure loss due to gap g is reduced, the differential pressure change due to changes in gap g becomes smaller, which lowers the measurement accuracy of the change in gap g. In this embodiment, such a decrease in measurement accuracy is prevented and suppressed.

[0044] Furthermore, compared to the configuration of the comparative example, the configuration of this embodiment has the following advantages. Specifically, in the comparative example (Figure 5), the throttle 72 is built into the pressure loss measurement unit 71 together with the differential pressure sensor 73 (provided in the same housing). While attaching the pressure loss measurement unit 71 to the rotating shaft 21 can reduce pipeline resistance, the differential pressure sensor 73 provided in the pressure loss measurement unit 71 rotates together with the rotating shaft 21. If the differential pressure sensor 73 measures the differential pressure while rotating, measurement errors may occur or the differential pressure sensor 73 may malfunction. In contrast, in the configuration of this embodiment, the differential pressure adjustment unit 70 (throttle 72) is attached to the rotating shaft 21, and the differential pressure sensor 73 (pressure loss measurement unit 71) can be provided at a position away from the rotating shaft 21. The throttle 72 is a mechanical part and is less affected by the rotation even if it rotates together with the rotating shaft 21. Thus, according to the configuration of this embodiment, only the differential pressure sensor 73, which is susceptible to the effects of rotation, can be installed away from the rotating shaft 21. As a result, piping of the required length can be used depending on the application of the machine tool.

[0045] In the first embodiment described above (Figure 1), the case in which compressed gas supply passages 64 and 65 extending axially within the housing 11 are formed was explained. However, the first embodiment is not limited to this configuration. The gas passage 66b of the gas connection portion 66 may be extended to the outer circumference and opened, and the differential pressure adjustment portion 70 may be connected to this opening. Alternatively, the compressed gas supply passage 65 may be omitted, and the compressed gas supply passage 64 may be opened on the outer circumference of the small outer diameter portion 12a, and the differential pressure adjustment portion 70 may be connected to this opening.

[0046] Furthermore, in the first embodiment described above (Figure 1), while the rotating shaft 21 of the bearing device 10 of the machine tool is rotating, and the radial displacement of the rotating shaft 21 is "0", the amount of restriction of the throttle 72 of the differential pressure adjustment unit 70 is adjusted so that the differential pressure detected by the differential pressure sensor 73 becomes a preset value. However, the first embodiment is not limited to this adjustment. For example, with the rotating shaft 21 of the bearing device 10 stopped without external load (0 rotations), the differential pressure of each pressure loss measurement unit 71 is adjusted to a certain value by the throttle 72 of the differential pressure adjustment unit 70, and this state is set as displacement 0. Then, when the rotation speed of the rotating shaft 21 is changed, the differential pressure of each pressure loss measurement unit 71 changes according to the rotation speed of the rotating shaft 21, and the differential pressure set as displacement 0 is offset by the same amount. Then, after the rotation speed has stabilized, a trigger signal is given from the outside in the same no-load state as above, and the value at that time is set to "0" again. As a result, if the rotation of the rotating shaft 21 is constant, measurements can be taken at different rotational speeds in the same way as in the first embodiment. In Figure 1, the differential pressure adjustment unit 70 is shown to be installed at a distance L1 from the rotating shaft 21. However, as described above, the differential pressure adjustment unit 70 may be attached to the rotating shaft 21 and rotate together with it. In other words, the distance L1 may be zero. In this specification, "nearby" includes contact (including cases where the distance L1 is greater than zero and cases where it is zero).

[0047] Second Embodiment Next, a second embodiment of the bearing device (spindle device) according to the present invention will be described with reference to Figure 10. Components similar to those in the first embodiment (for example, the differential pressure adjustment unit 70, the pressure loss measurement unit 71, the compressed gas supply unit 80, the piping 74, etc.) will not be shown or described, and the differences from the first embodiment will be explained.

[0048] The second embodiment employs a configuration that suppresses the influence of compressed gas on the front rolling bearing. More specifically, in the second embodiment, as shown in Figures 10(a) and 10(b), three displacement detection units 61 are provided at equal intervals in the circumferential direction. In each displacement detection unit 61, gas recovery grooves 81a and 81b are formed in the circumferential direction on the front and rear sides of the compressed gas discharge nozzle 62, respectively, on the inner surface of the outer ring spacer 36 which faces the outer surface of the inner ring spacer 38 via a gap g to be measured. As shown in the lower part of Figure 10(a) and Figure 10(b), cavities 86 communicating with the gas recovery grooves 81a and 81b are formed in each displacement detection unit 61 of the outer ring spacer 36 at positions facing each other across the central axis. On the other hand, a gas discharge passage 87a is formed at a position opposite the cavity 86 of the small outer diameter portion 12a, communicating with the cavity 86 and extending radially. Another gas discharge passage 87b is formed, with one end communicating with the gas discharge passage 87a and the other end opening to the front end. The gas recovery grooves 81a, 81b, the cavity 86, and the gas discharge passages 87a and 87b constitute a compressed gas discharge passage (compressed gas discharge section). The gas discharge passages 87a and 87b can be referred to as drain sections that discharge compressed gas to the outside of the bearing device.

[0049] According to the second embodiment, the compressed air discharged from the compressed gas discharge nozzle 62 of the displacement detection unit 61 into the gap g to be measured between the inner surface of the outer ring spacer 36 and the outer surface of the inner ring spacer 38 expands in the front-rear and circumferential directions and flows through the gap g to be measured. The compressed gas that has expanded in the front-rear direction flows into the gas recovery grooves 81a and 81b, and the gas flows through the gas recovery grooves 81a and 81b in the circumferential direction of Figure 10(b) in clockwise and counterclockwise directions to reach the cavity 86. From the cavity 86, the gas is discharged to the outside from the front end surface of the small outer diameter portion 12a through the gas discharge passages 87a and 87b of the small outer diameter portion 12a.

[0050] Therefore, it is possible to prevent compressed gas injected from the compressed gas discharge nozzle 62 from flowing into the space between the outer ring 33 and inner ring 34 of the angular contact ball bearings 31a and 31b, which are positioned in front of and behind the outer ring spacer 36 and the inner ring spacer 38. As a result, the effects of compressed gas flowing into the angular contact ball bearings 31a and 31b, i.e., the effects on oil-air lubrication and oil-mist lubrication of the angular contact ball bearings, can be reduced or prevented. Furthermore, the same effects as in the first embodiment can be obtained in this embodiment as well. That is, the pressure value input to the differential pressure sensor 73 is not affected by the distance from the rotating shaft 21 to the differential pressure sensor 73. As a result, the measurement accuracy of the differential pressure sensor 73 does not decrease depending on the installation position of the pressure loss measurement unit 71. Therefore, it becomes possible to freely change the distance between the rotating shaft 21 and the pressure loss measurement unit 71.

[0051] Third Embodiment Next, a fourth embodiment of the bearing device according to the present invention will be described with reference to Figure 11. Components similar to those of the first embodiment (for example, the differential pressure adjustment unit 70, the pressure loss measurement unit 71, the compressed gas supply unit 80, the piping 74, etc.) will not be shown or described, and the differences from the first embodiment will be explained. In the third embodiment, the displacement detection unit 61 is formed not as a spacer between the front rolling bearings 31, but at a position adjacent to the front rolling bearings 31 in the axial direction. In other words, in the third embodiment, as shown in Figure 11, the displacement detection unit 61 is positioned adjacent to the rear side of the rear angular contact ball bearing 31b that constitutes the front rolling bearing 31. Therefore, the bearing housing step portion 12c formed on the inner circumferential surface of the front cylindrical portion 12 of the housing 11 extends rearward from the angular contact ball bearing 31b that constitutes the front rolling bearing 31.

[0052] The displacement detection unit 61 has an outer ring side spacer 96, which has the same shape as the outer ring side spacer 36 in the first and second embodiments, positioned on the extension of the bearing housing step portion 12c, and the inner circumferential surface of the outer ring side spacer 96 is facing the outer circumferential surface of the rotating shaft 21 so as to form a predetermined gap g to be measured. The outer ring spacer 96 is equipped with the same outer ring spacer 36 as the outer ring spacer 36, including an outer ring portion 96a, an inner ring portion 96b, a recess 96c, and a compressed gas discharge nozzle 97. Furthermore, an opening 98 similar to the opening 63 is formed at a position opposite the outer ring side spacer 96 of the small outer diameter portion 12a of the housing 11, and a gas connection portion 99 is installed inside the opening 98, with gas passages 99a and 99b similar to those of the gas connection portion 66. Although not shown in the figures, the third embodiment also includes a gas recovery channel for recovering compressed gas and a gas discharge passage for discharging compressed gas to the outside, as described in the second embodiment.

[0053] According to the third embodiment, the displacement detection unit 61 itself operates in the same manner as in the first embodiment, and therefore can exhibit the same effects as in the first embodiment. That is, the pressure value input to the differential pressure sensor 73 is not affected by the distance from the rotating shaft 21 to the differential pressure sensor 73. As a result, the measurement accuracy of the differential pressure sensor 73 does not decrease depending on the installation position of the pressure loss measurement unit 71. Therefore, it is possible to freely change the distance between the rotating shaft 21 and the pressure loss measurement unit 71. Furthermore, in the third embodiment, as in the first and second embodiments, the compressed gas is discharged from the outer ring side spacer 96 directly into the gap g to be measured, which is formed between the outer ring side spacer and the rotating shaft 21, rather than into the inner spacer. Therefore, as in the first and second embodiments, the effect of misalignment between the rotating shaft 21 and the inner ring side spacer, which is a problem when using an inner ring side spacer that rotates integrally with the rotating shaft 21, is eliminated, and the shape accuracy of the gap g to be measured can be improved. Note that the first to third embodiments may be combined as appropriate within a non-contradictory range.

[0054] In the first to third embodiments, the bearing device 10 according to the present invention was described in the case where it is applied to the spindle device of a machine tool, but the application of the present invention is not limited to this. For example, the present invention can also be applied to a rotary table device 131 of a machine tool in which a rotary table 130 is arranged at the upper end of the rotating shaft 21 shown in Figure 12. In Figure 12, the same reference numerals are used for parts corresponding to those in Figure 1, and detailed explanations are omitted.

[0055] Fourth Embodiment Next, a fourth embodiment of the bearing device for a machine tool according to the present invention will be described with reference to Figures 13, 14, and 15. In the fourth embodiment, axial displacement is measured. Note that the same reference numerals are used for components and parts that are the same as in the first embodiment. The bearing device (spindle device) 10A of the machine tool is of a motor-built-in type, in which a hollow rotating shaft (spindle) 21, which is a rotating member, is rotatably supported by a front rolling bearing 31 and a rear rolling bearing 41 that constitute the bearing device, on a housing 11, which is a fixed member (stationary member). The rotating shaft 21 is rotationally driven by a drive motor 51 positioned between the front rolling bearing 31 and the rear rolling bearing 41.

[0056] The housing 11 is composed of a front cylindrical section 12 and a rear cylindrical section 13, which are divided between the front rolling bearing 31 and the drive motor 51. The front cylindrical portion 12 is composed of a small outer diameter portion 12a at the front, which has a smaller outer diameter, and a large outer diameter portion 12b at the rear, which has a larger outer diameter compared to the small outer diameter portion 12a. The inner circumferential surfaces of the small outer diameter portion 12a and the large outer diameter portion 12b are formed to have the same inner diameter, but a bearing housing step portion 12c for housing the front rolling bearing 31 is formed from the front end to the rear end of the small outer diameter portion 12a. The rear cylindrical portion 13 is formed by a large inner diameter portion 13a with a larger inner diameter and a small inner diameter portion 13b with an inner diameter smaller than that of the large inner diameter portion 13a.

[0057] The front rolling bearing 31 consists of a pair of angular contact ball bearings 31a and 31b of substantially the same dimensions, arranged in a back-to-back configuration. These angular contact ball bearings 31a and 31b each include an outer ring 33 which is a stationary raceway, an inner ring 34 which is a rotating raceway, and a plurality of balls 35 which are rolling elements arranged at a contact angle between the outer ring raceway groove (stationary raceway) and the inner ring raceway groove (rotating raceway). In other words, each bearing 31a, 31b has an inner ring 34, an outer ring 33, and balls (rolling elements) 35 which are rotatably arranged between the inner ring 34 and the outer ring 33. Each bearing 31a, 31b may also be provided with a cage to hold the rolling elements. Each angular contact ball bearing 31a and 31b has its outer ring 33 fitted into a bearing housing step portion 12c formed in the front cylindrical portion 12 of the housing 11 via an outer ring spacer 36, and is fixed by a front bearing outer ring retainer 37 that is bolted to the front cylindrical portion 12 of the housing 11. Furthermore, the inner rings 34 of each angular contact ball bearing 31a and 31b are fitted onto the rotating shaft 21 via inner ring spacers 38 and fixed to the rotating shaft 21 by nuts 39 fastened to the rotating shaft 21. The angular contact ball bearings 31a and 31b are subjected to a fixed position preload by the nuts 39. Therefore, the axial position of the rotating shaft 21 is positioned by the front rolling bearing 31.

[0058] The rear rolling bearing 41 is a cylindrical roller bearing and has an outer ring 42, an inner ring 43, and a plurality of cylindrical rollers 44 as rolling elements. The outer ring 42 of the rear rolling bearing 41 is fitted into the small inner diameter portion 13b of the rear cylindrical portion 13 of the housing 11 and is fixed to the small inner diameter portion 13b via an outer ring side spacer 46 by a rear bearing retainer 45 bolted to the small inner diameter portion 13b. The inner ring 43 of the rear rolling bearing 41 is fixed to the rotating shaft 21 via an inner ring side spacer 48 by another nut 47 fastened to the rotating shaft 21. The drive motor 51 consists of a stator 52 fitted inside the large inner diameter portion 13a of the rear cylindrical portion 13 of the housing 11, and a rotor 53 fitted outside the rotating shaft 21 which faces the inner circumference of the stator 52 with a gap in between.

[0059] Furthermore, the bearing device 10A of the machine tool having the above configuration is provided with a displacement measuring unit 60A for measuring the axial load acting on the rotating shaft 21. The displacement measuring unit 60A consists of a displacement detection unit 61A that uses compressed gas to detect the axial displacement of the rotating shaft 21, a pressure loss measuring unit 71 that measures the pressure loss of the compressed gas according to the gap between the outer ring spacer 36 and the inner ring spacer 38, and a differential pressure adjustment unit 70 that is connected to the compressed gas supply unit 80 and provided between the displacement detection unit 61A and the pressure loss measuring unit 71. At least one set of the displacement detection unit 61A, the differential pressure adjustment unit 70, and the pressure loss measuring unit 71 is provided in the circumferential direction of the housing 11. The displacement measuring unit 60A is equipped with a calculation processing unit PU that calculates the axial load acting on the rotating shaft 21 based on the measurement results of the pressure loss measuring unit 71. Compressed gas is supplied from a single compressed gas supply unit 80 to each set of displacement detection unit 61A, differential pressure adjustment unit 70, and pressure loss measurement unit 71.

[0060] As shown in Figures 14(a) and 14(b), the displacement detection unit 61A is formed at least at one location in the circumferential direction on the small outer diameter portion 12a of the front cylindrical portion 12 of the housing 11. Figure 14(b) is a cross-sectional view taken along the CC arrow in Figure 13. The displacement detection unit 61A is configured to include an outer ring spacer 36 and an inner ring spacer 38 of the front rolling bearing 31. Specifically, the outer ring spacer 36 comprises an outer circumference ring portion 36a that contacts the opposing axial end faces of the outer rings 33 of the angular contact ball bearings 31a and 31b, and an inner circumference ring portion 36b that is narrower than the outer circumference ring portion 36a. The outer ring portion 36a has a recess 36c formed in the axial center that is recessed from the outside to the inside. The inner ring portion 36b has a circumferential groove 36d formed between the outer ring 33 and inner ring 34 of the angular contact ball bearing 31a.

[0061] The inner ring spacer 38 consists of a cylindrical portion 38a fitted onto the rotating shaft 21, and an annular projection 38b with a rectangular cross-section that protrudes outward from the front end of the cylindrical portion 38a and extends into the circumferential groove 36d of the outer ring spacer 36. As shown in Figure 14(a), the gap to be measured g is formed on the axially opposing surfaces of the left side surface of the outer ring spacer 36 that forms the circumferential groove 36d and the right side surface of the annular projection 38b of the inner ring spacer 38. Furthermore, the gap between the bottom surface of the circumferential groove 36d and the outer surface of the annular projection 38b is set to the same gap as the gap to be measured g. Similarly, the gap between the inner surface of the outer ring spacer 36 and the outer surface of the cylindrical portion 38a of the inner ring spacer 38 is also formed to the same gap as the gap to be measured g. However, in this embodiment, gaps other than the gap to be measured g between the outer ring spacer 36 and the inner ring spacer 38 do not need to be matched to the gap to be measured g, and can be larger than the gap to be measured g.

[0062] The outer ring spacer 36 has a gas passage 36e that extends radially from the bottom surface of the recess 36c toward the inner circumferential surface, and a compressed gas discharge nozzle 62A is formed that opens axially toward the gap g to be measured toward the right side of the circumferential groove 36d from the tip of the gas passage 36e. Compressed gas is discharged from the compressed gas discharge nozzle 62A into the gap g to be measured between the circumferential groove 36d of the outer ring spacer 36 and the annular projection 38b of the inner ring spacer 38. The spindle of a machine tool is sometimes rotated at high speed to improve machining efficiency. Therefore, especially during spindle rotation, a temperature difference occurs between the housing 11 and the rotating shaft 21. In most cases, the rotating shaft 21 becomes hotter, causing the axial clearance between the housing 11 and the rotating shaft 21 to decrease by several to several tens of micrometers. The center of relative axial expansion due to the temperature difference varies depending on the fixing method, such as bearings, so the direction of the expansion changes each time. Furthermore, due to the effects of centrifugal force, the rotating shaft 21 may contract axially, and depending on the preloading method of the bearings (31a, 31b), the contact angle may change, causing the rotating shaft 21 to be displaced relative to the housing 11 by several to several tens of micrometers in the axial direction.

[0063] Furthermore, in the spindle of a machine tool, the gaps formed between the housing 11 and the rotating shaft 21, such as between the outer ring spacer 36 and the inner ring spacer 38, are set to a maximum of a few tenths of a millimeter in order to prevent foreign matter from entering the inside of the spindle or the rolling bearing 31. In machine tool spindles, an axial gap (restriction) is sometimes formed between the housing and the rotating body to prevent foreign matter from entering the spindle interior or bearings. In such cases, the size of this gap is set to be at most a few tenths of a millimeter. Therefore, the measured gap g between the outer ring spacer 36 and the inner ring spacer 38 is set to 0.05 mm to 0.5 mm when the rotating shaft 21 is stationary. However, since the change in pressure loss with respect to the axial displacement of the rotating shaft 21 increases as the gap size decreases, it is preferable to set the measured gap g to 0.05 mm to 0.2 mm.

[0064] In order to accurately measure the gap g between the outer ring spacer 36 and the inner ring spacer 38 during operation, it is desirable that the inner ring spacer 38 provided in the displacement detection unit 61A be as coaxial as possible with the rotation axis 21. In the small outer diameter portion 12a of the housing 11, a circular opening 63 is formed coaxially with the gas passage 36e, extending from the outer circumferential surface to the recess 36c of the outer ring side spacer 36, and its inner diameter is reduced in two stages. As shown in Figure 13, one end of a compressed gas supply passage 64 formed in the front cylindrical portion 12 opens into the rear side wall of the opening 63. The other end of the compressed gas supply passage 64 communicates with a compressed gas supply passage 65 formed in the rear cylindrical portion 13, which opens at the rear end and extends forward in the axial direction.

[0065] Furthermore, as shown in Figures 14(a) and 14(b), a gas connection section 66 is installed inside the opening 63, which serves as a gas direction changing section that changes the direction of the compressed gas supplied from the compressed gas supply passage 64 from axial to radial and supplies it to the compressed gas discharge nozzle 62A via the gas passage 36e of the outer ring side spacer 36. The gas connection portion 66 has a shape that can be fitted into the opening 63, for example, an outer circumference shape identical to the inner circumference shape of the opening 63, and has a gas passage 66a that communicates with the opening 63 and a gas passage 66b that communicates with the gas passage 66a at one end and with the other end communicating with the compressed gas discharge nozzle 62A. An O-ring 67 is placed between the side wall of the gas connection portion 66 and the inner wall of the opening 63, and an O-ring 68 is similarly placed between the bottom surface of the gas connection portion 66 and the bottom surface of the recess 36c, and these O-rings 67 and 68 prevent leakage of compressed air.

[0066] Furthermore, as shown in Figures 14(a) and 14(b), the gas connection portion 66 is positioned radially by the stepped portion on its outer circumferential surface contacting the stepped portion on the inner circumferential surface of the opening 63. In addition, the radially outer end face of the gas connection portion 66 contacts a retaining piece 69 that is screwed to the outer circumferential surface of the small outer diameter portion 12a, preventing it from coming out of the opening 63. It should be noted that the gas connection portion 66 can be fixed to the housing 11 using any method, not limited to the case where it is fixed to the housing 11 by the retaining piece 69, but also by forming a flange portion on the outer circumferential surface side of the gas connection portion 66 and screwing this flange portion.

[0067] The lubrication system, which supplies lubricating oil to the front rolling bearing 31 and the rear rolling bearing 41, is provided by an oil-air lubrication system or oil mist lubrication system (not shown) with compressed gas at approximately 4 atmospheres from a compressed gas supply unit 80. The compressed gas supply unit 80 includes a compressor 81 that discharges compressed gas, a regulator 82 for the lubrication system that regulates the pressure of the compressed gas discharged from the compressor 81, and a regulator 83 for measuring pressure loss connected in parallel with the regulator 82. Note that the lubrication of the bearings 31 and 41 is not limited to oil-air lubrication or oil mist lubrication. For example, grease lubrication may also be used.

[0068] The differential pressure adjustment unit 70 is connected to the compressed gas supply passage 65 of the housing 11 by the compressed gas supply path (piping) 74. The differential pressure adjustment unit 70 has a throttle 72 inserted into the compressed gas piping 74, a first branch pipe 76a branching from the first branching point 74a of the piping 74, and a second branch pipe 76b branching from the second branching point 74b of the piping 74. The first branch pipe 76a is connected to the low-pressure side of the differential pressure sensor 73, and the second branch pipe 76b is connected to the high-pressure side of the differential pressure sensor 73. The first branch point 74a is the branch point downstream of the aperture 72, and the second branch point 74b is the branch point upstream of the aperture 72.

[0069] The pressure loss measurement unit 71 is connected to the differential pressure adjustment unit 70 by the first branch pipe 76a and the second branch pipe 76b. The differential pressure sensor 73 included in the pressure loss measurement unit 71 detects the difference (differential pressure) between the pressure on the upstream side and the pressure on the downstream side of the throttle 72. The compressed gas supply path 74 extends downward from the second branching point 74b and connects to the compressed gas supply unit 80. In this routing configuration, no compressed gas flow velocity is generated between the first branching point 74a and the low-pressure side of the differential pressure sensor 73 (i.e., within the first branch pipeline 76a). Similarly, no compressed gas flow velocity is generated between the second branching point 74b and the high-pressure side of the differential pressure sensor 73 (i.e., within the second branch pipeline 76b).

[0070] The throttle 72 is interposed in a pipe 74 that connects the regulator 83 to the opening of the compressed gas supply passage 65 formed in the housing 11. The amount of throttling by the throttle 72 is set so that the differential pressure detected by the differential pressure sensor 73 when the axial displacement of the rotating shaft 21 is "0" during the rotation of the rotating shaft 21 becomes a preset value. As a result, the pressure downstream of the throttle 72 represents a pressure loss corresponding only to the axial displacement of the rotating shaft 21, taking into account the flow resistance due to the length and diameter of the pipe from the throttle 72 to the displacement detection unit 61A. The low-pressure side of the differential pressure sensor 73 is connected to the downstream pipe 74 of the restrictor 72 via the first branch pipe 76a (connected to the first branch point 74a), and the high-pressure side of the differential pressure sensor 73 is connected to the upstream pipe 74 of the restrictor 72 via the second branch pipe 76b (connected to the second branch point 74b). The second branch point 74b, which is the junction of the second branch pipe 76b and pipe 74, is connected to the regulator 83 via pipe 74. The differential pressure sensor 73 detects the differential pressure between the compressed air pressure supplied from the regulator 83 (pressure at the second branch point 74b) and the downstream pressure of the restrictor 72 connected to the displacement detection unit 61A (pressure at the first branch point 74a), that is, the pressure loss corresponding to the axial displacement of the rotation axis 21 at the displacement detection unit 61A, and outputs the detected differential pressure value as an analog or digital value.

[0071] The arithmetic processing unit (PU) is composed of an arithmetic processing unit such as a microcomputer, and receives the differential pressure detection value output from the differential pressure sensor 73 of each pressure loss measurement unit 71. This differential pressure detection value is proportional to the axial load acting on the rotating shaft 21. Therefore, by measuring or calculating the bearing stiffness (spring constant) of the angular contact ball bearings 31a and 31b that constitute the front rolling bearing 31 to which a fixed position preload is applied, and determining the relationship between the magnitude of the axial load and the differential pressure detection value based on the displacement of the rotating shaft 21, a load calculation map is formed and stored in the memory of the arithmetic processing unit (PU). By referring to the load calculation map based on the differential pressure detection value, the direction and magnitude of the axial load acting on the rotating shaft 21 can be determined. The calculated direction and magnitude of the axial load are output and displayed on the display unit DP. Alternatively, instead of using a load calculation map, the axial load can be calculated by deriving the equation for the characteristic curve of the load calculation map and substituting the differential pressure detected by the differential pressure sensor 73 into the obtained equation.

[0072] Next, the operation of the bearing device 10A of the fourth embodiment will be described. First, compressed gas is supplied from the compressed gas supply unit 80 to the differential pressure adjustment unit 70 and the pressure loss measurement unit 71. As described above, with the rotating shaft 21 of the bearing device 10A of the machine tool rotating and the axial load applied to the rotating shaft 21 being "0", the amount of throttling of the throttle 72 of the differential pressure adjustment unit 70 is adjusted so that the differential pressure detected by the differential pressure sensor 73 becomes a preset value. Then, with the rotating shaft 21 of the bearing device 10A stopped, the compressor 81 is started to regulate the pressure of the compressed gas with the regulator 82, and the compressed gas at the set pressure is supplied to the lubrication oil supply system for the front rolling bearing 31 and the rear rolling bearing 41 (not shown), thereby starting the supply of lubricant to the front rolling bearing 31 and the rear rolling bearing 41.

[0073] Simultaneously, or before or after, the compressed gas discharged from the compressor 81 is regulated by the regulator 83 and supplied to the differential pressure adjustment unit 70 and the pressure loss measurement unit 71. The compressed gas supplied to the differential pressure adjustment unit 70 is input to the compressed gas supply passage 65 of the housing 11 via the throttle 72. The compressed gas input to the compressed gas supply passage 65 is redirected by 90 degrees radially from the axial direction at the gas connection unit 66 from the compressed gas supply passage 64 connected to the compressed gas supply passage 65, and is supplied to the compressed gas discharge nozzle 62A via the gas passage 36e.

[0074] The compressed gas supplied to the compressed gas discharge nozzle 62A is supplied to the gap g to be measured between the right side surface forming the circumferential groove 36d of the outer ring spacer 36 and the right side surface of the annular projection 38b of the inner ring spacer 38. At this time, as the gap g to be measured, i.e., the axial displacement of the rotating shaft 21, increases from a state of "0", the gap g to be measured decreases, and the pressure loss decreases accordingly. Conversely, as the axial displacement decreases, the gap g to be measured increases, and the pressure loss increases accordingly. As described above, the gap g to be measured decreases due to the axial relative displacement of the rotating shaft 21 with respect to the housing 11 caused by the temperature difference and centrifugal force between the housing 11 and the rotating shaft 21 during spindle rotation.

[0075] Therefore, in an unloaded state where the axial displacement of the rotating shaft 21 is "0", the differential pressure detected by the differential pressure sensor 73 becomes a preset value, and the differential pressure detected value indicating that the axial displacement of the rotating shaft 21 is "0" is output to the arithmetic processing unit PU. Therefore, the arithmetic processing unit (PU) calculates the axial load by referring to a load calculation map based on the differential pressure detected by the differential pressure sensor (73). The calculated load is output and displayed on the display unit (DP). In this case, since the axial displacement is "0", the axial load displayed on the display unit (DP) will be "0".

[0076] From this state, for example, if a drill is attached to the rotating shaft 21 and drilling is started, an axial load is applied to the rotating shaft 21, and an axial displacement corresponding to this axial load occurs in the rotating shaft 21. Therefore, in accordance with the axial displacement of the rotating shaft 21, a pressure loss occurs in the compressed gas discharged from the compressed gas discharge nozzle 62A of the displacement detection unit 61A, corresponding to the axial displacement. This pressure loss is detected as a differential pressure value by the differential pressure sensor 73 of the pressure loss measurement unit 71. The detected differential pressure value is supplied to the arithmetic processing unit (PU), which then calculates the axial load applied to the rotating shaft 21 by referring to a load calculation map. The calculated axial load is output to the display unit (DP) and displayed.

[0077] As described above, according to the fourth embodiment, compressed gas is supplied to the displacement detection unit 61A, which detects axial displacement and is composed of the outer ring spacer 36 and inner ring spacer 38 of the front rolling bearing 31. Compressed gas is then discharged from the compressed gas discharge nozzle 62A into the gap g to be measured between the circumferential groove 36d of the outer ring spacer 36 and the annular projection 38b of the inner ring spacer 38. As a result, a pressure loss of compressed gas occurs in the gap g to be measured, i.e., in accordance with the axial displacement of the rotating shaft 21. This pressure loss is detected by the differential pressure sensor 73 of the pressure loss measurement unit 71 provided on the outside of the housing 11, and the detected differential pressure value is supplied to the calculation processing unit PU, thereby enabling the calculation of the axial load applied to the rotating shaft 21.

[0078] Therefore, the displacement detection unit 61A can generate pressure loss corresponding to the axial displacement of the rotating shaft 21 with a simple configuration that only requires the provision of a circumferential groove 36d of the outer ring side spacer 36 and an annular projection 38b of the inner ring side spacer 38, a gas passage 36e, a compressed gas supply passage 64, a gas connection part 66, and a compressed gas discharge nozzle 62A facing each other via a predetermined gap g to be measured. For this reason, the displacement detection unit 61A does not require any electrically operated components, so there is no need to consider wiring or electrical insulation.

[0079] Furthermore, the differential pressure adjustment unit 70 supplies compressed gas to the displacement detection unit 61A via the throttle 72, and can measure the pressure loss at the displacement detection unit 61A by detecting the differential pressure between the pressure downstream of the throttle 72, i.e., on the displacement detection unit 61A side, and the original pressure of the compressed gas supplied to the differential pressure adjustment unit 70. Then, by inputting the detected differential pressure value into the calculation processing unit PU, the axial load of the rotating shaft 21 can be calculated by referring to the load calculation map. Therefore, when the rotating shaft 21 is rotatably supported by rolling bearings, it is possible to calculate the axial displacement of the rotating shaft 21 or the axial load applied to the rotating shaft 21 using compressed gas with a simple configuration.

[0080] As explained in Figures 3 to 6 of the first embodiment, in the fourth embodiment as well, in order to suppress the influence of the distance from the rotating shaft 21 to the pressure loss measurement unit 71 (influence on differential pressure measurement), the differential pressure adjustment unit 70 (throttle 72) and the pressure loss measurement unit 71 (differential pressure sensor 73) are separated, the differential pressure adjustment unit 70 is placed between the rotating shaft 21 and the pressure loss measurement unit 71, and the differential pressure adjustment unit 70 is provided within a predetermined distance from the rotating shaft 21, and compressed gas is supplied to the differential pressure adjustment unit 70. Furthermore, the differential pressure adjustment unit 70 and the pressure loss measurement unit 71 are connected by branch pipes 76a and 76b. Therefore, the compressed gas supplied from the compressed gas supply unit 80 flows through the piping 74 toward the second branch point 74b as indicated by arrow A1, flows to the left from the second branch point 74b (arrow A2), then passes through the throttle 72 and the first branch point 74a, and is supplied to the rotating shaft 21 as indicated by arrow A3. The compressed gas is then supplied to the gap g to be measured, and if the rotating shaft 21 is rotating, a pressure change occurs in the gap g to be measured (the pressure decreases). The value of the decreased pressure is input to the low-pressure side of the differential pressure sensor 73 via the first branch pipe 76a. As described above, since no flow velocity of compressed gas is generated in the first branch pipe 76a from the first branch point 74a to the differential pressure sensor 73, the pressure at the first branch point 74a becomes the value on the low-pressure side of the differential pressure sensor 73. Furthermore, since no compressed gas flow velocity is generated in the second branch pipe 76b from the first branch point 74b to the differential pressure sensor 73, the pressure at the second branch point 74b becomes the high-pressure value of the differential pressure sensor 73.

[0081] Similar to the first embodiment, in this embodiment as well, the differential pressure adjustment unit 70 is installed near the rotating shaft 21 (at a distance L1), so that the pressure value input to the low-pressure side of the differential pressure sensor 73 becomes the pressure value at the first branching point 74a, and the pressure value input to the high-pressure side of the differential pressure sensor 73 becomes the pressure value at the second branching point 74b. In the first branch pipeline 76a extending from the first branching point 74a to the low-pressure side of the differential pressure sensor 73, the flow velocity of the compressed gas is zero, so the pressure value at the first branching point 74a is directly input to the low-pressure side of the differential pressure sensor 73. The compressed gas is subjected to pipeline resistance in the pipeline 74 from the rotating shaft 21 to the first branching point 74a, but the differential pressure adjustment unit 70 is provided near the rotating shaft 21, and in this embodiment, the pipeline length (distance L1) that is subjected to pipeline resistance is set to a distance that allows the pressure loss in the gap g under measurement to be input to the differential pressure sensor 73 with high accuracy. The pressure value input to the high-pressure side of the differential pressure sensor 73 is the pressure value at the second branching point 74b. Since the flow velocity of compressed gas is zero in the pipeline 76b, the pressure value of the compressed gas supplied from the compressed gas supply unit 80 is input to the high-pressure side of the differential pressure sensor 73 with high accuracy. In this embodiment, even if the distance between the differential pressure adjustment unit 70 and the pressure loss measurement unit 71 increases, the result is the same as in Figure 4 of the first embodiment. Therefore, even if the pressure loss measurement unit 71 is installed far from the rotating shaft 21, the flow velocity of the compressed gas in the first branch pipe 76a and the second branch pipe 76b is zero, so the pressure value input to the differential pressure sensor 73 is not affected by the length of the first branch pipe 76a or the second branch pipe 76b. Therefore, the measurement accuracy of the differential pressure sensor 73 does not decrease depending on the installation position of the pressure loss measurement unit 71.

[0082] In the fourth embodiment (Figure 13), a case was described in which compressed gas supply passages 64 and 65 extending axially within the housing 11 are formed. However, the fourth embodiment is not limited to this configuration. The gas passage 66b of the gas connection portion 66 may be extended to the outer circumference and opened, and the differential pressure adjustment portion 70 may be connected to this opening. Alternatively, the compressed gas supply passage 65 may be omitted, and the compressed gas supply passage 64 may be opened on the outer circumference of the small outer diameter portion 12a, and the differential pressure adjustment portion 70 may be connected to this opening. Furthermore, while the fourth embodiment described a case where the compressed gas discharge nozzle 62A extends in the axial direction, the invention is not limited to this. As shown in Figure 15(a), the compressed gas discharge nozzle 62A can be tilted upward, as shown in Figure 15(b), the compressed gas discharge nozzle 62A can be tilted downward, and as shown in Figure 15(c), the compressed gas discharge nozzle 62A can be rotated around the central axis of the gas passage 36e.

[0083] Furthermore, in the fourth embodiment, a case was described in which, with the rotating shaft 21 of the bearing device 10A of the machine tool rotating and the axial load applied to the rotating shaft 21 being "0", the amount of restriction of the throttle 72 of the differential pressure adjustment unit 70 is adjusted so that the differential pressure detected by the differential pressure sensor 73 becomes a preset value. However, this embodiment is not limited to this adjustment. For example, with the rotating shaft 21 of the bearing device 10A stopped without external load (0 rotations), the differential pressure of each pressure loss measurement unit 71 is adjusted to a certain value by the throttle 72 of the differential pressure adjustment unit 70, and this state is set as displacement 0. Then, when the rotation speed of the rotating shaft 21 is changed, the differential pressure of each pressure loss measurement unit 71 changes according to the rotation speed of the rotating shaft 21, and the differential pressure set as displacement 0 is offset by the same amount. Then, after the rotation speed has stabilized, a trigger signal is applied from the outside in the same no-load state as described above, and the value at that time is set to "0" again. As a result, if the rotation of the rotating shaft 21 is constant, measurements can be taken at different rotational speeds in the same way as in the fourth embodiment. As described above, in the fourth embodiment, just as in the first embodiment, the pressure value input to the differential pressure sensor 73 is not affected by the distance from the rotating shaft 21 to the differential pressure sensor 73. As a result, the measurement accuracy of the differential pressure sensor 73 does not decrease depending on the installation position of the pressure loss measurement unit 71. Therefore, it is possible to freely change the distance between the rotating shaft 21 and the pressure loss measurement unit 71.

[0084] Fifth Embodiment Next, a fifth embodiment of the bearing device according to the present invention will be described with reference to Figure 16. Figure 16(a) is a cross-sectional view taken along the EE arrow in Figure 16(b). The fifth embodiment is also a bearing device for measuring axial displacement, and its basic structure is the same as that of the fourth embodiment. In the fifth embodiment, a configuration is adopted to reduce or eliminate the effect of compressed gas on the front rolling bearing. Configurations similar to those in the fourth embodiment (for example, the differential pressure adjustment unit 70, the pressure loss measurement unit 71, the compressed gas supply unit 80, the piping 74, etc.) are omitted from the illustration and description, and the differences from the fourth embodiment will be explained.

[0085] In the fifth embodiment, as shown in Figures 16(a) and 16(b), a gas recovery groove 85a for recovering compressed gas is formed circumferentially on the bottom surface of the circumferential groove 36d of the outer ring spacer 36. In addition, a gas recovery groove 85b for recovering compressed gas is formed circumferentially on the end of the outer circumferential surface of the outer ring spacer 36 facing the angular contact ball bearing 31b, opposite the outer circumferential surface of the inner ring spacer 38. Furthermore, as shown in the lower part of Figure 16(a) and Figure 16(b), cavities 86 communicating with the gas recovery grooves 85a and 85b are formed on both sides of the displacement detection unit 61A of the outer ring spacer 36. Furthermore, a gas discharge passage 87a is formed at a position opposite the cavity 86 of the small outer diameter portion 12a, communicating with the cavity 86 and extending radially. Another gas discharge passage 87b is formed, with one end communicating with the gas discharge passage 87a and the other end opening to the front end. The gas recovery grooves 85a, 85b, the cavity 86, and the gas discharge passages 87a and 87b constitute a compressed gas discharge passage (compressed gas discharge section). The gas discharge passages 87a and 87b can be referred to as drain sections that discharge compressed gas to the outside of the bearing device.

[0086] According to the fifth embodiment, compressed air discharged from the compressed gas discharge nozzle 62A of the displacement detection unit 61A into the gap g to be measured, which is formed between the left side of the circumferential groove 36d of the outer ring spacer 36 and the right side of the annular projection 38b of the inner ring spacer 38, spreads in the front-rear and circumferential directions and flows through the gap g to be measured. The compressed gas that has spread in the front-rear direction flows into the gas recovery grooves 85a and 85b, and the gas flows through the gas recovery grooves 85a and 85b in the circumferential direction of Figure 16(b) in the clockwise and counterclockwise directions to reach the cavity 86. From the cavity 86, the gas is discharged to the outside from the front end surface of the small outer diameter portion 12a through the gas discharge passages 87a and 87b of the small outer diameter portion 12a. Therefore, it is possible to prevent compressed gas injected from the compressed gas discharge nozzle 62A from flowing between the outer ring 33 and inner ring 34 of the angular contact ball bearings 31a and 31b, which are positioned in front of and behind the outer ring spacer 36 and the inner ring spacer 38. This prevents the flow of compressed gas into the angular contact ball bearings 31a and 31b from affecting oil-air lubrication or oil-mist lubrication of the angular contact ball bearings.

[0087] In the fifth embodiment, the case in which only one displacement detection unit 61A is installed was described, but the fifth embodiment is not limited to this configuration, and two or more displacement detection units 61A may be installed. Also, the cavity 86 formed in the outer ring side spacer 36 and the gas passages 87a and 87b formed in the small outer diameter portion 12a may be provided in the intermediate part between adjacent displacement detection units 61A. In this case, by forming the cavity 86 in the intermediate part between adjacent displacement detection units 61A, it is possible to prevent compressed gas discharged from one adjacent displacement detection unit 61A from affecting the other displacement detection unit 61A. Also, multiple cavities 86 may be provided between adjacent displacement detection units 61A. In the fifth embodiment as well, the pressure value input to the differential pressure sensor 73 is not affected by the distance from the rotating shaft 21 to the differential pressure sensor 73. As a result, the measurement accuracy of the differential pressure sensor 73 does not decrease depending on the installation position of the pressure loss measurement unit 71. Therefore, it is possible to freely change the distance between the rotating shaft 21 and the pressure loss measurement unit 71.

[0088] Sixth Embodiment Next, a sixth embodiment of the bearing device according to the present invention will be described with reference to Figure 17. The sixth embodiment is also a bearing device for measuring axial displacement, and its basic structure is the same as that of the fourth embodiment. Components similar to those of the fourth embodiment (for example, the differential pressure adjustment unit 70, the pressure loss measurement unit 71, the compressed gas supply unit 80, the piping 74, etc.) will not be shown or described, and the differences from the fourth embodiment will be explained. In the sixth embodiment, the axial length of the gap g to be measured, formed between the inner surface of the outer ring spacer 36 and the outer surface of the inner ring spacer 38, is set to the minimum necessary. More specifically, in the sixth embodiment, the displacement detection unit 61A is formed not in the spacer between the front rolling bearings 31, but at a position adjacent to the front rolling bearings 31 in the axial direction. In other words, in the sixth embodiment, as shown in Figure 17, the displacement detection unit 61A is positioned adjacent to the rear side of the rear angular contact ball bearing 31b that constitutes the front rolling bearing 31.

[0089] Therefore, the bearing housing step portion 12c formed on the inner circumferential surface of the front cylindrical portion 12 of the housing 11 extends rearward from the angular contact ball bearing 31b that constitutes the front rolling bearing 31. The displacement detection unit 61A has an outer ring side spacer 96, which has the same shape as the outer ring side spacer 36 in the fourth and fifth embodiments, positioned on the extension of the bearing housing step portion 12c, and the inner circumferential surface of the outer ring side spacer 96 faces the inner ring side spacer 101 provided on the outer circumferential surface of the rotating shaft 21. The outer ring spacer 96, like the outer ring spacer 36, is equipped with an outer ring portion 96a, an inner ring portion 96b, a recess 96c, a circumferential groove 96d, a gas passage 96e, and a compressed gas discharge nozzle 97.

[0090] Furthermore, an opening 98 similar to the opening 63 is formed at a position opposite the outer ring side spacer 96 of the small outer diameter portion 12a of the housing 11, and a gas connection portion 99 is installed inside the opening 98, with gas passages 99a and 99b similar to those of the gas connection portion 66. The inner ring spacer 101 is composed of a cylindrical portion 101a and an annular projection 101b that protrudes into the circumferential groove 96d of the outer ring spacer 96. The gap to be measured g is formed between the right side of the annular projection 101b and the left side of the outer ring spacer 96 that forms the circumferential groove 96d opposite it. Compressed gas is discharged into the gap to be measured g from a compressed gas discharge nozzle 97 formed in the outer ring spacer 96.

[0091] According to the sixth embodiment, the displacement detection unit 61A itself operates in the same manner as in the fourth embodiment, and therefore the axial load can be calculated with the same effects as in the fourth embodiment. Furthermore, in the sixth embodiment as well, the pressure value input to the differential pressure sensor 73 is not affected by the distance from the rotating shaft 21 to the differential pressure sensor 73. As a result, the measurement accuracy of the differential pressure sensor 73 does not decrease depending on the installation position of the pressure loss measurement unit 71. Therefore, it is possible to freely change the distance between the rotating shaft 21 and the pressure loss measurement unit 71.

[0092] Although not shown in the figures, the sixth embodiment also includes a gas recovery groove for recovering compressed gas and a gas discharge passage for discharging compressed gas to the outside, as described in the fifth embodiment. Furthermore, the fourth to sixth embodiments may be combined as appropriate, as long as they do not contradict each other.

[0093] In the fourth to sixth embodiments described above, the case in which the bearing device 10A according to the present invention is applied to the spindle device of a machine tool was explained, but the application of the present invention is not limited to this. For example, the present invention can also be applied to a rotary table device 131 of a machine tool in which a rotary table 130 is arranged at the upper end of the rotating shaft 21 shown in Figure 12, and to other machine tools. Although specific embodiments are described above, these embodiments are merely illustrative and not intended to limit the scope of the present invention. Apparatuses and methods described herein can be embodied in forms other than those described above. Furthermore, the embodiments described above can be appropriately omitted, substituted, and modified without departing from the scope of the present invention. Such omitted, substituted, and modified forms fall within the scope of the claims and their equivalents and are within the technical scope of the present invention. [Explanation of symbols]

[0094] 10...Bearing device (spindle device) of a machine tool, 11...Housing, 21...Rotating shaft (rotating member), 31...Front rolling bearing, 31a,31b...Angular contact ball bearing, 33...Outer ring, 34...Inner ring, 35...Ball, 36...Outer ring spacer, 38...Inner ring spacer, 41...Rear rolling bearing, 51...Drive motor, 52...Stator, 53...Rotor, 61...Displacement detection unit, PU...Calculation processing unit, 62...Compressed gas discharge nozzle, g...Gap to be measured, 64,65...Compressed gas supply passage, 66...Gas connection part, 70...Differential pressure adjustment 71... Pressure loss measuring section, 72... Throttle, 73... Differential pressure sensor, 74, 75... Piping, 76a... First branch pipeline, 76b... Second branch pipeline, 77... Throttle, 80... Compressed gas supply section, 81... Compressor, 82, 83... Regulator, 81a, 81b... Gas recovery groove, 86... Cavity section, 87a, 87b... Gas discharge passage, 96... Outer ring side spacer, 97... Compressed gas discharge nozzle, 99... Gas connection section, 101... Compressed gas discharge nozzle, 130... Rotary table, 131... Rotary table device for machine tool

Claims

1. A bearing device comprising a displacement measuring unit that supports a rotating member on a stationary member via a rolling bearing, and measures the radial or axial displacement of the rotating member by supplying compressed gas to the gap to be measured between the rotating member and the stationary member around the rolling bearing, The displacement measuring unit is A displacement detection unit having a compressed gas discharge nozzle that discharges compressed gas into the gap to be measured, A pressure loss measuring unit for measuring the pressure loss of compressed gas supplied to the displacement detection unit, The system includes a throttling member provided near the rotating member and between the pressure loss measuring unit and the displacement detection unit, The compressed gas supply source is connected to a pipeline connecting the high-pressure side of the pressure loss measurement unit and the throttling member, and the low-pressure side of the pressure loss measurement unit is connected to a pipeline connecting the displacement detection unit and the throttling member. The pressure loss of the compressed gas is the pressure difference between the pressure of the compressed gas between the displacement detection unit and the throttling member and the pressure of the compressed gas output from the compressed gas supply source. A bearing device in which the installation position of the throttling member is fixed, the installation position of the pressure loss measuring unit can be changed, and the pressure loss measuring unit can be installed away from the installation position of the throttling member.

2. From the point where the compressed gas supply source is connected to the pipeline connecting the high-pressure side of the pressure loss measurement unit and the throttling member, to the high-pressure side of the pressure loss measurement unit, the flow velocity of the compressed gas is zero. The bearing device according to claim 1, wherein the flow velocity of the compressed gas is zero from the point where the low-pressure side of the pressure loss measuring unit is connected to the pipeline connecting the displacement detection unit and the throttling member to the low-pressure side of the pressure loss measuring unit.

3. The bearing device according to claim 2, wherein the displacement detection unit further comprises gas recovery grooves on one or both sides in the axial direction of the compressed gas discharge nozzle for recovering the compressed gas discharged from the compressed gas discharge nozzle into the gap to be measured.

4. The bearing device according to claim 3, wherein the displacement detection unit further comprises a compressed gas discharge unit for discharging the compressed gas recovered in the gas recovery groove to the outside.

5. The bearing device according to claim 4, further comprising a calculation processing unit that calculates the amount of load applied to the rotating member based on the differential pressure detected by the pressure loss measuring unit.

6. A spindle device for a machine tool, comprising a bearing device according to any one of claims 1 to 5, wherein the bearing device rotatably supports the spindle as the rotating member, and measures the load applied to the spindle.

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