Bearing device and spindle device

Abstract

The bearing device is designed to apply axial preload to the first and second bearings, and to accurately detect the magnitude of the preload load based on the output of a strain sensor attached to the outer ring spacer between the first and second outer rings. [Solution] The device includes a first shear deformation member 51 interposed between the first outer ring 32 and the outer ring spacer 26, which deforms radially in accordance with the radial deformation of the first outer ring 32, thereby preventing the transmission of the radial deformation of the first outer ring 32 to the outer ring spacer 26, and a second shear deformation member 52 interposed between the second outer ring 35 and the outer ring spacer 26, which deforms radially in accordance with the radial deformation of the second outer ring 35, thereby preventing the transmission of the radial deformation of the second outer ring 35 to the outer ring spacer 26.

Description

Technical Field

[0001] The present invention relates to a bearing device and a machine tool spindle device having the bearing device.

Background Art

[0002] In machine tools such as machining centers and lathes, and other industrial machines, a spindle device is used to rotatably support a rotating shaft to which an object such as a tool or a workpiece is attached. In the field of use of such spindle devices, in recent years, there has been a demand for enhancing the condition monitoring function for labor saving and unmanned operation. To meet this requirement, a bearing device has been proposed in which an outer ring spacer with a strain sensor is interposed between the outer rings of the first bearing and the second bearing, and the magnitude of the axial preload is monitored by the strain sensor (Patent Document 1).

[0003] The first bearing and the second bearing each have an outer ring, an inner ring, and a plurality of rolling elements incorporated between the outer ring and the inner ring. The first bearing and the second bearing are a pair of angular ball bearings provided in a back-to-back combination relationship. The outer ring spacer is a cylindrical body axially sandwiched between the first outer ring and the second outer ring. Preload is applied by tightening a preload nut between the axial end surface on the side opposite to the second bearing side of the inner ring of the first bearing and the axial end surface on the side opposite to the first bearing side of the inner ring of the second bearing. The preload load due to the tightening of the preload nut is transmitted through the inner ring, rolling elements and outer ring of the first bearing, the outer ring spacer, and the outer ring, rolling elements and inner ring of the second bearing. The strain sensor is attached to the outer circumference (or inner circumference) of the outer ring spacer. If the strain sensor detects the strain generated in the outer ring spacer due to the load applied from the first bearing and the second bearing to the outer ring spacer, it becomes possible to estimate the magnitude of the preload load applied to the first bearing and the second bearing based on the output of this strain sensor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] However, in the bearing device disclosed in Patent Document 1, the outer ring and rolling elements in each bearing are in contact at a contact angle, and due to the small deformation of each outer ring caused by the force in the direction of the contact angle, axial and radial loads are applied from each outer ring to the outer ring spacer. These loads cause small deformations (several μm) in the axial and radial directions of the outer ring spacer. Ideally, since the preload is an axial load, we would like to detect only the aforementioned small axial deformation with a strain sensor, but the aforementioned small radial deformation also affects the detection by the strain sensor, resulting in poor detection accuracy of the preload. In order to achieve high precision in the machining accuracy of machine tools, it is necessary to be able to control the bearing preload, which affects the axial support rigidity of the spindle main shaft, with high precision.

[0006] In light of the aforementioned background, the problem that this invention aims to solve is to provide a bearing device that can accurately detect the magnitude of the preload based on the output of a strain sensor attached to the outer ring spacer. [Means for solving the problem]

[0007] To solve the above problems, this invention provides a bearing device to which axial preload is applied, comprising: a first bearing having a first outer ring, a first inner ring, and a plurality of first rolling elements disposed between the first inner ring and the first outer ring; a second bearing having a second outer ring, a second inner ring, and a plurality of second rolling elements disposed between the second inner ring and the second outer ring; an outer ring spacer provided between the first outer ring and the second outer ring which are spaced apart in the axial direction; and a strain sensor attached to the outer ring spacer. The bearing device configuration 1 is characterized by further comprising: a first shear deformation member interposed between the first outer ring and the outer ring spacer, which deforms radially in accordance with the radial deformation of the first outer ring, thereby preventing the transmission of the radial deformation of the first outer ring to the outer ring spacer; and a second shear deformation member interposed between the second outer ring and the outer ring spacer, which deforms radially in accordance with the radial deformation of the second outer ring, thereby preventing the transmission of the radial deformation of the second outer ring to the outer ring spacer.

[0008] According to the above configuration 1, when the first outer ring and the second outer ring undergo elastic deformation in the radial expansion direction when preload is applied, the radial deformation of each outer ring is transmitted to the corresponding first shear deformation member or second shear deformation member. As a result, the corresponding first shear deformation member or second shear deformation member undergoes radial shear deformation between the first outer ring and the outer ring spacer, or between the second outer ring and the outer ring spacer. Therefore, the transmission of the radial deformations of the first and second outer rings to the outer ring spacer is prevented. In other words, according to the above configuration 1, the transmission of the radial deformations of the first and second outer rings to the outer ring spacer is reduced compared to when they are directly transmitted to the outer ring spacer, thereby reducing minute radial deformations of the outer ring spacer. Consequently, it becomes possible to accurately detect the magnitude of the preload based on the output of the strain sensor.

[0009] In the above configuration 1, a configuration 2 can be adopted in which a plurality of strain sensors are attached to the outer ring spacer at circumferential intervals, and a plurality of the first shear deformation members and a plurality of the second shear deformation members are each positioned at circumferential intervals corresponding to the plurality of strain sensors.

[0010] According to the above configuration 2, even if there is a circumferential bias in the load applied to the outer ring spacer, it is possible to detect the magnitude of the strain in the outer ring spacer in a manner that eliminates the effect of the circumferential bias, based on the outputs of multiple strain sensors arranged at intervals in the circumferential direction, and consequently, to accurately detect the magnitude of the preload. Furthermore, by limiting the position where the load from the first and second outer rings is applied to the outer ring spacer to the circumferential position corresponding to the multiple strain sensors, it becomes possible to generate a large amount of strain in the outer ring spacer due to that load at the surface portion in contact with each strain sensor. As a result, it becomes possible to increase the sensitivity of each strain sensor to the load, and consequently, to improve the load detection accuracy based on the output of each strain sensor.

[0011] In the above configuration 2, a configuration 3 can be adopted in which the outer ring spacer has a first end face that contacts the first shear deformation member and extends in the circumferential and radial directions, and a second end face that contacts the second shear deformation member and extends in the circumferential and radial directions, and each of the first end face and the second end face is provided at multiple locations spaced apart in the circumferential direction, the plurality of first end faces are in the axial position closest to the first outer ring within the outer ring spacer, and the plurality of second end faces are in the axial position closest to the second outer ring within the outer ring spacer.

[0012] According to configuration 3 above, in order to form the first and second end faces of the outer ring spacer into surfaces that extend circumferentially and radially at the corresponding axial position closest to the corresponding first or second outer ring, it is necessary to create irregularities on the outer ring spacer by machining, and finish the protruding end faces as the first or second end faces. The positions of the first and second end faces manufactured by machining are highly accurate. Since the preload load is transmitted via the corresponding first or second shear deformation member only between each of these first and second end faces and the corresponding first or second outer ring, it becomes possible to reduce the variation in the magnitude of the load applied to the strain sensor at each phase. Furthermore, since the first and second end faces are located in positions that protrude the most axially towards one end or the other end of the outer ring spacer, when attaching the first and second shear deformation members to the outer ring spacer, the positions on the outer ring spacer where the first and second shear deformation members should be attached are clear, and it is also possible to ensure that multiple first shear deformation members and multiple second shear deformation members are arranged in the appropriate phase.

[0013] In any one of the above configurations 1 to 3, configuration 4 can be adopted, in which the thickness of the first shear deformation member and the second shear deformation member is 100 μm or less.

[0014] According to the above configuration 4, the amount of displacement of each end face of the first shear deformation member and the second shear deformation member that are compressed in the axial direction by preload can be suppressed. In other words, the decrease in axial stiffness in the first shear deformation member and the second shear deformation member can be suppressed.

[0015] In any one of the above configurations 1 to 4, configuration 5 can be adopted in which the first shear deformation member and the second shear deformation member are each made of an adhesive.

[0016] According to the above configuration 5, the first and second shear deformation members, which are made of adhesive, can be easily shear-deformed in the radial direction, thus effectively reducing the transmission of radial deformation of the first and second outer rings to the outer ring spacer. Furthermore, since the first and second shear deformation members adhere to the corresponding first or second outer ring and the outer ring spacer, it is possible to prevent the first and second shear deformation members from falling off, improving the ease of assembly of the bearing device. In addition, it is possible to peel off the first and second shear deformation members without damaging the first and second outer rings and the outer ring spacer, making it easy to replace the first and second shear deformation members.

[0017] In any one of the above configurations 1 to 4, configuration 6 can be adopted, in which the first shear deformation member and the second shear deformation member each consist of a tape having an adhesive and a base material that supports the adhesive.

[0018] According to the above configuration 6, the first shear deformation member and the second shear deformation member can be easily shear-deformed radially in the adhesive layer, resulting in an excellent effect in reducing the transmission of radial deformation of the outer ring. Furthermore, since the first shear deformation member and the second shear deformation member are attached to the outer ring spacer or the corresponding first or second outer ring, it is possible to prevent the first and second shear deformation members from falling off, improving the ease of assembly of the bearing device. In addition, it is possible to peel off the first and second shear deformation members without damaging the first and second outer rings and the outer ring spacer, making it easy to replace the first and second shear deformation members. Moreover, since it is a tape containing a base material, it is easy to grasp the tape and attach or detach the first and second shear deformation members during assembly or replacement.

[0019] In the above configuration 5 or 6, configuration 7 can be adopted in which the adhesive consists of an acrylic adhesive or a silicone adhesive.

[0020] According to the above configuration 7, it is possible to use a first shear deformation member and a second shear deformation member that have excellent oil resistance, heat resistance, and weather resistance compared to rubber-based adhesives and urethane-based adhesives.

[0021] It is possible to adopt a configuration 8, which is a spindle device having a bearing device according to any one of the above configurations 1 to 7, a main shaft of a machine tool rotatably supported by the bearing device, and a motor that rotationally drives the main shaft.

[0022] According to the above configuration 8, it becomes possible to stably perform condition monitoring for labor saving and unmanned operation of a machine tool, and it also becomes possible to detect a machining load acting on the main shaft during cutting of the machine tool.

Effect of the Invention

[0023] As described above, by adopting the above configuration 1, this invention can be a bearing device capable of accurately detecting the magnitude of the preload based on the output of the strain sensor attached to the outer ring spacer.

Brief Description of the Drawings

[0024] [Figure 1] Cross-sectional view showing a spindle device using the bearing device according to the first embodiment of this invention [Figure 2] Enlarged view of the vicinity of the bearing device in FIG. 1 [Figure 3] Block diagram showing the connection relationship between the strain sensor and the preload calculation processing unit shown in FIG. 2 [Figure 4] Cross-sectional view taken along line IV-IV in FIG. 2 [Figure 5] Cross-sectional view taken along line V-V in FIG. 4 [Figure 6] Cross-sectional view showing the state where the first shear deformation member in FIG. 1 is attached to the outer ring spacer [Figure 7] Cross-sectional view showing the bearing device according to the second embodiment of this invention in the same manner as FIG. 4 [Figure 8] Cross-sectional view taken along line VIII-VIII in FIG. 7 [Figure 9]A cross-sectional view of a bearing device according to the third embodiment of this invention, similar to that shown in Figure 4. [Figure 10] Cross-sectional view along line XX in Figure 9 [Figure 11] A cross-sectional view of a bearing device according to the fourth embodiment of this invention, similar to that shown in Figure 6. [Figure 12] This is a cross-sectional view showing the first shear deformation member according to the fourth embodiment of this invention attached to the first outer ring. [Figure 13] Graph showing the results of load detection tests when comparative examples are used as the first and second shear deformation members. [Figure 14] Graph showing the results of the load detection test when Sample 1 was used as the first and second shear deformation members. [Figure 15] Graph showing the results of the load detection test when Sample 4 was used as the first and second shear deformation members. [Figure 16] Graph showing the results of the load detection test when Sample 5 was used as the first and second shear deformation members. [Modes for carrying out the invention]

[0025] Figure 1 shows a spindle device using a bearing device 1 (hereinafter simply referred to as "bearing device 1") according to a first embodiment as an example of the present invention. This spindle device comprises a spindle 2 of a machine tool, a spindle housing 3 that houses the spindle 2, a motor 4 that rotationally drives the spindle 2, a bearing device 1 that rotatably supports the spindle 2 axially forward of the motor 4, and a rear bearing device 5 that rotatably supports the spindle 2 axially rear of the motor 4.

[0026] Here, the axial direction is the direction parallel to the central axis of the main shaft 2, the radial direction is the direction perpendicular to the central axis of the main shaft 2, and the circumferential direction is the direction along the circumference that revolves around the central axis of the main shaft 2.

[0027] The spindle housing 3 is formed in a hollow cylindrical shape with both ends open. The spindle housing 3 houses the bearing device 1 and the motor 4 in order from the front to the rear in the axial direction. In the illustrated example, the part of the spindle housing 3 that houses the bearing device 1 and the part of the spindle housing 3 that houses the motor 4 are formed as a single, seamless piece. However, the part of the spindle housing 3 that houses the bearing device 1 and the part of the spindle housing 3 that houses the motor 4 may be formed as separate parts and then connected to form a single piece.

[0028] The spindle 2 is inserted into the spindle housing 3 with its front end protruding from the front end opening of the spindle housing 3. A chuck (not shown) for gripping a tool or workpiece is detachably attached to the front end of the spindle 2. A through hole 6 is formed in the spindle 2, which allows a drawbar (not shown) of the machine tool to be slidably housed in the axial direction.

[0029] The motor 4 has a rotor 7 mounted on the outer circumference of the main shaft 2 and an annular stator 8 that imparts rotational force to the rotor 7. The rotor 7 has a rotor sleeve 9 fitted to the outer circumference of the main shaft 2 and a rotor core 10 fixed to the outer circumference of the rotor sleeve 9. The rotor core 10 is, for example, a laminate of electrical steel sheets. The rotor sleeve 9 is fixed to the main shaft 2 so as to rotate integrally with the main shaft 2. The axial front end of the rotor sleeve 9 contacts a stepped portion 11 formed on the outer circumference of the main shaft 2, and is positioned axially by contact with the stepped portion 11.

[0030] The stator 8 has a stator core 12 fixed to the inner circumference of the spindle housing 3, and electromagnetic coils 13 wound around multiple teeth formed at circumferential intervals on the stator core 12. When current is supplied to the electromagnetic coils 13, the electromagnetic force acting between the stator core 12 and the rotor core 10 generates a rotational force in the rotor core 10, causing the rotor 7 and the spindle 2 to rotate together. Here, an electric motor that generates rotational force using electricity is used as the motor 4, but it is also possible to use a motor that generates rotational force using another power source such as compressed air instead of an electric motor.

[0031] The rear bearing device 5 includes an annular bearing support member 14 coaxially fixed to the rear end of the main shaft housing 3, and a rolling bearing 15 incorporated into the bearing support member 14. The rolling bearing 15 is a cylindrical roller bearing having an outer ring 16 fitted to the inner circumference of the bearing support member 14, an inner ring 17 fitted to the outer circumference of the main shaft 2, and a plurality of cylindrical rollers 18 incorporated between the outer ring 16 and the inner ring 17.

[0032] A retaining member 19 is attached to the bearing support member 14. The retaining member 19 fixes the axial position of the outer ring 16 by contacting the axial rear end surface of the outer ring 16. A nut member 20 that presses the inner ring 17 axially forward and an annular spacer 21 incorporated between the inner ring 17 and the nut member 20 are mounted on the outer circumference of the main shaft 2. The nut member 20 is screw-engaged with a male thread 22 formed on the outer circumference of the rear end of the main shaft 2. The axial front end surface of the spacer 21 is in contact with the axial rear end surface of the inner ring 17, and the axial rear end surface of the spacer 21 is in contact with the axial front end surface of the nut member 20. The axial front end surface of the inner ring 17 is in contact with the axial rear end surface of the rotor sleeve 9.

[0033] The bearing device 1 includes a hollow cylindrical bearing support cylinder 23 fixed to the main shaft housing 3, a first bearing 24 and a second bearing 25 assembled in the bearing support cylinder 23 at axial intervals, an outer ring spacer 26 and an inner ring spacer 27 provided between the first bearing 24 and the second bearing 25, a strain sensor 28 attached to the outer ring spacer 26, a preload nut 29 for applying preload to the first bearing 24 and the second bearing 25, and a cover member 30 for fixing the first bearing 24 and the second bearing 25 to the bearing support cylinder 23.

[0034] The bearing support cylinder 23 is fitted to the inner circumference of the main shaft housing 3. Cooling grooves 31 are formed on the outer circumference of the bearing support cylinder 23 through which a refrigerant for cooling the bearing device 1 flows. The cooling grooves 31 are a plurality of annular grooves formed at axial intervals on the outer circumference of the bearing support cylinder 23, or helical grooves extending spirally along the outer circumference of the bearing support cylinder 23.

[0035] As shown in Figure 2, the first bearing 24 includes a first outer ring 32 fitted to the inner circumference of the bearing support cylinder 23, a first inner ring 33 coaxially arranged radially inward of the first outer ring 32, and a plurality of first rolling elements 34 incorporated between the first outer ring 32 and the first inner ring 33 at circumferential intervals. The first outer ring 32 rotatably supports the first inner ring 33 via the first rolling elements 34.

[0036] The second bearing 25 includes a second outer ring 35 fitted to the inner circumference of the bearing support cylinder 23, a second inner ring 36 coaxially arranged radially inward of the second outer ring 35, and a plurality of second rolling elements 37 incorporated between the second outer ring 35 and the second inner ring 36 at circumferential intervals. The second outer ring 35 rotatably supports the second inner ring 36 via the second rolling elements 37.

[0037] The first bearing 24 is configured such that when an axial preload is applied between the first outer ring 32 and the first inner ring 33, the first rolling element 34 generates a radial component force that pushes the first outer ring 32 radially outward. The second bearing 25 is also configured such that when an axial preload is applied between the second outer ring 35 and the second inner ring 36, the second rolling element 37 generates a radial component force that pushes the second outer ring 35 radially outward.

[0038] In this bearing device 1, the first bearing 24 and the second bearing 25 are configured as a pair of angular contact ball bearings arranged in a back-to-back configuration.

[0039] The first rolling element 34 and the second rolling element 37 are each made of balls. The inner circumference of the first outer ring 32 and the inner circumference of the second outer ring 35 have raceway surfaces 38 and 39 with a cross-sectional arc shape that the corresponding first rolling element 34 or second rolling element 37 rolls into contact with. The first outer ring 32 and the second outer ring 35 are shouldered outer rings, each having a shape in which the corresponding axial front or axial rear shoulder portion has been removed from the corresponding raceway surface 38 or raceway surface 39.

[0040] The outer circumference of the first inner ring 33 and the outer circumference of the second inner ring 36 are provided with raceway surfaces 40 and 41 in a cross-sectional arc shape, to which the corresponding first rolling element 34 or second rolling element 37 rolls and makes contact. The first inner ring 33 and the second inner ring 36 are shouldered inner rings, each having a shape in which the shoulder portion corresponding to the axial rear or axial front side of the raceway surface 40 or raceway surface 41 to which the corresponding first rolling element 34 or second rolling element 37 rolls and makes contact has been removed. The imaginary straight line connecting the contact point between the first inner ring 33 and the first rolling element 34 and the contact point between the first outer ring 32 and the first rolling element 34 extends in a direction that is inclined axially rearward from the radially inward to the radially outward. The straight line connecting the contact point between the second inner ring 36 and the second rolling element 37 and the contact point between the second outer ring 35 and the second rolling element 37 extends in a direction that is inclined axially forward from the radially inward to the radially outward.

[0041] The first inner ring 33 and the second inner ring 36 are fitted to the outer circumference of the main shaft 2 with an overlap. The second inner ring 36 is positioned axially rearward from the first inner ring 33. The outer circumference of the first outer ring 32 and the outer circumference of the second outer ring 35 are fitted to the inner circumference of the bearing support cylinder 23 with a gap.

[0042] The outer ring spacer 26 and the inner ring spacer 27 are hollow cylindrical members with open ends. The central axes of the first bearing 24, the second bearing 25, and the outer ring spacer 26 coincide with the central axis of the main shaft 2.

[0043] The outer ring spacer 26 is fitted with a gap on the inner circumference of the bearing support cylinder 23. The outer ring spacer 26 is positioned between the first outer ring 32 and the second outer ring 35. The axial rear end face of the first outer ring 32 (the axial end face of the first outer ring 32 on the side of the second outer ring) is located axially forward relative to the outer ring spacer 26. The second outer ring 35 is positioned axially rearward from the first outer ring 32. The axial front end face of the second outer ring 35 (the axial end face of the second outer ring 35 on the side of the first outer ring 32) is located axially rearward relative to the outer ring spacer 26.

[0044] The inner ring spacer 27 is fitted to the outer circumference of the main shaft 2 with a gap. The inner ring spacer 27 is positioned between the first inner ring 33 and the second inner ring 36.

[0045] A shaft shoulder portion 42 is formed around the entire circumference of the main shaft 2, facing the axial front end face of the first inner ring 33 (the axial end face of the first inner ring 33 opposite to the side of the second inner ring 36) in the axial direction. The shaft shoulder portion 42 restricts the movement of the first inner ring 33 axially forward (away from the second outer ring 35), thereby positioning the first inner ring 33 in the axial direction.

[0046] Furthermore, a preload nut 29 is mounted on the outer circumference of the main spindle 2, axially rearward of the second inner ring 36. The preload nut 29 is screw-engaged with a male thread 43 formed on the outer circumference of the main spindle 2. An annular spacer 44 is incorporated between the second inner ring 36 and the preload nut 29. The axial front end face of the spacer 44 contacts the axial rear end face of the second inner ring 36, and the axial rear end face of the spacer 44 contacts the axial front end face of the preload nut 29.

[0047] The preload nut 29 is tightened with a predetermined force, and the axial force of the preload nut 29 applies a preload load in a direction that brings the first inner ring 33 and the second inner ring 36 closer together between the axial front end face of the first inner ring 33 (the axial end face of the first inner ring 33 opposite to the side of the second inner ring 36) and the axial rear end face of the second inner ring 36 (the axial end face of the second inner ring 36 opposite to the side of the first inner ring 33). Here, the preload load applied from the preload nut 29 is transmitted to the shaft shoulder portion 42 through the first inner ring 33, the first rolling element 34, the first outer ring 32, the outer ring spacer 26, the second outer ring 35, the second rolling element 37, and the second inner ring 36.

[0048] A housing shoulder 45 is formed around the entire inner circumference of the bearing support cylinder 23, facing the axial rear end face of the second outer ring 35 (the axial end face of the second outer ring 35 opposite to the side of the first outer ring 32) in the axial direction. The housing shoulder 45 positions the second outer ring 35 in the axial direction by restricting its movement axially rearward (away from the first outer ring 32).

[0049] The cover member 30 has an annular plate-shaped flange portion 46 fixed to the axial front end surface of the bearing support cylinder 23 with bolts (not shown), and an annular projection portion 47 that protrudes axially from the radial inner end of the flange portion 46 along the inner circumference of the bearing support cylinder 23. The axial rear end surface of the annular projection portion 47 abuts against the axial front end surface of the first outer ring 32 (the axial end surface of the first outer ring 32 opposite to the side of the second outer ring 35). Multiple bolts are provided at equal intervals in the circumferential direction.

[0050] The first outer ring 32 and the second outer ring 35 are assembled between the cover member 30 and the housing shoulder 45 with an axial overlap. This axial overlap applies an outer ring fixing load that brings the first outer ring 32 and the second outer ring 35 closer together between the axial front side of the first outer ring 32 (the axial end face of the first outer ring 32 opposite to the side of the second outer ring 35) and the axial rear side of the second outer ring 35 (the axial end face of the second outer ring 35 opposite to the side of the first outer ring 32). Here, the outer ring fixing load applied from the cover member 30 is transmitted to the housing shoulder 45 through the first outer ring 32, the outer ring spacer 26, and the second outer ring 35.

[0051] The strain sensor 28 is positioned at the axial center of the outer ring spacer 26. The strain sensor 28 is positioned such that the center of the strain detection part of the strain sensor 28 is at a position that bisects the distance between the axial front end and the axial rear end of the outer ring spacer 26, or the amount of axial displacement from that position to the center of the strain detection part of the strain sensor 28 is less than 10% of the total axial length of the outer ring spacer 26.

[0052] A strain gauge is used as the strain sensor 28, in which the electrical resistance changes according to the axial strain of the bonded portion.

[0053] The strain sensor 28 is electrically connected to the preload calculation processing unit 48, as schematically shown in Figure 3, and the output signal of the strain sensor 28 is input to the preload calculation processing unit 48. The preload calculation processing unit 48 is, for example, an electronic circuit or electronic control device provided outside the bearing device 1, and calculates the magnitude of the preload based on the output of the strain sensor 28.

[0054] As shown in Figures 4 and 5, three or more strain sensors 28 (three in this case) are provided at equal intervals in the circumferential direction on the inner circumference of the outer ring spacer 26. The same number of axial grooves 49 as the number of strain sensors 28 are formed at equal intervals in the circumferential direction on the inner circumference of the outer ring spacer 26. Each axial groove 49 has a planar groove bottom surface that extends in the axial direction, and a strain sensor 28 is fixedly attached to the bottom surface of each groove.

[0055] While it is possible to estimate the preload by forming flat surfaces at one or more locations in the circumferential direction on the inner or outer circumference of the outer ring spacer and attaching strain sensors to each flat surface, it is preferable to form three or more flat surfaces spaced apart in the circumferential direction and place strain sensors on each flat surface. Even if a distribution of load is created on the inner or outer circumference of the outer ring spacer, the strain sensors of different phases distributed at three or more locations in the circumferential direction can detect loads of different magnitudes on the circumference, making it possible to accurately detect the load by utilizing the output of each strain sensor.

[0056] The output of the strain sensor 28 changes according to the axial compression deformation, bending deformation, diameter expansion deformation, etc., at the location on the outer ring spacer 26 where the strain sensor 28 is attached. As mentioned above, two types of loads are applied simultaneously to the outer ring spacer 26: a preload from the preload nut 29 shown in Figure 2, and an outer ring fixing load from the cover member 30. Therefore, the outer ring spacer 26 experiences strain from both the preload from the preload nut 29 and the outer ring fixing load from the cover member 30 at the same time. The combined strain from these two loads is then detected by the strain sensor 28.

[0057] Here, if the magnitude of the outer ring fixing load by the lid member 30 is a known constant value, the magnitude of the preload can be detected by subtracting the axial load by the lid member 30 from the load value detected based on the output of the strain sensor 28. However, in reality, the magnitude of the outer ring fixing load by the lid member 30 is not a constant value, and it is difficult to know its magnitude accurately, so it is not easy to accurately detect the magnitude of the preload by the aforementioned subtraction.

[0058] Furthermore, when the preload applied by the preload nut 29 is transmitted to the outer ring spacer 26, the outer ring spacer 26 undergoes deformation (barrel-shaped deformation) that causes the axial center to bulge due to the axial compressive load. At this time, the first outer ring 32 undergoes elastic deformation in the radial direction due to the radial component force received from the first rolling element 34, and the second outer ring 35 also undergoes elastic deformation in the radial direction due to the radial component force received from the second rolling element 37. If the first outer ring 32 and the second outer ring 35 directly sandwich the outer ring spacer 26 in the axial direction, then when the first outer ring 32, the second outer ring 35 and the outer ring spacer 26 are pushing against each other under an axial compressive load, the aforementioned expansion deformation of the first outer ring 32 and the second outer ring 35 is transmitted to both ends of the outer ring spacer 26. As a result, the outer ring spacer 26 also undergoes deformation that expands the diameter of both axial ends of the outer ring spacer 26 (a deformation in which the axial center of the outer ring spacer 26 becomes constricted relative to the axial ends). Ideally, since the preload is an axial load, it would be ideal for the strain sensor 28 to detect only the minute axial deformation that occurs in the outer ring spacer 26. The aforementioned expansion deformation of the first outer ring 32 and the second outer ring 35 is transmitted to the outer ring spacer 26. In other words, the expansion load acting from the expanding first outer ring 32 and the second outer ring 35 onto the outer ring spacer 26 causes minute deformations on both axial sides of the outer ring spacer 26 in the expansion direction. This minute radial deformation also affects the detection of the strain sensor 28, which is undesirable. Therefore, in this bearing device 1, measures are taken to prevent the aforementioned expansion deformation of the first outer ring 32 and the second outer ring 35 from being substantially transmitted to the outer ring spacer 26.

[0059] Specifically, the first shear deformation member 51 is interposed between the first outer ring 32 and the outer ring spacer 26, so that the first outer ring 32 and the outer ring spacer 26 are not in contact. Furthermore, the second shear deformation member 52 is interposed between the second outer ring 35 and the outer ring spacer 26, so that the second outer ring 35 and the outer ring spacer 26 are not in contact. The first shear deformation member 51 and the second shear deformation member 52 are respectively sandwiched axially between the corresponding first outer ring 32 or second outer ring 35 and the outer ring spacer 26, and can undergo radial shear deformation in accordance with the radial deformation of the corresponding first outer ring 32 or second outer ring 35. The shear moduli of the first shear deformation member 51 and the second shear deformation member 52 with respect to the first outer ring 32, the outer ring spacer 26, and the second outer ring 35 are smaller than the shear moduli of the first outer ring 32, the second outer ring 35, and the outer ring spacer 26, respectively.

[0060] The first shear deformation member 51 and the second shear deformation member 52 are provided with the same specifications. Furthermore, the specifications of the contact surfaces between the first shear deformation member 51 and the first outer ring 32, and the specifications of the contact surfaces between the second shear deformation member 52 and the second outer ring 35 are also provided with the same specifications. Furthermore, the specifications of the contact surfaces between the first shear deformation member 51 and the outer ring spacer 26, and the specifications of the contact surfaces between the second shear deformation member 52 and the outer ring spacer 26 are also provided with the same specifications.

[0061] The first shear deformation member 51 is made of adhesive. As shown in Figures 4 and 5, the first shear deformation member 51 is a double-sided tape formed in an annular shape extending in the circumferential direction. In Figure 4, a portion of the first shear deformation member 51 in the circumferential direction is cut out, and the end face 53 of the outer ring spacer 26 is partially exposed in the axial direction.

[0062] The first shear deformation member 51 is attached to the first end face 53 on the axial front side (the side closer to the first outer ring 32) of the outer ring spacer 26 or to the first side surface 54 on the axial rear side (the side closer to the outer ring spacer 26) of the first outer ring 32, prior to the step of placing it between the first outer ring 32 and the outer ring spacer 26. For example, as shown in Figure 6, it is attached to the end face 53 of the outer ring spacer 26. After this attachment, when the first outer ring 32 and outer ring spacer 26 are positioned as shown in Figure 2 and the aforementioned outer ring fixing load and preload are applied, the first shear deformation member 51 becomes tightly attached to the first end face 53 of the outer ring spacer 26 and the first side surface 54 of the first outer ring 32 and is compressed in the axial direction by the axial components of the outer ring fixing load and preload.

[0063] The same applies to the second shear deformation member 52. When the second shear deformation member 52 is attached to the second end face 55 on the axial rear side (closer to the second outer ring 35) of the outer ring spacer 26 or the second side surface 56 on the axial front side (closer to the outer ring spacer 26) of the second outer ring 35, and the aforementioned outer ring fixing load and preload load are applied, the second shear deformation member 52 will be in close contact with the second end face 55 of the outer ring spacer 26 and the second side surface 56 of the second outer ring 35 and compressed in the axial direction.

[0064] The first side surface 54 of the first outer ring 32, the second side surface 56 of the second outer ring 35, and the first end surface 53 and second end surface 55 of the outer ring spacer 26 are each formed in an annular shape along the radial and circumferential directions, and are finished to a predetermined degree of flatness.

[0065] When the first outer ring 32 and the second outer ring 35 are deformed by the radial component of the aforementioned preload, the first shear deformation member 51 and the second shear deformation member 52 receive a force in the radial direction from the corresponding first side surface 54 of the first outer ring 32 or the second side surface 56 of the second outer ring 35, respectively. Therefore, the first shear deformation member 51 and the second shear deformation member 52 are shear-deformed such that the contact surface side that is in close contact with the corresponding first side surface 54 or second side surface 56 is displaced in the radial direction relative to the contact surface side that is in close contact with the outer ring spacer 26 (see enlarged area A in Figure 2. Note that the deformation of the first outer ring 32 and the first shear deformation member 51 is exaggerated and depicted with a dashed line here). As a result, the radial deformation of the first outer ring 32 or the second outer ring 35 is not directly transmitted to the outer ring spacer 26, and the radial expansion force applied by the first shear deformation member 51 or the second shear deformation member 52 to the end face 53 or end face 55 of the corresponding outer ring spacer 26 is significantly reduced compared to the radial expansion force applied from the corresponding first outer ring 32 or the second outer ring 35. In this way, the first shear deformation member 51 and the second shear deformation member 52 deform radially in response to the radial deformation of the corresponding first outer ring 32 or the second outer ring 35, thereby preventing the transmission of the radial deformation of the corresponding first outer ring 32 or the second outer ring 35 to the outer ring spacer 26. Therefore, it becomes possible to substantially prevent radial deformation of the outer ring spacer 26 from occurring to the extent that it would affect detection by the strain sensor 28. On the other hand, the axial load applied between the first outer ring 32, the first shear deformation member 51, the outer ring spacer 26, the second shear deformation member 52, and the second outer ring 35 is transmitted between the corresponding contact surfaces. Therefore, the radial deformation of the first outer ring 32 or the second outer ring 35 does not substantially affect the outer ring spacer 26, resulting in axial strain in the outer ring spacer 26. Based on the output of the strain sensor 28 that detects this strain, it becomes possible to calculate the magnitude of the preload. Consequently, the value of the preload calculated by the preload calculation processing unit 48 based on the output of the strain sensor 28 is made more accurate. The method for calculating this preload is not particularly limited, but for example, it can be done as follows.

[0066] First, a test bearing device 1 is prepared that replicates the same configuration as the bearing device 1. Using this test bearing device 1, a test is performed in which an outer ring fixing load by the cover member 30 and a preload load by the preload nut 29 are applied simultaneously, and the magnitude of the outer ring fixing load and the magnitude of the preload load are changed independently, and the change in the output of the strain sensor 28 is recorded. This test provides a correspondence between the output of the strain sensor 28 and the combination of the magnitude of the outer ring fixing load by the cover member 30 and the magnitude of the preload load by the preload nut 29, making it possible to create conversion data for converting the preload load (and outer ring fixing load) from the output of the strain sensor 28.

[0067] Next, the conversion data obtained as described above is stored in the preload calculation processing unit 48 shown in Figure 3. Based on this conversion data, the preload calculation processing unit 48 converts the output of the strain sensor 28 to the magnitude of the preload load. The conversion data may be obtained using a conversion map that individually stores the relationship between the output of the strain sensor 28 and the magnitude of the preload load from the preload nut 29, or it may be calculated using a mathematical formula that approximates the relationship between the output of the strain sensor 28 and the magnitude of the preload load.

[0068] The outputs of multiple strain sensors 28, which are spaced apart in the circumferential direction, can be used as the sum (or average) of their outputs.

[0069] As described above, when the radial shear deformation in the first shear deformation member 51 and the second shear deformation member 52 shown in Figure 2 reduces the small radial deformations occurring in the outer ring spacer 26 due to the expansion of the diameter of the first outer ring 32 and the second outer ring 35 to a substantially negligible degree, the output of the strain sensor 28 becomes substantially proportional to the magnitude of the preload. If there is good linearity in the relationship between the output of the strain sensor 28 and the magnitude of the preload, it becomes possible to express the conversion formula for converting the output of the strain sensor 28 to the preload as a linear equation, thus eliminating the need to use complex formulas such as terms and simplifying the calculations.

[0070] The first shear deformation member 51 and the second shear deformation member 52 are preferably each several μm to several hundred μm in thickness (total axial width). The thickness of the first shear deformation member 51 and the second shear deformation member 52 is set to 100 μm or less in order to suppress the amount of axial displacement of each end face of the first shear deformation member 51 and the second shear deformation member 52. This suppresses the decrease in axial rigidity in the first shear deformation member 51 and the second shear deformation member 52.

[0071] Furthermore, since the first bearing 24 and the second bearing 25 are angular contact ball bearings that require high rotational accuracy for supporting the spindle 2 of a machine tool, it is preferable to suppress the axial runout of the outer ring. The axial runout of the first outer ring 32, the second outer ring 35, and the outer ring spacer 26 is determined as the difference between the maximum and minimum readings of the measuring instrument when the corresponding first outer ring 32, second outer ring 35, or outer ring spacer 26 is rotated once. The first shear deformation member 51 and the second shear deformation member 52 are interposed between the corresponding first outer ring 32 or second outer ring 35 and the outer ring spacer 26, and the adhesive can smooth out undulations, etc., on the first side surface 54 of the first outer ring 32 and the second side surface 56 of the second outer ring 35, etc., with which it adheres (that is, the adhesive can penetrate minute undulations and irregularities on the contact surface and improve the contact condition), making it easy to control the axial runout of the first outer ring 32 and the second outer ring 35 with the desired precision. For example, in a spindle support application, if the bearing outer diameter (equivalent to the outer diameter of the outer ring) exceeds 250 mm and is 315 mm or less, it is desirable to set the axial runout of the first outer ring 32 and the second outer ring 35 to 0.018 mm or less, more preferably 0.007 mm or less. Furthermore, for main shaft support applications where the bearing outer diameter exceeds 180 mm but is 250 mm or less, the axial runout of the first outer ring 32 and the second outer ring 35 should be 0.015 mm or less, more preferably 0.007 mm or less. The axial runout values ​​listed here are obtained using a measurement method compliant with ISO-1132-2:2001 (corresponding Japanese Industrial Standard JIS B 1515-2).

[0072] Similarly, the runout of each end face 53, 55 of the outer ring spacer 26 should be 0.01 mm or less, more preferably 0.007 mm or less, in order to maintain a high level of rotational accuracy of the first bearing 24 and the second bearing 25. The first shear deformation member 51 and the second shear deformation member 52 are interposed between the corresponding first outer ring 32 or second outer ring 35 and the outer ring spacer 26, and the adhesive can smooth out any waviness, etc., of the end face 53 or end face 55 of the outer ring spacer 26 to which it adheres, making it easier to control the runout accuracy.

[0073] Generally, adhesives are classified by the material they contain as their main component. Examples of adhesives used for the first shear deformation member 51 and the second shear deformation member 52 include acrylic adhesives, silicone-based adhesives, rubber-based adhesives, and urethane-based adhesives. In environments where there is oil to lubricate the first bearing 24 and the second bearing 25, and coolant to lubricate the workpiece, the first shear deformation member 51 and the second shear deformation member 52 are required to have oil resistance. Also, since the first bearing 24 and the second bearing 25 that support the high-speed rotating spindle 2 become hot, the first shear deformation member 51 and the second shear deformation member 52 are required to have heat resistance. Considering these factors, acrylic adhesives or silicone-based adhesives are used as the adhesives for the first shear deformation member 51 and the second shear deformation member 52. Acrylic adhesives or silicone-based adhesives are also suitable when weather resistance is required.

[0074] The material of the first shear deformation member 51 and the second shear deformation member 52 is not limited to the adhesive described above, but it is preferable to use a resin. By using a resin, the first shear deformation member 51 and the second shear deformation member 52 can be made to have a shear modulus suitable for reducing the effect of the expansion deformation of the first outer ring 32 and the second outer ring 35 transmitted from the first outer ring 32 and the second outer ring 35 to the outer ring spacer 26 (effect of reducing the transmission of each expansion deformation of the first outer ring 32 and the second outer ring 35). The type of resin can be appropriately selected from, for example, polyamide, polyetheretherketone, polyphenylene sulfide, fluororesin, polyimide, polyamideimide, silicone resin (i.e., silicone), acrylic resin, phenolic resin, epoxy resin, urethane resin, etc., depending on the magnitude of the load applied to the first shear deformation member 51 and the second shear deformation member 52 and the usage environment.

[0075] If the first shear deformation member 51 and the second shear deformation member 52 are made entirely of a metal material such as iron, the shear modulus is larger than that of resin, making it difficult to obtain the effect of reducing the transmission of the expansion deformation of the first outer ring 32 and the second outer ring 35. Also, if the first shear deformation member 51 and the second shear deformation member 52 are made of a coating such as a solid lubricant film attached to the side surfaces 54, 56 of the first outer ring 32 and the second outer ring 35 or the end faces 53, 55 of the outer ring spacer 26, it is difficult to obtain the effect of reducing the transmission of the expansion deformation of the first outer ring 32 and the second outer ring 35, similar to the case with a metal material such as iron.

[0076] The first shear deformation member 51 and the second shear deformation member 52 are exemplified as being made of double-sided tape formed solely of adhesive, which can be attached to the first outer ring 32, the second outer ring 35, or the outer ring spacer 26 by the adhesiveness of their end faces. However, it is also possible to provide the first shear deformation member and the second shear deformation member by applying an adhesive or bonding resin coating agent to the first outer ring 32, the second outer ring 35, or the outer ring spacer 26.

[0077] As described above, this bearing device 1 (see Figures 1 and 2) comprises a first bearing 24 having a first outer ring 32, a first inner ring 33, and a plurality of first rolling elements 34 positioned between the first inner ring 33 and the first outer ring 32; a second bearing 25 having a second outer ring 35, a second inner ring 36, and a plurality of second rolling elements 37 positioned between the second inner ring 36 and the second outer ring 35; an outer ring spacer 26 provided between the first outer ring 32 and the second outer ring 35, which are spaced apart in the axial direction; and a strain sensor 28 attached to the outer ring spacer 26, and is provided with axial preload. Therefore, it becomes possible to adjust the preload load while checking the magnitude of the preload load converted based on the output of the strain sensor 28, and consequently, it becomes unnecessary to strictly control the accuracy of the width dimension of the outer ring spacer 26 (for example, to a tolerance of a few μm).

[0078] This bearing device 1 further includes, in particular, a first shear deformation member 51 interposed between the first outer ring 32 and the outer ring spacer 26 and which deforms radially in accordance with the radial deformation of the first outer ring 32, thereby preventing the transmission of the radial deformation of the first outer ring 32 to the outer ring spacer 26, and a second shear deformation member 52 interposed between the second outer ring 35 and the outer ring spacer 26 and which deforms radially in accordance with the radial deformation of the second outer ring 35, thereby preventing the transmission of the radial deformation of the second outer ring 35 to the outer ring spacer 26, thereby enabling the first outer ring 32 and the second outer ring spacer to be separated. When each of the rings 35 undergoes elastic deformation in the radial expansion direction when preload is applied, the radial deformation of the first outer ring 32 and the radial deformation of the second outer ring 35 are transmitted to the corresponding first shear deformation member 51 or second shear deformation member 52. As a result, the corresponding first shear deformation member 51 or second shear deformation member 52 undergoes radial shear deformation between the corresponding first outer ring 32 and the outer ring spacer 26 or between the second outer ring 35 and the outer ring spacer 26, thus hindering the transmission of the radial deformation of the first outer ring 32 and the radial deformation of the second outer ring 35 to the outer ring spacer 26. Therefore, the transmission of radial deformation of the first outer ring 32 and the second outer ring 35 to the outer ring spacer 26 is reduced compared to when it is directly transmitted to the outer ring spacer 26, thereby reducing minute radial deformation of the outer ring spacer 26 due to the radial deformation of the first outer ring 32 and the second outer ring 35. Consequently, it becomes possible to accurately detect the magnitude of the preload based on the output of the strain sensor 28. In this way, the bearing device 1 can be made capable of accurately detecting the magnitude of the preload based on the output of the strain sensor 28 attached to the outer ring spacer 26.

[0079] Furthermore, in this bearing device 1, since the thickness of the first shear deformation member 51 and the second shear deformation member 52 is 100 μm or less, the amount of displacement of each end face of the first shear deformation member 51 and the second shear deformation member 52 that are compressed in the axial direction by preload can be suppressed, and consequently, the decrease in axial rigidity of the first shear deformation member 51 and the second shear deformation member 52 can be suppressed.

[0080] Furthermore, since the first shear deformation member 51 and the second shear deformation member 52 are each made of adhesive, the first shear deformation member 51 and the second shear deformation member 52 can be easily shear-deformed in the radial direction, thus providing an excellent effect in reducing the transmission of the expansion of the diameter of the first outer ring 32 and the second outer ring 35 to the outer ring spacer 26.

[0081] Furthermore, in this bearing device 1, the first shear deformation member 51 and the second shear deformation member 52 adhere to the corresponding first outer ring 32 or second outer ring 35 and the outer ring spacer 26, preventing the first shear deformation member 51 and the second shear deformation member 52 from falling off, improving the ease of assembly of the bearing device 1. In addition, it becomes possible to peel off the first shear deformation member 51 and the second shear deformation member 52 without damaging the first outer ring 32, the second outer ring 35, and the outer ring spacer 26, thus making it easy to replace the first shear deformation member 51 and the second shear deformation member 52.

[0082] Furthermore, by using acrylic or silicone adhesives as the adhesives for the first shear deformation member 51 and the second shear deformation member 52 of this bearing device 1, the first shear deformation member 51 and the second shear deformation member 52 can have superior oil resistance, heat resistance, and weather resistance compared to rubber adhesives or urethane adhesives.

[0083] Furthermore, because this bearing device 1 has multiple strain sensors 28 mounted on the outer ring spacer 26 at circumferential intervals, even if there is a circumferential bias in the load applied to the outer ring spacer 26, it is possible to detect the magnitude of the strain in the outer ring spacer 26 in a manner that eliminates the influence of the circumferential bias, based on the outputs of the multiple strain sensors 28 arranged at circumferential intervals, and consequently, to accurately detect the magnitude of the preload.

[0084] Furthermore, since this bearing device 1 (see Figures 2 and 3) is equipped with three or more strain sensors 28 at equal intervals in the circumferential direction (three in this embodiment), even if there is a circumferential bias in the preload or fixed load applied to the outer ring spacer 26, it is easy to eliminate the effect of the circumferential bias based on the output of these strain sensors 28.

[0085] Furthermore, this spindle device, which includes the bearing device 1, the spindle 2 of a machine tool rotatably supported by the bearing device 1, and the motor 4 that rotates the spindle 2, enables stable monitoring of the machine tool's condition for labor-saving or unmanned operation, and also allows detection of the machining load acting on the spindle 2 during cutting operations. The first shear deformation member 51 and the second shear deformation member 52, which are provided on the non-rotating side (spindle housing 3 side), do not particularly adversely affect the rotational accuracy of the high-speed rotating spindle 2.

[0086] Figures 7 and 8 show the main parts of the bearing device according to the second embodiment of this invention. In the following, only the differences from the first embodiment will be described, and the same reference numerals will continue to be used for corresponding components.

[0087] The bearing device according to the second embodiment has a plurality of first shear deformation members 51 and a plurality of second shear deformation members 52. These first shear deformation members 51 and second shear deformation members 52 are each spaced apart in the circumferential direction. The phase of this arrangement corresponds to the phase of a plurality of strain sensors 28. The paths that can transmit the aforementioned preload load and outer ring fixed load between the first side surface 54 of the first outer ring 32 and the first end face 53 of the outer ring spacer 26 are limited to locations where the first shear deformation members 51 are interposed, and are therefore limited to a plurality of locations in the circumferential direction that are in phase with the strain sensors 28. Similarly, the paths that can transmit the aforementioned preload load and outer ring fixed load between the second side surface 56 of the second outer ring 35 and the second end face 55 of the outer ring spacer 26 are limited to locations where the second shear deformation members 52 are interposed, and are therefore limited to a plurality of locations in the circumferential direction that are in phase with the strain sensors 28. Therefore, the load applied to the outer ring spacer 26 is concentrated on the surface in contact with each strain sensor 28 (the groove bottom surface of the axial groove 49) compared to the first embodiment. As a result, the strain on the surface in contact with each strain sensor 28 increases, and the repeatability of the generated strain is also improved.

[0088] If the first and second shear deformation members are arranged to avoid the circumferential position corresponding to the strain sensor 28, the load will not be concentrated on the surface of the outer ring spacer 26 that is in contact with the strain sensor 28, and the sensitivity of the strain sensor 28 to the load will decrease, which is undesirable.

[0089] In the illustrated example, the first shear deformation member 51 and the second shear deformation member 52 are attached to the outer ring spacer 26, and the arrangement of the first shear deformation member 51 and the second shear deformation member 52 is determined so that the axial groove 49 can be used as a marker to indicate the attachment position. Specifically, the first shear deformation member 51 and the second shear deformation member 52 are positioned between a virtual plane that is parallel to the virtual axial plane passing through the circumferential center of the corresponding strain sensor 28 and the central axis of the outer ring spacer 26 and passing through one circumferential end of the axial groove 49, and a virtual plane that is parallel to that virtual axial plane and passing through the other circumferential end of the axial groove 49.

[0090] If the aforementioned load concentration effect is to be emphasized, it is preferable to arrange the first shear deformation member and the second shear deformation member in the smallest possible area. For example, they should be arranged across a virtual plane that is parallel to the aforementioned virtual axial plane and tangent to one circumferential end of the strain sensor 28, and a virtual plane that is parallel to the aforementioned virtual axial plane and tangent to the other circumferential end of the strain sensor 28.

[0091] Furthermore, in order to stabilize the first outer ring 32, the second outer ring 35, and the outer ring spacer 26, it is preferable to equally distribute the first shear deformation member 51 and the second shear deformation member 52 at three or more locations in the circumferential direction. The runout at the locations where the first shear deformation member 51 and the second shear deformation member 52 are provided can be managed as a common plane encompassing all locations.

[0092] In the bearing device according to the second embodiment, in particular, the plurality of first shear deformation members 51 and the plurality of second shear deformation members 52 are arranged at circumferential positions corresponding to the plurality of strain sensors 28, with intervals in the circumferential direction between them. This limits the position where the load from the first outer ring 32 and the second outer ring 35 is applied to the outer ring spacer 26 to the circumferential positions corresponding to the plurality of strain sensors 28. This makes it possible to generate a large amount of strain in the outer ring spacer 26 due to the load at the surface portion in contact with each strain sensor 28 (the groove bottom surface of the axial groove 49), thereby increasing the sensitivity of each strain sensor 28 to the load and, consequently, improving the load detection accuracy based on the output of each strain sensor 28.

[0093] Figures 9 and 10 show the main parts of the bearing device according to the third embodiment of this invention. Since the third embodiment is a further modification of the second embodiment, only the differences from the second embodiment will be described here, and the same reference numerals will continue to be used for corresponding components.

[0094] The outer ring spacer 26 according to the third embodiment has multiple first end faces 53 in contact with the first shear deformation member 51 and multiple second end faces 55 in contact with the second shear deformation member 52, each spaced apart in the circumferential direction. The axial front side (the side closer to the first outer ring 32) of the outer ring spacer 26 consists of multiple first end faces 53 and recesses 57, and the axial rear side (the side closer to the second outer ring 35) of the outer ring spacer 26 consists of multiple second end faces 55 and recesses 58.

[0095] The first end face 53 and the second end face 55 are equally spaced in the circumferential direction and are positioned in the circumferential direction corresponding to the multiple strain sensors 28 and axial grooves 49. All of these multiple first end faces 53 are located in the same axial position and are positioned on the axial front side (closer to the first outer ring 32) of the outer ring spacer 26. Similarly, all of these multiple second end faces 55 are located in the same axial position and are positioned on the axial rear side (closer to the second outer ring 35) of the outer ring spacer 26.

[0096] One first shear deformation member 51 is attached to each first end face 53. One second shear deformation member 52 is attached to each second end face 55. The first end face 53 and the second end face 55 have the same planar shape as the corresponding first shear deformation member 51 or second shear deformation member 52. In other words, the first end face 53 and the second end face 55 in the illustrated example are planar in shape, respectively, extending between a virtual axial plane that is parallel to the virtual axial plane passing through the circumferential center of the corresponding strain sensor 28 and the central axis of the outer ring spacer 26 and passing through one circumferential end of the axial groove 49, and a virtual plane that is parallel to that virtual axial plane and passing through the other circumferential end of the axial groove 49.

[0097] Each first end face 53 and each second end face 55 of the outer ring spacer 26 are surfaces aligned circumferentially and radially at corresponding axial positions (surfaces included in the same virtual radial plane), and therefore require high-precision machining. For this reason, recesses 57 and 58 are formed in the outer ring spacer 26 by machining, and the tip surfaces of the protrusions machined out by the formation of these recesses 57 and 58 are finished to become the first end face 53 or the second end face 55. The positions of the first end face 53 and the second end face 55, which are manufactured by machining, are highly precise. Because the preload is transmitted via the corresponding first shear deformation members 51 or the second shear deformation members 52 only between each first end face 53 and each second end face 55 with such high positional precision and the corresponding first side surface 54 of the first outer ring 32 or the second side surface 56 of the second outer ring 35, the load concentration on the surface in contact with each strain sensor 28 (the groove bottom surface of the axial groove 49) is also highly precise. In other words, it becomes possible to reduce the variation in the magnitude of the load applied to the strain sensor 28 at each phase.

[0098] As described above, since the multiple first end faces 53 and the multiple second end faces 55 are each formed on surfaces included in their corresponding virtual radial planes, the runout at these locations can be managed as a common surface (i.e., the corresponding virtual radial plane) encompassing all locations.

[0099] As described above, the bearing device according to the third embodiment has an outer ring spacer 26 having a first end face 53 that contacts the first shear deformation member 51 and extends in the circumferential and radial directions, and a second end face 55 that contacts the second shear deformation member 52 and extends in the circumferential and radial directions, and each of the first end face 53 and the second end face 55 is provided at multiple locations spaced apart in the circumferential direction, and the multiple first end faces 53 are located in the axial position closest to the first outer ring 32 in the outer ring spacer 26, and the multiple second end faces 55 are located in the axial position closest to the second outer ring 35 in the outer ring spacer 26, so that the preload is transmitted via the corresponding first shear deformation member 51 or second shear deformation member 52 only between each first end face 53 and each second end face 55 and the corresponding first outer ring 32 or second outer ring 35, thereby reducing the variation in the magnitude of the load applied to the strain sensor 28 at each phase.

[0100] Furthermore, in the bearing device according to the third embodiment, the first end face 53 and the second end face 55 are located in positions that protrude the most in the axial direction from one end or the other end (in the illustrated example, the axial front or axial rear) of the outer ring spacer 26. Therefore, when attaching the first shear deformation member 51 and the second shear deformation member 52 to the outer ring spacer 26, the positions on the outer ring spacer 26 where the first shear deformation member 51 and the second shear deformation member 52 should be attached are clear, and it is also possible to ensure that the multiple first shear deformation members 51 and the multiple second shear deformation members 52 are arranged in the appropriate phase.

[0101] In the embodiments described above, examples were shown in which double-sided tape made of adhesive was used for the first shear deformation member 51 and the second shear deformation member 52, respectively. However, the first shear deformation member and the second shear deformation member can also be made of multiple materials. As an example, the main parts of the bearing device according to the fourth embodiment are shown in Figures 11 and 12. Note that the fourth embodiment is a modification of the structures of the first shear deformation member and the second shear deformation member in the embodiments described above. Therefore, only the modifications will be described here, and the same reference numerals will continue to be used for corresponding components.

[0102] The first shear deformation member 51 according to the fourth embodiment consists of a tape having an adhesive 59 and a base material 60 that supports the adhesive 59. For example, paper, cloth, film, metal foil, etc., can be used as the base material 60. The entire surface of one side of the base material 60 is covered with the adhesive 59. The side of the base material 60 opposite to the adhesive 59 constitutes one side of the tape. The first shear deformation member 51 is attached to the first end face 53 of the outer ring spacer 26 in the layer of adhesive 59 as shown in Figure 11, or to the first side surface 54 of the first outer ring 32 as shown in Figure 12. A second shear deformation member 52 (see Figure 2), not shown, also consists of a tape with the same specifications as the first shear deformation member 51. In the illustration, an example is shown in which a single-sided tape, in which the adhesive layer 59 is provided only on one side of the base material 60, is used for the first shear deformation member, etc. However, it is also possible to use a double-sided tape, in which the adhesive layer is provided on both sides of the base material, for the first shear deformation member, etc.

[0103] In the bearing device according to the fourth embodiment (see Figures 2, 11, and 12), the first shear deformation member 51 and the second shear deformation member 52 are each made of a tape having an adhesive 59 and a base material 60 that supports the adhesive 59. As a result, the first shear deformation member 51 and the second shear deformation member 52 can be easily shear-deformed radially in the layer of adhesive 59, thus providing an excellent effect in reducing the transmission of radial deformation of the first outer ring 32 and the second outer ring 35.

[0104] Furthermore, in the bearing device according to the fourth embodiment, since the first shear deformation member 51 and the second shear deformation member 52 are attached to the outer ring spacer 26 or the corresponding first outer ring 32 or second outer ring 35 in layers of adhesive 59, it is possible to prevent the first shear deformation member 51 and the second shear deformation member 52 from falling off, improving the ease of assembly of the bearing device 1. In addition, it is possible to peel off the first shear deformation member 51 and the second shear deformation member 52 without damaging the first outer ring 32, the second outer ring 35, and the outer ring spacer 26, respectively, making it easy to replace the first shear deformation member 51 and the second shear deformation member 52.

[0105] Furthermore, since the bearing device according to the fourth embodiment is a tape that includes a base material 60 supporting the adhesive 59, it is less likely to tear when attaching or removing the first shear deformation member 51 and the second shear deformation member 52 during assembly or replacement, making the work easier.

[0106] As described above, the inventors of this application investigated the effect of preventing radial deformation transmission on various samples in order to find suitable materials and structures for the first shear deformation member and the second shear deformation member.

[0107] Sample 1 consists of a tape with a polyimide film as the base material and an adhesive layer on only one side of the base material. Sample 2 consists of a tape with copper as the base material and an adhesive layer on only one side of the base material. Sample 3 consists of a double-sided tape with an iron shim as the base material and adhesive layers on both sides of the base material. Sample 4 consists of adhesive (double-sided tape). Sample 5 consists of polyimide film. Sample 6 consists of iron-based shim (shim tape). Sample 7 consists of a solid lubricating film (DLC film). For samples that could not be attached by adhesive, they were attached to the aforementioned test specimens using an adhesive or by a coating treatment. When the effect of preventing the radial deformation of the first and second outer rings from being transmitted to the outer ring spacer was evaluated for these samples 1 to 7 using the same method, good effects were obtained for samples 1 to 3, which are tapes with a base material and adhesive, and for sample 4, which is a double-sided tape consisting of adhesive. However, sample 5, which is simply a polyimide film without adhesive properties, showed an inferior effect compared to samples 1 to 4. In other words, it is thought that the adhesive tends to have the effect of preventing radial deformation from being transmitted when a load is applied to the outer ring spacer via the adhesive. Furthermore, no significant effect was obtained for samples 6 and 7, which lacked adhesiveness and had poor radial shear deformation properties.

[0108] Therefore, samples 1, 4, and 5 were selected and load detection tests were conducted. Load detection tests were also performed on comparative examples without the first and second shear deformation members. In these load detection tests, an outer ring spacer of a certain shape was used as the test specimen, and the same test specimen and strain sensor were used in all tests.

[0109] Figure 13 shows a graph illustrating the relationship between the magnitude of the load obtained in the load detection test of the comparative example and the output of the strain sensor. Figure 14 shows a graph illustrating the relationship between the magnitude of the load obtained in the load detection test of Sample 1 and the output of the strain sensor. Figure 15 shows a graph illustrating the relationship between the magnitude of the load obtained in the load detection test of Sample 4 and the output of the strain sensor. Figure 16 shows a graph illustrating the relationship between the magnitude of the load obtained in the load detection test of Sample 5 and the output of the strain sensor. These graphs represent the change in output during the process of applying a load to a predetermined magnitude.

[0110] The graph of the comparative example shown in Figure 13 cannot express the relationship between the magnitude of the load and the output of the strain sensor as a linear function. On the other hand, the graph of Sample 1 (polyimide film + adhesive) shown in Figure 14 and the graph of Sample 4 (adhesive) shown in Figure 15 both show linearity throughout the entire process that can be expressed as a linear function, and the linearity is clearly improved compared to the graph shown in Figure 13. The graph of Sample 5 (polyimide film) shown in Figure 16 shows a clearly inferior improvement in linearity compared to Figures 14 and 15. From these load detection test results, it is considered that, as exemplified in each embodiment described above, adopting a first shear deformation member and a second shear deformation member made of adhesive, or a first shear deformation member and a second shear deformation member made of a tape having a base material and adhesive, is particularly effective in preventing the transmission of radial deformation of the first and second outer rings to the outer ring spacer.

[0111] Furthermore, as mentioned above, when the first shear deformation member and the second shear deformation member are fully attached to the corresponding first and second end faces of the outer ring spacer with an adhesive layer, it becomes possible to obtain accurate calibration values ​​for the strain gauge attached to the outer ring spacer.

[0112] For example, when converting to preload using the outputs of multiple strain sensors 28 as described above, the preload can be estimated with good accuracy. However, if there is a difference in sensitivity among the strain sensors 28, the accuracy of the preload estimation decreases. To accurately estimate the preload, it is necessary to correct the sensitivity of the strain sensors 28 to be as similar as possible. One factor that causes differences in the sensitivity of the strain sensors 28 is that the state in which the strain sensors 28 are attached to the outer ring spacer 26 using adhesive, etc., is not the same for each strain gauge 28 (hereinafter referred to as attachment error). Since the strain of the outer ring spacer 26 is transmitted to the strain sensor 28 via adhesive, etc., a difference in the sensitivity of the strain sensor 28 occurs depending on the attachment error relative to the reference attachment state. When multiple strain sensors 28 are attached to the outer ring spacer 26, the sensitivity of each strain sensor 28 may differ due to attachment errors, etc.

[0113] Before assembling the outer ring spacer 26 into the bearing device 1, the strain sensor 28 is calibrated, and then, based on the calibration values ​​obtained, calibration is performed to improve the accuracy of the conversion to preload. In this calibration, the first end face 53 and the second end face 55 of the outer ring spacer 26 are fully supported by a disc surface (not shown; the disc surface replaces the first outer ring 32 and the second outer ring 35 in Figures 5, 8, and 10), and a predetermined axial load is applied to the outer ring spacer 26 via the disc surface using an autograph or the like. Generally, the first end face 53 and the second end face 55 of the outer ring spacer 26 are controlled to a flatness of several μm, but there are minute surface undulations and irregularities. If the first end face 53 and the second end face 55 of the outer ring spacer 26 were directly supported by the disc surface, the contact state between the first end face 53 and the second end face 55 of the outer ring spacer 26 and the aforementioned disc surface would differ locally due to minute undulations, etc. Therefore, even if the same axial load is applied to the outer ring spacer 26 via the aforementioned disc surface, the load characteristics of the strain sensor 28 may differ from the reference load characteristics. For this reason, it is difficult to determine whether the calibration value obtained in the calibration includes the bonding error, and it is not possible to obtain a calibration value that can accurately correct the bonding error. As a result, there is a concern that calibration will be performed with a calibration value that includes the bonding error, leading to a large conversion error in the preload.

[0114] In contrast, during calibration, the first shear deformation member 51 (see Figures 4, 5, 7-10) and the second shear deformation member 52 are fully attached to the corresponding first end face 53 and second end face 55 of the outer ring spacer 26 with a layer of adhesive. When the aforementioned disc surface is brought into contact with the first shear deformation member 51 and the second shear deformation member 52, and a predetermined axial load is applied to the outer ring spacer 26 via the disc surface, the adhesive penetrates the aforementioned minute undulations and irregularities, improving the contact condition with the disc surface (the load distribution on the outer ring spacer 26 becomes uniform). As a result, calibration values ​​for correcting adhesion errors can be obtained with high accuracy.

[0115] For example, if strain sensors 28 are attached to multiple locations on the circumference of the outer ring spacer 26 at circumferential intervals, the same load is applied to each attachment point of the strain sensors 28 on the outer ring spacer 26. Therefore, the sensitivity of each strain sensor 28 will more accurately reflect the influence of the attachment error. Consequently, by performing calibration to adjust the sensitivity of all strain sensors 28 to match based on the acquired calibration values, the accuracy of the preload estimation can be improved.

[0116] One method for adjusting the sensitivity differences of the strain sensors 28 is to perform the aforementioned calibration and calculate a correction coefficient so that the sensitivity of one strain sensor 28 selected from among the multiple strain sensors 28 is used as a reference, and the sensitivity of the remaining strain sensors 28 is adjusted (matched) to that reference strain sensor 28.

[0117] Another example involves calculating the strain generated in the outer ring spacer 26 using numerical analysis (to determine a reference sensitivity), and then calculating a correction coefficient to adjust the sensitivity of each strain sensor 28 to match the aforementioned calculated reference sensitivity. This method can also be used when only one strain sensor 28 is attached to the outer ring spacer 26.

[0118] In the embodiments described above, angular contact ball bearings were used as examples for the first bearing 24 and the second bearing 25. However, other types of rolling bearings that generate a radial component force from an axial preload can also be used as the first bearing 24 and the second bearing 25, such as tapered roller bearings or deep groove ball bearings.

[0119] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than by the foregoing description, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0120] 1. Bearing device 2 spindle 4 motors 24 First bearing 25 Second bearing 26 Outer wheel spacer 28. Strain Sensor 29 Preload nut 32 First outer ring 33 First Inner Ring 34. First Rolling Element 35. Second outer ring 36. Second inner ring 37. Second rolling element 51 First shear deformation member 52 Second shear deformation member 53 1st end face 55 2nd end face

Claims

1. A first bearing having a first outer ring, a first inner ring, and a plurality of first rolling elements disposed between the first inner ring and the first outer ring, A second bearing having a second outer ring, a second inner ring, and a plurality of second rolling elements disposed between the second inner ring and the second outer ring, An outer ring spacer is provided between the first outer ring and the second outer ring, which are spaced apart in the axial direction, The system includes a strain sensor attached to the outer ring spacer, In a bearing device to which axial preload is applied, A first shear deformation member interposed between the first outer ring and the outer ring spacer, which deforms radially in accordance with the radial deformation of the first outer ring, thereby preventing the transmission of the radial deformation of the first outer ring to the outer ring spacer, A bearing device further comprising a second shear deformation member interposed between the second outer ring and the outer ring spacer, which deforms radially in accordance with the radial deformation of the second outer ring, thereby preventing the transmission of the radial deformation of the second outer ring to the outer ring spacer.

2. Multiple strain sensors are attached to the outer ring spacer at circumferential intervals. The bearing device according to claim 1, wherein a plurality of the first shear deformation members and a plurality of the second shear deformation members are each arranged at circumferential intervals and at circumferential positions corresponding to the plurality of strain sensors.

3. The outer ring spacer has a first end face that contacts the first shear deformation member and extends in the circumferential and radial directions, and a second end face that contacts the second shear deformation member and extends in the circumferential and radial directions, and each of the first end face and the second end face is provided at multiple locations spaced apart in the circumferential direction. The plurality of first end faces are located in the axial position closest to the first outer ring within the outer ring spacer, The bearing device according to claim 2, wherein the plurality of second end faces are in the axial position closest to the second outer ring in the axial direction among the outer ring spacers.

4. The bearing device according to any one of claims 1 to 3, wherein the thickness of the first shear deformation member and the second shear deformation member is 100 μm or less.

5. The bearing device according to any one of claims 1 to 3, wherein the first shear deformation member and the second shear deformation member are each made of an adhesive.

6. The bearing device according to any one of claims 1 to 3, wherein the first shear deformation member and the second shear deformation member each consist of a tape having an adhesive and a base material that supports the adhesive.

7. The bearing device according to claim 5, wherein the adhesive is an acrylic adhesive or a silicone adhesive.

8. A bearing device according to any one of claims 1 to 3, The spindle of a machine tool, which is rotatably supported by the aforementioned bearing device, A spindle device having a motor that rotates the main shaft.

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