JP2024067312A - Bearing device with strain sensor and spindle device for machine tool - Google Patents

Abstract

To provide a bearing device with a strain sensor which can detect a bearing pre-load with high accuracy.SOLUTION: At a first outer ring 30 side end of an outer ring spacer 26, a first annular cutout 57 having an annular shape is formed by cutting out one or both of an intersection part between a first axial end surface 52 and a cylindrical inner peripheral surface 50 and an intersection part between the first axial end surface 52 and a cylindrical outer peripheral surface 51 over whole circumference. At a second outer ring 35 side end of the outer ring spacer 26, a second annular cutout 58 having an annular shape is formed by cutting out one or both of an intersection part between a second axial end surface 53 and the cylindrical inner peripheral surface 50 and an intersection part between the second axial end surface 53 and the cylindrical outer peripheral surface 51 over whole circumference.SELECTED DRAWING: Figure 2

Description

This invention relates to a bearing device with a strain sensor and a spindle device for a machine tool that uses the bearing device with a strain sensor.

In machining centers, lathes and other machine tools, and other industrial machines, spindle devices are used that rotatably support a rotating shaft on which tools, workpieces, and other objects are attached. In recent years, there has been a demand in fields where such spindle devices are used to strengthen the status monitoring function in order to reduce manpower and achieve automation.

Therefore, the applicant of this application has already proposed a bearing device equipped with a strain sensor to meet the need for enhanced condition monitoring functions (Patent Document 1).

The bearing device with strain sensor in Patent Document 1 has a first bearing and a second bearing spaced apart in the axial direction, a cylindrical outer ring spacer provided between the first bearing and the second bearing, and a strain sensor attached to the outer ring spacer.

The first bearing has a first outer ring, a first inner ring provided radially inside the first outer ring, and a plurality of first rolling elements assembled between the first outer ring and the first inner ring. Similarly, the second bearing has a second outer ring, a second inner ring provided radially inside the second outer ring, and a plurality of second rolling elements assembled between the second outer ring and the second inner ring. The outer ring spacer is arranged by being sandwiched between the first outer ring and the second outer ring in the axial direction.

An axial preload is applied between the first bearing and the second bearing so that the preload is transmitted through the first inner ring, the first rolling element, the first outer ring, the outer ring spacer, the second outer ring, the second rolling element, and the second inner ring. The first bearing is an angular ball bearing configured so that the axial preload generates a radial component force that causes the first rolling element to press the first outer ring, and the second bearing is also an angular ball bearing configured so that the axial preload generates a radial component force that causes the second rolling element to press the second outer ring.

The outer ring spacer is a cylindrical member having a cylindrical inner peripheral surface, a cylindrical outer peripheral surface, a first axial end face, and a second axial end face. The first axial end face is an annular axis-perpendicular plane having a width equal to the radial thickness between the cylindrical inner peripheral surface and the cylindrical outer peripheral surface, and this axis-perpendicular plane is pressed against the first outer ring with an axial preload. Similarly, the second axial end face is an annular axis-perpendicular plane having a width equal to the radial thickness between the cylindrical inner peripheral surface and the cylindrical outer peripheral surface, and this axis-perpendicular plane is pressed against the second outer ring with an axial preload.

The strain sensor is attached to a flat sensor mounting surface formed by cutting out a portion of the cylindrical inner surface of the outer ring spacer, and the preload of the first bearing and second bearing (hereinafter referred to as "bearing preload") can be detected based on the output of this strain sensor.

JP 2021-014886 A

However, in the strain sensor-equipped bearing device of Patent Document 1, an error could occur in the magnitude of the bearing preload detected based on the output of the strain sensor on the inner circumference of the outer ring spacer. If this error could be eliminated and the bearing preload could be detected with high accuracy, it would be possible to improve the reliability of condition monitoring for labor-saving or unmanned operation.

The problem that this invention aims to solve is to provide a bearing device with a strain sensor that can detect bearing preload with high accuracy.

The inventors of the present application prototyped and evaluated the strain sensor-equipped bearing device of Patent Document 1 above, and found that when the bearing preload was changed, the first axial end face and the second axial end face of the outer ring spacer slipped radially between the first and second outer rings, and that this slippage caused the first axial end face and the second axial end face of the outer ring spacer to come into strong contact with the first and second outer rings at a position closer to the radial inside, and to come into strong contact with the first and second outer rings at a position closer to the radial outside.

When the first axial end face and the second axial end face of the outer ring spacer make strong contact at a position closer to the radial inside, the bearing preload is transmitted mainly through the inner circumference of the outer ring spacer, and the output of the strain sensor attached to the inner circumference of the outer ring spacer becomes large. Conversely, when the first axial end face and the second axial end face of the outer ring spacer make strong contact at a position closer to the radial outside, the bearing preload is transmitted mainly through the outer circumference of the outer ring spacer, and the output of the strain sensor attached to the inner circumference of the outer ring spacer becomes small.

In this way, even if the magnitude of the bearing preload is the same, the output of the strain sensor is not the same when the first axial end face and the second axial end face of the outer ring spacer make strong contact at a position closer to the radial inside and when they make strong contact at a position closer to the radial outside, and it was found that this causes an error in the bearing preload detected based on the output of the strain sensor.

The inventors of the present application came up with the idea that if the first axial end face and the second axial end face of the outer ring spacer are shaped in advance so that they come into contact within a specific narrow radial range, it would be possible to minimize the error in the bearing preload detected based on the output of the strain sensor.

Based on this idea, in order to solve the above problems, the present invention provides a bearing device with a strain sensor having the following configuration.
[Configuration 1]
The bearing has a first bearing and a second bearing spaced apart in the axial direction, a cylindrical outer ring spacer provided between the first bearing and the second bearing, and a strain sensor attached to the outer ring spacer,
the first bearing includes a first outer ring, a first inner ring provided radially inside the first outer ring, and a plurality of first rolling elements assembled between the first outer ring and the first inner ring;
the second bearing includes a second outer ring, a second inner ring provided radially inside the second outer ring, and a plurality of second rolling elements assembled between the second outer ring and the second inner ring,
an axial preload is applied between the first bearing and the second bearing such that the preload is transmitted through the first inner ring, the first rolling element, the first outer ring, the outer ring spacer, the second outer ring, the second rolling element, and the second inner ring;
the outer ring spacer has a cylindrical inner circumferential surface, a cylindrical outer circumferential surface, a planar sensor mounting surface formed by cutting out a portion of the cylindrical inner circumferential surface or the cylindrical outer circumferential surface, a first axial end face pressed against the first outer ring by the axial preload, and a second axial end face pressed against the second outer ring by the axial preload, and the strain sensor is attached to the sensor mounting surface,
a first annular notch is formed at an end of the outer ring spacer on the side of the first outer ring, the first annular notch being cut out over an entire circumference of one or both of an intersection of the first axial end face and the cylindrical inner circumferential surface and an intersection of the first axial end face and the cylindrical outer circumferential surface,
a second annular notch is formed on the end of the outer ring spacer on the second outer ring side, the second annular notch being cut out around the entire circumference of one or both of the intersection of the second axial end face and the cylindrical inner circumferential surface and the intersection of the second axial end face and the cylindrical outer circumferential surface.

By adopting this configuration, the first axial end face is narrowed in the radial direction by the amount of the first annular notch, so that the difference in the radial position of the strong contact point can be kept small between the case where the first axial end face strongly contacts the first outer ring at a position closer to the radial outside and the case where the first axial end face strongly contacts the first outer ring at a position closer to the radial inside. Similarly, the second axial end face is narrowed in the radial direction by the amount of the second annular notch, so that the difference in the radial position of the strong contact point can be kept small between the case where the second axial end face strongly contacts the second outer ring at a position closer to the radial outside and the case where the second axial end face strongly contacts the second outer ring at a position closer to the radial inside. Therefore, the radial position through which the bearing preload passes is stable between the first axial end face and the second axial end face of the outer ring spacer, and errors are less likely to occur in the output of the strain sensor. As a result, it is possible to detect the bearing preload with high accuracy.

[Configuration 2]
2. The bearing device with strain sensor according to claim 1, wherein the first annular notch and the second annular notch are formed so that the first axial end face and the second axial end face are aligned at the same radial position.

When this configuration is adopted, the first axial end face and the second axial end face are aligned at the same radial position, so the radial position through which the bearing preload passes between the first axial end face and the second axial end face of the outer ring spacer becomes particularly stable, making it particularly unlikely that errors will occur in the output of the strain sensor.

[Configuration 3]
3. The bearing device with a strain sensor as described in configuration 1 or 2, wherein the first annular notch and the second annular notch are formed so that the radial width of the first axial end face and the radial width of the second axial end face are 50% or less of the radial thickness between the cylindrical inner surface and the cylindrical outer surface.

By adopting this configuration, it is possible to effectively stabilize the radial position through which the bearing preload passes between the first axial end face and the second axial end face of the outer ring spacer.

[Configuration 4]
3. The bearing device with a strain sensor as described in configuration 1 or 2, wherein the first annular notch and the second annular notch are formed so that the radial width of the first axial end face and the radial width of the second axial end face are 20% or less of the radial thickness between the cylindrical inner surface and the cylindrical outer surface.

By adopting this configuration, it becomes possible to particularly effectively stabilize the radial position through which the bearing preload passes between the first axial end face and the second axial end face of the outer ring spacer.

[Configuration 5]
5. The bearing device with a strain sensor according to any one of configurations 1 to 4, wherein the strain sensor is disposed on an inner circumference of the outer ring spacer.

[Configuration 6]
5. The bearing device with a strain sensor according to any one of configurations 1 to 4, wherein the strain sensor is disposed on an outer periphery of the outer ring spacer.

[Configuration 7]
5. The bearing device with strain sensor according to any one of configurations 1 to 4, wherein the strain sensors are arranged on both the inner circumference and the outer circumference of the outer ring spacer.

By adopting this configuration, it is possible to detect the degree to which the radial position through which the bearing preload passes is biased radially inward or outward between the first axial end face and the second axial end face. In addition, by taking the sum of the output of the strain sensor arranged on the inner circumference of the outer ring spacer and the output of the strain sensor arranged on the outer circumference of the outer ring spacer, it is possible to cancel out the effect of the radial position through which the bearing preload passes being biased radially inward or outward, and to detect the axial preload load with stable accuracy.

[Configuration 8]
A bearing device with a strain sensor as described in any one of configurations 1 to 7, wherein the first axial end face is a surface that has been subjected to friction reduction treatment to reduce the friction coefficient with the first outer ring, and the second axial end face is also a surface that has been subjected to friction reduction treatment to reduce the friction coefficient with the second outer ring.

By adopting this configuration, friction reduction treatment is applied to the first axial end face and the second axial end face, so radial bias in the contact pressure of the first axial end face and the second axial end face is less likely to occur. Therefore, it is possible to particularly effectively stabilize the radial position through which the bearing preload passes between the first axial end face and the second axial end face of the outer ring spacer.

The present invention also provides a machine tool spindle device using the above-mentioned strain sensor-equipped bearing device, which has the following configuration.
[Configuration 9]
A bearing device with a strain sensor according to any one of configurations 1 to 8,
a main spindle of a machine tool rotatably supported by the bearing device with a strain sensor;
a motor that drives and rotates the main shaft.

By adopting this configuration, it becomes possible to stably monitor the status of machine tools to reduce the number of workers required or to operate them unmanned. It also becomes possible to detect the processing load acting on the spindle of the machine tool during cutting.

In the strain sensor-equipped bearing device of the present invention, the first axial end face is narrowed in the radial direction by the provision of the first annular notch, so the difference in the radial position of the strong contact point is small between when the first axial end face strongly contacts the first outer ring at a position closer to the radial outside and when the first outer ring strongly contacts the first outer ring at a position closer to the radial inside. Similarly, the second axial end face is narrowed in the radial direction by the provision of the second annular notch, so the difference in the radial position of the strong contact point is small between when the second axial end face strongly contacts the second outer ring at a position closer to the radial outside and when the second outer ring strongly contacts the second outer ring at a position closer to the radial inside. Therefore, the radial position through which the bearing preload passes is stable between the first axial end face and the second axial end face of the outer ring spacer, so that errors are unlikely to occur in the output of the strain sensor, and it is possible to detect the bearing preload with high accuracy.

FIG. 1 is a cross-sectional view showing a spindle device for a machine tool that uses a bearing device with a strain sensor according to an embodiment of the present invention. An enlarged view of the vicinity of the strain sensor-equipped bearing device of FIG. 3 is a cross-sectional view taken along line III-III in FIG. 2 . 4 is a cross-sectional view taken along line IV-IV of FIG. FIG. 5 is a diagram showing a modified outer ring spacer in which the first annular notch and the second annular notch shown in FIG. 4 are formed only on the radially outer portions of both axial ends of the outer ring spacer. FIG. 5 is a diagram showing a modified outer ring spacer in which the first annular notch and the second annular notch shown in FIG. 4 are formed only on the radially inner portions of both axial ends of the outer ring spacer. FIG. 4 shows a modified outer ring spacer in which the arrangement of the strain sensor shown in FIG. 3 is changed from the inner periphery of the outer ring spacer to the outer periphery. 7 is a cross-sectional view taken along line VII-VII of FIG. FIG. 4 is a diagram showing a modified outer ring spacer in which the strain sensor shown in FIG. 3 is provided on both the inner and outer peripheries of the outer ring spacer. 9. Cross-sectional view taken along line XX in FIG. FIG. 5 is a diagram showing a modified example of the first annular notch and the second annular notch shown in FIG. FIG. 5 is a diagram showing another modified example of the first annular notch and the second annular notch shown in FIG. 4 . FIG. 5 is an enlarged cross-sectional view of the vicinity of a first axial end surface, showing a modified example in which a friction reduction treatment is applied to the first axial end surface of the outer ring spacer shown in FIG.

Figure 1 shows a spindle device for a machine tool that uses a bearing device with a strain sensor 1 (hereinafter simply referred to as "bearing device 1") according to an embodiment of the present invention. This spindle device has a main spindle 2 of the machine tool, a main spindle housing 3 that accommodates the main spindle 2, a motor 4 that drives and rotates the main spindle 2, the bearing device 1 of the embodiment that rotatably supports the main spindle 2 axially forward of the motor 4, and a rear bearing device 5 that rotatably supports the main spindle 2 axially rearward of the motor 4.

The spindle housing 3 is formed in a hollow cylinder with both ends open. The spindle housing 3 accommodates the bearing device 1 and the motor 4 in that order from the front to the rear in the axial direction. In the figure, the part of the spindle housing 3 that accommodates the bearing device 1 and the part of the spindle housing 3 that accommodates the motor 4 are formed seamlessly as one piece, but the part of the spindle housing 3 that accommodates the bearing device 1 and the part of the spindle housing 3 that accommodates the motor 4 may be formed separately and then connected to form an integrated unit.

The spindle 2 is inserted into the spindle housing 3 with the front end of the spindle 2 protruding from the front end opening of the spindle housing 3. A chuck (not shown) for gripping a tool or workpiece is removably attached to the front end of the spindle 2. A through hole 6 is formed axially through the spindle 2 to accommodate a drawbar (not shown) of the machine tool so that it can slide axially.

The motor 4 has a rotor 7 attached to the outer periphery of the main shaft 2 and an annular stator 8 that applies a rotational force to the rotor 7. The rotor 7 has a rotor sleeve 9 that fits onto the outer periphery of the main shaft 2 and a rotor core 10 fixed to the outer periphery of the rotor sleeve 9. The rotor core 10 is, for example, a laminate of electromagnetic steel sheets. The rotor sleeve 9 is prevented from rotating on 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 step 11 formed on the outer periphery of the main shaft 2, and is positioned in the axial direction by the contact with the step 11.

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

The rear bearing device 5 has an annular bearing support member 14 that is coaxially fixed to the rear end of the spindle housing 3, and a rolling bearing 15 that is assembled into the bearing support member 14. The rolling bearing 15 is a cylindrical roller bearing that has an outer ring 16 that fits into the inner periphery of the bearing support member 14, an inner ring 17 that fits into the outer periphery of the spindle 2, and a number of cylindrical rollers 18 that are assembled between the outer ring 16 and the inner ring 17.

An outer ring pressing member 19 is attached to the bearing support member 14. The outer ring pressing member 19 fixes the axial position of the outer ring 16 by contacting the axial rear end face of the outer ring 16. A nut member 20 that presses the inner ring 17 axially forward and an annular spacer 21 assembled between the inner ring 17 and the nut member 20 are attached to the outer periphery of the main shaft 2. The nut member 20 is threadedly engaged with a male thread 22 formed on the outer periphery of the rear end of the main shaft 2. The axial front end face of the spacer 21 contacts the axial rear end face of the inner ring 17, and the axial rear end face of the spacer 21 contacts the axial front end face of the nut member 20. The axial front end face of the inner ring 17 contacts the axial rear end of the rotor sleeve 9.

The bearing device 1 has a bearing support tube 23 fixed to the spindle housing 3, a first bearing 24 and a second bearing 25 assembled in the bearing support tube 23 at an axial distance from each other, an outer ring spacer 26 and an inner ring spacer 27 provided between the first bearing 24 and the second bearing 25, and a strain sensor 28 attached to the outer ring spacer 26.

As shown in FIG. 2, the first bearing 24 has a first outer ring 30 that fits into the inner circumference of the bearing support tube 23, a first inner ring 31 that is rotatably provided on the radially inner side of the first outer ring 30, and a plurality of first rolling elements 32 that are assembled between the first outer ring 30 and the first inner ring 31. The first rolling elements 32 are balls here. The inner circumference of the first outer ring 30 is provided with a first outer ring raceway surface 33 that has an arc-shaped cross section with which the first rolling elements 32 roll and contact. The first outer ring 30 is a shoulder-drop outer ring that has a shape in which the axially front outer ring shoulder is removed from the outer ring shoulder on the axially front side and the outer ring shoulder on the axially rear side with respect to the first outer ring raceway surface 33. The outer circumference of the first inner ring 31 is provided with a first inner ring raceway surface 34 that has an arc-shaped cross section with which the first rolling elements 32 roll and contact. The first inner ring 31 is a shoulder-reduced inner ring with a shape in which the axially rear inner ring shoulder is removed from the axially front inner ring shoulder and the axially rear inner ring shoulder with respect to the first inner ring raceway surface 34 with which the first rolling element 32 rolls. The first inner ring 31 is fitted to the outer periphery of the main shaft 2 with a tightening margin.

The second bearing 25 has a second outer ring 35 that fits into the inner circumference of the bearing support tube 23, a second inner ring 36 that is rotatably provided radially inside the second outer ring 35, and a plurality of second rolling elements 37 that are incorporated between the second outer ring 35 and the second inner ring 36. The second rolling elements 37 are balls here. The inner circumference of the second outer ring 35 is provided with a second outer ring raceway surface 38 that has an arc-shaped cross section with which the second rolling elements 37 roll and contact. The second outer ring 35 is spaced axially rearward from the first outer ring 30, and the second inner ring 36 is also spaced axially rearward from the first inner ring 31. The second outer ring 35 is a shoulder-drop outer ring that has a shape in which the axially rear outer ring shoulder is removed from the axially front outer ring shoulder and the axially rear outer ring shoulder relative to the second outer ring raceway surface 38. The outer periphery of the second inner ring 36 is provided with a second inner ring raceway 39 with an arc-shaped cross section with which the second rolling element 37 rolls. The second inner ring 36 is a shoulder-reduced inner ring with an axially front inner ring shoulder removed from the axially rear inner ring shoulder with respect to the second inner ring raceway 39 with which the second rolling element 37 rolls. The second inner ring 36 is fitted to the outer periphery of the main shaft 2 with a tightening margin.

Here, the first bearing 24 is configured so that the first rolling body 32 generates a radial component force pressing the first outer ring 30 under axial preload, and similarly, the second bearing 25 is configured so that the second rolling body 37 generates a radial component force pressing the second outer ring 35 under axial preload. In this embodiment, the first bearing 24 is an angular ball bearing in which the straight line connecting the contact point of the first inner ring 31 and the first rolling body 32 and the contact point of the first outer ring 30 and the first rolling body 32 is inclined axially backward from the radial inner side toward the radial outer side. Also, the second bearing 25 is an angular ball bearing in which the straight line connecting the contact point of the second inner ring 36 and the second rolling body 37 and the contact point of the second outer ring 35 and the second rolling body 37 is inclined axially forward from the radial inner side toward the radial outer side. In other words, the first bearing 24 and the second bearing 25 are a pair of angular contact ball bearings arranged back-to-back with a gap in the axial direction.

The outer ring spacer 26 is a hollow cylindrical member with both ends open. The outer ring spacer 26 fits into the inner circumference of the bearing support tube 23 with a gap. The outer ring spacer 26 is sandwiched in the axial direction between the axial rear end face of the first outer ring 30 and the axial front end face of the second outer ring 35.

Like the outer ring spacer 26, the inner ring spacer 27 is a hollow cylindrical member with both ends open. The inner ring spacer 27 fits onto the outer periphery of the main shaft 2 with a gap. The inner ring spacer 27 is sandwiched axially between the first inner ring 31 and the second inner ring 36.

An outer ring pressing member 40 is fixed to the axial front end of the spindle housing 3. The outer ring pressing member 40 fixes the axial position of the first outer ring 30 by contacting the axial front end face of the first outer ring 30. The outer ring pressing member 40 has a cylindrical portion 41 that fits into the inner circumference of the bearing support tube 23 and a flange portion 42 that extends radially outward from the axial front end of the cylindrical portion 41. The flange portion 42 is fixed to the axial front end face of the bearing support tube 23. A step portion 43 that restricts the axial forward movement of the first inner ring 31 is provided on the outer circumference of the axial front end of the spindle 2. The step portion 43 contacts the axial front end face of the first inner ring 31 to position the first inner ring 31 in the axial direction.

A preload nut 44 that presses the second inner ring 36 axially forward and an annular spacer 45 that is assembled between the second inner ring 36 and the preload nut 44 are attached to the outer periphery of the main shaft 2. The preload nut 44 is threadedly engaged with a male thread 46 formed on a portion extending axially forward from a stepped portion 11 (see FIG. 1) on the outer periphery of the main shaft 2. The axial front end face of the spacer 45 contacts the axial rear end face of the second inner ring 36, and the axial rear end face of the spacer 45 contacts the axial front end face of the preload nut 44. A stepped portion 47 that restricts the axial rearward movement of the second outer ring 35 is provided on the inner periphery of the bearing support tube 23. The stepped portion 47 contacts the axial rear end face of the second outer ring 35 to position the second outer ring 35 in the axial direction.

As shown in FIG. 1, the bearing support cylinder 23 is fitted to the inner circumference of the spindle housing 3. A cooling groove 48 is formed on the outer circumference of the bearing support cylinder 23, through which a refrigerant for cooling the bearing device 1 flows. The cooling groove 48 is a plurality of annular grooves formed at intervals in the axial direction on the outer circumference of the bearing support cylinder 23, or a spiral groove extending in a spiral shape around the outer circumference of the bearing support cylinder 23.

2, the preload nut 44 is tightened with a predetermined force, and the axial force of the preload nut 44 is transmitted through the spacer 45, the second inner ring 36, the second rolling element 37, the second outer ring 35, the outer ring spacer 26, the first outer ring 30, the first rolling element 32, and the first inner ring 31, and is received by the step portion 43. In other words, the axial force of the preload nut 44 applies an axial preload between the first bearing 24 and the second bearing 25 so that the preload is transmitted through the first inner ring 31, the first rolling element 32, the first outer ring 30, the outer ring spacer 26, the second outer ring 35, the second rolling element 37, and the second inner ring 36 in this order.

The strain sensor 28 is attached to the axial center of the outer ring spacer 26. Specifically, the strain sensor 28 is attached to the outer ring spacer 26 so that the strain sensor 28 fits within an axial distance range of 1/4 of the total axial length of the outer ring spacer 26 from the axial center position of the outer ring spacer 26.

The outer ring spacer 26 is a cylindrical member having a cylindrical inner peripheral surface 50, a cylindrical outer peripheral surface 51, a first axial end face 52, and a second axial end face 53. The first axial end face 52 is an annular, axis-perpendicular plane formed at the axial front end of the outer ring spacer 26, and is pressed against the axial rear end face of the first outer ring 30 by axial preload. The second axial end face 53 is an annular, axis-perpendicular plane formed at the axial rear end of the outer ring spacer 26, and is pressed against the axial front end face of the second outer ring 35 by axial preload.

As shown in FIG. 3, multiple strain sensors 28 (four in this example) are provided at intervals in the circumferential direction on the inner circumference of the outer ring spacer 26. Each strain sensor 28 is attached to a planar sensor mounting surface 54 formed by cutting out a portion of the cylindrical inner circumference 50 of the outer ring spacer 26. The sensor mounting surface 54 is a plane parallel to the center line of the outer ring spacer 26, and is located radially outward of the cylindrical inner circumference 50 when viewed from the axial direction. Here, the sensor mounting surface 54 is the groove bottom surface of axial grooves formed at equal intervals in the circumferential direction on the inner circumference of the outer ring spacer 26.

As shown in FIG. 4, each strain sensor 28 has a strain detection unit 55 and a processing unit 56 connected to the strain detection unit 55. The strain detection unit 55 is a strain gauge whose electrical resistance changes according to strain. The processing unit 56 has a strain detection circuit that detects strain based on the change in the electrical resistance of the strain gauge, and an AD conversion circuit that converts the strain detected by the detection circuit from an analog signal to a digital signal and outputs it.

The strain detection unit 55 has an axial strain detection unit (strain gauge arranged with the axial direction as the strain detection direction) that detects the axial strain of the outer ring spacer 26 at the installation position of the strain sensor 28, and a circumferential strain detection unit (strain gauge arranged with the circumferential direction as the strain detection direction) that detects the circumferential strain of the outer ring spacer 26 at the installation position of the strain sensor 28. The processing unit 56 is configured to take the difference between the axial strain detected by the axial strain detection unit and the circumferential strain detected by the circumferential strain detection unit (i.e., the sum of the absolute value of the axial strain and the absolute value of the circumferential strain), and to use this difference as the output of the strain sensor 28.

At the end of the outer ring spacer 26 on the side of the first outer ring 30 (see FIG. 2), a first annular notch 57 is formed, which cuts out the intersection of the first axial end face 52 and the cylindrical inner peripheral surface 50 (the lower left corner of the square cross section of the outer ring spacer 26 in FIG. 4) and the intersection of the first axial end face 52 and the cylindrical outer peripheral surface 51 (the upper left corner of the square cross section of the outer ring spacer 26 in FIG. 4). Similarly, at the end of the outer ring spacer 26 on the side of the second outer ring 35 (see FIG. 2), a second annular notch 58 is formed, which cuts out the intersection of the second axial end face 53 and the cylindrical inner peripheral surface 50 (the lower right corner of the square cross section of the outer ring spacer 26 in FIG. 4) and the intersection of the second axial end face 53 and the cylindrical outer peripheral surface 51 (the upper right corner of the square cross section of the outer ring spacer 26 in FIG. 4).

The first annular notch 57 and the second annular notch 58 are steps formed by dropping axially from the first axial end face 52 and the second axial end face 53, respectively. In the figure, the axial depth of the first annular notch 57 and the second annular notch 58 is exaggerated for ease of understanding, but the axial depth of the first annular notch 57 and the second annular notch 58 is shallow, about 0.1 mm to 0.5 mm.

The first annular notch 57 and the second annular notch 58 are formed so that the first axial end face 52 and the second axial end face 53 are aligned at the same radial position. That is, the first annular notch 57 and the second annular notch 58 are formed so that the radial position of the radial outer end of the first axial end face 52 (the boundary between the first axial end face 52 and the first annular notch 57 on its radial outer side) and the radial position of the radial outer end of the second axial end face 53 (the boundary between the second axial end face 53 and the second annular notch 58 on its radial outer side) are the same radial position, and the radial position of the radial inner end of the first axial end face 52 (the boundary between the first axial end face 52 and the first annular notch 57 on its radial inner side) and the radial position of the radial inner end of the second axial end face 53 (the boundary between the second axial end face 53 and the second annular notch 58 on its radial inner side) are also the same radial position.

The first annular notch 57 is formed so that the radial width of the first axial end face 52 is 50% or less (preferably 20% or less) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51. In other words, the overall radial width of the first annular notch 57 is set to 50% or more (preferably 80% or more) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51.

Similarly, the second annular notch 58 is formed so that the radial width of the second axial end face 53 is 50% or less (preferably 20% or less) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51. In other words, the overall radial width of the second annular notch 58 is set to 50% or more (preferably 80% or more) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51.

In the bearing device 1 shown in FIG. 2, the preload of the first bearing 24 and the second bearing 25 (hereinafter referred to as "bearing preload") changes depending on the rotational speed of the main shaft 2 when the spindle device is in operation. The bearing preload can be detected based on the strain of the outer ring spacer 26 detected by the strain sensor 28.

In other words, when the rotational speed of the main shaft 2 changes during operation of the spindle device, the centrifugal force of the first rolling body 32 and the second rolling body 37 changes, and in response to the change in centrifugal force, the load with which the first rolling body 32 presses against the first outer ring raceway surface 33 (preload load of the first bearing 24) and the load with which the second rolling body 37 presses against the second outer ring raceway surface 38 (preload load of the second bearing 25) also change. Here, the first outer ring raceway surface 33 and the second outer ring raceway surface 38 are in contact with the first rolling body 32 and the second rolling body 37 at an angle inclined with respect to the axial direction, so when the load with which the first rolling body 32 presses the first outer ring raceway surface 33 and the load with which the second rolling body 37 presses the second outer ring raceway surface 38 change, the axial preload load applied from the first outer ring 30 and the second outer ring 35 to the outer ring spacer 26 changes, and the strain of the outer ring spacer 26 changes. Therefore, it is possible to detect the preload (bearing preload) of the first bearing 24 and the second bearing 25 based on the strain of the outer ring spacer 26 detected by the strain sensor 28.

In addition, when a moment load acts on the spindle 2, loads of different magnitudes are applied to the positions of the strain sensors 28 arranged at equal intervals in the circumferential direction. Therefore, it is possible to detect the moment load acting on the spindle 2 of the machine tool during cutting processing based on the output of each of the multiple strain sensors 28.

When the bearing preload increases, the first outer ring 30 elastically deforms in the radial expansion direction due to an increase in the radial component force it receives from the first rolling element 32, and at this time, a small amount of slippage occurs between the contact surfaces of the first outer ring 30 and the outer ring spacer 26, causing the first outer ring 30 to move radially outward relative to the outer ring spacer 26. On the other hand, when the bearing preload decreases, the first outer ring 30 elastically restores in the radial contraction direction due to a decrease in the radial component force it receives from the first rolling element 32, and at this time, a small amount of slippage occurs between the contact surfaces of the first outer ring 30 and the outer ring spacer 26, causing the first outer ring 30 to move radially inward relative to the outer ring spacer 26.

Similarly, when the bearing preload increases, the second outer ring 35 elastically deforms in the radial expansion direction due to an increase in the radial component force received from the second rolling element 37, and at this time, a small slip occurs between the contact surfaces of the second outer ring 35 and the outer ring spacer 26, where the second outer ring 35 moves radially outward relative to the outer ring spacer 26. On the other hand, when the bearing preload decreases, the second outer ring 35 elastically restores in the radial contraction direction due to a decrease in the radial component force received from the second rolling element 37, and at this time, a small slip occurs between the contact surfaces of the second outer ring 35 and the outer ring spacer 26, where the second outer ring 35 moves radially inward relative to the outer ring spacer 26.

When the above-mentioned radial slippage occurs between the contact surfaces of the first outer ring 30 and the outer ring spacer 26, or between the contact surfaces of the second outer ring 35 and the outer ring spacer 26, the first axial end face 52 and the second axial end face 53 may come into strong contact with the first outer ring 30 and the second outer ring 35 at a position closer to the radial inside, or may come into strong contact with the first outer ring 30 and the second outer ring 35 at a position closer to the radial outside.

Here, in the bearing device 1 shown in Figure 2, a comparative example is assumed in which the first annular notch 57 and the second annular notch 58 are not provided on both axial end faces of the outer ring spacer 26, and the first axial end face 52 and the second axial end face 53 are annular axis-perpendicular planes having a width equal to the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51, and the first axial end face 52 and the second axial end face 53 are in contact with the first outer ring 30 and the second outer ring 35. In this comparative example, the radial width of the first axial end face 52 and the second axial end face 53 is wide, so there is a large difference in the output of the strain sensor 28 between when the first axial end face 52 and the second axial end face 53 make strong contact with the first outer ring 30 and the second outer ring 35 at a position closer to the radial inside and when they make strong contact with the first outer ring 30 and the second outer ring 35 at a position closer to the radial outside, which causes an error in the bearing preload detected based on the output of the strain sensor 28.

In response to this problem, in the bearing device 1 of this embodiment, as shown in FIG. 4, the first axial end face 52 is narrowed in the radial direction by the provision of the first annular notch 57, so the difference in the radial position of the strong contact point is small when the first axial end face 52 makes strong contact at a position closer to the radial outside and when it makes strong contact at a position closer to the radial inside. Similarly, the second axial end face 53 is narrowed in the radial direction by the provision of the second annular notch 58, so the difference in the radial position of the strong contact point is small when the second axial end face 53 makes strong contact at a position closer to the radial outside and when it makes strong contact at a position closer to the radial inside. Therefore, the radial position through which the bearing preload passes is stable between the first axial end face 52 and the second axial end face 53, so that the output of the strain sensor 28 is less likely to have an error, and it is possible to detect the bearing preload with high accuracy.

In addition, as shown in FIG. 4, in this bearing device 1, the radial positions of the radial outer end and inner end of the first axial end face 52 and the radial positions of the radial outer end and inner end of the second axial end face 53 are aligned in the same radial position, so that the radial position through which the bearing preload passes is particularly stable between the first axial end face 52 and the second axial end face 53 of the outer ring spacer 26, making it possible to effectively prevent errors in the output of the strain sensor 28.

In addition, in this bearing device 1, the radial width of the first axial end face 52 and the radial width of the second axial end face 53 shown in FIG. 4 are set to 50% or less (preferably 20% or less) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51, so that it is possible to effectively stabilize the radial position through which the bearing preload passes between the first axial end face 52 and the second axial end face 53 of the outer ring spacer 26.

In the above embodiment, as shown in FIG. 4, the first annular notch 57 is formed on both the radial outer side and the radial inner side of the first axial end face 52, and the second annular notch 58 is formed on both the radial outer side and the radial inner side of the second axial end face 53. However, as shown in FIG. 5, the first annular notch 57 may be formed only on the radial outer side of the radial outer side and the radial inner side of the first axial end face 52, and the second annular notch 58 may be formed only on the radial outer side of the radial outer side and the radial inner side of the second axial end face 53. Also, as shown in FIG. 6, the first annular notch 57 may be formed only on the radial inner side of the radial outer side and the radial inner side of the first axial end face 52, and the second annular notch 58 may be formed only on the radial inner side of the radial outer side and the radial inner side of the second axial end face 53.

In FIG. 5, the first annular notch 57 is an annular step that cuts out the entire circumference of the intersection of the first axial end face 52 and the cylindrical outer circumferential surface 51, and the second annular notch 58 is an annular step that cuts out the entire circumference of the intersection of the second axial end face 53 and the cylindrical outer circumferential surface 51. The axial depth of the first annular notch 57 and the second annular notch 58 is shallow, about 0.1 mm to 0.5 mm.

The first annular notch 57 and the second annular notch 58 are formed so that the first axial end face 52 and the second axial end face 53 are aligned at the same radial position. That is, the first annular notch 57 and the second annular notch 58 are formed so that the radial position of the radial outer end of the first axial end face 52 (the boundary between the first axial end face 52 and the first annular notch 57) and the radial position of the radial outer end of the second axial end face 53 (the boundary between the second axial end face 53 and the second annular notch 58) are in the same radial position, and the radial position of the radial inner end of the first axial end face 52 (the intersection ridge of the first axial end face 52 and the cylindrical inner circumferential surface 50) and the radial position of the radial inner end of the second axial end face 53 (the intersection ridge of the second axial end face 53 and the cylindrical inner circumferential surface 50) are also in the same radial position.

In FIG. 6, the first annular notch 57 is an annular step that cuts out the entire circumference of the intersection of the first axial end face 52 and the cylindrical inner circumferential surface 50, and the second annular notch 58 is an annular step that cuts out the entire circumference of the intersection of the second axial end face 53 and the cylindrical inner circumferential surface 50. The axial depth of the first annular notch 57 and the second annular notch 58 is shallow, about 0.1 mm to 0.5 mm.

The first annular notch 57 and the second annular notch 58 are formed so that the first axial end face 52 and the second axial end face 53 are aligned at the same radial position. That is, the first annular notch 57 and the second annular notch 58 are formed so that the radial position of the radial outer end of the first axial end face 52 (the intersection ridge of the first axial end face 52 and the cylindrical outer peripheral surface 51) and the radial position of the radial outer end of the second axial end face 53 (the intersection ridge of the second axial end face 53 and the cylindrical outer peripheral surface 51) are in the same radial position, and the radial position of the radial inner end of the first axial end face 52 (the boundary between the first axial end face 52 and the first annular notch 57) and the radial inner end of the second axial end face 53 (the boundary between the second axial end face 53 and the second annular notch 58) are also in the same radial position.

5 and 6, the first annular notch 57 is formed so that the radial width of the first axial end face 52 is 50% or less (preferably 20% or less) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51. That is, the radial width of the first annular notch 57 is set to 50% or more (preferably 80% or more) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51. Similarly, the second annular notch 58 is formed so that the radial width of the second axial end face 53 is 50% or less (preferably 20% or less) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51. That is, the radial width of the second annular notch 58 is set to 50% or more (preferably 80% or more) of the radial thickness between the cylindrical inner peripheral surface 50 and the cylindrical outer peripheral surface 51.

In addition, in the above embodiment, the strain sensor 28 is disposed on the inner circumference of the outer ring spacer 26, but as shown in Figures 7 and 8, the strain sensor 28 may be disposed on the outer circumference of the outer ring spacer 26.

In Figures 7 and 8, multiple strain sensors 28 (four in this example) are provided at intervals in the circumferential direction on the outer periphery of the outer ring spacer 26. Each strain sensor 28 is attached to a planar sensor mounting surface 54 formed by cutting out a portion of the cylindrical outer periphery 51 of the outer ring spacer 26. The sensor mounting surface 54 is a plane parallel to the center line of the outer ring spacer 26, and is located radially inward of the cylindrical outer periphery 51 when viewed from the axial direction. Here, the sensor mounting surface 54 is the groove bottom surface of axial grooves formed at equal intervals in the circumferential direction on the outer periphery of the outer ring spacer 26.

Also, as shown in Figures 9 and 10, the strain sensors 28 may be arranged on both the inner and outer circumferences of the outer ring spacer 26. In this way, it is possible to detect the degree to which the radial position through which the bearing preload passes is biased radially inward or outward between the first axial end face 52 and the second axial end face 53. In addition, by taking the sum of the output of the strain sensor 28 arranged on the inner circumference of the outer ring spacer 26 and the output of the strain sensor 28 arranged on the outer circumference of the outer ring spacer 26, it is possible to cancel out the effect of the radial position through which the bearing preload passes being biased radially inward or outward, and to detect the axial preload load with stable accuracy.

In the above embodiment, the first annular notch 57 and the second annular notch 58 are exemplified by step portions that drop straight in the axial direction from the first axial end face 52 and the second axial end face 53, respectively, as shown in FIG. 4. However, as shown in FIG. 11, chamfered portions that drop in a tapered manner in the axial direction from the first axial end face 52 and the second axial end face 53 may also be used, and as shown in FIG. 12, fillet portions that drop in the axial direction in an arc-shaped cross section from the first axial end face 52 and the second axial end face 53 may also be used.

As shown in FIG. 13, the first axial end face 52 can be a surface that has been subjected to friction reduction treatment to reduce the friction coefficient with the first outer ring 30 (see FIG. 2). The friction reduction treatment is, for example, a coating treatment with a low-friction coating 59 (such as a fluororesin coating). Similarly, the second axial end face 53 shown in FIG. 4 can also be a surface that has been subjected to friction reduction treatment to reduce the friction coefficient with the second outer ring 35 (see FIG. 2). In this way, radial bias is less likely to occur in the contact pressure of the first axial end face 52 and the second axial end face 53. Therefore, it is possible to particularly effectively stabilize the radial position through which the bearing preload passes between the first axial end face 52 and the second axial end face 53.

In the above embodiment, angular contact ball bearings have been used as the first bearing 24 and the second bearing 25, but it is also possible to use other types of rolling bearings, such as tapered roller bearings and deep groove ball bearings, that generate a radial component force due to an axial preload, as the first bearing 24 and the second bearing 25.

In addition, in the above embodiment, the strain sensor 28 is exemplified as having a strain detection unit 55 and a processing unit 56, but the strain sensor 28 can also be configured with only the strain detection unit 55 (only a strain gauge).

In addition, in the above embodiment, the strain detection unit 55 has an axial strain detection unit and a circumferential strain detection unit, but the strain detection unit 55 can also be configured with only an axial strain detection unit or a circumferential strain detection unit.

In addition, in the above embodiment, the bearing device 1 that rotatably supports the main shaft 2 of a machine tool (such as a machining center or a lathe) has been described as an example, but the present invention can also be applied to a bearing device that rotatably supports the rotating shaft of other devices, such as the main shaft of a wind power generation device.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

REFERENCE SIGNS LIST 1 Bearing device with strain sensor 2 Main shaft 4 Motor 24 First bearing 25 Second bearing 26 Outer ring spacer 28 Strain sensor 30 First outer ring 31 First inner ring 32 First rolling element 35 Second outer ring 36 Second inner ring 37 Second rolling element 50 Cylinder inner peripheral surface 51 Cylinder outer peripheral surface 52 First axial end face 53 Second axial end face 54 Sensor mounting surface 57 First annular notch 58 Second annular notch

Claims (9)

The bearing has a first bearing (24) and a second bearing (25) spaced apart in the axial direction, a cylindrical outer ring spacer (26) provided between the first bearing (24) and the second bearing (25), and a strain sensor (28) attached to the outer ring spacer (26),
The first bearing (24) has a first outer ring (30), a first inner ring (31) provided radially inside the first outer ring (30), and a plurality of first rolling elements (32) assembled between the first outer ring (30) and the first inner ring (31),
The second bearing (25) has a second outer ring (35), a second inner ring (36) provided radially inside the second outer ring (35), and a plurality of second rolling elements (37) assembled between the second outer ring (35) and the second inner ring (36),
An axial preload is applied between the first bearing (24) and the second bearing (25) such that the preload is transmitted through the first inner ring (31), the first rolling element (32), the first outer ring (30), the outer ring spacer (26), the second outer ring (35), the second rolling element (37), and the second inner ring (36);
The outer ring spacer (26) has a cylindrical inner peripheral surface (50), a cylindrical outer peripheral surface (51), a planar sensor mounting surface (54) formed by cutting out a part of the cylindrical inner peripheral surface (50) or the cylindrical outer peripheral surface (51), a first axial end surface (52) pressed against the first outer ring (30) by the axial preload, and a second axial end surface (53) pressed against the second outer ring (35) by the axial preload, and in this bearing device with a strain sensor, the strain sensor (28) is attached to the sensor mounting surface (54),
a first annular notch (57) is formed at an end of the outer ring spacer (26) on the side of the first outer ring (30), the first annular notch (57) being cut out over the entire circumference of one or both of an intersection of the first axial end face (52) and the cylindrical inner circumferential surface (50) and an intersection of the first axial end face (52) and the cylindrical outer circumferential surface (51);
A bearing device with a strain sensor, characterized in that an end of the outer ring spacer (26) on the side of the second outer ring (35) is formed with a second annular notch (58) that is annular and cuts out one or both of the intersection of the second axial end face (53) and the cylindrical inner circumferential surface (50) and the intersection of the second axial end face (53) and the cylindrical outer circumferential surface (51) over the entire circumference. The bearing device with strain sensor according to claim 1, wherein the first annular notch (57) and the second annular notch (58) are formed so that the first axial end face (52) and the second axial end face (53) are aligned at the same radial position. The bearing device with a strain sensor according to claim 1 or 2, wherein the first annular notch (57) and the second annular notch (58) are formed so that the radial width of the first axial end face (52) and the radial width of the second axial end face (53) are 50% or less of the radial thickness between the cylindrical inner circumferential surface (50) and the cylindrical outer circumferential surface (51). The bearing device with strain sensor according to claim 1 or 2, wherein the first annular notch (57) and the second annular notch (58) are formed so that the radial width of the first axial end face (52) and the radial width of the second axial end face (53) are 20% or less of the radial thickness between the cylindrical inner circumferential surface (50) and the cylindrical outer circumferential surface (51). The strain sensor-equipped bearing device according to claim 1 or 2, wherein the strain sensor (28) is disposed on the inner circumference of the outer ring spacer (26). The strain sensor-equipped bearing device according to claim 1 or 2, wherein the strain sensor is disposed on the outer periphery of the outer ring spacer (26). The strain sensor-equipped bearing device according to claim 1 or 2, wherein the strain sensors are arranged on both the inner and outer circumferences of the outer ring spacer (26). The bearing device with strain sensor according to claim 1 or 2, wherein the first axial end face (52) is a surface that has been subjected to friction reduction treatment to reduce the coefficient of friction with the first outer ring (30), and the second axial end face (53) is also a surface that has been subjected to friction reduction treatment to reduce the coefficient of friction with the second outer ring (35). A bearing device with a strain sensor (1) according to claim 1 or 2,
A main spindle (2) of a machine tool that is rotatably supported by the bearing device (1) with a strain sensor;
and a motor (4) for rotating the main shaft (2).

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