Bearing devices, strain detection devices, motors

Abstract

To provide a sensor unit which allows a strain gage to be easily positioned on a motor.SOLUTION: A sensor unit includes: a cylindrical gauge fixing component mounted on an outer peripheral surface of a bearing housing; and a first strain gauge and a second strain gauge attached to the gauge fixing component. The first strain gauge is a stress sensor and the second strain gauge is a noise sensor.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention is, axis relates to a receiving device, a strain detection device, and a motor.

Background Art

[0002] In a motor provided with a rolling bearing, when the motor rotates, the balls in the rolling bearing rotate, and the rolling bearing is slightly strained. And a motor having a sensor for detecting such strain has been proposed. The sensor for detecting strain is provided, for example, between the side surface in the rotation axis direction of the rolling bearing and the housing of the motor (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, for example, when a strain gauge is used as a sensor for detecting strain, it is necessary to perform an attachment operation to a narrow and curved surface portion, so it is extremely difficult to arrange the strain gauge at a predetermined position inside the motor.

[0005] The present invention has been made in view of the above points, and provides a sensor unit in which a strain gauge can be easily arranged in a motor Bearing device having for the purpose.

Means for Solving the Problems

[0006] This Bearing device includes a rotating shaft, a first rolling bearing that supports the rotating shaft, a bearing housing that holds the first rolling bearing, and the bearing housing It comprises a cylindrical member attached to the outer surface of a device, and a stress sensor and a noise sensor attached to the member.The sensor unit comprises a member having a strain transmission section to which strain generated in the first rolling bearing by the rotation of the rotating shaft is transmitted, and a strain non-transmission section to which the strain is not transmitted, wherein the strain transmission section is located at a position that overlaps with the outer circumferential surface of the first rolling bearing in a radial view, and the strain non-transmission section is located at a position that does not overlap with the outer circumferential surface of the first rolling bearing in a radial view, the stress sensor is arranged in the strain transmission section, and the noise sensor is arranged in the strain non-transmission section. [Effects of the Invention]

[0007] According to the disclosed technology, a sensor unit is available that allows strain gauges to be easily mounted on a motor. Bearing device having We can provide this. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view illustrating a sensor unit according to the first embodiment. [Figure 2] This is a cross-sectional view illustrating a sensor unit according to the first embodiment. [Figure 3] This is a diagram (part 1) illustrating an example of a cylindrical member. [Figure 4] This is a diagram (part 2) illustrating an example of a cylindrical member. [Figure 5] This is a perspective view illustrating a bearing device according to the first embodiment. [Figure 6] This is a cross-sectional view (part 1) illustrating a bearing device according to the first embodiment. [Figure 7] This is a cross-sectional view (part 2) illustrating a bearing device according to the first embodiment. [Figure 8] This is a cross-sectional view (part 1) of the bearing device shown in Figure 7, perpendicular to the axis m. [Figure 9] Figure 7 is a magnified view of the vicinity of the sensor unit shown. [Figure 10] Figure 7 shows a magnified view of the vicinity of the first and second strain gauges. [Figure 11]It is a schematic diagram illustrating a strain detection device according to the first embodiment. [Figure 12] It is a cross-sectional view (part 2) in a direction perpendicular to the axis m of the bearing device shown in FIG. 7. [Figure 13] It is a plan view illustrating a strain gauge according to the first embodiment. [Figure 14] It is a cross-sectional view illustrating a strain gauge according to the first embodiment. [Figure 15] It is a cross-sectional view illustrating a motor equipped with a bearing device according to the first embodiment. [Figure 16] It is a cross-sectional view illustrating a bearing device according to Modification 1 of the first embodiment. [Figure 17] It is a cross-sectional view (part 1) illustrating a bearing device according to Modification 2 of the first embodiment. [Figure 18] It is a cross-sectional view (part 2) illustrating a bearing device according to Modification 2 of the first embodiment. [Figure 19] It is a cross-sectional view (part 3) illustrating a bearing device according to Modification 2 of the first embodiment. [Figure 20] It is a partially enlarged view (part 1) of a strain transmission part and a strain non-transmission part according to Modification 3 of the first embodiment. [Figure 21] It is a partially enlarged view (part 2) of a strain transmission part and a strain non-transmission part according to Modification 3 of the first embodiment. [Figure 22] It is a partially enlarged view (part 3) of a strain transmission part and a strain non-transmission part according to Modification 3 of the first embodiment. [Figure 23] It is a partially enlarged view (part 4) of a strain transmission part and a strain non-transmission part according to Modification 3 of the first embodiment. [Figure 24] It is a partially enlarged view (part 5) of a strain transmission part and a strain non-transmission part according to Modification 3 of the first embodiment. [Figure 25] It is a partially enlarged view (part 6) of a strain transmission part and a strain non-transmission part according to Modification 3 of the first embodiment. [Figure 26] It is a partially enlarged view (part 7) of a strain transmission part and a strain non-transmission part according to Modification 3 of the first embodiment. [Figure 27] This is a partially enlarged view (part 8) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment. [Figure 28] This is a partially enlarged view (part 9) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment. [Figure 29] This is a partially enlarged view (part 10) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment. [Figure 30] This is a partially enlarged view (part 11) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, the same reference numerals are used for identical components, and redundant explanations may be omitted.

[0010] <First Embodiment> (Sensor unit) Figure 1 is a perspective view illustrating a sensor unit according to the first embodiment. Figure 2 is a cross-sectional view illustrating a sensor unit according to the first embodiment, showing a cross-section passing through the central axis of the gauge fixing member 110.

[0011] As shown in Figures 1 and 2, the sensor unit 100 includes a gauge fixing member 110, a first strain gauge 120A, a second strain gauge 120B, a third strain gauge 120C, a fourth strain gauge 120D, and wiring 130A to 130D.

[0012] The gauge fixing member 110 is a cylindrical member attached to the outer circumferential surface of the bearing housing (described later). The gauge fixing member 110 is, for example, a hollow cylinder with both ends open in the direction of the central axis. The gauge fixing member 110 has an outer circumferential surface 110a and an inner circumferential surface 110b. The gauge fixing member 110 can be made of a metal such as brass, stainless steel, or aluminum. It is preferable to select a material for the gauge fixing member 110 that has a coefficient of thermal expansion close to that of the material forming the bearing housing 40 (described later). The thickness of the gauge fixing member 110 can be appropriately determined considering strain transmission and required rigidity, but for example, it may be about 1 mm.

[0013] Furthermore, cylindrical members include, for example, hollow cylindrical members that have been processed in part. Processing refers to cases where a slit, groove, hole, projection, step, etc., is provided in part of the hollow cylindrical member. For example, the gauge fixing member 110 shown in Figures 3 and 4 is also included in cylindrical members. In the example shown in Figure 3, a slit 110x is provided in the hollow cylindrical gauge fixing member 110. In the example shown in Figure 4, a groove 110y is provided in the hollow cylindrical gauge fixing member 110. Of course, the gauge fixing member 110 may have multiple slits or grooves, or both may be mixed. Also, a slit or groove may be provided in a part of the gauge fixing member 110 in the central axis direction. Such slits or grooves can be used, for example, as passages for wiring 130A to 130D.

[0014] Returning to the description of Figures 1 and 2, the first strain gauge 120A, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D are attached to the outer circumferential surface 110a of the gauge fixing member 110. The first strain gauge 120A, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D are fixed to the outer circumferential surface 110a of the gauge fixing member 110, for example, by adhesive.

[0015] The first strain gauge 120A and the second strain gauge 120B are positioned spaced apart from each other in the central axis direction of the gauge fixing member 110. The third strain gauge 120C and the fourth strain gauge 120D are positioned spaced apart from each other in the central axis direction of the gauge fixing member 110.

[0016] The first strain gauge 120A and the third strain gauge 120C are positioned at different circumferential positions on the gauge fixing member 110. For example, the first strain gauge 120A and the third strain gauge 120C are positioned at the same position in the central axis direction of the gauge fixing member 110.

[0017] The second strain gauge 120B and the fourth strain gauge 120D are positioned at different circumferential positions on the gauge fixing member 110. The second strain gauge 120B and the fourth strain gauge 120D may be positioned at the same position in the central axis direction of the gauge fixing member 110, or they may be positioned at different positions.

[0018] The first strain gauge 120A and the third strain gauge 120C are stress sensors, while the second strain gauge 120B and the fourth strain gauge 120D are noise sensors. The stress sensors and noise sensors will be described later.

[0019] In the examples shown in Figures 1 and 2, the first strain gauge 120A and the second strain gauge 120B are arranged such that the line connecting their respective centers is parallel to the central axis of the gauge fixing member 110, but this is not limited to this arrangement. Similarly, the third strain gauge 120C and the fourth strain gauge 120D are arranged such that, for example, they are parallel to the central axis of the gauge fixing member 110, but this is not limited to this arrangement.

[0020] Wiring 130A is connected to the electrode of the first strain gauge 120A. Wiring 130B is connected to the electrode of the second strain gauge 120B. Wiring 130C is connected to the electrode of the third strain gauge 120C. Wiring 130D is connected to the electrode of the fourth strain gauge 120D.

[0021] Although not shown in Figures 1 and 2, the first strain gauge 120A, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D each have two electrodes (see Figure 10, etc.). Therefore, each of the wirings 130A to 130D contains two conductive wires that are insulated from each other and connected to the two electrodes of each strain gauge.

[0022] (Bearing device) Figure 5 is a perspective view illustrating a bearing device according to the first embodiment. Figure 6 is a cross-sectional view (part 1) illustrating a bearing device according to the first embodiment, showing a cross-section passing through the axis m of the rotating shaft 20. Figure 7 is a cross-sectional view (part 2) illustrating a bearing device according to the first embodiment, showing a cross-section passing through the axis m of the rotating shaft 20. Figures 5 and 6 show the state before the sensor unit 100 is attached to the bearing housing 40, while Figure 7 shows the state after the sensor unit 100 is attached to the outer circumferential surface of the bearing housing 40.

[0023] As shown in Figures 5 to 7, the bearing device 1 includes a rotating shaft 20, a first rolling bearing 30A, a second rolling bearing 30B, a bearing housing 40, and a sensor unit 100.

[0024] The rotating shaft 20 is rotatably supported by a first rolling bearing 30A and a second rolling bearing 30B, which are spaced apart from each other in the axial direction m. The first rolling bearing 30A and the second rolling bearing 30B are fixed to the bearing housing 40 by press-fitting, adhesive, or the like, and are held by the bearing housing 40. The bearing housing 40 is a hollow cylindrical member made of a metal such as brass. Preferably, the bearing housing 40 presses against the outer circumferential surface of the outer ring 31 around its entire circumference.

[0025] The first rolling bearing 30A and the second rolling bearing 30B are held in the bearing housing 40, spaced apart from each other in the axial direction m. The first rolling bearing 30A and the second rolling bearing 30B are positioned, for example, on a stepped portion provided on the inner circumferential surface of the bearing housing 40. In the example shown in Figures 5 to 7, the second rolling bearing 30B is provided on one side in the axial direction m of the bearing housing 40, and the first rolling bearing 30A is provided on the other side in the axial direction m. For the sake of explanation, the side on which the second rolling bearing 30B is provided will be referred to as the upper side, and the side on which the first rolling bearing 30A is provided as the lower side.

[0026] The first rolling bearing 30A and the second rolling bearing 30B each have an outer ring 31, an inner ring 32, and a plurality of rolling elements 33. The outer ring 31 is a cylindrical structure with axis m as its central axis. The inner ring 32 is a cylindrical structure arranged coaxially with the outer ring 31 on its inner circumference. Each of the plurality of rolling elements 33 is a sphere placed in a raceway formed between the outer ring 31 and the inner ring 32. A lubricant such as grease is sealed inside the raceway.

[0027] The bearing housing 40 has a first outer circumferential surface 40a, a second outer circumferential surface 40b, and a third outer circumferential surface 40c. The first outer circumferential surface 40a, the second outer circumferential surface 40b, and the third outer circumferential surface 40c are arranged sequentially from the second rolling bearing 30B side toward the first rolling bearing 30A. The second outer circumferential surface 40b forms the bottom surface of a recess that is recessed from the first outer circumferential surface 40a toward the rotating shaft 20 side, and the third outer circumferential surface 40c forms the bottom surface of a recess that is recessed further toward the rotating shaft 20 side toward the second outer circumferential surface 40b.

[0028] The sensor unit 100 can be detachably fitted into one side of the bearing housing 40 in the axial direction m. As shown in Figure 7, when the sensor unit 100 is fitted into the bearing housing 40, the inner circumferential surface 110b of the gauge fixing member 110 comes into contact with the second outer circumferential surface 40b of the bearing housing 40.

[0029] Furthermore, a gap (the gap S shown in Figure 9, described later) is formed between the inner circumferential surface 110b of the gauge fixing member 110 and the third outer circumferential surface 40c of the bearing housing 40. The width of the gap S can be, for example, about 0.5 mm to 1 mm. When the sensor unit 100 is attached to the outer circumferential surface of the bearing housing 40, the central axis of the gauge fixing member 110 roughly coincides with the axis m.

[0030] As described above, the first strain gauge 120A and the third strain gauge 120C are stress sensors that detect strain occurring in the first rolling bearing 30A, and the second strain gauge 120B and the fourth strain gauge 120D are noise sensors that detect noise.

[0031] Here, a stress sensor is a sensor that primarily detects strain occurring in an object, but it can also detect noise occurring in the vicinity of the object. Similarly, a noise sensor is a sensor that primarily detects noise occurring in the vicinity of an object, but it may also detect strain occurring in the object. The strain detected by a stress sensor is greater than the strain detected by a noise sensor. In contrast, the noise detected by a stress sensor is approximately equal to the noise detected by a noise sensor.

[0032] The strain detected by the first strain gauge 120A and the third strain gauge 120C is greatest on the side of the center of the rolling element 33 (around the point where the distance from the center is minimum). Therefore, as shown in Figure 7, it is preferable to place the first strain gauge 120A and the third strain gauge 120C on the side of the center of the rolling element 33. On the other hand, the second strain gauge 120B and the fourth strain gauge 120D are noise sensors, and it is preferable to avoid detecting strain as much as possible, so it is preferable to place them at a position away from the side of the center of the rolling element 33.

[0033] Furthermore, it is preferable that the first strain gauge 120A and the third strain gauge 120C are positioned so that the rolling element 33 passes directly beneath each of their respective resistors at the same time. The resistor 123 will be explained separately with reference to Figure 10, etc.

[0034] Figure 8 is a cross-sectional view (part 1) of the bearing device shown in Figure 7, perpendicular to the axis m, and shows a cross-section passing through the center of each rolling element 33 of the first rolling bearing 30A. In the example of Figure 8, the first rolling bearing 30A has 6 rolling elements 33, and the resistors 123 of the first strain gauge 120A and the resistors 123 of the third strain gauge 120C are positioned opposite each other, and the rolling elements 33 pass directly beneath each resistor 123 at the same time.

[0035] In Figure 8, θ is the angle between the center of the resistor 123 of the first strain gauge 120A and the center of the resistor 123 of the third strain gauge 120C, as viewed from the direction of the axis m of the rotation axis 20. In the example in Figure 8, the angle θ between the center of the resistor 123 of the first strain gauge 120A and the center of the resistor 123 of the third strain gauge 120C is 180 degrees.

[0036] However, the preferred arrangement of the first strain gauge 120A and the third strain gauge 120C is not limited to θ = 180 degrees. If N is the number of rolling elements 33 and n is an integer between 1 and (N-1), the first strain gauge 120A and the third strain gauge 120C can be positioned at θ = (360 × n) / N. Note that an error of ±3 degrees is allowed for the angle θ. For example, if θ = 183 degrees or θ = 177 degrees, they are considered to be positioned at θ = (360 × n) / N.

[0037] In the example shown in Figure 8, since N=6, the first strain gauge 120A and the third strain gauge 120C can be placed at positions where θ=60 degrees, 120 degrees, 180 degrees, 240 degrees, or 300 degrees. In Figure 8, when the position of the first strain gauge 120A is fixed, the preferred positions for placing the third strain gauge 120C are indicated by dashed rectangles.

[0038] Since the second strain gauge 120B and the fourth strain gauge 120D are noise sensors, they may be placed at any position within the strain non-transmission section 112 described later, regardless of the above-mentioned θ.

[0039] Figure 9 is a magnified view of the vicinity of the sensor unit shown in Figure 7. As shown in Figure 9, in the sensor unit 100, the gauge fixing member 110 has a strain transmission section 111 to which the strain generated in the first rolling bearing 30A due to the rotation of the rotating shaft 20 is transmitted, and a strain non-transmission section 112 to which the strain generated in the first rolling bearing 30A due to the rotation of the rotating shaft 20 is not transmitted.

[0040] The strain transmission section 111 and the strain non-transmission section 112 are parts where the average value of strain when the rotating shaft 20 rotates at its rated rotational speed is relatively different. Specifically, the strain non-transmission section 112 is defined as the part where, when the average value of strain when the rotating shaft 20 rotates at its rated rotational speed is measured using a strain gauge of the same specifications, the average value of strain measured at the strain transmission section 111 is 1 / 2 or less of the average value of strain measured at the strain transmission section 111. In other words, the "strain non-transmission section 112, where strain generated in the first rolling bearing 30A is not transmitted" does not indicate a part where no strain is transmitted at all. Furthermore, when the average value of strain when the rotating shaft 20 rotates at its rated rotational speed is measured using a strain gauge of the same specifications, it is preferable that the average value of strain measured at the strain non-transmission section 112 is 1 / 5 or less of the average value of strain measured at the strain transmission section 111.

[0041] The strain transmission section 111 is located in a position that overlaps with the outer surface of the first rolling bearing 30A when viewed radially. The strain transmission section 111 is a part that is easily affected by the strain generated in the first rolling bearing 30A due to the rotation of the rotating shaft 20.

[0042] In the example shown in Figure 9, the position of the outer stepped portion 41b of the bearing housing 40 is the same as the position of the inner stepped portion 41a of the bearing housing 40 that abuts against the upper end of the first rolling bearing 30A in the direction of axis m. Also, the position of the outer stepped portion 41c of the bearing housing 40 is the same as the position of the lower end of the first rolling bearing 30A in the direction of axis m.

[0043] In other words, in the example shown in Figure 9, the entire second outer surface 40b of the bearing housing 40 is located in a position that overlaps with the outer surface of the first rolling bearing 30A in a radial view. On the other hand, the third outer surface 40c of the bearing housing 40 is located in a position that does not overlap with the outer surface of the first rolling bearing 30A in a radial view. Since the portion of the bearing housing 40 where the second outer surface 40b is provided is thinner than the portion where the first outer surface 40a is provided, strain generated in the first rolling bearing 30A is more easily transmitted to it.

[0044] Furthermore, in the bearing housing 40, it is sufficient to thin the portion that overlaps with the outer surface of the first rolling bearing 30A in a radial view. Therefore, the position of the outer step portion 41b of the bearing housing 40 may be above the position of the inner step portion 41a of the bearing housing 40 (towards the second rolling bearing 30B) in the direction of axis m.

[0045] The strain-non-transmission portion 112 is located in a position that does not overlap with the outer surface of the first rolling bearing 30A when viewed radially. The strain-non-transmission portion 112 is a part in which strain generated in the first rolling bearing 30A due to the rotation of the rotating shaft 20 is not easily transmitted.

[0046] The first strain gauge 120A and the third strain gauge 120C are located in the strain transmission section 111. In other words, the first strain gauge 120A and the third strain gauge 120C are positioned in a location where strain generated in the first rolling bearing 30A is easily transmitted. In contrast, the second strain gauge 120B and the fourth strain gauge 120D are located in the non-strain transmission section 112. In other words, the second strain gauge 120B and the fourth strain gauge 120D are positioned in a location where strain generated in the first rolling bearing 30A is not easily transmitted.

[0047] In the example shown in Figure 9, a gap S is formed between the inner circumferential surface 110b of the gauge fixing member 110 and the third outer circumferential surface 40c of the bearing housing 40. The gap S is provided in a position that does not overlap with the outer circumferential surface of the first rolling bearing 30A in a radial view. By providing the gap S, the strain generated in the first rolling bearing 30A is less likely to be transmitted to the second strain gauge 120B and the fourth strain gauge 120D, which are positioned on the outer circumferential surface 110a of the gauge fixing member 110. The gap S may be provided only in the region that overlaps with the second strain gauge 120B and the fourth strain gauge 120D in a radial view, or only in that region and its vicinity.

[0048] In the axial direction m, the lower side of the gauge fixing member 110 is an open end. Almost no strain from the first rolling bearing 30A is transmitted to the open end of the gauge fixing member 110. Therefore, it is preferable to position the second strain gauge 120B and the fourth strain gauge 120D near the open end of the gauge fixing member 110, where strain is particularly difficult to transmit, within the strain non-transmission section 112.

[0049] Here, the vicinity of the open end is defined as the range L / 2 from the open end, where L is the axial distance m between the open end and the end of the first rolling bearing 30A on the open end side, as shown in Figure 9. The second strain gauge 120B and the fourth strain gauge 120D are more preferably positioned within the range L / 3 from the open end, and even more preferably within the range L / 4 from the open end.

[0050] In this manner, by arranging the first strain gauge 120A and the third strain gauge 120C in the strain transmission section 111 of the gauge fixing member 110, the strain of the first rolling bearing 30A is transmitted to the first strain gauge 120A and the third strain gauge 120C via the gauge fixing member 110. This makes it possible to detect the strain of the first rolling bearing 30A using the first strain gauge 120A and the third strain gauge 120C. In this embodiment, the first strain gauge 120A and the third strain gauge 120C detect the strain of the first rolling bearing 30A as a change in the resistance value of the resistor 123.

[0051] Figure 10 is a partially enlarged view of the vicinity of the first strain gauge and the second strain gauge shown in Figure 7, etc. As shown in Figure 10, in the first strain gauge 120A, it is preferable that the resistor 123 is positioned with its longitudinal direction (gauge length direction) facing the circumferential direction of the gauge fixing member 110. Since the circumferential direction of the gauge fixing member 110 is more flexible than the axial direction m, a large strain waveform can be obtained by positioning the longitudinal direction of the resistor 123 facing the circumferential direction of the gauge fixing member 110.

[0052] The first strain gauge 120A has a pair of terminals 125 connected to both ends of a resistor 123 via wiring 124, and wiring 130A is electrically connected to each terminal 125 by solder or the like. Wiring 130A may be, for example, a coaxial cable, or it may be a structure in which a solid GND is formed on at least one side of a flexible substrate. The third strain gauge 120C shown in Figure 7 etc. has the same structure as the first strain gauge 120A.

[0053] The second strain gauge 120B, like the first strain gauge 120A, includes a resistor 123, wiring 124, and terminals 125. The second strain gauge 120B can have the same structure and size as the first strain gauge 120A, for example. In the second strain gauge 120B, the longitudinal direction of the resistor 123 can be the same as the longitudinal direction of the resistor 123 in the first strain gauge 120A, for example.

[0054] Each terminal portion 125 of the second strain gauge 120B is electrically connected to a wiring 130B by solder or the like. The wiring 130B may be, for example, a coaxial cable, or it may be a structure in which a solid GND is formed on at least one side of a flexible substrate. The fourth strain gauge 120D shown in Figure 7, etc., has the same structure as the second strain gauge 120B.

[0055] The first strain gauge 120A, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D are affected by electromagnetic noise interference. Therefore, the output of the first strain gauge 120A, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D includes electromagnetic noise in addition to the strain of the first rolling bearing 30A. Electromagnetic noise, in this context, refers to noise generated from the motor's coils, etc., when the bearing device 1 is mounted on a motor.

[0056] However, in the bearing device 1, the second strain gauge 120B and the fourth strain gauge 120D are located in the strain non-transmission section 112. Therefore, the second strain gauge 120B and the fourth strain gauge 120D hardly detect any strain in the first rolling bearing 30A, and the output of the second strain gauge 120B and the fourth strain gauge 120D consists almost entirely of electromagnetic noise.

[0057] As mentioned above, a large strain waveform can be obtained by aligning the longitudinal direction of the resistor 123 with the circumferential direction of the bearing housing 40. Therefore, in order to further reduce the strain detected by the second strain gauge 120B and the fourth strain gauge 120D, the second strain gauge 120B and the fourth strain gauge 120D may be oriented with the longitudinal direction of the resistor 123 in the direction of axis m.

[0058] Since the first strain gauge 120A, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D are all fixed to the gauge fixing member 110, the influence of electromagnetic noise is almost the same for all of them. Therefore, by placing the first strain gauge 120A and the third strain gauge 120C in the strain transmission section 111 of the gauge fixing member 110, and the second strain gauge 120B and the fourth strain gauge 120D in the non-strain transmission section 112 of the gauge fixing member 110, the influence of electromagnetic noise can be eliminated using the outputs of both, and strain with a good signal-to-noise ratio can be detected. A specific circuit connection example is shown below.

[0059] Figure 11 is a schematic diagram illustrating a strain detection device according to the first embodiment. As shown in Figure 11, the strain detection device 3 includes a bearing device 1 and a bridge circuit 2. R1, R2, R3, and R4 correspond to the resistors 123 of the first strain gauge 120A, second strain gauge 120B, third strain gauge 120C, and fourth strain gauge 120D, respectively.

[0060] In other words, in Figure 11, the first strain gauge 120A, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D of the bearing device 1 constitute one of the four sides of the bridge circuit 2. A DC voltage E is supplied between the connection point of resistor R1 and resistor R2, and between the connection point of resistor R3 and resistor R4. As a result, an output voltage e0 can be obtained as the output of the bridge circuit from between the connection point of resistor R1 and resistor R4, and between the connection point of resistor R2 and resistor R3.

[0061] The first strain gauge 120A forms one side of the four sides of the bridge circuit 2 on one side of the first output voltage extraction point, and the fourth strain gauge 120D forms one side of the four sides of the bridge circuit 2 on the other side of the first output voltage extraction point. Furthermore, the second strain gauge 120B forms one side of the four sides of the bridge circuit 2 on the side of the second output voltage extraction point that is connected to the first strain gauge 120A, and the third strain gauge 120C forms one side of the four sides of the bridge circuit on the side of the second output voltage extraction point that is connected to the fourth strain gauge 120D.

[0062] Specifically, for example, in Figure 11, if the connection point between resistors R1 and R4 is the first output voltage extraction point, and the connection point between resistors R2 and R3 is the second output voltage extraction point, then in Figure 11, R1 can be the first strain gauge 120A, R2 the second strain gauge 120B, R3 the third strain gauge 120C, and R4 the fourth strain gauge 120D. However, the same output voltage e0 can be obtained even if the positions of the first strain gauge 120A and the third strain gauge 120C, and the second strain gauge 120B and the fourth strain gauge 120D are swapped.

[0063] Furthermore, in Figure 11, if the connection point between resistors R1 and R4 is the second output voltage extraction point, and the connection point between resistors R2 and R3 is the first output voltage extraction point, then in Figure 11, R1 can be the second strain gauge 120B, R2 the first strain gauge 120A, R3 the fourth strain gauge 120D, and R4 the third strain gauge 120C. However, the same output voltage e0 can be obtained even if the positions of the first strain gauge 120A and the third strain gauge 120C, and the second strain gauge 120B and the fourth strain gauge 120D are swapped.

[0064] For example, if strain ε and electromagnetic noise N are detected in the first strain gauge 120A and the third strain gauge 120C, and only electromagnetic noise N is detected in the second strain gauge 120B and the fourth strain gauge 120D, then the electromagnetic noise N is canceled out, and the output voltage e0 = E / 2 × Ks × ε, where Ks is the gauge factor.

[0065] In this way, by arranging the first strain gauge 120A and the third strain gauge 120C in the strain transmission section 111 and the second strain gauge 120B and the fourth strain gauge 120D in the non-strain transmission section 112, a bearing device 1 can be realized that outputs a signal capable of reducing the influence of electromagnetic noise N. Then, by configuring a strain detection device 3 using the bearing device 1, a strain ε with a good signal-to-noise ratio, from which the influence of electromagnetic noise N has been removed, can be detected as the output voltage ε0.

[0066] The strain detection device 3 may further include a power supply capable of supplying a DC voltage E, an amplifier that amplifies the output voltage e0, an A / D converter that converts the output of the amplifier into a digital signal, and a signal processing unit that performs calculations on the output of the A / D converter. The state of the first rolling bearing 30A can be monitored by, for example, performing an FFT analysis (Fast Fourier Transform) on the output voltage e0 of the bridge circuit 2 in the signal processing unit.

[0067] Figure 12 is a cross-sectional view (part 2) of the bearing device shown in Figure 7, perpendicular to the axis m, and shows a cross-section passing through the center of each rolling element 33 of the first rolling bearing 30A. The first strain gauge 120A and the third strain gauge 120C may be arranged as shown in Figure 12, unlike in Figure 8. That is, the first strain gauge 120A and the third strain gauge 120C may be arranged such that when a rolling element 33 passes directly below the resistor 123 of the first strain gauge 120A, the resistor 123 of the third strain gauge 120C is located between two adjacent rolling elements 33.

[0068] In the example shown in Figure 12, the first rolling bearing 30A has seven rolling elements 33, and the resistors 123 of the first strain gauge 120A and the resistors 123 of the third strain gauge 120C are positioned opposite each other. In other words, in the example shown in Figure 12, the angle θ between the center of the resistor 123 of the first strain gauge 120A and the center of the resistor 123 of the third strain gauge 120C is 180 degrees.

[0069] However, the preferred arrangement of the first strain gauge 120A and the third strain gauge 120C is not limited to θ = 180 degrees. If N is the number of rolling elements 33 and n is an integer between 0 and (N-1), then the first strain gauge 120A and the third strain gauge 120C can be positioned at θ = (360 × n) / N + 360 / 2N. Note that an error of ±3 degrees is allowed for the angle θ. For example, if θ = 183 degrees or θ = 177 degrees, they are considered to be positioned at θ = (360 × n) / N + 360 / 2N.

[0070] In the example shown in Figure 12, since N=7, the first strain gauge 120A and the third strain gauge 120C can be positioned at a location where θ = approximately 26 degrees, approximately 77 degrees, approximately 129 degrees, 180 degrees, approximately 231 degrees, approximately 283 degrees, or approximately 334 degrees. In Figure 12, when the position of the first strain gauge 120A is fixed, the preferred position for positioning the third strain gauge 120C is indicated by a dashed rectangle.

[0071] Furthermore, since the second strain gauge 120B and the fourth strain gauge 120D are noise sensors, they may be placed at any position within the strain non-transmission section 112 that is unrelated to the above-mentioned θ.

[0072] Even when the first strain gauge 120A and the third strain gauge 120C are arranged as shown in Figure 12, the output voltage e0 can still be obtained with the circuit shown in Figure 11. However, in the circuit shown in Figure 11, the first strain gauge 120A constitutes one side of the four sides of the bridge circuit 2 on one side of the first output voltage extraction point, and the fourth strain gauge 120D constitutes one side of the four sides of the bridge circuit 2 on the other side of the first output voltage extraction point. Furthermore, the second strain gauge 120B constitutes one side of the four sides of the bridge circuit 2 on the fourth strain gauge 120D side of the second output voltage extraction point, and the third strain gauge 120C constitutes one side of the four sides of the bridge circuit 2 on the first strain gauge 120A side of the second output voltage extraction point.

[0073] Specifically, for example, in Figure 11, if the connection point between resistors R1 and R4 is the first output voltage extraction point, and the connection point between resistors R2 and R3 is the second output voltage extraction point, then in Figure 11, R1 can be the first strain gauge 120A, R2 the third strain gauge 120C, R3 the second strain gauge 120B, and R4 the fourth strain gauge 120D. However, the same output voltage e0 can be obtained even if the positions of the first strain gauge 120A and the third strain gauge 120C, and the second strain gauge 120B and the fourth strain gauge 120D are swapped.

[0074] Furthermore, in Figure 11, if the connection point between resistors R1 and R4 is the second output voltage extraction point, and the connection point between resistors R2 and R3 is the first output voltage extraction point, then in Figure 11, R1 can be the second strain gauge 120B, R2 the fourth strain gauge 120D, R3 the first strain gauge 120A, and R4 the third strain gauge 120C. However, the same output voltage e0 can be obtained even if the positions of the first strain gauge 120A and the third strain gauge 120C, and the second strain gauge 120B and the fourth strain gauge 120D are swapped.

[0075] For example, if strain ε and electromagnetic noise N are detected in the first strain gauge 120A and the third strain gauge 120C, and only electromagnetic noise N is detected in the second strain gauge 120B and the fourth strain gauge 120D, then the electromagnetic noise N is canceled out, and the output voltage e0 = E / 2 × Ks × ε, where Ks is the gauge factor.

[0076] (Strain gauge) Figure 13 is a plan view illustrating a strain gauge according to the first embodiment. Figure 14 is a cross-sectional view illustrating a strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 13. While the first strain gauge 120A will be described below, the second strain gauge 120B, the third strain gauge 120C, and the fourth strain gauge 120D can have the same structure as the first strain gauge 120A. However, each strain gauge may have a partially different structure as needed. For example, the size of the base material, the presence or absence of a cover layer, and other specifications may be changed as necessary.

[0077] Referring to Figures 13 and 14, the first strain gauge 120A includes a base material 121, a functional layer 122, a resistor 123, wiring 124, and a terminal portion 125. However, the functional layer 122 may be provided as needed.

[0078] In the explanation of Figures 13 and 14, for convenience, in the first strain gauge 120A, the side of the base material 121 on which the resistor 123 is provided will be referred to as the upper side or one side, and the side on which the resistor 123 is not provided will be referred to as the lower side or the other side. Also, the surface on which the resistor 123 is provided in each part will be referred to as one surface or the upper surface, and the surface on which the resistor 123 is not provided will be referred to as the other surface or the lower surface. However, the first strain gauge 120A can be used upside down or positioned at any angle. Furthermore, a plan view refers to viewing the object from the direction normal to the upper surface 121a of the base material 121, and a planar shape refers to the shape of the object viewed from the direction normal to the upper surface 121a of the base material 121.

[0079] The base material 121 is a member that serves as a base layer for forming the resistor 123, etc., and is flexible. The thickness of the base material 121 is not particularly limited and can be appropriately selected depending on the purpose, but for example it can be about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm for the base material 121 is preferable in terms of the transmission of strain from the surface of the strain-generating body (for example, the outer peripheral surface 110a of the gauge fixing member 110) that is joined to the lower surface of the base material 121 via the adhesive layer 150, and dimensional stability against the environment, and a thickness of 10 μm or more is even preferable in terms of insulation.

[0080] The base material 121 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, or polyolefin resin. Note that "film" refers to a flexible material with a thickness of approximately 500 μm or less.

[0081] Here, "formed from an insulating resin film" does not prevent the base material 121 from containing fillers or impurities in the insulating resin film. For example, the base material 121 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0082] Other materials for the substrate 121 besides resin include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3), as well as amorphous glass. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 121. In this case, an insulating film is formed on the metallic substrate 121.

[0083] The functional layer 122 is formed on the upper surface 121a of the base material 121 as a lower layer of the resistor 123. That is, the planar shape of the functional layer 122 is substantially the same as the planar shape of the resistor 123 shown in Figure 13.

[0084] In this application, the functional layer refers to a layer that has the function of promoting the crystal growth of the resistor 123, which is at least the upper layer. Preferably, the functional layer 122 further has the function of preventing oxidation of the resistor 123 by oxygen and moisture contained in the substrate 121, and the function of improving the adhesion between the substrate 121 and the resistor 123. The functional layer 122 may further have other functions.

[0085] Since the insulating resin film that makes up the base material 121 contains oxygen and moisture, and especially when the resistor 123 contains Cr (chromium), the Cr forms an oxidized film, it is effective for the functional layer 122 to have a function to prevent oxidation of the resistor 123.

[0086] The material of the functional layer 122 is not particularly limited as long as it is a material that has the function of promoting crystal growth of the upper layer resistor 123, and can be appropriately selected according to the purpose. Examples include Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), and Bi (bismuth). Examples include one or more metals selected from the group consisting of Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of these metals, or a compound of any of these metals.

[0087] Examples of the alloys mentioned above include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds mentioned above include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0088] When the functional layer 122 is formed from a conductive material such as a metal or alloy, it is preferable that the thickness of the functional layer 122 be 1 / 20 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor flows into the functional layer 122, preventing a decrease in strain detection sensitivity.

[0089] When the functional layer 122 is formed from a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer 122 be 1 / 50 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor flows through the functional layer 122, further preventing a decrease in strain detection sensitivity.

[0090] If the functional layer 122 is formed from a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer 122 be 1 / 100 or less of the thickness of the resistor. Within this range, it is possible to further prevent a decrease in strain detection sensitivity due to a portion of the current flowing through the resistor flowing into the functional layer 122.

[0091] When the functional layer 122 is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer 122 is preferably 1 nm to 1 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer 122 can be easily formed without cracking.

[0092] When the functional layer 122 is formed from an insulating material such as an oxide or nitride, the film thickness of the functional layer 122 is more preferably 1 nm to 0.8 μm. Within this range, the crystal growth of α-Cr can be promoted, and the film can be formed more easily without cracking in the functional layer 122.

[0093] When the functional layer 122 is formed from an insulating material such as an oxide or nitride, it is even more preferable that the film thickness of the functional layer 122 be 1 nm to 0.5 μm. Within this range, the crystal growth of α-Cr can be promoted, and the film can be formed more easily without cracking in the functional layer 122.

[0094] The planar shape of the functional layer 122 is patterned to be substantially the same as the planar shape of the resistor shown in Figure 13. However, the planar shape of the functional layer 122 is not limited to being substantially the same as the planar shape of the resistor. If the functional layer 122 is formed from an insulating material, it does not need to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer 122 may be formed as a solid block at least in the region where the resistor is formed. Alternatively, the functional layer 122 may be formed as a solid block over the entire upper surface of the substrate 121.

[0095] Furthermore, when the functional layer 122 is formed from an insulating material, forming the functional layer 122 relatively thick, such as 50 nm to 1 μm, and forming it in a solid form increases the thickness and surface area of ​​the functional layer 122, allowing the heat generated when the resistor heats up to be dissipated towards the base material 121. As a result, the decrease in measurement accuracy due to self-heating of the resistor can be suppressed in the first strain gauge 120A.

[0096] The resistor 123 is a thin film formed in a predetermined pattern on the upper surface of the functional layer 122, and is a sensitive part that undergoes a change in resistance when subjected to strain.

[0097] The resistor 123 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 123 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0098] The following explanation will use the case where the resistor 123 is a Cr multiphase film as an example. Here, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide. In addition, some of the material constituting the functional layer 122 may be diffused into the Cr multiphase film. In this case, the material constituting the functional layer 122 and nitrogen may form a compound. For example, if the functional layer 122 is made of Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0099] The thickness of the resistor 123 is not particularly limited and can be appropriately selected depending on the purpose, but for example, it can be about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more of the resistor 123 is preferable because it improves the crystallinity of the crystals constituting the resistor 123 (for example, the crystallinity of α-Cr), and a thickness of 1 μm or less is even preferable because it can reduce cracks in the film and warping from the substrate 121 caused by internal stress in the film constituting the resistor 123.

[0100] By forming the resistor 123 on the functional layer 122, the resistor 123 can be formed using a stable crystalline phase, thereby improving the stability of the gauge characteristics (gauge factor, gauge factor temperature coefficient TCS, and resistance temperature coefficient TCR).

[0101] For example, if the resistor 123 is a Cr multiphase film, a resistor 123 mainly composed of α-Cr (alpha-chromium) can be formed by providing a functional layer 122. Since α-Cr is a stable crystalline phase, the stability of the gauge characteristics can be improved.

[0102] Here, "main component" means that the substance in question accounts for 50% or more by mass of the total substances constituting the resistor. When the resistor 123 is a Cr multiphase film, from the viewpoint of improving gauge characteristics, it is preferable that the resistor 123 contains 80% or more by weight of α-Cr, and more preferably 90% or more by weight. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0103] Furthermore, if the resistor 123 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film at 20% by weight or less, the decrease in gauge factor can be suppressed.

[0104] Furthermore, the proportion of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the proportion of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes even more pronounced due to the semiconducting properties of Cr2N. In addition, brittle fracture is reduced by reducing the ceramicization.

[0105] On the other hand, if trace amounts of N2 or atomic N are mixed into the film, external environmental factors (such as high temperatures) can cause them to escape from the film, resulting in changes in film stress. By creating chemically stable CrN, the generation of the aforementioned unstable N is avoided, and a stable strain gauge can be obtained.

[0106] Furthermore, the gauge characteristics can be improved by the diffusion of the metal (e.g., Ti) constituting the functional layer 122 into the Cr multiphase film. Specifically, the gauge factor of the first strain gauge 120A can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C.

[0107] The terminal portion 125 extends from both ends of the resistor 123 via the wiring 124, and in a plan view, it is wider than the resistor 123 and the wiring 124 and is formed in a substantially rectangular shape. The terminal portion 125 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 123 caused by strain. The resistor 123 extends from one of the terminal portion 125 and the wiring 124, for example, by folding back in a zigzag pattern, and is connected to the other wiring 124 and terminal portion 125. The upper surface of the terminal portion 125 may be covered with a metal that has better solderability than the terminal portion 125.

[0108] Although the resistor 123, wiring 124, and terminal portion 125 are given different reference numerals for convenience, they can be formed integrally from the same material in the same process.

[0109] A cover layer 126 (insulating resin layer) may be provided on the upper surface 121a of the base material 121 so as to cover the resistor 123 and wiring 124 and expose the terminal portion 125. Providing the cover layer 126 prevents mechanical damage to the resistor 123 and wiring 124. In addition, providing the cover layer 126 protects the resistor 123 and wiring 124 from moisture, etc. The cover layer 126 may be provided so as to cover the entire portion excluding the terminal portion 125.

[0110] The cover layer 126 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin, polyolefin resin). The cover layer may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer, and it can be appropriately selected depending on the purpose, but for example, it can be about 2 μm to 30 μm.

[0111] To manufacture the first strain gauge 120A, first, a base material 121 is prepared, and a functional layer 122 is formed on the upper surface 121a of the base material 121. The materials and thicknesses of the base material 121 and the functional layer 122 are as described above. However, the functional layer 122 may be provided only if necessary.

[0112] The functional layer 122 can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming the functional layer 122 and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer 122 is deposited while etching the upper surface 121a of the substrate 121 with Ar, thus minimizing the amount of functional layer 122 deposited and achieving improved adhesion.

[0113] However, this is just one example of a method for forming the functional layer 122, and the functional layer 122 may be formed by other methods. For example, the upper surface 121a of the substrate 121 may be activated by plasma treatment using Ar or the like before forming the functional layer 122 to improve adhesion, and then the functional layer 122 may be formed in a vacuum by magnetron sputtering.

[0114] Next, a metal layer forming the resistor 123, wiring 124, and terminal portion 125 is formed on the entire upper surface of the functional layer 122. Then, the functional layer 122, resistor 123, wiring 124, and terminal portion 125 are patterned into the planar shape shown in Figure 13 by photolithography. The material and thickness of the resistor 123, wiring 124, and terminal portion 125 are as described above. The resistor 123, wiring 124, and terminal portion 125 can be formed integrally from the same material. The resistor 123, wiring 124, and terminal portion 125 can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming the resistor 123, wiring 124, and terminal portion 125. The resistor 123, wiring 124, and terminal portion 125 may also be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, etc., instead of magnetron sputtering.

[0115] There are no particular restrictions on the combination of materials for the functional layer 122 and the resistor 123, wiring 124, and terminal portion 125, and they can be appropriately selected according to the purpose. For example, Ti can be used as the functional layer 122, and a Cr multiphase film mainly composed of α-Cr (alpha-chromium) can be formed for the resistor 123, wiring 124, and terminal portion 125.

[0116] In this case, for example, the resistor 123, wiring 124, and terminal portion 125 can be formed by magnetron sputtering with Ar gas introduced into the chamber, using a raw material capable of forming a Cr multiphase film as the target. Alternatively, the resistor 123, wiring 124, and terminal portion 125 can be formed by reactive sputtering with pure Cr as the target, using an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, the ratio of CrN and Cr2N in the Cr multiphase film, as well as the ratio of Cr2N within CrN and Cr2N, can be adjusted by changing the amount and pressure (partial pressure of nitrogen) of nitrogen gas introduced or by adjusting the heating temperature by providing a heating step.

[0117] In these methods, the functional layer 122 made of Ti initiates the growth surface of the Cr multiphase film, enabling the formation of a Cr multiphase film mainly composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer 122 into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of the first strain gauge 120A can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C.

[0118] Furthermore, when the resistor 123 is a Cr multiphase film, the functional layer 122 made of Ti has all of the following functions: promoting crystal growth of the resistor 123, preventing oxidation of the resistor 123 by oxygen and moisture contained in the substrate 121, and improving the adhesion between the substrate 121 and the resistor 123. The same applies when Ta, Si, Al, or Fe is used instead of Ti as the functional layer 122.

[0119] Subsequently, if necessary, a cover layer 126 is provided on the upper surface 121a of the base material 121, covering the resistor 123 and wiring 124 and exposing the terminal portion 125, thereby completing the first strain gauge 120A. The cover layer 126 can be manufactured, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 121a of the base material 121 so as to cover the resistor 123 and wiring 124 and exposing the terminal portion 125, and then heating and curing it. Alternatively, the cover layer 126 may be manufactured by applying a liquid or paste-like thermosetting insulating resin to the upper surface 121a of the base material 121 so as to cover the resistor 123 and wiring 124 and exposing the terminal portion 125, and then heating and curing it.

[0120] In this way, by providing a functional layer 122 in the lower layer of the resistor 123, crystal growth of the resistor 123 can be promoted, and a resistor 123 consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics of the first strain gauge 120A can be improved. Furthermore, the diffusion of the material constituting the functional layer 122 into the resistor 123 can improve the gauge characteristics of the first strain gauge 120A.

[0121] Furthermore, the first strain gauge 120A, which uses a Cr multiphase film as the material for the resistor 123, achieves high sensitivity (more than 500% compared to conventional models) and miniaturization (less than 1 / 10 of conventional models). For example, while the output of a conventional strain gauge was about 0.04mV / 2V, the first strain gauge 120A can obtain an output of 0.3mV / 2V or higher. In addition, while the size (gauge length × gauge width) of a conventional strain gauge was about 3mm × 3mm, the size (gauge length × gauge width) of the first strain gauge 120A can be miniaturized to about 0.3mm × 0.3mm.

[0122] As described above, the first strain gauge 120A, which uses a Cr multiphase film as the material for the resistor 123, is small and therefore particularly suitable for use in a bearing device 1 that uses small first rolling bearings 30A and second rolling bearings 30B with a diameter (outer diameter of the outer ring 31) of 30 mm or less. Furthermore, the first strain gauge 120A, which uses a Cr multiphase film as the material for the resistor 123, is highly sensitive and can detect small displacements, making it possible to detect minute strains that were previously difficult to detect. In other words, by having the first strain gauge 120A, which uses a Cr multiphase film as the material for the resistor 123, a bearing device 1 equipped with the function of accurately detecting strain can be realized.

[0123] (motor) The bearing device 1 can be mounted on a motor. Figure 15 is a cross-sectional view illustrating a motor equipped with the bearing device according to the first embodiment. As shown in Figure 15, the motor 5 is an axial flow fan motor having the bearing device 1, an impeller 10, a stator 50, a rotor 60, and a casing 70. Note that the bearing device 1 can also be mounted on motors other than axial flow fan motors.

[0124] The impeller 10 has a rotor housing 11 and blades 12 provided on the outer circumference of the rotor housing 11. A bearing device 1 is fixed to the center of the impeller 10. The stator 50 has an insulator 51, a stator core 52, and a coil 53, and is arranged on the outer circumference of the bearing housing 40 of the bearing device 1. The stator core 52 is fixed to the outer circumference of the bearing housing 40 by, for example, press-fitting.

[0125] The rotor 60 has a rotor yoke 61 integrally provided inside the rotor housing 11 and a rotor magnet 62 mounted inside the rotor yoke 61. In the example shown in Figure 15, the rotor yoke 61 is integrally provided inside the rotor housing 11, but this is not limited to this, and the rotor yoke 61 may be mounted inside the rotor housing 11. Also, the rotating shaft 20 is mounted on the rotor yoke 61 and fixed to the center of the rotor housing 11, but the rotating shaft 20 may be directly fixed to the rotor housing 11.

[0126] The casing 70 includes a casing outer frame 71 that covers the outer circumference of the impeller 10, a base hub 72 that fixes the bearing housing 40, and stationary vanes 73 that connect the casing outer frame 71 and the base hub 72.

[0127] In the example shown in Figure 15, the casing outer frame 71 and the base hub 72 are connected by a stationary vane 73. However, the casing outer frame 71 and the base hub 72 may also be connected by a rod-shaped structure such as a connecting shaft.

[0128] Furthermore, the bearing housing 40 of the bearing device 1 may be fixed to the base hub 72 when the casing 70 is injection molded from resin, or the casing 70 may be molded first and then fixed to the base hub 72 later.

[0129] In motor 5, the motor section 80 is composed of a stator 50 and a rotor 60. By supplying current to a coil 53 from a power supply unit (not shown), the impeller 10 rotates around the central axis m of the rotating shaft 20, which is rotatably supported within the bearing housing 40. In other words, motor 5 is a so-called outer rotor type motor.

[0130] In motor 5, the upper side of Figure 15 is the intake side, and the lower side is the outlet side. Therefore, in motor 5, the impeller 10 is provided on the air intake side of the casing outer frame 71, and the base hub 72 is provided on the outlet side.

[0131] When the wiring 130A to 130D shown in Figure 7 has a shielded portion, it is preferable that the gauge fixing member 110 to which the first strain gauge 120A etc. is fixed be connected to a GND at the same potential as the shielded portion of the wiring 130A to 130D, from the viewpoint of suppressing the influence of electromagnetic noise. For example, by bonding the gauge fixing member 110 and the shielded portion of the wiring 130A to 130D with a conductive adhesive, both can be connected to a GND at the same potential. Examples of conductive adhesives include pastes in which particles such as silver, nickel, gold, copper, and carbon black are dispersed in the adhesive.

[0132] The wiring 130A to 130D may, for example, be directly routed from the sensor unit 100 to the outside of the motor 5, or it may be electrically connected to a circuit board located inside the motor 5.

[0133] In the bearing device 1, the bearing housing 40 and the sensor unit 100 are separate parts. Therefore, when assembling the motor 5, each strain gauge mounted on the sensor unit 100 can be easily placed on the motor 5. That is, after press-fitting the bearing housing 40 into the base hub 72 which will serve as the housing, the sensor unit 100 with the strain gauges mounted on it can be attached to the bearing housing 40.

[0134] Thus, in the motor 5, since the bearing housing 40 and the sensor unit 100 are separate parts, the sensor unit 100 is easy to handle, and strain gauges can be easily placed on the motor 5 using the sensor unit 100. Therefore, the assembly time for the motor 5 can be reduced. In addition, by attaching the sensor unit 100 to the bearing housing 40, the rigidity of the bearing housing 40 can be increased. Furthermore, by attaching the sensor unit 100 to the bearing housing 40 in a detachable manner, it is possible to replace the sensor unit 100 when necessary.

[0135] Furthermore, the motor 5 may have a strain detection device 3. That is, in addition to the bearing device 1, the motor 5 can also be equipped with the bridge circuit 2 shown in Figure 11. By monitoring the changes in the strain waveform of the first rolling bearing 30A using the strain detection device 3, it is possible to detect abnormalities in the first rolling bearing 30A and detect abnormalities before the motor 5 experiences rotational malfunctions. For example, an axial flow fan motor used for cooling servers is constantly operating, and even a temporary stop reduces its cooling capacity. In this case, monitoring the state of the first rolling bearing 30A is particularly effective in order to detect abnormalities in the axial flow fan motor as early as possible.

[0136] <Variation 1 of the First Embodiment> Modification 1 of the first embodiment shows an example of a sensor unit having two strain gauges. In Modification 1 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0137] Figure 16 is a cross-sectional view illustrating a bearing device according to Modification 1 of the First Embodiment, showing a cross-section passing through the axis m of the rotating shaft 20. Figure 16 shows the state after the sensor unit 100A has been attached to the outer circumferential surface of the bearing housing 40.

[0138] The bearing device 1A shown in Figure 16 differs from the bearing device 1 (see Figure 7, etc.) in that the sensor unit 100 has been replaced by the sensor unit 100A. The sensor unit 100A has a first strain gauge 120A and a second strain gauge 120B, but does not have a third strain gauge 120C and a fourth strain gauge 120D. The sensor unit 100A is otherwise the same as the sensor unit 100.

[0139] Even when using only the first strain gauge 120A and the second strain gauge 120B of the bearing device 1A, a strain ε with a good signal-to-noise ratio, in which the influence of electromagnetic noise N is removed, can be detected as the output voltage ε0, similar to the first embodiment.

[0140] Specifically, in the bridge circuit 2 shown in Figure 11, R1 is the first strain gauge 120A, R4 is the second strain gauge 120B, and R2 and R3 are fixed resistors R. This allows us to obtain an output voltage e0 as the output of the bridge circuit 2. For example, if strain ε and electromagnetic noise N are detected by the first strain gauge 120A, and only electromagnetic noise N is detected by the second strain gauge 120B, the electromagnetic noise N is canceled out, and the output voltage e0 = E / 4 × Ks × ε.

[0141] Thus, the sensor unit may have two or four strain gauges. By placing at least one strain gauge in both the strain transmission section 111 and the strain non-transmission section 112, the influence of electromagnetic noise N can be reduced. A sensor unit with four strain gauges is advantageous in that it can obtain a large output voltage e0. On the other hand, a sensor unit with two strain gauges is advantageous in that it can reduce the number of parts. Therefore, it is preferable to select either sensor unit according to the required specifications.

[0142] <Modification 2 of the First Embodiment> Modification 2 of the first embodiment shows an example of a bearing device equipped with two sensor units. In Modification 2 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0143] Figure 17 is a cross-sectional view (part 1) illustrating a bearing device according to modification 2 of the first embodiment, showing a cross-section passing through the axis m of the rotating shaft 20. Figure 18 is a cross-sectional view (part 2) illustrating a bearing device according to modification 2 of the first embodiment, showing an example of a cross-section along line BB in Figure 17. Figure 19 is a cross-sectional view (part 3) illustrating a bearing device according to modification 2 of the first embodiment, showing another example of a cross-section along line BB in Figure 17. Note that Figure 17 shows the state after the two sensor units 100 have been attached to the outer circumferential surface of the bearing housing 40.

[0144] As shown in Figures 17 to 19, the bearing device 1B includes a rotating shaft 20, a first rolling bearing 30A, a second rolling bearing 30B, a bearing housing 40, and two sensor units 100.

[0145] One end of the sensor unit 100 can be detachably fitted into one side of the bearing housing 40 in the axial direction m (the side with the first rolling bearing 30A). The structure near one end of the sensor unit 100 is the same as that of the bearing device 1 shown in Figure 6, etc. The other end of the sensor unit 100 can be detachably fitted into the other side of the bearing housing 40 in the axial direction m (the side with the second rolling bearing 30B).

[0146] On the other side of the sensor unit 100, the gauge fixing member 110 has a strain transmission section to which strain generated in the second rolling bearing 30B by the rotation of the rotation axis m is transmitted, and a strain non-transmission section to which strain is not transmitted. The strain transmission section is located in a position that overlaps with the outer circumferential surface of the second rolling bearing 30B in a radial view, and the strain non-transmission section is located in a position that does not overlap with the outer circumferential surface of the second rolling bearing 30B in a radial view. The first strain gauge 120A and the third strain gauge 120C are arranged in the strain transmission section, and the second strain gauge 120B and the fourth strain gauge 120D are arranged in the strain non-transmission section.

[0147] As shown in Figure 18, in the other sensor unit 100 (the sensor unit on the second rolling bearing 30B side), the wires (wiring 130A, etc.) connected to the electrodes of each strain gauge can be routed to the first rolling bearing 30A side, for example, through grooves 40x provided in the bearing housing 40. Alternatively, as shown in Figure 19, they may be routed to the first rolling bearing 30A side through holes 40y provided in the bearing housing 40.

[0148] Thus, a sensor unit 100 may be provided to detect the strain of the first rolling bearing 30A and the second rolling bearing 30B, respectively. Alternatively, instead of two sensor units 100, two sensor units 100A as shown in Figure 16 may be used. That is, each sensor unit may have four strain gauges (first strain gauge 120A, second strain gauge 120B, third strain gauge 120C, and fourth strain gauge 120D), or it may have two strain gauges (first strain gauge 120A and second strain gauge 120B).

[0149] <Modification 3 of the First Embodiment> Modification 3 of the first embodiment shows an example of variations in the strain transmission section and the strain non-transmission section. In Modification 3 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0150] Figure 20 is a partially enlarged view (part 1) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment. Figure 21 is a partially enlarged view (part 2) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment.

[0151] As shown in Figure 20, in the sensor unit 100, the gauge fixing member 110 may have a groove 110c that is recessed from the inner circumferential surface 110b toward the opposite side of the rotation axis 20 in the region located between the first strain gauge 120A and the second strain gauge 120B in the direction of the axis m of the rotation axis 20. In this case, the area further below the groove 110c becomes the strain non-transmission portion 112. Multiple grooves 110c may be arranged spaced apart in the direction of the axis m. In this case, the area further below the lowest groove 110c becomes the strain non-transmission portion 112. Furthermore, one or more grooves 110c may be provided around the entire circumference, or only in the portion where the first strain gauge 120A and the second strain gauge 120B face each other.

[0152] As shown in Figure 21, in the sensor unit 100, the gauge fixing member 110 may have a groove 110d that is recessed from the outer surface 110a toward the side of the rotation shaft 20 in the region located between the first strain gauge 120A and the second strain gauge 120B in the direction of the axis m of the rotation shaft 20. In this case, the area further below the groove 110d becomes the strain non-transmission portion 112. Multiple grooves 110d may be arranged spaced apart in the direction of the axis m. In this case, the area further below the lowest groove 110d becomes the strain non-transmission portion 112. Furthermore, one or more grooves 110d may be provided around the entire circumference, or only in the portion where the first strain gauge 120A and the second strain gauge 120B face each other.

[0153] By adopting the structure shown in Figures 20 and 21, strain is concentrated in the grooves 110c and 110d of the gauge fixing member 110, thereby further reducing strain transmission to the strain non-transmission section 112. The cross-sectional shape and length of the grooves can be determined arbitrarily. For example, grooves longer than the strain non-transmission section 112 in the axial direction m may be provided, such as groove 110e shown in Figure 22 and groove 110f shown in Figure 23. The fixing parts of the gauge fixing member 110 for the third strain gauge 120C and the fourth strain gauge 120D can also have the same structure as shown in Figures 20 to 23.

[0154] Figure 24 is a partially enlarged view (No. 5) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment. As shown in Figure 24, a thin-walled section 110g may be provided at a position that overlaps with the outer circumferential surface of the first rolling bearing 30A in a radial view, and the first strain gauge 120A may be placed on the thin-walled section 110g. In this case, the thin-walled section 110g of the gauge fixing member 110 becomes the strain transmission section 111. In this way, in order to more easily transmit the strain generated in the first rolling bearing 30A by the rotation of the rotating shaft 20, the strain transmission section 111 may be thinner than the strain non-transmission section 112. Note that the fixing sections of the third strain gauge 120C and the fourth strain gauge 120D in the gauge fixing member 110 can also have the same structure as in Figure 24.

[0155] Figure 25 is a partially enlarged view (6) of the strain transmission section and strain non-transmission section according to Modification 3 of the First Embodiment. As shown in Figure 25, a thin-walled portion 110h recessed on the outer circumference side may be provided on the gauge fixing member 110 at a position that does not overlap with the outer circumference surface of the first rolling bearing 30A in a radial view, and the second strain gauge 120B may be placed in the thin-walled portion 110h. In this case, the thin-walled portion 110h of the gauge fixing member 110 becomes the strain non-transmission section 112. Compared to the outer circumference surface of the gauge fixing member 110 that overlaps with the outer circumference surface of the first rolling bearing 30A in a radial view, strain generated in the first rolling bearing 30A is less likely to be transmitted to the thin-walled portion 110h. In addition, by providing the thin-walled portion 110h, it is easier to place the second strain gauge 120B. Furthermore, the fixing portion of the gauge fixing member 110 for the third strain gauge 120C and the fourth strain gauge 120D can also have the same structure as shown in Figure 25.

[0156] Figure 26 is a partially enlarged view (part 7) of the strain transmission section and the strain non-transmission section according to modification 3 of the first embodiment. As shown in Figure 26, the bearing housing 40 does not have to have a third outer circumferential surface 40c. In this case, the second outer circumferential surface 40b is a continuous surface without steps, and the entire second outer circumferential surface 40b is in contact with the inner circumferential surface 110b of the gauge fixing member 110, so the gap S shown in Figure 9 is not formed. Thus, the gap S shown in Figure 9 is provided as needed. In the case of a structure without a gap S as shown in Figure 26, the rigidity of the bearing housing 40 and the gauge fixing member 110 can be increased.

[0157] Figure 27 is a partially enlarged view (part 8) of the strain transmission section and the strain non-transmission section according to modification 3 of the first embodiment. As shown in Figure 27, the air gap S may not be provided, and the outer circumferential surface 110a of the gauge fixing member 110 may be made to protrude outward between the strain transmission section 111 and the strain non-transmission section 112. In this structure, when the bearing device is fixed to the motor housing 140, the outer circumferential surface 110a of the gauge fixing member 110 comes into contact with the inner circumferential surface of the motor housing 140, thereby increasing the rigidity of the bearing housing 40 and the gauge fixing member 110. In the case of the structure in Figure 27, grooves or holes may be provided in the outer circumferential region M1 of the gauge fixing member 110 to pass wiring that connects to the strain gauge. Alternatively, grooves or holes may be provided in the inner circumferential region M2 of the motor housing 140.

[0158] Figure 28 is a partially enlarged view (9th) of the strain transmission section and the strain non-transmission section according to Modification 3 of the First Embodiment. As shown in Figure 28, strain is not easily transmitted to the end face of the gauge fixing member 110, so the end face of the gauge fixing member 110 becomes a strain non-transmission section 112. Therefore, the second strain gauge 120B may be placed on the end face of the gauge fixing member 110, which is a strain non-transmission section.

[0159] When the second strain gauge 120B is placed on the end face of the gauge fixing member 110, in order to secure the mounting surface for the second strain gauge 120B, instead of making the entire gauge fixing member 110 thicker as shown in Figure 28, a flange type may be used, as shown in Figure 29, in which a projection 110i is provided that circumferentially protrudes outward from the lower end of the outer peripheral surface 110a of the gauge fixing member 110.

[0160] Furthermore, as shown in Figure 30, the outer circumferential surface 110a of the gauge fixing member 110 may be made to protrude outward in areas other than the strain transmission section 111. In this structure, when the bearing device is fixed to the motor housing 140, the outer circumferential surface 110a of the gauge fixing member 110 comes into contact with the inner circumferential surface of the motor housing 140, thereby increasing the rigidity of the bearing housing 40 and the gauge fixing member 110. In addition, grooves or holes may be provided in the outer circumferential region M3 of the gauge fixing member 110 to allow wiring to pass through for connection to the strain gauge in the structure of Figure 30. Alternatively, grooves or holes may be provided in the inner circumferential region M4 of the motor housing 140.

[0161] The structures shown in Figures 20 to 30 can be combined as appropriate to the extent technically feasible.

[0162] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

[0163] For example, if a gap S is formed between the inner circumferential surface 110b of the gauge fixing member 110 and the third outer circumferential surface 40c of the bearing housing 40, the second strain gauge 120B and the fourth strain gauge 120D may be placed on the inner circumferential surface 110b of the gauge fixing member 110.

[0164] For example, the present invention can also be applied to bearing devices having only one of the first rolling bearing and the second rolling bearing, strain detection devices, and motors. [Explanation of symbols]

[0165] 1,1A,1B Bearing device, 2 Bridge circuit, 3 Strain detection device, 5 Motor, 10 Impeller, 11 Rotor housing, 12 Blades, 20 Rotating shaft, 30A First rolling bearing, 30B Second rolling bearing, 31 Outer ring, 32 Inner ring, 33 Rolling element, 40 Bearing housing, 40a First outer surface, 40b Second outer surface, 40c Third outer surface, 40x Groove, 40y Hole, 41a Inner step, 41b,41c Outer step, 51 Insulator, 52 Stator core, 53 Coil, 60 Rotor, 61 Rotor yoke, 62 Rotor magnet, 70 Casing, 71 Casing outer frame, 72 Base hub, 73 Stator vanes, 80 Motor section, 100,100A Sensor unit, 110 Gauge fixing member, 110a outer surface, 110b inner surface, 110c, 110d, 110e, 110f groove, 110g, 110h thin-walled section, 110i projection, 110x slit, 110y groove, 111 strain transmission section, 112 non-strain transmission section, 120A first strain gauge, 120B second strain gauge, 120C third strain gauge, 120D fourth strain gauge, 121 base material, 122 functional layer, 123 resistor, 124 wiring, 125 terminal section, 126 cover layer, 130A, 130B, 130C, 130D wiring

Claims

1. The axis of rotation and A first rolling bearing supporting the aforementioned rotating shaft, A bearing housing that holds the first rolling bearing, The sensor unit comprises a cylindrical member attached to the outer circumferential surface of the bearing housing, and a stress sensor and a noise sensor attached to the member, In the aforementioned observation unit, The member has a strain transmission section that transmits the strain generated in the first rolling bearing by the rotation of the rotating shaft, and a strain non-transmission section that does not transmit the strain. The strain transmission portion is located in a position that overlaps with the outer circumferential surface of the first rolling bearing in a radial view. The strain non-transmission portion is located in a position that does not overlap with the outer circumferential surface of the first rolling bearing in a radial view. The stress sensor is positioned in the strain transmission section. The noise sensor is a bearing device located in the strain non-transmission section.

2. In the bearing device according to Claim 1, A second rolling bearing supporting the aforementioned rotating shaft, The system further comprises a second sensor unit attached to the bearing housing, In the second detection unit, The member has a strain transmission section that transmits the strain generated in the second rolling bearing by the rotation of the rotating shaft, and a strain non-transmission section that does not transmit the strain. The strain transmission portion is located in a position that overlaps with the outer circumferential surface of the second rolling bearing in a radial view. The strain non-transmission portion is located in a position that does not overlap with the outer circumferential surface of the second rolling bearing in a radial view. The stress sensor is positioned in the strain transmission section. The noise sensor is a bearing device located in the strain non-transmission section.

3. In the bearing device according to Claim 1, The first rolling bearing has rolling elements, The sensor unit comprises a first strain gauge and a third strain gauge as stress sensors, and a second strain gauge and a fourth strain gauge as noise sensors. The first strain gauge and the second strain gauge are arranged to be spaced apart from each other in the central axis direction of the member. A bearing device in which the third strain gauge and the fourth strain gauge are arranged to be spaced apart from each other in the axial direction of the central axis of the member.

4. In the bearing device according to claim 2, The first rolling bearing and the second rolling bearing each have rolling elements, The sensor unit and the second sensor unit each include a first strain gauge and a third strain gauge as stress sensors, and a second strain gauge and a fourth strain gauge as noise sensors, In each of the aforementioned sensor unit and the second sensor unit, The first strain gauge and the second strain gauge are arranged to be spaced apart from each other in the central axis direction of the member. A bearing device in which the third strain gauge and the fourth strain gauge are arranged to be spaced apart from each other in the axial direction of the central axis of the member.

5. The first strain gauge has a first resistor which serves as a sensing element, The third strain gauge has a third resistor which acts as a sensing element, The first strain gauge and the third strain gauge are positioned so that the rolling element passes directly beneath the first and third resistors at the same time. The bearing device according to claim 3 or 4, wherein, when viewed from the axial direction of the rotation shaft, the angle θ between the center of the first resistor and the center of the third resistor is θ = (360 × n) / N, where N is the number of rolling elements and n is an integer between 1 and (N-1).

6. The first strain gauge has a first resistor which serves as a sensing element, The third strain gauge has a third resistor which acts as a sensing element, The first strain gauge and the third strain gauge are arranged such that when the rolling element passes directly beneath the first resistor, the third resistor is positioned between two adjacent rolling elements. The bearing device according to claim 3 or 4, wherein, when viewed from the axial direction of the rotation shaft, the angle θ between the center of the first resistor and the center of the third resistor is θ = (360 × n) / N + 360 / 2N, where N is the number of rolling elements and n is an integer between 0 and (N-1) inclusive.

7. The bearing housing has a first outer circumferential surface and a second outer circumferential surface that forms the bottom surface of a recess that is recessed from the first outer circumferential surface toward the rotating shaft. The second outer surface is located in a position that overlaps with at least the outer surface of the first rolling bearing in a radial view. The bearing device according to any one of claims 1 to 6, wherein the inner circumferential surface of the member abuts against the second outer circumferential surface.

8. The bearing housing has a third outer surface that forms the bottom surface of a recess that is further recessed toward the rotating shaft side from the second outer surface, The third outer surface is located in a position that does not overlap with the outer surface of the first rolling bearing in a radial view. The bearing device according to claim 7, wherein a gap is formed between the inner circumferential surface of the member and the third outer circumferential surface.

9. The bearing device according to claim 3 or 4, and a bridge circuit, The first strain gauge constitutes one of the four sides of the bridge circuit, on one side of the first output voltage extraction point. The second strain gauge is a strain detection device that forms one of the four sides of the bridge circuit, on the other side of the first output voltage extraction point.

10. The bearing device according to claim 5 and the bridge circuit are provided, The first strain gauge constitutes one of the four sides of the bridge circuit, on one side of the first output voltage extraction point. The fourth strain gauge constitutes one of the four sides of the bridge circuit, on the other side of the first output voltage extraction point. The second strain gauge constitutes one of the four sides of the bridge circuit on the side of the second output voltage extraction point that is on the side of the first strain gauge. The third strain gauge is a strain detection device that forms one of the four sides of the bridge circuit on the side of the second output voltage extraction point that is connected to the fourth strain gauge.

11. The bearing device according to claim 6 and the bridge circuit are provided, The first strain gauge constitutes one of the four sides of the bridge circuit, on one side of the first output voltage extraction point. The fourth strain gauge constitutes one of the four sides of the bridge circuit, on the other side of the first output voltage extraction point. The second strain gauge constitutes one of the four sides of the bridge circuit on the side of the second output voltage extraction point that is connected to the fourth strain gauge. The third strain gauge is a strain detection device that forms one of the four sides of the bridge circuit on the side of the second output voltage extraction point that is on the first strain gauge side.

12. A motor having a bearing device according to any one of claims 1 to 8.

13. A motor having a strain detection device according to any one of claims 9 to 11.

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