Bearing device and spindle device

Abstract

To provide a bearing device and a spindle device that can accurately measure a machining load and a preload on each bearing.SOLUTION: A bearing device 50 comprises a first outer ring spacer 6g arranged between an outer ring 5ga of a bearing 5a and an outer ring 5gb of a bearing 5b, a housing 3 for fixing the outer ring 5ga of the bearing 5a and the outer ring 5gb of the bearing 5b, a second outer ring spacer 7 arranged between the outer ring 5gb of the bearing 5b and the housing 3, a first strain sensor 11, and a second strain sensor 8. The first strain sensor 11 is fixed to the first outer ring spacer 6g, which is located on a path through which a preload is transmitted to the bearing 5a and the bearing 5b. The second strain sensor 8 is fixed to the second outer ring spacer 7, which is not located on the path through which the preload is transmitted to the bearing 5a and the bearing 5b.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a bearing device and a spindle device. [Background technology]

[0002] In spindle devices such as machine tools, management of processing loads and bearing preloads is required to improve processing accuracy and efficiency. Spindle devices are also required to detect signs of bearing abnormalities before they occur and prevent bearing abnormalities before they occur.

[0003] Japanese Patent Laid-Open Publication No. 2-164241 (Patent Document 1) discloses a preload detection device for a pair of angular contact ball bearings arranged back-to-back with a spacer in between, in which a strain sensor is attached to the spacer and the amount of preload on the bearing is measured from the amount of strain on the spacer. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2-164241 Summary of the Invention [Problem to be solved by the invention]

[0005] The preload detection device disclosed in Patent Document 1 detects not only changes in bearing preload due to the rotation speed and the temperature difference between the inner and outer rings during spindle operation, but also changes in bearing preload due to the processing load input from the cutting tool.For this reason, the preload detection device disclosed in Patent Document 1 cannot determine whether the change in sensor output is due to the change in bearing preload or the processing load using only the strain sensor attached to the spacer, making it difficult to accurately detect the processing load.

[0006] Furthermore, in the preload detection device disclosed in Patent Document 1, when a processing load is applied in the axial direction, the preload of one of a pair of back-to-back angular contact ball bearings increases and the preload of the other decreases, resulting in a difference in preload between the bearings. For this reason, it is difficult to accurately detect the preload of each bearing using only a strain sensor attached to the spacer.

[0007] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a bearing device and a spindle device that are capable of accurately measuring the processing load and the preload of each bearing. [Means for solving the problem]

[0008] The present disclosure relates to a bearing device including a first bearing and a second bearing, each including an outer ring, an inner ring, and rolling elements. The bearing device includes a first outer ring spacer disposed between the outer ring of the first bearing and the outer ring of the second bearing, a fixing member that fixes the outer ring of the first bearing and the outer ring of the second bearing, a second outer ring spacer disposed between the outer ring of the second bearing and the fixing member, a first strain sensor, and a second strain sensor. The first strain sensor is fixed to the first outer ring spacer on a path along which a preload is transmitted to the first and second bearings, and the second strain sensor is fixed to the second outer ring spacer that is not on the path along which the preload is transmitted to the first and second bearings. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a bearing device and a spindle device that are capable of accurately measuring the processing load and the preload of each bearing. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a spindle device according to a first embodiment. [Figure 2] FIG. 2 is an enlarged view of the main part on the left side of FIG. [Figure 3] FIG. 2 is a diagram showing a schematic configuration of a first strain sensor. [Figure 4]FIG. 2 is a schematic structural diagram of a first strain sensor. [Figure 5] FIG. 3 is a cross-sectional view taken along the line X1-X1 in FIG. 2. [Figure 6] FIG. 2 is a block diagram of a strain sensor in a spindle device. [Figure 7] This is a flag that indicates the relationship between the load applied to the bearing device and the strain signal. [Figure 8] FIG. 10 is a schematic structural diagram of a first strain sensor in a spindle device according to a second embodiment. [Figure 9] FIG. 10 is a cross-sectional view of a spindle device according to a third embodiment. [Figure 10] FIG. 10 is a cross-sectional view of a spindle device according to a fourth embodiment. [Figure 11] FIG. 10 is a cross-sectional view of a spindle device according to a fifth embodiment. [Figure 12] FIG. 13 is a cross-sectional view of a spindle device according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the embodiments described below, when numbers, quantities, etc. are mentioned, the scope of the present disclosure is not necessarily limited to those numbers, quantities, etc., unless otherwise specified. The same reference numerals are used for the same or equivalent parts, and redundant descriptions may not be repeated. It is intended from the beginning that the configurations in the embodiments may be used in appropriate combinations.

[0012] [Embodiment 1] Fig. 1 is a cross-sectional view showing a schematic configuration of a spindle device 1 according to embodiment 1. Fig. 2 is an enlarged view of a main part on the left side of Fig. 1. Fig. 2 mainly shows a bearing device 50.

[0013] 1 is used, for example, as a built-in motor type spindle device for a machine tool. In this case, a motor 40 is built into one end of a spindle 4 supported by the spindle device 1 for the machine tool main shaft, and a cutting tool such as an end mill (not shown) is connected to the other end.

[0014] The spindle device 1 includes a bearing 5 including bearings 5a and 5b, a spacer 6 disposed adjacent to the bearings 5a and 5b, a spacer 9 disposed adjacent to one end of the bearing 5b opposite the spacer 6, a motor 40, and a bearing 16 disposed behind the motor. The main shaft 4 is rotatably supported about a rotation axis A by a plurality of bearings 5a and 5b provided in a housing 3 embedded in the inner diameter portion of the outer cylinder 2. The bearing 5a includes an inner ring 5ia, an outer ring 5ga, rolling elements Ta, and a cage Rta. The bearing 5b includes an inner ring 5ib, an outer ring 5gb, rolling elements Tb, and a cage Rtb. The spacer 6 includes an inner ring spacer 6i and a first outer ring spacer 6g.

[0015] An inner ring 5ia of bearing 5a and an inner ring 5ib of bearing 5b are fitted in an interference fit (press-fit) state onto the main shaft 4, the inner rings 5ia and 5ib being spaced apart in the axial direction, which is the direction along the rotation axis A. An inner ring spacer 6i is disposed between the inner rings 5ia and 5ib, and a first outer ring spacer 6g is disposed between the outer rings 5ga and 5gb.

[0016] The bearing 5a is a rolling bearing in which multiple rolling elements Ta are arranged between an inner ring 5ia and an outer ring 5ga. The spacing between these rolling elements Ta is maintained by a cage Rta. The bearing 5b is a rolling bearing in which multiple rolling elements Tb are arranged between an inner ring 5ib and an outer ring 5gb. The spacing between these rolling elements Tb is maintained by a cage Rtb.

[0017] The bearings 5a and 5b are bearings to which a preload can be applied by an axial force, and may be angular contact ball bearings, deep groove ball bearings, tapered roller bearings, etc. The bearing device 50 shown in Fig. 2 uses angular contact ball bearings, and the two bearings 5a and 5b are installed in a back-to-back (DB) configuration.

[0018] Here, a structure in which the main shaft 4 is supported by three bearings 5a, 5b, and 16 will be described as an example, but the main shaft 4 may be supported by two or four or more bearings.

[0019] Single-row rolling bearing 16 is a cylindrical roller bearing. Bearings 5a and 5b, which are angular contact ball bearings, support radial and axial loads acting on main shaft 4. Single-row bearing 16, which is a cylindrical roller bearing, supports radial loads acting on spindle device 1 for the machine tool main shaft.

[0020] The housing 3 functions as a fixing member that fixes the outer ring 5ga of the bearing 5a and the outer ring 5gb of the bearing 5b. A coolant flow path G is formed in the housing 3. The bearings 5a and 5b can be cooled by flowing a coolant between the housing 3 and the outer cylinder 2. If grease-lubricated bearings are used as the bearings 5a and 5b, no lubricant supply path is required. However, if lubrication such as air-oil lubrication is required, a lubricant supply path is provided in the first outer ring spacer 6g. Note that the lubricant supply path is not shown here.

[0021] During assembly, bearing 5a, spacer 6, bearing 5b, and spacer 9 are first inserted onto main shaft 4 in that order, and then nut 10 is tightened to apply an initial preload along the path shown by force line P1. Tightening nut 10 applies a pressing force to the end face of inner ring 5ib of bearing 5b via spacer 9, pressing inner ring 5ib toward inner ring spacer 6i. This pressing force is transmitted through inner ring 5ib, rolling element Tb, and outer ring 5gb, applying a preload between the raceway surfaces of inner ring 5ib and outer ring 5gb and rolling element Tb, and a pressing force also acts from the outer ring 5gb to first outer ring spacer 6g.

[0022] This pressing force is transmitted to the outer ring 5ga, rolling element Ta, and inner ring 5ia in bearing 5a, and also applies preload between the raceway surfaces of the inner ring 5ia and outer ring 5ga of left-side bearing 5a and the rolling element Ta. The preload applied to bearings 5a and 5b is determined by the amount of movement of nut 10, which is limited by the difference in width between first outer ring spacer 6g and inner ring spacer 6i, for example.

[0023] The first outer ring spacer 6g is cylindrical and has a plurality of flat portions 6ga formed on its outer diameter surface. First strain sensors 11 including first strain sensors 11a and 11b are fixed to the flat portions 6ga. The first strain sensors 11 detect the strain of the first outer ring spacer 6g. The initial preload is calculated from the strain detected by the first strain sensors 11 and information (e.g., a relational expression) indicating a relationship between the strain and the preload that has been determined in advance.

[0024] 2, one end of second outer ring spacer 7, which is disposed on the right side of outer ring 5gb of bearing 5b, abuts against step 3a provided on housing 3, and the other end of second outer ring spacer 7 abuts against the right end face of outer ring 5gb of bearing 5b. Finally, front cover 12 is fixed to housing 3 with bolts or the like (not shown), and the outer ring 5ga of bearing 5a, first outer ring spacer 6g, outer ring 5gb of bearing 5b, and second outer ring spacer 7 are pressed together, whereby main shaft 4 is rotatably fixed to housing 3 via bearings 5a and 5b.

[0025] When front cover 12 is fixed to housing 3, a load is applied in the direction of force line P2 shown in Fig. 2 according to the torque applied when tightening bolts (not shown). The load applied when fixing front cover 12 displaces outer ring 5ga, first outer ring spacer 6g, outer ring 5gb, and second outer ring spacer 7 in a direction parallel to main shaft 4, and the preload decreases according to the amount of displacement.

[0026] A second strain sensor 8 is fixed to the outer peripheral surface of the second outer ring spacer 7 to detect strain on the second outer ring spacer 7. The reduction in preload is calculated from the strain detected by the second strain sensor 8 and information indicating the relationship between the strain and preload obtained in advance. The preload after assembly is determined by subtracting the calculated reduction in preload from the initial preload. At this time, the load applied to the path of the force line P2 is also applied to the first outer ring spacer 6g. Therefore, instead of the output of the second strain sensor 8, the change in output of the first strain sensor 11 before and after the front cover 12 is attached may be used.

[0027] Additionally, inner ring 16a of single-row bearing 16 is positioned in the axial direction by cylindrical member 15 fitted onto the outer periphery of main shaft 4 and inner ring retainer 19. Inner ring retainer 19 is fixed by nut 20 threadedly attached to main shaft 4. Outer ring 16b of bearing 16 is sandwiched between positioning member 21 fixed to end member 17 and positioning member 18. Inner ring 16a slides integrally with main shaft 4 relative to end member 17 as main shaft 4 expands and contracts.

[0028] Motor 40, which drives main shaft 4, is disposed in a space 22 formed between main shaft 4 and outer cylinder 2, at an axially intermediate position sandwiched between bearings 5a, 5b and single-row bearing 16. Rotor 14 of motor 40 is fixed to a cylindrical member 15 fitted onto the outer periphery of main shaft 4. Stator 13 of motor 40 is fixed to the inner periphery of outer cylinder 2. Note that a coolant flow path for cooling motor 40 is not shown here.

[0029] During operation of the spindle device 1, as the rotational speed of the spindle 4 increases, the centrifugal force acting on the rolling elements Ta and Tb increases, causing the preload to increase. In this case, the first outer ring spacer 6g is compressed in the axial direction, and the second outer ring spacer 7 expands according to the amount of deformation of the first outer ring spacer 6g. During machining, in machining in which a load is applied vertically to the cutting tool, the load associated with the machining is applied from the spindle 4 to the inner rings 5ia and 5ib of the bearings 5a and 5b. As a result, the preload on bearing 5a increases and the preload on bearing 5b decreases. This machining load is ultimately supported by the stepped portion 3a of the housing 3 via the second outer ring spacer 7.

[0030] At this time, the compressive force acting on the first outer ring spacer 6g changes depending on the distribution of the machining load between bearing 5a and bearing 5b, causing the machining load and the increase in the preload applied to the first outer ring spacer 6g to no longer match. Therefore, the first strain sensor 11 alone cannot accurately detect the machining load. The second strain sensor 8 detects tensile strain when the preload increases due to an increase in rotational speed, and compressive strain when the preload increases due to the application of the machining load. Therefore, the second strain sensor 8 can easily distinguish the type of strain and accurately measure the machining load. Therefore, using the second strain sensor 8 can contribute to improved machining quality, increased productivity, and longer tool life.

[0031] In the spindle device 1, the preload of the bearing 5a can be calculated from the amount of change in the strain signal of the first strain sensor 11 immediately before the start of machining and during machining. In the spindle device 1, the preload of the bearing 5b can be calculated by calculating the difference between the preload of the bearing 5a and the machining load calculated from the strain detected by the second strain sensor 8. Therefore, in the spindle device 1, it is possible to prevent the bearing 5a from seizing due to an excessive preload and the bearing 5b from vibrating due to an insufficient preload.

[0032] The timing for acquiring data immediately before the start of machining and during machining may be determined using machining command information from the machine tool or the strain signal from the second strain sensor 8. For example, data from the first strain sensor 11 immediately before the start of machining may be acquired when machining command information for the machine tool has not yet been input or has just been input. Alternatively, data from the first strain sensor 11 immediately before the start of machining may be acquired when the value or rate of change of the strain signal from the second strain sensor 8 is lower than a preset threshold.

[0033] Furthermore, data from the first strain sensor 11 during machining may be acquired when machining command information for the machine tool has been input. Furthermore, data from the first strain sensor 11 during machining may be acquired when the value or rate of change of the strain signal from the second strain sensor 8 is higher than a preset threshold. The timing for acquiring data may also be determined based on other information, such as rotational speed information of the spindle 4 or motor 40, and temperature information of the bearings 5a and 5b.

[0034] Next, the first strain sensor 11 and the second strain sensor 8 will be described. The first strain sensor 11 and the second strain sensor 8 can have the same configuration. Below, the configuration will be described using the first strain sensor 11. FIG. 3 is a diagram showing a schematic configuration of the first strain sensor 11, and FIG. 4 is a schematic structural diagram of the first strain sensor 11.

[0035] The first strain sensor 11 includes a detection unit 24 formed from a strain gauge and a processing unit 25. The processing unit 25 includes an amplifier unit 25a that electrically amplifies the signal from the strain gauge, and an output unit 25b that calculates a strain signal based on the signal from the strain gauge and outputs it to the outside. This makes it possible to obtain a suitable strain signal. The processing unit 25 may also include a bridge circuit that converts resistance changes in the strain gauge into voltage changes and outputs the voltage changes as a pre-processing for the amplifier unit 25a.

[0036] As shown in Fig. 4, the first strain sensor 11 has a detection unit 24 and a processing unit 25 arranged on a substrate 23. The substrate 23 is, for example, a metal plate with a linear expansion coefficient similar to that of the first outer ring spacer 6g. The detection unit 24 is fixed onto the substrate 23 by adhesive or mechanical bonding. The processing unit 25 is an electric circuit board that is miniaturized and fixed onto the substrate 23. The detection unit 24 and processing unit 25 are electrically connected by wiring or the like.

[0037] The first strain sensor 11 may be composed of only a strain gauge that serves as the detection unit 24. The processing unit 25 may be provided outside the spindle device 1, but by arranging it close to the detection unit 24, the lead wires can be shortened. Therefore, the processing unit 25 is less susceptible to the effects of electrical noise than when the detection unit 24 and the processing unit 25 are separated from each other.

[0038] The detection unit 24 is fixed to the outer diameter surface of the first outer ring spacer 6g via the substrate 23. This allows the first strain sensor 11 to be constructed within the substrate 23, improving assembly ease. The substrate 23 is fixed to the flat portions 6ga, 6gb on the outer diameter surface of the first outer ring spacer 6g. This makes it easy to fix the substrate 23, improving the stability of the sensor output. Furthermore, the only additional processing required on the first outer ring spacer 6g is to provide the flat portions 6ga, 6gb. This allows for a simple configuration that does not significantly change the structure of the first outer ring spacer 6g, and does not significantly reduce rigidity. The same effect can be achieved when the second strain sensor 8 is installed on the second outer ring spacer 7.

[0039] To calculate the strain, a CPU (Central Processing Unit) may be installed in the output section 25b, and the CPU may execute a process to convert the strain into a numerical value using a pre-stored map, for example. When calculating the strain, it is possible that the resistance of the detection section 24 may change depending on the temperature of the first outer ring spacer 6g, causing temperature drift in the sensor output. However, if a material with a small temperature coefficient of resistance (the rate at which the resistance value changes with temperature) is used for the detection section 24, it is possible to reduce the temperature drift.

[0040] The processing unit 25 may be equipped with a temperature compensation function. For example, a temperature sensor may be mounted inside the substrate 23 or on the first outer ring spacer 6g on which the first strain sensor 11 is mounted, and temperature compensation may be performed by calculations performed by the processing unit 25 based on the detected value of the temperature sensor.

[0041] Next, the arrangement of the first strain sensor 11 will be described. FIG. 5 is a cross-sectional view taken along the line X1-X1 in FIG. 2. As shown in FIG. 5, in the spindle device 1 of the first embodiment, flat portions 6ga are provided at four locations spaced at 90-degree intervals on the outer diameter surface of the first outer ring spacer 6g. The first strain sensors 11a, 11b, 11c, and 11d are fixed to each of the flat portions 6ga. The second strain sensors 8 are fixed to positions corresponding to the first strain sensors 11a, 11b, 11c, and 11d, one each.

[0042] 6 is a block diagram of the strain sensors in the spindle device 1. Strain signals from the first strain sensor 11 and the second strain sensor 8 are output to a data processing unit 33 provided outside the bearing device 50. Note that the data processing unit 33 may also be provided inside the bearing device 50.

[0043] The data processing unit 33 includes a processing load calculation unit 27 that processes the outputs (strain signals Sa, Sb, Sc, Sd) of the second strain sensors 8 (8a, 8b, 8c, 8d), and a first memory unit 28 that stores information indicating the relationship between the strain signals and the load of the second outer ring spacer 7. The processing load calculation unit 27 calculates the processing load from the strain signals of the second strain sensors 8 and the data in the first memory unit 28.

[0044] The data processing unit 33 further includes a bearing preload calculation unit 29 that processes the outputs (strain signals Se, Sf, Sg, Sh) of the first strain sensors 11 (11a, 11b, 11c, 11d), and a second storage unit 30. The second storage unit 30 stores information indicating the relationship between the strain signal of the first outer ring spacer 6g and the preload. The bearing preload calculation unit 29 calculates the preload of the bearing 5a from the amount of change in the strain signal of the first strain sensor 11 before and during machining and the information stored in the second storage unit 30 that indicates the relationship between the strain signal of the first strain sensor 11 and the preload. The bearing preload calculation unit 29 further calculates the preload of the bearing 5b from the difference between the processing load data calculated by the processing load calculation unit 27 and the preload of the bearing 5a.

[0045] The timing for acquiring data from the first strain sensor 11 before the start of machining and during machining can be determined by determining whether the data is in a state immediately after or after the input of information such as machining commands, rotational speed, and temperature for the machine tool in the bearing preload calculation unit 29. Furthermore, the timing for acquiring data from the first strain sensor 11 before the start of machining and during machining can be determined by determining whether the value or rate of change of the strain signal from the second strain sensor 8 is lower or higher than a threshold value that is set in advance and stored in the second storage unit 30.

[0046] The data processing unit 33 includes a diagnosis unit 31 that determines whether the bearings 5a, 5b are in an abnormal state based on the preload calculated by the bearing preload calculation unit 29, and a third storage unit 32 that stores reference values ​​for the preload of the bearings 5a, 5b in advance. The diagnosis unit 31 outputs a bearing abnormality diagnosis signal when the reference values ​​stored in the third storage unit 32 are exceeded. In the spindle device 1, the abnormality diagnosis signal can be used to prevent heat generation and seizure due to excessive bearing preload, and vibration due to insufficient bearing preload.

[0047] Machine tools can increase production efficiency by increasing the rotational speed and processing load of the spindle device 1. For this reason, the reference values ​​of the preloads of the bearings 5a, 5b and the corresponding abnormality diagnosis signals stored in the third storage unit 32 are set at multiple stages, and by monitoring the state of the bearings in detail, the rotational speed and processing load of the spindle device 1 can be controlled to maximize productivity.

[0048] The first storage unit 28, the second storage unit 30, and the third storage unit 32 are configured, for example, by a memory circuit mounted on a microcontroller. The processing load calculation unit 27, the bearing preload calculation unit 29, and the diagnosis unit 31 are configured, for example, by a CPU mounted on a microcontroller. If necessary, a temperature sensor (not shown) may be installed to add temperature correction.

[0049] Fig. 7 shows flags indicating the relationship between the load and strain signal applied to the bearing device 50. Fig. 7 shows the relationship between the load and the output (strain signal) of each strain sensor when a load is applied to the first outer ring spacer 6g alone to which the first strain sensor 11 is fixed.

[0050] Each of the first strain sensors 11 (11a, 11b, 11c, 11d) detects strain signals Se, Sf, Sg, and Sh due to the axial load (bearing preload) applied to the first outer ring spacer 6g. As shown in FIG. 10, the detected strain signals are not uniform around the circumference of the first outer ring spacer 6g, but vary due to factors such as dimensional accuracy and assembly variations of the first outer ring spacer 6g, housing 3, front cover 12, and bearing 5, radial load, and misalignment of the load application point. It is also expected that the detected strain signals will fluctuate due to the effects of the moment load applied to the spindle 4 as it rotates and the movement of the rolling elements in the bearing 5.

[0051] For this reason, it is desirable to obtain a sensor output representative value by processing the strain signals Se, Sf, Sg, and Sh of each first strain sensor 11 in the bearing preload calculation unit 29. The sensor output representative value is, for example, the total value of each strain signal Se to Sh, or the average value of each strain signal Se to Sh. The sensor output representative value may also be the maximum or minimum value of the strain signal, or the difference between the maximum and minimum values. The bearing preload calculation unit 29 calculates the preload from a table showing the relationship between strain and load, which is stored in advance in the second storage unit 30, or from an approximate equation showing the relationship between strain and load.

[0052] As a countermeasure against electrical noise, the preload may be calculated after low-pass filtering the representative sensor output value. The obtained preload may also be low-pass filtered to suppress fluctuations in the preload measurement value.

[0053] The spindle device 1 is equipped with a processing unit 25 incorporating an amplifier unit 25a near a detection unit 24 consisting of a strain gauge. Therefore, in the spindle device 1, by converting strain into a digital value, electrical noise can be reduced and processed. Furthermore, by adding or averaging the strain signals from multiple first strain sensors 11, the detection variation of each first strain sensor 11 can be reduced and the preload detection accuracy can be improved. Note that the strain signal from the second strain sensor 8 is processed in the same way as the strain signal from the first strain sensor 11, so a description thereof will be omitted.

[0054] [Embodiment 2] FIG. 8 is a schematic structural diagram of a strain sensor in a spindle device according to the second embodiment. As shown in FIG. 8, the first strain sensor 110 in the spindle device according to the second embodiment is a one-chip IC 26 that integrates the detection unit 24 and processing unit 25 shown in FIGS. 3 and 4. The one-chip IC 26 is fixed onto a substrate 23. This allows the strain sensor to be miniaturized, making it easier to incorporate into the first outer ring spacer 6g. The second strain sensor 8 may also have a similar shape.

[0055] Although the IC 26 may be fixed directly to the outer or inner diameter surface of the first outer ring spacer 6g, using the substrate 23 allows the first strain sensor 11 to be constructed within the substrate 23, improving assembly ease. When fixing the substrate 23 to the outer or inner diameter surface of the first outer ring spacer 6g, providing a flat portion makes it easy to fix the substrate 23, improving the stability of the sensor output. The only additional processing required on the first outer ring spacer 6g is to provide a flat portion. This allows for a simple configuration that does not significantly change the structure of the first outer ring spacer 6g, and does not significantly reduce rigidity.

[0056] [Embodiment 3] Fig. 9 is a cross-sectional view of a spindle device according to a third embodiment. As shown in Fig. 9, in the spindle device according to the third embodiment, flat portions 6ga are provided at two locations 180 degrees apart on the outer diameter surface of a first outer ring spacer 6g. One first strain sensor 11a, 11b is fixed to each flat portion 6ga. One second strain sensor 8 is fixed at a position corresponding to each of the first strain sensors 11a, 11b.

[0057] [Embodiment 4] Fig. 10 is a cross-sectional view of a spindle device according to a fourth embodiment. As shown in Fig. 10, in the spindle device according to the fourth embodiment, flat portions 6ga are provided at three locations equally spaced at 120 degrees from the outer diameter surface of a first outer ring spacer 6g. One first strain sensor 11a, 11b, and 11c is fixed to each flat portion 6ga. One second strain sensor 8 is fixed to each of the positions corresponding to the first strain sensors 11a, 11b, and 11c.

[0058] [Embodiment 5] FIG. 11 is a cross-sectional view of a spindle device according to a fifth embodiment. As shown in FIG. 11, in the spindle device according to the fifth embodiment, flat portions 6gb are provided at three locations on the inner diameter surface of a first outer ring spacer 6g, spaced at equal intervals of 120 degrees. First strain sensors 11a, 11b, and 11c are fixed to each of the flat portions 6gb. Second strain sensors 8 are fixed to positions corresponding to the first strain sensors 11a, 11b, and 11c, respectively.

[0059] [Embodiment 6] Fig. 12 is a cross-sectional view of a spindle device according to a sixth embodiment. As shown in Fig. 12, in the spindle device according to the sixth embodiment, flat portions 6gb are provided at four locations spaced at 90-degree intervals on the inner diameter surface of a first outer ring spacer 6g. First strain sensors 11a, 11b, 11c, and 11d are fixed to each of the flat portions 6gb, one each. Second strain sensors 8 are fixed to positions corresponding to the first strain sensors 11a, 11b, 11c, and 11d, one each.

[0060] (Variation) In the spindle device, flat portions 6gb may be provided at two locations 180 degrees apart on the inner diameter surface of the first outer ring spacer 6g. One first strain sensor 11a, 11b may be fixed to each flat portion 6gb. One second strain sensor 8 is fixed at a position corresponding to each of the first strain sensors 11a, 11b. Five or more first strain sensors 11 and second strain sensors 8 may be arranged.

[0061] (summary) The present disclosure relates to a bearing device 50 including bearings 5a and 5b, each including outer rings 5ga and 5gb, inner rings 5ia and 5ib, and rolling elements Ta. The bearing device 50 includes a first outer ring spacer 6g disposed between the outer ring 5ga of the bearing 5a and the outer ring 5gb of the bearing 5b, a housing 3 that secures the outer ring 5ga of the bearing 5a and the outer ring 5gb of the bearing 5b, a second outer ring spacer 7 disposed between the outer ring 5gb of the bearing 5b and the housing 3, a first strain sensor 11, and a second strain sensor 8. The first strain sensor 11 is fixed to the first outer ring spacer 6g, which is located on a path along which a preload is transmitted to the bearings 5a and 5b, and the second strain sensor 8 is fixed to the second outer ring spacer 7, which is not located on a path along which the preload is transmitted to the bearings 5a and 5b.

[0062] With this configuration, the second strain sensor 8 can accurately detect changes in the processing load. Furthermore, the spindle device 1 can calculate the preload of the bearing 5a from the change in the strain signal of the first strain sensor 11 immediately before the start of processing and during processing. The spindle device 1 can calculate the preload of the bearing 5b by calculating the difference between the preload of the bearing 5a and the processing load calculated from the strain detected by the second strain sensor 8. In this way, the spindle device 1 can accurately measure the processing load and the preload of each bearing 5a, 5b.

[0063] Preferably, the first strain sensor 11 is fixed to flat portions 6ga, 6gb formed on either the outer peripheral surface or the inner peripheral surface of the first outer ring spacer 6g and the second outer ring spacer 7. The second strain sensor 8 is fixed to flat portions formed on either the outer peripheral surface or the inner peripheral surface of the first outer ring spacer 6g and the second outer ring spacer 7.

[0064] This configuration allows the first strain sensor 11 and the second strain sensor 8 to be easily fixed, improving the stability of the sensor output. Furthermore, the only additional processing required for the first outer ring spacer 6g is to provide the flat portions 6ga and 6gb. This allows for a simple configuration that does not significantly change the structure of the first outer ring spacer 6g, and does not significantly reduce rigidity. The same effect can be achieved when the second strain sensor 8 is installed on the second outer ring spacer 7.

[0065] Preferably, each of the first strain sensor 11 and the second strain sensor 8 includes a detection unit 24 and a processing unit 25 that processes a signal transmitted from the detection unit 24. The processing unit 25 includes an amplifier 25a that electrically amplifies the signal transmitted from the detection unit 24, and an output unit 25b that calculates a strain signal from the signal amplified by the amplifier 25a.

[0066] By providing such a configuration, it is possible to obtain a suitable strain signal, and to accurately measure the processing load and the preload of each of the bearings 5a and 5b.

[0067] Preferably, the detection unit 24 and the processing unit 25 are fixed on the same substrate 23, and the substrate 23 is fixed to the flat portions 6ga and 6gb.

[0068] By providing such a configuration, the substrate 23 can be easily fixed, and the stability of the sensor output is improved.

[0069] Preferably, the detection unit 24 and the processing unit 25 are built into a single integrated circuit, that is, a one-chip IC 26.

[0070] By providing such a configuration, the strain sensor can be made smaller, and can be easily incorporated into the first outer ring spacer 6g or the second outer ring spacer 7.

[0071] Preferably, the device further includes a first memory unit 28 that stores first information indicating the relationship between the strain signal of the second strain sensor 8 and the processing load, and a processing load calculation unit 27 that calculates the processing load from the strain signal of the second strain sensor 8 and the first information.

[0072] By providing such a configuration, the processing load can be measured accurately.

[0073] Preferably, the apparatus further includes a bearing preload calculation unit 29 that uses the strain signal from the first strain sensor 11 and the strain signal from the second strain sensor 8 to calculate the preload of either the bearing 5a or the bearing 5b.

[0074] By providing such a configuration, the preload of each of the bearings 5a and 5b can be measured accurately.

[0075] Preferably, the system further includes a second storage unit 30 that stores second information indicating the relationship between the strain signal of the first strain sensor 11 and the preload. The bearing preload calculation unit 29 calculates the preload from the strain signal of the first strain sensor 11 and the second information, and calculates the preload of either the bearing 5a or the bearing 5b from the calculated preload and the processing load calculated by the processing load calculation unit 27.

[0076] By providing such a configuration, the preload of each of the bearings 5a and 5b can be measured accurately.

[0077] Preferably, the device further includes a third memory unit 32 that stores a preset threshold value, and a diagnosis unit 31 that compares the bearing preload calculated by the bearing preload calculation unit 29 with the threshold value and diagnoses an abnormality if the bearing preload exceeds the threshold value.

[0078] By providing such a configuration, it is possible to prevent heat generation and seizure due to excessive preload of the bearing, and vibration due to insufficient preload of the bearing.

[0079] Preferably, the bearing device 50 may be applied to the spindle device 1 .

[0080] By providing such a configuration, the spindle device 1 can accurately measure the processing load and the preload of each of the bearings 5a and 5b.

[0081] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0082] 1 Spindle device, 2 Outer cylinder, 3 Housing (fixed member), 3a Step portion, 4 Main shaft, 5, 5a, 5b, 16 Bearing, 5ga, 5gb, 16b Outer ring, 5ia, 5ib, 16a Inner ring, 6, 9 Spacer, 6g First outer ring spacer, 6ga, 6gb Flat portion, 6i Inner ring spacer, 7 Second outer ring spacer, 8 Second strain sensor, 11, 11a, 11b, 110 First strain sensor, 10, 20 Nut, 12 Front cover, 13 Stator, 14 Rotor, 15 Cylindrical member, 17 End member, 18, 21 Positioning member, 19 Inner ring holder, 22 Space portion, 23 Board, 24 Detection portion, 25 Processing portion, 25a Amplification portion, 25b Output portion, 27 Processing load calculation portion, 28 First memory unit, 29 bearing preload calculation unit, 30 second memory unit, 31 diagnosis unit, 32 third memory unit, 33 data processing unit, 40 motor, 50 bearing device, A rotating shaft, G flow path, P1, P2 force lines, Rta, Rtb cage, Ta, Tb rolling elements.

Claims

1. A bearing device comprising a first bearing and a second bearing, each bearing including an outer ring, an inner ring, and rolling elements, a first outer ring spacer disposed between an outer ring of the first bearing and an outer ring of the second bearing; a fixing member that fixes an outer ring of the first bearing and an outer ring of the second bearing; a second outer ring spacer disposed between an outer ring of the second bearing and the fixed member; a first strain sensor; a second strain sensor; the first strain sensor is fixed to the first outer ring spacer located on a path through which a preload is transmitted to the first bearing and the second bearing; the second strain sensor is fixed to the second outer ring spacer that is not on a path through which a preload of the first bearing and the second bearing is transmitted; The processing load and the preload are calculated using the strain signal of the first strain sensor and the strain signal of the second strain sensor.

2. the first strain sensor is fixed to a flat portion formed on either an outer peripheral surface or an inner peripheral surface of the first outer ring spacer, The bearing device according to claim 1 , wherein the second strain sensor is fixed to a flat portion formed on either an outer peripheral surface or an inner peripheral surface of the second outer ring spacer.

3. each of the first strain sensor and the second strain sensor includes a detection unit and a processing unit that processes a signal transmitted from the detection unit; 3. The bearing device according to claim 1, wherein the processing unit includes an amplifier that electrically amplifies the signal transmitted from the detector, and an output unit that calculates a strain signal from the signal amplified by the amplifier.

4. Each of the first strain sensor and the second strain sensor includes a detection unit and a processing unit that processes a signal transmitted from the detection unit; the detection unit and the processing unit are fixed on the same substrate, The bearing device according to claim 2 , wherein the substrate is fixed to the flat portion.

5. The bearing device according to claim 4 , wherein the detection unit and the processing unit are built into a single integrated circuit.

6. a first storage unit that stores first information indicating a relationship between the strain signal of the second strain sensor and a processing load; The bearing device according to claim 1 , further comprising: a processing load calculation unit that calculates a processing load from the strain signal of the second strain sensor and the first information.

7. 7. The bearing device according to claim 1, further comprising a bearing preload calculation unit that calculates a preload of either the first bearing or the second bearing using the strain signal of the first strain sensor and the strain signal of the second strain sensor.

8. A bearing preload calculation unit that calculates a preload load of either the first bearing or the second bearing using the strain signal of the first strain sensor and the strain signal of the second strain sensor; a second storage unit configured to store second information indicating a relationship between the strain signal of the first strain sensor and the preload, 7. The bearing device according to claim 6, wherein the bearing preload calculation unit calculates a preload from the strain signal of the first strain sensor and the second information, and calculates the preload of either the first bearing or the second bearing from the calculated preload and the processing load calculated by the processing load calculation unit.

9. a third storage unit that stores a preset threshold value; 9. The bearing device according to claim 8, further comprising a diagnosis unit that compares the bearing preload calculated by the bearing preload calculation unit with the threshold value, and diagnoses an abnormality when the bearing preload exceeds the threshold value.

10. A spindle device comprising the bearing device according to any one of claims 1 to 9.

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