Bearing device and spindle device

Abstract

To provide a bearing device and a spindle device capable of detecting a preload of a bearing accurately.SOLUTION: A bearing device 30 comprises: at least one bearing 5a including an outer ring 5ga, an inner ring 5ia and a rolling element Ta; a first member (6g) arranged on a path P1 on which pressing force for generating a preload between each raceway surface of the outer ring 5ga and the inner ring 5ia and the rolling element Ta is transmitted; a load sensor 50 arranged on the first member (6g); a temperature detector 60 arranged on the outer ring 5ga or the first member (6g); and a load calculation processing unit 70 that estimates the preload based on a change amount of a load value applied to the load sensor 50 due to thermal expansion of the outer ring 5ga and the first member (6g) corresponding to the output of the load sensor 50 and the output of the temperature detector 60.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a bearing device and a spindle device including a preload sensor for detecting the preload (load) of a bearing used for a spindle of a machine tool or the like.

Background Art

[0002] In a spindle device such as a machine tool, preload management of bearings is required to improve machining accuracy and efficiency, and therefore there is a need to detect the preload (load) of the bearings. There is also a need to detect signs of abnormality in the bearings before an abnormality occurs in the bearings and prevent the abnormality of the bearings.

[0003] In Japanese Patent Application Laid-Open No. 2020-003385 (Patent Document 1), in a bearing device in which a spacer is interposed between a plurality of rolling bearings arranged in the axial direction, a preload (load) sensor is arranged between the end face of the stationary ring of the bearing and the end face of the spacer, thereby detecting a change in the preload of the bearing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the bearing device disclosed in Japanese Patent Application Laid-Open No. 2020-003385 (Patent Document 1), the bearing preload is also affected by a change in the axial pressing force accompanying a temperature change of the bearing or the spacer. For this reason, it is difficult to accurately detect the preload of the bearing only with the preload sensor provided between the stationary ring of the bearing and the end face of the spacer.

[0006] The present disclosure has been made to solve the above problems, and an object thereof is to disclose a bearing device and a spindle device capable of accurately detecting the preload of a bearing.

Means for Solving the Problems

[0007] The present disclosure relates to a bearing device. The bearing device includes at least one bearing including a stationary ring, a rotating ring, and rolling elements, a first member disposed on a path through which a pressing force that generates a preload between each raceway surface of the stationary ring and the rotating ring and the rolling elements is transmitted, a load sensor disposed on the first member, a temperature detector disposed on the stationary ring or the first member, and a processing unit that estimates the preload based on the output of the load sensor and the amount of change in the load value on the load sensor due to thermal expansion of the stationary ring and the first member corresponding to the output of the temperature detector.

Effect of the Invention

[0008] According to the bearing device of the present embodiment, since the change in the pressing force due to thermal expansion can be subtracted from the load value acquired by the load sensor, only the preload of the bearing can be accurately detected.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Best Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0011] FIG. 1 is a cross-sectional view showing a schematic configuration of the spindle device according to this embodiment. FIG. 2 is an enlarged view of the main part on the left side of FIG. 1. FIG. 2 mainly shows the bearing device 30.

[0012] The spindle device 1 shown in FIG. 1 is used, for example, as a built-in motor type spindle device of a machine tool. In this case, a motor 40 is incorporated in one end side of the spindle 4 supported by the spindle device 1 for the machine tool spindle, and a cutting tool such as an end mill (not shown) is connected to the other end side.

[0013] The spindle device 1 includes bearings 5a and 5b, a spacer 6 disposed adjacent to the bearings 5a and 5b, a load sensor 50 disposed so as to abut on the end face of the bearing 5a, a motor 40, and a bearing 16 disposed behind the motor. The spindle 4 is rotatably supported 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 an outer ring spacer 6g.

[0014] The load sensor 50 is fixed to one end face 6ga of the outer ring spacer 6g or one end face of the outer ring 5ga by adhesion or the like. When fixing by adhesion, it is desirable to use an adhesive excellent in oil resistance and heat resistance.

[0015] On the main shaft 4, the inner rings 5ia of the bearings 5a and the inner rings 5ib of the bearings 5b, which are axially spaced apart, are fitted in an interference fit state (press-fitted state). An inner ring spacer 6i is disposed between the inner rings 5ia - 5ib, and an outer ring spacer 6g is disposed between the outer rings 5ga - 5gb.

[0016] The bearing 5a is a rolling bearing in which a plurality of rolling elements Ta are disposed between the inner ring 5ia and the outer ring 5ga. These rolling elements Ta are spaced apart by a cage Rta. The bearing 5b is a rolling bearing in which a plurality of rolling elements Tb are disposed between the inner ring 5ib and the outer ring 5gb. These rolling elements Tb are spaced apart by a cage Rtb.

[0017] The bearings 5a, 5b are bearings capable of applying preload with an axial force, and angular ball bearings, deep groove ball bearings, tapered roller bearings, etc. can be used. Angular ball bearings are used in the bearing device 30 shown in FIG. 2, and two bearings 5a, 5b are installed in a back-to-back combination (DB combination).

[0018] Here, a structure in which the main shaft 4 is supported by three bearings 5a, 5b, 16 will be exemplified and described, but a structure in which the main shaft 4 is supported by three or more bearings may also be used.

[0019] The single-row rolling bearing 16 is a cylindrical roller bearing. The angular ball bearings 5a, 5b support the radial load and the axial load acting on the spindle device 1. The single-row bearing 16, which is a cylindrical roller bearing, supports the radial load acting on the spindle device 1 for a machine tool spindle.

[0020] A cooling medium flow path G is formed in the housing 3. By flowing a cooling medium between the housing 3 and the outer cylinder 2, the bearings 5a, 5b can be cooled. When grease-lubricated bearings are used as the bearings 5a, 5b, a lubricating oil supply path is not required, but when lubrication such as air-oil is necessary, a lubricating oil supply path is provided in the outer ring spacer 6g. Here, the lubricating oil supply path is not shown.

[0021] At the time of assembly, first, the bearing 5a, spacer 6, bearing 5b, and spacer 9 are inserted in order onto the main shaft 4, and an initial preload is applied by tightening the nut 10. Thereafter, the main shaft 4 with the bearings 5a and 5b attached is inserted into the housing 3 until the right side of the outer ring 5gb of the bearing 5b in FIG. 1 abuts against the stepped portion 3a provided on the housing 3. Finally, the main shaft 4 is fixed to the housing 3 by the front cover 12 pressing the outer ring 5ga of the left bearing 5a.

[0022] By tightening the nut 10, a pressing force acts on the end face of the inner ring 5ib of the bearing 5b via the spacer 9, and the inner ring 5ib is pushed toward the inner spacer 6i. This pressing force is transmitted through the inner ring 5ib, rolling elements Tb, and outer ring 5gb, applying a preload between the raceway surfaces of the inner ring 5ib and outer ring 5gb and the rolling elements Tb, and is also transmitted from the outer ring 5gb to the outer spacer 6g. A pressing force acts from the right outer ring 5gb to the outer spacer 6g, and force is also transmitted to the load sensor 50.

[0023] This pressing force is transmitted to the outer ring 5ga, rolling elements Ta, and inner ring 5ia in the bearing 5a, applying a preload between the raceway surfaces of the inner ring 5ia and outer ring 5ga of the left bearing 5a and the rolling elements Ta. The force line P1 of the preload is shown in FIG. 2. The preload applied to the bearings 5a and 5b is determined by the amount of movement of the nut 10 restricted by, for example, the dimensional difference between the combined width of the outer spacer 6g and the load sensor 50 and the width of the inner spacer 6i.

[0024] Thereafter, the main shaft 4 with the bearings 5a and 5b attached is inserted into the housing 3 until the right side of the outer ring 5gb of the bearing 5b in FIG. 1 abuts against the stepped portion 3a provided on the housing 3. Finally, the main shaft 4 is fixed to the housing 3 by the front cover 12 pressing the outer ring 5ga of the bearing 5a. When the front cover 12 is fixed to the housing 3, a load is applied in the direction of the force line P2 shown in FIG. 2.

[0025] Also, for the single-row bearing 16, the inner ring 16a is axially positioned by a cylindrical member 15 fitted on the outer periphery of the main shaft 4 and an inner ring retainer 19. The inner ring retainer 19 is prevented from coming off by a nut 20 screwed onto the main shaft 4. The outer ring 16b of the bearing 16 is sandwiched between a positioning member 21 fixed to the end member 17 and a positioning member 18 fixed to the end member 17. The inner ring 16a is configured to slide integrally with respect to the end member 17 in accordance with the expansion and contraction of the main shaft 4.

[0026] A motor 40 for driving the main shaft 4 is disposed at an axial intermediate position sandwiched between the bearing 5b and the single-row bearing 16 in a space portion 22 formed between the main shaft 4 and the outer cylinder 2. The rotor 14 of the motor 40 is fixed to a cylindrical member 15 fitted on the outer periphery of the main shaft 4, and the stator 13 of the motor 40 is fixed to the inner peripheral portion of the outer cylinder 2.

[0027] Note that a cooling medium flow path for cooling the motor 40 is not shown here. The load sensor 50 is disposed on the force transmission path (force line P1 in FIG. 2) to which the bearing preload is applied. In addition to the bearing preload, the load sensor 50 measures the axial pressing force (force line P2 in FIG. 2) due to the thermal expansion of the outer rings 5ga, 5gb, the spacer between the outer rings 6g, the front cover 12, and the housing 3.

[0028] The temperature detector 60 includes at least one of a temperature sensor 60gs for measuring the temperature of the spacer between the outer rings 6g, a temperature sensor 60ga for measuring the temperature of the outer ring 5ga, and a temperature sensor 60gb for measuring the temperature of the outer ring 5gb. More preferably, the temperature detector 60 includes a temperature sensor 60f for measuring the temperature of the front cover 12 and a temperature sensor 60h for measuring the temperature of the housing 3.

[0029] Using the temperature detector 60, the temperatures of the outer rings 5ga, 5gb, the spacer between the outer rings 6g, the front cover 12, and the housing 3 can be measured.

[0030] The temperature detector 60 is preferably attached at a position close to the force line P2. For example, the temperature sensors 60ga and 60gb are attached to the outer diameter portions of the outer rings 5ga and 5gb, and the temperature sensor 60gs is attached to the outer diameter portion of the intermediate ring 6g between the outer rings. For example, the temperature sensor 60f is attached to the inner diameter portion of the front cover 12 facing the outer diameter surface of the main shaft 4, and the temperature sensor 60h is attached to the inner diameter portion of the housing 3 facing the outer diameter surface of the intermediate ring 9.

[0031] The temperature sensor 60gs and the temperature sensors 60ga and 60gb may be attached by providing a notch or a flat portion or the like in a part of the outer diameter surfaces of the intermediate ring 6g between the outer rings and the outer rings 5ga and 5gb. Also, the temperature sensors 60f and 60h may be attached by providing a notch or a flat portion or the like in a part of the inner diameter portions of the front cover 12 and the housing 3.

[0032] As each temperature sensor of the temperature detector 60, those whose electrical resistance value changes in response to a temperature change, such as a measuring resistor, a thermistor, a thermocouple, an IC temperature sensor, or those that generate a thermoelectromotive force can be used, but any type of sensor may be used.

[0033] The load sensor 50 measures the force to which the bearing preload is applied and the axial pressing force (the force line P2 in Fig. 2) due to the thermal expansion of the outer rings 5ga, 5gb, the spacer 6g between the outer rings, the front cover 12, and the housing 3. Therefore, in order to accurately detect the bearing preload, it is necessary to remove the change in the axial pressing force due to the thermal expansion of the outer rings 5ga, 5gb, the spacer 6g between the outer rings, the front cover 12, and the housing 3. As a method for this, a relational expression for calculating the change amount of the axial pressing force applied to the load sensor 50 due to their thermal expansion is obtained in advance from the temperature changes of the outer rings 5ga, 5gb, the spacer 6g between the outer rings, the front cover 12, and the housing 3. A map showing the relationship between the temperature and the change amount may also be created. Using the relational expression or the map, the change in the axial pressing force due to thermal expansion can be calculated from the temperature measurement values of the outer rings 5ga, 5gb, the spacer 6g between the outer rings, the front cover 12, and the housing 3. Therefore, the bearing preload can be accurately obtained by calculating the difference between the load value measured by the load sensor 50 and the pressing force converted from the measurement value of the temperature detector 60. The calculated accurate bearing preload can be used for highly accurate detection of bearing overload, prevention of bearing seizure, or prediction of remaining life.

[0034] The relational expression for calculating the change amount of the pressing force from the temperature measurement value can be experimentally obtained, for example, in a state where there is no fluctuation in the bearing preload due to rotation in Fig. 1 (the main shaft 4 is in a rotation stop state). Specifically, in the rotation stop state, by heating the outer rings 5ga, 5gb and the spacer 6g between the outer rings with a heat source such as a heater, the axial pressing force accompanying the thermal expansion of the outer rings 5ga, 5gb and the spacer 6g between the outer rings is applied to the load sensor 50. Therefore, by simultaneously measuring the temperatures of the outer rings 5ga, 5gb and the spacer 6g between the outer rings, an expression for converting the temperature measurement value into the change amount of the axial pressing force due to thermal expansion can be obtained.

[0035] [Example of Arrangement of Load Sensor Elements] An example of the arrangement of load sensor elements in the load sensor used in the present embodiment will be described below.

[0036] FIG. 3 is a diagram showing a first arrangement example of the sensor elements of the load sensor 50 in the X1 cross section of FIG. 2. FIG. 4 is a diagram showing a second arrangement example of the sensor elements of the load sensor 50 in the X1 cross section of FIG. 2. Note that parts unnecessary for the description are not shown in FIGS. 3 and 4.

[0037] The first arrangement example in FIG. 3 is an arrangement example of the load sensor 50 arranged between the end face of the outer ring 5ga and the end face 6ga of the spacer 6g between the outer rings. In the first arrangement example, the load sensor elements 50a, 50b, 50c, and 50d are evenly arranged at intervals of 90 degrees in the circumferential direction of the spacer 6g between the outer rings.

[0038] In this case, based on the average value or the total value of the four outputs of the load sensor elements 50a, 50b, 50c, and 50d, the preload of the bearing 5 and the load including the change in the axial pressing force due to the thermal expansion of the bearing 5 and the spacer 6g between the outer rings during operation are calculated.

[0039] In the second arrangement example in FIG. 4, three load sensor elements 50a, 50b, and 50c are evenly arranged at intervals of 120 degrees in the circumferential direction of the spacer 6g between the outer rings.

[0040] The number of load sensor elements included in the load sensor 50 only needs to be able to evenly and well balance the end face of the outer ring 5ga via the load sensor elements, and three or more are preferable. Also, the plurality of load sensor elements are preferably arranged at equal intervals on substantially the same circumference.

[0041] [Configuration of Load Sensor Element] Next, the structure of the load sensor element used in each embodiment will be described with reference to FIGS. 5 and 6.

[0042] FIG. 5 shows a cross-sectional view of the load sensor element 50a in the X2 cross section of FIG. 3. FIG. 6 is a front view of the load sensor element 50a as viewed from the X3 direction of FIG. 5. Note that the load sensor elements 50b to 50d also have the same structure.

[0043] The load sensor element 50a outputs a signal corresponding to the load (pressure) applied to the load sensor 50. For example, the load sensor element 50a is a pressure sensor whose electrical resistance value changes according to the load, and a pressure sensor having high rigidity that does not significantly reduce the rigidity of the spindle device 1 is desirable. More specifically, the load sensor element 50a is a pressure-sensitive element formed of a metal thin film pattern (metal thin film resistor) whose resistance changes with a change in surface pressure.

[0044] The load sensor element 50a includes, for example, an insulating substrate 51, a metal thin film pattern (metal thin film resistor) 52 formed on the substrate 51 whose resistance changes with a change in surface pressure and an electrode 53 connected thereto, and an insulating protective layer 54 that protects the metal thin film pattern 52. Since the protective layer 54 is not formed on the electrode 53, wiring can be directly connected to the electrode 53.

[0045] For the substrate 51, a ceramic material mainly composed of, for example, zirconia (ZrO2) or alumina (Al2O3) is used. The ceramic material has high rigidity and high insulation, and the surface flatness of the substrate 51 can be processed with high precision, which is convenient. The thickness of the substrate 51 is preferably, for example, 0.3 mm or more and 5 mm or less from the viewpoint of thinning the load sensor element 50a and ensuring the strength in the compression direction.

[0046] The metal thin film pattern 52 is made of, for example, nickel chromium (NiCr), chromium (Cr)-based materials, and is formed by film deposition such as evaporation or sputtering. The thickness of the metal thin film pattern is, for example, 1 μm or less. Further, as the protective layer 54, a thin film of an insulating material, for example, alumina (Al2O3) or silicon dioxide (SiO2) formed by sputtering or the like can be used. The film thickness of the protective layer 54 is set to about 2 μm, for example.

[0047] In addition, the surface of the electrode 53 may be coated with a material such as copper, silver, or gold to facilitate soldering to the wiring.

[0048] Although a load sensor element using a metal thin film pattern has been described here, other types such as piezoelectric or strain gauge types may also be used as the load sensor element.

[0049] FIG. 7 is a circuit diagram of an amplifier section that detects the resistance change of the load sensor 50. An output value corresponding to the resistance change is obtained through an amplifier section 55 that detects and amplifies the resistance change of the load sensor 50.

[0050] The amplifier section 55 includes resistors R1 to R3 connected to the DC power supply VSDC, the load sensor 50, and a differential amplifier AMP. The resistors R1 to R3 and the load sensor 50 form a bridge circuit. Between the positive and negative electrodes of the DC power supply VSDC, the resistor R1 and the resistor R2 are connected in series. Also, between the positive and negative electrodes of the DC power supply VSDC, the load sensor 50 and the resistor R3 are connected in series. One input node of the differential amplifier AMP is connected to the connection node between the resistor R1 and the resistor R2. The other input node of the differential amplifier AMP is connected to the connection node between the load sensor 50 and the resistor R3.

[0051] By configuring a bridge circuit as shown in FIG. 7, the resistance change of the load sensor 50 when the load changes can be detected by the differential amplifier AMP.

[0052] FIG. 8 is a diagram showing a modification of an embodiment in which the arrangement of the load sensor 50 is changed. In the modification of the embodiment, the outer ring spacer is divided into two, and the load sensor 50 is arranged therebetween.

[0053] The load sensor 50 shown in FIG. 8 is arranged so as to abut on the end face 6g1a of one outer ring spacer 6g1 obtained by axially dividing the outer ring spacer 6g into two, and the end face 6g2a of the other outer ring spacer 6g2.

[0054] The end face 6g1a of the outer ring spacer 6g1 that abuts against the load sensor 50 and the end face 6g2a of the outer ring spacer 6g2 that presses the load sensor 50 need to be machined with high precision in terms of flatness, surface roughness, and the parallelism of these end faces 6g1a and 6g2a. However, since the outer ring spacers 6g1 and 6g2 can be machined individually, it is possible to achieve good machining accuracy.

[0055] At this time, it is desirable to attach temperature sensors 60gs1 and 60gs2 to the outer ring spacers 6g1 and 6g2 respectively, but it is also possible to attach a temperature sensor to only one of the outer ring spacers.

[0056] A convex surface (not shown) may be provided on the end face 6g2a of the outer ring spacer 6g2 so that the convex surface abuts against the load sensor element 50a. Also, a convex surface (not shown) may be provided on the end face 6g1a of the outer ring spacer 6g1 and the load sensor element 50a may be fixed to the convex surface. In this case, since the area that requires machining accuracy can be reduced, machining becomes easier and the machining time can be shortened. Furthermore, alignment may be performed with pins (not shown) so as to relatively position the two-part outer ring spacers 6g1 and 6g2.

[0057] The processing circuits of the load sensor 50 and the temperature detector 60 will be described below. FIG. 9 is a functional block diagram of a load arithmetic processing unit that processes the output of the load sensor. As shown in FIG. 9, the load arithmetic processing unit 70 processes the outputs of the load sensor 50 and the temperature detector 60 and outputs a bearing preload value.

[0058] The load arithmetic processing unit 70 includes a load arithmetic unit 71, a storage unit 72 that stores a load conversion coefficient, a change amount calculation unit 73 that calculates the change amount of the pressing force due to thermal expansion, a storage unit 74 that stores a pressing force conversion coefficient, and a bearing preload calculation unit 75.

[0059] The storage unit 72 stores a coefficient, an approximation formula, or a conversion map for converting the output value of the load sensor 50 into a load value. The load arithmetic unit 71 calculates the load value applied to the load sensor 50 from the coefficient, approximation formula, or conversion map stored in the storage unit 72 and the output of the load sensor 50.

[0060] The memory unit 74 stores a coefficient, an approximation formula, or a conversion map for converting into a change amount of the pressing force due to thermal expansion applied to the predetermined load sensor 50. The change amount calculation unit 73 calculates a change in the pressing force due to thermal expansion applied to the load sensor 50 based on the coefficient, the approximation formula, or the conversion map stored in the memory unit 74 and the output of the temperature detector 60.

[0061] The bearing preload calculation unit 75 calculates a difference between the load value calculated by the load calculation unit 71 and the change in the pressing force calculated by the change amount calculation unit 73, and outputs a bearing preload value.

[0062] Further, a life estimation unit 76 for estimating the remaining life of the bearing may be provided in the load calculation processing unit 70. The life estimation unit 76 receives the bearing preload value calculated by the bearing preload calculation unit 75 and at least one piece of information among the internal specifications of the bearing, the rotational speed of the bearing, the number of rotations, and the temperature, and is configured to notify the remaining life of the bearing and the bearing replacement timing.

[0063] Note that the above load calculation processing unit 70 may be provided outside the spindle device 1 or may be provided inside the spindle device 1, specifically, on the outer ring spacer 6g.

[0064] (Summary) Referring to the drawings again, the present embodiment will be summarized.

[0065] The present disclosure relates to a bearing device 30. The bearing device 30 shown in FIG. 2 includes at least one bearing 5a including an outer ring 5ga which is a stationary ring, an inner ring 5ia which is a rotating ring, and rolling elements Ta, a first member (6g) disposed on a path P1 through which a pressing force for generating a preload between each raceway surface of the outer ring 5ga and the inner ring 5ia and the rolling elements Ta is transmitted, a load sensor 50 disposed in contact with the first member (6g), a temperature detector 60 disposed on the outer ring 5ga or the first member (6g), and a load arithmetic processing unit 70 that estimates a preload based on an output of the load sensor 50 and a change amount of a load value to the load sensor 50 due to thermal expansion of the outer ring 5ga and the first member (6g) corresponding to an output of the temperature detector 60.

[0066] Preferably, as shown in FIG. 3 or FIG. 4, the load sensor 50 includes a plurality of load sensor elements 50a to 50d arranged at equal intervals on the same circumference centered on the main shaft 4 on an end face 6ga which is a plane perpendicular to the extending direction of the main shaft 4 supported by the bearing 5a.

[0067] Preferably, as shown in FIGS. 5 and 6, the load sensor 50 includes a metal thin film pattern 52 whose resistance changes according to the applied force, and a protective layer 54 that insulates and protects the metal thin film pattern 52.

[0068] Preferably, as shown in FIG. 2, the at least one bearing is a plurality of bearings 5a, 5b. The first member is a non-rotating side outer ring spacer 6g inserted between the two bearings 5a, 5b, and the load sensor 50 is disposed between an end face of the outer ring 5ga of one of the two bearings 5a, 5b and an end face 6ga of the outer ring spacer 6g. The pressing force is transmitted through the load sensor 50.

[0069] Preferably, as shown in FIG. 8, the first member is one of the first spacers 6g1 and the second spacers 6g2 obtained by dividing an outer ring spacer 6g disposed adjacent to at least one bearing 5a in the extending direction of the main shaft 4 supported by the bearing 5a, the load sensor 50 is disposed between an end face 6g1a of the first spacer 6g1 and an end face 6g2a of the second spacer 6g2, and the pressing force is transmitted through the load sensor 50.

[0070] Preferably, as shown in FIG. 9, the load calculation processing unit 70 includes a storage unit 72 which is a first storage unit that stores in advance first information for converting the output of the load sensor 50 into a load value, a load calculation unit 71 that calculates a first load value based on the first information stored in the first storage unit and the output of the load sensor 50, a storage unit 74 which is a second storage unit that stores in advance second information for converting the output of the temperature detector 60 into a force, and a change amount calculation unit 73 that calculates a change amount of the pressing force applied to the load sensor 50 based on the second information stored in the second storage unit and the output of the temperature detector 60, and a bearing preload calculation unit 75 that outputs a bearing preload value based on the first load value and the change amount of the pressing force. The first information includes, for example, a load conversion coefficient, an approximate formula, or a conversion map for converting the output of the load sensor 50 into a load value. The second information includes, for example, a conversion formula or a conversion map for converting the output of the temperature detector 60 into a force.

[0071] As shown in FIG. 1, the spindle device 1 in another aspect of the present embodiment includes the bearing device 30 described in any of the above, a housing 3 that supports the bearing 5, a front cover 12 for fixing the bearing 5 to the housing 3, a first detector (temperature sensor 60h) that detects the temperature of the housing 3, and a second detector (temperature sensor 60f) that detects the temperature of the front cover 12.

[0072] According to the bearing device of the embodiment described above, the following effects can be obtained. That is, if only a load sensor (pressure-sensitive sensor element) capable of measuring a load is arranged between the outer ring spacer on the path where a preload (load) is applied to the bearing and the bearing, the change in the pressing force due to the thermal expansion of the bearing and the outer ring spacer is also detected, and it has been difficult to accurately measure the bearing preload generated between the rolling element and the raceway surface. In contrast, in the present embodiment, the temperatures of the bearing, the outer ring spacer, the front cover, and the housing are measured, the axial pressing force due to their thermal expansion is calculated using the temperature measurement results, and the difference from the load value of the load sensor is calculated, whereby the bearing preload can be accurately calculated.

[0073] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Signs

[0074] 1 Spindle device, 2 Outer cylinder, 3 Housing, 3a Step portion, 4 Main shaft, 5, 5a, 5b, 16 Bearings, 5ga, 5gb, 16b Outer rings, 5ia, 5ib, 16a Inner rings, 6, 9 Intermediate seats, 6g, 6g1, 6g2 Outer ring intermediate seats, 6g1a, 6g2a, 6ga End faces, 6i Inner ring intermediate seat, 10, 20 Nuts, 12 Front cover, 13 Stator, 14 Rotor, 15 Cylindrical member, 17 End member, 18, 21 Positioning members, 19 Inner ring retainer, 22 Space portion, 30 Bearing device, 40 Motor, 50 Load sensor, 50a~50d Load sensor elements, 51 Substrate, 52 Metal thin film pattern, 53 Electrodes, 54 Protective layer, 55 Amplifying portion, 60 Temperature detector, 60f, 60ga, 60gb, 60gs, 60gs1, 60h Temperature sensors, 70 Load calculation processing unit, 71 Load calculation unit, 72, 74 Storage units, 73 Variation amount calculation unit, 75 Bearing preload calculation unit, 76 Life estimation unit, AMP Differential amplifier, G Flow path, R1, R2, R3 Resistors, Rta, Rtb Retainers, Ta, Tb Rolling elements.

Claims

1. A bearing device comprising: at least one bearing including a stationary ring, a rotating ring, and rolling elements; a first member disposed on a path through which a pressing force for generating preload between each raceway surface of the stationary ring and the rotating ring and the rolling elements is transmitted; a load sensor disposed in contact with the first member; a temperature detector disposed on the stationary ring or the first member; a processing unit configured to estimate the preload based on an output of the load sensor and a change amount of a load value applied to the load sensor due to thermal expansion of the stationary ring and the first member corresponding to an output of the temperature detector; wherein the processing unit includes a first storage unit that stores in advance first information for converting an output of the load sensor into the load value; a load calculation unit that calculates a first load value based on the first information stored in the first storage unit and the output of the load sensor; a second storage unit that stores in advance second information for converting an output of the temperature detector into a force; a change amount calculation unit that calculates a change amount of the pressing force applied to the load sensor based on the second information stored in the second storage unit and the output of the temperature detector; a bearing preload calculation unit that calculates a second load value corresponding to the preload based on the first load value and the change amount of the pressing force; and a life estimation unit that receives a bearing preload load value calculated by the bearing preload calculation unit and information of the bearing, and notifies a remaining life of the bearing and a bearing replacement timing, the information including at least one of internal specifications, a rotation speed, and a number of rotations of the bearing.

2. The bearing device according to claim 1, wherein the load sensor includes a plurality of load sensor elements arranged at equal intervals on the same circumference centered on the shaft in a plane perpendicular to an extending direction of the shaft supported by the bearing.

3. The load sensor includes a metal thin film pattern whose resistance changes according to a pressed force, and a protective layer that insulates and protects the metal thin film pattern.

4. The at least one bearing is a plurality of bearings, the first member is a non-rotating intermediate seat inserted between two of the plurality of bearings, the load sensor is disposed between an end face of a stationary ring of one of the two bearings and an end face of the intermediate seat, and the pressing force is transmitted through the load sensor.

5. The first member is one of the first seat and the second seat which are formed by dividing a seat adjacent to the at least one bearing into the first seat and the second seat in an extending direction of a shaft supported by the bearing, The load sensor is disposed between an end surface of the first seat and an end surface of the second seat, and the pressing force is transmitted through the load sensor. The bearing device according to any one of claims 1 to 3.

6. A bearing device according to any one of claims 1 to 5, A housing that supports the bearing, A front cover for fixing the bearing to the housing, A first detector that detects the temperature of the housing, A spindle device comprising a second detector that detects the temperature of the front cover.

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