JP7713792B2 - Bearing device and spindle device - Google Patents

Description

This disclosure relates to a bearing device and a spindle device equipped with a preload sensor that detects the preload (load) of bearings used in main spindles of machine tools, etc.

In spindle devices such as machine tools, bearing preload management is required to improve machining accuracy and efficiency, and as a result there is a need to detect bearing preload (load). There is also a need to detect signs of bearing abnormalities before they occur and prevent bearing abnormalities from occurring.

JP 2020-003385 A (Patent Document 1) describes a bearing device in which spacers are interposed between multiple rolling bearings aligned in the axial direction, and a preload (load) sensor is placed between the end face of the bearing's stationary ring and the end face of the spacer to detect changes in the bearing preload.

Japanese Patent Application Laid-Open No. 2020-003385

In the bearing device disclosed in JP 2020-003385 A (Patent Document 1), the bearing preload is also affected by changes in axial pressure due to temperature changes in the bearing and spacer. For this reason, it is difficult to accurately detect the bearing preload using only a preload sensor installed between the bearing's stationary ring and the spacer end face.

This disclosure has been made to solve the above-mentioned problems, and its purpose is to disclose a bearing device and spindle device that can accurately detect bearing preload.

The present disclosure relates to a bearing device. The bearing device comprises at least one bearing including a stationary ring, a rotating ring, and a rolling element; a first member arranged on a path along which a pressing force that generates a preload is transmitted between the rolling element and the raceway surfaces of the stationary ring and the rotating ring; a load sensor arranged on the first member; a temperature detector arranged 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 that corresponds to the output of the temperature detector.

With the bearing device of this embodiment, it is possible to subtract the change in pressing force due to thermal expansion from the load value acquired by the load sensor, thereby accurately detecting only the bearing preload.

1 is a cross-sectional view showing a schematic configuration of a spindle device according to an embodiment of the present invention. FIG. 2 is an enlarged view of the main part on the left side of FIG. 1 . 3 is a diagram showing a first example of arrangement of sensor elements of the load sensor 50 in the X1 cross section of FIG. 2. FIG. 3 is a diagram showing a second example of arrangement of sensor elements of the load sensor 50 in the X1 cross section of FIG. 2. FIG. 4 shows a cross-sectional view of the load sensor element 50a taken along 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 in FIG. 5. 4 is a circuit diagram of an amplifier that detects a change in resistance of the load sensor 50. FIG. 10 is a diagram showing a modified example of the embodiment in which the arrangement of the load sensor 50 is changed. FIG. FIG. 3 is a functional block diagram of a load calculation processing unit that processes the output of the load sensor.

Embodiments of the present invention will now be described with reference to the drawings. Note that identical or corresponding parts in the following drawings will be designated by the same reference numerals, and their description will not be repeated.

Figure 1 is a cross-sectional view showing the general configuration of the spindle device of this embodiment. Figure 2 is an enlarged view of the main part on the left side of Figure 1. Figure 2 mainly shows the bearing device 30.

The spindle device 1 shown in Figure 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 the 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.

The spindle device 1 includes bearings 5a and 5b, a spacer 6 positioned adjacent to bearings 5a and 5b, a load sensor 50 positioned to abut the end face of bearing 5a, a motor 40, and a bearing 16 positioned behind the motor. The main shaft 4 is rotatably supported by multiple bearings 5a and 5b provided in a housing 3 embedded in the inner diameter portion of the outer cylinder 2. Bearing 5a includes an inner ring 5ia, an outer ring 5ga, rolling elements Ta, and a cage Rta. Bearing 5b includes an inner ring 5ib, an outer ring 5gb, rolling elements Tb, and a cage Rtb. Spacer 6 includes an inner ring spacer 6i and an outer ring spacer 6g.

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

The inner ring 5ia of bearing 5a and the inner ring 5ib of bearing 5b, which are spaced apart in the axial direction, are fitted to the main shaft 4 in an interference (press-fit) state. An inner ring spacer 6i is disposed between the inner rings 5ia and 5ib, and an outer ring spacer 6g is disposed between the outer rings 5ga and 5gb.

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

Bearings 5a and 5b are bearings that can be preloaded with an axial force, and can be angular contact ball bearings, deep groove ball bearings, tapered roller bearings, or other bearings. The bearing device 30 shown in Figure 2 uses angular contact ball bearings, and the two bearings 5a and 5b are installed in a back-to-back (DB) configuration.

Here, we will explain an example of a structure in which the main shaft 4 is supported by three bearings 5a, 5b, and 16, but the main shaft 4 may also be supported by three or more bearings.

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

A coolant flow path G is formed in the housing 3. By flowing a coolant between the housing 3 and the outer cylinder 2, the bearings 5a and 5b can be cooled. 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 outer ring spacer 6g. Note that the lubricant supply path is not shown here.

During assembly, bearing 5a, spacer 6, bearing 5b, and spacer 9 are first inserted into the main shaft 4 in that order, and an initial preload is applied by tightening the nut 10. The main shaft 4, with bearings 5a and 5b attached, is then inserted into the housing 3 until the right side of the outer ring 5gb of bearing 5b in Figure 1 contacts the stepped portion 3a on the housing 3. Finally, the front cover 12 presses on the outer ring 5ga of the left-side bearing 5a, securing the main shaft 4 to the housing 3.

Tightening the nut 10 applies a pressing force to the end face of the inner ring 5ib of the bearing 5b via the spacer 9, pressing the inner ring 5ib toward the inner ring spacer 6i. This pressing force is transmitted through the inner ring 5ib, rolling element Tb, and outer ring 5gb, applying preload between the raceway surfaces of the inner ring 5ib and outer ring 5gb and the rolling element Tb, and is also transmitted from the outer ring 5gb to the outer ring spacer 6g. A pressing force acts from the right outer ring 5gb to the outer ring spacer 6g, and this force is also transmitted to the load sensor 50.

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 the left-side bearing 5a and the rolling element Ta. Figure 2 shows the preload force line P1. The preload applied to bearings 5a and 5b is determined by the amount of movement of the nut 10, which is limited by the dimensional difference between the combined width of the outer ring spacer 6g and load sensor 50 and the width of the inner ring spacer 6i, for example.

Then, the main shaft 4, to which the bearings 5a and 5b are attached, is inserted into the housing 3 until the right side of the outer ring 5gb of the bearing 5b in Figure 1 abuts against the stepped portion 3a provided on the housing 3. Finally, the front cover 12 presses the outer ring 5ga of the bearing 5a, thereby fixing the main shaft 4 to the housing 3. 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 Figure 2.

Furthermore, for the single-row bearing 16, the inner ring 16a is positioned axially by a cylindrical member 15 fitted onto the outer periphery of the main shaft 4 and an inner ring retainer 19. The inner ring retainer 19 is prevented from coming loose by a nut 20 threaded 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 slides integrally against the end member 17 in response to the expansion and contraction of the main shaft 4.

The motor 40 that drives the main shaft 4 is located in the space 22 formed between the main shaft 4 and the outer cylinder 2, at an axially intermediate position between the bearing 5b and the single-row bearing 16. The rotor 14 of the motor 40 is fixed to a cylindrical member 15 fitted onto the outer periphery of the main shaft 4, and the stator 13 of the motor 40 is fixed to the inner periphery of the outer cylinder 2.

It should be noted that the coolant flow path for cooling the motor 40 is not shown here.
The load sensor 50 is disposed on the force transmission path (line of force P1 in FIG. 2 ) along which the bearing preload is applied. The load sensor 50 measures not only the bearing preload but also the axial pressing force (line of force P2 in FIG. 2 ) due to thermal expansion of the outer rings 5ga, 5gb, outer ring spacer 6g, front cover 12, and housing 3.

The temperature detector 60 includes at least one of temperature sensor 60gs, which measures the temperature of the outer ring spacer 6g, temperature sensor 60ga, which measures the temperature of the outer ring 5ga, and temperature sensor 60gb, which measures the temperature of the outer ring 5gb, and more preferably includes temperature sensor 60f, which measures the temperature of the front cover 12, and temperature sensor 60h, which measures the temperature of the housing 3.

The temperature detector 60 can be used to measure the temperatures of the outer rings 5ga, 5gb, outer ring spacer 6g, front cover 12, and housing 3.

It is desirable to mount the temperature detector 60 in a position close to the line of force P2. For example, temperature sensors 60ga and 60gb are mounted on the outer diameter portions of the outer rings 5ga and 5gb, and temperature sensor 60gs is mounted on the outer diameter portion of the outer ring spacer 6g. For example, temperature sensor 60f is mounted on the inner diameter portion of the front cover 12, which faces the outer diameter surface of the spindle 4, and temperature sensor 60h is mounted on the inner diameter portion of the housing 3, which faces the outer diameter surface of the spacer 9.

Temperature sensors 60gs and 60ga, 60gb may be attached by providing a notch or flat portion on part of the outer diameter surface of outer ring spacer 6g and outer rings 5ga, 5gb. Temperature sensors 60f and 60h may also be attached by providing a notch or flat portion on part of the inner diameter surface of front cover 12 and housing 3.

The temperature sensors in the temperature detector 60 can be any type of sensor, including measuring resistors, thermistors, thermocouples, and IC temperature sensors, which change electrical resistance in response to temperature changes or generate thermoelectric power.

The load sensor 50 measures both the force applied by the bearing preload and the axial pressing force (force line P2 in Figure 2) due to thermal expansion of the outer rings 5ga, 5gb, outer ring spacer 6g, front cover 12, and housing 3. Therefore, to accurately detect the bearing preload, it is necessary to remove the change in the axial pressing force due to thermal expansion of the outer rings 5ga, 5gb, outer ring spacer 6g, front cover 12, and housing 3. To achieve this, a relational equation is first determined to calculate the change in the axial pressing force applied to the load sensor 50 due to thermal expansion of the outer rings 5ga, 5gb, outer ring spacer 6g, front cover 12, and housing 3 based on their temperature changes. A map showing the relationship between temperature and the amount of change may also be created. Using this relational equation or map, the change in the axial pressing force due to thermal expansion can be calculated from the measured temperature values of the outer rings 5ga, 5gb, outer ring spacer 6g, front cover 12, and housing 3. Therefore, the bearing preload can be accurately determined 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 to accurately detect bearing overload, prevent bearing seizure, or predict remaining life.

The relational equation for calculating the amount of change in pressing force from the measured temperature value can be experimentally determined, for example, when there is no fluctuation in bearing preload due to rotation as shown in Figure 1 (when the main shaft 4 is stopped). Specifically, when the rotation is stopped, the outer rings 5ga, 5gb and outer ring spacer 6g are heated with a heat source such as a heater, and the axial pressing force due to thermal expansion of the outer rings 5ga, 5gb and outer ring spacer 6g is applied to the load sensor 50. Therefore, by simultaneously measuring the temperatures of the outer rings 5ga, 5gb and outer ring spacer 6g, an equation can be determined for converting the measured temperature into the amount of change in axial pressing force due to thermal expansion.

[Example of arrangement of load sensor elements]
An example of the arrangement of the load sensor elements in the load sensor used in this embodiment will be described below.

Figure 3 is a diagram showing a first example of the arrangement of the sensor elements of the load sensor 50 in the X1 cross section of Figure 2. Figure 4 is a diagram showing a second example of the arrangement of the sensor elements of the load sensor 50 in the X1 cross section of Figure 2. Note that parts not necessary for the explanation have been omitted from Figures 3 and 4.

The first arrangement example in Figure 3 is an example of an arrangement of a load sensor 50 placed between the end face of the outer ring 5ga and the end face 6ga of the outer ring spacer 6g. In the first arrangement example, the load sensor elements 50a, 50b, 50c, and 50d are evenly spaced at 90-degree intervals around the circumferential direction of the outer ring spacer 6g.

In this case, the load is calculated based on the average or total value of the four outputs of the load sensor elements 50a, 50b, 50c, and 50d, including the preload of the bearing 5 and the change in axial pressure due to thermal expansion of the bearing 5 and outer ring spacer 6g caused by heat generation during operation.

In the second arrangement example shown in Figure 4, three load sensor elements 50a, 50b, and 50c are evenly spaced at 120-degree intervals around the circumferential direction of the outer ring spacer 6g.

The number of load sensor elements included in the load sensor 50 should be sufficient to press the end face of the outer ring 5ga evenly and in a balanced manner via the load sensor elements, and three or more is preferable. Furthermore, it is preferable to arrange multiple load sensor elements at equal intervals on approximately the same circumference.

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

Figure 5 shows a cross-sectional view of the load sensor element 50a taken along the X2 cross section in Figure 3. Figure 6 is a front view of the load sensor element 50a as seen from the X3 direction in Figure 5. Note that the load sensor elements 50b to 50d have a similar structure.

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-sensitive sensor whose electrical resistance value changes depending on the load, and it is desirable for the load sensor element 50a to be a pressure-sensitive sensor with high rigidity that does not significantly reduce the rigidity of the spindle device 1. More specifically, the load sensor element 50a is a pressure-sensitive element formed from a metal thin-film pattern (metal thin-film resistor) whose resistance changes with changes in surface pressure.

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 changes in surface pressure, an electrode 53 connected to the metal thin-film pattern 52, and an insulating protective layer 54 that protects the metal thin-film pattern 52. Because the protective layer 54 is not formed on the electrode 53, wiring can be connected directly to the electrode 53.

A ceramic material containing, for example, zirconia ( _ZrO2 ) or alumina ( _Al2O3 ) as _its main component is used for the substrate 51. Ceramic materials have high rigidity and insulating properties, and are advantageous because they allow the surface of the substrate 51 to be processed with high precision to achieve flatness. From the viewpoint of making the load sensor element 50a thin and ensuring strength in the compression direction, the thickness of the substrate 51 is preferably 0.3 mm or more and 5 mm or less.

The metal thin film pattern 52 is made of, for example, a nickel chromium (NiCr) or chromium (Cr)-based material and is formed by vapor deposition, sputtering, or the like. The thickness of the metal thin film pattern is, for example, 1 μm or less. The protective layer 54 can be made of an insulating material, for example, a thin film of alumina (Al ₂ O ₃ ) or silicon dioxide (SiO ₂ ) formed by sputtering, or the like. The thickness of the protective layer 54 is, for example, about 2 μm.

The surface of the electrode 53 may be coated with a material such as copper, silver, or gold to facilitate soldering to wiring.

Here we have explained a load sensor element that uses a metal thin film pattern, but other types of load sensor elements, such as piezoelectric or strain gauge types, may also be used.

Figure 7 is a circuit diagram of the amplifier that detects resistance changes in the load sensor 50. An output value corresponding to the resistance change is obtained via the amplifier 55, which detects and amplifies the resistance change in the load sensor 50.

The amplifier unit 55 includes resistors R1 to R3 connected to the DC power supply VSDC, a load sensor 50, and a differential amplifier AMP. Resistors R1 to R3 and the load sensor 50 form a bridge circuit. Resistors R1 and R2 are connected in series between the positive and negative terminals of the DC power supply VSDC. Furthermore, the load sensor 50 and resistor R3 are connected in series between the positive and negative terminals of the DC power supply VSDC. One input node of the differential amplifier AMP is connected to the connection node between resistors R1 and R2. The other input node of the differential amplifier AMP is connected to the connection node between the load sensor 50 and resistor R3.

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

Figure 8 shows a modified embodiment in which the placement of the load sensor 50 is changed. In this modified embodiment, the outer ring spacer is divided into two parts, and the load sensor 50 is placed between them.

The load sensor 50 shown in Figure 8 is positioned so that it abuts against the end face 6g1a of the outer ring spacer 6g1, one of the two outer ring spacers 6g that are axially divided into two, and the end face 6g2a of the other outer ring spacer 6g2.

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 against the load sensor 50, need to be machined with high precision to ensure flatness, surface roughness, and parallelism between these end faces 6g1a and 6g2a. However, because the outer ring spacers 6g1 and 6g2 can be machined separately, it is possible to achieve good machining precision.

In this case, it is desirable to attach temperature sensors 60gs1 and 60gs2 to 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.

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. Alternatively, 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, the area requiring machining precision can be reduced, making machining easier and shortening the machining time. Furthermore, the two split outer ring spacers 6g1 and 6g2 may be aligned with each other using a pin (not shown).

The processing circuits for the load sensor 50 and temperature detector 60 are described below. Figure 9 is a functional block diagram of the load calculation processing unit that processes the output of the load sensor. As shown in Figure 9, the load calculation processing unit 70 processes the output of the load sensor 50 and temperature detector 60 and outputs the bearing preload value.

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

The memory unit 72 stores coefficients, approximation formulas, or conversion maps for converting the output value of the load sensor 50 into a load value. The load calculation unit 71 calculates the load value to be applied to the load sensor 50 from the coefficients, approximation formulas, or conversion maps stored in the memory unit 72 and the output of the load sensor 50.

The memory unit 74 stores a coefficient, approximation formula, or conversion map that converts a predetermined amount of change in pressure applied to the load sensor 50 due to thermal expansion. The change amount calculation unit 73 calculates the amount of change in pressure applied to the load sensor 50 due to thermal expansion based on the coefficient, approximation formula, or conversion map stored in the memory unit 74 and the output of the temperature detector 60.

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

The load calculation processing unit 70 may also be provided with a life estimation unit 76 that estimates the remaining bearing life. The life estimation unit 76 is configured to receive the bearing preload value calculated by the bearing preload calculation unit 75, as well as at least one piece of information from the bearing's internal specifications and the bearing's rotational speed, number of rotations, and temperature, and to notify the remaining bearing life and the timing for bearing replacement.

The load calculation processing unit 70 may be provided outside the spindle device 1, or it may be provided inside the spindle device 1, specifically in the outer ring spacer 6g.

(summary)
Again, referring to the drawings, the present embodiment will be summarized.

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 (stationary ring), an inner ring 5ia (rotating ring), and a rolling element Ta; a first member (6g) arranged on a path P1 along which a pressing force that generates a preload between the raceway surfaces of the outer ring 5ga and the inner ring 5ia and the rolling element Ta is transmitted; a load sensor 50 arranged in contact with 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 the output of the load sensor 50 and the amount of change in the load value applied to the load sensor 50 due to thermal expansion of the outer ring 5ga and the first member (6g) that corresponds to the output of the temperature detector 60.

As shown in Figures 3 and 4, the load sensor 50 preferably includes multiple load sensor elements 50a-50d arranged at equal intervals on the same circumference centered on the main shaft 4 on the end face 6ga, which is a plane perpendicular to the extension direction of the main shaft 4 supported by the bearing 5a.

As shown in Figures 5 and 6, the load sensor 50 preferably includes a thin metal film pattern 52 whose resistance changes depending on the pressure applied, and a protective layer 54 that insulates and protects the thin metal film pattern 52.

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 outer ring spacer 6g inserted between the two bearings 5a, 5b, and the load sensor 50 is positioned between the end face of the outer ring 5ga of one of the two bearings 5a, 5b and the end face 6ga of the outer ring spacer 6g. The pressing force is transmitted via the load sensor 50.

As shown in FIG. 8, the first member is preferably one of the first spacers 6g1, which are obtained by dividing an outer ring spacer 6g arranged adjacent to at least one bearing 5a into a first spacer 6g1 and a second spacer 6g2 in the extension direction of the main shaft 4 supported by the bearing 5a, and the load sensor 50 is disposed between the end face 6g1a of the first spacer 6g1 and the end face 6g2a of the second spacer 6g2, and the pressing force is transmitted via the load sensor 50.

9, the load calculation processing unit 70 preferably includes a memory unit 72, which is a first memory unit that pre-stores first information for converting the output of the load sensor 50 into a load value; a load calculation unit 71 that calculates the first load value based on the first information stored in the first memory unit and the output of the load sensor 50; a memory unit 74, which is a second memory unit that pre-stores second information for converting the output of the temperature detector 60 into a force; a change amount calculation unit 73 that calculates the amount of change in the pressing force applied to the load sensor 50 based on the second information stored in the second memory 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 amount of change in the pressing force. The first information includes, for example, a load conversion coefficient, approximation formula, or conversion map that converts the output of the load sensor 50 into a load value. The second information includes, for example, a conversion formula or conversion map that converts the output of the temperature detector 60 into a force.

As shown in FIG. 1, the spindle device 1 in another aspect of this embodiment includes any of the bearing devices 30 described 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.

The bearing device of the embodiment described above offers the following advantages. Simply placing a load sensor (pressure-sensitive sensor element) capable of measuring load between the outer ring spacer and the bearing, which is on the path along which preload (load) is applied to the bearing, would also detect changes in pressing force due to thermal expansion of the bearing and outer ring spacer, making it difficult to accurately measure the bearing preload generated between the rolling elements and the raceway surface. In contrast, this embodiment measures the temperatures of the bearing, outer ring spacer, front cover, and housing, and uses the temperature measurement results to calculate the axial pressing force due to their thermal expansion. By calculating the difference with the load value of the load sensor, it is possible to accurately calculate the bearing preload.

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

1 Spindle device, 2 Outer cylinder, 3 Housing, 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, 6g1, 6g2 Outer ring spacer, 6g1a, 6g2a, 6ga End face, 6i Inner ring spacer, 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, 30 Bearing device, 40 Motor, 50 Load sensor, 50a to 50d Load sensor element, 51 Substrate, 52 Metal thin film pattern, 53 Electrode, 54 Protective layer, 55 Amplifying unit, 60 Temperature detector, 60f, 60ga, 60gb, 60gs, 60gs1, 60h temperature sensors, 70 load calculation processing unit, 71 load calculation unit, 72, 74 memory unit, 73 change amount calculation unit, 75 bearing preload calculation unit, 76 life estimation unit, AMP differential amplifier, G flow path, R1, R2, R3 resistors, Rta, Rtb cage, Ta, Tb rolling elements.

Claims (6)

A bearing device,
At least one bearing including a stationary ring, a rotating ring, and a rolling element;
a first member disposed on a path along which a pressing force that generates a preload between each of the raceway surfaces of the stationary ring and the rotating ring and the rolling element 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 that estimates the preload based on an output of the load sensor and a change in a load value applied to the load sensor due to thermal expansion of the stationary wheel and the first member, the change corresponding to the output of the temperature detector,
The processing unit
a first storage unit that stores in advance first information for converting the 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 an output of the load sensor;
a second storage unit that stores in advance second information for converting the output of the temperature detector into 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 an 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 an amount of change in the pressing force;
a lifespan estimation unit that receives the bearing preload value calculated by the bearing preload calculation unit and information about the bearing, and notifies the user of the remaining bearing lifespan and the timing for bearing replacement, wherein the information includes at least one of internal specifications, rotational speed, and number of rotations of the bearing. The bearing device described in 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 supported by the bearing in a plane perpendicular to the extension direction of the shaft. The load sensor is
A metal thin film pattern whose resistance changes depending on the pressure applied;
3. The bearing device according to claim 1, further comprising a protective layer that insulates and protects the thin metal film pattern. the at least one bearing is a plurality of bearings;
the first member is a non-rotating side spacer inserted between two bearings among the plurality of bearings,
4. The bearing device according to claim 1, wherein 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 spacer, and the pressing force is transmitted via the load sensor. the first member is one of the first spacers obtained by dividing a spacer disposed adjacent to the at least one bearing into a first spacer and a second spacer in an extension direction of a shaft supported by the bearing,
4. The bearing device according to claim 1, wherein the load sensor is disposed between an end face of the first spacer and an end face of the second spacer, and the pressing force is transmitted via the load sensor. The bearing device according to any one of claims 1 to 5,
a housing supporting the bearing;
a front cover for fixing the bearing to the housing;
a first detector for detecting a temperature of the housing;
a second detector for detecting the temperature of the front cover.