JP2003206925A - Bearing preload measuring method, preload measuring device, and spindle device. - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manage pre-load highly precisely by measuring load applied to a rolling body, as pre-load applied to a bearing, accurately and directly to prevent inconveniences such as seizure and wear of the bearing. <P>SOLUTION: A method is provided to measure pre-load amount of the rolling bearing 23 in which the rolling body 26 is arranged between an inner ring 25 and an outer ring 24. In this method, a pre-load amount is measured based on an electric characteristic value between the outer ring 24 having electroconductivity of the rolling bearing 23 or a member 21 connected with the outer ring 24 electrically and the inner ring 25 having electroconductivity of the rolling bearing 23 or a member 22 electrically connected to the inner ring 25. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique suitable for measuring a preload of a bearing used for supporting a spindle of a machine tool, for example.

[0002]

2. Description of the Related Art A spindle for a machine tool is supported by a plurality of preloaded bearings. In machine tools, it is necessary to increase the rigidity of the spindle so that high-precision machining can be performed, and in order to achieve this, a large preload is applied to the bearings that support the spindle for machine tools. Insufficient control of this preload causes problems such as bearing seizure and wear.

Conventionally, a method of measuring the preload has been considered for not only machine tools but also various devices. In Japanese Unexamined Patent Publication No. 58-196318, a load in the thrust direction is applied to a part of a ball bearing, the displacement due to the load is measured, and the preload is estimated from the value of the load at the time when the sudden displacement starts. Techniques for doing so are disclosed. Japanese Patent Publication 2-617
Japanese Patent Publication No. 00 discloses a technique in which vibration is applied to a ball bearing by a vibrating device, the resonance frequency of the ball bearing is detected, and the preload is estimated from the resonance frequency and a contact angle obtained separately. In addition to the above, there is also a technique of estimating the preload applied to the ball bearing by measuring the starting torque when the bearing starts to rotate.

[0004]

The above-mentioned methods cannot be used with a fixed position preload with a small amount of displacement (Japanese Patent Laid-Open No. 58-58).
No. 196318), an accurate contact angle cannot be obtained (Japanese Patent Publication No. 2-61700). In the method of measuring the starting torque, it is difficult to obtain an accurate preload because it is easily affected by the condition of the lubricating oil and the raceway surface, and the effects of displacement and rigidity change in parts other than the bearing appear.

The present invention has been made in view of the above circumstances, and an object thereof is to accurately and directly measure a load applied to a rolling element as a preload applied to a bearing, thereby performing highly accurate preload management. This is to prevent problems such as seizure and wear of the bearing.

[0006]

The object of the present invention is achieved by the following constitution. (1) A method for measuring a preload amount of a rolling bearing in which a plurality of rolling elements are arranged between an inner ring and an outer ring, the conductive outer ring of the rolling bearing or a member electrically connected to the outer ring. And a method for measuring a preload of a bearing, characterized in that a preload amount is obtained based on an electrical characteristic value between the conductive inner ring of the rolling bearing or a member electrically connected to the inner ring. (2) At least one of the rolling elements has conductivity, and the electrical characteristic value is a resistance value or a potential difference or a current difference that changes based on the resistance value. The resistance value, the potential difference, or the current difference. The preload measurement method according to (1) above, wherein the preload amount is appropriate when is within a predetermined range. (3) The bearing preload measuring method according to (1) or (2), wherein the rolling element is made of semiconductive ceramic. (4) A device for measuring a preload amount of a rolling bearing in which a plurality of rolling elements are arranged between an inner ring and an outer ring, wherein the outer ring having conductivity of the rolling bearing or a member electrically connected to the outer ring. A detecting means for detecting an electrical characteristic value between the inner ring having conductivity or a member electrically connected to the inner ring, and a calculating means for converting a detection result of the detecting means into a preload amount. A bearing preload measuring device characterized by being provided. (5) The bearing preload measuring device according to (4), further including a determining unit that notifies the outside when the amount of preload is inappropriate. (6) A spindle device incorporating the bearing preload measuring device according to (4) or (5).

According to the above construction, the outer ring having conductivity or a member (a housing or the like) electrically connected to the outer ring and the inner ring having conductivity or a member electrically connected to the inner ring ( The amount of preload is calculated based on the electrical characteristic value between the main shaft and the like). An oil film is formed between the inner and outer races and the rolling elements when the bearing rotates, but when the bearing is stopped and a preload is applied, the oil film becomes thin or broken. However, since the rolling elements and the inner and outer rings are in direct metal contact, the preload amount can be measured. The preload amount is measured by utilizing the thinned or broken state of the oil film. That is, when a preload is applied when the bearing is stopped, the contact areas of the rolling elements with respect to the inner ring raceway and the outer ring raceway change accordingly, and the electrical characteristic values between the inner and outer races also change. If the relationship between the preload and the electrical characteristic value is known in advance, the preload at that time can be accurately obtained in real time from the measured electrical characteristic value. In this way, highly accurate preload management can be performed. Further, when the amount of preload is improper, the determination means informs the outside of this, so that the abnormal preload can be reliably detected.

Examples of rolling elements made of semiconductive or conductive ceramics include, for example, Japanese Patent Laid-Open Nos. 62-87463, 62-265177, and 64-1552.
No. 3, JP-A-2-43699, and JP-A-3-297.
No. 44, No. 10-87370, and Japanese Patent Laid-Open No. 2000-2000.
Known ones described in Japanese Patent Publication No. 154064, Japanese Patent Publication No. 2000-192969, Japanese Patent Publication No. 8-16030 can be used. Furthermore, Japanese Patent Application No. 2001-203
No. 783, a transition metal nitride,
A rolling member made of a conductive ceramic containing 10 to 60% by weight of one or more selected from carbides, borides and oxides can also be used. The same type of rolling element is used for each rolling bearing. When rolling elements made of electrically conductive ceramics and rolling elements made of non-conductive ceramics are mixed, by making the main components of both types of rolling elements the same, make sure that the specific gravity, thermal expansion coefficient, etc. are as close as possible. use.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a bearing preload measuring device 40 according to a first embodiment of the present invention. The preload measuring device 40 includes a first spacer 41 that abuts the inner ring 52 of the rolling bearing 50 from one side in the axial direction, and a second spacer 42 that abuts the outer ring 51 of the rolling bearing 50 from the other side in the axial direction. There is. The first spacer 41 and the second spacer 42 are made of, for example, metal and have conductivity.

A pressing jig 43 is connected (mounted) to the first spacer 41, and the axial load F is applied to the pressing jig 43.
When a is applied, the first spacer 41 presses the inner ring 41. The second spacer 42 is fixed on the base 44, and the first spacer 41
Even if the inner ring 41 is pushed by the second spacer 42,
The outer ring 51 is supported without allowing the movement of the outer ring 51. Thus, the rolling bearing 50 is preloaded by the axial load Fa.

The electrodes of the tester 45 are connected to the first spacer 41 and the second spacer 42, respectively. Tester 45
Measures the resistance between the inner ring 52 and the outer ring 51 of the rolling bearing 50. Axial load Fa is applied and rolling element 53
As the contact area between the inner ring raceway and the outer ring raceway increases, the resistance value measured by the tester 45 decreases.

Three types of rolling elements 53 having different conductivity
As the rolling element, a rolling element (A) made of a steel ball, a rolling element (B) made of silicon nitride having conductivity, and a rolling element (C) made of silicon nitride having low conductivity are prepared and rolled respectively. Bearing (here, angular contact ball bearing (manufactured by NSK Ltd. 7
900)) 50. Inner ring 52 and outer ring 51
Is made of SUJ2 and has conductivity. And
Each rolling bearing 50 was set in the preload measuring device 40, and the relationship between the axial load Fa and the resistance between the inner and outer rings was obtained.

FIG. 2 shows the bearing preload measuring device 4 shown in FIG.
6 is a graph showing the relationship between the axial load Fa and the resistance between the inner and outer races, which is obtained by 0. The vertical axis of FIG. 2 shows the bearing resistance value ratio when the resistance value of the bearing incorporating the rolling element (A) made of steel balls is 1. In the bearing in which the steel rolling element shown in A in the figure is incorporated, the axial load is 10
The bearing resistance value ratio remained at 1 even when varied from N to 50N. In the bearing in which the rolling element made of silicon nitride having conductivity shown in B in the drawing is incorporated, when the axial load was changed from 10 N to 50 N, the bearing resistance value ratio was changed from 1 to 0.6. In the bearing in which the rolling element made of silicon nitride having low conductivity in C in the figure is incorporated, when the axial load was changed from 10 N to 50 N, the bearing resistance value ratio was changed from 1 to 0.35.

FIG. 3 shows a state in which the bearing preload measuring device 10 according to the second embodiment of the present invention is incorporated in a spindle device (spindle device for machine tool spindle) 20. The spindle device 20 includes a pair of rolling bearings in which a main spindle (also referred to as a “main spindle”) 22 also made of metal such as steel is axially spaced inside a housing 21 made of metal such as steel. (Combination of angular contact ball bearings)
It is rotatably supported by 23, 23. Each rolling bearing 23 has a metal outer ring 24 having an outer ring raceway on its inner peripheral surface and a metal inner race 2 having an inner ring raceway on its outer peripheral surface.
5, a plurality of rolling elements 26 rotatably provided between the outer ring raceway and the inner ring raceway, and a retainer (not shown) that rotatably holds these rolling elements 26.

The inner ring 25 of each rolling bearing 23 is composed of the main shaft 22.
It is fitted and fixed on. Outer ring 24 of each rolling bearing 23
Are fixedly fitted in the housing 21. In each rolling bearing 23, each inner ring 25 is in contact with the inner ring spacer 27 and each outer ring 24 is in contact with the outer ring spacer 28.

The inner ring 25 of one of the rolling bearings 23 (to the right in the figure) is in contact with the shoulder portion of the main shaft 22 via the receiving member 29 on the side opposite to the side in contact with the inner ring spacer 27. . The outer ring 24 of the rolling bearing 23 is in contact with the first outer ring member 30 fitted to the receiving member 29 on the side opposite to the side in contact with the outer ring spacer 28. The inner and outer rings of the rolling bearing 23 have conductivity. Further, each of the plurality of rolling elements 26 of the rolling bearing 23 is made of conductive ceramic or metal and has conductivity, but at least one of the plurality of rolling elements 26 has conductivity. Good. The first outer ring member 30 is externally fitted and fixed to the shoulder portion of the main shaft 22.

The inner ring 25 of the other (left in the figure) rolling bearing 23 is in contact with the pressing member 31 on the side opposite to the side in contact with the inner ring spacer 27. The outer ring 24 of the rolling bearing 23 is in contact with the second outer ring member 32 fitted to the pressing member 31 on the side opposite to the side in contact with the outer ring spacer 28.
The pressing member 31 is a preload nut 3 screwed into the main shaft 22.
By 3, it is pressed in the axial direction to apply preload. The rolling bearing 23 on the left side of the drawing is provided even when the rotation of the main shaft 22 is stopped.
It is preferable that the inner ring 25 and the outer ring 24 are not electrically connected to each other. As the rolling bearing 23, for example, the main shaft 22
When a structure in which the inner ring 25 and the outer ring 24 are electrically connected to each other when the rotation is stopped is used, it is preferable to interpose an insulator between the inner ring 25 and the outer ring 24 so that the rolling bearing 23 does not electrically connect to the rolling bearing 23 on the right side in the drawing. good.

The preload measuring device 10 has a closed circuit in which a rolling bearing 23 on the right side in the figure, a DC power source 11, and a resistor 12 are connected in series. One end of the lead wire 13 forming the closed circuit is directly connected to the outer ring 24 of the rolling bearing 23. The other end of the conductive wire 13 is electrically connected to the inner ring 25 of the rolling bearing 23 via the connector 14 and the internal conductive wire 13 a in the main shaft 22. When the main shaft 22 rotates, the other end of the conducting wire 13 can be removed from the main shaft 22 by removing the connector 14 from the main shaft 22. Instead of using the connector 14, a connecting means such as a brush (for example, a carbon brush) is used, and the conductive wire 1 is used even when the main shaft 22 rotates.
It is also possible to avoid removing 3 from the main shaft 22. Although not shown, one end of the lead wire 13 may be detachably electrically connected to the outer ring of the rolling bearing 23 via the connector and the inner lead wire in the housing 21.

A voltmeter 15 is provided in the middle of the lead wire 13 in parallel with the DC power supply 11 and the resistor 12. The voltmeter 15 detects the potential difference between the outer ring 24 and the inner ring 25 of the rolling bearing 23 on the right side in the figure. In the present embodiment, the DC power supply 11, the resistor 12 and the voltmeter 15 constitute a detecting means. The voltage value Ve of the DC power supply 11
Can be appropriately set within a range of about 0.1 to 10V. Further, the resistance value of the resistor 12 can be appropriately set within the range of 1 kΩ to 1 MΩ.

The measured value Va of the voltmeter 15 is given to the controller 16 having a built-in calculating means, judging means and the like. Controller 1
In 6, the measured value Va of the voltmeter 15 is converted into a preload amount in real time by the calculation means. More specifically, the measured value Va of the voltmeter 15 is converted into a preload amount using a data table stored in advance in a storage means such as a ROM.

In order to obtain the data table to be stored in the storage means such as the ROM of the controller 16, the bearing preload measuring device 40 as shown in FIG. 1 is used, and the preload (axial load) and the bearing are applied to various bearings. It is also possible to create a data table by obtaining the relationship with the resistance value.

The measurement of the preload by the preload measuring device 10 will be described in detail below. First, the type and material of the rolling bearing 23 that supports the main shaft 22 is input to the controller 16 via an input means (not shown) so that the data table corresponding to the bearing 23 can be referred to. When the preload is zero, an oil film, which is an insulating material, is present between the outer ring raceway and the inner ring raceway of the rolling bearing 23 on the right side of the figure and the rolling surface of the rolling element 26, so that the outer ring 24 and the inner ring 25 are separated from each other. Has a high electric resistance, and the potential difference between the outer ring 24 and the inner ring 25 is high (close to the voltage of the DC power supply 11). When the preload nut 33 is screwed in and a preload is applied to the pair of rolling bearings 23, 23,
Is the rolling element 26 coming into strong contact with the inner ring raceway and the outer ring raceway, and is there an oil film between the outer raceway or inner ring raceway and the rolling surface of the rolling element 26 in the rolling bearing 23 on the right side in the drawing? Even if it exists, it will be insufficient. In such a state, the contact state between the outer ring raceway and the inner ring raceway and the rolling surface of the rolling element 26 becomes a metal-metal contact state, and the outer ring 24
The electric resistance between the inner ring 25 and the inner ring 25 decreases, and the potential difference between the outer ring 24 and the inner ring 25 decreases. Therefore, the measured value Va of the voltmeter 15 becomes lower than the voltage Ve of the DC power supply 11.

The calculation means of the controller 16 refers to the data table and converts the measured value Va of the voltmeter 15 into a preload amount in real time. The determination means of the controller 16 is the voltmeter 1
When the amount of preload converted from the measured value Va of 5 exceeds the range of the predetermined threshold, it is determined that the load is abnormal preload, and the alarm device is activated.

FIG. 4 is a flow chart for explaining the control operation of the judging means in the preload measuring device 10. First,
The preload is sampled (S101). Here, the preload amount data X is calculated by the calculation means of the controller 16.
(N) is obtained. Next, the determination means determines whether the preload amount data X (n) is within the range between the upper limit threshold C and the lower limit threshold D (S102). Then, if the preload amount data X (n) is within the range between the upper limit threshold value C and the lower limit threshold value D, the preload load is sampled again (S101). If the preload amount data X (n) is out of the range between the upper limit threshold value C and the lower limit threshold value D, that is, the preload amount data X (n) exceeds the upper limit threshold value C,
If the preload amount data X (n) is below the lower limit threshold D, the alarm device is activated as a preload abnormal load (S1).
03). A lamp, a siren, or the like is used as the alarm device.

FIG. 5 shows a state in which the bearing preload measuring device 70 according to the third embodiment of the present invention is incorporated in the spindle device 20. Preload measuring device 70 of the present embodiment
Has a closed circuit in which the DC power supply 11 and the ammeter 75 are connected in series with each other. One end of the lead wire 13 forming the closed circuit is directly connected to the outer ring 24 of the rolling bearing 23. The other end of the lead wire 13 has a connector 14 and a spindle 2.
The inner ring 2 of the rolling bearing 23 via the inner conductor 13a in
5 is electrically connected. The ammeter 75 is the outer ring 24
And the current flowing between the inner ring 25 is detected.

The measured value A of the ammeter 75 is given to the controller 16 having a built-in calculating means, judging means and the like. Controller 16
Then, the measurement value A of the ammeter 75 is converted into a preload amount in real time by the calculating means. For details, see RO in advance.
Using the data table stored in the storage means such as M, the measured value A of the ammeter 75 is converted into the preload amount. When the preload nut 33 is screwed in and the preload is applied to the pair of rolling bearings 23, 23, the current flowing between the outer ring 24 and the inner ring 25 of the rolling bearing 23 on the right side in the drawing increases. That is, the difference (current difference) between the measured value of the ammeter 75 before the preload is applied and the measured value of the ammeter 75 after the preload is started becomes large. The determination means of the controller 16 is
When the amount of preload converted from the measured value A of the ammeter 75 exceeds the range of the predetermined threshold, it is determined that the load is abnormal preload, and the alarm device is activated.

The present invention is not limited to the above-described embodiment, but can be appropriately modified and improved. For example, a bearing other than an angular contact ball bearing may be used. The bearing preload measuring device 10 may be detachably incorporated in the spindle device 20, and when the preload setting in one spindle device 20 is completed, the preload measuring device 10 is removed to replace the preload measuring device 10 with another. It may be incorporated into the spindle device.

[0028]

As described above, according to the present invention,
By accurately and directly measuring the load applied to the rolling element as the preload applied to the bearing, it is possible to manage the preload with high precision and prevent seizure or wear of the bearing.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a bearing preload measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between axial load and bearing resistance.

FIG. 3 is a sectional view of a spindle device to which an embodiment of the present invention is applied and a circuit configuration diagram of a preload measuring device.

FIG. 4 is a flowchart illustrating a control operation of a determination unit in the preload measuring device.

FIG. 5 is a cross-sectional view of a spindle device to which an embodiment of the present invention is applied and a circuit configuration diagram of a preload measuring device.

[Explanation of symbols]

10, 40, 70 Preload measuring device 15 Voltmeter (detection means) 20 Spindle device 23,50 rolling bearings 24,51 outer ring 25,52 inner ring 26,53 rolling elements 45 tester (detection means) 75 Ammeter (detection means)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Morita             1-5-50 Kumei, Kugenuma, Fujisawa-shi, Kanagawa             Within NSK Ltd. F term (reference) 3C048 BB14                 3J012 AB02 AB20 BB03 CB06 FB10                       GB10 HB02                 3J101 AA02 AA42 AA54 AA62 BA10                       EA41 EA72 FA41 GA31

Claims (6)

[Claims] 1. A method for measuring a preload amount of a rolling bearing in which a plurality of rolling elements are arranged between an inner ring and an outer ring, wherein the rolling bearing has an electrically conductive outer ring or is electrically connected to the outer ring. Preload measuring method for a bearing, characterized in that the amount of preload is obtained based on an electrical characteristic value between a member that is electrically conductive and the inner ring having conductivity of the rolling bearing or a member that is electrically connected to the inner ring. . 2. At least one of the rolling elements has conductivity, and the electrical characteristic value is a resistance value or a potential difference or a current difference that changes based on the resistance value. The resistance value or the potential difference or The method for measuring preload of a bearing according to claim 1, wherein the preload amount is appropriate when the current difference is within a predetermined range. 3. The bearing preload measuring method according to claim 1, wherein the rolling element is made of semi-conductive ceramic. 4. A device for measuring a preload amount of a rolling bearing in which a plurality of rolling elements are arranged between an inner ring and an outer ring, the electrically conductive outer ring of the rolling bearing or being electrically connected to the outer ring. Detecting means for detecting an electric characteristic value between a member having a conductive inner ring or a member electrically connected to the inner ring, and a calculating means for converting a detection result of the detecting means into a preload amount. A bearing preload measuring device comprising: 5. The bearing preload measuring device according to claim 4, further comprising a determination means for notifying the outside when the amount of preload is inappropriate. 6. A spindle device in which the bearing preload measuring device according to claim 4 or 5 is incorporated.