JPH1043909A - Rotary body driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively prevent seizure and a release of a preload of a bearing. SOLUTION: This device is constituted so as to have a spindle 1 inserted into a housing 6, back face type multi-row combination angular ball bearings 3a to 3d which are interposed by four rows in the shaft direction of the spindle 1 between the housing 6 and the spindle 1 and rotatably support the spindle 1 and a driving motor M which is enclosed in the housing 6 and drives the spindle 1 in rotation. In this case, both a ball 15 of the bearing 3d arranged in a position closest to the driving motor M in the four-row angular ball bearings 3a to 3d and a ball 15 of the bearing 3c whose contact angle direction is the same as the bearing 3d are made of ceramics, and balls 15 of its other bearings 3a and 3b are made of bearing steel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotating body driving device incorporating a multi-row combination rolling bearing, for example, a spindle device for a machine tool.

[0002]

2. Description of the Related Art A multi-row combination ball bearing incorporated in a spindle device for a machine tool requires characteristics such as high rigidity, high rotational accuracy, and low heat generation in order to improve machining accuracy.
In recent years, in order to improve the processing efficiency of a workpiece, high-speed rotation (that can be used stably at a high rotation speed for a long time) is required.

In order to secure such characteristics, for example, high rigidity and high rotational accuracy, the internal clearance of the ball bearing is set to "0" or less at the time of assembling the bearing (the ball (rolling element) and the bearing ring are elastically deformed inside the bearing). And the preload is applied). Considering that ball bearings for general industrial machinery are often used so that the internal clearance of the bearing remains during operation from the viewpoint of prolonging the peeling life and suppressing the deterioration of the bearing function due to disturbance, such a bearing is considered. When the internal clearance at the time of assembly is "0" or less, it can be said that the use of the bearing is a severe condition in which internal parts are liable to be worn or seized.

[0004] As a method of applying a preload, a so-called constant pressure preload in which a load is applied in the axial direction by a spring, and a plurality of bearings in which the dimensions of the bearing race are adjusted in advance in the axial direction are fixed. There is a so-called fixed position preload in which the (contact portion between the bearing ring and the ball) is elastically deformed, but a fixed position preload is often used for a ball bearing incorporated in a spindle device for a machine tool. This is because the rigidity of the bearing can be further improved when the preload is in the fixed position, but it also has a drawback that when the preload is large and the speed is high, abnormal temperature rise or seizure easily occurs during operation.

Further, in the spindle device, the number of rows of bearings is increased to three or more in order to further increase the rigidity. In order to increase the bending stiffness of the spindle, the combination of the bearings is changed to a back type. May be inserted to increase the distance between action points.

[0006]

By the way, the rotary drive of the spindle has been performed by transmitting the power of the external drive source to the spindle via a transmission mechanism such as a belt, a gear, and a coupling. Recently, the so-called drive motor built-in type spindle device in which the drive motor is incorporated in the housing of the spindle device has been increasing due to a problem that a high speed operation is difficult to be realized due to a problem due to a loss in a mechanism or a decrease in rotation accuracy. is there.

However, in such a spindle device with a built-in drive motor, a spindle device of a type that transmits the power of an external drive source to a spindle via a transmission mechanism such as a belt (hereinafter referred to as an “external drive spindle device”). However, when used at the maximum rotational speed or the degree of preload (preload load) where no problem occurs, there is an inconvenience that seizure of the bearing occurs with a relatively high probability.

Here, the present inventors have conducted intensive studies and analyzed the mechanism of the occurrence of such image sticking.
During operation under high load, the heat generated by the drive motor becomes larger than expected, the temperature distribution in the axial direction of the spindle becomes uneven, and the temperature near the drive motor is high and the temperature at the shaft end is relatively low. It has been found that an equilibrium state is likely to occur, and it has been found that this phenomenon has a great effect on the seizure occurrence probability of the bearing.

That is, due to the temperature gradient in the axial direction of the spindle, the temperature difference between the inner and outer rings in each row of the bearings (difference of the inner ring temperature with respect to the outer ring temperature: the temperature on the inner ring side is usually higher) and the bearing near the drive motor ( Hereinafter, a difference between the inner bearing and the bearing on the shaft end side (hereinafter referred to as an “outer bearing”) tends to occur, and the difference is larger than that of the above-described externally driven spindle device. .

As a result, the contact angle of the inner bearing is reduced due to thermal expansion, and the axial load capacity of the inner bearing is smaller than that of the outer bearing. The increase in the preload during operation increases the contact surface pressure of the inner bearing. Centrifugal force acts on the ball for high-speed operation, and the contact surface pressure of the inner bearing is more likely to increase. The increase in the contact surface pressure makes it difficult for a lubricating oil film to be formed on the inner bearing.

According to the above, finally, the inner bearing is seized. It is known that all the balls of the bearing row are made of ceramics, thereby making it less susceptible to the influence of temperature and centrifugal force at the time of operation so that the operation can be performed stably even at an ultra-high speed. If the balls of all the bearing rows are made of ceramic as described above, the preload increase during operation becomes too small, and preload loss easily occurs when an external axial load is applied during operation. Not only causes a decrease in rigidity and machining accuracy, but also causes abnormal vibration and abnormal noise.Furthermore, since ceramic balls are more expensive than bearing steel balls, equipment costs are reduced. It also causes soaring.

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a disadvantage, and an object of the present invention is to provide a rotating body driving device capable of preventing seizure of a bearing and loss of preload at low cost.

[0013]

In order to achieve the above object, a rotating body driving device according to the present invention comprises a rotating body inserted into a housing, and a rotating body disposed between the housing and the rotating body. A rotating body driving device including a back-type multi-row combination rolling bearing interposed in a plurality of rows in the axial direction and rotatably supporting the rotating body, and a drive motor built in the housing and configured to rotationally drive the rotating body. Of the plurality of rolling bearings constituting the back-type multi-row combination rolling bearing, a rolling element of a rolling bearing arranged at a position closest to the drive motor and a rolling bearing having the same contact angle direction as the rolling bearing. The rolling elements are made of ceramics, and the rolling elements of other rolling bearings are made of bearing steel.

Here, among the plurality of rolling bearings constituting the multi-row combination rolling bearing, the rolling bearing disposed closest to the drive motor and the rolling bearing having the same contact angle as the rolling bearing are disposed inside the rolling bearing. Bearings and other rolling bearings are outer bearings.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory sectional view for explaining a spindle device with a built-in drive motor which is an example of an embodiment of the present invention.

First, the structure of a spindle device with a built-in drive motor will be described. A spindle (rotating body) 1 of the spindle device is inserted through a housing 2 and has a front end (left end) having a plurality of axial ends. Angular contact ball bearings 3a to 3d arranged in rows (four rows in the figure) have rear ends (right ends)
Are rotatably supported horizontally by a row of cylindrical roller bearings 4. The housing 2 includes a housing main body 6 including an outer cylinder 5a and an inner cylinder 5b, a front cover 7 fixed to a front end of the housing main body 6, and a bearing support member 8a and an outer ring pressing member at a rear end of the housing main body 6. 8b. In the drawing, reference numeral 2a is a coolant passage formed between the outer cylinder 5a and the inner cylinder 5b.

A rotor 10 of a built-in motor M is fixed to an outer peripheral surface of a central portion of the spindle 1 by interference fit. A stator 11 coaxially arranged on the rotor 10 so as to oppose the peripheral surface thereof has a housing body 6. Is fixed to the inner peripheral surface of the. The front end surface of the spindle 1 has a taper hole 12 for mounting a tool whose diameter gradually decreases toward the rear end side.
A shaft hole 13 is formed along the axis of the spindle 1 so as to extend from the back of the shaft 2 to the rear end of the spindle 1. Taper hole 1
2, a taper shank portion (not shown) of a tool holder for holding a tool is fitted.

Of the four rows of angular contact ball bearings 3a to 3d that support the front end of the spindle 1, two front rows of angular contact ball bearings 3a, 3b and two rear rows of angular contact ball bearings 3c, 3c near the motor M. 3d between the outer and inner spacer 14a,
14b, and the angular contact ball bearing 3
a, 3b and the angular contact ball bearings 3c, 3d are a back-to-back combination.

In this embodiment, two rear rows of angular contact ball bearings 3d near the motor M (rolling bearings arranged closest to the drive motor) and 3c (directions of contact angles with the rolling bearings) are provided. Are the same rolling bearings), each ball (rolling element) 15 is formed of a material mainly composed of, for example, silicon nitride ceramics Si ₃ N ₄ having a smaller coefficient of thermal expansion and a lower density than the bearing steel, and has two rows on the front side. Angular contact ball bearing 3
The balls 15 of a and 3b (other rolling bearings) are formed of ordinary bearing steel.

Here, the rear two rows of angular ball bearings 3c and 3d near the motor M are referred to as inner bearings A, and the front two rows of angular ball bearings 3a and 3b are referred to as outer bearings B. In addition, the outer and inner rings 16a of the frontmost angular contact ball bearing 3a,
16b is pressed by an outer ring pressing member 17 provided on the inner peripheral portion of the inner cylinder 5b and a nut 18 screwed to the outer peripheral portion of the spindle 1, and the outer inner rings 16a, 16b of the rearmost angular contact ball bearing 3d are Each is received by a step 21 formed on the inner periphery of the inner cylinder 5b and a step 22 formed on the outer periphery of the spindle 1.

On the other hand, the outer ring 23a of the cylindrical roller bearing 4 that supports the rear end of the spindle 1 has a front side bearing support member 8a.
And the rear surface is pressed by the outer ring pressing member 8b. The inner ring 23b of the cylindrical roller bearing 4 has its front side face received by a step portion 20 formed on the outer peripheral portion of the spindle 1, and
Nut 25 whose rear surface is screwed to the outer periphery of spindle 1
Is held down by In the figure, reference numeral 26 is used.
Are between the front lid 7 and the nut 18, and between the rear lid 9 and the nut 25.
And seal members provided between the two.

Next, such a drive motor built-in type spindle
The operation and effect of the device will be described with reference to Tables 1 and 2. What
Each ball of the inner bearing A of the above embodiment as an example of the present invention.
15 is smaller in thermal expansion coefficient and density than bearing steel
Silicon nitride ceramics Si _ThreeN_FourThe main ingredient is
Using the formed one, the conventional example 1
Each ball 15 of the inner bearing A is formed of normal bearing steel.
Using. Table 1 shows the operation of the outer bearing B and the inner bearing A of the present invention.
Rotational preload and the outer bearing B and inner bearing A of Conventional Example 1
The results of trial calculation of the operating preload are shown below. Trial calculation
The matter is as follows for both the present invention example and the conventional example 1. Table 2
Ceramics Si_ThreeN_FourAnd the material properties of the bearing steel are shown.

Bearing JIS number: 7014C Rotation speed: dm · n (product of ball pitch circle diameter (mm) and rotation speed (1 / min)) = 800000 (mm / mi)
n) equivalent Outer ring temperature: 20 ° C rise from room temperature Inner / outer ring temperature difference: Outer bearing B 3 ° C, inner bearing A 10
° C Preload method: Fixed position preload Preload load (at the time of assembly): 15kgf ... Equivalent to slight preload Lubrication method: Grease lubrication

[0024]

[Table 1]

[0025]

[Table 2]

As is evident from Table 1, in the example of the present invention in which each ball 15 of the inner bearing A is made of ceramics having a smaller coefficient of thermal expansion and a lower density than the bearing steel, the preload during operation is lower than that of the conventional example 1. As a result, during high-speed operation, the inner bearing A
Even if the temperature difference between the inner and outer rings of the inner bearing A is larger than that of the outer bearing B, the decrease in the contact angle of the inner bearing A is suppressed well, the axial load capacity of the inner bearing A is reduced, and the contact surface pressure between the ball and the raceway surface is reduced. It can be seen that the increase in the image quality can be suppressed and the possibility of image sticking can be reduced.

Further, by using ceramic balls having a density lower than that of the bearing steel for the inner bearing A, the weight of the balls of the inner bearing A is reduced as compared with the conventional example 1 so that the centrifugal force acting on the balls during high-speed operation is reduced. It is less likely to be affected, and as a result, an increase in the contact surface pressure can be further suppressed.

However, if the speed becomes higher than the above speed condition, the effect of the centrifugal force acting on the ball becomes large,
In particular, the operating conditions of the outer bearing B (using balls made of bearing steel) become severe. Therefore, in the above embodiment, the maximum rotation speed is dm · n (the product of the pitch circle diameter of the ball and the rotation speed) 500000 to 1,000,000 (mm / min).
The degree is preferable, and 650000 to 800000 (mm
/ Min) is more preferred.

By the way, as an ultra-high speed spindle device,
It is known that the balls of all bearing rows (inner bearing A and outer bearing B) are made of ceramics. This is used at a higher speed than the spindle device of the present invention, is less susceptible to temperature and centrifugal force during operation than the conventional example 1 and the present invention, and can be operated stably even at ultra high speed. .

However, as is evident from Table 1, the increase in the preload during operation is smaller in bearings using ceramic balls than in bearings using bearing steel balls. Although this is effective in preventing seizure due to an excessive increase in preload, it can be said that preload loss easily occurs when an external axial load is applied during operation. If the preload is lost during operation, the rigidity of the spindle is significantly reduced, which causes not only a decrease in machining accuracy but also causes abnormal vibration and abnormal noise.

Table 3 shows the results of a trial calculation of the external load at which the preload loss due to the ball material occurs. Table 3 shows the results of trial calculations of the preload during operation and the preload release load of the inner and outer bearings A and B of the present invention and the preload during operation and the preload release load of the inner and outer bearings A and B of Conventional Example 2, respectively. Show. The trial calculation conditions are the same as those in Table 1 for both the present invention example and the conventional example 2. In the second conventional example, each of the balls 15 of the inner bearing A and the outer bearing B of the above embodiment has a silicon nitride ceramic Si ₃ having a smaller coefficient of thermal expansion and a lower density than the bearing steel.
A material formed of a material mainly containing N ₄ was used.

[0032]

[Table 3]

As is clear from Table 3, in the example of the present invention which is used at the above-described maximum rotational speed, an appropriate preload is applied at the time of operation. Therefore, when an external axial load is applied during operation, preload loss is unlikely to occur, and the preload is not excessively increased as the possibility of seizure increases. Further, although ceramic balls are considerably more expensive than bearing steel balls, the present invention uses ceramic balls only for the inner bearing A, so that the cost of the apparatus can be reduced as compared with the conventional example 2. Can be planned.

In the above calculation conditions, the bearing specifications are the same except for the ball material. However, the contact angle, ball size, number of balls, and the like between the outer bearing B and the inner bearing A may differ depending on the use conditions. The number of rows of the outer bearing B and the number of rows of the inner bearing A may be arbitrarily increased or decreased according to the magnitude of a load applied from the outside during use.

Further, in this embodiment, a back-type four-row combination angular contact ball bearing is used, and bearing spacers 14a and 14b are arranged between the inner bearing A and the outer bearing B so as to increase the bending rigidity of the spindle 1. ing. Also, an appropriate amount of grease is applied to the inside of these bearings A and B, and a lubricating oil film is formed on the contact surface between the ball and the race. With such a structure, the temperature difference between the inner bearing A and the outer bearing B tends to be large, and the effect of the present invention is remarkably exhibited.

The above-described angular ball bearing uses a cage (not shown) for uniformly arranging the balls in the circumferential direction, in addition to the balls and the bearing rings. This retainer is usually injection-molded with a thermoplastic resin such as a polyamide resin to which an appropriate amount (10 to 30% by weight) of glass fiber or the like is added, or a thermosetting resin such as a phenol resin using a cotton cloth or the like as a base material. It is manufactured by cutting a conductive resin. In addition, in addition to the above-mentioned resin-based materials, a copper alloy may be manufactured by cutting. These cages are rotationally guided by races or balls.

[0037]

As is apparent from the above description, according to the present invention, it is possible to prevent the internal bearing from seizing due to the heat generated by the heat generated by the built-in drive motor at the time of high-speed operation, and to prevent the external axial during operation. Preload loss can be prevented when a load is applied.Moreover, expensive ceramic rolling elements are used only for the inner bearings. Cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view for explaining a spindle device with a built-in drive motor which is an example of an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Spindle (rotating body) 3a-3d ... Angular contact ball bearing (Back type multi-row combination rolling bearing) 3c ... Angular contact ball bearing (Rolling bearing whose contact angle direction is the same as that of the rolling bearing 3d) 3d ... Angular contact ball bearing 3a, 3b ... angular ball bearings (other rolling bearings) 6 ... housing 15 ... balls (rolling elements) M ... drive motor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuto Nakamura 3-2-1 Gion, Asaminami-ku, Hiroshima-shi, Hiroshima Mitsubishi Heavy Industries, Ltd. Hiroshima Koki Plant Hiroshima Koki Factory, Mitsubishi Heavy Industries, Ltd. 3-2-1 Gion, Asaminami-ku

Claims (1)

[Claims] A rotating body inserted into a housing; a back-type multi-row combination interposed between the housing and the rotating body in a plurality of rows in an axial direction of the rotating body to rotatably support the rotating body; A rotating body driving device comprising: a rolling bearing; and a drive motor built in the housing and configured to rotationally drive the rotating body, wherein the drive motor includes a plurality of rolling bearings constituting the back-type multi-row combination rolling bearing. The rolling element of the rolling bearing arranged closest to the rolling element and the rolling element of the rolling bearing having the same contact angle direction as the rolling bearing are made of ceramics, and the rolling elements of the other rolling bearings are made of bearing steel. Characteristic rotating body driving device.