JPH0751904A - Pre-load adjusting device for spindle bearing - Google Patents

Abstract

PURPOSE:To provide a pre-load adjusting device enabling an optimum pre-load to be automatically applied to the bearing according to an increase in the rotation of a main spindle without using additional equipment such as oil pressure. CONSTITUTION:Within a bearing box 3, a pre-load adjusting sleeve 8 for pressing a bearing 6, a compression coil spring 9 for urging the sleeve 8, and a sleeve stopper 10 are provided. During a low-speed rotation, the sleeve 8 is pressed against the stopper 10 by the spring force of the coil spring 9 to apply an initial pre-load that is a normal-position pre-load. When the rotation of a main spindle exceeds a predetermined speed, the sleeve 8 is pushed back by the increased in-bearing pressure to move the sleeve 8 away from the stopper, thereby a constant level of pre-load is applied by the spring force of the coil spring 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preload adjusting device for automatically changing the preload amount of a spindle bearing such as a machine tool spindle in accordance with a change in the spindle rotational speed.

[0002]

2. Description of the Related Art In a machine tool spindle that uses an angular contact ball bearing as a main shaft bearing, the pressure inside the bearing changes due to a change in the rotational speed of the main shaft, and the rotation speed increases. Since the preload increases, it is necessary to adjust the preload during operation so that the bearing preload does not become excessive.

As a method of adjusting such a preload, conventionally,
By adjusting the plane difference between the inner ring and the outer ring of the bearing, the initial preload is set so that the optimum preload is achieved at the maximum speed of the spindle (constant position preload method), and a constant preload is always applied to the bearing by using spring force, etc. There is a method of giving (constant pressure preload method).

However, in the fixed position preloading method, the rigidity of the main shaft certainly increases, but in order to achieve the optimum preloading at the maximum operating speed, it is necessary to reduce the initial preloading by the amount of increase in preloading due to the increase in rotation. . For this reason, the preload may be remarkably reduced at low speed, and there is a drawback that the rotation range used is limited.

On the other hand, the constant pressure preloading method is suitable for increasing the speed of the spindle, but has a problem that the rigidity of the spindle cannot be set as large as that of the constant position preloading method.

To solve the problems of the conventional method, for example, JP-A-62-124805 and JP-A-2-279.
In Japanese Patent Publication No. 203, etc., there is proposed a device for gradually changing the bearing preload to a preload suitable for the rotational speed during operation or before operation by controlling hydraulic pressure.

However, in the proposed switching device, control for switching the preload during or before the operation is required, so that the control structure of the spindle tends to be complicated, and in the stepwise preload switching, the preload is switched during the operation. There is a problem that a sudden change in preload occurs.

[0008] In addition, since auxiliary equipment such as a hydraulic pressure source for switching the preload, the outer cylinder of the spindle, and the inside of the bearing box are required to have a space for providing a pipeline for introducing hydraulic pressure and machining of the pipeline, There is also a problem that the device becomes large and the manufacturing cost rises.

In view of the above, the present invention solves the above-mentioned problems and enables automatic preload adjustment without the use of auxiliary equipment such as hydraulic pressure, high speed rotation, and high spindle rigidity in the low speed range. It is an object of the present invention to provide a preload adjusting device for a spindle bearing capable of achieving the above.

[0010]

In order to solve the above problems, the present invention is directed to a preload adjusting sleeve for axially pressing a bearing supporting a main shaft and a preload adjusting sleeve for increasing the preload of the bearing. It consists of an elastic member for urging and a stopper that stops the movement of the preload adjusting sleeve in the direction of increasing the preload of the bearing at an arbitrary position, and the urging force of the elastic member rotates the main shaft at a predetermined rotation speed or more. At times, the pressure was set to be lower than the pressure generated inside the bearing.

[0011]

In the above structure, when the main shaft is in operation, the preload adjusting sleeve moves to the position where it comes into contact with the stopper by the urging force of the elastic member, and the preload adjusting sleeve presses the initial preload of the fixed position preload on the bearing. Join.

On the other hand, when the main shaft rotates over a predetermined number of rotations, the increasing pressure inside the bearing causes the elastic member to contract, the preload adjusting sleeve and the stopper are separated, and a constant pressure preload is applied to the bearing by the urging force of the elastic member. .

As described above, the bearing preload is automatically switched to the fixed position preload at low speed and to the constant pressure preload at high speed according to the change of the preload of the bearing accompanying the rotation of the main shaft. Preload can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 and 2, 1 is a main shaft, 2 is an outer cylinder, 3 is a bearing box incorporated inside the outer cylinder 2, and both end portions of the main shaft 1 are angular contact ball bearings 4 arranged in pairs, respectively. It is rotatably supported inside the bearing box 3 via 5 and 6 and 7.

The angular ball bearings 4, 5 and 6, 7 are assembled in a parallel rear face combination, and the bearings 4, 5 arranged on the work mounting side of the main shaft 1 are axially arranged with respect to the bearing housing 3. It is fixed to.

On the other hand, the bearings 6 and 7 on the side opposite to the work mounting side are equipped with a preload adjusting device A for varying the bearing preload between the bearings 6 and 7 and the inner diameter surface of the bearing housing 3.

The preload adjusting device A comprises a preload adjusting sleeve 8, a compression coil spring 9 as an elastic member, and a sleeve stopper 10.
Are fixed to the stopper fixing plate 11 press-fitted inside the bearing box 3 with bolts 12.

The preload adjusting sleeve 8 can be slid in the bearing box 3 in the axial direction with an extremely small force by a ball slide bearing 13 incorporated between the outer diameter surface of the sleeve and the bearing box 3. And the spacer 14 on the inner diameter surface side.
Angular contact ball bearings 6 and 7 are fitted to each other via. The spacer 14 is incorporated between the step portion 15 provided on the inner diameter surface of the preload adjusting sleeve 8 and the outer ring end surface of the bearing 6, and presses the outer ring of the bearing 6 when the sleeve 8 moves in the axial direction. As a result, the outer rings of the bearings 6 and 7 move relative to the inner ring to change the bearing clearance, and the preload of the bearings 6 and 7 changes.

The compression coil spring 9 is incorporated between the end surface of the preload adjusting sleeve 8 and the end surface of the stopper fixing plate 11,
The elastic force biases the preload adjusting sleeve 8 in the direction in which the preload of the bearings 6 and 7 increases.

The step portion 1 corresponding to the step portion 16 of the preload adjusting sleeve 8 is formed on the outer diameter surface of the sleeve stopper 10.
7 is provided, and by the contact between the step portions 16 and 17,
The movement of the sleeve 8 in the direction in which the preload of the bearings 6 and 7 increases is stopped at a predetermined position, and the movement of the sleeve 8 in the opposite direction is allowed.

Here, the position of the sleeve stopper 10 and
The magnitude of the spring force Fs of the compression coil spring 9 is such that when the preload adjusting sleeve 8 comes into contact with the sleeve stopper 10 and stops as shown in FIG. 2, a bearing clearance δ is created between the inner ring of the bearing 6 and the outer shaft. The spring force Fs is set to be larger than the initial preload Fb _{0 of the} bearing 6 caused by the bearing clearance δ (Fs> Fb ₀ ).

The spring force Fs of the compression coil spring 9 is
Bearings 6 and 7 when the main shaft 1 rotates at a predetermined rotation speed n _1.
Is equal to the bearing preload Fb ₁ (Fs = Fb ₁ ), and is smaller than the pressure generated inside the bearings 6 and 7 when the main shaft 1 rotates at a rotation speed n ₁ or higher.

The passage 18 provided in the bearing housing 3 in FIG. 1 is a supply passage for supplying each bearing lubricating oil from the spacer.

This embodiment has the structure as described above,
When the main shaft 1 is stopped, the preload adjusting sleeve 8 is moved by the spring force Fs of the compression coil spring 9 until it comes into contact with the step portion 17 of the sleeve stopper 10 as shown in FIG.
The bearings 6 and 8 are loaded with an initial preload Fb ₀ by the bearing clearance δ (see FIG. 4).

In this case, since the relationship of Fs> Fb _{0 is} satisfied, the position of the sleeve 8 is held constant, and the bearing is in the state of constant position preload. This initial preload Fb ₀ can be arbitrarily adjusted by changing the position of the sleeve stopper 10 and changing the plane difference between the inner and outer rings of the bearings 6, 7.

The spindle 1 rotates, and the number of revolutions is the set number of revolutions n.
_In the range until reaching ₁ the bearing preload Fb gradually increases due to the pressure inside the bearings 6 and 7 which increases in proportion to the increase in rotation of the main shaft.

When the rotational speed of the main shaft 1 reaches the set rotational speed n ₁ , the spring force Fs and the bearing preload Fb are balanced, and when the main shaft rotation further rises from that point, the preload adjusting sleeve 8 is moved as shown in FIG. When pushed back, the compression coil spring 9 is deformed in the contracting direction. As a result, a gap is created between the sleeve 8 and the sleeve stopper 10, so that the compression coil spring 9
The spring force Fs itself becomes the bearing preload, and becomes the constant pressure preload state.

This constant pressure preload (Fb ₁ = Fs) needs to be set lower than the upper limit allowable value of the preload, and in actuality, it does not cause gyro-slip on the rolling elements of the bearing at the maximum rotation speed n ₂ of the main shaft. Set between the preload required for and the upper limit determined by bearing life.

As described above, when the apparatus of the embodiment is used, a constant position preload can be obtained at a low speed where the spindle rigidity is required, and the constant pressure preload can be automatically changed to a high speed direction as the rotation speed increases. Therefore, it is possible to obtain the optimum bearing preload corresponding to the rotation of the main shaft.

FIG. 5 shows changes in preload when the bearing preload is changed in multiple stages during the operation of the main shaft by using the conventional preload switching type device.

Comparing FIG. 5 with FIG. 4, in the conventional switching system, the preload changes abruptly during the operation of the spindle, and the rigidity of the spindle also changes greatly at that time. Since the adjusting device smoothly changes from the fixed position preload to the constant pressure preload without causing a rapid change in preload, there is no sudden change in the spindle rigidity, and stable spindle operation can be performed.

[0032]

[Effects] With the above-described structure, the present invention can achieve the following effects.

(1) As the main spindle rotation speed increases, the position automatically shifts to the constant position preload at low speed and to the constant pressure preload at high speed.
Control such as preload switching becomes unnecessary, and the control structure and control operation can be simplified.

(2) Since the fixed position preload is switched to the constant pressure preload without using hydraulic pressure, auxiliary equipment such as a hydraulic pressure source and hydraulic lines in the bearing box are not required, and the apparatus is made compact and manufactured. The cost can be reduced.

(3) Since there is no abrupt preload change during the spindle operation and the preload state changes smoothly, there is no abrupt change in the spindle rigidity, and a stable operating state can be maintained.

(4) Since the structure is simple and the number of parts is small,
The device can be unitized and easily installed inside the spindle.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment.

FIG. 2 is an enlarged sectional view of the main part of the above.

FIG. 3 is a sectional view showing an operating state of the above.

FIG. 4 is a chart showing a change in preload of an example.

FIG. 5 is a chart showing changes in preload of a conventional example.

[Explanation of symbols]

 1 Spindle 2 Outer Cylinder 3 Bearing Box 4, 5, 6, 7 Angular Contact Ball Bearing 8 Preload Adjusting Sleeve 9 Compression Coil Spring 10 Sleeve Stopper 11 Stopper Fixing Plate 13 Ball Slide Bearing

Claims (1)

[Claims] 1. A preload adjusting sleeve for axially pressing a bearing supporting a main shaft, an elastic member for urging the preload adjusting sleeve in a direction in which the preload of the bearing increases, and a direction in which the preload of the bearing increases. The spindle bearing, which comprises a stopper that stops the movement of the preload adjusting sleeve at an arbitrary position, and is set so that the urging force of the elastic member is smaller than the pressure generated inside the bearing when the main shaft rotates at a predetermined rotation speed or more. Preload adjusting device.