JP2000035036A - Preload adjusting method for spindle unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preload adjusting method for switching preload to be applied to a spindle unit to the maximum condition, in accordance with the rotation frequency of a main spindle and a thrust load. SOLUTION: A main spindle is supported by angular ball bearings 3 and 7 arranged with their back surfaces facing with each other. An inner spacer 11 is arranged between the inner races 4 and 8 of both the bearings, and an outer spacer 12, fitting with the inner peripheral surface of a casing 2, is arranged between the outer races 6 and 10 of both the bearings. The outer spacer 12 has a groove 23 formed in a circumferential direction on an outer surface thereof, and grooves 22a, 23b formed in a circumferential direction adjacent to the groove 23. On an outer side of outer races 6, 10, ring-shaped hydraulic piston 24, 25 are arranged. Pressure inside an oil chamber formed by the groove 23 and inner peripheral surface of the casing 2 and pressure inside oil chamber 18, 19 of the hydraulic piston 24, 26 are both of them regulated simultaneously, switching of preload of angular ball bearing can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a preload of a spindle unit used in a machine tool or the like, and more particularly to a spindle capable of coping with a wide range of cutting conditions from low-speed heavy cutting to high-speed light cutting. The present invention relates to a method for adjusting a preload of a unit.

[0002]

2. Description of the Related Art In order to support a thrust load in a spindle unit, a spindle is usually supported by a plurality of angular ball bearings arranged on the back. It is common practice to apply axial preload to angular contact ball bearings in order to increase the rotational speed and rigidity of these angular contact ball bearings, or to prevent vibration and noise of the spindle. I have.

As a method of giving a preload, there are a fixed position preload and a constant pressure preload. Generally, a fixed position preload is used for cutting. In the case of fixed-position preload, a thrust load generated inside the angular ball bearing due to centrifugal force during high-speed rotation results in heavy preload, and there is a possibility that seizure may occur in the angular ball bearing due to a rise in temperature.
On the other hand, the constant pressure preload has a low rigidity and is difficult to use for cutting work that needs to support a large thrust load, and is therefore mainly used for high-speed light cutting.

[0004] In order to respond to the demand for increasing the speed of the spindle of a machine tool or realizing a wide range of machining conditions, cutting (or grinding) from a low speed to an ultra-high speed is performed using one spindle. A method of switching the preload applied to the angular contact ball bearing at a predetermined rotation speed is adopted.

For example, Japanese Unexamined Patent Publication No. Sho 60-139911 discloses that an outer race spacer disposed between outer races of front and rear angular ball bearings arranged in a rear surface is formed in a shape which is easily elastically deformed, and one outer race is formed. A structure is described in which a ring-shaped hydraulic piston is disposed outside of the outer ring, and the preload is switched by driving the hydraulic piston to deform the outer ring spacer.

In such a structure, when the outer race spacer is elastically deformed, the parallelism of the spacer end surface in contact with the outer race of the adjacent front and rear angular ball bearings becomes poor, and the contact between the outer race end surface of the angular ball bearing is reduced. It may be worse.

FIG. 2 shows another example of a conventional spindle unit. In the figure, 1 is a main shaft, 2 is a casing, 3 and 7
Denotes an angular ball bearing, 4 and 8 denote an inner race of the angular ball bearing, 6 and 10 denote an outer race of the angular ball bearing, and 11 denotes an inner spacer. A tool (not shown) is fixed to the tip (left side in the figure) of the spindle 1. Hereinafter, spindle 1
Is referred to as front, and the rear end of the spindle 1 is referred to as rear.

The main shaft 1 is housed in a casing 2 via angular ball bearings 3 and 7, and the casing 2 is supported by housings 14 and 16 at front and rear end faces. In this spindle unit, two angular ball bearings 3 are arranged and fixed in the axial direction on the front side inside the casing 2, and two angular ball bearings 7 are arranged in the axial direction on the rear side. Two hydraulic pistons 4 are provided inside the casing 2 which is in front of the angular ball bearing 7.
1, 42 are connected in series and arranged. Pressure is applied to oil chambers 46 and 47 provided on the back side of the hydraulic pistons 41 and 42 to drive the hydraulic pistons 41 and 42 in the axial direction to move the position of the outer race 10 of the angular ball bearing 7 stepwise. As a result, the preload is switched.

(Problems of the prior art) a. In the spindle unit shown in FIG. 2, a mechanism that supports the outer race 10 of the angular ball bearing 7 disposed on the rear side from the inside of the casing 2 includes a plurality of hydraulic pistons 41 for switching preload,
As a result, the outer diameter of the casing 2 increases, and the span between the front and rear angular ball bearings 3 and 7 also increases.

B. Also, a hydraulic piston 4 for switching the preload is provided.
Although an O-ring for preventing oil leakage is used between the first and second casings 42 and the inner periphery of the casing 2, the accuracy of assembling the hydraulic pistons 41 and 42 to the casing 2 is deteriorated because of the O-ring. Therefore, it is difficult to support the outer race 10 of the angular ball bearing 7 within a predetermined accuracy.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional method of adjusting the preload of a spindle unit. An object of the present invention is to provide a spindle unit preload adjusting method capable of coping with a wide range of cutting conditions from high-speed light cutting to a non-ferrous material such as an alloy.

[0012]

According to the present invention, there is provided a method for adjusting a preload of a spindle unit, comprising: a main shaft on which a tool is mounted in front; a casing in which the main shaft is housed; A first angular contact ball bearing that supports the main shaft toward the first, a second angular contact ball bearing that is arranged on the rear side inside the casing and supports the main shaft with the back facing forward, and the first and second angular contact An inner spacer arranged between the inner races of the ball bearing and fitted on the outer peripheral surface of the main shaft, and an outer spacer arranged between the outer races of the first and second angular ball bearings and fitted on the inner peripheral surface of the casing. A spacer, a first hydraulic piston that presses the outer race of the first angular contact ball bearing in the axial direction from the front side, and an outer race of the second angular contact ball bearing in the axial direction from the rear side A second hydraulic piston for pushing, wherein a preload adjusting method of a spindle unit for applying a preload to the first and second angular ball bearings by an axial dimensional difference between the inner spacer and the outer spacer. The spacer has a first groove formed in the outer peripheral surface in a circumferential direction,
A second groove formed in the inner peripheral surface in the circumferential direction and adjacent to the first groove and arranged on the front side, and a second groove formed in the inner peripheral surface in the circumferential direction and adjacent to the first groove and thereafter A third groove arranged on one side, and by applying pressure to an oil chamber formed between the first groove and the inner peripheral surface of the casing, the outer spacer is axially moved. It is configured to elastically deform and expand and contract, and by simultaneously adjusting the pressure in the oil chamber and the driving pressure of the first and second hydraulic pistons, switches a preload condition of the angular ball bearing. I do.

According to the spindle unit preload adjusting method of the present invention, the pressure in the oil chamber formed between the first groove provided on the outer peripheral surface of the outer spacer and the inner peripheral surface of the casing; By controlling both the driving pressures of the first and second hydraulic pistons simultaneously, the amount of expansion and contraction of the outer spacer can be freely adjusted. Therefore, it is possible to finely switch the condition of the fixed position preload for the angular contact ball bearing according to the rotation speed of the spindle unit.

Further, according to the method for adjusting the preload of the spindle unit of the present invention, by changing the driving pressure of the first and second hydraulic pistons according to the number of revolutions, it is also possible to switch from the preload at the fixed position to the preload at the constant pressure. Therefore, at high speed light cutting, by switching to constant pressure preload,
Stable high-speed cutting becomes possible.

[0015]

(Embodiment 1) FIG. 1 shows an example of the structure of a spindle unit to which a preload adjusting method according to the present invention is applied. In the figure, 1 is a main shaft, 2 is a casing, 3 and 7 are angular ball bearings, 4 and 8 are inner races of angular ball bearings, 6 and 10 are outer races of angular ball bearings, 11 is an inner spacer, 12 is an outer spacer, 24 represents a first hydraulic piston, and 26 represents a second hydraulic piston. A tool (not shown) is fixed to the tip (left side in the figure) of the spindle 1. Hereinafter, the front end side (left side in the figure) of the spindle 1 is referred to as front, and the rear end side of the spindle 1 is referred to as rear.

Inside the casing 2, first and second angular ball bearings 3 and 7 for supporting the main shaft 1 are arranged with their backs facing each other. In this example, the first and second angular ball bearings 3 and 7 each have two bearings (3a, 3b and 7a, 7b) arranged in the axial direction. Between the inner races 4 and 8 of the first and second angular ball bearings 3 and 7,
An inner spacer 11 is arranged, and the inner spacer 11 is fitted on the outer peripheral surface of the main shaft 1. In addition, outer races 6, 1
Between 0, an outer spacer 12 is arranged, and the outer spacer 12 is fitted on the inner peripheral surface of the casing 2.

A groove 23 is formed circumferentially at the axial center of the outer peripheral surface of the outer spacer 12, and the groove 22a and the groove 22 are formed on the inner peripheral surface of the outer spacer 12 so as to sandwich the groove 23 therebetween. 22b is formed in the circumferential direction. Thus, the outer spacer 12 has a structure that can be expanded and contracted by elastic deformation in the axial direction, and at the same time, the end surfaces of the outer spacer 12 are less likely to fall.

A ring-shaped hydraulic piston 24 is disposed in front of the angular ball bearing 3 disposed on the front side, and is disposed between the housing 14 adjacent to the front end of the casing 2 and the rear surface of the hydraulic piston 24. An oil chamber 18 is formed. The front surface of the hydraulic piston 24 has a two-stage shape whose inner diameter side protrudes. When the hydraulic piston 24 is moved forward by applying pressure to the oil chamber 18, the hydraulic piston 24
The end face 31 of the outer race 6 of the angular contact ball bearing 3 is pressed by the step portion 24a on the inner diameter side of the front surface of the outer race 6.

Similarly, a ring-shaped hydraulic piston 26 is disposed behind the angular ball bearing 7 disposed on the rear side, and the housing 16 and the rear surface of the hydraulic piston 26 adjacent to the rear end of the casing 2 are arranged. And an oil chamber 19 is formed between them. The front surface of the hydraulic piston 26 has a two-stage shape whose inner diameter side protrudes. When the hydraulic piston 26 is advanced by applying pressure to the oil chamber 19, the end face 32 of the outer race 10 of the angular ball bearing 7 is pressed by the step 26 a on the inner diameter side on the front surface of the hydraulic piston 26.

Next, a method of adjusting the preload of the spindle unit will be described. First, the rotation of the main shaft 1 is started at a low speed. At this time, pressure is applied to the oil chamber 23 formed between the groove 23 on the outer peripheral surface of the outer spacer 12 and the inner peripheral surface of the casing 12, and the oil chambers 18 and 19 on the rear side of the hydraulic pistons 24 and 26 are pressed. Relieve pressure. As a result, the outer spacer 12 elastically deforms in the extension direction, the hydraulic pistons 24 and 26 move to the opposite sides of the respective outer spacers 12, and the step on the outer side of the back surface of the hydraulic pistons 24 and 26 and the end surface of the casing 2 And a gap corresponding to the maximum preload switching amount δ is formed. In this state, a heavy preload is applied to the angular ball bearings 3 and 7 as an initial preload.

Next, when the rotational speed of the main shaft 1 increases and the preload increases, the pressure in the oil chamber 23 is slightly reduced and the pressure in the oil chambers 18 and 19 is smaller than the pressure in the oil chamber 23. Apply pressure. As a result, the length of the outer spacer 12 is slightly reduced, and the value of the preload acting on the angular ball bearings 3 and 7 is reduced. The outer spacer 12 has a groove 23,
Since the groove 22a and the groove 22b are formed, the spring element is provided. However, since the pressure is applied to the oil chamber (groove) 23, the rigidity is not insufficient.

Further, when the rotational speed of the spindle increases and the preload increases, the pressure is adjusted so that the pressure in the oil chambers 18 and 19 becomes higher than the pressure in the oil chamber 23. As a result, the length of the outer spacer 12 is further reduced, and the angular contact ball bearing 3,
The value of the preload acting on 7 is further reduced. Such a preload reduction operation is performed until the hydraulic pistons 24 and 26 finally reach the forward limit, that is, advance by δ from the initial heavy preload state respectively, and the hydraulic pistons 24 and 26
Steps 24b and 26b on the outer side of the front surface of the casing 2 come into close contact with the front and rear end surfaces 33 and 34 of the casing 2, respectively.

As described above, the pressure in the oil chamber 23 and the oil chamber 1
By simultaneously adjusting the pressures in the inner and outer pressures 8 and 19, the amount of expansion and contraction of the outer spacer 12 is switched based on the pressure difference between the two, and the value of the preload acting on the angular ball bearings 3 and 7 is reduced. Can be adjusted. As a result,
As a result, it is possible to perform cutting under the optimal preload condition according to the rotation speed of the main shaft and the thrust load.

[0024]

According to the spindle unit preload adjusting method of the present invention, a heavy preload, that is, high rigidity can be realized when the rotation speed of the spindle is low, even though the spindle unit is a fixed position preload type spindle unit. When the rotation speed of the spindle increases, the preload can be reduced finely. Therefore, cutting can be performed under the optimal preload condition according to the rotation speed of the main shaft and the thrust load.

[Brief description of the drawings]

FIG. 1 is a front half sectional view showing an example of the structure of a spindle unit in which a preload adjusting method of the present invention is used.

FIG. 2 is a front half sectional view showing an example of a conventional spindle unit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Main shaft, 2 ... Casing, 3 ... Angular contact ball bearing (front side), 7 ... Angular contact ball bearing (rear side), 6, 10 ... Outer race, 4, 8, ... Inner race, 11 ... inner spacer, 12 ... outer spacer, 14, 16 ... housing, 18, 19 ... oil chamber, 22a, 22b ... groove, 23 ... groove (oil chamber) ,
24, 26: Hydraulic piston, 31, 32: End face of outer race, 33, 34: End face of casing,
41, 42 ... hydraulic piston, 46, 47 ... oil chamber.

Claims (1)

[Claims] 1. A main shaft on which a tool is mounted at the front, a casing accommodating the main shaft, a first angular ball bearing disposed at a front side inside the casing and supporting the main shaft with a rear surface facing rearward, A second angular contact ball bearing disposed on the rear side inside the casing and supporting the main shaft with the rear surface facing forward; and an outer peripheral surface of the main shaft disposed between inner races of the first and second angular contact ball bearings An inner spacer fitted between the outer race of the first and second angular contact ball bearings and an outer spacer fitted to the inner peripheral surface of the casing; and an outer race of the first angular contact ball bearing on the front side thereof. A first hydraulic piston that pushes the outer race of the second angular contact ball bearing axially from the rear side thereof, and a first hydraulic piston that pushes the outer race of the second angular contact ball bearing in the axial direction. A preload adjusting method for a spindle unit that applies a preload to first and second angular ball bearings by an axial dimensional difference with the outer spacer, wherein the outer spacer has a first circumferential surface formed on an outer peripheral surface thereof. The groove, the second groove formed in the inner peripheral surface in the circumferential direction and adjacent to the first groove and disposed on the front side, and the first groove formed in the inner peripheral surface in the circumferential direction. A third groove adjacent to and disposed on the rear side of the outer spacer by applying pressure to an oil chamber formed between the first groove and an inner peripheral surface of the casing. Is configured to be elastically deformed in the axial direction to expand and contract. By simultaneously adjusting the pressure in the oil chamber and the driving pressure of the first and second hydraulic pistons, the preload condition of the angular ball bearing is switched. Spindle unit preload Adjustment method.