JPH0653323B2 - Preload adjustable spindle unit - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle unit used as a main shaft of a machine tool such as a machining center, and more specifically, a child having an inner ring spacer that is axially divided into three parts. The present invention relates to a pressure adjustable spindle unit.

(Prior Art) In machine tools (especially, machining centers), speeding up of the spindle has been remarkably progressed for the purpose of improving productivity and machining accuracy. In addition, speeding up and reduction in temperature rise are also required. Generally, the spindle of a machine tool is used not only at a constant rotational speed but also at a wide range of rotational speeds from low speed for heavy cutting to high speed for light cutting. Therefore,
Ideally, the preload should be set to heavy preload at low speed and light preload at high speed.

(Problems to be Solved by the Invention) However, in the low position pressure system currently adopted by many machine tool spindles, there is a drawback in that the above relationship is reversed. That is, in the low position preload method, when the main shaft rotates at high speed, the axial preload is caused by the centrifugal force acting on the balls that are rolling elements, the expansion of the inner ring due to the centrifugal force, and the thermal expansion difference due to the temperature difference between the inner ring and the outer ring. Has been confirmed to increase. Therefore, it is required to suppress the influence of these phenomena as small as possible and prevent the preload from increasing during high speed rotation. Conventionally, in order to solve this, for example, the outer ring spacer is deformed by axially pressing the bearing outer ring in accordance with the number of rotations of the main shaft to prevent an increase in the axial preload during high-speed rotation. There is an example. However, with such a method, it is necessary to further provide drive means for pressing the bearing outer ring and control it according to the number of revolutions, which may complicate the overall configuration of the apparatus.

Therefore, an object of the present invention is to provide a spindle unit capable of reducing the preload when the main shaft rotates at a high speed as compared with the low speed and lowering the temperature rise region.

(Means for Solving the Problems) In order to achieve the above-mentioned object, a spindle unit of the present invention includes a rotating spindle (1) and a bearing (fitted to the spindle to rotatably support the spindle (1)). 5, 7) and the inner ring spacer (12, 12) which is axially closely attached to the inner ring of the bearing and is fitted to the main shaft.
22) and an outer ring spacer (11) that is in close contact with the outer ring of the bearing in the axial direction, wherein the inner ring spacer is divided into three parts in the axial direction, and the mating surface thereof is the shaft. It has a tapered shape that forms a predetermined angle with respect to the direction, and the central portion (15,
23) is a portion (13 and 17, 21 and 2) on both sides thereof.
It is characterized in that at least one of the inner and outer diameter dimensions is set larger than that in 5).

(Operation) With the configuration as described above, the central portion of the three-divided inner ring spacer is displaced in the radial direction according to the rotational speed of the main shaft, so that the axial preload applied to the bearing can be automatically adjusted.

Embodiments Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the drawings, the same parts are designated by the same reference numerals.

Before describing the embodiments, the relationship between the axial preload and the axial clearance, that is, the axial clearance will be described with reference to the fifth and fifth parts.
This will be described with reference to the drawings and FIGS. 6a and 6b. FIGS. 5a and 5b show a case where the angular bearings are combined in a single-row rear surface and a spacer is interposed therebetween. Also, the sixth
Similarly, FIGS. 6A and 6B show a case where angular bearings are combined in a single-row surface and a spacer is interposed therebetween. In the case of the single-row rear surface combination, as shown in FIG. 5a, an outer ring spacer 37 and an inner ring spacer 39 are arranged between angular bearings composed of balls 34, an outer ring 33a and an inner ring 33b. In this case, an axial gap Δa is provided between the inner ring spacer 39 and one of the bearings on both sides, and the inner ring is tightened by the axial force Fa shown in FIG. The total amount of elastic deformation is Δa
Is the preload.

In the case of the front combination, as shown in Fig. 6a, balls 4
6, an outer ring spacer 49 and an inner ring spacer 51 are arranged between the angular bearings composed of the outer ring 45a and the inner ring 45b. Contrary to the back face combination, as shown in FIG. 6a, an axial gap Δa is provided between the outer ring spacer and one of the bearings on both sides thereof. In this case, the outer ring is tightened by the axial force Fa shown in FIG. 6b, and the load at which the total elastic deformation amount of the left and right bearings becomes Δa is the preload.

Therefore, from the above, the axial gap Δa is changed,
That is, the adjustment can adjust the axial preload applied to the bearing. That is, if the axial gap Δa is set to be small, the preload will be small, and if the axial gap Δa is set to be large, the preload will be large. Normally, this axial gap tends to increase due to the centrifugal force applied to the ball and the temperature difference between the inner and outer rings of the bearing as already described when the spindle rotates at high speed, but in the present invention, this axial gap decreases. By doing so, the preload can be reduced.

Examples of the present invention will be described below. FIG. 1 is an axial sectional view of a spindle unit showing a first embodiment of the present invention. The main shaft 1 is rotatably fitted and supported by two left and right bearings 5 and 7 that are combined in a back surface. The bearings 5 and 7 are angular bearings here, but they may also be tapered roller bearings or deep groove ball bearings, for example. Bearing 5
An outer ring spacer 11 and an inner ring spacer 12 composed of three spacer portions are arranged between the bearings 7 and 7 in close contact with the bearings 5 and 7. The bearings 5 and 7, and the outer ring spacer 11 are the housing 3
Is held in contact with. A sleeve nut 9 is screwed onto the main shaft 1, and when the spindle unit is assembled, the bearing is positioned at a predetermined axial position to apply a predetermined preload.

As shown in FIG. 3 which is a detailed view of FIG. 1, the inner ring spacer 12 has one end in the axial direction brought into contact with the inner ring 5b of the bearing 5, and the other end is a tapered surface 13a. Spacer part 13
A second spacer portion 17 having one end abutting on the inner ring 7b of the bearing 7 and the other end being a tapered surface 17a, and the tapered surface is disposed between the second spacer portion 17 and the first and second spacer portions. 13a and 1
7a, and a central spacer portion having tapered surfaces 15a that abut and slide on the respective 7a at both axial end portions. The tapered surface 13a and the tapered surface 15a and the tapered surface 17a and the tapered surface 15a are mating surfaces that are in a sliding relationship with each other. Therefore, the central spacer portion 15 has an isosceles trapezoidal shape when viewed in cross section.

In the spindle unit having the above structure, when the main shaft 1 rotates, the inner spacer expands to the outer diameter side by centrifugal force. The expansion amount at this time is as follows.

Expansion amount of outer diameter surface ξ (b): Expansion amount of inner diameter surface ξ (a): Here, m: Poisson's ratio, E: Young's modulus, a: inner radius, b: outer radius, γ: specific gravity, ω: angular velocity, g: gravitational acceleration.

Assuming that the expansion amount at the center of the spacer mating surface is the average value of the expansion amounts of these inner and outer diameter surfaces, the central spacer having a large diameter expands more than the spacer parts on both sides. At this time, assuming that the taper angle of the mating surface of the spacer is 2 · α and the difference in expansion amount between the central spacer and the spacer portions on both sides thereof is ξ, Δa =
This means that the inner ring spacer has expanded by ξ · tan α. Therefore, in FIG. 3, the inner rings 5b and 7b of the bearing, which are closely arranged on both sides of the inner spacer, are subjected to a pressing force in the direction opposite to the axial direction. Therefore, in the case of the back surface combination as shown in FIG. 3, a pressing force is applied to the bearings 5 and 7 in a direction to reduce the preload. The broken line in FIG. 3 indicates the position of the central spacer 15 when the main shaft 1 rotates at high speed (when it is desired to reduce the preload applied to the bearing). The position of the central spacer 15 when the main shaft 1 is rotating at a low speed (when it is not necessary to reduce the preload applied to the bearing) is indicated by the solid line.

Here, as shown in FIG. 4, in the taper matching surface A between the first spacer portion 13 and the central spacer 15, the half angle of the taper angle is set to be larger than the friction angle. The same is set between the second spacer portion 17 and the central spacer 15. By setting in this way, the radial movement of the central spacer, that is, the expansion is performed smoothly, and when the main shaft 1 changes its rotation speed from high-speed rotation to low-speed rotation, or vice versa. The central spacer 1 can be smoothly moved between the broken line position and the solid line position shown in FIG. Therefore, the bearing 5
The adjustment of the preload applied to 7 and 7 is performed smoothly, automatically and surely.

An example of setting conditions of each component in the first embodiment is as follows.

Under the above setting conditions, the preload when the rotation speed is N = 15000 rpm is 750 kgf for the integrated spacer. On the other hand, when the three-divided spacer of the present invention is used, ξ = 0.0075 mm
, Δa = 0.013, the preload can be reduced to 630 kgf, and a sufficient effect was obtained.

Under the above-mentioned setting conditions, both the inner and outer dimensions of the central spacer are set to be larger than the inner and outer dimensions of the first and second spacer portions, but it is not always necessary to increase both the inner and outer diameters. Instead, at least one of them may be set to a large value.

FIG. 2 is a sectional view of a spindle unit showing a second embodiment of the present invention. In this embodiment, the bearings 5 and 7 are axially frontally assembled. The only difference between the first embodiment and the second embodiment shown in FIG. 1 is that the bearing is a front combination with respect to the spacer and the inner ring spacer has a different configuration. Here, the description of the other components is omitted.

Also in the case of the second embodiment, the taper angle is set to about 120 degrees as in the first embodiment, and the half angle of the taper angle is set to be larger than the friction angle. However, the method of cutting the taper angle is opposite to that in the first embodiment. When the main shaft 1 rotates at a high speed, the central spacer 23 of the inner ring spacer 22 expands due to centrifugal force while sliding on the tapered surfaces of the first and second spacer portions 21 and 25 that are axially adjacent to each other. And move radially outward. Therefore, the first and second spacer portions 21
And 25 approach each other towards the central spacer 23. As a result, the pressing force applied to the inner races of the bearings 5 and 7 is reduced, and the inner races are slightly moved so as to approach each other in the axial direction to reduce the preload. When the rotation speed of the main shaft 1 decreases and the rotation speed becomes low, the central spacer 23 contracts from the expanded state and moves inward in the radial direction. Therefore, a predetermined preload is applied to the bearings 5 and 7 via the first and second spacer portions 21 and 25.

In the first and second embodiments described above, if the center spacer of the inner ring spacer is made of a material having a larger specific gravity than the adjacent first and second spacer portions, a greater effect can be obtained. . Further, when the main shaft rotates at a high speed, the temperature rise also increases. Therefore, if the central spacer is made of a material having a larger linear expansion coefficient than the adjacent first and second spacer portions, a greater effect can be obtained. Is obtained.

Further, in the first and second embodiments, the spacer is interposed between the bearings supporting the main shaft, but this spacer may be arranged between the bearing and the sleeve nut if necessary.

(Effect of the Invention) According to the preload adjusting type spindle unit of the present invention described above, the following effects can be obtained.

It is possible to reduce the preload during high-speed rotation of the spindle, which was difficult in the past, with a simple structure.With a special controller configuration, the preload can be changed from heavy preload to light preload between low-speed and high-speed rotation of the spindle. It can be automatically adjusted to.

[Brief description of drawings]

FIG. 1 is an axial sectional view of a spindle unit showing a first embodiment of the present invention, and FIG. 2 is an axial sectional view of a spindle unit showing a second embodiment of the present invention. FIG. 4 is a cross-sectional view showing details of the inner ring spacer of FIG. 1, FIG. 4 is a schematic view showing details of the tapered mating surface A in FIG. 3, and FIGS. FIGS. 6a and 6b are diagrams showing the relationship between the axial gap and the preload. [Explanation of symbols of main parts] 1 ... spindle 12 ... inner ring spacer 5,7 ... bearing 15 ... central spacer

Claims (4)

[Claims] 1. A rotating main shaft, a bearing fitted to the main shaft to rotatably support the main shaft, an inner ring spacer closely fitted to the inner ring of the bearing in the axial direction and fitted to the main shaft, and A spindle unit including an outer ring of a bearing and an outer ring spacer closely contacting in the axial direction, wherein the inner ring spacer is divided into three parts in the axial direction, and a mating surface thereof has a predetermined angle with respect to the axial direction. The spindle unit is characterized in that at least one of the inner and outer diameter dimensions of the central portion of the three portions is set to be larger than that of the portions on both sides thereof. 2. The spindle unit according to claim 1, wherein a radius of a taper angle of the mating surface is set to be larger than a friction angle. 3. The spindle unit according to claim 1, wherein the central portion of the inner ring spacer is made of a material having a specific gravity larger than the specific gravity of the portions on both sides thereof. 4. The center part of the inner ring spacer is made of a material having a linear expansion coefficient larger than the linear expansion coefficients of the parts on both sides of the inner ring spacer. Spindle unit.