JP2602325B2 - Variable preload spindle unit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable preload type spindle unit, and more particularly, to a method in which a fixed position preload can always be applied to a bearing from a low speed to a high speed rotation of a spindle. The present invention relates to a variable preload spindle unit that adjusts the amount of preload according to the number of rotations of a spindle and achieves both rigidity and high speed of the spindle.

[Conventional technology]

Generally, a spindle of a machine tool is used by applying a preload to an angular ball bearing that supports a main spindle in order to obtain rotational accuracy and rigidity of the main spindle.

As described above, as a preloading method of applying a moderate axial load to the angular contact ball bearing to maintain a constant preload load state in the gap inside the bearing, a constant pressure preload using a spring or hydraulic pressure, a spacer, a shim, or the like is used. There is fixed position preload.

The former constant pressure preload is a preload method in which the relative position of the preloaded bearing changes during use, but the preload is substantially constant, and has a characteristic that the support rigidity of the main shaft is low.

The latter fixed-position preload is a preload method in which the relative position of the preloaded bearing does not change during use and remains constant, and has a characteristic that the support rigidity of the main shaft is high.

By the way, in a machine tool, since rotation accuracy and high speed are required, a preloading method without a means for varying a preload as in the related art is insufficient for a spindle used in this field.

That is, in the preloading method without the means for varying the preload, the rigidity and the number of revolutions of the spindle are determined by the initial preload setting, and if high rigidity is emphasized at low speed rotation, the preload must be increased.

However, recent spindles are required to cover rotation accuracy and rigidity from low speed to high speed.
If the bearing is rotated at high speed with the initial preload increased, an excessive load is applied to the bearing, exceeding the seizure limit. Normal operation is impossible.

Conversely, if the initial preload is set small so that the main shaft can rotate at a high speed, the preload at the time of low speed rotation becomes insufficient, and a problem arises in that high rigidity cannot be obtained at low speed rotation.

Therefore, in recent years, a preloading method has been considered in which the preload applied to the spindle bearing is made variable and the preload is switched between a heavy preload in a low-speed rotation range and a light preload in a high-speed rotation range.

The above preload variable method is such that a presser is externally fitted to an outer ring of a bearing supporting a main shaft so as to move integrally in the axial direction, and the presser is always placed in a housing that holds the presser so as to be movable in the axial direction. In addition to incorporating a constant-pressure preload spring that presses in the axial direction, a hydraulic chamber is provided on the back side of the piston incorporated in the housing so that it can move in the axial direction, and a hydraulic chamber is provided in the low-speed rotation range of the main shaft. The presser is pressed by the piston by supplying oil, a heavy preload is applied to the bearing by the fixed position preload, the oil in the hydraulic chamber is drained in the high speed rotation range of the main shaft, and the pressure is switched to the constant pressure preload by the elasticity of the spring. .

[Problems to be solved by the invention]

By the way, in the above-described method of switching from the fixed-position preload to the constant-pressure preload, there is a problem that it is difficult to obtain high rigidity with the constant-pressure preload, and thus it is difficult to obtain a sufficient preload in a high-speed rotation region.

In addition, when the constant pressure preloading means is used, the outer ring or the inner ring always moves in the axial direction, and it is necessary to maintain a constant pressure.However, the bearing is tightly fitted with the inner ring as the main shaft to increase rigidity, and the outer ring has Since the gap is fitted, there is a problem that when a temperature difference occurs, interference occurs, and it becomes difficult to move the bearing in the axial direction.

Accordingly, an object of the present invention is to solve the above-mentioned problems by adopting a fixed-position preload switching method for preloading a bearing, and changing the preload amount stepwise according to the number of revolutions of the main shaft, thereby achieving high-speed rotation. An object of the present invention is to provide a variable preload spindle unit that can apply a sufficient preload even in a low speed range and has high rigidity from a low speed rotation to a high speed rotation range.

[Means for solving the problem]

In order to solve the above-described problems, the present invention provides a bearing box that axially presses a bearing that rotatably supports a main shaft, and an intermediate ring that axially presses the bearing box in an outer cylinder. An adjusting member having a step for limiting the amount of movement of the bearing box and a step for limiting the amount of movement of the intermediate ring is fixed to the outer cylinder, and the end of the bearing box and A pressure chamber is provided at each end of the intermediate ring, and the amount of movement of the bearing box is adjusted in multiple stages by the adjustment member and the intermediate ring by supplying and discharging hydraulic pressure to and from the pressure chamber.

[Action]

The adjustment position of the bearing box and the intermediate ring in the axial direction is limited by the adjusting member.When the spindle is rotating at low speed, the bearing box is directly moved by hydraulic pressure to apply heavy preload to the bearing. The oil pressure to the box is released and the intermediate ring is moved by oil pressure to reduce the amount of preload on the bearing. When the main shaft rotates at high speed, the oil pressure of the intermediate ring is released and the amount of preload is switched.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 1, the main shaft 11 is rotatably supported by bearings 12, 13 and 14, 15 each having two ends arranged at each end. Each bearing 12, 13 and 14, 15 use angular contact ball bearings,
The pair of bearings 12, 13 and 14, 15 are in a parallel combination via spacers 16, 17, respectively, and the bearings 12, 13 and 14, 15 are arranged in a back-to-back arrangement.

The bearings 14 and 15 on one end are directly incorporated in the outer cylinder 18, and the bearings 12 and 13 on the other end are incorporated in a bearing box 19 inserted between the bearings 12 and 13 and the outer cylinder 18. .

In the outer cylinder 18, the bearing box 19, an intermediate ring 20 is inserted at a position on one end side of the bearing box 19 so as to be movable in the axial direction, and between the bearing box 19 and the intermediate ring 20. A hydraulic chamber 22 is formed between the end faces of the hydraulic chamber 21 and the intermediate ring 20 and the outer cylinder 18, and a hydraulic pressure is applied to each of the hydraulic chambers 21 and 22 from a hydraulic control device 23 so that the bearing box 19 and the intermediate ring 20 are pivoted. Direction.

The bearing box 19 applies a preload to the bearings 12 and 13 via a spacer 24 provided between the bearing 13 and the outer ring of the bearing 13 when the bearing box 19 moves in the axial direction.

An adjusting member 25 fixed inside the outer cylinder 18 has a bearing box 19
A step 26 for controlling the amount of movement of the intermediate ring 20 and a step 27 for limiting the amount of movement of the intermediate ring 20 are provided.
A step 28 corresponding to 26 and an end face 29 where the intermediate ring 20 abuts
The distance between the step 28 and the end face 29 of the bearing housing 19 is set shorter than the distance between the two steps 26 and 27 of the adjusting member 25.

Oil supply to both hydraulic chambers 21 and 22 by the hydraulic control device 23,
The oil discharge is switched by detecting the number of revolutions of the main shaft 11 with a sensor (not shown), and adjusting the preload amount by positioning the bearing box 19 by the steps 26 and 27 of the adjusting member 25.

In order to smoothly move the bearing box 19 in the axial direction, a spiral groove 30 is provided on the inner peripheral surface of the outer cylinder 18 in FIG. 1 and hydraulic pressure is applied to the spiral groove 30 by the hydraulic control device 23 in FIG. However, the spiral groove 30 may be provided on the outer periphery of the bearing box 19, and is not limited to such a spiral groove. It only needs to be generated during the movement in the direction.

In the example shown in FIG. 2, a ball slide 31 is inserted between the bearing box 19 and the fitting surface of the outer cylinder 18 instead of the spiral groove 30.

In order to perform air-oil lubrication for each of the bearings 12, 13, 14, and 15, a nozzle for air oil is provided at the spacer between bearings.
32 may be formed, and the bearings 12 and 13 may be configured to press the outer ring of the bearing with the end face of the bearing box 19 without being incorporated in the bearing box 19.

The spindle unit of the present invention is configured as described above, and a method of adjusting the preload amount will be described.

First, the outline of the adjustment of the preload amount will be described with reference to FIG. 7. adjust.

Startup pressured by supplying oil to the hydraulic chamber 21 so that the preload P ₁₀ according to the bearings, adjust the bearing box 19 step portion 28 is member 25
The inner ring surface pressure becomes P when the rotation speed reaches N ₁ , so oil is drained from the hydraulic chamber 21 and oil is supplied to the hydraulic chamber 22 to reduce the pressure. Over the middle ring
20 is moved to the position where it contacts the step 27, and the preload amount is
Switch to _20, when further rotational speed becomes N _2, the hydraulic chamber 22
Remove the oil, to preload P _30.

By doing so, it is possible to operated until the rotational speed N _3. In other words, it will be a preload amount shown by bold lines in FIG. 7 bearing receives, between the rotational speed zero to the rotational speed N _3, bearing constantly P
_10, P _20, will be P ₃₀ or more and less position preloading P is applied, it is possible to obtain a highly rigid spindle.

Next, a specific operation will be described with reference to FIGS.

FIG. 3 shows the state before the operation with a bearing plane difference of 0, and the sum of the initial clearances of the four bearings is δ ₁ (the total amount of preload during the highest speed operation), and the step 26 of the adjusting member 25 and the bearing box 19 are shown. ₂ of the gap between the stepped portion 28 _[delta], the gap between the stepped portion 27 and the intermediate ring 20 of the adjusting member 25 and [delta] _3. The relationship of this gap is δ ₂ > δ ₃ > δ ₁
And keep it.

In the figure, since two bearings 12 and 13 are shown, the sum of the initial clearances of the two bearings 12 and 13 is δ _1/2 .

When rotation of the main shaft 11 is in the low speed range, that is, between the rotational speed from 0 to N ₁ in FIG. 7, the boat P ₁ to the hydraulic chamber 21 in the state of FIG. 3
Then, the pressure is applied by applying oil, and as shown in FIG. 4, the bearing housing 19 is moved to a position where the steps 26 and 28 abut.

At this time, the preload amount according to the position is δ ₂ −δ ₁ , which is converted into a force, P _{10 in} FIG. 7, and when the rotation speed of the main shaft 11 increases, the preload amount increases along the line a in FIG. I do.

Assuming that the surface pressure of the inner and outer rings reaches a certain value P, for example, 200 kgf / mm ² when the rotation speed of the main shaft 11 reaches N ₁ , the oil pressure is switched here, the oil in the hydraulic chamber 21 is drained, and the port P ₂ From hydraulic chamber
Oil is fed into 22 and pressure is applied, and intermediate ring 20 is
Is moved to the state of FIG.

At this time, the preload amount at the position is (δ ₃ −δ ₁ ), and when this is converted into a force, it becomes a line C in FIG.
N ₂ from N ₁ is the preload amount increases along the line C of Figure 7. At the time of switching, it becomes the line b in FIG.

Next, when the rotation speed of the main shaft 11 becomes N ₂ and the surface pressure of the inner and outer rings reaches P, the oil in the hydraulic chamber 22 is drained, and the two hydraulic chambers 21 and 22 are drained.
When you turn off the hydraulic pressure source to the preload amount - [delta ₁ next by the position at this time, when this is converted into a force seventh view of a line e, and the rotational speed of the spindle 11 becomes N ₃ increases Up to the point e, the preload increases. At the time of switching at this time, it becomes a line d in FIG.

In the case of reducing the rotational speed of the spindle 11 from the N _3, the hydraulic chamber
The supply and discharge of oil to and from 21, 22 may be performed in the reverse manner.

Also, in the case shown, a bearing housing 19 and an intermediate ring 20 are used,
Although the example in which two switching operations are performed by the two step portions 26 and 27 of the adjusting member 25 has been described, if the number of intermediate rings and the number of step portions of the adjusting member 25 are increased, the number of switching of the preload can be increased. It is possible.

〔effect〕

As described above, according to the present invention, the bearing housing for pressing the bearing in the axial direction and the intermediate ring are made movable in the axial direction by supplying and discharging hydraulic pressure, and the amount of movement of the bearing housing and the intermediate ring is limited by the adjusting member. The amount of preload applied to the bearing is adjusted, so that the preposition can be applied to the bearing in accordance with the rotation speed of the main shaft. Spindle with high rigidity until rotation.

Further, since the fixed position preload is switched by the use of the adjusting member and the supply and discharge of the oil using the bearing housing and the intermediate ring, the switching rotation can be freely selected as needed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a spindle unit according to the present invention, FIG. 2 is a longitudinal sectional view of a main part showing another example of the same, and FIG.
6 to 6 are explanatory diagrams showing operating states, and FIG. 7 is a graph showing a process of switching the preload. 11 ... Spindle, 12-15 ... Bearing, 18 ... Outer cylinder, 19 ... Bearing box, 20 ... Intermediate ring, 21,22 ... Hydraulic chamber, 23 ... Hydraulic control device, 25 ... Adjustment member , 26, 27, 28 ... step, 29 ...
…End face.

Claims (5)

(57) [Claims] A bearing housing for axially pressing a bearing for rotatably supporting a main shaft and an intermediate ring for axially pressing the bearing housing are arranged in the outer cylinder so as to be movable in the axial direction. An adjusting member having a step for limiting the amount of movement of the bearing box and a step for limiting the amount of movement of the intermediate ring is fixed to the outer cylinder, and a pressure chamber is provided at each of the end of the bearing box and the end of the intermediate ring. A variable preload spindle unit that adjusts the amount of movement of the bearing housing in multiple stages by the adjustment member and the intermediate ring by supplying and discharging hydraulic pressure to both pressure chambers. 2. The variable preload spindle unit according to claim 1, wherein the bearing is disposed inside the bearing housing. 3. The preload variable spindle unit according to claim 1, wherein when the bearing housing is moved in the axial direction, high-pressure oil is fed into the bearing housing and the outer cylinder. 4. A helical groove for feeding high-pressure oil is provided in one of the regions where the bearing housing and the outer cylinder are in contact with each other.
2. A variable preload spindle unit according to item 1. 5. The variable preload spindle unit according to claim 1, wherein a ball slide is disposed between the bearing housing and the outer cylinder.