JP2008298250A - Feed driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent breaking of a bearing, to stabilize a service life, and to improving processing accuracy by stabilizing axial rigidity, in a feed driving device having the heat compensating function. <P>SOLUTION: Angular bearings 6 and 16 supporting the other end side of a ball screw 7 are constituted by combining the angular bearing 6 for tension for realizing a tension state to the ball screw 7 and the angular bearing 16 for compression for realizing a compression state to the ball screw 7, and are provided with a fixing part 100 composed of a holder 18 abutting on both an outer race 5 and a bearing housing 3 of the angular bearings 6 and 16, a frame body 20 fixed to the bearing housing 3 and an elastic member 19 pressed in a clearance in the axial direction between the holder 18 and the frame body 20. The elastic member 19 elastically displaces a position of the outer race 5 to the bearing housing 3 so that an axial load acting on the angular bearing 16 for compression does not exceed a specific value, and when the axial load acting on the angular bearing 16 for compression is the specific value or less, the outer race 5 is rigidly fixed to the bearing housing 3 by the holder 18. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a feed driving device having a thermal compensation function.

In the feed drive device according to the prior art, both ends of the ball screw are supported by angular bearings, and the motor side is loaded with an axial load in both directions by a double back (DB) or double front (DF) combination.
On the other hand, the angular bearing on the tension end side (opposite the motor side) is supported by applying pretension to the ball screw to prevent thermal displacement and excessive load on the angular bearing due to the temperature rise of the ball screw. ing.

  That is, three rows of angular bearings are held by the bracket with respect to the base, and one end of the ball screw passes through these angular bearings so as to be freely rotatable. A collar is attached to the shaft end of the ball screw with a spacer between three rows of angular bearings, and a nut is screwed to press the spacer and the collar against the angular bearing. Further, a locking nut is screwed on the outside of the nut.

In each of the three rows of angular bearings, the inner diameter of the outer ring held by the bearing housing is wide at the shaft end side and narrowed at the center side, and the outer diameter of the inner ring fitted to the ball screw is larger at the shaft end side. The center side is smaller. That is, the three rows of angular bearings can realize the tension state of the ball screw.
Here, the inner ring of the angular bearing closest to the shaft end contacts the spacer, and the outer ring of the angular bearing closest to the center is constrained in the axial direction by the bearing housing.

  Therefore, by adjusting the screwing amount by the nut, a force can be applied to the three rows of angular bearings via the collar and the spacer. A force in the direction oblique to the axial direction acts between the inner ring and the outer ring, while the pre-tension in the axial direction is applied to the ball screw via the collar and spacer. Is granted.

Further, a convex portion is formed on the spacer, and a disc spring is press-fitted between the convex portion and the collar. The disc spring expands when the ball screw is thermally deformed due to temperature rise and an axial gap is formed between the collar and the spacer, and applies a certain tension to the angular bearing through the spacer. is there.
Here, when the ball screw undergoes thermal deformation due to temperature rise, the pretension acting on the ball screw gradually decreases. Finally, there is no pretension, an axial gap is created between the collar and the spacer, and the disc spring expands to apply a constant tension to the angular bearing. That is, the constant position preload in which the positional relationship between the collar and the spacer does not change is changed to the constant pressure preload by the disc spring.

  Also, when a load due to acceleration / deceleration acts near the tension end position and a load in the direction opposite to the pretension is applied, and the pretension applied to the ball screw disappears, the fixed position preload is changed to the constant pressure preload as described above. Will change.

The problems when the pre-tension is lost in the ball screw are as follows. ~ 5. It is as follows.
1. The ball screw is fixed from both sides to one side, and the shaft rigidity is reduced to 1/2 to 1/4. As a result, the natural frequency in the extension direction becomes 1 / 1.4-1 / 2, and the controllability is deteriorated. In addition, shape accuracy and machined surface quality deteriorate.

2. During constant pressure preload, the inner ring of the angular bearing receives a load from the disc spring and is fixed in position. However, since the ball screw is displaced, the sliding displacement is absorbed between the inner ring of the angular bearing and the ball screw. Originally, the inner ring and the ball screw are fixed relatively tightly. For this reason, it is necessary to make them loose, and slipping in the rotational direction occurs between the inner ring and the ball screw during high-speed rotation, which may cause early damage. .

3. When an instantaneous load such as acceleration / deceleration is applied during constant pressure preload, if the angular bearing and ball screw tension is tight, the slip does not follow, the pre-tension of the angular bearing is lost, and the rolling elements of the bearing slip. there's a possibility that.

4). In order to give the pre-tension of the assumed thermal displacement of the ball screw, a bearing with high load capacity is required.
However, high-load bearings are large-diameter bearings and are expensive to manufacture. In addition, when loading is performed with a large number of bearings, the load cannot be evenly applied to the large number of bearings.

5. Since the pre-tension amount of the ball screw is increased, the change in the feed shaft rigidity due to the operating state is large, which causes deterioration in machining accuracy.
Japanese Patent No. 2773653

  In another feed driving device according to the prior art, as shown on the tension end side in FIG. 3, a pre-tension of about half of the estimated thermal displacement of the ball screw 07 is applied by a combination of double backs as in the motor side. It is known that the ball screw 07 is changed from the tension state to the compression state as the heat is displaced.

  That is, as shown in FIG. 3, two rows of angular bearings 06 and two rows of angular bearings 016 are held by the bracket 02 with respect to the base 01, and one end of the ball screw 07 is rotated around these angular bearings 06,016. It penetrates freely. A spacer 012 is attached to the shaft end of the ball screw 07, and a nut 08 is screwed to press the spacer 012 against the angular bearings 06, 016. On the outside of the nut 08, a locking nut 09 is further screwed.

  In the two rows of angular bearings 06 close to the shaft end, the inner diameter of the outer ring 05 held by the bearing housing 03 is wide at the shaft end side and narrowed at the center side. The diameter is larger on the shaft end side and smaller on the center side. That is, the two rows of angular bearings 06 can realize the tension state of the ball screw 07.

On the other hand, in the two rows of angular bearings 016 closer to the center, the inner diameter of the outer ring 015 held by the bearing housing 03 is narrower on the shaft end side and wider on the center side, and the inner ring 014 fitted to the ball screw 07 The outer diameter is smaller on the shaft end side and larger on the center side. That is, the two rows of angular bearings 016 can realize the compressed state of the ball screw 07.
Here, the inner ring 04 of the angular bearing 06 closest to the shaft end is in contact with the spacer 011, and the outer ring 05 is fixed to the bearing housing 03 by a bearing pressing lid 013. Further, the outer ring 05 of the most angular contact angular bearing 016 is restrained in the axial direction by the bearing housing 03, and an existing collar 017 is interposed in the axial gap between the bearing housing 03 and the bracket 02.

Therefore, by adjusting the thickness of the current collar 017, when a leftward force in the figure acts on the four rows of angular bearings 06, 016 via the spacers 012, the two rows of angular bearings 06 are: While a bearing rolling element is sandwiched between the inner ring 04 and the outer ring 05, an oblique force acts on the axial direction as shown by an arrow in the figure. An axial pretension can be applied to the screw 07.
Here, the pretension is set to about half of the estimated thermal displacement of the ball screw 07, and as the ball screw 07 is thermally displaced, the tension state is changed to the compressed state.

That is, as indicated by a dashed line A in FIG. 2, in the initial state (at room temperature), a load having the same magnitude as the pretension acting on the ball screw 07 acts on the two rows of angular bearings 06. According to the thermal deformation accompanying the 07 temperature rise, the value gradually decreases, and when the pretension is lost, the load becomes zero.
Further, when a compressive force is applied to the ball screw 07 in accordance with thermal deformation due to a temperature rise, as shown by a two-dot chain line B in FIG. 2, a load having the same magnitude as the compressive force applied to the ball screw 07 is formed in two rows. It will act on the bearing 016. At this time, in the two rows of angular bearings 016, the bearing rolling elements are sandwiched between them, and the inner ring 04 and the outer ring 05 are inclined with respect to the axial direction as indicated by an arrow (white) in the figure. Force acts.

When the thermal deformation due to the temperature rise reaches the thermal displacement estimated amount, a load having the same magnitude as the pretension acting on the ball screw 07 is applied to the two rows of angular bearings 016.
Furthermore, when the temperature of the ball screw 07 exceeds the assumed heat rise value (heat rise assumed value) and the thermal displacement exceeds the expected value, the two rows of angular bearings 016 have one point in FIG. As indicated by a chain line B, a load exceeding the pretension applied to the ball screw 07 acts.

Here, the two rows of angular bearings 016 can withstand the load up to the limit load even if the estimated amount of thermal displacement is exceeded, but if the limit load is exceeded, there is a risk of early failure.
The present invention has been made in view of the above prior art, and an object of the feed drive device having a heat compensation function is to prevent bearing breakage, to stabilize the life, and to improve machining accuracy by stabilizing shaft rigidity.

  The feed drive device according to claim 1 of the present invention that solves the above-described problems supports both ends of the ball screw rotatably via angular bearings, and connects a motor to one end of the ball screw, In the feed drive device that applies axial pretension to the ball screw from the other end side of the ball screw, the angular bearing that supports the other end side of the ball screw realizes a tension state with respect to the ball screw. An angular bearing for tension is combined with an angular bearing for compression that realizes a compression state with respect to the ball screw, and the axial load acting on the angular bearing for compression does not exceed a certain value, so that A fixing portion for elastically displacing the position of the outer ring is provided.

  The feed drive device according to claim 2 of the present invention for solving the above-mentioned problem is that in claim 1, when the axial load acting on the compression angular bearing is below a certain value, the outer ring is rigid with respect to the bearing housing. It is characterized by fixing.

  A feed driving device according to a third aspect of the present invention for solving the above-mentioned problems is the feed driving device according to the second aspect, wherein the fixing portion is fixed to the holder that contacts both the outer ring and the bearing housing, and the bearing housing. And an elastic member that is press-fitted into an axial gap between the holder and the frame, and the elastic member is configured so that the axial load acting on the angular contact bearing for compression does not exceed a certain value. The position of the outer ring relative to the bearing housing of the bearing is elastically displaced and the outer ring is rigidly fixed to the bearing housing by the holder when the axial load acting on the angular contact bearing for compression is below a certain value. It is characterized by that.

  According to the feed drive device of the first aspect of the present invention, the fixing portion for elastically displacing the position of the outer ring relative to the bearing housing is provided so that the axial load acting on the compression angular bearing does not exceed a certain value. Even when the ball screw undergoes thermal displacement due to temperature rise, the fixed part elastically displaces the position of the outer ring with respect to the bearing housing, so the axial load acting on the angular contact bearing for compression does not exceed a certain value. The limit load is not applied to the angular contact bearing for compression, and therefore, the bearing can be prevented from being broken and the life can be stabilized.

  According to the feed drive device of the second aspect of the present invention, the fixing portion for rigidly fixing the outer ring to the bearing housing is provided when the axial load acting on the compression angular bearing is below a certain value. The rigidity of the compression angular bearing is increased, and the machining accuracy can be improved by stabilizing the feed shaft rigidity.

  According to the feed driving device according to claim 3 of the present invention, the holder that contacts both the outer ring of the compression angular bearing and the bearing housing, the frame fixed to the bearing housing, and the holder and the frame A fixing portion made of an elastic member that is press-fitted into the axial gap is provided, and the elastic member elastically displaces the position of the outer ring relative to the bearing housing so that the axial load acting on the compression angular bearing does not exceed a certain value. At the same time, when the axial load acting on the compression angular bearing is below a certain value, the outer ring is rigidly fixed to the bearing housing with the holder. In addition to the effects of preventing and stabilizing the life, the rigidity of the angular contact bearing for compression can be increased, and the rigidity of the feed shaft can be stabilized. Improving by machining accuracy an effect that can be achieved.

  The mode described below as an example is the best mode for carrying out the present invention.

A feed driving apparatus according to a first embodiment of the present invention is shown in FIG. FIG. 1 shows only the tension end side and omits the motor side.
Also in the present embodiment, as with the motor side, a pretension of about half of the estimated thermal displacement of the ball screw 7 is applied, and as the ball screw 7 is thermally displaced, the tension state is changed to the compressed state. ing.

That is, as shown in FIG. 1, two rows of angular bearings 6 and two rows of angular bearings 16 are held by the bracket 2 with respect to the base 1, and one end of the ball screw 7 rotates around these angular bearings 6 and 16. It penetrates freely. A spacer 12 is attached to the shaft end of the ball screw 7, and a nut 8 is screwed to press the spacer 12 against the angular bearings 6 and 16. A nut 9 for preventing loosening is further screwed onto the outside of the nut 8.
In the two rows of angular bearings 6 close to the shaft end, the inner diameter of the outer ring 5 held by the bearing housing 3 is wider on the shaft end side and narrower on the center side. The diameter is larger on the shaft end side and smaller on the center side. That is, the two rows of angular bearings 6 can realize the tension state of the ball screw 7.

On the other hand, in the two rows of angular bearings 16 closer to the center, the inner diameter of the outer ring 15 held by the bearing housing 3 is narrower on the shaft end side and wider on the center side, and the inner ring 14 fitted to the ball screw 7 The outer diameter is smaller on the shaft end side and larger on the center side. That is, the two rows of angular bearings 16 can realize the compressed state of the ball screw 7.
Here, the outer ring 5 of the most angular contact bearing 16 is constrained in the axial direction by the bearing housing 3, and an existing collar 17 is interposed in the axial gap between the bearing housing 3 and the bracket 2.

Further, the inner ring 4 of the angular bearing 6 closest to the shaft end abuts against the spacer 11, and the outer ring 5 is fixed elastically and rigidly by a fixing part 100.
The fixed portion 100 elastically displaces the position of the outer ring 5 with respect to the bearing housing 3 so that the load acting on the two rows of angular bearings 16 does not exceed the estimated thermal displacement, and further acts on the two rows of angular bearings 16. The outer ring 5 is rigidly fixed to the bearing housing 3 when the load to be applied is equal to or less than the estimated thermal displacement.

That is, the frame 20 protrudes from the shaft end side of the bearing housing 3 and is bent inward so as to face the outer ring 5, and the outer ring 5 and the bearing housing 3 are connected via the disc spring (elastic member) 19. A holder 18 is mounted between them. The holder 18 has a step so as to contact both the outer ring 5 and the vicinity of the inner periphery of the bearing housing 3.
The disc spring (elastic member) 19 is ideally rigid enough to rigidly fix the outer ring 5 with the holder 18 when the load acting on the two rows of angular bearings 16 is less than half of the estimated thermal displacement. And the elasticity of the degree that elastically displaces the position of the outer ring 5 with respect to the bearing housing 3 to the right in the drawing so that the load acting on the two rows of angular bearings 16 does not exceed the thermal displacement assumption amount. is there.

Accordingly, by adjusting the amount of screwing by the nut 8, when a leftward force in the figure acts on the four rows of angular bearings 6, 16 via the spacers 12, the two rows of angular bearings 6 A slanting force acts on the axial direction between the inner ring 4 and the outer ring 5 between the inner ring 4 and the outer ring 5 as shown by the arrows in the figure. An axial pretension can be applied to the screw 7.
Here, the pretension is set to about half of the estimated thermal displacement of the ball screw 7, and the tension state is changed to the compressed state as the ball screw 7 is thermally displaced.

That is, as indicated by a one-dot chain line A in FIG. 2, in the initial state (at room temperature), a load having the same magnitude as the pretension acting on the ball screw 7 acts on the two rows of angular bearings 6. According to the thermal deformation accompanying the temperature rise of 7, the value gradually decreases, and when the pretension is lost, the load becomes zero.
Further, when a compressive force is applied to the ball screw 7 in accordance with the thermal deformation caused by the temperature rise, as shown by a two-dot chain line B in FIG. It will act on the bearing 16. At this time, in the two rows of angular bearings 16, the bearing rolling elements are sandwiched therebetween, and the inner ring 4 and the outer ring 5 are inclined with respect to the axial direction as indicated by arrows (outlined) in the figure. Force acts

When the thermal deformation due to the temperature rise reaches the estimated thermal displacement, a load having the same magnitude as the pretension acting on the ball screw 7 is applied to the two rows of angular bearings 16.
Further, when the temperature of the ball screw 7 exceeds the assumed heat rise value (heat rise assumed value) and the thermal displacement exceeds the expected value, the disc spring 19 is elastically deformed, and the holder 18 is 1, the load is not applied to the two rows of angular bearings 16 as indicated by the solid line C in FIG. In other words, when the estimated amount of thermal displacement is exceeded, switching to constant pressure preload is performed.

Therefore, the load exceeding the thermal displacement assumption amount does not act on the two rows of angular bearings 16, and the effect of preventing early breakage can be obtained.
Further, it is considered that a load due to acceleration / deceleration acts near the tension end side position, a load opposite to the pretension is applied, and the pretension applied to the ball screw 7 is lost.
Therefore, the disc spring 19 is designed to have rigidity and elasticity by adding a load caused by acceleration / deceleration acting near the tension end side position to the assumed thermal displacement amount, and the pre-tension applied to the ball screw 7. It is possible to prevent omission.

  Further, as shown by a solid line E in FIG. 2, the disc spring 19 is such that the outer ring 5 is rigidly fixed by the holder 18 when the load acting on the two rows of angular bearings 16 is equal to or less than the estimated thermal displacement. This is clearly different from Patent Document 1 in that it has rigidity, that is, functions as a rigid body.

That is, in Patent Document 1, for example, as shown in FIG. 1, when a ball screw (indicated by reference numeral 8) reaches a compressed state, a bearing (indicated by reference numeral 7) that realizes the compressed state of the ball screw is a disc spring. Since it can be elastically displaced at (shown by reference numeral 24), its rigidity is considerably low as shown by the broken line D in FIG.
On the other hand, in the present embodiment, even when the ball screw 7 is in a compressed state, the outer ring 5 is rigidly fixed to the bearing housing 3 by the disc spring 19 up to the estimated heat rise, that is, the disc spring 19. 2 functions as a rigid body rather than an elastic body, and as shown by a solid line E in FIG. 2, the same rigidity as when the two rows of angular bearings 16 are in tension can be secured.

  The present invention relates to a feed driving device having a heat compensation function, and can be widely used for machine tools and industrial machines in general.

It is sectional drawing which shows the feed drive device (tension end side) which concerns on 1st Example of this invention. It is a graph which compares and shows the bearing load and bearing rigidity with respect to a heat rise (thermal displacement of a ball screw). It is sectional drawing which shows the feed drive device (tension end side) which concerns on another prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base 2 Bracket 3 Bearing housing 4,14 Inner ring 5,15 Outer ring 6,16 Angular bearing 7 Ball screw 8 Nut 9 Loosening prevention nut 12 Spacer 17 Joint collar 18 Holder 19 Belleville spring 20 Bracket 100 Fixed part

Claims (3)

  Both ends of the ball screw are rotatably supported via angular bearings, and a motor is connected to one end side of the ball screw, while an axial pretension is applied to the ball screw from the other end side of the ball screw. The angular bearing for supporting the other end of the ball screw includes a tension angular bearing that realizes a tension state with respect to the ball screw, and a compression angular bearing that realizes a compression state with respect to the ball screw. A fixed part for elastically displacing the position of the outer ring with respect to the bearing housing of the bearing is provided so that an axial load acting on the angular contact bearing for compression does not exceed a certain value. Feed drive device.   The feed driving device according to claim 1, wherein the fixing portion rigidly fixes the outer ring to the bearing housing when an axial load acting on the compression angular bearing is equal to or less than a predetermined value.   The fixed portion includes a holder that contacts both the outer ring and the bearing housing, a frame fixed to the bearing housing, and an elastic member that is press-fitted into an axial gap between the holder and the frame. The elastic member elastically displaces the position of the outer ring with respect to the bearing housing of the bearing and acts on the compression angular bearing so that the axial load acting on the compression angular bearing does not exceed a certain value. 3. The feed driving device according to claim 2, wherein the outer ring is rigidly fixed to the bearing housing by the holder when the axial load is a predetermined value or less.

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