JP2002266976A - Ball groove shape of ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball groove shape capable of preventing damage on a ball groove even at high speed operation by improving the ball groove shape in a screw shaft of a ball screw. SOLUTION: An outside diameter part 4 of the screw shaft 1 and a semicircular shaped ball rolling part 5 of the ball groove 1a are connected with an arc part 11. A radius of curvature R of the arc part 11 is equal to or more than half and equal to or lower than twice of the radius of the ball 7. The arc part 11 is continuously connected with a smooth curve line at least to the ball rolling part 5. The outside diameter of the screw shaft 1 is equal to or slightly smaller than a center circle diameter of the ball 7 engaged with the ball groove 1a provided on the outer diameter of the screw shaft 1. The difference is 10% or less of the diameter of the ball 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a ball groove shape of a ball screw, and more particularly to a ball groove shape of a ball screw shaft capable of improving the durability of the ball screw.

[0002]

2. Description of the Related Art As a conventional cross-sectional shape of a ball groove of a screw shaft of a ball screw, there is, for example, one shown in FIG. As shown in FIG. 6, in a so-called tube-type ball screw provided with a ball circulation tube 3 on a nut 2 screwed to a screw shaft 1 via a number of balls, as shown in FIG. The cross-sectional shape is shown in an enlarged manner, and the ball groove 1a spirally formed on the screw shaft 1 has a land portion 4 which is a cylindrical outer diameter portion of the screw shaft and an arc shape with a radius r. The ball rolling portion 5 (that is, the land shoulder portion) is connected to the ball rolling portion 5 by a chamfered portion 6 formed of a linear inclined surface.

In general, a preload is applied to a ball screw in order to increase the rigidity of the ball screw against an axial load and secure positional accuracy. As means therefor, for example, there is one as shown in FIG. 7 (US Pat. No. 4,177,690). This slightly shifts the lead of the ball groove 2a of the nut 2 with respect to the ball groove 1a of the screw shaft 1. After the ball 7 rolls in the shifted grooves 1a and 2a, it is scooped up by the scooping-up end 3a of the ball circulation tube 3, moved into the ball circulation tube 3, and returned to the grooves 1a and 2a again. It is.
In the conventional example, at this time, the chamfered portion 6 is provided with the two grooves 1a,
By slightly relieving the ball 7 pre-loaded in 2a in the axial direction and assisting the upward movement, it is possible to prevent the ball 7 from being clogged at the scooping-up end 3a of the ball circulation tube and to prevent the ball from being clogged. This prevents the hooks from being returned into the two grooves 1a and 2a again. In this conventional example, the chamfered portion 6 is preferably a straight chamfer having an angle α of 30 ° to 60 ° shown in FIG. 5, and ideally, the angle α is restricted to 45 ° to 50 °. This allows
The intersection point P1 between the chamfered portion 6 of the ball groove 1a of the screw shaft and the arc-shaped ball rolling portion 5 has a projection shape.

Further, instead of such a straight chamfered portion 6, an arc-shaped chamfered portion 8 is known as shown in FIG. This arc-shaped chamfered portion 8 is mainly employed in a so-called top (piece) circulation type ball screw having a circulation top 9 as shown in FIG. This is a screw shaft 1
The cylindrical outer diameter portion (land portion) 4 and the ball rolling portion 5 having an arc shape with a radius r are connected by an arc-shaped chamfered portion 8 with a radius of curvature R. The radius of curvature R of the arc is reduced to 40% or less of the radius r of the ball 7 in order to connect the chamfer 8 and the chamfer 8 almost continuously. Also, in this case, the intersection P1 between the arc-shaped chamfered portion 8 of the ball groove 1a of the screw shaft and the arc-shaped ball rolling portion 5 has a more obtuse angle as compared with FIG. I have.

[0005] Incidentally, Y _2/2 of Y _1/2 and 8 of FIG. 5
Is both represent half of the difference between the diameter of the ball center circle passing through the center O of the ball 7 in the outer diameter of the ball groove 1a of the screw shaft 1, the case of the conventional ball groove shape, Y ₁ , Y ₂ are set to be relatively large, at least 10% of the diameter of the ball 7. Θ is the intersection point P1 between the ball rolling portion 5 and the linear chamfered portion 6 or the ball rolling portion 5 and the arc-shaped chamfered portion 8
Is an angle indicating the position of the intersection P1 with
About 70 °.

[0006]

When the ball screw is operated, the ball 7 rolls in a spiral load ball rolling path composed of a ball groove 1a of the screw shaft and a ball groove 2a of the nut opposed thereto. And ball circulation tube 3 and circulation top 9
The ball is re-circulated by being scooped up by the ball circulating portion and straddling the loaded ball rolling path, and is again sent to the loaded ball rolling path. At this time, the trajectory of the ball circulation motion has a certain range of variation. Such a variation in the locus is inevitably present due to differences in machining and assembly errors of the ball screw, operating speed and other use conditions, and is inevitable.

Due to the variation of the trajectory of the ball circulating motion, the ball 7 in the ball circulating portion is moved to the position P in FIG.
After colliding near one point, it is often sent to the loaded ball rolling path. However, in the ball groove shape of the screw shaft of the conventional ball screw as shown in FIGS. 5 and 8, the point P1 is protruding (and in the case of FIG. Even if it is arc-shaped, its radius of curvature is small), and the stress when the ball 7 collides with these points or in the vicinity thereof is large. In particular, in recent ball screws, the impact force increases as the operation speed increases, and damage occurs near the point P1 which is the land shoulder of the ball screw shaft. Had one problem.

Accordingly, the present invention has been made in view of the above-mentioned conventional problems. By improving the shape of the ball groove on the screw shaft of the ball screw, the ball groove is not damaged even at high speed operation. It is an object of the present invention to provide a ball screw capable of satisfying a required service life.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a ball screw having a substantially semicircular outer diameter portion and a ball groove in a cross section perpendicular to a groove of a ball groove of a screw shaft of a ball screw. The ball rolling portion is connected to the ball rolling portion by an arc portion, and the radius of curvature of the arc portion is set to not less than half and not more than twice the radius of the ball rolling in the ball groove, and at least the arc portion and the ball The rolling portion is characterized by being smoothly continuous.

Here, the outer diameter of the screw shaft is equal to or slightly smaller than the center circle diameter of the ball fitted in the ball groove provided in the outer diameter of the screw shaft, and the difference is determined by the diameter of the ball. 10% or less.

[0011]

[Effect] By making the shoulder opening of the land of the screw shaft of a ball screw into an arc, the radius of curvature is set to 1/2 to 2 times the radius of the ball, and it is continuously and smoothly connected to the arc surface of the ball rolling portion. However, the connection does not form a protrusion like the conventional point P1. As a result, the stress concentration is reduced even when the impact force of the ball collision acts, so that the land shoulder opening is not damaged even at high speed operation.

Further, the outer diameter of the screw shaft is equal to or slightly smaller than the center circle diameter of the ball fitted into the ball groove provided on the outer diameter of the screw shaft, and the difference is defined as 10 times the diameter of the ball. % Or less, it is possible to prevent the ball from colliding with the intersection P2 between the arc portion and the land even if the radius of curvature of the arc portion is increased.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. This embodiment is applied to a tube-type ball screw having a screw shaft diameter of 40 mm, a lead of 25 mm, and a ball diameter of 7.1438 mm. FIG. 1 shows a cross section of the ball shaft 1a of the screw shaft 1 at right angles to the groove. An outer diameter portion (land portion) 4 of the screw shaft 1 and a substantially semicircular ball rolling portion 5 of the ball groove 1a are connected by an arc portion 11 chamfered in an arc shape. The radius of curvature R of the arc 11
Is approximately equal to the radius r of the ball 7 in this embodiment, 3.57 mm, and is smoothly and continuously connected to the curve of the ball rolling portion 5 at the point P. In addition, a relief portion 12 at the time of grinding is formed at the groove bottom of the ball rolling portion 5.

The upper portion of the arc portion 11 is connected to the land portion 4 having the outer diameter of the screw shaft 1 to form a point P2 which is a projection-like intersection. Further, in this embodiment, the difference between the ball center circle diameter passing through the center O of the ball 7 in the ball groove 1 a of the screw shaft 1 and the outer diameter of the screw shaft 1, the magnitude of Y, is It is smaller than 10% of the diameter. In order to reduce the stress concentration due to the impact of the ball collision, it is desirable that the radius of curvature R of the arc portion 11 be as large as possible. On the other hand, as the radius of curvature R increases, the arc portion 11 and the land portion 4
As the position of the intersection point P2 approaches the center of the groove, its shape becomes a sharp projection. If the radius of curvature R exceeds the limit and becomes excessive, the chance of the ball colliding near the point P2 increases, and at the same time, the stress concentration at the time of the collision also increases, thereby increasing the risk of damage to the land shoulder opening. Therefore, it is necessary to set an upper limit on the radius of curvature R of the arc portion 11 to avoid the danger.

The inventor of the present invention has found that when the ball 7 passes through the ball circulation tube of the ball screw and is fed toward the ball groove 1a of the screw shaft 1, the ball 7 first collides with the surface of the ball groove 1a. The position is plotted, the obtained diagram is analyzed, and the upper limit of the radius of curvature R of the arc portion 11 is determined. FIG. 2 to FIG. 4 are diagrams when the results of continuously plotting the ball collision positions are viewed from the top of FIG. In each figure, when the ball center position came to most of a point on E ₁ level, the ball is shown to collide with the surface of the ball groove 1a in E ₂ point indicated directly below the E _1.

FIG. 2 shows a case where it is assumed that the trajectory of the ball sent into the ball groove 1a is ideal and there is no variation. In this case, the ball collides only with the ball rolling portion 5 irrespective of the radius of curvature R of the arc portion 11. Therefore, the upper limit of the radius of curvature R of the arc portion 11 does not matter. However, in the actual case, the trajectory of the ball inevitably varies within a certain range due to the use conditions such as the processing / assembly error of the ball screw and the operating speed. FIG. 3 and FIG. 4 show analysis results in consideration of the dimensional accuracy of the ball screw and the deviation of the ball trajectory estimated from experimental results.

[0017] FIG. 3 shows a case of the ball groove shape of the present embodiment shown in FIG. 1, E ₂ the ball collides with the surface of the ball groove 1a
The point is within the arc 11. The radius of curvature R of the arc 11
Is formed to a size substantially equal to the radius of the ball, so that the possibility of damage occurring therefrom is extremely small. When the radius of curvature R of the arc portion 11 is further increased, the ball collision position approaches the projecting boundary line L between the arc portion 11 and the screw shaft outer diameter portion (land portion) 4. When the radius of curvature R exceeds a predetermined value, there is a danger that the ball collides with the boundary line L to cause damage to the land shoulder opening. The inventor has performed the above analysis,
The upper limit of the radius of curvature R of the circular arc portion 11 is determined based on the results of the measurement with various changes in the radius of curvature R of the circular arc portion 11. I was able to ask. Its value should be less than twice the radius of the ball.

On the other hand, when the radius of curvature R of the arc portion 11 is less than 1/2 of the radius of the ball, it has been recognized that the arc portion 11 is damaged by the ball collision. FIG. 4 shows a case of the conventional ball groove shape shown in FIG. 5 (where the land shoulder portion is connected by a chamfered portion 6 formed of an inclined surface). In this case, the ball is in the ball groove 1a.
E ₂ points to a surface of a collision, is on the boundary line between the ball rolling unit 5 and the chamfered portion 6, therefore the boundary line is in the protruding, it has been found that damage occurs from there .

The size of Y of the screw shaft 1 (ball groove 1)
a ball center circle diameter passing through the center O of the ball 7 in
(The difference from the outer diameter of the screw shaft 1) to 0 or less than 10% of the ball diameter, that is, a ball groove shape in which the outer diameter of the screw shaft 1 is relatively large with respect to the ball center circle diameter In this case, even if the radius of curvature R of the arc portion 11 is increased, the ball collision on the boundary line L between the arc portion 11 and the land portion 4 can be prevented, so that the stress concentration at the time of collision can be further alleviated. It is possible.

Although the above embodiment has been described in connection with a tube circulation type ball screw, the present invention can be similarly applied to other frame circulation type ball screws.

[0021]

As described above, according to the present invention, in the cross-sectional shape perpendicular to the groove of the ball groove of the screw shaft of the ball screw, the ball rolling of the semi-circular shape between the outer diameter portion of the screw shaft and the ball groove. Are connected to each other by an arc portion, and the radius of curvature of the arc portion is set to be not less than の and not more than twice the radius of the ball rolling in the ball groove so as to be smoothly continuous with at least the ball rolling portion. It was assumed. As a result, even if the impact force of the ball collision acts on the vicinity of the arc, stress concentration is reduced, and damage to the land shoulder opening of the screw shaft can be prevented even at high speed operation. In the case where the center circle diameter of the ball fitted in the ball groove provided on the outer diameter of the shaft is equal to or slightly smaller than the center circle diameter and the difference is 10% or less of the diameter of the ball, Even if the radius of curvature is increased, the collision of the ball with the intersection between the arc portion and the land portion can be prevented, so that the effect of extending the life of the ball screw can be obtained.

[Brief description of the drawings]

FIG. 1 is a right-angle cross-sectional view of a ball groove of a screw shaft according to an embodiment of the present invention.

FIG. 2 is a continuous plot diagram of a ball collision position with respect to a ball groove shown by an arrow A in FIG. 1 and shows a case where a ball motion trajectory is ideal.

FIG. 3 is a continuous plot diagram of a ball collision position with respect to a ball groove in FIG. 1 in a case where a ball motion trajectory is realistic;

FIG. 4 is a continuous plot diagram of a ball collision position with a ball groove in a conventional ball screw, where a ball motion trajectory is realistic.

FIG. 5 is a right-angle cross-sectional view of a ball groove of a conventional screw shaft.

FIG. 6 is an external plan view of a tube-type ball screw.

FIG. 7 is a sectional view taken along line VII-VII of FIG. 6;

FIG. 8 is a right-angle cross-sectional view of a ball groove of another conventional screw shaft.

FIG. 9 is an external plan view of the top-circulating ball screw.

[Explanation of symbols]

 Reference Signs List 1 screw shaft 1a ball groove 4 outer diameter part (land) 5 ball rolling part 7 ball 11 arc part

Claims (2)

[Claims] In a cross-sectional shape perpendicular to a groove of a ball groove of a screw shaft of a ball screw, an outer diameter portion of the screw shaft and a substantially semicircular ball rolling portion of the ball groove are connected by an arc portion. The radius of curvature of the arc portion is set to be not less than 1/2 and not more than twice the radius of the ball rolling in the ball groove, and at least the arc portion and the ball rolling portion are smoothly connected. Ball screw ball groove shape. 2. An outer diameter of the screw shaft is equal to or slightly smaller than a center circle diameter of a ball fitted in a ball groove provided in the outer diameter of the screw shaft, and a difference between the diameter and the center diameter of the ball is defined as the diameter of the ball. The ball groove shape of the ball screw according to claim 1, wherein the ball groove shape is 10% or less.