JP2006105298A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw capable of preventing occurrence of flaking or the like caused by collision of a ball against a step formed on a boundary portion between a ball returning passage and a ball rolling passage, when the ball coming out from the ball returning passage enters into the ball rolling passage. <P>SOLUTION: A tapered ball guide passage 11 expanding toward the ball returning passage 7 is formed between the ball rolling passage 6 and the ball returning passage 7 to prevent the contact of the ball 5 coming out from the ball returning passage 7, with the step 10 when the ball enters into the ball rolling passage 6. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ball screw used in various industrial machines such as machine tools as means for mechanically converting rotational motion into linear motion.

  In various industrial machines such as machine tools, a ball screw as shown in the following document 1 is used as means for mechanically converting rotational motion into linear motion. However, such a ball screw has a U-shaped ball circulation tube made of metal as a part for circulating a ball rolling on a spiral ball rolling path formed by the ball screw groove and the ball screw groove. The ball is circulated by scooping up the ball in a direction perpendicular to the center line of the screw shaft by the tongue portion of the ball circulation tube. For this reason, when the ball is picked up by the tongue portion of the ball circulation tube, vibration and noise are generated, which may reduce the reliability of the ball screw.

  Therefore, the ball rolling on the ball rolling path is picked up in a direction inclined by the lead amount of the ball screw groove with respect to a straight line that is in contact with the ball center orbit circle and perpendicular to the center line of the screw shaft. Ball screws have been proposed. As shown in FIG. 6, the ball screw includes a screw shaft 1 and a nut 2, and a ball screw groove 3 s is formed on the outer peripheral surface of the screw shaft 1.

  The ball screw groove 3s faces the ball screw groove 3n formed on the inner peripheral surface of the nut 2, and a large number of balls 5 are provided between the ball screw groove 3s and the ball screw groove 3n. These balls 5 roll along a spiral ball rolling path formed between the ball screw grooves 3 s and 3 n in accordance with the rotational movement of the screw shaft 1 or the nut 2. A ball return passage 7 is provided for returning the ball 5 that has rolled on the ball rolling path.

  The ball return passage 7 penetrates the nut 2 in the axial direction, and ball circulation pieces 8 are incorporated at both ends of the nut 2 in order to circulate the balls 5. The ball circulation piece 8 is formed by injection molding of a resin material. The ball circulation piece 8 includes a ball 5 that rolls between the ball screw grooves 3s and 3n along a tangent line that contacts the ball center orbit circle. Further, a tongue portion 81 (see FIGS. 7 and 8) that scoops up in a direction inclined by an amount corresponding to the lead of the ball screw grooves 3s and 3n with respect to a straight line orthogonal to the center line of the screw shaft 1 is integrally formed.

Further, the ball circulation piece 8 has a ball guide piece 82 (see FIGS. 7 and 8). The ball circulation piece 8 has a ball circulation piece 8 at the end of the inner peripheral surface of the nut 2 into which the ball circulation piece 8 is incorporated. A ball guide surface 9 (see FIGS. 6 and 9) for guiding the ball 5 to the ball return passage 7 in cooperation with the ball guide piece 82 is formed.
In such a ball screw, the ball 5 that rolls between the ball screw grooves 3 s and 3 n moves between the ball screw grooves 3 s and 3 n with respect to a straight line orthogonal to the center line of the screw shaft 1 by the tongue portion 81 of the ball circulation piece 8. Since it can be picked up in a direction inclined by the lead, it is possible to suppress the generation of vibration and noise as compared with the method of picking up the ball in a direction perpendicular to the center line of the screw shaft and circulating the ball. .

Further, the ball guide surface 9 for guiding the ball 5 to the ball return passage 7 is formed on the nut 2 in cooperation with the ball guide piece 82 of the ball circulation piece 8, so that the leads of the ball screw grooves 3s and 3n are connected to the ball. The ball 5 can be circulated without causing the ball circulation piece 8 to interfere with the ball screw groove 3n of the nut 2 even when the diameter is smaller than 5 or when the ball screw grooves 3s, 3n are multi-threaded grooves.
JP 2003-269564 A

  However, in the ball screw described above, the ball guide surface 9 is formed by turning the inner peripheral surface of the nut 2 including a part of the ball screw groove 3n with a ball end mill. For this reason, a step 10 as shown in FIG. 10 may occur at the boundary between the ball rolling path 6 and the ball return path 7, and the ball 5 coming out of the ball return path 7 enters the ball rolling path 6. Flaking on the surface of the ball 5 or the groove surface of the ball screw groove 3n by colliding with the step 10, or metal powder generated by the flaking is caught between the ball screw grooves 3s, 3n and the ball 5 As a result, wrinkles such as indentations may occur on the groove surfaces of the ball screw grooves 3 s and 3 n and on the surface of the ball 5.

  The present invention has been made paying attention to such a problem, and occurred when the ball exiting from the ball return path enters the ball rolling path at the boundary between the ball return path and the ball rolling path. It is an object of the present invention to provide a ball screw that can prevent flaking and the like from colliding with a step.

  In order to achieve the above-mentioned object, the present invention provides a large number of rollers that roll between the ball screw grooves formed on the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut as the screw shaft or the nut rotates. A ball circulation piece for scooping up and circulating the ball in a direction inclined by the lead of the ball screw groove with respect to a straight line perpendicular to the center line of the screw shaft is provided at both ends of the nut, and the ball circulation piece A ball screw having a ball guide surface formed on the nut for guiding the ball to a ball return passage formed on the nut in cooperation with a ball guide piece provided on the nut, formed between the ball screw grooves. A tapered ball guiding path that extends toward the ball return path is formed at the boundary between the ball rolling path and the ball return path.

In this case, the ball guide path may be formed by crowning the boundary portion between the groove surface of the ball screw groove formed on the nut and the ball guide surface, or the ball guide groove of the ball screw groove formed on the nut. The boundary portion between the groove surface and the ball guide surface may be formed by crowning and then finishing with a rubber grindstone or the like.
In the ball screw according to the present invention, a spacer having a smaller elastic coefficient than that of two adjacent balls may be arranged between two adjacent balls. In this case, the spacer may be a resin retaining piece formed in a disk shape with a smaller diameter than the ball, or may be a resin spacer ball formed in a spherical shape with a smaller diameter than the ball. .

  According to the ball screw of the present invention, the tapered ball guiding path that extends toward the ball return path is formed between the ball rolling path and the ball return path. Steps are unlikely to occur at the boundary of the ball, so when the ball exiting from the ball return passage enters the ball rolling path, it collides with the step generated at the boundary between the ball return path and the ball rolling path, and flaking, etc. Can be prevented.

Hereinafter, a first embodiment of the present invention will be described with reference to FIG. 1, but the same parts as those shown in FIG. 10 are denoted by the same reference numerals, and detailed description thereof will be omitted.
FIG. 1 is a diagram schematically showing a main part of a ball screw according to a first embodiment of the present invention. As shown in FIG. 1, a boundary portion between a ball rolling path 6 and a ball return path 7 is A tapered ball guide path 11 extending toward the ball return path 7 is formed by smoothly crowning the boundary portion between the groove surface of the ball screw groove 3n and the ball guide surface 9.

  In the ball screw configured as described above, a tapered ball guide path 11 extending toward the ball return path 7 is formed at the boundary portion between the ball rolling path 6 and the ball return path 7, and as shown in FIG. Such a step 10 is less likely to occur at the boundary between the ball rolling path 6 and the ball return path 7, and the balls 5 that have exited the ball return path 7 can be smoothly introduced into the ball rolling path 6. Therefore, when the ball 5 exiting from the ball return path 7 enters the ball rolling path 6, it collides with a step generated at the boundary between the ball return path 7 and the ball rolling path 6 to cause flaking and the like. Can be prevented.

In the first embodiment described above, the ball guiding path 11 is formed by crowning the boundary portion between the groove surface of the ball screw groove 3n and the ball guide surface 9, but the second embodiment shown in FIG. As described above, after the boundary portion between the groove surface of the ball screw groove 3n and the ball guide surface 9 is smoothly crowned, the ball guide path 11 may be formed by finishing with a rubber grindstone or the like.
In this way, after the boundary portion between the groove surface of the ball screw groove 3n and the ball guide surface 9 is smoothly crowned, the ball 5 exiting from the ball return passage 7 is returned to the ball by finishing with a rubber grindstone or the like. Since the boundary portion between the passage 7 and the ball rolling path 6 rolls more smoothly, the ball return path 7 and the ball rolling path 6 when the ball 5 exiting the ball return path 7 enters the ball rolling path 6. It is possible to surely prevent flaking and the like from colliding with a step generated at the boundary portion.

FIG. 3 is a diagram showing a third embodiment of the present invention. The third embodiment is different from the second embodiment in that a plurality of balls 5 are adjacent to each other between two adjacent balls 5. The resin retaining piece 12 formed in a disk shape with a smaller diameter is arranged as a spacer.
Thus, by disposing the resin retaining piece 12 formed in a disk shape with a smaller diameter than the ball 5 between the two adjacent balls 5, 5, the ball rolling path 6 and the ball return path 7 are arranged. It is possible to suppress the occurrence of competition between the balls at the boundary portion between the two and the generation of noise and vibration due to the competition between the balls can be reduced.

FIG. 4 is a diagram showing a fourth embodiment of the present invention. The fourth embodiment is different from the second embodiment in that a plurality of balls 5 are adjacent to each other between two adjacent balls 5. The resin spacer ball 13 formed in a spherical shape with a smaller diameter is arranged as a spacer.
Thus, by arranging the resin spacer ball 13 formed in a spherical shape with a smaller diameter than the ball 5 between the two adjacent balls 5 and 5, the boundary between the ball rolling path 6 and the ball return path 7. Since it is possible to suppress the occurrence of competition between the balls at the portion, it is possible to reduce the occurrence of noise and vibration due to the competition between the balls as in the third embodiment.

The inventor uses a ball screw manufactured by NSK Ltd. (nominal number: BS2525, ball diameter: 4.7625 mm, Dm (ball center orbit circle diameter): 25.5 mm), preload load: 1000 N, rotation speed : N = 1000 to 8000 min ⁻¹ , Stroke: 500 mm, Lubricating grease: A ball screw durability test was performed under the test conditions of Multemp SRL (Kyodo Yushi). Then, the actual travel distance of the nut until flaking occurs on the groove surface of the ball screw groove or the surface of the ball and the damage is measured, and this is compared with the calculated travel distance to calculate the ball screw. The life ratio was determined. The results are shown in Table 1.

  In Table 1, sample number 1 shows the calculated life ratio of the ball screw according to the first embodiment shown in FIG. 1, and sample number 2 shows the calculated life of the ball screw according to the second embodiment shown in FIG. The ratio is shown. Sample number 3 shows the calculated life ratio of the ball screw according to the third embodiment shown in FIG. 3, and sample number 4 shows the calculated life ratio of the ball screw (conventional example) shown in FIG. .

  FIG. 5 is a diagram showing the relationship between the calculated life ratio of each ball screw shown in Table 1 and Dm · n (Dm: ball center orbit circle diameter, n: rotational speed). As is apparent from the figure, in the conventional ball screw, the calculated life ratio is greatly reduced when the value of Dm · n exceeds 70,000. On the other hand, in the case of the first embodiment, it can be seen that the life ratio is higher than that of the conventional example in both the low-speed and high-speed rotation regions. In the case of the second embodiment, the life ratio is higher than that of the first embodiment, but the life ratio is lower than that of the third embodiment. I understand.

  Therefore, as in the first to third embodiments, the tapered ball guide path 11 that spreads toward the ball return path 7 is formed between the ball rolling path 6 and the ball return path 7. 10 is less likely to occur at the boundary between the ball rolling path 6 and the ball return path 7, and the balls 5 coming out of the ball return path 7 can be smoothly introduced into the ball rolling path 6. it can. Therefore, when the ball 5 exiting from the ball return path 7 enters the ball rolling path 6, it collides with a step generated at the boundary between the ball return path 7 and the ball rolling path 6 to cause flaking and the like. Can be prevented.

It is a figure which shows typically the principal part of the ball screw which concerns on the 1st Embodiment of this invention. It is a figure which shows typically the principal part of the ball screw which concerns on the 2nd Embodiment of this invention. It is a figure which shows typically the principal part of the ball screw which concerns on the 3rd Embodiment of this invention. It is a figure which shows typically the principal part of the ball screw which concerns on the 4th Embodiment of this invention. It is a diagram which shows the relationship between the life ratio of a ball screw, and Dm * n value. It is a figure which shows schematic structure of the ball screw called a circulation top type. FIG. 7 is a plan view of the ball circulation piece shown in FIG. 6. It is a bottom view of the ball circulation piece shown in FIG. It is a perspective view which shows the ball | bowl guide surface formed in the nut. It is a figure which shows the level | step difference formed in the boundary part of a ball rolling path and a ball return path.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw shaft 2 Nut 3s, 3n Ball screw groove 5 Ball 6 Ball rolling path 7 Ball return path 8 Ball circulation piece 81 Tongue part 82 Ball guide piece part 9 Ball guide surface 10 Step 11 Ball guide path 12 Resin retaining piece made of resin 13 Resin spacer balls

Claims (6)

A large number of balls that roll between the ball screw grooves formed on the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut in accordance with the rotational movement of the screw shaft or the nut are linearly orthogonal to the center line of the screw shaft. In contrast, the ball circulation piece for scooping up and circulating in the direction inclined by the lead amount of the ball screw groove is provided in both ends of the nut, and in cooperation with the ball guide piece provided on the ball circulation piece. In the ball screw in which the ball guide surface for guiding the ball to the ball return passage formed in the nut is formed in the nut,
A ball screw characterized in that a tapered ball guide path that extends toward the ball return path is formed at a boundary portion between the ball rolling path formed between the ball screw grooves and the ball return path.   2. The ball screw according to claim 1, wherein the ball guiding path is formed by crowning a boundary portion between a groove surface of the ball screw groove formed on the nut and the ball guide surface.   The ball guide path is formed by performing a crowning process on a boundary portion between the groove surface of the ball screw groove formed on the nut and the ball guide surface, and then finishing with a rubber grindstone or the like. The ball screw according to claim 1.   The ball screw according to any one of claims 1 to 3, wherein a spacer having a smaller elastic coefficient than the ball is disposed between two adjacent balls among the plurality of balls.   The ball screw according to claim 4, wherein the spacer is a resin retaining piece formed in a disk shape with a smaller diameter than the ball.   6. The ball screw according to claim 5, wherein the spacer is a resin spacer ball formed in a spherical shape with a smaller diameter than the ball.

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