WO2015159508A1

WO2015159508A1 - Ball screw

Info

Publication number: WO2015159508A1
Application number: PCT/JP2015/001966
Authority: WO
Inventors: 水口　淳二
Original assignee: 日本精工株式会社
Priority date: 2014-04-14
Filing date: 2015-04-07
Publication date: 2015-10-22
Also published as: JPWO2015159508A1; TW201608150A; JP6187680B2; CN106133396B; TWI568955B; CN106133396A

Abstract

A ball screw equipped with a ball return path formation component having a tongue, wherein the end surface of the tongue (42) of the ball return path formation component (4) has a groove-bottom-opposing line (L) which, in a cross section at a groove bottom (110), which is the deepest positon of a spiral groove (11) of the screw shaft, opposes a circle formed by the groove bottom (110), with a clearance (S) therebetween. The groove-bottom-opposing line (L) is provided such that the clearance (S) decreases from the tip portion (42a) toward the base portion (42b) of the tongue (42).

Description

Ball screw

This invention relates to a ball screw provided with a circulating part having a tongue (part forming a ball return path).

The ball screw has a screw shaft, a nut, and a plurality of balls. The screw shaft passes through the nut, and a rolling path in which the ball rolls in a loaded state by a spiral groove formed on the outer peripheral surface of the screw shaft and a spiral groove formed on the inner peripheral surface of the nut. Is formed. The nut includes a ball return path for returning the ball from the end point of the rolling path to the start point. The balls are arranged in a circulation path composed of the rolling path and the ball return path. The nut and the screw shaft move relative to each other through the ball circulating in the circulation path.

Parts that form the ball return path (circulation parts) are parts that are used by inserting legs into holes that penetrate from the outer peripheral surface of the nut to the inner peripheral surface (a metal return tube and a line that indicates the moving direction of the ball) And an end deflector used in communication with a hole penetrating in the axial direction of the nut.
These parts have tongues for scooping the ball from the rolling path into the ball return path at the end of the rolling path and for guiding the ball from the ball return path to the rolling path at the start point. With these components attached, the end face of the tongue faces at least the spiral groove of the screw shaft. That is, the end face of the tongue has a groove bottom facing line that faces the spiral groove of the screw shaft at the deepest position (hereinafter referred to as “groove bottom”).

A conventional example of a ball screw having a metal return tube is shown in FIG. This figure is a partial cross-sectional view of the portion where the return tube 40 of the ball screw is disposed along the screw shaft 1 and the

spiral grooves

11 and 21 of the nut 2 (the rolling path 31 of the ball 3). A flat portion 2a is formed on the outer peripheral surface of the nut 2, and a through hole 22 penetrating from the flat portion 2a to the inner peripheral surface is formed.
The tip of the leg portion of the return tube 40 has an end surface 410 extending along the base line perpendicular to the tube axis direction in a range of more than half in the circumferential direction of the tube cross-section circle, and the other part is a tongue-like shape from the base line. The tongue 420 projects into The leg portion of the return tube 40 is inserted into the through hole 21 of the nut 2, the tongue 420 is disposed in the rolling path 31, and the end face M of the tongue 420 faces the spiral groove 11 of the screw shaft 1. The ball 3 in the rolling path 31 collides with the tongue 420 and is scooped up and guided into the return tube 40.

In the conventional ball screw shown in FIG. 6, the groove bottom facing line L provided on the end face of the tongue 420 is an arc along a circle C10 concentric with the circle forming the groove bottom 110 of the screw shaft. That is, in the conventional ball screw, the gap S between the groove bottom opposing line L of the tongue 420 and the groove bottom 110 of the screw shaft is the same from the front end side to the base end side of the tongue 420.
In FIG. 6, the thickness of the return tube 40 is shown thicker only at the portion where the tongue 420 is formed. As can be seen from FIG. 6, at the distal end portion (corner portion on the side guiding the ball 3) 420a of the tongue 420, the angle formed by the inner peripheral surface of the return tube 40 and the groove bottom facing line L is an acute angle. In the part 420b, the angle formed by the outer peripheral surface of the return tube 40 and the groove bottom facing line L is an obtuse angle.
In such a conventional method for setting the groove bottom facing line L, the smaller the gap S, the smaller the radius of curvature of the groove bottom facing line L, so that the tongue 420 can be formed longer, but the tip (acute angle portion) 420a of the tongue 420 can be formed. The thickness becomes thinner. The larger the gap S is, the larger the radius of curvature of the groove bottom facing line L is, so that the tip part (acute angle part) 420a of the tongue 420 can be thickened. However, when the gap S is increased, the length of the tongue 420 is shortened.

FIG. 7 shows the case where the gap S is larger than that in FIG.
The longer the tongue 420, the more smoothly the ball 3 can be directed to the ball return path 45. That is, in the conventional setting method of the groove bottom facing line L of the tongue 420 (method of causing the groove bottom facing line L to be along a circle concentric with the circle forming the groove bottom 110 of the screw shaft), the ball 3 is smoothly returned to the ball. In order to make it go to the path 45, it is better to make the gap S smaller. However, the larger the gap S, the easier the ball 3 enters the gap S when going from the tongue 420 to the ball return path 45.
On the other hand, when the ball 3 collides with the tongue 420 and the tongue 420 is deformed, as can be seen from the comparison between FIG. 6B and FIG. 7B, the case where the gap S is smaller (FIG. 6) The tip portion (acute angle portion) 420 a of the tongue 420 is easy to contact the groove bottom 110. When the gap S is large (FIG. 7), unless the tongue 420 is significantly deformed, the tip end portion (acute angle portion) 420 a of the tongue 420 does not contact the groove bottom 110.
In particular, a synthetic resin circulation part has a lower mechanical strength than a metal circulation part. Therefore, if the gap S is too small, the tongue may be damaged. Even when the gap S is small, the base end portion (obtuse angle portion) of the tongue is difficult to contact the groove bottom of the screw shaft when the ball collides with the tongue.

In Patent Document 1, regarding the ball screw, the minimum clearance between the groove bottom of the screw shaft and the tongue is set to 1 of the diameter of the ball for the purpose of preventing damage to the tongue of the circulating part (part forming the ball return path). It is described to be within the range of 15% to 15%. In the ball screw described in Patent Document 1, the groove bottom-facing line of the tongue is along a circle concentric with the circle forming the groove bottom of the screw shaft, as in the conventional method.
In Patent Document 2, regarding the ball screw, for the purpose of suppressing early damage to the tongue of the end deflector, the radius of curvature R of the roundness formed at the tip (acute angle portion) of the tongue is set to R in relation to the diameter Dw of the ball. /Dw≧0.015 is described.

JP 2007-107613 A JP 2004-278551 A

As described above, in the conventional method for setting the groove bottom facing line of the tongue (the method of setting the groove bottom facing line along a circle concentric with the circle forming the groove bottom of the screw shaft), the ball is smoothly directed to the ball return path. This is incompatible with the fact that the tip of the tongue is difficult to contact the groove bottom of the screw shaft and the mechanical strength of the tip of the tongue is high.
An object of the present invention is to provide a ball screw provided with a circulating part having a tongue (a part forming a ball return path), and by appropriately setting the groove bottom facing line of the tongue, the ball smoothly moves toward the ball return path. That is, both the fact that the front end of the tongue is difficult to contact the groove bottom of the screw shaft and the mechanical strength of the front end of the tongue is high.

In order to solve the above problems, a ball screw according to an aspect of the present invention has the following constituent elements (1) to (4).
(1) It has a screw shaft, a nut, and a plurality of balls. The screw shaft passes through the nut, and a rolling path in which the ball rolls in a loaded state by a spiral groove formed on the outer peripheral surface of the screw shaft and a spiral groove formed on the inner peripheral surface of the nut. Is formed. The nut includes a ball return path for returning the ball from the end point of the rolling path to the start point. The balls are arranged in a circulation path composed of the rolling path and the ball return path. The nut and the screw shaft move relative to each other through the ball circulating in the circulation path.
(2) The component forming the ball return path has a tongue for scooping up the ball into the ball return path.
(3) An end face of the tongue (at least a surface facing the spiral groove of the screw shaft) is a cross section at a groove bottom that is the deepest position of the spiral groove of the screw shaft, and a circle and a gap forming the groove bottom are formed. And a groove bottom facing line opposed to each other.
(4) The groove bottom facing line is provided so that the gap decreases from the distal end side to the proximal end side of the tongue.

According to the present invention, a ball screw having a circulating part having a tongue, the ball smoothly going to the ball return path, and the tip of the tongue is difficult to contact the groove bottom of the screw shaft. A ball screw compatible with high mechanical strength is provided.

It is a figure which shows the relationship between the return tube which comprises the ball screw of 1st embodiment, a ball | bowl, and the deepest position (groove bottom) of the spiral groove of a screw shaft. It is sectional drawing in the groove bottom explaining the relationship between the tongue of the ball return path formation component which comprises the ball screw of embodiment, and the groove bottom of a screw axis, Comprising: The thickness of a ball return path formation component is tongue Only the portion where is formed is displayed thick. It is a figure which shows the relationship between the end deflector which comprises the ball screw of 2nd embodiment, a ball | bowl, and the deepest position (groove bottom) of the spiral groove of a screw shaft. It is a figure which shows the relationship between the synthetic resin circulation components which comprise the ball screw of 3rd embodiment, an end deflector, a ball | bowl, and the deepest position (groove bottom) of the spiral groove of a screw shaft. It is sectional drawing which shows the conventional example of a ball screw. It is a figure explaining the relationship between the tongue of the ball return path forming part constituting the ball screw of the conventional example and the groove bottom of the screw shaft, and the thickness of the return tube is shown thicker only in the portion where the tongue is formed Has been. It is a figure explaining the relationship between the tongue of the ball return path forming part constituting the ball screw of the conventional example and the groove bottom of the screw shaft, and the thickness of the return tube is shown thicker only in the portion where the tongue is formed Has been. It is a figure explaining clearance gaps Sa and Sb and a test method, Comprising: The tongue of a ball return path formation component and the cross section in the groove bottom of a screw shaft are shown. It is a graph which shows the relationship between contact surface pressure ratio and clearance ratio (Sa / Sb).

Hereinafter, although embodiment of this invention is described, this invention is not limited to the following embodiment.
[First embodiment]
The ball screw of this embodiment has the same screw shaft 1, nut 2, and ball 3 as the conventional ball screw shown in FIG. 5, and the return tube 40 of FIG. 6 and the return tube 4 that differs only in the end face shape of the tongue.
As shown in FIGS. 1 and 2, the end face of the tongue 42 of the return tube 4 has a groove bottom facing line that is opposed to a circle that forms the deepest position (groove bottom) 110 of the spiral groove of the screw shaft through a gap S. L. The groove-facing line L is an arc along a circle C1 whose center is different from the circle forming the groove bottom 110 of the screw shaft, and as shown in FIG. 2 (a), the base end from the distal end portion 42a side of the tongue 42 The gap S is provided so as to decrease toward the portion 42b. Further, the gap S on the front end portion 42a side of the tongue 42 is set to an appropriate dimension (a dimension that is larger than the base end 42b side but is difficult for the ball 3 to enter).

Therefore, according to the ball screw of this embodiment, when the ball 3 collides with the tongue 42 and the tongue 42 is deformed, for example, the state shown in FIG. That is, compared with the state shown in FIG. 6B and FIG. 7B, the groove bottom opposing line L of the tongue 42 and the groove bottom 110 of the screw shaft on the base end (obtuse angle portion) 42b side of the tongue 42 The distance becomes smaller.
Further, since the gap S on the tip end (acute angle portion) 42a side of the tongue 42 is set to an appropriate size, the tongue 3 is smoothly tanged to the groove bottom 110 of the screw shaft while smoothly moving the ball 3 toward the ball return path 45. It is possible to make it difficult to contact the tip 42a of 42.

In the unlikely event that the tongue 42 contacts the groove bottom 110 of the screw shaft, not only the front end portion 42a but also the base end portion 42b of the tongue 42 contacts the groove bottom opposing line L and the groove bottom of the screw shaft. 110 is likely to be a line contact rather than a single point of contact. Therefore, compared with the state shown in FIG. 6B and FIG. 7B, the stress generated at the tip 42a of the tongue 42 can be relaxed.
Therefore, in the ball screw of this embodiment, the groove bottom facing line L of the tongue 42 of the return tube 4 is appropriately set, so that the ball 3 smoothly moves toward the ball return path 45 and the tip of the tongue 42. The portion 42a is unlikely to contact the groove bottom 110 of the screw shaft, and the mechanical strength of the tip 42a of the tongue 42 is high.

[Second Embodiment]
As shown in FIG. 3, the ball screw of this embodiment has an end deflector 4 </ b> A made of a synthetic resin as a part that forms a ball return path 45. The tongue 42 of the end deflector 4A and the groove bottom 110 of the screw shaft have the relationship shown in FIG.
That is, the groove bottom opposing line L of the tongue 42 is an arc along a circle C1 whose center is different from the circle forming the groove bottom 110 of the screw shaft, and as shown in FIG. The gap S is provided so as to decrease from the side toward the base end portion 42b. Further, the gap S on the front end portion 42a side of the tongue 42 is set to an appropriate dimension (a dimension that is larger than the base end 42b side but is difficult for the ball 3 to enter).

In the unlikely event that the tongue 42 contacts the groove bottom 110 of the screw shaft, not only the front end portion 42a but also the base end portion 42b of the tongue 42 contacts the groove bottom opposing line L and the groove bottom of the screw shaft. 110 is likely to be a line contact rather than a single point of contact. Therefore, compared with the state shown in FIG. 6B and FIG. 7B, the stress generated at the tip 42a of the tongue 42 can be relaxed.
Therefore, in the ball screw of this embodiment, the groove bottom facing line L of the tongue 42 of the end deflector 4A is appropriately set, so that the ball 3 smoothly moves toward the ball return path 45 and the tip of the tongue 42. The portion 42a is unlikely to contact the groove bottom 110 of the screw shaft, and the mechanical strength of the tip 42a of the tongue 42 is high.

[Third embodiment]
As shown in FIG. 4, the ball screw of this embodiment has a circulation part 4 </ b> B made of synthetic resin as a part for forming the ball return path 45. The synthetic resin circulation part 4B is composed of two divided bodies divided along a line indicating the moving direction of the ball. Each divided body is formed by injection molding of a synthetic resin, and the circulating component 4B is assembled by joining these divided bodies. The tongue 42 of the circulating component 4B and the groove bottom 110 of the screw shaft have the relationship shown in FIG.
That is, the groove bottom opposing line L of the tongue 42 is an arc along a circle C1 whose center is different from the circle forming the groove bottom 110 of the screw shaft, and as shown in FIG. The gap S is provided so as to decrease from the side toward the base end portion 42b. Further, the gap S on the front end portion 42a side of the tongue 42 is set to an appropriate dimension (a dimension that is larger than the base end 42b side but is difficult for the ball 3 to enter).

Therefore, according to the ball screw of this embodiment, when the ball 3 collides with the tongue 42 and the tongue 42 is deformed, for example, the state shown in FIG. That is, compared with the state shown in FIG. 6B and FIG. 7B, the groove bottom opposing line L of the tongue 42 and the groove bottom 110 of the screw shaft on the base end (obtuse angle portion) 42b side of the tongue 42 The distance becomes smaller.
Further, since the gap S on the tip end (acute angle portion) 42a side of the tongue 42 is set to an appropriate size, the tongue 3 is smoothly tanged to the groove bottom 110 of the screw shaft while smoothly moving the ball 3 toward the ball return path 45. It is possible to make it difficult to contact the tip 42a of 42.
In the unlikely event that the tongue 42 contacts the groove bottom 110 of the screw shaft, not only the front end portion 42a but also the base end portion 42b of the tongue 42 contacts the groove bottom opposing line L and the groove bottom of the screw shaft. 110 is likely to be a line contact rather than a single point of contact. Therefore, compared with the state shown in FIG. 6B and FIG. 7B, the stress generated at the tip 42a of the tongue 42 can be relaxed.

Therefore, in the ball screw of this embodiment, the groove bottom facing line L of the tongue 42 of the synthetic resin circulating component 4B is appropriately set, so that the ball 3 smoothly moves toward the ball return path 45, and the tongue The tip end portion 42a of the screw 42 is less likely to contact the groove bottom 110 of the screw shaft, and the mechanical strength of the tip end portion 42a of the tongue 42 is high.
That is, according to the setting method of the tongue bottom line of the tongue of each of the above embodiments, the risk of contact between the screw shaft and the tongue is reduced without reducing the mechanical strength of the tip of the tongue. The operability and acoustic characteristics can be improved.

[Description of Action of Ball Screw of One Embodiment of the Invention]
In the ball screw according to one aspect of the present invention, the groove bottom opposing line of the tongue is located at the deepest position of the gap (the groove bottom opposing line of the tongue and the spiral groove of the screw shaft from the distal end side to the proximal end side of the tongue. A gap formed between a circle forming a groove bottom and a circle is small. Therefore, when the ball collides with the tongue and the tongue is deformed, the ball screw of this aspect has a base end of the tongue compared to the ball screw provided with the groove bottom facing line so that the gap is constant. The distance between the end face of the tongue on the side and the groove bottom of the screw shaft is reduced.

Therefore, in the ball screw of this aspect, by setting the gap on the front end side of the tongue to an appropriate size (a size that is larger than the base end side, but difficult to enter the ball), the ball is smoothly directed to the ball return path. It is possible to make it difficult for the tip of the tongue to contact the groove bottom of the screw shaft.
Further, in the ball screw of this aspect, in the unlikely event that the tongue contacts the groove bottom of the screw shaft, there is a possibility that not only the front end portion of the tongue but also the proximal end side contacts. Therefore, since the groove bottom facing line and the groove bottom of the screw shaft are likely to be contact or line contact by a plurality of points instead of contact at only one point, stress generated at the tip (acute angle portion) of the tongue can be relieved.

The ball screw according to this aspect may have a configuration in which the groove bottom opposing line is an arc along a circle having a center different from a circle forming the groove bottom of the screw shaft.
Further, if the parts forming the ball return path are made of a synthetic resin, the mechanical strength is lower than that of a metal, so that it is preferable to use the ball screw of this aspect.
In this aspect, the ball screw has a distance (Sa) between the center of the cross-sectional circle of the groove bottom and a point farthest from the groove bottom of the groove-bottom line, and is opposed to the center of the cross-sectional circle of the groove bottom. The ratio (Sa / Sb) to the distance (Sb) between the line and the point closest to the groove bottom preferably satisfies the following expression (1).
1.2 ≦ Sa / Sb ≦ 2.6 (1)

[About equation (1)]
A large number of return tubes 4 having different groove bottom facing lines L of the tongue 42 were prepared. The tongues 42 of these return tubes 4 have various values of the ratio (Sa / Sb) between the gap Sa and the gap Sb shown in FIG. FIG. 8 corresponds to the enlarged mirror view of FIG.
The clearance Sa is a clearance at the front end portion 42a of the tongue 42, and in the cross section shown in FIG. 8, between the center of the sectional circle of the groove bottom 100 of the screw shaft and the point farthest from the groove bottom 110 of the groove bottom facing line L. Distance. The clearance Sb is a clearance at the base end portion 42b of the tongue 42, and is a distance between the center of the sectional circle of the groove bottom 100 and the point closest to the groove bottom 110 of the groove bottom opposing line L in the cross section shown in FIG. is there.
A ball screw incorporating each return tube 4 is used, and the tongue 42 is pressed against the groove bottom 110 of the screw shaft with the force F shown in FIG. Asked. Furthermore, a ratio was calculated with an area A of 1 when Sa / Sb = 1.6. This ratio corresponds to the contact surface pressure ratio. FIG. 9 is a graph showing the relationship between the obtained contact surface pressure ratio and the gap ratio (Sa / Sb).

From the graph of FIG. 9, when the gap ratio (Sa / Sb) satisfies the range of 1.2 or more and 2.6 or less, the contact pressure ratio becomes 1.5 or less, and the range of 1.3 or more and 2.2 or less. It can be seen that the contact pressure ratio becomes 1.4 or less by satisfying the above.
That is, the tongue 42 is pressed against the groove bottom 110 of the screw shaft by setting the groove bottom facing line L of the tongue 42 so that the gap ratio (Sa / Sb) satisfies the range of 1.2 to 2.6. In this case, the contact surface pressure generated at the time of pressing can be kept low, and the tip 42a of the tongue 42 can be hardly damaged. Further, if the groove bottom facing line L of the tongue 42 is set so that the gap ratio (Sa / Sb) satisfies the range of 1.3 or more and 2.2 or less, the tip 42a of the tongue 42 can be hardly damaged. The effect is greater.

1 Screw shaft 11 Screw shaft spiral groove 110 Screw shaft groove bottom (the deepest position of the spiral groove)
2 Nut 2a Flat part of nut outer peripheral surface 21 Spiral groove of nut 22 Through hole (return tube mounting hole)
3 Ball 31 Ball rolling path 4 Return tube (part forming the ball return path)
40 Return tube 4A End deflector (part that forms ball return path)
4B Synthetic resin circulation parts (parts that form a ball return path)
41 End surface of the leg portion of the return tube 410 End surface of the leg portion of the return tube 42 Tang of the part forming the ball return path 42a Tip of the tongue 42b Base end 420 Return tongue of the tube 45 Ball return path C1 Groove bottom of the screw shaft C10 Circle that has a different center from the circle C10 Circle that has the same center as the circle that forms the groove bottom of the screw shaft L Groove bottom facing line that the end face of the tongue M End face of the tongue S Groove bottom facing line of the tongue and the groove bottom of the screw shaft Gap with eggplant circle

Claims

A screw shaft, a nut, and a plurality of balls;
The screw shaft passes through the nut;
The spiral groove formed on the outer peripheral surface of the screw shaft and the spiral groove formed on the inner peripheral surface of the nut form a rolling path on which the ball rolls in a loaded state,
The nut includes a ball return path for returning the ball from the end point of the rolling path to the start point,
The ball is disposed in a circulation path composed of the rolling path and the ball return path,
The part forming the ball return path has a tongue for scooping the ball into the ball return path,
The end surface of the tongue has a groove bottom facing line that is opposed to the circle forming the groove bottom via a gap in a cross section at the groove bottom that is the deepest position of the spiral groove of the screw shaft,
The groove bottom facing line is provided so that the gap decreases from the distal end side to the proximal end side of the tongue,
A ball screw in which the nut and the screw shaft move relative to each other through the ball circulating in the circulation path.
The ball screw according to claim 1, wherein the groove bottom facing line is an arc along a circle whose center is different from a circle forming the groove bottom of the screw shaft.
The ball screw according to claim 1 or 2, wherein the parts forming the ball return path are made of synthetic resin.
The distance (Sa) between the center of the cross-sectional circle of the groove bottom and the point farthest from the groove bottom of the groove-bottom line is the center of the cross-sectional circle of the groove bottom and the groove bottom of the groove-bottom line. The ball screw according to any one of claims 1 to 3, wherein a ratio (Sa / Sb) to a distance (Sb) to a close point satisfies the following expression (1).
1.2 ≦ Sa / Sb ≦ 2.6 (1)