JP7494711B2 - Ball screw - Google Patents

Description

This disclosure relates to a ball screw.

A ball screw includes a screw shaft and a nut, and is used as a motion conversion mechanism that rotates the screw shaft to linearly move the nut. In detail, a helical screw groove is provided on the outer peripheral surface of the screw shaft, and a helical screw groove is provided on the inner peripheral surface of the nut, and a rolling path is formed by the opposing screw grooves, and multiple balls are accommodated in this rolling path. The ball screw also includes a circulation mechanism that connects the screw grooves of the nut and circulates balls in the rolling path. There are various types of circulation mechanisms, one of which is called a bridge type. This bridge type ball screw has a communication groove that connects adjacent screw grooves of the nut, and some have a circulation lid member attached to the nut, with the ball rolling path serving as a circulating path (see, for example, Patent Document 1).

JP 2007-211898 A

The lid member in Patent Document 1 is fixed to the nut using adhesive, so it takes a certain amount of time for the adhesive to reach a practical strength, and assembly time is required until the adhesive has fully hardened. Furthermore, it requires the cost of equipment to apply the appropriate amount of adhesive to the specified area, and the effort of storing and managing the adhesive.

This disclosure was made in consideration of the above-mentioned problems, and aims to provide a ball screw that can further simplify the task of attaching the lid member to the nut.

In order to achieve the above object, a ball screw according to one embodiment of the present disclosure comprises a cylindrical nut having a first helical screw groove on its inner circumferential surface, a circular through hole penetrating in the radial direction, and a bottomed hole located radially outside the through hole and overlapping the through hole in the radial direction, a screw shaft inserted into the nut and having a second helical screw groove on its outer circumferential surface, a number of balls housed in a rolling path surrounded by the first screw groove and the second screw groove, and a communication groove on one end surface that communicates the first screw grooves with each other, , and a lid member having a cylindrical portion that fits into the through hole of the nut and a hook portion having an elliptical shape that overlaps with the other end of the cylindrical portion, the bottomed hole of the nut is an elongated hole in which a first distance in the longitudinal direction is greater than the major axis of the hook portion and a second distance in the lateral direction is greater than the minor axis of the hook portion, a pair of recesses recessed in a direction away from the bottomed hole are provided on each of a pair of inner peripheral walls facing each other across the bottomed hole, and a portion of the hook portion is inserted into the recesses.

In this way, because a part of the hook portion is inserted into the recess, the lid member can be attached to the nut without using adhesive. Therefore, by omitting the work step of applying adhesive, the work of attaching the lid member to the nut can be further simplified. Also, because a part of the hook portion is inserted into the recess, even if a load is input to the lid member, the lid member is held without coming off the nut. And the bottomed hole of the nut is an elongated hole in which a first distance in the longitudinal direction is greater than the major axis of the hook portion and a second distance in the lateral direction is greater than the minor axis of the hook portion. Therefore, the lid member can be easily inserted into the bottomed hole of the nut.

In a preferred embodiment of the ball screw, the maximum distance between one of the pair of recesses is smaller than the major axis of the hook portion. This causes a portion of the hook portion to be compressed by the recess. Therefore, the lid member is more securely fixed to the nut by frictional force without the use of adhesive, and the lid member can be easily positioned radially relative to the nut.

In a preferred embodiment of the ball screw, the recess in the inner peripheral wall of the nut has an arc shape with a curvature smaller than the curvature of the portion of the hook portion when viewed from the radial direction of the nut. This allows a portion of the hook portion to be smoothly inserted into the recess by the simple action of rotating the lid member.

In a preferred embodiment of the ball screw, the outer surface of the lid member is provided with a groove that extends linearly along the long or short axis of the hook portion. This allows the lid member to be easily rotated by inserting a tool or jig with a sharp tip, such as a flathead screwdriver, into the groove and rotating it. In addition, the rotation angle of the lid member can be easily confirmed by visually checking the direction of the groove.

The ball screw disclosed herein can further simplify the task of attaching the lid member to the nut.

FIG. 1 is a side view, partly in section, showing a ball screw according to an embodiment. FIG. 2 is a side view of the nut of FIG. FIG. 3 is a front view of the nut of FIG. 1 as viewed from the axial direction. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a front view of the cover member of the embodiment as viewed from the front surface side. 7 is a rear view of the cover member of FIG. 6 as seen from the rear surface side. FIG. 8 is a side view of the cover member of FIG. 6 . FIG. 9 is a plan view of the cover member of FIG. 6 as seen from above. FIG. 10 is a front view of the cover member of FIG. 6 as seen from the front side, showing a state in which the cover member is inserted into the nut receiving portion. FIG. 11 is a front view of the cover member of FIG. 6 as viewed from the front surface side, showing a state in which the hook portion is elastically deformed after being rotated 90 degrees from the state of FIG.

The following describes in detail the form (embodiment) for carrying out the invention with reference to the drawings. The present invention is not limited to the contents described in the following embodiment. The components described below include those that a person skilled in the art would easily imagine and those that are substantially the same. Furthermore, the components described below can be combined as appropriate.

The following describes a ball screw according to an embodiment. Figure 1 is a side view, partially in cross section, showing a ball screw according to an embodiment. Figure 2 is a side view of the nut shown in Figure 1. Figure 3 is a front view of the nut shown in Figure 1 as viewed from the axial direction.

As shown in FIG. 1, the ball screw 1 includes a nut 2, a screw shaft 3, a ball 4, and a cover member 5.

As shown in FIG. 1, the screw shaft 3 extends along the axis Ax. The screw shaft 3 has a helical screw groove 31 (second screw groove) and a screw thread 32 on its outer circumferential surface. As shown in FIGS. 1 to 3, the nut 2 has a cylindrical portion 21 and a flange portion 22. The cylindrical portion 21 has a cylindrical shape located on the outer circumferential side of the screw shaft 3. That is, the screw shaft 3 is inserted into the cylindrical portion 21. A helical screw groove 213 (first screw groove) is provided on the inner circumferential surface 215 of the cylindrical portion 21. The cylindrical portion 21 has a storage portion 210 capable of storing the lid member 5. The storage portion 210 and the lid member 5 will be described in detail later.

The outer peripheral surface 216 of the cylindrical portion 21 has a recess 211 at one end in the axial direction (left-right direction in FIG. 1) and a chamfered portion 212 at the other end. The flange portion 22 spreads in a disk shape from one end of the cylindrical portion 21 toward the radial outside of the nut 2. The area surrounded by the screw groove 213 (first screw groove) and the screw groove 31 (second screw groove) is the rolling path 40. A plurality of balls 4 are housed in the rolling path 40, and the balls 4 move (roll) within the rolling path 40.

Figure 4 is a cross-sectional view taken along line IV-IV in Figure 2. Figure 5 is a cross-sectional view taken along line V-V in Figure 2. Note that Figures 4 and 5 show cross sections taken along a plane including the center CL of the through hole 233.

4 and 5, the accommodating portion 210 includes a circular through hole 233 and a bottomed hole 234. The through hole 233 is located on the radial inner side (lower side in Figs. 4 and 5) of the nut 2 and is a circular through hole extending through the nut 2 in the radial direction (up and down direction in Figs. 4 and 5). The diameter of the through hole 233 is L10. As shown in Fig. 2, the bottomed hole 234 is a rectangular long hole extending in the circumferential direction when viewed from the radial direction of the nut 2. Specifically, the bottomed hole 234 is formed by a pair of long sides 218 extending in the circumferential direction of the cylindrical portion 21 and a pair of short sides 217 extending in the axial direction. However, the bottomed hole of the present invention is not limited to a rectangular shape and may be, for example, an elliptical shape. The bottom of the bottomed hole 234 is the bottom portion 235 shown in Fig. 5, which is a surface obtained by cutting out a part of the outer circumferential surface of the cylindrical portion 21. As shown in FIG. 5, the length of the long side 218 of the blind hole 234 is a first distance L1. As shown in FIG. 4, the length of the short side 217 is a second distance L2.

4, the pair of long sides 218 are arranged opposite each other with the bottomed hole 234 in between. That is, the pair of inner peripheral walls 231 facing each other with the bottomed hole 234 in between correspond to the pair of long sides 218. The inner peripheral wall 231 is provided with a pair of recesses 214 recessed in a direction away from the bottomed hole 234 (left and right direction in FIG. 4). The direction away from the bottomed hole 234 is also the direction toward the outside of the short side direction of the bottomed hole 234. Specifically, the inner peripheral wall 231 on the left side of FIG. 4 is provided with a recess 214 recessed to the left side of FIG. 4, and the inner peripheral wall 231 on the right side of FIG. 4 is provided with a recess 214 recessed to the right side of FIG. 4. The third distance L3, which is the maximum distance between one recess 214 and the other recess 214, is smaller than the major diameter L20 of the hook portion 52 described later. That is, the maximum distance between one recess 214 and the other recess 214 is the distance at a position passing through the center CL of the through hole 233 shown in FIG. 2, which is the third distance L3 shown in the cross section of FIG. 4.

As shown in FIG. 2, the recess 214 has an arc shape centered on the center CL when viewed from the radial direction of the cylindrical portion 21 of the nut 2. As shown in FIG. 4, the recess 214 has a rectangular cross-sectional shape. In the cross section of FIG. 4, the recess 214 has a depth L4 and a height L5 in the axial direction of the bottomed hole 234. The recess 214 is formed, for example, by keyseed machining using a keyseed cutter.

Figure 6 is a front view of the lid member of the embodiment as viewed from the front side. Figure 7 is a rear view of the lid member of Figure 6 as viewed from the back side. Figure 8 is a side view of the lid member of Figure 6 as viewed from the side. Figure 9 is a plan view of the lid member of Figure 6 as viewed from above.

6 to 9, the lid member 5 includes a cylindrical portion 51 and a hook portion 52. The lid member 5 is made of elastic resin. The cylindrical portion 51 has a cylindrical shape that fits into the through hole 233 of the nut 2. As shown in FIG. 8, the axial end face 55 of the cylindrical portion 51 is curved along the inner circumferential surface 215 of the cylindrical portion 21 of the nut 2. A communication groove 54 is provided on the end face 55. The communication groove 54 communicates the screw grooves 213 (first screw grooves) of the nut 2 with each other. As shown in FIG. 7, the communication groove 54 is curved in an approximately S-shape. As a result, the communication groove 54 smoothly connects the adjacent screw grooves 213 (first screw grooves) of the nut 2. Metal materials such as aluminum, brass, and copper can also be used as the material of the lid member 5.

The hook portion 52 is fixed to the end of the cylindrical portion 51 in the axial direction (left-right direction in Figs. 8 and 9) and has an elliptical shape that overlaps with the cylindrical portion 51 when viewed from the axial direction of the cylindrical portion 51. In Figs. 6 and 7, the long axis (long side) of the hook portion 52 is D1, and the short axis (short side) is D2. The long axis D1 extends in the left-right direction in Figs. 6 and 7, and the short axis D2 extends in the up-down direction in Figs. 6 and 7. As shown in Figs. 6 and 7, the part of the periphery of the hook portion 52 that intersects with the long axis D1 is called the first periphery 57, and the part of the periphery of the hook portion 52 that intersects with the short axis D2 is called the second periphery 58. As shown in Fig. 6, the groove 53 extends linearly along the short axis D2. The outer surface 56 of the lid member 5 is provided with a groove 53 that extends linearly along the short axis D2 of the hook portion 52.

Here, the bottomed hole 234 of the nut 2 has a first longitudinal distance L1 that is greater than the major axis L20 (see FIG. 6) of the hook portion 52, and a second transverse distance L2 that is greater than the minor axis L30 (see FIG. 6) of the hook portion 52. As shown in FIG. 2, the recess 214 of the nut 2 has an arc shape with a curvature smaller than the curvature of the edge of the first peripheral portion 57 of the hook portion 52 when viewed from the radial direction of the nut 2. In other words, the radius of curvature of the arc of the recess 214 of the nut 2 is greater than the radius of curvature of the edge of the first peripheral portion 57. The axial height L5 of the recess 214 is greater than the thickness of the first peripheral portion 57 of the hook portion 52. This makes it possible to easily adjust the radial position of the lid member 5, and to set the step between the thread groove 213 of the nut 2 and the communication groove 54 to a small value.

Figure 10 is a front view of the lid member in Figure 6 as seen from the front side, showing the state in which it is inserted into the nut housing. Figure 11 is a front view of the lid member in Figure 6 as seen from the front side, showing the state in which the hook portion is elastically deformed after being rotated 90° from the state in Figure 10.

The procedure for placing the lid member 5 in the accommodating portion 210 of the nut 2 is briefly explained below.

First, as shown in FIG. 10, the lid member 5 is inserted into the bottomed hole 234 of the accommodating portion 210 shown in FIG. 2 with the long axis D1 of the lid member 5 arranged in the circumferential direction of the cylindrical portion 21 of the nut 2. At this time, the recessed groove 53 extends in the axial direction of the cylindrical portion 21 (the direction of the short axis D2) as shown in FIG. 10.

Next, the lid member 5 is positioned radially. At this time, adjustment is made by so-called actual fitting so that the radial step at the connection portion between the communication groove 54 of the lid member 5 and the screw groove 213 (first screw groove) of the nut 2 is small. Specifically, the radial position of the lid member 5 is determined using a positioning jig so that the communication groove 54 is at a predetermined radial position based on the screw groove 213.

Furthermore, the lid member 5 is rotated, for example, by an angle of 90° in a clockwise or counterclockwise direction while maintaining the radial position. At this time, the axial step at the connection portion between the communication groove 54 and the screw groove 213 is adjusted by actual fitting so as to be small. Then, as shown in FIG. 11, the concave groove 53 extends in the circumferential direction of the cylindrical portion 21. In addition, the axial height L5 of the recess 214 (see FIG. 4) is larger than the thickness of the first peripheral edge portion 57 of the hook portion 52, and the dimensional difference is larger than the maximum adjustment dimension in the actual fitting described above. Therefore, the first peripheral edge portion 57 of the hook portion 52 is inserted into the recess 214 without interfering with the inner peripheral wall 231. In addition, the third distance L3, which is the maximum distance between one recess 214 and the other recess 214, is smaller than the major axis L20 of the hook portion 52 (L3<L20). Therefore, the first peripheral edge 57 of the hook portion 52 is compressed from the left and right recesses 214 and elastically deforms, and as shown in FIG. 11, the first peripheral edge 57 is bent by a distance L40 in the direction along the long axis D1. As a result, the first peripheral edge 57 is positioned and fixed to the recess 214 by the frictional force caused by the elastic deformation. In this way, the lid member 5 is positioned and fixed to the accommodating portion 210 by matching the actual product, with the step at the connection portion between the communication groove 54 of the lid member 5 and the thread groove 213 of the nut 2 being reduced. Therefore, there is no need to increase the processing accuracy of the nut 2 (accommodating portion 210) (reducing the dimensional tolerance), and the cost of the nut 2 can be reduced.

As described above, the ball screw 1 according to this embodiment includes a cylindrical nut 2 having a spiral thread groove 213 (first thread groove) on its inner circumferential surface 215, a circular through hole 233 penetrating in the radial direction, and a bottomed hole 234 located radially outside the through hole 233 and overlapping the through hole 233 in the radial direction; a screw shaft 3 inserted into the nut 2 and having a spiral thread groove 31 (second thread groove) on its outer circumferential surface; a plurality of balls 4 housed in a rolling path 40 surrounded by the thread grooves 213 and 31; and a cover member 5 having a connecting groove 54 on one end face 55 that connects the thread grooves 213 to each other, a cylindrical portion 51 that fits into the through hole 233 of the nut 2, and a hook portion 52 having an elliptical shape that overlaps the other end of the cylindrical portion 51. The bottomed hole 234 of the nut 2 is an elongated hole in which the first longitudinal distance L1 is greater than the major axis L20 of the hook portion 52 and the second lateral distance L2 is greater than the minor axis L30 of the hook portion 52. A pair of recesses 214 recessed in a direction away from the bottomed hole 234 are provided on each of a pair of inner peripheral walls 231 facing each other across the bottomed hole 234, and a first peripheral portion 57 (part) of the hook portion 52 is inserted into the recesses 214.

In this way, since the first peripheral portion 57 (part) of the hook portion 52 is inserted into the recess 214, the lid member 5 can be attached to the nut 2 without using adhesive. Therefore, the work of applying adhesive can be omitted, and the work of attaching the lid member 5 to the nut 2 can be further simplified. In addition, since the first peripheral portion 57 (part) of the hook portion 52 is inserted into the recess 214, even if a load is input to the lid member 5, the lid member 5 is held without coming off the nut 2. Here, an example of a load input to the lid member 5 is, for example, a load applied to the lid member 5 by the ball 4 clogging the rolling path 40. The bottomed hole 234 of the nut 2 is an elongated hole in which the first distance L1 in the longitudinal direction is greater than the major axis L20 of the hook portion 52 and the second distance L2 in the lateral direction is greater than the minor axis L30 of the hook portion 52. Therefore, the lid member 5 can be easily inserted into the bottomed hole 234 of the nut 2.

The third distance L3 (maximum distance) between one recess 214 and the other recess 214 of the pair of recesses 214 is smaller than the major axis L20 of the hook portion 52. As a result, the first peripheral edge portion 57 (part) of the hook portion 52 is compressed by the recess 214. Therefore, the lid member 5 is more securely fixed to the nut by frictional force without using adhesive, and the lid member 5 can be easily positioned radially relative to the nut 2.

When viewed from the radial direction of the nut 2, the recess 214 in the inner peripheral wall 231 of the nut 2 has an arc shape with a curvature smaller than that of the first peripheral edge 57 of the hook portion 52. This allows the first peripheral edge 57 of the hook portion 52 to be smoothly inserted into the recess 214 by the simple action of rotating the lid member 5.

The outer surface of the lid member 5 is provided with a groove 53 that extends linearly along the minor axis D2 of the hook portion 52. This allows the lid member 5 to be easily rotated by inserting a tool or jig with a sharp tip, such as a flathead screwdriver, into the groove 53 and rotating it. In addition, the rotation angle of the lid member 5 can be easily confirmed by visually checking the orientation of the groove 53.

Although the embodiment has been described above, the embodiment is not limited to the above. For example, the outer surface of the lid member 5 is provided with a groove 53 that extends linearly along the minor axis D2 of the hook portion 52, but the groove 53 may be provided along the major axis D1 of the hook portion 52.

1 Ball screw 2 Nut 3 Screw shaft 4 Ball 5 Lid member 31 Screw groove (second screw groove)
40: rolling path 51: cylindrical portion 52: hook portion 53: groove 54: communicating groove 55: end surface 57: first peripheral portion (part)
213 Thread groove (first thread groove)
214 Recess 215 Inner circumferential surface 231 Inner circumferential wall 233 Through hole 234 Bottomed hole L1 First distance L2 Second distance L3 Third distance (maximum distance)
L20 Long diameter L30 Short diameter

Claims (4)

A cylindrical nut having a first helical thread groove on an inner peripheral surface thereof, and having a circular through hole penetrating in a radial direction and a bottomed hole positioned radially outward of the through hole and overlapping with the through hole in the radial direction;
A screw shaft that is inserted into the nut and has a second helical screw groove on its outer circumferential surface;
A plurality of balls are accommodated in a rolling path surrounded by the first screw groove and the second screw groove;
A cover member having a connecting groove that connects the first screw grooves to each other on an end surface on one side, and a cylindrical portion that fits into the through hole of the nut, and a hook portion having an elliptical shape that overlaps with an end portion on the other side of the cylindrical portion;
Equipped with
The blind hole of the nut is an elongated hole having a first distance in a longitudinal direction that is greater than a major axis of the hook portion and a second distance in a lateral direction that is greater than a minor axis of the hook portion, and a pair of recesses recessed in a direction away from the blind hole are provided on each of a pair of inner circumferential walls facing each other across the blind hole, and a part of the hook portion is inserted into the recesses.
Ball screw. a maximum distance between one recess and the other recess of the pair of recesses is smaller than a major axis of the hook portion;
2. The ball screw according to claim 1. The recess of the inner peripheral wall of the nut has an arc shape with a curvature smaller than a curvature of the part of the hook portion when viewed from a radial direction of the nut.
3. The ball screw according to claim 1 or 2. The outer surface of the lid member is provided with a groove extending linearly along the major axis or minor axis of the hook portion.
The ball screw according to any one of claims 1 to 3.

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