JP2001141019A - Ball screw device - Google Patents

Abstract

(57) [Problem] To provide a ball screw device capable of circulating a ball more smoothly and having high durability. A ball screw device includes a screw shaft, a nut, and a plurality of balls. The ball rolling groove 3 a of the screw shaft 1 and the ball screw groove 2 a of the nut 2 opposing each other form a ball rolling path 3. The nut 2 is provided with a connection path 6 that allows a part of the ball rolling path 3 to communicate with another part. The connection path 6 and the ball rolling path 3 form a ball circulation path 7 that communicates endlessly. Each ball 8 is arranged endlessly in the ball circulation path 7. By cutting off the corners of the connection part between the screw groove 2a of the nut 2 and the connection path 6 constituting the ball rolling path 3, a part of the screw groove 2a is formed.
A processing section 11 that is smoothly continuous is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw device used for a feed mechanism of various devices.

[0002]

2. Description of the Related Art A ball screw device is a mechanical element for converting a rotary motion into a linear motion. The ball screw device has a screw shaft having a ball screw groove formed on an outer peripheral surface thereof. A nut formed with a ball screw groove facing the ball screw groove of the shaft.

A helical ball rolling path is constituted by a ball screw groove of a screw shaft and a ball screw groove of a nut facing each other, and a part of the ball rolling path which is spaced apart from the other part is a nut. The ball rolling path and the connecting path constitute an endless ball circulation path, and are connected to each other by a connection path provided in the ball circulation path. In the ball circulation path, materials such as steel, ceramic, plastic, and resin are used. Are accommodated so as to be continuously arranged endlessly.

When the screw shaft rotates, its power is transmitted to the nut via a ball between the screw shaft and the nut, and the nut moves in the axial direction of the screw shaft. The ball circulates infinitely in the circulating path, and the axial movement of the nut in response to the rotation of the screw shaft is smoothly and accurately performed by the ball infinite circulation.

[0005] More specifically, referring to the drawings,
FIG. 6 schematically shows a cross section of a conventional ball screw device 100 of a tube type.
Is installed. A ball screw groove 1 a is formed on an outer peripheral surface of the screw shaft 1, and a helical ball screw groove 2 a facing the ball screw groove 1 a of the screw shaft 1 is formed on an inner peripheral surface of the nut 2. The ball screw groove 1a of the screw shaft 1 and the ball screw groove 2a of the nut 2 opposing each other constitute a spiral ball rolling path 3.

[0006] Through holes 4 a and 4 b are formed in the peripheral wall of the nut 2, and these through holes 4 a and 4 b are connected by a tube 5. This tube 5 is arranged on the outer periphery of the nut 2,
Both ends are inserted into the through holes 4a and 4b. The through holes 4a and 4b and the tube 5 form a connection path 6 that connects a part of the ball rolling path 3 apart from the other and another part to communicate with each other.

As a result, the ball rolling path 3 communicates endlessly through the connection path 6, and the endlessly communicating path is the ball circulation path 7, which is connected to the ball circulation path 7 endlessly. Steel, ceramic, plastic,
A large number of balls 8 formed of a material such as resin are accommodated therein,
These balls 8 roll in the ball circulation path 7 when the screw shaft 1 rotates, and circulate indefinitely.

In the ball screw device 100, when the nut 2 rotates, for example, in the direction indicated by the arrow R with respect to the screw shaft 1, each ball 8 rolls in the direction of the arrow R along the screw groove 1a. Here, since the moving speed of the ball 8 is lower than the rotation speed of the nut 2, each ball 8
Moves from the tube 5 toward the thread groove 2a of the nut 2 through one through hole 4a.

[0009]

However, in the conventional ball screw device 100, the connection portion between the ball rolling path 3 and the connection path 6, that is, the ball screw groove 2a of the nut 2 is provided.
As shown in FIG.
Therefore, the smooth circulation movement of the ball 8 circulating in the ball circulation path 7 is hindered by the corner portion 10, and there is a problem that the operability and durability are reduced.

On the other hand, when an external load acts on the ball screw device 100, the ball screw groove 1a of the screw shaft 1 and the ball 8
And the ball screw groove 2a of the nut 2 and the ball 8
And the distance between the thread grooves 1a and 2a is reduced due to the Hertz contact between them and the elastic deformation of the ball 8 itself. This condition is referred to herein as elastic approach.

In the state where the elastic approach is occurring, the thread grooves 1a and 2a which are the load zones are removed from the tube 5 which is the no load zone.
The ball 8 enters in between. Here, thread grooves 1a, 2
If the distance between "a" and "a" is narrow, the ball 8 cannot enter between the screw grooves 1a and 2a as it is. Therefore, the preceding ball 8 is pushed by the succeeding ball 8 to enter between the thread grooves 1a and 2a.

Conventionally, the ball screw groove 2a is continuously worked on the entire inner periphery of the nut 2 based on the center diameter of the ball 8. Therefore, when the above-described external load is applied, the ball screw grooves 1 a and 2 a equally approach each other over the entire inner circumference of the nut 2. As a result, the moment the ball 8 enters the ball screw grooves 1a, 2a from the tube 5, the ball 8 is rapidly compressed.

For example, a diameter of 100 mm, a lead of 25 mm,
In a ball screw device having a ball diameter of 19.05 mm,
When a load is applied, the amount of elastic approach between the thread grooves is 50
μm may be reached. That is, when the ball enters the load zone from the no-load zone, it is compressed by 50 μm. For this reason, there is a concern that the following problems may occur, particularly when the load is large.

(1) Stress concentrates on the corner 10 between the ball screw groove 2a and the end of the tube 5, and flaking occurs from that point. (2) The ball 8 is likely to be clogged in the vicinity of the corner 10, and the ball 8 cannot be circulated smoothly. (3) When the ball 8 enters the ball screw groove 2a from the tube 5, the preceding ball 8 is pressed by the succeeding ball 8, so that the ball is damaged or worn. The abrasion powder generated at that time causes a decrease in the durability of the ball screw device.

The present invention has been made in view of such a point, and an object of the invention is to provide a ball screw capable of circulating a ball more smoothly, maintaining good operability and improving durability. It is to provide a device.

[0016]

In order to achieve the above object, the present invention provides a screw shaft having a ball screw groove on an outer peripheral surface, a screw shaft fitted on the outer periphery of the screw shaft, and a screw shaft on an inner peripheral surface. A nut having a ball screw groove facing the ball screw groove of the above, a ball rolling path formed by a ball screw groove of the screw shaft and a ball screw groove of the nut facing each other, and the ball rolling provided on the nut; A connection path that connects a part of the path with another part, a ball circulation path that is formed by the connection path and the ball rolling path and that communicates endlessly; In a ball screw device including a plurality of balls housed so as to be arranged in a row, a processing section formed by processing a smooth shape by shaving off a corner of a connection portion between the ball rolling path and the connection path. Have.

The processing portion formed by a crowning process or the like has a tapered shape in which a distance between the screw grooves is gradually reduced in a direction in which a ball enters from the connection path into each of the screw grooves. The processing section may be formed in a range extending from the end of the connection path in the circumferential direction of the nut and not exceeding 90 ° from the corner in the circumferential direction of the nut. By doing so, when the ball enters the ball rolling path from the connection path, the ball is gradually compressed,
The occurrence of stress concentration in the ball screw groove is avoided. If the processing section exceeds the range of 90 ° from the corner in the circumferential direction of the nut, the load capacity of the ball screw device decreases, so the range is at most 90 ° from the corner.

It is desirable that the cut amount of the processing portion is larger than the elastic approach amount of the ball screw groove. Specifically, it is preferable that the diameter be in the range of 1/400 to 1/10 of the diameter of the ball in the radial direction of the nut. If the shaving amount is 1/400 or less of the ball diameter, the movement of the ball is not smooth, and the above problem cannot be solved. If the depth of cut exceeds one-tenth of the ball diameter, the operability of the ball screw device deteriorates.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG.
(A) shows the main part of the tube-type ball screw device 1A according to the first embodiment of the present invention. FIG.
(B) shows the structure of the corresponding part of the conventional tube type ball screw device 100 for comparison.

As shown in FIGS. 1A and 3, a nut 2 is mounted on the outer periphery of a screw shaft 1. A ball screw groove 1 a is formed on the outer peripheral surface of the screw shaft 1. A helical ball screw groove 2 a facing the ball screw groove 1 a of the screw shaft 1 is formed on the inner peripheral surface of the nut 2. A helical ball rolling path 3 is constituted by the ball screw groove 1a of the screw shaft 1 and the ball screw groove 2a of the nut 2 facing each other.

Through holes 4 a and 4 b are formed in the peripheral wall of the nut 2, and these through holes 4 a and 4 b are connected by a tube 5. This tube 5 is arranged on the outer periphery of the nut 2,
Both ends are inserted into the through holes 4a and 4b. The through holes 4a and 4b and the tube 5 form a connection path 6 that connects a part of the ball rolling path 3 apart from the other and another part to communicate with each other.

As a result, the ball rolling path 3 communicates endlessly through the connection path 6, and the path that communicates endlessly is the ball circulation path 7. A large number of balls 8 made of a material such as steel, ceramic, plastic, or resin are accommodated in the ball circulation path 7 so as to be continuously arranged in an endless manner. The ball is rolled in the ball circulation path 7 and circulates infinitely.

In the ball screw device 1A, when the nut 2 rotates in the direction indicated by the arrow R with respect to the screw shaft 1, each ball 8 rolls in the direction of the arrow R along the screw groove 1a. Here, since the moving speed of the ball 8 is lower than the rotation speed of the nut 2, each ball 8
It moves from the tube 5 to the thread groove 2a of the nut 2 through one through hole 4a.

In the conventional ball screw device 100 shown in FIG. 1 (B), a corner 10 is formed at a connection portion between the ball rolling path 3 and the connection path 6. On the other hand, in the ball screw device 1A of the present invention shown in FIG. 1 (A), a flat and smooth processing portion 11 is formed by shaving off the corner portion 10 in the manufacturing stage. The processing portion 11 is formed at a boundary portion between the ball screw groove 2a of the nut 2 and the connection path 6 over a length L in the circumferential direction of the nut 2 by chamfering using a grindstone or the like.

In such a configuration, the ball rolling path 3 and the connection path 6 are smoothly continuous, so that the ball 8 smoothly circulates in the ball circulation path 7 from the initial stage of operation of the manufactured ball screw device 1A. I do. For this reason, the ball 8 and the ball circulation path 7 hardly wear from the initial stage of the operation of the ball screw device 1A, so that the operability is maintained well and the durability can be enhanced.

FIG. 2A shows a structure of a main part of a tube type ball screw device 1B according to a second embodiment of the present invention. FIG. 2B shows the structure of a corresponding portion of a conventional tube-type ball screw device 100 for comparison. The configuration of the ball screw device 1B according to the second embodiment shown in FIG. 2A is the same as that of the ball screw device 1A according to the first embodiment except for the processing 12 formed on the inner surface of the nut 2. . Therefore, the ball screw device 1B of the first embodiment relates to the ball screw device 1B of the second embodiment.
Parts common to those of A are denoted by the same reference numerals as in the first embodiment, and description thereof is omitted.

The ball screw device 1B according to the second embodiment comprises:
A relatively long region including a portion corresponding to the corner 10 of the connection portion between the ball rolling path 3 and the connection path 6 in the conventional ball screw device 100 is gently smoothed by a crowning process using a polishing means such as a grindstone. The smooth processing portion 12 is formed by shaving in a circular arc shape.

As shown in FIG. 4, the processing section 12 extends from the end C of the connection path 6 in the circumferential direction of the nut 2. The processing portion 12 has a tapered shape such that the distance between the thread grooves 1a and 2a gradually decreases in the direction of entry of the ball 8 between the connection path 6 and each of the thread grooves 1a and 2a. The processing portion 12 extends in the circumferential direction of the nut 2 from the end C of the connection path 6 and extends 90 ° in the circumferential direction from the corner portion 12.
Is formed within the range not exceeding.

By providing such a processing portion 12, the ball 8 easily enters between the thread grooves 1a and 2a, and the ball 8 is gradually compressed as the ball 8 progresses. Is avoided. If the length of the processing portion 12 exceeds 90 ° in the circumferential direction of the nut 2, the load capacity of the ball screw device 1B decreases.

The shaving amount (cutting amount H shown in FIG. 5) of the processing section 12 is determined by the ball screw groove 1a,
2a, it is larger than the elastic approach amount. That is,
The cut amount H is in the range of 1/400 to 1/10 of the diameter of the ball 8 in the radial direction of the nut 2.

Also in such a configuration, since the ball rolling path 3 and the connection path 6 are smoothly connected, the ball 8 smoothly circulates in the ball circulation path 7 from the initial stage of operation of the ball screw device 1B immediately after the production. I do. Therefore, the wear of the ball 8 and the ball circulation path 7 is suppressed from the initial stage of the operation of the ball screw device 1B, so that good operability can be obtained and durability can be enhanced.

According to the present invention, in addition to a tube-type ball screw device in which the connection path 6 is constituted by the tube 5, an internal circulation type ball screw apparatus using a connection path top and a connection path formed in an end cap are provided. The present invention can be similarly applied to the ball screw device described above. In short, in the ball screw device of the present invention, a smoothly continuous processing portion may be formed by shaving off a corner between the connection path provided in the nut and the ball screw groove.

[0033]

As described above, according to the present invention,
By forming the processing portion at the connection portion between the ball rolling path and the connection path, the ball circulates smoothly from the initial stage of manufacturing the ball screw device. The ball screw device of the present invention has good operability and can enhance durability. In addition, since the ball easily enters the load zone between the screw grooves from the no-load zone inside the connection path, damage and wear due to contact between the balls can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a part of a ball screw device according to a first embodiment of the present invention and a part of a conventional ball screw device in comparison.

FIG. 2 is a sectional view showing a part of a ball screw device according to a second embodiment of the present invention and a part of a conventional ball screw device in comparison.

FIG. 3 is a perspective view showing the overall appearance of the ball screw device of the present invention.

FIG. 4 is a sectional view of the ball screw device according to the second embodiment shown in FIG. 2;

FIG. 5 is an enlarged sectional view showing a part of the ball screw device according to the second embodiment shown in FIG. 2;

FIG. 6 is a sectional view of a conventional ball screw device.

[Explanation of symbols]

 1A, 1B ... Ball screw device 1 ... Screw shaft 1a ... Screw groove 2 ... Nut 2a ... Screw groove 3 ... Ball rolling path 5 ... Tube 6 ... Connection path 7 ... Ball circulation path 8 ... Ball 10 ... Corner 11 ... Processing Processing unit 12: Processing unit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshiyuki Iku 78 Tobacho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd. (72) Inventor Kazuo Miyaguchi 78 Tobacho, Maebashi-shi, Gunma Nippon Seiko Co., Ltd.

Claims (3)

[Claims] A screw shaft having a ball screw groove on an outer peripheral surface;
A nut fitted on the outer periphery of the screw shaft and having a ball screw groove on the inner peripheral surface facing the ball screw groove of the screw shaft, and a ball screw groove of the screw shaft and a ball screw groove of the nut facing each other. Ball rolling path and nut
A connection path that connects a part of the ball rolling path to another part, a ball circulation path that is formed by the connection path and the ball rolling path and that communicates endlessly; In a ball screw device having a plurality of balls housed so as to be endlessly arranged therein, the ball screw device is processed into a smooth shape by shaving off a corner portion of a connection portion between the ball rolling path and the connection path. A ball screw device having a processing unit. 2. The processing section has a shape in which a distance between the thread grooves is gradually reduced in a direction in which a ball enters from the connection path to each of the thread grooves. The ball screw device according to claim 1, wherein the ball screw device extends in a circumferential direction of the nut from an end of the nut and does not exceed 90 ° in a circumferential direction of the nut from the corner. 3. The processing section has a shape in which a distance between the thread grooves is gradually reduced in a direction in which a ball enters between the connection paths and between the thread grooves, and a cut amount of the processing section is reduced. 3. The ball screw device according to claim 1, wherein the diameter of the ball is in a range of 1/400 to 1/10 of a diameter of the ball in a radial direction of the nut.