JP2009024720A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive ball screw with low noises at the time of actuation. <P>SOLUTION: This ball screw 1 comprises a screw shaft 3 having a spiral screw groove 3a on an outer periphery, a nut 5 having a screw groove 5a opposed to the screw groove 3a of the screw shaft 3, and a plurality of balls 9 rollably loaded in a spiral ball rolling path 7 formed by both of the screw grooves 3a, 5a. After grinding, shot-peening is applied to both of the screw grooves 3a, 5a by projecting approximate spherical glass particles of mean particle size of 200 μm or less, so surface roughness Ra is 0.15 μm or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ball screw.

A ball screw, which is a type of rolling linear motion device, is configured by loading a plurality of balls into a spiral ball rolling path formed between a screw groove of a screw shaft and a screw groove of a nut. The power is transmitted between the screw shaft and the nut through the rolling. In such a ball screw, since the ball rolls with sliding due to the combined force of the rotational force and the axial force, rolling friction is caused at the contact portion between the ball and the surface of both screw grooves. Sliding friction will occur at the same time.
For this reason, grease such as grease and solid lubricant is placed inside the ball screw, which reduces the coefficient of friction between the ball and the surface of both screw grooves and reduces the noise of the ball screw. And improve durability. However, in recent years, ball screws have been operating at higher speeds for the purpose of improving productivity, etc., and accordingly, the demand for lower noise of ball screws has become more severe.

In ball screws, the rolling element balls are super-finished, but the thread grooves are only ground, and after that, finishing such as super-finishing is performed. There wasn't. Therefore, it cannot be said that the surface of the thread groove is sufficiently smooth, and it has not been easy to meet strict requirements for noise reduction.
Patent Document 1 discloses a ball screw provided with a soundproofing device for reducing noise during operation. That is, by covering the ball return tube with a tube pressing member formed entirely of a buffer soundproofing material, noise and vibration generated when the ball screw is operated are reduced.
JP 63-163060 A

However, the method of reducing the noise by providing a soundproofing device as in Patent Document 1 has a problem that the ball screw is increased in size and the manufacturing cost is increased by the amount of the soundproofing device.
SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a ball screw that solves the problems of the prior art as described above and that has low noise during operation and is inexpensive.

  In order to solve the above-described problems, the present invention has the following configuration. That is, the ball screw according to claim 1 of the present invention includes a screw shaft having a helical screw groove on the outer peripheral surface, a nut having a screw groove facing the screw groove of the screw shaft on the inner peripheral surface, A ball screw comprising a plurality of balls rotatably arranged between screw grooves, and at least one of the two screw grooves is substantially spherical glass having an average particle diameter of 200 μm or less after being ground. Shot peening is performed by projecting particles, and the surface roughness Ra is 0.15 μm or less.

With such a configuration, since the surface of the thread groove is smoothed by the shot peening, noise during operation is small. In addition, shot peening is highly versatile, and the finishing process of the surface of the thread groove can be performed easily and in a short time, so that the manufacturing cost of the ball screw is not greatly increased. Therefore, the ball screw of the present invention is inexpensive.
If the average particle diameter of the glass particles exceeds 200 μm, the surface roughness of the screw groove after projecting the glass particles becomes excessive, and the surface finish of the screw groove becomes insufficient. Moreover, when the shape of the glass particles is a spherical shape that is a smooth curved surface or a shape having a corner instead of a spherical shape, the surface roughness of the thread groove after projecting the glass particles may be excessive.

  The ball screw of the present invention has a low noise during operation and is inexpensive.

Embodiments of a ball screw according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view of a ball screw according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA of the ball screw of FIG.
As shown in FIGS. 1 and 2, the ball screw 1 includes a screw shaft 3 having a helical screw groove 3 a on the outer peripheral surface, and a helical screw groove 5 a facing the screw groove 3 a of the screw shaft 3 on the inner peripheral surface. And a plurality of balls 9 movably loaded in a spiral ball rolling path 7 formed by both screw grooves 3a, 5a. Then, when the nut 5 and the screw shaft 3 screwed to the screw shaft 3 through the ball 9 are relatively rotated, the screw shaft 3 and the nut 5 are relatively moved in the axial direction through the rolling of the ball 9. It is designed to move in a straight line. The cross-sectional shape of the thread grooves 3a and 5a may be an arc shape or a gothic arc shape.

  A part of the outer peripheral surface of the nut 5 is cut flat, and a flat portion 13 parallel to the axial direction is formed. A return tube 15 bent in a substantially U-shape that connects the start point and end point of the ball rolling path 7 to form an endless ball circulation path is fixed to the flat portion 13 by a tube presser 17. That is, the nut 5 is provided with a pair of through holes that open to the flat portion 13 and communicate with the thread groove 5a of the nut 5, and both end portions of the return tube 15 are inserted into both through holes from the flat portion 13 side. Has been. A central portion of the return tube 15 located outside the through hole is disposed on the flat portion 13.

  The ball 9 rolling in the ball rolling path 7 is circulated through the return tube 15. That is, the ball 9 moves in the ball rolling path 7 and turns around the screw shaft 3 a plurality of times, and then returns at the end point of the ball rolling path 7 (intersection of the return tube 15 and the ball rolling path 7). The tube 15 is scooped up into the return tube 15 from one end (opening) of the tube 15. The scooped up ball 9 passes through the return tube 15 and is returned to the starting point of the ball rolling path 7 from the other end (opening) of the return tube 15. In this way, the ball 9 rolling in the ball rolling path 7 is infinitely circulated by the return tube 15 that connects the starting point and the end point of the ball rolling path 7, so that the screw shaft 3 And the nut 5 can continuously move in a relative straight line.

  Both the screw grooves 3a and 5a of the ball screw 1 are subjected to shot peening by projecting substantially spherical glass particles having an average particle diameter of 200 μm or less after being subjected to grinding, and the surface roughness Ra Is 0.15 μm or less. As described above, since the finish processing is applied to both the screw grooves 3a and 5a and the surface is smoothed, the ball screw 1 has low noise during operation. Also, shot peening is highly versatile, and the finishing of the surfaces of the thread grooves 3a and 5a can be performed easily and in a short time, so that the manufacturing cost of the ball screw 1 is not greatly increased. Therefore, this ball screw 1 is inexpensive.

  A general-purpose shot peening apparatus can be used for projecting the glass particles, and the injection pressure is preferably 0.196 to 0.588 MPa and the injection time is preferably 10 to 20 min. By performing such shot peening, a surface residual stress of −1200 MPa or more and −900 MPa or less is applied to the screw grooves 3 a and 5 a, thereby improving the durability of the ball screw 1.

As shown in FIG. 2, a retaining piece 21 may be interposed between the adjacent balls 9. The retaining piece 21 has two concave surfaces facing the rolling surface of the ball 9 and is for preventing direct contact between the balls 9, and is interposed between the balls 9. . The retaining piece 21 is made of, for example, polyamide having a lubricating action, fluororesin, or polyethylene impregnated with a lubricating oil, and has a concave spherical surface with a radius of curvature larger than the radius of the ball 9 at both ends. It is disk-shaped.
The shape of the concave spherical surface is not limited to the spherical shape, and may be a so-called Gothic arch-shaped concave surface formed by intersecting two arcs at an intermediate portion or a conical concave surface. . Further, a through hole may be provided on the concave surface, or a lubricant may be held in the through hole to reduce the contact resistance with the ball 9.

〔Example〕
The present invention will be described more specifically with reference to the following examples. A ball screw manufactured by Nippon Seiko Co., Ltd. having the same configuration as the above-described ball screw 1 is mounted on a noise measuring device and rotated at a rotational speed of 4000 rpm, and the generated noise is separated from the axis of the screw shaft by 400 mm. Measured in position.
The specifications of this ball screw are as follows.
-Screw shaft diameter: 20mm
・ Lead: 10mm
-Ball diameter: 3.969 mm
-Number of circuits: 2.5 windings x 1 row-Holding piece: None

  In the ball screws of Examples 1 to 5 and Comparative Examples 1 and 2 subjected to the noise measurement test, the surface roughness of the screw shaft and the thread groove of the nut is different (see Table 1). Although shot peening is performed in Examples 1 to 5 and Comparative Example 2, shot peening is not performed in Comparative Example 1, and only grinding is performed. The ball screw was lubricated with YS2 grease manufactured by Lube Co., Ltd.

  The results of the noise measurement test are shown in Table 1. In addition, the numerical value of the noise value of Table 1 is shown by the difference (the unit is dB) from this reference value with the noise value of Comparative Example 1 as the reference value. In Examples 1 to 5, since the surface roughness Ra of the thread groove was 0.15 μm or less by shot peening, the noise was lower than that of Comparative Example 1 in which shot peening was not performed. In Comparative Example 2, since shot peening was performed by projecting substantially spherical glass particles having an average particle size exceeding 200 μm, the surface roughness Ra of the thread groove was as large as 0.25 μm. Therefore, the noise was loud.

It is a top view of one embodiment of a ball screw concerning the present invention. It is AA sectional drawing of the ball screw of FIG.

Explanation of symbols

1 Ball screw 3 Screw shaft 3a Screw groove 5 Nut 5a Screw groove 7 Ball rolling path 9 Ball

Claims (1)

A screw shaft having a spiral thread groove on the outer peripheral surface, a nut having a screw groove facing the screw groove of the screw shaft on the inner peripheral surface, and a plurality of rolls arranged between the screw grooves. A ball screw comprising:
At least one of the two screw grooves is subjected to shot peening by projecting substantially spherical glass particles having an average particle diameter of 200 μm or less after being subjected to grinding, and the surface roughness Ra is 0.15 μm or less. The ball screw characterized by being said.

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