JP2010190305A - Ball screw - Google Patents

Abstract

The present invention provides a ball screw with a long life, particularly a ball screw with a long life, which is suitably used in a machine tool that applies a high load in a certain direction.
A screw shaft 2 having a spiral ball rolling groove 1a on an outer peripheral surface, a nut 3 having a spiral ball rolling groove 1b on an inner peripheral surface, and a ball rolling groove 1a of the screw shaft 2; A plurality of balls 5 arranged in a raceway 1 formed opposite to the ball rolling groove 1b of the nut 3, and a ball rolling that the screw shaft 2 has a Gothic arc groove including two arcs. A ball screw used for each of the groove 1a and the ball rolling groove 1b of the nut 3 and included in the gothic arc groove when a main load is applied in a certain direction along the axial direction of the screw shaft 2. Among the two arcs, the curvature of one arc that receives the main load is made larger than the curvature of the other arc that does not receive the main load.
[Selection] Figure 2

Description

  The present invention relates to a ball screw having a long life, and more particularly to a ball screw having a long life that is suitably used in a machine tool that receives a high load from a certain direction.

  A screw shaft having a spiral ball rolling groove on the outer circumferential surface, a nut having a spiral ball rolling groove on the inner circumferential surface, a ball rolling groove on the screw shaft, and a ball rolling on the nut. A ball rolling groove provided on the screw shaft and the nut provided with a plurality of balls arranged in a track formed so as to face the moving groove, and including two arcs. Ball screws used for the ball rolling grooves are currently used in machine tools such as electric injection molding machines and electric press machines.

  The ball screws used in these machine tools are relatively large and receive a heavy load. The high load momentarily acts in a certain direction, and after the load is applied, the ball screw is temporarily stopped and then reversely rotated. It is often used under the condition of reciprocating (reciprocating motion). For this reason, friction may be generated between the ball rolling groove of the screw shaft or the ball rolling groove of the nut and the ball as the rolling element, and the ball rolling groove may be damaged such as wear. This wear is a cause of shortening the life of the entire ball screw and is a problem.

  Conventionally, it has been studied to extend the life of the entire ball screw by reducing the friction generated in the ball rolling groove. For example, in the technique described in Patent Document 1, a contact state between a raceway formed by opposing a ball rolling groove of a screw shaft and a ball rolling groove of a nut and a plurality of balls arranged in the raceway is determined. It is disclosed that the friction on the ball rolling groove or the surface of the ball can be reduced by using two-point contact. Thereby, a durable life can be extended.

JP 2002-276765 A

  However, in order to extend the life of ball screws, especially those used in machine tools that apply a high load from a certain direction, in addition to reducing the friction, the rated load of the ball screw must be maintained. Is also necessary. As a method for maintaining the rated load, the radius of the ball, which is a rolling element, is increased without changing the curvature of the ball rolling groove, and the ball rolling groove is not changed without changing the radius of the ball. And a method of increasing the curvature.

However, the former method leads to an increase in the overall size of the ball screw and increases the occupied space. This is inconvenient for downsizing machine tools and the like. In the latter method, since the contact area between the ball rolling groove and the ball increases, the contact surface pressure can be reduced, but on the other hand, the friction generated between the ball rolling groove and the ball increases. . As a result, frictional heat increases, and the operability and lubricant characteristics of the ball screw may be deteriorated.
In this way, in a ball screw used for a machine tool or the like in which a high load is applied in a certain direction, there is still room for study in order to extend the life while maintaining the rated load. Therefore, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a ball screw that extends the life while maintaining the rated load.

Here, for example, a general ball screw using a Gothic arc groove as the ball rolling groove is considered. The “gothic arc groove” refers to a cross-sectional shape in which two circular arcs having different centers of curvature radii are connected. In this case, when a load is applied to the nut, the ball in contact with the nut receives the load and contacts one of the arcs of the ball rolling grooves provided on the screw shaft side and the nut side. As a result, a main load is applied to these arcs. The “main load” refers to a load in which a relatively large load acts on one arc of the ball and the ball rolling groove among axial loads acting on the reciprocating nut. Note that the friction generated when the ball rolls mainly occurs in an arc where the main load is not applied.
The inventor pays attention to the magnitude of curvature of the two arcs forming the gothic arc grooves provided on the screw shaft and nut, thereby maintaining the rated load of the ball screw and sufficiently increasing its durability life. I found that I could secure it.

  Therefore, in order to achieve the above object, the invention according to claim 1 includes a screw shaft having a spiral ball rolling groove on the outer peripheral surface and a spiral ball rolling groove on the inner peripheral surface. And a plurality of balls arranged in a raceway formed by opposing the ball rolling groove of the screw shaft and the ball rolling groove of the nut, the Gothic including two arcs A ball screw used for each of the ball rolling groove provided on the screw shaft and the ball rolling groove provided on the nut, wherein the arc groove is included in the Gothic arc groove of each of the ball rolling grooves. Among the two arcs, when a main load is applied from a certain direction along the axial direction, the curvature of one arc that receives the main load is made larger than the curvature of the other arc.

  With such a configuration, the contact area between the ball and the ball rolling groove can be reduced in an arc that does not receive the main load. Further, the contact area between the ball and the ball rolling groove can be increased in the arc that receives the main load. Thereby, the wear which arises in the circular arc which does not receive a main load can be reduced, and also the contact surface pressure in the circular arc which receives a main load can be reduced. Therefore, the durability can be improved while maintaining the rated load of the ball screw. Here, “increasing the curvature” means tightening the curved surface.

The invention according to claim 2 is the ball screw according to claim 1, characterized in that the curvature of one arc that receives the main load is equal to the curvature of the ball.
With such a configuration, the contact area between the ball and the ball rolling groove can be set to the maximum possible value in the arc that receives the main load. Thereby, the contact surface pressure in the circular arc which receives a main load can be made into the minimum value which can be taken, and the rated load of a ball screw can be maintained.

Sectional drawing which shows one Embodiment of the ball screw which concerns on this invention. The elements on larger scale which show the relationship between the shape of a ball rolling groove, and a ball | bowl.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view partially showing in cross section the configuration of a ball screw 100 according to an embodiment of the present invention. In FIG. 1, the nut 3 is shown by being broken along a plane including the center of the screw shaft 2 and extending along the axial direction of the screw shaft 2.
As shown in FIG. 1, the ball screw 100 includes a screw shaft 2, a nut 3, and a ball 5 as main components. The screw shaft 2 includes a spiral ball rolling groove 1a on the outer peripheral surface thereof. The nut 3 is provided with a spiral ball rolling groove 1 b facing the ball rolling groove 1 a of the screw shaft 2 on its inner peripheral surface, and is further screwed with the screw shaft 2. The balls 5 are slidably loaded in the raceway 1 formed by the ball rolling groove 1a of the screw shaft 2 and the ball rolling groove 1b of the nut 3, and the number thereof is plural.

  A circulation passage 6 made of a tube bent in a substantially U shape is disposed on the outer peripheral surface of the nut 3, and is fixed to the nut 3 by a circulation passage presser 7. Although a total of two circulation passages 6 are illustrated in FIG. 1, this is not restrictive. For example, both ends of each circulation passage 6 pass through the nut 3 to the track 1, and the balls 5 that roll in the track 1 circulate through the circulation passage 6. Therefore, the nut 3 screwed to the screw shaft 2 via the plurality of balls 5 and the screw shaft 2 can relatively move in the axial direction via the rolling of the balls 5. Since the ball 5 rotates randomly in the circulation passage 6 when passing through the circulation passage 6, the wear of the ball 5 caused by rolling in the track 1 uniformly spreads over the entire surface of the ball 5.

  Next, details of the ball rolling grooves 1a and 1b will be described with reference to FIG. 1 and FIG. FIG. 2 is an enlarged view of the region indicated by “II” in FIG. 1 and shows the relationship between the track 1 and the ball 5 in the ball screw 100. In order to simplify the description, FIG. 2 shows one ball 5 and ball rolling grooves 1a and 1b. Further, the lubricant interposed between the ball 5 and the ball rolling groove 1a of the screw shaft 2 or the ball rolling groove 1b of the nut 3 is omitted in the drawing. In addition, the arrow in a figure shows a pressurization and a holding | maintenance direction.

  Each of the ball rolling grooves 1a and 1b in the ball screw 100 is a Gothic arc groove, and its cross-sectional shape is formed by combining two arcs having different curvatures as well as the position of the center of curvature. In the present embodiment, one of the two arcs receives the main load. Here, among the arcs that receive the load of the main load (hereinafter referred to as load arcs), the one provided on the nut 3 side is the nut side load arc N1, and the one provided on the screw shaft 2 side is the screw side load arc S1. To do. On the other hand, among the arcs that are not subjected to the load of the main load (hereinafter referred to as non-load arcs), those provided on the nut 3 side are the nut-side non-load arc N2, and those provided on the screw shaft 2 side are the screw-side non-loads. Let arc S2. 2, the nut-side load arc N1 and the screw-side load arc S1, and the nut-side non-load arc N2 and the screw-side non-load arc S2 are provided to face each other.

  In the present invention, the curvatures of the nut-side load arc N1 and the screw-side load arc S1 are larger than the curvatures of the nut-side non-load arc N2 and the screw-side non-load arc S2. That is, when the curvature of the nut-side unloaded arc N2 is RN2, the curvature of the screw-side unloaded arc S2 is RS2, the curvature of the nut-side loaded arc N1 is RN1, and the curvature of the screw-side loaded arc S1 is RS1, RN1> The relationship is RN2 and RS1> RS2.

  Next, the operation and effect of the ball screw 100 having the above configuration will be described. As shown in FIG. 2, when a load is applied to the nut 3, the ball 5 in contact with the nut 3 receives the load and contacts the arcs of the ball rolling grooves 1a and 1b provided on the screw shaft 2 side and the nut 3 side, respectively. To do. At this time, the main load is applied to the nut-side load arc N1 and the screw-side load arc S1. According to the ball screw 100 of the present invention, the curvature of the ball 5 and the curvature of the nut-side load arc N1 are secured in order to ensure a sufficient contact area between the nut-side load arc N1 or the screw-side load arc S1 and the ball 5. Although it is preferable to make the curvature RS1 of the RN1 or the screw side load arc S1 substantially equal, it is not limited to this. Furthermore, the magnitude relationship between the curvature RN1 of the nut-side load arc N1 and the curvature RS1 of the screw-side load arc S1 may be RN1 = RS1, RN1> RS1, or RS1> RN1. With the above configuration, the contact surface pressure in the nut-side load arc N1 and the screw-side load arc S1 can be reduced, so that the rated load of the ball screw 100 can be maintained.

Further, in order to sufficiently reduce the contact area between the nut-side unloaded arc N2 and the screw-side unloaded arc S2 and the ball 5, the curvature of the nut-side unloaded arc N2 and the screw-side unloaded arc S2 is changed to the curvature of the ball 5. However, this is not a limitation. Thereby, since the friction which arises in the said 2 circular arc can be reduced, the fall of durability of the ball screw 100 is suppressed and the lifetime can be extended. The magnitude relationship between the curvature RN2 of the nut-side unloaded arc N2 and the curvature RS2 of the screw-side unloaded arc S2 is also particularly limited as in the case of the curvature RN1 of the nut-side loaded arc N1 and the curvature RS1 of the screw-side loaded arc S1. Not provided.
In the present embodiment, there is no particular restriction on the installation direction of the screw shaft 2. That is, even if the axial direction of the screw shaft 2 is a vertical direction or a parallel direction, the same operation and effect can be exhibited. Further, even if it is a so-called “left-handed screw” or “right-handed screw”, the same operation and effect can be exhibited.

100 Ball screw 1 Track 1a Screw shaft side ball rolling groove 1b Nut side ball rolling groove 2 Screw shaft 3 Nut 5 Ball 6 Circulating passage 7 Circulating passage presser N1 Nut side load arc N2 Nut side non-load arc S1 Screw side load arc S2 Thread side unloaded arc RN1 Nut side loaded arc radius of curvature RN2 Nut side unloaded arc radius of curvature RS1 Thread side loaded arc radius of curvature RS2 Thread side unloaded arc radius of curvature RS2

Claims (2)

A screw shaft having a spiral ball rolling groove on the outer circumferential surface, a nut having a spiral ball rolling groove on the inner circumferential surface, a ball rolling groove on the screw shaft, and a ball rolling on the nut. A plurality of balls arranged in a track formed so as to face the moving groove,
A ball screw using a Gothic arc groove including two arcs for a ball rolling groove provided on the screw shaft and a ball rolling groove provided on the nut, respectively.
Of the two arcs included in the Gothic arc groove of each of the ball rolling grooves, when a main load is applied from a certain direction along the axial direction, the curvature of one arc that receives the main load is expressed as A ball screw characterized by being larger than the curvature of the arc. 2. The ball screw according to claim 1, wherein a curvature of one arc that receives the main load is equal to a curvature of the ball.

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