JP2007107649A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw which reduces a nut outer diameter without reducing a ball outer diameter. <P>SOLUTION: The ball screw 1 is provided with: a screw shaft 3 having a spiral ball rolling groove 2 on an outer circumference face; a nut 6 having a nut inner cylinder 10 having a load ball rolling groove 4 facing the ball rolling groove 2 on an inner circumference face and a nut outer cylinder 20 fit on the nut inner cylinder 10; a ball return passage 8 formed between the nut inner cylinder 10 and the nut outer cylinder 20 and passing through the cylinders along an axial direction of the cylinders; a ball raceway 7 composed between the ball rolling groove 2 and the load ball rolling groove 4; a ball circulation member 30 having a ball circulation passage 32 communicated with the the ball raceway 7 and the ball return passage 8; and a plurality of balls 5 housed so as to freely circulate in an endless circulation passage 9 composed of the ball raceway 7, the ball return passage 8, and the ball circulation passage 32. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a ball screw, and more particularly, to a small ball screw suitable for use in rotating a ball screw nut.

As this type of ball screw, for example, a technique described in Patent Document 1 is known.
In the technique described in Patent Document 1, a ball raceway is formed by a ball rolling groove of a screw shaft and a load ball rolling groove of a nut corresponding to the ball rolling groove. Further, a ball return passage penetrating along the axial direction is formed in the thick portion of the nut. Further, at both ends of the ball return passage, a ball circulation member having a ball circulation passage can be mounted from the radial direction of the nut, and each ball circulation member is a separate member from the radially outer side of the nut. It is configured to be fixed with a lid. A plurality of balls are circulated in an infinite circulation path composed of the ball raceway, the ball return path, and the ball circulation path, whereby the screw shaft ( Or a nut) is relatively movable in the axial direction through rolling of the ball.
JP 2001-289302 A

However, in the technique described in Patent Document 1, when the wall thickness from the inner wall surface of the ball return passage to the outer peripheral surface of the nut is insufficient, when forming the ball return passage in the thick portion of the nut, It is difficult to reduce the wall thickness to a certain extent because there is a risk that the outer peripheral side of the nut may be broken due to the cutting resistance or the like. For this reason, this increase in thickness has become a bottleneck in reducing the size of the nut. If the ball outer diameter is reduced, the nut outer diameter can be reduced accordingly, but it is not preferable in view of performance such as the allowable load of the ball screw. Moreover, there is a possibility that the processing blade is also small (the rigidity is small) and the processing cannot be performed.
Therefore, the present invention has been made paying attention to such problems, and an object thereof is to provide a ball screw that can reduce the nut outer diameter without reducing the ball outer diameter.

  In order to solve the above-described problems, a ball screw according to the present invention has a screw shaft having a spiral ball rolling groove on the outer peripheral surface and a load ball rolling groove facing the ball rolling groove on the inner peripheral surface. A nut having a nut inner cylinder and a nut outer cylinder fitted around the nut inner cylinder; a ball return passage formed between the nut inner cylinder and the nut outer cylinder and penetrating along these axial directions; A ball raceway formed between the ball rolling groove and the load ball rolling groove, a ball circulation member having a ball circulation passage for communicating the ball raceway and the ball return passage, and the ball raceway And a plurality of balls circulated in an infinite circulation path composed of a ball return path and a ball circulation path.

According to the present invention, the nut includes a nut inner cylinder and a nut outer cylinder, and the ball return passage is formed between the nut inner cylinder and the nut outer cylinder. Thereby, for example, a groove that opens toward the outer peripheral side of the nut inner cylinder can be formed by cutting, and the ball return passage can be configured so that the opening side is covered with the inner wall surface of the nut outer cylinder itself. In this case, the nut inner cylinder does not need to take into consideration the meat breakage that may occur on the outer peripheral side of the nut exemplified in Patent Document 1. And, since the nut outer cylinder at this time can set its thickness without considering cutting resistance or the like in the machining process, for example, compared with the thickness of the portion in the nut exemplified in Patent Document 1, The wall thickness can be reduced.
Therefore, according to the present invention, it is possible to provide a ball screw capable of reducing the nut outer diameter without reducing the ball outer diameter.

Hereinafter, embodiments of a ball screw according to the present invention will be described with reference to the drawings as appropriate.
FIG. 1 is a schematic configuration diagram for explaining a first embodiment of a ball screw according to the present invention. FIG. 1 (a) is a view seen from an axial direction of the nut, and FIG. 1 (b) is a radial direction of the nut. It is the figure seen from.
As shown in the figure, the ball screw 1 includes a screw shaft 3 having a spiral ball rolling groove 2 on the outer peripheral surface and extending in the axial direction, and a nut 6 is loosened on the screw shaft 3. It is fitted.
The nut 6 includes a nut inner cylinder 10 and a nut outer cylinder 20 that is fitted on the nut inner cylinder 10.
The nut inner cylinder 10 is a member made of steel and having a substantially cylindrical shape, and has a spiral load ball rolling groove 4 corresponding to the ball rolling groove 2 of the screw shaft 3 on its inner peripheral surface. The load ball rolling groove 4 and the ball rolling groove 2 of the screw shaft 3 are opposed to each other to form a ball raceway 7 between them.

  The nut outer cylinder 20 is a thin cylindrical member formed of a synthetic resin material. The inner diameter of the nut outer cylinder 20 is slightly larger than the outer diameter of the nut inner cylinder 10. Is fitted with almost no gap. In the example of this embodiment, in addition to this fitting, as shown in FIG. 1B, a tap hole 52 is formed on the nut inner cylinder 10 side at a position that does not interfere with other mechanism portions. On the nut outer cylinder 20 side, a countersunk hole 53 is formed at a predetermined mounting position at a position facing the tap hole 52, and these can be fastened by a countersunk screw 54.

  The nut 6 is formed with a ball return passage 8 penetrating along the axial direction between the nut inner cylinder 10 and the nut outer cylinder 20. Specifically, as shown in FIG. 2, a groove 8 a that opens in the radial direction of the nut inner cylinder 10 is formed on the outer peripheral surface of the nut inner cylinder 10 by end milling or milling. And as shown to Fig.1 (a), the said ball | bowl return channel | path 8 is comprised by the inner wall surface 20a of the nut outer cylinder 20 facing this groove part 8a.

  Further, as shown in FIG. 1 (b), a set of two mounting grooves 40 for fitting the ball circulation member 30 is formed at each end of the ball return passage 8 from the ball return passage 8. It is processed over the moving groove 4. The mounting groove 40 has an R process (reference numeral in the figure) that matches the cutting edge of the tool used so that the bottom of the groove can be processed from either the axial direction or the radial direction of the nut inner cylinder 10. R).

And the ball circulation member 30 is detachably fitted to each mounting groove 40 at both end faces of the nut inner cylinder 10.
As shown in FIG. 3, the ball circulation member 30 is arranged on both sides in the axial direction of the nut inner cylinder 10 and has an annular part 34 having an inner and outer diameter equal to the inner and outer diameters, and the annular part 34 toward the nut inner cylinder 10 side. And a circulation passage forming portion 36 extending toward the outside, and these are integrally formed from a synthetic resin material by injection molding.

  The circulation passage forming portion 36 has a predetermined outer shape that can be fitted in alignment with the inner shape of the mounting groove 40. The predetermined outer shape is such that when the nut 6 is loosely fitted to the screw shaft 3 in a state where the circulation passage forming portion 36 is fixed to the nut inner cylinder 10 by being fitted into each mounting groove 40, the screw The shaft 3 is accommodated inside the ball rolling groove 2 so that mutual interference between the screw shaft 3 and the circulation passage forming portion 36 is prevented.

  The circulation passage forming portion 36 is formed with a ball circulation passage 32 inside thereof. The ball circulation passage 32 is a groove curved so as to allow the ball return passage 8 and the ball track 7 to communicate with each other. The curved groove has a substantially U-shaped cross section perpendicular to the longitudinal direction, and the ball 5 rolling on the ball raceway 7 is located on the ball raceway 7 side (lower side in FIG. 3). A scooping portion 38 for scooping up the scissors is formed in a tongue shape. The scooping portion 38 extends in a direction along the tangent line of the lead angle of the ball raceway 7 and is gently connected to the ball rolling surface 31 of the ball circulation passage 32. As a result, the ball 5 is smoothly guided into the ball circulation passage 32.

  Then, by inserting the ball circulation member 30 from both ends of the nut inner cylinder 10 in the axial direction, the infinite circulation path 9 including the ball raceway path 7, the ball return path 8, and the ball circulation path 32 can be configured. ing. In order to prevent the circulation passage forming portion 36 from coming off in the mounting groove 40 in the axial direction, the retaining protrusion 50 (see FIG. 3) of the ball circulation member 30 can be fitted in the retaining groove 40 in the mounting groove 40. Since it is regulated by fitting into the recess 51 (see FIG. 2), the ball circulation member 30 can be easily prevented from being detached from the nut inner cylinder 10 and fixed.

  A plurality of balls 5 as rolling elements are accommodated in the endless circulation path 9, and the nut 6 (or the screw shaft 3) is moved through the rolling of the ball 5 by the rotation of the screw shaft 3 (or the nut 6). The ball 5 moves in the axial direction, and the ball 5 can be endlessly circulated from one end of the ball raceway 7 by a set of ball circulation members 30 and returned to the other end of the ball raceway 7. ing.

Next, functions and effects of the ball screw 1 will be described.
In the ball screw 1 having the above configuration, when the ball 5 rolls in the endless circulation circuit 9 and reaches one end of the ball raceway 7, the ball 5 rolls from the scooping portion 38 of one ball circulation member 30. It is scooped up on the surface 31 and guided to the ball circulation path 32, passes through the ball return path 8, enters the ball circulation path 32 of the other ball circulation member 30, enters the other end of the ball raceway 7 again, and is infinitely circulated. It can circulate in the path 9.

  According to the ball screw 1, the nut 6 includes the nut inner cylinder 10 and the nut outer cylinder 20, and the ball return passage 8 is formed between the nut inner cylinder 10 and the nut outer cylinder 20. Has been. In particular, in the example of the present embodiment, the groove 8a that opens toward the outer peripheral side of the nut inner cylinder 10 is formed by end milling or milling, and the opening side is covered with the inner wall surface 20a of the nut outer cylinder 20 itself. A return passage 8 is formed. For this reason, the nut inner cylinder 10 does not need to take into consideration the breaking of meat on the outer peripheral side. And since the thickness of the nut outer cylinder 20 can be set without considering cutting resistance or the like in the machining process, the thickness can be reduced. Therefore, according to this ball screw 1, the outer diameter of the nut 6 can be reduced without reducing the outer diameter of the ball 5. Thereby, this ball screw 1 is suitable especially for the use which rotates the nut of a ball screw with a small size.

  Usually, when the hole of the ball return passage penetrating in the axial direction is drilled in the thick part of the nut, the hole processing is generally longer in the axial direction than the hole diameter. And the accuracy is difficult to achieve. In particular, when a ball return passage longer than the tool length is formed, it is difficult to accurately match the opposing position because the machining is performed from both end faces of the nut. On the other hand, according to this ball screw 1, the groove 8a that opens toward the outer peripheral side of the nut inner cylinder 10 can be easily formed by end milling or milling as described above, so that the processing cost is reduced. And the accuracy can be improved.

Furthermore, according to this ball screw 1, since the nut outer cylinder 20 is a thin cylindrical member, it is easy to manufacture and fit into the nut inner cylinder 10 when the outer diameter of the nut 6 is reduced.
Further, according to this ball screw 1, the nut outer cylinder 20 is made of a synthetic resin material, so that it can be made lighter than that made of steel. It is more suitable for the purpose of rotation.

Next, a second embodiment of the ball screw according to the present invention will be described. The second embodiment is the same as the first embodiment except that the configuration described below is different from the first embodiment except for the other configurations. The same reference numerals are given to the configurations, and the description thereof is omitted as appropriate.
As shown in FIG. 4, the second embodiment is different from the nut outer cylinder 20 in that the nut outer cylinder is constituted by a set of nut outer cylinder constituent members 23 in the first embodiment. It is different.

  Specifically, the set of nut outer cylinder constituent members 23 includes a flange portion 21 and a cylindrical portion 22, respectively. The flange portions 21 are annular portions that are arranged on both sides in the axial direction of the nut inner cylinder 10 and extend radially inward. The plate thickness is the same as that of the first embodiment, and the inner diameter thereof is slightly larger than the screw shaft 3 so as not to interfere with the screw shaft 3. The cylindrical portion 22 is a thin cylindrical portion extending from the flange portion 21 along the axial direction of the nut inner cylinder 10, and the inner and outer diameters thereof are the same as those of the nut outer cylinder 20 in the first embodiment. The axial length is half that of the nut outer cylinder 20. In each nut outer cylinder constituent member 23 having such a configuration, each cylindrical portion 22 is externally fitted to the nut inner cylinder 10 from both sides in the axial direction, and is opposed to each other in the axial direction. In this mounted state, the flange portion 21 of each nut outer cylinder component member has a surface 21a facing the nut inner tube 10 side of the flange portion 21 abutting against a surface 34a facing the outer side of the annular portion 34 of the ball circulation member 30. In contact therewith, the movement of the ball circulation member 30 in the removal direction is prevented. As shown in the figure, also in the second embodiment, the ball circulation member 30 and the nut inner cylinder 10 are each provided with a retaining protrusion 50 and a retaining recess 51 as in the first embodiment. Yes. Further, the nut inner cylinder 10 and each nut outer cylinder constituting member 23 are provided with a set of a tapped hole 52, a countersink hole 53, and a countersunk screw 54 as in the first embodiment.

With such a configuration, the ball circulation member 30 can be prevented from moving in the removal direction without providing the ball circulation member 30 and the nut inner cylinder 10 with the retaining protrusion 50 and the retaining recess 51. And the effect | action and effect in said 1st embodiment can be show | played similarly to said 1st embodiment.
As described above, according to the ball screw of the present invention, it is possible to provide a ball screw capable of reducing the nut outer diameter without reducing the ball outer diameter.

In addition, the ball screw which concerns on this invention is not limited to said each embodiment, A various deformation | transformation is possible unless it deviates from the meaning of this invention.
For example, in each of the above embodiments, the ball return passage 8 formed between the nut inner cylinder 10 and the nut outer cylinder 20 is formed in the outer peripheral surface of the nut inner cylinder 10 and is a groove that opens in the radial direction. 8a and the example constituted by the inner peripheral surface 20a of the nut outer cylinder 20 facing the groove 8a, but the present invention is not limited to this, and the groove is formed at a position of the nut outer cylinder 20 facing the groove 8a. And a ball return passage may be formed by the groove and the groove portion 8a.

  Moreover, in each said embodiment, although the nut outer cylinder 20 demonstrated the example made into the thin cylindrical member, it is not limited to a thin wall and is not limited to a cylindrical shape. For example, the cross section may be rectangular, or a plane for attachment to another structure may be provided in a part of the cylindrical shape. Note that the thickness of the thin wall only needs to have a necessary and sufficient thickness so that the ball passing through the ball return passage can be accommodated and maintained in a state of being externally fitted to the nut inner cylinder 10 under the use conditions. It can be set.

Moreover, although the nut outer cylinder 20 demonstrated in the said each embodiment the example currently formed from the synthetic resin material, it is not limited to this, For example, a stainless steel plate and other steel materials can be used. However, in order to obtain a small ball screw suitable for the purpose of rotating the nut of the ball screw, it is preferable to form the nut outer cylinder from a synthetic resin material.
In each of the above embodiments, the nut outer cylinder 20 (or each nut outer cylinder constituent member 23) has been described as being fitted to the outer peripheral surface of the nut inner cylinder 10 with almost no gap, but the present invention is not limited thereto. It can be set as various fittings. For example, an interference fit that can be press-fitted can be suitably applied as the fit related to this fitting. With such a fitting, for example, a fastening structure including a set of the tap hole 52, the countersink 53, and the countersunk screw 54 can be omitted.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram explaining 1st embodiment of the ball screw concerning this invention, The figure (a) is the figure seen from the axial direction of the nut, The figure (b) was seen from the radial direction of the nut. FIG. It is a figure explaining the nut inner cylinder of the ball screw of FIG. 1, The figure (a) is the figure seen from the axial direction left of the nut, The figure (b) is the figure seen from the radial direction of the nut, Fig. (C) is a view seen from the right in the axial direction of the nut. It is a figure explaining the ball | bowl circulation member of the ball screw of FIG. 1, The figure (a) is the figure seen from the radial direction of the nut, The figure (b) is the figure seen from the axial direction right side of the nut. . It is a schematic structure figure explaining a first embodiment of a ball screw concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ball screw 2 Ball rolling groove 3 Screw shaft 4 Loaded ball rolling groove 5 Ball 6 Nut 7 Ball raceway 8 Ball return path 9 Endless circulation path 10 Nut inner cylinder 20 Nut outer cylinder 21 Hook 22 Cylindrical part 23 Nut outside Cylindrical component 30 Ball circulation member 32 Ball circulation passage 40 Mounting groove 50 Retaining protrusion 51 Retaining recess 52 Tap hole 53 Countersink 54 Countersunk screw

Claims (6)

  A screw shaft having a spiral ball rolling groove on the outer peripheral surface, a nut inner cylinder having a load ball rolling groove facing the ball rolling groove on the inner peripheral surface, and a nut outer cylinder fitted on the nut inner cylinder A ball return passage formed between the nut inner cylinder and the nut outer cylinder and penetrating along these axial directions; and the ball rolling groove and the load ball rolling groove. An infinite circulation path composed of the ball raceway, a ball circulation member having a ball circulation path for communicating the ball raceway and the ball return path, and the ball raceway, the ball return path, and the ball circulation path. And a plurality of balls accommodated in a freely circulating manner.   The ball return passage is configured by a groove portion formed on an outer peripheral surface of the nut inner cylinder and opening in a radial direction thereof, and an inner wall surface of the nut outer cylinder facing the groove portion. The ball screw according to claim 1.   The ball screw according to claim 1, wherein the nut outer cylinder is a thin cylindrical member.   Each of the nut outer cylinders has an annular flange that is disposed on both axial sides of the nut inner cylinder and extends radially inward, and a cylindrical portion that extends from the flange along the axial direction. It consists of a set of nut outer cylinder constituent members, and the set of nut outer cylinder constituent members is configured such that each of the cylindrical portions is externally fitted to the nut inner cylinder from both sides in the axial direction, and is opposed to each other in the axial direction. The ball screw according to claim 1, wherein the ball screw is configured as described above.   The ball screw according to any one of claims 1 to 4, wherein the nut outer cylinder is formed of a synthetic resin material.   The ball screw according to claim 5, wherein each flange portion of the set of nut outer cylinder constituting members is configured to prevent the ball circulating member from moving in the pulling direction.

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