Ball screw

Abstract

A ball screw (10) comprises: a screw shaft formed with a screw shaft-side raceway groove (21); a nut (30) provided with a through-hole (32) formed with a circular cross-sectional shape to provide communication between an outer peripheral surface (33) and a nut-side raceway groove (31); a plurality of balls (26) that roll on a ball rolling path (25); and a circulation component (40) that forms a ball circulation path (45). The circulation component (40) has a cylindrical nut insertion part (42) that is fitted into the through-hole (32), and, at a tip of the nut insertion part (42), has a semi-cylindrical part (46) provided such that a rolling surface of the ball circulation path (45) is continuous with a rolling surface of the nut-side raceway groove (31), and a tongue part (47) provided so as to enter the screw shaft-side raceway groove (21). A center line (C1) of the nut insertion part (42) is closer to an axis (O) of the nut (30) relative to a ball center trajectory (L) of the ball (26) scooped up in a tangential direction from the screw shaft-side raceway groove (21).

Description

ball screw

[0001] The present invention relates to a ball recirculation type ball screw.

[0002] Ball recirculation ball screws used in machine tools and the like require balls, which are arranged in a spiral ball rolling path (loaded track) consisting of a raceway groove in the screw shaft and a raceway groove in the nut, to be scooped up from the ball rolling path and returned from one end of the ball rolling path to the other. Known ball circulation methods include the tube type, the top type (also called the deflector type), the end cap type, and the end deflector type.

[0003] Depending on the circulation method, circulation parts are used that have a ball scooping section and a ball return passage formed as one unit, circulation parts that have a tube that can be attached to the nut, or circulation parts that have a nut insertion section formed with a tang section (a protrusion for guiding the ball into the passage within the circulation part) that scoops up and guides the ball into the ball return passage formed in the nut.

[0004] Furthermore, in such a ball recirculation type ball screw, a tangential scooping method is used as a means for improving the allowable rotation speed of the ball screw. As shown in Patent Document 1, the tangential scooping method generally involves creating a circulation path that scoops up the balls on a tangent to the BCD (ball center circle diameter).

[0005] Japanese Patent Application Publication No. 2014-84948

[0006] However, in the structure of Patent Document 1, the ball passage (ball circulation path) in the circulation part requires a structure combining straight and curved lines, so the cross-sectional shape of the nut insertion part of the circulation part that is inserted into the nut is formed into an oval shape. This results in the problem that it takes time to drill the hole in the nut, leading to increased costs for the ball screw. Furthermore, as the lead angle of the ball rolling path (nut raceway groove) increases, the thickness of the outer diameter portion of the nut insertion part that is inserted into the nut and the inner diameter portion of the ball passage that is opened obliquely in the lead angle direction becomes thinner, making it difficult to ensure the wall thickness required to provide sufficient strength to the nut insertion part (especially the tang portion) that is inserted into the nut.

[0007] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a ball screw that can easily process the nut while providing sufficient strength to the nut insertion portion of the circulating part.

[0008] The above object of the present invention is achieved by the following configuration: A ball screw comprising: a screw shaft having a spiral screw-shaft-side raceway groove formed on its outer peripheral surface; a nut having a spiral nut-side raceway groove formed on its inner peripheral surface facing the screw-shaft-side raceway groove and provided with a pair of through holes communicating the outer peripheral surface with the nut-side raceway groove; a plurality of balls that roll in a ball rolling path formed by the screw-shaft-side raceway groove and the nut-side raceway groove; and a circulation part attached to the through holes and forming a ball circulation path for circulating the balls rolling in the ball rolling path, wherein the through holes are formed with a circular cross section that penetrates obliquely inwardly along the lead angle of the nut-side raceway groove and communicates with the nut-side raceway groove, the circulation component has a cylindrical nut insertion portion having a ball scooping portion at its tip and fitted into the through hole, a semi-cylindrical portion provided at the tip of the ball scooping portion so that the rolling surface of the ball circulation path is continuous with the raceway surface of the nut-side raceway groove, and a tang portion provided at the tip of the ball scooping portion so as to fit into the screw shaft-side raceway groove, and the center line of the nut insertion portion is closer to the axis of the nut with respect to the ball center locus of the balls scooped up tangentially from the screw shaft-side raceway groove.

[0009] According to the present invention, it is possible to provide a ball screw that can easily process the nut while providing sufficient strength to the nut insertion portion of the circulating part.

[0010] The present invention has been briefly described above. The details of the present invention will become clearer by reading the following detailed description of the invention (hereinafter referred to as "embodiments") with reference to the accompanying drawings.

[0011] FIG. 1 is a plan view of a ball screw according to a first embodiment of the present invention. FIG. 2 is a front view of the ball screw shown in FIG. 1, viewed from the axial direction. FIG. 3 is a partial cross-sectional front view of the ball screw shown in FIG. 2, viewed from the axial direction. FIG. 4 is a perspective view of the circulatory component shown in FIG. 1. FIG. 5 is an exploded perspective view of the circulatory component shown in FIG. 4. FIGS. 6(a) to 6(d) are a front view, a side view, a bottom view, and a plan view of the ball scooping unit shown in FIG. 5. FIG. 7 is an enlarged cross-sectional view of a main portion of the nut and circulatory component shown in FIG. 1, viewed from the axial direction, to show the positional relationship between the ball rolling path in which the balls roll, the nut insertion portion of the circulatory component, and the through-hole of the nut. FIG. 8 is a plan view of a ball screw according to a second embodiment of the present invention. FIG. 9 is a front view of the ball screw shown in FIG. 8, viewed from the axial direction. FIGS. 10(a) and 10(b) are a plan view and a bottom view of the circulatory component shown in FIG. 8. Figures 11(a) and 11(b) are an exploded plan view and an exploded bottom view of the circulating part shown in Figure 10. Figure 12 is an enlarged cross-sectional view of a main part of the nut and circulating part shown in Figure 8, viewed from the axial direction, to show the positional relationship between the ball rolling path in which the balls roll, the nut insertion portion of the circulating part, and the through hole of the nut.

[0012] A ball screw according to an embodiment of the present invention will be described in detail below with reference to the drawings. (First Embodiment) First, the ball screw according to the first embodiment will be described with reference to Figs. 1 to 6. Fig. 1 is a plan view of a ball screw 10 according to the first embodiment of the present invention. Fig. 2 is a front view of the ball screw 10 shown in Fig. 1 as seen from the axial direction. Fig. 3 is a partial cross-sectional front view of the ball screw 10 shown in Fig. 2 as seen from the axial direction.

[0013] As shown in Figures 1 and 2, a ball screw 10 of the first embodiment includes a screw shaft 20 having a spiral screw shaft-side raceway groove 21 formed on its outer peripheral surface, a nut 30 having a spiral nut-side raceway groove 31 formed on its inner peripheral surface facing the screw shaft-side raceway groove 21 and having a pair of through holes 32 connecting the outer peripheral surface 33 and the nut-side raceway groove 31, a plurality of balls 26 that roll in a ball rolling path 25 formed by the screw shaft-side raceway groove 21 and the nut-side raceway groove 31, and a circulation part 40 that is attached to the through hole 32 and forms a ball circulation path 45 that circulates the balls 26 rolling in the ball rolling path 25.

[0014] 2 and 3, the metal nut 30 is formed in a cylindrical shape, and a spiral nut-side raceway groove 31 is formed on its inner peripheral surface with the same lead as the screw shaft-side raceway groove 21. In addition, an attachment surface 33a that is parallel to the axis O of the nut 30 is formed on the outer peripheral surface 33 of the nut 30.

[0015] Furthermore, near both axial ends of the mounting surface 33a, through holes 32 having a circular cross section are formed, respectively, penetrating obliquely inwardly along the lead angle of the nut-side raceway groove 31 and communicating with the nut-side raceway groove 31. The through holes 32 communicate with the space within the ball rolling path 25 formed in the ball screw 10.

[0016] A circulation part 40 is attached to the mounting surface 33a. The circulation part 40 forms a ball circulation path that circulates the plurality of balls 26 rolling in the ball rolling path 25. The circulation part 40 is fixed to the nut 30 via a retaining member or the like (not shown) that is screwed onto the nut 30.

[0017] The balls 26 are spherical bodies made of steel such as alloy steel, and roll in the ball rolling path 25 consisting of the opposing screw shaft side raceway groove 21 and nut side raceway groove 31 to thread the screw shaft 20 and nut 30 together and support the load applied to the ball screw 10.

[0018] Fig. 4 is a perspective view of the circulating device 40 shown in Fig. 1. Fig. 5 is an exploded perspective view of the circulating device 40 shown in Fig. 4. Figs. 6(a) to 6(d) are a front view, a side view, a bottom view, and a plan view of the ball scooping portion 44 shown in Fig. 5. As shown in Fig. 4, the circulating device 40 includes a cylindrical nut insertion portion 42 having a ball scooping portion 44 at its tip and fitted into the through hole 32, and a direction changing portion 41 having a ball circulation path 45 for changing the movement direction of the scooped balls 26 from the direction of the ball scooping portion 44 along the lead angle to the other circulating portion along the axial direction.

[0019] 5, ball scooping portion 44 having rolling surface 45c with a circular cross section is formed as a separate body from base 43 of nut insertion portion 42. Circulation part 40 is composed of first and second parts 41a and 41b each having semicircular cross-sectional rolling surfaces 45a and 45b that divide ball circulation path 45 into two along the ball center locus so that base 43 of nut insertion portion 42 and direction change portion 41 are formed continuously.

[0020] By combining the first part 41a and the second part 41b with the ball scooping portion 44, a ball circulation path 45 for circulating the balls 26 is defined and formed by the rolling surfaces 45a, 45b, and 45c.

[0021] The first part 41a and the second part 41b, which have rolling surfaces 45a and 45b respectively for forming the ball circulation path 45, which is a complex path made up of a combination of curves, are formed by resin molding, which has a high degree of freedom in shape, or sintering molding using metal powder.

[0022] Furthermore, the ball scooping portion 44, which must have a linear section of several millimeters on the rolling surface 45c of the ball circulation path 45 adjacent to the ball rolling path 25, is formed by casting or cutting using a high-strength metal material in order to ensure the strength of the tip that scoops up the ball 26 and increase durability.

[0023] As shown in Figures 6(a) to 6(d), the ball scooping portion 44 has a semi-cylindrical portion 46 formed at the tip of the ball scooping portion 44 so that the rolling surface 45c of the ball circulation path 45 is continuous with the raceway surface 31a of the nut-side raceway groove 31, and a tang portion 47 formed at the tip of the ball scooping portion 44 so as to fit into the screw shaft-side raceway groove 21.

[0024] The circulation part 40 is integrally assembled by bonding together the first part 41a, the second part 41b, and the ball scooping part 44. An anti-rotation step 48 is formed on the contact surface between the base part 43 of the nut insertion part 42 and the ball scooping part 44 to prevent the ball scooping part 44 from rotating relative to the base part 43 around the center line C1 of the nut insertion part 42.

[0025] 1 and 2, the pair of circulation parts 40 are attached to the nut 30 with their nut insertion portions 42 inserted into their respective through holes 32 of the nut 30. The circulation parts 40 are attached to the nut 30 with the bottom surfaces of their direction change portions 41 placed on the mounting surface 33a of the nut 30 and their ball circulation paths 45 communicating with each other.

[0026] Figure 7 is an enlarged cross-sectional view of the key parts of the nut 30 and circulating part 40 shown in Figure 1 viewed from the axial direction to show the positional relationship between the ball rolling path 25 in which the ball 26 rolls, the nut insertion portion 42 of the circulating part 40, and the through hole 32 of the nut 30.

[0027] 7 , in the ball screw 10 according to the first embodiment, when the pair of circulation components 40 are attached to the nut 30, the tongue portion 47 of the ball scooping portion 44 enters the screw shaft-side raceway groove 21. The tongue portion 47 has the function of smoothly scooping up the balls 26 that have passed through the ball rolling path 25 into the ball circulation path 45 on a tangent to the BCD (ball center circle diameter) of the ball rolling path 25, and the function of smoothly guiding the balls 26 that have passed through the ball circulation path 45 into the ball circulation path 45.

[0028] When the cylindrical nut insertion portion 42 is inserted into the through hole 32 having a circular cross section, the center line C1 of the nut insertion portion 42, which coincides with the center line C2 of the through hole 32, is configured to be closer to the axis O of the nut 30 by a distance S with respect to the ball center locus L of the ball 26 scooped up tangentially from the screw shaft side raceway groove 21.

[0029] Furthermore, the raceway surface 31a of the nut-side raceway groove 31, which faces the tip end surface 46a of the semi-cylindrical portion 46, is formed with a step 35 that is on a plane F that includes the axis O of the nut 30 and is perpendicular to the center line of the through hole 32 and has a width that corresponds to the thickness of the tip end of the semi-cylindrical portion 46. Therefore, when the tip end surface 46a of the semi-cylindrical portion 46 inserted into the through hole 32 abuts against the step 35, the rolling surface 45c of the semi-cylindrical portion 46 can smoothly connect to the raceway surface 31a of the nut-side raceway groove 31.

[0030] As described above, in the ball screw 10 of the first embodiment, the through hole 32 provided in the nut 30 is formed to have a circular cross section. That is, the through hole 32 in the nut 30 can be formed by machining a single hole, eliminating the need for oval machining, which increases costs. Therefore, the ball screw 10 of the first embodiment can facilitate the machining of the nut 30.

[0031] In addition, the nut insertion portion 42 of the circulation part 40 that is inserted into the through hole 32 of the nut 30 is configured so that the center line C1 of the nut insertion portion 42 is closer to the axis O of the nut 30 by a distance S with respect to the ball center locus L of the ball 26 that is scooped up tangentially from the screw shaft side raceway groove 21.

[0032] That is, in the ball screw 10, by appropriately setting the distance S between the center line C1 of the nut insertion portion 42 and the ball center locus L, a thickness equivalent to the distance S can be ensured between the outer diameter of the nut insertion portion 42 and the inner diameter of the ball circulation path 45. Thus, according to the ball screw 10 of the first embodiment, it is possible to easily ensure a thickness that will give sufficient strength to the semi-cylindrical portion 46 and the tang portion 47 of the nut insertion portion 42.

[0033] Furthermore, in the ball screw 10 of the first embodiment, the ball scooping portion 44 is separate from the base 43 of the nut insertion portion 42. Therefore, the base 43 and the ball scooping portion 44 of the nut insertion portion 42 can be formed using optimal manufacturing methods according to their respective functions. In other words, it is possible to reduce the manufacturing cost of the nut insertion portion 42.

[0034] For example, the first component 41a and the second component 41b that make up the ball circulation path 45, which is a complex path, can be formed by resin molding, which allows for a high degree of freedom in shape, or sintering molding using metal powder. Also, the ball scooping portion 44, which needs to have sufficient strength at its tip, can be formed by casting or cutting using a high-strength metal material.

[0035] Furthermore, in the ball screw 10 of the first embodiment, a rotation prevention step 48 is formed on the contact surface between the base 43 of the nut insertion portion 42 and the ball scooping portion 44, preventing the ball scooping portion 44 from rotating relative to the base 43 about the center line C1 of the nut insertion portion 42. Thus, the cylindrical ball scooping portion 44 fitted into the through hole 32 with a circular cross section can be prevented from rotating about the center line C1 within the through hole 32.

[0036] Second Embodiment Next, a ball screw according to a second embodiment will be described with reference to FIGS. 8 to 11. FIG. 8 is a plan view of a ball screw 10A according to a second embodiment of the present invention. FIG. 9 is a front view of the ball screw 10A shown in FIG. 8, viewed from the axial direction. The ball screw 10A according to the second embodiment differs from the ball screw 10 of the first embodiment in that the circulating component 40 is replaced with a circulating component 60. Other configurations are substantially similar to those of the first embodiment, and therefore the same reference numerals are used and detailed description thereof will be omitted.

[0037] As shown in Figures 8 and 9, the ball screw 10A of this second embodiment comprises a screw shaft 20, a nut 30A, a plurality of balls 26, and a circulation part 60 attached to the through hole 32A of the nut 30A to form a ball circulation path 65 for circulating the balls 26 rolling in the ball rolling path 25.

[0038] 9, the nut 30A of the second embodiment has through holes 32A with a circular cross section formed near both axial ends of the mounting surface 33a, the through holes 32A penetrating obliquely inward along the lead angle of the nut-side raceway groove 31 and communicating with the nut-side raceway groove 31. The through holes 32A communicate with the space within the ball rolling path 25 formed in the ball screw 10A. The through holes 32A have an annular positioning portion 37 formed in the middle thereof, making them stepped holes.

[0039] A circulation component 60 is attached to the mounting surface 33a, forming a ball circulation path that circulates the plurality of balls 26 rolling in the ball rolling path 25. The circulation component 60 is fixed to the nut 30A via a retaining member or the like (not shown) that is screwed onto the nut 30A.

[0040] 10A and 10B are a plan view and a bottom view of the circulating component 60 shown in FIG. 8. FIGS. 11A and 11B are exploded plan views and bottom views of the circulating component 60 shown in FIG. 10. As shown in FIGS. 10A and 10B, the circulating component 60 includes a cylindrical nut insertion portion 63 having a ball scooping portion 66 at its tip and fitted into the through hole 32A, and a direction changing portion 64 having a ball circulation path 65 for changing the movement direction of the scooped balls 26 from the direction of the ball scooping portion 66 along the lead angle to another circulation portion along the axial direction. An annular positioning step 68 is formed on the outer circumferential surface of the nut insertion portion 63 and abuts against the positioning portion 37 of the through hole 32A.

[0041] Furthermore, as shown in Figures 11 (a) and (b), the circulation part 60 is constructed by combining together a first circulation part 61 and a second circulation part 62, each of which has a shape in which at least the ball scooping part 66 is divided into two parts in the direction of the axis O of the nut 30A.

[0042] The first circulation component 61 and the second circulation component 62 each have rolling surfaces 65a, 65b with a semicircular cross section that divide the ball circulation path 65 into two along the ball center locus so that the nut insertion portion 63 and the direction change portion 64 are continuously formed. That is, by combining the first circulation component 61 and the second circulation component 62, the ball circulation path 65 for circulating the balls 26 is defined and formed by the rolling surfaces 65a, 65b.

[0043] The first circulation part 61 and the second circulation part 62, which each have rolling surfaces 65a and 65b for forming the ball circulation path 65, which is a complex path made up of a combination of curves, are formed by resin molding, which has a high degree of freedom in shape, or sintering molding using metal powder.

[0044] 10 and 11 , the tip of the ball scooping portion 66 has a semi-cylindrical portion 69 formed at the tip of the ball scooping portion 66 so that the rolling surfaces 65a, 65b of the ball circulation path 65 are continuous with the raceway surface 31a of the nut-side raceway groove 31, and a tang portion 67 formed at the tip of the ball scooping portion 66 so as to fit into the screw shaft-side raceway groove 21. The semi-cylindrical portion 69 is made up of a first portion 69a formed integrally with the first circulation component 61 and a second portion 69b formed integrally with the second circulation component 62.

[0045] 8 and 9, the pair of circulation parts 60 are inserted into the respective through holes 32A of the nut 30A at their nut insertion portions 63. Then, the circulation parts 60 are attached to the nut 30A with the bottom surfaces of their direction change portions 64 placed on the mounting surface 33a of the nut 30A and their ball circulation paths 65 communicating with each other.

[0046] Figure 12 is an enlarged cross-sectional view of the key parts of the nut 30A and circulating part 60 shown in Figure 8, viewed from the axial direction, to show the positional relationship between the ball rolling path 25 in which the ball 26 rolls, the nut insertion portion 63 of the circulating part 60, and the through hole 32A of the nut 30A.

[0047] 12 , in the ball screw 10A according to the second embodiment, a pair of circulation components 60 are attached to the nut 30A, so that the tongue portion 67 of the ball scooping portion 66 enters the screw shaft-side raceway groove 21. The tongue portion 67 has the function of smoothly scooping up the balls 26 that have passed through the ball rolling paths 25 into the ball circulation path 65 on a tangent to the BCD (ball center circle diameter) of the ball rolling paths 25, and the function of smoothly guiding the balls 26 that have passed through the ball circulation path 65 into the ball circulation path 65.

[0048] When the cylindrical nut insertion portion 63 is inserted into the through hole 32A having a circular cross section, the center line C1 of the nut insertion portion 63, which coincides with the center line of the through hole 32A, is configured to be closer to the axis O of the nut 30A by a distance S with respect to the ball center locus L of the ball 26 scooped up tangentially from the screw shaft side raceway groove 21.

[0049] Furthermore, when the nut insertion portion 63 is inserted into the through hole 32A, a positioning step 68 formed on the outer peripheral surface of the nut insertion portion 63 abuts against the positioning portion 37 of the through hole 32A, thereby restricting the insertion position of the circulative component 60. Then, the tip surface of the semi-cylindrical portion 69 inserted into the through hole 32A abuts against the step 35, so that the rolling surfaces 65a, 65b of the semi-cylindrical portion 69 smoothly continue into the raceway surface 31a of the nut-side raceway groove 31.

[0050] As described above, in the ball screw 10A of the second embodiment, the through hole 32A provided in the nut 30A is formed to have a circular cross section. That is, the through hole 32A in the nut 30A can be machined as a stepped hole, eliminating the need for oval machining, which increases costs. Therefore, the ball screw 10A of the second embodiment makes it possible to easily machine the nut 30A.

[0051] In addition, the nut insertion portion 63 of the circulation part 60 that is inserted into the through hole 32A of the nut 30A is configured so that the center line C1 of the nut insertion portion 63 is closer to the axis O of the nut 30A by a distance S with respect to the ball center locus L of the ball 26 that is scooped up tangentially from the screw shaft side raceway groove 21.

[0052] That is, in the ball screw 10A, by appropriately setting the distance S between the center line C1 of the nut insertion portion 63 and the ball center locus L, it is possible to ensure a thickness equivalent to the distance S between the outer diameter of the nut insertion portion 63 and the inner diameter of the ball circulation path 65. Thus, according to the ball screw 10A of the second embodiment, it is possible to easily ensure a thickness that will give sufficient strength to the semi-cylindrical portion 69 and the tang portion 67 of the nut insertion portion 63.

[0053] However, if the lead angle of the ball rolling path 25 becomes large, the thickness of the outer diameter portion of the ball scooping portion 66 inserted into the through hole 32A and the inner diameter portion of the ball circulation path 65 opened at an angle in the lead angle direction will become thinner, and it may not be possible to ensure the strength of the semi-cylindrical portion 69 and the tang portion 67.

[0054] In the ball screw 10A of the second embodiment, at least the ball scooping portion 66 is configured by integrally combining a first circulation component 61 and a second circulation component 62, each having a shape divided into two in the direction of the axis O of the nut 30A. Therefore, at the butted end of the first circulation component 61 and the second circulation component 62, it is easy to form the ball scooping portion 66 of the nut insertion portion 63 so that the thin-walled portions that cannot ensure strength at the end of the semi-cylindrical portion 69 and the tongue portion 67 are removed.

[0055] Therefore, the ball scooping portion 66 of the nut insertion portion 63 in this second embodiment, in which the thin-walled portions with low strength have been removed, can be made into an excellent shape that does not adversely affect ball circulation even if the lead angle of the ball rolling path 25 becomes large.

[0056] As described above, according to the ball screws 10, 10A of the respective embodiments, the nuts 30, 30A can be easily machined, while the nut insertion portions 42, 63 of the circulating parts 40, 60 can be provided with sufficient strength.

[0057] The present invention is not limited to the above-described embodiments, and can be appropriately modified, improved, etc. Furthermore, the material, shape, size, number, location, etc. of each component in the above-described embodiments are arbitrary and not limited as long as they can achieve the present invention.

[0058] The ball screw of the present invention is used, for example, in XY stages used for positioning devices that perform high-precision machining and measurement, and in semiconductor manufacturing, etc. The ball screw is also used, for example, in machine tools (machining centers, lathes, grinders, etc.), measuring machines (three-dimensional measuring devices), semiconductor manufacturing equipment (tables for exposure devices, inspection probes, etc.), etc.

[0059] Here, the features of the above-described embodiments of the ball screw according to the present invention will be briefly summarized and listed below in [1] to [4].

[0060] [1] A ball screw (10, 10A) comprising: a screw shaft (20) having a spiral screw shaft-side raceway groove (21) formed on its outer peripheral surface; a nut (30, 30A) having a spiral nut-side raceway groove (31) formed on its inner peripheral surface facing the screw shaft-side raceway groove (21) and provided with a pair of through holes (32, 32A) connecting the outer peripheral surface (33) and the nut-side raceway groove (31); a plurality of balls (26) rolling in a ball rolling path (25) formed by the screw shaft-side raceway groove (21) and the nut-side raceway groove (31); and a circulation part (40, 60) attached to the through holes (32, 32A) and forming a ball circulation path (45, 65) for circulating the balls (26) rolling in the ball rolling path (25), the through holes (32, 32A) are formed to have a circular cross section that penetrates obliquely inwardly along the lead angle of the nut-side raceway groove (31) and communicates with the nut-side raceway groove (31), The circulation component (40, 60) has a cylindrical nut insertion portion (42, 63) having a ball scooping portion (44, 66) at its tip and fitted into the through hole (32, 32A), a semi-cylindrical portion (46, 69) provided at the tip of the ball scooping portion (44, 66) so that the rolling surface (45a, 45b, 45c; 65a, 65b) of the ball circulation path (45, 65) is continuous with the raceway surface (31a) of the nut-side raceway groove (31), and a tang portion (47, 67) provided at the tip of the ball scooping portion (44, 66) so as to enter the screw shaft-side raceway groove (21), a center line (C) of the nut insertion portion (42, 63) being closer to an axis (O) of the nut with respect to a ball center locus (L) of the ball (26) scooped up in a tangential direction from the screw shaft side raceway groove (21).

[0061] According to the ball screw (10, 10A) having the configuration [1] above, the through hole (32, 32A) provided in the nut (30, 30A) is formed to have a circular cross section. Therefore, the through hole (32, 32A) in the nut (30, 30A) can be machined as a single hole, eliminating the need for oval machining, which increases costs. Furthermore, in the ball screw (10, 10A) having this configuration, by appropriately setting the distance (S) between the center line (C) of the nut insertion portion (42, 63) and the ball center locus (L), a thickness equivalent to the distance (S) can be ensured between the outer diameter of the nut insertion portion (42, 63) and the inner diameter of the ball circulation path (45, 63). Therefore, with the ball screw (10, 10A) of this configuration, it is easy to ensure the thickness necessary to provide sufficient strength to the semi-cylindrical portion (46, 69) and the tang portion (47, 67) of the nut insertion portion (42, 63) of the ball screw (10, 10A).

[0062] [2] The ball screw (10) according to the above [1], wherein the ball scooping portion (44) is separate from the base portion (43) of the nut insertion portion (42).

[0063] According to the ball screw (10) having the configuration [2] above, the base portion (43) and the ball scooping portion (44) of the nut insertion portion (42) can be formed using the optimum manufacturing method according to their respective functions. In other words, it is possible to reduce the manufacturing cost of the nut insertion portion (42).

[0064] [3] The ball screw (10) described in [2] above, wherein a rotation prevention step (48) is formed on the contact surfaces of the base (43) of the nut insertion portion (42) and the ball scooping portion (44) to prevent the ball scooping portion (44) from rotating relative to the base (43) of the nut insertion portion (42) around the center line (C) of the nut insertion portion (42).

[0065] According to the ball screw (10) having the configuration [3] above, the cylindrical ball scooping portion (44) fitted into the through hole (32) having a circular cross section can be prevented from rotating around the center line (C) within the through hole (32).

[0066] [4] The ball screw (10A) according to the above [1], wherein at least the ball scooping portion (66) of the circulation component (60) has a shape divided into two in the direction of the axis (O) of the nut (30A).

[0067] According to the ball screw (10A) having the configuration [4] above, it is easy to form the ball scooping portion (66) of the nut insertion portion (63) so that the butted ends of the two divided circulating components (the first circulating component 61 and the second circulating component 62) have a shape in which thin-walled portions that do not ensure the strength of the ends of the semi-cylindrical portion (69) and the tang portion (67) are removed. Therefore, the ball scooping portion (66) of the nut insertion portion (63) from which the thin-walled portions with low strength have been removed can have a good shape that does not adversely affect ball circulation even when the lead angle of the ball rolling path (25) is large.

[0068] This application is based on a Japanese patent application (Patent Application No. 2023-204621) filed on December 4, 2023, the contents of which are incorporated herein by reference.

[0069] According to the ball screw of the present invention, it is possible to easily process the nut while providing sufficient strength to the nut insertion portion of the circulating part, thereby reducing manufacturing costs.

[0070] REFERENCE SIGNS LIST 10 ball screw 20 screw shaft 21 screw shaft side raceway groove 25 ball rolling path 26 ball 30 nut 31 nut side raceway groove 31a raceway surface 32 through hole 33 outer circumferential surface 40 circulation part 42 nut insertion portion 44 ball scooping portion 45 ball circulation path 45a rolling surface 45b rolling surface 45c rolling surface 46 semi-cylindrical portion 47 tongue portion

Claims

1. A ball screw comprising: a screw shaft having a helical screw shaft side raceway groove formed on its outer circumferential surface; a nut having a helical nut side raceway groove formed on its inner circumferential surface facing said screw shaft side raceway groove and provided with a pair of through holes communicating the outer circumferential surface with said nut side raceway groove; a plurality of balls rolling in a ball rolling path formed by said screw shaft side raceway groove and said nut side raceway groove; and a circulation part attached to said through holes and forming a ball circulation path for circulating the balls rolling in said ball rolling path, wherein the through holes are formed in a circular cross section penetrating obliquely inwardly along the lead angle of said nut side raceway groove and communicating with said nut side raceway groove, The circulation part has a cylindrical nut insertion portion having a ball scooping portion at its tip and being fitted into the through hole, a semi-cylindrical portion provided at the tip of the ball scooping portion so that the rolling surface of the ball circulation path is continuous with the raceway surface of the nut side raceway groove, and a tang portion provided at the tip of the ball scooping portion so as to fit into the screw shaft side raceway groove, and the center line of the nut insertion portion is closer to the axis of the nut with respect to the ball center locus of the ball scooped up tangentially from the screw shaft side raceway groove.

2. The ball screw according to claim 1, wherein the ball scooping portion is separate from a base portion of the nut insertion portion.

3. A ball screw as described in claim 2, wherein a rotation prevention step is formed on the contact surfaces between the base of the nut insertion portion and the ball scooping portion to prevent the ball scooping portion from rotating relative to the base of the nut insertion portion around the center line of the nut insertion portion.

4. The ball screw according to claim 1, wherein at least the ball scooping portion of the circulation component has a shape divided into two in the axial direction of the nut.

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