Ball screw

Abstract

To provide a ball screw that can more efficiently prevent the grease adhering to an end surface of a seal from depositing or scattering and can effectively utilize the grease.SOLUTION: A ball screw 10 includes a screw shaft 20, a nut 30, a plurality of balls 26, and a seal 40. The seal 40 sealing a gap between an outer peripheral surface of the screw shaft 20 and an inner peripheral surface of the nut 30 has an inner peripheral surface 40d facing the screw shaft 20; and a lateral surface 40a that is an axial outer end surface and formed into an inclination shape that is inclined on an axial inside toward a radial inside from a radial outside.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ball screw. [Background technology]

[0002] A ball screw includes a screw shaft with a spiral outer peripheral screw groove formed on its outer peripheral surface, a nut with a spiral inner peripheral screw groove formed on its inner peripheral surface, and a plurality of balls that are freely rollable in a ball rolling section formed by the outer peripheral screw groove and the inner peripheral screw groove, and converts the relative rotational motion between the screw shaft and the nut into linear motion. If the lubricant sealed in the ball screw leaks or foreign matter such as dust or wear powder enters the nut from the outside, smooth motion may be impaired. Generally, a sealing mechanism that seals the gap between the screw shaft and the nut is known to prevent the leakage of the lubricant sealed in the ball screw and the entry of foreign matter from the outside.

[0003] Patent Document 1 discloses a ball screw in which a grease reservoir is provided on the inner peripheral surface of a cylindrical portion exposed axially outward of the nut to form a space relative to the screw shaft, and the grease reservoir opens to the outer peripheral surface of the cylindrical portion and communicates with a slot formed on the outer peripheral surface of a seal. In the ball screw of Patent Document 1, grease (excess grease) that adheres to the surface of the screw shaft from inside the nut and attempts to escape to the outside is scraped off by the cylindrical portion and, due to the reaction of the cylindrical portion, is discharged from the nut through the grease reservoir and guided along the slot, where it accumulates on the outer peripheral surface of the seal, where centrifugal force does not act on the grease. As a result, the grease is not scattered around by centrifugal force, but instead drips under its own weight below the screw shaft, which is unaffected by the scattering, preventing the accumulation and scattering of excess grease inside the nut. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6252136 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the ball screw described in Patent Document 1 has a complicated seal structure for storing grease, which tends to increase manufacturing costs. Also, because the seal is exposed from the nut, grease can adhere to and accumulate on the outer circumferential surface of the seal or on the outer end surface of the seal, which is a surface perpendicular to the screw axial direction, which can result in the grease not being used effectively.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide a ball screw that more efficiently prevents the accumulation and scattering of grease adhering to the end face of the seal, and that allows the effective use of this grease. [Means for solving the problem]

[0007] The above object of the present invention is achieved by the following configuration of a ball screw. [1] A screw shaft having a spiral outer thread groove formed on its outer circumferential surface; a nut having a spiral internal thread groove formed on its inner peripheral surface; A plurality of balls rolling on a ball rolling section formed by an outer peripheral screw groove of the screw shaft and an inner peripheral screw groove of the nut; A seal provided at least at one axial end of the nut to seal between an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut; A ball screw comprising: The seal is The inner circumferential surface faces the screw shaft, and the axially outer end surface is formed in an inclined shape that inclines axially inward from the radially outer side toward the radially inner side. Ball screw. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a ball screw that can more efficiently prevent the accumulation and scattering of grease adhering to the end face of the seal and that can effectively utilize this grease. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1(a) is a front view of a ball screw according to a first embodiment of the present invention, and FIG. 1(b) is a cross-sectional view taken along line AA in FIG. 1(a). [Figure 2] FIG. 2(a) is a front view of the seal shown in FIGS. 1(a) and 1(b), and FIG. 2(b) is a cross-sectional view taken along line BB in FIG. 2(a). [Figure 3] FIG. 3(a) is a front view of a ball screw according to a second embodiment of the present invention, and FIG. 3(b) is a cross-sectional view taken along the line AA in FIG. 3(a). [Figure 4] FIG. 4(a) is a front view of the seal shown in FIGS. 3(a) and 3(b), and FIG. 4(b) is a cross-sectional view taken along line BB in FIG. 4(a). [Figure 5] FIG. 5(a) is a front view of a seal in a ball screw according to a third embodiment of the present invention, and FIG. 5(b) is a cross-sectional view taken along line BB in FIG. 5(a). [Figure 6] FIG. 6(a) is a front view of a seal in a ball screw according to a fourth embodiment of the present invention, and FIG. 6(b) is a cross-sectional view taken along line BB in FIG. 6(a). DETAILED DESCRIPTION OF THE INVENTION

[0010] (First embodiment) A ball screw according to a first embodiment of the present invention will be described in detail below with reference to the drawings. As shown in Figures 1(a) and (b), the ball screw 10 of this embodiment includes a screw shaft 20 that extends in the axial direction and has a spiral outer peripheral screw groove 21 on its outer peripheral surface, a nut 30 that has a spiral inner peripheral screw groove 31 on its inner peripheral surface that corresponds to the outer peripheral screw groove 21 of the screw shaft 20, and a seal 40 that is disposed at the axial end of the nut 30 and seals the gap between the screw shaft 20 and the nut 30.

[0011] The outer peripheral screw groove 21 of the screw shaft 20 and the inner peripheral screw groove 31 of the nut 30 face each other, forming a ball rolling section 25 therebetween, and a large number of balls 26 as rolling elements are loaded into the ball rolling section 25 together with grease so that they can roll. As a result, the ball screw 10 converts the rotational motion of the screw shaft 20 and the nut 30 into the linear motion of the nut 30 and the screw shaft 20. Note that only a portion of the large number of balls 26 are shown in FIG. 1(b).

[0012] A flange portion 32 is formed on one axial end side of the nut 30 (the left side in FIG. 1(b)). Circular recesses 33 having an inner diameter larger than the groove bottom 31a of the inner circumferential thread groove 31 of the nut 30 are formed concentrically with the inner circumferential thread groove 31 at both axial ends of the nut 30. A seal 40 for sealing the gap between the screw shaft 20 and the nut 30 is disposed in the circular recess 33. A moving platform or the like of a mechanical device (not shown) is fixed to the flange portion 32 with mounting bolts or the like.

[0013] Furthermore, a pair of pilot holes 36, 36 that penetrate radially from the outer peripheral surface 35 to the circular recess 33 are formed at both axial ends (including the flange portion 32) of the nut 30 at positions that are 180° out of phase with each other. The axial distance between the axial center of the pilot hole 36 and the side surface 33a of the circular recess 33 is set to L1.

[0014] Generally, in a tube circulation nut, tube mounting holes and the like are machined radially, so the pilot hole 36, which is a radial hole, can be machined in the same process, reducing the number of set changes compared to machining axial holes and reducing manufacturing costs. Also, as will be described later, the pilot hole 36 is a hole for a tapping screw, so there is no need to machine a female thread, and processing costs can be reduced.

[0015] The nut 30 also has a ball return passage (not shown) that penetrates the interior in the axial direction, and a circulating piece (not shown) is disposed therein to connect the ball return passage with the ball rolling section 25. The ball rolling section 25, one circulating piece, the ball return passage, the other circulating piece, and the ball rolling section 25 form an infinite circulation passage for the balls 26. A plurality of balls 26 are loaded into the infinite circulation passage together with a predetermined amount of lubricant (for example, grease).

[0016] 2(a) and 2(b), the seal 40 is fitted into the circular recess 33. The seal 40 has an inner peripheral surface 40d facing the screw shaft 20. In this example, the seal 40 has an outer diameter slightly smaller than the inner diameter of the circular recess 33 and is formed in a generally annular shape with a through-hole 41 in the center that is larger than the outer diameter of the screw shaft 20 so as to define a gap S between the seal 40 and the screw shaft 20. The seal 40 is made of, for example, metal or a synthetic resin such as nylon, POM, or PBT. A pair of pilot holes 42, 42 for tapping screws are formed in the outer peripheral surface 40b of the seal 40, 180° out of phase with each other. The pilot holes 42, 42 for tapping screws are simple holes and do not require female thread machining, so processing costs are low.

[0017] One side surface 40a of the seal 40 (the axially outer end surface in FIGS. 1(a) and 1(b)) is formed in an inclined shape (i.e., a downward slope) that slopes axially inward from the radially outer side toward the radially inner side. That is, the side surface 40a is inclined extending from the outer peripheral surface 40b toward the inner peripheral surface 40d. Referring also to FIGS. 2(a) and 2(b), the inclination angle α of the side surface 40a is preferably 10° or more to more efficiently prevent the accumulation and scattering of grease adhering to the side surface 40a of the seal 40 (achieving the effects of the invention), but is preferably 90° or less in consideration of the thickness and width of the seal 40, the manner in which the seal 40 is assembled into the circular recess 33, and the like.

[0018] Furthermore, since the seal 40 is simply an annular member, it is easy to process and can be used in common with ball screws having different leads as long as the screw shaft diameter is the same.

[0019] The other non-inclined side surface 40c is the side surface 40c that becomes the inner side in the axial direction of the nut 30 when assembled to the circular recess 33. The axial distance L2 between this side surface 40c and the axial center of the tapping screw pilot hole 42 is smaller than the axial distance L1 between the axial center of the screw pilot hole 36 of the nut 30 and the side surface 33a of the circular recess 33 (L2 < L1). Thereby, when the seal 40 is incorporated into the circular recess 33, a gap can be secured between the side surface 40c of the seal 40 and the side surface 33a of the nut 30, and the seal 40 can be assembled without trouble. The axial centers of the tapping screw pilot hole 42 and the screw pilot hole 36 substantially coincide.

[0020] Next, the assembly of the ball screw 10 will be described. First, while aligning the screw pilot hole 36 of the nut 30 and the tapping screw pilot hole 42 of the seal 40, the seal 40 is fitted into the circular recess 33. Next, a tapping screw 51 is inserted into the screw pilot hole 36 and screwed into the tapping screw pilot hole 42 to regulate the rotational direction and axial position of the seal 40 and fix it to the nut 30. Since the seal 40 is an annular shape without a circumferential phase, it is only necessary to generally align the screw pilot hole 36 and the tapping screw pilot hole 42, and an accurate alignment operation is not required, making the operation easier.

[0021] Next, a mechanism for suppressing the deposition and scattering of excess grease adhering to the end face (one side surface 40a) of the seal 40 and effectively utilizing this grease will be described. During the operation of the ball screw 10, it is operated with the space between the nut 30 and the screw shaft 20 filled with grease.

[0022] For example, when the screw shaft 20 is rotated in a predetermined direction, the nut 30 moves to the right or left side in FIG. 1 as it rotates. During this axial rotation and nut movement, as shown in FIG. 2(b), the grease adhering to the seal 40 is discharged into the gap S (center, screw shaft 20) by the air pressure difference because the air pressure applied to the side surface 40a of the seal 40 is greater on the upper side of the inclined surface (radial outer side) than on the lower side of the inclined surface (radial inner side).

[0023] Furthermore, for example, when the nut 30 is rotated in a predetermined direction, the screw shaft 20 moves to the right or left in Fig. 1 as the nut rotation shaft moves. When the nut rotation shaft moves, the grease adhering to the seal 40 tends to scatter radially outward due to the rotational centrifugal force, but this tendency to scatter is suppressed by the inclined side surface 40a.

[0024] As described above, according to this embodiment, it is possible to more efficiently prevent the accumulation and scattering of grease adhering to the side surface 40a of the seal 40, and also to effectively utilize this grease.

[0025] Next, a ball screw according to a second embodiment of the present invention will be described in detail. The ball screw 10 of the second embodiment differs only in the shape of the seal 40, and other structures are the same as the ball screw 10 of the first embodiment, so the same parts are given the same reference numerals and detailed explanations are omitted.

[0026] As shown in Figures 3(a) and 3(b) and 4(a) and 4(b), the seal 40 of this embodiment further has a plurality of (four in this example) holes 43 that penetrate from the side surface 40a to the inner circumferential surface 40d. The holes 43 are minute holes for discharging grease adhering to the side surface 40a of the seal 40 into the gap S. In this example, the holes 43 are formed in a substantially L-shape, but the shape is not particularly limited.

[0027] The hole 43 is provided near the radially outer edge of the side surface 40a. More specifically, the radial distance between the radially outer edge of the side surface 40a and the hole 43 is set to X, and it is preferable that the relationship between this radial distance X and the radial width H of the seal 40 satisfies X<0.5H. This is because, while grease near the radially inner edge of the side surface 40a is effectively guided to the center (gap S) by the inclined side surface 40a, grease is also effectively guided to the gap S near the radially outer edge, where grease is not as effectively guided to the gap S as near the radially inner edge. In other words, by providing the hole 43 at the above-described position, grease near the radially outer edge of the side surface 40a of the seal 40 is discharged to the gap S through the hole 43. As described above, according to this embodiment, accumulation and scattering of grease adhering to the side surface 40a of the seal 40 are more efficiently prevented and the grease can be effectively utilized.

[0028] Furthermore, it is preferable that the relationship between the hole diameter of the hole portion 43 and the radial width H of the seal 40 be (hole diameter)<0.5H, because if the hole diameter is too large, it may affect the rigidity of the seal 40.

[0029] Next, a ball screw according to a third embodiment of the present invention will be described in detail. The ball screw 10 of the third embodiment differs only in the shape of the seal 40, and other structures are the same as the ball screw 10 of the first embodiment, so the same parts are given the same reference numerals and detailed explanations are omitted.

[0030] 5(a) and 5(b), the seal 40 of this embodiment has a hole 43 on its side surface 40a, similar to the seal 40 of the second embodiment. The seal 40 of this embodiment also has a lip portion 44 on its inner circumferential surface 40d, which matches the spiral shape of the outer peripheral thread groove 21 of the screw shaft 20. This allows the lip portion 44 to be in sliding contact with the outer peripheral thread groove 21 over the entire circumference, thereby achieving high dustproofing and sealing effects.

[0031] In this example, the seal 40 has a lip portion 44 on the inner surface 40d, so that no gap S is defined between the seal 40 and the screw shaft 20 (there is a small gap), but the grease is discharged from the hole portion 43 to the screw shaft 20.

[0032] Next, a ball screw according to a fourth embodiment of the present invention will be described in detail. The ball screw 10 of the third embodiment differs only in the shape of the seal 40, and other structures are the same as the ball screw 10 of the first embodiment, so the same parts are given the same reference numerals and detailed explanations are omitted.

[0033] As shown in Figures 6(a) and (b), the seal 40 of this embodiment further has an annular slit 45 extending axially from the side surface 40a, and multiple (four in this example) through-hole portions 46 that penetrate radially from the outer peripheral surface 40b to the inner peripheral surface 40d and communicate with the slit 45.

[0034] The through-hole portion 46 communicates with the gap S, and the slit 45 communicates with the gap S via the through-hole portion 46. A sealing member such as an O-ring 47 is attached to the radially outer side of the through-hole portion 46. This prevents foreign matter from entering the through-hole portion 46 from the outer circumferential surface 40b.

[0035] The slit 45 and the through-hole portion 46 are intended to discharge grease adhering to the side surface 40a of the seal 40 into the gap S. That is, the slit 45 and the through-hole portion 46 correspond to the hole portion 43 in the second and third embodiments. As with the hole portion 43 in the second and third embodiments, the slit 45 is preferably formed, for example, near the radially outer edge portion of the side surface 40a. As such, according to this embodiment, it is possible to more efficiently prevent the accumulation and scattering of grease adhering to the side surface 40a of the seal 40, and to effectively utilize this grease.

[0036] Furthermore, by using the slits 45 and the through-holes 46 instead of the holes 43 of the second and third embodiments, hole processing becomes easier compared to the second and third embodiments, and manufacturing costs can be reduced.

[0037] The present invention is not limited to the above-described embodiments, and modifications, improvements, etc. are possible as appropriate. For example, the radially extending portion of the hole 43 in the second and third embodiments may be formed like the through-hole 46 in the fourth embodiment. In this way, the configurations of the respective embodiments can be adopted as appropriate.

[0038] As described above, the present specification discloses the following: (1) a screw shaft having a spiral outer peripheral thread groove formed on its outer peripheral surface; a nut having a spiral internal thread groove formed on its inner peripheral surface; A plurality of balls rolling on a ball rolling section formed by an outer peripheral screw groove of the screw shaft and an inner peripheral screw groove of the nut; A seal provided at least at one axial end of the nut to seal between an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut; A ball screw comprising: The seal is The inner circumferential surface faces the screw shaft, and the axially outer end surface is formed in an inclined shape that inclines axially inward from the radially outer side toward the radially inner side. Ball screw. (2) The ball screw according to (1), The seal is a hole portion that penetrates from the axially outer end surface to the inner peripheral surface; Ball screw. (3) The ball screw according to (2), The hole is provided in the axially outer end surface near a radially outer edge portion. Ball screw. (4) The ball screw according to (1), The seal is an annular slit extending in the axial direction from the axially outer end surface along the entire circumference; a through hole that penetrates from the outer peripheral surface of the seal to the inner peripheral surface and communicates with the slit; Ball screw.

[0039] According to the above configuration (1), it is possible to more efficiently prevent the accumulation and scattering of grease adhering to the end face of the seal, and it is possible to obtain a ball screw that can effectively utilize this grease. According to the above configuration (2), the grease adhering to the end face of the seal can be effectively utilized. According to the above configuration (3), it is possible to effectively utilize grease that is adhered particularly to the vicinity of the radially outer edge portion of the end face of the seal. According to the above configuration (4), the grease adhering to the end face of the seal can be effectively utilized. [Explanation of symbols]

[0040] 10 Ball screw 20 Screw shaft 21 Peripheral thread groove 25 Ball Rolling Section 26 balls 30 nuts 31 Internal thread groove 40 stickers 40a Side 40b Outer surface 40d Inner surface 41 Through hole 43 Hole 45 Slit 46 Through hole section H Radial width S Gap X radial distance α Incline angle

Claims

1. a screw shaft having a spiral outer peripheral thread groove formed on its outer peripheral surface; a nut having a spiral internal thread groove formed on its inner peripheral surface; A plurality of balls rolling on a ball rolling section formed by an outer peripheral screw groove of the screw shaft and an inner peripheral screw groove of the nut; A seal provided at least at one axial end of the nut to seal between an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut; A ball screw comprising: The seal is The inner circumferential surface faces the screw shaft, and the axially outer end surface is formed in an inclined shape that inclines axially inward from the radially outer side toward the radially inner side. Ball screw.

2. 2. The ball screw according to claim 1, The seal is a hole portion that penetrates from the axially outer end surface to the inner peripheral surface; Ball screw.

3. 3. The ball screw according to claim 2, The hole is provided in the axially outer end surface near a radially outer edge portion. Ball screw.

4. 2. The ball screw according to claim 1, The seal is an annular slit extending in the axial direction from the axially outer end surface along the entire circumference; a through hole that penetrates from the outer peripheral surface of the seal to the inner peripheral surface and communicates with the slit; Ball screw.

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