Ball screw device

Abstract

A ball screw device according to the present invention comprises: a screw shaft which has an outer circumferential raceway surface formed on an outer circumferential surface; a nut which has an inner circumferential raceway surface formed on an inner peripheral surface and through which the screw shaft passes; a plurality of balls which are disposed between the outer circumferential raceway surface and the inner circumferential raceway surface; and a tubular circulation component which has a return passage formed therein. The nut is provided with two through holes which pass through the outer circumferential surface and the inner peripheral surface. The circulation component has two leg portions which are inserted into the through holes and a main body unit which is disposed on the outer circumferential side of the nut and connects the two leg portions to each other. An inlet and an outlet of the return passage, which open toward an inner circumferential side of the nut, are formed at the tip parts of the leg portions. At least one sheet is disposed between the outer circumferential surface of the nut and the main body unit.

Description

Ball screw device

[0001] The present disclosure relates to a ball screw device.

[0002] A ball screw device is a device that converts rotational motion into linear motion, or converts linear motion into rotational motion. The ball screw device includes a screw shaft, a nut penetrated by the screw shaft, a plurality of balls, and a circulation component. The plurality of balls move along a raceway between the screw shaft and the nut. The circulation component returns a ball that has moved from one end of the raceway to the other end back to the one end of the raceway.

[0003] As shown in Patent Document 1, a cylindrical circulation component is cited as an example of a circulation component. The internal space of the cylindrical circulation component serves as a return path along which balls move. Further, the cylindrical circulation component includes a main body portion extending along the outer circumferential surface of the nut, and two leg portions extending radially inward from both end portions of the main body portion. An inlet / outlet of the return path is formed at the tip of each leg portion. The leg portions are inserted into through holes penetrating the outer circumferential surface and the inner circumferential surface of the nut. A ball moving along the raceway enters the return path from one of the two leg portions. The ball moving along the return path returns to the raceway from the other leg portion.

[0004] Further, a radial step between the inner circumferential raceway surface of the nut constituting the raceway and the return path causes vibration and noise when balls pass therethrough, so it is desirable that the step is as small as possible. Particularly in the case where the step is such that the leg portion of the circulation component protrudes further inward than the inner circumferential raceway surface, balls pass through while colliding with the tip of the return path, which may cause damage to the circulation component or early failure of the ball screw due to poor ball circulation. However, due to variations in the finish of the circulation component and processing variations in the depth of the nut raceway surface, variations also occur in the step for each combination of the circulation component and the nut, making it difficult to reduce the step.

[0005] In Patent Document 2, a deflector is exemplified as a circulation component. Further, Patent Document 2 proposes cutting with a cutting tool in order to reduce the step at the joint between the return path of the deflector and the inner circumferential raceway surface of the nut.

[0006] Japanese Unexamined Patent Application Publication No. 2003-269564 Japanese Patent No. 4483257

[0007] However, machining with cutting tools is too time-consuming. Therefore, it is desirable to be able to adjust the step difference at the joint between the return path and the inner circumferential raceway surface using a simple method.

[0008] This disclosure has been made in view of the above, and aims to provide a ball screw device that can easily adjust the step difference at the joint between the return path and the inner circumferential raceway surface.

[0009] To achieve the above objective, a ball screw device according to one aspect of the present disclosure comprises a screw shaft having an outer peripheral raceway surface formed on its outer peripheral surface, a nut having an inner peripheral raceway surface formed on its inner peripheral surface and passing through the screw shaft, a plurality of balls disposed between the outer peripheral raceway surface and the inner peripheral raceway surface, and a cylindrical circulating component having a return path formed inside. The nut is provided with two through holes that penetrate the outer peripheral surface and the inner peripheral surface. The circulating component has two legs inserted into the through holes and a main body disposed on the outer peripheral side of the nut and connecting the two legs. An inlet and outlet for the return path, opening toward the inner peripheral side of the nut, is formed at the tip of each leg. At least one sheet is disposed between the outer peripheral surface of the nut and the main body.

[0010] According to this disclosure, increasing the number of sheets reduces the amount of leg inserted into the through hole. Conversely, decreasing the number of sheets increases the amount of leg inserted into the through hole. In other words, by increasing or decreasing the number of sheets, the step difference at the joint between the return path and the inner raceway surface can be reduced. In addition to increasing or decreasing the number of sheets, the step difference at the joint can also be reduced by changing the thickness of the sheets. Furthermore, increasing or decreasing the number of sheets or changing the sheet thickness requires less effort than machining with cutting tools. Therefore, the step difference at the joint can be easily adjusted.

[0011] Furthermore, a preferred embodiment of a ball screw device according to one aspect of this disclosure includes a retaining part that covers the outer circumference of the circulating part, and a bolt that penetrates the retaining part and is screwed into the nut. The retaining part is provided with a flange that extends along the outer surface of the nut and is fastened to the head of the bolt. The seat is positioned between the outer surface of the nut and the flange.

[0012] If the sheet is placed only between the nut and the circulating component, changing the number of sheets will change the distance between the outer surface of the nut and the circulating component, but the distance between the outer surface of the nut and the retaining component will not change. In other words, the clamping allowance of the retaining component will increase or decrease. On the other hand, with the above configuration, if the thickness of the sheet is changed, the distance from the outer surface of the nut will change for both the circulating component and the retaining component. Therefore, the clamping allowance of the retaining component will not change.

[0013] Furthermore, the seat of the ball screw device according to one aspect of this disclosure may have a hole formed through which the shaft portion of the bolt passes.

[0014] Furthermore, in a preferred embodiment of the ball screw device according to one aspect of this disclosure, the seat is made of a resin material. The retaining part is made of a metal material. The hole is larger than the head of the bolt.

[0015] If a sheet made of resin material is interposed between the outer surface of the nut and the flange, the bolt will be more likely to loosen. On the other hand, with the above configuration, the portion of the flange that is fastened to the head of the bolt passes through the hole and makes close contact with the outer surface of the nut. Therefore, the bolt is less likely to loosen.

[0016] Furthermore, in a preferred embodiment of the ball screw device according to one aspect of this disclosure, the seat is made of a metal material. The retaining part is made of a metal material. The hole is smaller than the head of the bolt and larger than the shaft of the bolt.

[0017] The sheet with the above configuration can be used even in high-temperature environments. Furthermore, the sheet is made of the same metal as the retaining parts and nuts that are fastened and made contact with the bolts. Therefore, bolt loosening is less likely to occur. In addition, it can be manufactured using a die-cutting process, making it ideal for mass production.

[0018] Furthermore, in a preferred embodiment of the ball screw device according to one aspect of this disclosure, the edge of the sheet is provided with a concave notch through which a part of the circulating component passes.

[0019] According to the above configuration, the circulating component catches on the inner circumference of the notch. Therefore, when assembling the circulating component and the seat to the nut, misalignment of the seat is prevented.

[0020] Furthermore, in a preferred embodiment of the ball screw device according to one aspect of this disclosure, the outer shape of the outer circumferential surface of the main body is formed in a circular shape in cross-sectional view. A base that restricts the rotation of the main body is disposed between the outer circumferential surface of the nut and the main body. The seat is disposed between the outer circumferential surface of the nut and the base.

[0021] According to the above configuration, misalignment of the tip of the leg is suppressed, and the scooping up and returning of the ball becomes smoother.

[0022] According to the ball screw device of this disclosure, the step difference at the joint between the return path and the inner circumferential raceway surface can be easily adjusted.

[0023] Figure 1 is an exploded perspective view of a part of the ball screw device of Embodiment 1. Figure 2 is a cross-sectional view of the ball screw device of Embodiment 1. Figure 3 is a cross-sectional view of the axial central part of the circulating component of the ball screw device of Embodiment 1. Figure 4 is a plan view of the sheet of Embodiment 1 viewed from the vertical. Figure 5 is a perspective view of the circulating component of Embodiment 1 with the sheet attached, viewed from the first vertical direction. Figure 6 is a plan view of the sheet of Embodiment 2 viewed from the second vertical direction. Figure 7 is a perspective view of the ball screw device of Embodiment 3. Figure 8 is a cross-sectional view of the ball screw device of Embodiment 3. Figure 9 is a plan view of the base of Embodiment 3 viewed from the second vertical direction. Figure 10 is a perspective view of the circulating component of Embodiment 4 with the sheet attached, viewed from the first vertical direction.

[0024] The embodiments for carrying out the invention will be described in detail with reference to the drawings. This disclosure is not limited by the contents described below. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art, and those that are substantially the same. In addition, the components described below can be combined as appropriate.

[0025] (Embodiment 1) Figure 1 is an exploded perspective view of a part of the ball screw device of Embodiment 1. As shown in Figure 1, the ball screw device 100 of Embodiment 1 includes a screw shaft (not shown), a cylindrical nut 1, a plurality of balls 2 (see Figure 2), a circulation component 3, a seat 4, a retaining component 5, and a bolt 6.

[0026] Although not specifically illustrated, the screw shaft is a cylindrical component with an outer raceway surface formed on its outer surface. Hereafter, the direction parallel to the screw shaft will be referred to as the axial direction.

[0027] The cross-sectional shape of the outer surface 10 of the nut 1 is D-shaped. That is, the outer surface 10 of the nut 1 has an arcuate surface 11 and a flat surface 12. A ridge line 13 is provided at the boundary between the arcuate surface 11 and the flat surface 12. Two female screw holes 12a (not shown in Figure 1; see Figure 7) are formed in the flat surface 12.

[0028] Hereinafter, the direction parallel to plane 12 will be referred to as the plane direction. The direction in which the two edges 13 are positioned within the plane direction will be referred to as the intersection direction Y. The direction perpendicular to plane 12 will be referred to as the vertical direction. Within the vertical direction, the direction in which the screw axis is positioned as viewed from plane 12 will be referred to as the first vertical direction Z1, and the opposite direction will be referred to as the second vertical direction Z2.

[0029] Figure 2 is a cross-sectional view of the ball screw device of Embodiment 1. As shown in Figure 2, an inner circumferential raceway surface 16 is formed on the inner circumferential surface of the nut 1, facing the outer circumferential raceway surface of the screw shaft. A helical raceway is formed between the outer circumferential raceway surface and the inner circumferential raceway surface 16. Multiple balls 2 are arranged on this raceway.

[0030] The nut 1 has two through holes 17 that penetrate the outer circumferential surface 10 and the inner circumferential surface 15. The through holes 17 penetrate the nut 1 vertically and cut out a portion of the inner circumferential raceway surface 16.

[0031] As shown in Figure 1, the circulation component 3 is a cylindrical component. The internal space of the circulation component 3 is a return path 7 (see Figure 2) through which the ball 2 can move. The circulation component 3 comprises a main body portion 30 extending along the outer circumferential surface 10 (plane 12) of the nut 1, and two leg portions 31 extending in the first vertical direction Z1 from both ends of the main body portion 30. The two leg portions 31 are inserted into the through hole 17.

[0032] As shown in Figure 2, an entrance / exit 32 and a tongue 33 are formed at the tip of the leg portion 31. The entrance / exit 32 opens on the inner circumference side of the nut 1. The tongue 33 scoops up the ball 2 radially outward. With this configuration, the ball 2 moving from the track towards the return path 7 is scooped up by the tongue 33 at the entrance / exit 32 and enters the return path 7. In addition, the portion of the return path 7 within the leg portion 31 near the entrance / exit 32 extends tangentially to the track. Therefore, the ball 2 moves smoothly between the track and the return path 7. Furthermore, the edge 32a of the entrance / exit 32 abuts against the inner circumference 18 of the through hole 17.

[0033] Figure 3 is a cross-sectional view of the circulating component of the ball screw device of Embodiment 1, showing the axial central portion. The dashed line O30 in Figure 3 is the center line of the portion of the return path 7 formed on the main body 30. As shown in Figure 3, the bottom surface 37 of the main body 30 of the circulating component 3 is flat. If the bottom surface 37 were arc-shaped, the circulating component 3 could rotate around the main body 30, but according to this embodiment, the rotation of the circulating component 3 is restricted.

[0034] As shown in Figure 3, the sheet 4 is a thin plate-like object whose thickness is extremely small compared to its length and width. The sheet 4 is positioned between the outer circumferential surface 10 (flat surface 12) of the nut 1 and the main body 30 of the circulating component 3. The sheet 4 is a plate-like component formed from a resin material. In this disclosure, the thickness of the sheet 4 is not particularly limited.

[0035] Figure 4 is a plan view of the sheet of Embodiment 1, viewed from the vertical. The sheet 4, viewed from the vertical, has a central portion 40 that abuts the bottom surface 37 of the main body portion 30, and an extended portion 41 that extends from the central portion 40 in the intersecting direction Y. The central portion 40 extends along the center line O30. Notches 42, which are cut out in a concave (arc-shaped) manner, are provided at both ends of the central portion 40.

[0036] Figure 5 is a perspective view of the circulating component of Embodiment 1 with the sheet attached, viewed from a first vertical direction. As shown in Figure 5, the main body 30 is provided with a bulging portion 35 that bulges in the first vertical direction Z1 and connects to the leg portion 31. The bulging portion 35 is positioned inside the notch 42. The inner circumferential surface of the notch 42 is in contact with the side surface of the bulging portion 35. As a result, when the sheet 4 is placed on the plane 12 of the nut 1 with the bottom surface 37 of the circulating component 3 in contact with it, the bulging portion 35 catches on the inner circumferential surface of the notch 42. Therefore, displacement of the sheet 4 in the planar direction is restricted.

[0037] As shown in Figure 3, the expansion portion 41 is in contact with the plane 12. As shown in Figure 4, the expansion portion 41 has a hole 43 that opens the female screw hole 12a.

[0038] As shown in Figure 3, the retaining part 5 has a container portion 50 that opens in the first vertical direction Z1, and a flange 51 that extends in the intersecting direction Y from the edge of the opening of the container portion 50.

[0039] The container portion 50 houses the main body portion 30 inside and covers the outer circumference of the main body portion 30. Furthermore, the inner circumferential surface 52 of the container portion 50 is in contact with the outer circumferential surface of the main body portion 30. Therefore, the movement of the circulating component 3 in the second vertical direction Z2 is restricted, and it does not fall off the nut 1.

[0040] Furthermore, in this embodiment, the container portion 50 has a pressing surface. As a result, the main body portion 30 receives a load in the first vertical direction Z1 from the container portion 50 and is pressed against the flat surface 12 (sheet 4). This suppresses rattling of the circulating component 3, stabilizes the position of the tip of the leg portion 31, and ensures smooth transfer of the ball 2.

[0041] The flange 51 is superimposed on the expanded portion 41 of the seat 4. As shown in Figure 1, the flange 51 is provided with a hole 53. The shaft portion 60 of the bolt 6 is inserted into the hole 43 of the seat 4 and the hole 53 of the retaining component 5 and screwed into the female threaded hole 12a. The head 61 of the bolt 6 tightens the flange 51 in the second vertical direction Z2, and the retaining component 5 is fixed to the nut 1.

[0042] Next, the effects of Embodiment 1 will be explained. As shown in Figure 2, if the circulating component 3 is positioned vertically off from its predetermined position, a step will occur at the joint 19 between the return path 7 and the inner circumferential track surface 16. In such cases, the number of sheets 4 can be increased or decreased, or the thickness of the sheets 4 can be changed. This causes the main body portion 30 superimposed on the sheets 4 to move vertically, and the insertion amount of the leg portion 31 inserted into the through hole 17 increases or decreases. As a result, the amount of step that occurs at the joint 19 can be reduced or eliminated. Furthermore, this method requires less effort than machining with a cutting tool. Therefore, the step at the joint 19 can be easily adjusted.

[0043] The thickness of the sheet 4 is appropriately selected so that the return path 7 does not extend beyond the inner circumferential raceway surface 16 into the inner diameter of the nut at the joint 19, and so that the return path 7 is positioned within a predetermined range on the outer diameter side of the nut relative to the inner circumferential raceway surface 16. In this embodiment, the return path 7 is formed to be parallel to the tangential direction of the inner circumferential raceway surface 16 at the joint 19, and the ball 2 can be scooped up by the tongue 33 in the tangential direction of the inner circumferential raceway surface 16. In other words, since the direction of the return path 7 at the joint 19 intersects with the position adjustment direction of the circulating component 3 (Z1 direction in Figure 2), the step at the joint 19 can be easily adjusted. Furthermore, since the angle of the joint is obtuse when viewed from the axial direction, the impact when the ball 2 passes through can be mitigated.

[0044] Furthermore, in this embodiment, the retaining component 5 is also placed on top of the sheet 4. In other words, the vertical position of the retaining component 5 changes in response to changes in the number and thickness of the sheets 4. Therefore, the retaining allowance of the retaining component 5 does not change. Thus, there is no possibility that the circulating component 3 will become loose due to a lack of retaining allowance, or that the circulating component 3 will be crushed due to an increased retaining allowance.

[0045] The above is the description of Embodiment 1. Next, a ball screw device according to another embodiment will be described. In addition, the following description will focus only on the differences from Embodiment 1.

[0046] (Embodiment 2) FIG. 6 is a plan view of the sheet of Embodiment 2 viewed from the second vertical direction. As shown in FIG. 6, the sheet 4A of Embodiment 2 differs from the sheet 4 of Embodiment 1 in that the hole 43A is larger than the head 61 of the bolt 6. According to Embodiment 2, the portion of the flange 51 of the pressing component 5 that is tightened against the head 61 of the bolt 6 passes through the hole 43A and is in close contact with the flat surface 12 (outer circumferential surface 10) of the nut 1. In other words, the sheet 4 no longer intervenes between the flange 51 and the nut 1. It should be noted that if the sheet 4 is interposed between the flange 51 and the nut 1, the sheet 4 may deform and cause the bolt 6 to loosen. Therefore, in this embodiment, loosening of the bolt 6 is less likely to occur.

[0047] (Embodiment 3) FIG. 7 is a perspective view of the ball screw device according to Embodiment 3. FIG. 8 is a cross-sectional view of the ball screw device according to Embodiment 3. FIG. 9 is a plan view of the pedestal of Embodiment 3 viewed from the second vertical direction. In Embodiment 3, the pressing component 5 is not shown to make the pedestal 70 easily visible.

[0048] As shown in FIG. 7, the ball screw device 100B of Embodiment 3 differs from Embodiment 1 in that the outer circumferential surface of the circulation component 3B is circular. The ball screw device 100B of Embodiment 3 also differs from Embodiment 1 in that a pedestal 70 is disposed between the main body portion 30B and the outer circumferential surface 10 (flat surface 12) of the nut 1. The sheet 4A used in Embodiment 3 is the one described in Embodiment 2, and is disposed between the outer circumferential surface 10 (flat surface 12) of the nut 1 and the pedestal 70.

[0049] As shown in Figure 8, the outer surface of the circulating part 3B is circular. Therefore, the circulating part 3B is shaped to easily rotate around the main body 30B. When the circulating part 3B rotates around the main body 30B, the leg portion 31B is displaced in the direction indicated by arrow L1 or arrow L2. In other words, the tip of the leg portion 31B is not positioned in the predetermined location, and the transfer of the ball 2 between the circulating part 3B and the track is not smooth.

[0050] As shown in Figure 8, a concave surface 71 is formed on the second vertical Z2 surface of the base 70. The cross-sectional shape of the concave surface 71 is circular. The main body 30B is placed on the concave surface 71.

[0051] As shown in Figure 9, the concave surface 71 extends linearly along the main body portion 30B. One end of the concave surface 71 in the longitudinal direction is bent in one direction along the intersecting direction Y, and the other end is bent in the other direction along the intersecting direction Y. Two support surfaces 72, which are cut out in an arc shape when viewed from the vertical direction, are provided at one end and the other end of the concave surface 71. The leg portion 31B of the circulating component 3B extends in the first vertical direction Z1 along the support surfaces 72.

[0052] According to this, as shown in Figure 8, the support surface 72 abuts against the side surface of the leg portion 31B. In other words, of the two support surfaces 72, the support surface 72 shown in Figure 8 supports the leg portion 31B from the direction indicated by arrow L1. Therefore, the circulating component 3B does not rotate in the direction indicated by arrow L1. Also, of the two support surfaces 72, the support surface 72 not shown in Figure 8 supports the other leg portion 31B from the direction indicated by arrow L2. Therefore, the circulating component 3B does not rotate in the direction indicated by arrow L2. From the above, the rotation of the circulating component 3B is restricted. Therefore, the transfer of the ball 2 between the circulating component 3B and the track is performed smoothly.

[0053] (Embodiment 4) Figure 10 is a perspective view from a first vertical direction of the circulating component of Embodiment 4 with the sheet attached. As shown in Figure 10, the sheet 4C of Embodiment 4 differs from the sheet 4 of Embodiment 1, which is made of resin, in that it is made of metal. The sheet 4C of Embodiment 4 can be used even in high-temperature environments. The sheet 4C is also made of the same metal as the retaining part 5 and nut 1 that are tightened and come into contact with the bolt 6. Therefore, the bolt 6 is less likely to loosen. Also, because the sheet 4C is made of metal, it can be manufactured using a die-cutting mold, making it suitable for mass production. Furthermore, the hole 43C in the sheet 4C is smaller than the head 61 of the bolt 6 and larger than the shaft portion 60 of the bolt 6. Therefore, the shaft portion 60 can be inserted into the hole 43C.

[0054] Although each embodiment has been described above, this disclosure is not limited to the examples shown in the embodiments. For example, in the embodiments, a retaining part 5 is used to fix the circulating part 3, but other parts may be used in this disclosure. Also, when a retaining part 5 is used, the sheet 4 does not have to have an expanded portion 41. Also, although a notch 42 is formed in the sheet 4, in this disclosure, the sheet may not have a notch 42.

[0055] 1 Nut 2 Ball 3, 3B Circulation part 4, 4A, 4C Sheet 5 Retaining part 6 Bolt 7 Return path 10 Outer surface 12 Flat surface 16 Inner raceway surface 17 Through hole 19 Joint 30 Main body 31 Leg part 32 Inlet / outlet 40 Central part 41 Expansion part 42 Notch 43, 43A, 43C Hole 50 Container part 51 Flange 53 Hole 60 Shaft part 61 Head 70 Base 71 Concave surface 72 Support surface 100, 100B Ball screw device

Claims

1. A ball screw device comprising: a screw shaft having an outer circumferential raceway surface formed on its outer circumferential surface; a nut having an inner circumferential raceway surface formed on its inner circumferential surface and passing through the screw shaft; a plurality of balls disposed between the outer circumferential raceway surface and the inner circumferential raceway surface; and a cylindrical circulating component having a return path formed inside, wherein the nut is provided with two through holes that penetrate the outer circumferential surface and the inner circumferential surface; the circulating component has two legs inserted into the through holes; and a main body disposed on the outer circumferential side of the nut and connecting the two legs, wherein an inlet and outlet for the return path opening toward the inner circumferential side of the nut is formed at the tip of the legs; and at least one sheet is disposed between the outer circumferential surface of the nut and the main body.

2. The ball screw device according to claim 1, comprising: a retaining part that covers the outer circumference of the circulating part; and a bolt that penetrates the retaining part and is screwed into the nut, wherein the retaining part is provided with a flange that extends along the outer surface of the nut and is fastened to the head of the bolt, and the seat is positioned between the outer surface of the nut and the flange.

3. The ball screw device according to claim 2, wherein the sheet has a hole through which the shaft portion of the bolt passes.

4. The ball screw device according to claim 3, wherein the sheet is made of a resin material, the retaining part is made of a metal material, and the hole is larger than the head of the bolt.

5. The ball screw device according to claim 3, wherein the sheet is made of a metal material, the retaining part is made of a metal material, and the hole is smaller than the head of the bolt and larger than the shaft of the bolt.

6. The ball screw device according to any one of claims 1 to 5, wherein the edge of the sheet is provided with a concave notch through which the leg passes.

7. The ball screw device according to any one of claims 1 to 6, wherein the outer shape of the outer surface of the main body is formed in a circular shape in cross-section, a base that restricts the rotation of the main body is disposed between the outer surface of the nut and the main body, and the seat is disposed between the outer surface of the nut and the base.

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