Ball screw

Abstract

To provide a compact ball screw capable of rotating smoothly.SOLUTION: In a circulation passage (7) of a top member, an opening (79) opened inward in a radial direction is formed over the entire length. A locus (74) of the center of a ball in the circulation passage when viewed from an axial direction has a first part (76) which represents a tangent line of a ball center diameter (75) of a ball rolling passage at an introduction part (71), and a second part (77) which represents a single arc tangent to the tangent line. The ball (42) is located on the outer side of an outer diameter of a screw shaft at least at a vertex of the arc (77). A locus (80) of the center of the ball in the circulation passage when viewed from the radial direction has a third part (81) inclined at the same angle as a lead angle of the rolling passage 6 in the introduction part (71).SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] Conventionally, in a ball screw in which a ball return passage that returns the ball rolling groove by one turn is provided in a deflector to form an infinite track for the balls, it has been proposed to form the ball return passage in a tunnel shape to isolate the balls from the outer peripheral surface of the screw shaft, and to form U-shaped ball scooping sections at both ends of the ball return passage (see Patent Document 1).

[0003] With the deflector configured in this way, the U-shaped ball scooping parts gradually lift the ball from below on both sides, allowing the ball to be smoothly removed from the ball rolling groove. Also, since the ball return passage is formed in a tunnel shape, the ball can be held without contacting the screw shaft, and the generation of contact noise with the screw shaft can also be prevented. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2001-165274 A Summary of the Invention [Problem to be solved by the invention]

[0005] As with the configuration of Patent Document 1, various efforts have been made in the past to improve the rotational performance and reduce noise in ball screws. However, in recent years, there has been a strong demand for a ball screw that is compact and capable of rotating smoothly.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide a ball screw that is compact and capable of rotating smoothly. [Means for solving the problem]

[0007] One aspect of the present invention comprises a screw shaft having a screw groove on its outer peripheral surface, a nut fitted onto the screw shaft and having a screw groove formed on its inner peripheral surface that forms a ball rolling path together with the screw groove, a ball disposed in the ball rolling path, and a top member having a circulation path formed therein for returning the ball from an end point of the ball rolling path to a start point thereof, the circulation path having an opening that opens radially inward over its entire length, the circulation path including an introduction portion that guides the ball from the end point of the ball rolling path to the circulation path, an outlet portion that guides the ball from the circulation path to the start point of the ball rolling path, and an intermediate portion between the introduction portion and the outlet portion; the introduction portion is provided with a tongue portion that enters the screw groove of the screw shaft and scoops up the ball, the trajectory of the center of the ball in the circulation path when viewed in the axial direction has a first portion that is a tangent to the ball center diameter of the ball rolling path at the introduction portion and a second portion that is a single arc tangent to the tangent line, and the ball is positioned outside the outer diameter of the screw shaft at least at the apex of the arc, and the trajectory of the center of the ball in the circulation path when viewed in the radial direction has a third portion that is inclined at the same angle as the lead angle of the ball rolling path at the introduction portion. Effect of the Invention

[0008] According to the present invention, it is possible to provide a ball screw that is capable of smooth rotation and has a small outer diameter of the nut. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing a ball screw according to an embodiment of the present invention. [Diagram 2] FIG. 4 is a schematic diagram of a ball screw with the nut and the bearing member shown in a transparent state. [Diagram 3] FIG. 4A is a schematic diagram showing a top member according to the present embodiment, and FIG. 4B is a schematic diagram showing a nut according to the present embodiment. [Figure 4] Exploded view of the nut and bearing parts. [Diagram 5]FIG. [Figure 6] FIG. 13 is a diagram showing the movement trajectory of the balls in the circulation path when viewed from the axial direction. [Figure 7] FIG. 13 is a diagram showing the movement trajectory of the balls in the circulation path as viewed from the radial direction. [Figure 8] FIG. 11 is a schematic diagram showing another example of the top member. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Ball screw schematic configuration> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view showing a ball screw 1 according to this embodiment, which includes a screw shaft 2, a nut 3, balls 4 (see Fig. 2), and a top member 5. A helical screw groove 21 is formed on the outer circumferential surface of the screw shaft 2 with a predetermined lead angle, and a nut 3 is fitted onto the outside of the screw shaft 2.

[0011] The nut 3 has a generally cylindrical shape into which the screw shaft 2 is inserted, and has an inner diameter larger than the outer diameter of the screw shaft 2. As shown in Fig. 2, in which the nut 3 and the top member 5 are shown in a transparent state, a helical thread groove 31 is formed on the inner peripheral surface of the nut 3 with the same lead angle as that of the screw shaft 2. This thread groove 31 faces the thread groove 21 of the screw shaft 2 and constitutes the rolling path 6 for the balls 4 together with the thread groove 21.

[0012] The top member 5 is attached to the mounting holes 32 formed in the nut 3, and has a circulation path 7 that returns the balls from the end point of the rolling path 6 to the start point. The nut 3 is formed with a plurality of mounting holes 32 (three in this embodiment) at different positions in the circumferential and axial directions, and the top member 5 is attached to each mounting hole 32. In this embodiment, the nut 3 is provided with a plurality of mounting holes 32 at different phases, but these plurality of mounting holes 32 may be provided such that at least any combination of the mounting holes 32 are aligned at different axial positions in the same circumferential phase (in a horizontal row).

[0013] The circulation path 7 of the top member 5, together with the above-mentioned rolling path 6, forms an infinite circulation path in which the balls 4 circulate infinitely. For this reason, in the ball screw 1, when the screw shaft 2 rotates, the balls 4 in the above-mentioned rolling path 6 and circulation path 7 roll, and the nut 3, which is fixed to a mechanical part or the like so as not to rotate, moves linearly in the axial direction. The nut 3 is provided with an attachment part 33 for attaching the above-mentioned mechanical part or the like, and by rotating the screw shaft 2 relative to the nut 3, the mechanical part attached to the nut 3 can be positioned, etc.

[0014] <Detailed configuration of the top parts> Next, a detailed configuration of the top member 5 will be described. As shown in Fig. 3(a), the top member 5 is configured to include a main body portion 51 and a flange portion 52, and is attached to the attachment hole 32 of the nut 3. As shown in Fig. 3(b), the attachment hole 32 includes a bottom surface 321, a through hole 322 formed in the bottom surface 321, and an inner wall 323 erected from the bottom surface 321. The top member 5 is attached to the attachment hole 32 by inserting the main body portion 51 of the top member 5 into the through hole 322 and seating the flange portion 52 of the top member 5 on the bottom surface 321.

[0015] More specifically, the above-mentioned through hole 322 is an elongated hole that penetrates all the way to the hollow portion of the nut 3, and the main body 51 of the top member 5 also has an elliptical cross section that corresponds to the above-mentioned through hole 322. Therefore, the main body 51 of the top member 5 can be inserted into the above-mentioned through hole 322 with a predetermined tolerance, and the position of the top member 5 in the rotational direction is thereby determined.

[0016] As described above, the flange portion 52 of the top member 5 is configured to seat on the bottom surface 321 of the mounting hole 32, thereby positioning the top member 5 in the radial direction (height direction). As shown in Figs. 2 and 4, a stop ring 85 is disposed on the radial outer side of the top member 5 in the large-diameter circular recess 324 formed by the bottom surface 321 and the inner wall 323 to prevent the top member 5 from coming off. The stop ring 85 is a restricting member that restricts only the radial movement of the top member 5 without restricting the movement of the top member 5 in the rotational direction, thereby preventing the top member 5 from coming off the mounting hole 32, and the stop ring 85 prevents the top member 5 from coming off in the radial direction. In other words, the stop ring 85 as a fixing device does not fix the top member 5 in the rotational direction, but fixes it only in the radial direction, so that the top member 5 is in a floating state in the rotational direction.

[0017] Therefore, when the ball 4 is introduced into / exited from the circulation path 7 and a reaction force acts in the rotational direction, the top member 5 moves in the rotational direction within the gap between the main body portion 51 and the through hole 322, so that the circulation path 7 naturally aligns with the inlet / outlet of the rolling path 6.

[0018] In the above embodiment, the through hole 322 is an elongated hole, but is not limited to this. As long as the fit between the main body 51 and the through hole 322 can regulate the rotational position (rotation range) of the top member 5, the through hole 322 may have any shape, such as an elliptical shape or a rectangular shape.

[0019] Further, as shown in FIG. 4, the top member 5 is divided into a plurality of divided bodies 511, 512 (two in this embodiment). The first and second divided bodies 511, 512 are formed by dividing the top member 5 along a moving path 80 of the center of the ball 4, which will be described later, and are connected by metal shim plates 513, 514 so as not to be separated. Specifically, a circular protrusion 53 for connecting the divided bodies 511, 512 is provided on the outer surface of the flange portion 52 of the top member 5, and the circular protrusion 53 fits into a hole portion of the ring-shaped shim plate 513. In addition, the main body portion 51 of the top member 5 fits into a hole portion (long hole portion) of the ring-shaped shim plate 514. This improves the joining force between the first and second divided bodies 511, 512 of the top member 5, and can improve its strength. In addition, a metal spacer is interposed between the nut 3 and the retaining ring 85, and this spacer can adjust the radial position of the circulation path 7.

[0020] Next, the configuration of the circulation path 7 of the top member 5 will be described in detail. As shown in Fig. 5, the circulation path 7 includes an introduction section 71 that introduces the ball 4 from the end point of the rolling path 6 into the circulation path 7, an outlet section 72 that leads the ball 4 from the circulation path 7 to the start point of the rolling path 6, and an intermediate section 73 that is located between the introduction section 71 and the outlet section 72 and moves the ball 4 to the adjacent screw groove 21 (rolling path 6) by climbing over one thread of the screw thread 22 of the screw shaft 2. In addition, the introduction section 71 and the outlet section 72 are provided with tongue sections 800, 801 that enter the screw groove 21 of the screw shaft 2 and guide the ball 4, and the ball 4 is scooped up from the rolling path 6 into the circulation path 7 by the tongue sections 800, 801 and sent out from the circulation path 7 to the rolling path 6. In this embodiment, the first divided body 511 is provided with a tongue portion 800 for scooping up the ball 4, and the second divided body 512 is provided with a tongue portion 801 for sending out the ball 4 (see FIG. 7).

[0021] 6, the circulation path 7 is configured such that a movement locus 74 of the center of the ball 4 in the circulation path 7 is in the shape of a circular arc when viewed from the axial direction of the screw shaft 2. Specifically, the movement locus 74 is configured to include a tangent 76 to the ball center diameter 75 at an intersection T0 between the scoop angle α and the ball center diameter 75 of the nut 3 (rolling path 6), a circular arc 77 tangent to the tangent 76, and a tangent 78 described in detail below. At least a part of the tangent portion (first portion) 76 of the movement locus 74 between the point T0 and T1, which is the starting point of the arc 77, is located in the introduction portion 71 and scoops up the ball 41 and removes it from the rolling path 6, so that the ball 41 can be scooped up by the ball center diameter 75 of the nut 3 (rolling path 6) and smoothly removed from the rolling path 6.

[0022] The scooping angle α is the angle between an imaginary line L1 connecting the center C1 (above point T0) of the ball 41 at the starting point where guiding of the ball by the top member 5 begins and the central axis X of the nut 3, and an imaginary line L2 connecting the central axis X of the nut 3 and the center C2 of the ball 42 located at the apex position of the movement trajectory 74 (apex position of the arc 77). The ball center diameter, which can also be called the pitch circle diameter, is the diameter of a cylinder that includes the center of the ball 4 where the screw shaft 2 and the nut 3 are in contact at a theoretical contact point.

[0023] Furthermore, in the movement trajectory 74, at least a part of an arc portion (second portion) 77 between points T1 and T2 is located in the intermediate portion 73, where the ball 42 climbs over the thread 22, and at least the ball 42 at the apex position of the arc portion 77 is located radially outward from the outer diameter (thread 22) of the screw shaft 2. More specifically, in this embodiment, the arc 77 is tangent to the tangent 76 at point T1 of the introduction portion 71 of the circulation path 7 where the tongue portion 800 is provided. Therefore, the ball 41 that has moved in the direction of the tangent 76 can be smoothly placed on the trajectory 77, which is a single arc, and climb over the thread 22.

[0024] In addition, the ball 42 is designed to ride over the thread 22 at the apex of the arc 77, and the circulation path 7 is open toward the inside in the radial direction over its entire length as shown in FIG. 7. This, combined with the fact that the thickness of the top member 5 can be suppressed when forming the circulation path 7, makes it possible to achieve a compact configuration in the radial direction. The opening 79 of the circulation path 7 has an uneven opening width. More specifically, the opening width of the opening 79 is large at the introduction portion 71 and the discharge portion 72, narrows toward the middle portion 73, and is narrowest at the apex portion. In addition, when viewed in units of the first and second divided bodies 511 and 512, the circulation groove 700 of each of the first and second divided bodies 511 and 512 constituting the circulation path 7 is configured so that the cross section in the direction perpendicular to the axial direction is an arc that is less than a semicircle. More specifically, the circulation groove 700 of the first and second divided bodies 511, 512, including the tongue portions 800, 801, is configured with an arc of less than a semicircle in any cross section perpendicular to the axial direction, i.e., in any cross section at any position along the entire length of the inner circumferential surface forming the circulation groove 700 of each divided body 511, 512. For this reason, when the first and second divided bodies 511, 512 are produced using a metal mold, it is possible to remove the metal mold from the circulation groove 700.

[0025] 6, at least a part of the tangent portion (fifth portion) 78 between points T2 and T3 of the moving path 74 is located in the lead-out portion 72, and is a tangent to the ball center diameter 75 at the intersection (point T3) between the center C3 of the ball at the end point where the ball 4 is guided by the circulation path 7 and the ball center diameter 75 of the nut 3 (rolling path 6), and the arc 77 is tangent to the tangent 78 at point T2. Therefore, the ball 4 that has rolled in the circulation path 7 faces the tangent direction of the ball center diameter 75 of the rolling path 6 at point T3, and the ball 4 can be smoothly sent out from the circulation path 7 to the rolling path 6. In this embodiment, the angle that the virtual line L3 connecting point C3 and the central axis X of the nut 3 makes with the virtual line L2 is the same as the above-mentioned rake angle α.

[0026] 7, when viewed from the inside in the radial direction, the movement trajectory 80 of the center of the ball 4 is an S-shaped curve. Note that although the movement trajectory 80 is the same as the movement trajectory 74 described above, for the sake of convenience, the movement trajectory viewed from the axial direction is indicated by reference numeral 74, and the movement trajectory viewed from the radial direction is indicated by reference numeral 80.

[0027] Specifically, the movement path 80 includes connection parts 81, 82 inclined at the same lead angle as the screw groove 21 of the screw shaft 2 and the screw groove 31 of the nut 3 described above, and an intermediate part 83 connecting these connection parts 81, 82. The connection part (third part) 81 of the movement path 80 corresponds to the tangential part 76 described above, at least a part of which is located in the introduction part 71 and inclined at the same angle as the lead angle of the rolling path 6. The straight part of the connection part 81 inclined at this lead angle has the straight part having a length equal to or greater than the radius of the ball 4, and the circulation path 7 is configured so that the ball 41 rolling from the rolling path 6 smoothly enters the circulation path 7 at the same angle as the rolling path 6. The connection part 81 is connected to an intermediate part (fourth part) 83 described in detail later by a connection arc 811, and the connection arc 811 is a large arc having a radius equal to or greater than the radius of the ball. For this reason, the ball 4 smoothly rolls to the intermediate part 83. In addition, the straight line portion of the connection portion 81 has a length equal to or greater than the radius of the ball 4, and is therefore equal to or greater than the radius of the ball 4, with the connection point between the straight line portion and the connection arc 811 as its center.

[0028] Similarly, the connection portion (fifth portion) 82 of the movement path 80 corresponds to the tangential portion 78, at least a part of which is located in the lead-out portion 72 and is inclined at the same angle as the lead angle of the rolling path 6. The straight portion of the connection portion 82 inclined at this lead angle has a length equal to or greater than the radius of the ball 4, and is configured so that the ball 41 that rolls in the circulation path 7 is smoothly sent to the rolling path 6 at the same angle as the lead angle of the rolling path 6. The connection portion 82 is connected to the intermediate portion 83 by a connecting arc 821, and the connecting arc 821 is a large arc having a radius equal to or greater than the radius of the ball 4. Therefore, the ball 4 smoothly rolls from the intermediate portion 83 to the connection portion 82. The straight portion of the connection portion 82 has a length equal to or greater than the radius of the ball 4, and is therefore a straight portion having a radius equal to or greater than the radius of the ball 4, with the connecting point of the straight portion and the connecting arc 821 as the center.

[0029] Furthermore, the intermediate portion (fourth portion) 83 of the movement trajectory 80 corresponds to the above-mentioned arc portion 77, and at least a part of it is located in the intermediate portion 73, and is connected to the connection portion 81 at one end side (upstream side in the rolling direction of the ball 4) and is connected to the connection portion 82 at the other end side (downstream side in the rolling direction of the ball 4). In addition, this intermediate portion 83 is inclined at a predetermined S-shaped angle β so as not to overlap with the tongue portions 800, 801 when viewed from the radial direction. This S-shaped angle β is the angle formed by the plane P perpendicular to the central axis X of the nut 3 and the intermediate portion 83 of the movement trajectory 80, and is configured to be 30° or less. Therefore, the circulation path 7 is configured to return the ball 4 to the rolling path 6 via the shortest route, and the ball screw 1 can be rotated smoothly.

[0030] In the above-described embodiment, the main body 51 is formed in an oval shape, but the shape of the main body 51 is not limited to this, and may be formed so that the cross section of the main body 51 when viewed from the radial direction is circular, as shown in Fig. 8. In this case, since the through hole 322 of the nut 3 is also circular, an oval protrusion 52a is formed on the back side (radial inner side) of the flange 52 in order to position the top member 5 in the rotational direction. This protrusion 52a fits into an oval recess formed on the bottom surface 321 of the mounting hole 32 of the nut 3, and positions the top member 5 in the rotational direction.

[0031] In this way, by separating the function of the rotational direction positioning means for positioning the top member 5 in the rotational direction from the main body 51 and having the function performed by the flange portion 52, the degree of freedom in designing the shape of the main body 51 can be improved. For this reason, for example, the main body 51 can be formed in a circular shape as described above, and the circulation path 7 of the top member 5 can be formed as short as possible. This allows the length of the rolling path 6 of the nut 3 to be relatively long, and the number of balls 4 in the rolling path 6 to be increased, thereby increasing the rated load of the ball screw 1. In particular, the rated load can be increased in a ball screw 1 with a small diameter.

[0032] The shape of the main body 51 does not necessarily have to be circular, and may be any shape whose maximum length in a radial view is shorter than the maximum length of the protruding portion 52a (rotational direction positioning means). The rotational direction positioning means of the flange portion 52 does not necessarily have to be formed as the protruding portion 52a, and may have any configuration as long as the positioning of the top member 5 in the rotational direction is achieved by the engagement between the flange portion 52 and the mounting hole 32 of the nut 3. For example, the rotational direction positioning means may be formed by making the top member 5 a recess and the nut side a protrusion, or the positioning of the top member 5 in the rotational direction may be achieved by the engagement between the outer circumferential shape of the flange portion 52 and the inner wall 323 of the mounting hole 32.

[0033] <Summary> (Configuration 1) A screw shaft (2) having a screw groove (21) on its outer circumferential surface; a nut (3) fitted onto the screw shaft (2) and having a screw groove (31) formed on its inner circumferential surface, the screw groove (21) forming a ball rolling path (6); A ball (4) disposed in the ball rolling path (6); a ball member (5) having a circulation path (7) for returning the ball (4) from the end point of the ball rolling path (6) to the start point thereof; The circulation path (7) has an opening (79) that opens radially inward along its entire length, The circulation path (7) has an introduction portion (71) that guides the ball (4) from the end point of the ball rolling path (6) into the circulation path (7), an outlet portion (72) that guides the ball (4) from the circulation path (7) to the start point of the ball rolling path (6), and an intermediate portion (73) between the introduction portion (71) and the outlet portion (72), The introduction portion (71) is provided with a tongue portion (800) that enters the screw groove (21) of the screw shaft (2) and scoops up the ball (4), a locus (74) of the center of the ball in the circulation path when viewed from the axial direction has a first portion (76) that is a tangent to a ball center diameter (75) of the ball rolling path (6) in the introduction portion (71) and a second portion (77) that is a single arc tangent to the tangent line, and at least at a vertex of the arc (77), the ball (42) is located outside the outer diameter of the screw shaft (2); a locus (80) of the center of the ball in the circulation path when viewed from the radial direction has a third portion (81) inclined at the same angle as the lead angle of the ball rolling path (6) in the introduction portion (71); A ball screw (1) characterized by:

[0034] In this way, the circulation path 7 of the top member 5 is configured such that the locus of the center of the ball is a tangent to the ball center diameter 75 of the ball rolling path 6 (nut 3) in the introduction portion 71 when viewed from the axial direction, and is the lead angle of the ball rolling path 6 when viewed from the radial direction. As a result, the ball 4 that has rolled in the ball rolling path 6 is guided in the tangent direction of the ball center diameter 75 in the radial direction, and can smoothly leave the ball rolling path 6 and enter the circulation path 7. In addition, since the ball 4 is guided in the axial direction at the same angle as the lead angle of the ball rolling path 6, the ball 4 can be smoothly guided from the ball rolling path 6 to the circulation path 7. In addition, by making the second portion a circular arc tangent to the tangent line, the ball 4 can smoothly roll in the circulation path. And, by guiding the ball 4 that has rolled in the ball rolling path 6 smoothly into the circulation path 7 in this way and configuring the ball 4 to roll smoothly in the circulation path, the ball screw 1 can be rotated smoothly. In particular, in the case where the ball screw is of a size that allows a user to rotate it by hand, the tactile sensation felt when the user rotates the ball screw by hand can be improved.

[0035] Furthermore, by opening the circulation passage 7 radially inward over its entire length and positioning the balls 4 radially outward from the outer diameter of the screw shaft at the apex of the arc, the circulation passage 7 can be formed while suppressing the height of the top member 5, thereby making it possible to reduce the outer diameter of the nut 3. This allows the ball screw 1 to be configured compactly.

[0036] (Configuration 2) a locus (80) of the center of the ball (4) in the circulation path when viewed from the radial direction includes a fourth portion (83) that is connected to the third portion (81) at one end side and has an inclination angle different from that of the third portion (81); The third portion (81) has a straight portion having a length equal to or greater than the radius of the ball (4), the third portion (81) and the fourth portion (83) are connected by a circular arc (811) having a radius equal to or greater than the radius of the ball (4); The inclination angle of the fourth portion (83) is set to an angle such that the fourth portion (83) does not overlap with the tongue portion (800) when viewed from the radial direction. 2. The ball screw (1) according to configuration 1.

[0037] In this way, by having the third portion 81 have a straight portion with a length equal to or greater than the radius of the ball 4, the ball 4 that has rolled in the rolling path 6 can smoothly enter the circulation path 7, and by connecting the third portion 81 and the fourth portion 83 with an arc 811 having a radius equal to or greater than the radius of the ball 4, the ball 4 can be smoothly transferred from the third portion 81 to the fourth portion 83. In addition, coupled with the fact that the fourth portion is set at an angle such that it does not overlap with the tongue portion, the ball screw 1 can be rotated smoothly.

[0038] (Configuration 3) a locus (80) of the center of the ball (4) in the circulation path when viewed from the radial direction has a fourth portion (83) having an inclination angle different from that of the third portion; The fourth portion (83) is configured such that an inclination angle (β) of the fourth portion (83) with respect to a virtual plane (P) perpendicular to a central axis (X) of the nut (3) is 30° or less at the intermediate portion (73). 3. The ball screw (1) according to configuration 1 or 2.

[0039] In this way, by configuring the S-angle β to be 30° or less, the balls 4 can be returned to the ball rolling path 6 via a short path, and the ball screw 1 can be rotated smoothly.

[0040] (Configuration 4) a first portion (76) which is a tangent to a ball center diameter (75) of the ball rolling path (6) is a tangent to the ball center diameter (75) of the ball rolling path at a starting point where the circulation path (7) starts guiding the ball (41); 4. A ball screw (1) according to any one of configurations 1 to 3.

[0041] With this configuration, the ball 41 can be guided in the tangential direction of the ball center diameter when being transferred from the ball rolling path 6 to the circulating path 7, and the ball can be smoothly removed from the ball rolling path 6.

[0042] (Configuration 5) The opening (79) is an opening having a non-uniform opening width. 5. A ball screw (1) according to any one of configurations 1 to 4.

[0043] (Configuration 6) The top member (5) includes first and second divided bodies (511, 512) that are divided along a trajectory (80) of the center of the ball in the circulation path when viewed from the radial direction, The circulation groove (700) of the first and second divided bodies (511, 512) forming the circulation path (7) is configured so that a cross section in a direction perpendicular to the axial direction is an arc of less than a semicircle, and the tongue portion (800) is provided in the first divided body (511). 6. A ball screw (1) according to any one of configurations 1 to 5.

[0044] By dividing the piece 5 in this way, it is possible to perform molding using a metal mold, thereby reducing the cost of the parts. It is also possible to form the circulation path 7 in a Gothic shape.

[0045] (Configuration 7) The nut (3) has a mounting hole (32) for mounting the top member (5), The mounting hole (32) includes a bottom surface (321) on which the top member (5) is seated, an inner wall (323) surrounding the periphery of the bottom surface (321), and a through hole (322) formed in the bottom surface (321), The top member (5) is positioned in the rotational direction by fitting into the through hole (322), and is positioned in the radial direction by abutting against the bottom surface (321). 7. A ball screw (1) according to any one of configurations 1 to 6.

[0046] With this configuration, the top member 5 can be easily positioned.

[0047] (Configuration 8) and a restricting member (85) that does not restrict the movement of the top member (5) in the rotational direction but restricts the movement in the radial direction to prevent the top member (5) from coming off the mounting hole (32). 8. A ball screw (1) according to any one of configurations 1 to 7.

[0048] In this way, by floating the top member 5 in the rotational direction, the balls 4 are guided into the circulation path 7, so that the circulation path 7 naturally follows the ball rolling path 6 and the circulation path 7 and the ball rolling path 6 are aligned.

[0049] (Configuration 9) The top member (5) includes first and second divided bodies (511, 512) that are divided along a trajectory (80) of the center of the ball in the circulation path when viewed from the radial direction, a first spacer (514) that connects the first and second divided bodies (511, 512) and is interposed between a bottom surface (321) of the mounting hole (32) and the top member (5); a second spacer (513) that connects the first and second divided bodies (511, 512) and is interposed between the regulating member (85) and the top member (5); 9. A ball screw (1) according to any one of configurations 1 to 8.

[0050] With this configuration, the strength of the top member 5 can be improved, and the position in the radial direction (height direction) can be adjusted.

[0051] (Configuration 10) The nut (3) has a mounting hole (32) for mounting the top member (5), The mounting hole (32) has a bottom surface (321) on which the top member (5) is seated, an inner wall (323) surrounding the periphery of the bottom surface (321), and a through hole (322) formed in the bottom surface (321), The piece member (5) has a main body portion (51) that is inserted into the through hole (322) and in which the circulation path (7) is formed, and a flange portion (52) that is seated on the bottom surface (321), The top member (5) is positioned in the rotational direction by the engagement between the flange portion (52) and the mounting hole (32). The main body portion (51) has a circular cross-sectional shape when viewed from a radial direction. 10. A ball screw (1) according to any one of configurations 1 to 9.

[0052] With this configuration, it becomes possible to form the main body 51 in a circular shape, and the circulation path 7 can be made short, allowing the number of balls 4 housed in the rolling path 6 to be increased.

[0053] In the above-described embodiment, the circulation path 7 is configured so that the moving trajectory 74 has tangents 76, 78 and an arc 77, and the moving trajectory 80 has connection portions 81, 82 and an intermediate portion 83. However, this is not limited to the above, and for example, at the connection portion of the moving trajectories 74, 80, there may be a portion intervening that results in a trajectory with a different curvature or inclination than the above-described portions.

[0054] Moreover, the tangents 76, 78 do not necessarily have to be tangents to the ball center diameter at the starting point where the circulation path 7 starts guiding the ball 4 or at the release point where the ball 4 is sent out, but may be tangents to the ball center diameter at other points within the introduction part 71 or the outlet part 72. For example, the tangent at the introduction part 71 may be a tangent to the ball center diameter at the point where the tongue part 800 starts scooping up the ball 4.

[0055] Furthermore, in the above-mentioned embodiment, the restricting member is constituted by the snap ring 85, but the restricting member may be constituted by any material as long as it is possible to restrict the rotational position of the top member 5 in a floating state. Also, the inventions described in the above-mentioned embodiment may be combined in any manner. [Explanation of symbols]

[0056] 1: ball screw / 2: screw shaft / 3: nut / 4: ball / 5: ball bearing member / 6: ball rolling path / 7: circulation path / 21: screw groove / 71: introduction section / 72: outlet section / 73: middle section / 74: trajectory / 75: ball center diameter / 76: first section / 77: second section / 79: opening / 80: trajectory / 81: third section / 800: tongue section

Claims

1. A screw shaft having a screw groove on its outer circumferential surface; A nut is fitted onto the screw shaft and has a screw groove formed on an inner peripheral surface thereof, which forms a ball rolling path together with the screw groove; A ball disposed in the ball rolling path; a ball member having a circulation path formed therein for returning the ball from the end point of the ball rolling path to the start point thereof; The circulation path has an opening portion that opens radially inward along its entire length, the circulation path has an introduction portion that guides the ball from an end point of the ball rolling path to the circulation path, an introduction portion that guides the ball from the circulation path to a start point of the ball rolling path, and an intermediate portion between the introduction portion and the introduction portion, The introduction portion is provided with a tongue portion that enters the screw groove of the screw shaft and scoops up the ball, a locus of the center of the ball in the circulation path when viewed from the axial direction has a first portion that is a tangent to the ball center diameter of the ball rolling path in the introduction portion, and a second portion that is a single arc tangent to the tangent line, and the ball is positioned outside the outer diameter of the screw shaft at least at a vertex of the arc, a locus of a center of the ball in the circulation path when viewed from the radial direction has a third portion inclined at the same angle as a lead angle of the ball rolling path in the introduction portion; A ball screw characterized by:

2. a locus of a center of the ball in the circulation path when viewed from the radial direction includes a fourth portion that is connected to the third portion at one end and has an inclination angle different from that of the third portion, the third portion has a straight portion having a length equal to or greater than the radius of the ball, the third portion and the fourth portion are connected by an arc having a radius equal to or greater than the radius of the ball, The inclination angle of the fourth portion is set to an angle such that the fourth portion does not overlap with the tongue portion when viewed from the radial direction.

2. The ball screw according to claim 1.

3. a locus of a center of the ball in the circulation path when viewed from the radial direction has a fourth portion having an inclination angle different from that of the third portion, The fourth portion is configured such that an inclination angle with respect to a virtual plane perpendicular to a central axis of the nut at the intermediate portion is 30° or less.

2. The ball screw according to claim 1.

4. the first portion being a tangent to a ball center diameter of the ball rolling path is a tangent to a ball center diameter of the ball rolling path at a start point where the circulation path starts guiding the ball; 4. The ball screw according to claim 1, wherein the ball screw is a ball bearing.

5. The opening has a non-uniform opening width.

2. The ball screw according to claim 1.

6. the top member includes first and second divided bodies configured by being divided along a trajectory of a center of the ball in the circulation path when viewed from the radial direction, The circulation grooves of the first and second divided bodies forming the circulation path are configured so that a cross section in a direction perpendicular to the axial direction is an arc of less than a semicircle, and the tongue portion is provided on the first divided body.

2. The ball screw according to claim 1.

7. The nut has a mounting hole for mounting the top member, The mounting hole includes a bottom surface on which the top member is seated, an inner wall surrounding the bottom surface, and a through hole formed in the bottom surface, The top member is positioned in the rotational direction by fitting into the through hole, and is positioned in the radial direction by abutting against the bottom surface.

2. The ball screw according to claim 1.

8. a restricting member that does not restrict the movement of the top member in the rotational direction but restricts the movement in the radial direction to prevent the top member from coming out of the mounting hole; 8. The ball screw according to claim 7.

9. the top member includes first and second divided bodies configured by being divided along a trajectory of a center of the ball in the circulation path when viewed from the radial direction, a first spacer that connects the first and second divisional bodies and is interposed between a bottom surface of the mounting hole and the top member; a second spacer connecting the first and second divided bodies and interposed between the regulating member and the top member; 9. The ball screw according to claim 8.

10. The nut has a mounting hole for mounting the top member, The mounting hole has a bottom surface on which the top member is seated, an inner wall surrounding the periphery of the bottom surface, and a through hole formed in the bottom surface, The top member has a main body portion that is inserted into the through hole and in which the circulation path is formed, and a flange portion that is seated on the bottom surface, The top member is positioned in a rotational direction by engagement between the flange portion and the mounting hole, The main body has a circular cross-sectional shape when viewed from a radial direction.

2. The ball screw according to claim 1.

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