JP7823474B2 - Ball screw device - Google Patents

Description

This disclosure relates to a ball screw device.

A ball screw device is a device that converts rotary motion into linear motion, or linear motion into rotary motion. A ball screw device comprises a screw shaft, a nut, multiple balls that roll on a track between the screw shaft and the nut, and a circulating part that returns the balls that have rolled from one end of the track to the other end of the track.

One example of a circulation part is a tubular part as shown in Patent Document 1. This tubular circulation part has a main body extending along the outer surface of the nut, a bent part bent from the main body, and legs extending from the bent part. The legs are inserted into through holes that penetrate the outer and inner surfaces of the nut. The tips of the legs scoop up balls from the track and return balls to the track from the tips of the legs.

Japanese Patent Application Laid-Open No. 2003-269564

In recent years, ball screw devices have been developed in which the legs of the circulation component are inclined relative to the through-hole of the nut. Such legs cannot fit into the through-hole, and the tips of the legs end up misaligned from their intended assembly position. This makes it impossible to smoothly scoop up or return the balls.

The present disclosure has been made in light of the above, and aims to provide a ball screw device that suppresses positional deviation of the tip of the leg.

To achieve the above object, a ball screw device according to one aspect of the present disclosure comprises a screw shaft, a nut inserted through the screw shaft, a plurality of balls arranged in a track between the screw shaft and the nut, a circulation component having a cylindrical cross section for circulating the balls, and a fixed component for fixing the circulation component to the outer peripheral surface of the nut. When viewed from an axial direction parallel to the screw shaft, a direction parallel to an imaginary line connecting the screw shaft and the fixed component is the assembly direction. When viewed from the axial direction, a direction perpendicular to the assembly direction is the intersecting direction. The nut is provided with two through holes that penetrate the nut in the assembly direction and are long in the intersecting direction. The two through holes are arranged on one side and the other side of the intersecting direction, with the imaginary line as the boundary. The circulation component is arranged on the outer peripheral side of the nut and includes a main body portion fixed to the fixed component, two leg portions inserted into the through holes, and two bent portions connecting the main body portion and the leg portions. The inner circumferential surface of the through hole has a pair of opposing surfaces that face each other in the intersecting direction. The pair of opposing surfaces includes a first opposing surface positioned closer to the imaginary line and a second opposing surface positioned further away from the imaginary line. The leg portion is inclined so as to approach the second opposing surface from the first opposing surface toward the tip of the leg portion. The first opposing surface presses against the leg portion. The tip of the leg portion is pressed against the second opposing surface.

According to the present disclosure, the legs are pressed against the first opposing surface and rotate. As a result, the tips of the legs are pressed against the second opposing surface and positioned to abut against the second opposing surface. Note that in ball screw devices, for example, due to low precision in the circulation components, the through holes may be large, leaving gaps between the legs and the legs. Even in such cases, according to the present disclosure, the tips of the legs are positioned to abut against the second opposing surface. Furthermore, because the first opposing surface abuts against the legs, the legs are prevented from rotating so that their tips move away from the second opposing surface. Therefore, even if the legs are subjected to impact from a ball during use of the ball screw device, the tips of the legs remain in abutment against the second opposing surface. As a result, smooth ball scooping and return are continuously achieved.

In a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the second opposing surface has a concave shape with a recessed central portion in the axial direction when viewed from the assembly direction.

The legs are pressed against the second opposing surface. Therefore, with this configuration, the tips of the legs are aligned so that they fit into the concave recesses in the second opposing surface. This allows the tips of the legs to be positioned at a predetermined axial position.

In a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the second opposing surface has an arc shape when viewed from the assembly direction.

With this configuration, the tip of the leg comes into surface contact with the second opposing surface, making it less likely to shift axially.

In a preferred embodiment of the ball screw device according to the present disclosure, the first opposing surface is provided with a pressing surface that presses against the outer peripheral surface of the leg portion. The pressing surface is inclined with respect to the assembly direction and extends along the outer peripheral surface of the leg portion.

In the present disclosure, the first opposing surface extends in the assembly direction and intersects with the leg portion, which is inclined in the assembly direction. Therefore, the corners of the first opposing surface may press against the leg portion, potentially causing deformation of the leg portion. On the other hand, with the above configuration, the pressing surface comes into surface contact with the leg portion. This prevents the load from concentrating on one part of the leg portion, causing deformation of the leg portion.

Furthermore, in a preferred aspect of the ball screw device according to one aspect of the present disclosure, the through hole extends along the track when viewed from the assembly direction.

With this configuration, the through hole fits within the space of one of the inner raceway surfaces of the nut, and does not interfere with adjacent inner raceway surfaces. Therefore, it can be used even when the circulating part has a small lead.

Furthermore, in a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the angle of the inlet and outlet of the circulating component is less than 180° when viewed from the axial direction.

This configuration increases the number of balls placed on the track, improving the load-bearing capacity of the ball screw device.

In a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the circulating component is made of a metal material.

This configuration provides superior durability compared to plastic.

In a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the main body is divided into two parts in the longitudinal direction of the main body.

According to the present disclosure, the rotation of one leg and the other leg generates a torsional load on the main body. However, with the above configuration, the torsion is absorbed, preventing damage to the main body.

In a preferred embodiment of the ball screw device according to one aspect of the present disclosure, the inner peripheral surface of the through hole has a pair of side surfaces that face each other in the axial direction. The diameter of the circulating part is greater than the distance between the pair of side surfaces. The outer peripheral surface of the leg portion has a pair of flat portions that face the pair of side surfaces and are cut out in a flat shape.

This configuration allows the use of a circulation part that is larger than the distance between the pair of side surfaces, improving the strength of the circulation part. Furthermore, because it has a flat surface, it can also be inserted into a through hole.

The ball screw device disclosed herein prevents the tip of the leg from shifting out of position.

FIG. 1 is a perspective view of a ball screw device according to a first embodiment. FIG. 2 is a view of the ball screw device of the first embodiment, with the circulating component and the fixed component removed, viewed from the outer periphery of the nut. FIG. 3 is a cross-sectional view of the nut of the first embodiment cut in the axial direction, as viewed from the inner peripheral side. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. FIG. 5 is a view of only the circulating component of the first embodiment taken out and viewed from the axial direction. FIG. 6 is a view of the nut according to the first embodiment, showing a state in which a circulation component is inserted into a through-hole of the nut, as viewed from the outer periphery side of the nut. FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. FIG. 8 is a view of the circulating component of the first modification as viewed from the axial direction. FIG. 9 is a view of the circulating component of the second modification as viewed from the outside in the assembly direction. FIG. 10 is a view of the circulating component of the third modification as viewed from the axial direction.

The following describes in detail the mode for carrying out the invention, with reference to the drawings. The present disclosure is not limited to the content of the following description. Furthermore, the components described below include those that would be easily conceived by a person skilled in the art and those that are substantially identical. Furthermore, the components described below can be combined as appropriate.

(Embodiment 1)
Fig. 1 is a perspective view of a ball screw device of embodiment 1. As shown in Fig. 1, the ball screw device 100 of embodiment 1 includes a screw shaft 1 (see Fig. 2), a cylindrical nut 2, a plurality of balls 3 (see Fig. 7), a circulating component 4, and a fixed component 5.

Figure 2 is a view of the ball screw device of embodiment 1 with the circulating component and fixed component removed, viewed from the outer periphery of the nut. As shown in Figure 2, the screw shaft 1 is a solid rod-shaped component. The screw shaft 1 passes through the nut 2. An outer periphery raceway surface 1a is provided on the outer periphery of the screw shaft 1. Hereinafter, the direction parallel to the axis O1 of the screw shaft 1 will be referred to as the axial direction X.

Figure 3 shows the nut of embodiment 1 cut in the axial direction, with the cross section viewed from the inner peripheral side. As shown in Figure 3, an inner peripheral raceway surface 11 is provided on the inner peripheral surface 10 of the nut 2. Threads 12 are provided between each thread of the inner peripheral raceway surface 11. The inner peripheral raceway surface 11 faces the outer peripheral raceway surface 1a (see Figure 2). A spiral raceway 7 on which balls 3 roll is formed between the outer peripheral raceway surface 1a and the inner peripheral raceway surface 11 (see Figure 2).

Figure 4 is a cross-sectional view taken along line IV-IV in Figure 2. As shown in Figure 4, the outer peripheral surface 13 of the nut 2 is D-cut. This provides a flat surface 14 on the outer peripheral surface 13 of the nut 2. The circulating part 4 and fixed part 5 are mounted on the flat surface 14 (see Figure 1). The flat surface 14 is perpendicular to an imaginary line K1 that extends linearly from the axis O1. Note that the imaginary line K1 passes through the midpoint of the two through holes 20 when viewed from the axial direction.

Hereinafter, the direction parallel to the imaginary line K1 will be referred to as the assembly direction Y. Furthermore, within the assembly direction Y, the direction approaching the axis O1 will be referred to as the inside of the assembly direction Y, and the direction away from the axis O1 will be referred to as the outside of the assembly direction Y. Additionally, the direction perpendicular to (intersecting with) the imaginary line K1 when viewed from the axial direction will be referred to as the cross direction Z. Within the cross direction Z, the direction approaching the imaginary line K1 will be referred to as the inside of the cross direction Z, and the direction away from the imaginary line K1 will be referred to as the outside of the cross direction Z1.

As shown in FIG. 4, the nut 2 has a through hole 20 that penetrates the inner peripheral surface 10 and outer peripheral surface 13 of the nut 2. The through hole 20 extends in the assembly direction Y. The leg portions 42 of the circulating part 4 are disposed in the through hole 20. Therefore, two through holes 20 are provided corresponding to the two leg portions 42. When viewed from the axial direction, the two through holes 20 are arranged on one side and the other side of the intersecting direction Z, with the imaginary line K1 as the boundary.

When viewed from the assembly direction, the two through holes 20, the circulation part 4, and the fixed part 5 are symmetrical with respect to point P on the plane 14 (see Figure 2). Point P on the plane 14 is located at the center of the plane 14 in the axial direction X and at the center of the transverse direction Z. Therefore, the circulation part 4 and the fixed part 5 can be assembled to the nut 2 even when rotated to point P on the plane 14. In the following explanation, a configuration located on one side of point P will be described as a representative example, and a description of a configuration located on the other side of point P will be omitted. Furthermore, within the axial direction, the direction approaching point P will be referred to as the inside of the axial direction X, and the direction away from point P will be referred to as the outside of the axial direction X.

As shown in Figure 2, the length H2 of the through hole 20 in the transverse direction Z is longer than the length H1 in the axial direction X. This allows the leg portion 42 of the circulating part 4 to be positioned in the through hole 20 while tilted in the transverse direction Z.

The inner circumferential surface of the through hole 20 has a pair of side surfaces 21 facing in the axial direction X and a pair of opposing surfaces 22 facing in the transverse direction Z. The pair of side surfaces 21 has a first side surface 23 positioned closer to the inside of the through hole 20 in the axial direction X and a second side surface 24 positioned closer to the outside of the axial direction X. The pair of opposing surfaces 22 has a first opposing surface 25 positioned closer to the inside of the through hole 20 in the transverse direction Z and a second opposing surface 26 positioned closer to the outside of the transverse direction Z. The first side surface 23 and the second side surface 24 are linear. The first opposing surface 25 and the second opposing surface 26 are arc-shaped. As described above, the through hole 20 has a so-called oval shape.

The through hole 20 is inclined with respect to the transverse direction Z. More specifically, the through hole 20 is inclined so that it is positioned inward in the axial direction X as it moves outward in the transverse direction Z. In other words, the through hole 20 is inclined along the raceway 7. Therefore, as shown in FIG. 3, the through hole 20 penetrates one thread of the inner circumferential raceway surface 11. Furthermore, the first side surface 23 and the second side surface 24 extend along the thread 12. As a result, the thread 12 is not divided by the through hole 20 and is continuous in the spiral direction.

As shown in Figure 2, a recess 16 is provided on the outer surface 13 of the nut 2, at the edge of the through hole 20. The recess 16 is recessed toward the inner periphery of the nut 2 and is intended to avoid contact with the bent portion 43 of the circulatory component 4. In addition, two female threaded holes (not shown) are provided on the flat surface 14. Screws 6 that fasten the fixing component 5 are threaded into these female threaded holes (see Figure 1).

As shown in FIG. 4, a chamfered pressing surface 27 is provided on the portion of the first opposing surface 25 that is closer to the outside in the assembly direction Y. This pressing surface 27 is formed by chamfering the corner formed by the bottom surface of the recess 16 and the first opposing surface 25. The pressing surface 27 is also inclined so that it is positioned inward in the transverse direction Z as it extends outward in the assembly direction Y. The pressing surface 27 is positioned so that when the leg portion 42 of the circulable part 4 is inserted into the through hole 20, it abuts against the outer peripheral surface of the leg portion 42 and can press the leg portion 42 outward in the transverse direction Z (see FIG. 7).

Figure 5 shows only the circulation component of embodiment 1, viewed from the axial direction. As shown in Figure 5, the circulation component 4 is a cylindrical component, with its internal space serving as a return path 40. The circulation component 4 includes a main body 41 disposed on the outer periphery of the nut 2, two leg portions 42 inserted into the through-hole 20, and two bent portions 43 connecting the main body 41 and the leg portions 42. Note that the imaginary circle C shown in Figure 5 is a circle connecting the centers of the balls 3 disposed on the raceway 7.

A scooping portion 43a is provided at the tip of the leg portion 42 to scoop up the balls 3 from the track 7. The angle θ1 of the entrance and exit of the circulating part 4 (the angle at which the balls 3 are scooped up and returned by the two scooping portions 43a) is less than 180°.

The leg 42 has a first leg 44 that continues from the bent portion 43, and a second leg 45 that extends further from the first leg 44. The first leg 44 and the second leg 45 are not connected in a straight line but are slightly bent. Specifically, the second leg 45 extends parallel to a tangent D to the imaginary circle C. Meanwhile, the first leg 44 is inclined so as to be positioned outside the assembly direction Y relative to the tangent D. The scooping portion 43a is provided at the tip of the first leg 44. Therefore, in this embodiment, the balls 3 are scooped up by the first leg 44, not the second leg 45. This reduces the angle θ1 of the entrance and exit of the circulating component 4 compared to when the balls 3 are scooped up by the second leg 45. In other words, more balls 3 are placed on the track 7, improving the load-bearing capacity of the ball screw device 100.

In addition, in this embodiment, the main body 41, leg 42, and bent portion 43 of the circulable component 4 are manufactured by bending a cylindrical metal component using press processing. Therefore, the cross-sectional shapes of the main body 41, leg 42, and bent portion 43 are each circular.

Note that while the circulative part 4 in embodiment 1 is made of metal, the present disclosure may also be a circulative part made of resin. Furthermore, in the present disclosure, when the circulative part 4 is manufactured from a cylindrical metal part, the processing method is not limited to press working. Furthermore, while the circulative part 4 in embodiment 1 consists of a single part, the present disclosure may also be a circulative part made by joining multiple parts.

Figure 6 shows the state in which a circulatory component has been inserted into the through-hole of the nut in embodiment 1, viewed from the outer periphery of the nut. As shown in Figure 6, the main body 41 is linear. In other words, the main body 41 is cylindrical. The main body 41 is placed on the flat surface 14 of the nut 2. The main body 41 is also pressed toward the flat surface 14 from the outside in the assembly direction Y by the fixing part 5 (see Figure 1). This prevents the circulatory component 4 from slipping out to the outside in the assembly direction Y. The main body 41 is also positioned so that both ends point toward the two through-holes 20. Therefore, the center line M41 of the main body 41 is inclined with respect to the axial direction X.

Figure 7 is a cross-sectional view taken along line VII-VII in Figure 6. The bent portion 43 is bent and serves to change the direction of travel of the ball 3. As shown in Figure 7, a portion of the bent portion 43 is positioned in the recess 16 of the nut 2. This prevents interference between the bent portion 43 and the outer peripheral surface 13 of the nut 2.

The leg portion 42 is disposed in the through hole 20. When viewed from the axial direction, the leg portion 42 is inclined so that it is positioned outward in the transverse direction Z as it moves inward in the assembly direction Y. Therefore, the leg portion 42 does not extend parallel to the assembly direction Y, and is shaped in such a way that it cannot be fitted into the through hole 20.

Regarding the rotation directions of the main body 41 about the center line M41, one is referred to as the first rotation direction L1 and the other is referred to as the second rotation direction L2. The outer peripheral surface of the leg 42 has an outer peripheral surface 46 facing the first rotation direction L1 and an inner peripheral surface 47 facing the second rotation direction L2. The outer peripheral surface 46 faces the second opposing surface 26. The inner peripheral surface 47 faces the first opposing surface 25. The outer peripheral surface 46 at the tip of the leg 42 (the tip of the second leg 45) has a corner surface 48 formed by chamfering the corner. This corner surface 48 has an arc shape when viewed from the assembly direction Y.

Next, the through hole 20 and the leg 42 will be described in detail. When the circulating part 4 is assembled to the nut 2, the outer peripheral surface of the leg 42 comes into contact with the first opposing surface 25. In other words, the first opposing surface 25 is positioned in the transverse direction Z so that it comes into contact with the inner outer peripheral surface 47 of the leg 42 (first leg 44). As a result, the leg 42 receives a load from the outside in the transverse direction Z (see arrow F1). The main body 41 then twists about the center line M41, causing the leg 42 to rotate in the first rotation direction L1. As a result, the tip of the leg 42 (second leg 45) is pressed against the second opposing surface 26 (see arrow F2). From the above, when the circulating part 4 is assembled to the nut 2, the tip (corner surface 48) of the leg 42 (second leg 45) is positioned in contact with the second opposing surface 26.

In Figure 7, the other leg 42 (not shown) is pressed against the first opposing surface 25 and rotates in the second rotation direction L2. As a result, the two legs 42 rotate in different directions, increasing the distance between the legs 42 (angle θ1).

The portion of the first opposing surface 25 that comes into contact with the inner outer peripheral surface 47 of the leg portion 42 forms the pressing surface 27. The pressing surface 27 is an inclined surface that follows the inner outer peripheral surface 47 of the leg portion 42 and is in surface contact with the inner outer peripheral surface 47. This prevents the corners of the first opposing surface 25 from coming into contact with the leg portion 42 and causing deformation of the leg portion 42.

In addition, a cornered surface 48 is provided at the tip of the leg 42, which is pressed against the second opposing surface 26. Therefore, the tip (cornered surface 48) of the leg 42 is in surface contact with the second opposing surface 26. This prevents the load from concentrating on the corner at the tip of the leg 42, causing deformation of the tip.

As shown in Figure 6, the axial length H1 of the through hole 20 (see Figure 2) is slightly larger than the diameter of the circulating part 4. In other words, a minute gap is created between the outer surface of the leg 42 and the pair of side surfaces 21. Therefore, even if manufacturing errors occur in the circulating part 4, the leg 42 can be reliably inserted into the through hole 20.

The tip (cornered surface 48) of the leg 42 is pressed against the second opposing surface 26 (see F2 in Figure 7). Therefore, the tip (cornered surface 48) of the leg 42 is aligned so that it abuts the portion of the second opposing surface 26 that is recessed furthest outward in the transverse direction Z. Therefore, the tip (cornered surface 48) of the leg 42 is positioned at a predetermined position in the axial direction.

The corner surface 48 of the leg portion 42 is arc-shaped when viewed from the assembly direction Y. Furthermore, the curvature of the corner surface 48 of the leg portion 42 is the same as the curvature of the second opposing surface 26. Therefore, the corner surface 48 and the second opposing surface 26 abut against each other without any gaps. Therefore, even if vibration of the ball 3 occurs on the leg portion 42, it is difficult for the leg portion 42 to become misaligned in the axial direction.

As described above, according to the ball screw device 100 of embodiment 1, the tip (cornered surface 48) of the leg 42 is positioned at a predetermined position in the transverse direction Z and the axial direction X. Therefore, the effort required to position the tip (cornered surface 48) of the leg 42 when assembling the circulable component 4 is reduced. Furthermore, because the first opposing surface 25 (pressing surface 27) abuts against the inner outer peripheral surface 47 of the leg 42, the leg 42 does not rotate in the second rotation direction L2. Therefore, even if vibrations of the ball 3 are transmitted to the leg 42, the tip of the leg 42 is unlikely to separate from the second opposing surface 26. In other words, the tip of the leg 42 is unlikely to become displaced during use of the ball screw device 100. Furthermore, even if the tip of the leg 42 separates from the second opposing surface 26, the tip of the leg 42 will abut against the second opposing surface 26 due to elastic deformation. Therefore, smooth scooping and returning of the ball 3 can be continuously performed.

As described above, the ball screw device 100 of embodiment 1 comprises a screw shaft 1, a nut 2 inserted through the screw shaft 1, a plurality of balls 3 arranged in a raceway 7 between the screw shaft 1 and the nut 2, a circulation part 4 having a cylindrical cross section for circulating the balls 3, and a fixed part 5 for fixing the circulation part 4 to the outer peripheral surface 13 of the nut 2. When viewed from the axial direction X parallel to the axis O1 of the screw shaft 1, the direction parallel to the imaginary line K1 connecting the screw shaft 1 and the fixed part 5 is the assembly direction Y. When viewed from the axial direction X, the direction perpendicular to the assembly direction Y is the transverse direction Z. The nut 2 has two through holes 20 that penetrate in the assembly direction Y and are long in the transverse direction Z. The two through holes 20 are arranged on one side and the other side of the transverse direction Z, with the imaginary line K1 as the boundary. The circulation component 4 is disposed on the outer periphery of the nut 2 and includes a main body 41 fixed to the fixed component 5, two legs 42 inserted into the through hole 20, and two bent portions 43 connecting the main body 41 and the legs 42. The inner periphery of the through hole 20 has a pair of opposing surfaces 22 facing each other in the transverse direction Z. The pair of opposing surfaces 22 includes a first opposing surface 25 positioned closer to the imaginary line K1 and a second opposing surface 26 positioned further away from the imaginary line K1. The legs 42 are inclined so as to approach the second opposing surface 26 from the first opposing surface 25 toward the tip of the legs 42. The first opposing surface 25 presses against the legs 42, and the tip of the legs 42 is pressed against the second opposing surface 26.

According to embodiment 1, the tip of the leg 42 is positioned so that it abuts the second opposing surface 26. Furthermore, because the first opposing surface 25 presses against the leg 42, the tip of the leg 42 is prevented from moving away from the second opposing surface 26. As a result, the ball 3 can be smoothly and continuously scooped up and returned.

Furthermore, the second opposing surface 26 in embodiment 1 has an arc shape when viewed from the assembly direction Y.

This allows the tip of the leg 42 to come into surface contact with the second opposing surface 26, making it less likely to shift axially.

In addition, the first opposing surface 25 in embodiment 1 is provided with a pressing surface 27 that presses against the outer peripheral surface of the leg portion 42. The pressing surface 27 is inclined with respect to the assembly direction Y and extends along the outer peripheral surface of the leg portion 42.

This allows the pressing surface 27 to come into surface contact with the leg portion 42, preventing deformation of the leg portion 42.

Furthermore, the through hole 20 in embodiment 1 extends along the track 7 when viewed from the assembly direction Y.

This allows the through hole 20 to fit within one thread of the inner circumferential raceway surface 11, and the thread 12 is not broken. Therefore, it can be used even when the circulating part 4 has a small lead.

Furthermore, the angle θ of the inlet and outlet of the circulating part 4 in embodiment 1 is less than 180° when viewed from the axial direction.

As a result, the number of balls 3 placed on the track 7 is increased, improving the load-bearing capacity of the ball screw device 100.

Furthermore, the circulating part 4 in embodiment 1 is made of a metal material.

As a result, the recyclable part 4 is more durable than if it were made from a resin material.

Although the first embodiment has been described above, the present disclosure is not limited to the example shown in the first embodiment. For example, the first opposing surface 25 in the first embodiment has a pressing surface 27, but in the present disclosure, the first opposing surface 25 may press the leg 42. Furthermore, the outer peripheral surface 46 at the tip of the leg 42 is formed as a corner surface 48, but it may also be a rounded surface or may not be chamfered.

Furthermore, while the second opposing surface 26 in embodiment 1 has an arc shape when viewed from the assembly direction Y, in the present disclosure it may have a triangular shape, for example. In other words, the second opposing surface 26 in the present disclosure only needs to be concave, with a recessed central portion in the axial direction when viewed from the assembly direction Y. With this shape, the tip of the leg portion 42 is positioned so that it fits into the concave central portion of the second opposing surface 26. Therefore, the tip of the leg portion 42 is positioned at a predetermined position in the axial direction.

Furthermore, the rotatable parts of the present disclosure are not limited to the example shown in embodiment 1. Below, modified examples of rotatable parts will be described. The following explanation will focus on the changes.

(Variation 1)
8 is a view of the circulable component of Modification 1 as viewed from the axial direction. The circulable component 4A of Modification 1 differs from the circulable component 4 of Embodiment 1 in that the leg portions 42A are linear. The center line M42 of the leg portions 42A extends tangentially to the imaginary circle C. According to the circulable component 4A of Modification 1, the angle θ2 formed by the inlet and outlet of the circulable component 4A is less than 180° but is larger than the angle θ1 of Embodiment 1. In other words, the balls 3 arranged in the track 7 are smaller than those of Embodiment 1, resulting in a slight decrease in the durability of the ball screw device 100.

(Variation 2)
FIG. 9 is a view of the circulable component of Modification 2 as viewed from the outside in the assembly direction. The circulable component 4B of Modification 2 differs from the circulable component 4 of Embodiment 1 in that the main body 41B is divided into two parts in the longitudinal direction (parallel to the center line M41). That is, the circulable component 4B of Modification 2 is composed of two parts, and the main body 41B has a first main body 141 and a second main body 142. In the circulable component 4 of Embodiment 1, the main body 41 is twisted by pressure from the first opposing surface 25. In contrast, in Modification 2, the first main body 141 and the second main body 142 rotate in different rotational directions. This reduces the load on the main body 41B, making the main body 41B less susceptible to damage.

In Figure 9, to make the boundary between the first body portion 141 and the second body portion 142 easier to see, a gap is provided between the end portion 141a of the first body portion 141 and the end portion 142a of the second body portion 142; however, in the present disclosure, the end portion 141a of the first body portion 141 and the end portion 142a of the second body portion 142 may abut each other.

(Variation 3)
10 is a view of the circulation device of Modification 3 as viewed from the axial direction. The circulation device 4C of Modification 3 is similar to the circulation device 4 of Embodiment 1 in that it is manufactured by processing a cylindrical metal part. However, the circulation device 4C of Modification 3 differs from the circulation device 4 of Embodiment 1 in that the diameter of the circulation device 4C of Modification 3 is larger than the axial length H1 of the through-hole 20 (see FIG. 2). The circulation device 4C of Modification 3 has high rigidity and improved durability.

Moreover, variant 3 differs from the circulation component 4 of embodiment 1 in that each of the two leg portions 42C has a pair of flat portions 143 formed by cutting out a flat surface. Note that two (a pair of) flat portions 143 are provided for each leg portion 42C, but Figure 10 shows the flat portion 143 facing one side of the axial direction X, and does not show the flat portion facing the other side of the axial direction X. Furthermore, the pair of flat portions 143 face a pair of side surfaces 21 of the through hole 20 (see Figure 2). The pair of flat portions 143 reduces the axial length of the leg portion 42C, allowing it to be inserted into the through hole 20.

REFERENCE SIGNS LIST 100 Ball screw device 1 Screw shaft 2 Nut 3 Ball 4, 4A, 4B, 4C Circulation part 5 Fixed part 7 Raceway 11 Inner raceway surface 14 Flat surface 20 Through hole 21 Side surface 22 Opposing surface 23 First side surface 24 Second side surface 25 First opposing surface 26 Second opposing surface 27 Pressing surface 40 Return path 41, 41B Main body 42, 42A Leg 43 Bent portion 43a Scooping portion 44 First leg 45 Second leg 46 Outer outer peripheral surface 47 Inner outer peripheral surface 48 Angular surface 141 First main body 142 Second main body 143 Flat portion

Claims (9)

A screw shaft,
a nut inserted through the screw shaft;
a plurality of balls arranged in a raceway between the screw shaft and the nut;
a circulation part having a cylindrical cross section that circulates the balls;
a fixing part that fixes the circulation part to an outer peripheral surface of the nut;
Equipped with
When viewed from an axial direction parallel to the screw shaft, a direction parallel to an imaginary line connecting the screw shaft and the fixed part is an assembly direction,
When viewed from the axial direction, a direction perpendicular to the assembly direction is a cross direction,
The nut is provided with two through holes that penetrate the nut in the assembly direction and are long in the intersecting direction,
the two through holes are arranged separately on one side and the other side in the intersecting direction with the imaginary line as a boundary,
The circulating part is
a main body portion disposed on an outer circumferential side of the nut and fixed to the fixed component;
Two legs inserted into the through holes;
two bent portions connecting the main body portion and the leg portion;
and
an inner circumferential surface of the through hole has a pair of opposing surfaces that face each other in the intersecting direction;
The pair of opposing surfaces are
a first opposing surface disposed near the imaginary line;
a second opposing surface disposed away from the imaginary line;
and
the leg portion is inclined so as to approach the second opposing surface from the first opposing surface toward the tip of the leg portion,
the first opposing surface presses the leg portions to increase the angle between the two leg portions;
the tip of the leg is pressed against the second opposing surface. The ball screw device according to claim 1 , wherein the second opposing surface has a concave shape with a recessed central portion in the axial direction when viewed from the assembly direction. The ball screw device according to claim 2 , wherein the second opposing surface has an arc shape when viewed from the assembly direction. The first opposing surface is provided with a pressing surface that presses against an outer peripheral surface of the leg portion,
The ball screw device according to any one of claims 1 to 3, wherein the pressing surface is inclined with respect to the assembly direction and extends along the outer peripheral surface of the leg portion. The ball screw device according to any one of claims 1 to 4, wherein the through hole extends along the raceway when viewed from the assembly direction. The ball screw device according to any one of claims 1 to 5, wherein an angle of an inlet and outlet of the circulating part is less than 180° when viewed from the axial direction. The ball screw device according to any one of claims 1 to 6, wherein the circulating component is made of a metal material. The ball screw device according to any one of claims 1 to 7, wherein the main body is divided into two parts in a longitudinal direction of the main body. an inner circumferential surface of the through hole has a pair of side surfaces facing each other in the axial direction;
The diameter of the circulating part is greater than the distance between the pair of side surfaces,
The ball screw device according to any one of claims 1 to 8, wherein the outer peripheral surface of the leg portion is provided with a pair of flat portions that face the pair of side surfaces and are cut out in a flat shape.