Ball screw device

Abstract

To provide a ball screw device which does not require strict dimensional control for a hole.SOLUTION: A ball screw device of the present disclosure includes a screw shaft main body having an outer peripheral raceway surface formed on an outer peripheral surface, a nut having an inner peripheral raceway surface formed on an inner peripheral surface and penetrated by the screw shaft main body, a plurality of balls disposed between the screw shaft main body and the nut, and a circulation portion attached to the nut and configured to circulate the balls. A direction parallel to a central axis of the screw shaft body is defined as an axial direction. A hole recessed radially inward from an outer peripheral surface of the screw shaft body is formed in at least one of both ends of the screw shaft body in the axial direction. A spring pin is inserted into the hole. The spring pin has a fitting portion fitted into the hole and a protruding portion protruding radially outward from an outer peripheral surface of the screw shaft main body. The protruding portion can enter the inner peripheral side of the nut and come into contact with the ball or the circulation portion.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] A ball screw device has a nut, a screw shaft, and multiple balls, and converts rotational motion into linear motion and linear motion into rotational motion. Ball screw devices are used in a variety of products, such as actuators. For this reason, ordinary consumers sometimes perform maintenance on ball screw devices. However, ordinary consumers may accidentally move the screw shaft in the axial direction beyond a predetermined distance, causing the balls to fall out from between the nut and the screw shaft. Once the balls fall out, ordinary consumers are unable to assemble the ball screw device. Therefore, the following patent documents disclose a system in which pins are provided on both the nut and the screw shaft to limit the movement of the screw shaft so that it does not exceed a predetermined amount. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 63-68555 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned patent documents, a hole is formed on the outer peripheral surface of the screw shaft, and a pin is press-fitted into the hole. If the interference of the hole is too large, the press-fitting of the pin will deform the outer peripheral raceway surface of the screw shaft, hindering the smooth rolling of the balls. Therefore, strict dimensional control of the hole is required.

[0005] An object of the present disclosure is to provide a ball screw device that does not require strict dimensional control of the hole. [Means for solving the problem]

[0006] In order to achieve the above object, a ball screw device according to one aspect of the present disclosure includes a screw shaft body 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 inserted into the screw shaft body, a plurality of balls arranged between the outer peripheral raceway surface and the inner peripheral raceway surface, and a circulation unit attached to the nut and circulating the balls. The direction parallel to the central axis of the screw shaft body is defined as the axial direction. At least one of the axial ends of the screw shaft body is formed with a hole recessed radially inward from the outer peripheral surface of the screw shaft body. A spring pin is inserted into the hole. The spring pin has a fitting portion that fits into the hole and a protruding portion that protrudes from the hole. The protruding portion is capable of contacting the balls or the circulation unit.

[0007] In the present disclosure, the fitting portion (spring pin) deforms in accordance with the diameter of the hole. In other words, even if the diameter of the hole is formed smaller than a predetermined dimension, the outer peripheral raceway surface of the screw shaft body does not deform. Therefore, strict dimensional control of the hole is not required. Furthermore, in the present disclosure, the spring pin serves as a restricting component that restricts the amount of movement of the screw shaft body. The protrusion (spring pin) deforms upon contact with the circulating portion or the ball, reducing the load input to the circulating portion or the ball. Thus, according to the present disclosure, damage to the circulating portion or the ball is suppressed more than when a solid pin is used as a restricting component.

[0008] The screw shaft body of the ball screw device is heat treated.

[0009] If a hole is formed in the screw shaft body before heat treatment, the hole is deformed by the heat treatment, changing its diameter. Therefore, dimensional control is performed taking into account the hole diameter after heat treatment, or the hole is formed after heat treatment. According to the above configuration, even if the hole is formed before heat treatment, the fitting portion (spring pin) deforms in accordance with the hole diameter after deformation. Therefore, the effort of dimensional control taking into account the hole diameter after heat treatment can be eliminated.

[0010] In the ball screw device, the screw shaft body may have holes formed at both ends in the axial direction, and the spring pins may be inserted into the two holes, respectively.

[0011] In the ball screw device, a portion of the outer peripheral surface of the screw shaft body where the outer peripheral raceway surface is not formed is formed with a helical thread. The hole is formed in only one of the two ends in the axial direction of the screw shaft body. The other end of the screw shaft body in the axial direction may be formed with a crimped portion formed by crimping the thread.

[0012] In the ball screw device, the hole may be formed in the outer circumferential raceway surface.

[0013] In the ball screw device, a portion of the outer peripheral surface of the screw shaft body where the outer peripheral raceway surface is not formed is formed with a helical thread. At least a portion of the hole may overlap with the thread. [Effects of the Invention]

[0014] According to the present disclosure, there is no need to have strict dimensional control over the holes. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a view showing a ball screw device of the first embodiment cut in the axial direction. [Figure 2] FIG. 2 is a schematic view of the outer peripheral surface of the nut as viewed from the direction II in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a schematic view of the ball screw device of the first modification cut in the axial direction. [Figure 6] FIG. 6 is a schematic view of the ball screw device of the second modification cut in the axial direction. [Figure 7] FIG. 7 is a cross-sectional view of the ball screw device of the second modification cut in the spiral direction, showing the contact state between the spring pin and the ball. [Figure 8] FIG. 8 is a schematic view of the ball screw device of the third modification cut in the axial direction. [Figure 9] FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. [Figure 10] FIG. 10 is a schematic view of the ball screw device of the fourth modification cut in the axial direction. [Figure 11] FIG. 11 is a schematic view of the ball screw device of the fifth modification cut in the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present disclosure will be described in detail below with reference to the drawings. Note that the present disclosure is not limited to the following modes for carrying out the invention (hereinafter referred to as embodiments). Furthermore, the components in the following embodiments include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be combined as appropriate.

[0017] (Embodiment 1) FIG. 1 is a view of a ball screw device of embodiment 1 cut in the axial direction. FIG. 2 is a schematic view of the outer peripheral surface of a nut viewed from the direction II in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. The nut (piece) shown in FIG. 3 is a cross-sectional view taken along line IV-IV in FIG. 2. Therefore, the angle at which the piece and the spring pin are cut is different in FIG. 3. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 2.

[0018] 1, the ball screw device 100 includes a screw shaft 1, a nut 2 inserted through the screw shaft 1, a plurality of balls 3 disposed between the screw shaft 1 and the nut 2, and a plurality of circulation units 4 attached to the nut 2. In the following description, the direction parallel to the central axis O1 of the screw shaft 1 is referred to as the axial direction.

[0019] The screw shaft 1 includes a cylindrical connecting portion 10 and a screw shaft main body 11. The outer diameter of the connecting portion 10 is smaller than that of the screw shaft main body 11. The connecting portion 10 is a portion for connecting to another component. Examples of other components that can be connected to the connecting portion 10 include a carrier or a piston of a reduction gear, but the present disclosure does not particularly limit this. The present disclosure may also include a screw shaft 1 that is configured only with the screw shaft main body 11 and does not have the connecting portion 10. Hereinafter, the axial direction in which the screw shaft main body 11 is disposed as viewed from the connecting portion 10 is referred to as a first direction X1. The opposite direction to the first direction X1 is referred to as a second direction X2.

[0020] An end face 11a of the screw shaft body 11 in the first direction X1 is a flat surface. An outer circumferential raceway surface 13 is formed on an outer circumferential surface 12 of the screw shaft body 11. The outer circumferential raceway surface 13 is recessed radially inward and extends in the spiral direction. The outer circumferential raceway surface 13 is formed from the end of the screw shaft body 11 in the first direction X1 to the end of the screw shaft body 11 in the second direction X2. The outer circumferential raceway surface 13 is formed by cutting the outer circumferential surface 12 of the screw shaft body 11. Note that the portion of the outer circumferential surface 12 of the screw shaft body 11 on which the outer circumferential raceway surface 13 is not formed is formed as a screw thread 14.

[0021] In this embodiment, the screw shaft 1 is heat-treated after cutting to form the outer circumferential raceway surface 13. Specifically, the heat treatment is quenching and tempering. In the present disclosure, carburizing may be performed before quenching. Alternatively, induction hardening may be used as the quenching method. This heat treatment provides the outer circumferential raceway surface 13 with the desired hardness and toughness.

[0022] A crimped portion 15 is formed on the outer peripheral surface 12 of the screw shaft body 11. The crimped portion 15 is located at an end of the outer peripheral surface 12 in the second direction X2. The crimped portion 15 is formed by crimping a portion of the thread 14 radially inward. A portion of the crimped portion 15 protrudes into the outer peripheral raceway surfaces 13 on both axial sides. Therefore, the ends of the outer peripheral raceway surfaces 13 in the second direction X2 of the screw shaft body 11 have portions that are narrowed by the crimped portion 15, i.e., portions through which the balls 3 cannot pass. Note that the thread 14 after heat treatment is hardened and less likely to deform. For this reason, the screw shaft 1 is crimped to form the crimped portion 15 before heat treatment.

[0023] A circular hole 16 is formed in the outer peripheral surface 12 of the screw shaft body 11. The hole 16 is arranged at an end of the outer peripheral surface 12 in the first direction X1. As shown in FIG. 3, the hole 16 extends radially from a central axis O1 (not shown in FIG. 3; see FIG. 1). The hole 16 is formed in an outer peripheral raceway surface 13 of the outer peripheral surface 12 of the screw shaft body 11. The diameter of the hole 16 is smaller than the diameter of the balls 3.

[0024] The holes 16 are formed by cutting the outer peripheral raceway surface 13. Here, the outer peripheral raceway surface 13 after heat treatment is hardened and difficult to process. For this reason, the holes 16 are formed in the outer peripheral raceway surface 13 before heat treatment. Furthermore, since the holes 16 are deformed by heat treatment, the diameter of the holes 16 also changes before and after heat treatment.

[0025] A spring pin 50 is inserted into the hole 16. The spring pin 50 fits into the hole 16 while exerting an elastic deformation force (spring force). Note that the spring pin 50 in this embodiment is a grooved spring pin having a C-shaped cross section taken in a direction perpendicular to the center line of the spring pin 50, but the present disclosure may also be a double-wound spring pin, and is not particularly limited in terms of the type of spring pin.

[0026] A radially inner end 51 of the spring pin 50 abuts against a bottom surface 16a of the hole 16. The spring pin 50 has a fitting portion 53 that fits into the hole 16 and a protruding portion 54 that protrudes radially outward beyond the outer circumferential raceway surface 13. The distance from the central axis O1 (not shown in FIG. 3) to the radially outer end 52 of the spring pin 50 is L1.

[0027] As shown in FIG. 1, the nut 2 is formed in a cylindrical shape and has an annular first end face 20 facing the first direction X1 and an annular second end face 21 facing the second direction X2. A spiral inner circumferential raceway surface 23 is formed on an inner circumferential surface 22 of the nut 2. The inner circumferential raceway surface 23 extends in the spiral direction and faces the outer circumferential raceway surface 13. A raceway is formed between the inner circumferential raceway surface 23 and the outer circumferential raceway surface 13, and a plurality of balls 3 are arranged therein. The length of the inner circumferential raceway surface 23 is slightly shorter than one revolution (approximately one lead). Therefore, the length of the raceway is also slightly shorter than one revolution (approximately one lead).

[0028] The nut 2 has a through hole 26 formed therein that penetrates the outer peripheral surface 24 and the inner peripheral surface 22 (see FIG. 2). A block 40 (circulation portion 4) is inserted into the through hole 26. The block 40 has an inner diameter surface 41 that faces radially inward. An S-shaped circulation groove 42 is formed in the inner diameter surface 41. This circulation groove 42 connects one end and the other end of the inner peripheral raceway surface 23. Therefore, the balls 3 that move from one end of the raceway to the other end move along the circulation groove 42 and circulate back to one end of the raceway.

[0029] In this embodiment, there are four inner circumferential raceway surfaces 23 and four pieces 40. That is, there are four orbits. Hereinafter, the four inner circumferential raceway surfaces 23 will be referred to as the first inner circumferential raceway surface 23a, the second inner circumferential raceway surface 23b, the third inner circumferential raceway surface 23c, and the fourth inner circumferential raceway surface 23d in order from the first direction X1. Furthermore, the four pieces 40 will be referred to as the first piece 40a, the second piece (not shown), the third piece 40c, and the fourth piece (not shown) in order from the first direction X1. Note that, although there are four inner circumferential raceway surfaces 23 and four pieces 40 in this embodiment, the present disclosure may have a number other than four.

[0030] As shown in FIG. 3, the distance from the central axis O1 (not shown in FIG. 3, see FIG. 1) to the inner peripheral surface 22 of the nut 2 is L2. The inner diameter surface 41 of the link 40 protrudes radially inward from the inner peripheral surface 22 of the nut 2. The distance from the central axis O1 (not shown in FIG. 3, see FIG. 1) to the inner diameter surface 41 of the link 40 is L3. The distance L1 to the radially outer end 52 of the spring pin 50 is smaller than the distance L2 and larger than the distance L3 (L2>L1>L3).

[0031] Next, a method for assembling the ball screw device 100 of this embodiment will be described. First, a temporary shaft (not shown) is inserted into the nut 2, and the balls 3 are placed between the inner peripheral raceway surface 23 of the nut 2 and the temporary shaft. Next, the screw shaft 1 is placed in the second direction X2 of the nut 2, and the end face 11a (see FIG. 1) of the screw shaft body 11 is brought into contact with the temporary shaft. Next, the screw shaft 1 is rotated while the screw shaft body 11 is inserted into the nut 2. This pushes the temporary shaft out of the nut 2, and the balls 3 are placed between the screw shaft body 11 and the nut 2. Thereafter, a spring pin 50 is inserted into the hole 16, and the ball screw device 100 is completed. Therefore, when the screw shaft body 11 is inserted into the nut 2, the hole 16 is open. However, the diameter of the hole 16 is smaller than the diameter of the balls 3. Therefore, the balls 3 do not fall into the hole 16.

[0032] Next, the effects of the ball screw device 100 of the first embodiment will be described. When the screw shaft 1 is rotated and moved in the second direction X2 while the nut 2 is fixed, the spring pin 50 enters the inside of the nut 2. When the screw shaft 1 is further rotated and moved in the second direction X2, the protrusion 54 (spring pin 50) comes into contact with the first piece 40a, as shown in FIG. 4. Therefore, the spring pin 50 does not move further in the second direction X2 than the first piece 40a.

[0033] On the other hand, when the screw shaft 1 is moved in the first direction X1 while being rotated while the nut 2 is fixed, the crimped portion 15 (see FIG. 1) enters the inner peripheral side of the nut 2. Then, when the screw shaft is further moved in the first direction X1 while being rotated, the crimped portion 15 comes into contact with the balls 3 arranged on the fourth inner peripheral raceway surface 23d. Therefore, the crimped portion 15 does not move in the first direction X1 further than the fourth link (not shown).

[0034] As described above, according to the first embodiment, the end of the screw shaft body 11 in the first direction X1 does not move in the second direction X2 beyond the first block 40a. Moreover, the end of the screw shaft body 11 in the second direction X2 does not move in the first direction X1 beyond the fourth block (not shown). Therefore, the outer circumferential raceway surface 13 is always disposed radially inward of the balls 3. In other words, the balls 3 do not fall out from between the screw shaft 1 and the nut 2.

[0035] In addition, in this embodiment, a spring pin 50 is used as a component to be inserted into the hole 16. Even if the diameter of the hole 16 differs from a predetermined size, the spring pin 50 elastically deforms. In other words, in this embodiment, even if the spring pin 50 is inserted into the hole 16, the outer circumferential raceway surface 13 of the screw shaft 1 is not deformed. Therefore, strict dimensional control of the hole 16 is not required.

[0036] Similarly, although the diameter of hole 16 changes before and after heat treatment, spring pin 36 elastically deforms and fits into hole 16. This eliminates the need to manage dimensions by taking into account the diameter of hole 16 after heat treatment.

[0037] Furthermore, the spring pin 50 comes into contact with the first link 40a, and if a solid pin were to come into contact with the first link 40a, the first link 40a could be damaged. In this embodiment, the spring pin 50 deforms, reducing the load applied to the first link 40a. This prevents damage to the first link 40a.

[0038] The above has described embodiment 1. Next, a modified example that is a partial modification of embodiment 1 will be described. The following description will focus on the differences from embodiment 1.

[0039] (Variation 1) 5 is a schematic view of a ball screw device of Modified Example 1 cut in the axial direction. The ball screw device 100A of Modified Example 1 differs from Embodiment 1 in that a continuous thread groove surface 60 is formed on the inner peripheral surface 22 of the nut 2 from the end in the first direction X1 to the end in the second direction X2. A part of this thread groove surface 60 forms the inner peripheral raceway surface 23 (only the second inner peripheral raceway surface 23b is shown in FIG. 5). The remaining thread groove surface 60 forms the circuit outer thread groove surface 61. In other words, the balls 3 are arranged on the inner peripheral raceway surface 23, but the balls 3 are not arranged on the circuit outer thread groove surface 61.

[0040] Further, the first end face 20 and the second end face 21 (not shown in FIG. 5, see FIG. 1) are partially cut out by the thread groove surface 60. Therefore, the first end face 20 and the second end face 21 have openings 62 that open the thread groove surface 60 in the axial direction.

[0041] Furthermore, the spring pin 50A of Modification 1 differs from the spring pin 50 of Embodiment 1 in that it is longer than the spring pin 50 of Embodiment 1. Specifically, the distance L4 from the central axis O1 to the radially outer end 52 of the spring pin 50A is longer than the distance L2 from the central axis O1 to the inner circumferential surface 22 of the nut 2 (L4>L2). Furthermore, the spring pin 50 has a length that allows it to enter the thread groove surface 60.

[0042] According to the above-described first modification, when the screw shaft 1 is moved in the second direction X2 while being rotated with the nut 2 fixed, the spring pin 50A enters the circuit outer thread groove surface 61 from the opening 62 of the first end face 20 (see the dashed line 50Q in FIG. 5). Then, when the screw shaft 1 is further moved in the second direction X2 while being rotated, the spring pin 50A moves along the circuit outer thread groove surface 61 and comes into contact with the first block 40a. Therefore, the spring pin 50A does not move further in the second direction X2 than the first block 40a.

[0043] As described above, even in the first modification, the balls are prevented from falling out from between the screw shaft 1 and the nut 2.

[0044] (Variation 2) Fig. 6 is a schematic diagram of a ball screw device of Modification 2 cut in the axial direction. Fig. 7 is a cross-sectional view of the ball screw device of Modification 2 cut in the spiral direction, showing the contact state between the spring pin and the ball. As shown in Fig. 6, the ball screw device 100B of Modification 2 differs from Embodiment 1 in that the spring pin 50B is shorter than the spring pin 50. Specifically, the distance L5 from the central axis O1 to the radially outer end 52 of the spring pin 50B is shorter than the distance L3 from the central axis O1 to the inner diameter surface 41 of the link 40 (L3>L5).

[0045] According to the above-described second modification, when the screw shaft 1 is rotated and moved in the second direction X2 while the nut 2 is fixed, the spring pin 50B enters the inner peripheral side of the nut 2. When the screw shaft 1 is further rotated and moved in the second direction X2, as shown in Fig. 7, the spring pin 50B moves in a spiral direction on the inner peripheral side of the first block 40a and comes into contact with the ball 3. Therefore, the spring pin 50B does not move in the second direction X2 any further than the ball 3 arranged on the first inner peripheral raceway surface 23a.

[0046] From the above, Modification 2 also prevents the balls from falling out from between the screw shaft 1 and the nut 2. Note that in Modification 2, the spring pin 50B protrudes radially outward beyond the thread 14 of the screw shaft 1, but the present disclosure may also use a spring pin that does not protrude beyond the thread 14.

[0047] (Variation 3) FIG. 8 is a schematic diagram of a ball screw device of Modification 3 cut in the axial direction. FIG. 9 is a cross-sectional view taken along line IX-IX in FIG. 8. As shown in FIG. 8, a hole 16C of a ball screw device 100C of Modification 3 differs from that of Embodiment 1 in that it overlaps with the thread 14. Therefore, the spring pin 50C protrudes beyond the thread 14 toward the outer circumferential raceway surfaces 13 disposed adjacent to the thread 14 in the first direction X1 and the second direction X2. The circulation portion 4 of Modification 3 also differs from that of Embodiment 1 in that an S-shaped groove surface 40C is provided instead of the link 40. The S-shaped groove surface 40C is a groove surface formed on the inner circumferential surface 22 of the nut 2 by forging.

[0048] Also, the diameter of the hole 16C in Modification 3 is larger than the diameter of the ball 3, which is different from Embodiment 1. According to this, in assembling the ball screw device 100C, when the screw shaft 1 is inserted into the nut 2 while rotating the screw shaft 1, if the ball 3 moves from the outer peripheral raceway surface 13 toward the hole 16C, there is a possibility that the ball 3 will fall into the hole 16C. However, the ball 3 gets caught on the inner peripheral raceway surface 23 of the nut 2 and does not move toward the hole 16C. This prevents the ball 3 from falling into the hole.

[0049] Furthermore, the size H of the portion of the spring pin 50C that is arranged on the outer circumferential raceway surface 13 is smaller than the diameter of the ball 3. Therefore, when assembling the ball screw device 100C, when the screw shaft 1 is inserted into the nut 2 while being rotated, the ball 3 moves along the outer circumferential raceway surface 13, but the ball 3 does not fall into the portion of the spring pin 50C that is arranged on the outer circumferential raceway surface 13.

[0050] 9, the spring pin 50C of Modification 3 differs from Embodiment 1 in that it is shorter than the spring pin 50. Specifically, the distance L6 from the central axis O1 to the radially outer end 52 of the spring pin 50C is shorter than the distance L7 from the central axis O1 to the thread 14 of the screw shaft 1 (L7>L6). In other words, the protruding portion 54 of the spring pin 50B does not protrude radially outward beyond the outer circumferential surface 12 of the screw shaft 1. In other words, the spring pin 50C does not interfere with the nut 2 or the block 40.

[0051] According to the above-described modified example 3, when the screw shaft 1 moves in the second direction X2 with the nut 2 fixed, the spring pin 50C comes into contact with the ball 3 arranged on the first inner circumferential raceway surface 23a, as in modified example 2. Therefore, the spring pin 50C does not move further in the second direction X2 than the ball 3 arranged on the first inner circumferential raceway surface 23a, and therefore, the ball 3 is prevented from falling out from between the screw shaft 1 and the nut 2.

[0052] In the spring pin 50C of Modification 3, the distance L6 to the radially outer end 52 is smaller than the distance L7 to the thread 14 of the screw shaft 1 (see FIG. 9), but when using such a spring pin 50B, a top 40 may be used instead of the S-groove surface 40C, and a protrusion may be provided on the inner diameter surface 41 of the top 40 that protrudes radially inward and fits into the outer peripheral raceway surface 13 of the screw shaft 1. In this way, the spring pin 50C comes into contact with the protrusion of the top 40 instead of the ball 3, and movement of the screw shaft 1 in the second direction X2 is restricted.

[0053] (Variation 4) FIG. 10 is a schematic diagram of a ball screw device of Modification 4 cut in the axial direction. As shown in FIG. 10, a ball screw device 100D is similar to Modification 3 in that the hole 16D overlaps the screw thread 14. However, it differs from Modification 3 in that the hole 16D is formed only on the circumferential raceway surface 13 arranged in the first direction X1 of the screw thread 14. Therefore, the spring pin 50D protrudes toward the outer circumferential raceway surface 13 arranged in the first direction X1 of the screw thread 14. Even in Modification 4, as in Modification 3, the spring pin 50D comes into contact with the ball 3 arranged on the first inner circumferential raceway surface 23a. Therefore, the spring pin 50D does not move in the second direction X2 further than the ball 3 arranged on the first inner circumferential raceway surface 23a, preventing the ball 3 from falling out from between the screw shaft 1 and the nut 2.

[0054] (Variation 5) FIG. 11 is a schematic view of a ball screw device of Modified Example 5 cut in the axial direction. As shown in FIG. 11, a ball screw device 100E of Modified Example 5 differs from Embodiment 1 in that a hole 16E is formed instead of a crimped portion 15 at the end of the screw shaft body 11 in the second direction X2. A spring pin 50E is inserted into the hole 16. According to Modified Example 5, when the screw shaft 1 is moved in the first direction X1 while rotating with the nut 2 fixed, the spring pin 50E comes into contact with the balls 3 arranged on the fourth block (not shown) or the fourth inner peripheral raceway surface 23d. This prevents the balls 3 from falling out from between the screw shaft 1 and the nut 2.

[0055] Although the first embodiment and its modified examples have been described above, the present disclosure is not limited to the examples shown in the first embodiment and its modified examples. For example, although the block 40 and the S-shaped groove surface 40C are given as examples of the circulation portion 4, in the present disclosure, a tube may be used. Also, although the screw shaft 1 in the embodiment is heat-treated, in the present disclosure, a screw shaft that is not heat-treated may be used. Also, in the present embodiment, the outer circumferential raceway surface 13 is formed by cutting, but in the present disclosure, the outer circumferential raceway surface 13 may be formed by rolling.

[0056] Also, although the hole 16 has a circular shape when viewed from the outside in the radial direction, the present disclosure is not limited to a circular shape as long as the spring pin can be fitted in. In other words, the present disclosure also allows the hole to have a triangular, hexagonal, or other shape when viewed from the outside in the radial direction.

[0057] Furthermore, although the diameters of the holes 16, 16E formed in the outer peripheral raceway surface 13 are smaller than the diameter of the balls 3 in the first embodiment and the like, in the present disclosure, they may be the same as or larger than the diameter of the balls 3. When the diameters of the holes 16, 16E are the same as or larger than the diameter of the balls 3, the holes 16, 16E may be temporarily filled with a filler before assembling the ball screw device. This blocks the holes 16, 16E with the filler, preventing the balls 3 from falling out. After inserting the screw shaft 1 into the nut 2, the filler may be removed and the spring pin 50 may be inserted. Furthermore, the holes 16C, 16D overlapping the threads 14 described in Modifications 3 and 4 are larger in diameter than the balls 3. Therefore, the holes 16C, 16D may be temporarily filled with a filler as described above before assembling the ball screw device. However, if the diameters of the holes 16, etc. are smaller than the diameter of the balls 3, the work of filling and removing the filler is unnecessary, reducing the labor required for assembly.

[0058] Furthermore, the diameters of holes 16C and 16D that overlap thread 14 described in Modifications 3 and 4 are formed to be larger than the diameter of ball 3, but in the present disclosure, they may be the same as or smaller than the diameter of ball 3. Furthermore, if the diameters of holes 16C and 16D are smaller than the diameter of ball 3, ball 3 will not fit into holes 16C and 16D.

[0059] The present disclosure may also be implemented as a combination of the following configurations. (1) a screw shaft body having an outer circumferential raceway surface formed on its outer circumferential surface; a nut having an inner peripheral raceway surface formed on its inner peripheral surface and being inserted into the screw shaft body; a plurality of balls disposed between the outer circumferential raceway surface and the inner circumferential raceway surface; a circulation unit attached to the nut and circulating the balls; Equipped with A direction parallel to the central axis of the screw shaft body is defined as an axial direction, At least one of the two axial ends of the screw shaft body is formed with a hole recessed radially inward from the outer peripheral surface of the screw shaft body, A spring pin is inserted into the hole, The spring pin is a fitting portion that fits into the hole; a protrusion protruding from the hole; and The protrusion is capable of coming into contact with the ball or the circulating portion. (2) The screw shaft body is heat treated. The ball screw device according to (1). (3) The holes are formed at both ends of the screw shaft body in the axial direction, The spring pins are inserted into the two holes, respectively. A ball screw device according to (1) or (2). (4) a portion of the outer circumferential surface of the screw shaft body where the outer circumferential raceway surface is not formed has a helical thread, The hole is formed in only one of both ends in the axial direction of the screw shaft body, The other of the two ends in the axial direction of the screw shaft body is formed with a crimped portion formed by crimping the threads. A ball screw device according to (1) or (2). (5) The hole is formed in the outer circumferential raceway surface. A ball screw device according to any one of (1) to (4). (6) a portion of the outer circumferential surface of the screw shaft body where the outer circumferential raceway surface is not formed has a helical thread, At least a portion of the hole overlaps with the thread. A ball screw device according to any one of (1) to (4). [Explanation of symbols]

[0060] 1 Screw shaft 2 nuts 3 balls 4 Circulation section 10 Connection part 11 Screw shaft body 12 Outer surface 13 Outer raceway surface 14 threads 15 Crimping part 16, 16C, 16D, 16E holes 22 Inner surface 23 Inner raceway surface 40 frames 40C S-shaped groove surface 41 Inner diameter surface 42 Circulation groove 50, 50A, 50B, 50C, 50D, 50E spring pins 53 Fitting part 54 Protrusion 100, 100A, 100B, 100C, 100D, 100E Ball screw device

Claims

1. a screw shaft body having an outer circumferential raceway surface formed on its outer circumferential surface; a nut having an inner peripheral raceway surface formed on its inner peripheral surface and being inserted into the screw shaft body; a plurality of balls disposed between the outer circumferential raceway surface and the inner circumferential raceway surface; a circulation unit attached to the nut and circulating the balls; Equipped with A direction parallel to the central axis of the screw shaft body is defined as an axial direction, At least one of the two axial ends of the screw shaft body is formed with a hole recessed radially inward from the outer peripheral surface of the screw shaft body, A spring pin is inserted into the hole, The spring pin is a fitting portion that fits into the hole; a protrusion protruding from the hole; and The protrusion is capable of coming into contact with the ball or the circulating portion. Ball screw device.

2. The screw shaft body is heat treated. The ball screw device according to claim 1 .

3. The holes are formed at both ends of the screw shaft body in the axial direction, The spring pins are inserted into the two holes, respectively. The ball screw device according to claim 1 or 2.

4. a portion of the outer circumferential surface of the screw shaft body where the outer circumferential raceway surface is not formed has a helical thread, The hole is formed in only one of both ends in the axial direction of the screw shaft body, The other of the two ends in the axial direction of the screw shaft body is formed with a crimped portion formed by crimping the threads. The ball screw device according to claim 1 or 2.

5. The hole is formed in the outer circumferential raceway surface. The ball screw device according to claim 1 or 2.

6. a portion of the outer circumferential surface of the screw shaft body where the outer circumferential raceway surface is not formed has a helical thread, At least a portion of the hole overlaps with the thread. The ball screw device according to claim 1 or 2.

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