Ball screw

Abstract

To provide a ball screw for suppressing the deterioration of a fastening jig while stabilizing the position of a circulation member with respect to the fastening jig.SOLUTION: A ball screw include a circulation member 5 mounted into a fitting hole 6 provided in a nut 3 for circulating a rolling ball, the circulation member 5 having an engagement part 12 fastened to a fitting hole 6 to engage therewith in the state of being mounted into the fitting hole 6. The engagement part 12 engages with the fitting hole 6 in the state of being fastened circularly around a center P of the fitting hole 6 in view from the outer diameter side of the nut 3.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present invention relates to a ball screw including a circulating member that circulates balls. [Background technology]

[0002] A known ball screw used in general industrial machine tools or automotive actuators and the like comprises a nut having a helical thread groove on its inner peripheral surface, a screw shaft having a helical thread groove on its outer peripheral surface, a number of balls rollably accommodated between the thread grooves of the nut and the screw shaft inserted into the nut, and a circulation member for circulating the balls.

[0003] For example, Patent Document 1 (Patent Publication No. 4756645) discloses a method of fixing a circulation member in a fitting hole provided in a nut, in which, as shown in Figure 13, a circulation member 500 is inserted into a fitting hole 600 of a nut 300, and a convex engagement portion (guide wall) 120 provided on the circulation member 500 is tightened outward (see the dotted line portion in Figure 13) to engage the engagement portion 120 with the edge of the fitting hole 600.

[0004] Furthermore, in Patent Document 1, in order to reduce the amount of springback of the engaging portion after plastic deformation, a method is proposed in which, when tightening the engaging portion, a tightening jig is brought into point contact with both end portions 120a of the inner surface of the engaging portion 120 shown in FIG. 13 to press the engaging portion 120. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4756645 Summary of the Invention [Problem to be solved by the invention]

[0006] While the above-mentioned method of crimping by point contact can reduce the amount of springback after plastic deformation, excessive stress acts on the pressing part of the crimping jig when pressing the engagement part. This makes it easy for the crimping jig to deteriorate. In addition, when crimping by point contact, the position of the circulating member relative to the crimping jig is not stable, so there is also the problem that it is difficult to perform crimping with high accuracy. Specifically, in the ball screw described in Patent Document 1, the arm portion provided on the circulating member is fitted into the screw groove of the nut, so that the circulating member is roughly positioned in the axial direction of the screw shaft and in the rotational direction within the fitting hole, but is not positioned in a direction perpendicular to the axial direction of the screw shaft. Therefore, when attempting to fix the circulating member by the method described in Patent Document 1, there is a risk that the positional deviation of the circulating member in the direction perpendicular to the axial direction of the screw shaft will be particularly large.

[0007] Therefore, an object of the present invention is to suppress deterioration of the crimping jig and to stabilize the position of the circulating member relative to the crimping jig. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a ball screw comprising a nut having a helical thread groove on its inner surface, a screw shaft having a helical thread groove on its outer surface, a plurality of balls rollably accommodated between the opposing thread grooves of the nut and the screw shaft, and a circulation member that is mounted in a mating hole provided in the nut and circulates the rolling balls, wherein the circulation member has an engagement portion that is crimped and engages with the mating hole when mounted in the mating hole, and the engagement portion engages with the mating hole in a state in which it is crimped in an arc shape centered on the center of the mating hole when viewed from the outer diameter side of the nut.

[0009] As described above, in the ball screw according to the present invention, the engagement portion of the circulation member engages with the fitting hole in a state in which the engagement portion is crimped in an arc shape centered on the center of the fitting hole when viewed from the outer diameter side of the nut. Such an arc-shaped engagement structure is obtained by bringing a crimping jig into line contact with the engagement portion. In other words, the engagement portion is crimped in an arc shape by bringing the crimping jig into line contact with the engagement portion in an arc shape centered on the center of the fitting hole.

[0010] As described above, in the present invention, by making the crimping jig contact the engagement portion in a line, the contact area of ​​the crimping jig with the engagement portion is increased compared to the conventional crimping method using point contact, and the stress acting on the crimping jig can be reduced. This makes it possible to suppress deterioration of the crimping jig due to excessive stress acting on the crimping jig. In addition, by making the crimping jig and the engagement portion in a line contact, the position of the circulating member relative to the crimping jig is easily stabilized, so that the positional deviation of the circulating member can be suppressed, and crimping processing can be performed with high precision.

[0011] In addition, it is preferable that the contact area of ​​the crimping jig with the engaging portion is the entire circumferential direction of the engaging portion. In that case, a contact mark caused by contact with the crimping jig is formed over the entire circumferential direction of the engaging portion. In this way, by bringing the crimping jig into contact with the engaging portion over the entire circumferential direction of the engaging portion, the crimping process can be performed evenly and the stress acting on the crimping jig is also made even. In other words, it is possible to prevent the stress acting on the crimping jig from becoming locally large, and deterioration of the crimping jig can be more effectively suppressed. Effect of the Invention

[0012] According to the present invention, it is possible to suppress deterioration of the crimping jig and to stabilize the position of the circulating member relative to the crimping jig. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a plan view of a ball screw according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a vertical sectional view of the ball screw according to the embodiment. [Diagram 3] FIG. 2 is a vertical cross-sectional view of the nut according to the embodiment. [Figure 4] FIG. 4 is a cross-sectional perspective view showing a state before a circulation member is attached to the nut according to the embodiment. [Diagram 5] FIG. 2 is a perspective view of a crimping jig according to the embodiment. [Figure 6] FIG. 2 is a vertical cross-sectional view of the crimping jig according to the embodiment. [Figure 7] FIG. 2 is a front view of the crimping jig according to the embodiment, as viewed from the tip side. [Figure 8] 11A and 11B are diagrams for explaining a method of fixing the circulation member. [Figure 9] 11A and 11B are diagrams for explaining a method of fixing the circulation member. [Figure 10] FIG. 13 is a diagram showing a state before the engagement portion is crimped. [Figure 11] 13 is a diagram showing a state in which the inner surface of the engagement portion and the tapered surface of the crimping portion are in line contact with each other. FIG. [Figure 12] 13A and 13B are diagrams illustrating a state in which the engagement portion is crimped. [Figure 13] FIG. 1 is a diagram showing a conventional crimping method using point contact. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members or components having the same function or shape are given the same reference numerals as far as they can be distinguished. Therefore, the description of components that have been described once will be omitted.

[0015] The overall configuration of a ball screw according to an embodiment of the present invention will be described with reference to Fig. 1 to Fig. 4. Fig. 1 is a plan view of the ball screw according to this embodiment, Fig. 2 is a longitudinal sectional view of the ball screw, Fig. 3 is a longitudinal sectional view of a nut provided in the ball screw, and Fig. 4 is a sectional perspective view showing a state before a circulation member is attached to the nut.

[0016] As shown in FIGS. 1 and 2, a ball screw 1 according to this embodiment includes a screw shaft 2, a nut 3, a plurality of balls 4, and a circulation member 5.

[0017] The screw shaft 2 has a helical screw groove 2a on its outer circumferential surface, and is inserted into a cylindrical nut 3. On the other hand, the nut 3 has a helical screw groove 3a on its inner circumferential surface that faces the screw groove 2a of the screw shaft 2. A plurality of balls 4 are housed between these screw grooves 2a, 3a in a rollable manner.

[0018] The cross-sectional shape of each of the thread grooves 2a, 3a may be a circular arc shape or a gothic arc shape. In this embodiment, each of the thread grooves 2a, 3a is formed in a gothic arc shape that allows a large contact angle with the ball 4 and a small axial gap. This increases the rigidity of each of the thread grooves 2a, 3a against the axial load and suppresses the occurrence of vibration.

[0019] The nut 3 is provided with a circular fitting hole 6 that penetrates from the inner peripheral surface to the outer peripheral surface and cuts out a part of the thread groove 3a. A circulation member 5 having a substantially circular cross section is inserted into this fitting hole 6.

[0020] The circulation member 5 has a connecting groove 5a that connects adjacent screw grooves 3a of the nut 3 for one revolution, as shown in FIG. 3, when the circulation member 5 is inserted into the fitting hole 6, the adjacent screw grooves 3a of the nut 3 are connected by the connecting groove 5a curved in an S-shape, and the rolling path of the balls 4 is formed by the connecting groove 5a and the approximately one revolution portion of the screw groove 3a. As a result, the multiple balls 4 are guided by the connecting groove 5a of the circulation member 5, and are returned to the adjacent screw groove 3a by climbing over the screw thread of the screw shaft 2. Then, the multiple balls 4 roll again along the screw grooves 2a, 3a, thereby circulating. The depth of the connecting groove 5a is set to a depth that allows the balls 4 to climb over the screw thread of the screw shaft 2 in the connecting groove 5a.

[0021] 3, the circulation member 5 is provided with a pair of arm portions 9 protruding in opposite directions. When the circulation member 5 is inserted into the fitting hole 6 of the nut 3, each arm portion 9 of the circulation member 5 fits into the thread groove 3a of the nut 3, thereby positioning the circulation member 5 in the axial direction with respect to the nut 3 and preventing the circulation member 5 from falling off in the outer diameter direction of the nut. Each arm portion 9 engages with the thread groove 3a in which the balls 4 do not roll so as not to hinder the rolling of the balls 4.

[0022] 1, a pair of engagement portions 12 are provided on the nut outer diameter side of the circulation member 5 so as to protrude in the outer diameter direction. When the circulation member 5 is inserted into the fitting hole 6 of the nut 3, the engagement portions 12 are pressed down outward (in directions away from each other) and tightened, whereby the engagement portions 12 engage with the edges of the fitting hole 6. This fixes the circulation member 5 to the nut 3.

[0023] Next, a crimping jig for crimping and fixing the circulation member 5 to the nut 3 according to this embodiment will be described.

[0024] FIG. 5 is a perspective view of the crimping jig according to this embodiment, FIG. 6 is a vertical cross-sectional view of the crimping jig, and FIG. 7 is a front view of the crimping jig as viewed from the tip end side.

[0025] As shown in FIGS. 5 to 7, the jig 20 has a cylindrical main body 21 and a pair of crimping portions 23 protruding from the main body 21.

[0026] The pair of crimping portions 23 have tapered surfaces 23a that are inclined (reduced in diameter) toward the respective tips so as to approach the center line L (see FIG. 6) of the main body portion 21. The tapered surfaces 23a function as pressing portions that press the engaging portions 12 when the engaging portions 12 of the circulation member 5 are crimped.

[0027] Next, a method for fixing the circulation member 5 using the crimping jig 20 according to this embodiment (a method for manufacturing a ball screw) will be described.

[0028] 8, the circulation member 5 is inserted into the fitting hole 6 from the inner diameter side of the nut 3, and the arm portion 9 of the circulation member 5 is fitted into the screw groove 3a. As a result, the circulation member 5 is positioned relative to the nut 3.

[0029] 9, the crimping jig 20 is pressed against the circulation member 5 in the positioned state from the outer diameter side of the nut 3. At this time, the tapered surfaces 23a of the pair of crimping portions 23 are pressed against the inner surfaces 12a of the engagement portions 12 of the circulation member 5, causing each engagement portion 12 to plastically deform so as to fall outward. As a result, each engagement portion 12 engages with the edge of the fitting hole 6, and the circulation member 5 is fixed inside the fitting hole 6 of the nut 3.

[0030] Here, in a state where the circulation member 5 is inserted into the fitting hole 6 (a state before each engaging portion 12 is crimped), as shown in Fig. 10, each engaging portion 12 is formed in an arc shape centered on the center of the fitting hole 6. In this embodiment, a pair of crimping portions 23 having the same arc-shaped tapered surfaces 23a as each engaging portion 12 are pressed against each engaging portion 12 formed in such an arc shape.

[0031] 11, tapered surface 23a of each crimping portion 23 is in line contact with inner side surface 12a of each engaging portion 12. That is, since inner side surface 12a of engaging portion 12 and tapered surface 23a of crimping portion 23 are formed in arc-shaped cross sections of the same radius R centered on center P of fitting hole 6, these surfaces 12a, 23a are in line contact with each other.

[0032] As described above, in this embodiment, since the tapered surface 23a of the crimping portion 23 and the inner surface 12a of the engaging portion 12 are in line contact, when the crimping jig 20 is pressed in, as shown in Figure 12, each engaging portion 12, when viewed from the outer diameter side of the nut 3, is plastically deformed so as to spread radially from the center P of the fitting hole 6, and is crimped into an arc shape centered on the center P of the fitting hole 6.

[0033] In contrast, in the conventional case shown in FIG. 13, the crimping tool is brought into point contact with both end portions 120a of the engagement portion 120, so that, as shown by the dotted lines in the figure, both end portions 120a of the engagement portion 120 and the surrounding areas are locally plastically deformed to a large extent, and the shape after crimping is not arc-shaped.

[0034] As described above, in the embodiment of the present invention, the crimping jig 20 is brought into line contact with the engaging portion 12 of the circulation member 5, so that compared to the conventional method of bringing the crimping jig into point contact, the contact area of ​​the crimping jig 20 with the engaging portion 12 is increased, and the stress acting on the crimping jig 20 can be reduced. This makes it possible to avoid application of excessive stress to the crimping jig 20, and therefore makes it possible to suppress deterioration of the crimping jig 20.

[0035] In addition, by bringing the crimping jig 20 into line contact with the engagement portion 12, the position of the circulation member 5 relative to the crimping jig 20 is easily stabilized. Therefore, the positional deviation of the circulation member 5 is suppressed, and the crimping process can be performed with high accuracy. In this embodiment, as shown in FIG. 5, the pair of crimping portions 23 have tapered surfaces 23a, and when the tapered surfaces 23a are pressed against the inner surface 12a of the engagement portion 12, the engagement portion 12 is guided by the tapered surfaces 23a, and the circulation member 5 moves to follow the center line of the crimping jig 20, and the positional deviation of the circulation member 5 is corrected. In particular, in this embodiment, the positional deviation of the circulation member 5 in a direction perpendicular to the axial direction of the screw shaft 2 can be expected to be corrected. That is, in this embodiment, the arm portion 9 of the circulation member 5 is fitted into the screw groove 3a of the nut 3, so that the circulation member 5 is positioned in the axial direction of the screw shaft 2 and in the rotational direction in the fitting hole 6, and therefore the positional deviation of the circulation member 5 is mainly corrected in the direction perpendicular to the axial direction of the screw shaft 2. Furthermore, according to the present invention, correction of positional misalignment of the circulation member 5 is possible not only in the direction perpendicular to the axial direction of the screw shaft 2, but also in the axial direction of the screw shaft 2 and in the rotational direction within the fitting hole 6.

[0036] 1, the circulation member 5 according to this embodiment has a pair of flat surfaces 5b facing in opposite directions, so that when the circulation member 5 is inserted into the fitting hole 6, a gap 15 with a D-shaped cross section is formed between these flat surfaces 5b and the inner peripheral surface of the fitting hole 6. Also, since each flat surface 5b is a surface formed in a direction substantially perpendicular to the axial direction of the screw shaft 2, the presence or absence and the degree of misalignment of the circulation member 5 can be easily confirmed by appearance.

[0037] In addition, the contact area of ​​the crimping jig 20 with the engaging portion 12 is preferably the entire circumferential direction of the engaging portion 12. The "circumferential direction" of the engaging portion 12 here means the circumferential direction of a circle arranged along the arc-shaped engaging portion 12. In this case, the inner surface 12a of the engaging portion 12 crimped in an arc shape has contact marks caused by contact with the crimping jig 20 formed over the entire circumferential direction. In this way, the crimping jig 20 contacts the engaging portion 12 over the entire circumferential direction, so that the crimping process can be performed evenly over the entire circumferential direction of the engaging portion 12, and the stress acting on the crimping jig 20 can also be made even. In the case of crimping by conventional point contact, the contact marks are formed only at the crimping position of the engaging portion 12, and stress concentration occurs. In contrast, in the case where the contact area is the entire circumferential direction of the engaging portion 12 as in the embodiment of the present invention, it is possible to avoid the stress acting on the crimping jig 20 from becoming locally large, so that deterioration of the crimping jig 20 can be more effectively suppressed.

[0038] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be modified as appropriate without departing from the gist of the invention. [Explanation of symbols]

[0039] 1. Ball screw 2 Screw shaft 2a Thread groove 3 Nut 3a Thread groove 4. Ball 5 Circulating parts 6 Fitting hole 12 Engagement part 20 Crimping jig P Center of fitting hole

Claims

1. A nut having a helical thread groove on its inner circumferential surface; A screw shaft having a helical screw groove on an outer circumferential surface thereof; A plurality of balls rollably accommodated between the opposing thread grooves of the nut and the screw shaft; A ball screw including a circulation member that is attached to a fitting hole provided in the nut and circulates the rolling balls, the circulation member has an engagement portion that is crimped and engaged with the fitting hole when the circulation member is attached to the fitting hole, A ball screw characterized in that the engagement portion engages with the fitting hole in a state in which it is tightened in an arc shape centered on the center of the fitting hole when viewed from the outer diameter side of the nut.

2. 2. The ball screw according to claim 1, wherein the engaging portion that is crimped in an arc shape has a contact mark formed over the entire circumferential direction thereof due to contact with a crimping jig.

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