Ball screw

Abstract

To secure the smooth rolling of a ball by accurately performing the positioning of a circulation member with respect to a fitting hole.SOLUTION: In a ball screw including a circulation member 5 which is mounted into a fitting hole 6 provided in a nut 3 for circulating a rolling ball, a pair of gaps 15 are provided between the fitting hole 6 and the circulation member 5 into which jigs 20 are inserted, for positioning the circulation member 5 with respect to the fitting hole 6. The pair of gaps 15 are located on one side and on the other side in the extending direction of a screw shaft, respectively.SELECTED DRAWING: Figure 10

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 (JP Patent Publication No. 4756645) discloses a method of fixing a circulation member in a fitting hole provided in a nut. In this case, the circulation member is inserted into the fitting hole, and then a convex engagement portion provided on the circulation member is tilted outward to engage (cinch) with the edge of the fitting hole. This fixes the circulation member in the fitting hole and prevents the circulation member from falling off the nut. In addition, when the circulation member is fixed in the fitting hole, adjacent thread grooves of the nut are connected by the connecting groove of the circulation member, so that the balls are guided along the connecting groove to circulate in the thread groove. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4756645 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described configuration in which the circulation member is attached to the fitting hole of the nut, the fitting hole is formed slightly larger than the circulation member in order to make it easier to insert the circulation member into the fitting hole. Therefore, when the circulation member is attached to the fitting hole, a gap is generated between the connecting groove of the circulation member and the thread groove of the nut.

[0006] Since such gaps become steps when the balls roll, it is preferable that the gaps are uniform in order for the balls to roll smoothly. However, if the positioning accuracy of the circulation member relative to the fitting hole is poor, the installation position of the circulation member will vary, and the gaps will also vary. In that case, the steps will also become large in places where the gaps are particularly large, which may hinder the smooth rolling of the balls.

[0007] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a ball screw that can accurately position a circulation member relative to a fitting hole and ensure smooth rolling of the balls. [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 thread groove of the nut and the thread groove of the screw shaft inserted into the nut, and a circulation member mounted in a fitting hole provided in the nut and circulating the rolling balls, wherein a pair of gaps are provided between the fitting hole and the circulation member for inserting a jig for positioning the circulation member relative to the fitting hole, and the pair of gaps are located on one side and the other side in the extension direction of the screw shaft, respectively.

[0009] In this way, in the ball screw according to the present embodiment, a pair of gaps are provided between the fitting hole and the circulation member, into which a jig for positioning the circulation member can be inserted, so that the circulation member can be positioned with high precision by inserting the jig into the gap. As a result, the variation in the gap between the circulation member and the nut can be reduced, so that smooth rolling of the balls can be ensured. Here, the one side and the other side in the extending direction of the screw shaft refer to one side and the other side when the direction in which the axis of the screw shaft extends is the axial direction.

[0010] It is preferable that the center of the circulation member is arranged so as to coincide with the center of the fitting hole. By mounting the circulation member so that the center of the circulation member coincides with the center of the fitting hole, the gap between the circulation member and the nut becomes uniform, so that the balls can roll more smoothly.

[0011] The circulation member may also have a non-flat contact surface that comes into contact with the portion of the jig that is inserted into the pair of gaps. Effect of the Invention

[0012] According to the present invention, the circulation member can be accurately positioned relative to the fitting hole, and smooth rolling of the balls can be ensured. [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] 13 is a diagram showing a state in which the center of the circulation member coincides with the center of the fitting hole. FIG. [Figure 6] 13 is a diagram showing a state in which the center of the circulation member is offset from the center of the fitting hole. FIG. [Figure 7] FIG. 2 is a perspective view of a jig according to the present embodiment. [Figure 8] FIG. 2 is a side view of the jig according to the embodiment. [Figure 9] 9 is a cross-sectional view of the jig according to the present embodiment taken along line AA in FIG. 8. [Figure 10] 11A and 11B are diagrams for explaining a method of fixing the circulation member. [Figure 11] 11A and 11B are diagrams for explaining a method of fixing the circulation member. [Figure 12] FIG. 13 is a perspective view of a circulation member and a jig according to another embodiment of the present invention. [Figure 13] 13 is a diagram showing a state in which a circulation member is positioned by a jig according to another embodiment of the present invention. FIG. 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] Here, in the configuration in which the circulation member 5 is mounted in the fitting hole 6 of the nut 3 as in the above embodiment, the positioning accuracy of the circulation member 5 relative to the fitting hole 6 affects the rolling property of the balls 4. That is, as in the example shown in FIG. 5, when the circulation member 5 is mounted so that the center O of the circulation member 5 coincides with the center P of the fitting hole 6, the gaps S1 and S2 between the connecting groove 5a of the circulation member 5 and the screw groove 3a of the nut 3 can be made uniform, but as in the example shown in FIG. 6, when the center O of the circulation member 5 is shifted from the center P of the fitting hole 6 and the circulation member 5 is mounted offset, the gaps S1 and S2 between the connecting groove 5a of the circulation member 5 and the screw groove 3a of the nut 3 vary (S1>S2). In this way, when the gaps S1 and S2 vary, the step between the connecting groove 5a of the circulation member 5 and the screw groove 3a of the nut 3 becomes large, especially in the area where the gap is large (gap S1 in FIG. 6), so that the smooth rolling of the balls 4 may be hindered.

[0024] Therefore, in the ball screw according to this embodiment, in order to accurately position the circulation member 5 relative to the fitting hole 6, the following jig is used to fix the circulation member 5. The configuration of the jig used in this embodiment and the method of fixing the circulation member 5 using the jig (the manufacturing method of the ball screw) are described below.

[0025] 7 is a perspective view of a jig used in this embodiment, FIG. 8 is a side view of the jig, and FIG. 9 is a cross-sectional view of the jig taken along line AA in FIG.

[0026] 7 to 9, the jig 20 has a cylindrical main body 21, a pair of positioning portions 22, and a pair of crimping portions 23. The pair of positioning portions 22 and the pair of crimping portions 23 are each provided to protrude in the longitudinal direction from one end of the main body 21 in the longitudinal direction. The pair of positioning portions 22 protrude more than the crimping portions 23 and are disposed at a distance from each other. On the other hand, the pair of crimping portions 23 protrude less than the positioning portions 22 and are disposed at a distance from each other in a direction intersecting or perpendicular to the direction in which the positioning portions 22 face each other.

[0027] Each crimping portion 23 has an inclined surface 23a that is inclined toward the center line L (see FIG. 9) of the main body portion 21 toward its tip. The inclined surface 23a functions as a pressing portion that presses the engaging portion 12 when the engaging portion 12 of the circulation member 5 is crimped.

[0028] Meanwhile, the pair of positioning portions 22 are formed in a D-shaped cross section consisting of an arc portion and a straight portion in a cross section perpendicular to the center line L of the main body portion 21. That is, each positioning portion 22 has a flat surface portion 22a arranged so as to face the center line L side (inside) of the main body portion 21, and an arc surface portion 22b arranged so as to face the opposite side to the center line L side (outside).

[0029] To attach the circulation member 5 to the nut 3 using the jig 20 of the above embodiment, first, the circulation member 5 is inserted into the fitting hole 6 from the inner diameter side of the nut 3, and then, as shown in Figure 10, the positioning portion 22 of the jig 20 is inserted into the gap 15 between the circulation member 5 and the fitting hole 6.

[0030] 1 and 3, in this embodiment, the circulation member 5 has a pair of flat portions 5b facing in opposite directions, and therefore, when the circulation member 5 is inserted into the fitting hole 6, a gap 15 having a D-shaped cross section is formed between these flat portions 5b and the inner circumferential surface of the fitting hole 6. Then, into this D-shaped gap 15, a positioning portion 22 having the same D-shaped cross section is inserted.

[0031] In this manner, in this embodiment, D-shaped gaps 15 are provided at positions on one side and the other side in the extending direction of the screw shaft 2 between the fitting hole 6 and the circulation member 5, and the circulation member 5 can be positioned in the fitting hole 6 by inserting a pair of positioning parts 22 into these gaps 15. That is, as shown in FIG. 10, when the positioning parts 22 are inserted into the gaps 15, the flat surface parts 22a of the positioning parts 22 come into contact with the flat surface parts 5b of the circulation member 5, and the arc surface parts 22b of each positioning part 22 come into contact with the inner peripheral surface of the fitting hole 6, so that the displacement (positional deviation) of the circulation member 5 in the fitting hole 6 is restricted by the pair of positioning parts 22. As a result, the circulation member 5 is positioned with respect to the fitting hole 6 with high accuracy.

[0032] Then, when the circulation member 5 is positioned, the jig 20 is further pushed into the fitting hole 6, whereby the pair of engagement portions 12 of the circulation member 5 are pressed by the inclined surfaces 23a of the pair of crimping portions 23, and each engagement portion 12 is pressed down (crimped) outward, as shown by the two-dot chain lines in Fig. 11. As a result, each engagement portion 12 engages with the edge of the fitting hole 6, and the circulation member 5 is fixed to the nut 3.

[0033] As described above, in this embodiment, the gap 15 between the fitting hole 6 and the circulation member 5 is used as a gap for inserting the jig 20 (positioning portion 22) for positioning the circulation member 5, thereby enabling the circulation member 5 to be positioned with high precision relative to the fitting hole 6. As a result, as shown in Fig. 5, the center O of the circulation member 5 and the center P of the fitting hole 6 can be aligned, and the gaps S1 and S2 between the connecting groove 5a of the circulation member 5 and the thread groove 3a of the nut 3 can be made uniform, ensuring smooth rolling of the balls.

[0034] The position of the center O of the circulation member 5 does not necessarily have to coincide with the center P of the fitting hole 6. Even in such a case, by using the jig 20 according to this embodiment, it is possible to reduce the positional deviation of the circulation member 5 with respect to the fitting hole 6, thereby improving the positioning accuracy and achieving smooth rolling of the balls.

[0035] It is preferable that the pair of flat surfaces 5b of the circulation member 5 are machined surfaces such as by cutting or grinding. In this case, each flat surface 5b can be more accurately aligned with the surface of the positioning portion 22, thereby improving the positioning accuracy. In addition, 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.

[0036] Moreover, the jig 20 is preferably a jig having the positioning portion 22 and the crimping portion 23 integrally as in the above embodiment. By the jig 20 having the positioning portion 22 and the crimping portion 23 integrally, the positioning and fixing (crimping) of the circulation member 5 with respect to the fitting hole 6 can be performed using one jig 20, improving the working efficiency. Moreover, in the above embodiment, each engagement portion 12 is formed at a position perpendicular to the position of the gap 15 (flat portion 5b) so that the positioning and fixing (crimping) of the circulation member 5 can be performed simultaneously using one jig 20.

[0037] In addition, in the above-mentioned method, the case where the circulation member 5 is inserted into the fitting hole 6 and then the positioning portion 22 of the jig 20 is inserted has been described as an example, but the procedure for positioning the circulation member 5 is not limited to the above-mentioned method. For example, the positioning portion 22 may be inserted into the fitting hole 6 before the circulation member 5, and then the circulation member 5 may be inserted into the fitting hole 6 to be positioned.

[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.

[0039] 12, a convex portion 220 having a semicircular cross section may be provided on the flat surface portion 22a of each positioning portion 22 of the jig 20, and a concave portion 50 having a semicircular cross section may be provided on each flat surface portion 5b of the circulation member 5. In this case, as shown in FIG. 13, when the positioning portions 22 of the jig 20 are inserted on both sides of the circulation member 5, the convex portion 220 of the positioning portion 22 fits into the concave portion 50 of the circulation member 5, thereby positioning the circulation member 5 within the fitting hole 6. In this way, the convex portion 220 and the concave portion 50 that fit into each other may be provided on the flat surface portion 22a of the positioning portion 22 and the flat surface portion 5b of the circulation member 5, to position the circulation member 5. That is, the circulation member 5 and the jig 20 may have non-flat contact surfaces (convex portion 220 and concave portion 50) that come into contact with each other between the circulation member 5 and a portion (positioning portion 22) of the jig 20 inserted into a gap located on one side and the other side in the extension direction of the screw shaft 2 between the fitting hole 6 and the circulation member 5. Furthermore, the shapes of the convex portion 220 and the concave portion 50 may be shapes other than a semicircular cross section, and contrary to the examples of Figs. 12 and 13, a concave portion may be provided in the jig 20 and a convex portion that fits into the concave portion may be provided in the circulation member 5. [Explanation of symbols]

[0040] 1. Ball screw 2 Screw shaft 2a Thread groove 3 Nut 3a Thread groove 4. Ball 5 Circulating parts 5a Connection groove 6 Fitting hole 15. Gap 20 Jig 21 Main body 22 Positioning section 23 Crimping part

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 screw groove of the nut and the screw groove of the screw shaft inserted into the nut; A ball screw including a circulation member that is attached to a fitting hole provided in the nut and circulates the rolling balls, A ball screw characterized in that a pair of gaps are provided between the fitting hole and the circulation member, into which a jig for positioning the circulation member relative to the fitting hole is inserted, and the pair of gaps are respectively located on one side and the other side of the extension direction of the screw shaft.

2. The ball screw according to claim 1 , wherein the center of the circulation member is aligned with the center of the fitting hole.

3. 3. The ball screw according to claim 1, wherein the circulation member has a non-flat contact surface that contacts a portion of the jig that is inserted into the pair of gaps.

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