Ball screw

Abstract

To provide a ball screw which can be reduced in size, and can secure seal performance while suppressing a cost of a component.SOLUTION: A ball screw has a screw shaft in which a spiral external peripheral screw groove is formed at an external peripheral face, a nut disposed around the screw shaft, in which a spiral internal peripheral screw groove is formed at an internal peripheral face while opposing the external peripheral screw groove, a plurality of balls accommodated in a ball rolling path which is formed of the external peripheral screw groove and the internal peripheral screw groove which oppose each other, a circulation member for circulating the plurality of balls in the ball rolling path, and a contact seal arranged between an end part of the nut and the screw shaft. The external peripheral screw groove has a grinding relief groove, the contact seal is an elastically-deformable annular plate material, and an internal peripheral edge abuts on the external peripheral face of the screw shaft, and has a protrusion which is fit into the grinding relief groove.SELECTED DRAWING: Figure 3

Description

Technical Field

[0006] , , , ,

[0001] The present invention relates to ball screws.

Background Art

[0002] A ball screw includes a nut having a spiral groove formed on its inner peripheral surface, a screw shaft having a spiral groove formed on its outer peripheral surface, and balls disposed between the tracks formed by the spiral groove of the nut and the spiral groove of the screw shaft. The nut moves relative to the screw shaft as the balls roll within the tracks. Usually, in order to suppress the intrusion of foreign matter into the nut and prevent the lubricant inside the nut from leaking out to ensure the lubrication state inside the nut, contact seals that contact the surface of the screw shaft are attached to both ends of the nut.

[0003] By the way, during the manufacture of the screw shaft, a rotating grinding wheel is brought into contact with the surface of the screw groove to perform grinding of the screw groove. However, there is a risk that the grinding wheel and the surface of the screw groove may seize due to frictional heat, or the screw shaft may undergo thermal deformation. In order to avoid such problems, a grinding relief groove is formed at the center of the screw groove to suppress heat generation during grinding.

[0004] On the other hand, when a grinding relief groove is provided in a ball screw employing a contact seal, a gap may occur between the contact seal and the grinding relief groove, which may prevent the intrusion of foreign matter and the leakage of lubricant.

[0005] In contrast, Patent Document 1 discloses a ball screw having a screw shaft provided with a grinding relief groove and provided with a first seal and a second seal at the axial end portions of the nut. According to such a ball screw, during its operation, the first seal slidably contacts the groove surface of the screw groove of the screw shaft, and the second seal fits into and slidably contacts the grinding relief groove, thereby being able to prevent the intrusion of foreign matter and the leakage of lubricant despite having a grinding relief groove.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Application Publication No. 05-44810 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the ball screw described in Patent Document 1 has two seals, which increases the axial length of the nut, preventing miniaturization of the ball screw and increasing component costs. Furthermore, the presence of two seals increases the sliding resistance during ball screw operation.

[0008] This invention has been made in view of the above problems, and aims to provide a ball screw that can be miniaturized and parts costs can be reduced while ensuring sealing performance. [Means for solving the problem]

[0009] The ball screw of the present invention is A screw shaft having a helical outer thread groove formed on its outer surface, A nut is arranged around the screw shaft, and has a helical inner screw groove formed on its inner surface opposite to the outer screw groove, A plurality of balls housed in a ball rolling path formed by the opposing outer circumferential screw groove and the inner circumferential screw groove, A circulation member for circulating the plurality of balls in the ball rolling path, It has a contact seal positioned between the end of the nut and the screw shaft, The aforementioned outer circumferential screw groove has a grinding relief groove, The contact seal is an elastically deformable annular plate material, the inner edge of which abuts against the outer surface of the screw shaft, and the protrusion which fits into the grinding relief groove. It is characterized by the following: [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a ball screw that can be miniaturized and parts costs can be reduced while ensuring sealing performance. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a plan view of the ball screw according to this embodiment. [Figure 2] Figure 2 is a cross-sectional view AA of the ball screw in Figure 1. [Figure 3] Figure 3 shows the end of the nut as viewed in the direction of arrow B in Figure 1, with the seal retainer and contact seal attached. [Figure 4] Figure 4 shows the contact seal as viewed along the axial direction of the ball screw. [Figure 5] Figure 5 shows the contact seal viewed perpendicular to the axis of the ball screw. [Figure 6] Figure 6 is an enlarged cross-sectional view along the axial direction of the screw groove, showing the convex portion of the contact seal in place. [Figure 7] Figure 7 shows a modified contact seal viewed in the axial direction of the ball screw. [Figure 8] Figure 8 is an enlarged cross-sectional view of the modified screw groove along its axial direction. [Figure 9] Figure 9 illustrates the configuration of a contact seal according to another modified example. [Modes for carrying out the invention]

[0012] Hereinafter, one embodiment of the ball screw according to the present invention will be described in detail with reference to the drawings. Figure 1 is a plan view of the ball screw according to this embodiment, and Figure 2 is a cross-sectional view AA of the ball screw in Figure 1. Figure 3 is a view of the end of the nut in the direction of arrow B in Figure 1 with the seal retainer and contact seal attached. Figure 4 is a view of the contact seal in the direction of the axial direction of the ball screw, and Figure 5 is a view of the contact seal in the direction perpendicular to the axis of the ball screw.

[0013] As shown in FIGS. 1 and 2, the ball screw 1 includes a screw shaft 3 having a spiral screw groove (outer peripheral screw groove) 3a on its outer peripheral surface, a nut 5 disposed around the screw shaft 3 and having a spiral screw groove (inner peripheral screw groove) 5a on its inner peripheral surface facing the screw groove 3a of the screw shaft 3, a plurality of balls 9 rotatably accommodated in a spiral ball rolling path formed by both screw grooves 3a and 5a, a lubricant (not shown) for lubricating between both screw grooves 3a and 5a and the balls 9, and annular contact seals 19, 19 attached to both axial ends of the nut 5. A grinding relief groove 3b extending spirally is formed at the center of the screw groove 3a.

[0014] When the nut 5 screwed onto the screw shaft 3 via the balls 9 and the screw shaft 3 are relatively rotated by, for example, a motor not shown, the screw shaft 3 and the nut 5 relatively linearly move in the axial direction via the rolling of the balls 9. The cross-sectional shapes of the screw grooves 3a and 5a may be arc-shaped or may be a Gothic arc shape forming a substantially V shape by combining two arcs with different centers of curvature.

[0015] A part of the outer peripheral surface of the nut 5 is flattened to form a flat surface portion 13 parallel to the axial direction. A return tube (circulation member) 15 bent in a substantially U shape to form an endless ball circulation path by communicating the start point and the end point of the ball rolling path is fixed to the flat surface portion 13 by a tube retainer 17. The nut 5 is provided with a pair of through holes that open to the flat surface portion 13 and communicate with the screw groove 5a of the nut 5, and both ends of the return tube 15 are inserted into both through holes from the flat surface portion 13 side. And the central portion of the return tube 15 located outside the through holes is disposed on the flat surface portion 13.

[0016] The ball 9 that rolls within the ball rolling path is adapted to be circulated through this return tube 15. That is, the ball 9 moves within the ball rolling path and rotates around the screw shaft 3 a plurality of times, and then at the end point of the ball rolling path (the intersection of the return tube 15 and the ball rolling path), it is scooped up into the return tube 15 from one end (opening) of the return tube 15. The scooped-up ball 9 passes through the return tube 15 and is returned from the other end (opening) of the return tube 15 to the starting point of the ball rolling path. Thus, since the ball 9 rolling within the ball rolling path is infinitely circulated by the return tube 15 that connects the starting point and the end point of the ball rolling path, the screw shaft 3 and the nut 5 can continuously move relative to each other in a straight line.

[0017] In FIG. 4, the outer periphery of each contact seal 19 is circular, and the inner periphery has a non-circular shape substantially the same as the cross-sectional shape obtained when orthogonal to the axis of the screw shaft 3, but at one location on the inner periphery, it has a convex portion 19a that protrudes radially inward. The convex portion 19a of the present embodiment is arc-shaped when viewed in the axial direction of the screw shaft 3. Further, the contact seal 19 includes three through holes 19b at equal angles along the circumferential direction.

[0018] Each contact seal 19 preferably has a uniform plate thickness and is formed of an elastic material such as resin, rubber, or elastomer. For example, the contact seal 19 can be formed accurately and at low cost by irradiating a plate-shaped material with a laser for cutting or punching and forming with a mold.

[0019] By making the contact seal 19 an elastic body that can be elastically deformed, its inner peripheral edge can easily adhere to the outer peripheral surface of the screw shaft 3, and particularly when the convex portion 19a fits into the grinding relief groove 3b, it can easily adhere, so that the sealing performance can be ensured. Also, since the convex portion 19a is also elastically deformable, it is not necessary to accurately match the thickness of the convex portion 19a and the width of the grinding relief groove 3b, and it is possible to provide the merit of reducing the component cost.

[0020] In Figure 2, each end face of the nut 5 has three female screw holes 5b (only one shown) formed at equal angles along the circumferential direction. The annular seal retaining plate 21 attached to both end faces of the nut 5 has three through holes 21a (only one shown) at equal angles along the circumferential direction.

[0021] Each contact seal 19 is positioned so as to be sandwiched between the end face of the nut 5 and the annular seal retaining plate 21. The contact seal 19 is attached to the nut 5 by screwing a fixing screw 23, which is inserted through the through hole 21a of the seal retaining plate 21 and the through hole 19b of the contact seal 19, into the female screw hole 5b of the nut 5. With the screw shaft 3 assembled, the inner circumferential edge of the contact seal 19 abuts against the outer circumference of the screw shaft 3 almost all the way around. In addition, the protrusion 19a fits into the grinding relief groove 3b.

[0022] Figure 6 is an enlarged cross-sectional view along the axial direction of the screw groove 3a, showing the state in which the protrusion 19a of the contact seal is positioned. The plate thickness T of the contact seal 19 (i.e., the protrusion 19a) is approximately equal to the width W of the grinding relief groove 3b of the screw shaft 3. Also, the convex cross-sectional shape of the protrusion 19a is approximately equal to the concave cross-sectional shape of the grinding relief groove 3b. Note that plate thickness T refers to the thickness of the contact seal 19 in the axial direction of the ball screw, and width W refers to the groove width of the grinding relief groove 3b in the axial direction of the ball screw.

[0023] The contact seal 19 is pre-equipped with a tightening allowance that takes into account the shape of the screw shaft 3. Therefore, when assembled to the screw shaft 3, it undergoes elastic deformation that expands its inner circumference, allowing it to tightly adhere to the outer circumference of the screw shaft 3. Furthermore, because the contact seal 19 is elastically deformable, even if the convex cross-sectional shape of the protrusion 19a and the concave cross-sectional shape of the grinding relief groove 3b do not perfectly match, the protrusion 19a will elastically deform to conform to the grinding relief groove 3b when in contact with it, thus ensuring a sealing performance.

[0024] By making such a contact seal 19 contact the entire area of ​​the screw shaft 3 of the ball screw 1 (i.e., the outer circumference of the screw shaft 3, the screw groove 3a, and the grinding relief groove 3b), it is possible to perform a sealing function that prevents leakage of lubricant (grease or lubricating oil) and the intrusion of foreign matter. Furthermore, since the contact seal 19 that contacts the screw shaft 3 is only the inner circumference portion (including the protrusion 19a) which has a plate thickness T, the sliding resistance during the operation of the ball screw can be significantly reduced compared to when it contacts the entire screw groove 3a. Moreover, since the contact seal 19 is made of a thin plate material, it does not take up much space when attached to the nut 5, and the ball screw 1 can be made smaller.

[0025] (modified version) Figure 7 shows a modified contact seal 19A viewed in the axial direction of the ball screw. Figure 8 is an enlarged cross-sectional view along the axial direction of the screw groove 3Aa, showing the convex portions 19Aa of the contact seal spaced apart.

[0026] As shown in Figure 7, the contact seal 19A of this modified example has a protrusion 19Aa that projects in a rectangular shape when viewed in the axial direction of the ball screw. Also, as shown in Figure 8, when viewed in a direction perpendicular to the axis of the screw shaft 3A, the grinding relief groove 3Ab of the screw shaft 3A has a rectangular cross-section. The other configurations are the same as those of the embodiment described above.

[0027] According to this modified example, when the protrusion 19Aa is fitted into the grinding relief groove 3Ab, both sides of the protrusion 19Aa in the axial direction of the screw shaft 3A abut against both side walls of the grinding relief groove 3Ab, and the tip of the protrusion 19Aa abuts against the bottom surface of the grinding relief groove 3Ab. As a result, the sealing area is increased, and the sealing effect can be further enhanced.

[0028] Figure 9(a) is a plan view of a contact seal assembled on a screw shaft, viewed perpendicular to the axis, and schematically shows its deformation. Figures 9(a) and (b) are views of the area around the protrusion of a contact seal according to another modified example, viewed in the direction of arrow B in Figure 9(a).

[0029] Since the contact seal 19 is positioned to extend perpendicular to the axis of the screw shaft 3, when the inner circumference of the contact seal 19, which has been fitted with an overlap, comes into contact with the helical screw groove 3a, the contact seal 19 deforms in a complex manner along its curved surface. Specifically, as shown in Figure 9(a), when the screw shaft 3 is viewed from above, the inner circumference of one side of the contact seal 19 that abuts the right side of the screw groove 3a in the figure (left side when viewed in the direction of arrow B) deforms to the left as indicated by arrow L, and the inner circumference of the other side of the contact seal 19 that abuts the left side of the screw groove 3a in the figure (right side when viewed in the direction of arrow B) deforms to the right as indicated by arrow R. Thus, the direction of deformation of the contact seal 19 reverses with respect to the bottom of the screw groove 3a. Therefore, if a convex portion 19a is formed in the center of the upper part of the inner circumference of the contact seal 19, internal stress will be generated in the convex portion 19a such that it twists in opposite directions on both sides with respect to its center.

[0030] In contrast, the contact seal 19B according to another modification, as shown in Figure 9(b), has a slit 19Bc formed in the center of the protrusion 19Ba, extending radially outward from the inner periphery. As a result, when the deformation of the contact seal 19B reverses on both the left and right sides, the left side of the protrusion 19Ba tends to deform towards the front in Figure 9(b), and the right side of the protrusion 19Ba tends to deform towards the back in Figure 9(b). In this way, forming a slit 19Bc in the protrusion 19Ba can mitigate the effects of the reversal of the deformation direction of the contact seal 19B. It is preferable that the far end (upper end) of the slit 19Bc be formed in a curved shape (without a notch) as seen in Figure 9(b) to avoid stress concentration.

[0031] In the contact seal 19B shown in Figure 9(b), one slit 19Bc is provided. However, as in the contact seal 19C shown in Figure 9(c), three slits 19Cc can be formed parallel to each other on the protrusion 19Ca, or two or four or more slits can be formed.

[0032] It should be noted that the present invention is not limited to the embodiments described above. Within the scope of the present invention, any component of the embodiments described above can be modified. Furthermore, any component can be added to or omitted in the embodiments described above.

[0033] In this embodiment, the ball circulation method of the ball screw is a tube type, but the present invention is applicable to any circulation method of the ball screw, regardless of the ball screw circulation method, for example, a ball type, a deflector type, an end cap type, or an end deflector type. [Explanation of symbols]

[0034] 1 Ball screw 3. 3A Screw shaft 3a, 3Aa thread grooves 3b, 3Ab Grinding relief groove 5 nuts 5a Screw groove 9 Balls 15 Return Tube 19, 19A, 19B, 19C Contact seals 19a, 19Aa, 19Ba, 19Ca convex portion 19Bc, 19Cc slit 21 Seal retaining plate 23 Fixing screws

Claims

1. A screw shaft having a helical outer thread groove formed on its outer surface, A nut is arranged around the screw shaft, and has a helical inner screw groove formed on its inner surface opposite to the outer screw groove, A plurality of balls housed in a ball rolling path formed by the opposing outer circumferential screw groove and the inner circumferential screw groove, A circulation member for circulating the plurality of balls in the ball rolling path, It has a contact seal positioned between the end of the nut and the screw shaft, The aforementioned outer circumferential screw groove has a grinding relief groove, The contact seal is an elastically deformable annular plate material, the inner edge of which abuts against the outer surface of the screw shaft, The contact seal has a projection at least at one location on its inner periphery that protrudes radially inward from the inner periphery and fits into the grinding relief groove. A ball screw characterized by the following features.

2. The thickness of the protrusion of the contact seal is approximately equal to the width of the grinding relief groove. The ball screw according to feature 1.

3. The protrusion of the contact seal is arc-shaped when viewed in the axial direction of the screw shaft. A ball screw according to claim 1 or 2, characterized by the features described above.

4. The protrusion of the contact seal is rectangular in shape when viewed in the axial direction of the screw shaft. A ball screw according to claim 1 or 2, characterized by the features described above.

5. The protrusion of the contact seal has a slit that extends radially outward from the inner periphery of the contact seal. A ball screw according to claim 1 or 2, characterized by the features described above.

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