Ball screw

Abstract

A ball screw is provided with: a screw shaft in which a helical outer peripheral thread groove is formed in the outer peripheral surface; a nut disposed around the screw shaft and having a helical inner peripheral thread groove formed on the inner peripheral surface thereof so as to face the outer peripheral thread groove; a plurality of balls accommodated in a ball rolling path formed by the outer peripheral thread groove and the inner peripheral thread groove which face each other; a circulation means for circulating the plurality of balls in the ball rolling path; and a contact seal disposed between the end portion of the nut and the screw shaft, the outer peripheral thread groove having a grinding relief groove, the contact seal being an elastically deformable annular plate material, the inner peripheral edge of the contact seal being in contact with the outer peripheral surface of the screw shaft, and the contact seal having a convex portion fitted to the grinding relief groove.

Description

Technical Field

[0001] The present invention relates to a ball screw. Background Art

[0002] A ball screw includes: a nut having a spiral groove formed on an inner peripheral surface; a screw shaft having a spiral groove formed on an outer peripheral surface; and balls disposed between raceways formed by the spiral groove of the nut and the spiral groove of the screw shaft. The balls roll within the raceways, whereby the nut moves relative to the screw shaft. In general, in order to suppress foreign matter from entering the nut or to suppress leakage of the lubricant within the nut to the outside of the nut to ensure the lubrication state within the nut, contact seals that contact the surface of the screw shaft are attached to both ends of the nut.

[0003] However, when manufacturing the screw shaft, a rotating grinding wheel is brought into contact with the surface of the thread groove to perform grinding of the thread groove. However, there is a possibility that the grinding wheel and the surface of the thread groove are ablated due to frictional heat, or the screw shaft undergoes thermal deformation or the like. In order to avoid such problems, a grinding relief groove is formed in the center of the thread groove to suppress heat generation during grinding.

[0004] On the other hand, in the case where a grinding relief groove is provided in a ball screw employing contact seals, a gap is generated between the contact seal and the grinding relief groove, and thus there is a possibility that foreign matter cannot be prevented from entering or the lubricant cannot be prevented from leaking.

[0005] In contrast, Patent Document 1 discloses a ball screw having a screw shaft with a grinding relief groove, and a first seal and a second seal are provided at the axial end portions of the nut. According to this ball screw, during its operation, the first seal slidably contacts the groove surface of the thread groove of the screw shaft, and the second seal slidably contacts the grinding relief groove in an engaged state. Thus, even though there is a grinding relief groove, it is possible to prevent foreign matter from entering and the lubricant from leaking.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent Laid-Open No. 05-44810 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] However, in the ball screw of Patent Document 1, since two seals are provided, there are problems that the axial length of the nut becomes longer, miniaturization of the ball screw cannot be achieved, and the component cost also increases. Further, since two seals are provided, there is also a problem that the sliding resistance during the operation of the ball screw increases.

[0011] The present invention has been completed in view of the above problems, and an object thereof is to provide a ball screw that can be miniaturized, suppress component costs, and ensure sealing performance.

[0012] Means for Solving the Problems

[0013] The ball screw of the present invention is characterized by comprising:

[0014] a lead screw shaft having a spiral outer peripheral thread groove formed on an outer peripheral surface thereof;

[0015] a nut disposed around the lead screw shaft and having a spiral inner peripheral thread groove formed on an inner peripheral surface thereof so as to face the outer peripheral thread groove;

[0016] a plurality of balls housed in a ball rolling path formed by the opposed outer peripheral thread groove and inner peripheral thread groove;

[0017] a circulation member for circulating the plurality of balls in the ball rolling path; and

[0018] a contact seal disposed between an end portion of the nut and the lead screw shaft,

[0019] wherein the outer peripheral thread groove has a grinding relief groove,

[0020] the contact seal is an annular plate capable of elastic deformation, an inner peripheral edge thereof abuts against an outer peripheral surface of the lead screw shaft, and the contact seal has a convex portion fitted into the grinding relief groove.

[0021] Advantages of the Invention

[0022] According to the present invention, it is possible to provide a ball screw that can be miniaturized and ensure sealing performance while suppressing component costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a plan view of the ball screw according to the present embodiment.

[0024] Figure 2 is Figure 1 a sectional view taken along line A-A of the ball screw.

[0025] Figure 3 is a view of an end portion of the nut observed in the direction of arrow B in a state where a seal pressing member and a contact seal are mounted along Figure 1 the ball screw.

[0026] Figure 4 is a view of the contact seal observed along the axial direction of the ball screw.

[0027] Figure 5It is a view of the contact seal observed in the direction orthogonal to the axis of the ball screw.

[0028] Figure 6 It is an enlarged cross-sectional view along the axial direction of the thread groove shown in the state where the convex portion provided with the contact seal is arranged.

[0029] Figure 7 It is a view of the contact seal of the modified example observed from the axial direction of the ball screw.

[0030] Figure 8 It is an enlarged cross-sectional view along the axial direction of the thread groove of the modified example.

[0031] Figure 9 (a) to (c) of [] are views for explaining the structure of the contact seal of another modified example. Figure 9 (a) of [] is a plan view of the contact seal assembled to the screw shaft observed in the direction orthogonal to the axis, and is a view schematically showing its deformation. Figure 9 (b) and (c) of [] are respectively along Figure 9 Views of the periphery of the convex portion of the contact seal of another modified example observed in the direction of arrow B in (a). Detailed Description of the Invention

[0032] Hereinafter, an embodiment of the ball screw of the present invention will be described in detail based on the drawings.

[0033] Figure 1 It is a plan view of the ball screw of the present embodiment. Figure 2 is Figure 1 A - A cross-sectional view of the ball screw of []. Figure 3 It is a view of the end portion of the nut observed in the direction of arrow B in [] in the state where the seal pressing member and the contact seal are installed. Figure 1 Figure 4 It is a view of the contact seal observed from the axial direction of the ball screw. Figure 5 It is a view of the contact seal observed in the direction orthogonal to the axis of the ball screw.

[0034] As Figure 1 and Figure 2 shown, the ball screw 1 includes: a screw shaft 3 having a spiral thread groove (outer peripheral thread groove) 3a on its outer peripheral surface; a nut 5 disposed around the screw shaft 3 and having a spiral thread groove (inner peripheral thread groove) 5a opposed to the thread groove 3a of the screw shaft 3 on its inner peripheral surface; a plurality of balls 9 that are rotatably accommodated in a spiral ball rolling path formed by the two thread grooves 3a, 5a; a lubricant (not shown) that lubricates between the two thread grooves 3a, 5a and the balls 9; and annular contact seals 19, 19 that are installed at both axial ends of the nut 5. A grinding relief groove 3b that also extends spirally is formed at the center of the thread groove 3a.

[0035] Further, when a nut 5 screwed to a lead screw shaft 3 via balls 9 is rotated relative to the lead screw shaft 3 by a motor (not shown), for example, the lead screw shaft 3 and the nut 5 perform relative linear movement in the axial direction via the rolling of the balls 9. In addition, the cross-sectional shape of the thread grooves 3a and 5a may be an arc shape or a Gothic arc shape formed by combining two arcs with different curvature centers to form a substantially V shape.

[0036] A part of the outer peripheral surface of the nut 5 is flatly cut to form a flat surface portion 13 parallel to the axial direction. A return tube (circulation member) 15 bent in a substantially U shape that forms an annular ball circulation path by connecting the start point and the end point of the ball rolling path is fixed to the flat surface portion 13 by a tube pressing member 17. A pair of through holes that open in the flat surface portion 13 and communicate with the thread groove 5a of the nut 5 are provided in the nut 5, and both end portions of the return tube 15 are inserted into the two through holes from the flat surface portion 13 side. And, the central portion of the return tube 15 located outside the through hole is disposed on the flat surface portion 13.

[0037] The balls 9 rolling in the ball rolling path circulate through the return tube 15. That is, after the balls 9 move in the ball rolling path and rotate around the lead screw shaft 3 multiple times, at the end point of the ball rolling path (the intersection of the return tube 15 and the ball rolling path), the balls 9 are scooped up from one end portion (opening portion) of the return tube 15 into the return tube 15. The scooped-up balls 9 pass through the return tube 15 and return to the start point of the ball rolling path from the other end portion (opening portion) of the return tube 15. In this way, the balls 9 rolling in the ball rolling path circulate infinitely through the return tube 15 that connects the start point and the end point of the ball rolling path, so that the lead screw shaft 3 and the nut 5 can continuously perform relative linear movement.

[0038] In Figure 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 the lead screw shaft 3 is orthogonal to the axis, but a convex portion 19a protruding radially inward is provided at one place on the inner periphery. The convex portion 19a of the present embodiment is arc-shaped when viewed in the axial direction of the lead screw shaft 3. In addition, the contact seal 19 is provided with three through holes 19b at equal angles along the circumferential direction.

[0039] Each contact seal 19 has a uniform plate thickness and is preferably formed of an elastic material such as resin, rubber, or elastomer. For example, the contact seal 19 can be formed inexpensively and with high precision by cutting a plate-shaped raw material by irradiating laser or by blanking using a mold.

[0040] By making the contact seal 19 an elastomer capable of elastic deformation, its inner peripheral edge can easily adhere to the outer peripheral surface of the lead screw shaft 3. In particular, the convex portion 19a can easily adhere when engaged with the grinding retraction groove 3b, so that the sealing performance can be ensured. In addition, since the convex portion 19a can also be elastically deformed, it is not necessary to make the thickness of the convex portion 19a exactly the same as the width of the grinding retraction groove 3b, which has the advantage of reducing component costs.

[0041] In Figure 2 In this case, on both end faces of the nut 5, three internal threaded holes 5b (only one is shown in each figure) are formed at equal angles along the circumferential direction. In addition, the annular seal pressing plate 21 mounted on both end faces of the nut 5 has three through holes 21a (only one is shown in each figure) at equal angles along the circumferential direction.

[0042] Each contact seal 19 is arranged in a manner of being clamped between the end face of the nut 5 and the annular seal pressing plate 21. By screwing the fixing screw 23 inserted through the through hole 21a of the seal pressing plate 21 and the through hole 19b of the contact seal 19 into the internal threaded hole 5b of the nut 5, the contact seal 19 is mounted on the nut 5. In a state where the lead screw shaft 3 is assembled, the inner peripheral edge of the contact seal 19 abuts against the outer periphery of the lead screw shaft 3 over substantially the entire circumference. In addition, the convex portion 19a is engaged with the grinding retraction groove 3b.

[0043] Figure 6 It is an enlarged cross-sectional view along the axial direction of the thread groove 3a shown in a state where the convex portion 19a of the contact seal is arranged. The plate thickness T of the contact seal 19 (i.e., the convex portion 19a) is approximately equal to the width W of the grinding retraction groove 3b of the lead screw shaft 3. In addition, the cross-sectional convex shape of the convex portion 19a is approximately equal to the cross-sectional concave shape of the grinding retraction groove 3b. In addition, the plate thickness T refers to the wall thickness of the contact seal 19 in the axial direction of the ball screw, and the width W refers to the groove width of the grinding retraction groove 3b in the axial direction of the ball screw.

[0044] Considering the shape of the lead screw shaft 3, an interference amount is pre-given to the contact seal 19, so that it elastically deforms in a manner of expanding its inner circumference in a state of being assembled to the lead screw shaft 3 and can adhere tightly to the outer periphery of the lead screw shaft 3. In addition, since the contact seal 19 can be elastically deformed, even if it is assumed that the cross-sectional convex shape of the convex portion 19a and the cross-sectional concave shape of the grinding retraction groove 3b are not exactly the same, in a state where the convex portion 19a abuts against the grinding retraction groove 3b, it will elastically deform following the grinding retraction groove 3b, so that the sealing performance can be ensured.

[0045] By bringing such a contact seal 19 into contact with the entire area of the lead screw shaft 3 of the ball screw 1 (i.e., the outer periphery of the lead screw shaft 3, the thread groove 3a, and the grinding relief groove 3b), a sealing function of preventing leakage of lubricant (grease, lubricating oil) and preventing intrusion of foreign matter can be exerted. In addition, the contact seal 19 in contact with the lead screw shaft 3 is only the inner peripheral portion (including the convex portion 19a) of the plate thickness T, so the sliding resistance during the operation of the ball screw can be significantly reduced compared with the case of contacting the entire thread groove 3a. Furthermore, since the contact seal 19 is a thin plate, its volume does not increase when installed in the nut 5, and miniaturization of the ball screw 1 can be achieved.

[0046] (Modification example)

[0047] Figure 7 FIG. is a view of the contact seal 19A of the modification example as viewed in the axial direction of the ball screw. Figure 8 FIG. is an enlarged cross-sectional view along the axial direction of the thread groove 3Aa, showing the convex portion 19Aa of the contact seal in a separated state.

[0048] As Figure 7 shown, the contact seal 19A of this modification example has a convex portion 19Aa that protrudes in a rectangular shape when viewed in the axial direction of the ball screw. In addition, as Figure 8 shown, when viewed in the direction orthogonal to the axis of the lead screw shaft 3A, the grinding relief groove 3Ab of the lead screw shaft 3A has a rectangular cross-section. The other structures are the same as those of the above-described embodiment.

[0049] According to this modification example, when the convex portion 19Aa is fitted into the grinding relief groove 3Ab, both surfaces of the convex portion 19Aa in the axial direction of the lead screw shaft 3A are in contact with the side walls of the grinding relief groove 3Ab, and the top end of the convex portion 19Aa is in contact with the bottom surface of the grinding relief groove 3Ab. Therefore, the sealing area increases, and the sealing effect can be further improved.

[0050] Figure 9 (a) of FIG. is a plan view of the contact seal assembled to the lead screw shaft as viewed in the direction orthogonal to the axis, and is a diagram schematically showing its deformation. Figure 9 (b) and (c) of FIG. are views of the periphery of the convex portion of the contact seal of another modification example as viewed in the direction of arrow B in (a) of FIG. Figure 9 FIG.

[0051] The contact seal 19 is arranged so as to extend in the direction orthogonal to the axis of the lead screw shaft 3. Therefore, when the inner periphery of the contact seal 19 with an interference fit contacts the spiral thread groove 3a, the contact seal 19 deforms complexly along its curved surface. Specifically, as Figure 9As shown in (a) thereof, when looking down at the lead screw shaft 3, the inner periphery of one side (the left side when observed in the direction of arrow B) of the contact seal 19 that abuts against the right side surface in the drawing of the thread groove 3a deforms to the left as shown by arrow L, and the inner periphery of the other side (the right side when observed in the direction of arrow B) of the contact seal 19 that abuts against the left side surface in the drawing of the thread groove 3a deforms to the right as shown by arrow R. With the bottom of the thread groove 3a as the boundary, the deformation directions of the contact seal 19 are opposite. Therefore, if a convex portion 19a is formed at the center of the upper part of the inner periphery of the contact seal 19, internal stress that twists in opposite directions on both sides with its center as the boundary is generated in the convex portion 19a.

[0052] In contrast, as shown in (b) of Figure 9 , in the contact seal 19B of another modification example, a slit 19Bc extending from the inner peripheral edge toward the radially outer side is formed at the center of the convex portion 19Ba. Thus, when the deformation reverses on the left and right sides of the contact seal 19B, the left side of the convex portion 19Ba is likely to deform forward in Figure 9 (b), and the right side of the convex portion 19Ba is likely to deform inward in Figure 9 (b). In this way, by forming the slit 19Bc in the convex portion 19Ba, the influence brought about by the reversal of the deformation direction of the contact seal 19B can be alleviated. In addition, in order to avoid stress concentration, it is preferable that the inner end (upper end) of the slit 19Bc is formed in a curved shape (without a notch) when observed in Figure 9 (b) thereof.

[0053] In addition, in the contact seal 19B shown in (b) of Figure 9 , one slit 19Bc is provided, but for example, like the contact seal 19C shown in (c) of Figure 9 , three slits 19Cc can be formed in parallel on the convex portion 19Ca, or two or four or more slits can be formed.

[0054] In addition, the present invention is not limited to the above-described embodiments. Within the scope of the present invention, any constituent elements of the above-described embodiments can be deformed. In addition, any constituent elements can be added or omitted in the above-described embodiments.

[0055] In the present embodiment, the ball circulation method of the ball screw is set to the tube type, but the present invention does not limit the circulation method of the ball screw, and for example, it can also be applied to any one of the block type, the guide type, the end cap type, and the end guide type circulation methods.

[0056] As described above, various embodiments have been explained, but the present invention is of course not limited to this example. It is obvious that those skilled in the art can conceive of various modification examples or correction examples within the scope described in the claims, and these modification examples or correction examples of course also belong to the technical scope of the present invention. In addition, within the scope not departing from the gist of the invention, the constituent elements in the above-described embodiments can be arbitrarily combined.

[0057] In addition, this application is based on a Japanese patent application filed on October 21, 2022 (Japanese Patent Application No. 2022-169154), the content of which is incorporated herein by reference.

[0058] Explanation of Reference Numerals

[0059] 1 Ball screw

[0060] 3, 3A Lead screw shaft

[0061] 3a, 3Aa Thread groove

[0062] 3b, 3Ab Grinding retraction groove

[0063] 5 Nut

[0064] 5a Thread groove

[0065] 9 Ball

[0066] 15 Return pipe

[0067] 19, 19A, 19B, 19C Contact seal

[0068] 19a, 19Aa, 19Ba, 19Ca Protrusion

[0069] 19Bc, 19Cc Slit

[0070] 21 Seal pressing plate

[0071] 23 Fixing screw

Claims

1. A ball screw, characterized in that, it has: a lead screw shaft, on the outer peripheral surface of which a spiral outer peripheral thread groove is formed; a nut, which is arranged around the lead screw shaft, and on the inner peripheral surface, a spiral inner peripheral thread groove is formed so as to face the outer peripheral thread groove; a plurality of balls, and the plurality of balls are accommodated in a ball rolling path formed by the opposed outer peripheral thread groove and the inner peripheral thread groove; a circulation member for circulating the plurality of balls in the ball rolling path; and a contact seal, which is arranged between the end of the nut and the lead screw shaft, the outer peripheral thread groove has a grinding relief groove, the contact seal is an annular plate capable of elastic deformation, the inner peripheral edge abuts against the outer peripheral surface of the lead screw shaft, and has a convex portion fitted with the grinding relief groove.

2. The ball screw according to claim 1, characterized in that, the plate thickness of the convex portion of the contact seal is substantially equal to the width of the grinding relief groove.

3. The ball screw according to claim 1 or 2, characterized in that, when observed from the axial direction of the lead screw shaft, the convex portion of the contact seal is arc-shaped.

4. The ball screw according to claim 1 or 2, characterized in that, when observed from the axial direction of the lead screw shaft, the convex portion of the contact seal is rectangular.

5. The ball screw according to claim 1 or 2, characterized in that, the convex portion of the contact seal has a slit extending radially outward from the inner peripheral edge of the contact seal.

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