Ball screw

Abstract

To provide a ball screw for enabling common use of components of a sealing mechanism while having lower cost and high assembly accuracy.SOLUTION: A sealing mechanism 40 for sealing a gap between the outer peripheral face of a screw shaft 20 and the inner peripheral face of a nut 30 includes a through-hole 43 having an inner diameter larger than the outer diameter of the screw shaft 20, and further includes a seal base 41 to be fitted and fixed to a circular recessed part 33 formed at one axial end of the nut 30, and a thin type contact seal 42 having a lip part 47 formed in an inner peripheral edge shape similar to the axially right-angled cross section shape of the outer peripheral face of the screw shaft 20, formed in a thin-plate shape, and fixed to an axial side face 41a of the seal base 41 with a tapping screw 51.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a ball screw provided with a sealing mechanism for sealing a gap between a screw shaft and a nut.

Background Art

[0002] A ball screw includes a screw shaft having a spiral outer screw groove formed on its outer peripheral surface, a nut having a spiral inner screw groove formed on its inner peripheral surface, and a plurality of balls rotatably disposed in a ball rolling portion formed by the outer screw groove and the inner screw groove, and converts the relative rotational movement between the screw shaft and the nut into a linear movement. If the lubricant enclosed in the ball screw leaks or foreign matters such as dust and wear powder enter the nut from the outside, smooth movement may be hindered. Generally, in order to prevent leakage of the lubricant enclosed in the ball screw and prevent intrusion of foreign matters from the outside, a sealing mechanism for sealing the gap between the screw shaft and the nut is known.

[0003] Patent Document 1 discloses a ball screw in which one or more notches or slits are provided at the outer edge of a thin contact seal, the outer edge of the thin contact seal is fitted into an annular groove through a seal introduction groove communicating with the annular groove and attached to a nut, and fixed to the screw hole of the nut with screws.

[0004] Patent Document 2 discloses a seal member fixing structure for a ball screw in which radial holes are formed in a nut and a seal member, an anchor with a slit at its tip is inserted into both radial holes of the nut and the seal member, and then a pin member is passed through the anchor to expand the slit to fix the seal member to the nut.

[0005] Further, Patent Document 3 discloses a ball screw in which three through holes are provided in alignment in each of a seal, an annular portion of a seal cap, and an inward flange portion, three planar portions are provided in alignment in a nut, and the seal cap with the seal fixed is fitted onto the nut and screwed to the planar portions.

Prior Art Documents

Patent Document

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, according to the ball screw described in Patent Document 1, in order to fix the seal, it is necessary to machine a tapping hole along the axial direction in the nut, resulting in a problem that the manufacturing cost of the nut becomes high. Also, a method for aligning the screw shaft and the seal is not described.

[0008] Moreover, for the ball screw described in Patent Document 2, since the seal has a thick wall, if the inner peripheral surface shape is made similar to the cross-sectional shape perpendicular to the axis of the screw shaft, it becomes a three-dimensional complex spiral shape, requiring expensive milling. Also, seals with screw shafts having different leads require expensive milling for each lead of the screw shaft, increasing the production cost.

[0009] Furthermore, for the ball screw described in Patent Document 3, since the alignment state between the seal and the screw shaft is determined by the machining accuracy of the three through-screw holes of the seal, the three through-screw holes in the radial and axial directions of the seal cap, and the three flat portions of the nut, respectively, high-precision machining is required for each, resulting in a problem of increased production cost. Also, the assembly accuracy (phase) between the seal and the screw shaft is uniquely determined by the machining accuracy of the parts and cannot be adjusted to an optimal state according to the actual object.

[0010] The present invention has been made in view of the above-described problems, and its object is to provide a ball screw that enables component commonality of the sealing mechanism and has high assembly accuracy at low cost.

Means for Solving the Problem

[0011] Therefore, the above object of the present invention is achieved by the configuration of the following [1] related to the ball screw. [1] A screw shaft having a spiral outer thread groove formed on its outer peripheral surface, A nut having a spiral inner thread groove formed on its inner peripheral surface, A plurality of balls that roll on a ball rolling portion formed by the outer thread groove of the screw shaft and the inner thread groove of the nut, A sealing mechanism provided at at least one axial end of the nut for sealing between the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut, A ball screw comprising: The sealing mechanism is A seal base having a through hole with an inner diameter larger than the outer diameter of the screw shaft, and being fitted and fixed in a recess formed at at least one axial end of the nut, A thin contact seal having a lip portion with an inner peripheral edge shape similar to the axial cross-sectional shape of the outer peripheral surface of the screw shaft, formed in a thin plate shape, and fixed to the axial side surface of the seal base by a tapping screw, A ball screw comprising.

Advantages of the Invention

[0012] According to the ball screw of the present invention, it is possible to make the parts of the sealing mechanism common, and a ball screw with low cost and high assembly accuracy can be obtained.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0014] (First Embodiment) Hereinafter, the ball screw according to the first embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIGS. 1(a) and 1(b), the ball screw 10 of the present embodiment includes a screw shaft 20 having a spiral outer peripheral screw groove 21 on its outer peripheral surface and extending in the axial direction, a nut 30 having a spiral inner peripheral screw groove 31 corresponding to the outer peripheral screw groove 21 of the screw shaft 20 on its inner peripheral surface, and a sealing mechanism 40 disposed at the axial end of the nut 30 to seal the gap between the screw shaft 20 and the nut 30.

[0015] The outer peripheral screw groove 21 of the screw shaft 20 and the inner peripheral screw groove 31 of the nut 30 face each other to form a ball rolling portion 25 therebetween, and a large number of balls 26 as rolling elements are loaded in the ball rolling portion 25 so as to be able to roll together with grease. Thereby, the ball screw 10 converts the rotational motion of the screw shaft 20 and the nut 30 into the linear motion of the nut 30 and the screw shaft 20. Note that only a part of the large number of balls 26 is shown in FIG. 1(b).

[0016] A flange portion 32 is formed on one axial end side of the nut 30 (the left side in FIG. 1(b)). Circular recesses 33 having an inner diameter larger than the groove bottom 31a of the inner peripheral screw groove 31 of the nut 30 are formed coaxially with the inner peripheral screw groove 31 at both axial ends of the nut 30. A sealing mechanism 40 for sealing the gap between the screw shaft 20 and the nut 30 is disposed in the circular recess 33. A moving table of a mechanical device (not shown) or the like is fixed to the flange portion 32 with mounting bolts or the like.

[0017] Also, at both axial ends of the nut 30 (including the flange portion 32), a pair of pilot holes 36, 36 that penetrate radially from the outer peripheral surface 35 into the circular recess 33 are formed at positions with a phase difference of 180°. The axial distance between the axial center of the pilot hole 36 and the side surface 33a of the circular recess 33 is set to L1.

[0018] Generally, in a tube-circulating nut, since holes for tube attachment etc. are machined in the radial direction, the pilot holes 36, which are radial holes, can also be machined in the same process. Compared with axial hole machining, there are fewer setup changes, and the manufacturing cost can be reduced. Also, as will be described later, since the pilot hole 36 is a hole for a tapping screw, female screw machining is not required, and the processing cost can be suppressed.

[0019] The nut 30 also has a ball return passage (not shown) that penetrates axially inside it, and a circulating piece (not shown) that communicates the ball return passage with the ball rolling portion 25 is provided. Then, an infinite circulation passage for the balls 26 is formed by the ball rolling portion 25, one circulating piece, the ball return passage, the other circulating piece, and the ball rolling portion 25. A plurality of balls 26 are loaded into the infinite circulation passage together with a predetermined amount of lubricant (for example, grease).

[0020] The sealing mechanism 40 includes, with reference to FIGS. 2(a) and (b) and FIGS. 3(a) and (b) as well, a seal base 41 that fits into the circular recess 33, and a thin contact seal 42 that is screwed and fixed with a plurality of tapping screws 51 to the side surface 41a on the outer side in the axial direction of the seal base 41.

[0021] The seal base 41 has an outer diameter slightly smaller than the inner diameter of the circular recess 33 and is formed in a substantially annular shape having a through hole 43 at the center that is larger than the outer diameter of the screw shaft 20. The seal base 41 is made of a synthetic resin such as nylon or POM, for example. On the outer peripheral surface 41b of the seal base 41, a pair of tapping screw pilot holes 44, 44 are formed at phases different by 180°. On one side surface (the axially outer side surface in FIGS. 1(a) and (b)) 41a of the seal base 41, three tapping screw pilot holes 45, 45, 45 are provided at phases different by 120°. The tapping screw pilot holes 44, 45 are just holes and do not require female screw processing, so the processing cost is low.

[0022] Also, since the seal base 41 is a member with a simple annular shape, it is easy to process, and if the shaft diameters of the screw shafts are the same, it can be shared by ball screws with different leads.

[0023] The other side surface 41c without the tapping screw pilot hole 45 can be said to be the side surface 41c that becomes the axially inner side of the nut 30 when assembled into the circular recess 33. The axial distance L2 between this side surface 41c and the axial center of the tapping screw pilot hole 44 is smaller than the axial distance L1 between the axial center of the screw pilot hole 36 of the nut 30 and the side surface 33a of the circular recess 33 (L2 < L1). Thereby, when the seal base 41 is incorporated into the circular recess 33, a gap can be secured between the side surface 41c of the seal base 41 and the side surface 33a of the nut 30, and the seal base 41 can be assembled without trouble. Note that the axial centers of the tapping screw pilot hole 44 and the screw pilot hole 36 substantially coincide.

[0024] As shown in FIGS. 3(a) and 3(b), the thin contact seal 42 is formed into a substantially disc shape by press-working a thin resin sheet with a thickness t of 0.5 to 2 mm made of a low-friction engineering resin such as nylon, POM, or Teflon (registered trademark) at a low processing cost. At the center of the thin contact seal 42, a lip portion 47 having an inner peripheral edge shape similar to the cross-sectional shape perpendicular to the axis of the screw shaft 20 (the shape cut by a cross-section perpendicular to the axial direction) is provided. The lip portion 47 is in sliding contact with the screw shaft 20 over the entire circumference, and a high dust-proof effect and sealing effect can be obtained.

[0025] Next, the assembly of the ball screw 10 will be described. First, while aligning the screw counterbore 36 of the nut 30 and the tapping screw counterbore 44 of the seal base 41, the seal base 41 is fitted into the circular recess 33. Next, a tapping screw 51 is inserted into the screw counterbore 36 and screwed into the tapping screw counterbore 44 to restrict the rotational direction and axial position of the seal base 41 and fix it to the nut 30. Since the seal base 41 is an annular shape without a circumferential phase, it is only necessary to generally align the screw counterbore 36 and the tapping screw counterbore 44, and an accurate alignment operation is not required, which facilitates the work.

[0026] Next, after fitting the lip portion 47 of the thin contact seal 42 to the axial end of the screw shaft 20 and rotating it around the outer peripheral screw groove 21, the thin contact seal 42 moves axially inward along the outer peripheral screw groove 21, and the axially inner end face of the thin contact seal 42 contacts the side face 41a of the seal base 41. Even at the position where the axially inner end face of the thin contact seal 42 contacts the side face 41a of the seal base 41, the phases of the lip portion 47 and the screw shaft 20 coincide, and since the lip portion 47 is in sliding contact with the outer peripheral screw groove 21 over the entire circumference, a high sealing performance can be obtained.

[0027] Then, while making a hole in the thin contact seal 42 with the tapping screw 51, it is screwed into the tapping screw counterbore 45 of the seal base 41 to fix the thin contact seal 42 to the seal base 41.

[0028] Since the thickness t of the thin contact seal 42 is 0.5 to 2 mm, in a state where the phases of the lip portion 47 and the screw shaft 20 are aligned, a hole can be directly drilled and attached to the thin contact seal 42 by the tapping screw 51. That is, the thin contact seal 42 can be fixed by aligning the phases of the lip portion 47 and the screw shaft 20 in kind, and can be attached with high precision.

[0029] As described above, according to the ball screw 10 of the present embodiment, the seal base 41 is fixed to the nut 30 by the tapping screw 51, and further, the thin contact seal 42 is fixed to the side surface 41a of the seal base 41 by the tapping screw 51. Therefore, female screw processing of the nut 30 is not required, and the processing cost can be reduced.

[0030] Also, as described above, since the phase alignment between the lip portion 47 and the screw shaft 20 is naturally performed, the number of assembly steps of the thin contact seal 42 is reduced, the assembly accuracy is improved, and a ball screw 10 with high sealing performance at low cost can be obtained.

[0031] Also, if the shaft diameter of the screw shaft 20 is unified, the nut 30 and the seal base 41 can be made common even for ball screws 10 with different leads. By simply changing the shape of the lip portion 47 of the thin contact seal 42, it is possible to easily cope with variations in leads, and it can be assembled easily and accurately at low cost.

[0032] (Second Embodiment) Next, the ball screw according to the second embodiment of the present invention will be described in detail. The ball screw 10 of the second embodiment is the same as the ball screw 10 according to the first embodiment in other structures except that the mounting structure of the seal base 41 to the nut 30 is different. Therefore, the same reference numerals are given to the same parts, and detailed description thereof is omitted.

[0033] As shown in FIGS. 4(a) and 4(b), the nut 30 of the present embodiment further includes an annular groove 37 having an inner diameter larger than the inner diameter of the circular recess 33 on the axially outer side of the circular recess 33 of the nut 30. The axially outer surface 37a of the annular groove 37 is an inclined surface that becomes smaller in diameter toward the axially outer side.

[0034] Also, the axial depth L4 of the circular recess 33 (the distance from the stepped surface on the axially inner side of the annular groove 37 to the axially inner side surface 33a of the circular recess 33) is formed slightly shallower than the thickness L5 of the seal base 41 (L4 < L5). Therefore, when the seal base 41 is assembled into the circular recess 33, the side surface 41a of the seal base 41 protrudes axially outward from the circular recess 33 (the stepped surface on the axially inner side of the annular groove 37).

[0035] Here, when the C-ring 46 is assembled into the annular groove 37, the outer circumference of the C-ring 46 abuts against the axially outer surface 37a (inclined surface) of the annular groove 37 and is pushed axially inward. The C-ring 46 abuts against the side surface 41a of the seal base 41, and the elastic force of the C-ring 46 presses and fixes the seal base 41 against the side surface 33a of the circular recess 33. In this way, if the seal base 41 is fixed to the circular recess 33 by the C-ring 46, it becomes unnecessary to machine the threaded hole of the nut 30, and the manufacturing cost of the nut 30 can be reduced.

[0036] Also, the thin contact seal 42 of the present embodiment is disposed on the inner diameter side of the C-ring 46, and a flat washer 48 made of metal or a hard resin is stacked from the axially outer side and fixed to the seal base 41 with a tapping screw 51. By using the flat washer 48, deformation of the thin contact seal 42 due to the axial force of the tapping screw can be prevented.

[0037] Note that the present invention is not limited to the above-described embodiments, and modifications, improvements, etc. can be made as appropriate. For example, anti-rotation measures against the nut 30 may be added to the seal base 41 of the second embodiment. As anti-rotation means, it is possible to appropriately adopt, for example, engaging a pin provided to protrude from the side surface 33a of the circular recess 33 with a hole or notch formed on the outer circumferential surface of the seal base 41.

[0038] As described above, the following matters are disclosed in this specification. (1) A screw shaft having a spiral outer thread groove formed on its outer peripheral surface, a nut having a spiral inner thread groove formed on its inner peripheral surface, a plurality of balls that roll on a ball rolling portion formed by the outer thread groove of the screw shaft and the inner thread groove of the nut, a sealing mechanism provided at at least one axial end of the nut for sealing between the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut, A ball screw comprising: The sealing mechanism includes: a seal base having a through hole with an inner diameter larger than the outer diameter of the screw shaft, and being fitted and fixed in a recess formed at at least one axial end of the nut, a thin contact seal having a lip portion with an inner peripheral edge shape similar to the cross-sectional shape perpendicular to the axis of the outer peripheral surface of the screw shaft, being formed in a thin plate shape, and being fixed to the axial side surface of the seal base by a tapping screw, A ball screw comprising: According to this configuration, commonization of the components of the sealing mechanism is possible, and a ball screw with low cost and high assembly accuracy can be obtained.

[0039] (2) The nut has a screw hole that radially penetrates from the outer peripheral surface of the nut to the recess, The seal base is fixed to the nut by a tapping screw that is screwed into the screw hole, The ball screw according to (1). According to this configuration, female thread machining of the nut and the seal base is not required, and the processing cost can be suppressed.

[0040] (3) The nut further includes an annular groove having an inner diameter larger than the inner diameter of the recess on the outer side in the axial direction of the recess, A retaining ring is disposed in the annular groove, The seal base is fixed to the nut by being urged axially inward by the retaining ring, The ball screw according to (1) or (2). According to this configuration, it is not necessary to drill holes in the nut and the seal base, and the seal base can be fixed to the nut with a simple mechanism.

[0041] (4) The thickness of the thin contact seal is 0.5 to 2.0 mm. The ball screw according to any one of (1) to (3). According to this configuration, without performing expensive three-dimensional machining, the lip portion of the thin contact seal can be formed into a shape similar to the cross-sectional shape perpendicular to the axis of the outer peripheral surface of the screw shaft by an inexpensive processing method such as press working, and the manufacturing cost can be suppressed. In addition, the phase between the thin contact seal and the outer peripheral screw groove can be accurately aligned in the actual object and fixed by a tapping screw.

Explanation of symbols

[0042] 10 Ball screw 20 Screw shaft 21 Outer peripheral screw groove 25 Ball rolling part 26 Ball 30 Nut 31 Inner peripheral screw groove 33 Circular recess (recess) 35 Outer peripheral surface 36 Pilot hole 37 Annular groove 40 Sealing mechanism 41 Seal base 41a Side surface (axial side surface of the seal base) 42 Thin contact seal 43 Through hole 46 C-shaped retaining ring (retaining ring) 47 Lip portion 51 Tapping screw t Thickness of the thin contact seal

Claims

1. A screw shaft having a spiral outer thread groove formed on its outer peripheral surface, a nut having a spiral inner thread groove formed on its inner peripheral surface, a plurality of balls rolling on a ball rolling portion formed by the outer thread groove of the screw shaft and the inner thread groove of the nut, a sealing mechanism provided at at least one axial end of the nut for sealing between the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut, A ball screw comprising: The sealing mechanism is: A seal base having a through hole with an inner diameter larger than the outer diameter of the screw shaft and fitted and fixed in a recess formed at at least one axial end of the nut, A thin contact seal having a lip portion with an inner peripheral edge shape similar to the cross-sectional shape perpendicular to the axis of the outer peripheral surface of the screw shaft, formed in a thin plate shape and fixed to the axial side surface of the seal base by a tapping screw, A ball screw comprising.

2. The nut has a screw hole that radially penetrates from the outer peripheral surface of the nut to the recess, The seal base is fixed to the nut by a tapping screw that screws into the screw hole, The ball screw according to claim 1.

3. The nut further includes an annular groove having an inner diameter larger than the inner diameter of the recess on the outer side in the axial direction of the recess, A retaining ring is disposed in the annular groove, The seal base is fixed to the nut by being urged axially inward by the retaining ring, The ball screw according to claim 1.

4. The thickness of the thin contact seal is 0.5 to 2.0 mm, The ball screw according to any one of claims 1 to 3.

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