Ball screw

Abstract

To provide a ball screw excellent in dust-proof performance.SOLUTION: A dust intrusion preventing mechanism 40 preventing the intrusion of dust into an internal space between the outer periphery of a screw shaft 20 and the inner periphery of a nut 30 comprises: a non-contact seal 43 provided at one axial end of the nut 30 and having a radial clearance between the inner periphery and the screw shaft 20; a contact seal 41 provided on the axial inside further than the non-contact seal 43, via an axial clearance C and coming in elastically slide contact with the screw shaft 20; and a fluid supply portion 50 supplying fluid into the axial clearance C between the non-contact seal 43 and the contact seal 41.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ball screw, and more particularly to a ball screw that can prevent dust from entering from the outside. [Background technology]

[0002] Seals are generally known for preventing leakage of lubricant enclosed in a ball screw and preventing the intrusion of foreign matter from the outside. Seals are broadly classified into non-contact seals and contact seals, with contact seals being effective in preventing the intrusion of foreign matter from the outside. Patent Document 1 discloses a ball screw in which ring-shaped non-contact seals are arranged at both axial ends of the nut, and the nut is provided with suction holes that penetrate radially within the ball rolling path, separate from the grease supply holes, to minimize the release of dust generated inside the nut to the outside. Patent Document 2 also discloses a contact seal for a ball screw in which elastic seal pieces of the contact seal are arranged at the axial end of the nut, tilted outward from the nut, to prevent foreign matter attached to the screw shaft or the like outside the nut from invading the inside of the nut. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-190928 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-133944 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the ball screw described in Patent Document 1 is designed to prevent dust generated inside the nut during operation from escaping to the outside, and the seal that seals between the screw shaft and the nut is a non-contact seal, so it is not very effective at preventing foreign matter from entering from the outside. Furthermore, the contact seal for a ball screw described in Patent Document 2 has elastic seal pieces of the contact seal tilted outward from the nut to increase the effectiveness at preventing foreign matter from entering the inside, but it cannot actively expel foreign matter to the outside, so further improvements in dustproofing are required.

[0005] Furthermore, in recent years, 3D additive manufacturing has become widespread, and the powder used as the material, measuring a few microns in size, may adhere to the ball screw. When the ball screw is in operation, the screw shaft moves axially while rotating, making it easy for foreign matter to become trapped in the gap between the lip and the screw shaft, even with a contact seal. Dust particles on the order of a few microns are particularly difficult to effectively prevent from entering, and this could affect the performance of the ball screw.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a ball screw with excellent dustproof performance. [Means for solving the problem]

[0007] Therefore, the above object of the present invention is achieved by the following configuration [1] relating to a ball screw. [1] A screw shaft having a spiral outer thread groove formed on its outer circumferential surface; a nut having a spiral internal thread groove formed on its inner peripheral surface; A plurality of balls rolling on a ball rolling section formed by an outer peripheral screw groove of the screw shaft and an inner peripheral screw groove of the nut; A ball screw comprising: a dust intrusion prevention mechanism provided at least at one axial end of the nut to prevent dust from infiltrating into an internal space between an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut; The dust intrusion prevention mechanism includes: a non-contact seal provided at one axial end of the nut and having a radial gap between an inner circumferential surface and the screw shaft; a contact seal that is provided axially inward of the non-contact seal via an axial gap and that elastically slides against the screw shaft; a fluid supply unit that supplies fluid to the axial gap between the non-contact seal and the contact seal; A ball screw comprising: [Effects of the Invention]

[0008] According to the ball screw of the present invention, the dustproof performance of the ball screw can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a ball screw according to an embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view of the spacer shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of a ball screw according to the present invention will now be described in detail with reference to the drawings. As shown in Fig. 1, the ball screw 10 of this embodiment includes a screw shaft 20 extending in the axial direction and having a spiral outer peripheral screw groove 21 on its outer peripheral surface, a nut 30 having a spiral inner peripheral screw groove 31 on its inner peripheral surface that corresponds to the outer peripheral screw groove 21 of the screw shaft 20, and a dust intrusion prevention mechanism 40 disposed at the axial end of the nut 30 to seal the internal space between the outer peripheral surface of the screw shaft 20 and the inner peripheral surface of the nut 30 and prevent dust from entering from outside.

[0011] 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 and form a ball rolling section 25 therebetween, and a plurality of balls 26 as rolling elements are loaded rollably together with grease in the ball rolling section 25. As a result, 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.

[0012] The nut 30 has a flange portion 32 formed at one axial end (left side in FIG. 1 ). An annular recess 33 having an inner diameter larger than the groove bottom 31a of the internal thread groove 31 of the nut 30 is formed concentrically with the internal thread groove 31 at each of both axial end portions of the nut 30. A flow path 34 that connects the annular recess 33 with the outside of the nut 30 is connected to each of the pair of annular recesses 33. Each of the pair of flow paths 34 extends radially outward from the annular recess 33, and then extends axially outward to connect with the outside of the nut 30.

[0013] The flange portion 32 is fixed to a movable base or the like of a mechanical device (not shown) with mounting bolts or the like. A dust prevention mechanism 40 for sealing the internal space between the screw shaft 20 and the nut 30 is disposed in the annular recess 33.

[0014] The nut 30 also has a ball return passage (not shown) that penetrates the interior in the axial direction, and a circulation top (not shown) is disposed to connect the ball return passage with the ball rolling section 25. The ball rolling section 25, one circulation top, the ball return passage, the other circulation top, and the ball rolling section 25 form an infinite circulation passage for the balls 26. A plurality of balls 26 are loaded into the infinite circulation passage together with a predetermined amount of lubricant (for example, grease).

[0015] The dust intrusion prevention mechanism 40 includes a pair of contact seals 41, 41, a pair of spacers 42, 42, a pair of non-contact seals 43, 43, and a fluid supply unit 50. The contact seals 41, the spacers 42, and the non-contact seals 43 are respectively inserted into a pair of annular recesses 33, 33 of the nut 30 from the axially outer side (the left and right outer sides in FIG. 1) toward the axially inner side (the left and right center side in FIG. 1) of the nut 30. The contact seals 41, the spacers 42, and the non-contact seals 43 are arranged in the respective annular recesses 33 in this order, from the axially inner side toward the axially outer side.

[0016] The contact seal 41 includes a main body 44 and a lip 45, and is formed in a generally annular shape from an elastic material such as rubber or elastomer, such as acrylonitrile butadiene rubber (NBR), acrylic rubber (ACM), or fluororubber (FKM). The main body 44 is fitted and fixed into the annular recess 33 of the nut 30. The lip 45 extends radially inward from the main body 44, splitting into two parts, each with an arc-shaped cross section, and elastically sliding against the screw shaft 20. Forming the lip 45 in an arc-shaped cross section allows it to come into uniform contact with any portion of the screw shaft 20.

[0017] The radial interference between the lip portion 45 and the screw shaft 20 is set to 0.1 to 2 mm. The contact seal 41 in the embodiment shown in FIG. 1 is a two-piece seal (e.g., an X1 seal manufactured by NSK Ltd.) composed of a dustproof seal whose tip is inclined axially outward and a sealing seal whose tip is inclined axially inward, but it may also be a single-piece seal (e.g., a V1 seal manufactured by NSK Ltd.). A portion of the main body 44 may be formed by pressing a cold-rolled steel plate or the like. In this case, the lip portion 45 is integrally formed with the cold-rolled steel plate that is part of the main body 44.

[0018] The spacer 42 is a substantially annular member for ensuring an axial gap C between the contact seal 41 and the non-contact seal 43. As shown in FIG. 2 , the spacer 42 has a radial hole 46 penetrating radially in approximately the center in the width direction. The axial gap C can also be described as a substantially annular space surrounded by the contact seal 41, the spacer 42, the non-contact seal 43, and the screw shaft 20. The spacer 42 is fitted and fixed in the annular recess 33 between the contact seal 41 and the non-contact seal 43 so as to contact the contact seal 41 and the non-contact seal 43. In this state, the radial hole 46 of the spacer 42 communicates the axial gap C with the flow path 34. Therefore, the radial hole 46 can supply a fluid such as compressed air circulating from the flow path 34 to the axial gap C.

[0019] The non-contact seal 43 is made of synthetic resin and is formed in a substantially circular ring shape. The non-contact seal 43 is fitted and fixed into the annular recess 33 axially outward of the spacer 42. The radial gap between the inner peripheral surface of the non-contact seal 43 and the screw shaft 20 is set to 0.01 to 2 mm.

[0020] The fluid supply unit 50 is a mechanism for supplying fluid to the axial gap C, and has a fluid discharge port (not shown) connected to the flow path 34 of the nut 30. The fluid supply unit 50 is, for example, a compressor that compresses air, and supplies compressed air to the axial gap C via the flow path 34 and the radial hole 46 of the spacer 42.

[0021] The operation of this embodiment will be described below. Compressed air supplied from the fluid supply unit 50 is supplied to the axial gap C via the flow path 34 of the nut 30 and the radial hole 46 of the spacer 42, thereby increasing the pressure in the axial gap C.

[0022] The compressed air in the axial gap C is discharged in the direction of arrow A from the radial gap between the inner circumferential surface of the non-contact seal 43 and the screw shaft 20 toward the outside. At this time, dust D floating in the air and dust D adhering to the screw shaft 20, particularly powder of several microns in size that is the material for 3D additive manufacturing, is blown away and prevented from penetrating into the ball screw 10. This provides the ball screw 10 with high dustproofing performance.

[0023] Furthermore, the axial inside of the axial gap C is sealed by a contact seal 41 having a radial interference of 0.1 to 2 mm, so there is no risk of compressed air in the axial gap C flowing into the interior (ball rolling portion 25) of the ball screw 10. Furthermore, the high pressure in the axial gap C, along with the sealing action of the contact seal 41, prevents leakage of the lubricant sealed in the internal space, thereby maintaining a good lubricated state.

[0024] The pressure of the compressed air in the axial gap C can be set to any appropriate pressure by setting the radial gap between the inner surface of the non-contact seal 43 and the screw shaft 20 to a value of 0.01 to 2 mm.

[0025] In the above embodiment, compressed air is used as an example of the fluid, but the fluid is not limited to compressed air, and any fluid such as oil air, oil mist, lubricant, coolant, or organic solvent can be used.

[0026] For example, if oil air or oil mist is used as the fluid, the contact portion between the lip portion 45 of the contact seal 41 and the screw shaft 20 can be lubricated while obtaining high dust-proofing performance for the ball screw 10. If a lubricant is used as the fluid, foreign matter can be discharged while lubricating. If a coolant is used as the fluid, the ball screw 10 can be cooled while foreign matter is discharged. Furthermore, if an organic solvent is used as the fluid, foreign matter mixed with oil and grease can also be effectively discharged.

[0027] The present invention is not limited to the above-described embodiment, and modifications and improvements are possible as appropriate.

[0028] As described above, the present specification discloses the following: (1) a screw shaft having a spiral outer peripheral thread groove formed on its outer peripheral surface; a nut having a spiral internal thread groove formed on its inner peripheral surface; A plurality of balls rolling on a ball rolling section formed by an outer peripheral screw groove of the screw shaft and an inner peripheral screw groove of the nut; A ball screw comprising: a dust intrusion prevention mechanism provided at least at one axial end of the nut to prevent dust from infiltrating into an internal space between an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut; The dust intrusion prevention mechanism includes: a non-contact seal provided at one axial end of the nut and having a radial gap between an inner circumferential surface and the screw shaft; a contact seal that is provided axially inward of the non-contact seal via an axial gap and that elastically slides against the screw shaft; a fluid supply unit that supplies fluid to the axial gap between the non-contact seal and the contact seal; A ball screw comprising: This configuration can improve the dustproof performance of the ball screw.

[0029] (2) An annular spacer is further provided between the non-contact seal and the contact seal to ensure the axial gap, The spacer has a radial hole that penetrates radially and is capable of supplying the fluid to the axial gap. (1) The ball screw described in (1). According to this configuration, an axial gap for supplying fluid can be stably secured between the non-contact seal and the contact seal.

[0030] (3) The fluid is any one of air, oil air, oil mist, lubricant, coolant, and organic solvent. The ball screw according to (1) or (2). This configuration improves the dustproof performance of the ball screw, and also makes it possible to lubricate and cool the ball screw and to expel foreign matter mixed with oil and grease.

[0031] (4) A radial gap between the inner peripheral surface of the non-contact seal and the screw shaft is 0.01 to 2 mm, The radial interference between the lip portion of the contact seal and the screw shaft is 0.1 to 2 mm. The ball screw according to any one of (1) to (3). This configuration prevents leakage of the lubricant sealed inside the ball screw, and also makes it possible to set the pressure of the fluid in the axial gap to any appropriate pressure. [Explanation of symbols]

[0032] 10 Ball screw 20 Screw shaft 21 Peripheral thread groove 25 Ball Rolling Section 26 balls 30 nuts 31 Internal thread groove 40 Dust intrusion prevention mechanism 41 Contact seal 42 Maza 43 Non-contact seal 45 Lip 46 radial holes 50 Fluid supply unit C-axis clearance D Dust

Claims

1. a screw shaft having a spiral outer peripheral thread groove formed on its outer peripheral surface; a nut having a spiral internal thread groove formed on its inner peripheral surface; A plurality of balls rolling on a ball rolling section formed by an outer peripheral screw groove of the screw shaft and an inner peripheral screw groove of the nut; A ball screw comprising: a dust intrusion prevention mechanism provided at least at one axial end of the nut to prevent dust from infiltrating into an internal space between an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut; The dust intrusion prevention mechanism includes: a non-contact seal provided at one axial end of the nut and having a radial gap between an inner circumferential surface and the screw shaft; a contact seal that is provided axially inward of the non-contact seal via an axial gap and that elastically slides against the screw shaft; a fluid supply unit that supplies fluid to the axial gap between the non-contact seal and the contact seal; A ball screw comprising:

2. a ring-shaped spacer is further provided between the non-contact seal and the contact seal to ensure the axial gap; The spacer has a radial hole that penetrates radially and is capable of supplying the fluid to the axial gap.

2. The ball screw according to claim 1.

3. The fluid is any one of air, oil air, oil mist, lubricant, coolant, and organic solvent.

2. The ball screw according to claim 1.

4. The radial gap between the inner circumferential surface of the non-contact seal and the screw shaft is 0.01 to 2 mm, The radial interference between the lip portion of the contact seal and the screw shaft is 0.1 to 2 mm. The ball screw according to any one of claims 1 to 3.

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