Ball screw

Abstract

This ball screw is used in a state in which the axis line is inclined with respect to the horizontal direction, and is provided with: a screw shaft in which an outer peripheral thread groove is formed; a nut in which an inner circumferential thread groove is formed; a plurality of balls accommodated in a plurality of rolling paths formed by the outer peripheral thread groove and the inner peripheral thread groove which face each other; and a circulation member that returns the balls from one end to the other end of the rolling path, the ball screw is applied with compression preload, and the nut has a lubricating oil supply path having one end that opens toward the outside and the other end that opens toward the inner peripheral surface in the vicinity of the offset point.

Description

Technical Field

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

[0002] A ball screw used in a machine tool or the like is generally configured by rotatably arranging a plurality of balls between a thread groove formed on the outer peripheral surface of a screw shaft and a thread groove formed on the inner peripheral surface of a nut. For example, when a rotational torque about the axis is applied to the screw shaft, the plurality of balls roll between the two thread grooves of the screw shaft and the nut, and accordingly, the nut reciprocates in the axial direction of the screw shaft.

[0003] In a ball screw used for a gear grinder or the like, there is an application in which the axis is alternately inclined. When the ball screw is used in a state where the axis is inclined in the vertical direction or relative to the horizontal direction, there is a problem of where to arrange the lubricating oil supply hole.

[0004] For example, in a ball screw having a lubricating oil supply hole provided at the axial end of the nut, when the axis is inclined such that the supply hole is located at the uppermost position of the nut, the lubricating oil supplied from the supply hole to the inside of the nut is supplied to the entire area inside the nut by gravity. However, when the axis is inclined such that the supply hole is located at the lowermost position of the nut, the lubricating oil supplied from the supply hole to the inside of the nut stays near the supply hole, and the entire nut cannot be lubricated. No matter where the lubricating oil supply hole is arranged, although there are differences in degree, the same problem exists.

[0005] In Patent Document 1, a ball screw is disclosed in which a grease supply hole of the nut is formed at a position that forms the upper end portion of the raceway so that the axial direction of the screw shaft is along the vertical direction, and lubricant can be supplied to all the balls existing in the raceway.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015 - 108400 Summary of the Invention

[0009] Technical Problem to be Solved by the Invention

[0010] However, according to the ball screw of Patent Document 1, it is necessary to form grease supply holes at two positions according to the inclination direction of the screw shaft. This is not only troublesome in processing, but also the mechanism for selecting the grease supply hole and supplying lubricating oil becomes complicated, increasing the cost of the ball screw.

[0011] The present invention has been made in view of the above problems, and an object thereof is to provide a ball screw that can ensure lubricity, has a simple structure, and can be manufactured at low cost.

[0012] Means for Solving Technical Problems

[0013] The ball screw of the present invention is characterized in that it is a ball screw used in a state where the axis is inclined with respect to the horizontal direction, and has:

[0014] A screw shaft formed with an external thread groove on its outer periphery;

[0015] A nut formed with an internal thread groove on its inner periphery;

[0016] A plurality of balls, which are accommodated in a plurality of rolling paths formed by the opposed external thread groove and internal thread groove; and

[0017] A circulation member that returns the balls from one end of the rolling path to the other end,

[0018] The ball screw is applied with a compressive preload,

[0019] The nut has a lubricating oil supply path, and the lubricating oil supply path has one end opening to the outside and the other end opening to the inner peripheral surface near the offset point.

[0020] Advantages of the Invention

[0021] According to the present invention, it is possible to provide a ball screw that ensures lubricity, has a simple structure, and can be manufactured at low cost. Description of the Drawings

[0022] Figure 1 It is a cross-sectional view of the ball screw of this embodiment.

[0023] Figure 2 It is a schematic diagram for explaining the compressive preload.

[0024] Figure 3 (a) of is a schematic diagram of a ball screw arranged in a state where the axis is inclined with the left end side of the screw shaft being downward, Figure 3 and (b) of is a schematic diagram of a ball screw arranged in a state where the axis is inclined with the right end side of the screw shaft being downward.

[0025] Figure 4 (a) of is a schematic diagram of a ball screw to which a moment load is applied in a state where the axis is inclined with the left end side of the screw shaft being downward, Figure 4 and (b) of is a schematic diagram of a ball screw to which a moment load is applied in a state where the axis is inclined with the right end side of the screw shaft being downward.

[0026] Figure 5 It is a cross-sectional view of a modified ball screw.

[0027] Figure 6 It is a bottom view of a ball screw of another modified example. Detailed implementation mode

[0028] Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

[0029] Figure 1 It is a cross-sectional view showing the ball screw of this embodiment.

[0030] As Figure 1 shown, this ball screw is composed of a nut 1, a screw shaft 2, a plurality of balls 3, an annular seal 4, tubes (circulation components) 5, 5' and a tube pressing member 6. A spiral groove (inner peripheral thread groove) 1a is formed on the inner peripheral surface of the nut 1, and a spiral groove (outer peripheral thread groove) 2a is formed on the outer peripheral surface of the screw shaft 2. Balls 3 are arranged between the raceways formed by the spiral groove 1a of the nut 1 and the spiral groove 2a of the screw shaft 2. A flange 11 is formed at one axial end of the nut 1.

[0031] In this embodiment, the seals 4 arranged at both ends of the nut 1 are contact-type seals whose inner periphery contacts the outer periphery of the screw shaft 2, and the outer periphery of the seal 4 and the inner periphery of the nut 1 are sealed by an O-ring 7.

[0032] This ball screw has two circulation circuits composed of the raceways of the balls 3 (the rolling paths formed by the spiral groove 1a and the spiral groove 2a) and the tubes 5, 5'.

[0033] On the outer periphery of the part of the nut 1 other than the flange 11, a flat part 12 for arranging two tubes 5, 5' is formed. Tube mounting holes 16, 16' for mounting the tubes 5, 5' are formed in the flat part 12. The ends of the tubes 5, 5' bent into a U shape are inserted into the tube mounting holes 16, 16' and fixed respectively by the tube pressing member 6.

[0034] The supply of lubricating oil into the nut 1 is carried out via a lubricating oil supply path 17. The lubricating oil supply path 17 extends along the radial direction of the nut 1 and penetrates through the inner and outer peripheral surfaces, and has an opening 17a as the outer end opening to the outside and an opening 17b as the inner end located near the offset point W ( Figure 2 ) (or between the first nut and the second nut described later). Here, "near" means a range within ±1 pitch of the spiral groove 1a in the axial direction from the offset point W. It should be noted that an example is shown in which the lubricating oil supply path 17 is arranged to separate the spiral groove 1a by one row across the offset point W, but it can also be arranged between the spiral grooves 1a or at the bottom of the Gothic arc of the spiral groove 1a.

[0035] Generally, preloading is applied to the ball screw for the purpose of improving positioning accuracy and rigidity. The preloading method is classified into single-nut preloading and double-nut preloading according to the number of nuts used, and into tensile preloading and compressive preloading according to the preloading direction. The ball screw of the present embodiment is offset preloading or double-nut preloading, and compressive preloading is applied. As Figure 2 shown, compressive preloading means preloading in which the load acts in the direction in which the balls 3 arranged on both sides with respect to the offset point W approach each other.

[0036] The double-nut preloading includes spacer preloading in which a spacer is sandwiched between two mutually connected nuts (referred to as the first nut and the second nut) to apply preloading, and spring preloading in which a spring is sandwiched between the first nut and the second nut, and either one can be used.

[0037] As Figure 3 shown in (a) and (b) of Figure 1 , the ball screw of the present embodiment is arranged in a state where the axis X is inclined with respect to the horizontal direction. Assuming a ball screw using "tensile preloading" as the preloading method, in the state where the axis X is inclined, the region that bears the main load F generated by the gravity of the screw shaft 2 or the components mounted on the screw shaft 2 is the upper region B in the axial direction of the nut 1. Here, the lubricating oil supplied to the nut 1 from the lubricating oil supply path 17 ( Figure 1 ) provided at the central position in the axial direction of the nut 1 tends to move downward in the axial direction of the nut 1 as shown by the arrow C due to gravity, so there may be insufficient lubricating oil.

[0038] In contrast, according to the ball screw of the present embodiment, since "compressive preloading" is adopted, the region that bears the main load F generated by the gravity of the screw shaft 2 or the components mounted on the screw shaft 2 becomes the lower region A in the axial direction of the nut 1. Therefore, the lubricating oil supplied to the nut 1 from the lubricating oil supply path 17 ( Figure 1 ) provided at the central position in the axial direction of the nut 1 moves toward the region A as shown by the arrow C along with gravity. Therefore, even when the axis X is inclined in any direction (refer to Figure 3 (a), (b)), the region A can be sufficiently lubricated. In addition, the seals 4 and O-rings 7 ( Figure 1 ) provided on the side of the region A that bears the main load F prevent the leakage of the lubricating oil. Therefore, in the region A where there is no part where the lubricating oil leaks, the lubricating oil accumulates, so that the effect of being less likely to cause lubrication failure can be obtained.

[0039] According to the ball screw of the present embodiment, even when the up-and-down orientation or inclination is reversed, and thus the direction of the main load F is reversed, the direction of the lubricating oil flow is reversed due to gravity. Therefore, it has a structure in which the lubricating oil always covers the region A that bears the main load F, which is effective for early wear and early peeling.

[0040] In addition, in the ball screw according to the present embodiment, when a moment load M is applied in a state where the axis X of the screw shaft 2 is inclined, the region D that bears the load thereby becomes the lower region on the upper end side of the nut 1 as shown in (a) and (b) of Figure 4 . In addition, by bearing the moment load M, the region (axial load bearing region) A is closer to the upper part on the lower end side of the nut 1 than when the moment load M is not borne ( Figure 3 in (a) and (b)).

[0041] Here, the lubricating oil supplied to the nut 1 from the lubricating oil supply path 17 ( Figure 1 ) disposed at the central position of the nut 1 gravitates and is directed not only toward the region A but also toward the region (moment load bearing region) D, so that the region D can be sufficiently lubricated. When the moment load M and the axial main load F are applied simultaneously, lubrication of the regions A and D becomes important, but in the ball screw according to the present embodiment, the lubricating oil can be spread over any region.

[0042] (Modification 1)

[0043] Figure 5 is a cross-sectional view of a modified ball screw. In this modification, the nut 1A has a lubricating oil supply path 18 that passes through the inside of the nut 1A (between the spiral groove 1a and the outer peripheral surface of the nut 1A, and inside the flange 11). At least a part of the lubricating oil supply path 18 extending in the axial direction has an opening 18a as an inner end that opens at the central position in the axial direction on the inner periphery of the nut 1A, and has an opening 18b as an outer end that opens to the outside on the left end surface in the axial direction of the flange 11. The opening 18b may also be provided on the outer peripheral surface of the flange 11.

[0044] According to this modification, it is effective in cases where it is impossible to dispose a pipe for supplying lubricating oil at the central position in the axial direction of the nut 1A in order to avoid interference with other components.

[0045] (Modification 2)

[0046] For example, in the Figure 1 ball screw, when it is used upside down, the pipe 5 is located below. In this case, there is a possibility that the lubricating oil may leak from between the pipe 5 and the pipe mounting hole 16.

[0047] Figure 6It is a bottom view of a ball screw which is another modified example applicable to such a use. According to this modified example, the gap between the tube 5 and the tube mounting hole 16 of the nut 1, between the tube 5 and the tube pressing member 6, and between the mounting screw 20 for fastening the tube pressing member 6 to the nut 1 and a threaded hole (not shown) are sealed with a sealing material 19. Thereby, leakage of lubricating oil from the inside of the nut 1 can be suppressed. In addition, the sealing material 19 may be provided only for the gap between the tube 5 and the tube mounting hole 16.

[0048] The present invention is not limited to the above-described embodiments. Within the scope of the present invention, any constituent element of the above-described embodiments can be modified. In addition, any constituent element can be added or omitted in the above-described embodiments.

[0049] As described above, various embodiments have been described, 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 also of course 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.

[0050] In addition, this application is based on a Japanese patent application (Japanese Patent Application No. 2022-173621) filed on October 28, 2022, the content of which is incorporated herein by reference.

[0051] Explanation of reference numerals

[0052] 1, 1A Nut

[0053] 2 Lead screw

[0054] 3 Ball

[0055] 4 Seal

[0056] 5, 5’ Tube

[0057] 6 Tube pressing member

[0058] 7 O-ring

[0059] 11 Flange

[0060] 16, 16’ Tube mounting hole

[0061] 17, 18 Lubricating oil supply path

[0062] 19 Sealing material

[0063] 20 Mounting screw

Claims

1. A ball screw, It is characterized in that A ball screw used with its axis tilted relative to the horizontal direction, with: A screw shaft having an outer peripheral thread groove formed thereon; A nut having an inner circumferential thread groove; A plurality of balls, wherein the plurality of balls are accommodated in a plurality of rolling paths formed by the outer peripheral thread groove and the inner peripheral thread groove that are opposed to each other; as well as a circulation member for returning the balls from one end of the rolling path to the other end, The ball screw is applied with a compressive preload, The nut has a lubricating oil supply passage having one end opened to the outside and the other end opened to the inner peripheral surface near the offset point.

2. The ball screw according to claim 1, It is characterized in that The lubricating oil supply passage penetrates the nut in a radial direction.

3. The ball screw according to claim 1, It is characterized in that The lubricating oil supply passage extends at least along the axial direction of the nut.

4. The ball screw according to claim 3, It is characterized in that The nut has a flange, and the lubricating oil supply passage opens toward the outside at an end surface of the flange.

5. The ball screw according to any one of claims 1 to 4, It is characterized in that A contact type seal is provided between the end of the nut and the screw shaft at least on the side of the region receiving the main load.

6. The ball screw according to claim 5, It is characterized in that An O-ring is disposed between the contact seal and the nut.

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