ball screw

Abstract

To provide a ball screw which suppresses the clogging of rolling bodies, and is easy in assembling.SOLUTION: A ball screw comprises a screw shaft at which a spiral groove is formed at an external peripheral face, a nut at which a spiral groove is formed at an internal peripheral face, a plurality of rolling bodies arranged in a rolling path which is formed between the spiral groove of the screw shaft and the spiral groove of the nut, and a circulation component having a ball return passage for connecting both ends of the rolling path. The circulation component comprises a circulation top having a penetration hole penetrating a clearance between an external peripheral face and an internal peripheral face of the nut, a passage forming member inserted into the insertion hole, and having a groove constituting a part of the ball return passage, and an elastic member fixed into the insertion hole at an upper part of the passage forming member, and elastically fixing the passage forming member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Ball screws are used in devices that require precise positioning, such as machine tools and robots. A ball screw generally includes a screw shaft with a spiral groove formed on its outer circumferential surface, a nut with a spiral groove formed on its inner circumferential surface, a plurality of balls arranged in a rolling groove formed between the spiral groove of the screw shaft and the spiral groove of the nut, and a circulation part having a ball return passage connecting both ends of the rolling groove.

[0003] The circulation part is attached to the nut and guides balls scooped up from the end of the rolling groove into the ball return passage, and returns them from the return passage to the start of the rolling groove.When the screw shaft and the nut are rotated relative to each other, the balls circulate while rolling within the circulation circuit consisting of the rolling groove and the ball return passage, allowing the screw shaft and the nut to rotate relative to each other smoothly and with low torque.

[0004] In a ball circulation type ball screw, a circulation ball with a ball return passage formed in it is inserted and fixed into a hole that radially penetrates the outer and inner surfaces of the nut, and both ends of the nut spiral groove are connected by a ball return passage, thereby forming a circulation circuit.

[0005] Patent Document 1 discloses a ball screw with a top-type ball bearing, in which a through-hole for inserting a ball is provided in the top member, connecting the rolling path with the outer peripheral surface of the nut. The through-hole is sealed with a sealing means such as a plug. The top member is an internal fitting type with a positioning arm that engages with the thread groove of the nut.

[0006] Patent Document 2 discloses a ball screw in which multiple balls are interposed in a rolling path formed between the screw groove of the screw shaft and the screw groove of the nut. The ball screw has a circulation section whose both ends communicate with the screw groove of the nut and which circulates the balls in the rolling path. The rolling path and the circulation section form a circulating path. In this ball screw, the circulation section is provided with elasticity imparting means for imparting elasticity in the ball circulation direction between the balls at one end and the balls at the other end of the circulation section. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-202063 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-169881 Summary of the Invention [Problem to be solved by the invention]

[0008] A known factor that hinders smooth rotation (stable torque) of a ball screw is the phenomenon in which the balls do not roll properly in the ball return passage and become clogged. Patent Document 1 does not attempt to resolve this phenomenon.

[0009] In Patent Document 2, an elastic member absorbs the phenomenon of balls clogging in the circulating part, thereby realizing smooth rotation.

[0010] However, another factor that hinders the smooth rotation of the ball screw is the step at the connection between the ball groove of the nut and the ball groove of the top. In the configuration of Patent Document 2, the movement of the circulating top itself can change this step, which can hinder smooth rotation.

[0011] The present invention provides a ball screw that suppresses clogging of the rolling elements and is easy to assemble. [Means for solving the problem]

[0012] The above object of the present invention can be achieved by the following configuration. (1) a screw shaft having a spiral groove formed on its outer circumferential surface; a nut having a spiral groove formed on its inner circumferential surface; a plurality of rolling elements disposed in a rolling path formed between the spiral groove of the screw shaft and the spiral groove of the nut; a circulation component having a ball return passage connecting both ends of the rolling path, The circulating part is a circulation top fixed to the nut and having a through hole passing through between an outer peripheral surface of the nut and the inner peripheral surface; a passage forming member having a groove that is inserted into the through hole and that forms a part of the ball return passage; an elastic member that is fixed to the through hole on the passage forming member and elastically fixes the passage forming member; A ball screw comprising: (2) The circulation top is fixed to a notch formed in the nut so as to penetrate between the outer peripheral surface and the inner peripheral surface of the nut, and has a connecting groove on a surface facing the screw shaft, The groove of the passage forming member and the connecting groove of the circulation top are disposed in a missing portion of the spiral groove formed by the presence of the notch portion on the inner peripheral surface of the nut. (1) The ball screw described in (1). (3) The circulating top is positioned based on the seat surface formed in the notch portion. (2) The ball screw described in (2). (4) The side surface of the notch has a tapered shape. (2) The ball screw described in (2). (5) An adhesive hole for pouring adhesive into the notch is provided in the notch. (2) The ball screw described in (2). (6) The circulation top and the passage forming member are made of the same resin. A ball screw according to any one of (1) to (5). [Effects of the Invention]

[0013] According to the present invention, the passage forming member is movable by the elastic force of the elastic member, and moves in response to the behavior of the rolling elements, thereby preventing clogging of the rolling elements. Also, assembly is easy. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of a ball screw according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along a cross section perpendicular to the axial direction of the ball screw. [Figure 3] FIG. 3 is a perspective view of the nut. [Figure 4] FIG. 4 is a perspective view of the circulation top as seen from below. [Figure 5] FIG. 5 is a perspective view of the passage forming member as seen from below. [Figure 6] FIG. 6 is a perspective view of a ball screw according to a second embodiment of the present invention. [Figure 7] FIG. 7 is a perspective view of a ball screw according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The requirements of the embodiments described below can be combined as appropriate.

[0016] (First embodiment) A first embodiment of a ball screw according to the present invention will be described in detail below with reference to the drawings. Fig. 1 is a perspective view of a ball screw 100 according to the first embodiment of the present invention, specifically a perspective view of a portion of the configuration of the ball screw 100. Fig. 2 is a cross-sectional view taken along a cross section perpendicular to the axial direction of the ball screw 100. Fig. 3 is a perspective view of a nut 20.

[0017] The ball screw 100 is used in devices that require precise positioning, such as machine tools and robots. The ball screw 100 is installed on a stand or the like (not shown). The ball screw 100 includes a screw shaft 10 having a spiral groove 12 formed on its outer circumferential surface, a nut 20 having a spiral groove 27 formed on its inner circumferential surface, a plurality of rolling elements 30, and a circulating part 40.

[0018] The screw shaft 10 is connected to a power source such as a motor to rotate, and the nut 20, which is threaded onto the screw shaft 10 via multiple rolling elements 30, reciprocates along a straight line. In other words, the ball screw 100 converts rotational motion into linear motion. A device including components such as a slider and a table is connected to the nut 20. Figure 1 shows the nut 20 with the tip cut off, exposing its interior.

[0019] The rolling elements 30 are spherical bodies such as steel balls, and are arranged in a rolling path formed between the helical groove 12 of the screw shaft 10 and the helical groove 27 of the nut 20. The rolling elements 30 are also arranged in a ball return passage 41 of the circulating component 40. The rolling path is formed inside the nut 20, with one end of the rolling path connected to the ball return passage 41 shown in FIG. 1 and the other end of the rolling path connected to another ball return passage (not shown) provided inside the nut 20. In other words, the ball return passage connects both ends of the rolling path to form a loop-shaped path along which the rolling elements 30 can move.

[0020] As the ball screw 100 is driven, the screw shaft 10 and the nut 20 move relative to each other. As this movement occurs, the rolling elements 30 move through the rolling path and the ball return path 41. Specifically, a plurality of rolling elements 30 are sent out from the rolling path, move through the ball return path 41, and then return to the rolling path. The rolling of the rolling elements 30 in the rolling path reduces the contact resistance between the screw shaft 10 and the nut 20.

[0021] 3 is a perspective view of the nut 20. The nut 20 has a notch 21 that houses a circulating top 43, which will be described later. The notch 21 is formed to penetrate between the outer peripheral surface and the inner peripheral surface of the nut 20. Therefore, the spiral groove 27 on the inner peripheral surface of the nut 20 does not exist at the location of the notch 21. Furthermore, a pair of bearing surfaces 22 extending in the circumferential direction of the nut 20 are formed inside the notch 21.

[0022] 4 is a perspective view of the circulation top 43 as seen from below. The circulation component 40 is a component that forms the ball return passage 41, and includes the circulation top 43, a substantially cylindrical cylindrical member 44 as a passage-forming member, and an elastic member 45. The circulation top 43 is attached to the notch 21 of the nut 20, and has a through-hole 43a. The circulation top 43 is inserted into the notch 21 formed in the nut 20 by, for example, press-fitting, and fixed to the nut 20. When the circulation top 43 is fixed to the notch 21 of the nut 20, the through-hole 43a passes through between the outer peripheral surface and the inner peripheral surface of the nut 20. Note that the through-hole 43a in the illustrated example is a substantially cylindrical hole.

[0023] In this embodiment, the support portion 43b of the circulating top 43 is disposed on the seat surface 22 of the cutout portion 21. Therefore, the circulating top 43 is positioned based on the seat surface 22, and the circulating top 43 can be accurately positioned. However, the method of fixing the circulating top 43 is not particularly limited.

[0024] Furthermore, the circulating top 43 has two connecting grooves 43c formed on the surface (bottom surface) facing the screw shaft 10. When the circulating top 43 is fixed to the notch portion 21, the connecting grooves 43c are positioned in the missing portion (the location of the notch portion 21) where the spiral groove 27 does not exist on the inner peripheral surface of the nut 20, and connect to both ends of the interrupted spiral groove 27.

[0025] 5 is a perspective view seen from below of the cylindrical member 44. The cylindrical member 44 is fitted into the through-hole 43a of the circulating top 43, and has a groove 44a that forms part of the ball return passage 41. The groove 44a is formed in the bottom surface of the cylindrical member 44 and penetrates the cylindrical member 44 in the circumferential direction.

[0026] The cylindrical member 44 is inserted into the through-hole 43a by a method such as clearance fit, and is fitted into the through-hole 43a. The cylindrical member 44 inserted into the through-hole 43a is movable within the through-hole 43a, but is prevented from falling out by an elastic member 45, as will be described later. However, the method for fitting the cylindrical member 44 is not particularly limited.

[0027] The circulating top 43 and the cylindrical member 44 are made of, for example, the same resin, which makes it possible to prevent misalignment and loosening of the assembly caused by differences in thermal expansion coefficients.

[0028] When the cylindrical member 44 is fitted into the through-hole 43a, the groove 44a fits between the two connecting grooves 43c of the circulating top 43. As a result, both ends of the portion where the spiral groove 27 does not exist (the portion of the notch 21) are connected by the groove 44a of the cylindrical member 44 and the two connecting grooves 43c of the circulating top 43, and the ball return passage 41 is formed.

[0029] The elastic member 45 has, for example, a cylindrical shape and is made of a material such as resin or rubber having a predetermined elasticity. The elastic member 45 is fixed to the through-hole 43a on the top of the cylindrical member 44 (the side opposite to the groove 44a) by, for example, press-fitting, and elastically fixes the cylindrical member 44. However, the fixing method of the elastic member 45 is not particularly limited, but the elastic member 45 is fixed so as to at least not move within the through-hole 43a. The elastic member 45 may be formed by pouring a highly elastic adhesive (for example, an acrylic-modified silicone resin or epoxy resin-modified silicone elastic adhesive having a durometer A hardness of approximately 20 to 90) into the through-hole 43a.

[0030] The ball screw 100 is assembled as follows: After press-fitting the circulating top 43 into the notch 21 of the nut 20, the worker passes the screw shaft 10 through the nut 20. Next, the worker inserts the specified number of rolling elements 30 through the through-hole 43a of the circulating top 43, and then inserts the cylindrical member 44 into the through-hole 43a by a clearance fit. The worker then rotates the screw shaft 10, causing the rolling elements 30 to revolve on the rolling path, determining the optimal position of the cylindrical member 44, and then press-fits the elastic member 45 from above the cylindrical member 44. This completes the ball screw 100.

[0031] Since the elastic member 45 is fixed in the through-hole 43a by press-fitting, the movement of the cylindrical member 44 located below (on the screw shaft 10 side) is restricted, and the cylindrical member 44 is prevented from jumping out. In addition, since the rolling elements 30 are arranged below the cylindrical member 44, the cylindrical member 44 will not fall toward the screw shaft 10.

[0032] In the ball screw 100 of this embodiment, the circulating top 43 is fixed to the notch 21 formed in the nut 20 and has a connecting groove 43c on the surface facing the screw shaft 10. The groove 44a of the cylindrical member 44 and the connecting groove 43c of the circulating top 43 are located in the missing portion of the spiral groove 27 formed by the notch 21 on the inner surface of the nut 20. Under this premise, the elastic member 45 elastically fixes the cylindrical member 44. This allows the cylindrical member 44 to move due to the elastic force of the elastic member 45 and can move in response to the behavior of the rolling elements 30. This secures the ball return passage 41 and absorbs clogging of the rolling elements 30 within the circulating component 40, thereby preventing clogging. Furthermore, the spiral groove 27 on the inner surface of the nut 20 and the connecting groove 43c of the circulating top 43 are fixed at a position where a smooth connection is achieved. This simultaneously prevents two factors that hinder smooth rotation of the ball screw 100.

[0033] When the cylindrical member 44 moves due to the elastic force of the elastic member 45, a step may occur at the joint between the cylindrical member 44, in which the groove 44a is formed, and the connecting groove 43c of the circulating top 43. However, compared to the connection between the spiral groove 27 of the nut 20 and the connecting groove 43c of the circulating top 43, when the rolling elements 30 pass through this part (the joint between the groove 44a and the connecting groove 43c), the rolling elements 30 are not constrained and can move relatively freely, so this step does not hinder the smooth rotation of the ball screw 100.

[0034] In addition, in the assembly of a conventional ball screw, a ball screw without a through hole 43a as in this embodiment is fixed to a nut, a temporary shaft without a spiral groove is passed through the nut, and rolling elements are inserted between the temporary shaft and the spiral groove of the nut. After inserting the required number of rolling elements, the rolling elements are transferred from the temporary shaft to the actual screw shaft with a spiral groove. This process is time-consuming, and when inserting the rolling elements between the temporary shaft and the spiral groove of the nut, they may be inserted into a groove that does not have a circulation path for the rolling elements, rather than the groove that they should be inserted into. This prevents the rolling elements from circulating, which can hinder smooth rotation of the ball screw. In contrast, with the ball screw 100 of this embodiment, the rolling elements 30 are inserted through the circulation ball screw 43 with a through hole 43a, allowing the rolling elements 30 to be inserted reliably into the grooves they should be filled in, facilitating assembly and improving productivity.

[0035] Second Embodiment 6 is a perspective view of a ball screw 100 according to a second embodiment. In this embodiment, the side surface 23 of the notch 21 forms a tapered surface. The tapered surface ensures that the circulating top 43 is firmly fixed to the notch 21.

[0036] (Third embodiment) 7 is a perspective view of a ball screw 100 according to a third embodiment. In this embodiment, an adhesive hole 24 for pouring an adhesive is provided in the seating surface 22 of the cutout portion 21. By using the adhesive, the support portion 43b of the circulating top 43 can be firmly fixed to the seating surface 22 of the cutout portion 21.

[0037] The present invention is not limited to the above-described embodiments, and can be appropriately modified, improved, etc. In addition, the material, shape, dimensions, numerical values, form, number, location, etc. of each component in the above-described embodiments are arbitrary and not limited as long as they can achieve the present invention. [Explanation of symbols]

[0038] 10 Screw shaft 20 nuts 21 Notch 22 Seat 23 Side of notch 24 adhesive holes 30 rolling elements 40 Rotable Parts 41 Ball return passage 43 Circulation Top 43a Through hole 43b Support part 43c connection groove 44 Cylindrical member (passage forming member) 44a Groove in cylindrical member 45 Elastic member 100 ball screw

Claims

1. a screw shaft having a spiral groove formed on its outer circumferential surface; a nut having a spiral groove formed on its inner circumferential surface; a plurality of rolling elements disposed in a rolling path formed between the spiral groove of the screw shaft and the spiral groove of the nut; a circulation component having a ball return passage connecting both ends of the rolling path, The circulating part is a circulation top fixed to the nut and having a through hole passing through between an outer peripheral surface of the nut and an inner peripheral surface of the nut; a passage forming member having a groove that is inserted into the through hole and that forms a part of the ball return passage; an elastic member that is fixed to the through hole on the passage forming member and elastically fixes the passage forming member; Equipped with The circulating top has two connecting grooves formed on a surface facing the screw shaft, The passage forming member is movable relative to the connecting groove of the circulating top. Ball screw.

2. The circulation top is fixed to a notch formed in the nut so as to penetrate between the outer peripheral surface and the inner peripheral surface of the nut, The groove of the passage forming member and the connecting groove of the circulation top are disposed in a missing portion of the spiral groove formed by the presence of the notch portion on the inner peripheral surface of the nut.

2. The ball screw according to claim 1.

3. The circulating top is positioned based on a seat surface formed in the notch portion.

3. The ball screw according to claim 2.

4. The side surface of the notch portion has a tapered shape.

3. The ball screw according to claim 2.

5. An adhesive hole for pouring adhesive into the cutout portion is provided.

3. The ball screw according to claim 2.

6. The circulation top and the passage forming member are made of the same resin. The ball screw according to any one of claims 1 to 5.

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