Lead screw nut

Abstract

Provided is a screw nut that achieves a reduction in size and weight of a screw nut to which a pulley is attached. A screw nut (2) is provided with an outer ring (21), and a nut (23) that is rotatably attached to the outer ring (21) via first rolling elements. A nut (23) is provided with: a nut body (24) having a thread groove on the inner surface thereof; and a circulation member (25a) provided at an axial end of the nut body (24) and having a direction change path for circulating the second rolling body rolling in the thread groove. A pulley (41) attached to a nut (23) is fitted to an outer surface (24d) of a nut body (24), and the pulley (41) is brought into contact with an axial end surface (26a1) of the nut (23). The pulley (41) is attached to the end surface (26a1) of the nut (23) by means of a fastening member (42).

Description

[0001] This application is a divisional application of the invention patent application filed on October 18, 2018, with application number 201880069612.2 and invention title "Screw Nut or Spline Nut". Technical Field

[0002] The present invention relates to a lead screw nut or spline nut used in actuators, for example, industrial robots. Background Technology

[0003] In Zθ actuators used on the front axis of SCARA-type robots, ball screw splines are employed to meet the requirements of high functionality and high precision. These ball screw splines consist of a shaft, a screw nut mounted on the shaft, and a spline nut mounted on the shaft. Threaded grooves and spline grooves are formed in an overlapping manner on the outer surface of the shaft. By applying rotational input to the screw nut and spline nut respectively and controlling the amount of rotation, the shaft can perform arbitrary linear (Z), rotational (θ), and helical (Z+θ) motions.

[0004] A ball screw nut is an integral part of a bearing and a ball screw nut. That is, the ball screw nut comprises: an outer ring, and a ball screw nut rotatably assembled to the outer ring via bearing balls. The inner ring of the bearing is integral with the ball screw nut. The nut comprises: a nut body having threaded grooves on its inner surface; and a circulation component having a direction-changing path for circulating the ball screw balls rolling in the threaded grooves of the nut body.

[0005] A spline nut is an integral part of a bearing and a ball spline nut. That is, the spline nut comprises: an outer ring, and a nut rotatably assembled to the outer ring via bearing balls. The nut comprises: a nut body having spline grooves on its inner surface; and a circulation component having a direction-changing path for circulating the spline balls rolling in the spline grooves.

[0006] Both the lead screw nut and the spline nut are equipped with pulleys for rotating them. As a conventional method for installing pulleys, Patent Document 1 discloses a method in which a radially protruding, edge-shaped protrusion is integrally provided on the outer surface of the nut body. The pulley is engaged with the outer surface of the nut body while simultaneously abutting against the edge-shaped protrusion. Here, by engaging the pulley with the outer surface of the nut body, the pulley can be positioned radially. Furthermore, by abutting against the edge-shaped protrusion, the pulley can be positioned axially.

[0007] Another known method for installing pulleys involves a circulation member at the axial end of the nut body, and an annular outer diameter portion integrally formed on the nut body to surround the circulation member. The pulley is engaged with the outer surface of the nut body while simultaneously abutting against the annular outer diameter portion. Engaging the pulley with the outer surface of the nut body allows for radial positioning of the pulley. Furthermore, abutting the pulley against the annular outer diameter portion allows for axial positioning of the pulley.

[0008] Prior art literature

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 4-224351 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] In recent years, there has been a demand for further miniaturization and weight reduction of ball screw splines. This is because miniaturization and weight reduction of ball screw splines used in, for example, the front axis of SCARA robots can enable SCARA robots to move at high speeds, or can make motors smaller.

[0013] However, in the pulley installation method described in Patent Document 1, since a radially protruding, blade-shaped protrusion is integrally provided on the outer surface of the nut body, there is a problem that the outer diameter of the nut increases accordingly. Furthermore, since a return tube, serving as a circulation component, is provided on the outer surface of the lead screw nut body, there is also a problem that the outer diameter of the nut increases accordingly.

[0014] In the other pulley installation methods described above, since the nut body has an annular outer diameter portion that protrudes axially in a ring shape surrounding the circulation component, the outer diameter of the nut becomes larger corresponding to the presence of the annular outer diameter portion. Furthermore, since a gap is generated between the pulley and the circulation component, this gap may also contribute to pulley slack.

[0015] Therefore, the object of the present invention is to provide a miniaturized and lightweight lead screw nut with a pulley mounted on it.

[0016] Methods for solving problems

[0017] To address the aforementioned issues, one aspect of the present invention is a lead screw nut comprising an outer ring and a nut rotatably assembled to the outer ring via a first rolling element. The nut includes: a nut body having a threaded groove on its inner surface; and a circulation member disposed at an axial end of the nut body, having a direction-changing path for circulating the threaded groove or the second rolling element. A pulley mounted on the nut is engaged with the outer surface of the nut body, and the pulley abuts against the axial end face of the nut. The pulley is mounted to the end face of the nut by a fastening member.

[0018] Invention Effects

[0019] According to the present invention, since a circulation member is provided at the axial end of the nut body, the outer diameter of the nut can be reduced. Furthermore, since the pulley is abutted against the axial end face of the nut and mounted to the axial end face of the nut by a fastening member, the gap between the pulley and the end face of the nut can be eliminated, thus eliminating the cause of pulley slack. Moreover, since it is not necessary to provide an annular outer diameter portion for abutting the pulley in the nut body, the outer diameter of the nut can be further reduced. Attached Figure Description

[0020] Figure 1 This is a perspective view of a ball screw spline assembled from a lead screw nut and a spline nut according to an embodiment of the present invention (an example in which the lead screw nut is positioned on the front side).

[0021] Figure 2 This is a perspective view of a ball screw spline assembled from a lead screw nut and a spline nut according to an embodiment of the present invention (an example in which the spline nut is positioned on the front side).

[0022] Figure 3 This is an enlarged perspective view of the lead screw nut and shaft in this embodiment (a portion of the lead screw nut has been removed).

[0023] Figure 4 This is an enlarged perspective view of the lead screw nut of this embodiment (a portion of the cover component has been removed).

[0024] Figure 5 (a) is a side view showing the method for installing the pulley according to this embodiment. Figure 5 (b) is a side view showing the conventional method of installing pulleys.

[0025] Figure 6 This is an enlarged perspective view of the spline nut of this embodiment.

[0026] Figure 7 (a) is a cross-sectional view showing the pulley mounting method of this embodiment. Figure 7(b) is a cross-sectional view showing the conventional method of installing pulleys.

[0027] Explanation of reference numerals in the attached figures

[0028] 1…shaft, 1a…threaded groove, 1b…spline groove, 2…lead screw nut, 3…spline nut, 21, 31…outer ring, 22a, 22b, 32a, 32b…bearing balls (first rolling element), 23, 33…nut, 24, 34…nut body, 24b…threaded groove, 24d, 34d…outer surface of nut body, 24e…recess, 24g, 34g…outer diameter, 25a, 25b, 35a, 35b…circulation component, 26a, 26b…cover component, 26a1, 35a1…end face of nut, 27…lead screw ball (second rolling element), 28, 38…direction conversion path, 34b…spline groove, 37…spline ball (second rolling element), 41…pulley, 42…fastening component. Detailed Implementation

[0029] Hereinafter, the lead screw nut and spline nut of embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the lead screw nut and spline nut of the present invention can be embodied in various ways and are not limited to the embodiments described in this specification. These embodiments are provided so that those skilled in the art can fully understand the scope of the invention by making the specification sufficiently clear.

[0030] Figure 1 as well as Figure 2 This is a perspective view (partial sectional view) of a ball screw spline assembled from a lead screw nut and a spline nut according to an embodiment of the present invention. Figure 1 This is an example of placing the lead screw nut on the front side. Figure 2 This is an example of placing the spline nut on the front side. Figure 1 as well as Figure 2 In the diagram, 1 is the shaft, 2 is the lead screw nut, and 3 is the spline nut. They will be explained in order below.

[0031] (axis)

[0032] like Figure 1 As shown, a helical threaded groove 1a with a specified lead is formed on the outer surface of shaft 1, and a straight spline groove 1b extending axially is formed. The threaded groove 1a and the spline groove 1b partially overlap. In this embodiment, the number of threaded grooves 1a is 1 and the number of spline grooves 1b is 4, but these numbers can be appropriately set.

[0033] (Lead screw nut)

[0034] like Figure 1As shown, the ball screw nut 2 is an integral part of the bearing and the ball screw nut. That is, the ball screw nut has an outer ring 21 and a nut 23 that is rotatably assembled to the outer ring 21 via a plurality of bearing balls 22a, 22b, which serve as the first rolling elements. The inner ring of the bearing is integral with the nut 23.

[0035] like Figure 3 As shown in the enlarged view, the outer ring 21 is generally cylindrical and has a flange 21b at one end in the axial direction. The outer ring 21 is mounted to the housing of, for example, a Zθ actuator via the flange 21b. Two outer ring grooves 21a are formed, for example, on the inner surface of the outer ring 21. Two inner ring grooves 24a, for example, are formed on the outer surface of the nut body 24 of the nut 23, opposite to the outer ring grooves 21a. Two rows of bearing balls 22a, 22b are sandwiched between the outer ring grooves 21a and the inner ring grooves 24a in a rolling manner. The bearing balls 22a, 22b are held by an annular retainer. A seal 21c is installed on the outer ring 21 to seal the gap between the outer ring 21 and the nut body 24.

[0036] The nut 23 comprises a cylindrical nut body 24, circulation components 25a and 25b disposed at the axial ends of the nut body 24, and cap components 26a and 26b mounted on the axial end faces of the nut body 24. A helical thread groove 24b is formed on the inner surface of the nut body 24, opposing the thread groove 1a of the shaft 1. A plurality of lead screw balls 27, serving as second rolling elements, are arranged between the thread groove 24b of the nut body 24 and the thread groove 1a of the shaft 1 in a rolling manner. A direction-changing path 28 for circulating the lead screw balls 27 is formed in the circulation components 25a and 25b. A through hole 29 extending axially is formed in the nut body 24. The direction-changing path 28 connects to the thread groove 24b and the through hole 29 of the nut body 24.

[0037] The load rolling path 20, the direction changing path 28, and the through hole 29 between the threaded groove 24b of the nut body 24 and the threaded groove 1a of the shaft 1 constitute a circulation path. The screw ball 27, which moves to one end of the load rolling path 20, returns to the other end of the load rolling path 20 after passing through the direction changing path 28 and the through hole 29 of one circulation component 25a and the direction changing path 28 of the other circulation component 25b.

[0038] like Figure 4As shown, the circulation components 25a and 25b are housed in the recess 24e of the axial end face of the nut body 24. The circulation components 25a and 25b are covered and secured by annular cover members 26a and 26b. The circulation components 25a and 25b are made of resin, while the nut body 24 and cover members 26a and 26b are made of metal. The cover members 26a and 26b cover approximately the entire surface of the axial end face 24c of the nut body 24. The cover members 26a and 26b are fastened to the nut body 24 by fastening members 30 such as screws. It should be noted that the outer diameter of the cover members 26a and 26b is slightly smaller than the outer diameter of the nut body 24. This is to facilitate the engagement of the pulley 41 (described later) with the outer surface 24d of the nut body 24.

[0039] Figure 5 (a) indicates the pulley installation method of this embodiment. Figure 5 (b) indicates a conventional pulley mounting method. The pulley 41 is generally cylindrical with a bottom and has a cylindrical portion 41a and a bottom portion 41b. Multiple teeth 41c that mesh with the timing belt are formed on the outer surface of the cylindrical portion 41a. The pulley 41 is made of a metal such as aluminum.

[0040] like Figure 5 As shown in (a), the pulley 41 engages with the outer surface 24d of the nut body 24 and abuts against the axial end face 26a1 of the cover member 26a, i.e., the axial end face 26a1 of the nut 23. More specifically, the cylindrical portion 41a of the pulley 41 engages with the outer surface 24d of the nut body 24 in a predetermined fit, and the bottom 41b of the pulley 41 abuts against the end face 26a1 of the nut 23. By engaging the pulley 41 with the outer surface 24d of the nut body 24, the pulley 41 can be positioned radially. By abutting against the end face 26a1 of the nut 23, the pulley 41 can be positioned axially. After radial and axial positioning, the pulley 41 is fastened to the nut body 24 by fastening members 42 such as bolts. A threaded hole 24f is formed in the nut body 24 for the fastening member 42 to engage (see reference). Figure 4 A through hole 26a2 is formed in the cover member 26a for the fastening member 42 to pass through (see reference). Figure 4 (or an incision)

[0041] The nut body 24 and the cover member 26a are made of metal, thus enabling the pulley 41 to be securely fixed to the nut 23. Furthermore, almost the entire end face 26a1 of the nut 23 contacts the pulley 41, thereby eliminating any gap between the pulley 41 and the end face 26a1 of the nut 23. This allows for the control of the tightening torque of the fastening member 42 and eliminates the possibility of loosening.

[0042] like Figure 5As shown in (b), in conventional pulley installation methods, to prevent the resin-made circulation component 25a from contacting the pulley 41, an annular outer diameter portion 24g, which protrudes axially in a manner surrounding the circulation component 25a, is integrally formed with the nut body 24, causing the pulley 41 to abut against this outer diameter portion 24g. However, corresponding to the provision of the outer diameter portion 24g, the outer diameter of the nut body 24 becomes larger, and the diameter of the pulley 41 also becomes larger. Furthermore, since a gap 44 is generated between the pulley 41 and the circulation component 25a, this gap 44 may also become a cause of slackness in the pulley 41.

[0043] (Spline nut)

[0044] like Figure 2 As shown, the spline nut 3 is an integral part of the bearing and the ball spline nut. That is, the spline nut 3 has an outer ring 31 and a nut 33 that is rotatably assembled to the outer ring 31 via a plurality of bearing balls 32a, 32b, which serve as the first rolling elements. The inner ring of the bearing and the nut 33 are integral.

[0045] like Figure 6 As shown in the enlarged view, the outer ring 31 is generally cylindrical and has a flange 31b at one end in the axial direction. The outer ring 31 is mounted to the housing of, for example, a Zθ actuator via the flange 31b. Two outer ring grooves 31a are formed on the inner surface of the outer ring 31. Two inner ring grooves 34a, for example, are formed on the outer surface of the nut body 34, opposite to the outer ring grooves 31a. Two rows of bearing balls 32a and 32b are arranged between the outer ring grooves 31a and the inner ring grooves 34a in a rolling manner. The bearing balls 32a and 32b are held by an annular retainer. A seal 31c is installed on the outer ring 31 to seal the gap between the outer ring 31 and the nut body 34.

[0046] The nut 33 includes a cylindrical nut body 34 and circulation components 35a and 35b disposed at the axial ends of the nut body 34. A straight spline groove 34b is formed on the inner surface of the nut body 34, which is opposite to the spline groove 1b of the shaft 1 and extends axially. (It should be noted that...) Figure 6 The diagram shows a row of balls rolling in a spline groove 34b (the spline groove 34b is formed on the inner surface of the nut body 34). Multiple splined balls 37, acting as second rolling elements, are arranged between the spline groove 34b of the nut body 34 and the spline groove 1b of the shaft 1 in a manner capable of rolling motion. U-shaped direction-changing paths 38 for circulating the splined balls 37 are formed in the circulation components 35a and 35b. Figure 6 The image shows balls moving in a U-shaped direction-changing path 38, which is formed in the circulation components 35a and 35b. Additionally, a straight return path 39 parallel to the spline groove 34b is provided in the nut body 34. Figure 6The image shows balls moving in return path 39, which is provided in the nut body 34. Return path 39 is formed in the nut body 34 or in a retainer mounted on the nut body 34. Direction change path 38 connects to the spline groove 34b of the nut body 34 and the return path 39.

[0047] The load rolling path 36, direction changing path 38, and return path 39 between the spline groove 34b of the nut body 34 and the spline groove 1b of the shaft 1 constitute a circulation path. The spline ball 37 that moves to one end of the load rolling path 36 returns to the other end of the load rolling path 36 after passing through the direction changing path 38 and return path 39 of one circulation component 35a and the direction changing path 38 of the other circulation component 35b.

[0048] The circulation components 35a and 35b are mounted on the axial end face 34c of the nut body 34. The circulation components 35a and 35b are made of metal, for example, using MIM (Metal Injection Molding). The circulation components 35a and 35b are annular and cover approximately the entire surface of the end face 34c of the nut body 34. The outer diameter of the circulation components 35a and 35b is slightly smaller than the outer diameter of the nut body 34. This is to facilitate the engagement of the pulley 41 (described later) with the outer surface of the nut body 34. The circulation components 35a and 35b are fastened to the nut body 34 by fastening members 40 such as screws.

[0049] Figure 7 (a) indicates the pulley installation method of this embodiment. Figure 7 (b) indicates the conventional method of installing the pulley. The pulley 41 is the same as the pulley 41 installed on the lead screw nut 2, so the same reference numerals are used and its description is omitted.

[0050] like Figure 7 As shown in (a), the pulley 41 engages with the outer surface 34d of the nut body 34 and abuts against the axial end face 35a1 of the circulation member 35a, i.e., the axial end face 35a1 of the nut 33. More specifically, the cylindrical portion 41a of the pulley 41 engages with the outer surface 34d of the nut body 34 in a predetermined fit, and the bottom 41b of the pulley 41 abuts against the end face 35a1 of the nut 33. By engaging the pulley 41 with the outer surface 34d of the nut body 34, the pulley 41 can be positioned radially. By abutting against the end face 35a1 of the nut 33, the pulley 41 can be positioned axially. After radial and axial positioning, the pulley 41 is fastened to the nut body 34 by fastening members 42 such as bolts. Threaded holes for the fastening members 42 to engage are formed in the nut body 34. A through hole or cutout 25a2 is formed in the circulation component 35a for the fastening member 42 to pass through (see reference). Figure 6 ).

[0051] The nut body 34 and the circulation member 35a are made of metal, thus enabling the pulley 41 to be securely fixed to the nut 33. Furthermore, almost the entire end face 35a1 of the nut 33 contacts the pulley 41, thereby eliminating any gap between the pulley 41 and the end face 35a1 of the nut 33. This allows for the control of the tightening torque of the fastening member 42 and eliminates the possibility of loosening.

[0052] like Figure 7 As shown in (b), in conventional pulley installation methods, to prevent the resin-made circulation component 35a from contacting the pulley 41, an annular outer diameter portion 34g, which protrudes axially in a manner surrounding the circulation component 35a, is integrally formed with the nut body 34, causing the pulley 41 to abut against the outer diameter portion 34g. However, corresponding to the provision of the outer diameter portion 34g, the outer diameter of the nut body 34 becomes larger, and the diameter of the pulley 41 also becomes larger. Furthermore, since a gap 44 is generated between the pulley 41 and the circulation component 35a, this gap 44 may also become a cause of slackness in the pulley 41.

[0053] (The effect of the lead screw nut and spline nut in this embodiment)

[0054] By providing circulation components 25a and 35a at the axial ends of the nut bodies 24 and 34, the outer diameters of the nuts 23 and 33 can be reduced. Furthermore, by abutting the pulley 41 against the axial end faces 26a1 and 35a1 of the nuts 23 and 33 and mounting the pulley 41 to the axial end faces 26a1 and 35a1 of the nuts 23 and 33 via the fastening member 42, the gap between the pulley 41 and the end faces 26a1 and 35a1 of the nuts 23 and 33 can be eliminated, thus eliminating the possibility of pulley 41 becoming loose. Moreover, since it is not necessary to provide annular outer diameter portions 24g and 34g surrounding the circulation components 25a and 35a in the nut bodies 24 and 34, the outer diameters of the nuts 23 and 33 can be further reduced.

[0055] The pulley 41 abuts against the end faces 26a1 and 35a1 of the metal components (e.g., cover member 26a and circulation member 35a) mounted on the nut bodies 24 and 34, thus securing the pulley 41 firmly to the nuts 23 and 33.

[0056] The resin circulation component 25a of the lead screw nut 2 is housed in the recess 24e of the end face 24c of the nut body 24, and the circulation component 25a is covered by a metal cover component 26a. Therefore, it is not necessary to sandwich the resin circulation component 25a between the pulley 41 and the nut body 24, so that the pulley 41 can be firmly fixed to the nut 23.

[0057] The circulation part 35a of the spline nut 33 is made of metal, so the pulley 41 can be firmly fixed to the nut 33.

[0058] Furthermore, the present invention is not limited to the embodiments described above, and can be modified to other embodiments without changing the spirit of the present invention.

[0059] In the lead screw nut of the above embodiment, although the pulley abuts against the cover member, the cover member can also be omitted, and the pulley abuts against the end face of the nut body.

[0060] In the lead screw nut of the above embodiment, although the pulley abuts against the cover member, optional components such as a seal with a metal main body and a lubricating oil supply device can be sandwiched between them, so that the pulley abuts against the optional metal components.

[0061] In the lead screw nut of the above embodiment, although the cover member is installed on the end face of the nut body, optional components such as a seal with a metal body portion can also be sandwiched between them. Furthermore, the cover member can also function as an optional component such as a seal.

[0062] In the spline nut of the above embodiment, the pulley abuts against the circulation component, but optional components such as a seal with a metal main body and a lubricating oil supply device can also be sandwiched between them, and the pulley abuts against the optional metal component.

[0063] This specification is based on Japanese Patent Application No. 2017-210039, filed on October 31, 2017. All its contents are contained herein.

Claims

1. A lead screw nut, wherein, The lead screw nut includes an outer ring and a nut rotatably assembled to the outer ring via a first rolling element. The nut includes: a nut body having a threaded groove on its inner surface; and a circulation component disposed at an axial end of the nut body, having a direction-changing path for circulating a second rolling element that rolls in the threaded groove. The pulley mounted on the nut is fitted into the outer surface of the nut body, and the pulley abuts against the axial end face of the nut. The pulley is mounted to the end face of the nut by a fastening member.

2. The lead screw nut according to claim 1, characterized in that, The end face of the nut is the end face of a metal component mounted on the nut body.

3. The lead screw nut according to claim 2, characterized in that, The nut includes a metal cap member that covers the recirculating component, which is received in a recess on the axial end face of the nut body.

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