Ball screw

Abstract

A ball screw having a circulation member (5) attached to a fitting hole (6) provided in a nut (3), the circulation member (5) circulating rolling balls, in which a pair of gaps (15) into which a jig (20) is inserted is provided between the fitting hole (6) and the circulation member (5), the jig (20) positioning the circulation member (5) with respect to the fitting hole (6). The pair of gaps (15) are located on one side and the other side in the extending direction of the screw shaft, respectively.

Description

TECHNICAL FIELD

[0001] The present application relates to a ball screw having a circulation member that circulates balls. BACKGROUND

[0002] As a ball screw used for a general industrial machine tool or an actuator for an automobile and the like, there is known a ball screw having a nut having a helical thread groove on an inner peripheral surface, a screw shaft having a helical thread groove on an outer peripheral surface, a plurality of balls that are housed in a rollable manner between the thread grooves of the nut and the screw shaft inserted into the nut, and a circulation member that circulates the balls.

[0003] For example, in Patent Literature 1 (Japanese Patent No. 4756645), a method of fixing the circulation member in a fitting hole provided in the nut is disclosed. In this case, after the circulation member is inserted into the fitting hole, a convex engagement portion provided in the circulation member is tilted outward to be engaged with (pressed against) the edge of the fitting hole. Thus, the circulation member is fixed in the fitting hole, and the circulation member is prevented from falling off from the nut. In addition, in a state where the circulation member is fixed in the fitting hole, adjacent thread grooves of the nut are connected to each other by a connection groove of the circulation member, and thus the balls are circulated in the thread grooves by being guided along the connection groove.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 4756645 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, in the structure of mounting the circulation member in the fitting hole of the nut as described above, in order to easily insert the circulation member into the fitting hole, the fitting hole is formed to be slightly larger than the circulation member. Therefore, in a state where the circulation member is mounted in the fitting hole, a gap is generated between the connection groove of the circulation member and the thread groove of the nut.

[0009] Such a gap becomes a step when the balls roll, and thus in order to smoothly roll the balls, it is preferable that the gap be uniform. However, if the positioning accuracy of the circulation member with respect to the fitting hole is not good, the mounting position of the circulation member is deviated, and the gap is also deviated. In this case, in particular, at a portion where the gap is large, the step is also large, and thus it is possible to hinder the smooth rolling of the balls.

[0010] Therefore, an object of the present application is to provide a ball screw that can highly accurately perform positioning of a circulation member with respect to a fitting hole, and thus can ensure smooth rolling of balls.

[0011] Methods for solving problems

[0012] To address the aforementioned issues, the present invention provides a ball screw comprising: a nut having a helical threaded groove on its inner circumferential surface; a screw shaft having a helical threaded groove on its outer circumferential surface; a plurality of balls, which are rotatably housed between the threaded groove of the nut and the threaded groove of the screw shaft inserted into the nut; and a circulation member mounted in a fitting hole provided on the nut to circulate the rolling balls. The invention is characterized in that a pair of gaps are provided between the fitting hole and the circulation member for inserting a fixture, the fixture being used to position the circulation member relative to the fitting hole, the pair of gaps being located on one side and the other side of the extension direction of the screw shaft.

[0013] Thus, in the ball screw of this embodiment, a pair of gaps are provided between the fitting hole and the circulating component for inserting a fixture for positioning the circulating component. Therefore, by inserting the fixture into these gaps, the circulating component can be positioned with high precision. As a result, the deviation of the gap between the circulating component and the nut can be reduced, thus ensuring smooth rolling of the balls. Here, one side and the other side of the extending direction of the screw shaft are one side with the direction extending from the axis of the screw shaft as the axial direction and the other side opposite to that side.

[0014] Preferably, the center of the recirculating component is aligned with the center of the fitting hole. By installing the recirculating component with its center aligned with the center of the fitting hole, the gap between the recirculating component and the nut becomes uniform, thus enabling smoother ball rolling.

[0015] Alternatively, the circulation component may have a non-planar contact surface that contacts the portion of the fixture inserted into a pair of gaps.

[0016] Invention Effects

[0017] According to the present invention, the positioning of the circulating component relative to the fitting hole can be performed with high precision, thereby ensuring the smooth rolling of the ball. Attached Figure Description

[0018] Figure 1 This is a top view of a ball screw according to one embodiment of the present invention.

[0019] Figure 2 This is a longitudinal sectional view of the ball screw according to this embodiment.

[0020] Figure 3 This is a longitudinal sectional view of the nut in this embodiment.

[0021] Figure 4 This is a cross-sectional perspective view showing the state before the circulation component is installed on the nut in this embodiment.

[0022] Figure 5 This diagram shows the state in which the center of the circulation component aligns with the center of the fitting hole.

[0023] Figure 6 This is a diagram showing the state in which the center of the circulation component deviates from the center of the fitting hole.

[0024] Figure 7 This is a perspective view of the fixture in this embodiment.

[0025] Figure 8 This is a side view of the fixture in this embodiment.

[0026] Figure 9 The fixture of this embodiment is along Figure 8 A cross-sectional view cut off by line AA.

[0027] Figure 10 This is a diagram illustrating the method of fixing the circulating components.

[0028] Figure 11 This is a diagram illustrating the method of fixing the circulating components.

[0029] Figure 12 This is a perspective view of the circulation component and fixture according to other embodiments of the present invention.

[0030] Figure 13 This diagram illustrates the state in which a circulatory component is positioned using a fixture according to another embodiment of the present invention. Detailed Implementation

[0031] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Furthermore, in the drawings used to describe the present invention, components or constituent elements having the same function or shape are labeled with the same reference numerals whenever they can be identified. Therefore, the description of constituent elements that have been described once is omitted.

[0032] according to Figures 1-4 The overall structure of a ball screw according to one embodiment of the present invention will be described. Figure 1 This is a top view of the ball screw according to this embodiment. Figure 2 This is a longitudinal sectional view of the ball screw. Additionally, Figure 3 This is a longitudinal sectional view of the nut that is part of the ball screw. Figure 4 This is a cross-sectional perspective view showing the state before the circulation component is installed on the nut.

[0033] like Figure 1 and Figure 2 As shown, the ball screw 1 of this embodiment has a screw shaft 2, a nut 3, a plurality of balls 4, and a circulation component 5.

[0034] The lead screw 2 has a helical threaded groove 2a on its outer circumferential surface, and the lead screw 2 is inserted into a cylindrical nut 3. On the other hand, the nut 3 has a helical threaded groove 3a on its inner circumferential surface that is opposite to the threaded groove 2a of the lead screw 2. A plurality of balls 4 are accommodated in a rolling manner between these threaded grooves 2a and 3a.

[0035] The cross-sectional shape of each threaded groove 2a and 3a can be either a circular arc or a Gothic arch shape. In this embodiment, each threaded groove 2a and 3a is formed into a Gothic arch shape that allows for a larger contact angle with the ball 4 and a smaller axial clearance. Therefore, the rigidity of each threaded groove 2a and 3a relative to axial load is increased, and vibration can be suppressed.

[0036] In addition, a circular fitting hole 6 is provided in the nut 3, which extends from the inner circumference of the nut 3 to the outer circumference, cutting off a portion of the threaded groove 3a. Moreover, a circulation member 5 with a roughly circular cross-section is inserted into the fitting hole 6.

[0037] The circulation component 5 has a connecting groove 5a that connects adjacent turns of the threaded groove 3a of the nut 3 to each other. Therefore, as Figure 3 As shown, when the circulation component 5 is inserted into the fitting hole 6, the adjacent threaded grooves 3a of the nut 3 are connected to each other by a connecting groove 5a bent into an S-shape. The connecting groove 5a and approximately one circumference of the threaded grooves 3a form the rolling path of the balls 4. Thus, multiple balls 4 are guided by the connecting groove 5a of the circulation component 5, passing over the threads of the lead screw shaft 2 and returning to the adjacent lead screw groove 3a. Furthermore, the multiple balls 4 roll again along the threaded grooves 2a and 3a, thereby completing the cycle. The depth of the connecting groove 5a is set to the depth to which the balls 4 can pass over the threads of the lead screw shaft 2 within the connecting groove 5a.

[0038] In addition, such as Figure 3 As shown, a pair of arms 9 are provided on the circulation member 5, protruding in opposite directions. When the circulation member 5 is inserted into the engagement hole 6 of the nut 3, each arm 9 of the circulation member 5 engages with the threaded groove 3a of the nut 3, thereby positioning the circulation member 5 axially relative to the nut 3 and preventing the circulation member 5 from falling off in the direction of the nut's outer diameter. In addition, each arm 9 engages with the non-rolling threaded groove 3a of the ball 4 in a manner that does not impede the rolling of the ball 4.

[0039] In addition, such as Figure 1 As shown, a pair of engaging portions 12 are provided on the outer diameter side of the nut of the circulation component 5, protruding in the outward direction. When the circulation component 5 is inserted into the fitting hole 6 of the nut 3, each engaging portion 12 is pressed outward (in the direction of separation) and squeezed, thereby engaging each engaging portion 12 with the edge of the fitting hole 6. Thus, the circulation component 5 is fixed relative to the nut 3.

[0040] Here, as in the embodiment described above, in the structure where the circulation member 5 is installed within the fitting hole 6 of the nut 3, the positioning accuracy of the circulation member 5 relative to the fitting hole 6 affects the rolling performance of the ball 4. That is, in the case of... Figure 5 In the example shown, when the center O of the circulation component 5 is aligned with the center P of the fitting hole 6, the gaps S1 and S2 between the connecting groove 5a of the circulation component 5 and the threaded groove 3a of the nut 3 can be made equal. However, in cases where the circulation component 5 is installed with its center O aligned with the center P of the fitting hole 6, the gaps S1 and S2 between the connecting groove 5a of the circulation component 5 and the threaded groove 3a of the nut 3 can be made equal .... Figure 6 In the example shown, when the center O of the circulation component 5 is offset from the center P of the fitting hole 6 and the circulation component 5 is installed to one side, the gaps S1 and S2 between the connecting groove 5a of the circulation component 5 and the threaded groove 3a of the nut 3 deviate (S1 > S2). Thus, when the gaps S1 and S2 deviate, this is especially noticeable in areas with larger gaps ( Figure 6 The gap S1 in the middle), the step between the connecting groove 5a of the circulation component 5 and the thread groove 3a of the nut 3 becomes larger, which may hinder the smooth rolling of the ball 4.

[0041] Therefore, in the ball screw of this embodiment, in order to accurately position the circulation component 5 relative to the fitting hole 6, a fixture is used to fix the circulation component 5. Hereinafter, the structure of the fixture used in this embodiment and the method of fixing the circulation component 5 using the fixture (the manufacturing method of the ball screw) will be described.

[0042] Figure 7 This is a perspective view of the fixture used in this embodiment. Figure 8 This is a side view of the fixture. Figure 9 Is to place the jig along Figure 8 A cross-sectional view cut off by line AA.

[0043] like Figures 7-9 As shown, the fixture 20 has a cylindrical main body 21, a pair of positioning portions 22, and a pair of pressing portions 23. The pair of positioning portions 22 and the pair of pressing portions 23 are each provided such that they protrude from one end of the main body 21 along its length. The pair of positioning portions 22 protrude significantly more than the pressing portions 23 and are arranged spaced apart from each other. On the other hand, the protrusion of the pair of pressing portions 23 is smaller than that of the positioning portions 22, and the pair of pressing portions 23 are arranged spaced apart from each other in directions that intersect or are perpendicular to the directions opposite to the positioning portions 22.

[0044] In addition, each extrusion section 23 has a centerline L that approaches the main body section 21 toward its respective front end (see reference). Figure 9 The inclined surface 23a is tilted in a manner that allows it to be inclined. This inclined surface 23a functions as a pressing part that presses the engaging part 12 when the engaging part 12 of the compression circulation member 5 is pressed.

[0045] On the other hand, the pair of positioning portions 22 are formed in a cross section perpendicular to the center line L of the main body portion 21 as a D-shaped cross section composed of an arc portion and a straight portion. That is, each positioning portion 22 has a flat portion 22a arranged toward the center line L side (inner side) of the main body portion 21 and an arc portion 22b arranged toward the side opposite to the center line L side (outer side).

[0046] In order to install the circulation component 5 onto the nut 3 using the fixture 20 of this embodiment, firstly, the circulation component 5 is inserted into the fitting hole 6 from the inner diameter side of the nut 3, and then, as described above... Figure 10 As shown, the positioning part 22 of the fixture 20 is inserted into the gap 15 between the circulation component 5 and the fitting hole 6.

[0047] Here, in this embodiment, as Figure 1 and Figure 3 As shown, the circulation member 5 has a pair of flat portions 5b facing opposite directions, so that when the circulation member 5 is inserted into the fitting hole 6, a D-shaped gap 15 is formed between these flat portions 5b and the inner circumferential surface of the fitting hole 6. Then, a positioning portion 22 with the same D-shaped cross-section is inserted into the D-shaped gap 15.

[0048] Thus, in this embodiment, D-shaped gaps 15 are provided on one side and the other side of the lead screw shaft 2 extending in the direction between the fitting hole 6 and the circulation member 5. Therefore, by inserting a pair of positioning parts 22 into these gaps 15, the circulation member 5 can be positioned within the fitting hole 6. That is, as... Figure 10 As shown, when the positioning part 22 is inserted into the gap 15, the flat part 22a of the positioning part 22 contacts the flat part 5b of the circulation member 5, and the arcuate part 22b of each positioning part 22 contacts the inner circumferential surface of the fitting hole 6. Therefore, the displacement (position offset) of the circulation member 5 in the fitting hole 6 is limited by the pair of positioning parts 22. Thus, the circulation member 5 is positioned with high precision relative to the fitting hole 6.

[0049] Then, with the circulation component 5 positioned, the jig 20 is further pressed into the fitting hole 6, as... Figure 11 As shown by the double-dotted line, a pair of engaging portions 12 of the circulation component 5 are pressed by the inclined surfaces 23a of a pair of pressing portions 23, and each engaging portion 12 is pressed outward (compressed). As a result, each engaging portion 12 engages with the edge of the fitting hole 6, fixing the circulation component 5 relative to the nut 3.

[0050] As described above, in this embodiment, by using the gap 15 between the fitting hole 6 and the circulation member 5 as a gap for inserting the fixture 20 (positioning part 22) for positioning the circulation member 5, the circulation member 5 can be positioned with high precision relative to the fitting hole 6. Thus, as Figure 5 As shown, the center O of the circulation component 5 is aligned with the center P of the fitting hole 6, and the gaps S1 and S2 between the connecting groove 5a of the circulation component 5 and the threaded groove 3a of the nut 3 are equal, thereby ensuring the smooth rolling of the ball.

[0051] Furthermore, the position of the center O of the circulation member 5 does not necessarily need to coincide with the center P of the fitting hole 6. Even in such a case, by using the fixture 20 of this embodiment, the positional offset of the circulation member 5 relative to the fitting hole 6 can be reduced, thereby improving the positioning accuracy and enabling smooth rolling of the balls.

[0052] The pair of flat surfaces 5b of the circulation component 5 are preferably machined surfaces such as those produced by cutting or grinding. In this case, each flat surface 5b can be more accurately aligned with the surface of the positioning part 22, thus further improving the positioning accuracy. In addition, each flat surface 5b is formed in a direction substantially perpendicular to the axial direction of the lead screw shaft 2, so it is easy to visually confirm whether the circulation component 5 has any positional misalignment and the extent of it.

[0053] Furthermore, the jig 20 is preferably a jig that integrally has a positioning part 22 and a pressing part 23 as described in the above embodiment. Since the jig 20 integrally has the positioning part 22 and the pressing part 23, it is possible to use a single jig 20 to position and fix (press) the circulating component 5 relative to the fitting hole 6, thereby improving work efficiency. Additionally, in the above embodiment, each engaging part 12 is formed at a position perpendicular to the gap 15 (flat part 5b), so that the positioning and fixing (pressing) of the circulating component 5 can be performed simultaneously using a single jig 20.

[0054] Furthermore, the method described above is exemplified by inserting the positioning part 22 of the fixture 20 after inserting the circulation member 5 into the fitting hole 6. However, the process of positioning the circulation member 5 is not limited to the method described above. For example, the positioning part 22 may be inserted into the fitting hole 6 before the circulation member 5, and then the circulation member 5 may be inserted into the fitting hole 6 for positioning.

[0055] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and appropriate changes can be made without departing from the spirit of the invention.

[0056] For example, such as Figure 12As shown in the example, a semi-circular protrusion 220 can be provided on the flat portion 22a of each positioning portion 22 of the fixture 20, and a semi-circular recess 50 can be provided on each flat portion 5b of the circulation member 5. In this case, as... Figure 13 As shown, when the positioning part 22 of the fixture 20 is inserted into both sides of the circulation member 5, the protrusion 220 of the positioning part 22 engages with the concave part 50 of the circulation member 5, thereby positioning the circulation member 5 within the engagement hole 6. Alternatively, the engagement protrusion 220 and concave part 50 can be provided on the planar part 22a of the positioning part 22 and the planar part 5b of the circulation member 5 to position the circulation member 5. That is, the circulation member 5 and the fixture 20 can also have non-planar contact surfaces (protrusion 220 and concave part 50) where the portion of the fixture 20 inserted into the engagement hole 6 and the circulation member 5 in the extension direction of the lead screw shaft 2 (the positioning part 22) contacts the circulation member 5. Furthermore, the shapes of the protrusion 220 and concave part 50 can be shapes other than a semi-circular cross-section, and can also be... Figure 12 and Figure 13 In contrast, the fixture 20 has a recess, and the circulation member 5 has a protrusion that engages with the recess.

[0057] Label Explanation

[0058] 1: Ball screw; 2: Screw shaft; 2a: Threaded groove; 3: Nut; 3a: Threaded groove; 4: Ball; 5: Circulation component; 5a: Connecting groove; 6: Fitting hole; 15: Clearance; 20: Fixture; 21: Main body; 22: Positioning part; 23: Extrusion part.

Claims

1. A ball screw having: a nut having a helical thread groove on an inner peripheral surface; a screw shaft having a helical thread groove on an outer peripheral surface; a plurality of balls housed in a rollable manner between the thread groove of the nut and the thread groove of the screw shaft inserted to the nut; and a circulation member installed to a fitting hole provided on the nut to circulate the balls rolling, characterized in that a pair of gaps for insertion of a jig for positioning the circulation member with respect to the fitting hole are provided between the fitting hole and the circulation member, the pair of gaps being respectively located on one side and the other side in an extension direction of the screw shaft.

2. The ball screw according to claim 1, wherein a center of the circulation member is configured to coincide with a center of the fitting hole.

3. The ball screw according to claim 1 or 2, wherein the circulation member has a non-planar contact surface which contacts a portion of the jig inserted to the pair of gaps. ​ ​ ​ ​ ​ ​ ​ ​

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