JP2018091454A - Ball Screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a top-type ball screw having a structure which can adjust a position with respect to a penetration hole of a nut at the attachment of a top.SOLUTION: A top 4 is attached into a columnar penetration hole 22 formed at a nut 2 by using a fixing part 5. The top 4 is composed of a columnar body whose diameter is smaller than that of a column which forms the penetration hole 22, and a notch 42 for notching at least a part of an external peripheral part of the columnar body is formed at a first end face 41 out of two end faces of the columnar body in an axial direction. An S-shaped groove is formed at a second end face. The top 4 is inserted into the penetration hole 22 with the first end face 41 orientated toward an external peripheral side of the nut 2. The fixing part 5 fixes the top 4 into the penetration hole 22 by being pressure-inserted into the notch 42 of the top 4 which is inserted into the penetration hole 22, and pressing the penetration hole 22.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball screw having a top as a part forming a return path.

The ball screw has a screw shaft, a nut, and a plurality of balls. The screw shaft is disposed in the nut. A ball raceway is formed by the spiral groove of the screw shaft and the spiral groove of the nut. The nut has a return path for returning the ball from the end point of the track to the start point. The ball is disposed in a circulation path composed of a track and a return path. A ball screw is a device in which a screw shaft and a nut move relative to each other via a ball that circulates in a circulation path and rolls in a track (moves while rotating in a loaded state). The return path is formed by attaching a return tube or a piece to the nut.
In a top-type ball screw having a top as a part for forming a return path, the top is mounted in a through hole that penetrates a nut in a radial direction. Conventionally, in a top-type ball screw, in order to maintain the position of the top within the penetration, for example, a separate member is used or crimping or the like is performed to fix the top in the through hole. In addition, for the purpose of reducing working time and cost, proposals have been made regarding a structure for attaching a top to a through hole of a nut.

Patent Document 1 describes that a rectangular groove larger than the through hole is provided on the outer peripheral side of the through hole of the nut in which the piece is arranged, and a wedge member is inserted into the groove to fix the piece to the through hole. ing. The planar shape of the top is a shape in which both longitudinal ends of an elongated rectangle corresponding to the S-shaped groove forming the return path are arcuate.
Patent Document 2 describes a frame having a disk-shaped main body and a pair of protrusions protruding from the outer periphery thereof and having an S-shaped groove on the disk surface of the main body. A pair of recesses into which the pair of protrusions are fitted are formed at positions facing each other on the peripheral surface of the through hole of the nut. After the top is positioned in the through hole of the nut by alignment with the protrusions and the recesses, the top is fixed to the through hole using a fixing component whose attachment direction to the nut is different from that of the top.

Japanese Utility Model Publication No. 58-76851 JP2015-132369A

In the top-type ball screw, if a large step occurs at the connection between the S-shaped groove of the top and the spiral groove of the nut, the torque of the ball screw instantaneously increases when the ball passes through this step, and the ball screw Since there is a possibility of locking, it is necessary to reduce this step. At present, this step is reduced by increasing the processing accuracy of the top and nut. That is, the current piece type ball screw does not have a structure capable of reducing the step by adjusting the position of the nut relative to the through hole when the piece is attached.
In addition, since the demand for the operability of the ball screw is high, it is necessary to manage this step more strictly.

  An object of the present invention is to provide a top type ball screw having a structure capable of adjusting the position of a nut with respect to a through hole when the top is attached.

In order to solve the above problems, a ball screw according to an aspect of the present invention has the following configurations (1) to (4).
(1) A screw shaft having a spiral groove formed on the outer peripheral surface, and a nut made of a cylindrical body in which the screw shaft is inserted and a spiral groove is formed on the inner peripheral surface. A raceway is formed by the spiral groove of the nut and the spiral groove of the screw shaft. The nut has a columnar through hole penetrating in the radial direction of the cylindrical body.
(2) It has a frame having a return path as an S-shaped groove connecting the end point and the start point of the track to form a circulation path. The top is composed of a cylindrical body having a smaller diameter than the cylinder forming the through hole of the nut, and a notch that lacks at least a part of the outer peripheral portion of the cylindrical body on the first end surface of the two axial end surfaces of the cylindrical body. Part is formed, and an S-shaped groove is formed on the second end face.
(3) It has a fixing part that fixes the frame to the through hole of the nut. This fixed part is press-fitted into the notch portion of the frame inserted into the through hole with the first end surface facing the outer peripheral side of the nut, and presses the through hole.
(4) It has a plurality of balls arranged on the track and the return path. The screw shaft and the nut move relative to each other via a ball that rolls in the track.

  According to the ball screw of one aspect of the present invention, the position of the cylindrical body with respect to the through hole of the nut can be adjusted when the top is attached by moving or rotating the nut in the through hole of the nut in the radial direction of the nut. Yes. In addition, with this position adjustment, the top is fixed to the through-hole of the nut with a fixing part in a state where the level difference of the connecting portion between the S-shaped groove of the top and the spiral groove of the nut is reduced, so that the top type ball screw The operability of is improved.

It is a figure explaining the ball screw of a first embodiment, and is a figure which made a section of a portion where a part of a nut was broken to show a screw shaft and a ball, and a nut top was attached. It is the figure which looked at an example of the top which constitutes the ball screw of a first embodiment from each direction, (a) is a figure showing the field arranged at the perimeter side of a nut, (b) is a figure of (a) The figure seen from b direction, (c) is the figure seen from c direction of (b), (d) is the figure seen from d direction of (b). It is a figure which shows the fixed component which comprises the ball screw of 1st embodiment, Comprising: (a) is a figure which shows the surface arrange | positioned at the outer peripheral surface side of a nut, (b) was seen from b direction of (a). FIG. It is the figure which looked at an example of the top which constitutes the ball screw of a first embodiment from each direction, (a) is a figure showing the field arranged at the perimeter side of a nut, (b) is a figure of (a) The figure seen from b direction, (c) is the figure seen from c direction of (b), (d) is the figure seen from d direction of (b). It is a figure explaining the ball screw of 2nd embodiment, Comprising: While breaking a part of nut and showing a screw shaft and a ball | bowl, it is the figure which made the cross section the part to which the top of the nut was attached. It is the figure which looked at an example of the top which constitutes the ball screw of a 2nd embodiment from each direction, and (a) is a figure showing the field arranged at the perimeter side of a nut, and (b) is a figure of (a) The figure seen from b direction, (c) is the figure seen from c direction of (b), (d) is the figure seen from d direction of (b). It is a figure which shows the fixing component which comprises the ball screw of 2nd embodiment, Comprising: (a) is a figure which shows the surface arrange | positioned at the outer peripheral surface side of a nut, (b) was seen from the b direction of (a). FIG.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to embodiment shown below. In the embodiment described below, a technically preferable limitation is made for carrying out the present invention, but this limitation is not an essential requirement of the present invention.

[First embodiment]
As shown in FIG. 1, the ball screw of the first embodiment has a screw shaft 1, a nut 2, a plurality of balls 3, and three pieces 4. Each frame 4 has two fixing parts 5. Helical grooves 11 and 21 are formed on the outer peripheral surface 10 of the screw shaft 1 and the inner peripheral surface 20 of the nut 2. The screw shaft 1 passes through the nut 2. The nut 2 has a flange portion 2B at one axial end of the cylindrical portion 2A. A raceway on which the ball 3 rolls is formed by the spiral groove 11 of the screw shaft 1 and the spiral groove 21 of the nut 2.
The cylindrical portion 2A of the nut 2 has a columnar through hole 22 penetrating in the radial direction. The frame 4 is inserted into the through hole 22 and is fixed using the fixing component 5 by a method described later.

As shown in FIG. 2, the top 4 is formed of a cylindrical body. The diameter of the top 4 is slightly smaller than the diameter of the through hole 22 of the nut 2. A pair of notches 42 are formed on a first end surface (a surface disposed on the outer peripheral side of the nut 2) 41 of the two axial end surfaces of the cylindrical body forming the top 4.
The cutout portion 42 is a portion in which a part of the outer peripheral portion of the cylindrical body is cut off, and a bottom surface 42a parallel to the first end surface 41, a pair of opposing wall surfaces 42b, and a back surface that is a radially central surface. A surface 42c is provided. The wall surface 42 b and the back surface 42 c are surfaces perpendicular to the first end surface 41. The pair of notches 42 are formed at positions of a pair of arcs 40 that are opposite to each other in the radial direction of the cylindrical body.
The second end surface 43 of the top 4 is an arc surface facing the outer peripheral surface 12 of the screw shaft 1. The diameter of the arc surface forming the second end face 43 is larger than the outer diameter of the screw shaft 1 and is substantially the same as the inner diameter of the nut 2. An S-shaped groove 44 that forms a return path for the ball 3 is formed in the second end face 43. In FIG. 2C, the movement path 30 of the ball 3 is indicated by a one-dot chain line.

  As shown in FIG. 3, the fixed component 5 includes an arcuate surface 50 that is brought into contact with the through hole 22 of the nut 2, a lower surface 51 a that is brought into contact with the bottom surface 42 a of the cutout portion 42 of the top 4, and a wall surface 42 b of the cutout portion 42. And a top surface 51d parallel to the bottom surface 51a. The diameter of the circular arc surface 50 of the fixed component 5 is slightly larger than the diameter of the through hole 22 of the nut 2. A distance d51 between the side surfaces 51b of the fixed component 5 is slightly larger than a distance d41 between the wall surfaces 42b of the notch portion 42 of the top 4. The distance d52 between the lower surface 51a and the upper surface 51d of the fixed component 5 is the same as the axial dimension d42 of the notch portion 42 of the top 4.

In this embodiment, the top 4 is made of a synthetic resin, and the fixed part 5 is made of rubber or a thermoplastic elastomer. Examples of the synthetic resin forming the top 4 include PPS (polyphenylene sulfide), POM (polyacetal), PEEK (polyether ether ketone), 6 nylon, 4, 6 nylon, 6, 6 nylon and the like. The top 4 may be formed of a resin composition in which a reinforcing material made of glass fiber, potassium titanate fiber, or the like is mixed with these synthetic resins.
The top 4 may be made of metal, for example, may be formed by a metal powder injection molding method (MIM). Examples of the MIM alloy to be used include Fe—Ni—C (1 to 8% Ni, to 0.8% C).

The ball 3 is disposed in a circulation path composed of a track and an S-shaped groove (return path) 44 of the top 4. The ball 3 rolls in the track and circulates in the circulation path. The screw shaft 1 and the nut 2 move relative to each other via the ball 3.
When the ball screw is assembled, first, for example, the screw shaft 1 is inserted into the nut 2, and the ball 3 is filled into the track (between the spiral grooves 11 and 21) from the through hole 22. Alternatively, after the temporary shaft is inserted into the nut 2 and the ball 3 is disposed in the spiral groove 21, the temporary shaft is replaced with the screw shaft 1 which is the main shaft, whereby the ball 3 is filled in the track.

In this state, the top 4 is inserted into the through hole 22 of the nut 2 from the upper side of the nut 2 with the first end face 41 facing upward. Thereby, the first end face 41 of the top 4 faces the outer peripheral side of the nut 2, and the second end face 43 faces the screw shaft 1. Next, the step between the spiral groove 21 of the nut 2 and the S-shaped groove 44 of the top 4 is reduced by moving the top 4 in the radial direction of the nut 2 or rotating the top 4 within the through hole 22. Adjust so that
Next, the two fixing parts 5 are press-fitted into the two notches 42 of the top 4 in the through hole 22. At that time, the fixing component 5 is inserted in the axial direction until it contacts the bottom surface 42 a of the notch 42, presses the wall surface 42 b and the back surface 42 c, and presses the through hole 22 with the circular arc surface 50. Thereby, the top 4 is fixed to the through hole 22 of the nut 2 by the frictional force of the fixed component 5.

According to the ball screw of the first embodiment, as described above, the piece 4 made of a cylindrical body is moved or rotated in the radial direction of the nut 2 in the through hole 22 of the nut 2, so that the piece 4 is rotated. At the time of mounting, the position adjustment can be performed so that the level difference of the connecting portion between the S-shaped groove 44 of the top 4 and the spiral groove 21 of the nut 2 becomes small. As a result, when the ball 3 passes through the connecting portion between the S-shaped groove 44 of the top 4 and the spiral groove 21 of the nut 2, it is possible to prevent the torque of the ball screw from increasing instantaneously.
Moreover, it can be said that the measure for reducing the level difference due to the ball screw of the first embodiment is a method with a lower manufacturing cost than the current measure for reducing the level difference by increasing the machining accuracy of the top and nut.

  The top 4 of FIG. 2 has two notches 42 and is fixed to the through hole 22 of the nut 2 with two fixing parts 5. Instead of the frame 4, a frame 4A having only one notch 42 as shown in FIG. 4 may be used. In that case, like the top 4, the top 4A is inserted into the through hole 22 of the nut 2 and the above adjustment is performed, and then one fixed component 5 is press-fitted into the notch 42 of the top 4A. Then, the top 4 </ b> A is fixed to the through hole 22 of the nut 2.

[Second Embodiment]
As shown in FIG. 5, in the ball screw of the second embodiment, the top 4B shown in FIG. 6 is fixed to the through hole 22 of the nut 2 using the fixing component 6 shown in FIG. Other points are the same as the ball screw of the first embodiment.
As shown in FIG. 6, the top 4B is formed of a cylindrical body. The diameter of the top 4B is slightly smaller than the diameter of the through hole 22 of the nut 2. A notch 45 is formed on a first end surface (a surface disposed on the outer peripheral side of the nut 2) 41 of the two axial end surfaces of the cylindrical body forming the top 4B.

The cutout portion 45 is a portion where the entire outer peripheral portion of the cylindrical body is cut off. Therefore, the notch 45 has a bottom surface 45a parallel to the first end surface 41 and a back surface 45c that is a surface on the center side in the radial direction. However, the notch 45 has a wall surface 42b that the notch 42 of the top 4 in FIG. Does not have a corresponding surface. That is, in the top 4B, the notch 45 is formed in the entire circumferential direction of the cylindrical body.
The second end surface 43 of the top 4B is an arc surface facing the outer peripheral surface 12 of the screw shaft 1. The diameter of the arc surface forming the second end face 43 is larger than the outer diameter of the screw shaft 1 and is substantially the same as the inner diameter of the nut 2. An S-shaped groove 44 that forms a return path for the ball 3 is formed in the second end face 43. In FIG. 6C, the movement path 30 of the ball 3 is indicated by a one-dot chain line.

  Further, as shown in FIGS. 6B and 6D, the shape of the top 4B can be said to be a shape in which a columnar main body 410 and a disk-shaped attachment portion 420 are integrated coaxially. The main body 410 is formed of a cylindrical body that is slightly smaller than the diameter of the through hole 22 of the nut 2. The diameter of the mounting portion 420 is smaller than the diameter of the main body 410. At the boundary between the main body 410 and the mounting portion 420, the bottom surface 45a of the notch 45 is present in an annular shape.

As shown in FIG. 7, the fixing component 6 is an annular component having a rectangular cross section. The outer diameter (the diameter of the outer peripheral surface 61) of the fixed component 6 is slightly larger than the diameter of the through hole 22 of the nut 2, and the inner diameter (the diameter of the inner peripheral surface 62) is slightly smaller than the diameter of the inner surface 45 c of the notch 45. The axial dimension d6 of the fixed component 6 is the same as the axial dimension d420 of the mounting portion 420 of the top 4B.
The top 4B is made of synthetic resin or metal, and the fixed component 5 is made of rubber or thermoplastic elastomer. As a specific material of the top 4B, the same material as the top 4 described in the first embodiment can be used.

When the ball screw is assembled, first, for example, the screw shaft 1 is inserted into the nut 2, and the ball 3 is filled into the track (between the spiral grooves 11 and 21) from the through hole 22. Alternatively, after the temporary shaft is inserted into the nut 2 and the ball 3 is disposed in the spiral groove 21, the temporary shaft is replaced with the screw shaft 1 which is the main shaft, whereby the ball 3 is filled in the track.
In this state, the top 4B is inserted into the through hole 22 of the nut 2 from above the nut 2 with the first end face 41 facing upward. Thereby, the first end surface 41 of the top 4B faces the outer peripheral side of the nut 2, and the second end surface 43 faces the screw shaft 1. Next, the step between the spiral groove 21 of the nut 2 and the S-shaped groove 44 of the top 4B is reduced by moving the top 4B in the radial direction of the nut 2 or rotating the top 4B within the through hole 22. Adjust so that

Next, the fixed component 6 is press-fitted into the notch 45 of the top 4 </ b> B in the through hole 22. At that time, the fixed component 6 is inserted in the axial direction until it contacts the bottom surface 45 a of the notch 45, presses the back surface 45 c with the inner peripheral surface 62, and presses the through hole 22 with the outer peripheral surface 61. Thereby, the top 4 </ b> B is fixed to the through hole 22 of the nut 2 by the frictional force of the fixed component 6.
According to the ball screw of the second embodiment, as described above, the top 4B made of a cylindrical body is moved or rotated in the radial direction of the nut 2 within the through hole 22 of the nut 2 to thereby rotate the top 4B. At the time of mounting, the position adjustment can be performed so that the level difference of the connecting portion between the S-shaped groove 44 of the top 4B and the spiral groove 21 of the nut 2 becomes small. As a result, when the ball 3 passes through the connecting portion between the S-shaped groove 44 of the top 4B and the spiral groove 21 of the nut 2, it is possible to prevent the torque of the ball screw from increasing instantaneously.

Moreover, it can be said that the measure for reducing the level difference due to the ball screw of the second embodiment is a method with a lower manufacturing cost than the current measure for reducing the level difference by increasing the machining accuracy of the top and the nut.
Further, the top 4B of the second embodiment has the notch 45 formed in the entire circumferential direction of the cylindrical body and is fixed in the through hole 22 of the nut 2 by the annular fixing component 6. There is no gap between the frame 4B.

DESCRIPTION OF SYMBOLS 1 Screw shaft 10 Outer peripheral surface of screw shaft 11 Screw shaft spiral groove 2 Nut 2A Nut cylindrical portion 2B Nut flange portion 20 Nut inner peripheral surface 21 Nut spiral groove 22 Nut through hole 3 Ball 4 Top 4A Top 4B Frame 41 First end surface of frame 42 Notch portion of frame 43 Second end surface of frame 44 S-shaped groove 45 Notch portion of frame 410 Body of frame 420 Mounting portion of frame 5 Fixed component 6 Fixed component 61 Outer periphery of fixed component Surface 62 Inner peripheral surface of fixed part

Claims (3)

A screw shaft having a spiral groove formed on the outer peripheral surface;
A nut formed of a cylindrical body in which the screw shaft is inserted and a spiral groove is formed on an inner peripheral surface, and a raceway is formed by the spiral groove and the spiral groove of the screw shaft, and a radial direction of the cylindrical body A nut having a cylindrical through-hole penetrating into
A top having an S-shaped groove as a return path that connects the end point and the start point of the track to form a circulation path, and is composed of a cylinder having a diameter smaller than that of the cylinder forming the through hole. A top having a notch portion lacking at least a part of the outer peripheral portion of the cylindrical body on the first end surface of the two axial end surfaces, and the S-shaped groove formed on the second end surface;
A fixing component for fixing the top to the through hole, wherein the first end surface is press-fitted into the notch portion of the top inserted into the through hole with the first end surface facing the outer peripheral side of the nut. Fixing parts to press,
A plurality of balls disposed in the trajectory and the return path;
Have
A ball screw in which the screw shaft and the nut move relative to each other via the ball rolling in the track.   The ball screw according to claim 1, wherein the notch is formed at a position of a pair of arcs that are opposite to each other in the radial direction of the cylindrical body.   The ball screw according to claim 1, wherein the notch is formed in the entire circumferential direction of the cylindrical body.

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