JP6859688B2 - Ball screw - Google Patents

Description

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

A ball screw has a screw shaft, a nut, and a plurality of balls. The screw shaft is located inside the nut. A ball trajectory is formed by the spiral groove of the screw shaft and the spiral groove of the nut. The nut has a return path that returns the ball from the end of the trajectory to the start. The ball is arranged in a circulation path consisting of a trajectory 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 an orbit (moves while rotating under a load). The return path is formed by attaching a return tube or top to the nut.
In a top-type ball screw having a top as a component forming a return path, the top is mounted in a through hole that penetrates the nut in the radial direction. Conventionally, in a top type ball screw, in order to maintain the position of the top in the through hole, for example, another member is used or work such as caulking is performed to fix the top in the through hole. Further, for the purpose of reducing working time and cost, a proposal has been made regarding a structure for attaching a top to a through hole of a nut.

Patent Document 1 describes that a square groove larger than the through hole is provided on the outer peripheral side of the through hole of the nut on which the top is arranged, and a wedge member is inserted into the groove to fix the top to the through hole. ing. The planar shape of the top is a shape in which both ends in the longitudinal direction of an elongated rectangle corresponding to the S-shaped groove forming the return path are arcuate.
Patent Document 2 describes a frame composed of 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 for fitting the pair of protrusions are formed at positions facing each other on the peripheral surfaces of the through holes of the nut. After the top is arranged in the through hole of the nut by the alignment by these protrusions and recesses, the top is fixed to the through hole by using a fixing component whose attachment direction to the nut is different from that of the top.

Jikkai Sho 58-76851 Japanese Unexamined Patent Publication No. 2015-132369

In the top type ball screw, if a large step is generated at the connection between the S-shaped groove of the top and the spiral groove of the nut, the torque of the ball screw momentarily increases when the ball passes through this step, and the ball screw It is necessary to reduce this step because it may lock. At present, this step is reduced by increasing the processing accuracy of the top and nut. That is, the current top-type ball screw does not have a structure in which the step can be reduced by adjusting the position of the nut with respect to the through hole when mounting the top.
In addition, since the demand for the operability of the ball screw is high, it is necessary to control 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 mounting a top.

In order to solve the above problems, the ball screw of one aspect of the present invention has the following configurations (1) to (4).
(1) It has a screw shaft having a spiral groove formed on the outer peripheral surface and a nut made of a cylindrical body having the screw shaft inserted and a spiral groove formed on the inner peripheral surface. A trajectory is formed by the spiral groove of the nut and the spiral groove of the screw shaft. The nut has a columnar through hole that penetrates in the radial direction of the cylinder.
(2) It has a top having a return path as an S-shaped groove that connects the end point and the start point of the orbit to form a circulation path. The top consists of a cylinder whose diameter is smaller than that of the cylinder forming the through hole of the nut, and the first end surface of the two axial end faces of the cylinder is notched so as to have at least a part of the outer peripheral portion of the cylinder. A portion is formed, and an S-shaped groove is formed on the second end surface.
(3) It has a fixing part that fixes the top to the through hole of the nut. This fixing component is press-fitted into the notch of the top inserted into the through hole with the first end surface facing the outer peripheral side of the nut to press the through hole.
(4) Has multiple balls placed on the track and return path. The screw shaft and the nut move relative to each other through the ball that rolls in the orbit.

According to the ball screw of one aspect of the present invention, by moving or rotating the top made of a cylindrical body in the radial direction of the nut in the through hole of the nut, the position of the top with respect to the through hole of the nut can be adjusted when the top is attached. You can. In addition, by adjusting this position, the top is fixed to the through hole of the nut with a fixing part while the step at the connection between the S-shaped groove of the top and the spiral groove of the nut is reduced, so that the top ball screw Operability is improved.

It is a figure explaining the ball screw of 1st Embodiment, and is the figure which broke a part of a nut to show a screw shaft and a ball, and also made the part which attached the nut piece a cross section. An example of a piece constituting the ball screw of the first embodiment is viewed from each direction, (a) is a view showing a surface arranged on the outer peripheral surface side of the nut, and (b) is a view of (a). The view from the b direction, (c) is the view from the c direction of (b), and (d) is the view from the d direction of (b). It is a figure which shows the fixing part which comprises the ball screw of 1st Embodiment, (a) is the figure which shows the surface arranged on the outer peripheral surface side of a nut, (b) is seen from the b direction of (a). It is a figure. An example of a piece constituting the ball screw of the first embodiment is viewed from each direction, (a) is a view showing a surface arranged on the outer peripheral surface side of the nut, and (b) is a view of (a). The view from the b direction, (c) is the view from the c direction of (b), and (d) is the view from the d direction of (b). It is a figure explaining the ball screw of 2nd Embodiment, and is the figure which cut part of the nut to show a screw shaft and a ball, and has the part to which the piece of the nut is attached as a cross section. An example of a piece constituting the ball screw of the second embodiment is viewed from each direction, (a) is a view showing a surface arranged on the outer peripheral surface side of the nut, and (b) is a view of (a). The view from the b direction, (c) is the view from the c direction of (b), and (d) is the view from the d direction of (b). It is a figure which shows the fixing part which comprises the ball screw of 2nd Embodiment, (a) is the figure which shows the surface arranged on the outer peripheral surface side of a nut, (b) is seen from the b direction of (a). It is a figure.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the embodiments shown below. In the embodiments shown below, technically preferable limitations are 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. Further, each piece 4 has two fixing parts 5. Spiral 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 penetrates the nut 2. The nut 2 has a flange portion 2B at one end in the axial direction of the cylindrical portion 2A. The spiral groove 11 of the screw shaft 1 and the spiral groove 21 of the nut 2 form a trajectory on which the ball 3 rolls.
The cylindrical portion 2A of the nut 2 has a cylindrical through hole 22 penetrating in the radial direction. The frame 4 is inserted into the through hole 22 and is fixed by using the fixing component 5 by the method described later.

As shown in FIG. 2, the frame 4 is made 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 notched portions 42 are formed on the first end surface (the surface arranged on the outer peripheral side of the nut 2) 41 of the two axial end surfaces of the cylindrical body forming the frame 4.
The cutout portion 42 is a portion where a part of the outer peripheral portion of the cylindrical body is cut off, and has a bottom surface 42a parallel to the first end surface 41, a pair of wall surfaces 42b facing each other, and a back surface which is a surface on the central side in the radial direction. It has a surface 42c. The wall surface 42b and the back surface 42c are surfaces perpendicular to the first end surface 41. The pair of cutouts 42 are formed at positions of a pair of arcs 40 that are opposite to each other in the radial direction of the cylinder.
The second end surface 43 of the frame 4 is an arc surface facing the outer peripheral surface 12 of the screw shaft 1. The diameter of the arcuate surface forming the second end surface 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 forming a return path for the ball 3 is formed on the second end surface 43. FIG. 2C shows the moving path 30 of the ball 3 as a alternate long and short dash line.

As shown in FIG. 3, the fixing component 5 includes an arc surface 50 that contacts the through hole 22 of the nut 2, a lower surface 51a that contacts the bottom surface 42a of the notch 42 of the top 4, and a wall surface 42b of the notch 42. It has a side surface 51b that is in contact with the lower surface 51b and an upper surface 51d that is parallel to the lower surface 51a. The diameter of the arcuate surface 50 of the fixed component 5 is slightly larger than the diameter of the through hole 22 of the nut 2. The distance d51 between the side surfaces 51b of the fixed component 5 is slightly larger than the distance d41 between the wall surfaces 42b of the notch 42 of the frame 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 42 of the frame 4.

In this embodiment, the top 4 is made of synthetic resin, and the fixing part 5 is made of rubber or a thermoplastic elastomer. Examples of the synthetic resin forming the coma 4 include PPS (polyphenylene sulfide), POM (polyacetal), PEEK (polyetheretherketone), 6 nylon, 4, 6 nylon, 6, 6 nylon and the like. Further, the coma 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 coma 4 may be made of metal, and may be formed by, for example, a metal powder injection molding method (MIM). Examples of the MIM alloy used include Fe-Ni-C (1 to 8% Ni, to 0.8% C).

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

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 surface 41 facing upward. As a result, the first end surface 41 of the piece 4 faces the outer peripheral side of the nut 2, and the second end surface 43 faces the screw shaft 1. Next, by moving the top 4 in the radial direction of the nut 2 or rotating the top 4 in the through hole 22, the step between the spiral groove 21 of the nut 2 and the S-shaped groove 44 of the top 4 is small. 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 comes into contact with the bottom surface 42a of the notch portion 42, presses the wall surface 42b and the back surface 42c, and presses the through hole 22 at the arc surface 50. As a result, the top 4 is fixed to the through hole 22 of the nut 2 by the frictional force of the fixing component 5.

According to the ball screw of the first embodiment, as described above, the top 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. At the time of mounting, the position can be adjusted so that the step at the connection 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 connection portion between the S-shaped groove 44 of the frame 4 and the spiral groove 21 of the nut 2, it is possible to prevent the torque of the ball screw from increasing momentarily.
Further, it can be said that the measure for reducing the step by the ball screw of the first embodiment is a method in which the manufacturing cost is lower than the current measure for reducing the step by increasing the processing accuracy of the top and the nut.

The top 4 of FIG. 2 has two notches 42, and is fixed to the through hole 22 of the nut 2 by 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, after the piece 4A is inserted into the through hole 22 of the nut 2 and the above adjustment is made in the same manner as the piece 4, one fixing part 5 is press-fitted into the notch 42 of the piece 4A. Then, the frame 4A 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 frame 4B shown in FIG. 6 is fixed to the through hole 22 of the nut 2 by using the fixing component 6 shown in FIG. 7. Other than this, it is the same as the ball screw of the first embodiment.
As shown in FIG. 6, the frame 4B is composed 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 the first end surface (the surface arranged on the outer peripheral side of the nut 2) 41 of the two axial end surfaces of the cylindrical body forming the frame 4B.

The notch portion 45 is a portion where the entire outer peripheral portion of the cylindrical body is notched. Therefore, the notch portion 45 has a bottom surface 45a parallel to the first end surface 41 and a back surface 45c which is a surface on the center side in the radial direction, but the notch portion 42 of the frame 4 in FIG. 2 has a wall surface 42b. It has no corresponding surface. That is, in the frame 4B, the notch portion 45 is formed in the entire circumferential direction of the cylinder.
The second end surface 43 of the frame 4B is an arc surface facing the outer peripheral surface 12 of the screw shaft 1. The diameter of the arcuate surface forming the second end surface 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 forming a return path for the ball 3 is formed on the second end surface 43. FIG. 6C shows the moving path 30 of the ball 3 as a alternate long and short dash line.

Further, as shown in FIGS. 6 (b) and 6 (d), the shape of the frame 4B can be said to be a shape in which the columnar main body 410 and the disk-shaped mounting portion 420 are coaxially integrated. The main body 410 is made of a cylindrical body 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 portion 45 exists in an annular shape.

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

When assembling the ball screw, for example, the screw shaft 1 is inserted into the nut 2 and the ball 3 is filled in the track (between the spiral grooves 11 and 21) from the through hole 22. Alternatively, the temporary shaft is inserted into the nut 2 to arrange the ball 3 in the spiral groove 21, and then the temporary shaft is replaced with the screw shaft 1 which is the main shaft to fill the orbit with the ball 3.
In this state, the top 4B is inserted into the through hole 22 of the nut 2 from the upper side of the nut 2 with the first end surface 41 facing upward. As a result, the first end surface 41 of the frame 4B faces the outer peripheral side of the nut 2, and the second end surface 43 faces the screw shaft 1. Next, by moving the top 4B in the radial direction of the nut 2 or rotating the top 4B in the through hole 22, the step between the spiral groove 21 of the nut 2 and the S-shaped groove 44 of the top 4B is small. Adjust so that

Next, the fixing component 6 is press-fitted into the notch 45 of the top 4B in the through hole 22. At that time, the fixing component 6 is inserted in the axial direction until it comes into contact with the bottom surface 45a of the notch portion 45, and the inner peripheral surface 62 presses the inner surface 45c and the outer peripheral surface 61 presses the through hole 22. As a result, the top 4B is fixed to the through hole 22 of the nut 2 by the frictional force of the fixing 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 in the through hole 22 of the nut 2. At the time of mounting, the position can be adjusted so that the step at the connection 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 connection portion between the S-shaped groove 44 of the frame 4B and the spiral groove 21 of the nut 2, it is possible to prevent the torque of the ball screw from increasing momentarily.

Further, it can be said that the measure for reducing the step by the ball screw of the second embodiment is a method in which the manufacturing cost is lower than the current measure for reducing the step by increasing the processing accuracy of the top and the nut.
Further, in the top 4B of the second embodiment, since the notch portion 45 is 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, the through hole 22 and the top 4B There is no gap between the frame 4B and the frame 4B.

1 Screw shaft 10 Outer surface of screw shaft 11 Spiral groove of screw shaft 2 Nut 2A Cylindrical part of nut 2B Flange part of nut 20 Inner peripheral surface of nut 21 Spiral groove of nut 22 Through hole of nut 3 Ball 4 piece 4A piece 4B Frame 41 First end surface of the frame 42 Notch part of the frame 43 Second end surface of the frame 44 S-shaped groove 45 Notch part of the frame 410 Main body of the frame 420 Mounting part of the frame 5 Fixed parts 6 Fixed parts 61 Outer circumference of the fixed parts Surface 62 Inner peripheral surface of fixed parts

Claims (1)

A screw shaft with a spiral groove formed on the outer peripheral surface,
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 trajectory is formed by the spiral groove and the spiral groove of the screw shaft in the radial direction of the cylindrical body. A nut with a cylindrical through hole that penetrates through
A top having a return path as an S-shaped groove that connects the end point and the start point of the orbit to form a circulation path, and is composed of a cylinder having a diameter smaller than that of a cylinder forming the through hole. A top in which a notch portion lacking at least a part of the outer peripheral portion of the cylindrical body is formed on the first end surface of the two axial end faces and the S-shaped groove is formed on the second end face.
A fixing component for fixing the top to the through hole, the first end surface of which is pressed into the notch of the top inserted into the through hole with the first end surface facing the outer peripheral side of the nut, and the through hole is formed. And the fixed parts that press
With a plurality of balls arranged on the trajectory and the return path,
Have,
The notch is formed in the entire circumferential direction of the cylinder.
A ball screw in which the screw shaft and the nut move relative to each other via the ball that rolls in the track.

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