JP2017150647A - Linear motion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear motion apparatus that has remedied disadvantage of a ball screw without impairing advantage thereof, and is advantageous in terms of manufacturing cost, a product life, etc.SOLUTION: The linear motion apparatus is comprised of a plurality of balls 1, a screw shaft 2, a first component 3 covering a part of an outer circumferential surface of the screw shaft 2, a second component 4 covering a part, not covered with the first component, of the outer circumferential surface of the screw shaft 2, and rolling bearings 5, 6. The first component 3 has an axial size longer than an axial size of the screw shaft 2, and a spiral groove 32 opposite the spiral groove 212 of the screw shaft 2 and forming a first track K1 as a load rolling path for the balls 1 is formed in an inner circumferential surface 31 concentric with the screw shaft 2, of the first component 3. The second component 4 has an axial size shorter than the screw shaft 2 and equal to or larger than an axial size of the screw groove part 21 and concentric with the screw shaft 2. The second component 4 has an inner circumferential surface 41 formed of only a single arc surface having the same diameter with a circle showing a groove bottom line of the spiral groove 32 of the first component 3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a linear motion device that converts rotational motion into linear motion.

  As a linear motion device that converts rotational motion into linear motion, there are a rack and pinion and a ball screw. A rack and pinion requires a speed reducer. The rack and pinion has low mechanical efficiency due to sliding drive and has a short wear life, so it is necessary to perform maintenance in a short period of time. The ball screw does not require a speed reducer and has high mechanical efficiency, but cannot take a long stroke.

Patent Document 1 describes the disadvantages of ball screws (there is no backlash, less friction, and no reduction gears are required) and the disadvantages (the stroke cannot be lengthened, vibration problems, and the moment of inertia). A linear motion device with improved (increase) is described.
The linear motion device described in Patent Document 1 includes a ball gear, an outer guide, a plurality of balls, and a guide member. The ball gear has a substantially cylindrical shape and has a spiral ball rolling groove on the outer peripheral surface. The outer guide is a substantially cylindrical body that rotatably supports the ball gear, and a plurality of balls are interposed between the ball rolling grooves in a range facing the ball rolling grooves of the ball gear on the inner peripheral surface of the cylindrical body. A spiral ball rolling groove capable of holding the is formed. The substantially cylindrical body that forms the outer guide has a part in the radial direction cut out in the axial direction.

  The plurality of balls are in rolling contact with a raceway formed by both ball rolling grooves of the ball gear and the outer guide. The guide member has an axial dimension longer than that of the outer guide, is inserted into a notch portion of the outer guide, and has a spiral ball rolling groove capable of holding a plurality of balls between the ball rolling grooves of the ball gear. . The spiral ball rolling groove of the outer guide is continuous with the spiral ball rolling groove of the guide member.

Further, in the range where the ball rolling groove of the ball gear is formed, a ball communication hole extending in the axial direction is provided in the shaft core, and along the radial direction of the ball gear at the start point and the end point of the ball rolling groove. An extended ball reflux hole is provided. The ball return holes at the start point and the end point are connected to the ball communication hole. Thereby, the ball is returned from the start point to the end point of the ball rolling groove.
The linear motion device of Patent Document 1 has a guide protrusion on the side surface of the guide member that slidably supports the outer guide. A driving device for rotating the ball gear is fixed to the outer side of the outer guide.

JP 7-310802 A

The linear motion device described in Patent Document 1 has room for further improvement in terms of manufacturing cost and product life.
SUMMARY OF THE INVENTION An object of the present invention is to provide a linear motion device that has improved disadvantages without losing the advantages of the ball screw, and is advantageous in terms of manufacturing cost and product life.

In order to solve the above-described problems, a linear motion device according to an aspect of the present invention has the following configurations (1) to (5) and satisfies the following configurations (6) to (8).
(1) Multiple balls.
(2) A screw shaft having a screw groove portion in which a spiral groove for holding the ball is formed on an outer peripheral surface, and shaft end portions formed at both axial ends of the screw groove portion.
(3) A part that covers a part of the outer peripheral surface of the screw shaft, the axial dimension is longer than the axial dimension of the screw shaft, and has an inner peripheral surface concentric with the screw shaft, The 1st component by which the spiral groove which forms the 1st track | orbit which is the load rolling path of the said ball facing the said spiral groove of the said screw shaft is formed in the surrounding surface.

(4) A component that covers a portion of the outer peripheral surface of the screw shaft that is not covered with the first component, the axial dimension being shorter than the screw shaft and the same as the axial dimension of the thread groove portion. Or a second part having an inner peripheral surface which is longer than this, is concentric with the screw shaft, and has only a single arc surface having the same diameter as the circle indicating the groove bottom line of the spiral groove of the first part.
(5) The shaft end is rotatably supported with respect to the second component in a state where the screw groove portion of the screw shaft is inserted into the second component, and the screw shaft and the shaft of the second component Rolling bearing that restricts relative movement in the direction.

(6) The first component is disposed so as to form the first track with the spiral groove of the first component facing the spiral groove of the screw shaft with respect to the screw shaft in the state. ing.
(7) The ball by the first track, a second track formed between the screw groove and the inner peripheral surface of the second part, and a ball return path formed inside the screw shaft. A circulation path is formed.
(8) The rotation of the screw shaft is converted into a linear movement of the first part through the ball that rolls in a load state in the first track and circulates in the circulation path.

  According to the present invention, there is provided a linear motion device that has improved disadvantages without losing the advantages of the ball screw, and is advantageous in terms of manufacturing cost and product life.

It is sectional drawing (BB sectional drawing of FIG. 2) which shows the linear motion apparatus of 1st embodiment. It is a front view explaining the linear motion apparatus of 1st embodiment (The figure which abbreviate | omitted one part component from the A arrow directional view of FIG. 1). It is sectional drawing which shows the linear motion apparatus of 2nd embodiment. It is a front view explaining the linear motion apparatus of 3rd embodiment. FIG. 5 is a partial cross-sectional enlarged view illustrating a rolling guide mechanism included in the linear motion device of FIG. 4. FIG. 6 is an enlarged partial cross-sectional view illustrating an example having a rolling guide mechanism different from FIG. 5 in the linear motion device of the third embodiment.

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 linear motion device of the first embodiment includes a plurality of balls 1, a screw shaft 2, a first part 3, a second part 4, and radial bearings (rolling bearings) 5 and 6. Have.

  The screw shaft 2 includes a screw groove portion 21 and shaft end portions 22 and 23 formed at both ends of the screw groove portion 21 in the axial direction. A spiral groove 212 that holds the plurality of balls 1 is formed on the outer peripheral surface 211 of the thread groove portion 21. A through hole 24 extending in the axial direction is formed in the axial center of the screw shaft 2. Curved paths 241 and 242 extending from the through hole 24 to the spiral groove 212 are formed in the vicinity of both ends of the screw groove 21.

Circulating parts 25 and 26 are arranged mainly at the positions of the shaft end portions 22 and 23 of the through hole 24. The circulation parts 25 and 26 have guide surfaces 25 a and 26 a that guide the ball 1 in the through hole 24 to the curved paths 241 and 242. A ball return path K0 is formed by the through hole 24 and the curved paths 241 and 242 of the screw shaft 2 and the guide surfaces 25a and 26a of the circulation parts 25 and 26.
As shown in FIG. 2, the first component 3 is a component that covers a part of the outer peripheral surface 211 of the screw shaft 2, and is provided on both sides of the inner peripheral surface 31 concentric with the screw shaft 2 and the inner peripheral surface 31. It has a pair of continuous end surfaces 3a. As shown in FIG. 1, the axial dimension of the first component 3 is longer than the axial dimension of the screw shaft 2. A spiral groove 32 is formed on the inner peripheral surface 31 of the first component 3 so as to face the spiral groove 212 of the screw shaft 2 and form the first track K1. A convex portion 35 is integrally formed on the outer peripheral surface of the first component 3.

As shown in FIG. 2, the convex portion 35 extends in the direction perpendicular to the end surface 3 a from the center of the arc forming the outer peripheral surface of the first component 3. The convex portion 35 has a plurality of through holes 351 along the axial direction of the outer peripheral surface of the first component 3. The through hole 351 is a mounting hole for the first component 3.
As shown in FIG. 2, the second component 4 is a component that covers a portion of the outer peripheral surface 211 of the screw shaft 2 that is not covered with the first component 3, and an inner peripheral surface 41 that is concentric with the screw shaft 2, It has a pair of end surfaces 4 a continuous on both sides of the inner peripheral surface 41. The outer arc of the first part 3 and the outer arc of the second part 4 are arcs of the same circle 10. The end surface 3a of the first component 3 and the end surface 4a of the second component 4 are surfaces along a line parallel to the reference line L0 indicating the radial direction of the circle 10, and between these end surfaces 3a and 4a is actually There is a gap. That is, strictly speaking, one of the end surfaces 3a and 4a is a surface along a line L1 parallel to the reference line L0, and the other is a surface along a line parallel to the line L1 via a gap.

As shown in FIG. 1, the axial dimension of the second component 4 is slightly longer than the axial dimension of the thread groove 21 of the screw shaft 2. As shown in FIG. 2, the inner peripheral surface 41 of the second part 4 is composed of only a single circular arc surface. The diameter of the inner peripheral surface 41 is the same diameter as the circle E <b> 32 indicating the groove bottom line of the spiral groove 32 of the first part 3. No spiral groove is formed on the inner peripheral surface 41 of the second component 4.
As shown in FIG. 1, the screw groove 21 of the screw shaft 2 is inserted into the second part 4, and the outer diameter is the same as the second part 4 and the inner diameter is the second part 4 at both axial ends of the second part 4. Smaller rings 7 and 8 are fixed. Further, the first component 3 is disposed so as to form the first track K1 of the ball 1 with the spiral groove 32 facing the spiral groove 212 of the screw groove portion 21 with respect to the screw shaft 2. A second track K <b> 2 of the ball 1 is formed between the screw groove 21 of the screw shaft 2 and the inner peripheral surface 41 of the second component 4.

A circulation path of the ball 1 is formed by the first track K1, the second track K2, and the ball return path K0. That is, the ball 1 rolls on a track composed of the first track K1 and the second track K2 (the load in the first track K1), and then enters the ball return path K0 and is returned from the end point of the track to the start point. Circulate.
One shaft end portion 22 of the screw shaft 2 is rotatably supported with respect to the annular body 7 by a radial bearing 5 formed of a double row angular ball bearing. A pulley 9 for driving the screw shaft 2 is fixed on the outer side in the axial direction from the portion of the shaft end portion 22 supported by the radial bearing 5.

  A ring-shaped metal fitting 71 and a flange metal fitting 72 are fixed between the radial bearing 5 at the shaft end 22 and the pulley 9. The ring-shaped metal fitting 71 is fitted on the shaft end portion 22 of the screw shaft 2. The flange fitting 72 has a protrusion 72 a that comes into contact with the axial end surface of the outer ring of the radial bearing 5, is fitted on the ring fitting 71, and is fixed to the annular body 7. A nut 91 is disposed on the outermost portion of the shaft end 22 in the axial direction.

FIG. 2 is a view in which the ring-shaped metal fitting 71 and the annular body 7 are omitted from the A arrow view of FIG.
As shown in FIG. 1, in the linear motion device of this embodiment, the pulley 9 is fixed to the shaft end 22 of the screw shaft 2 by tightening the nut 91, and the radial bearing 5 is connected via the ring-shaped fitting 71. Preload is applied to the radial bearing 5 by pushing the inner ring in the axial direction. As a result, the relative movement of the screw shaft 2 in the axial direction with respect to the second component 4 is restricted.

The other shaft end 23 of the screw shaft 2 is rotatably supported with respect to the annular body 8 by a rolling bearing 6 formed of a deep groove ball bearing. A lid component 81 that covers the rolling bearing 6 and the shaft end portion 23 is disposed on the outer side in the axial direction of the annular body 8, and is fixed to the axial end portion of the second component 4 together with the annular body 8.
A belt 93 is stretched between a pulley that rotates by driving of the motor and a pulley 9 that is fixed to the shaft end 22 of the screw shaft 2. When the motor is switched on, the screw shaft 2 rotates as the pulley 93 rotates by driving the belt 93.

When the screw shaft 2 is rotated while the second component 4 is fixed, the rotation of the screw shaft 2 is performed through the ball 1 that rolls in the first track K1 in a loaded state and circulates in the circulation path. It is converted into a linear movement of the part 3.
When the screw shaft 2 is rotated while the first component 3 is fixed, the rotation of the screw shaft 2 is rotated through the ball 1 that rolls in the first track K1 in a loaded state and circulates in the circulation path. It is converted into a linear movement of the component 4. The screw shaft 2 moves linearly together with the second component 4 while rotating.

Compared with the linear motion apparatus described in Patent Document 1, the linear motion apparatus of this embodiment has the following effects.
In the linear motion device described in Patent Document 1, the outer guide, which is a substantially cylindrical body that rotatably supports the ball gear, is in a range facing the ball rolling groove of the ball gear on the inner peripheral surface of the cylindrical body. A spiral ball rolling groove capable of holding a plurality of balls is provided between the ball rolling grooves. The spiral ball rolling groove of the outer guide is continuous with the spiral ball rolling groove of the guide member. In addition, the rolling bearing that supports the rotating shaft of the ball gear is not given preload in the axial direction. An axial force is applied to the ball rolling groove of the outer guide.

However, it is difficult to process the outer guide and the ball rolling groove of the guide member, which are separate members, with the same accuracy, and a step is likely to occur between the ball rolling grooves. In other words, since it is difficult to make the ball rolling grooves smoothly continuous, there is a possibility that the ball may be damaged at the step portion when passing between the ball rolling grooves, leading to a decrease in the life of the linear motion device. .
On the other hand, in the linear motion device of this embodiment, the second component 4 corresponding to the outer guide has an inner peripheral surface 41 consisting of only a single arc surface and does not have a ball rolling groove. That is, since the boundary between the first component 3 and the second component 4 in the movement path of the ball 1 is not a portion where the ball rolling grooves are continuous, the ball 1 moves the first component 3 and the second component 4 together. It is prevented from being damaged when going back and forth.

[Second Embodiment]
As shown in FIG. 3, the linear motion device according to the second embodiment is a thrust bearing (rolling bearing) 5 </ b> A in place of the radial bearings 5 and 6 and the annular bodies 7 and 8 constituting the linear motion device according to the first embodiment. , 6A and annular bodies 7A, 8A. The axial dimensions of the annular bodies 7A and 8A are the same as the axial dimensions of the thrust bearings 5A and 6A. Further, a lid part 82 is provided instead of the ring-shaped metal part 71 and the flange metal part 72.

The shaft end portions 22A and 23A of the screw shaft 2A are shorter than the shaft end portions 22 and 23 of the screw shaft 2 constituting the linear motion device of the first embodiment. The axial dimensions of the circulating parts 25A and 26A are also shorter than the circulating parts 25 and 26 in accordance with the lengths of the shaft end portions 22A and 23A.
A lid part 82 that covers the thrust bearing 5A, the shaft end 22A, and the annular body 7A is disposed on the axially outer side of the annular body 7A, and is fixed to the axial end of the second part 4 together with the annular body 7A. A lid component 81 that covers the thrust bearing 6A, the shaft end 23A, and the annular body 8A is disposed on the axially outer side of the annular body 8A, and is fixed to the axial end of the second component 4 together with the annular body 8A.

  An inner ring of the thrust bearing 5A is fixed to a boundary portion with the shaft end portion 22A of the screw groove portion 21A of the screw shaft 2A, and an outer ring of the thrust bearing 5A protrudes from one axial end portion of the inner peripheral surface of the annular body 7A. It is being fixed to the corner | angular part formed with the part and the lid | cover component 82. FIG. The inner ring of the thrust bearing 6A is fixed to the boundary with the shaft end 23A of the screw groove 21A of the screw shaft 2A, and the outer ring of the thrust bearing 6A protrudes from the other axial end of the inner peripheral surface of the annular body 8A. It is fixed to a corner formed by the convex part and the lid part 81.

  Further, the spiral groove 212A of the screw groove portion 21A of the screw shaft 2A is formed in different shapes at the axial center portion and the end portion. Specifically, by making the gothic arc groove asymmetric (with a difference between both groove radii R1 and R2) and changing either of the groove radii R1 and R2, the spiral groove 212A of the screw shaft 2A is changed. The pitch is made larger than the spiral groove 32 of the first part 3 at the center in the axial direction, and smaller than the spiral groove 32 of the first part 3 at both ends in the axial direction.

As a result, the contact angle of the ball 1 changes in the axial direction in the first track K1 formed by the spiral groove 32 of the first part 3 and the spiral groove 212A of the screw shaft 2A. Is granted.
The pitch of the spiral groove 212A of the screw shaft 2A is made smaller than the spiral groove 32 of the first part 3 at the axial center, and larger than the spiral groove 32 of the first part 3 at both axial ends. A preload in the axial direction may be applied to the ball 1 by the first track K1 formed by the spiral groove 32 of the component 3 and the spiral groove 212A of the screw shaft 2A.

Except for the above, the linear motion device of the second embodiment is the same as the linear motion device of the first embodiment.
When the screw shaft 2A is rotated while the second part 4 is fixed, the rotation of the screw shaft 2A is performed through the ball 1 that rolls in the first track K1 in a loaded state and circulates in the circulation path. It is converted into a linear movement of the part 3.
When the screw shaft 2A is rotated while the first component 3 is fixed, the rotation of the screw shaft 2A is performed through the ball 1 that rolls in the loaded state in the first track K1 and circulates in the circulation path. It is converted into a linear movement of the component 4. The screw shaft 2A moves linearly together with the second component 4 while rotating.
The linear motion device of this embodiment has the effect of the linear motion device of the first embodiment described above. In addition to this, axial end portions 22A and 23A of the screw shaft 2A are rotatably supported with respect to the second part 4 using the thrust bearings 5A and 6A, and the axial direction of the screw shaft 2A and the second part 4 in the axial direction is supported. Since the relative movement is constrained, there is an effect that the number of parts is smaller than that of the linear motion device of the first embodiment.

[Third embodiment]
As shown in FIG. 4, the linear motion device according to the third embodiment is different from the first component 3 and the second component 4 constituting the linear motion device according to the first embodiment only in the shape of the outer peripheral portion. It has a second part 4A. Moreover, it has the rolling guide mechanism 53 which guides the relative linear movement of the 1st component 3A and the 2nd component 4A, restrict | limiting the movement to a radial direction. Except for the above, the linear motion device of the third embodiment is the same as the linear motion device of the first embodiment.

The outer peripheral portion of the first component 3A is not a circular arc surface, but has a planar guide surface 36 on the opposite side of the pair of end surfaces 3a. The guide surface 36 extends in the entire axial direction of the first part 3A.
The outer periphery of the second part 4A has a pair of arms 45 that have an outer shape line that is substantially hexagonal and extends to cover the end face 3a of the first part 3A. Each arm portion 45 has a facing surface 46 that faces each guide surface 36. The opposing surface 46 extends in the entire axial direction of the second component 4A.

Rolling grooves 532 in which the rollers 531 constituting the rolling guide mechanism 53 are disposed are formed on the opposing surfaces 46 of the respective arm portions 45 of the second part 4A. Further, a return path 533 and a direction change path 534 constituting the rolling guide mechanism 53 are formed in each arm portion 45 of the second part 4A.
As shown in FIG. 5, gaps exist between the return path 533 and 531 in the axial direction and the radial direction of the rollers 531. There is a gap in the axial direction of the roller 531 between the roller 531 and the rolling groove 532. A gap exists between the direction change path 534 and 531 in the axial direction and the radial direction of the roller 531.

Accordingly, when the second part 4A moves relative to the first part 3A in a straight line, the roller 531 in the rolling groove 532 rotates while contacting the guide surface 36 of the first part 3A, and the return path 533 and It circulates through the direction change path 534.
Therefore, according to the linear motion device of the third embodiment, in addition to the same effect as the linear motion device of the first embodiment, by having the rolling guide mechanism 53, the relative straight line of the second component 4A to the first component 3A. There is also an effect that the movement is smoothly performed while the movement in the radial direction is restricted.

The linear motion device according to the third embodiment may have a rolling guide mechanism using a rolling bearing 54 as shown in FIG. 6 instead of the rolling guide mechanism 53 shown in FIGS. 4 and 5. The rolling bearing 54 includes an inner ring 541, an outer ring 542, and a ball 543.
In the example of FIG. 6, a concave portion 47 in which the rolling bearing 54 and its rotation shaft 55 are arranged is formed on the facing surface 46 of each arm portion 45 of the second component 4 </ b> A. The recess 47 includes a first recess 47a on the facing surface 46 side and a second recess 47b corresponding to a recess with respect to the bottom surface of the first recess 47a.

The first recess 47a is formed in such a size that the outer peripheral portion of the outer ring 542 slightly protrudes from the opening surface of the first recess 47a and contacts the guide surface 36 of the first component 3A in a state where the rolling bearing 54 is installed inside. Has been. The second concave portion 47 b is formed to have a size that creates a gap between the axial end surface of the rolling bearing 54 and the outer peripheral surface of the outer ring 542.
The rolling bearing 54 is disposed in the concave portion 47 with the outer peripheral surface of the outer ring 542 facing the bottom surface of the second concave portion 47b in a state of being attached to the rotary shaft 5, and the boundary portion between the first concave portion 47a and the second concave portion 47b. The rotary shaft 5 is disposed on the arm portion 45. A retaining component 56 of the rotating shaft 5 is fixed to two opposing wall surfaces of the first recess 47a. There is a gap between the retaining component 56 and the axial end surface of the rolling bearing 54.

  Thus, when the second part 4A moves relative to the first part 3A in a straight line, the outer ring 542 of the rolling bearing 54 rotates while being in contact with the guide surface 36 of the first part 3A, whereby the second part 4A. The relative linear movement with respect to the first part 3A is smoothly performed while the movement in the radial direction is restricted.

1 Ball 2 Screw shaft 2A Screw shaft 21 Screw groove portion of screw shaft 21A Screw groove portion of screw shaft 211 Outer peripheral surface of screw groove portion 212 Spiral groove of screw groove portion 212A Spiral groove of screw groove portion 22 Screw shaft end portion 22A Screw shaft shaft End 23 Screw shaft end 23A Screw shaft end 24 Screw shaft through hole 241, 242 Curved path 25, 26 Circulating component 25A, 26A Circulating component 25a, 26a Guide surface 3 First component 3A First component 3a End surface 31 of the first part 31 Inner peripheral surface of the first part 32 Spiral groove of the first part 35 Convex part 351 of the first part 4 Through part of the convex part 4 Second part 4A Second part 41 Inner peripheral surface of the second part 4a End face of second part 5 Radial bearing (rolling bearing)
5A Thrust bearing (rolling bearing)
53 Rolling guide mechanism 54 Rolling guide mechanism 6 Radial bearing (rolling bearing)
6A Thrust bearing (rolling bearing)
7 annular body 7A annular body 71 ring-shaped bracket 72 flange bracket 72a projection of flange bracket 8 annular body 8A annular body 81, 82 annular body 9 pulley 91 nut 10 circle formed by outer arcs of the first part and the second part E32 first Circle indicating the groove bottom line of the spiral groove of the component K0 Ball return path K1 First track K2 Second track L0 Reference line indicating the radial direction of the circle 10 L1 A line parallel to the reference line L0

Claims (4)

With multiple balls,
A screw shaft having a screw groove portion in which a spiral groove for holding the ball is formed on an outer peripheral surface, and shaft end portions formed at both axial ends of the screw groove portion;
A part that covers a part of the outer peripheral surface of the screw shaft, the axial dimension is longer than the axial dimension of the screw shaft, and has an inner peripheral surface concentric with the screw shaft. A first part formed with a spiral groove that forms a first track that is a load rolling path of the ball facing the spiral groove of the screw shaft;
It is a part that covers a portion of the outer peripheral surface of the screw shaft that is not covered with the first part, and the axial dimension is shorter than the screw shaft and is the same as or more than the axial dimension of the screw groove portion. A second part having an inner peripheral surface that is long, concentric with the screw shaft, and has only a single arc surface having the same diameter as a circle indicating a groove bottom line of the spiral groove of the first part;
The shaft end is rotatably supported with respect to the second component in a state where the screw groove portion of the screw shaft is inserted into the second component, and the screw shaft and the second component in the axial direction are supported. A rolling bearing that restrains relative movement;
Have
The first component is arranged to form the first track with the spiral groove of the first component facing the spiral groove of the screw shaft with respect to the screw shaft in the state,
A circulation path of the ball by the first track, a second track formed between the screw groove and the inner peripheral surface of the second part, and a ball return path formed inside the screw shaft. Formed,
A linear motion device in which the rotation of the screw shaft is converted into a linear movement of the first part via the ball that rolls in a load state in the first track and circulates in the circulation path.   The rolling bearing is a radial bearing, and a preload is applied to the radial bearing that supports at least one of shaft end portions formed at both axial ends of the screw groove portion of the screw shaft, and the screw shaft and the screw shaft The linear motion device according to claim 1, wherein relative movement of the second part in the axial direction is restricted.   The linear motion device according to claim 1, wherein the rolling bearing is a thrust bearing.   The linear motion apparatus according to any one of claims 1 to 3, further comprising a rolling guide mechanism that guides relative linear movement of the first part and the second part while restricting movement in a radial direction.

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