TWI388745B - Roller screw - Google Patents

Description

Roller screw

The present invention relates to a roller screw (roller screw or roller screw) in which a rollable roller is sandwiched between a screw shaft and a nut.

A ball screw in which a ball can be rolled between a screw shaft and a nut is a screw that is in sliding contact with the screw, because the friction coefficient of the screw shaft is reduced relative to the nut, and thus has been actually Applied in machine tools. The positioning mechanism of the robot, the feed mechanism, or the steering gear of the automobile.

In recent years, in order to increase the allowable load, a roller screw using a roller instead of a ball as a rotor is used. For example, a roller screw of Patent Document 1 is proposed. The roller screw forms a roller track groove on the outer circumferential surface of the screw shaft, and a spiral roller groove groove that faces the roller groove groove of the screw shaft is formed on the inner circumferential surface of the nut, and On the load roller rolling path between the roller groove groove of the screw shaft and the roller track groove of the nut, a plurality of rollers serving as a rotating body are arranged. Moreover, the nut is provided with a circulating member forming a no-load roller return path which is connected to one end and the other end of the load rolling road, and the one end of the self-loading rolling road is rolled up on the rolling road of the load roller. The child is then sent back to the other end, whereby the roller rolling the load rolling road can be cycled.

(Patent Document 1) Japanese Patent Laid-Open No. Hei 11-210858

In a load roller rolling road, the roller receives a load on one side of the roller, and rolls on the roller rolling groove of the screw shaft and the roller rolling groove of the nut. Although the ball can roll in any direction, the direction of movement of the roller is limited to only one direction. In the roller road of the load roller, the posture of the roller is limited. Therefore, in order to return the roller picked up by the self-loading roller to the load rolling road, it must be returned in accordance with the posture of the roller which is determined by the load roller rolling road, that is, the side shape must be square. The shape of the roller is the same as the shape of the quadrilateral load roller rolling road. In order to cope with the necessity of returning this posture consistently, the conventional person twists the unloaded roller return path of the circulation member, and the roller moves along the unloaded roller return path to slowly change the posture of the roller. Finally, the posture of the roller and the cross-sectional shape of the roller of the load roller are matched.

However, when the unloaded roller return path of the circulation member is twisted, the resistance of the roller that moves the twisted portion on the unloaded roller return path increases, and becomes a problem that the roller cannot be smoothly moved.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a roller screw that can circulate a roller even without having to distort the unloaded roller return path following the load roller rolling path.

The invention is described below. Further, in order to facilitate the understanding of the present invention, the parentheses are attached to the component symbols of the drawings, but the present invention is not limited to the illustrated embodiments.

In order to solve the above problems, the invention of claim 1 relates to a roller screw characterized in that: a screw shaft (5) having a spiral roller groove groove (5) formed on an outer peripheral surface; And a nut (6) of a roller raceway groove (6a) which is formed to be spirally opposed to the roller runner groove (5a) of the screw shaft (5) on the inner circumferential surface; and is formed to be connected One end and the other end of the load roller rolling path (9) between the aforementioned roller rolling groove (5a) of the screw shaft (5) and the roller rolling groove (6a) of the nut (6) a circulating member (12, 13) of the unloaded roller return path (10); and a plurality of rollers arranged in the aforementioned load roller rolling path (9) and the aforementioned unloaded roller return path (10) (7) When viewed from the front surface of the nut (6), a pair of direction changing paths (16) at both end portions of the unloaded roller return path (10) linearly extend, and the pair of direction changing portions (16) The angle formed is substantially 90 degrees.

Here, the fact that the structure is substantially 90 degrees is because there is a slight gap between the roller (7) and the unloaded roller return path (10), and therefore, in consideration of the angle formed by even the pair of direction changing paths (16) When there is a slight deviation, it is not necessary to distort the unloaded roller return path (10).

The invention of claim 2, in addition to the roller screw of claim 1, is characterized in that the unloaded roller return path (10) has a nut (6) at a central portion thereof. The axis of the line extends linearly in a straight line (11).

The invention of claim 3, in addition to the roller screw of claim 1 or 2, is characterized in that the unloaded roller return path (10) is carried out from the aforementioned roller (7) In the state of the directional view, in order to make the axes of the adjacent rollers (7) orthogonal to each other, the plurality of rollers (7) are arranged in a cross shape.

The invention of claim 4, in addition to the roller screw of any one of claims 1 to 3, is characterized in that the ratio of the diameter to the length of the roller (7) is approximately 1:1. The cross-sectional shape of the unloaded roller return path (10) is square.

Here, the ratio of the diameter to the length is made to be about 1:1, and strictly speaking, the length is set to be slightly smaller than the diameter.

The invention of claim 5, in addition to the roller screw of any one of claims 1 to 4, characterized in that one of the circulation members formed by the direction changing path (16) is converted in direction The path forming portion (13) is attached to both end faces of the nut (6) in the axial direction.

According to the invention of claim 1, the roller is circulated because it is not necessary to twist the unloaded roller return path of the circulation member, so that the roller does not roll because of the no-load roller return path. There is resistance to the distortion of the sub-return path.

According to the invention of claim 2, it is possible to obtain a circulation member which can correspond to a case where the lead of the screw shaft is too large, or a case where the number of windings of the roller roller is excessive.

When the pair of direction changing paths are arranged as in the invention of the first application of the patent scope, the roller having the load in one direction (1) from the axis of the screw shaft is reversed by the unloaded roller return path. The state (that is, the state in which the load is loaded in the opposite direction (2) from the one direction (1) of the axis of the screw shaft) is returned to the load roller rolling path. According to the invention of claim 3, since the rollers are arranged in a cross, the load in one direction (1) and the other direction (2) of the axis of the screw shaft can be loaded even when the rollers are reversed.

According to the invention of claim 4, a roller having a diameter to length ratio of about 1:1 is used, and the cross-sectional shape of the unloaded roller return path is square, so that it can be designed as a straight line from the front of the nut. One of the extensions forms an angle of 90 degrees with respect to the direction change path.

According to the invention of claim 5, one of the direction changing paths forming the 90-degree intersection from the front surface of the nut can be attached to the nut.

Fig. 1 is a perspective view showing a roller screw in an embodiment of the present invention. The roller screw has a screw shaft 5 that forms a spiral roller groove groove 5a on the outer circumferential surface, and a spiral roller roller that forms a surface on the inner circumferential surface with respect to the roller track groove 5a. The nut 6 of the channel 6a. The load roller rolling path between the roller track groove 5a of the screw shaft 5 and the roller track groove 6a of the nut 6 is in a state of being viewed from the direction in which the roller 7 is viewed, for a plurality of rollers 7 The axes of adjacent rollers may be orthogonal to each other and arranged in a cross. In order to load the load in one direction (1) and the other direction (2) in the axial direction of the screw shaft 5 (see Fig. 3), the rollers 7 must be arranged in such a cross. In the present embodiment, the rollers 7 are arranged orthogonally with respect to one axis, and the ratio of the number of rollers 7 having parallel axes and the number of rollers orthogonal to the axis is 1:1. A retainer 8 that prevents the rollers 7 from contacting each other is interposed between the rollers 7.

When the nut 6 is relatively rotated about the screw shaft 5, a plurality of rollers 7 roll on the load roller rolling path 9 between the roller track groove 5a and the roller track groove 6a. The roller 7 of the roller to one end of the load roller rolling path 9 passes through the unloaded roller return path 10 and returns to the other end of the plurality of winding roller roads 9 wound on the front side.

2 is a perspective view showing the circulation members 12, 13 forming the unloaded roller return path 10. The unloaded roller return path 10 is composed of a linear path 11 at the center portion and a direction changing path 16 at both ends; The linear passage 11 and the axis of the nut 6 extend linearly in parallel. The direction change path 16 is curved, for example, in an arc shape.

The nut 6 is formed with a through hole extending in parallel with the axis of the screw shaft 5, and the through hole is inserted into the tubular straight portion 12. In the straight portion 12, a linear passage 11 having a rectangular cross section of a linear orbit is formed. The details will be described later, and the linear passage 11 is not twisted, and even if the roller 7 moves in the linear passage 11, the posture of the roller 7 does not rotate.

Directional switching path constituent portions 13 are attached to both end faces of the nut 6 in the axial direction. The direction changing path forming portion 13 has an arc-shaped track and a direction changing path 16 having a quadrangular cross section. The direction changing path configuration portion 13 is divided into two, that is, the inner circumferential side 13a and the outer circumferential side 13b, in the diagonal position of the quadrangular cross section of the direction changing path 16. The inner peripheral side 13a and the outer peripheral side 13b of the direction change path configuring portion 13 each have a flange portion. When the inner peripheral side 13a and the outer peripheral side 13b of the direction change path constituent portion 13 are overlapped and positioned on the end surface of the nut 6, the flange portion can be fixed to the end surface of the nut 6 by a fixing means such as a bolt. Since both ends of the straight portion 12 are fitted into the direction changing path forming portion 13, when the direction changing path forming portion 13 is fixed to the nut 6, the straight portion 12 is also fixed to the nut 6.

Figure 3 shows a side view of the roller screw. Fig. 4 is a view showing the arrow of the line IV-IV of Fig. 3. In order to remove foreign matter and to prevent leakage of lubricant from the inside of the nut 6 in the axial direction of both ends of the nut portion of the straight portion 12 and the direction changing path forming portion 13 , a labyrinth shaft seal is attached thereto ( Labyninth seal) 14. Further, a cover 15 covering the labyrinth shaft seal 14 is attached to the end surface of the nut 6.

Figure 5 shows the screw shaft 5. A spiral roller groove groove 5a having a predetermined lead is formed on the outer circumference of the screw shaft 5. In the present embodiment, in order to increase the allowable load, the number of the roller race grooves 5a is set to four in order to make the overall length of the nut 6 short. The roller raceway groove 5a can also be set to one, two or three.

Fig. 6 shows the cross-sectional shape of the roller race groove 5a of the screw shaft 5. The roller race groove 5a has a V-shaped cross section and an opening angle of 90 degrees. At the bottom of the roller chute groove 5a, a circular arc portion 5b having a grinding underout is formed in order to make the intersecting portion of 90 degrees.

FIG. 7 shows a detailed view of the nut 6. Fig. 7(A) is a front view of the nut 6, Fig. 7(B) is a cross-sectional view taken along the axial direction, and Fig. 7(C) is an internal view of the nut 6, and a surface is formed on the inner peripheral surface of the nut 6. The spiral roller race groove 6a of the roller race groove 5a of the screw shaft 5. Further, the nut 6 is formed with a through hole 17 extending in the axial direction of the nut 6. The through hole 17 has a central portion 17a formed in a small diameter, and both end portions 17a on both sides of the central portion are formed to be slightly larger than the central portion 17a. The linear portion 12 is inserted into the central portion 17a of the through hole 17, and the direction changing path constituent portion 13 is inserted into the both end portions 17b. A mounting seat 18 for mounting the nut 6 in the mounting direction switching path forming portion 13 is formed on the end surface of the nut 6. The linear portion 12 and the direction changing path forming portion 13 are provided in the same number as the roller rolling groove 6a (four in the present embodiment), and each of them is rolled in the four roller rolling grooves 6a. Sub 7 loops.

FIG. 8 shows a detailed view of the mount 18. In the mount 18, an arcuate balance groove 19 having a shape of a sheet portion (23, see FIG. 15(A)) of a direction change path forming portion 13 to be described later is formed. In a conventional end cap type ball screw, the end faces of the nuts are formed flat, and the balance grooves 19 are not formed. Further, a member constituting the direction changing path is attached to the flat portion. However, in the case of the roller screw, in order to allow the roller 7 to smoothly circulate, the radius of curvature of the direction changing path 16 tends to be larger than that of the ball screw. When the radius of curvature of the direction change path 16 is increased, the direction change path configuring portion 13 easily interferes with the roller track groove 6a of the nut 6. When the sheet portion 23 is formed in the direction changing path forming portion 13 and the balance groove 19 is formed by fitting the shape of the sheet portion 23 of the direction changing path forming portion 13 to the end surface of the nut 6, the radius of curvature of the direction changing path 16 is larger than that of the ball. The larger the screw, the more the direction change path forming portion 13 can be prevented from interfering with the roller track groove 6a.

Fig. 9 shows the cross-sectional shape of the roller race groove 6a of the nut 6. The cross section of the roller race groove 6a has a V shape and its opening angle is set to 90 degrees. At the bottom of the roller chute groove 6a, a circular arc portion 6b having an overrun groove can be formed for the 90-degree intersection portion.

Figure 10 shows a side view of the roller 7. The roller 7 that rolls on the load roller rolling path 9 has a cylindrical shape whose diameter D and length L are substantially equal (correctly, the diameter D of the roller 7 is slightly larger than the length L of the roller 7). Therefore, the shape of the roller 7 is close to a square when viewed from the side, and the ratio of the diameter to the length is roughly 1:1. In the present embodiment, the cross-sectional shape of the load roller rolling path 9 and the unloaded roller return path 10 is formed in a square shape in accordance with the side surface shape of the roller 7.

Fig. 11 shows the roller 7 housed in the load roller rolling path 9. The side surface of the roller 7 is compressed between the wall surface of the roller track groove 5a and the wall surface of the roller track groove 6a of the nut of the wall surface, and is loaded. Therefore, it can only load the load in one of the axial directions of the screw shaft 5. That is, the relative one roller 7 can only be loaded compared to the load in one direction (1) in the axial direction of the load screw shaft with one ball and the opposite direction (2) from the one direction (1). The load in either one direction (1) or the other direction (2) in the axial direction of the screw shaft 5 (the load in one direction (1) in Fig. 11). When the unloaded unloaded roller return path 10 is passed, the roller 7 that loads the load from the axis one direction (1) of the screw shaft 5 is in an inverted state (that is, the load has a self and a screw axis). The direction of the opposite direction (2) of the axis (1) in the direction of 5 is restored to the load roller rolling path 9. When the rollers 7 are arranged in a cross, even if the rollers 7 are reversed, the load in both the direction (1) and the other direction (2) of the axis of the screw shaft 5 can be loaded.

Further, in the case of the cross arrangement as in the present embodiment, the number of rollers 7 of the load in one direction of load (1) and the number of rollers 7 of the load in the other direction (2) can be made the same, but they are intended to be changed. In the case of the allowable load in both directions, the number of rollers 7 of the load in the load direction (1) and the number of the rollers 7 of the load in the other direction (2) may be different. In this case, when passing through the no-load roller return path 10, it must be noted that the roller 7 will reverse and the direction of the received load will also change.

The diameter D of the roller 7 is a so-called enlargement (oversize) which is slightly larger than the distance between the wall surface of the roller raceway 5a of the screw shaft 5 and the wall surface of the roller raceway groove 6a of the nut 6 of the wall surface. )By. Therefore, the roller becomes elastically deformable in the load roller rolling road 9, and the load balanced thereto exists as the preloading load in the inside of the nut 6. Since the rollers 7 are arranged in a cross in the load roller rolling path 9, the load applied from the rollers 7 to the nut 6 acts in the opposite direction by the adjacent rollers 7.

Fig. 12 shows the center line of the track of the roller 7 circulating on the spiral load roller rolling path 9, the circular direction changing path 16 and the linear path 11. (A) shows the trajectory of the roller 7 that moves on the load roller rolling path 9 (the state viewed from the axial direction of the screw shaft 5), and (B) shows the trajectory of the roller 7 that circulates in the entire infinite circulation path ( The state viewed from the side of the screw shaft 5). The track of the roller 7 of the load roller rolling path 9 is viewed from the axial direction of the screw shaft 5 and its radius is a circular shape of RCD/2. The track of the roller of the linear passage 11 of the unloaded roller return path 10 is a straight line on the axis 5c of the screw shaft 5. The track of the roller 7 in the direction changing path 16 is an arc of curvature radius R.

The joints of the load roller rolling path 9, the direction changing path 16, and the linear passage 11 are continuous to the wiring direction of the track of the roller 7, and therefore, the joints can be made smooth. Specifically, in the joint portion of the load roller rolling path 9 and the direction changing path 16, the wiring direction of the direction changing path 16 is in the state viewed from the axial direction of the screw shaft 5, and the center line of the load roller rolling path 9 The wiring direction is uniform, and when viewed from the side of the screw shaft 5, it coincides with the lead of the load roller rolling path 9. Further, in the joint portion between the linear passage 11 and the direction change path 16, the direction of the wiring of the direction change path 16 and the direction in which the center line of the linear passage 11 extends are aligned.

FIG. 13 shows the positional relationship between the direction change path constituting portion 13 attached to one end surface of the nut 6 and the direction changing path constituting portion 13 attached to the other end surface. The center line of the linear passage 11 of the above-described unloaded roller return path 10 extends in parallel with the axis 5c of the screw shaft 5. The center line of the direction change path 16 is linearly extended in the wiring direction of the center line of the load roller rolling path 9 when viewed from the front side of the nut 6 as shown in Fig. 13(A). Further, the center line of the direction change path 16 on the front side and the center line of the direction change path 16 on the inner side intersect at a predetermined opening angle of 90 degrees. The planes P1, P2 including the direction changing path 16 (correctly the plane including the center line of the direction changing path 16) are substantially parallel to the axis of the helical axis 5.

When a roller having a ratio of the roller diameter to the roller length of approximately 1:1 is used, as shown in Fig. 13(A), the cross-sectional shape of the linear passage 11 of the unloaded roller return path 10 can be made square. Therefore, the angle of formation of one of the linear extensions to the direction changing path 16 can be set to 90 degrees as viewed from the front of the nut. In this way, the roller can be circulated even without the unloaded roller return path 10 of the circulating member.

14 and 15 show the inner peripheral side 13a of the direction change path constituent portion. The inner peripheral side 13a of the direction changing path constituent portion has a main body portion 21 that forms a direction changing path of the radius of curvature R, and a flange portion 22 that is attached to the end surface of the nut 6. At one end of the main body portion 21, a scooping portion 21a that can pick up the roller 7 that has entered the load roller rolling path 9 is formed. The other end of the body portion 21 is embedded in the straight portion 12. The scooping portion 21a of the inner peripheral side 13a and the scooping portion of the outer peripheral side 13b can be picked up in the wiring direction to roll the roller 7 which rolls on the spiral load roller rolling path 9. The direction changing path 16 shifts the direction of the roller 7 after the lifting, and moves in the direction of the arc-shaped switching path 16. Here, even if the roller 7 moves along the direction changing path 16, the posture of the roller 7 does not rotate.

The inner peripheral side 13a of the direction changing member is formed to protrude from the end surface of the nut 6 of the mounting direction changing path forming portion 13 to the nut side, and the shape of the direction changing path 16 is curved into a curved sheet portion 23. The cross-sectional shape of the sheet portion 23 is formed in a V shape. This sheet portion 23 is fitted into the relief groove 19 formed in the end surface of the nut 6 (refer to FIG. 8).

16 and 17 show the outer peripheral side 13b of the direction change path constituent portion. The outer peripheral side 13b of the one-direction switching path configuration portion has a main body portion 25 that forms a direction change path 16 having a radius of curvature R, and a flange portion 26 that is attached to an end surface of the nut 6. At one end of the main body portion 25, a scooping portion 25a that can pick up the roller that has entered the loaded roller rolling path 9 is formed. The other end of the body portion 25 is embedded in the straight portion 12. The scooping portion 25a on the outer peripheral side and the scooping portion 21a on the inner peripheral side can pick up the roller 7 that rolls on the spiral load roller rolling path 9 in the wiring direction. The direction changing path 16 can change the direction of the roller 7 after the lifting and move in the direction of the arc-shaped switching path 16. Further, the outer peripheral side 13b of the direction changing path forming portion is formed with a protruding portion 27 that matches the shape of the roller track groove 5a of the screw shaft 5, whereby the strength of the scooping portion 25a can be secured. The direction change constituting portion 13 may be made of metal or resin.

FIG. 18 is a cross-sectional view showing the straight portion 12. The linear passage 11 is not twisted, and when the roller 7 passes through the linear passage 11 of the unloaded roller return passage 10, the posture of the roller 7 does not rotate. Further, the linear portion 12 may be made of metal or resin.

FIG. 19 shows the posture of the roller 7 that moves in the linear passage 11. As can be seen from Fig. 19, even if the linear passage 11 moves, the position of the angle A1 of the roller 7 does not change, and the posture of the roller 7 does not rotate.

Fig. 20 is a detailed view of a retainer 8 used in the present embodiment. The retainer 8 is a person who maintains the posture of the roller by maintaining the axis of the adjacent roller at a right angle. Further, in consideration of the fact that the retainer 8 itself is reversed, a flat retainer 8 whose thickness does not change on the inner circumferential side and the outer peripheral side of the annular load roller rolling path 9 can be used.

Further, the present invention is not limited to the above-described embodiments, and other embodiments may be embodied without departing from the scope of the invention. For example, the circulation member is not limited to the end cap method of the present embodiment, and various types of circulation members such as a return pipe method can be used.

The present specification claims priority from Japanese Patent Application No. 2005-083131, filed on March 23, 2005. This content is all included here.

5. . . Screw shaft

5a. . . Spiral shaft roller track groove

5b. . . Arc portion

5c. . . Axis

6. . . Nut

6a. . . Nut roller groove

7. . . Roller

8. . . Guard ring

9. . . Load roller rolling groove

10. . . No-load roller return path

11. . . Straight path

12. . . Circulating member (straight line)

13. . . Circulating member (direction change path constituent part)

13a. . . Inner circumference side

13b. . . Peripheral side

14. . . Curved shaft seal

15. . . cover

16. . . Direction conversion road

17. . . Through hole

17a. . . Central department

17b. . . Both ends

18. . . Mount

19. . . Gap

21, 25. . . Body part

21a, 25a. . . Pick up

22, 26. . . Flange

twenty three. . . Sheet portion

27. . . Protruding

D. . . diameter

L. . . length

P1, P2. . . flat

R. . . Radius of curvature

A1. . . Roller corner

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a roller screw in an embodiment of the present invention.

Figure 2 is an exploded perspective view of the main parts of the roller screw.

Figure 3 is a side view of the roller screw assembled from all parts.

Figure 4 is an arrow view of line IV-IV of Figure 3.

Figure 5 shows a side view of the screw shaft.

Fig. 6 is a view showing a cross-sectional shape of a groove of a roller groove groove of a screw shaft.

Fig. 7 is a detailed view of the nut 6 (Fig. (A) shows a front view of the nut, (B) shows a cross-sectional view along the axial direction, and (C) shows an internal view).

(A) is a detailed view of the mount of the direction change path constituent portion in Fig. 8 (Fig. (B) is a cross-sectional view taken along line B-B of (A)).

Fig. 9 is a view showing a cross-sectional shape of a groove of a roller chute groove of a nut.

Figure 10 is a side view of the roller.

Figure 11 is a cross-sectional view showing the roller in the roller of the load roller.

12(A) and (B) are center-line diagrams showing the trajectories of the rollers circulating on the spiral load roller rolling road, the arc-shaped direction changing path, and the straight path.

13(A) and 13(B) are diagrams showing the positional relationship of the direction changing path constituent portion of the end surface attached to one end side of the nut and the direction changing path forming portion of the end surface attached to the other side.

Fig. 14 is a view showing the inner peripheral side of the direction changing path constituent portion (Fig. (A) shows a front view, and Fig. 4(B) shows a side view).

Fig. 15 is a view showing the inner peripheral side of the direction changing path constituent portion (Fig. (A) shows a side view, and Fig. 5(B) shows an internal view).

Fig. 16 is a view showing the outer peripheral side of the direction change path constituting portion ((A) in the figure shows a front view, and (B) shows a side view).

Fig. 17 is a view showing the outer peripheral side of the direction changing path constituent portion (Fig. (A) shows a side view, and Fig. (B) shows a front view).

Figure 18 is a cross-sectional view of a straight portion.

Fig. 19 is a view showing a turning posture of a roller that moves in a straight path.

Figure 20 is a view showing a retainer (Fig. (A) shows a front view, (B) shows a cross-sectional view taken along the line X-X of (A), and (C) shows a cross-sectional view of the Y-Y line of (A). ).

5c‧‧‧ axis

9‧‧‧Load roller rolling groove

10‧‧‧Unloaded roller return path

11‧‧‧Linear access

13‧‧‧Circular members (direction change path components)

Claims (5)

A roller screw comprising: a screw shaft that forms a spiral roller groove groove on an outer peripheral surface; and the aforementioned inner circumferential surface and the aforementioned spiral shaft a nut of a roller raceway that is spirally opposed to the roller raceway; and a gap between the roller runner groove that is connected to the screw shaft and the roller track groove of the nut a circulating member of the unloaded roller return path at one end and the other end of the load roller rolling road; and a plurality of rollers arranged on the load roller rolling path and the unloaded roller return path; and the nut When viewed from the front, a pair of direction changing paths at both end portions of the unloaded roller return path extend linearly, and the pair of direction changing paths form an angle of substantially 90 degrees; the unloaded roller return path The pathway has not been distorted. The roller screw of the first aspect of the invention, wherein the unloaded roller return path has a linear passage extending linearly in parallel with an axis of the nut at a central portion thereof. The roller screw of claim 1 or 2, wherein the unloaded roller return path is viewed from a direction in which the roller is viewed, so that the axes of the adjacent rollers are orthogonal to each other, and the plurality of The rollers are arranged by the cross. The roller screw of claim 1 or 2, wherein the ratio of the diameter to the length of the roller is about 1:1. The cross-sectional shape of the unloaded roller return path is square. The roller screw according to claim 1 or 2, wherein one of the circulation members forming the direction change path is attached to both end faces of the nut in the axial direction.