JP2015155743A - Top-type ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive top-type ball screw having high circulation performance.

SOLUTION: A top-type ball screw comprises: a screw shaft 11 formed with a screw groove 12a; a nut 13 arranged at a periphery of the screw shaft 11, and formed with a screw groove 14; a plurality of balls arranged at a rolling passage 22 which is formed of both the screw grooves 12a, 14; and a top member 16 formed with a circulation groove 19. The nut 13 has an engagement groove 15 having a substantially-disc shape at a cross section, and formed at an internal peripheral face of the nut. The top member 16 comprises an irregularity part 17 which is slidably engaged with the screw groove 12a and a screw mount of the screw shaft 11 at an inner face side, and the circulation groove 19 formed at an external peripheral face forms a tunnel-shaped circulation passage 23 which circulates to the other end 22b from one end 22a of the rolling passage 22 together with the engagement groove 15 of the nut 13.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention relates to a ball screw used in various machine tools or an electric power steering or an actuator of an automobile, and more particularly to a piece type ball screw using a piece member as a ball circulation part.

  A piece-type ball screw is known as one of various types of ball screws with different ball circulation mechanisms, and many proposals have been made regarding the form of piece members (see, for example, Patent Documents 1 to 4). . The piece-type ball screw described in Patent Document 2 has a circulation groove that is curved in a substantially S-shape, and a piece formed in a circular shape or an oval shape is formed in a circular shape formed in a nut portion of a nut, Alternatively, it is inserted into an oblong piece window, and is fixed to the nut by fixing means such as caulking, press-fitting, and bonding to form a circulation path connecting between adjacent screw grooves of the nut.

  In the piece-type ball screw of Patent Document 3, a piece member that forms a ball circulation path together with a ball rolling path covers a metal pipe having a tunnel-like circulation path formed therein and the outside of the pipe. And a resin-made covering portion that fits into a mounting hole (frame window) provided in the nut. Further, the piece type ball screw of Patent Document 4 has a circulation block having a circulation groove installed in a concave groove of a nut, and a screw or C-shape is fitted after the localization key of the circulation block and the key groove of the nut are fitted. The circulating block is fixed to the nut by a ring or the like and positioned.

Japanese Patent Application No. 2013-115808 JP 2008-267523 A JP 2003-329097 A Utility Model Registration No. 3122121

  In the ball screw described in Patent Documents 1 and 4, since the concave groove for inserting the circulation block is provided over both axial end surfaces, the inner diameter of the end surface can be used as a processing standard in a subsequent process. was difficult. Moreover, since the radial thickness of the nut is uneven in the circumferential direction, uneven heat treatment deformation occurs in the heat treatment process after cutting. For this reason, it is necessary to set a machining allowance in a subsequent process in anticipation of unequal deformation, which may increase the manufacturing cost. In addition, the non-uniform deformation deteriorates the fitting accuracy between the concave groove and the circulation block, which may cause abnormal noise and vibration during the operation of the ball screw.

  In addition, in the piece type ball screw of Patent Documents 2 and 3, the circulation path that connects between adjacent thread grooves is formed by the circulation groove and the screw shaft of the piece member or the circulation block, and the rolling ball is Since it is scooped up by the R part of the thread of the screw shaft and circulates over the screw thread, the shape of the screw shaft affects the behavior of the ball. Therefore, in order to suppress abnormal noise and vibration and ensure a smooth operation, it is necessary to accurately manage the shape of the screw shaft.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an inexpensive piece-type ball screw having high circulation performance.

The above object of the present invention can be achieved by the following constitution.
(1) A screw shaft having a helical thread groove formed on the outer peripheral surface, a nut disposed around the screw shaft and having a helical thread groove formed on the inner peripheral surface, and the opposing screw grooves A piece comprising a plurality of balls accommodated in a rolling path formed by the above and a piece member provided with a circulation groove for rolling the ball circulating from one end to the other end of the rolling path. In the type ball screw, the circulation groove is formed on an outer surface side of the piece member, and a tunnel-like circulation path is formed by the circulation groove of the piece member and an inner peripheral surface of the nut, A fitting groove for accommodating the piece member having substantially the same shape and size as the shape and size of the outer surface side of the piece member is formed only in the axially intermediate portion of the inner peripheral surface of the nut. A ball screw characterized by that.
(2) On the inner surface side of the piece member, there is formed an uneven portion that is slidably fitted into at least one of a thread groove and a thread of the screw shaft, and the nut extends along the axial direction on the inner peripheral surface. And the piece member is fitted into the fitting groove of the nut, and the concavo-convex portion is fitted into at least one of the screw groove and the thread of the screw shaft. The piece member is positioned relative to the nut, and the tunnel-shaped circulation path is formed by the circulation groove of the piece member and the fitting groove of the nut. The piece type ball screw according to (1).
(3) The fitting groove is formed in a substantially arc-shaped cross section, and a protrusion having a substantially arc-shaped cross section corresponding to the shape of the fitting groove is formed on the outer surface side of the piece member. The piece type ball screw according to (2), characterized in that the piece type ball screw is formed so as to cross the circumferential direction.
(4) In any one of (1) to (3), the piece member includes a guide portion that scoops up the ball from the rolling path to the circulation path at at least one of the one end and the other end of the circulation groove. The piece-type ball screw described.
(5) The piece type ball screw according to any one of (1) to (4), wherein the plurality of piece members are arranged at equal intervals in the circumferential direction on the inner circumferential surface of the nut.

  According to the piece type ball screw of the present invention, since the fitting groove into which the piece member is fitted exists only in the intermediate portion in the axial direction of the nut, the radial thickness in the vicinity of both end portions in the axial direction has the fitting groove. The circumferential position and the non-existing circumferential position are the same, and the shape of the inner diameter in the vicinity of both axial ends is circular. Therefore, high-accuracy machining is possible by using the inner diameter of the end face as a machining reference in a subsequent process. In addition, since uneven heat treatment deformation hardly occurs in the heat treatment process, deterioration of the dimensional accuracy of the fitting groove can be prevented, and appropriate fitting with the piece member can be realized. Furthermore, it is possible to reduce the manufacturing cost by reducing the processing cost in the post process.

  Further, on the inner surface side of the piece member, an uneven portion is formed that is slidably fitted to at least one of the thread groove and the thread of the screw shaft, and the nut is formed on the inner peripheral surface along the axial direction. The piece member has a fitting groove, and the piece member is fitted into the fitting groove of the nut, and the uneven portion is fitted into at least one of the screw groove and the thread of the screw shaft, so that the piece member is attached to the nut. Relatively positioned. Accordingly, the piece member can be positioned on the nut without providing a fixing means for fixing the nut and the piece member, and the piece type ball screw can be manufactured at low cost. In particular, in the case of a conventional nut provided with a hole for attaching a circulation piece or tube, it is necessary to measure the position of the hole and to process the screw groove so that the axial position of the hole and the screw groove matches. However, in the case of the present invention, it is not necessary to precisely match the axial positions of the thread groove and the fitting groove, so that the processing of the nut is simplified and the processing cost can be reduced. Further, since the tunnel-like circulation path is formed by the circulation groove of the piece member and the fitting groove of the nut, the fitting groove is shared as the positioning portion of the piece member and the raceway surface of the circulation path. Can do.

  Furthermore, the fitting groove is formed in a substantially arc shape in cross section, and a protrusion having a substantially arc shape in cross section corresponding to the shape of the fitting groove is formed on the outer surface side of the piece member. Since it forms so that it may lie over the circumferential direction, a piece member can be designed compactly, sharing a fitting groove as a positioning part of a piece member, and a track surface of a circulation path.

  In addition, since the piece member has a guide portion for scooping the ball from the rolling path to the circulation path at at least one of the one end and the other end of the circulation groove, the thread of the screw shaft is provided like a conventional piece type ball screw. Since the ball is not used for picking up, a smooth operation can be realized and the operating noise can be reduced.

  Further, according to the piece type ball screw of the present invention, the circulating portion is formed on the outer surface side of the piece member, so that the ball is circulated from one end of the rolling path to the other end on the outer surface side of the piece member. Since the ball does not contact the thread of the screw shaft during circulation, the operation noise is reduced and the life of the ball screw can be extended. In addition, on the inner surface side of the piece member, an uneven portion that is slidably fitted to at least one of the thread groove and the thread of the screw shaft is formed, and the nut is formed on the inner peripheral surface along the axial direction. The piece member has a fitting groove, and the piece member is fitted into the fitting groove of the nut, and the concavo-convex portion is fitted into at least one of the screw groove and the screw thread of the screw shaft, so that the piece member is attached to the nut. Accordingly, the piece member can be positioned on the nut without providing a fixing means for fixing the nut and the piece member, and the piece type ball screw can be manufactured at low cost. In particular, in the case of a conventional nut provided with a hole for attaching a circulation piece or tube, it is necessary to measure the position of the hole and process the thread groove so that the axial position of the hole and the thread groove exactly matches each other. However, in the case of the present invention, since it is not necessary to match the axial positions of the screw groove and the fitting groove so closely, the processing of the nut is simplified and the processing cost can be reduced.

It is a perspective view of the piece type ball screw concerning the present invention. (A) is a disassembled perspective view of the piece type ball screw shown in FIG. 1, (b) is a perspective view of essential parts of the nut and the piece member. (A) is a perspective view of the piece member seen from the outside, (b) is a perspective view of the piece member seen from the diagonally inside, and (c) is a piece member portion showing one circulation groove. It is a perspective view. It is a partially broken perspective view which shows the state which the thread groove of a screw shaft and the uneven | corrugated | grooved part of a piece member fit, and a piece member is positioned. It is sectional drawing which shows the circulation path | route of a ball | bowl. It is a schematic diagram which shows the method of processing a fitting groove using a cutter tool. It is a perspective view of the piece type ball screw concerning the present invention using a plurality of piece members. It is a schematic diagram which shows the method of processing the nut which concerns on this invention by using the internal diameter of an axial direction both end surface as a process reference.

  Hereinafter, an embodiment of a piece type ball screw according to the present invention will be described in detail with reference to the drawings. As shown in FIGS. 1 and 2, the piece ball screw 10 includes a screw shaft 11 having a spiral thread groove 12a formed on the outer peripheral surface and a screw thread 14 formed on the inner peripheral surface. A rolling path 22 formed by a nut 13 arranged around the shaft 11, a piece member 16 fitted in the fitting groove 15 of the nut 13, a screw groove 12 a of the screw shaft 11 and a screw groove 14 of the nut 13. (See FIG. 5) and a plurality of balls (not shown) arranged so as to roll freely.

  The cross-sectional shapes of the screw shafts 12 and the screw grooves 12a and 14 of the nut 13 are preferably gothic arc shapes that have a large allowable axial load and can suppress vibration, but may be circular arc shapes. On the inner peripheral surface of the nut 13, a fitting groove 15 having a substantially arc-shaped cross section for accommodating the piece member 16 is formed in an intermediate portion in the axial direction of the nut. The axial length and circumferential length (width) of the fitting groove 15 and the shape of the axial cross section are substantially the same as or slightly larger than those of the piece member 16. A slight difference occurs in the position where the piece member 16 is stabilized in the fitting groove 15 due to variations in the component accuracy of the piece member 16. In the present invention, it is not necessary to firmly fix the piece member 16 to the fitting groove 15, so that the difference can be allowed by forming the fitting groove 15 slightly larger, thereby reducing the manufacturing cost. Can do.

  3 and 4, the piece member 16 has substantially the same cross-sectional shape as the screw groove 12 a and the screw thread 12 b of the screw shaft 11 on the surface that becomes the inner diameter side when fitted into the fitting groove 15. And the uneven | corrugated | grooved part 17 formed in the same pitch as the pitch of the thread groove 12a and the thread 12b is formed. Each concavo-convex portion 17 is slidably fitted into the screw groove 12a and the screw thread 12b of the screw shaft 11.

  Further, the surface which is on the outer diameter side when fitted in the fitting groove 15 extends in the longitudinal direction of the piece member 16 and has a substantially arc-shaped cross section having substantially the same sectional shape as the fitting groove 15 of the nut 13. A protrusion 18 is formed. In the protrusion 18, two circulation grooves 19 that are recessed in a substantially U shape from the outer diameter side toward the inner diameter side cross the protrusion 18 in the circumferential direction, and both end portions in the circumferential direction of the piece member 16. It is formed in a substantially S shape so as to connect 16a and 16b.

  One end 19a of each circulation groove 19 corresponds to one protrusion 17a among the adjacent protrusions 17a and 17b in the concavo-convex portion 17, and the other end 19b of the circulation groove 19 is the other protrusion. Corresponding to the part 17b, it is formed over both end parts 16a, 16b of the piece member 16, respectively. Between both ends 19a and 19b of each circulation groove 19, a curved shape is formed in a substantially S shape so that the ball rolls smoothly.

  As a result, the circulation groove 19 connects one end 22a and the other end 22b of the rolling path 22, and more specifically, connects one end and the other end of the adjacent screw groove 12a of the screw shaft 11. The end portions 19 a and 19 b of the circulation groove 19 are integrally formed with a guide portion 20 that scoops up a ball rolling on the rolling path 22 from the rolling path 22 and guides it to the circulation groove 19.

As shown in FIGS. 4 and 5, in the piece member 16, the protrusion 18 is fitted in the fitting groove 15 of the nut 13, and each uneven portion 17 is fitted in the screw groove 12 a and the screw thread 12 b of the screw shaft 11. Then, the screw shaft 11 and the nut 13 are assembled. Thus, a rolling path 22 is formed by the thread groove 12 a of the screw shaft 11 and the thread groove 14 of the nut 13, and the rolling path 22 is formed by the circulation groove 19 of the piece member 16 and the fitting groove 15 of the nut 13. A tunnel-like circulation path 23 that circulates from one end 22a to the other end 22b is formed.
FIG. 4 shows the piece member 16 and the nut 13 in a separated state for explanation.

  Further, the nut 13 and the piece member 16 are relatively positioned without using the fixing means. That is, by fitting the protrusion 18 with the fitting groove 15 of the nut 13, the radial position and the circumferential position of the piece member 16 with respect to the nut 13, and by fitting the concavo-convex part 17 with the screw groove 12 a and the thread 12 b. The axial position of the piece member 16 is restricted. Therefore, at the time of operation, the piece member 16 is held in the axial direction with respect to the nut 13 while sliding with the screw shaft 11. Thereby, the fixing means for fixing the piece window and the piece member inserted in the piece window which were necessary with the conventional piece type ball screw becomes unnecessary.

  The plurality of balls that roll in the rolling path 22 are scooped up from the one end 22a of the rolling path 22 by the guide portion 20 formed in the end portions 19a and 19b of the circulation groove 19 and guided to the circulation path 23. It returns to the other end 22b (adjacent screw grooves 12a, 14 shifted by one pitch) of the moving path 22 and rolls along the rolling path 22 again.

  The guide portion 20 is integrally formed corresponding to the concavo-convex portion 17, and the concavo-convex portion 17 is fitted into the screw groove 12 a and the screw thread 12 b of the screw shaft 11. 12a is assembled with a high positional accuracy. Accordingly, the ball scooped up by the guide unit 20 is smoothly guided from the rolling path 22 to the circulation path 23 and returned to the adjacent rolling path 22 through the tunnel-shaped circulation path 23.

  Thus, in the conventional piece type ball screw, the ball contacts the screw shaft 11 and circulates over the screw thread, and the shape of the screw shaft 11 affects the behavior of the ball. Since the piece-type ball screw 10 circulates without contacting the screw shaft 11, it is not necessary to manage the shape of the thread of the screw shaft 11.

  The piece member 16 of the present embodiment is integrally formed by a mold (not shown). When the piece member 16 is made of metal, for example, it can be formed by so-called MIM (Metal Injection Molding) in which a metal powder and a binder are heated and melted and pressed into a mold by an injection molding machine. By integrally molding the piece member 16 using a mold in this way, the relative positions of the concavo-convex portion 17, the protrusion 18, the circulation groove 19, and the guide portion 20 can be formed with high accuracy, which is favorable. Circulation performance is easily obtained. Note that the piece member 16 is not limited to the MIM as long as it is manufactured by a mold, and may be formed by injection molding a sintered alloy obtained by press-molding metal powder and firing, or synthetic resin. Good.

  As a processing method of the thread groove 14, turning processing, milling processing, grinding processing, and the like are possible. Moreover, the fitting groove 15 of the nut 13 can be formed by cutter processing using a milling machine etc. as shown in FIG. 6, for example. For example, when machining the screw groove 14 using a helical cutter, the screw groove 14 and the fitting groove 15 can be machined only by exchanging the tool, so that the relative position between the screw groove 14 and the piece member 16 is maintained with high accuracy. be able to.

  As described above, according to the piece type ball screw 10 of the present embodiment, the circulation groove 19 is formed on the outer surface side of the piece member 16, and is formed by the circulation groove 19 of the piece member 16 and the inner peripheral surface of the nut 13. Since the tunnel-like circulation path 23 is formed, the ball can be circulated from the one end 22a of the rolling path 22 to the other end 22b on the outer surface side of the piece member 16. Therefore, the ball does not come into contact with the screw thread 12b of the screw shaft 11 during the circulation, the operation noise is reduced, the ball is prevented from being damaged, and the life of the ball screw 10 can be extended. Furthermore, since members other than the circulation path such as a tube fixture required in the tube type ball screw are not necessary in this embodiment, an inexpensive piece type ball screw can be provided.

  Further, on the inner surface side of the piece member 16, an uneven portion 17 that is slidably fitted into the screw groove 12 a and the screw thread 12 b of the screw shaft 11 is formed, and the nut 13 is formed on the inner peripheral surface along the axial direction. By having the fitting groove 15 formed, the piece member 16 is fitted into the fitting groove 15 of the nut 13, and the concave and convex portion 17 is fitted into the screw groove 12 a and the screw thread 12 b of the screw shaft 11. The piece member 16 is positioned relative to the nut 13. Accordingly, the piece member 16 can be positioned on the nut 13 without providing a fixing means for fixing the nut 13 and the piece member 16, and the piece type ball screw 10 can be manufactured at low cost. In particular, in the case of a conventional nut provided with a hole for attaching a circulation piece or tube, it is necessary to measure the position of the hole and to process the screw groove so that the axial position of the hole and the screw groove matches. However, in the case of the present embodiment, it is not necessary to match the axial positions of the screw groove 14 and the fitting groove 15 so closely, so the processing of the nut 13 is simplified and the processing cost can be reduced. Further, since the tunnel-shaped circulation path 23 is formed by the circulation groove 19 of the piece member 16 and the fitting groove 15 of the nut 13, the fitting groove 15 serves as a positioning portion for the piece member 16, and the circulation path 23. It can be shared as a raceway surface.

  In addition, the fitting groove 15 is formed in a substantially arc shape in cross section, and a protrusion 18 having a substantially arc shape in cross section corresponding to the shape of the fitting groove 15 is formed on the outer surface side of the piece member 16. Since the projection 18 is formed so as to cross the circumferential direction, the piece member 16 can be used while sharing the fitting groove 15 as a positioning portion of the piece member 16 and as a raceway surface of the circulation path 23. It can be designed compactly.

  Further, unlike the prior art, the present invention is characterized in that the fitting groove 15 is formed only at the intermediate portion in the axial direction of the nut, and the radial thickness of both end faces of the nut 13 is the same over the entire circumference. Yes. As a result, as shown in FIG. 8, the inner diameter surfaces of the both end surfaces or the chamfered portions thereof can be used as a processing reference in a subsequent process, and the nut 13 can be processed with high accuracy. Further, since the nut 13 does not cause uneven heat treatment deformation in the circumferential direction in the heat treatment process, the processing cost in the subsequent process can be minimized, and the manufacturing cost can be reduced. In addition, since the uneven heat treatment deformation does not occur, the fitting groove 15 and the piece member 16 can be properly fitted, and the operation of the ball screw without abnormal noise or vibration can be realized.

  In addition, when a plurality of circulation grooves 19 are provided in one piece member 16, the cost can be reduced because only one piece member 16 and one fitting groove 15 are required, but the circumferential direction of the nut can be reduced. May cause unevenness in weight. If the weight is uneven in the circumferential direction, abnormal noise and vibration may occur when the nut is rotated, which may shorten the life of the ball screw. Therefore, it is preferable to use a plurality of piece members 16 for the usage of rotating the nut. FIG. 7 shows a configuration in which two piece members 16 are accommodated in two fitting grooves 15 arranged at equal intervals in the circumferential direction. Such a configuration can alleviate uneven load in the circumferential direction, suppress abnormal noise and vibration, and extend the life of the ball screw.

  Since the piece member 16 is provided with guide portions 20 for scooping the ball from the rolling path 22 to the circulation path 23 at both ends 19a and 19b of the circulation groove 19, the screw of the screw shaft 11 is provided like a conventional piece type ball screw. Since the balls are not picked up using the mountain 12b, a smooth operation can be realized and the operating noise can be reduced.

  Further, since the piece member 16 is integrally formed by a mold, the relative position between the concave and convex portion 17 and the circulation groove 19 and the guide portion 20 can be manufactured with high accuracy. Thereby, the positional accuracy of the thread groove 12a of the screw shaft 11 with which the uneven part 17 is fitted, the circulation groove 19 and the guide part 20 is improved, and the ball runs smoothly while suppressing the generation of abnormal noise and vibration. Can be made.

In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably.
For example, in the above-described embodiment, the screw groove 12a and the screw thread 12b of the screw shaft 11 and the uneven portion 17 of the piece member 16 are described as being fitted. If it restrict | limits a position, it will not be limited to this, You may make it fit only with the thread groove of the screw shaft 11, or only a thread.

  Further, the piece member 16 having the two circulation grooves 19 and the two circulation paths 23 has been described. However, the number of the circulation grooves 19 may be one, or three or more. It can be selected appropriately according to the specifications. When the piece type ball screw 10 includes a plurality of circulation paths 23, the piece member 16 having a plurality of circulation grooves 19 may be integrally formed, or a plurality of piece members 16 having one circulation groove 19. May be arranged in combination.

  In the piece type ball screw of the present invention, the circulating portion is formed on the outer surface side of the piece member, and the inner surface side of the piece member is slidably fitted into at least one of the screw groove and the thread of the screw shaft. The nut has a fitting groove formed along the axial direction on the inner peripheral surface, the piece member is fitted into the fitting groove of the nut, and the concave and convex portion is the screw shaft. It is sufficient that the piece member is positioned relative to the nut by fitting in at least one of the thread groove and the thread. For example, instead of configuring the circulation portion of the piece member by the circulation groove, Alternatively, a circulation hole may be used.

DESCRIPTION OF SYMBOLS 10 Piece type ball screw 11 Screw shaft 12a, 14 Thread groove 13 Nut 15 Fitting groove 16 Piece member 22 Rolling path 17 Uneven part 19 Circulation groove (circulation part)
19a One end of the circulation groove 19b Other end of the circulation groove 20 Guide part 23 Circulation path 30 Cutter tool

Claims (5)

It is formed by a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut disposed around the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and the opposing screw grooves. A piece type ball screw comprising: a plurality of balls housed in a rolling path; and a piece member provided with a circulation groove for rolling the ball circulating from one end to the other end of the rolling path. The circulation groove is a ball screw formed on the outer surface side of the piece member, and a tunnel-like circulation path is formed by the circulation groove of the piece member and the inner peripheral surface of the nut, A fitting groove for accommodating the piece member having substantially the same shape and size as the shape and size of the outer surface side of the piece member is formed only in the axially intermediate portion of the inner peripheral surface. And ball screw. On the inner surface side of the piece member, there is formed an uneven portion that is slidably fitted into at least one of a thread groove and a thread of the screw shaft, and the nut is formed on the inner peripheral surface along the axial direction. The piece member is fitted into the fitting groove of the nut, and the concavo-convex portion is fitted into at least one of the screw groove and the thread of the screw shaft. A piece member is positioned relative to the nut, and the tunnel-shaped circulation path is formed by the circulation groove of the piece member and the fitting groove of the nut. The piece type ball screw according to claim 1. The fitting groove is formed in a substantially arc shape in cross section, a protrusion having a substantially arc shape in cross section corresponding to the shape of the fitting groove is formed on the outer surface side of the piece member, and the circulation groove is formed in the protrusion. The piece type ball screw according to claim 2, wherein the piece type ball screw is formed so as to cross the circumferential direction. The piece according to any one of claims 1 to 3, wherein the piece member includes a guide portion that scoops up the ball from the rolling path to the circulation path at least one of the circulation groove and the other end. Ball screw. 5. The piece type ball screw according to claim 1, wherein the plurality of piece members are arranged at equal intervals in the circumferential direction on an inner circumferential surface of the nut.

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