WO2024048362A1

WO2024048362A1 - Ball screw device

Info

Publication number: WO2024048362A1
Application number: PCT/JP2023/030105
Authority: WO
Inventors: 太中村
Original assignee: Thk株式会社
Priority date: 2022-09-01
Filing date: 2023-08-22
Publication date: 2024-03-07
Also published as: JP2024034667A

Abstract

This ball screw device prevents contact of a ball rolling within an unloaded passage with a corner section of a nut member exposed to the interior of the passage, and enables favorable rolling conditions of the ball to be maintained over a long period. The nut member comprises: a nut body that has a pair of ball circulation holes which pass through in a radial direction so as to correspond to both ends of a loaded passage, and that has a ball return groove formed between the pair of ball circulation holes; a pair of circulation members that are mounted in the pair of ball circulation holes of the nut body and that has formed therein first direction-changing grooves; and a lid member that is installed on the nut body so as to cover the ball return groove and the pair of circulation members, that has a guide groove which, by overlapping with the ball return groove, forms a return passage, and that has a second direction-changing groove which, by continuing from the guide groove and overlapping with the first direction-changing grooves of the circulation members, forms a direction-changing path. The groove width of the ball return groove is set to be greater than the groove width of the guide groove.

Description

ball screw device

The present invention relates to a ball screw device that can mutually convert rotational motion and linear motion.

A ball screw device is a mechanical element that can mutually convert rotational motion and linear motion, and its purpose is to convert the rotational motion generated by a servo motor into linear motion in various machine tools, conveyance devices, industrial robots, etc. It is widely used in The ball screw device has a screw shaft and a cylindrical nut member screwed together through a large number of balls, and the screw shaft has a predetermined spiral rolling groove on the outer peripheral surface in which the balls roll. It is made of reeds. Therefore, when the screw shaft is rotated once, the nut member moves in the axial direction of the screw shaft by the lead of the rolling groove. Therefore, if the number of rotations applied to the screw shaft is the same, the larger the lead of the rolling groove, the faster the nut member moves in the axial direction of the screw shaft.

An endless circulation path in which the large number of balls are arranged is formed in the nut member. This endless circulation path connects a spiral load path in which the ball rolls while applying a load between the screw shaft and the nut member, and both ends of the load path, and the ball is released from the load. It consists of an unloaded passageway that rolls in a suspended state. The ball rolls in the endless circulation path as the screw shaft and the nut member rotate relative to each other.

In conventional ball screw devices, many structures of the no-load passage in the nut member have been proposed. For example, the larger the lead of the rolling groove, the more difficult it is to move the ball from the terminal end to the starting end of the spirally formed load passage. When returning the ball, it is necessary to move the ball largely in the axial direction of the nut member within the no-load passage.

A ball screw device having such a no-load passage is disclosed in Document 1. In the ball screw device disclosed in this document 1, the no-load passage is constructed by attaching a pair of circulation pieces and a return passage member that interconnects these circulation pieces to the nut member. The pair of circulation pieces have a connecting passage for separating the balls that have finished rolling in the load passage from the rolling groove of the screw shaft, and release the balls from the load and move the balls from the inside to the outside of the nut member. lead to. On the other hand, the return passage member has a linear return passage connecting between the pair of circulation pieces and extending in the axial direction of the nut member, and by attaching the return passage member to the nut member, the circulation The connection passage of the piece and the return passage are combined to complete the no-load passage.

JP2017-137953

In a ball screw device in which the lead of the rolling groove is large as described above, the no-load passage for the balls is constructed by attaching a pair of circulation pieces and a return passage member to the nut member. In this case, since the connecting portions of each member are exposed in the no-load passage, the presence of steps at these connecting portions will impede smooth circulation of the balls within the no-load passage.

In particular, since the ball applies a load between the screw shaft and the nut member, the nut member is usually made of a metal material such as bearing steel. For this reason, if a step occurs at the connection between the nut member and the circulation piece or the return passage member, the ball rolling in the no-load passage may hit the corner of the metal nut member at the connection portion. There was a concern that contact would cause abnormal wear on the ball's surface.

The present invention has been made in view of these problems, and its purpose is to prevent balls from rolling in the no-load passage when constructing a no-load passage for the ball relative to the nut member by combining a plurality of members. An object of the present invention is to provide a ball screw device that can prevent moving balls from coming into contact with corners of a nut member exposed in the passage and maintain a good rolling state of the balls over a long period of time.

The ball screw device of the present invention includes a large number of balls, a screw shaft in which rolling grooves for the balls are spirally formed on an outer peripheral surface, and a through hole through which the screw shaft is inserted, and a nut member that is screwed onto the screw shaft through the nut member and has an endless circulation path for the plurality of balls. The endless circulation path includes a load path in which the plurality of balls spirally roll between the screw shaft and the nut member, a pair of direction change paths located at both ends of the load path, and a pair of direction change paths located at both ends of the load path. It consists of a return passage connecting the direction change passage. The nut member has the through hole, the load passage is formed between the nut member and the screw shaft, and a pair of ball circulation holes that correspond to both ends of the load passage and penetrate in the radial direction, and further, A nut body having a ball return groove formed between the pair of ball circulation holes on the outer peripheral surface, and a pair of circulation grooves that are attached to the pair of ball circulation holes of the nut body and have a first direction change groove formed therein. a guide groove that is attached to the nut body and covers the ball return groove and the pair of circulation members, overlaps with the ball return groove and forms the return passage, and continues from the guide groove and includes the circulation member. and a lid member having a second direction change groove that overlaps with the first direction change groove of the member and forms the direction change path.

As a first feature, the groove width of the ball return groove is set larger than the groove width of the guide groove.

Moreover, as a second feature, the depth of the ball return groove is set larger than the depth of the first direction change groove.

According to the present invention, when constructing a no-load passage for a ball relative to a nut member by combining a plurality of members, it is possible to prevent a corner of the nut member from protruding into the no-load passage as a step. As a result, it is possible to prevent scratches from occurring on the surface of the ball and maintain a good rolling state of the ball for a long period of time.

FIG. 1 is a perspective view showing an example of a ball screw device to which the present invention is applied. It is an enlarged perspective view showing the state where the circulation member was attached to the nut main body. FIG. 3 is a perspective view showing the front side of the circulation member. It is a perspective view showing the back side of a circulation member. It is a perspective view showing a lid member. FIG. 3 is an enlarged perspective view showing a connecting portion between a ball circulation hole and a ball return groove of the nut body. It is a perspective view which shows the connection state of the direction change path and the return path provided in the nut member. It is a figure which shows the cross section of the direction change path formed by the overlapping of the circulation member and the lid member. FIG. 6 is a diagram showing a cross section of a return passage formed by overlapping the nut body and the lid member. FIG. 3 is a cross-sectional view of the connecting portion between the direction change path and the return path, viewed from a direction perpendicular to the rolling direction of the ball.

Hereinafter, the ball screw device of the present invention will be explained in detail using the accompanying drawings.

FIG. 1 shows an example of a ball screw device to which the present invention is applied. This ball screw device 1 includes a screw shaft 2 having a ball rolling groove 20 spirally formed on its outer circumferential surface, and a cylindrical nut member that is screwed around the screw shaft 20 via a large number of balls 5. It is composed of 3. Further, the nut member 3 is provided with an endless circulation path for the balls. The ball 5 is interposed between the screw shaft 2 and the nut member 3. For example, by rotating the screw shaft 2 with respect to the nut member 3, the nut member 3 rotates around the axis of the screw shaft 2. By moving in the direction or rotating the nut member 3 with respect to the screw shaft 2, the screw shaft 2 moves in the axial direction of the nut member 3.

A line of the rolling grooves 20 is formed with a predetermined lead on the outer peripheral surface of the screw shaft 2, and the rolling grooves 20 are present at a constant pitch along the axial direction of the screw shaft 2. Further, between the rolling grooves 20 adjacent to each other is a threaded portion 21, and the threaded portion 21 indicates the outer diameter of the screw shaft 2. In this embodiment, the lead of the rolling groove 20 is set larger than the outer diameter of the screw shaft 2.

The nut member 3 is formed into a cylindrical shape and has a through hole through which the screw shaft 2 is inserted. A spiral load rolling groove having the same lead as the rolling groove 20 of the screw shaft 2 is formed on the inner peripheral surface of the nut member 3. The balls 5 roll between the rolling groove of the screw shaft and the load rolling groove of the nut member, and apply a load between the screw shaft 2 and the nut member 3.

The nut member 3 has a cylindrical shape with no unevenness on the outer peripheral surface. This nut member 3 includes a metal nut body 30 having the through hole and the load rolling groove formed on the inner peripheral surface of the through hole, and a pair of circulation members 31 attached to the nut body 30. and a cover member 32 fixed to the nut main body 30 so as to cover the pair of circulation members 31. The rolling groove 20 of the screw shaft 2 and the load rolling groove of the nut body 30 face each other and constitute a load passage for the ball 5, and the ball 5 is inserted between the screw shaft 2 and the nut member 3. It rolls spirally within the load passage while applying the applied load.

The pair of circulation members 31 and the lid member 32 are made of synthetic resin, and by attaching the pair of circulation members 31 and the lid member 32 to the nut main body 30, the nut member 3 has balls 5. A no-load passage 50 is constructed in which the wheels roll in a state where they are released from a load, and both ends of the loaded passage are connected by the no-load passage. Note that FIG. 1 shows a state in which the lid member 32 is removed from the nut main body 30 and the no-load passage 50 of the ball 5 is exposed.

The nut body 30 has a flat mounting surface 34 with a part of its outer peripheral surface cut out, and by fixing the lid member 32 to this mounting surface 34, the nut member 3 is shaped into a cylindrical shape. is doing. A ball return groove extending linearly in the axial direction of the nut body 30 is formed in the mounting surface 34 of the nut body 30, and constitutes a part of the no-load passage 50. Further, the mounting surface 34 is provided with a pair of ball circulation holes into which each of the pair of circulation members 31 is fitted. These pair of ball circulation holes are located at both ends of the ball return groove.

FIG. 2 is an enlarged perspective view showing how the circulation member 31 is attached to the ball circulation hole. The ball circulation hole 35 passes through the nut body 30 in the radial direction, and is provided at a position corresponding to an end of a load rolling groove formed on the inner peripheral surface of the nut body 30. The circulation member 31 is provided with a first direction change groove 40, and when the circulation member 31 is installed in the ball circulation hole 35 of the nut body 30, one end of the first direction change groove 40 is connected to the ball return groove. 36.

The ball return groove 36 has a rectangular cross section perpendicular to its longitudinal direction, and the depth of the ball return groove 36 is the same as the radius of the ball 5 or slightly deeper than the radius of the ball 5. has been done. Further, the width of the ball return groove 36 is set to be slightly larger than the diameter of the ball 5.

3 and 4 are views showing the circulation member 31. FIG. 3 is a view of the circulation member 31 observed from the surface side of the circulation member, that is, the circulation member 31 is observed from the outside in the radial direction of the nut member 3, and FIG. 4 is a view of the circulation member 31. FIG. 3 is a view of the circulation member 31 observed from the back side of the circulation member 31, that is, the circulation member 31 viewed from the inside of the nut member 3 in the radial direction. The circulation member 31 includes a guide portion 310 located so as to close the end of the load rolling groove, and a guide portion 310 that extends around the guide portion 310 and contributes to fixing the circulation member 31 to the nut body 30. The fitting portion 311 is configured to include a fitting portion 311. As shown in FIG. 3, the first direction changing groove 40 is formed across the guide part 310 and the fitting part 311. Further, the cross section of the first direction changing groove 40 is formed in a semicircular shape similar to the spherical surface of the ball 5, and the radius thereof is set to be slightly larger than the radius of the ball 5.

A scooping part is provided at the end of the first direction change groove 40 on the guiding part 310 side for transferring the ball 5 between the first direction change groove 40 and the rolling groove 20 of the screw shaft 2. 312 is provided. The scooping portion 312 is provided by cutting out the first direction changing groove 40 in a substantially U-shape. Further, as shown in FIG. 4, the guide portion 310 is provided with a protrusion 313 that enters the rolling groove 20 of the screw shaft 2 while maintaining a gap. Therefore, as shown in FIG. 3, the scooping portion 312 has a generally M-shape as a whole.

On the other hand, FIG. 5 shows the lid member 32 fixed to the nut main body 30, and shows the back side of the lid member 32, that is, the side of the contact surface with the nut main body 30. As shown in the figure, a guide groove 321 corresponding to the ball return groove 36 of the nut body 30 is formed in the cover member 32. The guide groove 321 has a semicircular cross section perpendicular to its longitudinal direction that approximates the spherical surface of the ball 5, and its radius is set to be slightly larger than the radius of the ball 5. When the cover member 32 is attached to the nut body 30, the guide groove 321 overlaps with the ball return groove 36 of the nut body 30, thereby forming a ball return path.

Furthermore, a pair of guide protrusions 322 are provided on the lid member 32 so as to be located at both ends of the guide groove 321. When the lid member 32 is attached to the nut main body 30, these guide protrusions 322 overlap the circulation member 31, fit into the ball circulation hole 35, and cover the circulation member 31. A second direction changing groove 323 continuous from the guide groove 321 is formed in each guide protrusion 322 . The cross section of the second direction change groove 323 is formed in a semicircular shape similar to the spherical surface of the ball 5, similarly to the guide groove 321 and the first direction change groove 40 formed in the circulation member 31. , its radius is set slightly larger than the radius of the ball 5. The second direction change groove 323 overlaps with the first direction change groove 40 of the circulation member 31 when the cover member 32 is attached to the nut body 30, and allows the ball 5 to be moved between the load path and the return path. Configure the turning path for handover.

When the balls 5 that have rolled on the helical load rolling path provided between the screw shaft 2 and the nut body 30 reach the ball circulation hole 35 of the nut body 30, the balls 5 pass through the circulation member and the lid member. The vehicle enters the turning path formed by the vehicle and is released from the load. Further, the traveling direction of the ball 5 changes by approximately 90 degrees within the direction change path, and the ball 5 is sent into a linear return path formed by the ball return groove 36 of the nut body 30 and the guide groove 321 of the lid member 32. It will be done. The balls 5 that have rolled in the return path under no load are sent into the spiral loaded rolling path again via the direction change path on the opposite side. In this way, the balls 5 circulate endlessly inside the nut member 3.

FIG. 6 shows a connecting portion between the ball circulation hole 35 formed in the nut body 30 and the ball return groove 36. A housing part 351 into which the fitting part 311 of the circulation member 31 fits is provided around the ball circulation hole 35, and an end of the ball return groove 36 is open to the housing part 311.

FIG. 7 shows a state in which the circulation member 31 is attached to the ball circulation hole 35 and the lid member 32 is fixed to the attachment surface 34 of the nut body 30. However, a portion of the lid member 32 is illustrated with a cutout so that the connection state between the first direction changing groove 40 of the circulation member 31 and the ball return groove 36 of the nut body 30 can be understood. As can be understood from the figure, the ball return groove 36 of the nut main body 30 and the guide groove 321 of the lid member 32 overlap each other, and the linear return path 51 in which the ball 5 rolls under no load as described above. Configure. Further, a first direction change path 40 of the circulation member 31 is continuous with the ball return groove 36 of the nut body 30, and the balls 5 can go back and forth between the ball return groove 36 and the first direction change path 40. It looks like this.

FIG. 8 is a sectional view showing a direction change path 52 for the ball 5 formed by overlapping the first direction change groove 40 of the circulation member 31 and the second direction change groove 323 of the lid member 32. The cross sections of the first direction change groove 40 and the second direction change groove 323 are formed in a semicircular shape with the same inner diameter _D1 , and the inner diameter is set slightly larger than the diameter _D0 of the ball 5. There is. Therefore, the direction change path 52 becomes a passage having a circular cross section with an inner diameter D ₁ larger than the diameter D ₀ of the ball 5, and the ball 5 rolls inside the direction change path 52 under no load.

FIG. 9 is a sectional view showing a return passage 51 for the ball 5 formed by overlapping the ball return groove 36 of the nut body and the guide groove 321 of the lid member 32. The cross section of the guide groove 321 is formed in a semicircular shape with an inner diameter D ₁ , like the second direction change groove 323 which is continuous therewith. On the other hand, the ball return groove 36 facing the guide groove 321 is formed in a channel shape having a pair of side walls and a bottom surface, and the groove width of the ball return groove 36 is slightly larger than the diameter D ₀ of the ball 5. It is set to ₁ . Further, the depth of the ball return groove 36 is set to H ₁ which is slightly larger than the diameter D ₀ /2 of the ball 5. Therefore, the ball 5 rolls in the return passage 51 formed by overlapping the guide groove 321 and the ball return groove 36 under no load.

Here, when comparing the inner diameter D ₁ of the guide groove 321 and the groove width W 1 of the ball return groove 36, the groove width _{W 1} _of the ball return groove 36 is slightly smaller than the inner diameter D ₁ of the guide groove 321. Largely formed. Therefore, in the return passage 51, the corner of the upper edge of the ball return groove 36, that is, the corner where the mounting surface 34 of the nut main body 30 and the side wall of the ball return groove 36 intersect, is located in the cover member. 32 is slightly recessed with respect to the side edge of the guide groove 321, and the cover member 32 covers the corner of the upper end edge of the ball return groove 36.

Since the ball return groove 36 is formed in the metal nut body 30, if the ball 5 rolling in the return passage 51 comes into contact with the corner of the upper edge of the ball return groove 36, There is a concern that scratches may occur on the surface of the ball 5, leading to poor lubrication or abnormal wear of the ball 5. However, in the nut member 3 of this embodiment, the corner of the upper edge of the ball return groove 36 is covered by the lid member 32, and the ball 5 rolling in the return passage 51 comes into contact with the corner. Therefore, it is possible to maintain a good rolling state of the balls 5 for a long period of time.

FIG. 10 is a cross-sectional view of the connecting portion between the direction change path 52 and the return path 51, viewed from a direction perpendicular to the direction in which the ball 5 travels. The direction change path 52 is configured such that the second direction change groove 323 of the lid member 32 and the first direction change groove 40 of the circulation member 31 face each other. Further, the return passage 51 is formed such that the guide groove 321 of the lid member 32 and the ball return groove 36 of the nut body face each other. As described above, the first direction changing groove 40 is formed in a semicircular shape with an inner diameter _D1 , and the depth of the first direction changing groove 40 shown in the figure is 1/2 of _D1 . Meanwhile, the ball return groove 36 is formed in a channel shape, and its depth is _H1 .

Here, when comparing the depth of the first direction change groove 40 and the depth of the ball return groove 36, the depth H ₁ of the ball return groove 36 is the depth D ₁ /of the first direction change groove 40. It is set slightly larger than 2. Therefore, the circulation member 31 is fitted into the ball circulation hole 35 of the nut body 30, and the lid member 32 is fixed to the mounting surface 34 of the nut body 30, and the lid member 32 and the circulation When the member 31 is in contact with the member 31, the deepest part of the first direction change groove 40 is slightly higher than the bottom surface of the ball return groove 36, and there is a slight gap between the return path 51 and the direction change path 52. A difference in level occurs.

Since the ball return groove 36 is formed in the metal nut body 30, if the bottom surface of the ball return groove 36 becomes higher than the deepest part of the first direction change groove 40, the ball 5 When the ball enters the return path 51 from the direction change path 52, it collides with the edge of the ball return groove, and there is a concern that the surface of the ball 5 may be damaged. However, in the nut member 3 of this embodiment, since the deepest part of the first direction change groove 40 is slightly higher than the bottom surface of the ball return groove 36, the ball 5 moves from the direction change path 52 to the return path 51. When entering the ball, the ball does not collide with the edge of the ball return groove 36. On the other hand, when the ball 5 enters the direction change path 52 from the return path 51, there is a concern that the ball 5 will collide with the edge of the first direction change groove 40; Since the circulating member 31 is made of synthetic resin, it is possible to prevent the surface of the ball 5 from being damaged by such a collision.

As explained above, according to the ball screw device 1 of this embodiment, the groove width of the ball return groove 36 formed in the nut main body 30 is set to the groove width of the guide groove 321 formed in the cover member 32. Furthermore, the groove depth of the ball return groove 36 is set to be larger than the depth of the deepest part of the first direction changing groove 40 formed in the circulation member 31. Therefore, when the ball 5 rolls in the return passage 51 or enters and leaves the direction change passage 52 from the return passage 51, it comes into contact with the edge of the ball return groove formed in the metal nut body. It is possible to keep the surface of the ball in good condition for a long period of time without causing any damage, and to maintain a smooth circulating state of the ball in the endless circulation path.

Claims

many balls and
a screw shaft having a rolling groove for the balls spirally formed on the outer peripheral surface;
a nut member having a through hole through which the screw shaft is inserted, screwed onto the screw shaft via the plurality of balls, and having an endless circulation path for the plurality of balls;
The endless circulation path is
a load path in which the plurality of balls rolls in a spiral between the screw shaft and the nut member;
a pair of direction change paths located at both ends of the load passage;
a return path connecting the pair of direction change paths;
The nut member is
The load passage has the through hole and is formed between the load passage and the screw shaft, and a pair of ball circulation holes that correspond to both ends of the load passage and penetrate in the radial direction, and further have ball circulation holes on the outer peripheral surface thereof. a nut body in which a ball return groove is formed between a pair of ball circulation holes;
a pair of circulation members installed in the pair of ball circulation holes of the nut body and having a first direction change groove formed therein;
It has a guide groove which is attached to the nut body and covers the ball return groove and the pair of circulation members, overlaps with the ball return groove and forms the return passage, and which is continuous from the guide groove and covers the ball return groove and the pair of circulation members. a lid member having a second direction change groove that overlaps with the one direction change groove to constitute the direction change path;
A ball screw device characterized in that a groove width of the ball return groove is larger than a groove width of the guide groove.
The ball screw device according to claim 1, wherein the depth of the ball return groove is set larger than the depth of the first direction change groove.
The guide groove, the first direction change groove, and the second direction change groove are formed in a semicircular shape with an inner diameter larger than the diameter of the ball, while the ball return groove has a cross section perpendicular to its longitudinal direction. The ball screw device according to claim 2, wherein the ball screw device is formed in a rectangular shape.
many balls and
a screw shaft having a rolling groove for the balls spirally formed on the outer peripheral surface;
a nut member having a through hole through which the screw shaft is inserted, screwed onto the screw shaft via the plurality of balls, and having an endless circulation path for the plurality of balls;
The endless circulation path is
a load passage in which the plurality of balls roll spirally between the screw shaft and the nut member; a pair of direction change paths located at both ends of the load passage;
a return path connecting the pair of direction change paths;
The nut member is
The load passage has the through hole and is formed between the load passage and the screw shaft, and a pair of ball circulation holes corresponding to both ends of the load passage and penetrating in the radial direction, and a pair of ball circulation holes on the outer peripheral surface thereof. A nut body in which a ball return groove is formed between a pair of ball circulation holes;
a pair of circulation members attached to the pair of ball circulation holes in the nut body and having a first direction changing groove formed therein;
It has a guide groove that is attached to the nut body and covers the ball return groove and the pair of circulation members, overlaps with the ball return groove and constitutes the return passage, and includes a guide groove that is continuous from the guide groove and covers the ball return groove and the pair of circulation members. a lid member having a second direction change groove that overlaps with the one direction change groove to constitute the direction change path;
A ball screw device characterized in that the depth of the ball return groove is set larger than the depth of the first direction change groove.