JP2021110373A - Ball screw device - Google Patents

Abstract

To provide a ball screw device which can easily construct a non-load passage even if a lead of a rolling groove formed at a screw shaft is long, can reduce a size and weight of a nut member, and can contribute to high speeds of linear drive parts of a variety of industrial devices.SOLUTION: A nut member 3 has one or a plurality of infinite circulation paths of balls 5 making a round around a screw shaft 2, and the infinite circulation path comprises a non-load path for connecting both end parts of a load passage in which the balls roll while being applied with loads. The non-load passage has a linear passage part formed along an axial direction of the nut member 3, and a pair of transition passage parts formed at both ends of a linear communication part, and extending to mutual opposite sides along a peripheral direction of the nut member 3. The nut member also comprises a ball forwarding path 6 which is formed while penetrating an external peripheral face and an internal peripheral face of the nut member 3, and a cover plate 4 for blocking the ball forwarding path 6 from the outside of the nut member 3.SELECTED DRAWING: Figure 1

Description

The present invention relates to a ball screw device capable of mutually converting rotational motion and linear motion.

The ball screw device is a mechanical element capable of mutually converting rotary motion and linear motion, and is intended to convert rotary motion generated by a servomotor into linear motion in various machine tools, transfer devices, industrial robots, and the like. It is often used in. In the ball screw device, a screw shaft and a cylindrical nut member are screwed together via a large number of balls, and a spiral rolling groove on which the ball rolls is defined on the outer peripheral surface of the screw shaft. It is made up of leads. Therefore, when the screw shaft is rotated once, the nut member moves in the axial direction of the screw shaft by the lead amount of the rolling groove. Therefore, if the number of rotations given 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 infinite circulation path in which a large number of balls are arranged is formed in the nut member. This infinite circulation path connects a spiral load passage in which the ball rolls between the screw shaft and the nut member while applying a load, and both ends of the load passage, and the ball is released from the load. It is composed of a no-load passage that rolls in the loaded state. The ball rolls in the infinite circulation path with the relative rotation of the screw shaft and the nut member.

The conventional ball screw device can be classified into several types according to the structure of the no-load passage in the nut member. For example, in a type called a deflector type, a piece member having a deflection groove serving as a no-load passage is embedded in the nut member, and an infinite circulation path for one turn around the screw shaft is formed. The deflection groove forcibly changes the traveling direction of the ball that has reached the end of the load passage, whereby the ball gets over the threaded portion of the screw shaft and is returned to the start end of the load passage. ing.

In this deflector type ball screw device, the infinite circulation path is completed only by embedding the piece member in the nut member, so that the outer diameter of the nut member can be reduced and the weight of the nut member can be reduced accordingly. Is. On the other hand, the deflector type is difficult to apply to a ball screw device having a large lead of the screw shaft, for example, a ball screw device having the lead larger than the shaft diameter of the screw shaft, and the deflector type ball screw device is the nut. It was not suitable for applications that required a high moving speed of members.

On the other hand, as a ball screw device capable of setting a large lead of the screw shaft, there is a type called an end cap type. In this end cap type ball screw device, a ball return passage forming a part of the no-load passage of the ball is formed through the nut member along the axial direction, and at both ends of the nut member in the axial direction. An end cap for passing the ball between the load passage and the ball return passage is provided. Since the ball return passage is provided over the entire axial length of the nut member, it is possible to easily construct a no-load passage even when the lead of the rolling groove is large as described above.

Since the end cap type ball screw device can set a large lead of the rolling groove, it is most suitable for applications where a high moving speed of the nut member is required. On the other hand, since it is necessary to form the ball return passage through the nut member, the outer diameter of the nut member becomes larger than the outer diameter of the screw shaft, and the nut member is downsized. And there was a disadvantage that it was difficult to reduce the weight.

Patent Document 1 discloses a ball screw device that can be said to be a compromise of these deflector type or end cap type ball screw devices. In this ball screw device, a pair of piece members are embedded in the nut member corresponding to the start and end of the spiral load passage, and the nut member is connected between the pair of piece members. A straight groove is provided. The straight groove is provided along the axial direction of the nut member with respect to the inner peripheral surface of the nut member. Further, the deflection groove described above is formed in each of the pair of piece members, and when these piece members are fitted into the nut member, the deflection groove of each piece member and the straight groove are connected to form a ball. No-load passage is completed.

The ball screw device of Patent Document 1 can flexibly correspond to the length of the lead of the rolling groove by changing the length of the straight groove, and the piece member can be used as the nut member. Since the infinite circulation path is completed only by embedding it in, there is an advantage that it is easy to achieve miniaturization and weight reduction of the nut member.

JP-A-2017-2956

However, in the ball screw device of Patent Document 1, it is necessary to form the straight groove on the inner peripheral surface of the nut member, and a mounting hole for embedding the pair of piece members is formed in the nut member. It is necessary, and there is a problem that it takes time and effort to process the nut member.

Further, since each of the pair of piece members has a ball deflection groove, there is a limit to the miniaturization of each piece member, and the strength of the nut member having a mounting hole for the piece member is reduced. There is a concern that it is easy.

Further, the deflection groove provided in the piece member limits the traveling direction of the ball, whereby the ball itself is configured to crawl up the rolling groove of the screw shaft to the outer peripheral surface of the screw shaft, and thus is infinite. The resistance acting on the circulation of the ball in the circulation path also tends to be large, and it is not suitable for high-speed circulation of the ball in the infinite circulation path, that is, high-speed movement of the nut member with respect to the screw shaft.

The present invention has been made in view of such a problem, and an object of the present invention is that an infinite circulation path of a ball can be easily constructed with respect to a nut member, and the nut member is downsized. -It is possible to reduce the weight, and even when the lead of the spiral rolling groove is large, it is possible to easily construct a no-load passage, which contributes to speeding up the linear drive unit of various industrial equipment. Is to provide a ball screw device capable of.

That is, the ball screw device of the present invention has a large number of balls, a screw shaft in which a rolling groove of the ball is spirally formed on the outer peripheral surface, and a through hole through which the screw shaft is inserted. A load rolling groove facing the rolling groove is spirally formed on the inner peripheral surface of the hole, and is provided with a nut member screwed to the screw shaft via the large number of balls, and further. The nut member has one or a plurality of infinite circulation paths of balls that go around the screw shaft, and the infinite circulation path is a load passage formed by the rolling groove and the load rolling groove facing each other. And a non-load passage connecting both ends of the load passage. Then, the no-load passages are formed at both ends of the linear passage portion formed along the axial direction of the nut member and the linear connecting portion, and in opposite directions along the circumferential direction of the nut member. A ball forwarding path having a pair of extending transition passages and penetrating the outer peripheral surface and the inner peripheral surface of the nut member, and a cover plate that closes the ball forwarding path from the outside of the nut member. I have.

According to the present invention, the nut member has an infinite circulation path of a ball that goes around the screw shaft, but the no-load passage forming a part of the infinite circulation path is an outer peripheral surface of the nut member. Since the ball forwarding path penetrating the inner peripheral surface is constructed only by closing the ball forwarding path from the outside of the nut member with a cover plate, it is possible to easily construct an infinite circulation path with respect to the nut member. , It is possible to reduce the size and weight of the nut member. Further, the ball forwarding path is formed at both ends of the linear passage portion formed along the axial direction of the nut member and the linear connecting portion, and in opposite directions along the circumferential direction of the nut member. Since it has a pair of extending transition passage portions, even if the lead of the spiral rolling groove formed on the screw shaft is large, the length of the straight passage portion can be changed according to the lead. For example, a no-load passage can be easily constructed. This makes it possible to provide a ball screw device that can contribute to increasing the speed of the linear drive unit of various industrial devices.

It is a perspective view which shows an example of the ball screw apparatus to which this invention is applied. It is a top view which shows the nut member of the ball screw device shown in FIG. It is a figure which shows the trajectory of the ball arranged in the infinite circulation path of a nut member. It is an enlarged perspective view which shows the ball forwarding path provided in the nut member. It is a perspective view which shows the cover plate attached to the nut member. It is an enlarged perspective view which shows the main part of a cover plate. It is a perspective view which shows the state which observed the ball arranged in the ball forwarding path from the through hole of a nut member.

Hereinafter, the ball screw device of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an example of a ball screw device to which the present invention is applied. The ball screw device 1 has a screw shaft 2 in which a ball rolling groove 20 is spirally formed on the outer peripheral surface, and a cylindrical nut member 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 infinite circulation path for the ball. 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 becomes the shaft 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 single rolling groove 20 is formed on the outer peripheral surface of the screw shaft 2 with a predetermined lead, and the rolling groove 20 exists at a constant pitch along the axial direction of the screw shaft 2. Further, there is a thread portion 21 between the rolling grooves 20 adjacent to each other, and the thread portion 21 indicates the outer diameter of the screw shaft 2. In the present embodiment, the lead of the rolling groove 20 is set to be larger than the outer diameter of the screw shaft 2.

The nut member 3 has a through hole through which the screw shaft 2 is inserted and is formed in a cylindrical shape, and a flange portion 30 for connecting the nut member 3 to another mechanical device is formed at one end in the axial direction. Is provided. The flange portion 30 is provided with a plurality of mounting holes 31 for inserting fixing bolts. 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 ball 5 rolls between the rolling groove of the screw shaft and the load rolling groove of the nut member, and loads a load between the screw shaft 2 and the nut member 3.

The nut member 3 has three circuits of infinite circulation paths for balls that go around the screw shaft 2, and for constructing each infinite circulation path at three locations of the main body portion 32 of the nut member 3. The cover plate 4 is attached. The number of circuits in the infinite circulation path may be appropriately selected according to the load-bearing capacity required for the ball screw device 1. In order to clarify that the balls 5 are arranged in the infinite circulation path, FIG. 1 shows the infinite circulation path located at the second position among the infinite circulation paths of the three circuits provided on the nut member 3. The state in which the cover plate 4 is removed is shown.

A ball forwarding path 6 forming a part of the infinite circulation path is formed in the nut member 3, and by removing the cover plate 4 from the nut member 3, the ball forwarding path 6 is outside the nut member 3. It can be visually recognized from. In the present embodiment, since the nut member 3 has three circuits of infinite circulation paths for the balls 5, the ball forwarding paths 6 are formed at three locations of the nut member 3.

FIG. 2 is a plan view showing the arrangement of the ball forwarding path 6 with respect to the nut member 3. The alternate long and short dash line in the figure shows a spiral load rolling groove formed on the inner peripheral surface of the through hole 33 of the nut member 3. Each ball forwarding path 6 forms a part of the infinite circulation path, and functions as a no-load passage in which the ball 5 rolls in a no-load state. As described above, the ball forwarding path 6 is closed from the outside of the nut member 3 by the cover plate 4, thereby completing the no-load passage.

Each ball forwarding path 6 is provided for each turn of the load rolling groove, and is provided in series with the load rolling groove of one line. Further, in order to reduce the size of the nut member 3, the three ball forwarding paths are not arranged in a row along the axial direction of the nut member, and the positions of the three ball forwarding paths are shifted in the circumferential direction of the nut member 3. Arranged to minimize the spacing between adjacent infinite circulation paths.

FIG. 3 shows the balls 5 arranged in the infinite circulation path. The black-painted ball 5a is a ball that is released from the load and is in a no-load state, that is, a ball that exists in the no-load passage. This no-load passage corresponds to the ball forwarding path 6. The other white-painted balls 5b are balls that are rolling while applying a load between the rolling groove 20 of the screw shaft 2 and the load rolling groove of the nut member 3, that is, a load passage. It is a ball that exists in. This load passage is slightly shorter than the circumference of the screw shaft 2. Both ends of the load passage are connected to each other by the no-load passage, and an infinite circulation path of the ball 5 is constructed. Therefore, the ball 5 repeats loading and non-loading while circulating in the infinite circulation path.

FIG. 4 is an enlarged view showing the details of the ball forwarding path 6. Each ball forwarding path 6 is composed of a straight passage portion 60 formed along the axial direction of the nut member 3 and a pair of transition passage portions 61 formed at both ends of the linear connecting portion 60. Each transition passage portion 61 extends in opposite directions along the circumferential direction of the nut member 3 at both ends of the straight passage portion 60. The straight passage portion 60 and the pair of transition passage portions 61 are formed so as to penetrate between the outer peripheral surface and the inner peripheral surface of the nut member 3. Reference numeral 34 in FIG. 3 is the load rolling groove formed on the inner peripheral surface of the nut member 3, and can be visually recognized from the outside of the nut member 3 through the ball forwarding path 6.

The straight passage portion 60 is formed with a width slightly larger than the diameter of the ball 5, and the ball 5 rolls on the straight passage portion 60 in a no-load state. When the screw shaft and the nut member are combined, the straight passage portion 60 overlaps the thread portion 21 of the screw shaft and crosses the thread portion 21, and the ball rolls on the straight passage portion 60. Reference numeral 5 is in contact with the thread portion 21. Therefore, the length of the straight passage portion 60 corresponds to the lead of the rolling groove 20 of the screw shaft 2.

On the other hand, each transition passage portion 61 overlaps with the rolling groove 20 of the screw shaft 2, and the introduction portion 61a provided by cutting out a part of the load rolling groove 34 of the nut member 3 and this introduction portion. It is composed of a curved conversion portion 61b that connects the 61a to the straight passage portion 60. When the ball 5 that has rolled in the load passage while applying a load between the nut member 3 and the screw shaft 2 reaches the formation position of the ball forwarding path 6, the introduction portion 61a is first released from the load. The introduction portion 61a is moved in the tangential direction of the load rolling groove 34, and is separated from the rolling groove 20 of the screw shaft 2. After that, the ball 5 changes its traveling direction at the conversion portion 61b in the axial direction of the nut shaft 3, and the ball 5 enters the straight passage portion 60 from the transition passage portion 61. The opposite is true when the ball 5 enters the load passage from the ball forwarding path 6.

Further, on the outer peripheral surface of the nut member 3, a seat surface 62 for accommodating the cover plate 4 is formed around the ball forwarding path 6, and when the cover plate 4 is attached to the nut member 3, the seat surface 62 is formed. The cover plate 4 is fixed without protruding from the outer peripheral surface of the nut member 3. The seat surface 62 is provided with a female screw hole 63 for screwing the cover plate. The cover plate 4 is not limited to screwing, and may be fixed to the nut member 3 by another method such as adhesion.

The ball forwarding path 6 and the seating surface 62 around the ball forwarding path 6 can be machined from the outside of the nut member 3 by an end mill, for example.

FIG. 5 is a perspective view of the cover plate 4 and shows a surface of the nut member 3 on the side that abuts on the seat surface 62. A guide groove 40 that overlaps the ball forwarding path 6 is formed in the cover plate 4, and when the cover plate 4 is screwed into a predetermined position of the nut member 3, the guide groove 40 becomes a ball of the nut member 3. It covers the forwarding path 6 and thus completes the no-load passage of the ball 5 in the nut member 3. The guide groove 40 is composed of a straight groove 40a corresponding to the straight passage portion 60 of the ball forwarding path 6 and a pair of curved grooves 40b corresponding to the pair of transition passage portions 61 of the ball forwarding path 6. There is. The cross section orthogonal to the longitudinal direction of the guide groove 40 is formed in a curved surface shape that encloses a part of the spherical surface of the ball 5, but the depth thereof is set to be smaller than the radius of the ball 5. Therefore, the rolling direction of the ball 5 in the no-load passage is guided by the ball forwarding path 6, and the cover plate 4 functions only as a lid of the ball forwarding path 6. The shape of the cross section orthogonal to the longitudinal direction of the guide groove 40 is not limited to the curved surface shape described above, and is a flat surface as long as it overlaps with the ball forwarding path 6 of the nut member 3 and closes the cross section. There is no problem.

FIG. 6 is an enlarged view of a main part showing the details of the cover plate 4. Auxiliary protrusions 41 that fit into the transition passage portion 61 of the ball forwarding path 6 are provided at both ends of the cover plate 4 in the longitudinal direction. The curved groove 40b is formed on the auxiliary protrusion 41. When the auxiliary protrusion 41 is fitted into the transition passage portion 61 of the ball forwarding path 6, the auxiliary protrusion 41 cooperates with the transition passage portion 61 to form the entrance of the no-load passage portion. That is, the auxiliary protrusion 41 fills a part of the transition passage portion 61 to form a no-load passage connected to the load passage in the tangential direction.

FIG. 7 shows a state in which the balls 5 arranged in the ball forwarding path 6 are observed from the through hole 33 of the nut member 3. As shown in the figure, a part of the auxiliary protrusion 41 of the cover plate 4 penetrates the ball forwarding path 6 and appears on the inner peripheral surface of the nut member 3. All the balls 5 arranged in the ball forwarding path 6 are exposed on the inner peripheral surface of the nut member 3, and the balls 5 rolling on the ball forwarding path 6 are always in contact with the screw shaft 2. There is. Further, when the ball 5 rolls in the load rolling groove 34 of the nut member 3 and reaches the formation position of the ball forwarding path 6, it gradually sinks into the inside of the ball forwarding path 6 and becomes a no-load state. The ball forwarding path 6 is rolled.

The cover plate 4 can be formed including the guide groove 40 and the auxiliary protrusion 41 by, for example, injection molding of a synthetic resin.

In the ball screw device 1 configured as described above, it is possible to include one or a plurality of infinite circulation paths of the ball 5 that go around the screw shaft 2 with respect to the nut member 3. The no-load passage of each infinite circulation path is constructed by a ball forwarding path 6 formed in the nut member 3 and a cover plate 4 that closes the ball forwarding path 6 from the outside of the nut member 3. The ball forwarding path 6 penetrates the nut member 3 from the outer peripheral surface to the inner peripheral surface, and can be easily formed by, for example, cutting using an end mill. Further, the cover plate 4 can be formed by injection molding of a synthetic resin. Therefore, the ball screw device 1 can be easily and inexpensively manufactured.

Further, the ball forwarding path 6 is open to the inner peripheral surface of the nut member 3 over its entire length. In other words, the ball 5 that rolls on the ball forwarding path 6 in a no-load state is always the screw shaft 2. Therefore, when forming a no-load passage in the nut member 3, the outer diameter of the nut member 3 can be suppressed to a small size, and a compact and lightweight ball screw device 1 can be realized. ..

Further, since the ball forwarding path 6 is provided across the thread portion 21 of the screw shaft 2 in a state where the screw shaft 2 and the nut member 3 are combined, the roll formed on the screw shaft 2 is formed. By changing the length of the ball forwarding path 6 according to the lead of the moving groove 20, it is possible to flexibly correspond to the screw shaft 2 of various leads. For example, even when the lead is larger than the shaft diameter of the screw shaft 2, a compact and lightweight ball screw device 1 can be realized. By using the ball screw device 1 of the present invention, a linear drive unit of various industrial devices can be realized. It is possible to increase the speed and size of the ball.

Furthermore, by forming the straight passage portion 60 of the ball forwarding path 6 along the axial direction of the nut member 3, the ball 5 is loaded in the infinite circulation path of the ball 5 that goes around the screw shaft 2. It is possible to maximize the length of the load passage that rolls while loading the nut member 3, and it is possible to provide the ball screw device 1 with a sufficient load load capacity while reducing the size of the nut member 3.

Further, since the connecting portion between the no-load passage and the load passage of the infinite circulation passage, that is, the inlet portion of the no-load passage is connected to the load passage in the tangential direction of the screw shaft 2, it is connected to the load passage. The balls 5 can be smoothly transferred between the no-load passages, the resistance acting on the circulation of the balls 5 in the infinite circulation path is reduced, and the rotational resistance of the screw shaft 2 with respect to the nut member 3 is reduced. It becomes possible to do.

Further, the cover plate 4 is provided with a guide groove 40 that overlaps the ball forwarding path 6 formed in the nut member 3, but the depth of the guide groove 40 is set to be smaller than the radius of the ball 5. Therefore, the shape of the cover plate 4 becomes simple, and in this respect as well, the cover plate 4 can be easily and inexpensively formed.

Furthermore, even when the nut member 3 includes an infinite circulation path of a plurality of circuits, according to the present invention, a plurality of ball forwarding paths 6 corresponding to each infinite circulation path are provided in the circumferential direction of the nut member 3. The positions can be staggered, and the distance between adjacent infinite circulation paths can be minimized. Also in this respect, it is possible to provide the ball screw device 1 which is small in size and has a high load-bearing capacity.

1 ... ball screw device, 2 ... screw shaft, 3 ... nut member, 4 ... cover plate, 5 ... ball, 6 ... ball forwarding path, 20 ... rolling groove, 21 ... threaded portion, 34 ... load rolling groove, 40 ... Guide groove, 41 ... Auxiliary protrusion, 60 ... Straight passage part, 61 ... Transition passage part

Claims (4)

With many balls
A screw shaft in which the rolling groove of the ball is spirally formed on the outer peripheral surface,
The screw shaft has a through hole through which the screw shaft is inserted, and a load rolling groove facing the rolling groove is spirally formed on the inner peripheral surface of the through hole, and the screw shaft is formed through a large number of balls. With a nut member that is screwed into
The nut member has one or more infinite circulation paths of balls that go around the screw shaft.
The infinite circulation path includes a load passage formed by the rolling groove and the load rolling groove facing each other, and a non-load passage connecting both ends of the load passage.
The no-load passage
It has a straight passage portion formed along the axial direction of the nut member, and a pair of transition passage portions formed at both ends of the linear connecting portion and extending in opposite directions along the circumferential direction of the nut member. Then, the ball forwarding path formed through the outer peripheral surface and the inner peripheral surface of the nut member, and
A cover plate that closes the ball forwarding path from the outside of the nut member, and
A ball screw device characterized by being equipped with. The ball screw according to claim 1, wherein the straight passage portion of the ball forwarding path crosses the thread portion of the screw shaft, while the pair of transition passage portions overlaps the rolling groove of the screw shaft. Device. The cover plate is provided with an auxiliary protrusion that fits into the transition passage portion of the ball forwarding path, and the auxiliary protrusion cooperates with the transition passage portion to form an inlet portion of the no-load passage. The ball screw device according to claim 2, wherein the ball screw device is connected to the load passage in a tangential direction of the screw shaft. The cover plate has a guide groove that overlaps the ball forwarding path, and the cross section orthogonal to the longitudinal direction of the guide groove is formed in a curved surface shape that wraps a part of the spherical surface of the ball, and the depth of the guide groove is the ball. The ball screw device according to claim 2, wherein the ball screw device is set to be smaller than the radius of.

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