阅读说明：本技术 滚珠丝杠装置 (Ball screw device ) 是由 大桥智史 赵彬 岩城翔 工藤佳明 齐藤航 大木美香 宫崎拓也 于 2018-12-07 设计创作，主要内容包括：一种能够具有足够的载荷负载能力并且实现螺母构件的小型化的所谓多条螺纹类型的滚珠丝杠装置,其具备：丝杠轴(2),其设置有N条具有相同的导程的滚动槽(20),并且N为2以上的整数；滚珠(4),其在所述滚动槽(20)中滚动；以及螺母构件(3),其经由所述滚珠(4)而组装于所述丝杠轴(2),并且具有一个或多个使所述滚珠(4)在所述丝杠轴(2)的周围绕一圈的无限循环路(40),其中,所述螺母构件(3)的各无限循环路(40)包括：N个负载部(32),它们使所述滚珠(4)一边负载载荷一边滚动并且与所述N条滚动槽(20)分别对应；以及N个无负载部(33),它们将相互相邻的负载部彼此连结而使所述滚珠(4)在所述N条滚动槽(20)之间移动。(A ball screw device of a so-called multiple thread type capable of achieving a sufficient load bearing capacity and a reduction in size of a nut member, comprising: a screw shaft (2) provided with N rolling grooves (20) having the same lead, wherein N is an integer of 2 or more; balls (4) that roll in the rolling grooves (20); and a nut member (3) which is assembled to the screw shaft (2) via the balls (4) and has one or more endless circulation paths (40) for circulating the balls (4) one turn around the screw shaft (2), wherein each endless circulation path (40) of the nut member (3) includes: n load sections (32) which roll the balls (4) while bearing a load and which correspond to the N rolling grooves (20); and N unloaded portions (33) that connect mutually adjacent loaded portions to each other and move the balls (4) between the N rolling grooves (20).)

1. A ball screw device (1) is provided with:

a screw shaft (2) provided with N rolling grooves (20) having the same lead, wherein N is an integer of 2 or more;

balls (4) that roll in the rolling grooves (20); and

a nut member (3) which is assembled to the screw shaft (2) via the balls (4) and has one or more endless circulation paths (40) for circulating the balls (4) one turn around the screw shaft (2),

the ball screw device (1) is characterized in that,

each endless circulation path (40) of the nut member (3) includes:

n load sections (32) which roll the balls (4) while bearing a load and which correspond to the N rolling grooves (20); and

n unloaded portions (33) which connect mutually adjacent loaded portions to each other and move the balls (4) between the N rolling grooves (20).

2. The ball screw device according to claim 1,

the combination of the load part (32) and the no-load part (33) is used as a group, and N groups are evenly arranged around the screw shaft (2).

3. The ball screw device according to claim 2,

the length of each load section (32) in the axial direction of the threaded shaft (2) is 1/N of the lead of each rolling groove (20).

4. The ball screw device according to claim 1,

the nut member (3) includes a plurality of nut elements (3a, 3b, 3c) arranged to overlap in the axial direction of the threaded shaft (2),

at the joint portions of the nut elements (3a, 3b, 3c) adjacent to each other, an endless circulation path (40) of the balls (4) including the N loaded portions (32) and the N unloaded portions (33) forms one circuit.

Technical Field

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

Background

Ball screw devices are mechanical elements that can mutually convert rotational motion and linear motion, and are often used for the purpose of converting rotational motion generated by a servo motor into linear motion in various machine tools, conveying devices, industrial robots, and the like. The ball screw device includes: the nut member includes a plurality of balls, a screw shaft having a spiral rolling groove formed on an outer peripheral surface thereof, and a nut member screwed around the screw shaft via the balls. Further, the nut member includes an endless circulation path for the balls. The endless circulation path of the nut member includes a load path through which the balls roll while being loaded between the screw shaft and the nut member, and an unloaded path having one or more turns connecting both ends of the load path to return the balls to the rolling grooves.

The spiral rolling groove formed in the screw shaft is formed at a constant lead. The "lead" is a distance that the nut member travels in the axial direction when the screw shaft is rotated once, and the larger the lead is, the higher the speed at which the nut member can be moved when the screw shaft is rotated. In order to increase the rated load of the ball screw device and to increase the rigidity of the nut member with respect to the screw shaft, the screw shaft having a large lead is formed as a plurality of threads, and a plurality of spiral rolling grooves are formed in the outer peripheral surface of the screw shaft. Further, the nut member corresponding to the plurality of threads includes an infinite circulation path of balls having the same number of loops as the number of rolling grooves, and the number of balls to be loaded between the screw shaft and the nut member is increased.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open No. 2010-106895

Disclosure of Invention

Problems to be solved by the invention

In general, in the endless circulation path provided in the nut member, the length of the load path is set to be about one turn or about several turns around the screw shaft. This is to maximize the number of balls loaded by securing a sufficient length of the load path and to facilitate the construction of the no-load path connecting both ends of the load path.

On the other hand, when the length of the load path is set to be equal to or greater than about one turn around the screw shaft, the axial length of the nut member becomes longer than the lead of the rolling groove formed in the screw shaft even if the axial length is the lowest. Therefore, as in the case of the above-described multiple threads, the nut member combined with the screw shaft having a large lead of the rolling groove cannot be shortened in axial length, and it is difficult to downsize the nut member.

Means for solving the problems

The present invention has been made in view of the above problems, and an object thereof is to provide a so-called multi-thread type ball screw device capable of setting the length of an endless circulation path in the axial direction of a screw shaft to be shorter than the lead of a rolling groove, sufficiently securing the length of the load path, having a sufficient load bearing capacity, and realizing a reduction in size of a nut member.

That is, the present invention is a ball screw device including: a screw shaft provided with N rolling grooves having the same lead, wherein N is an integer of 2 or more; balls that roll in the rolling grooves; and a nut member that is assembled to the screw shaft via the balls and has one or more endless circulation paths for circulating the balls around the screw shaft. In the ball screw device, each endless circulation path of the nut member includes: n load parts which roll the balls while loading the balls and correspond to the N rolling grooves, respectively; and N unloaded portions that connect mutually adjacent loaded portions to each other and move the balls between the N rolling grooves.

Effects of the invention

According to the present invention, in a so-called multi-thread ball screw device in which the rolling grooves have a large lead, the length of the endless circulation path in the axial direction of the screw shaft can be set to be shorter than the lead of the rolling grooves, and the length of the load path can be sufficiently secured, and it is possible to achieve a sufficient load bearing capacity and a reduction in size of the nut member.

Drawings

Fig. 1 is a perspective view showing an example of a ball screw device to which the present invention is applied.

Fig. 2 is an exploded perspective view of the ball screw device shown in fig. 1.

Fig. 3 is a perspective view showing an end element of the nut member.

Fig. 4 is a perspective view showing an intermediate element of the nut member.

Fig. 5 is a perspective view showing a state in which balls are arranged in an end element of the nut member.

Fig. 6 is a view from direction a of fig. 5.

Fig. 7 is an explanatory diagram showing a relationship between the rolling groove of the screw shaft and the endless circulation path of the balls.

Fig. 8 is a longitudinal sectional view showing another example of the nut member.

Detailed Description

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

Fig. 1 is a diagram showing an example of a ball screw device to which the present invention is applied. The ball screw device 1 includes a screw shaft 2 having a rolling groove 20 formed in a spiral shape on an outer peripheral surface thereof, and a cylindrical nut member 3 screwed around the screw shaft 20 via a plurality of balls. The nut member 3 is provided with an endless circulation path for the balls. The balls are interposed between the screw shaft 2 and the nut member 3, and for example, the nut member 3 is moved in the axial direction of the screw shaft 2 by rotating the screw shaft 2 relative to the nut member 3, or the screw shaft 2 is moved in the axial direction of the nut member 3 by rotating the nut member 3 relative to the screw shaft 2.

The threaded shaft 2 is a so-called multi-thread screw, and a plurality of rolling grooves 20 are formed in the outer peripheral surface of the threaded shaft 2. In the ball screw device shown in fig. 1, three rolling grooves 20 are formed in the outer peripheral surface of the screw shaft 2, and the rolling grooves 20 have the same lead. Therefore, the rolling grooves 20 are present on the outer peripheral surface of the screw shaft 2 at a pitch of 1/3 degrees of the lead in the axial direction, and three rolling grooves 20 are equally spaced and arranged on the outer peripheral surface of the screw shaft 2 in the circumferential direction. Between the rolling grooves 20 adjacent to each other, thread portions 21 are formed, and the thread portions 21 indicate the outer diameter of the screw shaft 2. The number of the rolling grooves 20 formed in the screw shaft 2 may be 2 or more, and the design may be appropriately changed.

The nut member 3 has a through hole through which the threaded shaft 2 is inserted, and is formed in a cylindrical shape. The nut member is composed of a plurality of nut elements 3a, 3b, and 3c formed in a ring shape, and these nut elements 3a, 3b, and 3c are arranged to overlap in the axial direction of the threaded shaft 2. The nut element is composed of a pair of end elements 3a and 3b and an intermediate element 3c sandwiched between the end elements 3a and 3 b. In the example shown in fig. 1, two intermediate elements 3c are arranged between a pair of end elements 3a and 3 b. The pair of end elements 3a and 3b are members having the same shape and are arranged so as to face each other in opposite directions. The two intermediate elements 3c are members having the same shape.

Fig. 2 is an exploded perspective view showing a state where the end element 3a is removed from the nut member 3. An endless circulation path 40 of balls 4 is provided around the periphery of the screw shaft 2 at the joint portion of the nut elements 3a, 3b, and 3c adjacent to each other. That is, the endless circulation paths 40 of the balls 4 are provided at the boundary portion between the end element 3a and the intermediate element 3c, the boundary portion between the two intermediate elements 3c, and the boundary portion between the intermediate element 3c and the end element 3b, which are adjacent to each other, and the endless circulation paths 40 of the three circuits are provided in the entire nut member 3.

The number of loops of the endless loop path 40 can be arbitrarily increased or decreased depending on the number of the intermediate elements 3 c. For example, if one intermediate element 3c is sandwiched between a pair of end elements 3a and 3b, the endless circulation paths 40 of the two circuits are provided in the nut member 3. In addition, if the number of the intermediate elements 3c is three, four endless circulation paths 40 are provided in the nut member 3. Further, by directly joining the pair of end elements without using the intermediate element, only the endless circulation path 40 of one circuit can be provided in the nut member 3.

Fig. 3 is a perspective view showing the end elements 3a and 3b, and fig. 4 is a perspective view showing the intermediate element 3 c. The end elements 3a, 3b and the intermediate element 3c are formed in a ring shape having an inner diameter larger than the outer diameter of the threaded shaft 2, and a joint surface 30 to which the adjacent nut elements 3a, 3b, 3c are joined is formed in a curved surface shape. The end elements 3a and 3b are different from the intermediate element 3c in that only one end surface in the axial direction is formed as the joint surface 30, and both end surfaces in the axial direction are formed as the joint surface 30 in the intermediate element 3 c.

Circulation grooves 31 that constitute endless circulation paths 40 for the balls 4 are formed in the corners of the inner circumferential surfaces of the end elements 3a and 3b and the intermediate element 3c and the joint surface 30. For example, at the boundary portion between the end element 3a and the intermediate element 3c, the endless circulation path 40 for the balls 4 is constructed by combining the circulation groove 31 of the end element 3a and the circulation groove 31 of the intermediate element 3c in a manner to face each other. The end elements 3a and 3b have the circulation grooves 31 only on one end surface in the axial direction, and the intermediate element 3c has the circulation grooves 31 on both end surfaces in the axial direction.

One circulation groove 31 formed in the end elements 3a and 3b or the intermediate element 3c corresponds to a plurality of rolling grooves 20 provided in the screw shaft 2. If N (N is a natural number of 2 or more) rolling grooves 20 are provided in the screw shaft 2, the one circulation groove 31 is configured by N load portions 32 and N no-load portions 33. The load portion 32 faces the rolling groove 20 of the screw shaft 2, and the balls 4 roll between the load portion 32 and the rolling groove 20 of the screw shaft 2 while applying a load. On the other hand, the no-load portion 33 connects the load portions 32 to each other and faces the thread portion 21 of the screw shaft, and the balls 4 rolling in the no-load portion 33 are released from the load and pass over the thread portion 21 of the screw shaft 2. The loaded portions 32 and the unloaded portions 33 are alternately provided along the circumferential direction of the circulation groove 31, and as a result, the circulation groove 31 is formed in an annular shape. The end elements 3a and 3b and the intermediate element 3c shown in fig. 3 and 4 correspond to a case where three rolling grooves 20 are formed in the screw shaft 2, and the circulation groove 31 has a combination of three sets of the load portion 32 and the no-load portion 33.

Since the circulation groove 32 is provided at a corner portion between the inner peripheral surface of the end element 3a or 3b or the intermediate element 3c and the joint surface 30, the joint surface 30 is formed in a curved surface shape along the trajectory of the circulation groove 31, that is, the trajectory of the endless circulation path 40.

Fig. 5 and 6 show a case where balls are arranged in the circulation grooves 31 provided in the end elements 3a and 3b, and fig. 6 is a front view of the end elements 3a and 3b shown in fig. 5 as viewed from the direction of arrow a. The plural sets of the load portions 32 and the no-load portions 33 included in one circulation groove 31 are arranged equally around the screw shaft 2. Fig. 6 corresponds to an example in which three rolling grooves 20 are formed in the screw shaft 2, and therefore three sets of combinations of the load portions 32 and the no-load portions 33 are arranged by dividing the periphery of the screw shaft 2 at intervals of 120 degrees. Therefore, when the threaded shaft 2 has N rolling grooves, the periphery of the threaded shaft is divided into N360 degrees, and N sets of combinations of the load portions 32 and the no-load portions 33 are arranged uniformly.

The one-dot chain line in fig. 6 indicates the outer diameter of the screw shaft 2. A plurality of load portions 32 included in one circulation groove 31 correspond to different rolling grooves 20 formed in the screw shaft 2, respectively, and the balls 4 roll in the rolling grooves 20 at the load portions 32. On the other hand, the no-load part 33 connects the load parts 32 adjacent to each other, and the ball 4 rolling in the no-load part 33 moves between the rolling grooves 20 adjacent to each other by passing over the thread part 21 of the screw shaft. The balls 4 rolling in the load portion 32 move in the axial direction of the screw shaft 2 while revolving around the periphery of the screw shaft 2 in a spiral shape, but the no-load portion 33 moves the balls 4 in the axial direction opposite to the direction of the movement and delivers the balls 4 to the subsequent load portion 32. Therefore, the endless circulation path 40 through which the balls 4 circulate is formed as a track that undulates around the screw shaft 2.

In fig. 5 and 6, the state in which the balls 4 are arranged in the circulation grooves 31 of the end elements 3a and 3b is shown, but the case in which the balls 4 are arranged in the circulation grooves 32 of the intermediate element 3c is also the same as the above-described state. The end elements 3a and 3b have the circulation grooves 32 only on one end surface in the axial direction, but the intermediate element 3c has the same circulation grooves 32 on both end surfaces in the axial direction, and the difference is only in this point.

The end elements 3a and 3b and the intermediate element 3c thus configured are superposed on each other in the axial direction of the threaded shaft 2, thereby completing the nut member 3 having the endless circulation path 40 having a plurality of circuits. The end elements 3a and 3b and the intermediate element 3c can be coupled to each other by using bolts that axially penetrate these elements. Alternatively, the nut member 3 may be constructed by providing a cylindrical housing having an accommodation space for the end elements 3a and 3b and the intermediate element 3c, and closing the accommodation space into which the end elements 3a and 3b and the intermediate element 3c are inserted. When the housing is provided, a flange portion for fixing the nut member 3 to another device can be provided in the housing, and the shape of the end elements 3a and 3b or the intermediate element 3c can be simplified.

Fig. 7 is a perspective view showing the relationship between the balls 4 arranged in the endless circulation path 40 and the three rolling grooves 20a, 20b, and 20c formed in the screw shaft 2, and the single-dot chain lines in the drawing show the rolling grooves 20a, 20b, and 20c, respectively. In this case, the endless circulation path 40 has a combination of three sets of the load portions 32 and the no-load portions 33, and each load portion 32 corresponds to one of the three rolling grooves 20a, 20b, and 20 c.

As described above, when the balls 4 circulate in the endless circulation path 40, the load portion 32 revolves around the screw shaft 2 in a spiral shape along the rolling groove 20 (alternate long and short dash line in fig. 7) of the screw shaft 2, and moves in the axial direction of the screw shaft 2. The rolling groove 20 travels in the axial direction by 1 lead when wound around the screw shaft 2 for one circumference, but since the set of the load portion 32 and the no-load portion 33 is provided so as to trisect the circumference of the screw shaft 2 at every 120 degrees, the ball 4 rolling in one load portion 32 travels in the axial direction of the screw shaft 2 by 1/3 leads. That is, when N rolling grooves 20 are provided in the threaded shaft 2, the length of each load portion 32 in the axial direction of the threaded shaft 2 is 1/N of the lead of the rolling groove 20 for the N load portions 32 included in the endless circulation path 40.

On the other hand, when the N rolling grooves 20 are provided in the screw shaft 2, since the N load portions 32 are included in one circuit of the endless circulating path 40, the entire length of the load portion 32 included in the one circuit of the endless circulating path 40 is substantially the same as the length of the rolling groove 20 around the screw shaft 2. Therefore, the number of balls that can apply a load between the screw shaft 2 and the nut member 3 can be sufficiently ensured.

Therefore, in the ball screw device of the present invention, the axial length of each endless circulation path 40, that is, the width of the endless circulation path 40 along the axial direction of the screw shaft 2 can be set small with respect to the lead of the rolling groove 20, and when the ball screw device is applied to a multi-thread type ball screw device in which the lead is set large, the axial length of the nut member 3 can be shortened, and the ball screw device can be downsized.

In addition, even when the nut member 3 is reduced in size, the number of balls 4 that can apply a load between the screw shaft 2 and the nut member 3 can be sufficiently ensured, and the nut member 3 can be reduced in size without reducing the load capacity of the load.

Further, since the combination of the plurality of loaded portions 32 and unloaded portions 33 included in the endless circulation path 40 of one circuit is disposed uniformly around the screw shaft 2, even when either the screw shaft 2 or the nut member 3 is rotated, the balance of the behavior of the balls 4 with respect to the rotation center is improved. Therefore, it is possible to use the screw shaft 2 or the nut member 3 so as to rotate at a high speed, by making it difficult for vibration to occur in accordance with the rotation of the screw shaft 2 or the nut member 3.

That is, according to the present invention, the ball screw device 1 capable of high-speed conveyance of a mechanical device can be realized by combining the multiple types of large lead screw shafts 2 with the compact nut member 3.

In the above-described embodiment, the nut member 3 is formed by combining the plurality of nut elements 3a, 3b, and 3c, but the nut member 3 is not problematic as a single member as long as the endless circulation path 40 including the plurality of load portions 32 and the plurality of no-load portions 33 can be formed on the inner circumferential surface of the nut member 3. For example, as shown in fig. 8, a block-shaped reverser 34 in which the no-load part 33 is formed may be fitted to the nut member 3 from the outer peripheral surface of the nut member 3, thereby providing the no-load part 33 on the inner peripheral surface of the nut member.