Circulation device and ball screw equipped with circulation device

Abstract

To provide a circulation device with modular assembly capabilities. [Solution] The circulation device (100) comprises a first reflux device (110), a second reflux device (120), and an intermediate reflux device (130). The first reflux device comprises a first upper assembly (111) and a first lower assembly (112). A curved first passage pipe (113) is provided between the first upper assembly and the second lower assembly, and a first reflux passage (113a) is formed within the first passage pipe. The second reflux device comprises a second upper assembly (121) and a second lower assembly (122). A curved second passage pipe (123) is provided between the second upper assembly and the second lower assembly, and a second reflux passage (123a) is formed within the second passage pipe. The intermediate reflux device is interchangeably disposed between the first reflux device and the second reflux device. The intermediate reflux passage of the intermediate reflux device communicates with the first reflux passage and the second reflux passage.

Description

[Technical Field]

[0001] The present invention relates to the technical field of circulation devices, and in particular to a circulation device and a ball screw equipped with a circulation device. [Background technology]

[0002] Ball screws are commonly found in mechanical transmissions and are primarily used to convert rotary motion into linear motion. They are basically composed of a screw, balls, ball guideway, and nut. The operating principle of a ball screw is that the radial contact of the balls between the screw and the nut generates rolling motion, converting rotary motion into linear motion. The ball screw structure distributes the balls evenly on the radial ball guide of the nut, reducing the contact pressure between the balls and the guide, reducing rolling resistance, and improving transmission efficiency.

[0003] Another advantage of ball screws is their high rigidity. The structural design of ball screws distributes the balls evenly across the radial ball guide of the screw shaft, increasing the contact area between the balls and the radial ball guide. This improves the rigidity of the transmission system and allows the ball screw to withstand greater loads during operation. This makes ball screws particularly suitable for applications requiring high loads and rigidity, such as the cutting loads of machine tools and the high-load operations in robotics. Furthermore, the high precision of ball screws enables high-speed, high-precision motion control in many applications, leading to their use in a wide range of applications, including machine tools, automation equipment, precision measuring instruments, and semiconductor devices.

[0004] Ball screws convert the rotational motion of the screw into linear motion by rolling balls along the radial ball guideway between the screw and nut. Therefore, the rolling motion of the balls in the entire ball circulation system plays a key role. The assembly accuracy and geometric parameter design of the balls, the balls themselves, and the ball circulation system significantly affect ball screw performance, including transmission ratio, displacement accuracy, load capacity, and transmission efficiency. Conventional ball screws have complex structures, difficult assembly, and require complete replacement when damaged. This results in reduced assembly efficiency and higher maintenance costs. Furthermore, improper design of the geometric parameters of the assembly position often leads to uneven ball movement, reducing the overall performance and lifespan of the ball screw. Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE INVENTION The main object of the present invention is to provide a circulation device with modular assembly capabilities and a ball screw with a circulation device. [Means for solving the problem]

[0006] The circulation device according to the present invention includes a first circulation device including a first upper assembly and a first lower assembly assembled to the first upper assembly, a curved first passage pipe assembled between the first upper assembly and the first lower assembly, and a first circulation passage formed in the first passage pipe; a second reflux device comprising a second upper assembly and a second lower assembly assembled to the second upper assembly, wherein a second passage pipe having a curved shape is assembled between the second upper assembly and the second lower assembly, and a second reflux passage is formed in the second passage pipe; an intermediate reflux device that is replaceably assembled between the first reflux device and the second reflux device, and has an intermediate reflux passage provided therein, the intermediate reflux passage communicating with the first reflux passage and the second reflux passage; Equipped with The first return passage, the intermediate return passage and the second return passage are combined to form a ball circulation passage.

[0007] According to the circulation device of the present invention, the first passage pipe and the second passage pipe are made by 3D printing.

[0008] According to the circulation device of the present invention, the first upper assembly and the second upper assembly are made by plastic injection molding.

[0009] According to the circulation device of the present invention, the first lower assembly and the second lower assembly are formed by injection molding to enclose the first passage pipe and the second passage pipe, respectively.

[0010] The circulation device according to the present invention is characterized in that the hardness of the first lower assembly and the second lower assembly is lower than the hardness of the first upper assembly and the second upper assembly.

[0011] According to the ball screw of the present invention, the ball screw is provided with the circulation device according to claim 1, a nut having a number of internal threads, a first return flow device of the circulation device assembled at one end thereof, a second return flow device of the circulation device assembled at the other end thereof, an intermediate return flow device being interchangeably connected to the first return flow device and the second return flow device, and the first return flow passage, the intermediate return flow passage and the second return flow passage being combined to form a ball circulation passage; a screw shaft through which a nut is inserted, and on the outside of which a number of threads corresponding to the positions of the threads of the nut are provided, the outer threads of which are combined with the inner threads of the nut to form a ball rolling passage; a number of balls that are rollably disposed within the ball rolling passage, and that roll through the first return passage of the first return device, the intermediate return passage, the second return passage of the second return device, and the ball rolling passage, thereby forming a ball return circulation path; Equipped with When you try to assemble these parts, The first lower assembly and the first passage pipe of the first reflux device are combined and positioned on one end of the nut, and the second lower assembly and the second passage pipe of the second reflux device are combined and positioned on the other end of the nut. An intermediate reflux device is connected and positioned to the first lower assembly and the second lower assembly, so that the first reflux passage, the intermediate reflux passage and the second reflux passage communicate with each other to form a ball circulation passage. A large number of balls are placed in the ball circulation passage and pass through the ball circulation passage. The first upper assembly and the first lower assembly are combined and integrated, and the second upper assembly and the second lower assembly are combined and integrated, so that the ball circulation passage is closed. The first lower assembly and the first passage pipe of the first reflux device are combined and positioned on one end of the nut, the second lower assembly and the second passage pipe of the second reflux device are combined and positioned on the other end of the nut, balls are placed inside the first passage pipe and the second passage pipe, an intermediate reflux device is connected and positioned to the first lower assembly and the second lower assembly, the first reflux passage, the intermediate reflux passage and the second reflux passage are connected to form a ball circulation passage, the balls pass through the ball circulation passage, the first upper assembly and the first lower assembly are assembled and integrated, and the second upper assembly and the second lower assembly are assembled and integrated, closing the ball circulation passage.

[0012] According to the ball screw of the present invention, the first lower assembly of the first circulation device has a finger structure, and the second lower assembly of the second circulation device has another finger structure, the first finger structure of the first lower assembly and the second finger structure of the second lower assembly correspond to the threads of the screw shaft and the nut, respectively, and the balls can roll smoothly through the ball circulation passage and the ball rolling passage.

[0013] In the ball screw according to the present invention, the ball tangent position of the first return passage or the second return passage is offset by a distance d from the radial direction of the ball center diameter (BCD) when the ball is rolling, and the distance d satisfies the following condition: It is characterized by d = 0.02 x Dw, where Dw is the ball center diameter. [Effects of the Invention]

[0014] The circulation device and ball screw equipped with the circulation device of the present invention combine 3D printing and overmolding technologies to create a circulation device that not only improves component versatility but also simplifies the manufacturing and assembly processes, enabling a wide range of lead and thread specifications, resulting in a highly efficient and standardized ball screw circulation system. Furthermore, the modular structure allows for nuts with different cycle numbers to be accommodated by simply replacing the intermediate circulation device. Furthermore, as long as the ball diameter and lead are the same, the same intermediate circulation device can be used with screw shafts with different rod diameters, improving structural versatility and assembly efficiency. Furthermore, the present invention optimizes the ball tangent position of the circulation passage relative to the ball center diameter (BCD) and offsets it 0.02 times the ball diameter, thereby achieving smoother ball insertion and removal. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is an exploded perspective view showing the structure of a circulation device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a side view showing the circulation device of FIG. 1. [Figure 3] FIG. 2 is a top view showing the circulation device of FIG. 1. [Figure 4] FIG. 2 is a bottom view showing the circulation device of FIG. 1. [Figure 5] FIG. 2 is a side view showing a cross section of the circulation device of FIG. 1. [Figure 6] FIG. 2 is a side view showing an intermediate reflux device of the circulation device of FIG. 1. [Figure 7] 2 is a diagram showing the structure of the first and second passage pipes and the first and second lower assemblies of the circulation device of FIG. 1 before being enclosed by injection molding. FIG. [Figure 8] 2 is a diagram showing the structure of the circulation device of FIG. 1 after the first and second passage pipes and the first and second lower assemblies are enclosed by injection molding. FIG. [Figure 9] 1 is a perspective view showing the structure of a ball screw according to an embodiment of the present invention; [Figure 10] FIG. 10 is an exploded perspective view showing the ball screw of FIG. 9. [Figure 11] FIG. 10 is an exploded perspective view of the ball screw of FIG. 9 as seen from another angle. [Figure 12] FIG. 10 is a diagram showing a combination of a circulation device and a screw shaft in the ball screw of FIG. 9. [Figure 13] FIG. 13 is a cross-sectional view of FIG. [Figure 14] FIG. 12 shows the state in which the ball passes through the first circulation device. [Figure 15] FIG. 12 shows the state in which the ball passes through the second circulation device. [Figure 16] FIG. 10 is a cross-sectional view showing the ball screw of FIG. [Figure 17] 1 is a diagram showing the first step of assembling the circulation device to the ball screw in accordance with an embodiment of the present invention; FIG. [Figure 18] 10 is a view showing a second step of assembling the circulation device to the ball screw in accordance with an embodiment of the present invention; FIG. [Figure 19] 10 is a diagram showing a third step of assembling the circulation device to the ball screw in accordance with an embodiment of the present invention; FIG. [Figure 20] FIG. 10 is a view showing the fourth step of assembling the circulation device to the ball screw in accordance with an embodiment of the present invention. [Figure 21] FIG. 10 is a diagram showing the offset of the cut-in position of the ball. [Figure 22] FIG. 10 is a diagram showing a step at the cut-in position of a ball without adjustment. [Figure 23] FIG. 10 is a diagram showing a step after the cut-in position of the ball has been adjusted. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings. For clarity of explanation, the following description includes many practical details, but it should be understood that these practical details should not be construed as limiting the present invention. In other words, in some embodiments of the present invention, these practical details are not necessarily required. Furthermore, in order to simplify the drawings and focus on the main technical features of the present invention, some conventional non-essential structures and components are shown in simplified schematic diagrams or omitted.

[0018] In this invention, the terms "first," "second," "upper," "lower," and "between" are used to indicate relative positions. In practice, the possibility of changing the arrangement order according to circumstances is not excluded. When the viewing angle is different, the relative positional relationship of "first," "second," "upper," and "lower" may also change accordingly.

[0019] 1 to 8, the circulation device 100 includes a first reflux device 110, a second reflux device 120, and an intermediate reflux device .

[0020] The first reflux device 110 includes a first upper assembly 111 and a first lower assembly 112 assembled to the first upper assembly 111. A first passage pipe 113 having a curved shape is assembled between the first upper assembly 111 and the first lower assembly 112, and a first reflux passage 113a is formed within the first passage pipe 113.

[0021] The second reflux device 120 includes a second upper assembly 121 and a second lower assembly 122 assembled to the second upper assembly 121. A second passage pipe 123 having a curved shape is assembled between the second upper assembly 121 and the second lower assembly 122, and a second reflux passage 123a is formed in the second passage pipe 123.

[0022] The intermediate reflux device 130 is replaceably assembled between the first reflux device 110 and the second reflux device 120. An intermediate reflux passage 131 is provided within the intermediate reflux device 130. When the first reflux device 110, the second reflux device 120, and the intermediate reflux device 130 are assembled, the intermediate reflux passage 131 communicates with the first reflux passage 113a and the second reflux passage 123a, so that the first reflux passage 113a, the intermediate reflux passage 131, and the second reflux passage 123a combine to form a ball circulation passage.

[0023] The first lower assembly 112 and the second lower assembly 122 are respectively formed by combining with the first passage pipe 113 and the second passage pipe 123 using an overmolding technique. In other words, first, the first lower assembly 112 and the second lower assembly 122 are respectively formed by combining with the first passage pipe 113 and the second passage pipe 123 using an overmolding technique, then the intermediate reflux device 130 is assembled between the first lower assembly 112 and the second lower assembly 122, and finally, the first upper assembly 111 and the second upper assembly 121 are respectively assembled with the first lower assembly 112 and the second lower assembly 122 to form a unit, thereby forming the main body of the circulation device 100. The first upper assembly 111 can be attached to the first lower assembly 112, or the second upper assembly 121 can be attached to the second lower assembly 122, using a removable method such as a screw connection, a snap connection, a mortise and tenon connection, a hinge connection, an elastic clamp, a magnetic attraction, or a groove connection. Similarly, the intermediate reflux device 130 can be attached to the first reflux device 110 and the second reflux device 120 using the same method. This assembly method allows each component of the first reflux device 110, the second reflux device 120, and the intermediate reflux device 130, or each component itself, to be modularly connected, facilitating assembly, maintenance, and repair. Furthermore, by replacing the intermediate reflux device 130 with a different specification, it is possible to accommodate nut designs with different cycle numbers. The intermediate reflux device 130 can be used with different screw diameters as long as the ball diameter and lead are consistent.

[0024] In some embodiments, the first and second passage tubes 113 and 123 are made by 3D printing. The geometric shapes of the first and second passage tubes 113 and 123 are designed according to the ball circulation path, and thermoplastic plastics such as PP, PA, and ABS can be selected. Engineering materials with higher mechanical properties and thermal stability can also be selected according to actual needs. The first and second lower assemblies 112 and 122 are fabricated by overmolding technology to combine with the 3D-printed first and second passage tubes 113 and 123, respectively. The first and second lower assemblies 112 and 122 are used to precisely fit with the nut body and withstand local stress. For this reason, the covering material can be a plastic with low hardness or hole-forming properties to improve fitting and assembly stability. The first and second upper assemblies 111 and 121 are fabricated by resin injection molding. The first upper assembly 111 and the second upper assembly 121 are for precise mating with the intermediate reflux device 130, the first lower assembly 112 and the second lower assembly 122 to form a closed ball circuit. To this end, the first upper assembly 111 and the second upper assembly 121 are injection molded from hard plastic to seal the reflux passages and ensure structural integrity and secure installation.

[0025] In summary, based on different applications and properties, in the present invention, the hardness of the first lower assembly 112 and the second lower assembly 122 is lower than the hardness of the first upper assembly 111 and the second upper assembly 121.

[0026] 9 to 16. The ball screw 200 provided with the circulation device 100 includes a nut 210, a screw shaft 220, and a large number of balls 230.

[0027] Numerous threads 211 are provided inside the nut 210. The first reflux device 110 of the circulation device 100 is assembled to one end of the nut 210, and the second reflux device 120 of the circulation device 100 is assembled to the other end of the nut 210. An intermediate reflux device 130 is replaceably disposed between the first reflux device 110 and the second reflux device 120. The first reflux passage 113a, the intermediate reflux passage 131, and the second reflux passage 123a combine to form a ball circulation passage.

[0028] The screw shaft 220 is inserted through the nut 210. The outer surface of the screw shaft 220 is provided with threads 221 that correspond to the positions of the threads 211 of the nut 210. The threads 221 on the outer surface of the screw shaft 220 and the threads 211 on the back surface of the nut 210 combine to form a ball rolling passage. A number of balls 230 are provided in the ball rolling passage so as to be able to roll. As the balls 230 roll, they pass through the first return passage 113a of the first return passage 110, the intermediate return passage 131 of the intermediate return passage 130, the second return passage 123a of the second return passage 120, and the ball rolling passage, thereby forming a ball return circulation path.

[0029] 17 to 20 , the circulation device 100 according to the present invention has a modular assembly structure. The assembly order of the first reflux device 110, the second reflux device 120, and the intermediate reflux device 130 can be changed depending on the assembly requirements. When assembling the ball screw 200, the first lower assembly 112 of the first reflux device 110 is assembled and positioned on one end of the nut 210, the second lower assembly 122 of the second reflux device 120 is assembled and positioned on the other end of the nut 210, and the intermediate reflux device 130 is connected and positioned with the first lower assembly 112 and the second lower assembly 122. A ball circulation passage is formed by connecting the first reflux passage 113a, the intermediate reflux passage 131, and the second reflux passage 123a. A number of balls 230 are placed inside the intermediate circulation device 130, and the balls 230 pass through the first circulation passage 113a, the intermediate circulation passage 131, and the second circulation passage 123a. The first upper assembly 111 and the first lower assembly 112 are assembled into a single unit, and the second upper assembly 121 and the second lower assembly 122 are assembled into a single unit, thereby closing the ball circulation passage. Meanwhile, the assembly order of the intermediate circulation device 130 can be changed depending on the assembly conditions. For example, first, the first lower assembly 112 of the first reflux device 110 is assembled to one end of the nut 210 and positioned, and then the second lower assembly 122 of the second reflux device 120 is assembled to the other end of the nut 210 and positioned. Then, a large number of balls 230 are inserted, and the large number of balls 230 pass through the first reflux passage 113a of the first reflux device 110 and the second reflux passage 123a of the second reflux device 120. Then, the first upper assembly 111 and the first lower assembly 112 are assembled into one body, and then the second upper assembly 121 and the second lower assembly 122 are assembled into one body. Finally, the intermediate reflux device 130 is assembled between the first reflux device 110 and the second reflux device 120. This allows the large number of balls 230 to pass through the first reflux passage 113a, the intermediate reflux passage 131, and the second reflux passage 123a.

[0030] In some embodiments, the first lower assembly 112 of the first reflux device 110 includes a first finger structure 114. The second lower assembly 122 of the second reflux device 120 includes a separate second finger structure 124. When assembling, the first finger structure 114 and the second finger structure 124 correspond to the threads 221 of the screw shaft 220 and the threads 211 of the nut 210, respectively, so that the multiple balls 230 can smoothly roll through the ball circulation passage and the ball rolling passage.

[0031] See Figures 21 to 23. When assembling the ball 230 according to the present invention, to improve the step at the connection point between the return hole S of the first return passage 113a or the second return passage 123a and the thread 211 of the nut 210 in the ball screw 200, the present invention optimizes the ball tangent position in the return passage relative to the ball center diameter (BCD) and provides an offset of 0.02 times the ball diameter (Dw) to achieve smoother ball insertion and removal. Therefore, the ball tangent position of the ball 230 in the first return passage 113a or the second return passage 123a is offset by a distance d from the radial direction of the ball center diameter (BCD) when the ball rolls, and the distance d satisfies the following condition: d = 0.02 x Dw, where Dw is the ball center diameter. See Figure 21. The original tangential path P1 and the offset tangential path P2 are offset by a distance d. Optimizing this parameter improves ball movement efficiency, reduces system noise, and extends the life of the ball screw 200. As shown in Figures 22 and 23, the original tangential path P1 creates a large step H1 at its intersection with the ball circulation path, which can hinder ball movement and increase wear. By slightly offsetting the entry point radially by a distance d, the step H2 of the offset tangential path P2 is significantly smaller than H1, reducing the step to nearly zero. This allows for a smoother geometric transition between the return hole S and the thread 211 of the nut 210, significantly reducing the step and improving the stability and smoothness of the overall circulation.

[0032] In summary, the present invention provides a circulation device 100 with modular assembly capabilities and a ball screw 200 equipped with the circulation device 100. The combination of 3D printing and overmolding technologies for manufacturing the circulation device 100 not only increases component versatility, but also simplifies the manufacturing and assembly processes, enabling a wide range of lead and thread specifications, resulting in a highly efficient and standardized ball screw circulation system. Furthermore, the modular structure allows for the use of a nut 210 with a different cycle number by simply replacing the intermediate circulation device 130. Furthermore, as long as the ball 230 diameter and lead are the same, the same intermediate circulation device 130 can be used with screw shafts 220 with different rod diameters, improving structural versatility and assembly efficiency. Furthermore, the present invention optimizes the ball tangent position of the circulation passage relative to the ball center diameter (BCD) and offsets it 0.02 times the ball diameter, thereby achieving smoother ball insertion and removal. The shape transition between the return hole and the screw is smoother, the step is significantly reduced, and the stability and smoothness of the entire circulation are improved. [Explanation of symbols]

[0033] 100 Circulation device 110 First reflux device 111 First Upper Assembly 112 First Lower Assembly 113 First Passage Pipe 113a First reflux passage 120 Second reflux device 121 Second Upper Assembly 122 Second Lower Assembly 123 Second Passage Pipe 123a Second reflux passage 130 Intermediate reflux device 131 Intermediate reflux passage 200 ball screw 210 Nut 211 Screw 220 screw shaft 221 Screw 230 balls 114 First finger-like structure 124 Second finger-like structure S Reflux hole BCD ball center diameter d distance P1 Original tangent path P2 offset tangent path H1 step H2 step

Claims

1. a first reflux device comprising a first upper assembly and a first lower assembly assembled to the first upper assembly, wherein a first passage pipe having a curved shape is assembled between the first upper assembly and the first lower assembly, and a first reflux passage is formed within the first passage pipe; a second reflux device comprising a second upper assembly and a second lower assembly assembled to the second upper assembly, wherein a second passage pipe having a curved shape is assembled between the second upper assembly and the second lower assembly, and a second reflux passage is formed within the second passage pipe; an intermediate return flow device that is replaceably assembled between the first return flow device and the second return flow device, and has an intermediate return flow passage provided therein, the intermediate return flow passage communicating with the first return flow passage and the second return flow passage; Equipped with The circulation device, characterized in that the first return passage, the intermediate return passage, and the second return passage are combined to form a ball circulation passage.

2. The circulation device according to claim 1 , wherein the first passage pipe and the second passage pipe are made by 3D printing.

3. 2. The circulation device of claim 1, wherein the first upper assembly and the second upper assembly are made by plastic injection molding.

4. 2. The circulation device according to claim 1, wherein the first lower assembly and the second lower assembly are formed by injection molding to encase the first passage pipe and the second passage pipe, respectively.

5. 2. The circulation device according to claim 1, wherein the hardness of the first lower assembly and the second lower assembly is lower than the hardness of the first upper assembly and the second upper assembly.

6. A circulation device according to claim 1, a nut having a number of internal threads, the first return flow device of the circulation device being assembled at one end thereof, the second return flow device of the circulation device being assembled at the other end thereof, the intermediate return flow device being interchangeably connected to the first return flow device and the second return flow device, and the first return flow passage, the intermediate return flow passage and the second return flow passage being combined to form a ball circulation passage; a screw shaft through which the nut is inserted, the screw shaft having a number of threads on the outside thereof corresponding to the positions of the threads of the nut, the outside threads being combined with the threads on the inside of the nut to form a ball rolling passage; a number of balls that are provided in the ball rolling passage so as to be able to roll, and that pass through the first return passage of the first return flow device, the intermediate return passage, the second return passage of the second return flow device, and the ball rolling passage while rolling, thereby forming a ball return circulation path; Equipped with When you try to assemble these parts, the first lower assembly and the first passage pipe of the first reflux device are combined and positioned on one end of the nut, the second lower assembly and the second passage pipe of the second reflux device are combined and positioned on the other end of the nut, and an intermediate reflux device is connected and positioned to the first lower assembly and the second lower assembly, thereby communicating the first reflux passage, the intermediate reflux passage and the second reflux passage to form the ball circulation passage, a large number of the balls are placed in the ball circulation passage and pass through the ball circulation passage, combining the first upper assembly and the first lower assembly to form a unit, and combining the second upper assembly and the second lower assembly to form a unit, thereby closing the ball circulation passage; the first lower assembly and the first passage pipe of the first circulation device are combined and positioned on one end of the nut, the second lower assembly and the second passage pipe of the second circulation device are combined and positioned on the other end of the nut, the balls are placed inside the first passage pipe and the second passage pipe, the intermediate circulation device is connected to the first lower assembly and the second lower assembly and positioned, the first circulation passage, the intermediate circulation passage and the second circulation passage communicate with each other to form the ball circulation passage, the balls pass through the ball circulation passage, the first upper assembly and the first lower assembly are assembled and integrated, and the second upper assembly and the second lower assembly are assembled and integrated to close the ball circulation passage.

7. 7. The ball screw according to claim 6, wherein the first lower assembly of the first circulation device includes a finger structure, and the second lower assembly of the second circulation device includes another finger structure, the first finger structure of the first lower assembly and the second finger structure of the second lower assembly correspond to the thread of the screw shaft and the thread of the nut, respectively, and the balls can roll smoothly through the ball circulation passage and the ball rolling passage.

8. The ball is configured such that a ball tangent position of the first return passage or the second return passage is offset by a distance d from a radial direction of a ball center diameter (BCD) when the ball is rolling, and the distance d satisfies the following condition:

7. The ball screw according to claim 6, wherein d = 0.02 x Dw, Dw being the ball center diameter.

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