Splined ball screw

Abstract

To provide a ball screw with a spline that can improve a rated load, can obtain good operability, and can reduce manufacturing cost.SOLUTION: A ball screw 10 with a spline comprises a screw shaft 101. A helical ball screw groove 101a having a predetermined lead, and a linear ball spline groove 101b extending in an axial direction are formed in an outer surface of the screw shaft 101. A screw groove bottom radius r11 indicating a distance from a center O in a radial direction of the screw shaft 101 to a groove bottom P11 of the ball screw groove 101a is nearly equal to a spline groove bottom radius r12 indicating a distance from the center O in the radial direction of the screw shaft 101 to a groove bottom P12 of the ball spline groove 101b.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a ball screw with splines.

Background Art

[0002] When a ball screw nut rotates, for example, the screw shaft moves in the axial direction, and when a ball spline nut rotates, the screw shaft rotates. Therefore, it is suitably used, for example, as a Z-θ axis actuator of a scalar robot.

[0003] For example, as shown in FIG. 3, the ball screw 10 with splines described in Patent Document 1 includes a screw shaft 1, a ball spline nut 20, a ball screw nut 50, and a large number of spline balls 5 and screw balls 6.

[0004] On the outer surface of the screw shaft 1, a spiral ball screw groove 1a having a predetermined lead and a linear ball spline groove 1b extending in the axial direction are formed.

[0005] The ball spline nut 20 is rotatably supported by a ball bearing 2. The outer ring 3 of the ball bearing 2 is substantially cylindrical, and at one end in the axial direction, it has a flange 3a attached to the housing of the Z-θ axis actuator. A ball 4 is disposed between an outer ring groove 3b formed on the inner surface of the outer ring 3 and an inner ring groove 3c formed on the outer surface of the ball spline nut 20 so as to be freely rotatable. [[ID=2ό]]

[0006] The ball spline nut 20 includes a cylindrical nut body 21 and ring-shaped end caps 22A and 22B attached to the axial end portions of the nut body 21. On the inner surface of the nut body 21, a linear ball spline groove (not shown) that faces the ball spline groove 1b of the screw shaft 1 and extends in the axial direction is formed. The two ball spline grooves constitute a ball rolling path 26, and a large number of spline balls 5 are disposed between the two ball spline grooves so as to be freely rotatable.

[0007] Furthermore, a linear ball circulation path 25 is formed in the nut body 21, running axially through the nut body 21 parallel to the ball spline groove. In addition, U-shaped connecting passages 24 are formed in the end caps 22A and 22B for circulating the spline balls 5. In Figure 3, the ball rolling path 26 formed by the ball spline groove 1b of the screw shaft 1 and the ball spline groove of the nut body 21, the ball circulation path 25 formed by the nut body 21, and the connecting passages 24 formed by the end caps 22A and 22B are shown by the spline balls 5 moving within their respective passages.

[0008] In this way, the connecting passage 24 of the end cap 22A or 22B guides the spline balls 5, which roll along the linear ball track 26, to the ball circulation path 25, and then returns them to the ball track 26 again via the connecting passage 24 of the opposite end cap 22B or 22A.

[0009] The ball screw nut 50, like the ball spline nut 20, is rotatably supported by a ball bearing 2. The ball bearing 2 comprises an outer ring 3 having a flange 3a and an outer ring groove 3b, a ball screw nut 50 having an inner ring groove 3c formed on its outer surface, and balls 4 that are rotatably disposed between the outer ring groove 3b and the inner ring groove 3c.

[0010] The ball screw nut 50 comprises a cylindrical nut body 51, end caps 52A and 52B provided at the axial ends of the nut body 51, and a cover member 53 that covers the end caps 52A and 52B. The end caps 52A and 52B are fixed to the axial end faces of the nut body 51 by the cover member 53.

[0011] A helical ball screw groove 54 is formed on the inner circumferential surface of the nut body 51, opposite to the ball screw groove 1a of the screw shaft 1, and numerous screw balls 6 are arranged to roll freely between the two screw grooves 1a and 54.

[0012] The end caps 52A and 52B have a roughly arc-shaped connecting passage 55 for circulating the screw balls 6. The nut body 51 has a straight ball circulation path 56 that penetrates axially. The connecting passage 55 connects the ball rolling path 57 formed by the ball screw groove 54 of the nut body 51 and the ball screw groove 1a of the screw shaft 1, and the straight ball circulation path 56 to form a circulation path.

[0013] The connecting passage 55 of the end cap 52A or 52B guides the screw balls 6, which roll along the spiral ball track 57, to the ball circulation path 56, and then returns them to the ball track 57 again via the connecting passage 55 of the opposite end cap 52B or 52A.

[0014] For SCARA robots equipped with such splined ball screws, high-speed movement and rotation are required to improve cycle time, making weight reduction and low inertia of the splined ball screw itself crucial factors. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] International Publication No. 2019 / 107122 [Overview of the Initiative] [Problems that the invention aims to solve]

[0016] However, reducing the size of each component to lower weight and inertia raises concerns about reduced durability. Also, since the number of spline balls 5 moving along the ball track 26 is less than the number of screw balls 6 moving along the ball track 57, the load on the spline side increases, resulting in a lower rated load.

[0017] Furthermore, depending on the shape and depth of the groove formed on the screw shaft 1, at the point where the ball screw groove 1a and the ball spline groove 1b of the screw shaft 1 intersect, for example, the screw ball 6 may fall into the ball spline groove 1b, causing deterioration of operation or making operation impossible.

[0018] This invention has been made in view of the aforementioned problems, and aims to provide a splined ball screw that can improve the rated load, achieve good operability, and reduce manufacturing costs. [Means for solving the problem]

[0019] The above objective of the present invention is achieved by the following configuration. [1] A screw shaft having a helical ball screw groove and a linear ball spline groove on its outer surface, A ball screw nut having a helical ball screw groove on its inner circumferential surface that faces the ball screw groove of the screw shaft, A number of screw balls are arranged to roll freely in a ball rolling path formed between the ball screw groove of the screw shaft and the ball screw groove of the ball screw nut, A ball spline nut having a linear ball spline groove on its inner circumferential surface that faces the ball spline groove of the screw shaft, A number of spline balls are rotatably disposed in a ball rolling path formed between the ball spline groove of the screw shaft and the ball spline groove of the ball spline nut, A splined ball screw equipped with, At least one set of the following is different from each other: the diameter of the spline ball and the diameter of the screw ball; the ratio of the radius of curvature of the ball spline groove to the diameter of the spline ball and the ratio of the radius of curvature of the ball screw groove to the diameter of the screw ball and the initial contact angle between the spline ball and the ball spline groove and the initial contact angle between the screw ball and the ball screw groove. The distance from the center in the radial direction of the screw shaft to the groove bottom of the ball screw groove is substantially the same as the distance from the center to the groove bottom of the ball spline groove. Ball screw with spline.

[0020] [2] A screw shaft having a spiral ball screw groove and a linear ball spline groove on the outer peripheral surface, A ball screw nut having a spiral ball screw groove on the inner peripheral surface facing the ball screw groove of the screw shaft, A large number of screw balls arranged to be freely rotatable in a ball rolling path formed between the ball screw groove of the screw shaft and the ball screw groove of the ball screw nut, A ball spline nut having a linear ball spline groove on the inner peripheral surface facing the ball spline groove of the screw shaft, A large number of spline balls arranged to be freely rotatable in a ball rolling path formed between the ball spline groove of the screw shaft and the ball spline groove of the ball spline nut, A ball screw with spline, comprising: Among the diameter of the spline ball, the diameter of the screw ball, the initial contact angle between the spline ball and the ball spline groove, and the initial contact angle between the screw ball and the ball screw groove, at least one set has different values from each other. The distance from the center in the radial direction of the screw shaft to the initial contact point of the screw ball with the ball screw groove is substantially the same as the distance from the center to the initial contact point of the spline ball with the ball spline groove. Ball screw with spline.

Advantages of the Invention

[0021] According to the ball screw with spline of the present invention, the rated load can be improved, good operability can be obtained, and the manufacturing cost can be reduced.

Brief Description of the Drawings

[0022] [Figure 1] This is a cross-sectional view of the screw shaft in a splined ball screw according to a first embodiment of the present invention. [Figure 2] This is a cross-sectional view of the screw shaft in a splined ball screw according to a second embodiment of the present invention. [Figure 3] This is a partial fracture perspective view of a conventional splined ball screw. [Modes for carrying out the invention]

[0023] The inventors of the present invention have conducted various studies on the structure of a splined ball screw that can solve the above problems. As a result, they found that the rated load can be improved by increasing the diameter of only the spline balls 5 that roll in the spline section consisting of a ball rolling path 26, a ball circulation path 25, and a connecting passage 24. However, increasing the diameter of the spline balls 5 requires deepening the ball spline groove 1b of the screw shaft 1, which results in the problem that the screw balls 6 are more likely to fall into the ball spline groove 1b.

[0024] Two possible solutions to the above problems are as follows: (1) Ensure that the ball screw groove and the ball spline groove do not overlap. (2) Provide a retaining mechanism to prevent the screw ball from falling out. However, (1) would result in a long screw shaft, making it difficult to apply to SCARA robots and other devices that require a compact design. Also, as in (2), it is difficult to provide a holding mechanism to ball screws arranged in a helical shape, and even if it could be realized, the number of parts and assembly processes would increase significantly, leading to increased manufacturing time and thus increased costs.

[0025] Therefore, in the first embodiment of the present invention, the ball spline groove of the enlarged spline ball is made shallower, and the groove bottom of the ball screw groove and the groove bottom of the ball spline groove are made to be approximately the same depth. Hereinafter, splined ball screws according to each embodiment of the present invention will be described in detail with reference to the drawings.

[0026] (First Embodiment) First, a splined ball screw 10 according to the first embodiment of the present invention will be described. The splined ball screw 10 of the first embodiment is an improved version of the conventional splined ball screw 10 shown in Figure 3, with an improved screw shaft 101. Therefore, the basic configuration of the splined ball screw 10 is the same as that of the conventional splined ball screw 10 already described in Figure 3, so the screw shaft 101, which is the main part of this embodiment, will be described with reference to the same figure as needed.

[0027] As shown in Figure 1, the outer surface of the screw shaft 101 of this embodiment has a helical ball screw groove 101a with a predetermined lead and a linear ball spline groove 101b extending in the axial direction. In this embodiment, the depth of the ball screw groove 101a and the ball spline groove 101b is controlled, so in Figure 1, the ball screw groove 101a and the ball spline groove 101b are shown as being formed in the same direction for comparison.

[0028] Furthermore, as shown in Figure 1, the ball spline groove 101b is configured to roll large-diameter spline balls. Similarly, the ball screw groove 101a is configured to roll screw balls that are smaller in diameter than the spline balls. In this embodiment, the depth of the ball screw groove 101a and the depth of the ball spline groove 101b are made approximately the same. That is, the screw groove bottom diameter r11, which represents the distance from the radial center O of the screw shaft 101 to the groove bottom P11 of the ball screw groove 101a, and the spline groove bottom diameter r12, which represents the distance from the radial center O of the screw shaft 101 to the groove bottom P12 of the ball spline groove 101b, are approximately the same.

[0029] In this embodiment, which has a screw shaft 101 configured in this way, the ball diameter of the spline ball 5 is made larger than the ball diameter of the screw ball 6, thereby improving the rated load of the splined ball screw 10. Furthermore, since the depth of the ball screw groove 101a and the depth of the ball spline groove 101b are made approximately the same, it is possible to prevent the screw ball 6 from falling into the ball spline groove 101b at the point where the ball screw groove 101a and the ball spline groove 101b of the screw shaft 101 intersect. Therefore, good operability is obtained. Moreover, even if the ball diameter of the spline ball 5 is increased, it is not necessary to increase the depth of the ball spline groove 101b, so the time required for groove machining can be shortened, and manufacturing costs can be reduced.

[0030] Note that the screw groove bottom diameter r11 and the spline groove bottom diameter r12 may differ slightly from each other depending on the machining method of the grooves, etc. Therefore, if the two are approximately the same value, it is possible to prevent the screw ball 6 from falling into the ball spline groove 101b. However, it is preferable that the screw groove bottom diameter r11 and the spline groove bottom diameter r12 are the same.

[0031] In this embodiment, the rated load of the splined ball screw 10 is improved by increasing the diameter of the spline balls 5 that roll in the spline section consisting of a ball rolling path 26, a ball circulation path 25, and a connecting passage 24. However, the rated load can also be improved by making the ratio of the radius of curvature of the ball spline groove 101b to the diameter of the spline ball 5 (spline side groove R ratio) smaller than the ratio of the radius of curvature of the ball screw groove 101a to the diameter of the screw ball 6 (screw side groove R ratio). Furthermore, if the shape of the ball spline groove 101b is a Gothic arc shape, the rated load can also be improved by adjusting the initial contact angle between the spline ball 5 and the ball spline groove 101b (spline side initial contact angle) to a value larger than the initial contact angle between the screw ball 6 and the ball screw groove 101a (screw side initial contact angle). The initial contact angle will be described in detail in the second embodiment.

[0032] Therefore, even when improving the rated load by methods other than making the ball diameter of the screw ball 6 and the ball diameter of the spline ball 5 different, such as making the spline groove R ratio and the screw groove R ratio different, or making the initial contact angle on the spline side and the initial contact angle on the screw side different, good operating performance can be obtained by making the screw groove bottom diameter r11 and the spline groove bottom diameter r12 approximately the same.

[0033] (Second Embodiment) Next, a splined ball screw 10 according to a second embodiment of the present invention will be described. The splined ball screw 10 of the second embodiment, like the first embodiment, is an improved version of the conventional splined ball screw 10 shown in Figure 3, with an improved screw shaft 1. Therefore, the basic configuration of the splined ball screw 10 is the same as that of the conventional splined ball screw 10 already described in Figure 3. Thus, the screw shaft 102, which is the main part of this embodiment, will be described with reference to the same figure as necessary.

[0034] As shown in Figure 2, the outer surface of the screw shaft 102 of this embodiment has a helical ball screw groove 102a with a predetermined lead and a linear ball spline groove 102b extending in the axial direction. In this embodiment, the initial contact points of the ball screw groove 102a and the ball spline groove 102b are controlled, so in Figure 2, the ball screw groove 102a and the ball spline groove 102b are shown to be formed in the same direction for comparison.

[0035] As shown in Figure 2, the ball spline groove 102b is configured to roll a large-diameter spline ball 5. Similarly, the ball screw groove 102a is configured to roll a screw ball 6 which has a smaller diameter than the spline ball 5. Here, when the screw ball 6 is placed in the ball screw groove 102a, the two initial contact points between the screw ball 6 and the ball screw groove 102a are defined as the screw ball contact points P21. Similarly, when the spline ball 5 is placed in the ball spline groove 102b, the initial contact point between the spline ball 5 and the ball spline groove 102b is defined as the spline ball contact point P22.

[0036] In this embodiment, the screw groove contact point diameter r21, which represents the distance from the radial center O of the screw shaft 102 to the screw ball contact point P21, and the spline groove contact point diameter r22, which represents the distance from the radial center O of the screw shaft 102 to the spline ball contact point P22, are substantially the same.

[0037] In the second embodiment having the screw shaft 102 configured in this way, similar to the first embodiment, the ball diameter of the spline ball 5 is made larger than the ball diameter of the screw ball 6, thereby improving the rated load of the splined ball screw 10. Furthermore, since the screw groove contact point diameter r21 and the spline groove contact point diameter r22 are made substantially the same, it is possible to prevent the screw ball 6 from falling into the ball spline groove 102b at the point where the ball screw groove 102a and the ball spline groove 102b of the screw shaft 102 intersect. Therefore, good operability is obtained. Moreover, even if the ball diameter of the spline ball 5 is increased, it is not necessary to increase the depth of the ball spline groove 102b, so the time required for groove machining can be shortened, and manufacturing costs can be reduced.

[0038] Note that the screw groove contact point diameter r21 and the spline groove contact point diameter r22 may differ slightly from each other depending on the machining method of the grooves, etc. Therefore, if the two are approximately the same value, it is possible to prevent the screw ball 6 from falling into the ball spline groove 102b. However, it is preferable that the screw groove contact point diameter r21 and the spline groove contact point diameter r22 are the same.

[0039] Furthermore, in the second embodiment, the rated load of the splined ball screw 10 is improved by increasing the diameter of the spline balls 5 that roll in the spline section consisting of the ball rolling path 26, the ball circulation path 25, and the connecting passage 24. However, the rated load can also be improved by adjusting the initial contact angle θ2 (spline-side initial contact angle θ2) between the spline balls 5 and the ball spline groove 102b to a value greater than the initial contact angle θ1 (screw-side initial contact angle θ1) between the screw balls 6 and the ball screw groove 102a.

[0040] The initial contact angle θ1 on the screw side refers to the angle formed by the lines connecting the center of the screw ball 6 and the two screw ball contact points P21 when the screw ball 6 is placed in the ball screw groove 102a. Similarly, the initial contact angle θ2 on the spline side refers to the angle formed by the lines connecting the center of the spline ball 5 and the two spline ball contact points P22 when the spline ball 5 is placed in the ball spline groove 102b.

[0041] Thus, even when improving the rated load by adjusting the initial contact angle θ2 on the spline side and the initial contact angle θ1 on the screw side, in addition to the method of setting different ball diameters for the screw ball 6 and the spline ball 5, good operating performance can be obtained by making the screw groove contact point diameter r21 and the spline groove contact point diameter r22 approximately the same.

[0042] Furthermore, the present invention is not limited to the embodiments described above, and can be modified, improved, and so on as appropriate.

[0043] As described above, the following matters are disclosed in this specification: (1) A screw shaft having a helical ball screw groove and a linear ball spline groove on its outer surface, A ball screw nut having a helical ball screw groove on its inner circumferential surface that faces the ball screw groove of the screw shaft, A number of screw balls are arranged to roll freely in a ball rolling path formed between the ball screw groove of the screw shaft and the ball screw groove of the ball screw nut, A ball spline nut having a linear ball spline groove on its inner circumferential surface that faces the ball spline groove of the screw shaft, A number of spline balls are rotatably disposed in a ball rolling path formed between the ball spline groove of the screw shaft and the ball spline groove of the ball spline nut, A splined ball screw equipped with, At least one set of the following is different from each other: the diameter of the spline ball and the diameter of the screw ball; the ratio of the radius of curvature of the ball spline groove to the diameter of the spline ball and the ratio of the radius of curvature of the ball screw groove to the diameter of the screw ball and the initial contact angle between the spline ball and the ball spline groove and the initial contact angle between the screw ball and the ball screw groove. The distance from the radial center of the screw shaft to the bottom of the ball screw groove is approximately the same as the distance from the center to the bottom of the ball spline groove. Splined ball screw.

[0044] This configuration allows for an improvement in the rated load because at least one set of ball diameter, radius of curvature, and initial contact angle are different values ​​from each other. Furthermore, because the distance from the radial center of the screw shaft to the bottom of the ball screw groove and the distance from the radial center of the screw shaft to the bottom of the ball spline groove are approximately the same, good operability can be obtained, and manufacturing costs can be reduced.

[0045] (2) The splined ball screw according to (1), wherein the diameter of the spline ball is larger than the diameter of the screw ball.

[0046] This configuration allows for an even greater increase in the rated load.

[0047] (3) The splined ball screw according to (1), wherein the ratio of the radius of curvature of the ball spline groove to the diameter of the spline ball is smaller than the ratio of the radius of curvature of the ball screw groove to the diameter of the screw ball.

[0048] This configuration allows for an even greater increase in the rated load.

[0049] (4) The splined ball screw according to (1), wherein the initial contact angle between the spline ball and the ball spline groove is greater than the initial contact angle between the screw ball and the ball screw groove.

[0050] This configuration allows for an even greater increase in the rated load.

[0051] (5) A screw shaft having a helical ball screw groove and a linear ball spline groove on its outer surface, A ball screw nut having a helical ball screw groove on its inner circumferential surface that faces the ball screw groove of the screw shaft, A number of screw balls are arranged to roll freely in a ball rolling path formed between the ball screw groove of the screw shaft and the ball screw groove of the ball screw nut, A ball spline nut having a linear ball spline groove on its inner circumferential surface that faces the ball spline groove of the screw shaft, A number of spline balls are rotatably disposed in a ball rolling path formed between the ball spline groove of the screw shaft and the ball spline groove of the ball spline nut, A splined ball screw equipped with, At least one set of the following is different in value: the diameter of the spline ball and the diameter of the screw ball, and the initial contact angle between the spline ball and the ball spline groove and the initial contact angle between the screw ball and the ball screw groove. The distance from the radial center of the screw shaft to the initial contact point of the screw ball with the ball screw groove is approximately the same as the distance from the center to the initial contact point of the spline ball with the ball spline groove. Splined ball screw.

[0052] This configuration allows for an improvement in the rated load by making at least one set of ball diameters and initial contact angles different from each other. Furthermore, since the distance from the radial center of the screw shaft to the initial contact point of the screw balls with the ball screw groove and the distance from the radial center of the screw shaft to the initial contact point of the spline balls with the ball spline groove are approximately the same, good operability can be obtained, and manufacturing costs can be reduced.

[0053] (6) The splined ball screw according to (5), wherein the diameter of the spline ball is larger than the diameter of the screw ball.

[0054] This configuration allows for an even greater increase in the rated load.

[0055] (7) The splined ball screw according to (5), wherein the initial contact angle between the spline ball and the ball spline groove is greater than the initial contact angle between the screw ball and the ball screw groove.

[0056] This configuration allows for an even greater increase in the rated load. [Explanation of Symbols]

[0057] 1, 101, 102 Screw shaft 1a, 54, 101a, 102a Ball screw groove 1b, 101b, 102b Ball spline groove 2 ball bearings 3c Inner groove 5 Spline balls 6. Ball for screws 10 Splined ball screws 20 Ball Spline Nuts 21, 51 Nut body 22A, 22B, 52A, 52B end caps 24, 55 Connecting passage 25, 56 Ball circulation path 26, 57 Ball rolling path 50 Ball screw nuts

Claims

1. A screw shaft having a helical ball screw groove and a linear ball spline groove on its outer surface, A ball screw nut having a helical ball screw groove on its inner circumferential surface that faces the ball screw groove of the screw shaft, A number of screw balls are arranged to roll freely in a ball rolling path formed between the ball screw groove of the screw shaft and the ball screw groove of the ball screw nut, A ball spline nut having a linear ball spline groove on its inner circumferential surface that faces the ball spline groove of the screw shaft, A number of spline balls are rotatably disposed in a ball rolling path formed between the ball spline groove of the screw shaft and the ball spline groove of the ball spline nut, A splined ball screw equipped with, At least one set of the following is different from each other: the diameter of the spline ball and the diameter of the screw ball; the ratio of the radius of curvature of the ball spline groove to the diameter of the spline ball and the ratio of the radius of curvature of the ball screw groove to the diameter of the screw ball and the initial contact angle between the spline ball and the ball spline groove and the initial contact angle between the screw ball and the ball screw groove. The distance from the radial center of the screw shaft to the bottom of the ball screw groove is approximately the same as the distance from the center to the bottom of the ball spline groove. Splined ball screw.

2. The splined ball screw according to claim 1, wherein the diameter of the spline ball is larger than the diameter of the screw ball.

3. The splined ball screw according to claim 1, wherein the ratio of the radius of curvature of the ball spline groove to the diameter of the spline ball is smaller than the ratio of the radius of curvature of the ball screw groove to the diameter of the screw ball.

4. The splined ball screw according to claim 1, wherein the initial contact angle between the spline ball and the ball spline groove is greater than the initial contact angle between the screw ball and the ball screw groove.

5. A screw shaft having a helical ball screw groove and a linear ball spline groove on its outer surface, A ball screw nut having a helical ball screw groove on its inner circumferential surface that faces the ball screw groove of the screw shaft, A number of screw balls are arranged to roll freely in a ball rolling path formed between the ball screw groove of the screw shaft and the ball screw groove of the ball screw nut, A ball spline nut having a linear ball spline groove on its inner circumferential surface that faces the ball spline groove of the screw shaft, A number of spline balls are rotatably disposed in a ball rolling path formed between the ball spline groove of the screw shaft and the ball spline groove of the ball spline nut, A splined ball screw equipped with, At least one set of the following is different in value: the diameter of the spline ball and the diameter of the screw ball, and the initial contact angle between the spline ball and the ball spline groove and the initial contact angle between the screw ball and the ball screw groove. The distance from the radial center of the screw shaft to the initial contact point of the screw ball with the ball screw groove is approximately the same as the distance from the center to the initial contact point of the spline ball with the ball spline groove. Splined ball screw.

6. The splined ball screw according to claim 5, wherein the diameter of the spline ball is larger than the diameter of the screw ball.

7. The splined ball screw according to claim 5, wherein the initial contact angle between the spline ball and the ball spline groove is greater than the initial contact angle between the screw ball and the ball screw groove.

Images