Ball screw seal and ball screw

Abstract

To provide a ball screw seal capable of greatly reducing a passage rate of a foreign substance and suppressing reduction of a slidable property of a screw shank, on the other hand, and a ball screw.SOLUTION: A ball screw seal is an annular ball screw seal which includes a hole in which a screw shank penetrates in a center and in which an edge of the hole becomes an interference where the screw shank is fastened. The interference includes an outer peripheral surface contact part in contact with an outer peripheral surface of the screw shank, and a thread groove contact part in contact with a bottom of a thread groove of the screw shank. The outer peripheral surface contact part includes an interference fixed portion where a size of the interference is set to a first predetermined amount, and a pair of interference varied portions which extends from both ends of the interference fixed portion and continued with the thread groove contact part, and in which a size of the interference is varied with movements in a circumferential direction. The size of the interference in the thread groove contact part is set to a second predetermined amount greater than the first predetermined amount, and the size of the interference in the interference varied portions is increased from the first predetermined amount to the second predetermined amount as directed from the interference fixed portion to the thread groove contact part.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a seal for a ball screw and a ball screw. [Background technology]

[0002] A ball screw includes a cylindrical nut, a screw shaft that passes through the nut, and a number of balls disposed inside the nut. In the ball screw of Patent Document 1 below, ball screw seals are attached to both end faces of the nut. These ball screw seals seal between the nut and the screw shaft. This makes it difficult for foreign matter to enter the inside of the nut. Furthermore, it makes it difficult for grease inside the nut to leak out. Hereinafter, the ball screw seal may be simply referred to as a seal or a ball screw seal.

[0003] The seal has a hole in the center through which the screw shaft passes, and is annular. The outer periphery of the seal is attached to the end face of the nut. The inner periphery of the seal seals between the nut and the screw shaft. The edge of the seal hole comes into contact with the screw shaft and serves as an interference portion that tightens the screw shaft. Since a screw groove is provided on the outer periphery of the screw shaft, the interference portion has an outer periphery contact portion that comes into contact with the outer periphery of the screw shaft and a screw groove contact portion that comes into contact with the bottom surface of the screw groove. This interference portion allows the seal to come into contact with the screw shaft even if there is a manufacturing error in the screw shaft or an installation error in the seal, making it difficult for foreign matter to enter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-214407 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is desirable for the seal to have a low rate of passage of foreign matter. In fact, most of the foreign matter that passes through the seal is foreign matter attached to the thread groove. This is because, when the seal is attached to the nut and the screw shaft is tightened with the seal, wrinkles are generated in the seal. These wrinkles often overlap with the thread groove contact portion in the circumferential direction of the seal. The wrinkles generated in the thread groove contact portion deform the thread groove contact portion, and a gap is generated in a part of the thread groove contact portion. This is because the foreign matter attached to the thread groove passes through the gap in the thread groove contact portion. In response to this, it is possible to increase the interference over the entire circumference of the interference portion to make it difficult for a gap to be generated in the thread groove contact portion, but this greatly reduces the slidability of the screw shaft.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a seal for a ball screw and a ball screw that can significantly reduce the rate at which foreign matter passes through, while minimizing the deterioration of the slidability of the screw shaft. [Means for solving the problem]

[0007] In order to achieve the above object, a ball screw seal according to one embodiment of the present disclosure is an annular ball screw seal having a hole in the center through which a screw shaft passes, and an edge of the hole serving as an interference portion for tightening the screw shaft, the interference portion having an outer peripheral surface contact portion that contacts an outer peripheral surface of the screw shaft and a thread groove contact portion that contacts a bottom surface of a thread groove of the screw shaft, the outer peripheral surface contact portion having a constant interference portion whose magnitude of interference is set to a first predetermined amount, and a pair of varying interference portions extending from both ends of the constant interference portion and continuing to the thread groove contact portion, the magnitude of the interference changing as the screw groove contact portion moves in the circumferential direction, the magnitude of the interference of the thread groove contact portions being set to a second predetermined amount greater than the first predetermined amount, and the magnitude of the interference of the varying interference portions increasing from the first predetermined amount to the second predetermined amount as the constant interference portion moves toward the thread groove contact portion.

[0008] When the magnitude of the interference is considered to be a first predetermined value as a reference, the interference of the thread groove contact portion is a second predetermined value, which is large. This makes it difficult for a gap to occur between the thread groove contact portion and the bottom surface of the thread groove, improving the sealing performance of the thread groove. Furthermore, according to the conventional technology, the thread groove is the portion in which foreign matter passing through the seal is most distributed. In this case, the seal of the present disclosure greatly reduces the amount of foreign matter passing through the seal. From the above, it is possible to greatly reduce the rate at which foreign matter passes through.

[0009] On the other hand, when the interference of only the thread groove contact portion is increased, both circumferential ends of the outer peripheral surface contact portion adjacent to the thread groove contact portion are lifted by the thread groove contact portion that contacts the bottom surface of the thread groove. As a result, both circumferential ends of the outer peripheral surface contact portion float from the outer peripheral surface of the thread groove, resulting in a gap. According to the ball screw seal of the present disclosure, both circumferential ends of the outer peripheral surface contact portion are provided with interference change portions in which the interference increases from the constant interference portion toward the thread groove contact portion. This prevents both circumferential ends of the outer peripheral surface contact portion from floating from the outer peripheral surface. Furthermore, the portion of the interference portion in which the interference is larger than the first predetermined value is limited to a part of the whole (the thread groove contact portion and the interference change portion). This makes it possible to suppress the deterioration of the slidability of the screw shaft.

[0010] As one aspect of the above-mentioned ball screw seal, it is preferable that the pair of interference change portions occupy the same circumferential proportion of the outer peripheral surface contact portion and are linearly symmetrical with respect to a virtual line passing through a circumferential midpoint of the thread groove contact portion and the axis of the screw shaft.

[0011] This provides great convenience since the ball screw seal maintains the same shape even when turned over.

[0012] Moreover, a ball screw according to one aspect of the present disclosure includes a cylindrical nut, a screw shaft passing through the nut, a plurality of balls arranged between the screw groove of the nut and the screw groove of the screw shaft, and the above-mentioned ball screw seal attached to an end face of the nut.

[0013] According to the ball screw of the present disclosure, the amount of foreign matter passing through the seal is greatly reduced. In addition, the problem of both ends of the seal in the circumferential direction in contact with the outer circumferential surface floating from the outer circumferential surface is prevented. Furthermore, the deterioration of the sliding properties of the screw shaft is suppressed to a low level. Effect of the Invention

[0014] The ball screw seal and ball screw disclosed herein can significantly reduce the rate at which foreign matter passes through, while keeping degradation of the slidability of the screw shaft to a minimum. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view of a ball screw in which the nut is cut along the axis of the ball screw. [Diagram 2] FIG. 2 is a front view of the ball screw seal according to the first embodiment. [Diagram 3] FIG. 3 is an enlarged view of a portion of the ball screw seal of FIG. [Figure 4] FIG. 4 is a front view of the ball screw seal according to the second embodiment. [Diagram 5] FIG. 5 is a graph showing the measurement results of the passage rate of foreign matter for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the following modes for carrying out the invention (hereinafter, referred to as embodiments). Furthermore, the components in the following embodiments include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the components disclosed in the following embodiments can be appropriately combined.

[0017] Fig. 1 is a cross-sectional view of a ball screw in which a nut is cut along the axis of the ball screw. Fig. 2 is a front view of a seal for a ball screw according to embodiment 1. Fig. 3 is an enlarged view of a portion of the seal for a ball screw in Fig. 2. Before describing the seal 10 of embodiment 1, a ball screw 1 to which the seal 10 is attached will be described.

[0018] (Embodiment 1) As shown in FIG. 1, the ball screw 1 includes a cylindrical nut 2, a screw shaft 3 penetrating the nut 2, and a plurality of balls 4 disposed inside the nut 2. A first screw groove 5 is provided on an inner peripheral surface 2a of the nut 2. A second screw groove 6 corresponding to the first screw groove 5 is provided on an outer peripheral surface 3a of the screw shaft 3. The balls 4 are disposed between the first screw groove 5 and the second screw groove 6. The second screw groove 6 may also be simply referred to as a screw groove.

[0019] When the nut 2 rotates around the axis X of the screw shaft 3, the balls 4 roll and the screw shaft 3 moves in a direction along the axis X. A recess 2c is provided on both end faces 2b of the nut 2. A seal 10, an annular spacer 7, and a plurality of bolts 8 are provided inside the recess 2c. The spacer 7 is annular, and the entire circumference of the spacer 7 is in contact with the seal 10. Then, when the bolt 8 is tightened, the entire circumference of the seal 10 is tightened to the spacer 7, and the seal 10 is attached to the nut 2.

[0020] Next, the seal of the first embodiment will be described with reference to FIG. 2. The imaginary circle C1 in FIG. 2 indicates the inner peripheral surface 2a of the nut 2. The imaginary circle C2 is the outline of the screw shaft 3 cut by a plane perpendicular to the axis X. A part of the imaginary circle C2 is an imaginary arc portion C3 that protrudes in an arc shape toward the inside in the radial direction. This imaginary arc portion C3 indicates the bottom surface of the second screw groove 6. Furthermore, the imaginary lines L1 and L2 are lines that pass through the boundary between the outer peripheral surface contact portion 15 and the screw groove contact portion 16 and the axis X. The imaginary lines L3 and L4 are lines that pass through the boundary between the constant interference portion 17 and the varying interference portions 18 and 19 and the axis X. The imaginary line L5 is a line that passes through the circumferential midpoint 16a of the screw groove contact portion 16 and the axis X.

[0021] As shown in Fig. 2, the seal 10 has a hole 11 provided in the center and is annular. The seal 10 is made of a resin material or rubber. The seal 10 has an outer shape that is circular about an axis X. The seal 10 includes an outer circumferential portion 12 located radially outward from an imaginary circle C1, an inner circumferential portion 13 located between the imaginary circles C1 and C2, and an interference portion 14 that protrudes radially inward from the inner circumferential portion 13.

[0022] When the seal 10 is attached to the nut 2, the outer peripheral portion 12 is a portion that is sandwiched between the spacer 7 and the nut 2. The outer peripheral portion 12 is also provided with a plurality of bolt holes 12a through which the shanks of the bolts 8 pass. Note that in the seal 10, the number and circumferential positions of the bolt holes 12a are not limited to the example shown in the first embodiment.

[0023] The inner peripheral portion 13 is a portion that seals between the nut 2 and the screw shaft 3. The inner peripheral portion 13 has an arc portion 13a that forms an arc shape centered on the axis X, and a protruding portion 13b that protrudes radially inward from the arc portion 13a. The arc portion 13a seals between the nut 2 and the outer peripheral surface 3a of the screw shaft 3. The protruding portion 13b seals between the nut 2 and the bottom surface 6a of the second screw groove 6. If there is no manufacturing error in the screw shaft 3 or the like, or if there is no mounting error of the seal 10 relative to the nut 2, the radial inner end of the inner peripheral portion 13 overlaps with the outline of the screw shaft 3 (see imaginary circle C2).

[0024] The interference portion 14 is formed by the edge of the hole 11 of the seal 10, and tightens the outer periphery of the screw shaft 3. The interference portion 14 includes an outer periphery surface contact portion 15 that contacts the outer periphery 3a of the screw shaft 3, and a thread groove contact portion 16 that contacts the bottom surface 6a of the second thread groove 6.

[0025] The outer peripheral surface contact portion 15 includes a constant interference portion 17 in which the magnitude of the interference is constant in the circumferential direction, and a pair of varying interference portions 18, 19 in which the magnitude of the interference changes in the circumferential direction. The pair of varying interference portions 18, 19 extend from both ends of the constant interference portion 17 and are continuous with the thread groove contact portion 16. In other words, the pair of varying interference portions 18, 19 are interposed between the constant interference portion 17 and the thread groove contact portion 16. The seal 10 is formed line-symmetrically with respect to the imaginary line L5. Therefore, the pair of varying interference portions 18, 19 have the same configuration, and the varying interference portion 18 will be described as a representative example, and the description of the varying interference portion 19 will be omitted.

[0026] The constant interference portion 17 is in contact with a portion of the outer circumferential surface 3a of the screw shaft 3 that is circumferentially separated from the second thread groove 6. The varying interference portion 18 is in contact with a portion of the outer circumferential surface 3a of the screw shaft 3 that is circumferentially adjacent to the second thread groove 6.

[0027] As shown in FIG. 3, the magnitude L1 of the interference of the constant interference portion 17 is set to a first predetermined value. The magnitude L2 of the interference of the thread groove contact portion 16 is set to a second predetermined value. This second predetermined value β is larger than the first predetermined value α. Therefore, even if wrinkles are generated in the thread groove contact portion 16 and the thread groove contact portion 16 is deformed, a gap is unlikely to be generated between the thread groove contact portion 16 and the bottom surface 6a of the second thread groove 6. In addition, since the interference of the thread groove contact portion 16 is large, both circumferential ends (interference changing portions 18, 19) of the adjacent outer peripheral surface contact portions 15 are likely to be lifted outward in the radial direction due to contact between the thread groove contact portion 16 and the bottom surface 6a of the second thread groove 6.

[0028] The magnitude L3 of the interference of the interference changing portion 18 increases from a first predetermined value to a second predetermined value from one end 18a continuing with the constant interference portion 17 toward the other end 18b continuing with the thread groove contact portion 16. In other words, the amount of protrusion of the interference changing portion 18 radially inward increases from one end 18a toward the other end 18b. Therefore, even if the interference changing portion 18 is lifted by the thread groove contact portion 16, a gap is unlikely to occur between the interference changing portion 18 and the outer peripheral surface 3a of the screw shaft 3.

[0029] Since the ratio of the variable interference portion, which has a larger interference than the constant interference portion 17, can be reduced, a significant decrease in the slidability of the screw shaft can be suppressed.

[0030] Next, the effects of the seal 10 will be described. According to the seal 10 of embodiment 1, the thread groove contact portion 16 improves the sealing performance for the second thread groove 6. Furthermore, according to the conventional technology, the second thread groove 6 is the portion to which most of the foreign matter passing through the seal 10 adheres. Therefore, according to the seal 10 of embodiment 1, the amount of foreign matter that adheres to the second thread groove 6 and passes through the seal 10 is greatly reduced. For the above reasons, the passage rate of foreign matter through the seal 10 of embodiment 1 is greatly reduced.

[0031] On the other hand, the portion of the interference portion 14 where the interference is greater than the first predetermined value is limited to a part of the whole (the thread groove contact portion 16 and the interference change portions 18, 19). Therefore, the decrease in the slidability of the screw shaft 3 is kept small.

[0032] As described above, the seal 10 for a ball screw of the first embodiment is an annular seal 10 for a ball screw having a hole 11 through which the screw shaft 3 passes in the center, and an edge of the hole 11 serving as an interference portion 14 for tightening the screw shaft 3. The interference portion 14 has an outer peripheral surface contact portion 15 that contacts the outer peripheral surface 3a of the screw shaft 3, and a thread groove contact portion 16 that contacts the bottom surface of the thread groove of the screw shaft. The outer peripheral surface contact portion 15 has a constant interference portion 17 in which the magnitude L1 of the interference is set to a first predetermined amount, and a pair of varying interference portions 18, 19 that extend from both ends of the constant interference portion 17, are continuous with the thread groove contact portion 16, and the magnitude L3 of the interference changes as the screw shaft moves in the circumferential direction. The magnitude L2 of the interference of the thread groove contact portion 16 is set to a second predetermined amount that is larger than the first predetermined amount. The magnitude L3 of the interference of the varying interference portions 18, 19 increases from a first predetermined amount to a second predetermined amount from the constant interference portion 17 toward the thread groove contact portion 16.

[0033] This improves the sealing performance for the second thread groove 6, greatly reducing the rate at which foreign matter passes through. Also, the portion where the interference is increased is only a part of the whole, and the decrease in the sliding performance of the threaded shaft 3 is kept low. Furthermore, although the interference changing portions 18, 19 are raised by the thread groove contact portion 16, the interference increases toward the thread groove contact portion. Therefore, gaps are unlikely to occur between the interference changing portions 18, 19 and the outer peripheral surface 3a of the threaded shaft 3, making it difficult for foreign matter to pass through.

[0034] In the seal 10 for a ball screw in the first embodiment, the pair of interference change portions 18, 19 occupy the same proportion in the circumferential direction of the outer circumferential surface contact portion 15, and are line symmetrical with respect to an imaginary line L5 that passes through a circumferential midpoint 16a of the thread groove contact portion 16 and the axis X of the screw shaft 3. This provides high convenience since the shape remains the same even when the seal is turned over.

[0035] (Embodiment 2) FIG. 4 is a front view of the seal for a ball screw according to the second embodiment. In the following description, the same components as those described in the first embodiment are denoted by the same reference numerals, and the duplicated description will be omitted. The seal for a ball screw 10A of the second embodiment differs from the seal for a ball screw 10 of the second embodiment in that the angle θ3 of the interference change portion 19A is larger than the angle θ2 of the interference change portion 18A. That is, the seal for a ball screw 10A of the second embodiment is not symmetrical with respect to the imaginary line. However, the seal for a ball screw 10A of the second embodiment can also significantly reduce the passage rate of foreign matter while suppressing the deterioration of the slidability of the screw shaft 3.

[0036] (Example) A test was performed on the passage rate of foreign matter for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Example 1 is the seal 10 shown in the embodiment 1. The magnitude of the interference of the constant interference portion 17 of Example 1 is α mm. The magnitude of the interference of the thread groove contact portion 16 of Example 1 is α × 2 mm. The interference change portions 18, 19 of Example 1 increase in magnitude from α mm to α × 2 mm as they approach the thread groove contact portion 16. The angles θ2, θ3 of the interference change portions 18, 19 are 10°. Comparative Example 1 is a seal that has an outer periphery portion 12 but does not have an inner periphery portion 13 and an interference portion 14. Therefore, Comparative Example 1 has an annular gap between the outer periphery of the screw shaft. Comparative Example 2 is a seal that has an outer periphery portion 12 and an inner periphery portion 13, but does not have an interference portion 14. Comparative Example 3 is a seal that has an outer periphery portion 12, an inner periphery portion 13, and an interference portion 14. Moreover, the size of the interference portion in Comparative Example 3 is α mm, and is formed uniformly over the entire circumference.

[0037] In the test method, lubricating oil containing foreign matter was applied to the outer periphery of the screw shaft that was exposed to the outside of the nut. The foreign matter was sputtered powder of 200 μm or less. The nut was rotated, and the screw shaft was reciprocated so that the part of the screw shaft to which the lubricating oil was applied passed through the seal. The amount of foreign matter adhering to the screw shaft was measured, and the percentage of the foreign matter remaining was calculated. As a measurement method, the state before and after passing through the seal were photographed, and the amount of adhesion was measured. FIG. 5 is a graph showing the measurement results of the passage rate of foreign matter for Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. The measurement results are shown in FIG. 5.

[0038] In Example 1, the foreign matter passage rate was 13%. In Comparative Example 1, the foreign matter passage rate was 50%. In Comparative Example 2, the foreign matter passage rate was 18%. In Comparative Example 3, the foreign matter passage rate was 24%. Considering this, it is considered that the reason why the foreign matter passage rate is higher in Comparative Example 3 than in Comparative Example 2 is that the seal in Comparative Example 3 is deformed due to the interference, and foreign matter adhering to the second thread groove passes through. Also, in Example 1, although there is an interference portion, the interference of the thread groove contact portion 16 is large and there are interference change portions 18 and 19, so it is considered that the foreign matter passage rate is significantly lower than in Comparative Example 3. [Explanation of symbols]

[0039] 1. Ball screw 2 Nuts 3 Screw shaft 3a Outer surface 4. Ball 5 First screw groove (screw groove) 6 Second screw groove (screw groove) 6a Bottom 7 Spacer 8 Volts 10, 10A Seal (Ball screw seal) 11 holes 12 Outer periphery 13 Inner circumference 14 Interference 15 Outer periphery contact part 16 Thread groove contact area 17 Constant interference 18, 19 Tightening margin change area

Claims

1. A ring-shaped ball screw seal having a hole in the center through which a screw shaft passes, and an edge of the hole serving as a tightening portion for tightening the screw shaft, The interference portion is An outer peripheral surface contact portion that contacts the outer peripheral surface of the screw shaft; A thread groove contact portion that contacts a bottom surface of the thread groove of the screw shaft; having The outer circumferential surface contact portion is A constant interference portion in which the magnitude of the interference is set to a first predetermined amount; a pair of varying interference portions extending from both ends of the constant interference portion and continuing to the thread groove contact portion, the magnitude of the interference changing as the thread groove moves in the circumferential direction; having The magnitude of the interference of the thread groove contact portion is set to a second predetermined amount that is greater than the first predetermined amount, The magnitude of the interference of the varying interference portion increases from the first predetermined amount to the second predetermined amount from the constant interference portion toward the thread groove contact portion. Ball screw seal.

2. The pair of the interference change portions have the same circumferential proportion in the outer circumferential surface contact portion, The thread groove contact portion is symmetrical with respect to a virtual line passing through a circumferential midpoint of the thread groove contact portion and the axis of the thread shaft. The seal for a ball screw according to claim 1.

3. A cylindrical nut; A screw shaft passing through the nut; A plurality of balls arranged between the screw groove of the nut and the screw groove of the screw shaft; The ball screw seal according to claim 1 or 2, which is attached to an end surface of the nut; A ball screw comprising:

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