JP7600831B2 - Ball screw seal and ball screw - Google Patents

Description

The present invention relates to a seal for a ball screw and a ball screw.

A ball screw comprises a cylindrical nut, a screw shaft that passes through the nut, and a number of balls arranged 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 the space 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.

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, forming a tightening portion that tightens the screw shaft. In addition, since a thread groove is provided on the outer periphery of the screw shaft, the tightening portion has an outer periphery contact portion that comes into contact with the outer periphery of the screw shaft, and a thread groove contact portion that comes into contact with the bottom surface of the thread groove. This tightening 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.

JP 2005-214407 A

It is desirable for seals to have a low rate of passage of foreign matter. In fact, most of the foreign matter that passes through a seal is foreign matter attached to the thread groove. This is because wrinkles occur in the seal when the seal is attached to a nut and the screw shaft is tightened with the seal. These wrinkles often overlap with the thread groove contact part in the circumferential direction of the seal. The wrinkles that occur in the thread groove contact part deform the thread groove contact part, causing a gap to form in part of the thread groove contact part. This is because foreign matter that adheres to the thread groove passes through the gap in the thread groove contact part. To address this, it is possible to increase the tightening margin around the entire circumference of the tightening margin to make it less likely for gaps to form in the thread groove contact part, but this would significantly reduce the sliding properties of the screw shaft.

The present disclosure has been made in consideration of the above problems, and aims to provide a ball screw seal and a ball screw that can significantly reduce the rate of foreign matter passing through while minimizing the deterioration of the sliding properties of the screw shaft.

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 a tightening portion for tightening the screw shaft, the tightening portion having an outer peripheral surface contact portion that contacts the outer peripheral surface of the screw shaft and a thread groove contact portion that contacts the bottom surface of the thread groove of the screw shaft, the outer peripheral surface contact portion having a constant tightening portion whose tightening amount is set to a first predetermined amount, and a pair of varying tightening portions that extend from both ends of the constant tightening portion and are continuous with the thread groove contact portion, and whose tightening amount changes as the screw groove contact portion moves in the circumferential direction, the tightening amount of the thread groove contact portion is set to a second predetermined amount that is greater than the first predetermined amount, and the tightening amount of the varying tightening portion increases from the first predetermined amount to the second predetermined amount as it moves from the constant tightening portion to the thread groove contact portion.

When the magnitude of the interference is considered to be based on the first predetermined value, the interference of the thread groove contact portion is larger than the second predetermined value. 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 conventional technology, the thread groove is the portion in which foreign matter passing through the seal is most prevalent. Given this, 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.

On the other hand, if the tightening margin 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 disclosed herein, both circumferential ends of the outer peripheral surface contact portion are provided with a tightening margin change portion in which the tightening margin increases as the tightening margin approaches the thread groove contact portion from the constant tightening portion. This prevents both circumferential ends of the outer peripheral surface contact portion from floating from the outer peripheral surface. Furthermore, the part of the tightening margin portion where the tightening margin is larger than the first predetermined value is limited to a part of the whole (the thread groove contact portion and the tightening margin change portion). This makes it possible to keep the deterioration of the slidability of the screw shaft low.

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

This means that the ball screw seal will have the same shape even if it is turned over, making it highly convenient.

The ball screw according to one aspect of the present disclosure includes a cylindrical nut, a screw shaft that passes through the nut, a number of balls that are arranged between the screw groove of the nut and the screw groove of the screw shaft, and the above-mentioned ball screw seal that is attached to the end face of the nut.

The ball screw disclosed herein significantly reduces the amount of foreign matter passing through the seal. It also prevents both circumferential ends of the seal's outer peripheral surface contact portion from floating off the outer peripheral surface. Furthermore, the deterioration of the sliding properties of the screw shaft is kept low.

The ball screw seal and ball screw disclosed herein can significantly reduce the rate of foreign matter passing through while minimizing the deterioration of the sliding properties of the screw shaft.

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 the ball screw seal according to the first embodiment. FIG. 3 is an enlarged view of a portion of the ball screw seal of FIG. FIG. 4 is a front view of a ball screw seal according to the second embodiment. 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 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 combined as appropriate.

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

(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.

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. Inside the recess 2c, a seal 10, an annular spacer 7, and a number of bolts 8 are provided. The spacer 7 is annular, and its entire circumference is in contact with the seal 10. Then, by tightening the bolts 8, the entire circumference of the seal 10 is tightened to the spacer 7, and the seal 10 is attached to the nut 2.

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 axis X and the boundary between the outer peripheral surface contact portion 15 and the screw groove contact portion 16. The imaginary lines L3 and L4 are lines that pass through the axis X and the boundary between the constant tightening portion 17 and the varying tightening portion 18, 19. 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.

As shown in FIG. 2, the seal 10 has a hole 11 in the center and is annular. The seal 10 is made of a resin material or rubber. The seal 10 has a circular shape centered on the axis X. The seal 10 has an outer circumferential portion 12 located radially outward from the imaginary circle C1, an inner circumferential portion 13 located between the imaginary circles C1 and C2, and a tightening portion 14 protruding radially inward from the inner circumferential portion 13.

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

The inner circumferential portion 13 is a portion that seals between the nut 2 and the screw shaft 3. The inner circumferential 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, etc., or if there is no installation error of the seal 10 relative to the nut 2, the radial inner end of the inner circumferential portion 13 overlaps with the outline of the screw shaft 3 (see imaginary circle C2).

The tightening 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 tightening 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 6a of the second thread groove 6.

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

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 screw groove 6. The variable 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 screw groove 6.

As shown in FIG. 3, the magnitude of the interference L1 of the constant interference portion 17 is set to a first predetermined value. The magnitude of the interference L2 of the thread groove contact portion 16 is set to a second predetermined value. This second predetermined value β is greater than the first predetermined value α. Therefore, even if wrinkles occur in the thread groove contact portion 16 and the thread groove contact portion 16 is deformed, a gap is unlikely to occur 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, the contact between the thread groove contact portion 16 and the bottom surface 6a of the second thread groove 6 tends to cause both circumferential ends (variable interference portions 18, 19) of the adjacent outer peripheral surface contact portions 15 to be lifted radially outward.

The size 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, which is continuous with the constant interference portion 17, toward the other end 18b, which is continuous 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.

The proportion of variable interference sections with a larger interference than the constant interference section 17 can be reduced, preventing a significant decrease in the sliding properties of the screw shaft.

Next, the effect of the seal 10 will be described. According to the seal 10 of embodiment 1, the sealability for the second thread groove 6 is improved by the thread groove contact portion 16. 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. From the above, the passage rate of foreign matter through the seal 10 of embodiment 1 is greatly reduced.

On the other hand, the part 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 sliding properties of the screw shaft 3 is kept small.

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 a tightening portion 14 for tightening the screw shaft 3. The tightening 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 tightening portion 17 in which the tightening amount L1 is set to a first predetermined amount, and a pair of tightening amount changing portions 18, 19 that extend from both ends of the constant tightening portion 17, are continuous with the thread groove contact portion 16, and the tightening amount L3 changes as the screw groove contact portion 16 moves in the circumferential direction. The tightening amount L2 of the thread groove contact portion 16 is set to a second predetermined amount that is greater than the first predetermined amount. The size L3 of the interference change portion 18, 19 increases from a first predetermined amount to a second predetermined amount as it moves from the constant interference portion 17 toward the thread groove contact portion 16.

This improves the sealing performance of 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 properties of the screw shaft 3 is kept low. Furthermore, although the interference change 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 form between the interference change portions 18, 19 and the outer peripheral surface 3a of the screw shaft 3, making it difficult for foreign matter to pass through.

In the ball screw seal 10 of the first embodiment, the pair of interference change portions 18, 19 occupy the same proportion of the outer peripheral surface contact portion 15 in the circumferential direction, and are linearly symmetrical with respect to an imaginary line L5 that passes through the circumferential midpoint 16a of the thread groove contact portion 16 and the axis X of the screw shaft 3. This allows the seal to have the same shape even when turned over, making it highly convenient.

(Embodiment 2)
4 is a front view of the ball screw seal 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 overlapping description will be omitted. The ball screw seal 10A of the second embodiment differs from the ball screw seal 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 ball screw seal 10A of the second embodiment is not symmetrical with respect to the imaginary line. However, the ball screw seal 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.

(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 first embodiment. The size of the interference of the constant interference portion 17 of Example 1 is α mm. The size of the interference of the thread groove contact portion 16 of Example 1 is α×2 mm. The interference change portions 18 and 19 of Example 1 increase in size from α mm to α×2 mm as they approach the thread groove contact portion 16. The angles θ2 and θ3 of the interference change portions 18 and 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. The size of the interference portion in Comparative Example 3 is α mm, and is formed uniformly around the entire circumference.

In the test method, lubricating oil containing foreign matter was applied to the outer circumference of the screw shaft that was exposed to the outside of the nut. The foreign matter was spattered powder of 200 μm or less. The nut was then rotated, and the screw shaft was reciprocated so that the part of the screw shaft on which the lubricating oil was applied passed through the seal. The amount of foreign matter adhering to the screw shaft was then measured, and the percentage of the foreign matter remaining was calculated. The measurement method involved taking images of the state before and after passing through the seal, and measuring the amount of adhesion. Figure 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 Figure 5.

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, the foreign matter passage rate is higher in Comparative Example 3 than in Comparative Example 2 because the seal in Comparative Example 3 has a tightening margin and is deformed, allowing foreign matter adhering to the second thread groove to pass through. Also, in Example 1, although it has a tightening margin, the tightening margin of the thread groove contact portion 16 is large and it has tightening margin changing portions 18 and 19, so it is believed that the foreign matter passage rate is significantly lower than in Comparative Example 3.

1 Ball screw 2 Nut
3 Screw shaft 3a Outer circumferential surface 4 Ball 5 First screw groove (screw groove)
6 Second screw groove (screw groove)
6a Bottom surface 7 Spacer 8 Bolt 10, 10A Seal (ball screw seal)
REFERENCE SIGNS LIST 11 hole 12 outer periphery 13 inner periphery 14 interference portion 15 outer periphery contact portion
16 Thread groove contact portion
17 Constant interference part
18, 19 Tightening margin change part

Claims (3)

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,
a 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. The pair of the interference change portions have the same circumferential proportion in the outer circumferential surface contact portion,
The seal for a ball screw according to claim 1 , wherein the seal is symmetrical with respect to an imaginary line passing through a circumferential midpoint of the thread groove contact portion and an axis of the screw shaft. A cylindrical nut;
A screw shaft that passes 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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