JP2021004640A - Screw mechanism, linear motion device, and actuator - Google Patents

Abstract

To prevent deterioration of lubrication performance due to depletion of a lubricant.SOLUTION: A screw mechanism includes: a shaft part in which a spiral screw is provided on an outer peripheral surface; a nut part in which a spiral screw which is directly or indirectly engaged with the spiral screw of the shaft part is provided on an inner peripheral surface; and a bearing part for receiving the shaft part in a rotatable manner being fitted with the spiral screw of the shaft part, arranged adjacent to the nut part, and made of a material from which a lubricant oozes.SELECTED DRAWING: Figure 1

Description

The present invention relates to screw mechanisms, linear motion devices, and actuators.

Conventionally, a linear motion device incorporating a screw mechanism and an actuator using such a linear motion device are known.

For example, in Patent Document 1, a ball that converts a rotational force input from a drive source such as an electric motor into an axial force (axial force) and outputs the ball by using a ball screw that converts a rotary motion into a linear motion. A screw type linear motion actuator is described.

Japanese Unexamined Patent Publication No. 2012-4250

In a screw mechanism incorporated in an actuator or a linear motion device, a solid or semi-solid lubricant such as grease is injected between a male screw and a female screw for the purpose of preventing wear and smooth operation of the screw. There are many.

However, since the male screw side and the female screw side slide each time the screw mechanism operates, the lubricant gradually comes out from between the male screw and the female screw, and there is a risk that the lubricant will eventually be exhausted. Especially for actuators that are used vertically, the lubricant drops down due to the influence of gravity, so the lubricant tends to run out. If the lubrication performance at the part where the male screw and the female screw slide is deteriorated, not only the performance of the linear motion device and the actuator is affected, but also the life itself is shortened. In addition, increasing maintenance to prevent deterioration of lubrication performance increases costs.
Therefore, an object of the present invention is to prevent deterioration of lubrication performance due to depletion of the lubricant.

In order to solve the above problem, in one aspect of the screw mechanism according to the present invention, a shaft portion provided with a spiral screw on the outer peripheral surface and a spiral screw directly or indirectly engaged with the spiral screw of the shaft portion are inside. A bearing portion made of a material that fits with the nut portion provided on the peripheral surface and the spiral screw of the shaft portion to rotatably receive the shaft portion, is arranged adjacent to the nut portion, and exudes a lubricant. And.
According to such a screw mechanism, since the lubricant is supplied from the bearing portion when the lubricant is reduced, it is possible to prevent the lubrication performance from being deteriorated due to the depletion of the lubricant.

In the screw mechanism, it is desirable that the bearing portion is in contact with and fixed to the nut portion. The bearing part can supply the lubricant even if there is a gap between it and the nut part, but if the bearing part is in contact with the nut part and fixed, the nut part will be compared to the case where there is a gap. Since the lubricant is supplied at a close position, the ability to maintain the lubricity between the nut portion and the shaft portion is high.

Further, in the screw mechanism, it is desirable that the bearing portion extends over two pitches or more of the spiral screw of the shaft portion, or in the bearing portion, the shaft portion can protrude from the nut portion at the maximum. It is also desirable that it extends beyond the distant part. By extending the bearing portion in this way, the lubricant supply capacity is improved, and the bearing portion also functions as a sealing member for suppressing the leakage of the lubricant.

Comparing the thickness of such a long bearing portion from the inner peripheral surface to the outer peripheral surface, the extension portion extending from the end portion along the shaft portion is better than the end portion on the nut portion side. It may be thin. If the extension portion is thin, it is less likely to interfere with other members when assembling, and the assembling property is excellent.

The screw mechanism is integrally or separately from the nut portion, extends from the nut portion along the shaft portion, and further includes a hollow portion containing the tip of the shaft portion and the bearing portion in a hollow internal space. In the bearing portion, the distance between the inner wall of the hollow portion and the tip of the bearing portion may be equal to or less than the diameter of the shaft portion in the direction extending from the nut portion along the shaft. Since the tip of the bearing portion extends close to the inner wall of the hollow portion, the lubricant leaking into the internal space of the hollow portion is absorbed by the bearing portion and returned to the nut portion.

Further, in the screw mechanism, the bearing portion may have a storage chamber for storing the lubricant on the outer peripheral side. Since the bearing portion has a storage chamber, the period during which the lubricant can be supplied is extended, and the lubricity can be maintained for a longer period of time.

In order to solve the above problems, the linear motion device according to the present invention includes the screw mechanism, one of the shaft portion and the nut portion receives a rotational driving force, and the other with respect to the one receives rotation of the other. Along with this, it moves linearly along one of the above. According to such a linear motion device, it is possible to prevent deterioration of lubrication performance due to depletion of the lubricant.

In order to solve the above problems, the actuator according to the present invention includes the screw mechanism, one of the shaft portion and the nut portion receives a rotational driving force, and the other with respect to the one is accompanied by the rotation of the one. Further includes an output shaft that moves linearly along one of the above and is connected to the other that moves linearly to output an axial force along the direction of the linear movement. According to such an actuator, it is possible to prevent deterioration of lubrication performance due to depletion of the lubricant.

According to the present invention, deterioration of lubrication performance due to depletion of lubricant can be prevented.

It is sectional drawing which shows 1st Embodiment of the actuator of this invention. It is sectional drawing which shows the 2nd Embodiment of the actuator of this invention. It is sectional drawing which shows the 3rd Embodiment of the actuator of this invention. It is sectional drawing which shows 4th Embodiment of the actuator of this invention. It is sectional drawing which shows 5th Embodiment of the actuator of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing a first embodiment of the actuator of the present invention. FIG. 1 shows a cross-sectional view cut along a plane along the center of the output shaft of the actuator. Also, for convenience of understanding, some elements are shown in appearance rather than in cross section.

The actuator 1 of the present embodiment converts a rotational force input from a drive source such as an electric motor into an axial force (force in a direction along the axis) by using a ball screw that converts a rotary motion into a linear motion. It is a ball screw type linear motion actuator that outputs.

The actuator 1 of the present embodiment includes a ball screw 10 that converts a rotational motion into a linear motion, a transmission gear 20 that receives a rotational force from a drive source such as an electric motor (not shown) and transmits the rotational force to the screw shaft 11 of the ball screw 10. It is connected to the nut 13 of the ball screw 10 and includes a hollow output shaft 30 that outputs the axial force converted from the rotational force by the ball screw 10.

Further, the actuator 1 includes a substantially tubular housing member 40 including a ball screw 10 and an output shaft 30, a ball bearing 51 for rotatably holding the screw shaft 11 of the ball screw 10, and a housing member 40 for the ball bearing 51. A bearing housing 50 fixed to the bearing housing 50 and an oil-impregnated bearing 60 fixed to the nut 13 are further provided. The transmission gear 20 is fixed to the screw shaft 11 with a gear fixing nut 21.
The combination of the ball screw 10 and the output shaft 30 corresponds to one embodiment of the screw mechanism of the present invention and also corresponds to one embodiment of the linear motion device of the present invention.

The screw shaft 11 of the ball screw 10 corresponds to an example of the shaft portion referred to in the present invention, and the nut 13 of the ball screw 10 corresponds to an example of the nut portion referred to in the present invention. In the screw mechanism, linear motion device, and actuator of the present invention, bolts and nuts in which spiral screws are directly engaged with each other may be used instead of ball screws that are indirectly engaged with each other via a ball. Further, the output shaft 30 corresponds to an example of the output shaft referred to in the present invention.

The ball screw 10 includes a screw shaft 11 having a spiral screw groove 11a on the outer peripheral surface, a nut 13 having a spiral screw groove 13a facing the screw groove 11a of the screw shaft 11 on the inner peripheral surface, and both screw grooves. A plurality of balls (not shown) rotatably loaded in the spiral ball rolling path formed by 11a and 13a, and a ball that circulates the ball from the end point of the ball rolling path to the starting point. It has a circulation path (not shown). That is, the screw shaft 11 and the nut 13 are indirectly engaged with each other via the ball.

A lubricant such as grease is injected between the outer peripheral surface of the screw shaft 11 and the inner peripheral surface of the nut 13 in order to prevent wear and maintain the smooth operation of the ball screw 10. The lubricant spreads in a film shape over the entire area between the outer peripheral surface of the screw shaft 11 and the inner peripheral surface of the nut 13.

The ball moves around the screw shaft 11 while moving in the ball rolling path to reach the end point of the ball rolling path, where the ball is scooped up from the ball rolling path and is one of the ball circulation paths. Enter the end. The ball that has entered the ball circulation path passes through the ball circulation path and reaches the other end of the ball circulation path, from which the ball is returned to the starting point of the ball rolling path.

The materials of the screw shaft 11, the nut 13, and the ball are not particularly limited, and general materials can be used, and examples thereof include metals such as steel and ceramics. Further, the cross-sectional shape of the screw grooves 11a and 13a may be an arc shape or a Gothic arc shape.

In the ball screw 10, when the nut 13 indirectly engaged with the ball and the screw shaft 11 are relatively rotationally moved, the screw shaft 11 and the nut 13 are brought together via the rolling of the ball. It moves linearly relative to the axial direction. Then, an endless ball passage is formed by the ball rolling path and the ball circulation path so that the ball rolling in the ball rolling path circulates infinitely in the endless ball passage. Therefore, the screw shaft 11 and the nut 13 can be continuously linearly moved. The linear movement direction of the nut 13 is determined by the rotation direction of the screw shaft 11.

The ball screw 10 and the output shaft 30 connected to the nut 13 are contained in the internal space of the housing member 40, and the screw shaft 11 and the output shaft 30 of the ball screw 10 are arranged coaxially with the housing member 40. ing. Further, the nut 13 is included in one end in the axial direction (the opening at the left end in FIG. 1) of the internal space 30a of the output shaft 30, and the nut 13 and the output shaft 30 are coaxially and nested.

The nut 13 is connected to the output shaft 30 by two connecting elements 53. When the nut 13 moves linearly, the axial force is transmitted to the output shaft 30 by the connecting element 53, and the output shaft 30 moves linearly together with the nut 3, so that the axial force is output from the output shaft 30. The output shaft 30 corresponds to an example of the hollow portion referred to in the present invention. In the example of FIG. 1, the output shaft 30 and the nut 13 are separate members connected by the connecting element 53, but the hollow portion referred to in the present invention may be integrally formed with the nut portion referred to in the present invention. Good.

A ring-shaped slide bearing 55 that orbits the output shaft 30 is provided between the output shaft 30 and the housing member 40 so as to cover the connecting element 53. The slide bearing 55 is fixed to the outer surface of the output shaft 30 and supports the output shaft 30 with respect to the housing member 40. The slide bearing 55 slides on the inner peripheral surface of the housing member 40 and moves in the housing member 40 in the axial direction together with the output shaft 30.

The oil-impregnated bearing 60 has a concavo-convex structure on the inner peripheral surface that fits with the thread groove 11a of the screw shaft 11, and the outer peripheral surface of the screw shaft 11 and the inner peripheral surface of the oil-impregnated bearing 60 are fitted and directly in contact with each other. There is. The oil-impregnated bearing 60 rotatably receives the screw shaft 11. The oil-impregnated bearing 60 is made of, for example, a porous resin, and the lubricant permeates the oil-impregnated bearing 60.

The lubricant that has penetrated into the oil-impregnated bearing 60 seeps out from the oil-impregnated bearing 60 when the temperature of the oil-impregnated bearing 60 rises. Therefore, for example, when the lubricant on the 11th peripheral surface of the screw shaft decreases and the friction increases, the temperature of the oil-impregnated bearing 60 rises due to the heat of the friction, and the lubricant exudes to lubricate the 11th peripheral surface of the screw shaft. The agent will be supplied. The supply of the lubricant by the oil-impregnated bearing 60 suppresses the depletion of the lubricant on the peripheral surface of the screw shaft 11, and the lubricity between the screw shaft 11 and the nut 13 is maintained for a long period of time. As a result, the maintenance interval such as lubrication of the actuator 1 is extended, and the life of the actuator 1 is also extended.

The oil-impregnated bearing 60 may have a gap between it and the nut 13, but it is desirable that the oil-impregnated bearing 60 is fixed in contact with the nut 13. When it is in contact with the nut 13, the lubricity is supplied in the immediate vicinity of the nut 13, so that the ability to maintain the lubricity between the screw shaft 11 and the nut 13 is high.

Next, the second embodiment of the present invention will be described. Since the second embodiment is the same as the first embodiment except that the structure of the oil-impregnated bearing 60 is different, the description focusing on the differences will be described below, and duplicate description will be omitted.
FIG. 2 is a cross-sectional view showing a second embodiment of the actuator of the present invention.

In the second embodiment, the length of the oil-impregnated bearing 60 is longer than the two pitches of the thread groove 11a of the screw shaft 11. Such a long oil-impregnated bearing 60 has not only the ability to supply the lubricant but also the sealing ability to suppress the leakage of the lubricant from the nut 13. Therefore, the lubricity between the screw shaft 11 and the nut 13 is maintained for a longer period of time, and the maintenance interval and the life of the actuator 1 are further extended.

Further, when comparing the thickness of the oil-impregnated bearing 60 of the second embodiment from the inner peripheral surface in contact with the screw shaft 11 to the outer peripheral surface facing the inner wall of the output shaft 30, the thickness of the main body 62 on the nut 13 side is compared. As a result, the thickness of the extension portion 61 extending in the axial direction from the main body portion 62 is thinner. Since the extension portion 61 is thin, the extension portion 61 is less likely to hit the edge of the opening of the output shaft 30 when the output shaft 30 is connected to the ball screw 10, and is excellent in assembling property.
It is desirable that the main body portion 62 has a length of one pitch or more of the screw groove 11a in the direction along the screw shaft 11. When the length of the main body 62 is one pitch or more, sufficient strength to support the entire oil-impregnated bearing 60 can be obtained.

Next, a third embodiment of the present invention will be described. The third embodiment is the same as the second embodiment except that the stroke of the ball screw and the structure of the oil-impregnated bearing 60 are different. Therefore, the following description focuses on the differences and omits duplicate explanations. To do.
FIG. 3 is a cross-sectional view showing a third embodiment of the actuator of the present invention.

In the actuator 1 of the third embodiment, the lengths of the screw shaft 11, the output shaft 30, and the housing member 40 of the ball screw 10 are shorter than those of the second embodiment. Therefore, the stroke of the ball screw 10 is short, and the output stroke of the actuator 1 is also short.
Further, in the third embodiment, the extension portion 61 of the oil-impregnated bearing 60 extends longer than that in the second embodiment, and the tip of the screw shaft 11 reaches when the screw shaft 11 penetrates the internal space 30a of the output shaft 30 most. The extension portion 61 extends further into the output shaft 30 than the position. Therefore, the oil-impregnated bearing 60 always comes into contact with the peripheral surface of the output shaft 30, and the lubricant is reliably supplied.

The gap d between the tip of the extension portion 61 protruding in the axial direction (that is, the tip on the right side of FIG. 3) and the portion of the inner wall of the output shaft 30 located in the axial direction is narrowed. Since the gap d is narrow, the oil-impregnated bearing 60 can come into contact with the lubricant leaking into the internal space 30a of the output shaft 30 and absorb the lubricant. The lubricant absorbed by the oil-impregnated bearing 60 is supplied to the peripheral surface of the screw shaft 11 and contributes to maintaining the lubricity between the screw shaft 11 and the nut 13. In order for such an absorption action to occur, it is desirable that the gap d is as narrow as possible, but the diameter of the screw shaft 11 or less is a guideline for the narrowness of the gap d.

When the diameter of the screw shaft 11 is large, the area of the peripheral surface of the screw shaft 11 is large, so that a large amount of lubricant is injected between the screw shaft 11 and the nut 13. Therefore, since many lubricants leak into the internal space 30a of the output shaft 30, the oil-impregnated bearing 60 can absorb the lubricant even if the gap d is large. On the other hand, when the diameter of the screw shaft 11 is small, the area of the peripheral surface of the screw shaft 11 is small, so that the amount of lubricant injected between the screw shaft 11 and the nut 13 is small. Therefore, since the amount of lubricant that leaks into the internal space 30a of the output shaft 30 is small, the oil-impregnated bearing 60 cannot absorb the lubricant unless the gap d is sufficiently narrow.

The structure in which the gap d between the oil-impregnated bearing 60 and the inner wall of the output shaft 30 is narrow is particularly suitable for the actuator 1 having a short output stroke. This is because when the output stroke of the actuator 1 is long, the length of the extension portion 61 of the oil-impregnated bearing 60 also becomes long, and the resistance force between the oil-impregnated bearing 60 and the screw shaft 11 increases.

Next, a fourth embodiment of the present invention will be described. Since the fourth embodiment is the same as the first embodiment except that the structure of the oil-impregnated bearing 60 is different, the description focusing on the differences will be described below, and duplicate description will be omitted.
FIG. 4 is a cross-sectional view showing a fourth embodiment of the actuator of the present invention.

In the fourth embodiment, a storage chamber 63 in which the lubricant is stored is provided on the outer peripheral surface side of the oil-impregnated bearing 60. The storage chamber 63 goes around the screw shaft 11 once, and the lubricant is stored in the storage chamber 63 in advance.

The lubricant stored in the storage chamber 63 is absorbed into the oil-impregnated bearing 60 when the lubricant is supplied from the oil-impregnated bearing 60 to the peripheral surface of the screw shaft 11 and the lubricant of the oil-impregnated bearing 60 is reduced. Therefore, since the storage chamber 63 is provided, the period during which the lubricant can be supplied by the oil-impregnated bearing 60 is extended, the lubricity between the screw shaft 11 and the nut 13 is maintained longer, and maintenance in the actuator 1 is performed. Intervals and lifespan are further extended.

Next, a fifth embodiment of the present invention will be described. Since the fifth embodiment is the same as the first embodiment except that it has an additional oil-impregnated bearing, the following description focuses on the differences and omits duplicate description.
FIG. 5 is a cross-sectional view showing a fifth embodiment of the actuator of the present invention.

In the fifth embodiment, an additional oil-impregnated bearing 64 is provided at a position separated in the axial direction from the oil-impregnated bearing 60 fixed to the nut 13. The additional oil-impregnated bearing 64 is fixed to the inner wall of the output shaft 30, and the distance between the oil-impregnated bearings 60 and 64 is constant. By providing the additional oil-impregnated bearing 64, the ability to supply the lubricant to the peripheral surface of the screw shaft 11 is increased. Further, the additional oil-impregnated bearing 64 serves to block the lubricant leaking from the nut 13 side and store it between the lubricating bearing 60 and the oil-impregnated bearing 60 on the nut 13 side. As a result, the lubricant is absorbed by the oil-impregnated bearings 60 and 64 and returned to the peripheral surface of the screw shaft 11.

In the description of each of the above embodiments, the screw mechanism incorporated in the linear motion device and the linear motion device applied to the actuator are exemplified, but the screw mechanism of the present invention is used for devices other than the linear motion device. It may be incorporated, and the linear motion device of the present invention may be applied to a device other than the actuator.
Further, in the description of each of the above embodiments, as an example of the linear motion device and the actuator, the one in which the screw shaft rotates and the nut moves linearly is shown, but the linear motion device of the present invention and the actuator of the present invention , The nut may rotate and the screw shaft may move linearly.

1 ... Actuator, 10 ... Ball screw, 20 ... Transmission gear, 30 ... Output shaft, 31 ... Through hole, 40 ... Housing member, 11 ... Screw shaft, 13 ... Nut, 60, 64 ... Oil bearing, 61 ... Extension, 62 ... Main body, 63 ... Storage room

Claims (9)

A shaft with a spiral screw on the outer peripheral surface and
A nut portion having a spiral screw directly or indirectly engaged with the spiral screw of the shaft portion provided on the inner peripheral surface, and a nut portion.
A bearing portion made of a material that fits with the spiral screw of the shaft portion to rotatably receive the shaft portion, is arranged next to the nut portion, and exudes a lubricant.
A screw mechanism characterized by being equipped with. The screw mechanism according to claim 1, wherein the bearing portion is in contact with and fixed to the nut portion. The screw mechanism according to claim 1 or 2, wherein the bearing portion extends over two pitches or more of the spiral screw of the shaft portion. The screw mechanism according to any one of claims 1 to 3, wherein the bearing portion extends beyond the farthest portion that can protrude from the nut portion. Comparing the thickness of the bearing portion from the inner peripheral surface to the outer peripheral surface, it is found that the extension portion extending from the end portion along the shaft portion is thinner than the end portion on the nut portion side. The screw mechanism according to claim 3 or 4. A hollow portion extending from the nut portion along the shaft portion and containing the tip of the shaft portion and the bearing portion is further provided in a hollow internal space, integrally or separately from the nut portion.
Claim 1 is characterized in that the distance between the inner wall of the hollow portion and the tip of the bearing portion is equal to or less than the diameter of the shaft portion in the direction extending from the nut portion along the shaft. The screw mechanism according to any one of 5 to 5. The screw mechanism according to any one of claims 1 to 6, wherein the bearing portion has a storage chamber for storing the lubricant on the outer peripheral side. The screw mechanism according to any one of claims 1 to 7 is provided.
A linear motion device, characterized in that one of the shaft portion and the nut portion receives a rotational driving force, and the other with respect to the one moves linearly along the one with the rotation of the one. The screw mechanism according to any one of claims 1 to 7 is provided.
One of the shaft portion and the nut portion receives a rotational driving force, and the other with respect to the one moves linearly along the one with the rotation of the one.
An actuator further provided with an output shaft that is connected to the other linearly moving and outputs an axial force along the direction of the linear movement.

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