JP2000161461A - Ball screw type linear actuator - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To improve the durability and extend the service life and to realize a clean and compact structure. A ball nut (9) screwed to a ball screw shaft (1) via a plurality of balls (12) and an output shaft member (17) having a base end coupled to the ball nut (9) are arranged inside a casing (2). I do. One end of the ball screw shaft 1 is rotatably supported by a rolling bearing 4 provided inside the first opening 3, and the outer peripheral surface of the output shaft member 17 is fixed to the inner peripheral surface of the second opening 20. The sliding bearing 21 is supported movably in the axial direction. A predetermined amount of lubricating oil is sealed inside the casing 2, and further between the inner peripheral surface of the first opening 3 and the outer peripheral surface of the ball screw shaft 1 and the inner peripheral surface of the second opening 20. And the outer peripheral surface of the output shaft member 17 are sealed by oil seals 23, 23, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The ball screw type linear actuator according to the present invention is incorporated into various machine devices such as a machine tool such as a machining center, a molding machine such as an injection molding machine or a press machine, and is designed to reduce a relatively small input torque. It is used as a power converter for obtaining an output in a large linear motion direction.

[0002]

2. Description of the Related Art A ball screw type linear actuator has been widely used as a power conversion device for obtaining an output in a large linear motion direction from a relatively small input torque by utilizing a boosting function of a ball screw. When using such a ball screw type linear actuator, a relatively small input torque from an electric motor or the like as a driving source is input to a ball screw shaft (or a ball nut) constituting a ball screw via a speed reduction mechanism. Then, the ball screw shaft (or ball nut) is rotated in a desired direction. Then, the rotational motion of the ball screw shaft (or ball nut) is converted into a linear motion of a ball nut (or ball screw shaft) screwed to the ball screw shaft (or ball nut) via a plurality of balls. Convert. Then, the linear motion of the ball nut (or the ball screw shaft) is taken out from the output shaft member (or directly from the ball screw shaft).

In the case of the above-described ball screw type linear actuator, lubricating oil or grease is often used as a lubricant for lubricating a threaded portion between the ball screw shaft and the ball nut. When lubricating oil is used as the lubricant, the lubricating oil is supplied to the threaded portion by a method such as dripping lubrication or oil bath lubrication. However, when this lubricating oil is used, the lubricating oil is scattered around with the rotation of the ball screw shaft (or ball nut). Causes inconvenience such as soiling. Therefore, in order to avoid such inconveniences, grease that is less likely to scatter around than the lubricating oil is often used as the lubricant.

[0004]

In recent years, applications of the ball screw type linear actuator as described above under high load have been expanding. That is, with the recent electrification of various mechanical devices, for example, in the case of an injection molding machine or a press machine, in order to obtain a large power in a linear motion direction, a conventional hydraulic cylinder is used instead. Therefore, a ball screw type linear actuator using an electric motor as a driving source is often used. For example, in the case of an injection molding machine, there is an example in which the ball screw linear actuator is used for controlling a force exceeding 50 tons. By the way, in the case of a ball screw type linear actuator that is used by being incorporated in such an injection molding machine or the like, the lubricant for lubricating the threaded portion between the ball screw shaft and the ball nut as described above is more lubricated than grease. It is preferable to use oil. Hereinafter, the reason will be described.

FIG. 6 shows the relationship between the rotational speed of the ball screw shaft and the dynamic friction torque (rotational resistance) acting on the ball screw shaft when lubricating oil and grease are used as the lubricant. ing. In FIG. 6, solid lines a to c
Shows three examples of commonly used lubricating oils, and similarly, a broken line d shows one example of commonly used grease. As is clear from FIG. 6, the magnitude of the dynamic friction torque at the time of starting the ball screw shaft and at the time of low-speed rotation is substantially the same when lubricating oil is used as a lubricant and when grease is used. However,
As the rotational speed of the ball screw shaft increases, the dynamic friction torque increases linearly when grease is used as a lubricant, but hardly changes when lubricating oil is used. . Accordingly, when the ball screw shaft is used while rotating at a high speed, it is preferable to use a lubricating oil as the lubricant in order to reduce the rotation resistance of the ball screw shaft. On the other hand, in the case of the ball screw type linear actuator incorporated in the above-described injection molding machine or the like, during operation, the ball screw shaft is rotated at a high speed in order to quickly open and close and press the mold constituting the injection molding machine and the like. There is a need. Therefore, in the case of a ball screw type linear actuator incorporated in the injection molding machine or the like, it is preferable to use lubricating oil as the lubricant.

When the ball screw shaft is rotated at a high speed as described above, grease may be scattered around with the rotation of the ball screw shaft. The amount of grease attached to the ball screw shaft is reduced. On the other hand, in the case of the ball screw type linear actuator incorporated in the injection molding machine or the like, since the opening and closing and pressing of the mold are repeated during use, the relative displacement between the ball screw shaft and the ball nut in the axial direction is short and reciprocating. And the reciprocating displacement is repeated.
Therefore, as described above, the amount of grease adhered to the hole screw shaft decreases, and when the lubrication of the screw portion between the ball screw shaft and the ball nut is not performed well, these ball screw shaft and ball nut, The life of a plurality of balls that transmit power between these two members is reduced. On the other hand, in the case of lubricating oil, the lubricating oil can be continuously supplied to the screwed portion by the above-described method such as drop oiling or oil bath oiling. For this reason, lubrication of this threaded portion can be favorably performed over a long period of time. Therefore, from such a viewpoint, it is preferable to use a lubricating oil as the lubricant.

As described above, in the case of a ball screw type linear actuator used by being incorporated in an injection molding machine or the like, from the viewpoint of lubrication performance, it is better to use lubricating oil than grease as the above-mentioned lubricant. It is preferable. However, as described above, when using the lubricating oil as the lubricant, the lubricating oil scatters around with the rotation of the ball screw shaft, so depending on the environment in which the ball screw linear actuator is installed, Inconveniences such as soiling the surroundings occur. Therefore, regardless of the environment in which the ball screw type linear actuator is installed, it is desired to realize a structure that does not cause the above-described inconvenience even when lubricating oil is used as the lubricant. The ball screw type linear actuator of the present invention was invented in view of the above-mentioned circumstances.

[0008]

A ball screw linear actuator according to the present invention comprises a casing and first and second openings provided at both ends in the axial direction of the casing so as to communicate with the inside and outside of the casing. Part, with one end for receiving the transmission of rotational force from the drive source protruding outside the casing through the first opening of the one,
A ball screw shaft rotatably supported inside the casing, and an inner peripheral surface of the first opening and an outer peripheral portion of the intermediate portion of the ball screw shaft for rotatably supporting the ball screw shaft inside the casing. A first bearing provided between the first bearing and the surface;
A first helical groove having an arc-shaped cross section formed on the outer peripheral surface of a portion of the ball screw shaft disposed inside the casing relative to the first bearing, and a first helical groove having an arc-shaped cross section on the inner peripheral surface. A ball nut having two helical grooves, and displaceable in the axial direction inside the casing; and a plurality of balls rotatably provided between the first helical groove and the second helical groove. By connecting the base end to the ball nut while the center axis is disposed so as to coincide with or be parallel to the center axis of the ball nut, the ball nut can be displaced in the axial direction together with the ball nut. An output shaft member that can move in and out of the casing through the second opening with displacement in the direction, and an inner peripheral surface of the second opening portion for supporting the output shaft member with respect to the casing so as to be movable in the axial direction. Between the outer circumference of the output shaft member It comprises a second bearing provided on the inner side of the casing, and a lubricant oil sealed by an amount less than the gap space volume within the casing. Further, a portion between the inner peripheral surface of the first opening and the outer peripheral surface of the intermediate portion of the ball screw shaft, with respect to the inner space of the casing, outside the first bearing, and the second opening. The portion between the inner peripheral surface of the output shaft member and the outer peripheral surface of the output shaft member, the outer portion of the inner space of the casing with respect to the inner space of the casing, is sealed with an oil seal. The sealed lubricating oil is prevented from leaking outside the casing.

[0009]

In the case of the ball screw type linear actuator of the present invention constructed as described above, a lubricating oil sealed inside the casing is used as a lubricant for lubricating a threaded portion between the ball screw shaft and the ball nut. For this reason, even when the ball screw shaft is rotated at a high speed while a high load is applied to the screw portion, and the ball nut screwed with the ball screw shaft is reciprocated in a short range in the axial direction. ,
The resistance (dynamic friction torque) to the high-speed rotation of the ball screw shaft can be kept small, and the lubricating state at the threaded portion can be favorably maintained for a long period of time. As a result, the lubricating state can be maintained satisfactorily, so that a highly durable and long-life ball screw linear actuator can be realized.

Further, in the case of the present invention, the ball screw shaft which rotates during use is covered by a casing. For this reason, the lubricating oil does not scatter around with the rotation of the ball screw shaft. Further, a portion between the inner peripheral surface of the first opening communicating with the inside and the outside of the casing and the outer peripheral surface of the ball screw shaft, and an inner peripheral surface of the second opening communicating with the inside and the outside of the casing and the output shaft member. The portion between the outer peripheral surface and the outer peripheral surface is sealed by an oil seal. For this reason, the lubricating oil sealed inside the casing does not leak out of the casing. As a result, it is possible to eliminate the inconvenience that occurs when using a lubricating oil as a lubricant with the conventional structure, that is, the inconvenience of contaminating the surroundings depending on the installation environment. An actuator can be realized.

[0011]

1 and 2 show a first embodiment of the present invention. A ball screw shaft 1 that rotates based on an input torque from an electric motor (not shown) as a driving source is rotatably supported inside a cylindrical casing 2. That is, a part of the ball screw shaft 1 is inserted into the first opening 3 provided at one axial end (the left end in FIG. 1) of the casing 2, and a part of the intermediate portion is provided inside the casing 2. It is arranged in. A rolling bearing 4 as a first bearing is provided between the outer peripheral surface of the intermediate portion of the ball screw shaft 1 and the inner peripheral surface of the first opening 3. The outer end face (the left end face in FIG. 1) of the outer ring 5 that constitutes the rolling bearing 4 has a stepped surface 6 formed on the inner peripheral surface of the first through hole 3.
The inner end surface of the inner ring 7 (the right end surface in FIG. 1) is a step surface 8 formed on the outer peripheral surface of the ball screw shaft 1 near one end.
To each other. In the illustrated example, an angular type ball bearing capable of supporting a radial load and a thrust load is used as the rolling bearing 4.

A ball nut 9 is provided inside the casing 2 around the ball screw shaft 1 so as to be displaceable in the axial direction. A first helical groove 10 having an arc-shaped cross section formed on a part of the outer peripheral surface of the ball screw shaft 1 located inside the casing 2 with respect to the rolling bearing 4, A plurality of balls 12, 1 and 2 are provided between the second spiral groove 11 having an arc-shaped cross section formed on the peripheral surface.
2 is provided so as to roll freely, and the ball nut 9 can be displaced in the axial direction based on the rotation of the ball screw shaft 1. Further, a flat surface 13 is formed on a part of the outer peripheral surface of the ball nut 9, and ends of a pair of feed holes (not shown) for allowing the balls 12 to pass through the flat surface 13. Is opened. The end openings of the two feed holes are communicated with each other by the circulation tube 14. The pair of feed holes and the circulation tube 14 are connected to the balls 12, 1, which have moved to one end of the second spiral groove 11.
2 is returned to the other end of the second spiral groove 11 to circulate the plurality of balls 12, thereby constituting a circulation mechanism.

In the case of the present embodiment, the ball nut 9 is placed inside the casing 2 with a small clearance extending over the entire circumference between the outer peripheral surface of the ball nut 9 and the inner peripheral surface of the casing 2. And it is fitted. In addition, a plurality of locations in the circumferential direction of the outer peripheral surface of the ball nut 9 (three locations in the illustrated example).
, Grooves 15, 15 are formed over the entire length in the axial direction, and portions surrounded by these grooves 15, 15 and the inner peripheral surface of the casing 2 are passages 16, 16. When the ball nut 9 is displaced in the axial direction,
As described later, the lubricating oil sealed in the casing 2 can move to both sides of the ball nut 9 through these passages 16, 16. The circulation tube 1
The gap formed between the flat surface 13 provided with the inner surface 4 and the inner peripheral surface of the casing 2 also functions as a passage 16 for flowing the lubricating oil.

The output shaft member 17 is connected to one end (the right end in FIG. 1) of the ball nut 9 by connecting the base end (the left end in FIG. 1) of the output shaft member 17. The ball nut 9 is displaced in the axial direction together with the ball nut 9. That is, the output shaft member 17 has a tip (the right end in FIG. 1).
Is formed in a cylindrical shape, and a male screw portion 18 formed on an outer peripheral surface of a base end portion is screwed and fixed to a female screw portion 19 formed on an inner peripheral surface of one end portion of the ball nut 9. In this state, a part of the ball screw shaft 1 is made to enter the inside of the output shaft member 17. The output shaft member 17
Is projected outside the casing 2 through a second opening 20 provided at the other axial end (the right end in FIG. 1) of the casing 2 and a part of the outer peripheral surface of the output shaft member 17. Is movably supported in the axial direction by a sliding bearing 21 as a second bearing fixed to the inner peripheral surface of the second through hole 20. A passage 22 communicating between the inner peripheral surface and the outer peripheral surface of the output shaft member 17 is formed near the base end of the output shaft member 17. When the output shaft member 17 is displaced in the axial direction, the lubricating oil can move inside and outside the output shaft member 17 through the passage 22.

A predetermined amount of lubricating oil for lubricating the threaded portion between the ball screw shaft 1 and the ball nut 9 is provided inside the casing 2 so as to be smaller than the clearance space volume in the casing 2. {For example, a state in which the amount of protrusion of the output shaft member 17 from the casing 2 is minimized (FIG. 1)
In this state, the ball nut 9 is moved to the leftmost position in the casing 2).
Only about 60% of the volume of the gap space inside is enclosed.
If the amount of such lubricating oil is too large, the dynamic torque (rotational resistance) of the ball screw shaft 1 based on the agitation resistance of the lubricating oil increases during the operation described below, and smooth operation cannot be performed. In addition, when the output shaft member 17 is pulled into the casing 2, the pressure inside the casing 2 increases significantly. For this reason, the amount of the lubricating oil charged is such that the dynamic torque of the ball screw shaft 1 does not increase and the pressure fluctuation in the casing 2 does not become remarkable.
It is determined by appropriate adjustment. Further, a portion outside the rolling bearing 4 (left side in FIG. 1) between the inner peripheral surface of the first opening 3 and the outer peripheral surface near one end of the ball screw shaft 1, and the second opening 20 Oil seals 23 are provided between the inner peripheral surface of the shaft and the outer peripheral surface of the output shaft member 17 on the outer side of the slide bearing 21 (on the right side in FIG. 1). Intrusion prevention and this casing 2
It prevents leakage of lubricating oil inside. The sealing performance of each of the oil seals 23 and the amount of the lubricating oil filled therein is determined by the displacement of the output shaft member 17 irrespective of the pressure fluctuation in the casing 2 and the suction of the foreign matter into the casing 2. Set the range so that lubricating oil leakage can be prevented.

When using the ball screw type linear actuator of the present invention configured as described above, an input torque from an electric motor (not shown) is input to the ball screw shaft 1 directly or via a speed reduction mechanism (not shown). Ball screw shaft 1
Is rotated in the desired direction. As a result, the ball nut 9 screwed to the ball screw shaft 1 via the plurality of balls 12 is displaced in a desired direction in the axial direction. As a result, a large output in the linear motion direction can be taken out from the output shaft member 17 connected to the ball nut 9.
When the ball nut 9 and the output shaft member 17 are displaced in the axial direction in the casing 2 as described above,
The lubricating oil enclosed therein moves through the passages 16 and 22 on both axial sides of the ball nut 9 and inside and outside the output shaft member 17. At the same time, the lubricating oil is fed into a threaded portion between the ball screw shaft 1 and the ball nut 9 from an appropriate axial direction. For this reason, lubrication of this threaded part can be performed appropriately. In the case of the present example, the rolling bearings 24, 24 that constitute the rolling bearing 4 provided inside the first opening 3, and the sliding bearing 21 provided inside the second opening 20. The peripheral surface portion (the portion that slidably supports the outer peripheral surface of the output shaft member 17) is also made lubricable by the lubricating oil sealed in the casing 2. For this reason, a seal ring is not provided in a portion closer to the center of the casing 2 than the space in which the rolling elements 24 of the rolling bearing 4 are installed.

In the case of the ball screw type linear actuator of the present embodiment, which is constructed and operates as described above, a lubricating oil sealed in the casing 2 is used as a lubricant for lubricating the threaded portion between the ball screw shaft 1 and the ball nut 9. You are using Because of this,
When the ball screw type linear actuator of this example is used in a state where it is incorporated in an injection molding machine or the like as described above,
The ball screw shaft 1 is rotated at a high speed in a state where a high load is applied to the threaded portion between the ball screw shaft 1 and the ball nut 9, and the ball nut 9 screwed with the ball screw shaft 1 is moved in the axial direction. Even when the ball screw shaft 1 is reciprocated within a short range, the resistance (dynamic friction torque) against the high speed rotation of the ball screw shaft 1 can be kept small, and the lubricating state at the threaded portion can be favorably maintained for a long period of time. As a result of maintaining a good lubrication state in this manner, a highly durable and long-life ball screw linear actuator can be realized.

Further, in the case of the present invention, the ball screw shaft 1 which rotates during use is covered by the casing 2 described above. For this reason, the lubricating oil does not scatter around as the ball screw shaft 1 rotates. Also, a portion between the inner peripheral surface of the first opening 3 communicating with the inside and the outside of the casing 2 and the outer peripheral surface of the ball screw shaft 1, and an inner peripheral surface of the second opening 20 communicating the inside and the outside of the casing 2 The portion between the output shaft member 17 and the outer peripheral surface is sealed by oil seals 23, 23, respectively. For this reason, the lubricating oil sealed inside the casing 2 does not leak outside the casing 2. As a result, with the conventional structure, the disadvantage that occurs when using the lubricating oil as the lubricant, that is, the disadvantage that the surroundings are soiled depending on the installation environment can be solved,
A clean and compact ball screw type linear actuator can be realized.

FIGS. 3 and 4 show a second embodiment of the present invention. In the case of this example, a pair of rods 2 each serving as an output shaft member is provided on one end surface of the ball nut 9.
Base ends 5 and 25 (the left end in FIG. 3) are connected and fixed. Further, the tip of each of the rods 25, 25 is projected out of the casing 2 through a pair of second openings 20, 20 formed in the other end of the casing 2 (the right end in FIG. 3). The distal ends of the rods 25 are connected to each other by a connecting plate 26. And this connecting plate 26
Thereby, the load in the thrust direction can be freely supported.
Also in the case of this example, the outer peripheral surface of each of the rods 25, 25 was fixed to the inner peripheral surface of each of the second through holes 20, 20,
The sliding bearings 21, 21 as the second bearings support the second opening portions 20, 2 in such a manner as to be freely movable in the axial direction.
Between the inner peripheral surface of the shaft 0 and the outer peripheral surface of each of the rods 25, the outer portions of the slide bearings 21, 21 are hermetically sealed by oil seals 23, 23.

On the other hand, the other end of the ball screw shaft 1 (the right end in FIG. 3) is a closing plate 2 for closing the other end of the casing 2.
7, a sliding bearing 29 is formed in a receiving hole 28 formed in the center of the inner surface.
It is rotatably supported via. At one end (left end in FIG. 3) of the ball screw shaft 1, a portion projecting from the casing 2 is provided with a rotation transmitting member 3 such as a stepped pulley, a gear, or the like.
0 is externally fixed to the ball screw shaft 1 so as to be non-rotatable by key connection, non-circular fitting, or the like. A stepped belt (not shown) for transmitting input torque from an electric motor (not shown) serving as a driving source is wound around or meshed with a drive gear on the outer peripheral surface of the rotation transmitting member 30. Also in the case of the present embodiment having such a configuration, a large output in the linear motion direction is output from the connecting plate 26 connecting the tips of the pair of rods 25, 25 by the same operation as that of the above-described first example. Can be taken out. Other configurations and operations are the same as those of the above-described first example.

FIG. 5 shows a third embodiment of the present invention.
An example is shown. In the case of this example, inside the casing 2,
A pair of ball screw mechanisms each including a ball screw shaft 1, a ball nut 9, and a plurality of balls 12, 12,
They are provided in parallel with each other. That is, ball nuts 9, 9 are screwed around a pair of ball screw shafts 1, 1 disposed parallel to each other inside the casing 2 via a plurality of balls 12, 12, respectively. The phases of the ball nuts 9 in the axial direction are matched with each other, and the ball nuts 9 are connected to each other by a connecting plate 31. That is, the connecting plate 31 is attached to one end surface of the outward flange-shaped flange portions 32, 32 provided on the outer peripheral surface of one end portion (right end portion in FIG. 5) of each of the ball nuts 9, 9, and the two flange portions 32, 32 are provided. It is fixed in a state of being bridged between them.

The base end (the left end in FIG. 5) of the cylindrical output shaft member 17a is fixedly connected to the center of the connecting plate 31. In the illustrated example, a male screw 33 formed at the base end of the output shaft member 17a is screwed and fixed to a screw hole 34 formed at the center of the connection plate 31. Thus, the central portion of the connection plate 31 and the base end of the output shaft member 17a are connected. The intermediate portion of the output shaft member 17a is the other end of the casing 2 (right end in FIG. 5).
The output shaft member 17a is inserted into the second opening 20 and the outer peripheral surface of the output shaft member 17a is fixed to the inner peripheral surface of the second opening 20. It is freely supported. Also, in the case of this example, an oil seal (the right side in FIG. 5) outside the slide bearing 21 between the inner peripheral surface of the second opening 20 and the outer peripheral surface of the output shaft member 17a is used. Sealed by 23.

In the case of this embodiment, each of the ball screw shafts 1,
The one end portion is rotatably supported by a pair of rolling bearings 4, 4 provided inside the first opening 3, respectively. In the illustrated example, each of these rolling bearings 4, 4
Are angular contact type ball bearings. And
By assembling these angular ball bearings in a back-to-back combination, the thrust loads acting on the ball screw shafts 1, 1 in both directions can be freely supported. In the illustrated example, the outer races 5, 5 that constitute the rolling bearings 4, 4 are
A step surface 35 formed at the inner end (right end in FIG. 5) of the first opening 3 and a holder screwed to the inner peripheral surface of the outer end (left end in FIG. 5) of the first opening 3. Similarly, between the inner end face 36 (the right end face in FIG. 5), the inner ring 7, 7 is provided with a stepped surface 8 formed at a portion near one end of the ball screw shaft 1; Between a ring-shaped retaining ring 38 locked in a locking groove 37 formed over the entire outer peripheral surface,
Each is pinched.

In the state where the retaining ring 38 is locked in the locking groove 37 as described above, an appropriate preload is applied to the plurality of rolling elements 24 constituting each of the rolling bearings 4. To
The position where the locking groove 37 is formed and the thickness of the retaining ring 38 are restricted. Oil seals 23 are provided between the inner peripheral surfaces of the holders 36 and 36 and the outer peripheral surfaces of the intermediate portions of the ball screw shafts 1 and 1 to prevent foreign matter from entering the casing 2 and to prevent To prevent leakage of lubricating oil. A hexagonal hole 39 is provided on the outer end surface (left end surface in FIG. 5) of the holders 36, 36 so that the tip end of a tool for tightening the holders 36, 36 can be engaged.

When using the ball screw type linear actuator of this embodiment constructed as described above, an electric motor (not shown) is energized to rotate the pair of ball screw shafts 1, 1 in the same direction and synchronously with each other. . As a result, the ball nuts 9, 9 screwed into the respective ball screw shafts 1, 1 via the plurality of balls 12, 12 are in phase with each other in the axial direction.
Displace in the desired direction. Thereby, the output shaft member 1 coupled to the connecting plate 31 fixed to each of the ball nuts 9, 9
7a, a large output in the linear motion direction can be obtained. In particular, in the case of this example, a pair of ball screw mechanisms for converting the input torque from the electric motor into an output in the direction of linear motion are provided. For this reason, the output which can be taken out from the output shaft member 17a can be made larger than in the case of the above-described first and second examples. Other configurations and operations are the same as in the case of the above-described first example.

[0026]

The ball screw type linear actuator of the present invention is constructed and operated as described above, so that not only the durability and the service life can be improved, but also the ball screw shaft and the ball nut are screwed together. A clean and compact structure that does not stain the surroundings with the lubricating oil that lubricates the parts can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first example of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a cross-sectional view showing the second example.

FIG. 4 is a sectional view taken along line BB of FIG. 3;

FIG. 5 is a sectional view showing a third example of the embodiment of the present invention.

FIG. 6 is a diagram showing the effect of the type of lubricant on the relationship between the rotational speed of the ball screw shaft and the dynamic friction torque.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ball screw shaft 2 Casing 3 First opening 4 Rolling bearing 5 Outer ring 6 Stepped surface 7 Inner ring 8 Stepped surface 9 Ball nut 10 First spiral groove 11 Second spiral groove 12 Ball 13 Flat surface 14 Circulation tube 15 Concave groove 16 Passage 17, 17a Output shaft member 18 Male screw part 19 Female screw part 20 Second opening 21 Sliding bearing 22 Passage 23 Oil seal 24 Rolling element 25 Rod 26 Connecting plate 27 Closing plate 28 Receiving hole 29 Sliding bearing 30 Rotating transmitting member 31 Connecting plate 32 Flange 33 Male thread 34 Screw hole 35 Step surface 36 Holder 37 Lock groove 38 Retaining ring 39 Hexagon hole

Claims (1)

[Claims] 1. A casing, first and second openings respectively provided at both ends in the axial direction of the casing so as to communicate between the inside and the outside of the casing, and a casing for receiving transmission of rotational force from a drive source. A ball screw shaft rotatably supported inside the casing, with one end protruding outside the casing through the first opening, and the ball screw shaft rotatable inside the casing. In order to support, a first bearing provided between the inner peripheral surface of the first opening and the outer peripheral surface of the intermediate portion of the ball screw shaft, and a part of the ball screw shaft, A first helical groove having an arc-shaped cross section formed on the outer peripheral surface of a portion disposed inside the casing, and a second helical groove having an arc-shaped cross section on the inner peripheral surface. A ball nut provided to be freely displaceable over A plurality of balls provided rotatably between the first helical groove and the second helical groove, and a base end portion in a state where the central axis is arranged to be coincident with or parallel to the central axis of the ball nut. An output shaft member which is displaceable in the axial direction together with the ball nut by being connected to the ball nut, and which is capable of moving in and out of the casing through the second opening with the displacement in the axial direction; In order to support the output shaft member movably in the axial direction, a second bearing provided between the inner peripheral surface of the second opening and the outer peripheral surface of the output shaft member, and inside the casing, A lubricating oil filled by an amount smaller than the clearance space volume in the casing, and in a space between the inner peripheral surface of the first opening and the outer peripheral surface of the intermediate portion of the ball screw shaft in the inner space of the casing. For the first The outer part of the casing and the outer part of the casing with respect to the inner space of the casing at the portion between the inner peripheral surface of the second opening and the outer peripheral surface of the output shaft member. A ball screw linear actuator that seals with a seal to prevent the lubricating oil sealed inside the casing from leaking outside the casing.