JPH09146642A - Protective mechanism for linear actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protective mechanism capable of protecting the damage of constitutional parts of a linear actuator when excess torque is generated in a rotary driving source. SOLUTION: A braking body formed by a cylindrical elastic material held between two thrust washers 15, 16 is engaged between a thrust receiving stage part 10B formed on the outer periphery of a ball, screw shaft 10 and the thrust receiving face 11A of a bearing part 11 and a braking hole 7B of which inner diameter is slightly larger than the outer diameter of the braking body is formed on a fixing member provided with the bearing part 11 so as to concentrically arrange the braking body in the hole 7B. When thrust load applied to the shaft 10 is increased, the braking body is elastically deformed, its outer and inner peripheries respectively depress the inner periphery of the hole 7B and the outer periphery of the shaft 10 to brake the rotation of the shaft 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection mechanism for a linear actuator, and more particularly, to a thrust load acting on a ball screw shaft of a linear actuator having a structure in which a nut is screwed on a ball screw shaft driven by a rotary drive source. The present invention relates to a protection mechanism that prevents a load.

[0002]

2. Description of the Related Art Conventionally, a linear actuator having a ball screw type driving mechanism as shown in FIG. 4 has been widely used as a driving means for moving a movable part of a mechanical device forward and backward. In the figure, in the linear actuator 1, an inner cylinder 3 is arranged inside the outer cylinder 2 so as to be able to expand and contract. At the tip of the inner cylinder 3, there is attached a tip fitting 4 which is connected to a movable part of a mechanical device (not shown) for moving the movable part forward and backward. The inner cylinder 3 has a slider 5 fixed to the base end thereof. The slider 5 is slidably fitted on the inner peripheral surface of the outer cylinder 2, and guides the base end side of the outer cylinder 2 when the inner cylinder 3 extends and contracts with respect to the outer cylinder 2. The outer peripheral surface of the inner cylinder 3 is slidably held in the inner cylinder support hole 6A of the front end side flange portion 6 fixed to the front end of the outer cylinder 2.

A rotary drive source 8 composed of an electric motor or a fluid motor is attached to a base end side flange portion 7 fixed to the base end of the outer cylinder 2, and the drive shaft of the rotary drive source 8 is attached. A base end of a ball screw shaft 10 arranged coaxially with the central axis of the outer cylinder 2 is connected to 8A via a coupling 9. The ball screw shaft 10 is rotatably supported at a position near the base end thereof by a bearing portion 11 provided at the center of the base end side flange portion 7. The tip side of the ball screw shaft 10 is rotatably supported by a tip support member 12 slidably fitted on the inner peripheral surface of the inner cylinder 3 via a tip side bearing portion 13. The tip support member 12 is restricted from moving in the axial direction with respect to the ball screw shaft 10.

A slider 5 fixed to the base end of the inner cylinder 3.
A nut 14 to which the ball screw shaft 10 is screwed is integrally connected to the, and by the rotation of the ball screw shaft 10,
The inner cylinder 3 is driven to expand and contract with respect to the outer cylinder 2 via the nut 14, and the movable portion of the mechanical device is moved forward and backward via the tip fitting 4 of the inner cylinder 3.

[0005]

In the conventional linear actuator constructed as described above, an electric motor is generally used as a rotary drive source, and when a large current flows through the electric motor, the linear actuator is driven. There is a problem that the torque becomes excessively large, and as a result, the thrust load applied to the linear actuator becomes an overload state and the components of the linear actuator are damaged.

Therefore, the present invention solves the problem of the conventional linear actuator as described above, and when the rotary drive source generates an excessive torque, the thrust load applied to the ball screw shaft becomes overloaded. It is an object of the present invention to provide a protection mechanism capable of preventing damage and avoiding breakage of parts constituting the linear actuator.

[0007]

For the above-mentioned purpose, a protective device for a linear actuator provided with a ball screw shaft driven by a rotary drive source and a nut screwed with the ball screw shaft to perform a linear motion. According to the present invention, there are provided two thrust washers having substantially equal outer diameters, each having a through hole of the ball screw shaft in a central portion in a portion where the screw of the ball screw shaft is not formed, and the two thrust washers. And a cylindrical braking body formed of an elastic material having an outer diameter substantially equal to that of the above-mentioned braking body are fitted in a state where the braking body is sandwiched between two thrust washers, and one of the two thrust washers is the ball. While contacting the thrust receiving portion formed on the outer peripheral surface of the screw shaft, the other thrust washer contacts the thrust receiving surface of the bearing portion that rotatably supports the ball screw shaft, The thrust load applied to the ball screw shaft is supported by the thrust receiving surface of the bearing portion via the two thrust washers and the braking body, and the fixing member provided with the bearing portion has a thrust member of the braking body. A braking hole having an inner diameter slightly larger than the outer diameter is formed so that the braking body is concentrically arranged in the braking hole, and when the thrust load acting on the ball screw shaft is increased, the outer peripheral surface of the braking body is increased. A structure in which the diameter of the ball screw shaft is expanded to press the inner peripheral surface of the braking hole, and the diameter of the through hole at the center of the braking body is reduced to press the outer peripheral surface of the ball screw shaft to brake the rotation of the ball screw shaft. Is.

[0008]

In the above construction, when the ball screw shaft is rotated by the rotary drive source, the nut screwed on the ball screw shaft advances and retreats. While the thrust load acting on the ball screw shaft is small, there is a slight gap between the outer peripheral surface of the braking body and the inner peripheral surface of the braking hole formed in the fixing member, and the braking body works together with the ball screw shaft. It can rotate freely in the braking hole.

When the thrust load acting on the ball screw shaft increases above a certain limit, the thrust washer abutting the thrust receiving portion of the ball screw shaft and the thrust washer abutting the thrust receiving surface of the bearing portion. The compressive force acting on the braking body sandwiched between and increases, and as a result,
The braking body, which was initially cylindrical, is elastically deformed into a barrel shape, the outer peripheral surface of which expands radially outward to press the inner peripheral surface of the braking hole of the fixing member, and the ball formed at the center. The diameter of the through hole of the screw shaft is reduced to press the outer peripheral surface of the ball screw shaft to brake the rotation of the ball screw shaft.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. The basic structure of the linear actuator 1 shown in FIG. 1 is the same as that shown in FIG. 4 described above. Therefore, the members having the same functions as those shown in FIG. It is indicated by a number. Further, since the basic expansion / contraction operation of the linear actuator 1 is the same as that of the linear actuator 1 of FIG. 4 described above, the description thereof will be omitted.

In the linear actuator 1 of the present invention, the ball screw shaft 10 is not restricted in axial displacement with respect to the bearing portion 11, and the coupling 9 has a flexible joint like the flexible joint. A structure is used in which the ball screw shaft 10 can move in the axial direction by a minute distance with respect to the drive shaft 8A of the rotary drive source 8. In this embodiment, an electric motor is used as the rotary drive source. It should be noted that the inner cylinder 3 is prevented from rotating by being dragged by the rotation of the ball screw shaft 10 by a regulating means (not shown).

The screw portion 10A screwed onto the nut 14 is provided in a range in which the nut 14 moves on the ball screw shaft 10 when the inner cylinder 3 expands and contracts with respect to the outer cylinder 2. The base end side of the ball screw shaft 10 on which the screw portion 10A is not formed is a small diameter portion 10C with the thrust receiving step portion 10B as a boundary.

As shown in FIG. 2, a disk-shaped thrust washer 15 having a through hole at its center is brought into contact with the thrust receiving portion 10B in the small-diameter portion 10C so that the ball screw shaft 10 is supported. On the other hand, the ball screw shaft is fitted in a state in which the movement in the direction of the screw portion 10A is regulated, and the thrust washer 16 having substantially the same shape is in contact with the thrust receiving surface 11A of the bearing portion 11 in the hole thereof. The small diameter portion 10C of 10 is fitted so as to be freely slidable.

Further, the two thrust washers 1
Cylindrical braking body 17 having an outer diameter substantially equal to that of Nos. 5 and 16 and having a through hole at the center is provided with two thrust washers 1.
It is fitted in the small-diameter portion 10C in a state of being sandwiched between 5 and 16. The braking body 17 is formed of rubber so as to be largely elastically deformed when an external force is applied.

Further, in the base end side flange portion 7 as a fixing member, a space S is normally formed between the outer peripheral surface of the braking body 17 and a bearing holding hole 7A formed at the center thereof. A braking hole 7B having concentric inner peripheral surfaces facing each other is formed, and the braking hole 7B is rotated as the ball screw shaft 10 rotates.
The braking body 17 can rotate in B.

In the above-described structure, the ball screw shaft 10 is rotated through the coupling 9 by driving the rotary drive source 8 from the state shown in FIG. 1, and the ball screw shaft 10 is screwed into the screw portion 10A of the ball screw shaft 10. The rotating nut 14 moves toward the tip side of the ball screw shaft 10. As a result, the nut 14
The inner cylinder 3 integrated with the outer cylinder 2 extends from the tip of the outer cylinder 2.

At this time, the thrust load applied from the movable portion side of the mechanical device (not shown) connected to the tip fitting 4 to the inner cylinder 3 side is transmitted from the nut 14 to the ball screw shaft 10, As shown in detail in FIG.
From the thrust washer 15 that is in contact with the thrust receiving portion 10B of the thrust washer 16 through the braking body 17.
And is received by the thrust receiving surface 11A of the bearing portion 11.

When the thrust load is less than the allowable value, the bearing portion 11 sandwiched between the thrust washers 15 and 16 as shown in FIG.
A thrust load applied to the ball screw shaft 10 causes a compressive force in the axial direction to elastically deform, but the amount of deformation is small, and a gap S is formed between the outer peripheral surface of the braking body 17 and the inner peripheral surface of the braking hole 7B. Being present, the ball screw shaft 10 is free to rotate.

When the torque of the electric motor 8 increases for some reason and the thrust load applied to the ball screw shaft 10 increases, the braking body 17 sandwiched between the thrust washers 15 and 16 acts in the axial direction. The compressive force increases, and as a result, the outer peripheral surface of the braking body 17 is elastically deformed into a barrel shape and pressed against the inner peripheral surface of the braking hole 7B as shown in FIG. Since the diameter of the surface is also reduced and pressed against the outer peripheral surface of the ball screw shaft 10, the rotation of the ball screw shaft 10 is braked and damage to the components of the linear actuator 1 due to overload is prevented.

In the above-described embodiments, the linear actuator has a structure in which the inner cylinder is housed in the outer cylinder, but the invention is not limited to this, and the protection mechanism of the present invention is driven by a rotary drive source. If the nut screwed to the ball screw shaft is a linear actuator having a structure in which the nut moves linearly, it can be similarly implemented.

Further, in the present embodiment, rubber is used as the material of the braking body, but the amount of elastic deformation is large, and a large braking torque is generated due to the sliding contact with the inner peripheral surface of the hole of the fixed side member. Any material having a large friction coefficient can be used, and for example, a foamable resin such as urethane can be used. Further, in this embodiment, the electric motor is used as the rotary drive source, but it can be used as a protection mechanism for the linear actuator using a fluid motor or the like.

[0022]

As described above, according to the protection mechanism of the linear actuator of the present invention, the thrust load applied to the ball screw shaft is made simple with the braking body sandwiched between the two thrust washers. Since the rotation of the ball screw shaft is effectively braked when the torque increases, it is possible to prevent the thrust load from becoming excessive and prevent damage to the components of the linear actuator due to the overload. .

Further, since the protection mechanism of the present invention can be easily incorporated in the linear actuator having the conventional structure, it is possible to suppress an increase in manufacturing cost of the linear actuator due to the incorporation of the protection mechanism. further,
Since the braking body mounted on the ball screw shaft also has a function as a vibration damping material that absorbs vibration of the ball screw during rotation, a stable operating state is ensured.

[Brief description of the drawings]

FIG. 1 is a sectional view of a linear actuator showing one embodiment of the present invention.

FIG. 2 is an enlarged sectional view of a protection mechanism in a normal state.

FIG. 3 is an enlarged cross-sectional view of the protection mechanism in a state where the thrust load applied to the ball screw shaft is increased.

FIG. 4 is a sectional view of a conventional linear actuator.

[Explanation of symbols]

1 Linear actuator 7 Base side flange part (fixing member) 7B
Braking hole 8 Rotary drive source 10
Ball screw shaft 10A Screw part 10B
Thrust receiving part 11 Bearing part 11A
Thrust receiving surface 14 Nuts 15 and 16
Thrust washer 17 Braking body 15A, 16A, 17A Through hole

Claims (1)

[Claims] 1. A linear actuator including a ball screw shaft driven by a rotary drive source and a nut screwed on the ball screw shaft to perform a linear motion, wherein a portion of the ball screw shaft where the screw is not formed. A pair of thrust washers each having a substantially equal outer diameter and each having a through hole of the ball screw shaft at its center, and a cylindrical braking body formed of an elastic material having an outer diameter substantially equal to the two thrust washers. Is fitted in a state where the braking body is sandwiched between two thrust washers, and one of the two thrust washers is brought into contact with a thrust receiving portion formed on the outer peripheral surface of the ball screw shaft. At the same time, the other thrust washer is brought into contact with the thrust receiving surface of the bearing portion that rotatably supports the ball screw shaft, and the thrust load applied to the ball screw shaft is applied to the two thrust washers. A braking member having an inner diameter slightly larger than the outer diameter of the braking member is supported in the thrust receiving surface of the bearing unit through the shear and the braking member, and the fixing member provided with the bearing unit has a braking hole in the braking hole. The braking bodies are formed so as to be arranged concentrically, and when the thrust load acting on the ball screw shaft increases, the outer peripheral surface of the braking body expands and presses the inner peripheral surface of the braking hole. A protective mechanism for a linear actuator, characterized in that a through hole in the center of the body is reduced in diameter to press the outer peripheral surface of the ball screw shaft to brake the rotation of the ball screw shaft.