WO2022154043A1

WO2022154043A1 - Linear actuator

Info

Publication number: WO2022154043A1
Application number: PCT/JP2022/000886
Authority: WO
Inventors: 隆英齋藤; 慎太朗石川
Original assignee: Ntn株式会社
Priority date: 2021-01-15
Filing date: 2022-01-13
Publication date: 2022-07-21
Also published as: JP2022109519A

Abstract

In the present invention, in order to prevent the occurrence of a lock state when a linear screw element of a linear actuator has moved fully backward, a screw mechanism that converts the rotational force of a first screw element (1) into thrust in the axial direction of a second screw element (2) and a driving mechanism (3) that imparts rotational force to the first screw element (1) are supported by a case (4). The second screw element (2) stops rotating with respect to the case (4). The friction coefficient of a site that resists the rotation of the first screw element (1) is reduced by interposing a backward movement stopper (7), which comprises a thrust needle bearing, between a front end surface (1c) of the first screw element (1) and a rear end surface (2d) of the second screw element (2), which has moved fully backward relative to the case (4) by means of thrust in the rearward direction.

Description

Linear actuator

The present invention relates to a linear motion actuator including a screw mechanism that converts one rotary motion of a screw shaft and a nut into a linear motion of the other, and a drive mechanism that rotates one of the screw shaft and the nut in the forward and reverse directions. It relates to a case unitized mechanism and drive mechanism.

The linear motion actuator is roughly divided into a screw shaft rotation type in which the screw shaft is rotated to linearly move the nut and a nut rotation type in which the nut is rotated to linearly move the screw shaft.

Conventionally, the linear motion screw element of the screw mechanism (nut for screw shaft rotation type, screw shaft for nut rotation type) is configured as the output part of the linear motion actuator.

Since the output unit of the linear actuator limits the stroke that linearly moves in the axial direction to a certain level, the axial movement of the linear screw element may be restricted at the end position of the stroke. As a regulating means, a stopper is provided on the case or the screw shaft so that the linear motion screw element, which is an output unit, is stopped by contact with the stopper (for example, Patent Document 1).

A usage environment in which the linear motion screw element, which is the output unit of the linear motion actuator, is arranged unconnected to the mating member is also conceivable. In such a usage environment, the mating member may be displaced in the axial direction when the mating member is positioned with respect to the linear actuator, or the mating member may move in the axial direction independently of the linear actuator. There is. Therefore, when the linear screw element is advanced by the drive mechanism, the linear screw element collides with the mating member, and when the rotary screw element and the linear screw element are engaged, the screw mechanism is subsequently moved from the drive mechanism to the rotary screw element. Even if a reverse rotation force is applied to the screw element, the linearly acting screw element may not be able to move, resulting in a locked state.

In the linear actuator of Patent Document 1, the backlash of the screw mechanism and the elastic member are combined to prevent biting during forward movement.

Japanese Unexamined Patent Publication No. 2020-148213

However, in the linear motion actuator, if the position of the stopper that determines the end position of the linear motion screw element in the backward progress is not appropriate due to the influence of various errors, or if the reverse control of the linear motion screw element is not appropriate, the linear motion by the drive mechanism When the screw element is moving backward, the linear screw element may collide with the stopper at the end position of the backward progress, and the rotary screw element and the linear screw element may be caught and locked.

In view of the above background, the problem to be solved by the present invention is to prevent the occurrence of a locked state when the linear screw element of the linear actuator is fully moved backward.

In order to achieve the above problems, the present invention comprises a screw mechanism that converts the rotational force of the first screw element into an axial thrust of the second screw element, and a drive mechanism that applies the rotational force to the first screw element. In a linear motion actuator including a case that supports the drive mechanism and the screw mechanism, the rear end surface of the second screw element and the first screw element that have completely moved backward with respect to the case due to the thrust in the reverse direction. The second screw element is further prevented from rotating with respect to the case, and the retract stopper resists the rotation of the first screw element. A configuration is adopted in which the friction coefficient of the portion is smaller than the friction coefficient of the front end surface of the first screw element and the rear end surface of the second screw element.

By adopting the above configuration, the second screw element that is prevented from rotating with respect to the case is moved backward with respect to the case as the first screw element rotates, and the second screw element reaches the end position in the backward progress. At that time, the retracting stopper is interposed between the rear end surface of the second screw element and the front end surface of the first screw element. Since the friction coefficient of the portion where the retracting stopper resists the rotation of the first screw element is smaller than the friction coefficient of the front end surface of the first screw element and the rear end surface of the second screw element, the reverse movement is performed. When advancing the cut second screw element, the frictional force that resists the rotation of the first screw element is the frictional force when the front end surface of the first screw element and the rear end surface of the second screw element are directly slid. Can be made smaller than. Therefore, even if the first screw element and the second screw element are bitten when the second screw element is fully moved backward, the drive mechanism rotates the first screw element to easily eliminate the bite. Thereby, the occurrence of the locked state can be prevented.

The retracting stopper may be made of a thrust rolling bearing. In this way, most of the portion that resists the rotation of the first screw element becomes rolling friction, which is suitable for reducing the coefficient of friction.

Further, the retracting stopper may be made of a thrust needle bearing. In this way, since the rolling element and the raceway surface are in line contact, the contact portion of the raceway surface is less likely to be dented when a thrust load is applied, and when the first screw element is rotated, the contact portion is less likely to be dented. The rolling element can easily roll, and rolling resistance can be suppressed.

Further, the retracting stopper may have a raceway surface with the front end surface of the first screw element and the rear end surface of the second screw element as raceway surfaces. By doing so, the number of parts can be reduced.

Further, the output shaft arranged so as to be reciprocally movable in the axial direction with respect to the first screw element, the second screw element and the case, and the thrust in the forward direction of the second screw element are transmitted to the output shaft. The second screw element and the output shaft are moved in the forward direction when the thrust force in the forward direction is transmitted in a state where the output shaft can move forward. When the thrust force in the forward direction is transmitted in a state where the output shaft cannot move forward, the second screw element is given an elastic repulsive force in the reverse direction and the output shaft is given an elastic repulsive force in the forward direction. It is preferable that the second screw element is further provided with an elastic element, and a locking portion that transmits the thrust in the reverse direction to the output shaft and restricts the advance of the output shaft with respect to the second screw element is provided. .. In this way, the output shaft serves as the output unit of the linear motion actuator, the second screw element serves as the linear motion screw element, and the thrust in the forward direction of the second screw element is elastic during the forward drive of the second screw element by the drive mechanism. Since it is transmitted to the output shaft via the element, the second screw element and the output shaft can be interlocked in the forward direction. Further, during the reverse drive of the second screw element by the drive mechanism, the thrust in the backward direction of the second screw element is transmitted to the output shaft via the locking portion, and the advance of the output shaft with respect to the second screw element is restricted. Therefore, it is possible to link the second screw element and the output shaft in the reverse direction. When the output shaft collides with the mating member during the forward drive of the second screw element, the elastic repulsive force of the elastic element is given to the second screw element in the backward direction and is given to the output shaft in the forward direction. , The impact at the time of collision is absorbed by the elastic element, and the forward speed of the second screw element is reduced. Therefore, the biting of the first screw element and the second screw element is prevented, and thereby the occurrence of the locked state in the screw mechanism can be prevented.

Further, the second screw element has a hollow shaft portion extending in the axial direction and a rear wall portion that receives the rear end of the elastic element arranged inside the hollow shaft portion, and the output shaft is the output shaft. It may have a rear portion arranged inside the hollow shaft portion so as to receive the front end of the elastic element, and the rear end surface of the second screw element may be formed on the rear wall portion. In this way, the elastic element and the rear part of the output shaft are held in the hollow shaft part of the second screw element by the locking part and the rear wall part, and then the retracting stopper is received at the rear end surface using the wall part. Can be done.

Further, the first screw element has a crossguard portion protruding in the radial direction, and the front end surface of the first screw element is formed on the crossguard portion, and the first screw element is formed at a position rearward with respect to the retracting stopper. It is preferable that a thrust rolling bearing interposed between the collar portion and the case is arranged. In this way, the retracting stopper is received at the front end surface of the flange portion of the first screw element, and at that time, the collar portion is supported by the thrust rolling bearing from the rear side to prevent the flange portion from being deformed by the thrust load from the retracting stopper. As a result, it is possible to prevent deformation of the retracting stopper and prevent an increase in rotational resistance with respect to the first screw element.

As described above, the present invention can prevent the occurrence of a locked state when the linear screw element of the linear actuator is fully moved backward by adopting the above configuration.

Longitudinal sectional view showing a linear actuator according to the first embodiment of the present invention. A vertical cross-sectional view showing a state in which the output shaft of the linear actuator is advanced from the state shown in FIG. A vertical sectional view showing a linear actuator according to a second embodiment of the present invention.

Hereinafter, the first embodiment of the present invention will be described with reference to FIGS. 1 and 2 attached.

This linear actuator shown in FIG. 1 includes a screw mechanism that converts the rotational force of the first screw element 1 into an axial thrust of the second screw element 2, and a drive mechanism 3 that applies a rotational force to the first screw element 1. , A case 4 that supports the drive mechanism 3 and the above-mentioned screw mechanism, an output shaft 5 that is arranged so as to be reciprocally movable in the axial direction with respect to the first screw element 1, the second screw element 2, and the case 4, and an output. An elastic element 6 that urges the shaft 5 in the forward direction with respect to the second screw element 2, a retracting stopper 7 arranged between the first screw element 1 and the second screw element 2, and the first screw element 1 A thrust rolling bearing 8 arranged between the case 4 and the case 4 is provided.

Here, the axial direction means the direction along the rotation axis of the first screw element 1. Hereinafter, the direction perpendicular to the rotation axis is referred to as a radial direction, and the direction that goes around the rotation axis is referred to as a circumferential direction. Further, the direction in which the second screw element 2 moves axially to the right in the drawing toward the mating member P is the forward direction (forward), and the direction in which the second screw element 2 moves axially to the left in the figure. Is the backward direction (backward).

The first screw element 1 is arranged so as to be rotatable with respect to the case 4 and immovable in the axial direction. The first thread element 1 is composed of a male threaded component in which a male threaded portion 1a, a crossguard portion 1b protruding in the radial direction from the rear side of the male threaded portion 1a, and a front end surface 1c formed on the male threaded portion 1b are integrally formed. The entire first screw element 1 is formed of a metal, for example, an iron-based material.

The first screw element 1 has a hollow shaft shape opened at the rear end thereof. The drive shaft 3a of the drive mechanism 3 is connected to the hollow portion of the first screw element 1. The collar portion 1b of the first screw element 1 is radially supported by the inner circumference of the case 4. The front end surface 1c of the first screw element 1 is formed in an annular surface shape that is continuous along the entire circumference in the circumferential direction along the radial direction.

The drive mechanism 3 includes an electric motor that outputs rotation from the drive shaft 3a. The drive mechanism 3 can rotate the drive shaft 3a in the forward and reverse directions. The hollow portion of the drive shaft 3a and the first screw element 1 is fitted so as to be able to transmit a rotational force in any of the forward and reverse rotation directions. A polygonal shape such as a width across flats or a D-cut, a spline, or the like is applied to this rotation transmission structure. An example in which the drive shaft 3a of the drive mechanism 3 and the first screw element 1 are directly connected is shown, but the drive shaft and the first screw element are arranged in parallel, or a rotational force is applied between the drive shaft and the first screw element. It is also possible to add a gear mechanism for transmission.

In the case 4, the screw case 4a that supports the first screw element 1 and the second screw element 2, the front cover 4b that fits the front end of the screw case 4a, and the front cover 4b are fastened to the front end of the screw case 4a. It is composed of a plurality of bolts 4c, a motor holder 4d that supports the drive mechanism 3, and a bolt 4e that fastens the motor holder 4d to the rear end of the screw case 4a. The motor holder 4d maintains the coaxial arrangement and the coupled state of the drive shaft 3a of the drive mechanism 3 and the first screw element 1.

The second screw element 2 is arranged so as to be non-rotatable and movable in the axial direction with respect to the case 4. The second screw element 2 includes a female screw portion 2a screw-fitted to the male screw portion 1a of the first screw element 1, a hollow shaft portion 2b extending axially so as to surround the female screw portion 2a, and a hollow shaft portion 2b and a female screw. It has a nut in which a rear wall portion 2c connecting the rear side of the portion 2a and a rear end surface 2d formed on the rear wall portion 2c are integrally formed.

The outer diameter surface of the hollow shaft portion 2b includes a fitting surface that slidably contacts the inside of the screw case 4a in the axial direction, and is supported in the radial direction by the inside of the screw case 4a.

Further, the hollow shaft portion 2b is formed with a pin insertion hole extending in the radial direction from the outer diameter surface of the hollow shaft portion 2b. A pin 9 for preventing the second screw element 2 from rotating with respect to the case 4 is press-fitted into the pin insertion hole of the hollow shaft portion 2b.

The screw case 4a is formed with a slit portion 4f extending in the axial direction. The pin 9 fixed to the hollow shaft portion 2b is inserted into the space of the slit portion 4f of the screw case 4a. When a rotational force is applied to the second screw element 2, the pin 9 engages with the slit portion 4f in the rotational direction, so that the second screw element 2 cannot rotate with respect to the case 4. The detent structure may be another structure, and a nut having a polygonal cross-sectional shape and a screw case may be fitted without using a pin.

The output shaft 5 has a stepped shaft portion 5a extending in the axial direction and a rear portion 5b arranged inside the hollow shaft portion 2b.

The stepped shaft portion 5a has a smaller diameter toward the front. The stepped shaft portion 5a faces the mating member P in the axial direction through the through port of the front cover 4b. The small diameter side shaft portion of the stepped shaft portion 5a is abutted against the mating member P in the axial direction. The mating member P and the output shaft 5 are arranged in a non-connected state in which they can move independently in the axial direction, and do not always move integrally in the axial direction.

The rear portion 5b of the output shaft 5 is fitted so as to be slidable in the axial direction with respect to the inside of the hollow shaft portion 2b. Inside the hollow shaft portion 2b, a locking portion 10 is provided to prevent the rear portion 5b of the output shaft 5 from coming off from the hollow shaft portion 2b. The locking portion 10 is composed of a retaining ring. The locking portion 10 is attached to a retaining ring groove formed inside the hollow shaft portion 2b.

The elastic element 6 is made of an annular spring. A compression coil spring is used as the annular spring. The elastic element 6 may be composed of a plurality of spring members.

The elastic element 6 is arranged inside the hollow shaft portion 2b between the rear wall portion 2c and the rear portion 5b of the output shaft 5. The rear wall portion 2c and the rear portion 5b receive the rear end or the front end of the corresponding elastic element 6, respectively. The locking portion 10 transmits the thrust in the backward direction of the second screw element 2 to the output shaft 5, and advances the output shaft 5 with respect to the hollow shaft portion 2b against the elastic repulsive force generated by the elastic element 6. Stop.

As shown in FIG. 2, the front cover 4b has a rear end surface 4g that faces the front end of the large-diameter side shaft portion of the stepped shaft portion 5a of the output shaft 5 in the axial direction. The rear end surface 4gb of the front cover 4b is formed of an annular flat surface along the radial direction. The rear end surface 4g of the front cover 4b is a portion that stops the advance of the output shaft 5 with respect to the case 4 by contact with the output shaft 5. Further, the rear end surface 4g of the front cover 4b comes into contact with the front end of the hollow shaft portion 2b when the second screw element 2 further advances after the contact with the output shaft 5, so that the second screw element 2 advances with respect to the case 4. It becomes a part to stop. That is, the rear end surface 4g of the front cover 4b has a forward end position (advance limit position) of the stroke of the reciprocating movement of the output shaft 5 with respect to the case 4 and a terminal position of the second screw element 2 with respect to the case 4 in the forward progress. It will be the specified part.

As described above, the output shaft 5 is arranged so as to be reciprocally movable in the axial direction with respect to the case 4 within a range of a constant reciprocating stroke. The output shaft 5 is a portion that serves as an output unit of the linear actuator, and the stroke of the reciprocating movement of the output shaft 5 corresponds to a drive range in which the axial position of the mating member P can be adjusted by the linear actuator.

Here, FIG. 1 shows a state in which the second screw element 2 is completely moved backward by a thrust in the reverse direction based on the drive mechanism 3, and FIG. 2 shows a state in which the output shaft 5 comes into contact with the rear end surface 4g of the front cover 4b. The state when the second screw element 2 moves forward by the thrust in the forward direction is shown. The forward / backward stroke of the second screw element 2 by the drive mechanism 3 is longer than the stroke of the reciprocating movement of the output shaft 5, and the redundant portion further compresses the elastic element 6 from the state of FIG. 2 by the drive mechanism 3. Based on axial length.

The elastic element 6 is arranged inside the hollow shaft portion 2b in a predetermined compressed state in advance. This is the elastic element 6 due to the thrust transmitted via the locking portion 10 and the output shaft 5 when the second screw element 2 and the output shaft 5 move forward or backward without receiving resistance from the mating member P or the case 4 side. Is prevented from being compressed in the axial direction by one layer, and the output shaft 5 is advanced or moved forward in conjunction with the forward or backward movement of the second screw element 2, and the stroke of the output shaft 5 with respect to the forward or reverse movement of the second screw element 2 This is to virtually eliminate the loss.

Consider a case where the second screw element 2 shown in FIG. 1 is driven forward by the drive mechanism 3. In this case, the second screw element 2 and the output shaft 5 are provided by the rear wall portion 2c, the elastic element 6 and the locking portion 10 of the second screw element 2 until the output shaft 5 comes into contact with the rear end surface 4g of the front cover 4b. Advances are linked. When the output shaft 5 reaches the position shown in FIG. 2, the output shaft 5 comes into contact with the rear end surface 4g of the front cover 4b and is stopped. When the second screw element 2 further advances from the state of FIG. 2, the second screw element 2 advances with respect to the output shaft 5, and the rear portion 5b of the output shaft 5 and the rear wall portion 2c of the second screw element 2 The axial distance between and is getting narrower. Therefore, the elastic element 6 is compressed in the axial direction, and the elastic rebound force is applied to the rear wall portion 2c in the backward direction, and is applied to the output shaft 5 in the forward direction to be received by the case 4. Therefore, the elastic rebound force in the reverse direction applied to the rear wall portion 2c acts to slow down the advance of the second screw element 2. The elastic rebound force in the reverse direction gradually increases until the front end of the hollow shaft portion 2b comes into contact with the rear end surface 4g of the front cover 4b and the second screw element 2 is stopped. Therefore, the advancing speed of the second screw element 2 at the end position of the second screw element 2 in the forward progress is reduced, and the front end of the hollow shaft portion 2b and the rear end surface 4g of the front cover 4b come into contact with each other. It is difficult for the momentum to become so strong that a locked state occurs due to the biting of the male threaded portion 1a of the first screw element 1 and the female threaded portion 2a of the second screw element 2, and the front end of the hollow shaft portion 2b and the rear end surface 4g of the front cover 4b are assumed. Even if the collision occurs, the impact absorbing action of the elastic element 6 prevents the male screw portion 1a and the female screw portion 2a from being caught. As a result, when the second screw element 2 is advanced, the male screw portion 1a and the female screw portion 2a do not become in a high friction state, and a locked state in the screw mechanism is prevented from occurring.

In this embodiment, the end position of the second screw element 2 in the forward advance is determined by the contact with the case 4, but the elastic repulsive force of the elastic element 6 determines the end position of the second screw element 2 in the forward advance. May be set. That is, if the elastic element 6 capable of generating an elastic repulsive force equal to or higher than the thrust of the second screw element 2 based on the maximum output of the drive mechanism 3 is adopted, the elasticity of the elastic element 6 increases after the output shaft 5 stops moving forward. The position where the advance of the second screw element 2 is stopped by the repulsive force is the end position of the forward advance.

Now, consider a case where the second screw element 2 is driven backward by the drive mechanism 3 from the state of FIG. In this case, the locking portion 10 of the second screw element 2, the rear portion 5b of the output shaft 5, and the elastic element 6 interlock the reverse movement of the second screw element 2 and the output shaft 5, and return to the state of FIG. The retreat stopper 7 is abutted from the rear end surface 2d of the second screw element 2 that moves backward to stop the backward movement of the second screw element 2, and is a pure thrust that acts between the first screw element 1 and the second screw element 2. Support the load. Even when the second screw element 2 is fully moved backward, the first screw element 1 and the second screw element 2 are kept in a non-contact state by the intervention of the retracting stopper 7.

The retracting stopper 7 is composed of a bearing fitted between the outer circumference of the crossguard portion 1b of the first screw element 1 and the inner circumference of the screw case 4a. The retreat stopper 7 is arranged so as to be interposed between the rear end surface 2d of the second screw element 2 and the front end surface 1c of the first screw element 1 that have been completely moved backward with respect to the case 4 by the thrust in the backward direction. ..

The front end surface 1c of the crossguard portion 1b of the first screw element 1 and the rear end surface 2d of the rear wall portion 2c of the second screw element 2 are positioned so as to face each other in the axial direction. The front end surface 1c and the rear end surface 2d are annular surfaces facing each other along the radial direction.

The retracting stopper 7 is a plurality of track discs 7a in contact with the front end surface 1c of the crossguard portion 1b, a track disc 7b in contact with the rear end surface 2d of the rear wall portion 2c, and a plurality of raceway planes formed on the

track discs

7a and 7b. It is composed of a rolling element 7c and a cage 7d that holds these rolling elements 7c. The rolling element 7c is composed of a needle. That is, the retracting stopper 7 is made of a thrust needle bearing, which is a kind of thrust rolling bearing. The cage 7d of the retracting stopper 7 is guided in the radial direction by the outer circumference of the crossguard portion 1b of the first screw element 1. The outer diameter of the cage fitting portion where the collar portion 1b supports the retracting stopper 7 in the radial direction is smaller than the outer diameter of the collar portion 1b. This is to reduce the area of the contact portion that guides the cage 7d in the radial direction and suppress the slip resistance during guidance.

The portions where the retracting stopper 7 resists the rotation of the first screw element 1 are a plurality of rolling friction portions generated between the raceway surfaces of the

track discs

7a and 7b and the rolling elements 7c, the rolling elements 7c and the cage. It is substantially determined by the sliding friction portion of 7d, the cage 7d and the sliding friction portion of the flange portion 1b. That is, the coefficient of friction based on these friction portions is given to the first screw element 1 by the retracting stopper 7 when the first screw element 1 is rotated in the direction in which the second screw element 2 is advanced by the driving force given by the drive mechanism 3. Corresponds to rotational resistance. The coefficient of friction is smaller than the coefficient of friction of the front end surface 1c of the first screw element 1 and the rear end surface 2d of the second screw element 2. That is, in a virtual comparative example in which the rear end surface 2d of the second screw element 2 that has completely moved backward abuts on the front end surface 1c of the first screw element 1, the contact between the annular surfaces in which the rear end surface 2d and the front end surface 1c are in close contact with each other. The bearing rotational torque of the bearings constituting the retracted stopper 7 shown in the figure is clearly smaller than the rotational resistance determined by the coefficient of friction in the portion. Therefore, even if the male screw portion 1a of the first screw element 1 and the female screw portion 2a of the second screw element 2 are bitten when the second screw element 2 is fully moved backward, the drive mechanism 3 has the first screw element. It becomes easy to eliminate the biting by rotating 1. As a result, when the second screw element 2 is moved backward, the occurrence of a locked state in the screw mechanism is prevented.

The retracting stopper may have a friction coefficient of a portion that resists rotation of the first screw element smaller than the friction coefficient of the front end surface of the first screw element and the rear end surface of the second screw element. It may be a thrust ball bearing, or a thrust sliding bearing such as a solid lubricated bearing, a non-lubricated bearing, a self-lubricating bearing, or a sintered oil-impregnated bearing.

The thrust rolling bearing 8 is fitted to the inner circumference of the screw case 4a so as to be interposed between the crossguard portion 1b of the first screw element 1 and the rear end wall of the screw case 4a. The thrust rolling bearing 8 includes

track discs

8a and 8b facing in the axial direction, a plurality of rolling elements 8c interposed between the raceway surfaces formed on the

track discs

8a and 8b, and a cage 8d holding these rolling elements 8c. It consists of. The rolling element 8c is composed of a needle. That is, the thrust rolling bearing 8 is composed of a thrust needle bearing.

The thrust rolling bearing 8 supports a pure thrust load acting between the flange portion 1b of the first screw element 1 and the rear end wall of the screw case 4a. This support prevents the collar portion 1b from being deformed when the thrust load in the reverse direction from the retracting stopper 7 is received by the collar portion 1b, and as a result, the raceway surface of the retracting stopper 7 becomes distorted and the bearing rotation torque increases. Is prevented.

As described above, this linear actuator has a screw mechanism that converts the rotational force of the first screw element 1 into an axial thrust of the second screw element 2, and a drive mechanism 3 that applies the rotational force to the first screw element 1. The case 4 that supports the drive mechanism 3 and the screw mechanism, the rear end surface 2d of the second screw element 2 that has completely moved backward with respect to the case 4 due to the thrust in the reverse direction, and the front end surface 1c of the first screw element 1. The retreat stopper 7 is provided between the two, and the second screw element 2 is prevented from rotating with respect to the case 4, and the retreat stopper 7 determines the friction coefficient of the portion that resists the rotation of the first screw element 1. The second screw element 2 which is prevented from rotating with respect to the case 4 by making it smaller than the friction coefficient of the front end surface 1c of the first screw element 1 and the rear end surface 2d of the second screw element 2 is the first screw. When the second screw element 2 is moved backward with respect to the case 4 as the element 1 rotates and the second screw element 2 reaches the end position of the backward progress, the retracting stopper 7 is moved to the rear end surface 2d of the second screw element 2 and the first screw. It is interposed between the front end surface 1c of the element 1. The friction coefficient of the portion where the retracting stopper 7 resists the rotation of the first screw element 1 is smaller than the friction coefficient of the front end surface 1c of the first screw element 1 and the rear end surface 2d of the second screw element 2. Therefore, when the second screw element 2 that has been completely moved backward is advanced, the frictional force that resists the rotation of the first screw element 1 is applied to the front end surface 1c of the first screw element 1 and the rear end surface 2d of the second screw element 2. Can be made smaller than the frictional force when sliding directly. Therefore, even if the first screw element 1 and the second screw element 2 are bitten when the second screw element 2 is fully moved backward, the drive mechanism 3 rotates the first screw element 1 to bite the first screw element 1. It becomes easy to solve. As a result, the linear actuator can prevent the occurrence of a locked state when the second screw element 2, which is the linear screw element, is fully moved backward.

Further, this linear actuator is suitable for reducing the friction coefficient because most of the portion that resists the rotation of the first screw element becomes rolling friction because the retracting stopper 7 is made of a thrust rolling bearing. Is.

Further, in this linear motion actuator, since the retreat stopper 7 is made of a thrust needle bearing, the rolling element 7c and the raceway surface are in line contact with each other. The minute dents formed in the contact portions of the raceway surfaces of the

plates

7a and 7b become shallower, and at the beginning of rotating the first screw element 1, the bearing rotation torque required for the rolling element 7c to roll out of the minute dents becomes smaller, which in turn reduces the bearing rotation torque. When the first screw element 1 is rotated, the rolling element 7c is easily rolled, and the rolling resistance between the rolling element 7c and the raceway surface can be suppressed.

Further, this linear actuator has an output shaft 5 arranged so as to be reciprocally movable in the axial direction with respect to the first screw element 1, the second screw element 2 and the case 4, and the thrust in the forward direction of the second screw element 2. Is arranged between the output shaft 5 and the second screw element 2 so as to transmit to the output shaft 5, and when the output shaft 5 transmits the thrust in the forward direction while the output shaft 5 can move forward, the second screw element 2 and the output are transmitted. When the shaft 5 is interlocked in the forward direction and the output shaft 5 transmits the thrust in the forward direction in a state where the output shaft 5 cannot move forward, the second screw element 2 is given an elastic repulsive force in the reverse direction and the output shaft 5 is elastic in the forward direction. The second screw element 2 is further provided with an elastic element 6 that gives a repulsive force, and a locking portion 10 that transmits a thrust in the reverse direction to the output shaft 5 and regulates the advance of the output shaft 5 with respect to the second screw element 2. As a result, the output shaft 5 serves as the output unit of the linear motion actuator, the second screw element 2 serves as the linear motion screw element, and the second screw element 2 is being driven forward by the drive mechanism 3. Since the thrust in the forward direction is transmitted to the output shaft 5 via the elastic element 6, the second screw element 2 and the output shaft 5 are interlocked in the forward direction, and the drive mechanism 3 reverses the second screw element 2. During driving, the backward thrust of the second screw element 2 is transmitted to the output shaft 5 via the locking portion 10, and the advance of the output shaft 5 with respect to the second screw element 2 is restricted. 2 and the output shaft 5 are interlocked in the reverse direction, and when the output shaft 5 collides with the mating member P during the forward drive of the second screw element 2, the elastic repulsive force of the elastic element 6 with respect to the second screw element 2. Is given in the reverse direction and is given in the forward direction with respect to the output shaft 5, the impact at the time of collision is absorbed by the elastic element 6, and the forward speed of the second screw element 2 is decelerated, thereby causing the second screw element. Engagement of the one-screw element 1 and the second-thread element 2 can be prevented, and by extension, the occurrence of a locked state in the screw mechanism can be prevented.

Further, this linear actuator has a hollow shaft portion 2b in which the second screw element 2 extends in the axial direction, and a rear wall portion 2c that receives the rear end of the elastic element 6 arranged inside the hollow shaft portion 2b. The output shaft 5 has a rear portion 5b arranged inside the hollow shaft portion 2b so as to receive the front end of the elastic element 6, and the rear end surface 2d of the second screw element 2 is formed on the rear wall portion 2c. As a result, the elastic element 6 and the rear portion 5b of the output shaft 5 are held in the hollow shaft portion 2b of the second screw element 2 by the locking portion 10 and the rear wall portion 2c, and then the rear end surface using the wall portion 2c is used. The retreat stopper 7 can be received at 2d.

Further, in this linear motion actuator, the first screw element 1 has a bearing portion 1b protruding in the radial direction, and the front end surface 1c of the first screw element 1 is formed on the bearing portion 1b with respect to the retracting stopper 7. Since the thrust rolling bearing 8 interposed between the flange portion 1b and the case 4 is arranged at the rear position, the retracting stopper 7 is received by the front end surface 1c of the flange portion 1b of the first screw element 1. At this time, the flange portion 1b is supported by the thrust rolling bearing 8 from the rear side to prevent the flange portion 1b from being deformed by the thrust load from the retreat stopper 7, and by extension, the retreat stopper 7 is prevented from being deformed to prevent the rotation resistance with respect to the first screw element 1. Can be prevented from increasing.

The linear actuator according to the second embodiment will be described with reference to FIG. In the following, only the differences from the first embodiment will be described.

The retracting stopper 7 and the thrust rolling bearing 8 according to the second embodiment are different from the first embodiment in that the racetrack is omitted from each of them. Therefore, the retracting stopper 7 is configured by using the front end surface 1c of the first screw element 1 and the rear end surface 2d of the second screw element 2 as raceway surfaces, and arranging a needle with a cage between them. Further, the thrust rolling bearing 8 is configured by using the rear end surface of the crossguard portion 1b of the first screw element 1 and the rear end wall of the case 4 as raceway surfaces and arranging a needle with a cage between them.

This linear actuator has a simple structure because the raceway board is omitted from the retracting stopper 7 and the thrust rolling bearing 8, and the number of parts can be reduced.

In each of the above-described embodiments, the first screw element 1 is provided with a male screw portion and the second screw element 2 is provided with a female screw portion. However, the screw is provided with a female screw portion on the first screw element and a male screw portion on the second screw element. It is also possible to change to a mechanism. This change can be realized, for example, by providing a portion corresponding to the hollow shaft portion on the screw shaft of the first screw element and holding the output shaft and the elastic element inside these hollow shaft portions.

Further, as the screw mechanism, a sliding screw in which the threads of the first screw element 1 and the second screw element 2 are directly screwed together is adopted, but a ball screw can also be adopted.

The embodiments disclosed this time should be considered to be exemplary in all respects and not restrictive. Therefore, the scope of the present invention is indicated by the scope of claims rather than the above description, and it is intended that all modifications within the meaning and scope equivalent to the scope of claims are included.

1 1st thread element 1b Crossguard 1c Front end surface 2 2nd thread element 2b Hollow shaft part 2c Rear wall part 2d Rear end surface 3 Drive mechanism 4 Case 4f Slit part 5 Output shaft 5b Rear part 6 Elastic element 7 Retreat stopper 8 Thrust rolling bearing 9 pin 10 locking part

Claims

It supports a screw mechanism that converts the rotational force of the first screw element into an axial thrust of the second screw element, a drive mechanism that applies the rotational force to the first screw element, and the drive mechanism and the screw mechanism. In a linear actuator equipped with a case,
Further provided with a retracting stopper interposed between the rear end surface of the second screw element and the front end surface of the first screw element that has been completely moved backward with respect to the case by the thrust in the reverse direction.
The second screw element is prevented from rotating with respect to the case.
The retracting stopper has a friction coefficient of a portion that resists rotation of the first screw element smaller than the friction coefficient of the front end surface of the first screw element and the rear end surface of the second screw element. A linear actuator characterized by.
The linear actuator according to claim 1, wherein the retracting stopper is a thrust rolling bearing.
The linear actuator according to claim 2, wherein the retracting stopper includes a thrust needle bearing.
The linear actuator according to claim 2 or 3, wherein the retracting stopper has a front end surface of the first screw element and a rear end surface of the second screw element as raceway surfaces.
An output shaft arranged so as to be reciprocally movable in the axial direction with respect to the first screw element, the second screw element, and the case.
The thrust in the forward direction of the second screw element is arranged between the output shaft and the second screw element so as to transmit the thrust in the forward direction to the output shaft, and the thrust in the forward direction in a state where the output shaft can move forward. The second screw element and the output shaft are interlocked in the forward direction when transmitting the thrust, and when the thrust force in the forward direction is transmitted in a state where the output shaft cannot move forward, the elasticity in the reverse direction is transmitted to the second screw element. Further provided with an elastic element that gives a repulsive force and gives an elastic repulsive force in the forward direction to the output shaft.
Any one of claims 1 to 4 in which the second screw element is provided with a locking portion that transmits the thrust in the reverse direction to the output shaft and restricts the advance of the output shaft with respect to the second screw element. The linear actuator described in the section.
The second screw element has a hollow shaft portion extending in the axial direction and a rear wall portion that receives the rear end of the elastic element arranged inside the hollow shaft portion.
The output shaft has a rear portion arranged inside the hollow shaft portion so as to receive the front end of the elastic element.
The linear actuator according to claim 5, wherein the rear end surface of the second screw element is formed on the rear wall portion.
The first threaded element has a flange that protrudes in the radial direction.
The front end surface of the first screw element is formed on the crossguard portion.
The linear actuator according to any one of claims 1 to 6, wherein a thrust rolling bearing interposed between the crossguard and the case is arranged at a position rearward with respect to the retracting stopper.