JP5983040B2 - Actuator - Google Patents

Description

  The present invention relates to an actuator used for automobile parts, machine part devices, and the like.

  As an actuator used in an electric drive device for a transmission, an actuator using a ball screw device that converts a rotational motion transmitted from an electric motor as a drive source into a linear motion is known as disclosed in Patent Document 1. In the ball screw device, the ball screw shaft is rotated by the electric motor, and the ball screw nut screwed to the ball screw shaft moves in the axial direction of the ball screw shaft. One end of a swing arm that can swing in a plane formed by the axis of the ball screw shaft and a direction perpendicular to the axis is connected to the ball screw nut, and the other end of the swing arm is connected to the other end of the swing arm. The output shaft arranged in the direction perpendicular to the axis of the ball screw shaft is connected, and the output shaft is rotated by the swinging motion of the swinging arm so that the gear is switched.

  By the way, the swing arm of the actuator of Patent Document 1 (referred to as a shift arm in Patent Document 1) protrudes from one pair of outer surfaces that are opposite to each other of the ball screw nut. A long hole that engages with the pair of engagement pins is formed, and the other end is fixed to the output shaft. When the pair of engaging pins move in the longitudinal direction of the long hole by the linear motion of the ball screw nut, the swing arm performs the swing motion, and the linear motion of the ball screw nut is transmitted to the output shaft as a rotational motion. It is like that.

However, since the actuator of Patent Document 1 has a structure in which the swing arm and the output shaft do not rotate relative to each other, at least one of a ball screw shaft, a ball screw nut, a housing, a swing arm, and an output shaft is manufactured. If an error occurs in the arrangement angle of the ball screw shaft and the output shaft due to the error, a torsion occurs between the swing arm and the ball screw shaft, which may cause assembly failure of the actuator or impair operability.
Therefore, a telescopic swing arm is composed of a plurality of arms, and the plurality of arms are slidable in the direction of the arm axis and connected to each other so as to be rotatable relative to each other, resulting in manufacturing errors in the actuator components. However, there is known one that absorbs it and improves the operability of the actuator (for example, Patent Document 2).

JP 2002-317871 A JP 2011-112193 A

However, the actuator of Patent Document 2 has a complicated structure in which a plurality of arms constituting the swing arm are slidable in the arm axis direction and coupled to each other so as to be rotatable relative to each other in order to absorb manufacturing errors of components. There is a problem in terms of assembly.
Therefore, the present invention has been made paying attention to the above-mentioned unsolved problems of the conventional example, and an object thereof is to provide an actuator that can improve assembly and absorb manufacturing errors with a simple configuration. To do.

In order to achieve the above object, an actuator according to claim 1 of the present invention includes a ball screw shaft to which a rotational motion is transmitted from a rotational drive source, and a ball screw nut that performs a linear motion by the rotational motion of the ball screw shaft. And one swing arm that engages with the ball screw nut and swings in a plane formed by the axis of the ball screw shaft and a first direction perpendicular to the axis of the ball screw shaft. , Orthogonal to the axis of the ball screw shaft and the first direction, extending in a second direction passing through the swing center of the swing arm and connected to the other end of the swing arm, An output shaft to which a rotational motion is transmitted by a swing motion of the swing arm by a linear motion, and the other end of the output shaft and the swing arm is free to translate the swing arm in the second direction. And the swinging Over arm is coupled to regulate the movement in the direction of linear motion of the ball screw nut, the other end of the swing arm, the output has a rotational degree of freedom about the axis of the swing arm It is connected to the shaft.

According to a second aspect of the present invention, in the actuator according to the first aspect, a pair of output-side flat surfaces extending in parallel with each other in the second direction are provided at the end of the output shaft, and the swing arm is provided. An engagement hole for inserting the end of the output shaft is provided at the other end of the pair, and a pair of swing side inner planes on which the pair of output side flat surfaces slide in a surface contact state are provided in the engagement hole. And providing a protrusion on at least one of the pair of output side flat surfaces, and the protrusion on at least one of the pair of swing side inner planes sliding on at least one of the pair of output side flat surfaces. An engaging groove for entering was provided extending in the second direction.

According to a third aspect of the present invention, in the actuator according to the second aspect, a pin insertion hole that opens at the pair of output side flat surfaces is formed at an end of the output shaft, and the pin insertion hole includes the pin insertion hole. A pin was inserted with the end portion protruding from at least one of the pair of output side flat surfaces as the protrusion.
According to a fourth aspect of the present invention, in the actuator according to the second aspect, a protrusion that enters the engagement groove is integrally formed on at least one of the pair of output side flat surfaces of the output shaft.

According to a fifth aspect of the present invention, in the actuator according to the second aspect, a recess is formed in at least one of the pair of output side flat surfaces of the output shaft, and a sphere is fitted into the recess, and the sphere is The protrusion is inserted into the engagement groove.
Further, the invention according to claim 6 is the actuator according to any one of claims 1 to 5 , wherein one end of the swing arm is engaged with the ball screw nut so that the ball screw nut cannot be rotated. doing.

Furthermore, the invention according to claim 7 is the actuator according to claim 6 , wherein the ball screw nut is provided with a pair of anti-rotation planes facing each other in a direction orthogonal to the linear motion direction of the ball screw nut. A pair of engagement rods that slidably contact the pair of rotation stop planes are provided at one end of the swing arm.

  According to the actuator of the present invention, the other end of the output shaft and the swing arm is connected by restricting the swing arm from moving in the linear motion direction of the ball screw nut. It has translational freedom in the second direction. As a result, the interference between the swing arm and the ball screw nut can be prevented, the assembly of the actuator can be improved, and the manufacturing error can be absorbed with a simple configuration.

It is a perspective view which shows the actuator of 1st Embodiment which concerns on this invention. It is the figure which showed the actuator of 1st Embodiment from the 2nd direction (Z-axis direction). It is an AA arrow directional view of FIG. It is a figure which shows the principal part of the actuator of 2nd Embodiment which concerns on this invention. It is a figure which shows the principal part of the actuator of 3rd Embodiment which concerns on this invention. It is a figure which shows the principal part of the actuator of 4th Embodiment which concerns on this invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.
FIGS. 1 to 3 are views showing a first embodiment of an actuator 1 used in an automatic transmission of an automobile according to the present invention.
The actuator 1 according to the present embodiment is a shift actuator that performs a shift operation among shift select actuators. The ball screw shaft is arranged such that the axis P1 extends in the X-axis direction and the rotational motion is transmitted from the motor 2. 3 and a ball in which a plurality of balls (not shown) are interposed between the outer peripheral surface of the ball screw shaft 3 and the inner peripheral surface of the ball screw shaft 3, and the rotational motion transmitted to the ball screw shaft 3 is converted into a linear motion. One that engages with the screw nut 4 and one end of the ball screw nut 4 and swings in a plane formed by the axis P1 of the ball screw shaft 3 and the Y-axis direction orthogonal to the axis P1 of the ball screw shaft 2. The swing arm 5 and the axis P1 and the Y-axis direction of the ball screw shaft 3 are orthogonal to the Z axis direction passing through the swing center of the swing arm 5 and connected to the other end of the swing arm. An output shaft 6; That. Further, bearings 7 and 8 fixed to a housing (not shown) rotatably support both end sides of the ball screw shaft 2 in the axial direction.

  The output shaft 6 is a rod-like member that is rotatably supported by the housing via a bearing (not shown). An annular groove 28 is formed on the outer periphery of the output shaft 6, and a part of an output shaft pin 29 fixed to the housing is engaged with the annular groove 28. By such engagement of the annular groove 28 and the output shaft pin 29, the output shaft 6 is disposed so as to be rotatable about the Z axis while being restricted from moving in the Z-axis (axis P2) direction.

  An output lever 11 is provided on the middle portion in the longitudinal direction of the output shaft 6 so as to protrude outward. The output lever 11 receives a shift operation that rotates around the Z axis together with the output shaft 6 from the actuator 1 of the present embodiment, which is a shift actuator, and has a different structure from the actuator 1 of the present embodiment. A select operation that moves in the Z-axis direction is transmitted from (not shown). Note that when the selection operation is transmitted to the output lever 11, the output shaft 6 does not move in the Z-axis direction.

Here, on one end side of the output shaft 6 (the side to which the other end of the swing arm 5 is connected), a pair of output-side flat surfaces 9 which are parallel planes extending along the axis P2 of the output shaft 6 are provided. , 10 are formed.
As shown in FIG. 3, a pin insertion hole 12 is formed on one end side of the output shaft 6 so as to extend in a direction perpendicular to the axis P2 and open at a pair of output side flat surfaces 9, 10. The pin 13 is inserted into the pin insertion hole 12 with the end 13a protruding from the one output side flat surface 9.

The ball screw nut 4 has a rectangular parallelepiped appearance, and as shown in FIG. 3, cylindrical convex portions 14 protrude from both side surfaces 4a and 4b facing the Z-axis direction.
As shown in FIG. 2, the swing arm 5 includes an arm portion 15, a pair of nut engagement rods 17 formed at one end of the arm portion 15, and an output shaft engagement hole portion formed at the other end of the arm portion 15. 16.

  As shown in FIG. 2, the output shaft engagement hole 16 is provided with a hole extending in a direction perpendicular to the axis P <b> 3 of the arm portion 15 (Z-axis direction in FIG. 2), and a pair of output sides of the output shaft 6. A pair of oscillating side inner planes 18 and 19 formed as planes parallel to each other so as to come into surface contact with the flat surfaces 9 and 10, and an inner surface other than the pair of oscillating side inner planes 18 and 19, and the output shaft 6 Are formed on the non-contact inner surfaces 20 and 21 that do not contact the outer peripheral surface between the pair of output-side flat surfaces 9 and 10 and provide a gap, and on one of the swing side inner planes 18, and intersect the axis P3. And an engaging groove 22 extending in a direction (Z direction) orthogonal to the axis P3.

2 and 3, the pair of nut engaging rods 17 has a shape bifurcated in the Z-axis direction from the other end side of the arm portion 15, and a notch slit 23 is formed on the distal end side. It is a member. The distance between the inner walls of the pair of nut engaging rods 17 is set to be approximately the same as the distance between both side surfaces 4a and 4b facing the Z-axis direction of the ball screw nut 4.
Next, a procedure for assembling the actuator 1 having the above configuration will be described.
First, the output shaft 6 is supported at two points on the housing via a bearing (not shown).

  Next, one end side of the output shaft 6 is inserted into the output shaft engagement hole 16 of the swing arm 5 from the Z-axis direction. At that time, one output side flat surface of the output shaft 6 is formed in the engagement groove 22 extending in the direction (Z direction) orthogonal to the axis P3 of the one swing side inner plane 18 of the output shaft engagement hole portion 16. The end 13 a of the pin 13 protruding from 9 enters. Then, the pair of output side flat surfaces 9 and 10 of the output shaft 6 are brought into surface contact with the pair of swing side inner planes 18 and 19 of the output shaft engagement hole portion 16. Further, the non-contact inner surfaces 20 and 21 of the output shaft engaging hole 16 are in a state where a gap is provided between the output shaft engaging hole portion 16 and the outer peripheral surface between the pair of output side flat surfaces 9 and 10 of the output shaft 6.

Next, the ball screw shaft 3 having the bearings 7 and 8 mounted on both ends is extended in the X-axis direction, and the ball screw nut 4 disposed on the outer periphery of the ball screw shaft 3 is extended from both side surfaces 4a and 4b in the Z-axis direction. The convex part 14 is protruded.
Next, the peripheral edges of the notch slits 23 provided in the pair of nut engaging rods 17 of the swing arm 5 are engaged with the convex portions 14 protruding from both side surfaces 4 a and 4 b of the ball screw nut 4. At that time, as shown in FIG. 3, the side surfaces 4 a and 4 b facing the Z-axis direction of the ball screw nut 4 are located in a space surrounded by a portion including the inner walls of the pair of nut engaging rods 17.

Then, bearings 7 and 8 mounted on both end sides of the ball screw shaft 2 in the axial direction are fixed to the housing.
Thereafter, the ball screw shaft 3 is connected to the motor 2 through a coupling (not shown).
When the rotary motion is transmitted from the motor 2 to the ball screw shaft 3 in the assembled actuator 1, the inner walls of the pair of nut engaging rods 17 of the swing arm 5 are connected to the side surfaces 4 a and 4 b of the ball screw nut 4. By making contact, the ball screw nut 4 cannot be rotated, and the ball screw nut 4 performs linear motion in the X-axis direction.

Since the peripheral edges of the notch slits 23 of the pair of nut engaging rods 17 are slidably engaged with the pair of convex portions 14 of the ball screw nut 4, the linear motion of the ball screw nut 4 is applied to the output shaft. This is transmitted as the rotational motion of the swing arm 5 with the engagement hole 16 side as the center of rotation.
The rotational movement of the swing arm 5 is transmitted from the pair of swing side inner planes 18 and 19 to the pair of output side flat surfaces 9 and 10 of the output shaft 6, and the output lever 11 is rotated by the rotation of the output shaft 6. Swing and change gears.

Next, the effect of the actuator 1 described above will be described.
In the actuator 1 of the present embodiment, the swing arm 5 having one end of the output shaft 6 inserted into the output shaft engaging hole portion 16 tries to move in the X-axis direction. The end portion 13a of the pin 13 of the output shaft 6 entering the engaging groove 22 extending in the Z direction is regulated. Thereby, it is possible to prevent the swing arm 5 from being translated along with the ball screw nut 4 in the X-axis direction.

Even if the positional accuracy of the ball screw shaft 3 is poor due to a manufacturing error, the swing arm 5 has translational freedom in the Z-axis direction (the direction along the axis P2 of the output shaft 6). There is no risk of interference with the screw nut 4.
Even if the accuracy of the arrangement angle of the ball screw shaft 3 and the output shaft 6 is poor due to manufacturing errors, the swing arm 5 enters the engagement groove 22 of the output shaft engagement hole 16 of the swing arm 5. Since there is a degree of freedom of rotation around the pin 13 (end portion 13a), there is no possibility of interference between the swing arm 5 and the ball screw nut 4.

  As described above, the actuator 1 of this embodiment improves the assembly of the actuator with a minimum increase in the number of parts that uses the swing arm 5 and the pin 13 formed separately from the output shaft 6. The manufacturing error can be absorbed with a simple configuration. Here, the structure in which the other end of the swing arm described in the present invention is connected to the output shaft with a degree of freedom of rotation about the axis of the swing arm is provided in the output shaft engagement hole portion 16. The engaging groove 22 and the pin 13 formed in the rocking side inner plane 18 are set to positions close to the axis P3 but not crossing the axis P3, and the pin 13 (end portion) where the rocking arm 5 enters the engaging groove 22 13a) The case where it has a degree of freedom of rotation around is also included.

Further, the ball screw nut 4 has a simple structure in which the peripheral edge of the notch slit 23 of the pair of nut engaging rods 17 of the swing arm 5 is slidably engaged with the convex portion 14 of the ball screw nut 4. The linear motion can be transmitted as the rotational motion of the swing arm 5 with the output shaft engagement hole 16 side as the center of rotation.
Further, the pin 13 inserted into the pin insertion hole 12 on one end side of the output shaft 6 is the other swing side inner plane of the output shaft engagement hole portion 16 of the swing arm 5 after the actuator 1 is assembled. 19 and the inner wall of the engagement groove 22 prevent the pin from falling off, so that a pin press-fitting step, a pin drop-off prevention step, or a pin press-fitting and removal prevention step are not required.

Further, since there is no possibility of interference between the swing arm 5 and the ball screw nut 4, the gap between the inner wall of the engagement rod 17 and the side surfaces 4a and 4b of the ball screw nut 4 can be further reduced. Thereby, the time until the rotational motion of the motor 2 is transmitted to the ball screw nut 4 as a linear motion is shortened, and the actuator 1 with improved controllability can be obtained.
The Y-axis direction of the present embodiment corresponds to the first direction of the present invention, the Z-axis direction of the present embodiment corresponds to the second direction of the present invention, and the end portion 13a of the present embodiment is the protrusion of the present invention. It corresponds to the part.

Next, what is shown in FIG. 4 is a diagram showing a second embodiment of the actuator according to the present invention.
In the present embodiment, the protrusion 24 is integrally formed on the output side flat surface 9 of the output shaft 6. The protrusion 24 has a shape such as a cylinder, a cone, or the like that gives a degree of freedom of rotation. The protrusion 24 is formed on the swing side inner plane 18 of the output shaft engagement hole 16 of the swing arm 5 and intersects the axis P3. It enters into the engaging groove 22 extending in the direction orthogonal to the axis P3 (Z direction).

According to the present embodiment, the output shaft engaging hole 16 of the swing arm 5 is about to move in the X-axis direction orthogonal to the axis P2 in the Z direction of one swing side inner plane 18. Since the protrusion 24 entering the existing engagement groove 22 is regulated, the swing arm 5 can be prevented from translational movement in the X-axis direction together with the ball screw nut 4.
Even if the positional accuracy of the ball screw shaft 3 is poor due to a manufacturing error, the swing arm 5 has translational freedom in the Z-axis direction (the direction along the axis P2 of the output shaft 6). There is no risk of interference with the screw nut 4.

Even if the accuracy of the arrangement angle of the ball screw shaft 3 and the output shaft 6 is poor due to a manufacturing error, the swing arm 5 rotates around the protrusion 24 entering the engagement groove 22 of the output shaft engagement hole 16. Since there is a degree of freedom, there is no possibility of interference between the swing arm 5 and the ball screw nut 4.
Moreover, since the protrusion 24 is integrally formed on the output side flat surface 9 of the output shaft 6, the number of parts of the actuator 1 can be reduced.
Note that the protrusion 24 of the present embodiment corresponds to the protrusion of the present invention.

Next, FIGS. 5A and 5B are views showing a third embodiment of the actuator according to the present invention.
In this embodiment, a pair of output side flat surfaces 9 and 10 are formed on one end side of the output shaft 6 (the side to which the other end of the swing arm 5 is connected), and a conical portion is formed on a part of the one output side flat surface 9. A recess 25 having a shape is formed, and a sphere 26 is fitted in the recess 25.

In addition, a V-shaped groove 27 extending in a direction (Z direction) intersecting the axis P3 and orthogonal to the axis P3 is formed on one of the swing side inner planes 18 of the output shaft engagement hole 16 of the swing arm 5. When the one end side of the output shaft 6 is inserted from the Z-axis direction, the sphere 26 fitted in the recess 25 of the one output side flat surface 9 enters the V-shaped groove 27.
According to the present embodiment, the output shaft engaging hole 16 of the swing arm 5 is about to move in the X-axis direction orthogonal to the axis P2 in the Z direction of one swing side inner plane 18. Since the sphere 26 that enters the existing V-shaped groove 27 and fits in the recess 25 of the output side flat surface 9 is regulated, the swing arm 5 is prevented from translating in the X-axis direction together with the ball screw nut 4. can do.

Even if the positional accuracy of the ball screw shaft 3 is poor due to a manufacturing error, the swing arm 5 has translational freedom in the Z-axis direction (the direction along the axis P2 of the output shaft 6). There is no risk of interference with the screw nut 4.
Even if the accuracy of the arrangement angle of the ball screw shaft 3 and the output shaft 6 is poor due to a manufacturing error, the swing arm 5 has a rotational degree of freedom around the sphere 26 entering the recess 25 of the output shaft 6. There is no possibility of interference between the swing arm 5 and the ball screw nut 4.

Further, the sphere 26 fitted in the recess 25 of the one output side flat surface 9 has a V-shaped groove 27 formed in the output shaft engaging hole 16 of the swing arm 5 after the actuator 1 is assembled. Falling off can be prevented by the inner wall.
In addition, the spherical body 26 of this embodiment corresponds to the protrusion part of this invention, and the V-shaped groove 27 of this embodiment corresponds to the engagement groove | channel of this invention.
Further, FIGS. 6A and 6B show a fourth embodiment of the actuator according to the present invention.

The swing arm 5 of the present embodiment has a pair of nut engaging rods 30 formed at the other end of the arm portion 15. In other words, the pair of nut engaging rods 30 are disk-shaped members formed via a branching portion 31 that is bifurcated in the Z-axis direction from the other end side of the arm portion 15.
On both side surfaces 4a and 4b facing the Z-axis direction of the ball screw nut 4, a disc-shaped nut engaging rod 30 is inserted, and an engaging groove 32 is formed to engage the periphery of the nut engaging rod 30. Yes.
The distance between the inner walls of the pair of nut engaging rods 30 is set to be approximately the same as the distance between the side surfaces 32a of the engaging grooves 32 formed on both side surfaces 4a and 4b of the ball screw nut 4. .

According to the present embodiment, the inner surfaces of the pair of nut engaging rods 30 of the swing arm 5 abut on the side surfaces 32 a of the engaging grooves 32 formed on the side surfaces 4 a and 4 b of the ball screw nut 4, so that the ball screw nut 4 is Since the rotation is disabled, when the rotational motion is transmitted from the motor 2 to the ball screw shaft 3, the ball screw nut 4 can perform a linear motion in the X-axis direction.
The ball screw nut 4 has a simple structure in which the peripheral edges of a pair of nut engaging rods 30 having a disk shape of the swing arm 5 are slidably engaged with the engaging grooves 32 of the ball screw nut 4. This linear motion can be transmitted as a rotational motion of the swing arm 5 with the output shaft engagement hole 16 side as the center of rotation.

  DESCRIPTION OF SYMBOLS 1 ... Actuator, 2 ... Motor, 3 ... Ball screw shaft, 4 ... Ball screw nut, 4a, 4b ... Side surface of ball screw nut, 5 ... Swing arm, 6 ... Output shaft, 7, 8 ... Bearing, 9, 10 ... Output side flat surface, 11 ... Output lever, 12 ... Pin insertion hole, 13 ... Pin, 13a ... End part, 14 ... Convex part, 15 ... Arm part, 16 ... Output shaft engagement hole part, 17 ... Nut engagement １９, 18, 19 ... rocking side inner plane, 20, 21 ... non-contact inner surface, 22 ... engagement groove, 23 ... notch slit, 24 ... projection, 25 ... dent, 26 ... sphere, 27 ... V groove, 28 ... annular groove, 29 ... output shaft pin, 30 ... nut engaging rod, 31 ... branching portion, 32 ... engaging groove, 32a ... side surface of the engaging groove, P1 ... axis of the ball screw shaft, P2 ... output shaft Axis, P3 ... axis of swing arm

Claims (7)

A ball screw shaft to which rotational motion is transmitted from a rotational drive source;
A ball screw nut that performs linear motion by the rotational motion of this ball screw shaft;
One swinging arm that has one end engaged with the ball screw nut and swings in a plane formed by an axis of the ball screw shaft and a first direction orthogonal to the axis of the ball screw shaft;
The ball screw nut extends in a second direction perpendicular to the axis of the ball screw shaft and the first direction, passes through the swing center of the swing arm, and is connected to the other end of the swing arm. An output shaft to which a rotational motion is transmitted by a swinging motion of the swinging arm by motion,
The other end of the output shaft and the swing arm is such that the swing arm has a degree of freedom of translation in the second direction, and the swing arm moves in the linear motion direction of the ball screw nut. Regulated and consolidated ,
2. The actuator according to claim 1, wherein the other end of the swing arm has a degree of freedom of rotation about the axis of the swing arm and is connected to the output shaft . A pair of output-side flat surfaces extending in parallel with each other in the second direction are provided at the end of the output shaft, and an engagement hole for inserting the end of the output shaft into the other end of the swing arm. Provided with a pair of swing side inner planes in which the pair of output side flat surfaces slide in a surface contact state in the engagement hole,
Providing a protrusion on at least one of the pair of output side flat surfaces,
An engaging groove into which the protrusion enters is provided in at least one of the pair of swing side inner planes that slide on at least one of the pair of output side flat surfaces, extending in the second direction. The actuator according to claim 1. A pin insertion hole that opens at the pair of output-side flat surfaces is formed at an end of the output shaft, and an end that protrudes from at least one of the pair of output-side flat surfaces into the pin insertion hole. The actuator according to claim 2 , wherein a pin is inserted . The actuator according to claim 2 , wherein a protrusion that enters the engagement groove is integrally formed on at least one of the pair of output side flat surfaces of the output shaft. Claim 2 recess is formed on at least one of the pair of output side flat surface of the output shaft, fit the sphere to the recessed portion, the spherical body is equal to or enter into the engaging groove as said protrusion The actuator described. The actuator according to any one of claims 1 to 5 , wherein one end of the swing arm is engaged with the ball screw nut so that the ball screw nut cannot be rotated . The ball screw nut is provided with a pair of anti-rotation planes facing each other in a direction perpendicular to the linear motion direction of the ball screw nut,
The actuator according to claim 6 , wherein a pair of engagement rods slidably abutting against the pair of rotation stop planes are provided at one end of the swing arm .

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