JP2010102114A - Slot measuring method and device for optical fiber spacer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a slot measuring method for an optical fiber spacer that prevents a detecting accuracy degradation caused by the effect of the inertia forces of an eyeboard, even if the running speed of the optical fiber spacer is increased in the process of manufacturing the optical fiber spacer. <P>SOLUTION: An inertia force nullifying means 43 is disposed on the optical fiber spacer 3 together with a slot inverted angle measuring means 31 that has the eyeboard 33, the means 43 being used to nullify the inertia force of the eyeboard 33 rotated according to twist of the slot 3a of the optical fiber spacer 3. In this condition, the inverted angle of the slot 3a is measured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  According to the present invention, an inversion angle of a slot in an optical fiber spacer in which a slot for storing an optical fiber is inverted at a constant period and formed continuously in a longitudinal direction on a substantially cylindrical outer surface is rotated according to the twist of the slot. The present invention relates to a method and an apparatus for measuring a slot of an optical fiber spacer that is detected from a rotation amount of a plate.

  A tape slot type optical fiber cable is one in which a plurality of tape type optical fibers are accommodated in a laminated state in each slot (groove) formed in multiple strips on the outer periphery of a polyethylene optical fiber spacer.

The slot is continuously formed in the longitudinal direction by being inverted at a constant period in order to enable intermediate post-branching (the tape-type optical fiber accommodated in the slot is taken out from the slot for branching later).
5A and 5B illustrate a state in which the slot 3a of the optical fiber spacer 3 is inverted at a constant period. FIG. 5A is a side view of the optical fiber spacer 3, and FIG. 5B is a sectional view taken along line BB in FIG. (C) is CC sectional drawing of (a), (d) is DD sectional drawing of (a). For ease of understanding, (b) to (d) show a cross section of a tape slot type optical fiber cable in which a tape type optical fiber is accommodated in a slot.

In FIG. 5A, the position p1 of the CC cross section is an inversion position (neutral position) where the twisting direction of the slot 3a is reversed. The separation distance from the position p1 to the position p2 of the BB cross section and the separation distance from the position p1 to the position p3 of the DD cross section are both equal to L.
At the position p2, as compared with the position p1, the position of the slot 3a is twisted counterclockwise by an angle θ1. Further, at the position p3, the position of the slot 3a is twisted clockwise by an angle θ1 as compared with the position p1.
That is, the position of the slot 3a is reversed between the position p2 and the position p3. In FIG. 5A, the separation distance 2L from the position p2 to the position p3 is a half cycle pitch at which the direction of the slot 3a is reversed. It has become.

In the slot 3a of the optical fiber spacer 3, the direction of the slot 3a is reversed at every half cycle pitch shown in FIG. The slot movement angle 2θ1 at this time is referred to as a slot inversion angle.
The inversion angle of the slot greatly affects the transmission characteristics of the tape slot type optical fiber cable 1.
Therefore, conventionally, in the manufacturing process of the optical fiber spacer 3, the slot reversal angle is measured.

  The slot inversion angle measuring means for measuring the inversion angle of the slot measures whether or not the inversion angle of the slot in the manufactured optical fiber spacer is appropriate.

FIG. 6 shows a configuration example of the slot inversion angle measuring means.
This slot reversal angle measuring means 31 has the same configuration as the device disclosed as the slot shape detection unit in the following Patent Document 1, and is attached to the optical fiber spacer 3 at a fixed position on the travel path of the optical fiber spacer 3. The inversion angle of the slot is detected from the amount of rotation of the eye plate 33 that rotates according to the twist of the slot 3a.

  The eye plate 33 is a spacer similar to the cross-sectional shape of the optical fiber spacer 3 at the center of the disk by providing a pin (not shown) that fits into the slot 3a on the inner periphery of the disk portion through which the optical fiber spacer 3 is inserted. An insertion hole 33c is formed.

The eye plate 33 rotates according to the twist of the slot 3a when the optical fiber spacer 3 passes through the spacer insertion hole 33c.
The eye plate 33 is rotatably supported together with a first gear 34 integrated with the eye plate 33, and the amount of rotation of the eye plate 33 is engaged with the first gear 34 via the first gear 34. Is transmitted to.

The second gear 36 is the same gear as the first gear 34 and is rotatably supported at a fixed position meshing with the first gear 34. An angle detection device (rotary encoder) 38 for detecting the rotation amount of the second gear 36 is provided at the shaft end of the second gear 36.
Therefore, the rotation amount of the eye plate 33 is transmitted to the second gear 36 via the first gear 34 and detected by the angle detection device 38.

Japanese Patent No. 3852374

By the way, when the twist of the slot 3a is reversed, the inertial force to maintain the rotation until then is applied to the eyeplate 33 engaged with the optical fiber spacer 3 due to the inertia weight of the eyeplate 33.
This inertial force increases as the traveling speed of the optical fiber spacer 3 increases. When the traveling speed of the optical fiber spacer 3 exceeds a certain level, the inertial force exceeds the rigidity of the optical fiber spacer 3. As shown in FIG. 7, when the inversion position of the slot 3a is reached, the optical fiber spacer 3 is torsionally deformed, and the eye plate 33 is further rotated by θ2.

When the traveling speed of the optical fiber spacer 3 is higher than a certain level, the amount of rotation of the eye plate 33 that increases due to the inertial force becomes a non-negligible magnitude, and the inversion detected by the slot inversion angle measuring means 31. The reliability of the angle is impaired.
Therefore, in the optical fiber spacer slot measuring method and apparatus for detecting the slot reversal angle from the rotation amount of the eye plate 33 as described above, in the manufacturing process of the optical fiber spacer 3, the traveling speed of the optical fiber spacer 3 is increased. There was a problem that productivity could not be improved.

  The present invention has been made to solve the above-mentioned problems, and even when the traveling speed of the optical fiber spacer is increased, the slot reversal angle is highly accurate without lowering the detection accuracy due to the inertial force acting on the eyeplate. It is an object of the present invention to provide a method and an apparatus for measuring a slot of an optical fiber spacer, which can be detected in a short time, and thus can improve the productivity of the optical fiber spacer.

(1) In order to solve the above-described problems, the optical fiber spacer slot measuring method according to the present invention is such that a slot for storing an optical fiber is inverted on a substantially cylindrical outer surface and continuously formed in the longitudinal direction. A slot measuring method of the optical fiber spacer, wherein the inversion angle of the slot in the optical fiber spacer is detected from a rotation amount of the eyeplate rotating according to the twist of the slot,
An inertial force extinguishing means for generating an inertial force having the same magnitude and the opposite direction to the inertial force due to the rotation of the eyeplate is disposed on the optical fiber spacer together with the slot inversion angle measuring means having the eyeplate. The inversion angle of the slot is measured.

  (2) Further, in the slot measuring method of the optical fiber spacer according to the above (1), the inertia force extinguishing means has the same configuration as the slot inversion angle measuring means, and the slot inversion angle measuring means is equipped with the position. The slot may be mounted at a position shifted by a half cycle pitch, and the inversion angle of the slot may be measured.

(3) Further, in order to solve the above-described problem, an optical fiber spacer slot measuring device according to the present invention is mounted on a fed-out optical fiber spacer and rotates according to the twist of the slot on the optical fiber spacer. Slot reversal angle measuring means for detecting the reversal angle of the slot from the amount of rotation of the eyeplate, and the inertial force and magnitude due to the rotation of the eyeplate disposed on the optical fiber spacer together with the slot reversal angle measuring means. An inertial force extinguishing means that generates an inertial force that is the same and opposite in direction,
The inertial force extinguishing means has the same configuration as the slot inversion angle measuring means, and is provided at a position shifted by a half cycle pitch of the slot from the installation position of the slot inversion angle measuring means.

(4) Further, in order to solve the above-described problem, an optical fiber spacer slot measuring device according to the present invention is mounted on a fed-out optical fiber spacer and rotates in accordance with the twist of the slot on the optical fiber spacer. Slot reversal angle measuring means for detecting the reversal angle of the slot from the amount of rotation of the eyeplate, and the inertial force and magnitude due to the rotation of the eyeplate disposed on the optical fiber spacer together with the slot reversal angle measuring means. Multiple pairs of inertial force extinguishing means that generate inertial forces that are the same and opposite in direction,
The inertial force extinguishing means has the same configuration as the slot inversion angle measuring means,
The slot reversal angle measuring means and the inertial force extinguishing means which are paired with each other are arranged at positions equidistant from the reversal position across the reversal position of the slot.

According to the present invention, even when the traveling speed of the optical fiber spacer in the manufacturing process of the optical fiber spacer is increased and the inertial force generated by the eyeplate exceeds the rigidity of the optical fiber spacer, Since the inertial force extinguishing means for canceling the generated inertial force is provided, it can be avoided that the inertial force generated by the eyeplate causes torsional deformation in the optical fiber spacer.
Therefore, even when the traveling speed of the optical fiber spacer is increased to a certain level or more, the detection accuracy does not deteriorate due to the inertial force of the eyeplate, and the slot reversal angle can be detected with high accuracy. Productivity of the optical fiber spacer can be improved by increasing the traveling speed of the optical fiber spacer in the manufacturing process of the fiber spacer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an optical fiber spacer slot measuring method and apparatus according to the present invention will be described below in detail with reference to the drawings.
FIG. 1 is an explanatory view of a manufacturing process of an optical fiber spacer using the first embodiment of the slot measuring device for an optical fiber spacer according to the present invention, and FIG. 2 shows a main configuration of the slot measuring device shown in FIG. It is a perspective view.

In the manufacturing process of the optical fiber spacer shown in FIG. 1, the speed is adjusted by the capstan 21 and the dancer roll 23 on the downstream side of the apparatus in order to continuously manufacture the optical fiber spacer 3 having the cross-sectional structure shown in FIG. The wire is stored in the reel 25.
Further, the slot inversion angle is measured between the dancer roll 23 and the capstan 21 arranged in the front stage of the reel 25 by the slot measuring device 41 according to the first embodiment of the present invention.

The manufacturing process of the optical fiber spacer shown in FIG. 1 is substantially the same as the conventional manufacturing process except for the reversal angle measuring process performed by the slot measuring device 41, and the tensile body 9 stored in the reel 11 on one end side is the same. The capstan 13 is fed into a pair of extruders 14 and 15. Among the pair of extruders 14 and 15, the upstream extruder 14 applies an adhesive to the outer periphery of the tensile body 9, and the downstream extruder 15 coats the tensile body 9 with a polyethylene resin. The adhesive applied by the extruder 14 improves the adhesive strength of the polyethylene resin layer covered by the downstream extruder 15.
The downstream extruder 15 incorporates a die 15a for extruding a polyethylene resin layer coated with the strength member 9 into the cross-sectional shape of the optical fiber spacer 3 shown in FIG.
The extruded product 17 formed into a predetermined cross-sectional shape by the die 15a is cooled by the cooling device 18 and finished into the optical fiber spacer 3 having a predetermined cross-sectional shape.

  The slot measuring device 41 according to the first embodiment of the present invention is installed between the capstan 21 and the dancer roll 23 that feeds the optical fiber spacer 3 that has been molded through the cooling device 18 to the reel 25.

This slot measuring device 41 is mounted on the optical fiber spacer 3 drawn out from the capstan 21, and the inversion angle of the slot 3 a is determined from the rotation amount of the eye plate 33 that rotates according to the twist of the slot 3 a on the optical fiber spacer 3. The slot reversal angle measuring means 31 to be detected and the slot reversal angle measuring means 31 and the slot reversal angle measuring means 31 are arranged on the optical fiber spacer 3 to generate the inertial force having the same magnitude and the opposite direction due to the rotation of the eye plate 33. Inertial force extinguishing means 43 for canceling out the inertial force generated by the eye plate 33 is provided.
When the traveling speed of the optical fiber spacer 3 becomes higher than a certain level, the relationship between the reversal angle difference of the eyeplate 33 that increases due to the inertial force generated at that time and the traveling speed is proportional as shown in FIG. The relationship was confirmed.

The slot inversion angle measuring means 31 has the configuration shown in FIG.
In the present embodiment, the inertial force extinguishing means 43 has the same configuration as the slot inversion angle measuring means 31.

  The inertial force extinguishing means 43 is a position shifted on the optical fiber spacer 3 by a distance 2L (see FIG. 5A) corresponding to the half-cycle pitch of the slot 3a on the downstream side from the installation position of the slot inversion angle measuring means 31. Equipped with. That is, as shown in FIG. 2, the eye plate 33A constituting the inertia force extinguishing means 43 is separated from the eye plate 33 of the slot reversal angle measuring means 31 by a distance 2L corresponding to the half-cycle pitch of the twist of the slot 3a. And mounted on the optical fiber spacer 3.

  In this embodiment, the inertia force extinguishing means 43 has the same configuration as that of the slot inversion angle measuring means 31 and, for example, the inertia force generated in the gears 34 and 36 of the slot inversion angle measuring means 31 and the gear of the inertia force extinction means 43. In other words, the eye plate 33A of the inertial force extinguishing means 43 and the eye plate 33 of the slot inversion angle measuring means 31 are the same. Further, the eye plate 33A of the inertial force extinguishing means 43 is separated from the eye plate 33 of the slot reversal angle measuring means 31 by the half cycle pitch of the twist of the slot 3a. An inertial force having an opposite direction can be generated.

In the slot measuring device 41 described above, the slot reversal angle measuring means 31 shown in FIG. 6 determines the amount of rotation of the eye plate 33 that rotates according to the twist of the slot 3a via the gears 34, 36. By detecting at, the slot inversion angle 2θ1 is detected.
At that time, when the twist of the slot 3a is reversed, the inertial force (rotational moment) for maintaining the rotation until then is applied to the eyeplate 33 of the slot inversion angle measuring unit 31 due to the inertia weight of the eyeplate 33. work.

  However, the slot measuring device 41 of the present embodiment is equipped with inertia force extinguishing means 43. The inertia force extinguishing means 43 has the same configuration as the slot inversion angle measuring means 31 and is shifted from the slot inversion angle measuring means 31 by a distance 2L corresponding to the half-cycle pitch of the twist of the slot 3a. Therefore, the twist of the slot 3a at the position where the eye plate 33A of the inertia force extinguishing means 43 is mounted is reversed with respect to the twist of the slot 3a at the position where the eye plate 33 of the slot reversal angle measuring means 31 is mounted. It is twisted.

  Therefore, as shown in FIG. 2, the inertial force disappearing means 43 has an inertial force M1 having the same magnitude as that of the inertial force M1 acting on the eyeplate 33 of the slot reversal angle measuring means 31 and a reverse direction. M2 is generated and the inertial force M1 generated by the eye plate 33 of the slot reversal angle measuring means 31 is canceled.

  Accordingly, it is possible to prevent the optical fiber spacer 3 from being twisted and deformed by the inertial force generated by the eyeplate 33, and the influence of the inertial force of the eyeplate 33 even when the traveling speed of the optical fiber spacer 3 is increased to a certain level or more. Thus, the inversion angle of the slot 3a can be detected with high accuracy without lowering the detection accuracy. In addition, the productivity of the optical fiber spacer 3 can be improved by increasing the traveling speed of the optical fiber spacer 3 in the manufacturing process of the optical fiber spacer 3.

  Furthermore, since the inertia force extinguishing means 43 may have the same configuration as the slot reversal angle measuring means 31, it is unnecessary to develop a new inertial force extinguishing means 43, and the existing slot reversal angle measuring means 31 is installed in the conventional equipment. The slot measuring device 41 of the above embodiment can be obtained simply by adding to the above.

The measuring method performed by the slot measuring device 41 described above is the eye plate 33 that rotates the inversion angle of the slot 3a of the optical fiber spacer 3 continuously manufactured in the manufacturing process of the optical fiber spacer according to the twist of the slot 3a. The slot measurement method of the optical fiber spacer which detects from the amount of rotation is improved.
The improvement is that the inertial force extinguishing means 43 that cancels the inertial force M1 generated by the eyeplate 33 by generating the inertial force M2 having the same magnitude and the opposite direction as the inertial force M1 due to the rotation of the eyeplate 33, It is arranged on the optical fiber spacer 3 together with the slot inversion angle measuring means 31 having the plate 33 to measure the inversion angle of the slot 3a.

  Further, in the above-described embodiment, the inertia force extinguishing means 43 having the same configuration as the slot inversion angle measuring means 31 is mounted on the optical fiber spacer 3 from the installation position of the slot inversion angle measuring means 31. The slot 3a is installed at a position shifted by a half-cycle pitch, and the inversion angle of the slot 3a is measured.

However, the inertial force extinguishing means, which is an essential component in the slot measuring method of the present invention, only needs to cancel the inertial force generated by the eyeplate 33 of the slot reversal angle measuring means 31, and the specific configuration is the slot reversal angle measuring means. The configuration is not limited to 31.
For example, in the configuration shown in FIG. 6, the gears 34 and 36, the angle detection device 38, and the like may be omitted, and instead, a large eye plate in which the inertia weights of these omitted members are added may be used. .

  Further, when the eye plate used for the inertial force extinguishing means is changed to one having a size and weight different from that of the eye plate 33, the separation distance from the slot inversion angle measuring means 31 is also the half cycle shown in the above embodiment. It is not limited to the pitch. The inertial force generated by the eyeplate as the inertial force extinguishing means is the same as the inertial force generated by the eyeplate 33 of the slot reversal angle measuring means 31 and is separated from the eyeplate 33 so that the direction is reversed. The distance may be adjusted appropriately.

  Further, in the slot measuring method and apparatus for the optical fiber spacer according to the present invention, the number of slot inversion angle measuring means and inertial force extinguishing means provided on the traveling path of the optical fiber spacer 3 is the same as that shown in the above embodiment. The case is not limited. A plurality of pairs of slot reversal angle measuring means and inertial force extinguishing means may be provided.

FIG. 3 is a perspective view showing the configuration of the main part of the second embodiment of the slot measuring apparatus according to the present invention.
The slot measuring device 51 of the second embodiment is mounted on the optical fiber spacer 3 that is fed out, and the slot 3a is rotated from the amount of rotation of the eye plate 33 that rotates according to the twist of the slot 3a on the optical fiber spacer 3. Two slot inversion angle measuring means 31 and 32 for detecting the inversion angle, and the slot inversion angle measuring means 31 and 32 are arranged on the optical fiber spacer 3 and have the same inertial force and magnitude due to the rotation of the eye plate 33. There are provided two inertia force extinguishing means 43 and 44 that generate inertial forces of opposite directions and cancel the inertial force generated by the eye plate 33.

  The slot inversion angle measuring means 31 and 32 have the same configuration and the configuration shown in FIG. In order to simplify the drawing, the slot reversal angle measuring means 31 and 32 are not shown except for the eye plate 33.

The inertia force extinguishing means 43 is paired with the slot inversion angle measuring means 31 and cancels out the inertia force generated by the eye plate 33 of the slot inversion angle measuring means 31. The inertia force extinguishing means 44 is paired with the slot inversion angle measuring means 32 and cancels out the inertia force generated by the eye plate 33 of the slot inversion angle measuring means 32.
That is, the slot measuring device 51 of this embodiment includes two pairs of slot inversion angle measuring means and inertial force extinguishing means that make a pair with each other.

  In the case of this embodiment, the inertial force extinguishing means 43 and 44 have the same configuration as the slot inversion angle measuring means 31 shown in FIG. In these inertial force extinguishing means 43 and 44, reference numeral 33 </ b> A is a eyeplate that rotates according to the twist of the slot 3 a of the optical fiber spacer 3. The eye plate 33A has the same dimensions and weight as the eye plate 33.

  The slot reversal angle measuring means 31 and the inertial force extinguishing means 43 that are paired with each other are arranged at a distance L from the reversal position p1 across the reversal position p1 of the slot 3a, as shown in FIG. ing. In FIG. 3, the distance 2L between the slot reversal angle measuring means 31 and the inertial force extinguishing means 43 is the length of the half-cycle pitch of the slot 3a.

  Further, as shown in FIG. 3, the slot reversal angle measuring means 32 and the inertia force extinguishing means 44 are disposed at a position separated by a distance L1 from the reversal position p1 across the reversal position p1 of the slot 3a.

  That is, the slot inversion angle measuring means 31 and the inertial force extinguishing means 43 and the slot inversion angle measuring means 32 and the inertial force extinguishing means 44 that are paired with each other are equidistant from the inversion position p1 across the inversion position p1 of the slot 3a. Placed in position.

With this arrangement, the inertia force extinguishing means 44 generates the inertia force M4 having the same magnitude and the opposite direction as the inertia force M3 generated by the eyeplate 33 of the paired slot reversal angle measuring means 32. The inertial force generated by the eyeplate 33 of the slot reversal angle measuring means 32 is canceled out.
Further, the inertia force extinguishing means 43 generates an inertia force M6 having the same magnitude and the opposite direction as the inertia force M5 generated by the eye plate 33 of the paired slot inversion angle measuring means 31, and the slot inversion angle measuring means. The inertial force generated by the 31 eye plates 33 is canceled out.

  In the slot measuring device 51 of the second embodiment described above, the inertia force canceling action is doubled by providing two pairs of the slot reversal angle measuring means for canceling the inertia force and the inertia force extinguishing means. Therefore, the influence of the inertial force of the eyeplate in the slot reversal angle measuring means can be eliminated more reliably, and further improvement in detection accuracy of the reversal angle of the slot 3a can be expected.

It is explanatory drawing of the manufacturing process of the optical fiber spacer using 1st Embodiment of the slot measuring apparatus of the optical fiber spacer which concerns on this invention. It is a perspective view which shows the principal part structure of the slot measuring apparatus shown in FIG. It is a perspective view which shows the structure of the principal part of 2nd Embodiment of the slot measuring device which concerns on this invention. It is the figure which showed the relationship between the manufacturing speed of an optical fiber spacer, and a reversal angle difference. It is a figure explaining the slot of an optical fiber spacer, (a) is a side view of an optical fiber spacer, (b) is BB sectional drawing of (a), (c) is CC sectional drawing of (a), (D) is DD sectional drawing of (a). It is a perspective view of the slot measuring device of the optical fiber spacer used in the manufacturing process of the optical fiber spacer. It is explanatory drawing of the rotation amount of the eyeplate which increases by the influence of an inertial force.

Explanation of symbols

3 Optical fiber spacer 31 Slot reversal angle measuring means 32 Slot reversal angle measuring means 33, 33A Eye plate 33c Spacer insertion hole 34 First gear 36 Second gear 38 Angle detection device (rotary encoder)
41 Slot measuring device 43 Inertial force extinguishing means 44 Inertial force extinguishing means 51 Slot measuring device

Claims (4)

The reversing angle of the slot in the optical fiber spacer in which the optical fiber spacer is continuously formed in the longitudinal direction by reversing the slot containing the optical fiber on the outer surface of the substantially cylindrical shape is rotated according to the twist of the slot. A method of measuring a slot of an optical fiber spacer that is detected from a rotation amount,
An inertial force extinguishing means for generating an inertial force having the same magnitude and the opposite direction to the inertial force due to the rotation of the eyeplate is disposed on the optical fiber spacer together with the slot inversion angle measuring means having the eyeplate. A method for measuring the slot of an optical fiber spacer, comprising measuring the inversion angle of the slot.   As the inertial force extinguishing means, the same configuration as the slot inversion angle measuring means is installed at a position shifted by a half cycle pitch of the slot from the installation position of the slot inversion angle measuring means, and the inversion angle of the slot is adjusted. 2. The slot measurement method for an optical fiber spacer according to claim 1, wherein the measurement is performed. Slot reversal angle measuring means for detecting the reversal angle of the slot from the amount of rotation of the eye plate mounted on the optical fiber spacer to be fed and rotated in accordance with the twist of the slot on the optical fiber spacer, and the slot reversal angle An inertial force extinguishing means disposed on the optical fiber spacer together with the measuring means and generating an inertial force having the same magnitude and the opposite direction of the inertial force due to the rotation of the eyeplate,
The inertial force extinguishing means has the same configuration as the slot inversion angle measuring means, and is installed at a position shifted from the installation position of the slot inversion angle measuring means by a half cycle pitch of the slot. Fiber spacer slot measuring device. Slot reversal angle measuring means for detecting the reversal angle of the slot from the amount of rotation of the eye plate mounted on the optical fiber spacer to be fed and rotated in accordance with the twist of the slot on the optical fiber spacer, and the slot reversal angle A plurality of pairs of inertial force extinguishing means arranged on the optical fiber spacer together with the measuring means and generating inertial force having the same magnitude and the opposite direction of the inertial force due to rotation of the eyeplate,
The inertial force extinguishing means has the same configuration as the slot inversion angle measuring means,
The slot measuring device for an optical fiber spacer, wherein the slot inversion angle measuring means and the inertial force extinguishing means that are paired with each other are arranged at an equal distance from the inversion position with the inversion position of the slot interposed therebetween.

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