Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Optical fiber – waveguide – or preform
Reexamination Certificate
1998-09-22
2001-02-20
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Optical fiber, waveguide, or preform
C264S171130, C264S177170, C264S211120
Reexamination Certificate
active
06190583
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method for making a slotted rod which is accommodated in an optical cable and protects a plurality of optical fibers.
2. Related Background Art
Employed as a slotted rod for an optical cable is a slotted rod S (spacer) shown in
FIG. 1
in which a slot G accommodating an optical fiber is formed to meander as a so-called SZ groove in order to prevent extraordinary tension from being applied to the accommodated optical fiber and improve workability for taking out the optical fiber for branching. In general, such a slotted rod S is manufactured in a manner that, while a molten resin is extruded around a tension member L
0
by an extruder through its rotatable die, the die is rotated alternately in reverse directions to form the above-mentioned slot G in the outer peripheral face of the resin layer thus extruded.
In the above-mentioned method, however, due to the alternate reversing operation of the rotatable die (operation for alternating its rotational direction), the tension member L
0
maybe twisted, thereby the reversing angle &thgr; of the slot G in thus molded slotted rod S (the center angle formed on the slotted rod cross-section corresponding to the slot formed in a cycle of reversing rotation of the rotatable die(i.e. a period between any two consecutive reversions of the rotational direction of the die); see
FIG. 2
) may become smaller than the rotational angle of the rotatable die (the angle formed by a cycle of reversing rotation of the rotatable die). Consequently, in order for the slot G to attain a desired reversing angle, the rotatable die must have a large rotational angle, thus making it difficult to improve the manufacturing speed that depends on the speed of the alternate reversing operation. Here, in
FIG. 2
, P is a pitch for a cycle of reversing rotation of the rotatable die and corresponds to the distance which the tension member L
0
passes during such a single cycle (hereinafter referred to as a ‘reversing pitch’).
Known as the manufacturing apparatus having a rotatable die which alternately reverses its rotational direction are those disclosed in Japanese Patent Application Laid-Open No. 3-110509 and No. 1-303408. Japanese Patent Application Laid-Open No. 3-110509 discloses a manufacturing apparatus in which, for restraining the tension member from being twisted, the tension member is grasped upstream the rotatable die. Japanese Patent Application Laid-Open No. 1-303408 discloses a manufacturing apparatus in which, in the state where the tension member is grasped upstream the rotatable die, the grasping unit is synchronized with the reversing operation of the rotatable die such as to twist the tension member in the same direction as the rotation of the rotatable die.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus and method for making a slotted rod for an optical cable, which can lower the rotational angle of the rotatable die so as to improve manufacturing efficiency, while alleviating the load applied to the manufacturing apparatus.
The present invention relates to an apparatus and method for making a slotted rod for an optical cable. This slotted rod is constituted by a tension member placed at a center thereof and a resin layer disposed around the tension member, and a surface of the resin layer is formed with at least one slot in which a plurality of optical fibers are collectively accommodated.
For making the above-mentioned slotted rod for an optical cable, the apparatus according to the present invention comprises, at least, a grasping unit for grasping a tension member; and an extruder having a head portion with a space through which the tension member paid out from the grasping unit penetrates and, while injecting a molten resin into the head portion, extruding the resin coating around the tension member from a resin extruding orifice of the head portion. Arranged at the resin extruding orifice of the head portion is a rotatable die having a through hole for passing the tension member therethrough and a plurality of protrusions for forming the slots in the resin surface surrounding the tension member. While the resin is extruded around the tension member, the rotatable die is rotated about the pay-out direction of the tension member as its axis, alternately reversing its rotary direction at every reversing pitch of the tension member, thereby to form a slotted rod having measuring slots such as shown in FIG.
1
.
The apparatus according to the present invention further comprises a first driving system for rotating the grasping unit about the pay-out direction of the tension member as its axis as to twist the tension member by a predetermined amount, and a second driving system for rotating, about the pay-out direction of the tension member, the rotatable die disposed at the resin extruding orifice of the head portion. The first and second driving systems are driven and controlled by a controller electrically connected thereto. Specifically, the controller controls the second driving system such that the rotational direction of the rotatable die is alternately reversed in every predetermined pitch of the tension member, and controls the first driving system such that the tension member is alternately twisted in rotational directions opposite to the rotational directions of the rotatable die in synchronization with the rotation of the rotatable die. According to such a driving and controlling operation, the rotatable die and the grasping unit are always rotated in directions opposite to each other.
In other words, in the manufacturing method according to the present invention employing the apparatus configured as mentioned above, while the above-mentioned tension member is introduced into the extruder, the resin is extruded from the head portion to cover the tension member, the rotatable die is rotated about the moving direction of the tension member such that the rotatable die alternately reverses its rotational direction for every predetermined reversing pitch of the tension member, and the tension member is alternately twisted in rotational directions opposite to that of the rotatable die in synchronization with the rotation of the rotatable die. The grasping unit is disposed so as to apply an external force to twist the tension member that is introduced into the orifice of the head portion.
In accordance with the present invention, since the rotating operation of the grasping unit is made opposite to the rotating operation of the rotatable die, the rotational angle of the rotatable die can be made sufficiently small. As a result, even when the linear manufacturing speed is increased, the rotatable die can fully follow it, thus allowing the manufacturing efficiency to improve due to the higher linear speed. Also, since the driving load for the rotatable die can be alleviated, the apparatus can be made smaller and less expensive.
Since the rotational angle of the rotatable die is small, the shearing stress applied to the resin at the time of extrusion can be made small. As a result, the surface of thus made slotted rod (bottom part of the slot in particular) can be made smoother. When the surface roughness is high, irregularities in the surface are likely to apply stress to the optical fiber, thereby yielding a possibility of transmission characteristics being affected. Further, the mechanism for alternately rotating the grasping unit can have a configuration simpler than that of the mechanism for rotating the rotatable die incorporated in a complicated extruding mechanism, whereby a higher production efficiency can be easily realized.
Preferably, the rotational angle of the grasping unit (i.e. a rotational angle formed by the rotation of the grasping unit between any two consecutive reversions of its rotation) is set such that the rotational angle of the rotatable die and the reversing angle of the slot in the molded slotted rod equal each other. In this case, at the position where the rotatable
Okada Takehiko
Suemori Shigeru
Yasui Shigeki
Pillsbury & Winthrop LLP
Sumitomo Electric Industries Ltd.
Vargot Mathieu D.
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