JP2004035345A - Optical fiber preform heating furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating furnace of an optical fiber preform that eliminates unnecessary excess in opening. <P>SOLUTION: This heating furnace is for heating a vertically supported optical fiber preform 1 and has opening and closing shutters 4 and 5, one installed at the upper opening 31 and the other at the lower opening. The shutters 4 and 5 are each comprised of a plurality of shutter plates 4A, 4B; 5A, 5B; 11 arranged so as to be one on top of the other in the axial direction or arranged so as to contact with each other at the same level in the axial direction. The opening areas of the openings are adjusted by shifting each of shutter plates 4A, 4B; 5A, 5B;11 in the radial direction. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber preform heating furnace, and more particularly to an optical fiber preform heating furnace having open / close shutters at both upper and lower openings.
[0002]
[Prior art]
Referring to FIG. 4, a process of suspending the optical fiber preform 1 in the heating furnace 3 via the dummy bar 2 attached to the upper end thereof and performing the spinning process while heating with the heater 3A will be examined.
[0003]
As is well known, a clean gas such as an inert gas, air, or oxygen (not possible in the case of a furnace using carbon) is introduced into the heating furnace 3 to make the inside of the furnace positive pressure, and dust and unnecessary It is common practice to prevent gas from entering and extend the life of consumables.
[0004]
FIG. 4 (a) shows the state at the start of the spinning process. At this time, the upper and lower openings of the heating furnace 3 are almost completely closed by lids 14 and 15, respectively, and the temperature inside the furnace is reduced. Also, the inert gas and the like introduced and circulated into the heating furnace 3 are not consumed unnecessarily.
[0005]
However, in the state shown in FIG. 2B, where the spinning process proceeds and the portion of the dummy rod 2 reaches the upper opening, the inner diameter of the hole of the upper lid 14 that has passed through the main body portion of the optical fiber preform 1 earlier is smaller than the inner diameter of the hole. The outer diameter of the dummy rod 2 is too large, so that the hot air inside the furnace escapes from the gap e that is generated, the inert gas or the like is wasted, and there is a possibility that an unnecessary gas may enter.
[0006]
FIGS. 5A and 5B show a conventional countermeasure for remedying such inconvenience. FIG. 5A shows an upper lid having an inner diameter large enough to accommodate the optical fiber preform 1 and being machined in the axial direction. A hollow cylindrical lid 16 having a height sufficient to cover its length protruding into the upper part of the furnace at the start and having a hole at the upper end through which the dummy rod 2 can pass is shown.
[0007]
FIG. 5B shows a countermeasure for connecting the dummy rod 2A having the same diameter as the optical fiber preform 1. In this case, the processing proceeds as much as possible, and the portion of the optical fiber preform 1 is moved to the upper cover 14A. Therefore, even if the dummy rod 2A is displaced downward from the passage hole, the dummy rod 2A having the same diameter is replaced instead, so that there is no gap.
[0008]
[Problems to be solved by the invention]
However, in the former measure, the volume in the heating furnace 3 increases, so that the cost for maintaining the heating temperature and the cost of inert gas and the like increase, and the length of the dummy rod 2 also needs to be increased. This is not an advantageous measure, and the latter measure has the drawback that the cost for increasing the size of the dummy rod 2A is extremely large, and that the work time for connecting the dummy rod 2A to the optical fiber preform 1 becomes too long.
[0009]
[Means for Solving the Problems]
The present invention has been made to solve all the above-mentioned problems, and a solution according to the invention of claim 1 is a heating furnace that heats an optical fiber preform in a vertically supported state. Opening / closing shutters are respectively provided at the upper opening and the lower opening, and the opening / closing shutters are formed of a plurality of shutter plates that are arranged in an axially overlapping or abutting state at the same height in the axial direction. An optical fiber preform heating furnace characterized in that an opening area of the opening can be adjusted by moving a shutter plate in a radial direction.
[0010]
The optical fiber preform heating furnace according to claim 1, wherein the solution according to the invention of claim 2 is such that one or both of the opening and closing shutters are provided in a plurality in the axial direction. It is.
[0011]
According to another aspect of the present invention, an outer diameter measuring device is provided just above the upper opening, and the amount of movement of each of the shutter plates is determined according to the momentarily measured result of the outer diameter measuring device. 3. The light according to claim 1, wherein the optical fiber is moved in accordance with a movement amount instruction program which is prepared and input in advance in accordance with a numerical value of the shape of the optical fiber preform which is measured and known in advance. This is a fiber preform heating furnace.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. An opening / closing shutter 4 is provided at an upper opening 31 of the heating furnace 3, and an opening / closing shutter 5 is provided at a lower opening. An outer diameter measuring device 6 for measuring the outer diameter of the optical fiber preform 1 or the dummy rod 2 moving in the axial direction and passing therethrough is provided above the upper opening / closing shutter 4.
[0013]
Since the open / close shutters 4 and 5 have the same structure, this will be described with reference to FIG. At a symmetrical position symmetrical with respect to the center axis YY of the heating furnace 3, a plurality of, in the illustrated example, two shutter plates 4 </ b> A and 4 </ b> B overlap in the axial direction or abut against each other at the same height in the axial direction. Will be arranged.
[0014]
The opposing ends 41 of the shutter plates 4A and 4B are formed in an arc shape that partitions the opening into a substantially circular shape so that the opening is in the maximum open state if the two shutter plates are configured to overlap each other. The shutter plates 4A and 4B move close to each other, and their openings are sequentially reduced from the maximum state.
[0015]
When the shutter plates 4A and 4B are configured to abut each other, the opposing end 41 defines a substantially circular shape having a minimum opening when the shutter plates 4A and 4B are closest to each other, and the shutter plates 4A and 4B are separated from each other. As the opening area increases, the opening area increases.
[0016]
The above description is for the simplest case of two sheets, and it is natural that a gap can be prevented from being formed in the opening by increasing the number of sheets and adding an auxiliary shielding plate. For example, by installing a plurality of shutters that open and close in the axial direction in such a manner as to be close to and away from each other in the radial direction, and by stacking the shutters in a direction in which the opening and closing operations are angularly shifted, the gap in the closed state can be reduced. The overall size can be reduced.
[0017]
The mechanism for moving the shutter plates 4A and 4B in the radial direction with respect to the center axis YY is provided by a pinion 7 rotated by a drive motor M1 (M2 for the open / close shutter 5, which is optimally a servo motor) as shown in the figure. A mechanism for moving the rack 8 forward and backward may be used, and a fluid pressure cylinder or the like (not shown) may be used.
[0018]
The whole mechanism of the opening / closing shutters 4 and 5 is integrated on the frame F, and a specific mechanism (not shown) is configured to enable adjustment in an angle direction different from the adjustment direction by the rack 8. You may.
[0019]
Next, control for adjusting the degree of opening of the upper and lower openings of the heating furnace 3 will be described. Since the optical fiber preform 1 moves vertically from top to bottom, an outer diameter measuring device 6 is provided immediately above the upper opening / closing shutter 4 so that the optical fiber preform 1 passes therethrough. The outer diameter of the part is measured.
[0020]
According to the measurement data, the degree of opening of the upper opening 31 through which the measurement portion passes immediately after and the lower opening through which the measurement portion passes after a certain period of time is controlled. The control method may be real-time feedback control based on the outer diameter measurement data every moment.
[0021]
Alternatively, a previously measured and known shape numerical value of the optical fiber preform 1 to be used, that is, for example, how many millimeters the outer diameter of the end portion is, and how many millimeters the outer diameter at the position where it is raised in the axial direction by how many millimeters. It is also easy to prepare a control program in advance based on such information and adjust the degree of opening of the upper and lower openings according to the program.
[0022]
In some cases, the center axis of the optical fiber preform 1 may not coincide with the center axis YY of the heating furnace 3. Since the center axis position of the optical fiber preform 1 can be determined from the edge data measured by the outer diameter measuring device 6, the centering operation is first performed in this case. This is performed by the mechanism of the open / close shutters 4, 5 shown in FIG. What is necessary is just to move the frame F including the whole in a required direction by a required amount.
[0023]
The one shown in FIG. 3 is used for a diaphragm mechanism of a camera, and according to this, the size of the area can be adjusted while keeping the target opening in a very precise circular shape. Since the mechanism is a well-known mechanism, a disk 10 having substantially the same diameter can be relatively concentrically rotated on the disk 9 around the center O (9A is a handle for the relative rotation). Assuming that the opening circumference is indicated by reference numeral 32, a large number of shutter plates are rotatable around a point P on a circumferential line 10A having a diameter exactly intermediate the diameter of the circumference 32 and the outer diameter of the disk 10. 11 are provided in an overlapping state.
[0024]
The shutter plate 11 has a shape obtained by cutting a circle having a width b having the outer circumference and the circumference 32 of the disk 1O as the outer circumference and the inner circumference, respectively, by a predetermined center angle. In the drawing, when the inner peripheral line is placed at a position passing through the center O, the end 11B opposite to the end 11A rotatably attached to the point P is exactly at the position of the outer peripheral line of the disk 10. Is the central angle. The end 11B of the lever is attached to the disk 9.
[0025]
With the above configuration, if the disc 9 is rotated counterclockwise relative to the disc 10 with the handle 9A, the disc 9 is opened to the maximum opening state shown in FIG. If it is turned until it stops, it can be brought into a nearly completely closed state with an opening area of zero.
[0026]
Although not shown, there is another embodiment of the present invention in which a plurality of upper and lower opening and closing shutters are provided so as to be overlapped in the axial direction. Alternatively, a plurality of upper openings 31 may be provided, and a single opening / closing shutter may be provided in the lower opening.
[0027]
The types of these opening / closing shutters may be all the same, or one of them may be used as the mechanism shown in FIG. 2 and the other as the mechanism shown in FIG.
[0028]
【The invention's effect】
According to the present invention, unnecessary outside air does not enter the vicinity of the optical fiber preform during the heating step, so that dust and the like do not adhere to the optical fiber of the product, which is greatly effective in improving transmission characteristics.
In addition, there is an advantage that running temperature of a heating process such as spinning can be reduced because temperature reduction due to convection and radiation from the inside of the heating furnace is prevented, and consumption of an inert gas or the like to be used is reduced.
[0029]
Specifically, unnecessary external air is oxygen in the case of a carbon furnace, and the intrusion of this oxygen prevents the furnace body and parts from being oxidized and worn, and the zirconia furnace prevents nitrogen from entering. In addition, there is an advantage that deterioration of the furnace and parts due to the reduction reaction can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic side sectional view schematically showing an apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view showing an example of a mechanism for driving a shutter plate of an opening / closing shutter.
FIG. 3 is a plan view showing another example of a mechanism for driving a shutter plate of an opening / closing shutter.
FIG. 4 is a side sectional view for explaining a drawback of a conventional heating furnace in a spinning process.
FIG. 5 is a simplified side sectional view for explaining a conventional measure against the drawback.
[Explanation of symbols]
Reference Signs List 1 optical fiber preform 2, 2A dummy rod 3 heating furnace 31 upper opening 4, 5 opening / closing shutter 4A, 5A, 11 shutter plate 6 outer diameter measuring instrument 7 pinion 8 rack 9 disk 10 disk

Claims (3)

A heating furnace for heating an optical fiber preform (1) in a vertically supported state, wherein open / close shutters (4, 5) are provided at an upper opening (31) and a lower opening, respectively. Each of the shutter plates (4, 5) comprises a plurality of shutter plates (4A, 4B; 5A, 5B; 11) which are arranged in the axial direction or arranged at the same height in the axial direction so as to abut against each other. (4A, 4B; 5A, 5B; 11) is configured so that the opening area of the opening can be adjusted by moving in the radial direction. 2. An optical fiber preform heating furnace according to claim 1, wherein one or both of said open / close shutters (4, 5) are provided in a plurality in the axial direction. An outer diameter measuring device (6) is provided immediately above the upper opening (31), and the amount of movement of each of the shutter plates (4A, 4B; 5A, 5B; 11) is measured by the outer diameter measuring device (6). The optical fiber preform (1) is moved according to a momentary measurement result or according to a movement amount instruction program previously created and input according to the shape numerical value of the optical fiber preform (1) measured and known in advance. The optical fiber preform heating furnace according to claim 1 or claim 2.

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