Temperature control by means of a CCD-camera in welding...

Glass manufacturing – Fiber making apparatus – With measuring – controlling – sensing – timing – inspecting,...

Reexamination Certificate

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C065S501000, C065S488000

Reexamination Certificate

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06499319

ABSTRACT:

The present invention relates to control of temperature by means of a CCD-camera when welding optical fibers, in particular optical fiber ribbons and devices for accomplishing such control, and it also relates to a method and a device adapted to weld fiber ribbons to each other.
BACKGROUND
A very important parameter when splicing optical fibers by welding is the temperature at the welding location. To be able to maintain the temperature of the fibers at a sufficiently high level and during a sufficient long time period are determining factors in order to obtain a low attenuation and a high mechanic strength in the splice produced.
A known method for an indirect control of the temperature of the fibers, which is used in some known welding devices, is called “Meltback”, see the article by G. Kiss, “High yield fusion splicing in the outside plant: using fiber meltback to monitor electrode condition”, National Fiber Operation Engineering Conference, Denver, USA, September 1996.
In Patent Abstracts of Japan, abstract of the Japanese patent application No. 2129607, a fusion splicing device is disclosed, in which the brightness of an optical fiber heated in an arc discharge is observed. The discharge heating temperature is checked from the area of the bright part of the optical fiber.
When optical fibers assembled to optical fiber ribbons are to be spliced by melting the ends of the optical fibers in an electric arc, a problem exists of making the ends of the opposite individual fibers contact each other before and/or in the very fusioning process. This is due to the fact that it is very difficult to cut off such fiber ribbons at an exactly straight angle in relation to the longitudinal direction of the respective fiber ribbon. Also, the operation of stripping the polymer protective coating of a fiber ribbon and the force then used can result in that some fibers in a fiber ribbon will be elongated more than other fibers. Hence, the end surfaces of the fiber ribbon will not even be located in a plane.
In Patent Abstracts of Japan, abstract of the Japanese patent application No. 5-142442, a fusion splicing method for “multiple fibers” is disclosed, in which the connecting ends of optical fibers are preheated “at a low temperature to the extent of not attaining an excess molten state. The molten end faces of the optical fibers are then pressed to each other and while the end faces are heated in the state at the temp. higher than the above-mentioned preheating temp., the optical fibers are pushed in, by which the optical fibers are fusion spliced.”
SUMMARY
It is an object of the invention to provide methods and devices for temperature control in welding optical fibers, which only use devices existing in conventional automatic welding machines, and in particular to provide methods for a simple determination of a suitable welding temperature.
It is another object of the invention to provide a method and a device which in a secure way can accomplish welded splices of fiber ribbons.
Thus the optical system and the CCD-camera, which is arranged in conventional automatic welding devices, are used for determining the light intensity in a picture of the optical fiber, when it is heated, a locked control of the CCD-camera being used, so that the automatic light intensity setting system thereof is shut off.
The light intensity in a picture captured of heated optical fibers is directly related to the fiber temperature according to Planck's radiation law. It is used for an active control of the fiber temperature in the procedure and when in advance determining suitable welding currents.
The method makes it possible for the welding device and the user to compensate for the influence of some environmental factors such as under-atmospheric pressures and electrode condition, which often cause a lowering of the temperature during the welding process, when welding parameters are used which are programmed for normal situations.
When welding optical fibers to each other, which can be optical fibers assembled to optical fiber ribbons, the following steps are used:
a. The optical fibers are heated to a welding temperature by means of an electric arc between electrodes, between which an earlier determined electrode current passes. The electrode current has here preferably been determined to always give a not to high temperature suited for welding the fibers.
b. The intensity of light emitted by the heated optical fibers is determined and is compared to a predetermined set value.
c. Thereupon, in the case where the intensity of the emitted light has been determined to deviate from the desired value by more than a predetermined amount, the electrode current is changed, preferably increased by a predetermined step, whereby the temperature of the optical fibers is also changed by a corresponding step, and thereupon the steps b. and c. are again repeated, and in the case, where the intensity of the emitted light has been determined to deviate from the set value by less than the predetermined amount, the heating is allowed to continue at this electrode current, whereby the welding is made.
A similar procedure is as follows:
a. The optical fibers are first heated to a temperature, at which they emit visible light but which temperature is well below the temperature, at which the material of the fibers melt and at which the welding is to be made.
b. The intensity of light emitted by the heated optical fibers is determined and is compared to a predetermined set value.
c. Thereu{acute over (p)}on, in the case where the intensity of the emitted light has been determined to be less than the set value, the temperature of the optical fibers is increased by a predetermined step, and thereupon steps b. and c. are again performed, and in the case where the intensity of the emitted light has been determined to be greater than or equal to the set value or to deviate from the set value by less than some small, predetermined value, the welding is made at that temperature.
A corresponding method can preferably be used for in advance determining an electrode current, which gives a desired temperature of an optical fiber, e.g. the temperature to be used in welding the fiber to a similar fiber or a temperature to be used in a softening step. The optical fiber is as above heated in an electric arc, through which an electrode current passes. The following steps are then performed:
a. An electrode current having a first value is made to pass in the electric arc in order to heat the optical fiber to a temperature, at which it emits visible light, but which is well below the desired temperature.
b. The intensity of light emitted by the heated optical fiber is determined and is compared to a predetermined set value, which is determined depending on the desired temperature.
c. Thereupon, in the case where the intensity of the emitted light has been determined to be less than the set value or generally to deviate from the set value by not less than a small, predetermined value, the electrode current is increased by a predetermined step and thereupon steps b. and c. are again performed, and in the case where the intensity of die emitted light has been determined to be equal to or higher than the set value or generally to deviate from the set value by less than the small predetermined value respectively, the used electrode current is taken as the electrode current, which gives the desired temperature. If the desired temperature is the welding temperature, the determined electrode current can then be used for welding the fiber to another fiber, whereby a correct temperature during the welding process can be achieved. The predetermined step can e.g. be equal to the small predetermined value or a little smaller.
In the step b. of the procedures described above for determining the intensity of light emitted by a heated optical fiber this determination can be made by
capturing a picture of the heated optical fiber, and
analysing the picture to find values corresponding to the intensity of light only in regions of the pictures of the optical fib

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