Electric heating – Metal heating – By arc
Reexamination Certificate
1997-10-17
2001-03-27
Paschall, Mark (Department: 3742)
Electric heating
Metal heating
By arc
C219S121460, C219S121540, C385S096000
Reexamination Certificate
active
06207922
ABSTRACT:
The present invention relates to electronic control in welding and/or heating optical fibers by means of an electric discharge, in particular a control of the electric quantities of the electric discharge.
BACKGROUND
When optical fibers are welded by means of the intense heat in an electric discharge the physical characteristics of the discharge change when the surrounding air pressure varies. Thus the electric voltage over the electrodes between which the discharge is formed is reduced when the air pressure decreases, which in turn results in a reduction of the electric current in the electric discharge and thus a lower temperature in the discharge region and thus in the region of the fibers heated by the discharge. It results in turn in inferior welded splices generally having a larger attenuation than splices welded at normal air pressure.
Thus, when welding optical fibers an electric discharge in air of atmospheric pressure is used, the discharge being self-igniting and self-sustaining and obtained when only applying a sufficiently high voltage between the cold, stationary welding electrodes, such a discharge being called a glow discharge, using the strict language of plasma physics. In the glow discharge electrons are emitted by secondary emission, principally owing to positive ions hitting the electrodes. When the current between the electrodes is increased from the values existing in the glow discharge, an arc discharge is obtained, and then the voltage between the electrodes is reduced to a very low value. A diagram illustrating the conditions when increasing from zero and on the voltage/current between two cold electrodes is shown in
FIG. 1
a
. In region R
1
a small voltage is applied over the electrodes and a very small current will then pass between the electrodes, which increases up to a saturation current. Region R
2
is a transitional region reached when increasing the voltage even more and finally region R
3
is reached which is the normal glow discharge region, producing a constant voltage between the electrodes called the burn voltage, the voltage in region R
2
just before continuing to region R
3
being called the ignition voltage. The glow voltage is determined by the exterior electrical circuit in which the electrodes are connected. When then increasing the current between the electrodes region R
4
is obtained called abnormal glow discharge. Finally, in region R
5
which is obtained when the current has been increased even more, an arc discharge is produced. In region R
4
and even more in region R
5
the high current density at the electrodes causes a heating thereof, finally resulting in that the negative electrode, the cathode, is so hot that electrons are emitted thermally and that the electrode voltage reaches a few or some ten of volts. The region R
5
is used for ordinary welding of metals or similar materials, the initial heating of the negative electrode then being accomplished by heat generated in a contact resistance between the electrodes or between an electrode and the material to be welded, so that no high voltage is ever applied.
Different ways for compensating variations in the exterior air pressure when welding optical fibers using a glow discharge have been proposed:
The published European patent application EP A1 0 504 519 for Fujikura Ltd. discloses an optical fiber welding device comprising a discharge unit 2 for obtaining an electric discharge for melt-fusioning optical fibers, a pressure sensor 6 for providing a signal corresponding to the ambient atmospheric pressure and a “discharge control unit 3” for controlling the discharge in relation to the pressure signals so that to the discharge unit 2 an optimal current is delivered during the discharge. By using feedback through a line from a resistor 251 in the welding electrode circuit the welding current can be maintained constant. The Japanese patent application JP A 63-106706, which is available to the public, also for Fujikura Ltd. relates to an optical fiber welding device of a similar kind.
The German patent application DE A1 37 24 914 made available to the public, for kabelmetal electro GmbH, describes a procedure for connecting two optical fibers by means of the energy from an electric discharge. The procedure comprises among other things a control of the (gas) pressure which exists around the electric discharge and of the current through the electric discharge.
U.S. Pat. No. 5,002,351 for Szanto et al. relates to a melt welding device for optical fibers where it, according to the abstract, is arranged that “Once an arc is established between opposed electrodes, constant power is provided during the splicing.” From the specification of this patent it is not apparent what is meant by “power” of how “constant power” can be achieved.
SUMMARY
It is an object of the invention to provide means whereby a good quality of welded splices and thus splices having a low attenuation and a good strength can be obtained when welding optical fibers to each other using an electric discharge.
It is another object of the invention to provide a control of the electric quantities in an electric discharge which is used for welding optical fibers together, so that essentially the same quality of a finished splice is obtained at a varying surrounding air pressure.
These objects are achieved by a method and a device according to the invention, the detailed characteristics of which appear from the appended claims.
Thus, in welding optical fibers a glow discharge between welding electrodes is used, and in the discharge region the ends of the fibers are located to be heated by the energy of the discharge. The electric power developed in the electric discharge is fed back to a control unit controlling the heating process. The electric power is measured for instance as a product of a voltage which corresponds to an average value of the rectified, for instance full wave rectified, voltage, between the welding electrodes and a current which in the same way corresponds to an average value of the rectified, for instance full wave rectified, current flowing in the discharge from one electrode to the other.
A first voltage can then be produced which is proportional to the instantaneous electric power developed in the electric discharge when making the welding. It is fed back to a control circuit for controlling circuits for generating the high voltage over the electrodes, so that the electric power is maintained substantially constant during the welding operation. Then, a second voltage can be produced which is representative of or proportional to the electrical current between the welding electrodes, and a third voltage which is representative of or proportional to the voltage over the welding electrodes. The second and third voltages are multiplied by each other in a multiplying circuit for generating the first voltage.
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I. Yokohama et al., “Fiber-Coupler Fabrication with Automatic Fusion-Elongation Processes for Low Excess Loss and High Coupling-Ratio Accuracy,”IEEE Journal of Lightware Technology, vo. LT-5, No. 7, pp. 910-915 (Jul. 1987).
Dumitriu Ion
Hulten Ola
Burns Doane Swecker & Mathis L.L.P.
Paschall Mark
Telefonaktiebolaget LM Ericsson (publ)
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