PURPOSE: To improve the accuracy and reproducibility of the shape in a tapered part by twisting a hollow glass tube contg. an optical fiber bundle to form a glass rod during heating and heating and stretching the glass rod.
CONSTITUTION: Headstocks 3, 3' are rotated in arrow 11, 11' directions by motors 17, 17' to apply preliminarily a tension Pm on a twisted glass rod in the stage of stretching said rod and forming a tapered part 12. The Pm is the sum of the tension Pa for moving the headstocks and the tension Pl when the rod 9 is softened by heating and is stretched. The Pe is as large as ≥several 100g and the headstocks 3, 3' do not move while the rod 9 is not heated. When the rod is rotated in the direction of an arrow 10 and is heated by a burner 5, the headstocks 3, 3' move by L and are stopped by switches 20, 20'. The motors 17, 17' are stopped by switches 19, 19' as well. The tension during stretching is measured with a tension analyzer 14 and the value thereof is compared with a reference tension value. A signal is generated in the output from a circuit 16 according to the result thereof and when the measured value is lower than the reference value, switches 22, 23 are turned off to stop supplying gaseous H2 and O2.
IKUTA YASUSHI
MAEDA MINORU
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