| 摘要 |
PROBLEM TO BE SOLVED: To surely detect the occurrence of abnormality to crack a porous glass body during the production of this porous glass body by a VAD method even at the time of thermal shrinking without addition of a special device. SOLUTION: While a target rod 12 is rotated by a rotary pulling up device 13, this target rod is pulled up and the glass particulates formed from a burner 16, etc., are deposited at the bottom end thereof to form the porous glass body 11. The image near the bottom end of the porous glass body 11 is picked up by a TV camera 21 and the bottom end position thereof is detected by an image processor 22. The detection region for detecting this position is kept narrow at the stationary time but this detecting region is expanded to avoid overlooking of the cracked and fallen soot at the time of thermal shrinking, by which the abnormality is surely detected. |
