Response of fiber diameter to a continuously changing draw ratio in a laser drawing process

The controllability of the fiber diameter profile with a changing draw ratio in a laser drawing process is discussed in comparison with model calculations. The take-up speed in the continuous drawing process was changed under constant acceleration, and the diameter profile of the resultant fiber was monitored on-line. It was revealed that the diameter profile was consistent with a profile predicted by a model calculation up to a certain acceleration. The profile was calculated by assuming a stationary neck-drawing point and elastic deformation of the fiber in the drawing system. Video observation revealed that the neck-drawing point did in fact move with changes in the draw ratio. Moreover, it moved faster at higher accelerations, particularly when the draw ratio was increased from low to high. It seems that the faster movement of the neck-drawing point causes the observed diameter change to lag behind that predicted by the model. The responsiveness of the diameter change could be further improved by shortening the distance between the feed and take-up rollers. The minimum response length was 5 cm as the draw ratio decreased from 8.0 to 4.0.