Process for drawing glass fiber using prediction of future geometric parameter of the fiber

A method of producing an elongated component of glass, said method comprising:

• heating a glass blank to form a softened region;
• drawing the component from the softened region in a drawing direction at a drawing rate to form a drawing bulb;
• continually taking measurements of a first geometric variable at a first measurement site adjacent the drawing bulb;
• continually taking measurements of a second geometric variable at a second measurement site displaced from the first site in said drawing direction by an intersite distance;
• determining for each measurement at the first site a respective value for a controlled variable, each value representing a first estimate of a value of an actual process parameter for a point in time that follows said respective first site measurement by a period of dead time, the actual process parameter being equal or related to the second geometric variable measured at the second site;
• each value for the controlled variable being determined from the respective first site measurement and on a comparison of a value of the actual process parameter determined from the most recent measurement at the second site with an earlier one of the values of the controlled variable, which value was determined based on the measurement at the first measurement site preceding said most recent second-site measurement by the respective period of dead time;
• comparing each of the values of the controlled variable with a desired controlled variable to obtain a respective value of a controlling variable;
• and
• controlling the drawing of the component responsive to the values of the controlling variable.