PROCESS AND APPARATUS FOR CONTROLLING LATERAL DEVIATIONS IN A MOVING WEB

摘要

14 The invention relates to a process and apparatus for controlling lateral deviations of a moving web from its correct position. The process involves determining the actual position of the web and creating a positioning signal for a mechanism that controls the web's position, depending on the deviation of the actual position from the correct position. This is achieved with the help of an image/signal converter scanning at least a lengthwise portion of the web as it passes by the converter. A recognizable feature present in or on the web serves as a guidance criterion contained in the lengthwise portion is scanned at regular intervals and for each scan the image signals are stored and the actual position of the web is determined by analysis of the signals. For each scan the entire content of the image of the scanning field of the web covered by the image/signal converter is translated into image signals of only one single row of image dots extending crosswise to the web's direction of motion over the entire width of the scanning field. These image signals are stored. Before the control process begins, the image signals representing the guidance criterion are stored by themselves as fixed reference signals. During the control process the row of image dots with the image signals stored from each scan are regularly stepped against the row of image dots with the stored reference signals and for each stepping increment a similarity function is calculated from the signals of the two rows of image dots stepped against each other, the value of which function for each stepping increment is a measure for the degree of congruence of the two series of signals. The respective actual position of the guidance criterion is determined from the stepping with the function value that provides the best congruence.