Patent ID: 7751923

Claim:
A process for the automatic control of the thickness of an extruded film, comprising: measuring a thickness value profile of the extruded film with a thickness-measuring probe that is moved at a uniform speed along a surface of the film in a direction (x) that is substantially perpendicular to a conveying direction (z) of the extruded film, the thickness-measuring probe recording for each measuring cycle the thickness value profile of the film at least across parts of an expansion area of the film in the direction (x) perpendicular to the conveying direction (z) by measuring thickness values at definite positions in the x-direction in each measuring cycle; transmitting the measured values to a control unit; storing the measured values in a storage unit; determining statistical values of the film thickness with a computer using a definite number of measuring cycles (N) and the stored measured values from recent and previous measuring cycles with different weighting factors (k), determining deviations in the statistical values of the film thickness from a target value; and generating control commands to a device for controlling the film thickness based at least in part on the deviations; wherein the number of measuring cycles used during the predetermined time-frame at the start of the extrusion process is smaller than a number of measuring cycles used subsequent to the predetermined start time-frame, and/or wherein at least one weighting factor used during the predetermined time-frame at the start of the extrusion process is larger than the weighting factor used subsequent to the predetermined start time-frame; and wherein the determining statistical values includes dividing the sum of the weighted measured values by the number of measuring cycles (N) and/or by the sum of the weights (k); and wherein the number of the measuring cycles (N) and/or at least one weighting factor(s) (k) used during the predetermined start time at the start of the extrusion process is/are traced back in a series of steps within a large number of measuring cycles to a larger number of measuring cycles and/or an at least one smaller weighting factor(s) used in the operation subsequent to the predetermined start time-frame.