Method and apparatus for calibration of blown-film extrusion apparatus

A method of autonomously calibrating product output width from a blown-film extrusion apparatus, the method comprising the steps of:

• extruding, from a tube extrusion die including a width controller, a polymer tube;
• flattening the tube and accumulating the flattened tube at an accumulation point;
• continuously measuring, proximal the tube extrusion die, a diameter of tube extruded by the die, to produce a plurality of layflat samples;
• continuously measuring, downstream of the tube extrusion die and proximal the accumulation point of flattened tube, a width of the flattened tube, to produce a plurality of flat-width samples;
• monitoring relative positions of each edge of the flattened tube and calculating a rate of change of the relative positions, and, if the rate of change of the relative position of one edge oscillates above a selected threshold, indicating a wrinkle at the edge of the flattened tube, and, if the rate of change of the relative position of one edge exceeds a threshold for a selected period of time, indicating a curl at the edge of the flattened tube;
• calculating a slope value over each of a plurality of selected intervals of the layflat samples and the flat-width samples to determine the stability of the diameter of the tube and the width of the flattened tube;
• calculating a y-intercept value over each of the selected intervals of the layflat samples and the flat-width samples to determine a forecast trend of the diameter of the tube and the width of the flattened tube;
• calculating a variance value of the slope values of each of the layflat samples and flat-width samples;
• and
• when the slope values, y-intercept values, and variance values are within selected parameters indicative of a stable operation of the tube extrusion die and wrinkles and curls at the edges have been absent for selected intervals, calibrating the tube extrusion die by inputting one of the flat-width samples to the width controller.

A method of autonomously detecting curl and wrinkle conditions in flattened tubing in a blown-film extrusion apparatus, the method comprising the steps of:

• extruding, from a tube extrusion die including a width controller, a polymer tube;
• flattening the tube and accumulating the flattened tube at an accumulation point;
• measuring a width of the tube;
• monitoring relative positions of at least one edge of the flattened tubing prior to the accumulation point and calculating a rate of change of the relative positions;
• if the rate of change of the relative position of the edge oscillates above a selected threshold, indicating a wrinkle at the edge of the flattened tube;
• if the rate of change of the relative position of the edge exceeds a threshold for a selected period of time, indicating a curl at the edge of the flattened tube;
• and
• when the measured width is within selected parameters indicative of a stable operation of the tube extrusion die and wrinkles and curls at the edge have not been indicated for a selected interval, calibrating the tube extrusion die by inputting the measured width to the width controller.