Industrial Nucleonics Corporation

Bruce A Huber

Robert Lee Heiks

Ronald W Brand

Richard A Forbes

Thickness of a sheet being produced by an extruder is controlled in response to measurements of: sheet thickness, the speed at which material is fed through a screw of the extruder, as determined by screw speed, and the speed with which material is taken away from the extruder, as determined by sheet speed. Measured thickness is compared with a setpoint for sheet thickness and a determination is made as to whether the thickness is in a predetermined, deadband region relative to the setpoint, or if the sheet is out of the deadband because it is excessively thin or excessively thick. In response to the sheet thickness being in the deadband region, the screw speed is changed in response to a signal indicative of the product of sheet speed error and rate of change of screw speed with respect to sheet speed. Sheet speed is controlled by multiplying sheet speed error by a predetermined constant. In response to the sheet being excessively thin, screw speed, if it has not reached a maximum value, is changed by multiplying sheet thickness error by rate of change of screw speed with respect to sheet thickness; if the screw speed has reached a maximum value, sheet speed is changed by multiplying the thickness error by the rate of change of sheet speed with respect to thickness. In response to the sheet being excessively thick outside of the deadband region and the sheet speed has not reached a predetermined maximum, line speed is changed by multiplying sheet thickness error by the rate of change of sheet speed with respect to sheet thickness; if the line speed has reached the predetermined maximum, screw speed is changed in response to an indication of the product of sheet thickness error and rate of change of screw speed with respect to sheet thickness. The various rates of change are calculated from an equation which models sheet thickness, T, screw speed, V.sub.S, and sheet speed, V.sub.L, in accordance with: ##EQU1## where: A, B AND C ARE PREDETERMINED CONSTANTS DETERMINED FOR EACH EXTRUDER MACHINE AND ASSOCIATED APPARATUS.

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Boston, MA, United States of America

Bruce A Huber