ON-LINE COMPUTER CONTROL OF A PLASTICATING EXTRUDER.

On-line computer control of the extrudate thickness was carried out using a 2-1/2 inch extruder. Predried PMMA (polymethyl methacrylate) was extruded through a slit die. Three control methods, a conventional PI (proportional and integral) feedback controller, the Smith predictor and a feedforward plus feedback controller were tried for both set point changes (i. e. the extrudate thickness change) and load changes (i. e. the screw speed change). Results showed that both the PI feedback controller and the Smith predictor were satisfactory for set point change but not for load change. The feedforward plus feedback controller worked well for load change. To make the control algorithm more intelligent, an on-line adaptive control can be added to the feedforward controller.