Model reference optimal steady‐state adaptive computer control of plastics extrusion processes

The first true hierarchical automatic optimal control scheme for plastics extrusion has operated satisfactorily in the laboratory. The process operator is only required to specify desired output rate and die inlet melt temperature set‐points. The control variable set‐points are continually set by computer in line with an optimal policy pre‐programmed from off‐line solutions using models for extruder and die behavior. Feedback and feedforward control strategies are used to hold the melt temperature and pressure at die inlet within close tolerances using control actions calculated via process models and applied by a hierarchical cascade controller. The methodology is described by reference to a specific 40 mm diameter screw extruder fitted with a variable geometry annular blow molding die head, processing specific polymers. However, the control procedures are completely general and can be applied to any extruder‐die combination.