Model identification in extrusion cooking

Abstract : In this paper extrusion cooking is reduced to a single input-single output process and identification techniques are applied to derive transfer function models. A study is reported of the open-loop relationships between screw speed as the manipulated variable and die pressure as the controlled variable when extruding wheat flour with a twin-screw co-rotating extruder. Step tests were performed in various ranges from different working points. The auto-regressive moving average and external input model structure was used; in this model the parameters are estimated by the output error with extensive predictive model. The pressure responses to these step tests are complicated in that the steady-state gain is not constant, the identified transfer functions are of two types and the estimated model parameters fluctuate.