Internal Model Control of an Industrial Extruder

For some industrial extruders it is difficult to maintain constant torque on the screw. One cause of this control problem is the highly non-linear dynamic behavior exhibited by these extruders. This paper describes the design and production experience of a non-linear Internal Model Controller for torque control. The controller is based on a non-linear dynamic model which relates the screw speed and screw torque. The theory of non-linear IMC is covered and its important differences to linear IMC are stressed. The design of the non-linear torque controller is covered in detail and plant operating data is presented to demonstrate its performance.