Design of a feedback control system for real-time control of flow in a single-screw extruder

The topic of this paper is the design and experimental testing of a prototype feedback control system for the regulation of the volumetric flow in a polymer single-screw extruder. Flow regulation is achieved by means of joint regulation of the temperature and the pressure at the die. The overall controller architecture is constituted by three control sub-tasks: the inner-loop control of the local temperatures along the barrel; the outer-loop control of the temperature at the extruder output; the control of the pressure at the extruder output. In this work, the whole design procedure (modeling, controller design, and testing) is presented. Extensive tests have shown that the system reacts rapidly to changes in the operating conditions and effectively rejects disturbances due to unexpected changes in the quality of the material. The achieved regulation provides very small steady state errors both for pressure and temperature. Moreover, it is shown that this control system is a cost-effective alternative to mechanical volumetric pumps.