Control System Design for a Continuous Gravimetric Blender

Previdi F., D. Belloli, A. Cologni, S.M. Savaresi, D. Cazzola, M. Madaschi

In this work the control system for a continuous gravimetric blender for polymer extrusion process has been designed. The plant considered in this paper is a blending machine that mixes two different polymers, a bulk one and an additive. Each component of the mix is metered by a dedicated screw meter system. The mass delivered by each meter is measured by a load cell. The two components are poured into a hopper (the mixer) directly embedded on the extruder input. The control objectives are manifold and include: accurate mass flow estimate on the basis of the weight and screw speed measurements; accurate mass flow regulation of each meter; keeping of the relative proportions among
all the components that are metered in all the operating conditions; guarantee that inside the mixer there is always material enough to fulfill the mass flow variation request of the extruder.