Model Predictive Control of Cavity Pressure in an Injection Moulding Process

Cavity pressure control is a means of improving repeatability and product quality in injection moulding processes. As the system behaviour is greatly dependent on the mould which is interchangeable and typically designed and manufactured independently of the machine’s control system challenges arise in designing a controller that yields high performance and robustness to be suitable for universal use. A cavity pressure controller intended to be used for a wide variety of moulds will likely need some form of reparametrisation. In order to gain user acceptance, the process of manual or automatic parametrisation of the controller to a new mould needs to be simple enough to be performed and understood by staff that are not necessarily control experts. Addressing this issue, the authors suggest an approach using a Model Predictive Controller that is based on a physically motivated grey-box model. The model is simple enough to be intuitively checked for plausibility but sophisticated enough to reproduce the dominant behaviour of the system. For automated parametrisation, a strategy based on two experiments is suggested. The experiments are tailored to be suitable for incorporation into the regular production process. The concept is presented and first experimental results are shown.