Modeling and control of an electro-hydraulic injection molding machine with smoothed fill-to-pack transition

In this paper the modeling of a typical injection cycle for an injection-molding machine (IMM) is examined. Both the mold filling and mold packing phases of the cycle are examined along with a critical fill-to-pack transition. The novelty in this modeling work is that the nonlinear model considers both the machine hydraulic actuator and polymer flow characteristics in extensive detail. The simulation model is validated against experimental data and demonstrates the availability of a relatively accurate system model for full cycle control design of this electro-hydraulic system. The accurate process model is used in the design of a controller for the injection cycle including the fill-to-pack transition. The overall algorithm includes two Iterative Learning Controllers connected by a bumpless transfer scheme between them. The algorithm is successfully tested through model simulations and machine experiments. The simulation and experimental results presented demonstrate a significantly smoother control signal and pressure transient between the two learning controlled phases as well as overall tracking convergence for each phase.