CONTROL OF PLASTIC MELT TEMPERATURE - A MULTIPLE-INPUT MULTIPLE-OUTPUT MODEL-PREDICTIVE APPROACH

Good control of plastic melt temperature for injection molding is very important in reducing operator setup time, ensuring product quality, and preventing thermal degradation of the melt. The controllability an d setpoints of other process parameters also depend on the precise mon itoring and control of plastic melt temperatures. We experimentally in vestigated the thermal interactions between the barrel zones of an ins trumented plastic injection molding machine (IMM). These interactions result from the zone temperature differences that are used in normal m achine operations. From these experimental interactions, multiple-inpu t-multiple-output (MIMO) and single-input-single-output (SISO) models were derived for controlling these zone temperatures using a Model Pre dictive Control (MPC) strategy. An experimental comparison was made be tween MIMO MPC and SISO MPC of plastic melt temperature, which showed that the MIMO MPC scheme is more energy efficient, having zero oversho ot.