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Abstract

Proper control of packing is critical to the quality of injection molded parts. To control the packing phase, nozzle pressure was chosen as a better indicator of the degree of packing than cavity pressure. This allows one nozzle pressure transducer to be used for different molds and is more suitable for industrial applications. The dynamics of nozzle pressure during the packing stage were studied and found to be both nonlinear and time varying. Therefore, an adaptive self-tuning controller was designed and implemented. Several improvements—an anti-windup estimate, an adaptive feedforward, and cycle-to-cycle adaptation—were incorporated to produce excellent packing pressure control results. The controller works well for a wide range of different conditions, such as set point profiles, barrel temperatures, molds, and materials.