Cycle-to-cycle and within-cycle adaptive control of nozzle pressure duringpacking-holding for thermoplastic injection molding

Proper control of packing is critical to the quality of injection molded pa rts. To control the packing phase, nozzle pressure was chosen as a better i ndicator of the degree of packing than cavity pressure. This allows one noz zle pressure transducer to be used for different molds and is more suitable for industrial applications. The dynamics of nozzle pressure during the pa cking stage were studied and found to be both nonlinear and time varying. T herefore, 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 pr essure control results. The controller works well for a wide range of diffe rent conditions, such as set point profiles, barrel-temperatures, molds, an d materials.