Digital command feedforward and PID temperature control for PET stretch blow molding machines

In this paper, a novel but simple control method using command feedforward and feedback PID control, or called two degrees-of-freedom (Two-DOF) control, is presented for temperature control of a stretch polyethylene terephthalate (PET) blow molding machine. To achieve required temperature control of PET bottle performs passing through both heating ovens, our proposed controller consists of a digital command-feedforward controller designed to improve the transient performance and track quickly temperature set-points, and a digital feedback proportional-integral-derivative (PID) controller proposed to eliminate temperature errors and accomplish disturbances rejection. Such a controller not only carries out precise temperature setpoint tracking under any arbitrary ambient environment, but also uses the practical expertise of the control practitioners working for PET blow molding machines. Excellent set-point tracking and disturbance rejection of the proposed control method are well illustrated by computer simulations and experimental results. The results also clearly show applicability and superiority of the proposed method in comparison with other existing controllers.