Cavity pressure control by iterative learning control with zero-phase filtering in injection molding

Cavity pressure featured by cycle is a crucial process variable to determine the product quality in injection molding. A feedforward and feedback control method based on iterative learning control (ILC) with zero-phase filtering is proposed. ILC is used as feedforward part to realize accurate trajectory tracking with information of previous cycle and proportional control is used as feedback part to reject disturbances present at current cycle. In order to overcome bad learning transients in ILC, the convergence condition in frequency domain is derived and the implementation method of monotonic decay of learning transients is presented. The experimental results show that the proposed method makes ILC with monotonic decay of learning transients and the accurate tracking of cavity pressure setting curve achieved.