A feed-forward/feedback run-to-run control of a mixed product process: Simulation and experimental studies

Abstract

Run-to-run (RtR) control is an important quality assurance method for batch-based manufacturing process. Usually, products of different grades are produced on a tool that will experience gradual drift between maintenance cycles. A feed-forward/feedback RtR control strategy that compensates this drift for all products manufactured on this tool was proposed. This and other RtR control schemes were analyzed and validated by simulation and experimentally using a bench scale reactor that produces silica particles with different diameters by a sol-gel process. A simple EWMA (exponentially weighted moving average) RtR control scheme based on products of the same grade was found to be stable but inefficient for infrequent products. A simple EWMA RtR control scheme that attributed disturbance entirely as the effect of tool drift was found to be unstable. The feed-forward/feedback RtR control proposed was able to maintain stable quality by effectively utilizing information about tool changes to adjust recipes of infrequent products. � 2007 American Chemical Society.