Feedforward Control and Process Improvement for Some Time Series Disturbance Models

Thesis (Ph.D.)--University of Washington, 2012Process adjustment strategy is an important part of the process improvement methods, which is also called engineering process control (EPC), and it is often integrated with statistical process control (SPC) to improve the process control performance. While feedback control is used to compensate for the output deviation, feedforward control is a proactive control strategy based on a direct measurement of the disturbance, and it acts before the disturbance affects the system. Feedforward control is usually combined with feedback control for variation reduction. In this article, rationales for feedforward control are explained, and a new philosophy on its application is given. The feasibility condition for feedforward control application is illustrated from a new disturbance decomposition viewpoint, and the validity of some disturbance models which work well for feedforward control is investigated. Some relevant issues on process monitoring, feedback control and feedforward control are discussed and addressed