Closed-Loop Analysis and Tuning of Cross-Direction (CD) Control for Sheet-Forming Processes

Abstract This paper presents the closed-loop performance analysis of a cross-direction (CD) control system and explores the tuning criterion for CD control applications. The paper extends the closed-loop analysis from a linear time-invariant causal (or temporal) control system to a linear non-causal (or spatial) CD control system. Although the CD controllers are different from the temporal controllers, both controllers exhibit similar closed-loop behavior, particularly, their disturbance rejection responses. The disturbance rejection expressed in the spectral domain is key to the performance analysis of a CD closed-loop control system. The spectral amplitude ratio can be used for establishing a tuning criterion for CD control applications. Combining the spectral response of disturbance rejection and the power specuum of process disturbances, the potential reduction of process variations can be estimated.