Performance analysis of cross-direction process control using multivariable and spectral models

The paper addresses two interrelated problems in cross-directional (CD) control of papermaking processes. The first problem is that of paper property streaks observed in many CD control installations. The streaks usually correspond to the high-resolution error profile harmonics with wavelength dose to twice the actuator spacing. Typically, the streaks of paper weight or moisture are very stable. A question, which often arises, is if the streaks can be compensated by better tuning of the CD controller. The second, related, problem addressed in this paper is how the achievable high-resolution error profile and its spectrum depend on the CD controller tuning. The paper compares the performances of a mapped controller and an optimal multivariable controller. It also describes spectral characteristics of CD error profile around the Nyquist frequency. Applications of the developed analysis methodology to a paper mill data where weight streaks are a problem are demonstrated