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

This paper addresses two interrelated problems in cross-directional (CD) co ntrol of paper making processes. The first problem is explaining paper prop erty streaks observed in many CD control installations. The streaks usually correspond to the high-resolution error profile harmonics with wavelength close to twice the actuator sparing. Typically, the streaks of paper weight or moisture are very stable, A question that often arises is whether the s treaks can be compensated by better tuning of the CD controller, The second , related, problem addressed in this paper is how the achievable high-resol ution error profile and its spectrum depend on the CD controller tuning. Th is paper compares the performances of a mapped controller and an optimal mu ltivariable controller. It also describes spectral characteristics of CD er ror profile around the Nyquist frequency, We demonstrate applications of th e developed analysis methodology to paper mill data where weight streaks ar e a problem.