Optimal digital control of a laboratory-scale paper machine headbox

This paper describes the design of a multiinput multioutput (MIMO) digital-linear-quadratic-regulator (DLQR) control system for the headbox of a paper machine. The complete design procedure is described from development of a mathematical model of the nonlinear headbox system, through experimental identification of linear model, to demonstration of closed-loop system performance on a laboratory-scale mock-up of an actual headbox. The important role of computer-aideddesign tools is illustrated using Matlab and associated toolboxes. The control algorithm is implemented on a personal computer running the Labtech Notebook control program. The controlled system satisfactorily controls set point changes in total pressure and water level, and rejects disturbances in feedwater pressure. The material presented in the paper is used in a senior level course in digital process control at the University of Idaho. The course is jointly offered by the chemical and electrical engineering departments.