Multivariable CD Control of a Large Linerboard Machine Utilizing Multiple Multivariable MPC Controllers, PaperCon '09 Conference

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The paper presents the application of multivariable cross-direction (CD) control to a large linerboard machine (9.6 m trim) equipped with a dilution profiling headbox with narrow actuator spacing, a steam shower, a water spray with narrow actuator spacing, and induction heating actuators. The use of multivariable CD control has significantly improved the quality of its finished product but has also generated new challenges specific to applying multivariable model predictive control (MPC) for large applications where the total number of manipulated actuators exceeds 600.

The paper shows how these challenges have been addressed by utilizing two multivariable cross-direction model predictive control (CD-MPC) systems: one is configured to minimize the dry weight and moisture variability by coordinating dilution profiling, steam shower and water spray actuators, and the second is configured to minimize caliper variability by coordinated control of induction heating actuators with feed-forwards from the actuators operating under the first CD-MPC controller. The advantage of using these two systems is that induction heating actuators will anticipate and react to any dilution profiling, steam shower, and water spray actuator setpoint changes that may adversely impact the caliper profile.