Basis Adjustment
Caliper stability across the width of a paper web relies upon this feedback mechanism to manage moisture and fibre distribution. Automatic profile control adjusts slice lips or spray headers in real time to counteract localized variations in grammage. Sensors located at the dry end of the machine monitor density and thickness across the sheet.
Discrepancies between the set target and the measured output trigger corrections to the headbox or the press section settings. Precise actuators respond to these deviations without manual intervention to ensure the final product meets specified uniformity standards.
Correction Dynamics
The system maintains sheet flatness by dividing the width of the web into zones that correspond to independent control elements. Each element receives an instruction based on the deviation measured by the scanners at the reel. The controller calculates the necessary shift in aperture or pressure to bring the localized grammage back within the specified variance limit.
Processing speed determines how frequently the system updates these positions to prevent harmonic oscillation or uneven drying. High frequency adjustments handle transient disturbances during reel changes while stable operation requires damping to avoid overcorrection.
Operational Constraints
Mechanical limits of the headbox hardware define the maximum correction range available to the control loop. Physical travel of slice screws dictates how much the system modifies the basis weight in a single zone. Friction within the linkages or dead time in the signal loop introduces latency between detection and the resulting change in the paper product.
Accurate calibration of the sensor array is mandatory because the system assumes the measurement reflects the actual state of the dry sheet. Errors in the alignment of the scanner path produce false readings that drive the actuators toward incorrect positions. Effective maintenance of the hardware keeps the deviation within the narrow tolerance required for high-grade packaging materials.
