Patent ID: 6080278
Filing Date: 2000-06-27
Classification: D21G,Y10S

Abstract:
A control system for a sheetmaking machine having a wet end including a headbox for discharging wetstock onto a mesh conveyer, and forming elements residing beneath said conveyor at an impingement region of said wetstock onto said conveyer, each of said headbox and forming elements having associated adjustable operating variables controllable by one of fast response actuators, slow response actuators, and both of said fast response and slow response actuators for affecting dry end basis weight, said control system comprising:a first control loop including a means for obtaining basis weight (BW) measurements within said dry end and a means for converting said dry end basis weight into first control signals, and providing said first control signals to said headbox and forming elements to perform on-line adjustments of said operating variables, said first control loop having an associated first response time;a second control loop including:1) a means for obtaining wet-end basis weight (BW) measurements based on measurements of physical properties of said wetstock on said mesh conveyor within said wet end, wherein said wet end BW measurements including at least one of independent cross direction basis weight measurements and machine direction basis weight measurements,2) a means for predicting said dry end basis weight from said wet end basis weight measurements, and3) a means for converting said predicted dry end basis weight into second control signals and providing said second control signals to said headbox andforming elements to perform on-line adjustments of said operating variables, saidsecond control loop having an associated second response time;wherein said second response time is faster than said first response time and wherein said slow response actuators responding to said first control signals so as to perform coarse operating variable adjustments and said fast response actuators responding to said second control signals to perform fine operating variable adjustments.