Abstract A method of paper machine drier limited control wherein grade changes are executed in a continuous feedback manner. One control loop drives conditioned weight from one value to another value via action on stock flow while a second control loop maintains moisture at a constant value via action on master speed. The conditioned weight and moisture control loops are coordinated so that a control action in one loop will not upset the controlled variable in the other loop. The change in conditioned weight is also coordinated with a corresponding change in the headbox slice opening. Changes in master speed necessary to maintain a constant moisture content are fed forward to a headbox jet-to-wire ratio control loop so that the headbox head may be adjusted for speed changes to keep the jet-to-wire ratio constant. An additional coupling is made between the jet-to-wire ratio control loop and the slice opening so that the fiber concentration of the jet is not thrown out of control by head changes and the rotational velocity of the rectifier rollers is controlled to eliminate pressure differentials at the slice.
IN A METHOD OF CONTROLLING A PAPER MACHINE HAVING A PULP STREAM FLOW FEEDING INTO A HEADBOX AND CONTROLLED BY A PULP STREAM VALVE TO THEREBY CONTROL TOTAL HEAD, TH, SAID HEADBOX BEING PROVIDED WITH RECTIFIER ROLLERS AND A SLICE THAT PERMITS PULP TO JET ONTO A MOVING WIRE TO FORM A PAPER SHEET AND FROM WHICH THE WATER PASSING THROUGH IS COLLECTED, MIXED WITH STOCK FROM A STOCK FLOW LINE CONTROLLED BY A STOCK FLOW VALVE AND SUPPLIED TO THE PULP STEAM, SAID SHEET THEN BEING PASSED AT A CHARACTERISTIC MASTER SPEED THROUGH A DRIER SECTION TO WHICH STEAM IS SUPPLIED IN A DRYER LIMITED MODE, THE STEPS COMPRISING: SCANNING SAID SHEET AFTER THE DRYER SECTION AND DETERMINING A VALUE RELATED TO THE MOISTURE OF SAID SHEET, COMPARING SAID MEASURED VALUE WITH A TARGET VALUE FOR SAID MOISTURE CONTENT, AND UTILIZING THE MOISTURE ERROR SIGNAL THEREFROM TO MANIPULATE AT SUBSTANTIALLY EVERY SCAN SAID MASTER SPEED SO THAT SAID MOISTURE CONTENT IS MAINTAINED WITHIN SPECIFICATIONS; DETERMINING A VALUE RELATED TO CONDITIONED WEIGHT OF SAID SHEET, COMPARING SAID MEASURED VALUE WITH A TARGET VALUE FOR SAID CONDITIONED WEIGHT, AND UTILIZING THE ERROR SIGNAL THEREFROM TO MANIPULATE SAID STOCK FLOW VALVE SO THAT CONDITIONED WEIGHT REMAINS WITHIN SPECIFICATIONS; CROSS-COUPLING CONDITIONED WEIGHT ERROR SIGNALS TO MASTER SPEED AND TO SAID MOISTURE ERROR SIGNAL SO THAT CHANGES IN CONDITIONED WEIGHT ERROR SIGNALS WILL NOT UPSET MOISTURE, CROSSCOUPLING SAID MOISTURE
Claim 2
Dependent Claim
235 words
IN A METHOD OF CONTROLLING A PAPER MACHINE HAVING A PULP STREAM FLOW FEEDING INTO A HEADBOX AND CONTROLLED BY A PULP STREAM VALVE TO THEREBY CONTROL TOTAL HEAD, TH, SAID HEADBOX BEING PROVIDED WITH RECTIFIER ROLLERS AND A SLICE THAT PERMITS PULP TO JET ONTO A MOVING WIRE TO FORM A PAPER SHEET AND FROM WHICH THE WATER PASSING THROUGH IS COLLECTED, MIXED WITH STOCK FROM A STOCK FLOW LINE CONTROLLED BY A STOCK FLOW VALVE AND SUPPLIED TO THE PULP STEAM, SAID SHEET THEN BEING PASSED AT A CHARACTERISTIC MASTER SPEED THROUGH A DRIER SECTION TO WHICH STEAM IS SUPPLIED IN A DRYER LIMITED MODE, THE STEPS COMPRISING: SCANNING SAID SHEET AFTER THE DRYER SECTION AND DETERMINING A VALUE RELATED TO THE MOISTURE OF SAID SHEET, COMPARING SAID MEASURED VALUE WITH A TARGET VALUE FOR SAID MOISTURE CONTENT, AND UTILIZING THE MOISTURE ERROR SIGNAL THEREFROM TO MANIPULATE AT SUBSTANTIALLY EVERY SCAN SAID MASTER SPEED SO THAT SAID MOISTURE CONTENT IS MAINTAINED WITHIN SPECIFICATIONS; DETERMINING A VALUE RELATED TO CONDITIONED WEIGHT OF SAID SHEET, COMPARING SAID MEASURED VALUE WITH A TARGET VALUE FOR SAID CONDITIONED WEIGHT, AND UTILIZING THE ERROR SIGNAL THEREFROM TO MANIPULATE SAID STOCK FLOW VALVE SO THAT CONDITIONED WEIGHT REMAINS WITHIN SPECIFICATIONS; CROSS-COUPLING CONDITIONED WEIGHT ERROR SIGNALS TO MASTER SPEED AND TO SAID MOISTURE ERROR SIGNAL SO THAT CHANGES IN CONDITIONED WEIGHT ERROR SIGNALS WILL NOT UPSET MOISTURE, CROSSCOUPLING SAID MOISTURE