Control of Papermaking Processes with Respect to Square Point Conditions

Abstract

A system, method, and/or apparatus is provided for establishing targets or setpoints of speed parameters for the operation of a papermaking machine that is based on the square point of the paper sheet being produced. The square point of the paper sheet is determined in response to one or more speed parameters and associated one or more fiber distribution parameters for the paper sheet that are measured a plurality of times during the papermaking process and analyzed to determine the square point based on the measurements.

What is claimed is: 
     
         1 . A method for producing a paper sheet with a papermaking machine, the method comprising:
 determining a square point for the paper sheet from a plurality of measurements of one or more speed parameters for the papermaking machine and a plurality of measurements of one or more fiber distribution parameters for the paper sheet, wherein the plurality of measurements for the one or more speed parameters and the plurality of measurements for the one or more fiber distribution parameters are taken during operation of the papermaking machine; and   setting one or more speed parameters for the papermaking machine to produce the paper sheet based on the determined square point.   
     
     
         2 . The method of  claim 1 , wherein the one or more speed parameters are set at values corresponding to the determined square point for the paper sheet. 
     
     
         3 . The method of  claim 1 , wherein the one or more speed parameters are set at values offset from the determined square point for the paper sheet. 
     
     
         4 . The method of  claim 1 , wherein the one or more speed parameters include at least one of a jet speed, a wire speed, a jet-to-wire speed ratio, and a rush-to-drag speed difference of the papermaking machine. 
     
     
         5 . The method of  claim 1 , wherein the one or more fiber distribution parameters include at least one of a width of the paper sheet, a strength measurement of the paper sheet, and a fiber orientation ratio of the paper sheet. 
     
     
         6 . The method of  claim 1 , wherein determining the square point includes stepping the at least one of the one or more speed parameters of the papermaking machine depending on the one or more fiber distribution parameters of the paper sheet moving toward the square point or away from the square point. 
     
     
         7 . The method of  claim 1 , wherein determining the square point includes modelling a relationship between the plurality of measurements of the one or more speed parameters and the plurality of measurements of the one or more fiber distribution parameters with second order polynomial functions. 
     
     
         8 . The method of  claim 1 , wherein determining the square point includes modelling a relationship between the plurality of measurements of the one or more speed parameters and the plurality of measurements of the one or more fiber distribution parameters with fourth order polynomial functions. 
     
     
         9 . The method of  claim 1 , further comprising determining a plurality of start conditions are satisfied before taking the plurality of measurements of the one or more speed parameters and the one or more fiber distribution parameters. 
     
     
         10 . The method of  claim 1 , wherein determining the square point includes:
 monitoring start conditions to initiate probing of the papermaking machine;   probing the papermaking machine by making a plurality of adjustments to at least one of the one or more speed parameters with the start conditions being met;   obtaining the plurality of measurements of the one or more speed parameters and the plurality of measurements of the one or more fiber distribution parameters while probing the papermaking machine by making the plurality of adjustments to the at least one of the one or more speed parameters; and   modeling a relationship between the plurality of measurements of the one or more speed parameters with the plurality of adjustments to the at least one of the one or more speed parameters and the plurality of measurements of the one or more fiber distribution parameters.   
     
     
         11 . The method of  claim 10 , wherein the start conditions include a set of AND conditions and a set of OR conditions. 
     
     
         12 . The method of  claim 11 , wherein probing the papermaking machine is started in response to the AND conditions and the OR conditions being satisfied. 
     
     
         13 . A control apparatus for a papermaking machine to produce a paper sheet, the control apparatus including at least one computer processor that operates on the papermaking machine to:
 determine a square point for the paper sheet from a plurality of measurements of one or more speed parameters for the papermaking machine and a plurality of measurements of one or more fiber distribution parameters for the paper sheet, wherein the plurality of measurements for the one or more speed parameters and the plurality of measurements for the one or more fiber distribution parameters are taken during operation of the papermaking machine; and   set one or more speed parameters for operation of the papermaking machine based on the determined square point.   
     
     
         14 . The control apparatus of  claim 13 , wherein the one or more speed parameters include at least one of a jet speed, a wire speed, a jet-to-wire speed ratio, and a rush-to-drag speed difference of the papermaking machine. 
     
     
         15 . The control apparatus of  claim 13 , wherein the one or more fiber distribution parameters include at least one of a width of the paper sheet, a strength measurement of the paper sheet, and a fiber orientation ratio of the paper sheet. 
     
     
         16 . The control apparatus of  claim 13 , wherein at least one computer processor operates on the papermaking machine to step at least one of the one or more speed parameters of the papermaking machine depending on the one or more fiber distribution parameters of the paper sheet moving toward its square point or away from its square point. 
     
     
         17 . The control apparatus of  claim 13 , wherein at least one computer processor operates on the papermaking machine to determine the square point by modelling a relationship between the plurality of measurements of the one or more speed parameters and the plurality of measurements of the one or more fiber distribution parameters with at least one of second order polynomial or fourth order polynomial functions. 
     
     
         18 . The control apparatus of  claim 13 , wherein the one or more speed parameters are set at values corresponding to the determined square point for the paper sheet. 
     
     
         19 . The control apparatus of  claim 13 , wherein the one or more speed parameters are set at values offset from the determined square point for the paper sheet. 
     
     
         20 . The control apparatus of  claim 13 , wherein at least one computer processor operates on the papermaking machine to:
 monitor start conditions to initiate probing of the papermaking machine;   probe the papermaking machine by making a plurality of adjustments to at least one of the one or more speed parameters with the start conditions being met;   obtain the plurality of measurements of the one or more speed parameters and the plurality of measurements of the one or more fiber distribution parameters while probing the papermaking machine by making the plurality of adjustments to the at least one of the one or more speed parameters; and   model a relationship between the plurality of measurements of the one or more speed parameters with the plurality adjustments to the at least one of the one or more speed parameters and the plurality of measurements of the one or more fiber distribution parameters.   
     
     
         21 . The control apparatus of  claim 20 , wherein the start conditions include a set of AND conditions and a set of OR conditions. 
     
     
         22 . The control apparatus of  claim 21 , wherein probing the papermaking machine is started in response to the AND conditions and the OR conditions being satisfied. 
     
     
         23 . A method for determining a square point for a paper sheet produced by a papermaking machine, the method comprising:
 a) measuring one or more speed parameters and associated one or more fiber distribution parameters of the paper sheet during operation of the papermaking machine;   b) stepping at least one of the one or more speed parameters of the papermaking machine in a first direction;   c) measuring, after stepping the at least one of the one or more speed parameters in the first direction in step b), the one or more speed parameters and associated one or more fiber distribution parameters of the paper sheet;   d) in response to the one or more fiber distribution parameters moving away from the square point in step b), stepping the at least one of the one or more speed parameters of the papermaking machine in a second direction opposite the first direction and measuring the one or more speed parameters and the associated one or more fiber distribution parameters of the paper sheet; and   e) in response to the one or more fiber distribution parameters approaching the square point in step b) or step d), repeatedly stepping the at least one of the one or more speed parameters of the papermaking machine and measuring the one or more speed parameters and associated one or more fiber distribution parameters of the paper sheet until the one or more fiber distribution parameters move away from the square point.   
     
     
         24 . The method of  claim 23 , further comprising:
 f) determining the square point by modelling the measurements of the one or more speed parameters and the associated one or more fiber distribution parameters with one of second order polynomial or fourth order polynomial functions.   
     
     
         25 . The method of  claim 24 , further comprising:
 g) setting one or more speed parameters for the papermaking machine to produce the paper sheet based on the determined square point.   
     
     
         26 . A control apparatus for determining a square point for a paper sheet produced by a papermaking machine, the control apparatus being configured to:
 a) measure one or more speed parameters and associated one or more fiber distribution parameters of the paper sheet during operation of the papermaking machine;   b) step at least one of the one or more speed parameters of the papermaking machine in a first direction;   c) measure, after stepping the at least one of the one or more speed parameters in the first direction in step b), the one or more speed parameters and the associated one or more fiber distribution parameters of the paper sheet;   d) in response to the one or more fiber distribution parameters moving away from the square point in step b), step the at least one of the one or more speed parameters of the papermaking machine in a second direction opposite the first direction and measure the one or more speed parameters and the associated one or more fiber distribution parameters of the paper sheet; and   e) in response to the one or more fiber distribution parameters approaching the square point in step b) or step d), repeatedly step the at least one of the one or more speed parameters of the papermaking machine and measure the one or more speed parameters and the associated one or more fiber distribution parameters of the paper sheet until the one or more fiber distribution parameters move away from the square point.   
     
     
         27 . The control apparatus of  claim 26 , wherein the control apparatus is configured to:
 f) determine the square point by modelling the measurements of the one or more speed parameters and the associated one or more fiber distribution parameters with one of second order polynomial or fourth order polynomial functions.   
     
     
         28 . The control apparatus of  claim 27 , wherein the control apparatus us configured to:
 g) set one or more speed parameters for the papermaking machine to produce the paper sheet based on the determined square point.