CA2379228A1 - Method of estimating unknown or imprecisely known variables in a paper making process - Google Patents
Method of estimating unknown or imprecisely known variables in a paper making process Download PDFInfo
- Publication number
- CA2379228A1 CA2379228A1 CA002379228A CA2379228A CA2379228A1 CA 2379228 A1 CA2379228 A1 CA 2379228A1 CA 002379228 A CA002379228 A CA 002379228A CA 2379228 A CA2379228 A CA 2379228A CA 2379228 A1 CA2379228 A1 CA 2379228A1
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- CA
- Canada
- Prior art keywords
- variable
- measured
- headbox
- unknown
- reference variable
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21G—CALENDERS; ACCESSORIES FOR PAPER-MAKING MACHINES
- D21G9/00—Other accessories for paper-making machines
- D21G9/0009—Paper-making control systems
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Abstract
Method of estimating unknown or imprecisely known variables in a paper makin g process wherein a mathematical model of a process is formed, the model including at least one target variable which is unknown or imprecisely known . A plurality of process variables and at least one property of a manufactured paper are measured. At least one of said measured variables or properties is chosen as a reference variable. An initial value is chosen for the target variable for solving the mathematical model and a difference between the simulated reference variable and the measured reference variable is determined. The difference constitutes a cost function which is optimized to estimate the unknown or imprecisely known value of the target variable.</SDO AB>
Description
METHOD OF ESTIMATING UNKNOWN OR IMPRECISELY KNOWN
VARIABLES IN A PAPER MAKING PROCESS
The invention relates to a method of estimating unknown or imprecisely known variables in a paper making process.
US patent 5 812 404 discloses a method for the continuous overall regulation of a headbox of a paper machine. A physical fluid flow model of a pulp suspension flow discharged from the headbox to be regulated is formed and solved to obtain a simulated flow state based, e.g., on data on the geometry of the headbox and initial and boundary conditions related to the headbox. A target flow state based on the quality requirements of the paper produced from the pulp suspension flow, the costs of operation and runnability of the machine is obtained and a difference between the simulated flow state obtained as the solution of the flow model and the target flow state is ~5 determined. This difference constitutes a cost function which is optimized to determine optimal regulation values and set values for instrumentation devices and actuators of the headbox which affect the pulp suspension flow.
Provision of accurate initial and boundary conditions is advantageous in a method disclosed in US 5812404 but the solution of US
20 5 821 404 relies on measurements alone to provide said conditions.
Measurements alone cannot provide all required initial values with adequate accuracy. The values of variables are also too imprecise or unknown at several other points of the paper making process, and thus it would be necessary to obtain a more accurate estimate of the variable values.
25 An object of the present invention is to provide a method for obtaining a more accurate estimate of unknown or imprecisely known variables of a .paper making process.
The method of the invention is characterized by comprising the steps of 3o forming a mathematical model of a process, the model including at least one target variable which is unknown or imprecisely known, measuring a plurality of process variables and at least one property of a manufactured paper web, utilizing the measurements as initial and boundary values of the 35 model, choosing at least one of said measured process variables or measured web properties as a reference variable, choosing an initial value for the target variable, solving the mathematical model, simulating a value of the reference variable utilizing the model, determining a difference between the simulated reference variable and the measured reference variable, the difference constituting a cost function, and optimizing the cost function to estimate the unknown or ~o imprecisely known value of the target variable.
The essential idea of the invention is that a mathematical model of a process is formed, the model including at least one target variable which is unknown or imprecisely known. Plural process variables are measured and at least one property of the manufactured paper web is measured. At least one of ~5 said measured process variables or measured web properties is chosen as a reference variable. Boundary conditions for the mathematical model are obtained from the remaining measured process variables and measured web properties. An initial value is chosen for the target variable for solving the mathematical model, the reference variable is thereby simulated, and a 2o difference between the simulated reference variable and the measured reference variable is determined. This difFerence constitutes a cost function which is optimized to estimate the unknown or imprecisely known value of the target variable. The idea of a preferred embodiment is that the process is a flow process in a headbox and the target variable is a variable of the headbox.
25 An advantage of the invention is that variables of the paper making process can be estimated in a more accurate and diverse manner than earlier, which allows ~to improve control of the paper making process. The method applies particularly to estimation of unknown or imprecisely known variables which are multivariate or vector quantities, such as the cross machine profile 3o of a process variable or web property, or the statistical distribution of a variable whose value changes with position or time.
In this disclosure the term "paper" also refers to paper board and tissue.
The invention will be described in greater detail in the 3s accompanying drawings, in which Figure 1 is a schematic side view of a paper making process, Figure 2 is a simplified block diagram of a method of the invention, and Figure 3 is a simplified flowchart for an optimizing controller in which the method of the invention can be utilized.
Figure 1 schematically shows a paper machine. The paper machine comprises a headbox 1, from which pulp is fed into a former 2, where a fiber web 3 is formed of the pulp. The web 3 is conveyed to a press 4 and further to a dryer unit 5. From the dryer unit 5 the web 3 is conveyed to a reel 6. A
paper machine may also comprise, for example, a size press, coaters or a calender, 1o which are not illustrated in the Figure 1 for the sake of clarity.
Furthermore, the function of the paper machine is known per se for those skilled in the art, and will therefore not be further explained in this context.
The paper machine also comprises at least one measuring device 7 for measuring properties of the paper web 3. The measuring device 7 is used ~5 for measuring e.g. the basis weight BW, dry weight profile DWP and the fiber orientation angle profile FO of the paper web 3. The paper machine also comprises other measuring devices for measuring values and properties at different parts of the paper machine. Headbox pressure P, headbox consistency Cs, a profile of dilution valve positions DVP and headbox upper lip 2o profile ULP are given as examples of such measurements in Figure 1.
Additional properties of the paper web or of process streams can be measured from samples taken from the manufactured paper or process streams using instruments located elsewhere.
The invention relates to a method for estimating unobserved 25 variables or imprecisely measured process variables in a paper machine during operation, and especially for estimating an unknown or imprecisely measured process variable in the headbox 1 of a paper machine or in the sheet formed of the headbox discharge. A mathematical model of the process is formed based for example on the geometry of the headbox 1 and physical 3o models of the flow phenomena occurring therein, and including at least one target variable which is unknown or imprecisely known. Plural process variables are measured, for example using instruments in or around the headbox 1 and the various process streams leading to or from the headbox, and ~at least one property of the manufactured paper web 3 is measured using 35 instruments elsewhere on the machine or in a laboratory. At least one of said measured process variables or measured web properties is chosen as a reference variable. Boundary conditions for the mathematical model are obtained from the remaining measured process variables and measured web properties. An initial value is chosen for the target variable for solving the mathematical model, the reference variable is thereby simulated, and a difference between the simulated reference variable and the measured reference variable is determined. This difference constitutes a cost function which is optimized to estimate the unknown or imprecisely known value of the target variable. The initial value chosen can be, for example, an imprecise measurement of the target variable, so that the optimization produces an ~o estimate which is of superior accuracy to the measurement.
A simplified flow chart for the estimation process is depicted in Figure 2. The physical and geometric parameters are known a priori. The measurements of known states are provided by measuring instruments or operator input. The initial estimate of the unknown variable or state may be ~5 supplied from an approximate measurement, or may be provided by other means of estimation, or by an operator.
For example, in the headbox 1 the slice opening profile is approximately known. The profile of the upper lip ULP is measured at a number of locations across the slice, but the shape of the lower lip is generally 2o unknown. However, various profiles which depend on the slice opening profile are measured, such as the basis weight profile BW or dry weight profile DWP
and the fiber orientation angle profile FO.
The optimization uses the measured slice lip shape as an initial estimate of the slice opening profile. One or more suitable measurements, 25 such as the fiber orientation angle profile FO or dry weight profile DWP or basis weight profile BW are used as reference variables. Other measurements, such as headbox pressure P, consistency Cs, temperatures, flows, a profile of dilution valve positions DVP etc. are used as inputs to a mathematical model of the flow process in the headbox 1 and jet. By solving 3o the mathematical model of the headbox 1, a simulation of the fiber orientation angle profile is obtained. A penalty to be optimized is calculated from the difference between the measured fiber orientation angle profile and simulated fiber orientation angle profile. This penalty is optimized by adjusting the estimate of the slice opening profile, the optimum being reached when the 35 simulated fiber orientation angle profile most closely matches the measured fiber orientation angle profile.
This invention solves a mathematical model of the headbox to estimate unknown or imprecisely known current operating parameters consistent with measured properties of the current product.
The present invention is particularly well suited for estimation of the 5 initial conditions for a method of optimizing control such as that disclosed in US 5 812 404 which is incorporated herein by reference. The present invention uses inverse modeling to provide such a controller with improved estimates of its initial and boundary conditions. The present invention can utilize similar mathematical and physical models to those used by such a controller, or can use different ones.
A simplified flow chart for an optimizing controller is depicted in Figure 3. One or more of the "measurements of known variables/states" in that figure can be supplied by the estimation process of this invention.
The drawings and the description thereof are merely intended to ~5 illustrate the inventive idea. The details of the invention may vary within the scope of the claims. Thus the method of the invention can in principle be applied at any point of the paper making process.
VARIABLES IN A PAPER MAKING PROCESS
The invention relates to a method of estimating unknown or imprecisely known variables in a paper making process.
US patent 5 812 404 discloses a method for the continuous overall regulation of a headbox of a paper machine. A physical fluid flow model of a pulp suspension flow discharged from the headbox to be regulated is formed and solved to obtain a simulated flow state based, e.g., on data on the geometry of the headbox and initial and boundary conditions related to the headbox. A target flow state based on the quality requirements of the paper produced from the pulp suspension flow, the costs of operation and runnability of the machine is obtained and a difference between the simulated flow state obtained as the solution of the flow model and the target flow state is ~5 determined. This difference constitutes a cost function which is optimized to determine optimal regulation values and set values for instrumentation devices and actuators of the headbox which affect the pulp suspension flow.
Provision of accurate initial and boundary conditions is advantageous in a method disclosed in US 5812404 but the solution of US
20 5 821 404 relies on measurements alone to provide said conditions.
Measurements alone cannot provide all required initial values with adequate accuracy. The values of variables are also too imprecise or unknown at several other points of the paper making process, and thus it would be necessary to obtain a more accurate estimate of the variable values.
25 An object of the present invention is to provide a method for obtaining a more accurate estimate of unknown or imprecisely known variables of a .paper making process.
The method of the invention is characterized by comprising the steps of 3o forming a mathematical model of a process, the model including at least one target variable which is unknown or imprecisely known, measuring a plurality of process variables and at least one property of a manufactured paper web, utilizing the measurements as initial and boundary values of the 35 model, choosing at least one of said measured process variables or measured web properties as a reference variable, choosing an initial value for the target variable, solving the mathematical model, simulating a value of the reference variable utilizing the model, determining a difference between the simulated reference variable and the measured reference variable, the difference constituting a cost function, and optimizing the cost function to estimate the unknown or ~o imprecisely known value of the target variable.
The essential idea of the invention is that a mathematical model of a process is formed, the model including at least one target variable which is unknown or imprecisely known. Plural process variables are measured and at least one property of the manufactured paper web is measured. At least one of ~5 said measured process variables or measured web properties is chosen as a reference variable. Boundary conditions for the mathematical model are obtained from the remaining measured process variables and measured web properties. An initial value is chosen for the target variable for solving the mathematical model, the reference variable is thereby simulated, and a 2o difference between the simulated reference variable and the measured reference variable is determined. This difFerence constitutes a cost function which is optimized to estimate the unknown or imprecisely known value of the target variable. The idea of a preferred embodiment is that the process is a flow process in a headbox and the target variable is a variable of the headbox.
25 An advantage of the invention is that variables of the paper making process can be estimated in a more accurate and diverse manner than earlier, which allows ~to improve control of the paper making process. The method applies particularly to estimation of unknown or imprecisely known variables which are multivariate or vector quantities, such as the cross machine profile 3o of a process variable or web property, or the statistical distribution of a variable whose value changes with position or time.
In this disclosure the term "paper" also refers to paper board and tissue.
The invention will be described in greater detail in the 3s accompanying drawings, in which Figure 1 is a schematic side view of a paper making process, Figure 2 is a simplified block diagram of a method of the invention, and Figure 3 is a simplified flowchart for an optimizing controller in which the method of the invention can be utilized.
Figure 1 schematically shows a paper machine. The paper machine comprises a headbox 1, from which pulp is fed into a former 2, where a fiber web 3 is formed of the pulp. The web 3 is conveyed to a press 4 and further to a dryer unit 5. From the dryer unit 5 the web 3 is conveyed to a reel 6. A
paper machine may also comprise, for example, a size press, coaters or a calender, 1o which are not illustrated in the Figure 1 for the sake of clarity.
Furthermore, the function of the paper machine is known per se for those skilled in the art, and will therefore not be further explained in this context.
The paper machine also comprises at least one measuring device 7 for measuring properties of the paper web 3. The measuring device 7 is used ~5 for measuring e.g. the basis weight BW, dry weight profile DWP and the fiber orientation angle profile FO of the paper web 3. The paper machine also comprises other measuring devices for measuring values and properties at different parts of the paper machine. Headbox pressure P, headbox consistency Cs, a profile of dilution valve positions DVP and headbox upper lip 2o profile ULP are given as examples of such measurements in Figure 1.
Additional properties of the paper web or of process streams can be measured from samples taken from the manufactured paper or process streams using instruments located elsewhere.
The invention relates to a method for estimating unobserved 25 variables or imprecisely measured process variables in a paper machine during operation, and especially for estimating an unknown or imprecisely measured process variable in the headbox 1 of a paper machine or in the sheet formed of the headbox discharge. A mathematical model of the process is formed based for example on the geometry of the headbox 1 and physical 3o models of the flow phenomena occurring therein, and including at least one target variable which is unknown or imprecisely known. Plural process variables are measured, for example using instruments in or around the headbox 1 and the various process streams leading to or from the headbox, and ~at least one property of the manufactured paper web 3 is measured using 35 instruments elsewhere on the machine or in a laboratory. At least one of said measured process variables or measured web properties is chosen as a reference variable. Boundary conditions for the mathematical model are obtained from the remaining measured process variables and measured web properties. An initial value is chosen for the target variable for solving the mathematical model, the reference variable is thereby simulated, and a difference between the simulated reference variable and the measured reference variable is determined. This difference constitutes a cost function which is optimized to estimate the unknown or imprecisely known value of the target variable. The initial value chosen can be, for example, an imprecise measurement of the target variable, so that the optimization produces an ~o estimate which is of superior accuracy to the measurement.
A simplified flow chart for the estimation process is depicted in Figure 2. The physical and geometric parameters are known a priori. The measurements of known states are provided by measuring instruments or operator input. The initial estimate of the unknown variable or state may be ~5 supplied from an approximate measurement, or may be provided by other means of estimation, or by an operator.
For example, in the headbox 1 the slice opening profile is approximately known. The profile of the upper lip ULP is measured at a number of locations across the slice, but the shape of the lower lip is generally 2o unknown. However, various profiles which depend on the slice opening profile are measured, such as the basis weight profile BW or dry weight profile DWP
and the fiber orientation angle profile FO.
The optimization uses the measured slice lip shape as an initial estimate of the slice opening profile. One or more suitable measurements, 25 such as the fiber orientation angle profile FO or dry weight profile DWP or basis weight profile BW are used as reference variables. Other measurements, such as headbox pressure P, consistency Cs, temperatures, flows, a profile of dilution valve positions DVP etc. are used as inputs to a mathematical model of the flow process in the headbox 1 and jet. By solving 3o the mathematical model of the headbox 1, a simulation of the fiber orientation angle profile is obtained. A penalty to be optimized is calculated from the difference between the measured fiber orientation angle profile and simulated fiber orientation angle profile. This penalty is optimized by adjusting the estimate of the slice opening profile, the optimum being reached when the 35 simulated fiber orientation angle profile most closely matches the measured fiber orientation angle profile.
This invention solves a mathematical model of the headbox to estimate unknown or imprecisely known current operating parameters consistent with measured properties of the current product.
The present invention is particularly well suited for estimation of the 5 initial conditions for a method of optimizing control such as that disclosed in US 5 812 404 which is incorporated herein by reference. The present invention uses inverse modeling to provide such a controller with improved estimates of its initial and boundary conditions. The present invention can utilize similar mathematical and physical models to those used by such a controller, or can use different ones.
A simplified flow chart for an optimizing controller is depicted in Figure 3. One or more of the "measurements of known variables/states" in that figure can be supplied by the estimation process of this invention.
The drawings and the description thereof are merely intended to ~5 illustrate the inventive idea. The details of the invention may vary within the scope of the claims. Thus the method of the invention can in principle be applied at any point of the paper making process.
Claims (8)
1. A method of estimating unknown or imprecisely known variables in a paper making process, the method comprising the steps of forming a mathematical model of a process, the model including at least one target variable which is unknown or imprecisely known, measuring a plurality of process variables and at least one property of a manufactured paper web, utilizing the measurements as initial and boundary values of the model, choosing at least one of said measured process variables or measured web properties as a reference variable, choosing an initial value for the target variable, solving the mathematical model, simulating a value of the reference variable utilizing the model, determining a difference between the simulated reference variable and the measured reference variable, the difference constituting a cost function, and optimizing the cost function to estimate the unknown or imprecisely known value of the target variable.
2. A method according to claim 1, wherein the process is a flow process in a headbox and the target variable is a variable of the headbox.
3. A method according to claim 2, wherein the target variable is a slice opening profile of the headbox.
4. A method according to claim 3, wherein the reference variable is a fiber orientation angle profile.
5. A method according to claim 3, wherein the reference variable is a basis weight profile.
6. A method according to claim 3, wherein the reference variable is a dry weight profile.
7. A method according to claim 2, wherein the measured process variables comprise headbox pressure and headbox consistency.
8. A method according to claim 2, wherein the measured process variables comprise a profile of dilution valve positions.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US35388499A | 1999-07-15 | 1999-07-15 | |
| US09/353,884 | 1999-07-15 | ||
| PCT/FI2000/000648 WO2001006056A1 (en) | 1999-07-15 | 2000-07-14 | Method of estimating unknown or imprecisely known variables in a paper making process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2379228A1 true CA2379228A1 (en) | 2001-01-25 |
Family
ID=23391006
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002379228A Abandoned CA2379228A1 (en) | 1999-07-15 | 2000-07-14 | Method of estimating unknown or imprecisely known variables in a paper making process |
Country Status (5)
| Country | Link |
|---|---|
| AT (1) | AT410846B (en) |
| AU (1) | AU6284000A (en) |
| CA (1) | CA2379228A1 (en) |
| DE (1) | DE10084794T1 (en) |
| WO (1) | WO2001006056A1 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4913510B2 (en) * | 2006-09-05 | 2012-04-11 | 横河電機株式会社 | Simulation method, fiber orientation control method, and fiber orientation control device |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5812404A (en) * | 1996-04-18 | 1998-09-22 | Valmet Corporation | Method for overall regulation of the headbox of a paper machine or equivalent |
-
2000
- 2000-07-14 AT AT0912300A patent/AT410846B/en not_active IP Right Cessation
- 2000-07-14 WO PCT/FI2000/000648 patent/WO2001006056A1/en active Application Filing
- 2000-07-14 DE DE10084794T patent/DE10084794T1/en not_active Withdrawn
- 2000-07-14 CA CA002379228A patent/CA2379228A1/en not_active Abandoned
- 2000-07-14 AU AU62840/00A patent/AU6284000A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| ATA91232000A (en) | 2002-12-15 |
| WO2001006056A1 (en) | 2001-01-25 |
| DE10084794T1 (en) | 2002-09-05 |
| AU6284000A (en) | 2001-02-05 |
| AT410846B (en) | 2003-08-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |