Miniscan for dynamic correlation

Abstract

To provide a method for correlating on-line scanning sensor reading values to laboratory test results of sheet materials produced by continuous processes.SOLUTION: Correlating on-line scanning sensor reading values to laboratory test results for verification of accuracy and reproducibility can be facilitated by changing scanning parameters of a scanner so that it only scans a small portion of a sheet that is to be sampled; this feature makes the sensor's mini-scan reading values more relevant and more likely to be a repeatable result, thus the entire dynamic correlation process achieves more reliable results in a shorter length of time. A technique of operating a continuous sheet making system that includes actuators and a downstream scanning sensor, includes: (a) measuring a sheet physical characteristic of a continuous sheet with the scanning sensor and displaying a cross directional profile of measurements; (b) selecting a cross directional region within the profile; and (c) measuring the sheet physical characteristic with the scanning sensor within the region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to quality control techniques for manufacturing sheet materials, and more particularly to methods that facilitate correlating online scanning sensor readings with laboratory test results for sheet materials produced in a continuous process. [Background technology]

[0002] Online measurements are used to detect sheet material properties during production to enable accelerated control of the sheet making process, thus ensuring sheet quality while reducing the amount of substandard sheet material produced. One of the main problems with performing online measurements during sheet making is that the physical properties of the sheet material typically vary in the machine direction and the cross direction. (The term "machine direction" refers to the direction of movement of the sheet material during production, and the term "cross direction" refers to the direction across the surface of the sheet perpendicular to the machine direction.)

[0003] To detect variations in sheet material, scanning sensors are used that traverse back and forth periodically across the sheet-making machine in the transverse direction, detecting the value of a selected sheet characteristic, such as basis weight or caliper, along each scan. Typically, the sheet being produced is traversed edge-to-edge during each scan. The time required for a typical scan is generally on the order of a few seconds to tens of seconds, depending on the transverse length, which can be several meters. The rate at which measurement readings are provided by such scanners is usually adjustable, with a typical rate being about one measurement reading every millisecond.

[0004] In practice, the measurement information provided by the scanning sensors is typically assembled after each scan to provide a "profile" of detected sheet properties in the cross direction. In other words, each profile consists of a series of sheet measurements at adjacent locations in the cross direction. The purpose of the profile is to allow for easy detection of lateral variations in the sheet properties. Based on the detected lateral variations in the detected sheet properties, appropriate control adjustments can be made to the sheet making machine with the goal of reducing profile variations in both the cross direction and the machine direction.

[0005] A scanning sensor that periodically traverses a sheet at a constant velocity cannot measure selected sheet properties at locations aligned exactly perpendicular to the sheet's longitudinal edge. Because of the sheet velocity, the scanning sensor actually moves diagonally across the sheet surface, and as a result, successive scan paths have a zigzag pattern relative to the direction perpendicular to the sheet's longitudinal edge. In practice, it is typical to calculate an average of the profile measurements over each scan.

[0006] On industrial paper machines, often called Fourdrinier machines, scanning sensors are tested periodically, but this testing process is time consuming. Summary of the Invention

[0007] The present invention is based, in part, on the recognition that by changing the scanning parameters of the scanner so that it scans only a small portion of the sampled sheet, it can be facilitated to correlate online scan sensor readings with laboratory test results for accuracy and repeatability verification. This feature makes the sensor's mini-scan readings more relevant and more likely to be repeatable results. The overall dynamic correlation process achieves more reliable results in a shorter period of time.

[0008] In one aspect, the present invention relates to a method of operating a continuous sheet manufacturing system including a plurality of actuators positioned along a lateral direction and a scanning sensor positioned downstream of the plurality of actuators for measuring and acquiring property data of a moving sheet of material, the method comprising: (a) measuring sheet physical properties of a continuous sheet using a scanning sensor and displaying a cross-direction profile of the measurements; (b) selecting a lateral region within the profile; (c) measuring a sheet physical property of the continuous sheet with a scanning sensor within the area, wherein one or more of the actuators can be adjusted in response to the measurement.

[0009] In another aspect, the present invention relates to a method of correlating scanning sensor measurements with laboratory analysis employed in a system for producing a continuous sheet product moving in a machine direction (MD), the system employing a scanning sensor that periodically traverses back and forth across the width of the moving sheet during a production mode, the method comprising: (a) operating a scanning sensor in a production mode to periodically traverse back and forth across the width of a sheet in a cross-machine direction (CD) to detect values ​​of selected sheet properties along each scan; (b) operating the scanning sensor in a verification mode by varying the lateral width of each scan to be substantially less than the overall width of the sheet being scanned and detecting values ​​of selected sheet properties along each scan to generate detected values; (c) obtaining a sample of the sheet of material produced during the verification mode; and (d) testing the samples obtained during the verification mode to confirm the test results; (e) comparing the test results with the detection values ​​obtained in the verification mode.

[0010] In a further aspect, the present invention provides a method for measuring a process variable in a continuous sheet process having a machine direction and a cross direction, the method comprising: (i) providing an elongated member supporting a mounting head including a sensor; (ii) actuating the actuator to produce a continuous sheet of material; (iii) orienting a moving continuous sheet of material along a machine direction, the sheet having a first edge and a second edge, and a first elongated member positioned adjacent to the moving continuous sheet of material along the transverse direction; (iv) guiding the mounting head back and forth between a first scanning position and a second scanning position such that the sensor measures a property of the sheet of material between a first edge and a second edge of the sheet of material, the sensor generating a first signal corresponding to the measurement; (v) controlling the actuator in response to the first signal; (vi) ceasing control of the actuator in response to the first signal; (vii) guiding the mounting head back and forth between a third scan position and a fourth scan position such that the sensor measures a property of the sheet of material between an area of ​​the sheet of material within the first edge and the second edge, the sensor generating a second signal corresponding to the measurement; (viii) taking a sample of the sheet of material produced during step (vii); (ix) analyzing the sample obtained in step (viii) to obtain a test result; (x) comparing the test result with a second signal.

[0011] Although the invention is illustrated as being practiced in papermaking, it is understood that the invention is applicable to other continuous sheet making processes, for example, in the manufacture of rubber sheets, plastic films, electrodes, metal foils, textiles, etc. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a papermaking system. [Figure 2] It is a scanning sensor. [Figure 3] The scanning pattern is shown. [Figure 4] 1 is a cross-sectional profile of the sheet properties. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1 shows a sheet manufacturing system 10 including a papermaking machine 2, a control system 4, and a network 6. The papermaking machine 2 produces a continuous sheet of paper material 12 that is collected by a take-up reel 14. The paper material 12 has a specific width and is produced from a pulp suspension feedstock containing an aqueous mixture of wood fibers and other materials, which undergoes various unit operations that are monitored and controlled by a quality control system 4. The network 6 facilitates communication between the components of the system 10. Papermaking is described in U.S. Pat. No. 9,309,625 to Backstrom and Forbes and U.S. Pat. No. 8,021,517 to Hughes and Tixier, which are incorporated herein by reference.

[0014] The papermaking machine 2 includes a headbox 8, which distributes an aqueous pulp suspension evenly across the machine onto a continuous screen or wire 30 moving in the machine direction (MD). The headbox 8 includes slice openings through which the pulp suspension is distributed onto the screen or wire 30, the slice openings having a suitable structure, such as a mesh, to receive the pulp suspension and allow water or other materials to drain or be removed from the pulp suspension. Formation of the paper sheet 12 is influenced by a plurality of linear actuators 3 extending transversely across the paper sheet 12 being formed. The actuators 3 control the sheet weight in the cross direction (CD). Sensors positioned downstream of the actuators measure sheet properties. The feedstock is fed from the headbox through gaps or elongated orifices 5 onto the wire section 30. The orifices or gaps are relatively narrow openings extending across the width of the machine. Weight profile control of such an arrangement is achieved by locally adjusting the position of the slice lip across the machine with a motorized linear actuator 3 to vary the size of the gap or orifice immediately adjacent to the actuator. As used herein, the "wet end" forming portion of the sheet making system 10 includes the headbox 8 and wire 30 and the section before the wire 30, and the "dry end" includes the section downstream of the wire 30.

[0015] The sheet 12 then enters a press section 32, which includes multiple press rolls, and the sheet 12 advances through openings (called "nips") between multiple pairs of counter-rotating rolls in the press section 32. In this manner, the rolls in the press section 32 compress the pulp material forming the sheet 12. This may help remove more water from the pulp material and equalize the properties of the sheet 12 on both sides.

[0016] As the sheet 12 advances over a series of heated rolls in the dryer section 34, more water in the sheet 12 evaporates. The calender 36 processes and finishes the sheet 12, for example, by smoothing the sheet 12 and imparting a final finish, thickness, gloss, or other properties. Other materials (such as starch or wax) may also be added to the sheet 12 to achieve a desired finish. An array of induction heating actuators 24 applies heat to one or more of the rollers along the CD to control the roll diameter, and thereby the size of the nip. After processing by the calender 36, the sheet 12 is collected onto the reel 14.

[0017] The sheet making system 10 further includes an array of steam actuators 20 that control the amount of hot steam injected along the CD. The hot steam increases the surface temperature of the paper, allowing for easier water removal from the paper sheet in the cross direction. The paper material 14 is also sprayed with water in the CD to reduce or prevent over-drying of the paper sheet. Similarly, an array of rewet shower actuators 22 controls the amount of water applied along the CD.

[0018] To control the papermaking process, selected properties of the sheet 12 are continuously measured, and the papermaking machine 2 is adjusted to ensure sheet quality. Typical physical properties of paper that can be measured include, for example, thickness, basis weight, moisture content, chemical composition such as ash content, surface roughness, gloss, caliper, color, and crepe pattern surface characteristics. Control of CD can be achieved by measuring sheet properties using one or more scanners 26, 28 capable of scanning the sheet 12 to measure one or more properties of the sheet 12. For example, the scanner 28 can carry sensors for measuring the dry weight, moisture content, ash content, or any other or additional properties of the sheet 12. The scanner 28 includes a suitable structure for measuring or detecting one or more properties of the sheet 12, such as a set or array of sensors. The scanner 28 is particularly well-suited for measuring the dry-end dry weight and ash content of paper products.

[0019] Measurements from scanners 26 and 28 are provided to control system 4, which adjusts various actuators or operations of papermaking machine 2 that affect the machine direction and cross direction properties of sheet 12. Machine direction properties of sheet 12 generally refer to the average properties of sheet 12 that vary and are controlled in the machine direction. In this example, control system 4 may control the dry weight of the paper sheet by adjusting the supply of pulp to headbox 8. For example, control system 4 may provide information to a feedstock flow controller, which controls the flow of feedstock through a valve to headbox 8. Control system 4 may include any hardware, software, firmware, or combination thereof for controlling the operation of sheet making machine 2 or other machinery. Control system 4 may include, for example, a processor and memory for storing instructions and data used, generated, and collected by the processor. CD scanner sheet property measurements may be stored for future reference and / or accessed for real-time observation and analysis. Control systems for papermaking machines are described, for example, in U.S. Pat. No. 9,309,625 to Backstrom and Forbes, U.S. Pat. No. 10,174,456 to Backstrom and Forbes, and U.S. Pat. No. 10,358,771 to He et al., which are incorporated by reference.

[0020] FIG. 2 shows one specific implementation of a scanning sensor located at the dry end, just before the take-up reel of FIG. 1 . In particular, the radiation source and detector are housed within a dual-mounting head scanner 58 of a scanner system 50, which can be used to measure one or more properties of the paper being produced. The upper scanner head 54 moves repeatedly back and forth in the CD across the width of a moving sheet 60 moving in the MD so that properties of the entire sheet can be measured. The scanner 58, or gauge, is supported by two beams 52 and 62 to which the upper and lower scanning heads 54 and 56 are attached, respectively. The operating surfaces of the lower and upper scanner heads 56 and 54 define a measurement gap or window that accommodates the sheet 60. The lower scanner head 56 can include a sheet stabilization system, such as an air-bearing stabilizer (not shown), to maintain the sheet on a consistent plane as it passes through the measurement window. The movement of the dual scanner heads 54, 56 is synchronized in speed and direction so that they are aligned with each other. The sheet width in an industrial CD can exceed 10 meters, and typically, in normal production mode, the scanner head moves at a speed of 0.3 to 0.7 meters per second.

[0021] Depending on the property being monitored, the scanning sensors can be configured to operate in a transmission mode or a reflection mode. For example, scanner head 54 may contain a radiation source that directs a beam of radiation into moving web or sheet 26, and scanner head 56 contains a radiation receiver that detects the radiation transmitted through the material. As the dual scanner heads advance back and forth along the CD, the sensors measure one or more properties of web or sheet 60. Sensors operating in a transmission mode are described, for example, in U.S. Pat. No. 9,182,360 to Tixier and Hughes, U.S. Pat. No. 8,527,212 to Hughes and Tixier, U.S. Pat. No. 7,298,492 to Tixier, U.S. Patent Application Publication No. 2021 / 0382173 to Hughes et al., and U.S. Patent Application Publication No. 2021 / 0262776 to Tixier and Hughes, which are incorporated herein by reference. Typically, in normal production mode, the sampling rate of a scanning sensor ranges from one sample every 10 to 200 milliseconds.

[0022] In reflective mode, the upper scanner head 54 may house both a radiation source and a detector to measure one or more properties of the web or sheet 26. Sensors operating in reflective mode are described, for example, in U.S. Patent Nos. 9,182,360, 8,527,212, 7,298,492, and U.S. Patent Application Publication No. 2020 / 0096308, which are incorporated herein by reference.

[0023] A camera may be fixed to the upper or lower scanner head to capture an image of the surface of sheet 60. Cameras are described in U.S. Patent No. 7,695,592 to Shakespeare and Kellomaki, which is incorporated herein by reference.

[0024] The moving scanner does not measure selected sheet properties at locations aligned exactly perpendicular to the longitudinal edge of the moving sheet 60. Instead, due to the sheet velocity, the scanning device moves diagonally across the sheet surface, with the result that successive scan paths have a zigzag pattern relative to the direction perpendicular to the longitudinal edge of the sheet.

[0025] FIG. 3 shows an example of a zigzag scan pattern 76 traced by a gauge during normal operation of a papermaking machine as a scanning device 78 traverses the surface of a sheet during successive back-and-forth scans. The gauge has interrogation spots 74, and pattern 76 represents the locations where measurements are made on a moving sheet between edge 70 and edge 72 of the sheet. The angle of the scan path relative to the true CD depends on the lateral velocity of the scanning device 78 and the machine direction velocity of the sheet. The zigzag pattern of interrogation spots 74 covers a relatively small portion of the sheet surface. Note that in actual operation, the scanner 78 decelerates as it approaches the edge of the sheet, stops at the edge, and then accelerates as it moves away from the edge toward the center of the sheet. Thus, the zigzag pattern is actually curved rather than exhibiting sharp corners as shown.

[0026] In practice, the measurement information provided by the scanning sensor is typically assembled after each scan to provide a "profile" of the detected sheet properties in the lateral direction. In other words, each profile consists of a series of sheet measurements at adjacent locations in the lateral direction. The property measurements are averaged in bins of finite size in the CD segment. The purpose of the profile is to allow for easy detection of lateral variations in the sheet properties. Maps displaying the scanner measurements are typically divided into points or bins across their width. For example, each bin may represent a distance of approximately 5 mm.

[0027] Figure 4 is an exemplary cross-sectional profile produced by scanner 28 (Figure 1) measuring paper properties at the dry end. The scanner is operating in production mode, scanning the entire width of a moving sheet from edge to edge. Property levels, expressed in arbitrary units, vary across the width of the paper from bin 1 to 600.

[0028] According to the present invention, a mini-scan can be performed at any time to correlate online sensor readings with laboratory tests to verify accuracy and repeatability. In this procedure, paper being sampled in the laboratory is matched with the corresponding readings from the sensor. In normal scanning mode, the sensor traverses the entire sheet in x seconds (scan time). Since only a small portion of the sheet is inspected, much time is spent reading paper that is not relevant to the inspection.

[0029] In a mini-scan, scanning parameters are changed so that the scanner scans only the portion of the sheet that is to be sampled, thereby increasing the likelihood that all sensor readings are related and reproducible. In practice, the operator examines the lateral profile and selects a CD region that exhibits relatively consistent readings. The circled "flat region" in Figure 3 indicates an area with less variability and is easier to correlate. The length of this CD region for a mini-scan is typically less than 10% of the CD length for a full scan, preferably about 2-6%. Typically, in mini-scan verification mode, the scanner head moves at a speed of 0.3-0.7 meters per second, and the scanning sensor sampling rate ranges from one sample every 10-200 milliseconds.

[0030] FIG. 3 shows the zigzag pattern 86 generated during the mini-scan, which is traced during the verification operation by the gauge as the scanning device 78 traverses the surface of the sheet during successive back-and-forth scans within the area defined by boundaries 80, 82. The gauge has an interrogation spot 88, and the pattern 86 represents where on the moving sheet measurements will be taken. As is apparent, the mini-scan path involves much of the reading of the actual sampled product. The sensor data generated in the mini-scan is averaged, printed, displayed, and used for comparison with laboratory values ​​obtained when testing the sample. During the mini-scan, the scanning sensor control operation is preferably halted. That is, because the sheet being measured represents only a small portion of the entire product, there is no need to use the signals generated by the scanning sensor to adjust MD or CD control, as is the case during normal operation. Otherwise, the papermaking machine could be disrupted by being controlled with a small subset of data.

[0031] A mini-scan may be performed when the take-up reel 14 (FIG. 1) reaches the desired size. Upon completion of the mini-scan, the running sheet being produced is transferred to a new spool and the full sheet is removed for testing. A paper sample is taken from the portion of the sheet that was subjected to the mini-scan, and the sample is analyzed for caliper, basis weight, ash content, etc.

[0032] Mini-scans can also be used to diagnose upstream actuators. For example, as shown in FIG. 1, the formation of a paper sheet 12 is affected by multiple linear actuators 3 extending in the CD direction. The actuators 3 control the weight of the sheet in the CD. If one of the actuators malfunctions, the effect will be indicated in the measurements of the scanner 28. Mini-scans on selected narrow segments of the CD can be used to determine which actuators require tuning, adjustment, or replacement.

[0033] The foregoing has described the principles, preferred embodiments, and modes of operation of the present invention. However, the invention should not be construed as limited to the particular embodiments discussed. Accordingly, the above-described embodiments are to be considered illustrative rather than restrictive, and it will be understood that modifications can be made therein by those skilled in the art without departing from the scope of the invention as defined by the following claims.

Claims

1. 1. A method for producing a continuous sheet product moving in a machine direction (MD), comprising: operating the scanning sensor in a production mode to periodically traverse back and forth across the width of the sheet in a cross direction (CD) to detect a first set of values ​​of selected sheet properties; operating the scanning sensor in a verification mode by varying the lateral width of each scan to be substantially less than the width of the sheet to detect a second value of the selected sheet characteristic; wherein one or more control functions associated with the scanning sensor in the production mode are suspended while the scanning sensor is operating in the verification mode.

2. 2. The method of claim 1, wherein the method includes analyzing a CD profile of the detected values ​​before operating the scanning sensor in the verification mode and during operation of the scanning sensor in the production mode, and receiving input corresponding to a selection of a region of the CD profile, wherein the scanning sensor operates on the selected region of the CD profile in the verification mode.

3. 1. A method of operating a continuous sheet manufacturing system including a plurality of actuators positioned along a cross-machine direction (CD) and a scanning sensor positioned downstream of the plurality of actuators for measuring and acquiring property data of a moving sheet of material, comprising: measuring sheet physical properties of the moving sheet of material using the scanning sensor and displaying a lateral profile of the measurements; selecting a lateral region within the lateral profile, the lateral region having a lateral width less than 10% of an overall width of the moving sheet of material; measuring a sheet physical property of the moving sheet of material with the scanning sensor in the lateral region.

4. 1. A method for measuring process variables in a continuous sheet process having a machine direction and a cross direction, comprising: providing an elongated member supporting a mounting head containing a sensor; activating the actuator to produce a moving sheet of material; orienting the moving sheet of material along a machine direction, the moving sheet of material having a first edge and a second edge, the elongated member positioned adjacent the moving sheet of material along a lateral direction; guiding the mounting head back and forth between a first scan position and a second scan position such that the sensor measures a sheet property between the first edge and a second edge of the moving sheet of material, the sensor generating a first signal corresponding to the measurement; controlling the actuator in response to the first signal; ceasing control of the actuator in response to the first signal; guiding the mounting head back and forth between a third scan position and a fourth scan position such that the sensor measures a property of the moving sheet of material between areas within the first edge and the second edge, and the sensor generates a second signal corresponding to the measurement; obtaining a sample of the moving sheet of material produced during the inducing; analyzing the obtained sample to obtain a test result; comparing the test result with the second signal.

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