Measurement of the Machine Direction Position Profile in a Sheet Manufacturing System

Abstract

To reduce variations in profiles in both the cross and machine directions based on the detected lateral variations in detected sheet properties.SOLUTION: Machine direction (MD) position profile measurements of moving sheets record the MD positions of each cross direction (CD) measurement. A sheet monitoring system includes: means for measuring MD speed of a material sheet; means for associating measured MD velocity with time to produce a time-related MD velocity; means for recording time-related MD velocity; a first scanning sensor for measuring first properties of a sheet material, the first scanning sensor being located at a first position along the MD and a first scanner sensor traversing back and forth along the CD; and means for associating a first property measurement value with time to produce a time-related first property measurement value. Single and multiple scanning sensors are employed.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority under 35 U.S.C.§ 119(e) to co - pending application Ser. No. 63 / 349,500, filed Jun. 6, 2022, which is incorporated herein by reference.

[0002] (Field of the Invention) The present invention generally relates to quality control techniques for manufacturing sheet materials, and more particularly, to aligning measurements taken during the production of uncoated or coated sheet products, such as electrochemical cell electrodes, accurately with finished products, such as electrochemical batteries incorporating anodes and cathodes, and enabling tracking of defects discovered at later stages of production back to the source of the measured characteristics.

Background Art

[0003] Online measurements are used to detect the properties of sheet materials during manufacturing to enable facilitated control of the sheet - making process and, thus, ensure sheet quality while reducing the amount of off - specification sheet material produced. One of the main problems in performing online measurements during sheet making is that the physical properties of the sheet material typically vary in the machine direction (MD) and the cross - direction. The MD refers to the direction of movement of the sheet material during manufacturing, and the term “cross - direction” refers to the direction across the surface of the sheet perpendicular to the MD.

[0004] To detect variations in the sheet material, a scanning sensor that periodically traverses back and forth across the width of the sheet - making machine in the cross - direction is used while detecting the values of selected sheet properties, such as basis weight or caliper, along each scan. Typically, the sheet being produced traverses from edge to edge during each scan. The time required for a typical scan is generally on the order of several seconds to tens of seconds, depending on the cross - direction length, which can be several meters. The rate at which measurement readings are provided by such scanners is usually adjustable, and a typical rate is about one measurement reading per millisecond.

[0005] In practice, the measurement information provided by the scanning sensor is typically assembled after each scan to provide a "profile" of the sheet characteristics detected in the lateral direction. In other words, each profile is composed of a series of sheet measurements at adjacent locations in the lateral direction. The purpose of the profile is to enable the easy detection of lateral variations in the sheet characteristics. Based on the detected lateral variations in the detected sheet characteristics, appropriate control adjustments can be made to the sheet manufacturing machine for the purpose of reducing the variations in the profiles in both the lateral and machine directions.

[0006] A scanning sensor that periodically traverses the sheet at a constant speed cannot measure the sheet characteristics selected at a location that is precisely perpendicular to the longitudinal edge of the sheet. Due to the sheet speed, the scanning sensor actually moves diagonally across the sheet surface, and as a result, the successive scanning paths have a zigzag pattern with respect to the direction perpendicular to the longitudinal edge of the sheet. In practice, it is typical to calculate the average of the profile measurements over each scan.

[0007] Conventional scanning systems that use one or more scanners deliver to the customer one or more lateral profiles that are periodically updated at the end of each scan. In a multiple scanner system, these scanner profiles are acquired at different MD positions. No attempt has been made to correlate the downstream scanner with the upstream scanner at a time slightly after a sheet has actually been (re)measured at the upstream scanner.

[0008] In the production of an anode electrode or a cathode electrode, the metal foil from the metal roll is continuously coated with a mixture of active materials. For achieving and maintaining the quality of the continuous roll-to-roll production of the electrode, there is a certain on-line measurement of a quality factor that is strongly related to the battery performance. The cutting machine cuts the completed coated metal foil into electrode sheets that are assembled into cells and batteries.

[0009] With current manufacturing techniques, once a battery is assembled, there is no readily available means to identify and access specific data related to the electrodes incorporated into a particular battery. In the art, there is a need to improve product traceability such that online measurements taken during electrode production can be tracked all the way to the assembled electrochemical cells and batteries by the purchaser. SUMMARY OF THE INVENTION

[0010] The present invention is based, in part, on the generation of machine direction (MD) position profile measurements of a moving sheet or product that record each MD position of cross-direction (CD) measurements. This technique enables the reproduction of an actual zigzag measurement path that is not possible with current flat sheet scanning systems.

[0011] The present invention can be applied to a single scanning frame for measuring cross-directional sheet material properties, or to a plurality of scanning frames spaced along a production process. In the case of multiple scanners, a computer network-based synchronization protocol such as IEEE 1588v2 can be employed to ensure that all scanners are accurately time synchronized.

[0012] In one aspect, the present invention is directed to a material sheet moving in a machine direction (MD), means for measuring the MD speed of the material sheet, means for associating the measured MD speed with time to generate a time-related MD speed, means for recording the time-related MD speed, a first scanning sensor for measuring a first property of the sheet material, the first scanning sensor being disposed at a first position along the MD, the first scanner sensor traversing back and forth along a cross-direction (CD) perpendicular to the MD, and means for associating the first property measurement with time to generate a time-related first property measurement and a sheet monitoring system including the same.

[0013] In another aspect, the present invention is directed to a technique for producing an MD position profile of a moving material sheet moving in the MD, the technique including a scanning sensor for measuring physical properties. This technique (a) measuring the MD speed of the moving material sheet and generating a measured MD speed signal with a time stamp; (b) recording the measured MD speed signal with a time stamp; (c) receiving a measured physical property value with a time stamp from the scanning sensor; (d) correlating the recorded measured MD speed signal with a measured physical property value with a time stamp; (e) generating an MD position profile showing the measured physical property values of the CD with respect to the length of the moving material sheet produced within a specific time and including.

[0014] In yet another aspect, the present invention is directed to a technique for producing an MD position profile of a moving material sheet moving in the MD, the technique including two or more scanning sensors for measuring physical properties. This technique (a) measuring the MD speed of the moving material sheet and generating a measured MD speed signal with a time stamp; (b) recording the measured MD speed signal with a time stamp; (c) receiving a first measured physical property value with a time stamp from a first scanning sensor; (d) receiving a second measured physical property value with a time stamp from a second scanning sensor; (e) correlating the recorded measured MD speed signal with the first and second measured physical property values; (f) generating an MD position profile showing the first and second measured physical property values of the CD with respect to the length of the moving material sheet produced within a specific time and including.

[0015] In the present invention, by including the MD positioning information obtained by recording the time at which each measurement was made and the machine line speed (at one or more positions during the process), not only the profile of the measured values but also the "profile of the MD sheet position" is provided. Regarding the characteristic zigzag measurement pattern generated by the scanning sensor, the MD position profile of the present invention provides the position with respect to the CD value and the MD position. For example, when the scanning sensor is measuring basis weight (measured in grams per square meter), for the MD position profile of each specific MD position of the sheet (measured in millimeters from a user-defined reference), corresponding data exists for both the CD position (measured in millimeters from one edge of the moving sheet) and the basis weight measured at that CD position.

[0016] The improvement is that all measurements obtain extra coordinates. This provides complete traceability because the manufacturer can ultimately track and know which part of the sheet (e.g., the electrode) went into a specific battery. Thus, battery defects can be traced back to the exact physical location on the sheet product using the MD position profile.

[0017] In the present invention, two or more scanner systems can be set up to perform synchronized cross measurements that can increase the true measurement range. For example, two scanners can be set up to create an X-shaped measurement profile instead of the current zigzag pattern profile and, thus, calculate the true CD profile for the imaginary perpendicular line between the two scanners. Additionally, two scanner systems can be set up to perform synchronized cross (X-shaped) measurements that enable the calculation of a more accurate measurement average value. Similarly, a downstream follower scanner can be set up to retrace the MD position profile of the reader scanner to perform the same spot measurement. It is also possible to perform the same spot measurement in batch production, in which case the sheet product being measured is transferred discontinuously between the two scanning systems.

[0018] Finally, the MD position profile can be employed to prepare the MD position profile on each downstream scanner in the event of material breakage in the production process.

[0019] Although the present invention is illustrated as being implemented in lithium-ion battery production, it is understood that the present invention is applicable to other continuous sheet production processes, such as in the manufacture of paper, rubber sheets, plastic films, metal foils, and the like.

Brief Description of the Drawings

[0020]

Figure 1

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Embodiments for Carrying Out the Invention

[0021] Figure 1 shows a process for coating a metal web or sheet used in fabricating electrodes for lithium-ion electrochemical cells and batteries. To fabricate an anode, the electrode coating includes an anode active material such as graphite, and to fabricate a cathode, the electrode coating includes a cathode active material such as a lithium metal oxide. The electrode includes a current collector metal foil, and one or both sides of the current collector metal foil are coated with an electrode slurry that may also include carbon black, a binder, and a solvent. After applying the electrode slurry onto the side surface of the foil, the wet-coated foil is heated in a dryer to extract the solvent, leaving a solid layer of the electrode material adhering to the metal foil. Copper foil is a preferred anode current collector material, and aluminum foil is a preferred cathode current collector material. The foil is typically 9 - 50 μm thick, and the electrode coating ranges in thickness from 75 - 400 μm on one or both sides of the foil, such that a double-sided coated electrode can have a caliper of up to 850 μm, most typically about 250 μm thick.

[0022] As shown in Figure 1, roll 2 is unwound by an unwinder, and the sheet is fed as a continuous sheet of a metal web or sheet 30 that is coated with a layer of electrode slurry by a coater 4 whose upper (or first) surface may include a tape casting coating device. The basis weight, thickness, and other characteristics of the sheet of metal web 30 from roll 2 are well known. A tachometer 22 measures the line speed, and a scanning gauge 8 measures the basis weight, thickness, and other characteristics of the electrode slurry. The input from the tachometer can be used to calculate the MD position of the sheet being measured. As the scanning gauge 8 scans across the sheet, the MD position of each CD bin is recorded to create a MD position profile of the transient sensor. CD / MD offset correction can be applied to an additional sensor within the scanning head. A roll end signal or other dedicated signal can be used to set a reference ("zero") position for MD position measurement.

[0023] Coater 4 includes an actuator that controls a doctor blade to adjust the amount of slurry extruded onto sheet 30. Dryer 10 removes excess solvent and cures the slurry on the moving coated sheet 32 to form an electrode layer on the sheet. Tachometer 56 measures the line speed, and gauge 12 measures one or more characteristics of the coated sheet moving out of dryer 10. Thereafter, rolling supports 34, 36 reverse the orientation of the moving sheet so that the second surface becomes the upper surface that is not coated, and immediately thereafter, coater 14 applies a layer of electrode slurry onto the moving sheet 38, i.e., the second surface. Tachometer 46 measures the line speed, and the characteristics of the double-sided coated sheet 40 are measured by gauge 16 before entering dryer 18.

[0024] Tachometer 48 measures the line speed, and scanner device 24 measures the characteristics of the electrode layers on the first and second surfaces. After calendar 52, the winder takes in the double-sided coated sheet 42 onto roll 44. Surface defects on the coating are monitored by camera-based web inspection systems 26, 28. Although the process is illustrated as being continuous, it is understood that the various steps and attendant measurements can be carried out separately in discrete batch operations. For example, roll 44 is then subjected to a cutting operation to form individual electrodes suitable for assembly into cells and batteries.

[0025] Sensors 8, 12, 16, and 24 are shown as operating in transmission mode. For example, each includes a radiation source that directs a beam of radiation into the moving sheet and a radiation receiver that detects the radiation transmitted through the material. Sensors operating in transmission mode are described, for example, in U.S. Patent No. 9,182,360, U.S. Patent No. 8,527,212, U.S. Patent No. 7,298,492, and U.S. Patent Application No. 2021 / 0382173 and U.S. Patent Application No. 2021 / 0262776, which are hereby incorporated by reference. Alternatively, the sensors can operate in reflection mode. For example, each sensor has an upper head that houses both the radiation source and the detector. Sensors operating in reflection mode are described, for example, in U.S. Patent No. 9,182,360, U.S. Patent No. 8,527,212, U.S. Patent No. 7,298,492, and U.S. Patent Application No. 2020 / 0096308, which are hereby incorporated by reference. The sensors can also comprise a combination of reflective and transmissive sensors.

[0026] Maps that display scanner measurements are typically divided into points or bins across the width. For example, each bin can represent a distance of about 5 mm.

[0027] FIG. 2 shows a system for measuring the MD position profile of a continuous electrode sheet 100 that moves to MD and is supported by rollers 102 and 122. Roller 102 that supports electrode sheet 100 at position 124 includes magnet 104 that is monitored by line tachometer 106. The MD speed can be measured at any position of moving sheet 100. Since the sheet is stretchable, it is preferred to measure the MD speed near scanning sensor 110. Alternatively, an optical tachometer can be used.

[0028] Located downstream are the scanning sensors 110 and 112. The distances of the two scanners from position 124 are known. The line tachometer pulses are counted at a specified speed such as 2KHz and are accurately time-stamped. The system includes a controller 108 having a processor 118 and a memory 126, and a signal generator 116. During operation, the line tachometer measures the rotational speed of roller 102 and transmits a pulse signal to the controller 108 that converts the rotational speed to the MD speed by associating it with the radius of roller 102. The scanners 110 and 112 each measure the characteristics of the sheet and transmit the corresponding signals to the controller. The signal generator 116 transmits a synchronization signal to the scanner 110 that establishes the origin of the MD position axis. In this system, the synchronization signal only needs to be supplied to one of the scanners on the line. The integration of the speed over time results in a change in position along the MD.

[0029] In particular, the scanners 110 and 112 perform binning of the MD position such that instances are accurately time-stamped when the scanning gauge enters and exits each of the user-defined lateral measurement regions (bins). The tachometer counts the values within these time-stamps that are accumulated and averaged to generate the MD position for each of such lateral bins. Thereafter, the MD positions of each bin of the sensor measurement profile are aggregated as an array and displayed as an MD position profile for each lateral profile. Each sensor signal that measures the sheet characteristics is also aggregated as an array and displayed as a lateral profile.

[0030] Time synchronization is particularly suitable for coordinate MD position measurement in a production line. By time-synchronizing multiple scanners in a production line, it becomes possible to wire the MD reference position synchronization signal to only one scanner. The time stamp of the synchronization signal is accurately measured by the scanner to which it is wired. These time stamps are transferred to other scanners using a conventional TCP / IP network. Since all scanners are time-synchronized, a scanner receiving the synchronization signal time stamp can accurately associate it with its local tachometer time stamp to establish the MD reference position.

[0031] Each scanner can be configured to reset its position relative to the MD reference position when triggered by the synchronization signal. The amount designated as the "synchronization offset" compensates for the true distance between each scanner downstream in the production line so that the position on the sheet measured by one scanner appears at the same MD position when measured by a second scanner further downstream in the production line. Even if the scanners are not adjusted, scans from similar spots on the sheet can be grouped according to a program.

[0032] Figure 3 is a diagram of MD position measurement showing CD vs. MD sensor measurements. The profile is that of a scanner moving back and forth along the CD at a constant speed, and the scanner measures the physical characteristics of a moving sheet moving at a constant speed. Curve 170 is the measurement by sensor 110, and curve 172 is the measurement by sensor 112 (shown in Figure 2). Measurements at each point along the CD curves 170 and 172 can also be obtained. (The values are not shown in Figure 3.) The values can be shown on the curves by color codes or icons where different shades or icons represent specific values (such as basis weight ranges). It should be noted that in actual operation, each scanner decelerates as it approaches the edge of the sheet, stops at the edge, and then accelerates as it moves away from the edge towards the center of the sheet. Therefore, the zigzag pattern of the CD profile in this configuration and the figures in this specification curves rather than presenting sharp angles as shown.

[0033] Figure 4 is another system for measuring the MD position profile of the continuous electrode sheet 130 that moves to the MD and is supported by the rollers 132 and 152. The roller 132 that supports the electrode sheet 130 at position 154 includes a magnet 134 that is monitored by the linear tachometer 136. Downstream are arranged the scanning sensors 140 and 142. The distances of the two scanners from position 154 are known. The signal generator that functions as an external clock master transmits synchronization signals to the sensors 140 and 142.

[0034] Figure 5 shows the use of the MD position profile in tracking different measurements of the (one or more) electrode layers on the moving sheet to improve the traceability of the battery electrodes. The electrode layer 200 is coated on a moving substrate (foil) that is supported by the roller 202 operated by the motor 204 and conveyed to the MD. The tachometer 206 monitors the speed of the roller 202. The frame 210 supports the scanning device 212 that includes a gauge for measuring the basis weight and / or thickness of the coated sheet. The scanning device generally moves across the coated sheet 200 periodically at a constant speed. A gauge for measuring spots or regions 214 of the coated sheet 200 is shown. The gauge does not measure the sheet properties selected at a location that is exactly perpendicular to the longitudinal edge of the sheet. Instead, due to the sheet speed, the scanning device moves diagonally across the surface of the coated sheet, and as a result, the continuous scanning path has a zigzag pattern with respect to the direction perpendicular to the longitudinal edge of the coated sheet 200. An example of such a zigzag pattern is the scanning path 218 that is traced by the gauge when the scanning device 212 crosses the surface of the sheet during successive forward and backward scans. The angle of the scanning path with respect to the true CD depends on the lateral speed of the scanning device and the known machine direction speed of the coated sheet 200. The zigzag pattern of the investigation spots covers a relatively small portion of the surface of the coated sheet 200.

[0035] The computer 220 adjusts the measurements by the scanning device 212 so that the locations of the interrogation spots within the pattern 218 are recorded in the database 222 together with the corresponding MD positions. In this way, when the coated sheet 200 is cut into individual electrodes, the measurement values taken on each electrode are known, and furthermore, the electrochemical cells and batteries incorporating these electrodes can be identified by a serial number that enables the retrieval of the measurement values.

[0036] Another feature of the present invention is that an MD position profile can be employed to synchronize subsequent measurements with previous ones. For example, the coated sheet 200 of FIG. 5 measured by the sensor 212 can be moved to another line for further processing such as drying or calendaring. Thereafter, a coated sheet 230 thus processed is formed and subjected to a second measurement. The movement of the sheet is supported on a frame 240 fixed to the rollers 232 and the second scanner device 242. The release time and CD speed of the downstream scanner device 242 are adjusted by the computer 220 so as to synchronize the second measurement by the scanner device 242 with the first measurement performed downstream by the scanner device 212. The scanning device 242 can be reset to start the measurement at the interrogation spot 244 such that the interrogation spots within the pattern 248 coincide with the interrogation spots within the zigzag pattern 218.

[0037] When the second measurement by the scanning device 242 is performed, the locations of the interrogation spots within the pattern 248 are recorded in the database 222 together with the corresponding MD position profile. Thus, the database has a library of the first and second measurements taken on essentially the same interrogation spots. When the coated sheet is cut into individual electrodes and assembled into electrochemical cells and batteries, these electrodes can be identified by a serial number that enables the tracking of both the first and second measurement sets.

[0038] Referring to FIG. 5, the MD speeds of sheets 200 and 230 may be different such that the position of the downstream scanner 242 is adjusted so that its CD motion matches the CD motion of scanner 212. In most cases, the MD speeds of both sheets are the same so that the scanners have the same speed profile. Note that the CD motion of the scanner is more complex than just a constant speed since the scanner is often accelerating or decelerating at the sheet edges.

[0039] FIG. 6 shows the use of two scanners 312 and 342 to develop an X-shaped pattern on sheet 330. The zigzag pattern 318 is generated by scanner 312 and the downstream scanner 342 uses the MD position information from the upstream scanner 312 to generate a zigzag pattern 348 such that the two zigzag patterns form an X-shaped area along the MD of the sheet. The advantage of this arrangement is that there is a better sheet area and the average of the CD profile is more accurate.

[0040] The foregoing has described the principles, preferred embodiments, and modes of operation of the present invention. However, the present invention should not be construed as being limited to the specific embodiments considered. Accordingly, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be understood that modifications can be made by those skilled in the art to those embodiments without departing from the scope of the present invention.

Claims

Claim 1 A method for generating an MD position profile of a moving material sheet moving in the machine direction (MD), comprising: (a) measuring the MD speed of the moving material sheet moving in the machine direction and generating a measured MD speed signal with a time stamp; (b) recording the measured MD speed signal with the time stamp; (c) receiving a first measured physical property value of the moving material sheet with a time stamp from a first scanning sensor that periodically traverses along a cross direction (CD) perpendicular to the machine direction and measures the physical properties of the moving material sheet; (d) receiving a second measured physical property value of the moving material sheet with a time stamp from a second scanning sensor that is disposed downstream of the first scanning sensor and periodically traverses along the cross direction and measures the physical properties of the moving material sheet; (e) correlating the recorded measured MD speed signal with the first measured physical property value with the time stamp and the second measured physical property value with the time stamp; (f) generating an MD position profile showing the first and second measured physical property values in the cross direction with respect to the length of the moving material sheet produced within a specific time and a method comprising the steps thereof.

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