Patent Application
20230391571
The present invention generally relates to quality control techniques for fabricating sheet materials and, more particularly, to methods of precisely matching measurements made during the production of uncoated or coated sheet products such as electrochemical cell electrodes to finished products such as electrochemical batteries incorporating anodes and cathodes so as to permit defects found at a later stage of production to be traced to the sources of the measured properties.
On-line measurements are used to detect properties of sheet materials during manufacture to enable prompt control of the sheetmaking processes and, thus, to assure sheet quality while reducing the quantity of substandard sheet material which is produced. One of the main complications in making on-line measurements during sheetmaking is that the physical properties of sheet materials usually vary in the machine direction (MD) as well as in the cross direction. MD refers to the direction of travel of the sheet material during manufacture, and the term “cross direction” refers to the direction across the surface of a sheet perpendicular to the MD.)
To detect variations in sheet materials, scanning sensors are employed that periodically traverse back and forth across a sheetmaking machine in the cross direction while detecting values of a selected sheet property such as basis weight or caliper along each scan. Normally, the sheet being produced is traversed from edge to edge during each scan. The time required for a typical scan is generally between a few seconds to tens of seconds depending on the cross-direction length Which can be many meters. The rate at which measurement readings are provided by such scanners is usually adjustable; a typical rate is about one measurement reading every millisecond.
In practice, measurement information provided by scanning sensors is usually assembled after each scan to provide a “profile” of the detected sheet property in the cross direction. In other words, each profile is comprised of a succession of sheet measurements at adjacent locations in the cross direction. The purpose of the profiles is to allow cross-directional variations in sheet properties to be detected easily. Based upon the detected cross-directional variations in the detected sheet property, appropriate control adjustments may be made to the sheetmaking machine with the goal of reducing profile variations both in the cross direction and in the machine direction.
A scanning sensor that periodically traverses a sheet at generally constant speed cannot measure the selected sheet property at locations which are aligned exactly perpendicular to the longitudinal edges of the sheet. Due to finite sheet velocity, scanning sensors actually travel diagonally across the sheet surface, with the result that consecutive scanning paths have a zigzag pattern with respect to the direction perpendicular to the longitudinal edges of the sheet. In practice, it is typical to calculate an average of profile measurements over each scan.
Conventional scanning systems using one or more scanners deliver to the customer one or more cross-directional profiles that are updated periodically at the end of each scan. In multiple scanner systems these scanner profiles are taken at different MD positions. No attempt is made to correlate when a piece of sheet at an upstream scanner is actually (re)measured a little bit later with a down-stream scanner.
In fabricating anode or cathode electrodes, a metal foil from metal rolls is continuously coated with a mixture of active material. To achieve and maintain the quality of continuous, roll-to-roll production of electrodes, there are constant, online measurements of quality factors that are strongly linked to battery performance. Slitting machines cut the finished coated metal foils into sheets of electrodes that are assembled into the cells and batteries.
With current manufacturing techniques, once a battery is assembled, there is no readily available means of identifying and accessing specific data associated with the electrodes that are incorporated into a particular battery. The art is demanding improved production traceability so that purchasers can trace on-line measurements made during production of the electrodes all the way to the assembled electrochemical cells and batteries.
The present invention is based, in part, on the generation of a machine direction (MD) position profile measurement of the moving sheet or product that records the MD position of each of the cross direction (CD) measurements. The technique will enable recreation of the real zig-zag measurement path which is not possible with current flat sheet scanning systems.
The invention can apply to a single scanning frame for measuring sheet material properties in the cross direction or to multiple scanning frames spaced along the production process. In the case of multiple scanners, a computer network-based time synchronization protocol, such as the IEEE 1588v2, can be employed to ensure that all scanners are precision time synchronized.
In one aspect, the invention is directed to a sheet monitoring system that includes:
In another aspect, the invention is directed a technique for a producing MD position profile of a moving sheet of material which travels in a MD, that includes a scanning sensor that measures a physical property. The technique includes:
In yet another aspect, the invention is directed a technique for a producing MD position profile of a moving sheet of material which travels in a MD, that includes two or more scanning sensors that measures physical properties. The technique includes:
With the present invention, the inclusion of MD positioning information, which is obtained by recording the time when each measurement was taken and the machine line speed (at one or more positions in the process) yields not just a profile of measurements but also a “profile of MD sheet positions”. With respect to the characteristic zig-zag measurement pattern produced by a scanning sensor, the MD position profile of the present invention will provide the CD values and positions vs. the MD position. For instance, in the case where the scanning sensor is measuring basis weight (measured in grams per square meter), with the MD position profile for each specific MD position of the sheet (as measured in millimeters from a user defined reference) there will be corresponding data for both the CD position (as measured by distance in mm from one edge of the moving sheet) and the basis weight as measured at that CD position.
The improvement is that every measurement gets an extra coordinate. This gives full traceability as the manufacturer can trace and know that in the end the what parts of the sheet (e.g., electrode) went into a specific battery. Thus, defects in the batteries can be traced back using the MD position profile to the exact physical location on the sheet product.
With the present invention, two or more scanner systems can be setup to make synchronized crisscross measurements that can increase the true measurement coverage. For example, two scanners can be setup to create X-shaped measurement profiles instead of the current zig-zag pattern profiles and hence calculate a true CD profile for a fictitious perpendicular line between the two scanners. In addition, two or more scanner systems can be setup to make synchronized crisscross (X-shaped) measurements that will enable computing more accurate measurement averages. Similarly, downstream follower scanners can be setup to retrace the MD position profile of a leader scanner to make same spot measurements. Same spot measurements can be done in batch production as well, where the sheet product that is under measurement is transferred between two scanning systems in a discontinuous manner.
Finally, the MD position profile can be employed to adjust the MD position profile on each downstream scanner in the case of a material break in the production process.
While the invention will be illustrated as being implemented in lithium-ion battery production, it is understood that the invention is applicable in other continuous sheet making processes such as, for example, in the manufacture of paper, rubber sheets, plastic film, metal foil, and the like.
As shown in
Coater 4 includes actuators that control the doctor blade to regulate the amount of slurry that is extruded onto sheet 30. Dryer 10 removes excess solvents and cures the slurry that is 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 properties of the moving coated sheet exiting dryer 10. Thereafter rolling supports 34. 36 reverse the orientation of the moving sheet so that the second surface is now the uncoated top side whereupon coater 14 applies a layer of electrode slurry on the top or second surface of the moving sheet 38. Tachometer 46 measures the line speed and properties of the double-side coated sheet 40 are measured with gauge 16 before entering dryer 18.
Tachometer 48 measures the line speed and scanner device 24 measures properties of the electrode layers on the first and second surfaces. After calendar 52 a rewinder takes up the double-side coated sheet 42 into roll 44. Surface defects on the coatings 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 performed in separately in discrete, discontinuous batch operations. For example, the roll 44 is subsequently subject to a slitting operation to form individual electrodes suitable for assembling into cells and batteries.
Sensors 8, 12, 16 and 24 are depicted as operating in the transmissive mode. For instance, each comprise a radiation source that directs a beam of radiation into a moving sheet and a radiation receiver that detects radiation that is transmitted through the material. Sensors operating in the transmission mode are described, for instance, in U.S. Pat. Nos. 9,182,360, 8,527,212, 7,298,492 and US 2021103821173 and US 2021/0262776, which are incorporated herein by reference. Alternatively, the sensors can operate in the reflective mode. For instance, each sensor has an upper head housing both a radiation source and detector. Sensors operating in the reflective mode are described, for instance, in U.S. Pat. Nos. 9,182,360, 8,527,212, 7,298,492 and US2020/0096308, which are incorporated herein by reference. The sensors can also comprise a combination of reflective and transmissive sensors.
Maps displaying the scanner measurements are typically divided into points or bins across the width; for example, each bin can represent a distance of about 5 mm.
Located downstream are scanning sensors 110 and 112; the distances of the two scanners from position 124 are known. Line tachometer pulses are counted at a designated rate, such as 2 KHZ, and accurately time stamped. The system includes a controller 108 which has a processor 118 and memory 126 and a signal generator 116. In operation, line tachometer measures the rotation speed of roller 102 and sends pulse signals to controller 108 which converts the rotation speed to MD speed by relating; to the radius of roller 102. Scanners 110 and 112 each measures characteristics of sheet and transmits corresponding signals to the controllers. The signal generator 116 sends synchronizing signals to scanner 110 which establishes the origin for the MD position axis. In this system, the synchronization signals need only be provided to one of the scanners on the line. Integration of the velocity over time yields the change in position along the MD.
In particular, the scanners 110 and 112 perform binning of MD positions such that instances when the scanning gauge enters and exits in each of the user-defined, cross direction measurements regions (bins) are accurately timestamped. The tachometer counts values that fall within these timestamps which are accumulated and averaged to generate a MD position of each such cross directional bin. Thereafter, the MD position of each bin of the sensor measurement profile is aggregated as an array and displayed as an MD position profile for each cross directional profile. Each sensor signal measuring a sheet property is also aggregated as an array and displayed as a cross direction profile.
Time-synchronized is particularly suited for coordinate MD position measurements in a production line. Time synchronizing multiple scanners in a production line allows the MD reference position synchronization signal to be wired to only one scanner. Time stamps of the synchronization signals are 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, the scanner receiving synchronization signal timestamp can accurately associate it with its local tachometer timestamps to establish the MD reference position.
Each scanner can be configured to reset its position relative to the MD reference position when triggered by synchronization signals. A quantity designated “Sync Offset”, for instance, compensates for the true distance between each scanner down the production line so that a point on the sheet measured by one scanner appears at the same MD position when measured by a second scanner further down the production line. Even if the scanners are not coordinated, the scans from a similar spot on the sheet can be programmatically put together.
Computer 220 coordinates the measurements by scanning device 212 so that the locations of interrogation spots in pattern 218 are recorded in database 222 along with the corresponding MD positions. In this fashion, when the coated sheet 200 is cut into individual electrodes, the measurements made on each electrode are known; moreover, electrochemical cells and batteries incorporating these electrodes can be identified by serial numbers that will allow the measurements to be retrieved.
Another feature of the present invention is that the MD position profiles can be employed to synchronize subsequent measurements to prior measurements. For example, coated sheet 200 of
As the second measurements by scanning device 242 are made, the locations of the interrogation spots in pattern 248 are recorded in database 222 along with the corresponding MD position profile. The database thus has a library of first and second measurements that were made 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 serial numbers that will allow both first and second sets of measurements to be traced.
Referring to
The foregoing has described the principles, preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive, and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention.
This application claims priority under 35 U.S.C.§ 119(e) to co-pending application No. 63/349,500 filed Jun. 6, 2022, which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63349500 | Jun 2022 | US |
