System and method for calculating additional local stretch in a web - Patents.com

Abstract

The present invention relates to a system and method for calculating an additional local stretch of a web moving through a conversion process, the system and method being aimed at locating defects in the web identified during winding during unwinding and stopping the web with the web defect located near or at a defect correction station. The method comprises the steps of detecting position marks (PM(n)) applied during winding of the web (5) during unwinding of the web, measuring the distance between the position marks, calculating an additional local stretch between the position marks generated during unwinding, and applying the calculated additional local stretch to a known position of a subsequent web defect to determine an estimated position of this web defect in the unwound web. The method for correcting the web defect then comprises the step of stopping the web with the web defect located near or at a defect repair station (38).

Description

[Technical field]

[0001] The present invention relates to a system and method for locating pre-identified features, such as defects, of a moving web undergoing a converting process. The system and method calculates a change in local stretch in the moving web during the converting process. The calculated local stretch can be used to calculate a new position of the feature in the web relative to coded position marks on the stretched web during the converting process. The present invention also relates to a system and method for correcting defects in the web, and for slowing or stopping the web when the calculated new position of the feature approaches a defect repair station. [Background technology]

[0002] In web processing and converting, for example in paper making and roll winding, it is necessary to locate and repair significant web defects, such as holes or lumps, or web contamination, such as chemical contaminants such as oil, or foreign objects, such as metal chips. Locating and correcting / repairing such defects (hereafter referred to as defect repair for simplicity) is particularly important when the paper roll is subsequently subjected to coating or other converting operations, because even small holes in the web can cause sheet breaks that are time consuming to correct.

[0003] For example, when a web defect is detected by a web inspection system during winding, it is important to identify and record the location of the web defect on the web. This information can then be utilized in subsequent conversion processes, such as rewinding, to stop the unwinder so that the web defect is located at a defect repair station where an operator can correct or repair the defect on the web. A printing system can be used in the web inspection system to apply uniquely coded machine direction (MD) position marks (hereafter referred to as coded position marks for brevity) to the web being wound at a predetermined distance from the origin of the web. These marks can be detected by a position mark detector during inspection and can be used to identify the machine direction (MD) position of the web defect from the position marks during winding. The cross direction (CD) position of the defect can be recorded by an appropriate sensor. These coordinates of the web defect relative to the last identified coded position mark can be electronically recorded, such as in a table or database, along with a description of the web defect.

[0004] The web is then unwound and a coded position mark just prior to the web defect is detected on the unwinder, either automatically or by an operator, and the machine speed must be slowed down so that the operator can locate the web defect before the unwinder finally stops at the location of the web defect, so that the web defect can be repaired.

[0005] A problem with such systems is that the coded position marks are applied when the web is running in a first machine direction ("winding direction"), for example in a winder, at a first web speed and with a first web tension, while the correction of the web defect is performed when the web is running in the opposite machine direction ("unwinding direction"), for example in an unwinder, at a second web speed and usually with a different second web tension. Such differences in running conditions mean that during the winding and unwinding runs, the coded position marks are no longer spaced a predetermined distance apart, since the web material may stretch by different amounts and thus the distance between the coded position marks may be different in the different runs. As a result, during web defect correction in the unwinder, where the location of the web defect is recorded as a specific distance from a specific coded mark on the web, the web may be stopped too early if the web has stretched compared to the first run, or too late if the web length has decreased compared to the first run. If the web stops in the wrong location, an operator or the web inspection system must search for the web defect, find the defect, and then move the web so that the defect is located at the defect repair station, which is time consuming.

[0006] US20090028416 relates to a system that uses pairs of fiducial marks on a web to generate a scaling factor according to a process performed on the web, which is used to scale anomaly locations between pairs of fiducial marks for use in subsequent processes. Summary of the Invention

[0007] This problem of correcting the stretch difference between two processes performed on a web can be solved by a method and a system for calculating the additional local stretch experienced by a portion of a moving web and for applying this calculated local stretch in real time to one or more subsequent portions of the moving web. In the present invention, the term real time means that the calculation is performed and ready to be applied within an elapsed time of less than one second after the necessary measurement of the distance between a pair of coded position marks has been performed. The calculation is preferably performed and ready to be applied within 0.5 seconds or less, more preferably 0.1 seconds or less, even more preferably 0.01 seconds or less, most preferably 0.001 seconds or less after the necessary measurement has been performed. Even if it takes 1 second to be calculated and ready to be applied for a web moving at, for example, 10 m / s, the web has only moved 10 meters in this time, and if the calculated additional local stretch is 5%, the new position of a defect that was currently located 10 meters from the coded position mark will be at most 50 cm from its current position. Such a system is provided with one or more web length sensors, for example linear encoders. This(e) measures the actual length of the web passing the sensor(s). This actual length can then be compared to a calculated length of the web using previously applied coded position marks on the web detected as passing the sensor location. The system is provided with software which calculates the amount of additional local stretch experienced by the web material by comparing the actual length of material measured by the additional sensor(s) with the calculated length of material identified by the number or identity of the coded position marks passing the additional sensor(s). Such a simple calculation can be performed in the software in a fraction of a second, meaning that the results of the calculation can be used before any significant length of web from the next portion of the web has passed the subsequent defect repair station.Thus, for example, if the predetermined distance between the first coded position mark and the second coded position mark is set as 100 meters in a first winding run, but the actual distance between the two marks in a subsequent second unwinding run is measured as 105 meters, the software will calculate the additional local stretch in the second run compared to the first run (i.e. the stretch between these two position marks) as 5%. Generally, the process conditions that cause the web stretching do not change abruptly, so that the additional local stretch measured for adjacent sections of the web will be approximately the same. This means that the additional local stretch calculated for the first section of the web can be applied to a subsequent section of the web and the change in the position of the defect in the subsequent section of the web can be calculated. Thus, the amount of additional local stretch of the first section of the web can be applied to the recorded position of the web defect in the subsequent section of the web and the calculated new position of the web defect. For example, if a web defect was recorded as being 60 m behind a first coded position mark and 40 m ahead of a second coded position mark, and the calculated local stretch of the web in a first section of the web immediately preceding said first coded position mark was 5% greater than in the first run, then, using the 5% calculated local stretch for the first section of the web, the calculated location of the web defect would be 63 m (105% x 60) from said first coded position mark and 42 m (105% x 40) from the second coded position mark. Of course, if, as is normal, the direction of web travel is opposite to that used when the web was wound, the second coded position mark will be closer to the first coded position mark than the first coded position mark. First To be detected, the software locates the web defect on a second coded position mark. from At the first coding position mark Head toThe new distance between the first coded position mark and the second coded position mark is 105 m, so the web defect will be 105-63=42 m from the second coded position mark in the direction towards the first coded position mark. Information about the calculated new location of the defect from the second coded position mark can then be used during the same run to slow down or stop the web when the defect approaches the defect repair station. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 shows diagrammatically a side view of a winding system used in a system for calculating the additional local stretch in a web according to the invention. [Diagram 2] FIG. 2 shows a schematic side view of an unwinder used in a system for calculating additional local stretch in a web according to the invention. [Diagram 3] FIG. 3 illustrates a schematic of a system for calculating additional local stretch in a web according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] FIG. 1 shows a schematic of a winder system 1 having a winder 2 for winding a native web 3 from a papermaking machine or other web source 5. The web 3 is wound on a core 7 held on a rotatable shaft 9 of the winder to form a reel 11. The web is inspected during its progression from the web source 5 to the reel so that web defects can be detected for further correction. The inspection may comprise an optical defect detector such as a transverse linear scanner 13 and a transverse linear metal detector 15. The transverse linear scanner 13 extends across the width of the web (transverse direction "CD") to detect defects such as visible web features, e.g. holes, folds, scars, etc. The transverse linear metal detector 15 is capable of detecting web defects in the form of metallic contamination of the web. These optical and metal detectors generate defect signals that contain information about the location of the detected web defects across the web. To be able to correct the web defects, the location of the web defects in the direction of web progression in the machine direction ("MD") must also be known. The system includes a distance encoder, e.g., a linear distance encoder 17, which measures the length of the web in the winder direction past the distance encoder. The encoder is connected to a control system 19, which may be any automatic control system 19, such as a PC, analog computer, control server, etc., with appropriate control software or programs. The control system is operatively connected to a marking device 21, e.g., an ink marker. The marking device 21 may be operated to apply a uniquely coded MD position mark (PM(L times n)) to the web, preferably near the edge, preferably printed with an easily erasable ink, e.g., a UV erasable ink, every predetermined distance L of the web, e.g., every 100 m (i.e., L=100 m), in the winder direction, as measured by the distance encoder. Each coded position mark indicates the position of the mark in the MD direction from an origin, which may be the start of the reel or other fixed point, e.g., the first applied mark. The web may be transported in the machine direction at a constant linear velocity V m / s or at a continuously measured linear velocity V(t) m / s. The optical flaw detector is at a fixed distance A from the marking device and the metal detector is at a fixed distance B from the marking device.Thus, the time taken for each coded position mark to pass each of the detectors after being applied to the web can be calculated from the known values ​​of V or V(t). Similarly, the location of each individual web defect in MD can be calculated from the time that has elapsed from the time the last print was applied to the web to the time that the individual web defect was detected. For example, if the web is traveling in the MD at 10 m / s and the distance A is 1 meter, it will take 0.1 seconds for a newly applied coded position mark to pass the optical defect detector. At this speed, if an optically visible web defect (D1) is detected by the optical defect detector 1 second after the marking device prints coded position mark PM(1000) (corresponding to a position of 1000 meters in MD from the origin) and a signal is sent to the control system indicating the CD location of the web defect and the time it was detected, the control system can calculate that the web has traveled 10 meters from the marking device 21 in this 1 second, because the control device has a clock and information about the linear MD speed of the web. Since the optical defect detector 13 is 1 meter away from the marker device in the machine direction, the actual location of web defect D1 is 1009 meters in the machine direction from the origin of the reel in the winding direction, which is 9 meters behind the 1000 meter coding position mark in the winding direction, in other words, it is 91 meters ahead of the 1100 meter coding position mark (PM1100) in the winding direction.

[0010] A similar calculation can be made for the metal web defect (D2) found by the metal detector. If the distance B is 2 meters, then at a web speed of 10 m / s, it will take 0.2 seconds for the newly applied coded position mark to pass the metal defect detector. If the metal defect detector detects the metal web defect (D2) 1 second after the marking device prints the coded position mark (PM1000) corresponding to the position of 1000 meters in MD, the control system can calculate that the web has traveled 10 meters from the marking device in this 1 second. Since the metal defect detector 15 is located 2 meters from the marking device 21 in the machine direction, the actual position of the metal web defect D2 is 1008 meters from the origin in the reeling direction in the machine direction and 8 meters behind the coded position mark at 1000 meters in the reeling direction. In other words, it is 92 meters ahead of the coded position mark at 1100 meters in the reeling direction (PM1100).

[0011] Thus, the control system can be programmed to determine the location in the machine direction MD from the reel origin of a web defect found by an optical defect scanner or metal detector by utilizing the speed of the web and the time difference between when the defect signal is sent to the control unit and when the mark is applied to the web. The location in CD of the web defect can be indicated by the lateral position recorded in the defect signals of the optical defect scanner and metal detector.

[0012] The type of web defect, its CD location, and its MD distance from the origin of the web on the reel in the winding direction are preferably stored in a web defect log or list or database or the like for the uniquely identifiable reel being processed. This web defect log or the like may be stored on the system server 20 and associated with this uniquely identifiable reel 11 for future use in correcting web defects on this uniquely identifiable reel.

[0013] An unwinding system 30 for unwinding a web is shown in FIG. 2. It comprises an unwinder 31 for reels. In the system according to the invention for calculating the additional local stretch of a web, the reel on the unwinder 31 is a uniquely identifiable reel on which the unique web 3 has been wound using a winder system of the type described above. Also, the location of the web defects on the unique web is recorded in a web defect log or the like associated with this uniquely identifiable reel. When this uniquely identifiable reel 11 is ready to be unwound in order to correct the web defects, it is placed on a rotatable shaft 33 of the unwinder 31. The unwinder 31 unwinds the unique web from this uniquely identifiable reel and feeds it to another core 35 of a further device, for example a further winder 37. Web defects of the unique web can be corrected or repaired in an automatic or user-operated defect repair station 38. The unwinder is provided with a distance encoder, for example a linear distance encoder 39, which measures the length of the unique web in the unwinder direction past the distance encoder. The encoder is connected to a control system 19'. The control system 19' may be any automatic control system 19' with appropriate control software or programs, such as a PC, analog computer, control server, etc., that contains or has access to web defect logs etc. for the reels being processed. This access may be achieved by using the same control system 19, 19' for the unwinder system and the winder system, or by storing the web defect logs etc. on a server 20 that is accessible to both the winder control system 19 and the unwinder control system 19'. The defect logs etc., with details of the type and location of defects, may be provided on a movable storage medium that is accessible to the control systems 19, 19'. The distance encoder 39 provides a signal to the control system regarding the actual length of the web that has passed the encoder.

[0014] The unwinder is provided with a coded position mark reader, e.g. an ink reader 41, at a linear distance D (e.g. 1 meter) in the machine direction from the distance encoder. Similarly, the coded position mark reader is located at a linear distance C (e.g. 1 meter) in front of the defect correction station 38. The ink reader detects each coded position mark as it passes the coded position mark reader and sends a signal to the control system each time it detects a coded position mark. This signal contains information about the identity of the coded position mark, e.g. if it is the coded position mark at 1100 meters in the winding direction (PM(1100)), the control system is provided with software that registers the actual length (A1) of the web that has passed the distance encoder at the moment when all coded position marks, e.g. the coded position mark (PM(1100)), have been detected. When the next coded position mark, for example the 1000 meter coded position mark PM(1000), is detected by the ink reader, the control system registers the actual length of the web A1, for example 110 meters, that has passed the encoder since the previous coded position mark, the 1100 meter mark, was detected. In this example, the actual amount of the web A1 that has passed the encoder is 110 meters, while the coded position marks are nominally only a distance L that is, in this case, 100 meters apart. This means that the web has been locally stretched additionally (i.e. between these two coded position marks) by 10 meters (10%) during unwinding. The amount of additional local stretch SL between two successive coded position marks, for example PM(n) and PM(n+L), can be calculated by the control system and recorded for the portion of the web P(n) between each pair of successive coded position marks. The amount of additional local stretching of the web during unwinding can be used directly by the control system to estimate where a web defect detected during winding actually is in this subsequent unwinding. For example, as in the winding example above, if a web defect is detected 91 meters from the coded position mark at 1100 meters in the winding direction, forwardIf there is no additional local stretching, the web defect will be located 91 meters from the 1100 meter coded position mark in the unwinding direction. backward If the additional local stretch SL in the portion of the unwound web between the 1100 coded position mark and the 1000 coded position mark is a constant 10%, then on unwinding, the actual location of the web defect D1 is not 91 meters behind the 1100 portion mark, but 91 + 9.1 (additional 10% stretch) = 100.1 meters in the direction from the 1100 coded position mark towards the 1000 coded position mark.

[0015] However, the additional local stretch LS of the portion of the web containing the web defect (P(n)) can only be found after both the beginning and ending coded position marks (P(n) and P(n+L)) for the portion of the web containing the web defect have passed the ink reader. In practice, this means that the location of the web defect can only be estimated after the coded position mark following the web defect has been detected by the ink reader. If the coded position marks are nominally 100 m apart, then theoretically, for the portion of the web containing the web defect, the defect repair station would need to be at least 100 meters away from the ink reader (plus a distance to compensate for web stretch) in order for the additional local stretch to be calculable before the web defect reaches the web defect repair station. This is unrealistic, and instead the controller uses the additional local stretch calculated for the previous portion of the web between two position marks (portion P(n-(x*L))) to estimate in real time the additional local stretch for the actual portion of the web being processed between two coded position marks (portion P(n)). Preferably, the additional local stretch for the previous portion of the web is for the portion of the web between the two position marks immediately preceding the portion of the web being processed (i.e. x=1), because this previous portion of the web is subjected to very similar process conditions as the subsequent portion of the web and is therefore expected to experience similar local stretch as the subsequent portion of the web. However, if the web is moving very fast and there is a risk that a defect at the beginning of the portion of the web will pass the defect repair station before a new opposition of the defect can be calculated, the additional local stretch from an even earlier portion of the web can be used to calculate a new position of the defect in the web that has been subjected to the additional local stretch. The portion of the web may be a portion of the web between two consecutive coded position marks, or may be a portion of the web between multiple position marks.The greatest accuracy in estimating the local additional stretch for any portion of the web (P(n)) is achieved by utilizing the value of the additional local stretch calculated for the previous portion of the web (P(n-1)), which may be the additional local stretch of an earlier portion of the web (i.e. x>1, e.g. P(n-2) or P(n-3), etc.) or the average additional local stretch of two or more earlier portions of the web between two coded position marks (e.g. the average value of the additional local stretch of the portion P(n-1) and the portion P(n-2) of the web). In fact, the additional local stretch may also be calculated over a longer portion of the web, e.g. a portion of the web between a number of consecutive coded position marks, e.g. the portion between the preceding 3 or 4 or 5 coded position marks.

[0016] FIG. 3 shows diagrammatically a system for calculating the additional local stretch in a web 43 according to an embodiment of the invention comprising a winder and an unwinder according to the invention as described above.

[0017] This information regarding the estimated location of the web defect, taking into account the additional local stretching of the web with respect to the unique coded position marks on the web, allows the system to estimate in real time (e.g., while the web is being unwound) the web while it is being unwound and before the web reaches the defect repair station, where the information about the local additional stretching or shrinkage in the web is utilized to stop the web such that a portion of the web corresponding to the estimated location of the web defect is located near or at the defect repair station, thereby reducing the time required to run the equipment at slower speeds and / or move backwards or forwards when searching for the web defect. Thus, using the distances for C and D above, if the defect repair station 38 is 2 meters (distance D) from the distance encoder and only 1 meter (distance D minus distance C) from the ink reader, in order to stop the web so that a web defect estimated to be 100.1 meters from the 1100 meter coded position mark is located at the repair station, the web would simply be stopped 101.1 meters after the 1100 meter coded position mark is detected by the ink reader.

[0018] The method for calculating the additional local stretch of a web moving through a conversion process comprises the following steps: Providing a moving web of material; Providing a control system; applying a plurality of coded position marks to the moving web at predetermined intervals measured by a distance encoder while the web is being wound onto a reel; unwinding the web from the reel, detecting coded position marks, and measuring the distance between a plurality of pairs of consecutive coded position marks; using the control system to divide the measured distance between each of the plurality of pairs of consecutive coded position marks by the predetermined distance between each of the pairs of consecutive coded position marks to calculate in real time the additional local stretch of the web between each of the pairs of consecutive coded position marks; Equipped with.

[0019] A further method for calculating the additional local stretch of a web moving through a conversion process is: Follow these steps: Providing a moving web of material; Providing a control system; applying a plurality of coded position marks to the moving web at predetermined intervals measured by a distance encoder while the web is being wound onto a reel; unwinding the web from the reel, detecting coded position marks, and measuring the distance between a plurality of pairs of coded position marks; using the control system to divide the measured distances between the plurality of pairs of coded position marks by the predetermined distance between each pair of coded position marks to calculate in real time the additional local stretch of the web between each pair of coded position marks; Equipped with.

[0020] A method for calculating in real time additional local stretch of a moving web during a converting process and using said calculated additional local stretch to estimate locations of web defects in the web during unwinding comprises: Providing a moving web of material; Providing a control system; applying a plurality of coded position marks to the moving web at predetermined intervals, preferably measured by a distance sensor; scanning the web for web defects while winding the web onto a reel and recording the distance of each web defect from at least one coded position mark; unwinding the web from the reel and, during unwinding, detecting position marks and measuring the distance between at least one pair of coded position marks; using the control system to divide the measured distance between the at least one pair of coded position marks by the predetermined distance between the pair of coded position marks to determine the additional local stretch of the unwound web between the pair of coded position marks; multiplying the recorded distance of the web defect from the nearest coded position mark by the additional local stretch of the web calculated for the at least one pair of coded position marks upon approaching or immediately after passing the nearest coded position mark ahead of the web defect to identify the estimated location of the web defect in the machine direction on the unwound web; Equipped with.

[0021] In such a method, the pair of coded position marks may be consecutive position marks, or may be a pair of coded position marks separated by one or more further coded position marks, they may be two coded position marks immediately preceding the web defect in the current travel direction, or they may be other coded position marks ahead of the web defect.

[0022] The method for locating a web defect at a defect repair station additionally comprises the steps of calculating when the estimated location of the web defect is located at the defect repair station, and stopping the web when the estimated location of the web defect is located at the defect repair station or a predetermined distance in front of the defect repair station, the predetermined distance may be 2 meters or less, or 1 meter or less, so that an operator or an automated device can detect and / or identify the defect before it reaches the defect repair station.

[0023] A method for correcting a web defect includes the additional steps of stopping the web so that the web defect is located at the defect repair station and correcting the defect.

[0024] An alternative method for calculating additional local stretch of a moving web during a converting process and using said calculated additional local stretch to estimate the location of web defects in the web during unwinding comprises: Providing a moving web of material; Providing a control system; applying a plurality of coded position marks to the moving web at predetermined intervals, preferably measured by a linear distance encoder; scanning the web for web defects while winding the web onto a reel and recording the distance of each web defect from a next succeeding coded position mark; unwinding the web from the reel and, during unwinding, detecting coded position marks and measuring the actual distance between at least one pair of coded position marks; using the control system to divide the actual measured distance between each pair of coded position marks by the predetermined distance between the pair of coded position marks to determine at what additional local stretch of the unwound web between the pair of coded position marks during unwinding; multiplying the recorded distance of the web defect from the coded position mark closest to the web defect by the additional local stretch of the web determined with respect to the pair of coded position marks prior to approaching the coded position mark closest to the web defect to determine the estimated location of the web defect in the machine direction on the unwound web; Equipped with.

[0025] The method for locating a web defect at a defect repair station additionally comprises the steps of calculating when the estimated location of the web defect is at the defect repair station, and stopping the web when the estimated location of the web defect is at the defect repair station or at a predetermined distance in front of the defect repair station, the predetermined distance may be less than 2 meters, preferably less than 1 meter, so as to allow an operator or an automatic device to detect the defect before it reaches the defect repair station.

[0026] A method for correcting a web defect includes the additional steps of stopping the web so that the web defect is located at the defect repair station and correcting the defect.

[0027] Preferably, the control system for the method of the present invention comprises software running on a digital processing device such as a computer, server or the like, and the method includes the steps of providing such software and a digital processing device.

[0028] In some circumstances, a coded position mark may become damaged and unexpectedly unreadable, or may disappear or even fall off (e.g., an operator removes a sample of a web for testing because it is damaged and the removed sample had a coded position mark). For the sake of simplicity, any coded position mark that is unusable will be referred to as an "unusable coded position mark" in the following. When an unusable coded position mark occurs, the defect repair device is not able to calculate the additional local stretch between the unusable coded position mark (UCPM) and the coded position mark (PM(UCPM-1)) immediately preceding the unusable coded position mark, nor between the coded position mark PM ((UCPM+1)) immediately following the unusable coded position mark and the unusable coded position mark. To deal with such cases, a method for compensating for the unusable coded position mark may be provided in any method for calculating the additional local stretch of a moving web.

[0029] To avoid missing defects, in a method for compensating for unusable coded position marks, the software may be programmed to have an upper limit of the allowable additional local stretch. This upper limit may be predetermined and preprogrammed into the software. The upper limit may be set, for example, to any suitable value that exceeds the normally expected additional local stretch.

[0030] For example, if it is known that an additional local stretch of more than 10% would cause the preceding material batch to split or burst, then the additional local stretch calculated by the system obviously cannot exceed 10%. In such a case, when during use the actual measured distance from the coded position mark exceeds a distance that would correspond to an additional local stretch of 10% and no subsequent coded position mark is detected, the system may apply the last previously calculated local additional stretch or may apply a predefined value for the local additional stretch (e.g. 8%, 5%, 0%, -5%, -8%) until two consecutively numbered coded position marks are detected apart at an actual measured distance that corresponds to an additional local stretch of less than 10%. In this way, errors that may be introduced by unusable coded position marks may be reduced.

Claims

1. 1. A method for calculating additional local stretch of a web moving through a conversion process, comprising the steps of: Providing a moving web (3) of material; Providing a control system (19, 19'); applying a plurality of coded position marks at predetermined intervals to the moving web while winding the web onto a reel (11); unwinding the web from the reel, detecting coded position marks, and measuring the distance between a plurality of pairs of coded position marks; using said control system (19, 19') to divide the measured distance between each of said plurality of pairs of coded position marks by said predetermined distance between each of said plurality of pairs of coded position marks in real time within a time period of one second or less after measuring said distance between said at least one pair of coded position marks, to calculate said additional local stretch of said web between each of said pairs of consecutive coded position marks; A method comprising:

2. 1. A method for calculating in real time an additional local stretch of a web moving through a converting process and using said calculated additional local stretch to estimate locations of web defects in the web being unwound, comprising: Providing a moving web (5) of material; Providing a control system (19, 19'); applying a plurality of coded position marks at predetermined intervals to the moving web; scanning the web for web defects while winding the web onto a reel (11) and recording the distance of each web defect from at least one of the two nearest coded position marks; unwinding the web from the reel (11), detecting coded position marks and measuring the distance between at least one pair of coded position marks; using the control system, within a time period of one second or less after measuring the distance between the at least one pair of coded position marks, to divide the measured distance between the at least one pair of coded position marks by the predetermined distance between the pair of coded position marks to determine the additional local stretch of the unwound web between the pair of coded position marks, and multiplying the recorded distance of the web defect from the coded position mark in front of the web defect upon approaching or immediately after passing the coded position mark in front of the web defect by the additional local stretch of the web determined for the at least one pair of coded position marks to determine the estimated location of the web defect in the machine direction on the unwound web. A method comprising:

3. 1. A method for calculating in real time additional local stretch of a web moving through a converting process and using said calculated local stretch to estimate locations of web defects in the web being unwound, comprising: Providing a moving web (3) of material; Providing a control system (19, 19'); applying a plurality of coded position marks at predetermined intervals to the moving web; scanning the web for web defects while winding the web onto a reel (11) and recording the distance of each web defect from at least the next succeeding coded position mark; unwinding the web from the reel (11), detecting the coded position marks and measuring the distance between at least one pair of coded position marks; using the control system, within a time period of one second or less after measuring the distance between the at least one pair of coded position marks, to divide the measured distance between each pair of coded position marks by the predetermined distance between the pair of coded position marks to determine the additional local stretch of the rewound web between the pair of coded position marks, and multiplying the recorded distance of the web defect from the coded position mark ahead of the web defect upon approaching or immediately after passing the coded position mark closest to the web defect by the local additional stretch of the web determined for the pair of coded position marks to determine the estimated location of the web defect in the machine direction on the rewound web. A method comprising:

4. the pair of coded position marks are consecutive position marks; The method according to any one of claims 1 to 3.

5. the pair of coded position marks are separated by one or more further coded position marks, The method according to any one of claims 1 to 3.

6. the method comprising: a step of compensating for unusable coded position marks by applying the last previously calculated local additional stretch or by applying a predefined value for the local additional stretch, The method according to any one of claims 1 to 3.

7. The method is implemented in software on a digital processing device. The method according to any one of claims 1 to 3.

8. the method comprising the further step of locating the web defect at or near a defect repair station by calculating when an estimated location of the web defect is at the defect repair station and stopping the web when the estimated location of the web defect is at the defect repair station or a predetermined distance in front of the defect repair station. The method according to any one of claims 1 to 3.

9. The predetermined distance is 2 meters or less, preferably 1 meter or less. The method according to claim 8.

10. The method of any of claims 1 to 3, comprising the additional steps of stopping the web so that a web defect is located at the defect repair station, and repairing the defect.

11. The digital processing device is a server. The method according to any one of claims 1 to 3.

12. the time after measuring the distance between the at least one pair of coded position marks is preferably within 0.5 seconds or less, more preferably within 0.1 seconds or less, even more preferably within 0.01 seconds or less, and most preferably within 0.001 seconds or less; The method according to any one of claims 1 to 3.

13. A system for calculating an additional local stretch in a web, comprising a winder system (1), an unwinder system (30) and a control system (19, 19') having software adapted to implement the method according to any one of claims 1 to 3.

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