System and method for calculating additional local stretch in a web

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, e.g., defects, in a moving web undergoing a converting process. The system and method calculates changes in local stretch in the moving web during the converting process. The calculated local stretch can be used to calculate new positions of features 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 positions of the features approach a defect repair station. [Background technology]

[0002] In web processing and converting, for example, in papermaking 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 like oil, or foreign objects, such as metal chips. Locating and correcting / repairing such defects (hereinafter referred to as defect repair for simplicity) is particularly important when the paper roll undergoes subsequent coating or other converting operations, because even small holes in the web can cause sheet breaks, which can be time-consuming to correct.

[0003] For example, if 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 used during subsequent conversion processes, such as rewinding, to stop the rewinder 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 with the web inspection system to apply uniquely coded machine direction (MD) position marks (hereinafter referred to for brevity as coded position marks) to the web as it is 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) location of the web defect from the position mark during winding. The cross direction (CD) location of the defect can be recorded by an appropriate sensor. These coordinates of the web defect relative to the last identified coded position mark, along with a description of the web defect, can be recorded electronically, such as in a table or database.

[0004] The web is then unwound and the coded position mark immediately preceding the web defect is detected on the unwinder, either automatically or by an operator, causing the machine speed to be slowed down so that the operator can locate the web defect before the unwinder finally stops at the location of the web defect, and 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") at a first web speed and a first web tension, for example, in a winder, while web defect correction is performed when the web is running in the opposite machine direction ("unwinding direction") at a second web speed and usually a different second web tension, for example, in an unwinder. This difference in running conditions means that the coded position marks are no longer spaced a predetermined distance apart because the web material may stretch different amounts during the winding and unwinding runs, so the distance between the coded position marks may be different in different runs. As a result, during web defect correction in the unwinder, where the location of a web defect is recorded as a specific distance from a particular coded mark on the web, the web may be stopped too early if the web has stretched compared to the first run, or may be stopped too late if the web's length has decreased compared to the first run. If the web stops in the wrong position, 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 for differences in stretch between two processes performed on a web can be solved by a method and system for calculating the additional local stretch experienced by a portion of a moving web and applying this calculated local stretch to one or more subsequent portions of the moving web in real time. In the present invention, the term real time means that the calculation is performed and ready to apply within an elapsed time of less than one second after the necessary measurement of the distance between a pair of coded position marks is made. The calculation is preferably performed and ready to apply within 0.5 seconds or less, more preferably 0.1 seconds or less, even more preferably 0.01 seconds or less, and most preferably 0.001 seconds or less after the necessary measurement is made. For example, if it takes one second for the calculation to be performed and ready to apply to a web moving at 10 m / s, but the web only moves 10 meters during this time, and the calculated additional local stretch is 5%, the new location of a defect originally located 10 meters from the coded position mark will be at most 50 cm from its original location. Such a system is equipped with one or more web length sensors, such as linear encoders. These measure 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 having passed the sensor location. The system is provided with software that 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 coded position marks that passed the additional sensor(s). This simple calculation can be performed in the software in a matter of seconds, 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 to 100 meters in a first rewinding run, but the actual distance between the two marks in a subsequent second unwinding run is measured to be 105 meters, the software would calculate an additional local stretch (i.e., the stretch between these two position marks) of 5% in the second run compared to the first run. Generally, the process conditions that cause web stretching do not change rapidly, so 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 subsequent sections of the web to calculate the change in the location of the defect in the subsequent section of the web. Thus, the amount of additional local stretch for the first section of the web can be applied to the recorded location of the web defect and the calculated new location of the web defect in the subsequent section of the web. 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 usual, the direction of web movement is opposite to that used when the web was wound, then 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 maps the location of the web defect to a second coded position mark. from To the first coding position mark HeadingThe new distance between the first coded position mark and the second coded position mark must be calculated in the direction towards the first coded position mark. Since the new distance between the first coded position mark and the second coded position mark is 105 m, 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 to slow down or stop the web during the same run as the defect approaches the defect repair station. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows a schematic side view of a winding system used in a system for calculating additional local stretch in a web according to the invention. [Figure 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 present invention. [Figure 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 INVENTION

[0009] FIG. 1 schematically illustrates 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 onto a core 7 held on a rotatable shaft 9 of the winder to form a reel 11. The web is inspected as it travels from the web source 5 to the reel so that web defects can be detected for further correction. The inspection may include 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 (crosswise direction, "CD") to detect visible web features, such as holes, folds, and scars. The transverse linear metal detector 15 can detect web defects in the form of metallic contamination of the web. These optical and metal detectors generate defect signals that contain information regarding the location of the detected web defect across the web. To enable web defects to be corrected, the location of the web defect 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 take-up direction past the distance encoder. The encoder is connected to a control system 19, which can be any automatic control system, such as a PC, analog computer, control server, or the like, 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 can be operated to apply a uniquely coded MD position mark (PM(L times n)) to the web, preferably near the edge, printed with an easily erasable ink, e.g., a UV-erasable ink, every predetermined distance L of the web measured by the distance encoder, e.g., every 100 meters (i.e., L=100 m), in the take-up direction. Each coded position mark indicates the position of the mark in the MD direction from an origin, which can be the start of the reel or other fixed point, e.g., the first applied mark. The web can 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 defect 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 it takes 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 elapsed between the time the last print was applied to the web and the time that the individual web defect was detected. For example, if the web is traveling in the MD at 10 m / s and 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 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 traveled 10 meters from the marking device 21 in that 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 spaced 1 meter 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 in the winding direction behind the 1000 meter coding position mark, or in other words, 91 meters in the winding direction ahead of the 1100 meter coding position mark (PM1100).

[0010] A similar calculation can be made for the metal web defect (D2) found by the metal detector. If distance B is 2 meters, 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) one second after the marking device prints the coded position mark (PM1000) corresponding to the 1000 meter position in the MD, the control system can calculate that the web has traveled 10 meters from the marking device in this one second. Because the metal defect detector 15 is located two meters from the marking device 21 in the machine direction, the actual location of metal web defect D2 is 1008 meters from the origin in the rewinding direction and 8 meters behind the 1000 meter coded position mark in the rewinding direction. In other words, it is 92 meters ahead of the 1100 meter coded position mark (PM1100) in the rewinding direction.

[0011] Thus, the control system can be programmed to determine the location in the machine direction MD from the origin of the reel 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 signal 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, list, database, or the like for the uniquely identifiable reel being processed. This web defect log, or the like, can be stored on system server 20 and associated with this uniquely identifiable reel 11 for future use in correcting web defects on this uniquely identifiable reel.

[0013] FIG. 2 shows a rewinding system 30 for rewinding a web. It includes a reel rewinder 31. In the system according to the present invention for calculating the additional local stretch of a web, the reel on the rewinder 31 is a uniquely identifiable reel onto which a specific web 3 has been wound using a winder system of the type described above. The locations of web defects on the specific web are recorded, such as in a web defect log associated with the uniquely identifiable reel. When the uniquely identifiable reel 31 is ready to be unwound for web defect correction, it is placed on a rotatable shaft 33 of the rewinder 31. The rewinder 31 unwinds the specific web from the uniquely identifiable reel and feeds it to another core 35 of a further device, such as a further winder 37. Web defects in the specific web can be corrected or repaired in an automated or user-operated defect repair station 38. The rewinder is equipped with a distance encoder, such as a linear distance encoder 39, that measures the length of the specific web in the direction of the rewinder past the distance encoder. The encoder is connected to a control system 19'. The control system 19' may be any automatic control system 19', such as a PC, analog computer, control server, or the like, with appropriate control software or programs 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 rewinder system, or by storing web defect logs, etc., on a server 20 accessible to both the rewinder control system 19 and the unwinder control system 19'. Defect logs, etc., with details of defect type and location, may be provided on a removable storage medium accessible to the control systems 19, 19'. The distance encoder 39 provides the control system with a signal regarding the actual length of the web that has passed through the encoder.

[0014] The unwinder is provided with a coded position mark reader, e.g., ink reader 41, located a linear distance D (e.g., 1 meter) in the machine direction from the distance encoder. Similarly, the coded position mark reader is located a linear distance C (e.g., 1 meter) ahead 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., the coded position mark at 1100 meters in the rewinding 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 time every coded position mark, e.g., coded position mark (PM(1100)), is 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 web A1 that has passed the encoder since the previous coded position mark, the 1100-meter mark, was detected, for example 110 meters. In this example, the actual amount of web A1 that has passed the encoder is 110 meters, while the coded position marks are nominally only a distance L, in this case 100 meters apart. This means that the web has been locally stretched (i.e., between these two coded position marks) by an additional 10 meters (10%) during unwinding. The amount of additional local stretch SL between two consecutive 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 consecutive 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, forward, without additional local stretching, the web defect is 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 web defect D1 is not 91 meters behind the 1100 portion mark, but rather 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 (P(n)) containing the web defect 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 meters apart, then theoretically, 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 for the portion of the web containing the web defect before the web defect reaches the web defect repair station. This is unrealistic. Instead, the controller uses the additional local stretch calculated for the preceding 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 preceding 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). This is because this preceding 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 for the defect can be calculated, the additional local stretch from an earlier portion of the web can be used to calculate a new position for the defect in the web that has undergone the additional local stretch. The portion of the web may be the portion of the web between two consecutive coded position marks, or may be the 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 immediately preceding portion of the web (P(n-1)), but it may also 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 stretches of portion P(n-1) and portion P(n-2) of the web). In fact, the additional local stretch can also be calculated over a longer portion of the web, e.g., a portion of the web between multiple consecutive coded position marks, e.g., the portion between the preceding three, four, or five coded position marks.

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

[0017] This information about the estimated location of the web defect, taking into account the additional local stretching of the web relative 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 as it is being unwound and before the web reaches the defect repair station. At the defect repair station, the information about the local additional stretching or shrinkage in the web is used to stop the web so that a portion of the web corresponding to the estimated location of the web defect is located near or at the defect repair station. This reduces the time required to run the equipment at slower speeds and / or move backward or forward when searching for the web defect. Thus, using the distances for C and D above, if the defect repair station 38 is 2 meters from the distance encoder (distance D) and only 1 meter from the ink reader (distance D minus distance C), 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 transformation process is: Steps below: 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 distance 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 direction of travel, 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 includes 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, where the predetermined distance can be 2 meters or less, or 1 meter or less, to allow an operator or automated equipment to detect and / or identify the defect before it reaches the defect repair station.

[0023] The method for correcting a web defect comprises 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 the calculated additional local stretch to estimate the location of web defects in the unwinding web includes: 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 the next subsequent 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 the additional local stretch of the unwound web between the pair of coded position marks during unwinding; determining an estimated location of the web defect in the machine direction on the unwound web by 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 before approaching the coded position mark closest to the web defect; 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 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, where the predetermined distance can be 2 meters or less, preferably 1 meter or less, so that an operator or an automatic device can detect the defect before it reaches the defect repair station.

[0026] A method for repairing a web defect includes the additional steps of stopping the web so that the web defect is located at the defect repair station and repairing 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 step of providing such software and a digital processing device.

[0028] In some situations, coded position marks may become unusable because they are damaged and unexpectedly become unreadable, or they may disappear or even fall off (e.g., an operator removes a test web sample because it is damaged and the removed sample had coded position marks). For simplicity, any unusable coded position mark will be referred to hereinafter as an "unusable coded position mark." When an unusable coded position mark occurs, the defect repair device is unable to calculate the additional local stretch between the unusable coded position mark (UCPM) and the coded position mark immediately preceding the unusable coded position mark (PM(UCPM-1)), nor between the coded position mark immediately following the unusable coded position mark (PM(UCPM+1)) and the unusable coded position mark. To address such cases, a method for compensating for unusable coded position marks may be provided in any method for calculating the additional local stretch of a moving web.

[0029] To avoid undetected defects, in a method for compensating for unusable coded position marks, the software may be programmed with an upper limit for 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% will cause the preceding batch of material to split or burst, the additional local stretch calculated by the system clearly cannot exceed 10%. In such a case, when, during use, the actual measured distance from a 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 previously calculated additional local stretch or a predetermined value for the additional local stretch (e.g., 8%, 5%, 0%, -5%, -8%) until two consecutively numbered coded position marks are detected at an actual measured distance apart 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 the control system (19, 19') to divide the measured distance between each of the plurality of pairs of coded position marks by the length of the predetermined interval between each of the plurality of pairs of coded position marks in real time within one second or less after measuring the distance between the at least one pair of coded position marks; A method comprising:

2. 1. A method for calculating, in real time, additional local stretch of a web moving through a converting process and using the calculated additional local stretch to estimate locations of web defects in the web during unwinding, 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 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 length of the predetermined interval 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 upon approaching or immediately after passing the coded position mark in front of the web defect, multiplying the recorded distance of the web defect from 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 during unwinding, 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 subsequent 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 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 length of the predetermined interval 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 upon approaching or immediately after passing the coded position mark closest to the web defect, multiplying the recorded distance of the web defect from the coded position mark ahead of the web defect by the determined local additional stretch of the web 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 calculated local additional stretch or by applying a predetermined 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 will be 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 of claim 8.

10. 4. The method of claim 1, further comprising the steps of stopping the web so that a web defect is located at a defect repair station, and repairing the defect.

11. the digital processing device is a server; The method of claim 7.

12. the time after measuring the distance between the at least one pair of coded position marks is preferably 0.5 seconds or less, more preferably 0.1 seconds or less, even more preferably 0.01 seconds or less, and most preferably 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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