Process and system for monitoring characteristics of defects in a web which is moving in a web-making machine and for identifying the causes of the web defects

FIELD OF THE INVENTION

0001The present invention generally relates to techniques for monitoring and controlling continuous web-making systems such as a papermaking machine and more specifically to techniques for detecting repetitive defects on web sheet products, identifying the sources of the defects and initiating corrective measures.

BACKGROUND OF THE INVENTION

0002In the manufacture of paper on continuous papermaking machines, a web of paper is formed from an aqueous suspension of fibers (stock) on a traveling mesh of papermaking fabric and water drains by gravity and suction through the fabric. The web is then transferred to the pressing section where more water is removed by pressure and vacuum. The web next enters the dryer section where steam heated dryers and hot air completes the drying process. The paper machine is, in essence, a water removal system. A typical forming section of a papermaking machine includes an endless traveling papermaking fabric or wire, which travels over a series of water removal elements such as table rolls, foils, vacuum foils, and suction boxes. The stock is carried on the top surface of the papermaking fabric and is de-watered as the stock travels over successive de-watering elements to form a sheet of paper. Finally, the wet sheet is transferred to the press section of the papermaking machine where enough water is removed to form a sheet of paper. Many factors affect the quality of the paper produced.

0003The presence of defects and holes in the papermaking process can be disastrous since even a small hole can catch to result in a roll tear. Most of paper defects are repetitive but if the causes of the defects are not identified and corrected quickly the equipment damage can be extensive, which requires time consuming shut downs and expensive repairs. Current web inspection systems (WIS) can deliver quality data to support decisions that need to be made in subsequent processing steps. Based on web inspection technology, all relevant process images and data are captured and analyzed on-line. Interlinking WIS with events capturing already exists where, in addition to the defects detected, the WIS system also displays the corresponding video sequences recorded by cameras. Unfortunately, existing WISs do not include root cause analysis for repetitive defects which identifies the nature of web sheet defects, their locations relative to the papermaking machine, and the specific sources or names of the equipment that caused the defects. There are no solutions available for non-repetitive defects.

0004<patcit id="pcit0001" dnum="GB2304195A"><text>GB2304195A</text></patcit> discloses an apparatus and method for identifying periodic roughness variations on a paper surface. Such devices of this type, generally, collect topography data from the paper surface, analyze the data, and compare the data with known signature topographies of paper machine clothing and equipment to determine the location in the paper manufacturing process where the periodic roughness variations on the paper surface are being produced. Adjustment of the paper making machine or components thereof may be made to obviate the variations.

0005<patcit id="pcit0002" dnum="US7155356B2"><text>US 7,155,356 B2</text></patcit> discloses a method of controlling the quality and/or condition of a fibre web in a process for manufacturing and/or finishing the fibre web, which includes, monitoring the fibre web with at least one optical spectrum separating measurement device, determining a quality variable of the fibre web, measuring electromagnetic radiation reflected from the fibre web using an optical spectrum separating measurement device synchronously with a movement of the fibre web, and measurements in the form of spectral data, generating a continuous quality variable chart, dividing the continuous quality variable chart into successive matched partial charts having a cycle length, detecting deviations and/or discontinuities of the quality variable from the successive matched partial charts, and detecting malfunctioning of a rotating/moving means using the detected deviations and/or discontinuities of the quality variable.

SUMMARY OF THE INVENTION

0006The present invention in its various aspects is as set out in the appended claims.

0007The present invention is based in part on the recognition that the root causes of repetitive or cyclical web defects can be detected by creating unique diagnostic patterns associated with selected components of the papermaking machine and employing pattern recognition techniques to analyze and classify the moving (dynamic) paper defects and to identify their root causes. Once the locations of the paper defects and the equipment causing the paper defects are identified, corrective actions can be effected to resolve the problem. The invention enhances machine run-time thereby minimizing late deliveries and improves overall product quality.

0008In web production processes, machine or equipment defects or malfunctions manifest as web defects or deviations. The present invention traces the web defects to the exact equipment components that caused the problems. With respect to papermaking, equipment defects and malfunctions include, for example, the presence of foreign substances adhered to the equipment surface, uneven surfaces due the presence of holes or gaps in clothing (wire or felts) or on rolls (size press or calendar), uneven distribution of moisture, steam, or chemicals by spray nozzles, leaking nozzles, and cutting mechanism (slitter) malfunctions. Such equipment defects result in the production of paper web products that are not within physical and/or chemical property specification.

0009While the invention will be illustrated as being implemented in papermaking, it is understood that the invention is applicable in other continuous web-making processes such as, for example, in the manufacturer of packaging, rubber sheets, plastic film, metal foil, and the like. A web generally comprises a continuous sheet of moving material that is relatively thin and preferably elongated. The final product is flat and can be stored as rolls of material.

0010In one aspect, the invention is directed to a process to monitor characteristics of web defects according to claim 1.

0011In a further aspect, the invention is directed to a a web making system according to claim 4.

BRIEF DESCRIPTION OF THE DRAWINGS

0012<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIGS. 1</figref>, <figref idref="f0002">2</figref> and <figref idref="f0003">3</figref> illustrate a papermaking system;</li><li><figref idref="f0004">FIGS. 4A, 4B, and 4C</figref> are exemplary diagnostic patterns;</li><li><figref idref="f0005">FIG. 5A</figref> depicts measurements of a web sheet characteristic that are presented in a two-dimensional map format;</li><li><figref idref="f0005">FIG. 5B</figref> is a cross directional profile of a web sheet characteristic;</li><li><figref idref="f0006">FIG. 6</figref> is a flow diagram for identification of root cause of a defect; and</li><li><figref idref="f0007">FIG. 7</figref> is a flow diagram for automatic re-trimming of a defective jumbo roll.</li></ul>

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

0013The continuous web sheet defect analytics, classification and remediation will be illustrated by implementing the techniques in a sheet or web making system 10 that includes papermaking machine 2, control system 4 and network 6 as illustrated in <figref idref="f0001">Fig. 1</figref>. The papermaking machine 2 produces a continuous sheet or web of paper material 12 that is collected in take-up reel 14. The paper material 12, having a specific width, is produced from a pulp suspension, comprising of an aqueous mixture of wood fibers and other materials, which undergoes various unit operations that are monitored and controlled by control system 4. The network 6 facilitates communication between the components of system 10.

0014The papermaking machine 2 includes a headbox 8, which distributes a pulp suspension uniformly across the machine onto a continuous moving screen or wire 30 that moves in the machine direction (MD). The wire 30 is typically an open mesh material that can be made of metal such woven bronze or copper. Alternatively, the wire can be made of synthetic materials such as plastics (polyamides), in which case the wire is often referred to as a fabric. Headbox 8 includes any suitable structure for distributing a dilute, aqueous pulp suspension and includes a slice opening through which the pulp suspension is distributed onto moving screen or wire 30 which comprise a suitable structure such as a mesh for receiving a pulp suspension and allowing water or other materials to drain or leave the pulp suspension. The wire 30 is driven by and supported on motorized rolls 31, 33. A plurality of shower nozzles 35 is arranged in the cross direction (CD) for cleaning the wire (30). As used herein, the "wet end" forming portion of sheetmaking system 10 comprises headbox 8 and wire 30 and those sections before the wire 30, and the "dry end" comprises the sections that are downstream from wire 30. The wet end is also referred to as the fourdrinier section. As further described herein the dry end typically includes the press, drying, and finishing (or calendaring) sections.

0015Sheet 12 enters a press section 32, where the dehydration and thickening of the web takes place, and which includes multiple press rolls where sheet 12 travels through the openings (referred to as "nips") between pairs of counter-rotating rolls. In this way, the rolls in press section 32 compress the pulp material forming sheet 12. This may help to remove more water from the pulp material and to equalize the characteristics of the sheet 12 on both of its sides.

0016As sheet 12 travels over a series of heated rolls in dryer section 16, more water in sheet 12 is evaporated. At the finishing end, size press 17 and calendar 18 processes and finishes sheet 12, for example, by smoothing and imparting a final finish, thickness, gloss, or other characteristic to sheet 12. In particular, sizing operations provide paper with resistance to penetration by aqueous solutions. The chemical treatment also imparts better surface characteristics and improves certain physical properties. Sizing solution is applied within a two-roll nip 17. Other materials (such as starch or wax) can also be added to sheet 12 to obtain the desired finish. An array of induction heating actuators 24 applies heat along the CD to one or more of the rollers to control the roll diameters and thereby the size of the nips. Once processing by calendar 18 is complete, sheet 12 is collected onto reel 14.

0017Sheetmaking system 10 further includes an array of steam actuators 20 that controls the amount of hot steam that is projected along the CD. The hot steam increases the paper surface temperature and allows for easier cross directional removal of water from the paper sheet. Also, to reduce or prevent over drying of the paper sheet, paper material 12 is sprayed with water in the CD. Similarly, an array of rewet shower actuators 22 controls the amount of water that is applied along the CD.

0018In order to control the papermaking process, the properties of sheet 12 are continuously measured and the papermaking machine 2 adjusted to ensure sheet quality. This control may be achieved by measuring sheet properties using one or more scanners 26, 28 that are capable of scanning sheet 12 and measuring one or more characteristics of sheet 12. For example, scanner 28 could carry sensors for measuring the dry weight, moisture content, ash content, or any other or additional characteristics of sheet 12. Scanner 28 includes suitable structures for measuring or detecting one or more characteristics of sheet 12, such as a set or array of sensors. Scanner 28 can measure the dry end dry weight, ash content, or other physical properties of the paper product and generate dry-end signals. Measurements from scanner 28 are provided to control system 4 that adjusts various operations of papermaking machine 2 that affect MD and/or CD characteristics of sheet 12. An MD characteristic of sheet 12 generally refers to an average characteristic of sheet 12 that varies and is controlled in the machine direction.

0019In this example, control system 4 is capable of controlling the dry weight of the paper sheet by adjusting the supply of pulp to the headbox 8. For example, control system 4 could provide information to a stock flow controller that regulates the flow of stock through valves and to headbox 8. Control system 4 includes any hardware, software, firmware, or combination thereof for controlling the operation of the sheetmaking machine 2 or other machine. Control system 4 could, for example, include a processor and memory storing instructions and data used, generated, and collected by the processor. Scanner measurements control operations of the papermaking machine with both the dry end control and wet end control loops operating.

0020<figref idref="f0002">Fig. 2</figref> depicts a representative press section which is situated between the end of the forming section and beginning of the dryer section. The press section consists of a number of cooperating endless circulating loops, through which a sheet of wet stock is transformed into a sheet of partially de-watered wet-stock. This exemplary press arrangement includes three separate closed loops that include: (1) upper press felt 40, (2) lower press felt 42, and (3) dryer felt 44. Press felts 40, 42 serve as reservoirs to collect (absorb) water from the sheet of wet stock by pressing and capillary action. The forming wires, press felts, and dryer felts are collectively referred to as papermaking clothing. Dryer felt 44 is heated and water evaporates from the partially de-water wet stock as it is carried by the dryer felt. Upper and lower press felt 40, 42 are typically made of synthetic materials whereas dryer felt 44 is typically made of cotton or synthetic materials. The structure of the felts used in the dryer section can have veiy high open areas to afford rapid evaporation. Coarse or grainy characteristics, chocking of felts, sticky materials on the felts, degraded porosity and excessive hardness on the press and dryer felts can cause marks or imperfections on the paper formed.

0021A sheet of aqueous wet stock 46 is transported from wire 30 of the forming section onto the wet-press section. A wet-end sensor 61 can measure characteristics of the wet stock 46 such as basis weight or caliper and generate wet-end signals. Vacuum devices 62, 64 referred to as Uhle boxes (vacuum boxes) under the wire and press felt remove water from the web. A sheet of wet stock 46 is transferred by suction to the bottom side of upper press felt 40 that is held by suction roll 62 and is thereafter retained and supported by surface tension on the upper press felt 40 as the sheet becomes disposed between the upper press felt 40 and the lower press felt 42. The sheet of wet of stock, which is sandwiched between the two felts, advances toward a press nip that is created by press rolls 48 and 50 where compression forces water from the wet stock and into the felts. Papermaking machine can have multiple press sections depending on the machine configuration. Upon exiting the wet-press step, the partially de-watered and consolidated sheet is transferred onto the first dryer felt 44 which carries and supports the sheet as it passes over dryer cylinders 52 and 54 where some residual water is removed by evaporation. The sheet is then transferred onto the second dryer felt 58 which is heated by dryer cylinder 56. Only one dryer cylinder is shown whereas a commercial papermaking machine typically has thirty to sixty, depending on the paper machine configuration. At this stage in the process, the relatively thin sheet dried paper product 60 is available for further papermaking processing, such as coating and calendaring, where the moisture content is reduced.

0022Dryer felts can be cleaned and washed in the process is generally referred as conditioning using chemicals and water. For example, a spray device 72 directs cleaning fluid onto the fabric and vacuum device 74 removes the cleaning fluid. Lower press felt 42 is similarly conditioned with spray device 84 and vacuum device 86 and dryer felt 44 is equipped spray device 78 and vacuum device 80. Typically each spray device includes a plurality of shower nozzles arranged in the CD adjacent the felt.

0023<figref idref="f0003">Fig. 3</figref> is a schematic of the top view of a papermaking machine 102 with a wet end 130 and dry end consisting of press section 132, drying section 134, and finishing section 136. Headbox 104 discharges a fibrous suspension onto a wire (not shown) to form a sheet or web of aqueous fibers 100 that is supported on the wire which is situated between rolls 106 and 108. Positioned above the web which is moving in the machine direction is camera 152. Press section 132 includes camera 154 that is positioned between rolls 110 and 112. Drying section 134 includes camera 156 that is positioned between rolls 114 and 116 and finishing section 136 includes camera 158 that is positioned between rolls 118 and 120. A slitter 122 shears the paper when jumbo reel 124 reaches a preselected size. Digital images of the web are taken by the cameras, such as CCD or CMOS devices, and the images are processed and recorded in computer controller 160. Instead of using cameras, an optical reflective or transmission sensor consisting of a laser and associated detector can be used to obtain information characteristics of the web.

0024With the present invention, components of the wet end and dry end that can produce repetitive defects on the web 100 are selected for analysis by creating diagnostic patterns associated with the components. The diagnostic patterns are compared with operational web defect patterns of the corresponding components to determine the source(s) of web defects that are detected. For instance, for wet end 130, a diagnostic pattern for the wire 30 (<figref idref="f0001">Fig. 1</figref>) can be generated by capturing images of the web at the wet end when a new wire with no defects is used. The dimensions of diagnostic pattern for the wire are determined by the overall length of the wire circumference. Diagnostic patterns for rolls 106, 108 are captured and recorded by cameras 152 or with sensors. The dimensions of the diagnostic patterns for rolls are determined by their diameters. Similar diagnostic patterns are generated for components in the press, drying, and finishing (which includes the size press and calendar) sections. Another set of diagnostic patterns is also generated for the shower and spray arrangements in the wet and dry ends. They are used during production and during the cleaning or conditioning cycles. The dimensions of the diagnostic patterns are determined by the positions of the shower nozzles.

0025During operation of a papermaking machine, the quality control system (QCS) measures various physical properties of the paper, such as basis weight, thickness and moisture level, at different stages of the process. CD scanner sheet property measurements are stored for future reference and/or accessed for real-time observation and analysis. Other physical characteristics that can be measured include, for example: chemical composition, surface roughness, gloss, caliper, crepe pattern surface features.

0026With the present invention, diagnostic patterns are created for selected components of the papermaking machine. <figref idref="f0004">Fig. 4A</figref> is a diagnostic pattern 180 for wire 30 (<figref idref="f0001">Fig. 1</figref>) at the wet end. The 2-dimensional pattern is created by using sensors data that measure one or more properties of interest of a moving web along a CD at a designated MD location at the wet end. The length of pattern 180 corresponds to the entire length of outer boundary or circumference of wire 30. The property levels can be measured when the wire 30 is new or just cleaned and is free of defects so that the diagnostic pattern represents the standard for a particular grade of paper being manufactured under specific operating conditions. Preferably, when the 2-D pattern 180 is created, the CD measurements are initiated at specific and recorded location of wire 30. In this fashion, each position in the 2-D pattern of the web can be associated with an identifiable position on the wire.

0027If defects are present in wire 30, such as a hole in the wire mesh or the presence of a foreign material, then the diagnostic pattern will exhibit corresponding web sheet deviations from standard that are caused by said defects. In this example, the presence of deviations 182, 186 and 190 on the diagnostic pattern 180 suggests that there are corresponding defects on wire 30. Moreover, the specific locations of the defects on the wire can be identified. These defects on the wire are considered the root causes of the corresponding web-sheet deviations. Defects on wire 30 will cause repeated deviations on the moving web as the endless wire continues to operate.

0028Similarly, <figref idref="f0004">Fig. 4B</figref> is a diagnostic pattern 184 for press felt 40 (<figref idref="f0002">Fig. 2</figref>). The 2-D is created by sensors data that measure one or more properties of interest of a moving web along a CD at a designated MD location at press end. The length of pattern 184 corresponds to the entire length of outer boundary or circumference of press felt 40. For instance, the pattern can represent the preferred moisture levels or thicknesses of a web of fibrous stock exiting the press section. Defects in the press felt will result in repeated deviation 186 on the web.

0029<figref idref="f0004">Fig. 4C</figref> is a diagnostic pattern 188 for a roll such as size press 17 or calendar 18 (<figref idref="f0001">Fig. 1</figref>). The 2-D is created by sensors data that measure one or more properties of interest of a moving web along a CD at a designated MD location at finishing end. The length of pattern 188 corresponds to the entire length of outer boundary or circumference of a roll. For instance, the pattern can represent the preferred thicknesses or gloss of a web of dried paper. Defects in the press or calendar generate corresponding repeating deviations 190 on the web.

0030There are many potential sources of web quality deviations in the papermaking process. For example, with respect to deviations in web thickness, potential sources are present throughout the machine from the headbox to the finishing end. In the case of gloss deviations, the potential sources are most likely located at the finishing end where calendaring and added coatings produce glossy paper. The present invention affords a technique to identify the source(s) of repetitive web defects.

0031Both during production and cleaning, web inspection system defect identification sensors capture defects of the web to create operational patterns that are compared to the diagnostic patterns. In addition, the papermaking machine quality control system, which measures physical properties and optimizes the machine, is also operating and integrated with the web defect detection, classification and identification process. <figref idref="f0005">Fig. 5B</figref> is a cross-directional profile or scan of a representative physical property such as web caliper or basis weight at one location along the machine direction. The upper and lower profiles represent the acceptable range or standard for the physical property.

0032<figref idref="f0005">Fig. 5A</figref> shows a map which is a compilation of CD measurements vs. standard over a period of time. The most recent scan is at the bottom and the oldest one on top. The map depicts regions D where the measured parameters are within specification. The map also depicts successive regions 170, 172, and 174 of the moving web exhibiting quality deviations from standard. Moreover, each area encompasses acceptable and non-acceptable portions. For example, within the web portion designated 170A, the quality is within a tolerance range whereas the web portion designated 170B represent web where the quality with respect to the measured property is not acceptable. The data represented in <figref idref="f0005">Fig. 5A</figref> correlate to defects in the moving web along the MD with respect to the papermaking machine. In practice, for ease of observation, the measurement values are usually represented by different colors.

0033<figref idref="f0006">Fig. 6</figref> shows the steps in the process of identifying the cause(s) of paper defects generated during production. Diagnostic patterns (220) are created for selected wire parameters (202), press parameters (204), dryer/calendar parameters (206) and size press (210). Clothing refers to the wire at the wet end and felts at the dry end. Robo-cleaner refers to automatic cleaning mechanism in the dryer and felts. Diagnostic patterns are created for (i) selected rolls based on their diameters, (ii) clothing based on their lengths, and (iii) cleaning devices based their shower nozzle locations.

0034At step 208, web defect data is collected and analyzed as illustrated in <figref idref="f0005">Fig. 5A</figref>. In steps 214 and 212, quality deviations and defects are classified as repetitive defects or non-repetitive defects in the machine direction. Using standard pattern recognition software, the information in <figref idref="f0005">Fig. 5A</figref> and in particular, the regions exhibiting web deviations is analyzed and each region is classified as being a repetitive defect or non-repetitive (interval) defect in the machine direction. In <figref idref="f0005">Fig. 5A</figref>, regions 170, 172, and 174 represent repetitive or cyclical defects. A partitional clustering algorithm such as a K-means clustering algorithm can be employed to determine the right group or category to which repetitive defects belong. Repetitive defects are further classified in steps 224 and 218 into two categories: continuous web defects and non-continuous (or interval) web defects in steps 218, 220 and 224. For example, moisture lines and groove impressions from rolls and dryers appear as continuous web defects. Holes, calendar stamping, size press impressions are examples of non-continuous web defects.

0035As shown in steps 212, 228, 216, and 218, web defects on a moving web are classified as continuous web defects or non-continuous web defects. For a web with repeating defects that are non-continuous, diagnostic patterns for the rolls and clothing (including wire and felts) are compared to the repeating defects. The diagnostic pattern which matches the exact length of the repeating defect is identified. A technique for correlating the detected dynamic and deterministic web defect patterns to circulating web machine components uses a naive bayes statistical machine leaning technique. The probability method uses prior data to identify the machine component(s) or root causes of web defects. The Baysian model is constructed using information relating to machine component defects history data, machine parameters, and felt/wire/equipment replacement or reconditioning times and dates. The model applies historical data and when new data relating to defect incidences becomes available, the model prioritizes the equipment from where the defect(s) originate.

0036The unique features of the identified diagnostic pattern in turn yield information as to the specific component causing the defect. In steps 236, 230, 234, for a web with repeating defects that are continuous, shower and robo-cleaner patterns are applied and the diagnostic nozzle pattern which matches the exact length of the repeating defects is found and the identity and location of the cause of the defect are determined. In step 234, once a solution is generated and operator of papermaking machine is notified of cause and solution. As specified in steps 226, 232, for non-repetitive web defects, the defects are matched using conventional fault location metrics to identify the equipment(s) causing the non-repetitive web defects. For continuous web defects, when comparison shows a match in the exact pattern length and/or exact shower length, machine operator is notified (234).

0037Once the papermaking machine component(s) causing web defects are known, the operator can execute a number of solutions to remedy the situation. Re-trim removes selected defective portions of the material from the jumbo reel. In most papermaking operations, the jumbo reel is rewound into small paper rolls or to form another reel for coating, treatment or converting. As part of the re-winding operations, defective paper is removed.

0038As indicated in steps 208 and 228, when web defects are identified on a moving web, distance along the MD of the defects to the jumbo reel 14 (<figref idref="f0001">Fig. 1</figref>) are recorded as an input on the reel's length. When the web material is wound onto the reel, this synchronization procedure marks the locations, including the starting points, on the reel where web material containing defects can be found. The removed defective paper can be sold as paper of a lower grade.

0039When web defects are detected, control system 4 (<figref idref="f0001">Fig. 1</figref>) can initiate appropriate action to remove or minimize the defect. For example, if the defect in caused by tacky material on the wire mesh or felt, the foreign substance may be easily removed by application of an on-line spray. In the case where the web defects are caused by an upstream machine defect, it may be possible to minimize or correct the defect by the appropriate adjustments of actuators located downstream. For instance, if a slice in the headbox 8 malfunctions so that the sheet of aqueous wet stock 46 transported from wire 30 (<figref idref="f0002">Fig. 2</figref>) has an unacceptable CD thickness measurement, then one or more of the presses or rolls downstream can be adjusted so that the final product is within specification with respect to caliper. For either of these scenarios, it desirable to record when web defects first appear and when the defects cease. Finally, in some instances where web defects are caused by machine components that cannot be fixed online or where the web defects are too severe to be corrected, then the only effective remedy is to replace the defect machine parts.

0040The jumbo roll 14 (<figref idref="f0001">Fig. 1</figref>) is the parent roll that is manufactured and is typically undergoes a rewinding process whereby the parent roll is unwound, cut and wind into suitable size rolls. Defective material in the jumbo roll is identified and removed in a re-trimming process shown in <figref idref="f0007">Fig. 7</figref>. When a web defect is first detected, its location along the machine direction is recorded and simultaneously the anticipated location of the initial web defect in the jumbo rolls is noted. Since the machine speed is known, the time required for the initial web defect to reach the jumbo roll can be determined. In this fashion, the position of the initial web defect relative to the length of the roll can be marked in step 238. Once the web defect is removed, the position of when the defect ceases to appear relative to the length of the roll is also remarked in step 240.

0041Moisture and thickness profiles are also analyzed in step 252. The locations on the jumbo roll where moisture and thickness profile deviations occur, that is, the positions along the length of the paper where such defects are found are inputted in control system in step 254. These defects are also removed during re-trimming. In steps 244, 246, and 248, the operator takes appropriate corrective action. The initial appearance and cessation of web defects are marked on the jumbo roll. When the roll is unwound, the defective paper in the jumbo reel is removed or trimmed in steps 242, 250 and 256.

0042The foregoing has described the principles, preferred embodiment and modes of operation of the present invention. However, the invention should not be construed as limited to the particular embodiments discussed. Instead, 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 present invention as defined by the following claims.