Patent Publication Number: US-2007102556-A1

Title: Apparatus and method for measuring roll sidewall quality

Description:
FIELD OF THE INVENTION  
      The invention relates to manufacturing a roll of material, such as photographic paper, and more particularly, to an apparatus and method for determining the roll quality of a wound roll of material.  
     BACKGROUND OF THE INVENTION  
      Paper and other materials are manufactured using a continuous process that produces a traveling web of material. The web is wound in a roll of a specific size for further processing or distribution. Variables in the manufacturing process can affect the aesthetic appearance of the roll. For example, improperly controlled web tension during winding can cause conveyance weave and air entrapment between the winding layers, which can cause poor sidewall quality. Uneven web caliper (i.e., thickness) from one side of the web to the other can cause dishing wherein the edges of the roll lie in a different plane than the center, like a dish. Also, as the web travels over rollers, imperfections in the web or rollers or temperature fluctuations can cause the edges of the web to be uneven so that all individual windings do not lie in the same plane. These defects give the appearance that the roll quality is poor. Poor sidewall can cause functional failures during conveyance in printers; but without a tool to quantify sidewall profile and maximum roll width, the evaluation of roll quality in the factory can be subjective and unnecessary waste may be taken when acceptable rolls are rejected and discarded. There thus is a need to have a quality standard and a quantitative method and apparatus for measuring roll sidewall quality to provide both functionally and visually acceptable rolls.  
      Some paper or other material typically leaves the manufacturing facility as rolls that are to be photographically printed and cut to sheets of desired dimensions. A roll that is not perfectly wound may require extra effort to print and cut to desired dimensions, and may cause jams/stops in photo-processing equipment. Such rolls require careful monitoring as sheets are cut to ensure uniformity which translates to higher machinery costs and/or higher processing costs which is undesirable. A need therefore also exists for a method of quantifying roll sidewall quality and comparing to existing specifications for width in order to reduce extra processing costs.  
     SUMMARY OF THE INVENTION  
      The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, an apparatus for measuring a sidewall characteristic of a wound roll, where the wound roll comprises a strip of material wound about an axis, thereby forming a wound roll having concentric windings parallel to the axis with upstanding sidewall edges extending radially from the axis, includes a housing, a platform mounted in the housing having a surface adapted to receive the wound roll, a distance measuring sensor supported in the housing for movement along a predetermined line of measurement extending across at least a portion of a sidewall of the wound roll for measuring the sidewall characteristic, and a processor for processing the sidewall characteristic and generating at least one quality metric representative of the quality of the roll.  
      According to another aspect of the present invention, a method for measuring sidewall quality of a wound roll comprises the steps of positioning the wound roll on a planar surface with the axis perpendicular to the planar surface and with one edge of the sidewall exposed in an upstanding position, positioning a distance measuring sensor above the sidewall for movement along a predetermined line of measurement extending across at least a portion of the sidewall of the wound roll, moving the distance measuring sensor along the line of measurement and generating a plurality of data points, and processing the data points to generate at least one quality metric representative of the quality of the roll.  
      The wound roll has a width determined from the surface of the platform to one or more of the upstanding sidewall edges and the data points measured by the distance measuring sensor comprise distance data taken along the line of measurement. This distance data corresponds to the distance of the upstanding edges of the sidewall windings from the platform surface.  
      In another aspect of the invention, a quality metric is derived from a profile of the width dimension as seen from the sidewall of the wound roll. For example, the quality metric comprises a maximum roll width quality metric based on the profile of the width dimension of the sidewall. In yet another aspect of the invention, the quality metric correlates roll quality with the visual appearance of the sidewall. In particular, the metric involves determining shadowed data points by the presence of shadow areas comprising data points that are shadowed if the sidewall were to be illuminated by light of low incident angle, and accumulating shadowed data points and determining a length of the shadow areas. The quality metric is a shadow quality metric that is obtained by determining the ratio of ((total number of data points)−(the number of data points comprising shadow areas each greater than a predetermined length)/(total number of data points)).  
      In particular, defining an appearance metric as the ratio of the width of lighted edges in the radial direction to the total radial width of the wound roll provides a metric with special advantage for measuring roll sidewall quality. Counting only shadowed edges having a length greater than about 1.5 mm in the radial direction provides a useful, quantitative metric for gauging the quality of a roll of photographic paper.  
      These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a diagram illustrating a wound roll and a magnified portion of its sidewall.  
       FIG. 1B  is a diagram illustrating the basic components of the sidewall quality measuring apparatus and system according to the present invention.  
       FIG. 2  is perspective view of a housing for a roll sidewall quality gauge according to the present invention with the door open and a side panel removed.  
       FIG. 3  is a front view of the apparatus of  FIG. 2 .  
       FIG. 4  is top view of the apparatus of  FIG. 2  with the top panel removed.  
       FIG. 5  is a sectional view taken along line  5 - 5  of  FIG. 4 .  
       FIG. 6  shows a flowchart of the steps involved in using the sidewall quality gauge according to the invention to take sidewall measurements and generate quality metrics.  
       FIG. 7  shows a logical sequence for calculating the roll width quality metric.  
       FIG. 8  is a diagram illustrating the positioning of the roll in the sidewall quality gauge and the line of measurement across the sidewall of the roll.  
       FIG. 9  is an illustration of a sidewall profile as shown on the display of  FIG. 1B , also showing a pass/fail quality metric.  
       FIG. 10  shows how a virtual light source is used to illustrate the development of a shadow quality metric.  
       FIG. 11  is a plot of the shadow metric against a visual rating of a group of sample rolls.  
       FIG. 12  shows a flowchart of a two-dimensional rotation of a set of (x,y) data generated by the sidewall gauge of  FIG. 2 , in preparation for generating the shadow metric.  
       FIGS. 13A and 13B  show a flowchart for determining which data points of  FIG. 12  would be in shadow if the stock roll is viewed under light at a specified angle, for both “left” and “right” views.  
       FIGS. 14A and 14B  show a flowchart of a procedure using the “shadow” information from  FIGS. 13A and 13B  to compute the shadow metric. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Because surface measurement techniques employing laser or like devices and related circuitry are well known, the present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus and method in accordance with the present invention. Elements not specifically shown or described herein may be selected from those known in the art. Certain aspects of the embodiments to be described may be provided in software. Given the apparatus and method as shown and described according to the invention in the following materials, software not specifically shown, described or suggested herein that is useful for implementation of the invention is conventional and within the ordinary skill in such arts.  
      Referring to  FIG. 1A , a strip of material, such as photographic paper for example, is wound about a core  11  relative to an axis  10 , thereby forming a wound roll  12  with a sidewall  13  perpendicular to the axis  10  and extending radially therefrom. This forms a wound roll having concentric windings parallel to the axis with upstanding sidewall edges extending radially from the axis. (Note that the term “upstanding” merely refers to a position taken relative to a reference surface, and therefore is not limited to a position “above” a horizontal plane, for example.) A magnified sidewall area  14  of the sidewall  13  shows the sidewall profile  15  of a small number of laps  16 . It should be noted that the laps  16  typically do not form a planar surface, and instead individually extend from the nominal sidewall to a variable degree.  FIG. 1B  shows the basic elements of a sidewall quality measuring apparatus and system, including a distance measuring sensor  17  that reflects a laser beam  18  from the sidewall  13 . The distance measuring sensor  17  is supported for movement across the sidewall  13  (as shown by the arrow  17   a ) to produce a large number of measurements. Typically, each measurement is less than the thickness of an individual lap. The output of the distance measuring sensor  17  is provided to a computer  19  for further processing of the measurement data, and the computer  19  uses the processed data to drive a display  20  to provide, e.g., a suitable plot of the profile  15 .  
      The distance measuring sensor  17  used in the preferred embodiment of the invention is a Model AR600-1 Laser Displacement Sensor from Acuity Research. The AR600-1 sensor is a laser diode based distance measurement sensor that uses triangulation to measure distance. The laser beam is projected from the housing of the sensor  17  and is reflected from the sidewall surface to a collection lens. The lens focuses an image of the spot on a linear array camera (not shown) within the housing of the sensor  17 . The camera views the measurement range from an angle that varies from 45 to 65 degrees at the center of the measurement range. The position of the spot image on the pixels of the camera is then processed to determine the distance to the sidewall  13 . The AR600-1 sensor has a measuring distance of 2.5 inches and measures distances over its full scale span with an accuracy of 0.001 inches. This means, referring to  FIG. 1B , that in addition to translation in the horizontal direction  17   a,  the distance measuring sensor  17  must be movable perpendicular to that direction to bring the sensor within the measuring range of the device for rolls of different roll widths w. While, in the preferred embodiment, the distance measuring sensor  17  uses an infra red laser diode to prevent the exposure of light sensitive photographic materials, other types of lasers may be used, particularly if exposure of the roll is not a concern. While a triangulation measurement device is the preferred type of distance measurement sensor, other types of non-contact sensors may be used.  
      Referring now to  FIGS. 2 through 5 , an apparatus for measuring sidewall quality of a wound roll  12  with a sidewall  13  includes a housing  22  having left, right and rear panels  25   a,    25   b  and  25   c.  The housing  22  preferably has a plurality of left tubular framing members  24  connected in a rectangular configuration and covered with the left panel  25   a  (which is removed in  FIG. 2 ), and a plurality of right tubular framing members  26  connected in a rectangular configuration and covered with the right panel  25   b.  Rear portions of the left and right framing members  24 ,  26  accept the rear panel  25   c.  Top and front portions of the left and right framing members  24 ,  26  have a door  28  mounted thereon that slides up so that roll  12  can be inserted for determining quality. Door  28  preferably has a rear portion that slides along the rear of housing  22  parallel to the rear panel so that when door  28  closes both the top and front of housing  22  are covered. The door and panels shield the roll from air turbulence during the measurement process, protect the operator from moving components of the distance measuring sensor  17  and from its laser radiation, and help to prevent ambient light or other radiation from affecting the measurements. The housing  22  is not intended as shown to be light tight because measurements of photosensitive materials are intended to be done in a dark environment, such as a darkroom. As such, moving components should be properly guarded/contained so as not to allow contact with the operator&#39;s body, which could cause injury.  
      A bottom panel is connected to the left and right frame members  24 ,  26  forming a platform  30 . Platform  30  has a rigid planar surface for receiving wound roll  12 . Roll position stops  32 ,  34  in housing  22  adjacent platform  30  are arranged in a V-shape. An ultrasonic sensor  36  is arranged near the vertex of the V-shaped stops  32 ,  34 . As shown in  FIG. 4 , the ultrasonic sensor  36  is positioned so as to provide an ultrasonic signal representative of the distance  35  between the sensor  36  and the edge of the roll  12 . Because of the known positions of the stops  32 ,  34 , the distance  35  is a direct function of the diameter of the roll  12 . The ultrasonic signal from the sensor  36  is applied to the computer  19 , which provides a check on the roll diameter, ensuring that the roll is in position and enabling the distance measuring sensor  17  to know where to begin the scan.  
      Referring to  FIGS. 2, 3  and  5 , the distance measuring sensor  17  is mounted on a powered slide  42  that is capable of vertical movement along a direction  42 ′ on a track  43  with respect to the roll  12 . As a consequence, the distance measuring sensor  17  is preferably adjustable vertically to accommodate rolls of different widths. The track  43  is further mounted on a powered slide  41  that is capable of horizontal movement along a direction  41 ′ on a track  40  with respect to the roll  12 . The track  40  is firmly mounted to the housing panel  25   b . The powered slide movements are provided by ball screw and nut arrangements driven by electric motors (not shown) that are controlled by the computer  19 . The combined movements of the powered slides  41 ,  42  allow the distance measuring sensor  17  to be positioned near the sidewall  13  within the measurement range of the distance measuring sensor  17  and then to be moved horizontally across the sidewall  13  to take the sidewall surface profile measurements.  
      While  FIGS. 2-5  show a preferred embodiment of the sidewall quality gauge, it should understood that many variations can be made, all within the scope of the invention as claimed. For example, instead of being an enclosure, the housing  22  may simply be a frame for supporting the measuring sensor  17  and its associated movable supports and components. Further, for example, instead of being attached to the platform, the positioning stops  32 ,  34  may be formed in the platform  30  and may constitute any of various designs for locating the roll in a predetermined place on the platform. The ultrasonic sensor  36  is not essential, especially if the operator is willing to ensure that the correct roll is correctly placed and the distance measuring sensor is properly instructed as to where to begin the scan, both vertically and horizontally. And the concept of a platform as herein used is mainly to have some way of defining a reference surface to which the data points are related.  
      As shown in  FIG. 1B , the computer  19  receives measurement signals from the distance measuring sensor  17 . The computer  19  also receives position signals from the ultrasonic sensor  36 , and provides positioning commands to the powered slides  41 ,  42  to cause the distance measuring sensor  17  to undertake a scan of the sidewall  13  on the roll  12 . The data processed by the computer  19  can be output to a display  20  of the type associated with a desktop or laptop computer, or workstation for operating the sidewall gauge and viewing the calculated measurements. Alternatively, and referring now to  FIG. 2 , the computer may output the display data to a monitor  44  that is mounted on the outside of housing  22  for operating the sidewall gauge and, in some circumstances, viewing the measurements calculated. Monitor  44  is pivotally mounted and can fold flat against the side of the housing to facilitate transport or can be removed for transport. In the preferred embodiment, the monitor  44  includes a touch screen display having a darkroom-enabled faceplate that emits light toward the red end of the visible spectrum, which enables its use in a darkroom environment.  
      In the preferred embodiment, the sidewall gauge is capable of measuring the maximum width and profile of one half of the sidewall, from an outer lap to the core  11 , on a roll of photographic paper. Roll widths, for example, from 3.25 to 14 inches and diameters from 4.5 to 18 inches can be measured by the distance measuring sensor  17 . Obviously, the gauge can be modified to handle other widths and diameters. The gauge was designed for non-destructive measurements and, although the gauge housing is not itself light tight in the preferred embodiment, it can be used in both dark and light environments. More specifically, the gauge uses the touch screen monitor  44  for operation in the dark but can also utilize a typical large screen monitor  20 , mouse and keyboard while in a lighted condition. Referring now to  FIG. 6 , which shows a flowchart of the steps involved in using the sidewall quality gauge according to the invention to take sidewall measurements and generate one or more quality metrics, an operator first performs a calibration check procedure (in a calibration step  100 ) before starting any measurements. The calibration procedure, which can be done in either a white light or dark conditions, uses a multi-step calibration fixture that is placed against the v-shaped stops  32 ,  34 . The distance measuring sensor  17  moves into position and measures each step on the calibration fixture. Calibration coefficients are subsequently generated and written to a file that is used in the main program by the computer  19  to determine lap height from the surface of the platform  30 .  
      In the monitor selection step  102 , either the touch screen monitor  44  or the large screen computer monitor  20  is selected. The touch screen monitor  44  is to be used in the dark and the large screen monitor  20  can be used in white light. In the roll preparation step  104 , the roll  12  is manually prepared for placement in the sidewall quality gauge. In white light conditions, the operator should visually inspect the roll  12  for any singular or nearly single lap protrusions or “stick-outs” in the sidewall of the roll. If only one side has such protruding laps, it is this side that should be placed facing upward on the platform  30  so as to be “seen” by the laser beam  18  of the distance measuring sensor  17 . In a dark environment, the operator is limited to what can be felt of these protruding laps. After the roll is placed on the platform  30 , whether in white light or in the dark, the operator should push downward on the outer laps, all around the roll circumference  50  as shown in  FIG. 8 , in case they are loose. This is to assure that the outer laps are against the surface of the platform  30 , and as such do not enter into the maximum roll width measurement. Moreover, a few slightly loose outer laps that can easily be flattened by a customer or are part of the thread-up of the machine using the roll are of little practical concern and should not affect the quality metric.  
      In a roll placement step  106 , and as shown in  FIG. 8 , the roll  12  is pushed onto the platform  30  until it meets the v-shaped roll position stops  32 ,  34 . Once the roll  12  is in position, the operator closes the door  28  (door closing step  108 ). Next, in a roll width entering step  110  the nominal roll width w (see  FIG. 1B ) is entered via the touch screen  44  or the mouse connected to the computer  19 . This width is obtained, e.g., from slit width specifications or customer requirements. After this information is entered, a measurement step  114  is initiated when the operator touch/clicks a start button on the touch screen  44  or the display  20  to begin the measurement by the distance measuring sensor  17 . The powered slides  41 ,  42  begin to move and bring the distance measuring sensor  17  down to the roll surface, where it horizontally traverses the sidewall of the roll  12  from the outer edge to the inside of the core  11 , as shown along a line of measurement  52  in  FIG. 8 . During, or perhaps before, this sidewall scanning step, in the roll position checking step  112  the ultrasonic sensor  36  is used to ensure that the roll is in position and that the distance measuring sensor  17  begins the measurement at the proper point.  
      After the measurement is completed, the measurement data is processed in a processing stage  116  and used to generate a data file in the file generation stage  118 . Then, several quality metrics are generated in the quality metrics generating stage  120 . More specifically, depending upon the measurements obtained from step  114 , a maximum roll width quality determination is also displayed in the quality metric generating stage  120 . For example, the measurement data is first processed in a profile generating program and displayed to the operator on a screen  60  (in the quality metric generating stage  120 ) as a quality metric in the form of a sidewall profile  62 , as shown in  FIG. 9 . The screen  60  also shows the maximum width  64  determined from the nominal width step  110 . For example, the quality specification for maximum roll width may be established as the maximum slit width (entered in step  110 ) plus a small tolerance amount. If the sidewall profile  62  shows that none of the laps exceed the maximum roll width specification, then another quality metric  66  indicating PASS is shown on the screen  60 ; otherwise, the metric  66  indicates FAIL.  
      The screen  60  is initially interactive and allows the operator to magnify (zoom) portions of the profile by engaging a zoom button  68 . If there are any concerns with the data, the operator can engage the EXIT button  70  and repeat the measurement. Finally, a data file is created and saved in a data file creation step  118 . This file will contain the measurement height data in millimeters for each point of resolution. In the preferred embodiment, and in accordance with use of the Model AR600-1 Laser Displacement Sensor from Acuity Research as the distance measuring sensor  17 , each data point represents a radial distance of 0.0008 inch (0.02 mm) on the X-axis (horizontal axis) of the sensor. The laser spot diameter is 0.005 inch, so approximately  11  to  12  data points will span each 0.009 inch thick lap of paper. Plotting roll height (width) vs. data point produces the sidewall profile  62  of one half of the roll  12 .  
      As mentioned above, one quality metric relates to the maximum roll width, which in the sidewall gauge is determined by the bottom to top width w (see  FIG. 1B ) of the roll as it is placed into the gauge, that is, equal to the roll width dimension as measured from the surface of the platform  30  to the top edge of any lap protruding from the sidewall. Note that any core offset and even single lap protrusions will be detected and included in the value for the roll width, as is required by the quality specification.  FIG. 7  shows a logical sequence for calculating the roll width quality metric. Initially, a nominal width is called in the width data block  122 , as also described in connection with step  110  in  FIG. 6 . Then, the program looks up the upper specification limit for the nominal width in the specification look up block  124 . The maximum roll width is calculated in roll max width block  126  as the upper specification limit plus a small tolerance value, in the case of the preferred embodiment 1 mm. Then in the metric determination block  128 , the measurement data is tested to determine if one or more laps have returned a height (width) measurement that is greater than the maximum roll width. If the answer to the test is yes, that is, there are one or more laps or any part of the core greater than the maximum roll width, then the quality metric is set to FAIL. Otherwise, that is, if no lap or any part of the core are greater than the maximum roll width, the quality metric is set to PASS.  
      Another quality metric relates to sidewall appearance rather than to any particular roll dimensional attribute, such as roll width. As it turns out, some customers tend to correlate roll quality with the visual appearance and feel of the sidewall. In other words, a “rough” or “uneven” sidewall as seen and felt by the customer connotes poor quality, while a “smooth” sidewall connotes high quality. What has been lacking in the quality inspection process has been some way to rate and quantify the aesthetic appearance of the roll sidewall. Thus, there is a need to create a metric that would correlate to the visual appearance of the sidewall, since this is what customers see and feel. Considering this problem from the vantage of a customer&#39;s “sight”, when one views a roll laid on its side, the best way to “see” the roughness in the sidewall is to shine a light at a low incident angle in the radial direction and view the sidewall from above, as shown by the visualization in  FIG. 10 . Illuminating the upstanding exposed edge of the sidewall  13  creates edges in light and edges in shadow according to irregularities in the wound roll. Light rays  80  at a low incident angle  82  from a light source  84  graze the laps in the sidewall. As viewed in the axial direction from an observer&#39;s viewpoint  86 , the light rays  80  illuminate some laps that stick out and leave others in the shadows. As shown in the magnified portion  88  of the sidewall, this differentiation between light and shadow is seen by the effect of the grazing light rays  80 , which produce the lightly-rendered laps  90  with edges that are “illuminated” and the darkly-rendered laps  92  with edges that are in “shadow”. As shown in the magnified portion  88 , a number of consecutive laps may have edges that are in shadow. When the shadow length  94  of these consecutive laps exceed a certain quantity, depending on lap thickness, the overall “look” and “feel” of the sidewall is compromised in the view of the observer, and poor quality is the perceived result.  
      In order to develop the shadow quality metric, a test set of rolls were used to empirically develop the requirements for incident angle  82  and minimum shadow length  94  as perceived by the human eye that results in the best correlation of this metric to the visual appearance of a roll. A 3-degree angle  82  and a minimum shadow length of 1.5 mm (0.060 inch) were found to work well. (Obviously, other angles and minimum shadow lengths may work sufficiently well, depending on customer requirements and tastes, and are intended to be within the purview of the claimed invention.) Therefore, unless a shadow is at least 1.5 mm long, the laps within the shadow are counted as “illuminated”. (Note that there is no actual illumination by a real light source associated with practice of the method according to this invention. Reference to using a low incident light source to view sidewall roughness is only intended to explain the approach. In actuality, the determination of the shadow metric is achieved solely by mathematical manipulation of the profile data as disclosed in connection with  FIGS. 12-14 .)  
      The shadow quality metric is then defined as the ratio of “illuminated” data points to the total number of data points. Thus a rating of 1.0 or 100% would mean that the roll was smooth enough that there were no shadows longer than 1.5 mm, and a lesser rating—less than 1.0 or less than 100%—would mean that a corresponding smaller proportion of the roll was “illuminated”. For example, a rating of 23% would mean that 23% of the sidewall was “illuminated” and 77% of the sidewall appeared to be in shadow. Several caveats are in order. This metric does not include the core or start zones, that is, the initial few laps, but only the wind zone between the start zone and the outer diameter of the roll. Since a different result might occur depending on whether the light were shone from the outside of the roll in or from the inside out, the program does the computation for both directions and returns the worst case. Note that subtle dishing of the laps in the sidewall is generally not discernible by the human eye, and so does not have an impact on this metric. Generally, large shadow values as defined actually correspond to “smoother” sidewalls.  
      The goal of the shadow metric computation is to mimic the subjective reaction of a person viewing a roll sidewall. If a person would rate a roll&#39;s sidewall quality from 0 (terrible) to 1 (perfect), this routine should generate a similar number based on the information returned from the sidewall quality gauge.  FIG. 11  is a plot of the shadow metric against a visual rating of a group (16) of sample rolls, with one on the Y-axis being the highest rating. The sixteen rolls were ranked from 1 to 16, with number 1 being the best looking. The plot is a second order fit to a number of observers&#39; ratings and confirms that the shadow parameters were chosen correctly and provide a quantifiable metric that correlates to a visual roll appearance.  
      While the shadow metric can be calculated in a number of ways once the light/shadow analogy is understood as explained in connection with  FIG. 10 , it is advantageous to take the data file from step  118  in  FIG. 6  and perform a manipulation of the data points such that the modified data set emulates a rotation of the data about the incident angle  82  produced by the grazing light rays  80  from the (virtual) light source  84 . (In practice, of course, no such light source is used by the roll sidewall gauge, but the data is manipulated so as to emulate the effect of such light.) The data points are evaluated in sequential order to determine whether they are in shadow or illuminated, were they to be exposed to such a light source. Initially, the height of the first lap is used as a marker. In effect, the data set is set up so that the height of each lap can be compared to the previous lap (initially, the first lap) used as a marker to determine whether it is less than (in shadow) or greater than or equal to (illuminated) the height of the marker. When the height of the measured lap turns out to be equal to or greater than the marker lap (i.e., illuminated), then the measured lap is set to be the new marker lap, and the process continues. Along the way, a 0 is returned for those data points that are less than the marker (in shadow), and a 1 is returned for data points that are equal to or greater than the marker (illuminated). Then, the 0&#39;s are totaled up according to run lengths and the short runs are changed to 1&#39;s. The shadow metric is then computed as the ratio of the illuminated data points (1&#39;s) to the total number of data points.  
       FIGS. 12-14  show basic, self-explanatory flowchart information about each routine used in the computation of the shadow metric from data provided by the sidewall quality gauge. The sidewall quality gauge returns a set of two-dimensional data points, with “x” being the x-coordinate or horizontal position of each data point and “y” being the vertical distance to the edge of the paper wound in the roll at that point. “x” is a radial distance; “y” is axial. Both are in millimeters. “x” is uniformly spaced at about 0.02 mm, and is in numerical order. Three functions are used and shown in the flowcharts in  FIGS. 12-14  as follows: 
          1. rot 2 d (two-dimensional rotation of a set of (x,y) data) in  FIG. 12 .     2. shadow (determines which data points would be in shadow if the roll is viewed under light at a specified angle, for both “left” and “right” views) in  FIGS. 13A and 13B .     3. shadowcalc (a procedure using “shadow” to compute the shadow metric) in  FIGS. 14A and 14B . 
 
 Function rot 2 d ( FIG. 13 ) is characterized by [xo,yo]=rot 2 d(x,y,alpha,xc,yc) with inputs and outputs as follows: 
    x, column vector of x-coordinates of a set of points     y, corresponding vector of y-coordinates of a set of points     alpha, the angle in radians to rotate the set of point (x,y) about the rotation center (xc,yc)     xc, x-coordinate of center of rotation (defaults to 0)     yc, y-coordinate of center of rotation (defaults to 0)     xo, column vector of rotated x-coordinates     yo, corresponding column vector of rotated y-coordinates 
 
 Function shadow ( FIGS. 13A and 13B ) is characterized by the function [seenleft,seenright]=shadow(x,d,ang), where function “shadow” computes 0-1 vector results for a “left” view (looking from the core outward) and a “right” view (looking from the outside of the roll toward the core). Inputs and outputs to function shadow include: 
    x is the x-coordinate (radius) in mm     d is the y-coordinate (height in gauge) in mm     ang is the angle of the “light” used to “view” the roll     seenleft is a vector the same length as x and d, containing 0 if the data point is in shadow as viewed from the core of the roll looking out; otherwise 1     seenright is a vector the same length as x and d, containing 0 if the data point is in shadow as viewed from the outside of the roll looking in; otherwise 1. 
 
 The shadowcalc procedure ( FIGS. 14A and 14B ) uses the results from function shadow to compute the “shadow metric”. The procedure operates by finding all the results files from data processed by another program called “sidewall”, and adding the shadow metric to those results (or replacing them if the shadow metric is already present). 
       
      The invention has been described with reference to a preferred embodiment; However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. For example, other quality metrics may be derived from the data, including without limitation web-to-core offset, web offset at start, maximum peak-to-valley sidewall amplitude, and the average sidewall slope (a measure of dishing). The advantage of the sidewall gauge as described, which provides the data associated with the roll sidewall profile, is that it gives a process engineer an insight into the process, thereby enabling the engineer to determine, for example, whether the problem is at the winder (e.g., a wobble problem) or further into the web travel (e.g., a weaving problem).  
     Parts List  
     
         
           10  vertical axis  
           11  core  
           12  wound roll  
           13  sidewall  
           14  magnified sidewall area  
           15  profile  
           16  lap  
           17  distance measurement sensor  
           17   a  direction  
           18  laser beam  
           19  computer  
           20  display  
           22  housing  
           24  left framing members  
           25   a  left panel  
           25   b  right panel  
           25   c  rear panel  
           26  right framing members  
           28  door  
           30  platform  
           32  roll position stop  
           34  roll position stop  
           35  distance  
           36  ultrasonic sensor  
           40  track (horizontal)  
           41  powered slide (horizontal)  
           41 ′ direction (horizontal)  
           42  powered slide (vertical)  
           42 ′ direction (vertical)  
           43  track (vertical)  
           44  monitor (touch screen, dark capable)  
           50  roll circumference  
           52  line of measurement  
           60  screen  
           62  sidewall profile (raw data)  
           64  maximum width  
           66  max width quality metric  
           68  zoom button  
           70  exit button  
           80  light rays (for illustration of concept only)  
           82  low incident angle  
           84  light source (for illustration of concept only)  
           86  observer&#39;s viewpoint  
           88  magnified portion  
           90  illuminated laps  
           92  shadow laps  
           94  minimum shadow length  
           100  calibration step  
           102  monitor selection step  
           104  roll preparation step  
           106  roll placement step  
           108  door closing step  
           110  roll width entering step  
           112  roll position checking step  
           114  measurement step  
           116  processing stage  
           118  data file generation stage  
           120  max width quality metric generation stage  
           122  width data block  
           124  specification look up block  
           126  max width block  
           128  metric determination block