Abstract:
A method for measuring and displaying the flatness of a rolled steel sheet is disclosed that includes the steps of measuring tension in the sheet at a plurality of locations on the surface of the sheet and determining a plurality of tension ranges into which the sensed tension level can fall. A color is associated with each of the tension ranges, and a representation of the sheet is produced that is made up of a plurality of regions, each region having a color corresponding to tension range into which the tension sensed at the corresponding location on the surface of the sheet falls. A device for carrying out this method is also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation in part of U.S. application Ser. No. ______ filed Jan. 21, 2003, entitled “Graphical Rolled Steel Sheet Flatness Display and Method of Using Same” by inventors Thomas J. Russo, et. al. under attorney docket number 6219.880. 
     
    
     REFERENCE TO COMPUTER PROGRAM LISTING APPENDIX  
       [0002]     The computer program listing appendix contained in the file “FlatnessDisplayListing.txt” on compact disc  1  of 1, which has been filed with the United States Patent and Trademark Office in duplicate, is hereby incorporated by reference. The file was created on Dec. 10, 2002, and is 17,363 bytes in size.  
       FIELD OF THE INVENTION  
       [0003]     The present invention is directed toward a graphical flatness indicator for a sheet of rolled material and a method of using this device, and, more specifically, toward a device that receives signals indicative of tension levels in a rolled steel sheet and produces output signals that generate, on a display, in real time, a color representation of a surface of the rolled steel sheet, wherein different colors on the representation correspond to different sensed tension levels in the rolled steel sheet, and toward a method of using the device.  
       BACKGROUND OF THE INVENTION  
       [0004]     Steel sheet may be processed by cold rolling in a rolling mill to increase its strength. This is done by passing the sheet between a pair of rollers spaced by a distance less than the thickness of the sheet. In practice, owing to bending or expansion of the rollers, the pressure applied to the sheet is not completely uniform in either the length or width direction. This lack of uniformity produces internal compression and tensile stresses in the sheet that vary along its length and/or across its width.  
         [0005]     In general, a steel sheet that has a uniform tension distribution will lie flat on a horizontal table if it is unwound and set down with the tension removed. Steel sheet having a non-uniform tension distribution does not generally lie flat, but instead has wavy or buckled portions that correspond to the areas of the sheet rolled with the lowest tension. Thus, the flatness of a sheet may be determined by measuring its tension distribution. Examples of tension measuring devices that make use of this fact can be found, for example, in U.S. Pat. No. 5,537,878 to Sendzimir and U.S. Pat. No. 3,499,306 to Pearson, the disclosures of which are hereby incorporated by reference.  
         [0006]     The data produced by such tension sensors may be analyzed by computer to detect tension distributions that are outside normal ranges. However, merely detecting whether tension levels are too high or too low does not give complete information regarding the flatness of the sheet. Prior art devices may allow a sheet to be generally characterized as either acceptable or unacceptable, but provide little useful information as to how the tension varies across the length and width of the sheet. If more details concerning the tension distribution were available, decisions could be made concerning which portions of the sheet might be acceptable for some uses. Moreover, if information concerning the flatness of the sheet were available in real time, an operator might quickly determine what was causing an out-of-flatness condition and take the appropriate steps to correct the problem.  
         [0007]     It is therefore desirable to provide a method and apparatus for receiving tension signals from a plurality of sensors measuring tension in a rolled sheet, and providing an output that produces, on a display, in real time, a representation of the flatness of the sheet.  
       SUMMARY OF THE INVENTION  
       [0008]     In a first aspect, the invention comprises a graphical flatness display for a rolled steel sheet that includes at least one sensor for measuring a property of a rolled steel sheet at a plurality of locations on the sheet and producing a property output signal corresponding to a magnitude of the sensed property at each of the plurality of locations. A processor is operatively connected to the sensor and receives the sensor property output signals. Property magnitude ranges and a color corresponding to each of the property magnitude ranges are stored in a memory connected to the processor, and a color display is operatively connected to the processor. The processor receives a property output signal, determines the property magnitude range indicated by the output signal, and plots a point in the color corresponding to the property magnitude range on the display. The plot is made at a point on the display related to the location on the rolled steel sheet at which the property was sensed.  
         [0009]     Another aspect of the invention comprises a method of indicating the flatness of a rolled steel sheet that involves measuring tension at a plurality of points across a first segment of the sheet and generating an output signal related to the tension sensed at each of the plurality of points. Then a representation of the first segment of the rolled steel sheet is displayed that includes regions corresponding to each of the plurality of points. A color at each region is related to the tension measured at the corresponding one of the plurality of points on the sheet.  
         [0010]     Another aspect of the invention comprises a device for depicting the flatness of a rolled steel sheet in real time. The device includes a processor operatively connected to a sensing device that measures tension at a number of points on a rolled steel sheet and produces tension output signals related to sensed tensions. Numeric values based on the tension output signals are stored in a database, while colors corresponding to ranges of the numeric value are stored in a memory. The processor produces signals on a real-time basis to create a color image of the rolled steel sheet on a display with regions on the display corresponding to points on the rolled steel sheet, wherein the colors of the regions on the display are related to the tension level sensed at the corresponding points on the rolled steel sheet.  
         [0011]     Another aspect of the invention is a device for monitoring the performance of a steel rolling mill that includes a plurality of sensors positioned to sense tension at selected points along the width of a rolled steel sheet being processed in the rolling mill. Each of the sensors produces an output signal proportional to the sensed tension. A processor is operatively connected to the tension sensors for receiving the sensor output signals, while a memory is operatively connected to the processor. The memory stores tension ranges and a color corresponding to each of the tension ranges. A color display is operatively connected to the processor. The processor produces a representation of the surface of each sheet of rolled steel being processed in the rolling mill on the display. The representation comprises a plurality of regions corresponding to selected points on the surface of the sheet with the color of each region corresponding to the tension range into which the sensed tension at the corresponding selected point falls. The representations of the surfaces of each sheet emerging from the rolling mill also includes a centerline, and the centerlines of adjacent sheets of rolled steel are aligned.  
         [0012]     Another aspect of the invention is a device for displaying tension levels in a steel sheet that includes a processor operatively connected to a plurality of tension sensors for measuring tension at a plurality of locations spaced across the width of the sheet and producing an output signal corresponding to the sensed tension. A memory is operatively connected to the processor and stores tension ranges and a color corresponding to each of the tension ranges. A color display is operatively connected to the processor. The processor produces processor output signals for generating a color image on a color display, the image comprising regions corresponding to the plurality of locations, the color of each of the regions corresponding to the range into which the sensed tension falls.  
         [0013]     An additional aspect of the invention comprises a method of measuring the flatness of a sheet of rolled steel that includes the steps of measuring the tension at a plurality of measurement points on the surface of a sheet of rolled steel, determining a plurality of tension ranges into which the sensed tension level can fall, associating a color with each of the determined tension ranges, and displaying a representation of the sheet of rolled steel. The representation comprises a plurality of regions corresponding to the plurality of measurement points and the color of each region is the color associated with the tension range into which the measured tension for each measurement point corresponding to each display point falls.  
         [0014]     Another aspect of the invention comprises a real time flatness display that includes a processor connectable to a sensing device for measuring flatness at a number of points on a rolled steel sheet and producing an output signal corresponding to sensed flatness. A memory is operatively connected to the processor and stores color information for each sensed flatness. The output signal produces on a display a two-dimensional image of the sheet of rolled steel comprising a plurality of regions each corresponding to one of the plurality of points on the sheet of rolled steel. The color of each region is related to the sensed flatness at the corresponding point on the rolled steel sheet.  
         [0015]     Still another aspect of the invention comprises a display having first and second display fields where the first display field displays a colored representation of a planar surface of a rolled sheet of steel with different colors on the colored representation representing different tension levels in the at least one rolled sheet of steel. The second display field comprises a colored representation of average tension levels along a portion of the rolled steel sheet.  
         [0016]     Another aspect of the invention comprises a method of indicating the flatness of a first rolled sheet of steel rs i  comprising the following steps:  
         [0017]     a) providing a first rolled sheet of steel rs i  having a plurality of width segments w l  . . . w m  along a length of the first sheet of rolled steel rs l ;  
         [0018]     b) providing a sensing device having a plurality of sensors d l  . . . d l ;  
         [0019]     c) measuring a tension at a number of points x l  . . . x n across each width segment W l  . . . W m  of the first sheet of steel rs l  ;  
         [0020]     d) generating output signals having a value s l  . . . s n  related to the tension sensed at each point x l  . . . X n  for each width segment w l  . . . w m ;  
         [0021]     e) for each width segment w l  . . . w m  storing the values s l  . . . s n  in a row r l  . . . r n of a table t l  wherein each column of the table comprises signals from one of the sensors d l  . . . d n ;  
         [0022]     f) associating a color with each of the output signals S l  . . . S n  based on the level of tension represented by the output signal; and  
         [0023]     g) for each width w l  . . . w n  plotting points p l  . . . p n  on a display corresponding to points x l  . . . x f  on the width of the steel rs l  wherein the color of each point p l  . . . p n  is based on the level of tension represented by the output signals S l  . . . s n . 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The invention will be better understood after a reading of the detailed description of the invention provided below together with the following drawings.  
         [0025]      FIG. 1  is a schematic side elevational view of a cold rolling mill and a rolled steel sheet traveling over a tension sensor to a take-up roll.  
         [0026]      FIG. 2  is a schematic representation of the system of the present invention including the tension sensor of  FIG. 1 , a central processor and a display.  
         [0027]      FIG. 3  is a flow chart showing how data is gathered by the central processor of the present system.  
         [0028]      FIG. 4  is a flow chart showing how data from a database is used to generate images on a display.  
         [0029]      FIG. 5  is a detail view of region V of the display of  FIG. 2 .  
         [0030]      FIG. 6  is a detail view of region VI of the display of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     Referring now to the drawings, wherein the showings are for purposes of illustrating a preferred embodiment of the invention only, and not for the purpose of limiting same,  FIG. 1  shows a cold rolling mill  10  comprising a pair of rollers  12  supported on a frame  14 , a tension sensing device  16 , a take-up roll  18  and a steel sheet  20 . Steel sheet  20  passes between the rollers  12  to strengthen the steel and is wound onto take-up roll  18  under tension. The tension in rolled steel sheet  20  holds the rolled steel sheet  20  against tension sensing device  16 , thereby allowing the internal tension at the portion of the rolled steel sheet  20  in contact with tension sensing device  16  to be measured. It should be noted that, while the invention herein is described in connection with a cold rolled steel sheet, it could also be used to measure tension in a hot-rolled steel sheet or in a sheet of another material.  
         [0032]     As best shown in  FIG. 2 , tension sensing device  16  comprises a plurality of tension sensors  22  positioned along a rotatable drum  24  supported for rotation by supports  26 . Such tension sensing devices are known in the art. The number and exact arrangement of sensors on the drum can be varied as desired for a particular application. The preferred tension sensing device  16  described herein has fifty-four tension sensors  22 .  
         [0033]     Each tension sensor  22  generates a signal indicative of the load against the sensor  22  when the sensor  22  engages sheet  20 . The sensors  22  may, for example, include a piezoelectric element that generates a signal proportional to applied load. Because drum  24  rotates, each of the sensors  22  will be in contact with rolled steel sheet  20  for part of a rotation only, and will thus periodically generate a signal each time it comes into contact with rolled steel sheet  20 . The sensors  22  are preferably arranged in a spiral around the circumference of the drum  24 , so that fewer than all sensors  22  are in contact with the rolled steel sheet  20  at any one time. Each sensor  22  will contact rolled steel sheet  20  once for each rotation completed by drum  24 .  
         [0034]     The tension sensors  22  are operably connected to a local processor  28  having a memory  30 . Processor  26  is connected to a network  32 , such as a LAN, WAN or the Internet, so that data concerning the sensed tension can be remotely retrieved. Preferably, tension data is sent over network  32  using UDP (user datagram protocol), a transmission protocol that offers a minimal transport service without the cumbersome error checking and other features of protocols like TCP.  
         [0035]     A central processor  34  is also connected to network  32  and includes a memory  36 . Various software runs on central processor  34  including data collection software  38 , a database  40 , preferably a SQL Server Tm database, and shape display software  42 . The operation of this software will be described herein. Central processor  34  is operably connected to a display  44 , either by line  46  shown in  FIG. 2  or over network  32 , and to a secondary database  48  and various users  50  over network  32 .  
         [0036]     The collection of tension data is well known from the prior art. However, prior art methods and devices were generally unable to extract useful information from the data in a timely and informative way. For example, it would be useful to learn that one of the rollers in a rolling mill had developed a defect as soon the effects of the defect began to become apparent in the sheet of material being rolled, instead of hours later when the defect has degraded the quality of many rolls of steel sheet and potentially rendered them unusable.  
         [0037]     The collection of data by data collection software  38  will be explained with reference to the flow chart of  FIG. 3 . References L 1 -L 9  in the flowchart refer-to listings  1 - 9  in the code provided in the Appendix to this application to indicate which listing is responsible for which function. In a startup step  60 , central processor  34  initializes local and global variables, and at step  62  initializes a communications socket to prepare to receive information over network  32 . At step  64  a connection to SQL Server database  40  is opened, and record sets are initialized at step  66 . At step  68 , arrays are initialized to temporarily hold data received from tension sensing device  16 . At step  70 , central processor  34  waits for data to arrive over network  32 , and this data is read at step  72 . Socket data is copied from memory  36  into a global variable at step  74 , and the distance that strip  20  has moved for each packet of data received from local processor  28  is calculated at step  75 . For example, if drum  24  includes fifty-four sensors  22  distributed evenly about a six foot circumference, and local processor  28  sends data at 250 ms intervals, the receipt of  27  tension readings from local processor  28  would indicate that drum  24  had completed one half of a revolution and that strip  20  had moved three feet in that quarter-second period. There is little if any slippage between strip  20  and drum  24 , and drum rotation thus provides a good indication of strip movement. A determination is made at step  76  whether mill  10  is running. If mill  10  is not running, a debugging operation is carried out at step  78 . If mill  10  is running, data is entered into arrays in the database  40  at step  80 , the main database index value is incremented at step  82  and the database main index is put into database arrays where needed at a step  84 .  
         [0038]     At step  86 , a check is made to determine whether a new roll has been started. Steel sheet  20  and other sheets processed by mill  10  are joined together, such a by welding, to produce a continuous sheet with the end of one sheet pulling the beginning of a subsequent sheet through mill  10 . Sensors, which may be optical sensors  52  shown in  FIG. 2 , for example, detect the presence of a weld and send a signal to central processor  34  to indicate that a sheet end has been detected. If a new roll is not detected at step  86 , additional data from local processor  28  is placed into database  40  at a step  88 . If a new sheet is detected at step  86 , new coil entry work is done at step  90  and product data information (PDI) data is loaded into database  40  and associated with tension data from the new sheet. This PDI data is stored in a secondary database  48  and includes detailed information on the sheet being rolled. This information includes, for example, tolerance information for a given sheet and the degree of flatness required for that sheet.  
         [0039]     At step  92  a determination is made as to whether an event has occurred in the mill, and if an event has occurred, data concerning the event is stored in database  40  at step  94 . If no event has occurred, a determination is made at step  96  as to whether the sheet has moved a given distance, such as six meters. This determination is made from the calculation performed at step  75 . If the sheet  20  has not moved the given distance, sheet data is averaged at step  98 . If strip  20  has moved the given distance, shape data is placed into a main shape display table in step  100  before step  98  is carried out. From step  98 , central processor  40  returns to step  70  and waits for data to arrive over network  32 .  
         [0040]     By following the above steps, database tables are created that include tension data from fifty-four points across the width of strip  20 , this tension data being related to the tension in a short segment  102  of strip  20  equal to the circumference of drum  24  , and these tension levels are stored in a row of a database table. Each time drum  24  rotates, fifty four additional data points are generated and stored in the table. Each column in the table will correspond to the tension levels sensed by one of the sensors  22  on drum  24 . Thus the first column of the table will represent tension levels sensed at six foot intervals along a first longitudinal band  104  of strip  20  and the second column of the table will represent tension levels sensed at six-foot intervals along a second longitudinal band  106  of strip  20 . The points at which tension is sensed along each band will be slightly offset given the circumferential offset of adjacent sensors  22  on drum  24 .  
         [0041]     The output signals from tension sensors  22  may be in any form, but are preferably converted to “I-units,” a measure of flatness that uses positive and negative numbers to express the amount and direction of flatness deviations. I-units are explained in detail in ASTM standard A568/A568M which is hereby incorporated by reference.  
         [0042]     Table 1 below is populated with arbitrary data to illustrate the operation of the present invention. The values in the table are in I-units.  
                                                                                   TABLE 1                           TENSION LEVELS                Sensor#   0   1   2   3   n-1   n                            Width 1   1.2   −4.5   −6.1   5.6   3.1   −0.6           Width 2   1.5   −5.0   −7.2   6.1   4.0   1.1           Width 3   1.1   −4.7   −6.8   5.9   4.1   1.0           Width 4   1.1   −4.5   −6.1   6.0   3.1   −0.2           Width 5   2.1   −3.8   −5.9   6.3   3.9   −0.5           . . .            Width m-1   1.3   −4.4   −6.2   6.4   3.2   −0.3           Width m   2.2   −3.7   −5.8   6.2   3.8   −0.4                      
 
         [0043]     5.99 to −4, −3.99 to −2, −1.99 to −1, −0.99 to 0, 0 to 0.99, 1-1.99, 2-3.99, 4-5.99, 6-7.99 and 8-10. A color is assigned to each of these ranges. A preferred example of such a color assignment appears below. While other color schemes could be used, the below color assignment provides certain benefits that make it desirable. Specifically, under the below assignment, tension levels plotted in green colors are at acceptable levels. Orange and red are indicative of tension levels that require immediate attention, and blue regions indicate problems that require less immediate attention. This use of red to identify serious conditions is consistent with most user&#39;s associate of red with a warning or alert.  
                             TABLE 2                           COLORS ASSIGNED TO TENSION LEVEL RANGES                Tension level   Color                         −10 to −8   Dark Blue           −7.99 to −6   Blue           −5.99 to −4   Light Blue           −3.99 to −2   Aqua           −1.99 to −1   Green-Blue           −0.99 to 0   Green               0 to 0.99   Light Green               1 to 1.99   Yellow-Green               2 to 3.99   Yellow               4 to 5.99   Orange               6 to 7.99   Red-Orange               8 to 10   Red                      
 
         [0044]     From this information, processor  34  creates another table wherein the tension levels are replaced with their corresponding colors. Table 3 below is based on the above data:  
                                                             COLORS ASSIGNED TO TENSION RANGES OF TABLE 1            Sensor #   0   1   2   3   n-1   n               Width 1   Yellow-   Light   Blue   Orange   Yellow   Green           Green   Blue       Width 2   Yellow-   Light   Blue   Red-Orange   Orange   Yellow-           Green   Blue               Green       Width 3   Yellow-   Light   Blue   Orange   Orange   Yellow-           Green   Blue               Green       Width 4   Yellow-   Light   Blue   Red-Orange   Yellow   Green           Green   Blue       Width 5   Yellow   Aqua   Light Blue   Red-Orange   Yellow   Green       . . .        Width m-1   Yellow-   Light   Blue   Red-Orange   Yellow   Green           Green   Blue       Width m   Yellow   Aqua   Light Blue   Red-Orange   Yellow   Green                  
 
         [0045]     This data is used by a graphing program, such as Olectra Chart by ComponentOne, to create two separate graphical outputs shown in display  44  in  FIG. 2  and in more detail in  FIGS. 5 and 6 . The different steps described above may also be divided between software modules in different manners. For example, the color assignments may be made by the charting software itself rather by another program running on central processor  34 .  
         [0046]     The first graphical output  110  is displayed in a first region  112  of display  44  and shown in detail in  FIG. 5 . First graphical output  110  comprises an image  114  of rolled steel sheet  20  plotted in color with different colors representing different tension levels sensed by sensors  22 . Image  114  comprises a plurality of contiguous portions  116  corresponding to the short segments  102  of rolled steel sheet  20  measured each time drum  24  rotates. Each of these portions  116  is divided into a number of regions  118 , each corresponding to an area on rolled steel sheet  22  at which a given sensor has taken a measurement. Thus, even though each measurement taken by each of sensors  22  will be a different distance from an end of the rolled steel sheet, all will be within one short segment  102 , and tension along the entire length of the short segment  114  will be treated as constant. The length of short segments  114  can be decreased, for example, by using a drum having a smaller circumference. Based on the above data, the colors of the regions  118  in the first portion  116  of the image  114  , from the bottom to the top of the display, will be yellow-green, light blue, blue and orange. As data is added to Table 1, additional plots are made so that image  114  of strip  20  lengthens as more and more of the strip passes over tension measuring device  16 .  
         [0047]     The process can also be understood by treating rolled steel sheet  20  as a first sheet, rs l , of a plurality of similar steel sheets rs l  . . . rs n , each of which is divided in a lengthwise direction into a plurality of width segments w l  . . . w m . Each of sensors  22  on sensing device  26  is labeled, in the direction from left to right as seen in  FIG. 2 , d l  . . . d n . In the preferred embodiment, n=54, but n could be larger or smaller depending on the type of sensing device used. On a single revolution of drum  24  of sensing device  26 , each of the sensors d l  . . . d n  measures tension at a point x l  . . . x n  across a single width segment, with sensors d l  . . . d n  corresponding to points d l  . . . d n  along the width segment. Each time drum  24  rotates, n measurements are taken at a group of points x l  . . . x n  on another one of the width segments w l  . . . w m . Each time the drum rotates, the n sensors generate n output signals having values s l  . . . s n  related to the tension sensed at each point x l  . . . X n  on the width segment being sensed. For each width segment, these values are stored in a row r l  . . . r m  of a table t l  so that all the values for a particular width segment are stored in a single row. Each column of the table therefore comprises signals from one of the sensors d l  . . . d n . A color is associated with each of the output signals s l  . . . s n  based on the level of tension represented by the output signal. Finally, for each width segment w l  . . . w f , points p l  . . . p n  are plotted on display  44  which points correspond to points x l  . . . X n  on the width of the steel rs l . The color of each point p l  . . . p n  is based on the level of tension represented by the output signals s l  . . . s n  at the corresponding point x l  . . . x n .  
         [0048]     This display provides an operator with the ability to visualize the flatness of the rolled steel sheet  20  in real time and to detect patterns indicative of a problem with the rolling mill  10  or the steel itself much more readily than could be done by reviewing raw numerical data from the sensors  22 . In addition, first graphical output  110  comprises additional images  120 ,  122 ,  124 ,  126 ,  128  and  130  of previously rolled steel sheets (not shown) so that tension variations from one sheet to the next can be compared. The images  120 ,  122 ,  124 ,  126 ,  128  and  130  are aligned along their respective centerlines so that portions of each sheet that were rolled by the same portions of rollers  12  are aligned and can be compared. This allows defects in the surface of rollers  12  to be quickly detected by observing the similar tension levels they impart to aligned areas of successive rolled steel sheets  20 .  
         [0049]     The data in Table 1 is also used to produce a second graphic output  132 , namely a waterfall chart, shown in a second region  133  of display  44 . This second region  132  is shown in greater detain in  FIG. 6 . To produce this second graphical output  132  , tension values in each of the fifty-four columns for a given rolled steel sheet are summed and divided by the number of rows in the column. This provides an average value for the tension level sensed by a given sensor over the length of sheet  20 .  
         [0050]     The width of the strip is shown along the x axis of the graph, and the magnitude of the average tension value for each longitudinal band  104 ,  106  of the rolled steel sheet is plotted on the Y-axis, this plurality of points forming a first slice  134  of the waterfall plot. Nine additional slices  135 - 143  are also shown in  FIG. 6 ; the front-most slice displayed represents data from the most recently rolled sheet.  
         [0051]     The points are plotted in color based on the color correspondence of Table 2. Thus the average of the numbers shown in column 0 of Table 1 above is 1.5 which corresponds to the color yellow-green. The leftmost point on first slice  134  is thus plotted in yellow-green. Each point on first slice  134  thus has a color, even though it may be difficult to distinguish the colors of the fifty-four points along this line. However, the color data becomes more useful when a second slice  136  and subsequent slices are plotted adjacent first slice  134  in the same manner because corresponding points on each slice are connected by lines that indicate the change between the point on one line and the point on the other. Thus, for example, if a first point on the first slice  134  is yellow-green while the first point on the second slice  136  is yellow, a line will be plotted that shades gradually from yellow-green to yellow to show the transition.  
         [0052]     First graphic output  110  and second graphic output  132  together provide an operator with a detailed real-time data concerning the tension in a given sheet and allow corrective action to be taken when tension levels indicative of a problem are noted. Line  146 , for example in  FIG. 5  shows a low tension area in a rolled steel sheet that varies little from sheet to sheet. Observations at a greater level of detail may reveal that this line  146  is actually a series of periodic points. This might suggest that a surface defect on one of the rollers  12  is periodically decreasing tension in the sheets as they are rolled. Likewise, the somewhat random distribution of colors at location  148  shows what appear to be normal operating conditions, and/or variations that are due more to the structure of the rolled steel sheet  20  than to the effects of the rollers  12 . Likewise, stripe  150  in  FIG. 5  shows an area of generally consistently high tension. This real time view also allows the effects of changes to be seen in close to real time. For example, if, in order to lower the tension represented by line  146  in  FIG. 5 a  certain adjustment is made to rolling mill  10 , the effects of this adjustment on the next sheet will be readily observable from the corresponding illustration on display  44 .  
         [0053]      FIG. 4  illustrates the steps followed in retrieving data from database  40 . At step  152 , local and global variables are initialized. At step  154  shape display software  42 , which is preferably Olectra Chart shape display software, connects to database  40 . At steps  156  and  158 , the shape display software is configured to create first graphic output  110  and second graphic output  132 . At step  160 , PDI data for the sheet  20  being processed in mill  10  is obtained from secondary database  48  and displayed on display  44  in step  162 . At step  164 , data representing 60,000 feet of rolled steel sheet is obtained from database  40  and plotted in first region  112  at step  166 . At step  168 , a check is made to determine whether a new sheet has entered the mill, by checking the output of optical sensor  52 , for example. If a new sheet is not detected, data representing the current 60,000 feet of sheet is updated at step  164 . This process continues, with new colored regions corresponding to short segments  102  of sheet  20  being plotted in first region  112 . Only data concerning the current 60,000 feet of sheet is maintained; older data is removed from the tables of database  40  to prevent the size of the database  40  from slowing down the operation of the system. If a new sheet is detected, average tension values for each band on each of the previous ten sheets are obtained from database  40  at step  170  and used to form the waterfall plot in second region  133  at step  172 . PDI data for the new sheet is also obtained from secondary database  48  and displayed on display  44  at step  174 . The system then returns to step  164  and updates the display in first region  112 .  
         [0054]     It has been found that this use of color allows operators to quickly spot trends and identify problems. While the numerical data generated by such as system could conceivably be processed to locate numbers suggestive of a problem, an experienced operator can often spot patterns more quickly and more reliably than a machine relying upon statistical analyses. Moreover the information generated can be stored and later associated with the particular rolled steel sheet. If a particular rolled steel sheet is not sufficiently flat to satisfy the requirements of a certain customer, for example, the saved date concerning its flatness may allow persons to determine another use for which the rolled steel sheet is suitable and/or to find portions of the rolled steel sheet that are acceptable for other uses. For example, if a problem is corrected after 10 percent of the rolled steel sheet has been rolled, the 90 percent of the rolled steel sheet that is defect free may be usable for other purposes. By associating PDI data with each sheet, an operator can also quickly determine whether the sheet is being produced to specification, as the degree of flatness variation that will be acceptable in a given sheet will vary.  
         [0055]     The present invention has been described in terms of a preferred embodiment, it being understood that obvious modifications and additions to this preferred embodiment will become apparent to those skilled in the relevant art upon a review of this disclosure. It is intended that all such obvious modifications and additions be covered by the present invention to the extent that they are included within the scope of the several claims appended hereto.