Abstract:
A method including: displacing a plurality of sheets through a defined portion of a process path; generating, using an encoder, a first number of encoder pulses associated with displacing a first sheet from the plurality of sheets along the defined portion; applying first indicia to a first side of the first sheet; displacing the first sheet through the defined portion; generating, using the encoder, a second number of encoder pulses associated with displacing the first sheet along the defined portion; calculating, using a processor, a ratio including the first and second numbers; applying second indicia to the respective second side of the first sheet or third indicia to the respective first side of a second sheet from the plurality of sheets, or fourth indicia to the respective second side of the second sheet; and adjusting, using the processor, application of the second, third, or fourth indicia according to the ratio.

Description:
TECHNICAL FIELD 
     The present disclosure relates to a system and method for measuring a change in dimension for a sheet of paper due to operations applying indicia to the paper. In particular, the system and method use a ratio of encoder pulses related to respective movement of oppositely facing sides of the sheet of paper in a process path to determine a dimension change, due to operations on one side of the paper, to adjust application of indicia on the other side of the paper. 
     BACKGROUND 
     When applying indicia to both sides of a sheet of paper, it is desirable to maintain a specified registration between indicia on a front side of the sheet and indicia of the back side of the sheet. The registration noted above assumes a particular dimensionality of the sheet. Known systems and methods for applying indicia, such as xerography, dry ink printing, aqueous ink printing, and lithography, to two sides of a sheet of paper involve operations on the first/top side of the sheet, such as applying heat and pressure, or adding liquid, which can change the dimensions, for example length, of the sheet, for example by changing the moisture content of the sheet or stretching the sheet. When the application of indicia to the top sheet changes the dimensions of the sheet, the assumed dimensionality is no longer accurate and subsequently, the indicia applied to the back side can be out of registration with indicia on the front side. 
     For example, a xerographic machine passes a sheet through a fuser to fix indicia on a front side of a sheet. The fuser applies heat and pressure which can drive moisture out of the sheet, shrinking the sheet and changing the length of the sheet. Thus, the image magnification for the front side is not appropriate for image magnification for a back side of the sheet, and mis-registration occurs between print on the front and back sides of the sheet. It is known to use a manual measurement procedure to measure mis-registration on a sheet of paper. However, the procedure requires an operator to manually measure a test pattern on both sides of a printed sheet, which is time consuming and prone to operator error. 
     Many factors contribute to the dimensional change, for example an amount of paper shrinkage through the fuser of a xerographic machine. These factors include: paper type, environmental conditions, and machine settings/conditions. In addition to the time and error problems noted above, the manual measurement described above is only a snapshot in time and needs to be performed again whenever there is a change in any of these factors. 
     SUMMARY 
     According to aspects illustrated herein, there is provided an apparatus for compensating application of indicia to a sheet of paper according to a change in dimension for the sheet, including: a processor; a measuring system including a plurality of rollers and an encoder connected to a first roller from the plurality of rollers and configured to generate a pulse for each rotation of the first roller by a specified angle; and an indicia system. The apparatus is arranged to perform the following sequence: displace, using the plurality of rollers, a first plurality of sheets along a defined portion of a process path for the apparatus, each sheet having respective first and second sides; generate, using the encoder, a first number of pulses associated with displacement of a first sheet, from the first plurality of sheets, along the defined portion; apply, using the indicia system, first indicia to the respective first side of the first sheet; displace, using the plurality of rollers, the first sheet along the defined portion of the process path; generate, using the encoder, a second number of pulses associated with displacement of the first sheet along the defined portion; calculate, using the processor, a ratio including the first and second numbers and apply, using the indicia system: second indicia to the respective second side of the first sheet; or third indicia to the respective first side of a second sheet from the first plurality of sheets; or fourth indicia to the respective second side of the second sheet. The apparatus is arranged to adjust, using the processor, application of the second, third, or fourth indicia according to the ratio. 
     According to aspects illustrated herein, there is provided a computer-based method for compensating application of indicia to a sheet according to a change in dimension for the sheet, including: displacing each sheet in a first plurality of sheets through a defined portion of a process path of an apparatus; generating, using an encoder for the apparatus, a first number of encoder pulses associated with displacing a first sheet from the plurality of sheets along the defined portion of the process path; applying first indicia to a first side of the first sheet; displacing the first sheet through the defined portion of the process path of the apparatus; generating, using the encoder, a second number of encoder pulses associated with displacing the first sheet along the defined portion of the process path; calculating, using a processor for the apparatus, a ratio including the first and second numbers; applying second indicia to the respective second side of the sheet or third indicia to the respective first side of a second sheet from the plurality of sheets or fourth indicia to the respective second side of the second sheet; and adjusting, using the processor, application of the second, third, or fourth indicia according to the ratio. 
     According to aspects illustrated herein, there is provided a printer for compensating application of indicia to a sheet according to a change in dimension for the sheet of paper, including: a processor; a plurality of pairs of rollers, each pair of rollers including a respective first roller and a respective second roller arranged to engage each sheet from a plurality of sheets and displace said each sheet along a process path for the printer in a process direction; first and second edge sensors in the process path and separated from each other by a distance in the process direction; an encoder connected to the respective first rollers in the plurality of pairs of rollers and arranged to generate a pulse for each rotation of the respective first rollers by a specified angle; and an indicia system. Said each sheet includes respective first and second sides and respective first and second edges. The plurality of pairs of rollers is arranged to displace, at a first point in time, a first sheet from the plurality of sheets along the process path in the process direction. The first and second edge sensors are configured to detect the respective first and second edges of the first sheet at first and second times, respectively. The encoder is arranged to generate a first number of pulses for a first duration between the first and second times. The indicia system is arranged to print on the respective first side of the first sheet. The plurality of pairs of rollers is arranged to displace, at a second point in time, the first sheet along the process path in the process direction. The first and second edge sensors are configured to detect the first and second edges of the first sheet at third and fourth times, respectively. The encoder is arranged to generate a second number of pulses for a second duration between the third and fourth times. The processor is configured to calculate a ratio including the first and second number of pulses. The indicia system is arranged to print on the respective second side of the first sheet or the respective first side of a second sheet from the plurality of sheets or the respective second side of the second sheet. The processor is configured to adjust a position of print on the respective second side of the first sheet, the respective first side of the second sheet, or the respective second side of the second sheet according to the ratio. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are disclosed, by way of example only, with reference to the accompanying schematic drawing in which corresponding reference symbols indicate corresponding parts, in which: 
         FIG. 1A  is a schematic block diagram of an apparatus with compensation of application of indicia to a sheet according to a change in dimension for the sheet of paper; 
         FIG. 1B  is a schematic block diagram of an apparatus with compensation of application of indicia to a sheet according to a change in dimension for the sheet of paper; 
         FIG. 2  is a schematic representation of a sheet with indicia on both sides; 
         FIG. 3  is a schematic representation of a printer with compensation of application of indicia to a sheet according to a change in dimension for the sheet of paper; and, 
         FIG. 4  is a flow chart illustrating a method of compensating application of indicia to a sheet according to a change in dimension for the sheet. 
     
    
    
     DETAILED DESCRIPTION 
     Moreover, although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of these embodiments, some embodiments of methods, devices, and materials are now described. 
     It should be understood that the use of “or” in the present application is with respect to a “non-exclusive” arrangement, unless stated otherwise. For example, when saying that “item x is A or B,” it is understood that this can mean one of the following: (1) item x is only one or the other of A and B; (2) item x is both A and B. Alternately stated, the word “or” is not used to define an “exclusive or” arrangement. For example, an “exclusive or” arrangement for the statement “item x is A or B” would require that x can be only one of A and B. 
       FIG. 1A  is a schematic block diagram of apparatus  100  for compensating application of indicia to a sheet according to a change in dimension for the sheet. 
       FIG. 1B  is a schematic block diagram of apparatus  100  for compensating application of indicia to a sheet according to a change in dimension for the sheet of paper. 
       FIG. 2  is a schematic representation of a sheet with indicia on both sides. The following should be viewed in light of  FIGS. 1A through 2 . Apparatus  100  includes: processor  102  and measurement system  104 , including plurality of rollers  106  and encoder  108 , in process path  110  for the apparatus. The encoder is connected to at least one roller from the plurality of rollers and is configured to generate signal  112  including pulse  114  for each rotation of the roller, for example in direction RD, by a specified angle, as is known in the art. Apparatus  100  includes indicia system  116 . Apparatus  100  is arranged to displace a plurality of sheets  118 , for example sheets  118 A and  118 B, along defined portion  120  of the process path. Each sheet  118  includes sides S 1  and S 2  and edges E 1  and E 2 . Apparatus  100  is arranged to perform the following sequence: displace one sheet from the plurality of sheets  118 , for example, sheet  118 A, along defined portion  120  of the process path; generate, using the encoder, N 1  number of pulses  114  associated with displacement of sheet  118 A along portion  120 ; and apply, using the indicia system, indicia  122 A to side S 1  of sheet  118 A. Apparatus  100  is arranged to then: flip sheet  118 A in duplex portion  123 ; displace sheet  118 A along portion  120 ; generate, using the encoder, N 2  number of pulses  114  associated with displacement of sheet  118 A along portion  120 ; calculate, using the processor, ratio  124  including N 1  and N 2 ; apply, using system  116 , indicia  122 B to side S 2  of sheet  118 A; and move sheet  118 A from path  110  to exit portion  125 . 
     Apparatus  100  is arranged to perform the following sequence: move another sheet from the plurality of sheets  118 , for example sheet  118 B, from feed system  127  to path  110 ; displace sheet  118 B along defined portion  120 ; apply, using the indicia system, indicia  122 C to side S 1  of sheet  118 B; flip sheet  118 B in duplex portion  123 ; displace sheet  118 B along portion  120 ; apply, using system  116 , indicia  122 D to side S 2  of sheet  118 B. Apparatus  100  is arranged to adjust, using processor  102 , application of indicia  122 B,  122 C, or  122 D according to ratio  124 . It should be understood that sheet  118 B can be immediately after sheet  118 A in a sequence or can be separated from sheet  118 A by one or more other sheets in the sequence. 
     In an example embodiment, measurement system  104  includes edge sensors  126 A and  126 B separated from each other in process direction PD by distance D, which defines portion  120 . PD is the direction in which each sheet  118  is displaced along the process path. That is, portion  120  is the portion of the process path between sensors  126 A and  126 B. In an example embodiment, system  104  includes at least one pair of rollers  106 A/B. One of rollers  106 A/B is arranged to apply pressure to grip each sheet  118  between rollers  106 A/B and rotate to displace each sheet  118  along path  110  in direction PD. The other of rollers  106 A/B is connected to the encoder. For example in  FIG. 1 , roller  106 A applies the pressure and rotation and roller  106 B is the roller connected to the encoder as noted above. In an example embodiment, length L of each sheet  118  is greater than distance D, such that each sheet  118  is gripped by rollers  106 A/B as each end E 1  is detected by sensor  126 A and as each end E 2  is detected by sensor  126 B. 
     In an example embodiment, to generate N 1 : sensor  126 A is configured to: detect leading edge E 1  of sheet  118 A, moving in the process direction, at time T 1 ; sensor  126 B is configured to detect trailing edge E 2  of sheet  118 A at time T 2 , following T 1 ; and sheet  118 A is arranged to rotate roller  106 B such that encoder  108  generates N 1  pulses between T 1  and T 2 . In an example embodiment, to generate N 2 : sensor  126 A is configured to: detect leading edge E 2  of sheet  118 A, moving in the process direction, at time T 3 ; sensor  126 B is configured to detect trailing edge E 2  at time T 4 , following T 3 ; and sheet  118 A is arranged to rotate roller  106 B such that encoder  108  generates N 2  pulses between T 3  and T 4 . 
     In an example embodiment, ratio  124  is calculated as N 1 /N 2  or N 2 /N 1 . In an example embodiment, to make the ratio calculation more robust, a nominal number of pulses N 3  from the encoder for distance D are determined by any means known in the art. Then, the ratio is calculated as: [N 1 +N 3 ]/[N 2 +N 3 ] or [N 2 +N 3 ]/[N 1 +N 3 ]. In an example embodiment, respective positions of indicia  122 B,  122 C, or  122 D are adjusted along respective length L of sheet  118 A or sheet  118 B. 
     Apparatus  100 , in particular, system  116 , can use any process known in the art for applying indicia to a sheet. Such processes can include, but are not limited to: applying heat to the sheet, applying pressure to the sheet, removing moisture from the sheet, adding moisture to the sheet, and stretching the sheet. Such processes can include, but are not limited to xerography, dry ink printing, aqueous ink printing, and lithography. In an example embodiment, application of indicia  122 A  122 B,  122 C, and  122 D includes magnifying indicia  122 A,  122 B,  122 C, and  122 D, and adjusting application of indicia  122 B,  122 C, or  122 D according to ratio  124  includes adjusting magnification of indicia  122 B,  122 C, or  122 D according to the ratio. Any magnification known in the art can be used with apparatus  100 . For example, magnification can be performed by use of hardware, such as lenses; or, magnification can be performed by operating on digital data, for example, digital data obtained from use of a light emitting diode bar. 
     Respective ratios  124  can be calculated for each sheet in a plurality of sheets. In an example embodiment, the processor is configured to calculate running average  128  of the respective ratios  124 . That is, as ratio  124  is calculated for a particular sheet, the ratio is averaged with the ratios for the previous sheets in the plurality of sheets. Average  128  can be determined for a particular type of sheet material, a particular process, a particular machine or type of machine, or for sheets coming from particular manufacturing or storage situations. Then, when the same type of sheet is used, the respective average  128  can be used as a default setting for adjusting application of indicia. 
       FIG. 3  is a schematic top view of a portion of printer  200  for compensating application of indicia to a sheet according to a change in dimension for the sheet. The following should be viewed in light of  FIGS. 1A through 3 . In an example embodiment, apparatus  100  is printer  200 . The discussion for  FIGS. 1A and 1B  regarding apparatus  100  is applicable to printer  200  except as noted. Processor  102  is not shown in  FIG. 3  and can be located anywhere within and without printer  200  as is known in the art. In an example embodiment, printer  200  includes feeder module  202  that feeds sheets (e.g., paper or other print media) into process path  203 , for example, into marker module  204 , which outputs printed sheets to stacker module  206 . Marker module  204  includes photoreceptor  208  and a plurality of rollers that apply toner to the sheets as the sheets pass by each respective roller. According to an example, marker module  204  includes a plurality of color rollers  210 ,  212 ,  214 , and  216 . It will be appreciated that the described systems and methods are not limited to any marking techniques, and may use any suitable monochrome or color marking technique. In general, module  204  includes indicia system  116  described above. 
     As key roller  216  begins to lay down indicia on leading edge E 1  of a given sheet  118  (e.g., as the leading edge passes the key roller) with side S 1  up, a digital signal is generated and includes a timestamp or other information indicating a time of arrival of the leading edge of the sheet. Since the speed at which the image is traveling on photoreceptor belt  218  is known, and since the distance between imaging stations (e.g., registration points) is known, the system knows when to begin writing with each respective imaging station. Additionally, marker module  204  comprises registration entrance sensor  220  that senses sheet position for adjusting a duplex “eject-to-transfer” time. In an example embodiment, sensor  220  is included in system  104 , for example, as sensor  126 A or  126 B. In an example embodiment, system  104  is proximate sensor  220 . A sheet  118  is flipped on duplex path  222 , for example, such that side S 2  is up. 
     The following provides further detail regarding apparatus  100 . In an example embodiment, apparatus  100  is a xerographic machine and pressure and heat are applied to the sheet as part of xerographic operations on side S 1 . The pressure and heat can drive moisture from sheet  118 A, shrinking the sheet, in particular along length L of the sheet. By using ratio  124 , indicia  122 B,  122 C, or  122 D can be adjusted to ensure registration between respective indicia on respective sides S 1  and S 2 . That is, ratio  124  provides automatic adjustment of the registration to accommodate a change in the dimensions of a sheet  118 , in particular, a decrease in length L. 
     In an example embodiment, apparatus  100  is an aqueous ink or lithographic machine and the application of indicia  122 A  122 B,  122 C, and  122 D involves adding liquid, for example ink, to each sheet  118  as part of the printing or lithographic process. The addition of a liquid, plus possible stretching of each sheet  118 , as part of the process of transporting the sheet and applying the liquid, can result in an increase in L. In this case, by using ratio  124 , registration of respective indicia on respective sides S 1  and S 2  for each sheet  118  is ensured. That is, ratio  124  provides automatic adjustment of the registration to accommodate a change in the dimensions of a sheet  118 , in particular, an increase in length L. In general, change in dimension to a sheet due to any chemical processing of the sheet can be accounted for by apparatus  100 . 
     In an example embodiment, operations performed by apparatus  100  include stretching sheet  118 , as a result of the architecture for processing upon the sheet. As noted above, the use of ratio  124  enables adjust to account for such stretching and maintain a desired registration between respective indicia on respective sides S 1  and S 2  for each sheet  118   
     In an example embodiment, change to width W of a sheet  118  can be determined. For example, a ratio of a change in W with respect to a change in L can be calculated or otherwise obtained and this ratio can be used to determine the change in W when the change in L is known. 
     Advantageously, apparatus  100  enables real time, dynamic, and constant registration adjustment. For example, dimensional change is measured for a single sheet in real time and registration adjustment is made for that sheet or a subsequent sheet in real time. Thus, there is no lag in the measuring of dimensional change and appropriate adjustment to that change. Further, the real time measurements enable appropriate adjustment responsive to actual conditions and materials. 
     Apparatus  100  provides the following advantages as well. Apparatus  100  enables accurate correction for side  1  (S 1 ) to side  2  (S 2 ) magnification differences under all conditions, including changing environmental conditions, such as humidity levels and temperature, which affect paper dimensions. Apparatus  100  enables accurate correction for changing sheet media types, such as cover stock and lightweight stock, which change dimensions to differing degrees in the face of varying environmental, such as humidity or temperature, and machine conditions, for instance, fuser setpoints. Apparatus  100  saves operator and service technician time by reducing the time and frequency necessary to perform image to paper registration setup. Apparatus  100  enables registration adjustment for all size sheets supported by a particular embodiment of apparatus  100 . 
     Apparatus  100  enables simple and cost-effective implementation. In some instances, the components of system  104  are already in place and only relatively simple programming adjustments are required. Apparatus  100  reduces front to back show-through error. Apparatus  100  does not depend on accurately measuring an absolute length of the page (an inherent problem with other approaches). Rather, apparatus  100  measures a difference between S 1  to S 2  and calculates ratio  124 . Any error in the S 1  measurement is normalized with the same error in the S 2  measurement. Apparatus  100  enables, for example through the use of a run-time average, accurate default adjustment. 
       FIG. 4  is flow chart  300  illustrating a method for compensating application of indicia to a sheet according to a change in dimension for the sheet of paper. The following should be viewed in light of  FIGS. 1A through 4 . Step  302  begins the process. At step  304 , leading edge E 1  of sheet  118 A is detected by sensor  126 A and counting of encoder pulses begins. At step  306 , trailing edge E 2  of sheet  118 A is detected by sensor  126 B and counting of encoder pulses stops. At step  308  a determination is made as to whether S 1  or S 2  is being processed. For S 1 , (indicia  122 A not yet applied), branch  310  is made to step  312 , which saves the encoder counts as N 1 . For S 2 , (indicia  122 A applied, indicia  122 B not yet applied), branch  314  is made to step  316 , which saves the encoder counts as N 2 . Step  318  calculates ratio  124 . Optional step  320  calculates running average  128  of ratio  124 . Step  322  applies indicia  122 B to side S 2  of sheet  118 A. Step  324  applies indicia  122 C to side S 1  of sheet  118 B. Step  326  applies indicia  122 D to side S 2  of sheet  118 B. Step  328  adjusts magnification for application of indicia  122 B,  122 C, or  122 D. 
     It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.