Patent Publication Number: US-2011052292-A1

Title: Two-sided image on paper skew registration

Description:
TECHNICAL FIELD 
     This disclosure generally relates to a method for determining an angular orientation positioning of an image on a sheet of printing material during two-sided printing, and a system for monitoring the angular orientation of an image on a sheet of printing material during two-sided printing. 
     BACKGROUND 
     For precisely positioning an image on a sheet of printing material, it is necessary to monitor, and if necessary or desirable, to correct the position of the image. The precise position of an image on the sheet of printing material may be important when, for example, images are printed on both sides of the sheet. 
     Since the sheet gets inverted between printing on a first side and a second side the lead edge for the first side is the trail edge for the second side and the trail edge for the first side is the lead edge for the second side. By not registering the position of the sheet just before printing on both sides of the sheet using the appropriate side of the sheet, the first side to the second side image on paper registration may not match due to cut sheet tolerances and lead edge/trail edge non-parallelism. 
     There are other methods that eliminate the problem of using different reference edges for skew registration between the first side and the second side, such as using side edge sensing. Using the side edges can be difficult in center registered systems and even if a side edge registered system uses side edge sensors, the CCD (charge-coupled device) sensors are expensive and low cost CIS (contact image sensor) array sensors do not provide the proper resolution for an accurate registration. Therefore, it would be advantageous to provide a system and method for registering both sides of the sheet such that the first side to the second side image on paper registration matches. 
     SUMMARY 
     According to aspects illustrated herein, there is provided a method for registering a sheet of paper along a feed path. The method begins by, moving the sheet in a process direction along the feed path and past a first optical sensor and a second optical sensor to determine a first skew of a first edge of the sheet. The first optical sensor and the second optical sensor being configured to determine: a first time interval, the first time interval being equal to time elapsed between the first edge of the sheet passing the first optical sensor and the second optical sensor; and a first distance, the first distance is a distance between the first optical sensor and the second optical sensor. Next, the method calculates a first velocity of the sheet along the feed path at the first time interval and the first skew of the first edge of the sheet using the first time interval, the first distance, and the first velocity. After that, the method uses the first skew to register a first side of the sheet prior to printing a first image on the first side of the sheet. Then, the method inverts and refeeds the sheet on a second side. Thereafter, the method moves the sheet in the process direction along the feed path and past a third optical sensor and a fourth optical sensor to determine a second skew of the first edge of the sheet, the third optical sensor and the fourth optical sensor being configured to determine a second time interval, the second time interval being equal to time elapsed between the second edge of the sheet passing the third optical sensor and the fourth optical sensor; and a second distance, the second distance is the distance between the third optical sensor and the fourth optical sensor. Subsequently, the method calculates a second velocity of the sheet and the second skew of the first edge of the sheet using the second time interval, the second distance, and the second velocity. Finally, the method uses the second skew to register the second side of the sheet prior to printing a second image on the second side of the sheet, with the registration aligning the first image on the first side of the sheet with the second image on the second side of the sheet. 
     According to other aspects illustrated herein, there is provided a system for registering a sheet of paper using a printmaking device. The system includes a feed path configured to move in a process direction; at least one pair of optical sensors; and a control module. The at least one pair of optical sensors are configured to measure a first position of a first edge of the sheet and a second position of a first edge of the sheet. The control module is configured to register a first side of the sheet by: determining a first time interval being equal to time elapsed between the first edge of the sheet passing the first optical sensor and the second optical sensor; determining a first distance between the first optical sensor and the second sensor; calculating a first velocity of the sheet along the feed path of the first time interval; and calculating a first skew using the first time interval, the first distance, and the first velocity. Next, the control module is configured to register a second side of the sheet by: determining a second time interval being equal to time elapsed between the first edge of the sheet passing the third optical sensor and the fourth optical sensor; determining a second distance between the third optical sensor and fourth optical sensor; calculating a second velocity of the sheet along the feed path at the second time interval; and calculating a second skew using the second time interval, the second distance, and the second velocity. Then, the system moves the sheet along the feed path and past the first optical sensors and the second optical sensor to determine the first skew of the first edge of the first side of the sheet. The control module uses the first skew to register the first side of the sheet prior to printing a first image on the first side of the sheet. After that, the sheet is refed on the second side and moves along the feed path and past the third optical sensor and the fourth optical sensor to determine the second skew of the first edge with respect to the second side of the sheet. Finally, the control module uses the second skew to register the second side of the sheet prior to printing a second image on the second side of the sheet. The registration by the control module aligns the first image on the first side of the sheet with the second image on the second side of the sheet. 
     According to other aspects illustrated herein, there is provided a printmaking device for registering a sheet of paper along a feed path. The printmaking device including a feed path, a printing module, and a two-sided deskewing system. The feed path is adapted to move a sheet of paper, the sheet including a first edge and a second edge, with the first edge being approximately parallel to the second edge. The printing module configured to print an image on the sheet. The two-sided deskewing system along the feed path including at least one pair of optical sensors and a control module. The at least one pair of optical sensors include a first optical sensor and a second optical sensor being configured to measure a first position of the first edge of the sheet. The at least one pair of optical sensors further include a third optical sensor and a fourth optical sensor being configured to measure a second position of the second edge of the sheet. The control module is configured to register a first side of the sheet and a second side of the sheet. As the feed path moves the sheet in a process direction past the first optical sensor and the second optical sensor and the control module registers the first side of the sheet, prior to printing the first image on the first side of the sheet. The control module registers the first side by: determining a first time interval being equal to time elapsed between the first edge of the sheet passing the first optical sensor and the second optical sensor; determining a first distance between the first optical sensor and second optical sensor; calculating a first velocity of the sheet along the feed path at the first time interval; and calculating a first skew using the first time interval, the first distance, and the first velocity. Next, the printmaking device inverts and refeeds the sheet on the second side, the feed path moves the sheet in the process direction and past the third optical sensor and the fourth optical sensor, and the control module registers the second side of the sheet, prior to printing the second image on the second side of the sheet, by: determining a second time interval being equal to time elapsed between the first edge of the sheet passing the third optical sensor and the fourth optical sensor; determining a second distance between the third optical sensor and the fourth sensor; calculating a second velocity of the sheet along the feed path at the second time interval; and calculating a second skew using the second time interval, the second distance, and the second velocity. The registration by the control module is configured to align a first image on the first side of the sheet with a second image on the second side of the sheet. 
     Additional features and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a method for registering two sides of a sheet of paper along a feed path of a printmaking device using at least on pair of optical sensors. 
         FIG. 2  illustrates a system with two pairs of optical sensors for use with the method of  FIG. 1 , where the first side of the sheet is being registered. 
         FIG. 3  illustrates a system with two pairs of optical sensors for use with the method of  FIG. 1 , where the second side of the sheet is being registered. 
         FIG. 4  illustrates a system with one pair of optical sensors for use with the method of  FIG. 1 , where the first side of the sheet is being registered. 
         FIG. 5  illustrates a system with one pair of optical sensors for use with the method of  FIG. 1 , where the second side of the sheet is being registered. 
         FIG. 6  illustrates a printmaking device for use with the method and system shown in  FIGS. 1-5 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The method and system disclosed herein provide for registering both sides of a sheet of paper along a feed path of a printmaking device to ensure that the positions of the images on both sides of the paper are aligned. 
     As used herein, the phrase “printmaking device” encompasses any apparatus, such as a digital copier, a bookmaking machine, a facsimile machine, and a multi-function machine, which performs a printing outputting function for any purpose. 
     As used herein, the term “sheet” encompasses, for example, one or more of a usually flimsy physical sheet of paper, heavy media paper, coated papers, transparencies, parchment, film, fabric, plastic, or other suitable physical print media substrate on which information can be reproduced. 
     As used herein, the phrase “feed path” encompasses any apparatus for separating and/or conveying one or more sheets into a substrate conveyance path inside a printmaking device. 
     As used herein, the phrase “process direction” refers to a direction that the feed path moves a sheet. 
     As used herein, the phrase “lead edge” refers to the edge of a sheet that first advances along the substrate conveyance path. 
     As used herein the phrase “printing module” refers to a marking device that uses marking technologies, such as xerographic, inkjet, and offset markings. 
     As used herein, the term “skew” refers to an angular error in the placement of an image printed onto a sheet. 
     As used herein, the phrase “optical sensors” refer to a sensor that detects the intensity or brightness of light. 
     As used herein, the phrase “fixed reference” refers the alignment and configuration of the sensor, which points at a non-changing location to where the sensor collects information. The reference is a fixed reference because the sensor will only detect activity at the configured location. For example, a fixed reference may be a specific location on the feed path and the sensor may detect when a sheet is at that specific location. 
     As used herein, the terms “register” and “registration” refer to determining the proper alignment of a sheet and/or a printing apparatus with respect to a fixed reference. 
     As used herein, the terms “invert,” “inverting,” and “inverted” refer to the action of reversing the position of the sheet, such as flipping the sheet from a first side to a second side. 
     As used herein, the terms “refeed,” “refeeding,” and “refed” refer to a sheet being conveyed on a feed path for a second time after first moving along the feed path and having an image printed thereon. For example, in a duplex printmaking device, a sheet is fed along the feed path a first time to print an image on a first side, and then the sheet is inverted and then refed along the feed path a second time to print another image on a second side. 
     As used herein, the phrase “time interval” refers to a time period between two events. For example, a time period between a sheet crossing a first sensor and a second sensor. 
       FIG. 1  provides a method  10  for registering both sides of a sheet of paper along a feed path of a printmaking device to ensure that the positions of the images on both sides of the paper are aligned. In step  12 , the printmaking device moves the sheet in a process direction along the feed path and past a first optical sensor and a second optical sensor to determine a first skew of the first edge. A first skew of the first edge of the sheet is calculated by the control module in step  14 . The first skew is calculated using a first time interval between a sheet crossing the first optical sensor and the second optical sensor, a first distance between the first optical sensor and the second optical sensor, and a first sheet velocity. Next, in step  16 , the control module uses the first skew to register a first side of the sheet prior to printing a first image on the first side of the sheet. 
     After that, the printmaking device inverts the sheet and refeeds the sheet on a second side in step  18 . Then, in step  20 , the printmaking device moves the sheet in a process direction along the feed path and past a third optical sensor and a fourth optical sensor to determine a second skew of the first edge. The second skew of the first edge of the sheet is calculated by the control module in step  22 . The second skew is calculated using a second time interval between the sheet crossing the third optical sensor and the fourth optical sensor, a second distance between the third optical sensor and the fourth optical sensor, and a second velocity. Finally, in step  24 , the control module uses the second skew to register a second side of the sheet prior to printing a second image on the second side of the sheet. 
     The method  10  registers the first side of the sheet using skew information calculated using an equation that establishes the skew as substantially equal to v 1 *(t 1 −t 2 )/y 1 , where v 1  is the first velocity, (t 1 −t 2 ) is the first time interval, and y 1  is the first distance. The method  10  then registers the second side of the sheet using skew information calculated using a similar equation that establishes the skew as substantially equal to v 2 *(t 3 −t 4 )/y 2 , where v 2  is the second velocity, (t 3 −t 4 ) is the second time interval, and y 2  is the second distance. 
     The method  10  may use a printing module to print the first and second images on the first and second sides of the sheet. The method  10  may be modified to use one pair of optical sensors. In that case, the method  10  would use the first optical sensor and the second optical sensor to measure the skew of both the first and the second side of the sheet. Furthermore, the method may be configured such that the first edge is the lead edge of the first side of the sheet and the second edge is the trail edge of the first side of the sheet. Accordingly, the first edge is the trail edge of the second side of the sheet and the second edge is the lead edge of the second side of the sheet. 
       FIGS. 2-3  provide an exemplary system  30  for use with the method  10  of  FIG. 1 . The system  30  having a control module  32 , a first and second pair of optical sensors including a first optical sensor  34 , a second optical sensor  36 , a third optical sensor  38 , a fourth optical sensor  40 , and a feed path  42  for registering a sheet  44  of paper. The sheet  44  having a first edge  46  and a second edge  48  with the first edge  46  and the second edge  48  being approximately parallel. 
     The first optical sensor  34  and the second optical sensor  36  are configured to measure a first position and determine a first skew a of the first edge  46  of a first side  50  of the sheet  44 . The third optical sensor  38  and the fourth optical sensor  40  are configured to measure a first position and determine a second skew b of the first edge  46  of a second side  52  of the sheet  44 . 
     The control module  32  is configured to register the first side  50  and the second side  52  of the sheet  44 . The first side  50  of the sheet  44  is registered by determining a first time interval being equal to time elapsed between the first edge  46  of the sheet  44  passing the first optical sensor  34  and the second optical sensor  36 ; determining a first distance, y 1 , between the first optical sensor  34  and the second optical sensors  36 ; and calculating a first velocity of the sheet  44  along the feed path  42  during the first time interval. After that, the first skew a is calculated using the first time interval, the first distance, and the first velocity. 
     Similarly, after the sheet  44  is inverted and refed, the control module  32  registers the second side  52  of the sheet  44 . The second side  52  of the sheet  44  is registered by determining a second time interval being equal to time elapsed between the first edge  46  of the sheet  44  passing the third optical sensor  38  and the fourth optical sensor  40 ; determining a second distance, y 2 , between the third optical sensor  38  and the fourth optical sensor  40 ; and calculating a second velocity of the sheet  44  along the feed path  42  during the second time interval. Then, the second skew b is calculated using the second time interval, the second distance, and the second velocity. 
     In operation, as the sheet  44  moves along a feed path  42  in a process direction v and past the first optical sensor  34  and the second optical sensor  36  to determine a first skew a of the first edge  46  of the sheet  44 . Next, the control module  32  uses the first skew a to register the first side  50  of the sheet  44  prior to printing a first image  54  on the first side  50  of the sheet  44 . To register the first side  50  of the sheet  44  the following equation is used to estimate the sheet skew: r 1 =v 1 *(t 1 −t 2 )/y 1 , where the first velocity is v 1 , the first time interval is (t 1 −t 2 ), and the first distance is y 1 . 
     After that, the printmaking device inverts and refeeds the sheet  44  and moves the sheet  44  along the feed path  42  in the process direction v and past the third optical sensor  38  and the fourth optical sensor  40  to determine a second skew b of the first edge  46  of the sheet  44 . Then, the control module  32  uses the second skew b to register the second side  52  of the sheet  44 . The second side  52  of the sheet  44  is registered using the sheet skew estimated using the equation: r 2 =v 2 *(t 3 −t 4 )/y 2 , where the second velocity is v 2 , the second time interval is (t 3 −t 4 ), and the second distance is y 2 . The registration of the first and second sides  50 ,  52  of the sheet  44  by the control module  32  is designed to properly align the first image  54  on the first side  50  of the sheet  44  with the second image  56  on the second side  52  of the sheet  44 . 
     The system  30  of  FIGS. 2-3  may further include a printing module  58  for printing the first image  54  on the first side  50  of the sheet  44  and the second image  56  on the second side  52  of the sheet  44 . The type of printing module  58  contemplated may include any marking technology known to one of skill in the art for use with a system for duplex printing. 
     In  FIGS. 2-3  the first edge  46  is the lead edge of the first side  50  of the sheet  44  in relation to the process direction v and the second edge  48  is the trail edge of the second side  52  of the sheet  44  after the sheet  44  is refed. The system  30  of  FIGS. 2-3  is not limited to the first edge  46  being the lead edge of the first side  50  of the sheet  44 . Thus, the first edge  46  may be the trail edge of the first side  50  of the sheet  44  and the second edge  48  may be the lead edge of the first side  50  of the sheet  44 . An important aspect is that the system  30  uses the sensors to accurately determine the position of the same edge of the sheet  44  during registration of both sides. 
     Referring to  FIGS. 4-5 , a further exemplary system  60  is provided. The system  60  of  FIGS. 4-5  is a variation of the system  30  of  FIGS. 2-3 , for use with the method  10  of  FIG. 1 . The system  60  of  FIGS. 4-5  uses one pair of optical sensors, the first optical sensor  34  and the second optical sensor  36  to register both the first and second sides  50 ,  52  of the sheet  44 . In  FIGS. 4-5 , the first optical sensor  34  and the second optical sensor  36  determine the first skew a of the lead edge (first edge) of the first side  50  of the sheet  44  and the second skew b of the trail edge (first edge) of the second side  52  of the sheet  44 . All other aspects of the system  60  are the same as the system  30  of  FIGS. 2-3 . 
     Alternatively, the system  60  of  FIGS. 4-5  may use the first optical sensor  34  and the second optical sensor  36  to determine the first skew a of the trail edge (second edge) of the first side  50  of the sheet  44  and the second skew b based on the lead edge (second edge) of the second side  50  of the sheet  44 . 
       FIG. 6  provides a printmaking device  70  for use with the method  10  and systems  30 ,  60  of  FIGS. 1-5 . The printmaking device  70  includes a control module  32 , feed path  42 , a printing module  58 , and a two-sided deskewing system  72 , similar to that described in  FIGS. 2-5 . 
     The feed path  42  is adapted to move the sheet  44  in a process direction v. The sheet  44  having the first edge  46  and the second edge  48 , with the first edge  46  and the second edge  48  being approximately parallel. The printing module  58  being configured to print the first image  54  on the first side  50  of the sheet  44  and the second image  56  on the second side  52  of the sheet  44  using any marking means known to those skilled in the art. The two-sided deskewing system  72  is along the feed path  42  and includes at least one pair of optical sensors and a control module  32 . The at least one pair of optical sensors are shown as the third optical sensor  38  and the fourth optical sensor  40  in  FIG. 6 . 
     The control module  32  is configured to register a first side  50  and a second side  52  of the sheet  44 . The first side  50  of the sheet  44  is registered by determining a first time interval being equal to time elapsed between the first edge  46  of the sheet  44  passing the third optical sensor  38  and the fourth optical sensor  40 ; determining a first distance between the third optical sensor  38  and the fourth optical sensor  40 ; and calculating a first velocity of the sheet  44  along the feed path  42  during the first time interval. After that, the first skew a is calculated using the first time interval, the first distance, and the first velocity. 
     Similarly, after the sheet  44  is inverted and refed, the control module  32  registers the second side  52  of the sheet  44 . The second side  52  of the sheet  44  is registered by determining a second time interval being equal to time elapsed between the first edge  46  of the sheet  44  passing the third optical sensor  38  and the fourth optical sensor  40 ; determining a second distance between the third optical sensor  38  and the fourth optical sensor  40 ; and calculating a second velocity of the sheet  44  along the feed path  42  during the second time interval. Then, the second skew b is calculated using the second time interval, the second distance, and the second velocity. 
     In operation, as the sheet  44  moves along a feed path  42  in a process direction v and past the third optical sensor  38  and the fourth optical sensor  40  to determine a first skew a of the first edge  46  of the sheet  44 . Next, the control module uses the first skew a to register the first side  50  of the sheet  44  prior to printing a first image  54  on the first side  50  of the sheet  44 . To register the first side  50  of the sheet  44  the following equation is used to calculate the skew a: r 1 =v 1 *(t 1 −t 2 )/y 1 , where the first velocity is v 1 , the first time interval is (t 1 −t 2 ), and the first distance is y 1 . 
     After that, the printmaking device  70  refeeds the sheet  44  and moves the sheet  44  along the feed path  42  in the process direction v and past the third optical sensor  38  and the fourth optical sensor  40  to determine a second skew b of the first edge  46  of the sheet  44 . Then, the control module  32  uses the second skew b to register the second side  52  of the sheet  44 . The second side  52  of the sheet  44  is registered using the skew b calculated using the equation: r 2 =v 2 *(t 3 −t 4 )/y 2 , where the second velocity is v 2 , the second time interval is (t 3 −t 4 ), and the second distance is y 2 . The registration of the first and second sides  50 ,  52  of the sheet  44  by the control module  32  is designed to properly align the first image  54  on the first side  50  of the sheet  44  with the second image  56  on the second side  52  of the sheet  44 . 
     Alternatively, the one pair of optical sensors may be the first optical sensor  34  and the second optical sensor  36  as shown and discussed with reference to  FIGS. 4-5 . A further variation of  FIG. 6  includes using two pairs of optical sensors, the first optical sensor  34 , the second optical sensor  36 , the third optical sensor  38 , and the fourth optical sensor  40 , as shown and discussed in  FIGS. 2-3 . 
     The benefits of the method, system, and printmaking device provided herein include aligning images based on the skew for the same edge of both the first side  50  and the second side  52  of the sheet  44 . Using the system and method provided herein eliminates the first side  50  to second side  52  image on paper registration errors caused by cut sheet tolerances and lead edge/trail edge non-parallelism. An additional benefit is that the system and method provided herein enable the use of low cost point sensors. 
     It will be appreciated that variations of the above-disclosed and other features and functions, or alternative 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. In addition, the claims can encompass embodiments in hardware, software, or a combination thereof.