Patent Publication Number: US-7210758-B2

Title: Media feed calibration

Description:
FIELD OF THE INVENTION 
   The present embodiments relate generally to manners of banding related to media feed. 
   BACKGROUND OF THE INVENTION 
   For desktop printers, such as ink jet printers, a media sheet is picked from an input tray and moved along a media path into a print zone where characters, symbols or graphics are printed onto the media sheet. For scanning-type ink jet printers, the media sheet is fed incrementally as a printhead scans across the media sheet. Typically, the media sheet is moved by a linefeed distance between or during printing to a given line. 
   The media handling system for an ink jet printer includes a set of rollers which move a media sheet along a media path. The rollers are driven by a drive shaft, which is driven by a drive motor. In many instances, an intermediary gearing is used to vary the motion of the rollers. A print controller controls the drive motor. 
   For printing from a desktop computer, a user typically issues a print command within an application program environment. A file specified by the user then is downloaded to the printer for printing. Typically, a printer driver handles the communication interface between the computer and the printer. For text printing, a conventional print driver issues linefeed commands within a stream of character data so that the character data is printed in a desired visual format, (e.g., with desired margins and desired line spacing). The print controller controls timing for printing characters that achieve the desired format. Such timing is determined by the print driver commands, the data stream and fixed parameters. The fixed parameters are based upon a given physical configuration of a printer. Linefeed distance typically is based upon one or more of these fixed parameters for text, graphic and imaging processing. For example, for text printing the line spacing (e.g., 1, 1.5 or 2) is based upon the fixed linefeed parameter. 
   The present embodiments are directed to methods for adjusting the linefeed distance. 
   SUMMARY OF THE INVENTION 
   A novel method for calibration of paper feed in an ink jet printing system is used to remove overfeed bands and underfeed bands from an image. The method begins by feeding print media into the ink jet printing system. A color density test target is formed by simultaneously applying an on/off pattern print mask to print numerous print swaths while incrementing paper feed values. Each paper feed value corresponds respectively to each print swath. The color density test target reveals shifts from light to dark to light in order to identify a maximum optical density region. The paper feed value from the color density test target corresponding to a maximum optical density region on the color density test target is selected and entered into the printing system. The entered value calibrates printing system in order to minimize the presence of overfeed bands and underfeed bands while printing. 
   The present embodiments are advantageous over the prior art because the method enables calibration to reduce overfeed and underfeed banding in images from ink jet printing system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description of the preferred embodiments presented below, reference is made to the accompanying drawings, in which: 
       FIG. 1  is a schematic of an embodiment of a method to calibration of paper feed in an ink jet printing system. 
       FIG. 2   a  depicts an example of an overfeed band. 
       FIG. 2   b  depicts an example of an underfeed band. 
       FIG. 3  examples an on/off pattern print mask with a checkerboard embodiment. 
       FIG. 4  examples a color density test target formed from the embodied methods. 
       FIG. 5  depicts a schematic of a system for printing a color density test target on print media to calibrate paper feed in an ink jet printing system. 
   

   The present embodiments are detailed below with reference to the listed Figures. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Before explaining the present embodiments in detail, it is to be understood that the embodiments are not limited to the particular descriptions and that it can be practiced or carried out in various ways. 
   Media feed related banding is a gross image quality anomaly. Media feed calibration is typically done through printing a target while continuously changing media feed advance distance. At an ideal paper feed value, the target looks uniform no horizontal banding. This ideal paper feed value is selected and input into the printer as the calibrated paper feed value. Banding is thereby eliminated or substantially reduced. 
   The present embodiments relate to a feed calibration method in an ink jet printer. The methods entail printing a target over a range of paper feed values. The user can identify the densest area on the printed sheet that corresponds to a given paper feed value. The paper feed value is then entered into the printer, thereby setting the paper feed. 
   The present embodiments relate to a major improvement over the known art taught in U.S. Pat. No. 6,137,592, which is hereby incorporated by reference. 
   The present embodiments provide the advantageous manner for calibration by providing color density test targets that are shorter than other targets. The shorter color density test targets saves on paper, thereby saving money and helping the environment. The embodied methods print color density test targets that typically range in length from 6 inches to 13 inches. This size is at least 50% shorter than known calibration systems, such as those taught in U.S. Pat. No. 6,137,592. 
   The embodied methods provide a calibration that can be done with the human eye. Additional measurement devices, such as line measure using a ruler, are not needed. 
   The embodied methods provide a calibration method that can be automated. The embodied methods can be completed without human aid at all. The ink jet printing systems can print a color density test target created by the embodiments, then automatically optically scan the targets using a robot operated optical scanner. The optimized paper feed value can be selected from the scan of the targets and compared to preset color density values. The optimized paper feed value can then be input automatically input to the printing system, thereby reducing the overfeed bands and underfeed bands automatically. The automatic advantage of the embodied methods provides a significant reduction in labor costs. 
   The present embodiments provide a calibration method that is faster to complete than the known methods. The faster calibration saves energy by reducing the amount of time needed to do the testing of the printing system and allows for print system problem to be identified quicker in order to solve problems before they become too costly. 
   The embodied method allow for recalibrations to be carried out over the life of the print system, thereby reducing the need to replace the print system. The print systems utilizing these methods thereby have lengthened life spans and can print high quality documents, typically resolutions over 300 dpi, without overfeed and underfeed banding. The print systems can be recalibrated to accommodate different media types and different media weights, which greatly improve the versatility of the ink jet printing system. 
   The present embodiments provide an advantage of reducing the under-advancing of the media image on a regular basis. Using the embodied methods, the under-advancing of the media image can be routinely monitored, thereby allowing for better control of image size and more accurate reproduction of images. 
   With reference to the figures,  FIG. 1  is a schematic of an embodiment of a method for calibration of paper feed in an ink jet printing system. The methods are used to remove overfeed bands and underfeed bands from an image. Overfeed bands are light bands that appear in printing. Underfeed bands are dark bands that appear in the printing.  FIG. 2   a  depicts an example of an overfeed band  12  on an image  16 .  FIG. 2   b  depicts an example of an underfeed band  14  on an image  16 . 
   The method begins by feeding print media into the ink jet printing system (Step  100 ) and forming a color density test target  22  (Step  110 ). 
   The color density test target  22  is formed by simultaneously, which involves applying an on/off pattern print mask  26  (Step  120 ) and incrementing paper feed values  30   a ,  30   b , and  30   c  (Step  130 ).  FIG. 3  examples an on/off pattern print mask  26  with a checkerboard embodiment. The on/off pattern print mask  26  is applied using a plurality of print swaths  28   a ,  28   b , and  28   c  to print the test target while the paper feed values  30   a ,  30   b , and  30   c  are incremented. 
   The method continues by selecting the paper feed value from the color density test target  22  that corresponds to a maximum optical density region  24  on the color density test target  22  (Step  140 ). 
   The method ends by inputting the paper feed value that corresponds to the maximum optical density region  24 —“4809” shown in FIG.  4 —into the ink jet printing system (Step  150 ). Inputting the paper feed value calibrates the printing system in order to minimize the presence of overfeed bands and underfeed bands while printing. 
   Returning to  FIG. 3 , the on/off pattern print mask  26  can be made of other patterns, such as square patterns and rectangular patterns. The checkerboard print mask includes dark color areas and light color areas that correspond to the on/off pattern  26  for each print swath  28   a ,  28   b , and  28   c  that are shown in  FIG. 4 . If the calibration is incorrect, repeated printing passes reveal a overfeed or underfeed banding which can lead to inconsistent color density. The on/off pattern print mask  26  is sensitive to vertical changes in the printer. 
     FIG. 4  shows the color density test target  22  with the print swaths. 
   Each incremented paper feed value  30   a ,  30   b , and  30   c  corresponds respectively to a print swath  28   a ,  28   b , and  28   c . At least one paper feed value can correspond to up to six print swaths. The paper feed values  30   a ,  30   b ,  30   c  and  30   d  can be incremented by sequentially incrementing individual paper feed values or sequentially incrementing groups of paper feed values. 
   The color density test target  22  is created by performing these steps or “passes” numerous times. Typically between three and sixteen passes are required to create the color density test target  22 . The preferred number of passes to create the color density test target  22  is six. 
   The color density test target  22  is adapted to shift from light to dark to light in order to identify a maximum optical density region  24 . The maximum optical density region  24  is a maximum color concentration region on the color density test target  22 . The color density test target  22  can include color information, such as black, cyan, magenta, yellow, and combinations thereof. In  FIG. 4 , the paper feed value that corresponds to the maximum optical density region  24  is “4812” which is designed as element  30   d.    
   The embodied method can be used on ink jet printing systems with rollers for vertical feed. 
     FIG. 5  depicts a schematic of a system for printing a color density test target on print media to calibrate paper feed in an ink jet printing system. The system includes a drive motor  1 , a drive shaft  2  driven by the drive motor; and one or more rollers  3  coupled to the drive shaft  2 . The rollers  3 , therefore, move with the drive shaft  2 . 
   The system includes controller  4  coupled to the drive motor.  1 . The controller is connected to a processor  5  that includes memory  6  for storing a color density test target  22 . 
   A printhead  8  is located on a moveable carriage  9  to print the color density test target  22  onto print media  10 . A user interface  11  connects to the processor  5  to allow a user to provide input paper feed values to the processor  5  and store paper feed values into memory  6 . 
   The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
   PARTS LIST 
   
       
         1 . drive motor 
         2 . drive shaft 
         3 . roller 
         4 . controller 
         5 . processor 
         6 . memory 
         8 . printhead 
         9 . carriage 
         10 . print media 
         11 . user interface 
         12 . overfeed band 
         14 . underfeed band 
         16 . image 
         22 . color density test target 
         24 . maximum optical density region 
         26 . on/off pattern print mask 
         28   a . print swath 
         28   b . print swath 
         28   c . print swath 
         30   a . paper feed value 
         30   b . paper feed value 
         30   c . paper feed value 
         30   d . paper feed value 
         100 . step of feeding print media into the ink jet printing system 
         110 . step of forming a color density test target 
         120 . step of applying an on/off pattern print mask 
         130 . step of incrementing paper feed values 
         140 . step of selecting the paper feed value from the color density test target that corresponds to a maximum optical density region on the color density test target 
         150 . step of inputting the paper feed value that corresponds to the maximum optical density region into the ink jet printing system