Abstract:
A technique for assessing nozzle health of a printhead nozzle array in a printing system includes printing a swath portion of an image, optically scanning the printed swath portion to capture a scanned image, comparing an expected image of the swath portion of the image with the scanned image, and assessing whether any nozzles of the nozzle array have malfunctioned. A sensor can be mounted on a printhead carriage to accomplish the image capture.

Description:
BACKGROUND  
       [0001]     Inkjet printers employ printheads for ejecting ink through nozzles of fluid drop generators onto a print media. For various reasons, the fluid ejectors or nozzles can fail to operate properly, which can adversely affect print quality. Nozzle health tests can be done to detect nozzles which are not operating normally. It is known to use isolated drop detection systems with optical detectors to detect nozzle health during special test modes. These systems are expensive and use up ink and time for the testing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0002]     Features and advantages of the disclosure will readily be appreciated by persons skilled in the art from the following detailed description when read in conjunction with the drawing wherein:  
         [0003]      FIG. 1  illustrates an embodiment of a printer.  
         [0004]      FIG. 2  is a close-up simplified cross-sectional view of the carriage portion of the printing mechanism of  FIG. 1  showing a carriage-mounted optical scanner.  FIG. 2A  shows in diagrammatic plan view an exemplary orifice plate with a plurality of nozzles.  FIG. 2B  is an enlarged fragmentary view of a portion of  FIG. 2A , showing rows printed by the staggered nozzles of the two arrays.  
         [0005]      FIG. 3  is an exemplary block diagram of a printing system with an optical scanner.  
         [0006]      FIG. 4  is a simplified process flow diagram illustrating an exemplary process for printing and performing a nozzle heath assessment. 
     
    
     DETAILED DESCRIPTION  
       [0007]     In the following detailed description and in the several figures of the drawing, like elements are identified with like reference numerals.  
         [0008]     For simplicity and illustrative purposes, the principles of the present invention are described by referring mainly to an exemplary embodiment thereof. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent however, to one of ordinary skill in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structure have not been described in detail so as to not to unnecessarily obscure the disclosure.  
         [0009]     As used throughout the present disclosure, the terms “optical scanner” generally refer to a scanner module for image capturing. One exemplary embodiment of optical scanner includes an image capturing device such as a CCD for capturing images from a print media.  
         [0010]      FIG. 1  illustrates an embodiment of a printer  20 , which may be used for recording information onto a recording medium, such as paper, textiles, and the like, in an industrial, office, home or other environment. Embodiments of a nozzle health assessment technique disclosed herein may be practiced in a variety of printers. For instance, it is contemplated that an embodiment may be practiced in large scale textile printers, desk top printers, portable printing units, copiers, cameras, video printers, and facsimile machines, to name a few. For convenience, the concepts of the nozzle heath assessment techniques are illustrated in the environment of the printer  20 .  
         [0011]     While the printer components may vary from model to model, the printer  20  includes a chassis  22  surrounded by a housing or casing enclosure  24 , typically of a plastic material, together forming a print assembly portion  26  of the printer  20 . Additionally, the print assembly portion  26  may be supported by a desk or tabletop, however; however in this embodiment, the print assembly portion  26  is supported with a pair of leg assemblies  28 . The printer  20  also has a printer controller  30 , illustrated schematically as a microprocessor, that receives instructions from a host device (not shown), typically a computer, such as a personal computer or a computer aided drafting (CAD) computer system. The printer controller  30  may also operate in response to user inputs provided through a key pad and a status display portion  32 , located on the exterior of the casing  24 . A monitor coupled to the host device may also be used to display visual information to an operator, such as the printer status or a particular program being run on the host device. Personal and drafting computers, their input devices, such as a keyboard and/or a mouse device, and monitors are all well known to those skilled in the art.  
         [0012]     A recording media handling system may be used to advance a continuous sheet of recording media  34  from a roll through a print zone  35 . Moreover, the illustrated printer  20  may also be used for printing images on pre-cut sheets, ratherthan on media supplied in roll  34 . The recording media may be any type of suitable sheet material, such as paper, poster board, fabric, transparencies, mylar, vinyl, and the like. A carriage guide rod  36  is mounted to the chassis  22  to define a scanning axis  38 , with the guide rod  36  slideably supporting a carriage  40  for travel back and forth, reciprocally, across the print zone  35 . A carriage drive motor (not shown) may be used to propel the carriage  40  in response to a control signal received from the controller  30 . To provide carriage positional feedback information to controller  30 , an encoder strip (not shown) may be extended along the length of the print zone  35  and over a servicing region  42 .  
         [0013]     An optical encoder reader may be mounted on the back surface of carriage  40  to read positional information provided by the encoder strip. The manner of providing positional feedback information via the encoder strip reader, may be accomplished in a variety of ways.  
         [0014]     The printer  20  of this exemplary embodiment includes four print cartridges  50 - 56 . In the print zone  35 , the recording medium receives ink from cartridges  50 - 56 . The cartridges  50 - 56  are also often called “pens” by those in the art. One of the pens, for example pen  56 , may be configured to eject black ink onto the recording medium, where the black ink may contain a pigment-based or a dye-based ink. Pens  50 - 54  may be configured to eject variously colored inks, e.g., yellow, magenta, cyan, light cyan, light magenta, blue, green, red, to name a few. For the purposes of illustration, pens  50 - 54  are described as each containing a dye-based ink of the colors yellow, magenta and cyan, respectively, although it is apparent that the color pens  50 - 54  may also contain pigment-based inks in some implementations. It is apparent that other types of inks may also be used in the pens  50 - 56 , such as paraffin-based inks, as well as hybrid or composite inks having both dye and pigment characteristics.  
         [0015]     The printer  20  of this exemplary embodiment uses an “off-axis” ink delivery system, having main stationary reservoirs (not shown) for each ink (black, cyan, magenta, yellow) located in an ink supply region  74 . In this respect, the term “off-axis” generally refers to a configuration where the ink supply is separated from the print heads  50 - 56 . In this off-axis system, the pens  50 - 56  may be replenished by ink conveyed through a series of flexible tubes (not shown) from the main stationary reservoirs so only a small ink supply is propelled by carriage  40  across the print zone  35  which is located “off-axis” from the path of printhead travel. As used herein, the term “pen” or “cartridge” may also refer to replaceable printhead cartridges where each pen has a reservoir that carries the entire ink supply as the printhead reciprocates over the print zone.  
         [0016]     The illustrated pens  50 - 56  have printheads, e.g. printhead  62 , which selectively eject ink to form an image on a sheet of media  34  in the print zone  35 . In an exemplary embodiment, these printheads have a large print swath, for instance about 22.5 millimeters high or higher, although the concepts described herein may also be applied to smaller printheads. In an exemplary embodiment, the printheads each have an orifice plate with a plurality of nozzles formed there through.  FIG. 2A  shows in diagrammatic plan view an exemplary orifice plate  62  A with a plurality of nozzles.  
         [0017]     The nozzles of each printhead are typically formed in at least one, but typically two or more linear arrays along the orifice plate. For example, as shown in  FIG. 2A , the nozzles are formed in linear arrays  62  A- 1  and  62  A- 2 . The term “linear” as used herein may be interpreted as “nearly linear” or substantially linear, and may include nozzle arrangements slightly offset from one another, for example, in a zigzag arrangement. Each linear array is typically aligned in a longitudinal direction substantially perpendicular to the scanning axis  38 , with the length of each array determining the maximum image swath for a single pass of the printhead. The arrays can be staggered with respect to each other, so that an offset along the longitudinal direction enables higher resolution printing. For example, say the nozzles in array  62  A- 1  and array  62  A- 2  are spaced by 1/300 inch or 1/600 inch spacings. With the staggered array feature, the resolution can be increased to 1/600 or 1/1200, or to 600 dpi or 1200 dpi.  FIG. 2B  is an enlarged fragmentary view of the indicated region of  FIG. 2A , showing rows  63  printed by the staggered nozzles of the two arrays.  
         [0018]     The printer  20  also includes an optical scanner  80  configured to scan across images printed by the pens  50 - 56 . As shown in  FIG. 2 , in this embodiment of the printer  20 , the optical scanner  80  is connected to the carriage  40 . The optical scanner  80  may be connected to the carriage  40  in any reasonably suitable manner that enables the optical scanner to scan over the print zone  35  in a manner that follows the movement of the pens  50 - 56  (i.e., the optical scanner is in line with the pens). In an exemplary embodiment, the optical scanner is on a side of the pens which is downstream of the printing. If the printer supports bidirectional printing, i.e. printing each swath movement direction, then two optical scanners may be used, one on each side of the pens along a swath movement direction so that the just printed image portions can be scanned and captured by one of the optical scanners.  
         [0019]     For high quality full-color printing, the colors from the individual pens should be precisely applied to the printing medium, and this generally means that the pens should be precisely aligned with the carriage assembly. Paper slippage, paper skew, and mechanical misalignment of the pens in inkjet printing mechanisms often result in offsets along both the medium or paper-advance axis and the scan or carriage axis. A group of test patterns can be generated (by activation of selected nozzles in selected pens while the carriage scans across the print medium  90  ) whenever any of pens is distributed, e.g., just after a pen is replaced. The test patterns are then read by scanning the optical scanner  80  over them and analyzing the results.  
         [0020]     In an exemplary embodiment, the optical scanner can be used to perform nozzle health assessment. The optical scanner  80  senses the pixel patterns laid down by the pens  50 - 56  in normal printing modes, and provides electrical signals to, for example, processor  30 , indicative of the portions of the image in the field of view of the scanner  80  which has been printed on the medium  92 . The optical scanner  80  may include a field of view having a height substantially equal to the swath height of the nozzle arrays of the pens. It is, however, envisioned that the field of view of the optical scanner  80  may be relatively greater than the swath height of the pens  50 - 56 .  
         [0021]     In an exemplary embodiment, the optical scanner  80  may comprise a charge coupled device (CCD) scanner that is sized to fit on the carriage  40 . The optical scanner  80  includes a light source  82 , one or more reflective surfaces  84  (only one reflective surface is illustrated), a light focusing device  86 , and a CCD  88 . The optical scanner  80  captures images by illuminating the images with the light source  82  and sensing reflected light with the CCD  88 . The CCD  88  may be configured to include various channels (e.g., red, green, and blue) to detect various colors using a single lamp or a one channel CCD (monochrome) with various color sources (e.g., light emitting diodes (LED)). A more detailed description of one exemplary manner in which the CCD  88  may operate to detect pixels of an image may be found in U.S. Pat. No. 6,037,584. The disclosure contained in that patent is hereby incorporated by reference in its entirety.  
         [0022]     Referring to  FIG. 3 , there is illustrated an exemplary block diagram of elements of an embodiment of the printer  20 . The following description illustrates one exemplary manner in which a printer  20  having an optical scanner  80  may be operated. In this respect, it is to be understood that the following description of  FIG. 3  is but one manner of a variety of different manners in which such a printer  20  may be operated.  
         [0023]     The printer  20  is shown as including four printheads  50 - 56 . However, the nozzle health assessment techniques described herein may operate with a single printhead, or with more than one printheads.  
         [0024]     The printer  20  may also include interface electronics  306  configured to provide an interface between the controller  30  and the components for moving the carriage  40 , e.g., encoder, belt and pulley system (not shown), etc. The interface electronics  306  may include, for example, circuits for moving the carriage, the medium, firing individual nozzles of each printhead, and the like.  
         [0025]     The controller  30  may be configured to provide control logic to implement programmed processes for the printer  20 , e.g. to serve as a print engine, which provides the functionality for the printer. In this respect, the controller  30  may be implemented by a microprocessor, a micro-controller, an application specific integrated circuit (ASIC), and the like. The controller  30  may be a computer program product interfaced with a memory  110  configured to provide storage of a computer software, e.g. a computer readable code means, that provides the functionality of the printer  20  and may be executed by the controller. The memory  110  may also be configured to provide a temporary storage area for data/files received by the printer  20  from a host device  112 , such as a computer, server, workstation, and the like. The memory  110  may be implemented as a combination of volatile and non-volatile memory, such as dynamic random access memory (“RAM”), EEPROM, flash memory, hard drive storage and the like. Alternatively the memory  110  may be included in the host device  112 .  
         [0026]     The controller  30  may further be interfaced with an I/O interface  114  configured to provide a communication channel between the host device  112  and the printer  20 . The I/O interface  112  may conform to protocols such as RS-232, parallel, small computer system interface, universal serial bus, etc.  
         [0027]     Optical scanner interface electronics  124  may interface the optical scanner  304  and the controller  30 . The optical scanner interface electronics  124  may operate to convert instruction signals from the controller  30  to the optical scanner  304 . In addition, the optical scanner interface electronics  124  may also operate to convert information sensed by the optical scanner  304  into a format capable of being interpreted by the controller  30 .  
         [0028]     An exemplary embodiment of a nozzle health assessment technique uses the scanner  80  on the carriage in order to detect changes in nozzle health. The scanner is attached to the carriage, so it scans the same data being printed. That means that after a pass of a swath has been completely printed, the printer will have stored in memory the original image data (i.e. the image to be printed in the swath), the image portion to be printed this pass, and the scanned image. All the other images corresponding to the passes that are not being printed do not have to be stored in memory, as the original image data can be “anded” with the print mask at every pass. The scanned version of the image contains all the artifacts derived from the ink-on-paper interaction. One of those artifacts is nozzle health.  
         [0029]     In an exemplary embodiment, a print mode is used to print an image. One of the parameters of the print mode is the number of passes needed to print the image. For an n-pass print mode the printer uses n passes to finish a given swath. This means that at every printing pass only one nth of the dots are being printed. The splitting of the image data in passes is done using a print mode mask. This mask contains the pass number when each pixel is going to be printed. Then this mask is converted into ‘n’ binary masks that are logically “anded” with the image data. If there is a ‘1’ value in the same position for the image and for the mask, a drop is going to be fired.  
         [0030]     The following is an example of how this works. Assume that the image to be printed is the following:  
                                                                                   0   0   0   0   1   0   0   0   0           0   0   0   1   1   1   0   0   0           0   0   1   1   1   1   1   0   0           0   1   1   1   1   1   1   1   0           1   1   1   1   1   1   1   1   1           0   1   1   1   1   1   1   1   0           0   0   1   1   1   1   1   0   0           0   0   0   1   1   1   0   0   0                      
 
         [0031]     For this example, a 4-pass print mode mask is employed, splitting the printing into 4 binary masks:  
                                                                                   1   2   3   4   1   2   3   4   1           3   4   1   2   3   4   1   2   3           1   2   3   4   1   2   3   4   1           4   1   2   3   4   1   2   3   4           2   3   4   1   2   3   4   1   2           1   2   3   4   1   2   3   4   1           3   4   1   2   3   4   1   2   3           1   2   3   4   1   2   3   4   1                      
 
         [0032]     For pass 1, the print mode mask is as follows:  
                                                                                   1   0   0   0   1   0   0   0   1           0   0   1   0   0   0   1   0   0           1   0   0   0   1   0   0   0   1           0   1   0   0   0   1   0   0   0           0   0   0   1   0   0   0   1   0           1   0   0   0   1   0   0   0   1           0   0   1   0   0   0   1   0   0           1   0   0   0   1   0   0   0   1                      
 
         [0033]     For pass 2, the print mode mask is as follows:  
                                                                                   0   1   0   0   0   1   0   0   0           0   0   0   1   0   0   0   1   0           0   1   0   0   0   1   0   0   0           0   0   1   0   0   0   1   0   0           1   0   0   0   1   0   0   0   1           0   1   0   0   0   1   0   0   0           0   0   0   1   0   0   0   1   0           0   1   0   0   0   1   0   0   0                      
 
         [0034]     For pass 3, the print mode mask is as follows:  
                                                                                   0   0   1   0   0   0   1   0   0           1   0   0   0   1   0   0   0   1           0   0   1   0   0   0   1   0   0           0   0   0   1   0   0   0   1   0           0   1   0   0   0   1   0   0   0           0   0   1   0   0   0   1   0   0           1   0   0   0   1   0   0   0   1           0   0   1   0   0   0   1   0   0                      
 
         [0035]     For pass 4, the print mode mask is as follows:  
                                                                                   0   0   0   1   0   0   0   1   0           0   1   0   0   0   1   0   0   0           0   0   0   1   0   0   0   1   0           1   0   0   0   1   0   0   0   1           0   0   1   0   0   0   1   0   0           0   0   0   1   0   0   0   1   0           0   1   0   0   0   1   0   0   0           0   0   0   1   0   0   0   1   0                      
 
         [0036]     So, the image data applied every pass is:  
                                                                                   0   0   0   0   1   0   0   0   0           0   0   0   1   1   1   0   0   0           0   0   1   1   1   1   1   0   0           0   1   1   1   1   1   1   1   0           1   1   1   1   1   1   1   1   1           0   1   1   1   1   1   1   1   0           0   0   1   1   1   1   1   0   0           0   0   0   1   1   1   0   0   0                      
 
         [0037]     At pass 1, anding the image data with the first pass mask results in:  
                                                                                   0   0   0   0   1   0   0   0   0           0   0   0   0   0   0   0   0   0           0   0   0   0   1   0   0   0   0           0   1   0   0   0   1   0   0   0           0   0   0   1   0   0   0   1   0           0   0   0   0   1   0   0   0   0           0   0   1   0   0   0   1   0   0           0   0   0   0   1   0   0   0   0                      
 
         [0038]     At pass 2, anding the image with the second pass mask results in:  
                                                                                   0   0   0   0   0   0   0   0   0           0   0   0   1   0   0   0   0   0           0   0   0   0   0   1   0   0   0           0   0   1   0   0   0   1   0   0           1   0   0   0   1   0   0   0   1           0   1   0   0   0   1   0   0   0           0   0   0   1   0   0   0   0   0           0   0   0   0   0   1   0   0   0                      
 
         [0039]     At pass 3, anding the image with the third pass mask results in:  
                                                                                   0   0   0   0   0   0   0   0   0           0   0   0   0   1   0   0   0   0           0   0   1   0   0   0   1   0   0           0   0   0   1   0   0   0   1   0           0   1   0   0   0   1   0   0   0           0   0   1   0   0   0   1   0   0           0   0   0   0   1   0   0   0   0           0   0   0   0   0   0   0   0   0                      
 
         [0040]     At pass 4, anding the image with the fourth pass print mask results in:  
                                                                                   0   0   0   0   0   0   0   0   0           0   0   0   0   0   1   0   0   0           0   0   0   1   0   0   0   0   0           0   0   0   0   1   0   0   0   0           0   0   1   0   0   0   1   0   0           0   0   0   1   0   0   0   1   0           0   0   0   0   0   1   0   0   0           0   0   0   1   0   0   0   0   0                      
 
         [0041]     So, after four passes, the first two rows have been printed with all the 4 passes, the rows 3 and 4 have been printed only with passes 1, 2 and 3, rows 5 and 6 with passes 1 and 2 and rows 7 and 8 only with pass 1. Assume that, in this exemplary embodiment, the print medium advance system is actuated to advance the print medium by two rows between each pass. So, what is to be scanned is:  
                                                   after passes 1, 2, 3 and 4:           Row 1 0 0 0 0 1 0 0 0 0           Row 2 0 0 0 1 1 1 0 0 0           after passes 1, 2, and 3:           Row 3 0 0 1 0 1 1 1 0 0           Row 4 0 1 1 1 0 1 1 1 0           after passes 1 and 2:           Row 5 1 0 0 1 1 0 0 1 1           Row 6 0 1 0 0 1 1 0 0 0           after pass 1:           Row 7 0 0 1 0 0 0 1 0 0           Row 8 0 0 0 0 1 0 0 0 0                      
 
         [0042]     In this example for a 4-pass print mode, the print medium is advanced four times, i.e. once per pass, in order to print the complete swath. At every pass in this example, there is only one nozzle printing every row, so after the four advances, four nozzles have printed the same row. So after each pass, the scanner can observe if a nozzle is dead because there is no ink (or not enough ink) on a given row. The expected printed image (the respective images in the tables above) can be compared with the scanned image. If a nozzle is missing, it can be detected when comparing both images because of the lower density in a given row and in expected firing positions of this nozzle. This information can be used to modify the print masks to compensate for inoperative nozzles or nozzles which are not operating properly. Alternatively, detection of malfunctioning masks could trigger a printhead service routine, e.g. spitting and wiping, at a printer service station.  
         [0043]     The nozzle health assessment technique can also be employed with a single pass print mode, wherein the entire swath is printed with a single pass of the printhead carriage. In a single pass print mode, all the nozzles are ready to print, and so if a nozzle is not printing, the scanned image can be processed to detect this condition.  
         [0044]      FIG. 4  is a simplified process flow diagram illustrating an exemplary process for printing and performing a nozzle heath assessment. Data for an input image is provided at  202 . This data may define a swath of an image to be printed. The print mode masks are then applied at  204  to the input data, and a swath pass is printed at  206 . As the pass is being printed, the image of the printed image is captured by the scanner module  80  at  208  to provide a scanned image  210 . The scanned image is compared with the expected image  212  at  214 , to provide an assessment of the nozzle health at  216 . In one exemplary embodiment, using the information about the current swath printed (after masking), a target pattern can be generated (convoluting the image with the scanner transfer function) for a non-defect printing. The target pattern and the scanned image for the pass can be processed and compared (using image phase-correlation techniques to synchronize them spatially and cross-correlation to isolate the individual defects) and characterize the different parts of the nozzle array. Different health weights can be assigned depending on the magnitude of the difference from the printed image to the non-defect image.  
         [0045]     If malfunctioning nozzles are detected, then the print mode masks are modified at  218  to compensate for the malfunctioning nozzle(s). For example, if a nozzle is defective, rows printed by that nozzle will be blank. Another nozzle can be assigned to print rows previously assigned to the defective nozzle (by a 1 in a print mode mask, for example). For example, there may be a back up table of masks to use if a given nozzle goes bad, i.e. so that instead of modifying a print mask, the printer retrieves a mask from memory to use. Exemplary techniques for adjusting or modifying masks to compensate for non-working nozzles are described in U.S. Pat. No. 6,443,556, the entire contents of which are incorporated herein by this reference.  
         [0046]     Although the foregoing has been a description and illustration of specific embodiments of the invention, various modifications and changes thereto can be made by persons skilled in the art without departing from the scope and spirit of the invention as defined by the following claims.