Patent Publication Number: US-6217168-B1

Title: Transparency detection in a tray

Description:
BACKGROUND OF THE INVENTION 
     The disclosed invention generally relates to hardcopy printing systems, and more particularly to a printing system that optically detects transparency print media. 
     Printing devices such as ink jet printers apply a printing composition (e.g., ink or toner) to print media in controlled patterns to print text, graphics, images, etc. The print media may be of a variety of different types such as paper, transparency films, special purpose coated paper, fabric, etc. Different types of print media have various characteristics that are ideally accounted for during printing by selection of appropriate printing attributes. Otherwise, a less than optimal printed output may occur, which could be time consuming, costly, and wasteful if print jobs need to be repeated. 
     One way in which a printing device can be configured to a particular type of print medium is to have a user make adjustments to the printing device based upon the particular print medium. A consideration with this approach is that it requires user intervention, which may be undesirable. Further considerations with this approach are that a user might incorrectly configure the printing device, or a user might not configure the printing device. 
     One type of print medium that is more costly than standard paper and requires different printing attributes is transparency film. There is accordingly a need for detection of the presence of transparency film in an input tray of a printer. 
     SUMMARY OF THE INVENTION 
     The disclosed invention provides a printing system that includes a transparency film detector having a light source for illuminating a sheet of input media and a detector for detecting whether a portion of the light provided by the light source propagated by internal reflection within the volume of the illuminated media sheet is detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The advantages and features of the disclosed invention will readily be appreciated by persons skilled in the art from the following detailed description when read in conjunction with the drawing wherein: 
     FIG. 1 is a perspective view of an ink jet print printing device incorporating a transparency film detector in accordance with the present invention. 
     FIG. 2 is a perspective view of a transparency film detector in accordance with the invention. 
     FIG. 3 is a cross-sectional view of the transparency film detector of FIG.  2 . 
     FIG. 4 is a ray diagram illustrating the operation of the transparency film detector of the invention. 
     FIG. 5 is a simplified block diagram of a printer controller for controlling the ink jet printing device of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     In the following detailed description and in the several figures of the drawing, like elements are identified with like reference numerals. 
     FIG. 1 sets forth a schematic perspective view of an example of a printing device  10  in which the disclosed invention can be employed. By way of illustrative example, the printing device  10  comprises an ink jet printing device that includes ink jet printheads for applying marks on print media, and in accordance with the invention includes a transparency film detector that detects the presence of a transparency film by sensing whether source illumination propagates internally in a top sheet of print media disposed in a print tray of the printing device. More particularly, the transparency film detector detects whether source illumination provided to the top print media sheet propagates within the illuminated sheet and exits an edge of the print media sheet. If so, the top print media sheet is considered to be a transparency film, and the printing device is configured to use printing attributes appropriate for transparency film. 
     The ink jet printing device  10  of FIG. 1 more particularly includes a frame or chassis  22  surrounded by a housing, casing or enclosure  24 , commonly made of a plastic material. Individual sheets of print media “picked” from a stack  27  of sheets of print media are individually fed through a print zone  25  by a media handling system  26 . The print media may be any type of suitable sheet material such as paper, card-stock, transparencies, coated paper, fabric, and the like. 
     The media handling system includes an input media supply feed tray  28  for storing the stack  27  of sheets of print media before printing. A print media drive roller assembly  154  formed of a plurality of laterally spaced drive wheels or tires  30  co-axially mounted on a common axle  31  and conventionally driven by a stepper motor and drive gear assembly (not shown) may be used to move the print media from the feed tray  28 , through the print zone  25 , and, after printing, onto a pair of extended output drying wing members  38 , shown in a retracted or rest position in FIG.  1 . The wing members  38  hold the newly printed sheet for a short time above any previously printed sheets still drying in an output tray  32 , and then retract to the sides to drop the newly printed sheet into the output tray  32 . The media handling system  26  may include a series of adjustment mechanisms for accommodating different sizes of print media, including letter, legal, A-4, envelopes, etc., such as a sliding length adjustment lever  34  and a sliding width adjustment lever  36 . 
     A carriage slider or guide rod  44  is supported by the chassis  22  to slidably support an off-axis ink jet print carriage system  45  for back and forth, or reciprocating, motion across the print zone  25  along a carriage axis  46  which is substantially parallel to the X-axis of an XYZ coordinate system shown in FIG. 1. A carriage scan axis drive motor  112  drives an endless belt  49  that is secured in a conventional manner to the print carriage  45 , and a linear encoder strip  73  is utilized to detect position of the print carriage system  45  along the carriage scan axis, for example in accordance with conventional techniques. 
     In the print zone  25 , a media sheet receives ink from an ink jet cartridge, such as a black ink cartridge  50  and three single color ink cartridges  52 ,  54  and  56  which include respective printheads that selectively eject ink drops to form an image on the media sheet in the print zone  25 . By way of illustrative example, the print zone  25  is below the cartridges  50 ,  52 ,  54  and  56 , and the printheads eject ink drops downwardly. Ink jet cartridges  50 ,  52 ,  54 , and  56  are also commonly called “pens” by those in the art. In accordance with what is known as an “off-axis” ink delivery system, each of the pens  50 ,  52 ,  54  and  56  includes a small on-board reservoir for storing ink that is received from a replaceable main ink reservoir located separately from the pen. In the illustrated printer  10 , ink of each color for each printhead is delivered via a conduit or tubing system  58  from a group of replaceable stationary ink reservoirs  60 ,  62 ,  64  and  66  to the on-board reservoirs of respective pens  50 ,  52 ,  54  and  56 . 
     While the printhead cartridges  50 ,  52 ,  54 , and  56  are disclosed as printhead cartridges that receive ink from respective remote ink reservoirs  60 ,  62 ,  64  and  66 , it should be appreciated that the printhead cartridges can comprise self-contained printhead cartridges that have on-board ink reservoirs that are not coupled to remote ink reservoirs. 
     Each of the printheads of the pens  50 ,  52 ,  54  and  56  includes an orifice or nozzle plate having a plurality of ink ejecting nozzles formed therein in a manner well know to those skilled in the art. By way of illustrative example, the printheads of the pens  50 ,  52 ,  54  and  56  comprise thermal ink jet printheads. Other types of printheads may also be used, such as piezoelectric printheads. 
     As more particularly shown in FIG. 2, The printing device  10  of FIG. 1 includes a transparency film detector  20  that spans an edge portion of a top sheet  29  of the media stack  27  and detects whether the top media sheet  29  is a transparency film by sensing whether source illumination propagates by internal reflection in the volume of the top sheet  29 . 
     Referring now to FIGS. 3 and 4, the transparency film detector  20  more particularly includes a light source  111  that illuminates the top media sheet  29  with an incident beam IB, and an optical detector  113  for intercepting light that exits an edge of the top media sheet  29 . The light source  111  is located in a baffle recess  115  in a horizontal portion  111   a  of a housing  111 , while the optical detector  113  is in a vertical portion  111   b  of the housing  111  that is outboard of the media stack and adjacent the edge of the top media sheet  29  that is spanned by the transparency film detector. The baffle recess  115  extends to an opening in a bottom surface of the horizontal housing portion  111   a . The bottom surface of the horizontal housing portion  111   a  rests on the top surface  29   a  of the top sheet  29  of the media stack  27 , whereby light from the light source is incident on the top surface  29   a  of the top sheet  29 . The baffle recess  115  reduces the amount of light source illumination that would otherwise reach the optical detector by reflection at the top surface  29   a  of the top media sheet  29 . 
     The housing  111  is fixedly attached to one end of a pivot arm  117  (FIG. 2) that is pivotally attached to one side of the input media slot or tray for pivotal rotation about a pivot axis PA that is substantially parallel to the carriage scan axis and is elevationally located such that pivot arm  117  extends downwardly to allow for insertion of media into the media tray  28 . The input media tray  28  can include a pressure plate  28   a  that selectively upwardly biases the media stack  27  so that the top sheet  29  of the media stack  27  is at substantially a predetermined elevation for picking, and the housing  111  and the pivot arm  117  are configured so that the bottom surface of the horizontal portion  111   a  of the housing  111  lies generally flat against the top sheet  29  of the media stack  27  when the media stack is upwardly biased for picking. 
     As shown in FIG. 4, the light source  111  is more particularly configured to illuminate the top surface  29   a  of a top sheet  29  of the print media stored in the media input tray  28  with a substantially collimated or partially collimated incident beam IB at an incidence angle A selected such that if the top print media sheet  29  is a transparency film, a portion of the incident beam would enter the transparency film, propagate by internal reflection within the transparency film, and exit the edge adjacent the detector  113 . In other words, the beam angle is selected so that if the top print media sheet  29  is a transparency film, a portion of the incident beam IB is refracted as it passes into the volume of the transparency film and propagates within the volume of the transparency film by a series of internal reflections at the top and bottom surfaces of the transparency film. It is well understood that at appropriate beam angles reflection occurs at the boundary or interface between materials of different indices of refraction, which in this case comprise the interface between the top surface of the transparency film and air, and the interface between the bottom surface of the transparency film and air. 
     Thus, if a portion of the incident light enters the top media sheet  29 , travels in the volume of the top media sheet to the edge thereof, and exits such edge, then the top media will be regarded as a transparency film. Such propagation by internal reflection would not occur a sheet of media that is not film transparency (e.g., paper or cloth). 
     The light source  111  and the optical detector  113  are oriented such that intersection of the edge of the top media sheet  29  adjacent the detector  113  and the plane of incidence (which contains the centerline of the incident beam and the normal  211  to the top surface  29   a  at the point of incidence, and which is also the plane of FIG. 4) is within the viewing angle of the detector  113 . 
     By way of illustrative example, the light source  111  comprises a light emitting diode (LED) or a laser diode, and the angle of incidence A is optimized for example for the peak wavelength of the LED or laser diode. In other words, the angle of incidence A is selected to optimize the amount of light of the peak wavelength that passes into the volume of a transparency film and propagates or travels therein by internal reflection. Also by way of illustrative example, the detector  113  comprises a photo-transistor. 
     Referring now to FIG. 5, set forth therein is a simplified block diagram of a control system for controlling the ink jet printer of FIG. 1 in which the techniques of the invention can be implemented. The control system includes an interface  51  which receives print data from a host computer, for example, and stores the print data in a buffer memory  53 . A microprocessor controller  55  is configured to process the print data to produce raster data that is stored in a bit-map raster memory  57   a  contained in a random access memory (RAM)  57  provided for the use of the microprocessor controller  55 . A read-only memory  59  is also provided as appropriate for the use of the microprocessor controller  55 . 
     A print controller  61  transfers portions of the raster data from the bit-map raster memory  57   a  to a swath memory  63  and provides swath data to a printhead driver controller  43  which controls printhead drivers  67  that drive the ink firing elements of printhead cartridges  50 ,  52 ,  54  and  56  that are implemented as single color printhead cartridges and/or as multi-compartment cartridges. The printhead cartridges  50 ,  52 ,  54  and  56  include respective printheads  70 ,  72 ,  74  and  76  which in turn include respective nozzle arrays  80 ,  82 ,  84  and  86  that emit a single color or multiple colors, wherein for example a nozzle array the emits multiple colors is arranged in subarrays that emit ink drops of respective colors. 
     The printhead cartridges  50 ,  52 ,  54  and  56  also include memory elements  90 ,  92 ,  94  and  96 , for example resistor patterns, each of which contains information about the cartridge such as type, as well as a unique identifier. When a cartridge is installed, the control system reads the information stored in the associated memory element, for example to ensure that the cartridge is of the appropriate type for the particular printer. The control system can also determine whether the newly installed cartridge is a cartridge that had been removed subsequent to an earlier installation. 
     The print controller  61  further controls a media axis drive motor  152  which moves the print drive roller assembly  154  (FIG. 1) pursuant to media motion commands from the print controller  61 . The media position encoder  156  provides information for the feedback control of the media axis drive motor  152 . Similarly, the carriage axis encoder  73  provides feedback information for the feedback control of the carriage scan axis drive motor  112  which positions the print carriage  45  (FIG. 1) pursuant to carriage motion commands from the print controller  61 . 
     The microprocessor controller further controls the light source  111 , and receives the output an analog-to-digital converter  119  that provides a digital version of the analog output of the optical detector  113 . In response to the output of the optical detector  113 , the printer employs the printing attributes appropriate for printing on transparency film if transparency film is detected. 
     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.