Abstract:
A contact printer including a liquid crystal display (LCD) for presenting an image for printing; a supply adapted to contain at least one sheet of photosensitive media; and a structure for pressing the photosensitive media sheet from the supply against the LCD. The printer further includes electronics for driving the LCD for causing an image to be presented against a pressed photosensitive sheet for contact printing of such image.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention is related to commonly assigned U.S. patent application Ser. No. 08/824,694 (75543) filed Apr. 8, 1997, entitled “Printing Variable Density Pixels” to Stanley W. Stephenson. The disclosure of this related application is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to the printing of images produced from Liquid Crystal Displays (LCDs). More specifically, the present invention relates to contact printing using Liquid Crystal Displays. 
     BACKGROUND OF THE INVENTION 
     It is known to print on light sensitive media using a liquid crystal display as a shutter. Typically, the image bearing surface of a LCD is optically focused onto a sheet bearing a light sensitive emulsion. A source of light is provided behind the LCD to illuminate an image on the surface of the LCD. When color images are being produced, the media supports three types of color-sensitive chemistries that form the color image. It is further known to use a display to create color images using a monochrome LCD and various colors of light. The monochrome LCD is sequentially loaded with separated color planes of a source image, and the corresponding light is used to illuminate a color printing media 
     U.S. Pat. No. 4,811,089 discloses the use of a linear electrostatic head or ink jet head to write separate color records to an electrostatic mask. Red, green and blue light sources are then used to illuminate each mask to expose color-sensitive media. 
     U.S. Pat. No. 4,935,820 uses a white light source to illuminate a LCD. The LCD carries color separate information, and a dichroic mirror is used to provide the appropriate light color for each separation. Because the dichroic mirror absorbs the other two unused portions of the white light, the system is energy inefficient. This patent, &#39;820, is used to expose media with very low light sensitivity, which is stated as “. . . in the range of 103 ergs/c 2  to 107 ergs/cm 2 .” Such a media requires a very high output light source such as “. . . a 220 watt Tin Halide Arc Lamp type SN 220 manufactured by Phillips.” In addition, the LCD must also se high-efficiency liquid crystals, specifically called out as a smectic liquid crystal. 
     U.S. Pat. No. 5,337,068 discloses the use of a monochrome LCD, and a multiple sets of red, green and blue lamps to create color images on the monochrome display. Separate color information is written to multiple areas simultaneously at a rapid rate to project all three colors through common pixels. Appropriate lamps are activated simultaneously in separate areas as data are written to each area. Multiple lamps are required for each color of the separate areas and multiple lamps are energized simultaneously during display. An optic is needed to focus an image onto the light-sensitive media 
     It is known to focus emitted light from the image display onto the light sensitive sheet. Such optics are expensive, and require space for operation of the optical element. It would be advantageous to eliminate the need for an optical element between the display and the light receiving media. It would be useful to create a small, inexpensive printer to print images. Such a printer could be battery powered and portable. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to create a highly efficient, high effective and compact printer of digital images. It is a further object of the present invention to produce a printer which is portable. 
     These objects are achieved by a contact printer comprising: 
     a) a liquid crystal display (LCD) for presenting an image for printing; 
     b) supply means adapted to contain at least one sheet of photosensitive media; 
     c) means for pressing the photosensitive media sheet from the supply against the LCD; and 
     d) means for driving the LCD for causing an image to be presented against a pressed photosensitive sheet for contact printing of such image. 
     ADVANTAGES 
     A feature of this invention is that costly optic elements are eliminated and the volume of the printer is reduced. Another feature of this invention is that the printer can be made compact and thus portable. The printer uses a display having a structure that permits direct printing onto a light sensitive media. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top sectional view of a printer in accordance with the present invention; 
     FIG. 2 is an electrical schematic of the printer of FIG. 1 in accordance with the present invention; 
     FIG. 3 is a front sectional view showing portions of the printer in FIG. 1; and 
     FIG. 4 is a flow chart of the operation of the printer in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is directed to a compact printer used in conjunction with electronic cameras. Such a printer must be small, light and energy efficient to provide portability. Turning now to FIG. 1, a top sectional view of the printer  12  is shown. The operation of printer  12  is controlled by printer electronics  16 . Printer link  28  provides for communication to other apparatus, such as an electronic camera that stores digital images. Printer link  28  can be a two-connection serial port, an infrared sensor or other standard communication interfaces. An image is received, processed and printed by printer electronics  16 . 
     FIG. 2 is an electrical schematic of part of printer electronics  16  and shows the transfer of an image from a data stream to a print. Data is received by data receiver  54 , and is operated on by processor  52 . Processor  52  stores a received image in memory,  50 . Processor  52  transmits the image in memory  50  through display driver  56  to LCD  18 . The LCD  18  is driven to present an image to be presented against a pressed photosensitive sheet for contact printing of such image. 
     LCD  18  is a monochrome display such as Sharp Corp. model LM64P101. Display  18  has 640 horizontal square pixels in 480 vertical lines on 0.23 millimeter spacing to form a display having a 7.43 inch diagonal. This LCD display is currently used to display black and white data. In the present invention, data are loaded in parallel units of 8 bits that represent on and off conditions for each pixel. The display is written in 38,400 8 bit words in 11.7 milliseconds. Data can be written to the display by a method set forth in above identified co-pending U.S. patent application Ser. No. 08/824,694. Data for a given color plane are written 256 times, each time representing an increased exposure time. At the end of the 256 times, a continuous tone color plane will be written from the source image data. 
     During the writing process, LCD display  18  is sequentially illuminated by one of three separate lamps; red fluorescent lamp  20 , green fluorescent lamp  22  and blue fluorescent lamp  24  which are disposed around integrating bar  26 . The fluorescent lamps are individually and sequentially actuated by processor  52  for each color plane. One integrating bar  26  can be used for all three lamps  20 ,  22 , and  24  if the lamps are disposed around three of the sides of integrating bar  26  as shown in FIG.  3 . Each lamp is oriented to emit a specific color of light into integrating bar  26 . 
     Fluorescent lamps  20 ,  22  and  24  are conventional fluorescent lamps using an ultra-violet (254 nm) glow discharge from an excited mercury vapor. Phosphor coatings on the inside of the lamps support phosphors that emit in one of the three primary colors red, green and blue. Lamp  20  emits red fluorescent light and can be Harison lamp HMB4-150B, doped with the “R” phosphor. Such a lamp is 4.1 mm in diameter, 150 mm long and emits 8000 candela/m 2 . Lamp  22  has the same part number and dimensions but is coated with “G” phosphors to emit green light. Similarly, lamp  24  is the same mechanical package and part number, but coated with the “B” phosphor to emit blue light. 
     Using phosphors dedicated to a single color in each lamp permits the energy delivered to a lamp to be concentrated on the emission of a single color required for a given printed color plane of the image. Using multiple lamps for each color as in U.S. Pat. No. 5,337,068 requires many more lamps, and more energy will be used than using a unitary lamp for each color. If one or more white light lamps are used, ⅔ of the energy is wasted by filtering out the other two colors. Energizing three separate lamps at separate times for each of three separate color planes reduces power requirements and provides sufficient illumination to permit the development of a portable, battery powered printer. The processor  52  drives the LCD  18  and sequentially controls the colored light sources for causing three separate color images to be presented against a pressed photosensitive sheet  42  for contact printing of such image. 
     FIG. 4 is a flow chart of the process that is used to create a print according to the present invention. In step one,  60 , processor  52  turns on red fluorescent lamp  20 . In step two,  62 , processor  52  writes red image data to liquid crystal display  18  from memory  50 . In step three,  64 , processor switches illumination power to green fluorescent lamp  22 . In step four,  66 , processor loads green data into liquid crystal display  18  from memory  50 . In step  5 ,  68 , processor  52  switches illumination power to blue fluorescent lamp  24 . In step six,  70 , processor  52  writes blue image data to liquid crystal display  18 . The sequential illumination for specific colors reduces peak power demand on the printer. Processor  52  writes the color plane associated with the illuminant color to liquid crystal display  18 . 
     Printer  12  is provided with a supply structure  39  which contains a stack of photosensitive media sheets  38  to receive the image illuminated on LCD display  18 . These sheets are light sensitive and are loaded into the camera and stored in light sensitive manner as is known in the art. Springs  39   a  continuously urge the supply and hence the stack of photosensitive sheets to move such that the top photosensitive sheet  42  of the media sheet stack  38  is pressed against the LCD. Photosensitive sheets can be found in current art as instant silver halide sheets or pressure sensitive microencapsulated crushable color particles such as disclosed in U.S. Pat. Nos. 4,768,050; 5,049,902; and 5,122,432. Alternatively, images can be stored on photographic film and then stored and chemically processed at a later time. 
     In an experiment, light sensitive instant media, specifically Polaroid 600 media was pressed directly to liquid crystal display  18  and an exposure made to determine the resolution of LCD  18  without an optic. The resulting image was well focused, with a minimum of blurring between adjacent pixels. This is due to the fact that the Sharp Corp. LM64P101 display is a common twisted-nematic (TN) design. Polarizers on either side of the liquid crystals are used to permit light of a given polarity to pass through LCD  18 . Liquid crystals within the display are electrically directed to vary the polarity of light passing through the liquid crystal material. When the crystals are in a first state, light passes through the display in an alternative state, light is blocked. Modulating light at each pixel varies the intensity of each pixel. 
     Such displays generate highly collimated beams of light from each pixel of light emitted by LCD  18 . The glass substrate to the front of the display is relatively thin, so that the surface of the front of the display is relatively well focused. Using a display with relatively large pixels, such as the 0.23 mm pixels on the Sharp display permits the elimination of a focusing optic. The image does have some light bleed between adjacent pixels. This is not a problem if the display has a significantly greater resolution than the image being printed. For instance the 640 by 480 pixel resolution of the display is more than suitable for lower resolution images such as a 320 by 240 pixel image. As a general rule, pixel size, pixel count, degree of light collimation, and the front cover thickness of LCD  18  can be selected to permit contact printing from the display using lower-resolution images. 
     After the exposure process, exposed photosensitive sheet  42  is urged by picker  32  using picker drive  34  into processing rollers  40  under the control of printer electronics  16 . Processing rollers  40  are driven by roller drive  36  under control of printer electronics  16  and receive urged photosensitive sheet  42 . Processing rollers  40  or other means are used to apply pressure to photosensitive sheet  42  to process and stabilize the latent image on the surface of photosensitive sheet  42 . 
     In the case of silver halide imaging, a pod of chemicals at the beginning of photosensitive sheet  42  is burst by processing rollers  40 . The chemicals are spread across the image of photosensitive sheet  42  as photosensitive sheet  42  passes through processing rollers  40 . Said chemicals operate on the latent image to create a permanent colored dye image on photosensitive sheet  42 . In the case of crushable media, the rollers apply pressure to micro-beads containing the latent image. Burst micro-beads release dye chemistries onto photosensitive sheet  42  to create a permanent color image. 
     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 
       12  printer 
       16  printer electronics 
       18  LCD display 
       20  red fluorescent lamp 
       22  green fluorescent lamp 
       24  blue fluorescent lamp 
       26  integrating bar 
       28  printer link 
       32  picker 
       34  picker drive 
       36  roller drive 
       38  stack of media sheets 
       39  supply structure 
       39   a  springs 
       40  processing rollers 
       42  photosensitive sheet 
       50  memory 
       52  processor 
       54  data receiver 
       56  display driver 
       60  step one 
       62  step two 
       64  step three 
       66  step four 
       68  step five 
       70  step six