Abstract:
A camera having an electronic flash unit which provides a source of high voltage and having a display for displaying an image, which includes the display including material which is effective in a first condition in response to a selectively applied high voltage for changing the state of the material to display the image and to be effective in a second condition for preventing the display of an image, the material being selected so as after displaying an image to continue to display the image after the removal of applied voltages; and circuitry for coupling and selectively applying the high voltage source in the flash unit to the display for changing the state of the material in the display to produce the image.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned U.S. patent application Ser. No. 08/990,853 filed Dec. 15, 1997, entitled “A Sheet Having Patternable Conductive Traces for Use in a Display” by Stanley W. Stephenson; U.S. patent application Ser. No. 09/027,321 filed Feb. 20, 1998, entitled “Selectively Presenting Viewable and Conductive Images” by Stanley W. Stephenson and U.S. patent application Ser. No. 09/045,016 filed Mar. 20, 1998, entitled “Display Having Viewable and Conductive Images” by Stanley W. Stephenson, the disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to cameras having displays. 
     BACKGROUND OF THE INVENTION 
     Current silver halide film cameras have displays for indicating settings and status conditions, such as frame number, of the camera. Often, the display uses twisted nematic liquid crystals that that requires continuous electrical drive to display information. Cameras with this type of display can be turned on only for short periods of time to preserve battery life. When the cameras are turned off, the liquid crystal display goes blank. An operator must turn on the camera to determine the status of the camera. These cameras typically incorporate a high voltage power supply to drive an electronic flash built into the camera. 
     Many digital cameras use liquid crystal displays to display a captured image. Displays in these cameras are also nematic liquid crystals displays that can drain an electronic camera power supply in a short period of time. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a display in a camera that displays data, even when the power to the display is removed. 
     This object is achieved in a camera having an electronic flash unit which provides a source of high voltage and having a display for displaying an image, comprising: 
     (a) the display including material which is effective in a first condition in response to a selectively applied high voltage for changing the state of the material to display the image and to be effective in a second condition for preventing the display of an image, the material being selected so as after displaying an image to continue to display the image after the removal of applied voltages; and 
     (b) means for coupling and selectively applying the high voltage source in the flash unit to the display for changing the state of the material in the display to produce the image. 
     An advantage of the present invention is that it permits the use of displays which require a high voltage source to display images. 
     A feature of the present invention is that the high voltage supply in the electronic flash unit can be used as a source of power for the display. 
     It is a feature of the present invention it permits display of images when power to the display is turned off. 
     It is a further feature of the present invention to provide an arrangement which reduces the consumption of power required by a camera display. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top sectional view of a silver halide camera with a memory display in accordance with the present invention; 
     FIG. 2 is a top sectional view of an electronic capture camera with a memory display in accordance with the present invention; 
     FIG. 3 is a side sectional view of the memory display of FIG. 1; 
     FIG. 4 is a top view of the memory display of FIG. 3; 
     FIG. 5 shows an electrical circuit which drives the display of FIG. 3 by selectively coupling the flash unit high voltage supply to the display; 
     FIG. 6A is a partial top view of the memory display of the electronic capture camera of FIG. 2; 
     FIG. 6B is a magnified view of the memory display of FIG. 6A; 
     FIG. 7 is an electrical schematic circuit which drives the memory display of FIGS. 6A and 6B; 
     FIG. 8A is a waveform to drives a memory material to a reflecting, or bright state; 
     FIG. 8B is a waveform to drives a memory material to a transmitting, or dark state; and 
     FIG. 8C is a waveform to drive a memory material to an intermediate state between transmission and reflection. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A top sectional view of a silver halide film camera  10  is shown in FIG. 1. A film cassette  20  in camera  10  holds a strip of film  22  that captures images from optic  26 . Film  22  is sequentially taken up onto take-up spool  24  to capture a set of images. After image exposure is complete, film  22  is returned to film cassette  20 . Camera controller  30  receives commands from an operator and controls the sequential motion of film  22  and optic  26 . Camera controller  30  can provide supplemental illumination to a scene by discharging a high energy pulse through flash tube  42 . Flash tube  42  requires a flash capacitor  40  to store energy for flash tube  42 . Flash capacitor  40  typically stores energy in a capacitor having over 50 micro-farads capacitance at over 100 volts. 
     The status of camera  10  is shown on a display  35  in camera  10 . Typically, display  35  shows the number of the current frame of film, the operational mode of flash tube  42 , and operating parameters of optic  26 . In more complex cameras, display  35  is a conventional nematic liquid crystal display. Nematic liquid crystal fluids act in conjunction with polarizing filters to act as a shutter to reflect or transmit light. Transmitted light is selectively reflected from a surface behind the display to provide light indicia. The reflected light provides a white indicia. When light is blocked by the polarizing filters, the imager area is dark. Nematic liquid crystals must have a continuous electrical field across the display to display information. 
     FIG. 2 is a top sectional view of an electronic camera  12 . Many of the components operate as in conventional camera  10 . Film  22  is replaced by electronic sensor  50 . Electronic sensor  50  captures a scene and camera controller  30  stores a captured image in memory  52 . Display  35  in electronic camera  12  displays the status of electronic camera  12 , and in certain cases displays images from memory  52 . A flash tube  42  is often provided in electronic camera  12  to supply additional light to a scene at the time of image capture. Flash tube  42  requires a flash capacitor  40  to store energy for flash tube  42 . Flash capacitor  40  typically stores energy in a capacitor having over  50  micro-farads capacitance at over 100 volts. 
     FIG. 3 is a diagram of display  35  in accordance with the present invention. Memory material  60  is disposed between a transparent top conductor  62  and a bottom conductor  64 . Bottom conductor  64  can be a transparent electrical conductor such as Indium-Tin-Oxide or a light absorbing conductor formed by an oxide of a metal such as platinum or nickel. Memory material  60  can be a chiral doped nematic liquid crystal such as those disclosed in U.S. Pat. No. 5,695,682. Applied fields of various intensity and duration change the state of chiral doped nematic materials from a reflective to a transmissive state. These materials have the advantage of maintaining a given state indefinitely after the field is removed. Ambient light striking memory material can be reflected light  70 , providing a “light” image or can become absorbed light  72  which provides a “dark” image. 
     In one experiment, two glass plates were coated with transparent Indium-Tin-Oxide (ITO) to form transparent top conductor  62  and bottom conductor  64 . A laser beam was used to pattern the ITO coatings and 4 micron spacer beads were applied to one of the plates. The two plates were bonded together, with the spacer beads providing a 4 micron gap between the two plates. Black paint was applied to the back of the display over bottom conductor  64  to absorb light passing through memory material  60 . The gap between the plates was filled with E. M. Industries (Hawthorne, New York) chiral nematic fluid BL126 to act as memory material  60 . A 3 millisecond pulse at 100 volts across areas on transparent top conductor  62  and bottom conductor  64  would convert the BL126 memory material  60  to a reflective “bright” areas. A 3 millisecond pulse at 40 volts would clear memory material  60  so that incident light was absorbed by the black paint and create “dark” areas. Such a display can be used to display camera status on display  35  for either conventional camera  10  or electronic camera  12 . 
     FIG. 4 shows such display  35  having memory material  60 . A reflecting segment  80  has had a 100 volt pulse applied to memory material  60 . A transparent segment  82  has received a 40 volt pulse. Transparent segment  82  passes incident light to a light absorbing surface to create a dark The individual segments retain a given state indefinitely after being pulsed. A camera can be shut off and continue to have an operating display. 
     FIG. 5 is a schematic for driving display  35  in conventional camera  10 . Flash capacitor  40  is used as a source of high voltage for pulsing display  35 . Flash capacitor  40  stores power at well over 100 volts. Voltage regulator  90  converts a voltage from flash capacitor  40  to either a high or low voltage. In one case, voltage regulator  90  is resistor network that changes 330 volts on flash capacitor  40  to either 100 or 40 volts in response to high-low voltage select line  92  which is used by camera controller  30  to select a pulse voltage for display  35 . Using the pre-existing high voltage on flash capacitor  40  eliminates the need for an additional high voltage generating system in conventional camera  10 . 
     Camera controller  30  uses high-low voltage select line  92  to changes the voltage applied to display  35 . Display  35  contains chiral nematic liquid crystal memory material  60  to hold either a reflective or transmissive state for each segment of display  35 . FIG. 8A show the voltage forms applied by camera controller  30  to a segment of display  35  to write the segment into the reflective mode. Camera controller  30  sets voltage regulator  90  to a low voltage and pulses all segment switches  94  to clear all the segments with low voltage pulse P L . Voltage regulator  90  is then set to a high voltage, and selected ones of segment drivers  94  are pulsed with a high voltage pulse P H  to convert those segments to the reflective mode. FIG. 8B is waveform across a segment that has been kept in the transmissive mode. Because P H  was not applied across that segment, the segment remains in a transmissive, dark state from P L . After the write pulses P L  and P H  are applied, display  35  will continue to display status information indefinitely without the use of additional power. Conventional camera  10  can be de-energized and display  35  will continue to display information such as the number of images left on film  22 . 
     FIG. 6A is a partial top view and FIG. 6B is a magnified view of display  35  in electronic capture camera  12 . A substrate supports a plurality of transparent row traces  100 . A second set of transparent traces form column traces  105 . A memory material  60  is disposed between row traces  100  and column traces  105 . Memory material  60  is a chiral nematic material that can be written into either a reflective or transmissive state. Chiral nematic materials can be tuned to red green and blue wavelengths of reflection and three color planes can be stacked to create a full color display. 
     FIG. 7 is a schematic for driving display  35  in electronic camera  12 . Flash capacitor  40  is used as a source of high voltage for pulses to display  35 . Flash capacitor  40  stores power at well over 100 volts. Voltage regulator  90  converts a voltage from flash capacitor  40  to either a high or low voltage. In one case, voltage regulator  90  is resistor network that changes 330 volts on flash capacitor  40  to either 100 or 40 volts in response to high-low voltage select line  92 . Using the pre-existing high voltage on flash capacitor  40  eliminates the need for a high voltage generating system in electronic camera  12 . 
     FIG. 8C is the drive signals applied across a single color plane of display  35  when used as to display a color, gray scale image stored in memory  52  using the electrical drive of FIG.  7 . Camera controller  30  selects a first column using column selector  120 . Camera controller  30  sets voltage regulator  90  to a low voltage, and row drivers  15  write a first clearing pulse P L  to all pixels in the row. Camera controller  30  then sets voltage regulator  90  to a high voltage. Row drivers  115  are energized for various gray level times tg. A chiral nematic material changes state from the transmissive to the reflective state progressively over time. By selecting an appropriate drive time tg for each pixel, a column of pixels can be written to various degrees of reflection, creating a column of pixels written to various gray levels. Camera controller  30  uses to column selector  120  to select the next column of pixels for writing. The process is repeated for each column, and each color plane to create a full-color, gray scale image on display  35 . Other driving schemes can be used such as one proposed by Hashimoto et al, “Reflective Color Display Using Cholesteric Liquid Crystals”, SID 98 Digest, Article 31.1, 1998, pp. 897-900. 
     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 
       10  conventional camera 
       12  electronic camera 
       20  film cassette 
       22  film 
       24  take-up spool 
       26  optic 
       30  camera controller 
       35  display 
       40  flash capacitor 
       42  flash tube 
       50  sensor 
       52  memory 
       60  memory material 
       62  transparent top conductor 
       64  bottom conductor 
       70  reflected light 
       72  absorbed light 
       80  reflecting segment 
       82  transmitting segment 
       90  voltage regulator 
       92  high-low voltage select 
       94  segment switch 
       100  row traces 
       105  column traces 
       110  pixel 
       115  row drivers 
       120  column selector