ELECTRONIC IMAGING APPARATUS FOR PRODUCING STATIC LIGHT IMAGES

Abstract: Electronic imaging apparatus comprising an electro-optic device (50) which, upon being electrically addressed with image information and flood illuminated, provides a static two-dimensional light image display. The apparatus of the invention comprises electronic means (60, 51, 52, 13) for forming an electrostatic charge pattern (corresponding to the light image to be displayed) on a surface of an electro-optic panel (11). A pattern of electrodes (12) connected to a reference voltage (e.g. ground) cooperates with the charge pattern to produce light-modulating electric fields in the panel which, in turn, are used to imagewise modulate the intensity of light passing through the panel. The light image produced by the apparatus lasts until the charge pattern dissipates (which can take several hours, depending on the dielectric constant of the surface which supports the charge pattern).

Description: ELECTRONIC IMAGING APPARATUS FOR PRODUCING STATIC LIGHT IMAGES The present invention relates to electronic imaging apparatus for producing a static (stationary) display of a light image. For many years there have been extensive development efforts relating to electro-optic devices of the kind that are addressable by electric field patterns to provide light-modulating image patterns. Many different kinds of devices have evolved from such efforts, e.g. panels of dipole particles in a liquid suspension or elastomeric matrix, panels of liquid crystal material, and panels of ferroelectric ceramic material. Generally, in the presence of an image field pattern, these panels exhibit a change of a light-modulating'characteristic(s) , e.g. a change in light transmission, reflectivity or birefringence. The problem of generating and maintaining the desired electric field pattern on such electro-optic panels has received a substantial portion of the development work in this area, and a number of different approaches has been described in the prior art. One general approach is to provide an x-y electrode grid across the operative area of the panel and to address picture element (pixel) portions of the panel, a line at a time, with the desired electrical field pattern. But, the light image produced by such an addressing scheme lasts only as long as the addressing fields are applied. In order to view (or project) the image for a substantial time period (e.g. longer than a few milliseconds) , it is necessary to repeatedly re-address the grid pattern with the same image information so that the light modulation effect of the panel addressed in this manner appears static to the eye. See, e.g., International Patent Publication No. WO 82/02638, published 5 August 1982. One approach for providing a truly static two-dimensional field pattern is to provide a photoconductor layer overlying the operative area of an electro-optical panel and to optically address the panel with a light image pattern under conditions creating the desired electrical field pattern. This approach requires i agewise optical addressing, and therefore it is redundant where the aim is to use the electro-optic panel to form an optical image directly from electrical signals. Also, care must be taken when viewing the image so that the photoconductor is not discharged by ambient light. In view of the foregoing, the object of this invention is to provide an electronic imaging apparatus having an electro-optic panel which, upon being electrically addressed only once with image information and flood illuminated, displays such image information for a substantial time period (e.g. several hours or more) . The electronic imaging apparatus of the invention basically comprises (a) an electro-optic panel having first and second electrically-insulative surfaces sandwiching an operative region that is adapted to imagewise modulate light in response to application of an imagewise electrical field pattern; (b) a plurality of linear reference electrodes located in a generally parallel and uniformly spaced relation on said first panel surface; (c) a plurality of l-inear signal electrodes located on said second panel surface in a generally parallel and interleaved relation with the normal projections through said panel of said reference electrodes; (d) line enable means constructed for relative movement with respect to said first panel surface in a direction generally parallel to said signal electrodes, for applying a reference potential sequentially along successive image lines, generally _ O FI perpendicular to said signal electrodes, on said first electrode surface; (e) line address means for addressing said signal electrodes in synchronization with each reference potential application of said line enable means and in accordance with image line data; (f) logic means for selectively grounding the reference and signal electrodes; and (g) illumination means for directing uniform illumination along an optical path onto said electro-optic panel. The subsequent detailed description of preferred embodiments of the invention refers to the attached drawings wherein: Figures 1 and 2 are respectively top and bottom plan views of one embodiment of electro-optic element for practice of the present invention; Figure 3 " is a cross-sectional view of the Figures 1 and 2 element; Figures 4 and 5 are perspective views illustrating structures and procedures for practicing one preferred embodiment of the present invention; Figure 6 is a schematic diagram illustrating an exemplary field pattern achieved by address of the present invention; Figure 7 is a perspective schematic view of one electronic imaging apparatus in accord with the present invention; Figure 8 is a cross-sectional view of a portion of one alternative embodiment of electro-optic element for practice of the present invention; and Figure 9 is a plan view illustrating another alternative embodiment for electro-optic elements according to the present invention. Figures 1-3 illustrate one preferred embodiment of an electro-optical element 10 useful for static, two-dimensional light modulation in accordance with the present invention. The element 10 in general OMH comprises an electro-optic panel 11 (of the kind adapted to modulate the intensity of light passing therethrough in accordance with the amplitude of an applied electric field) having predeterminedly configured electrode patterns 12 and 13 located respectively on opposing panel surfaces 14 and 15. One preferred construction for panel 11 is a PLZT (lanthanum doped lead zirconate titanate) ceramic material which, in the presence of a transverse electrical field, changes from a non-polar, isotropic state to a polar, birefringent state. Such a panel can be used, e.g. in cooperation with crossed polarizing means, to control light transmission in response to an applied electrical field. However, other electro-optic panel constructions, e.g. mentioned in the description of the prior art section above, are useful in accordance with the present invention to provide similar or different light modulation effects. It is important in accord with the present invention that the surfaces 14 and 15 have a generally dielectric, i.e. electrically insulative characteristic, to prevent the discharge of electrostatic charges created on the panel. It is highly preferred that the volume of the operative electro-optic region of the panel (between surfaces 14 and 15) also be dielectric to prevent discharge of fields created within the panel. PLZT material is a preferred panel material and exhibits these properties. Preferred panel thicknesses are of the same order of magnitude as the reference electrode spacings discussed below. As shown in Figures 1-3, the electrode pattern 12 on dielectric surface 14 comprises a plurality of linear electrodes (herein termed reference electrodes for reasons described below) located in a generally uniformly spaced, parallel relation. It should be noted at this stage that, for clarity of explanation, the number of electrodes and spacings shown in the drawings are not representative of what is normally used in actual imaging applications. That is, the panel 11 can have an actual operative area corresponding to the two-dimensional image pattern, and the number and spacing of electrodes 12 can be selected to provide the desired resolution for the image. Thus, in one useful embodiment, the spacing between electrodes 12 defines the width of a "pixel" (i.e. picture element) for the desired image resolution. Electrodes 12 of the reference electrode construction can be commonly coupled, as shown in the drawings, or be separate. Certain advantages pertain to the coupled reference electrode construction shown in Figure 1 as will be more apparent subsequently. The electrodes 13 (herein termed signal electrodes for reasons described below) are located on the opposing dielectric surface 15 generally parallel to electrodes 12 and in interleaved relation with the projections (normally through the panel thickness) of electrodes 12. Each signal electrode 13 is separately addressable and comprises a contact pad 16 for coupling to a source of activating voltage. Referring now to Figures 4 and 5, preferred constructions and procedures for providing static, two-dimensional electrical address with a light- modulating device 20, will be described. In general, device 20 includes -electro-optic element 10, line enable electrode means 21 and electrode line address means 22. As indicated schematically by the arrows in Figure 4, line enable electrode 21 is constructed to move in a direction generally parallel to signal electrodes 13 and, as it moves, to sequentially apply -6- a reference potential (here ground) to successive lines (i.e. lines of the light image to be produced) on dielectric surface 14 opposite electrodes 13. At each line stage of this movement, i.e. while reference potential is applied at a given line on surface 14, signal electrodes 13 on opposing surface 15 are all simultaneously addressed by line address means 22. That is, line address means selectively applies a voltage +V or no-voltage (ground) to each of the signal electrodes 13 in accordance with the image information pertaining to that line. These procedures cooperatively cause an induced electrostatic charge to be formed selectively on pixel portions of each line (i.e. portions of each line between electrodes 12) in accordance with the image information pertaining to that line. When each line has been so addressed, electrostatic charges reside on surface 14 in a static, two-dimensional pattern corresponding to the successive lines of image information electronically input by the repetitive activations of signal electrodes 13. It is important that the electrode 21 be adapted to inject charge onto surface 14. Thus electrode 21 should be adapted for closely spaced or contacting movement across surface 14. A highly preferred structure for electrode 21 provides a slightly resilient contact surface to enhance close spacing and or contact. Another highly preferred feature of the electrode 21 is a sharp contacting edge which enhances charge injection and maintains sharp resolution for line address. Referring to Figure 5, the next stage of the field generating procedure is to ground both the signal and reference electrodes. The transverse electric field provided to an activated pixel portion of the panel 11 by an induced electrostatic charge and surrounding grounded electrodes 12 and 13 is shown in Figure 6. A reference potential other than ground, which maintains a transverse electric field distribution within the panel such as illustrated, can also provide equivalently useful results. The function(s) of the device 20 will be further understood by consideration of its operation in the electronic imaging apparatus shown in Figure 7. In that imaging apparatus, light source 41 is located to direct uniform illumination through a twodimensional light valve array 50, which includes light-modulating device 20 positioned between crossed polarizing means 42 and 43. Lens means 46 images the pattern of light passing the light valve array 50 at image zone 47, which can be, e.g., a display surface, such as a front Or rear projection screen, or a support surface for a light-sensitive recording media. To commence an imaging operation, line enable electrode 51 (here a roller electrode making line contact with the dielectric surface 14 of element 10) is moved to sequentially apply ground potential successively to lines on surface 14 (e.g. see L-, and Lc in Figure 7). In synchronism with the movement of roller 51, control logic 60 provides pixel address information (for each line of an image to be displayed or recorded) to line address means 52, e.g. a serial- in/parallel-out shift register. The data in the shift register 52 in turn controls the selective application of signal voltage (+V) or ground (0) to signal electrodes 13 to generate induced electrostatic charge regions on surface-14 in accordance with the image data from logic 60. After roller 21 has completed its movement from line L- to L (with respective, cooperative line addresses of signal electrodes 13) , control logic activates the application of ground potential to electrodes 12 and 13. A static, two-dimensional light-modulating field pattern of pixel portions is generated in the manner illustrated in Figure 6. At this stage, illumination means 41 is activated to direct uniform light through the light valve array 50 and a static light image pattern is provided for display or recording at image station 47. Light source 41 need not be of linear geometry. For example, it can be a bright screen such as used in light table devices. Also it should be noted that light valve array 50 can be viewed directly, as well as projected for display. After the desired imaging operation is complete the charge pattern on surface 14 can be erased by moving grounded electrode 21 back across the surface. Alternatively, an A.C. or grid controlled corona dischrage device can be used to erase the field pattern. As shown in Figure 8, the element 10 could include a photoconductive insulator layer 81 overlying surface 14, and the charge at surface 14 can be erased by flood illumination of the photoconductor 81. In such embodiment care must be taken that the photoconductive layer not interfere with field penetration into the volume of the panel as shown in Figure 6. Another alternative embodiment of modulating element 90 is shown in Figure 9. In this embodiment the reference electrode configuration includes electrically conductive islands 97 intermediate linear electrodes 92. The other portions of the element 90 can be as previously described with respect to Figures 1-3. In the Figure 9 embodiment the charge islands 97 improve the efficiency of charge injection onto surface 94. Various other modifications will occur to those skilled in the art. For example, a high frequency AC voltage can be applied to line enable electrode 21 rather than ground. Similarly, the light-modulating element 10 can be moved under a stationary line enable electrode. Also a voltage +V can be applied to the line enable electrode and charge ' formed on surface 14 by addressing signal electrodes with ground potential (a no-charge address being effected by application of a +V potential to the signal electrode) .

Claims: CLAIMS : 1. Electronic imaging apparatus for producing a static, two-dimensional light image, said apparatus being characterized by: (a) an electro-optic panel (11) having first and second electrically-insulative surfaces (14, 15) sandwiching an operative region that is adapted to imagewise modulate light in response to application of an imagewise electrical field pattern; (b) a plurality of linear reference electrodes (12) located in a generally parallel and uniformly spaced relation proximate said first panel surface; (c) a plurality of linear signal electrodes (13) located proximate said second panel surface in a generally parallel and interleaved relation with the normal projections through said panel of said reference electrodes; (d) line enable means (21, 51) , constructed for relative movement with respect to said first panel surface in a direction generally parallel to said signal electrodes, for applying a reference potential sequentially along successive image lines, generally perpendicular to said signal electrodes, on said first electrode surface; (e) line address means (22, 60) for addressing said signal electrodes in synchronization with each reference potential application of said line enable means and in accordance with image line data; (f) logic means (60) for selectively grounding said reference and signal electrodes; and (g) illumination means (41) for directing uniform illumination along an optical path onto said electro-optic panel. 2. The apparatus defined in Claim 1 characterized in that said panel is formed of PLZT ceramic material, and in that first and second, crossed, polarizing means are positioned on opposite sides of said panel along said optical path. 3. The apparatus defined in Claim 1 characterized in that said line enable means is constructed for movement with a portion thereof in closely spaced or contacting relation with said first panel surface. 4. The apparatus defined in Claim 1 characterized in that said contacting portion of said line enable means is resilient and electrically conductive.

Inventors: MIR JOSE MANUEL, MIR, JOSE, MANUEL
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1983
Main classification: H04N5
IPC codes: G02F1, G09G3