WO1987003708A1

WO1987003708A1 - Multicolor electrophotographic reproduction apparatus and method for producing color accented copies

Info

Publication number: WO1987003708A1
Application number: PCT/US1986/002674
Authority: WO
Inventors: Michael Mosehauer; Jerome G. Spitzner (Deceased); Michael David Stoudt; Eric K. Zeise
Original assignee: Eastman Kodak Company
Priority date: 1985-12-16
Filing date: 1986-12-15
Publication date: 1987-06-18
Also published as: JPS62502920A; EP0250556A1; EP0250556B1; JPH0670725B2

Abstract

A multicolor electrophotographic reproduction apparatus and method for reproducing a copy in selected colors. The apparatus includes a digitizer for inputting information denoting the location(s) of the pictorial information and the location(s) for which selected coloration is desired. The respective colors desired for reproduction of the information may be chosen from a menu of twenty-five or more colors stored in memory. In addition to an exposure source for reproducing an image of the original upon a photoconductor the apparatus also includes an illumination source for selective erase and a second illumination source which illuminates the photoconductor through a halftone screen to control the charge level on areas of a color separation image frame in accordance with the color selected to thereby effect the color which a reproduction will have.

Description

MU TICOLOR ELECTROPHOTOGRAPHIC REPRODUCTION APPARATUS AND METHOD FOR PRODUCING COLOR ACCENTED COPIES BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to multicolor electrophotographic reproduction apparatus and methods and. more specifically, to the improved production of copy in selected colors. Brief Description of the Prior Art In U.S. Patent 4.045,218 an apparatus is described for producing color accented reproductions from originals of a single color. In^' this method, an original such as a letter is placed at a copier's exposure station and an indicator member adjusted to identify which lines are to be reproduced in which colors. For example, the first ten lines of an original black-on-white letter may be desired to be reproduced in say red and the remainder.of the letter to be reproduced in its original color black. In this example the patent discloses that the entire original may be exposed onto a primary charged photoconductor to produce a latent electrostatic image thereof and the portion to be reproduced in black is erased by an electroluminescent panel. The remaining image is then developed with red toner. The original is then again exposed onto the photoconductor but this time the information to be reproduced in red is erased and the electrostatic latent image developed with black: toner. The two toner images are then transferred to a copy sheet in registration with one another to provide the multicolored reproduction. The patent discloses that three colors may be provided in the reproductions where three developer stations are used.

A problem with the apparatus described in this patent, as well as with that described in U.S. Patent No. 4.204.728 (Goshi a et al). is in the reproduction of originals with composite information. For example, it is often desirable to reproduce with its original coloration a multicolored pictorial while providing color accenting to line-type material such as alphanumerics and logos, etc. It would also be desirable to provide color accenting in many colors, for example 25, without providing significantly more color development units.

SUMMARY OF THE INVENTION The invention is directed to an electrophotographic reproduction method and apparatus for producing copies with color accenting, i.e.. in colors different from that of an original.

In a^' preferred embodiment of the invention signals are provided related to the desired color and position of an image area to be color accented. A plurality of image frames are used to reproduce the original and these image frames are developed with differently colored toners that are superimposed when transferred to a copy sheet to form a reproduction of the area to be color accented in a color different than that of the original. Further according to the invention, the charge level on one of these image frame(s) is reduced from its primary voltage to an intermediate level needed for the color accenting. Information not to be reproduced by color accenting is selectively erased entirely from this image frame. In a three color copier using subtractive colored toners of cyan, magenta and yellow, more than three image frames may be used to produce copy. The additional frames being used to provide intermediate charge levels needed for color accenting. For example, where up to six image frames are used to produce copy, three of the frames may be devoted to reproducing information near the primary charge level of Vo with selected areas erasable to a level below which will permit development. In a system constrained to use

3 only these three frames with three colors, 2 , or

8 color combinations are possible. In the apparatus and method of the invention the use of an extra three frames available for charge levels at say

3 one-half Vo allows for 3 . or 27 colors, i.e., 25 colors plus black and white.

In the preferred embodiment the charge level is reduced to one-half Vo on the selected image frame by exposure of a non-image information bearing light source through a half-tone screen. BRIEF DESCRIPTION OF THE DRAWINGS The subsequent description of the preferred embodiments of the present invention refers to the attached drawings wherein:

FIG. 1 is a perspective view of a multicolor electrophotographic reproduction apparatus for practice of the present invention.

FIG. 2 is a schematic side view of the operating elements of the multicolor electrophotographic reproduction apparatus for practice of the present invention.

FIG. 3 is a schematic illustration in cross- section of some of the elements forming a multi- layered photoconductive member for use in the apparatus of Fig. 2.

FIG. 4 is a schematic illustrating a data input station and block diagrams of controls for control¬ ling the apparatus shown in Figs. 1 and 2. FIG. 5 is an illustration of a document that is to be reproduced with selected color accenting. FIG. 6 is an illustration of various image frames on the photoconductor used to produce a color accented copy.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Because electrophotographic reproduction apparatus are well known, the present description will be directed in particular to elements forming part of or cooperating more directly with the present invention. Apparatus not specifically shown 0 or described herein are selectable from those known in the prior art.

With reference now to FIG. 1 and 2, a four color multicolor electrophotographic reproduction apparatus is shown. -5 The apparatus 10 includes a closed loop, flexible image transfer member, or photoconductive web 12. The web 12. which may be of the type described in FIG. 3 is supported on rollers 5 - 8. The rollers are mounted on the copier frame (not 0 shown) with one of the rollers, for example roller 5. rotatively driven by a motor 16 to effect continuous movement of the web 12 in a clockwise direction about its closed loop path. The web has a plurality of sequentially spaced, nonoverlapping 5 image areas which pass successively through electrophotographic processing stations (charge, expose, develop, transfer, clean) located about the path of the web. The web also includes timing marks (or regularly spaced perforations) which are sensed 0 by appropriate means, such as timing signal generator 17 to produce timing signals. Such signals are sent to a computer controlled logic and control unit 31. The LCU 31 controls the entire electrophotographic process based on the 5 instantaneous location of the web in the travel path. An encoder 18 associated with the roller drive motor 16 also produces timing signals for the LCU. The signals from the encoder cause the LCU to fine tune the process timing. The LCU 31 has a digital computer, preferably a microprocessor. The microprocessor has a stored program responsive to the input signals for sequentially actuating, then de-actuating the work stations as well as for controlling the operation of many other machine functions. Programming of a number of commercially available microprocessors such as one or more INTEL model 8086 microprocessor (which along with others can be used in accordance with the invention), is a conventional skill well understood in the art. This disclosure is written to enable a programmer having ordinary skill in the art to produce an appropriate control program for the microprocessor. The particular details of any such program would, of course, depend on the architecture of the designated microprocessor.

With reference also now to FIG. 4, a block diagram of logic and control unit (LCU) 31 is shown which interfaces with the apparatus 10. The LCU 31 consists of temporary data storage memory 42, central processing unit 43. timing and cycle control unit 44. and stored program control 46. Data input and output is performed sequentially under program control. Input data are applied either through input signal buffers 50 to a input data processor 41 or to interrupt signal processor 45. The input signals are derived from various switches, sensors, and analog-to-digital converters. The output data and control signals are applied to storage latches 47 which provide inputs to suitable output drivers 48, directly coupled to leads. These leads are connected to the various work stations, mechanisms and controlled components associated with the apparatus.

A multicolored original document sheet D to be reproduced is placed, image side down, on a 5 transparent glass platen 20 supported by the copier frame. Exposure lamps 22, such as xenon flash tubes, are located beneath the platen 20 within the frame. The lamps flood the document sheet with light and a reflected image of the document sheet is 0 transmitted via mirror 24, lens 26, and mirror 28 in focus to an area 30 lying in the plane of the web 12. The original document could, of course, be a transparency illuminated from the back side thereof. To reproduce an ordinary multicolored 5 document in its original colors, the document sheet D is illuminated, for example, four times in succession to form four separate electrostatic latent image frames of the document. On successive illuminations a red filter 32R, a green filter 32G, o o∑ a blue filter 32B is inserted into the light path to form color separation images at the area 30. A fourth filter comprising a neutral density filter 32N for providing what is known as a skeletal black image is inserted during a fourth exposure of the 5 original or may be used for coloring areas to be developed in black. The timing of the flash of lamps 22 and the insertion of the colored filters are controlled by the LCU and related to the travel of the web 12 to expose adjacent, nonoverlapping 0 areas of the web to the color separation images and the skeletal black image. One or more corona charging units, exemplified by corona charger 34, is located upstream of the exposure area 30, and applies a generally uniform primary electrostatic charge, of say negative polarity, to the web 12 as it passes the charger and before it enters the exposure area. A programmable power supply may be provided to selectively apply to each image frame a predetermined generally uniform electrostatic primary charge level Vo suitable for developing the particular color toner used to develop that image frame. The photoconductive properties of the web cause the primary charge in the exposed areas of the web to be discharged in that portion struck by the exposure light. This forms latent imagewise charge patterns on the web in the exposed areas corresponding to the respective black and color separation images. Travel of the web then brings the areas bearing the latent images into a development area 36. The development area has a plurality of magnetic brush development stations, corresponding to the number of formed black and color separation images, in juxtaposition to. but spaced from, the travel path of the, web. Magnetic brush development stations are well known; for example, see U.S. Patent 4.473,029 to Fritz et al and 4.546,060 to Miskinis et al. When the color separation images are red. green, blue and a skeletal black image is also to be provided, there are four development stations respectively containing complementary colored toner particles, i.e., cyan particles in station 36C, magenta particles in station 36M, yellow particles in station 36Y, and black particles in station 36B. The toner particles are agitated in the respective developer stations to exhibit a triboelectric charge of opposite polarity to the latent imagewise charge pattern. Backup rollers 38C, 38M, 38Y, and 38B, located on the opposite side of web 12 from the development area, are associated with respective developer stations 36C, 36M, 36Y and 36B. Actuators 40C, 40M. 40Y and 40B selectively move respective backup rollers into contact with the web 12 to deflect the web from its travel path into operative engagement with respective magnetic brushes. The charged toner particles of the engaged magnetic brush are attracted to the oppositely charged latent imagewise pattern to develop the pattern.

The logic and control unit 31 selectively activates the actuators in relation to the passage of the image areas containing corresponding latent color separation images through the development area 36. That is, as the area containing the latent red color separation image reaches the development station 36C. actuator 40C moves the backup roller 38C to deflect the web so that the latent charge image is developed by attracting cyan toner particles from the station 36C. As soon as the image area leaves the effective development area of the station 36C, the actuator 40C returns the backup roller 38C to its nondefleeting position. Thus., as the areas containing the green and blue color separation images and the neutral density latent image pass the developer station 36C, no development takes place. A similar cycle is accomplished by the logic and control unit 31 for the developer stations 36M. 36Y and 36B. In this manner, the red latent color separation image is developed only with cyan toner particles, the green latent color separation image is developed only with magenta toner particles, the blue latent color separation image is developed only with yellow toner particles, and the neutral density latent image is developed only with black toner.

The developed black and color separation images must be transferred to a receiver sheet in accurately registered superimposed relation to form a full color reproduction of the original document. Apparatus for providing such registered transfer are known, for example one of which is fully described in U.S. Patent No..4.477.176. issued October 16. 1984 in the name of Matthew J. Russel. Briefly, this is accomplished by feeding a receiver sheet S from a supply stack stored in hopper 27 in synchronism with movement of the first image sector so that the copy sheet engages the web and is registered by mechanism 80 with the first image frame. A transfer roller 68 includes a compliant insulating surface thereon and is biased to a potential suitable for transfer of the developed image on the first image sector to the copy sheet S and to tack copy sheet S to roller 68. Roller 68 is driven by a stepper motor 19 which receives actuating signals from the LCU 31.

Roller 68 may also be a biased vacuum roller or a roller with sheet clamping mechanisms to clamp the sheet to it. Continued movement of web 12 and synchronized rotation of roller 68 brings the lead edge of copy sheets back into transferable relationship with the web as the lead edge of the next toner image arrives at roller 68. At this point, sheet S remains tacked to roller 68 and the second toner image is transferred in superimposed registration with the first toner image on sheet S. The process is repeated until toner images on each of the first three image sectors have been transferred to the same surface of sheet S and the leading edge of copy sheet has been brought back into transferable relationship with the fourth toner image on the web. When the lead edge of copy sheet S is brought back into transferable relationship with web 12 for the last time, the bias on roller 68 is reversed to repel sheet S away from roller 68 back into contact with web 12. Copy sheet S will be carried by web 12 so that the copy sheet is in registration with the image on the fourth image sector. This image is transferred to the copy sheet by transfer charger 25. The copy sheet is separated from the web and conveyed by vacuum transport 60 or an air transport to roller fuser 62 where the transferred images are then fixed or fused onto the sheet. The sheet is then delivered to exit hopper 64 or an accessory finishing unit 69. While the image is being fixed to the receiver sheet, the web 12 continues to travel about its path and proceeds through a cleaning area 66.

To facilitate toner removal from the web, a corona charging station 70 and a rear erase lamp 71 may be located upstream of the cleaning unit 66 to neutralize any charge remaining on the web and thus reduce the adherence forces of the toner to the web. In order to reproduce a document sheet such as document sheet D (see FIG. 5) having composite information comprised of line-type information in areas A. B and C and multicolor continuous-tone information in areas E and F. the document sheet D is placed face up on a digitizing tablet 52 and registered against an appropriate corner (or centered relative to a predetermined edge) as shown in FIGS. 1, 4 and 5. A wand 53 is associated with the tablet and used by the operator to determine the format of the original and the locations of the various parts of the image information. Assuming line-type information on the original is in black and that the reproduction desired requires each to be in a different color the operator calls up a special program for accomplishing this task via inputs of a code on a keyboard 51 which is part of the control panel. Next, the operator presses a for at input button 57 and moves the wand in turn to points e, f (or just point g which contains the coordinates of e and f) on the digitizing tablet to define the format of the document D. Transducers may be located beneath the sheet to produce signals relating the position of the points touched relative to the registered upper left corner of the sheet. Alternatively, the tablet may be of the known sonic type wherein a spark formed by a wand creates sound waves in the air which are sensed by microphones placed along the sides of the tablet or wherein a sensor is placed in the wand and sources at known points on the sides of the tablet emit sonic signals (see. for example. U.S. patents Nos. 4.012,588 in the name of Davis et al and 4.124.838 in the name of Kiss). A digitizer controller 54 knowing the times of emitting of the signals and their receipt can through triangulation principles calculate the location of a point on the platen relative to a known point such as the upper-left corner shown.

Next, the operator inputs the desired color for the information appearing in area A by de¬ pressing an accent input button 58 and one of the 25 color buttons 61 in the apparatus' menu of available colors and moves the wand to four or more points to define an imaginary rectangle or other area which encloses the information in area A and encloses no other information. For example, assume the selected color for this information is to be reproduced in red. The LCU is programmed to recognize that the area is bordered by the straight lines joining adjacent points and the coordinates for the rectangular area to be selectively colored are thus stored in temporary memory. Alternatively, the LCU may be programmed to recognize two diagonally opposite points as defining a rectangle. The LCU may also be programmed to receive inputs regarding other geometrical shapes. This information is outputted on the display 55 showing the relative position of the area A on the display, indicating the desired color accent for area A. and also illustrates the format of the document sheet D.

The operator then proceeds to repeat this for the next block of line-type information by indicating the color that it is to be reproduced. 0 In this example, assume that area B is to be reproduced in its original black color using black toner only. An input, therefore, is needed to be provided to define area B and its color in a similar manner described for area A and a button 59 pressed - to input this color.

Area C on the other hand is desired to be reproduced in a color, for example, a particular shade of orange that is included within the menu. To reproduce Area C^'in this color the operator, 0 identifies the rectangular area C using the digitizer and depresses the button assigned for this color.

Inputs from the digitizer and the color select buttons are inputted into the LCU through 5 interrupt signal processor 45 and are stored in temporary memory 42.

The operator next takes the document sheet D and places it on the exposure platen (using feeder 15 for example) so that the side to be reproduced 0 faces the exposure lamps and registers the sheet with the appropriate corner (or centers it against a registration edge). The stored program control on the LCU has a program for compensating for the reversal of the sheet vis-a-vis the location of 5 areas when the sheet is face-up versus the location of these areas when the sheet is turned over for exposure. Alternatively, format input may not be needed where the same point on the sheet is registered when the sheet is both face up and face down. For example, where the sheet is registered when face-up using centering of its left edge for digitizing and then inverted for exposure so that the same edge is again centered, the location of the digitized areas is known without need of format input. The operator then indicates through a suitable means, such as a coded input or special button therefore, whether three color or four color processing is desired. Assumption will be made that four color exposure and processing is desired for the multicolored continuous tone photographs E and F. Upon actuation of the print button, the apparatus operates as described above. However, as shown in FIG. 4, each color frame subsequent to exposure is passed between two linear illumination elements which extend across the width of the photoconductive web 12 transverse to the direction of web movement. A first illumination element 80 coupled to drivers 48 comprises LED's (light emitting diodes) 81 whose illumination is picked up by optical fibers 82 at one end thereof and carried to linear banks or holders where the fibers are aligned and spaced from a gradient index lens array 86 such as a Selfoc (trademark of Nippon Sheet Glass Co.. Ltd.) array. This array focuses illumination exiting the fibers onto a photoconductive surface of web 12. Alternatively, a linear array of LED's may be located proximate the web to expose the web directly or through a Selfoc lens without use of optical fibers. With reference now to FIG. 3. it will be noted that the photoconductive web 12 comprises a transparent support 90. a halftone screen 91. a conductive layer 92, and a photoconductive layer 93. The integral screen photoconductor may have the dot pattern that is printed therein rotated on adjacent frames so as to avoid moire patterns.

With reference now also to FIGS. 5 and 6, it will be noted that key points or coordinates associated with the original document D have corresponding coordinates associated with each image frame 87 (designated by the x' , y' axes) which relate to the coordinates of the original and which are used to enable illumination from respective portions on the linear exposure element 80 (y" axes) at respective times established by corresponding x' abscissa coordinates.

The second linear exposure element 85 is an electroluminescent light panel which is also coupled to drivers 48. The illumination from the panel as controlled by the drivers 48, is such in this embodiment as to image a screen pattern onto the photoconductive surface of each image frame. The screen 91 is preferably formed of rows of dots. The dots may be colored such as magenta to operate with a complementary-colored (green) screen exposure light source of electroluminescent panel 85 which provides an exposure of the screen pattern on the photoconductive surface from the rear of the web. The screen, may be of "hard" or "soft" dots or may be comprised of lines or other shapes. Where the apparatus is primarily used to reproduce line-type information, the screen is preferably formed of "hard" dots or lines to form more uniform dots or lines over an image frame where the electro¬ luminescent panel may be providing nonuniform output over its length. The panel 85 in response to signals from the drivers is capable of generally uniformly outputting two levels of light throughout its linear length. The first level is a relatively low level that is adapted to image a screen pattern on an image frame of the photoconductor to screen all image areas thereof. However, the level of screen exposure will be relatively low and reduce the primary voltage level V to a new level only about 60 volts or so from its normal level of about

500 volts. This new level of V would be measured o over a large area and comprises an average of charge levels in this area. The effect of this will be to screen continuous tone areas and to break up large solid areas which might show mottling of developer if not screened. The second level illumination level is the relatively higher one and is adapted to not only image a screen pattern on an image frame but will reduce the average charge level of the image frame to one-half Vo.

The black frame is the first to be exposed to illumination from the document sheet D and is exposed through the neutral density filter 32N. As this frame passes between the linear exposure elements, those LED's 81 providing illumi ination to the upper (as viewed in FIG. 4, lower as viewed in FIG. 2) linear exposure element between the ordinates corresponding to y 0. y.1 and y4. , y_b are all turned on to substantially erase all charge on the portion of this image frame between abscissa lines corresponding to xo and x,1, and 4, and xb respectively, to erase the charge areas on this frame reproducing the information in rectangles A and C. respectively. The electroluminescent light panel 85 is turned on to its low level and illuminates a screen pattern over this entire image frame.

The cyan frame is the next to be exposed to illumination from the document sheet D and is exposed through a red filter 32R. As this frame passes between the linear exposure elements. selected LED's provide illumination between the ordinate line pairs corresponding to y . y . y , y and y . y . commencing with the 2 3 4 5 abscissa lines corresponding with x . x„ and

O 2 x . respectively and terminating with x, , x_

4 1 and x , respectively. This being done to erase all charge information in areas on this frame reproducing information in rectangles A. B and C.

The electroluminescent panel is kept turned on for this frame too at its low level to image a screen pattern on this image frame where charge remains. τ_ne first magenta frame is the next to be exposed to illumination from the document sheet D and is exposed through a green filter 32G. As this frame passes between the linear illumination elements, selected LED's provide illumination between the ordinate line pairs corresponding to y . y and y . y . commencing with the abscissa lines x , x . respectively, and terminating with the abscissa lines x , x ,

3 5 respectively. This being done to erase all charge information in areas in this frame reproducing information in rectangles B and C. The electro¬ luminescent panel 85 is kept turned on at its low level for this frame, too.

The yellow frame is the next to be exposed to illumination from the document sheet D and is exposed through a blue filter 32B. As this frame passes between the linear illumination elements, selected LED's provide illumination between the ordinate line pair corresponding to y , y commencing with the abscissa line corresponding to x and terminating with the abscissa line corresponding to x . This being done to erase all charge information on areas in this frame reproducing information in rectangle B. The electroluminescent light panel 85 is illuminated at its low level for this image frame, too.

A fifth image frame to be developed with magenta toner is also provided with a primary charge and is also exposed to document D by flashlamps 22. As this frame passes between the linear illumination elements, selected LED's are illuminated to erase all charge information but for the information in areas on this frame reproducing information in rectangle C. The electroluminescent panel 85 is turned on at its high level for this frame to reduce the charge level at unexposed areas of this frame in rectangle C to a level of one-half Vo The five image frames are serially developed with respective colored toners (the fifth image frame being developed with magenta toner in this example) and the developed images thereon transferred in register to receiver sheet S. With the apparatus shown in FIG. 2, the first four image frames are transferred using transfer roller 68 and the fifth image frame transferred using. transfer charger 25. Alternatively all image frames may be transferred using transfer roller 68. The developed images are fixed and delivered to hopper 64 or accessory finishing unit 69.

The resulting copy sheet includes reproductions of the photographs E and F which are reproduced in 4 colors and halftone screened to reduce contrast. The reproduction of area A originally in black is reproduced in red through combination or super position of magenta and yellow colored toners. The reproduction of area B is in black using only black toner. The reproduction of area C is in orange comprising a combination of a substantially V charge level in the yellow developed frame and one-half V charge level to one of the magenta developed frames. The screening of all information will be particularly beneficial to large solid areas which tend to appear mottled and of non-uniform color when developed without such screening.

The apparatus as described herein is adapted to provide transfer of up to seven image frames, four devoted to images having charge levels averaging about V and three devoted to images having charge levels averaging about one-half V .

Where additional colors beyond 25 are desired, additional f ames at still another voltage level may be provided for.

• The invention also contemplates the use of a light source which can accurately•reduce charge levels in selected areas of an image frame based on color accenting desired. Where, for example in response to inputs from the document digitizer, a one half Vo level can be established on selected areas of the first magenta frame while leaving other areas on the same frame at substantially V then the use of additional frames beyond three and four may be dispensed with. For example, variable output light sources with variable aperture arrays such as mechanically movable masks or alternatively electrically actuated masks such as PLZT arrays may be used to control screen illumination. PLZT is an abbreviation for a lead lanthanum zirconate titanate electro-optical material whose optical properties can be changed by an electric field. Illuminating panels or aperture arrays need not be linear, but can be areal and cover the area of the frame so that as a respective frame of the photoconductive web underlies the panel array illumination may then be selectively provided.

An interesting feature of some LED's emitting green colored light is that they are known (see U.S. Patent 4.538.900 to Lutus et al. issued

September 3. 1985). when providing a different level of drive current thereto, to change spectral content such as to red. Where a magenta colored ink is used for the halftone screen, the green colored light content of the LED's may be used to image a screen pattern on the electrostatic charge on the photoconductor in accordance with the requirements of the areas requiring selective screening and reduction of the average charge level to say one-half V . On the other hand, whenever areas of o the photoconductor are required to be substantially erased of charge such as areas in an image frame to be selectively erased or interframe and edge areas of the photoconductor the current level to the LED's may be adjusted to provide light outputs in the red color. Red color light is absorbed substantially less by the magenta dots compared with green colored light and thus the magenta colored screen is substantially transparent to light of red color. Control programs are known for illuminating a linear light source lying transverse to the direction of movement of a photoconductor for providing selective erase of charge from interframe and edge areas in accordance with encoded signals to the LCU determining the timing for illuminating a light source, at say. when the interframe area is positioned to be exposed to the light from the light source. An apparatus thus providing currents to selected LED's at levels suitable for generating light of a color to which the screen is transparent, for providing selective erase, and providing different currents to the LED's for generating light of a color to which the screen is not transparent, for providing selective screening, allows for the elimination of the need for an additional light source to provide the erase function.

The invention is not limited to the use of a photoconductor with an integral screen. The screen may be separate from the photoconductor and when it is so, may be positioned adjacent the surface of the photoconductor that is to be developed.

While the invention has been described with regard to a flash exposure of a document, other types of exposure are also contemplated. For example, the image may be scanned upon the electrostatically charged photoconductor and may be imaged thereon using either a scanning reflection or transmission exposure of the original or using light which has been electronically generated from say a bit stream. In the former segments of the original are scanned by a light source and the light modulated by the document is imaged upon the photoconductor. In the latter the information contents of a document are digitized into electrical signals by a suitable electronic image "reading" device and these signals used to modulate a light source such as a laser or LED arrangement which are then imaged upon the photoconductor. The image for the screen itself would be imaged upon the photo- conductor independently of the imaging source by the techniques described herein or their equivalent, however the selective erase function provided by the LED's could be incorporated into an electronic imaging device. The advantage to this would allow the electronic imaging source to be fed by a black only bit generator; yet 25 or more colors are available for accenting.

Additional color levels may be provided for by incorporating a multicolor screen within the photoconductor and using multicolor illumination to illuminate a screen pattern on the image frames. As used herein, light modulated only with a screen pattern is still considered to be "non-image information bearing light." For example, a screen may be used comprising a 60% dot magenta screen with a 30% dot cyan screen placed so that the dots of the two colored screens do not overlap. When an image frame is illuminated by the non-image information bearing red light, the charge level on the frame is reduced to 30* of V ; i.e., a 70* discharge level. When an image frame is illuminated by non-image information bearing green light, the charge level on the frame is reduced to 60% of V ; i.e.. a 40% discharge level. With both lights on the charge on the image frame would be reduced to a level below which development can occur or 100% discharged. With no lights on. there is no discharge and the charge on the image frame remains at V . Thus, four discharge levels are possible

°₃ and 4 or 6.4 colors are possible using three different color toners such as cyan, magenta and yellow. In a three color station apparatus no more than nine image frames would be needed to produce copy with all 64 colors.

Other modifications may include the use of a high percentage dot screen over a non-image bearing light source and repeated exposure of the photoconductor layer through the screen by the light source. The screen frequency can be varied in the direction of film motion by varying the frequency of light pulses exposing the photoconductor layer under the dot screen. The effective percent dot exposure is directly proportional to the frequency. For a

90% opaque dot pattern, exposures of zero to one hundred percent (0-100%) in 10% increments are

3 possible producing 10 or 1000 possible colors;

5 for an 80% opaque dot pattern, exposures of zero to one hundred (0-100%) in 20% increments are possible

3 producing 5 or 125 possible colors.

While the invention in its preferred embodiments has been described with regard to the

10 use of exposure to a screen to effect the charge level on a frame, the invention in its broader aspects contemplates other means which will be suggested by this specification for accomplishing more than 2 colors in a three color apparatus (or

I2B more than 22 colors in a two color apparatus).

For example, illumination sources or even charging devices which can be accurately controlled without use of a' screen may be used to reduce the charge to a predetermined percentage of V on a desired

20 image frame to obtain an accent or spot color effect. The advantage, however, to use of a screen is that the resulting reproduction appears to be more appealing and forgiving with regard to non-uniformities in light output. In lieu of using

25 a screen, a high-resolution addressable light source may be used to synthesize a screen-like pattern.

Description has been provided herein with regard to reproduction apparatus using belts or webs or sheets where exposure of different image sectors

30 refers to spatially different portions of the photoconductors described. It should be appreciated, however, that where smaller photoconductor-ductors are used, the image sectors may be considered different in the temporal sense. 5 For example, a photoconductor may be exposed to an image of an original, be developed and transferred to a copy sheet, the photoconductor cleaned, and the next exposure of the original be on the same photoconductor-ductor portion.

It will be appreciated that signals from the LCU based on the menu colors selected determines the number of image frames to be exposed to the original document. The stored program control 46 stores the information regarding, for each color selected, the number of image frames needed to produce that color and how many of such frames are to be at about the average V level and how many that are to be at the averag^ae one-half Vo level

(in an apparatus having 25 color levels plus black and white). The selective erase light source and the screen light source locations are not critical other than each being locatable between the primary charging station and the development station.

The invention has been described in detail with particular reference to the preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

We Claim:

1. In a method for reproducing a document including different information portions, at least one of which is to be reproduced in a selected color different from that of the original, the method including, storing signals related to the selected color and the location relative to a reference of the portion which is to be reproduced in the selected color; forming on a plurality of image frames of an electrostatic charge supporting member a plurality of separate developable latent electrostatic images representing the information to be reproduced; developing the image frames with differently colored toners; transferring the developed images in register to a copy sheet to form the reproduction; and the improvement which comprises wherein the portion to be reproduced in the selected color has corresponding latent electrostatic images thereof existant on more than one image frame and the corresponding latent images are developed with different colored toners and the corresponding developed images are transferred in register to a copy sheet to produce a reproduction wherein the said one portion is reproduced in the selected color that is different in color from that of the original and different in color from that of each of the toners used in forming the reproduction.

2. The method of Claim 1 and wherein the levels of charge of the corresponding latent electrostatic images in the more than one image frames are established in response to signals related to said selected color.

3. The method of Claim 2 and wherein in reproducing the document a plural number of image frames are developed with toner of the same color.

4. The method of Claim 3 and wherein the charge level of the latent electrostatic image in one image frame of the said plural number of image frames developed with toner of the same color is different than the charge level of the latent electrostatic image in another image frame of the said plural number of image frames developed with toner of the same color and the charge levels of said one and another image frames are related to respective colors selected for reproduction of different information portions of said document.

5. The method of Claims 1. 2. 3 or 4 and wherein in forming the latent electrostatic image a primary electrostatic charge level is provided to each image frame used to produce the reproduction and a non-image information bearing light source reduces the primary charge level in response to the signal related to selected color.

6. The method, of Claim 5 and wherein illumination from the light source is modulated by a halftone screen pattern.

7. The method of Claims 1. 2. 3 or 4 and wherein a multicolor portion is provided on said document and said multicolor portion is reproduced in approximately the same colors as it appears in the document by forming respective color separation latent electrostatic images of the multicolor portion upon respective image frames and at least one of said corresponding latent electrostatic images is also provided on at least one of the image frames containing one of the said color separation electrostatic images.

8. In an apparatus for reproducing a document including different information portions, at least one of which is to be reproduced in a selected color different color from that of the original, the apparatus including means for storing signals related to the selected color and the location relative to a reference of the portion which is to be reproduced in a different color; means for forming on a plurality of image frames of an electrostatic charge supporting member a plurality of separate developable latent electrostatic images representing the information to be reproduced; means for developing the image frames with differently colored toners; means for transferring the developed images in register to a copy sheet to form the reproduction; and the improvement which comprises means for establishing for the portion to be reproduced in the selected color corresponding latent electrostatic images thereof that are existant on more than one image frame and for causing the corresponding latent images to be developed with different colored toners that are transferred in register to a copy sheet to produce a reproduction wherein the said one of which portion is reproduced in the selected color that is different from that of the original and different from that of each of the toners used in forming the image.

9. The apparatus of Claim 8 and wherein the means for establishing establishes levels of charge of the corresponding latent electrostatic images in the more than one image frames in response to the signals related to the selected color.

10. In a method for producing copy in a color selected from a group of selectable colors, the method including storing signals related to the said color selected; depositing a respective primary electrostatic charge upon each of two or more image frames of an electrostatic charged supporting member used to produce said copy; modifying the charge level on said image frames to form electrostatic latent images of information; developing the latent images with differently colored toners; transferring the developed images to a copy sheet with the developed images superimposed on the sheet to form the copy in a color different than that of any of the said developed images and the improvement which comprises wherein the charge level of an electrostatic latent image in an image frame is caused to be established in response to the signals related to color selection of the copy.

11. In an apparatus for producing copy in a color selected from a group of selectable colors, the apparatus including means for storing signals related to the said color selected; means for depositing a respective primary electrostatic charge upon each of two or more image frames of an electrostatic charge supporting member used to produce said copy; means for modifying the charge level on said image frames to form electrostatic latent images of information; means for developing the latent images with differently colored toners; means for transferring the developed images to a copy sheet with the developed images superimposed on the sheet to form the copy in a color different than that of any of the said developed images and the improvement which comprises means for causing the charge level of an electrostatic latent image in an image frame to be established in response to the signals related to color selection of the copy.