Apparatus and method for electrophotographically producing color copy continuous-tone originals and other content of selective color

The technical field

The present invention relates to electrophotographic reproduction methods and apparatus and more specifically to the improved production of color copy of the kind having both continuous-tone (e.g. pictorial) and other (e.g. uniform background and/or line-type) content.

The background art

U.S. 4,053,216 discloses apparatus for electrophotographically producing color reproductions of continuous tone images. In this apparatus a color transparency is transmission-illuminated via successive color-separation filters onto successive, primary-charged photoconductor sectors. The sectors are then developed with different color toner and the toner images are transferred in register onto a copy sheet. In one disclosed embodiment a half-tone screen is placed on the exposure platen to modulate the light from a source which illuminates the transparency. A composition border is also placed on the exposure platen and is reflection illuminated by a second light source. The composition border can contain textured information.

The approach of the above-described patent requires that composition borders be constructed in a precise configuration and with the precise color information content that is to be reproduced. This presents a problem with regard to the productivity of the apparatus and method, particularly in handling reproductions of more complex content.

The invention

The purpose of the present invention is to provide improved apparatus and techniques for coping with the problems such as outlined above, and thereby improve the art of electrophotographically producing high quality reproductions containing such different types of information content.

In one constitution the present invention provides a method of electrophotographically producing a color reproduction which includes the steps of primary charging a plurality of photoconductor sectors, exposing said sectors to image patterns having continuous-tone and other content to form color-separation electrostatic images, developing said electrostatic images respectively with different toners and transferring the resulting toner images onto a copy sheet, wherein said exposure step includes exposing said sectors to a first-component original having continuous-tone portions and to a second-component original having (i) mask portions complementary to such continuous-tone portions and having (ii) line information portions; and in that said exposure of said second-component original is made to form electrostatic images of said line information portions on a selected one or more but less than all of said sectors so as to selectively vary the color of reproduced line information.

In a closely related constitution the present invention provides electrophotographic imaging apparatus comprising: <ul id="ul0001" list-style="none"><li>(a) a plurality of photoconductor image sectors movable along an operative path of said apparatus;</li><li>(b) means, located along said path, for forming an electrostatic primary charge on photoconductor image sectors moving therepast;</li><li>(c) first support means for accurately positioning a first-component original in a first location which is registered relative to said operative path;</li><li>(d) first exposing means, operative at a first exposure zone along said path for exposing half-tone-screened, different spectral content light images of a first-component-original that is positioned by said first support means, respectively onto different ones of said primary-charged photoconductor image sectors;</li><li>(e) second support means for accurately positioning a second-component-original in a second location which is registered relative to said first location and said operative path;</li><li>(f) second exposing means, operative at a second exposure zone along said path, for exposing at least one of said photoconductor sectors to the unscreened light image of a second-component-original that is positioned by said second support means;</li><li>(g) control means for synchronizing said first and said second exposing means and the movement of said photoconductor sectors at said first and. second exposure'zones so that said exposure by said second exposing means is in predetermined register with said exposure by said first exposing means;</li><li>(h) means for developing the exposed photoconductor image sectors respectively with different color toners; and</li><li>(i) means for transferring said developed toner images in register to a copy sheet; said first exposing means including (1) means for imagewise exposing the photoconductor sectors, at exposure levels that are optimized for tone-scale reproduction, to continuous-tone portions of a first-component-original at said first support means, (2) means for background exposing other portions of the photoconductors sectors which border the continuous-tone exposed portions, at an exposure level that discharges such other portions below a predetermined development level, and said control means activating (i) both said imagewise and background exposing means with respect to at least one of said photoconductor sectors and activating (ii) said imagewise exposing means and said second exposing means with respect to another of said photoconductor sectors.</li></ul>

The subsequent description of preferred embodiments of the present invention refers to the attached drawings wherein: <ul id="ul0002" list-style="none"><li>Figure 1 is a schematic side view of one exemplary embodiment of electrophotographic apparatus for practice of the present invention;</li><li>Figure 2 is a schematic side view of another exemplary embodiment of electrophotographic apparatus for practice of the present invention.</li></ul>

Referring now to Figure 1, there is shown an apparatus 30 which is adapted, in accord with one aspect of the present invention, to produce color electrophotographic reproductions of documents including continuous-tone image areas and surrounding white (or low density) background border zones. The Figure 1 structure and technique have the capability to produce good tone-scale (particularly in difficult highlight portions) together with backgrounds which are "substantially clean" (i.e. do not have an objectionable density level). The apparatus 30 includes a photoconductor 11 (e.g. a belt comprising a photoconductive insulator layer overlying a conductive layer on a support) having one or more image sectors adapted for movement along an operative path past primary charging station 12, exposure zones E₁ and E₂, development stations 14-1, 14-2, 14-3 and 14-4 and transfer station 15. The corona charger at station 12, magnetic brushes at station 14 and transfer roller at station 15 can be of the various types known in the art and equivalent devices can be utilized.

In accord with the present invention, the apparatus 30 includes two exposure stations 13 and 23. The exposure station 13 includes means for supporting an original 0₁ (e.g. transparent platen 16) at the illumination zone of apparatus 30, a first illumination source 17 located between the illumination zone and the photoconductor 11 and second illumination source 18 located on the opposite side of the illumination zone from photoconductor 11. Lens means L₁ is provided to image the original 0₁ at the illumination zone onto the photoconductor 11 at exposure zone E₁. A Fresnel-type field lens element (not shown) can be provided to image the transmission source 18 on the lens L₁. (If the background area B is diffuse, the Fresnel lens is not needed; however, the source 18 should be of a higher intensity.) This preferred embodiment includes a half-tone screen 19 located in the optical path of lens L₁ and proximate the exposure zone.

Apparatus 30 also comprises a second exposure station 23 constructed to expose a second component original 0₂ at a second exposure zone E₂. Positioning structure 21 and 22 is provided respectively at exposure stations 13 and 23 to accurately locate originals on the exposure platens. A photoconductor location detector D and logic and control unit 35 are provided to coordinate exposure of component original 0₂ in register on a common photoconductor image sector with the electrostatic image of a first component original 0₁ (previously exposed on that photoconductor sector at station E₁). Station 23 includes a light-transmissive document platen 26, illumination sources 27 (e.g. xenon flash lamps) coupled to a power source P₃, mirror 29 and lens means L₂ for imaging a component original 0₂ at exposure zone E₂.

The exposure procedure and structure of the present invention involve provision and use of originals 0₁ and O₂ of predetermined format. Specifically, the original 0, comprises a light reflective continuous-tone area(s) C formed within a light-transmissive background area 8₁. One preferred embodiment comprises photographic prints mounted on a light-transmissive plastic support.

The component original O2 is predeterminedly constructed to cooperate with original component 0₁, and for this purpose 0₂ has mask portions M which prevent source 27 illumination from passing to predetermined portions of exposure zone E₂ (viz. those portions which correspond to portions C of the original O₁). In this manner component original 0₂ is complementary to component original O₁. In embodiments where sources 27 are located to reflectively illuminate component original O2, the portions M can be light-absorptive (e.g. black) or light-transmissive. In such an embodiment, the background portions B₂ of component original 0₂ are desirably highly light-reflective (e.g. white) and line-type portions LT are light-absorptive (e.g. black). If desired the illumination sources 27 can be on the opposite side of platen 26 from exposure zone E₂ and in such an embodiment the component original 0₂ can have light-reflective or opaque mask portions M, light-transmissive background portions B₂ and light-blocking line-type portions LT (e.g. black, light-reflective or light-scattering alphanumerics). As will be understood by those skilled in the art, the background portions B₁ of component original 0₁ can be light-absorptive rather than light-transmissive. The desired function is to mask (e.g. be non-reflective to) source 17 light and thus prevent it from passing to the photoconductor sector corresponding to portions B of original O₁. A platen cover formed of light-absorptive material also could be used for this purpose.

The exposure station 13 can function in two modes upon a photoconductor imate sector, which is first moved past the charging station 12 where it receives a uniform primary electrostatic charge. In a first mode sources 17 and 18 are both actuated to illuminate the original 0₁ (which is in place on platen 16 with its light-reflective, continuous-tone portions facing the exposure zone E). More particularly, sources 17, e.g. xenon flash lamps are energized by power source P₁ at an intensity level selected for optimizing tone-scale of the electrostatic latent image formed on the photoconductor by light reflected from the continuous-tone portions C. The light source 18, e.g. a xenon flash tamp, is energized by its power source P₂ to provide an exposure level at the photoconductor which substantially discharges portions of the photoconductor (corresponding to background B) by transmission exposure. That is, the intensity of this transmission exposure is selected to reduce the electrostatic charge level of portions corresponding to document background below the development level of the apparatus (e.g. to a level proximate or below the bias on magnetic brushes at development station). The discharge of transmission-exposed photoconductor portions therefore is preferably more than the maximum discharge (minimum development density level) of the reflection-exposed portions. The exposure from source 18 is selected to discharge the screen pattern in the background areas below the development level of the apparatus. Thus, continuous-tone photoconductor regions can be exposed at one of a plurality of preselectable levels (chosen to optimize tone-scale of the electrostatic image) and such continuous-tone exposure need not be concerned with the need for complete discharge in document background areas. This allows substantial improvement in the quality of electrophotographic reproductions of images which contain different content types like 0₁,

The level of photoconductor exposure of the continuous-tone images can be varied in ways other than adjustment of the illumination intensity of source P_i, e.g. such as by aperture adjustment and/or illumination time control. Similarly one skilled in the art may readily substitute other exposure techniques, e.g. scan exposure techniques, for the flash exposure system described with respect to Figure 1. In certain applications the portions B of original 0₁ may desirably be selectively light-transmissive, light diffusive and/ or contain opaque line-type information. Also, if desired a graphic transparency image can be overlaid in a desired register with the original 0₁, e.g. in register with a portion of background B.

In a second mode of operation, a photoconductor image sector is primary-charged at station 12, transported to exposure zone E₁ and exposed to component original 0₁ by sources 17 without transmission exposure by source 18. This provides a screened electrostatic latent image of the desired tone-scale on photoconductor sector portions corresponding to continuous-tone information areas C of component original 0₁. The uniform primary charge remains on portions of the photoconductor sector that correspond to background portions B₁ of original O₁. The photoconductor sector next moves to exposure zone E₂; and when it is in proper alignment with respect to exposure station 23 (as sensed by detector D), logic unit 35 effects a high-contrast exposure of that photoconductor image sector to cooperative component original 0₂. Thus sources 27 are energized and the photoconductor sector is exposed to O2 via lens L₂ and mirror 29 at a high exposure level. This forms a high-contrast, non- screened image of line-type information areas LT and, in addition, discharges the photoconductor image sector portions corresponding to background areas 8₂ (to a level below the development level of apparatus 20). The photoconductor image sector now bears the composite electrostatic image.

Apparatus 30 also has structure which provide capabilities in regard to reproducing color originals. In this regard an array 31 of color filters e.g. including red, green and blue filters, is mounted along the optical path of exposure station 13. The array 31 is indexable by shaft 32 to selectively position each particular color filter in the optical path during the successive color-separation exposures of continuous-tone portions C of a color original 0₁. Also, in apparatus 30 the magnetic brush devices 14-1, 14-2, 14-3, 14-4, of the development station are operable, in response to signals from logic and control unit 35, to selectively apply different colors of toner (e.g. cyan, magenta, yellow and black toner) to different photoconductor image sectors. The functioning of these additional devices in cooperation with the other structure of electrophotographic apparatus 30 will be easily understood by considering the following operational descriptions of its different modes.

To commence operation of a color copy run, component originals 0₁ and 0₂ are prepared and positioned at predetermined positions respectively on platens 16 and 26. In the illustrated embodiment, component original 0₁ comprises a plurality of color continuous-tone information areas C (e.g. color prints) mounted on a light-transmissive support which forms background areas B₁. The component original 0₂ for the Figure 1 embodiment comprises a light-reflective (e.g. white) background B₂ with black mask areas M located in register with areas C of component original 0₁ and with high-contrast, line-type information LT (e.g. black alphanumeric information) located in adjacent areas on the white support. Index or positioning means, e.g. guide rails 36, 37, are provided to assure proper relative location of the component originals and thus proper register of their light images at exposure stations E₁ and E₂. With the originals 0₁ and 0₂ thus prepared and positioned, the operator inputs control data to logic and control unit 35, e.g. by a keyboard (not shown). Such data can include: (1) the desired operational mode (color or black-and-white), (2) desired number of reproductions and (3) special exposure level information regarding the respective color-separation exposures of composite original O₁. With regard to the last-mentioned input data, the operator often will perform pre-runs of the color-separation exposures at varying levels to determinate optimum exposure levels for the particular pictorial information involved. Logic and control unit 35 preferably contains memory to store selected exposure levels for each respective color-separation exposure.

When the above data is input, a "run" command is actuated by the operator, and the photoconductor belt 11 moves successive photoconductor image sectors thereof past primary charger 12 and onto exposure zone E,. Position of the photoconductor image sectors is detected by a sensor, e.g. a detector D of perforations in the photoconductor, and a position signal is input to unit 35. Logic and control unit 35 effects control of successive red, green and blue color exposures onto successive photoconductor sectors. For example, such control from unit 35 can include synchronization of: (1) the indexing of filter array 31, (2) energization of power source P, at the desired level(s) and (3) energization of source P₂ to actuate background clean-up. The three photoconductor image sectors, thus exposed, respectively comprise screened, continuous-tone red, green and blue color-separation electrostatic images corresponding to portions C of the original 0₁ and background portions discharged by source 18 to a level below the development level of apparatus 30 (e.g. below the bias level applied to the brushes of stations 14 by means not shown). As the sector bearing the red color-separation electrostatic image moves over magnetic brush 14-1, the brush is activated by unit 35 to apply cyan toner in accordance with the electrostatic image. Similarly brushes 14-2 and 14-3 are activated to apply magenta and yellow toner respectively to the subsequent green and blue electrostatic color-separation images on successive sectors of the photoconductor.

As a fourth primary-charged sector of the photoconductor belt 11 passes zone E_i, a panchromatic light exposure of selected tone-scale is effected by sources 17, without the activation of source 18. It may be preferred to filter this exposure, e.g. with another element of array 31, to achieve a more panchromatic system response for this exposure. At this stage, the electrostatic pattern on the fourth photoconductor image sector includes a screened, continuous-tone latent image pattern of the pictorial areas C and uniform primary charge on other areas corresponding to background 81, The fourth sector moves next to exposure zone E₂, and, in proper timed relation with movement of belt 11, unit 35 activates sources 27 to effect a high-contrast exposure of component original 0₂, in register with the image of component original 0₁, onto the fourth sector. The electrostatic image on the fourth sector leaving zone E₂ thus comprises (1) the continuous-tone electrostatic image component exposed at zone E₁ (and undisturbed by the zone E₂ exposure because of mask portions M on original 0₂), (2) the high-contrast, unscreened, alphanumeric electrostatic patterns corresponding to areas LT of composite original 0₂ and (3) the clean background portions discharged below the development level. The fourth sector subsequently is developed with black toner by magnetic brush 14-4. It will be appreciated that logic and control unit 35 can be constructed to effect the above-described exposures of the four photoconductor image sectors in any desired sequence. Also, it will be appreciated that logic and control can effect exposures so that the line information is in a color(s) other than black. For example, cyan line information can be provided by omitting the source 18 illumination and providing source 27 illumination to the red filter exposed image sector rather than the neutral density exposed sector. Of course the apparatus 30 can employ less than four colors, if desired.

After exposure and development and in proper timed relation with movement of the photoconductor image sectors to transfer station 15, unit 35 signals actuation for feeding a copy sheet S to the transfer roller. Successive cyan, magenta, yellow and black toner images are then transferred to the copy sheet, in register, by the first, second, third and fourth image sectors of the photoconductor 11. Unit 35 then signals pick-off of the copy sheet by detack device 39, and copy sheet S is fed through fixing device F to a receiver bin. It will be appreciated that the successive reproductions of the composite original can be made in a continuous mode by repeating the above-described operation as the belt recirculates. Appropriate photoconductor cleaning and rejuvination (known in the art) can be provided along the return path from station 15 to station 12.

Apparatus 30 also can be operated in a black-and-white copy mode. In such operation, appropriate control information is input to unit 35, e.g. to select the black-and-white mode, the number of copies desired and any exposure level information for sources 17. Start of the copy run is commanded and control unit 35 effects repeated cycles of charge exposure and development as described above with respect to the fourth (black toner) sector on successive photoconductor image sectors. Copy sheet feed in this mode is activated for each photoconductor image sector, in contrast to the color mode where four toner images are transferred between each copy sheet detack and replacement cycle.

Figure 2 discloses another embodiment of electrophotographic apparatus 40 in accord with the present invention. Apparatus 40 is similar in functional capabilities to the Figure 1 apparatus, and again, corresponding structural features are indicated with corresponding designators. The apparatus 40 differs from the Figure 1 embodiment primarily with respect to the construction of the photoconductor image sectors and the operative path of the apparatus. Specifically, the photoconductor image sectors of apparatus 40 are in discrete sheet form and have separate paths within the development portion of the apparatus.

In operation in a color copy mode, originals 0₁ and O2 are prepared as described with respect to Figure 3 and placed in register on platens 16 and 26. Appropriate control signals are input to a control and logic unit (not shown) and a start command is actuated. A first sheet sector 11-1 then is fed from a supply, primary-charged and exposed by device 13 via a red filter to original 0₁ at zone E₁ (in the same manner described with respect to the first photoconductor image sector of the belt 11 of apparatus 30). The sheet 11-1 next is moved past exposure station 23 (without an exposure actuation), is developed by brush 14-1 with cyan toner and is moved to hold position P_i. Subsequently green and blue color-separation images are exposed on sheets 11-2 and 11-3 and the resulting electrostatic images are developed by magnetic brushes 14-2 and 14-3 and forwarded to hold positions P₂ and P₃. A sheet 11-4 is then primary-charged, exposed at station 13 (by source 17 only) and at station 23 by source 27, all in a manner like that described above regarding the fourth sector of apparatus 30. The composite image on sheet 11-4 is developed with black toner and sheet 11-4 is moved to position P₄. From this stage of the operation, the sheets can be forwarded to station 15 in any desired order for transfer of toner to a copy sheet S. As was the case with the Figure 1 embodiment, apparatus 40 can be operated in a black only mode by successively repeating the sheet 11-4 sequence coordinated with successive copy sheet feed for each exposure sequence.

Industrial effect

As explained above and illustrated in the exemplary embodiments, the present invention provides a method which produces electrophotographic reproductions having screened, continuous-tone color portions, clean background areas and high contrast line information, and which is characterized by the capability to selectively vary the color in which line information is reproduced, without changing the original input. The apparatus constitutions of the present invention provide simple yet highly productive structures for achieving such desirable capabilities.