GB1564875A - Electrophotographic printing machine - Google Patents

Description

(54) ELECTROPHOTOGRAPHIC PRINTING MACHINE (71) We, XEROX CORPORATION, of Rochester, New York State, United States of America, a Body Corporate organized under the laws of the State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates generally to an electrophotographic printing machine, and more particularly, concerns a printing machine arranged to produce prints from color transparencies.

One process of electrophotographic printing comprises exposing a charged photoconductive member to a light image of an original document being reproduced. The exposed areas of the photoconductive surface are discharged to record thereon an electrostatic latent image corresponding to the original document. A development system moves a developer mix of magnetic carrier granules and toner particles into contact with the photoconductive surface.

The toner particles are attracted electrostatically from the carrier granules to the latent image forming a toner powder image thereon. Thereafter, the toner powder image is transferred to a sheet of support material. After transferring the toner powder image to the sheet of support material, a fusing device permanently affixes the toner powder image thereto.

Numerous types of machines have been devised for implementing the electrophotographic printing process. Exemplary of these, are special purpose printing machines which reproduce microfilm. Machines of this type are described in U.S. Patents Nos.

3,424,525, 3,542,468 and 3,547,533. Generally, a machine of this type produces an enlarged copy of the micro-film original.

The enlarged light image is projected onto the charged portion of the photoconductive surface and reproduced as hereinbefore described. However, it is difficult to produce copies having pictorial quality. Moreover, high quality reproduction of color slides has only been recently achieved.

With the advent of color electrophotographic printing, it became highly desirable to produce enlarged opaque color copies from color transparencies. Multi-color electrophotographic printing essentially is the same as the process hereinbefore described. However, in multi-color electrophotographic printing the light image is filtered to record an electrostatic latent image on the photoconductive member corresponding to a single color of the original document. This single color electrostatic latent image is thereupon developed with toner particles of a color complementary to the color of the filtered light image.

Thereafter, the toner powder image is transferred to a sheet of support material.

This process is repeated for successively differently colored light images. Each toner powder image formed is transferred, in superimposed registration with the prior toner powder image, to the sheet of support material. In this manner, a multi-layered toner powder image is deposited on the sheet of support material. The multilayered toner powder image is permanently affixed to the sheet of support material as it passes through the fusing device forming a permanent color copy of the original document.

Hereinbefore, reproduction of color transparencies has been achieved by projecting a single color light image of the color transparency through a screen and field lens disposed on the machine platen. The filtered modulated light image selectively discharges the charged portion of the photoconductive surface. Successive single color light images are formed and the resultant opaque copy corresponds to the color transparency being reproduced. This type of multiplicative screening is more fully described in British Patent Specification No. 1,489,142.

Alternatively, rather than disposing the screen on the platen, the screen is positioned closely adiacent to the photoconductive surface in the optical system. This is another type of multiplicative screening, and is more fully described in British Patent Specification No. 1,547,468.

In all of the foregoing processes, the light image of the transparency passes through the screen so as to be modulated thereby. In systems of this type, the screen is interposed directly into the light image path requiring a light image of greater illuminating intensity than is normally utilized. This frequently poses a difficult problem for the projector and increases the cost and complexity of the system. Contrawise, a sequential screen system, wherein the screen is located prior to or subsequent to the optical light path remedies the foregoing situation. Sequential screening systems have been employed to reproduce opaque original documents. For example, British Patent Specification No. 1,535,426 discloses such a system. However, it does not appear that a screening system of this type has been employed to print from transparencies.

According to the invention there is provided an electrographic printing machine for printing from a transparency, including: a photoconductive member; means for charging at least a portion of said photoconductive member to a substantially uniform level; means for forming a light image of the transparency on the charged portion of said photoconductive member to selectively dissipate the charge thereon recording an electrostatic latent image of the transparency; a screen member positioned closely adjacent to said photoconductive member, a light source positioned to transmit light rays through said screen member forming a light image of the screen pattern which exposes the charged portion of said photoconductive member to record thereon an electrostatic latent image of the screen pattern in superimposed registration with the electrostatic latent image of the transparency; a transparent plate; a composition frame disposed on said platen; a field lens positioned on said composition frame; and means for exposing the charged portion of said photoconductive member to a light image of said composition frame recording thereon a combined electrostatic latent frame in superimposed registration with the image of the transparency and composition electrostatic latent image of the screen pattern.

An example of the invention will now be described with reference to the accompanving drawings in which: Figure 1 is a schematic perspective view of an electrophotographic printing machine incorporating the features of the present invention therein: and Figure 2 is a schematic illustration of the Figure 1 printing machine optical system.

For a general understanding of a color electrophotographic printing machine incorporating the features of the present invention therein, continued reference is had to the drawings. In the drawings, like reference numeral have been used throughout to designate identical elements. Although the color electrophotographic printing machine in the present invention is particularly well adapted for reproducing color transparencies as enlarged opaque color copies, it should become evident from the following discussion that it is equally well suited for producing black and white copies from black and white transparencies and is not necessarily limited to the particular embodiment illustrated herein.

As depicted in Figure 1, the electrophotographic printing machine employs a photoconductive member comprising a drum 10 mounted rotatably within the machine frame (not shown) having photoconductive surface 12 secured thereto and entrained thereabout. Preferably, photoconductive surface 12 is made from a panchromatic selenium alloy of a type described in U.S. Patent No. 3,655,377.

Drum 10 rotates at a substantially constant angular velocity in the direction of arrow 14 to pass through a series of processing stations disposed about the periphery thereof. A signal generator is operatively associated with drum 10 to provide an indication of the angular orientation thereof. The signal generator develops a series of pulses which are transmitted to the machine logic to control the activation of each processing station in synchronism with the rotation of drum 10. Hereinafter, each of the processing stations will be discussed briefly.

Initially, drum 10 rotates through charging station A. Charging station A includes a corona generating device, indicated generally by the reference numeral 16, which sprays ions onto photoconductive surface 12 producing a relatively high, substantially uniform charge thereon. A suitable corona generating device is described in U.S. Patent No. 3,875,407 issued to Hayne in 1975.

After photoconductive surface 12 is charged to a substantially uniform potential, drum 10 rotates the charged portion thereof to exposure station B. Exposure station B includes a system, indicated generally by the reference numeral 18, for projecting a light image of a screen pattern onto the charged portion of photoconductive surface 12. Screening system 18 comprises a light source 20 arranged to illuminate screen member 22. The screen light pattern exposes the charged portion of photoconductive surface 12, selectively discharging the charge thereon to record a screen electrostatic latent image on photo conductive surface 12. As drum 10 continues to rotate in the direction of arrow 14, a light image of the transparency being reproduced, is superimposed over the screen electrostatic latent image.The color filtered light image of transparency 24, as exemplified by a 35mm slide, is projected onto the screen electrostatic latent image recorded on photoconductive surface 12, in registration therewith. Color transparency 24 is positioned in slide projector 26. Slide projector 26 includes a light source 28 adapted to illuminate transparency 24. In addition, slide projector 26 comprises a lens 30 having an adjustable focus to produce an enlarged or magnified image of color transparency 24. A suitable type of slide projector is sold under the tradename Carousel, Model No. 600, manufactured by the Eastman Kodak Corporation of Rochester, N.Y. A projector of this type has an F/35 Ektaner C projection lens.

Light source 28 is a quartz lamp. An enlarged image of color transparency 24 is directed onto mirror 32. Mirror 32 reflects the enlarged image through field lens 34.

A suitable type of field lens is a Fresnel lens. Interposed between field lens 34 and transparent platen 36 is a composition frame 38 having an aperture therein, i.e. a picture frame or informational frame which may optionally have indicia inscribed thereon.

Composition frame 38 defines an opaque border extending outwardly from the color transparency image. A scanning system is disposed beneath platen 36 which includes a moving lens system designated generally by the reference numeral 40, and a color filter mechanism, shown generally at 42.

Lamps 44 move in a timed relationship with lens 40 and filter mechanism 42 to scan and illuminate successive incremental areas of composition frame 38 which may be optionally placed on platen 36. In this manner, a light image of the transparency is combined with a light image of the composition frame to form a combined light image.

This combined light image is projected onto the screen electrostatic latent image recorded on photoconductive surface 12 selectively dissipating the charge thereon to record a modulated electrostatic latent image. The exposure system will be discussed hereinafter in greater detail with reference to Figure 2.

After the modulated electrostatic latent image is recorded on photoconductive sur iace 12, drum 10 rotates to development station C. At development station C, the individual developer units generally indicated by the reference numerals 46, 48 and 50, respectively, are arranged to render visible the electrostatic latent image recorded on photoconductive surface 12.

Preferably, each of the developer units are of a type generally referred to in the art as "magnetic brush developer units". A typical magnetic brush system employs a magnetizable developer mix which includes magnetic carrier granules and heat settable toner particles. In operation, the developer mix is continually brought through a directional flux field forming a chain-like array of fibers extending outwardly from the developer unit. This chain-like array of fibers is frequently termed a brush. As drum 10 rotates, the electrostatic latent image recorded on photoconductive surface 12 contacts the brush of developer mix.

Toner particles are attracted from the carrier granules to the latent image. Each of the developer units contain appropriately colored toner particles. For example, a green filtered light image is developed by depositing magenta toner particles thereon, a red filtered light image with cyan toner particles, and a blue filtered light image with yellow toner particles. This type of development process is termed subtractive.

A development system of this type is described in U.S. Patent No. 3,854,449.

After the single color electrostatic latent image is developed with toner particles, drum 10 rotates to transfer station D. At transfer station D, the toner powder image adhering electrostatically to photoconductive surface 12 is transferred to a sheet of support material 52. Support material 52 may be a sheet of paper or plastic material, amongst others. Transfer station D includes a corona generating device, indicated generally at 54, and a transfer roll, designated generally by the reference numeral 56. Corona generator 54 is excited with an alternating current and arranged to precondition the toner powder image adhering electrostatically to photoconductive surface 12.Transfer roll 56 recirculates support material 52 and is electrically biased to a potential of sufficient magnitude and polarity to electrostatically attract the preconditioned toner particles from the latent image recorded on photoconductive surface 12 to support material 52. Transfer roll 56 rotates in the direction of arrow 58, in synchronism with drum 10, to maintain support material 52 secured releasably thereon in registration with the toner powder image deposited on photoconductive surface 12. This enables successive toner powder images to be transferred to support material 52 in superimposed registration with one another. U.S. Patent No.

3,838,918 discloses a suitable transfer station.

Prior to proceeding with the remaining processing stations, the sheet feeding path will be briefly described. Support material 52 is advanced from a stack 60 mounted on a tray 62. Feed roll 64, in operative com munication with retard roll 66, advances and separates the uppermost sheet from stack 60. The advancing sheet moves into chute 68 which directs it into the nip between register rolls 70. Register rolls 70 align and forward the sheet to gripper finger 72 mounted on transfer roll 56. Gripper fingers 72 secure support material 52 releasably on transfer roll 56. After the requisite number of toner powder images have been transferred to support material 52, gripper fingers 72 release support material 52 and space it from transfer roll 56. As transfer roll 56 continues to rotate in the direction of arrow 58, stripper bar 74 is interposed therebetween.Support material 52 passes over stripper bar 74 onto endless belt conveyor 76. Endless belt conveyor 76 advances support material 52 with the toner powder image transferred thereto to fixing station E.

At fixing station E, a fuser, indicated generally by the reference numeral 78, generates sufficient heat to permanently affix the transferred toner powder image to support material 52. A suitable fusing device is described in U.S. Patent No.

3,781,516.

After the fixing process, support material 52 is advanced by endless belt conveyors 80 and 82 to catch tray 84. The machine operator may readily remove the finished color copy from catch tray 84.

Although a preponderance of the toner particles are transferred to support material 52, invariably some residual toner particles remain adhering to photoconductive surface 12 after the transfer of the toner powder image therefrom. These residual toner particles are removed from photoconductive surface 12 as it rotates through cleaning station F. At cleaning station F, the residual toner particles are brought under the influence of a cleaning corona generating device (not shown) adapted to neutralize the electrostatic charge remaining on the residual toner particles and photoconductive surface 12. The neutralized toner particles are then cleaned from photoconductive surface 12 by a rotatably mounted fibrous brush 86 in contact therewith. A suitable brush cleaning device is described in U.S. Patent No. 3,590,412 issued to Gerbasi in 1971.

It is believed that the foregoing description is sufficient for the purpose of the present application to depict the general operation of an electrophotographic printing machine incorporating the features of the present invention therein. Referring now to the specific subject matter of the present invention, Figure 2 depicts exposure station B in greater detail.

As shown in Figure 2, a screen 22 is positioned at exposure station B prior to the path of the light image. It should be noted that screen 22 may be located either prior to or subsequent to the light image path.

Light source 20 projects light rays through screen 20 forming a light image of a screen pattern which exposes the charged portion of photoconductive surface 12. This records an electrostatic latent image of the screen pattern on photoconductive surface 12. The electrostatic latent image of the screen pattern moves in the direction of arrow 14 so as to enable the combined light image to be projected thereon in superimposed registration therewith. Thus, the resultant electrostatic latent image formed on photoconductive surface 12 is modulated.

In the pictorial mode of operation, the screen member 22 and light source 20 are operational. Light source 20 is excited by voltage source 88. In order to place the printing machine in the functional mode of operation, i.e. wherein an un-modulated electrostatic latent image is recorded on photoconductive surface 12, voltage source 88 is de-energized, thereby de-activating light source 20. This precludes the formation of a light image of the screen pattern.

Thus, the single color light image exposing the charged portions of photoconductive surface 12 produces a single color electrostatic latent image which is un-modulated.

Hence, in the functional mode of copying the latent image is un-modulated whereas in the pictorial mode the latent image is modulated. Modulation is achieved by the formation of a screen pattern latent image on the photoconductive surface in superimposed registration with the latent image of the transparency. Thereafter, the modulated latent image is rendered visible by the development process heretofore described.

With continued reference to Figure 2, lamps 44 move across platen 36 illuminating incremental widths of composition frame 38.

Lamps 44 are mounted on a suitable carriage which is driven by a cable pulley system from the drive motor rotating drum 10. As the lamp carriage traverses platen 36, another cable pulley system moves lens 40 and filter 42 at a correlated speed therewith. Filter assembly 42 is mounted on a suitable bracket extending from lens 40 to move in conjunction therewith. Lamps 44, lens 40 and filter 42 scan the combined image to produce a flowing light image thereof. Slide projector 26 projects an enlarged image of color transparency 24 onto mirror 32. Projector 26 includes a light source 28 adapted to illuminate color transparency 24 with lens 30 being arranged to produce an enlarged light image thereof.

Lens 30 has an adiustable focus to vary the magnification while maintaining the resultant image in focus. The color transparency image transmitted to mirror 32 is reflected through field lens 34 and platen 36. Preferably, field lens 34 has the general characteristics of being composed of small, recurring light deflecting elements that will, as an entire unit, perform to achieve a uniform distribution of light over a predetermined area. The gratings or grooves therein are preferably about 200 or more per inch. Field lens 34 converges the diverging light rays from lens 30 of projector 26.

Other suitable field lenses may be employed in lieu of a Fresnel lens. However, without such a lens, the light rays reflected by mirror 32 would continue to diverge. The light rays from the color transparency and composition frame 38 are reflected by mirror 94 through lens 40 and filter 42 forming a single color light image thereof. This single color light image is reflected by mirror 92 onto the screened electrostatic latent image recorded on photoconductive surface 12.

A suitable field lens is described in greater detail in U.S. Patent No. 3,424,525.

Filter 42 is adapted to interpose selected color filters into the optical light path to create single color electrostatic latent images on photoconductive surface 12. Upon reaching the end of the path of scan, lamps 44, lens 40 and filter 42 are spring biased to return to their original position for the start of the next successive cycle. It should be clear that the movement of lens 40, filter 42 and lamps 44 are correlated with the speed of rotation of drum 10 for exposure of the charged portion of photoconductive surface 12. Greater details regarding the drive mechanism of the optical system are given in U.S. Patent No. 3,062,108.

Preferably, lens 40 is a six-element split dagor type of lens having front and back compound lens components with a centrally located diaphragm therebetween. The lens system forms a high quality image with a field angle of about 31 and a speed ranging from about F/45 to about F/85 at about a 1:1 magnification. In addition, lens 40 is designed to minimize the effect of secondary color in the image plane. The front lens component has three elements including, in the following order; a first lens element of positive power, a second lens element of negative power cemented to the first lens element and a third lens element of positive power disposed between the second lens element and the diaphragm. The back lens component also has three similar lens elements positioned so that lens 40 is symmetrical.In a specific embodiment of the lens, the first lens element in the front component is a double convex lens, the sec ond element a double concave lens and the third element a convex-concave lens element. Greater details regarding: lens 40 are given in U.S. Patent No. 3,592.531.

With continued reference to Figure 2, filter 42 includes a housing which is mounted on lens 40 by a suitable bracket and moves with lens 40 during scanning as a single unit. The housing of filter 42 includes a window which is positioned relative to lens 40 permitting the light rays reflected by mirror 94 to pass therethrough. Bottom and top walls of the housing include a plurality of tracks which extend the entire width thereof. Each track has a filter mounted movably therein. The filters move from an inoperative position to an operative position. In the operative position, the filter is interposed in the window of the housing permitting the light rays to pass therethrough. Individual filters are made from any suitable filter material such as coated glass.Preferably, three filters are employed in the electrophotographic printing machine shown in Figure 1, a red filter, a blue filter and a green filter. As pre viously noted, each of the filters is associated with its respectively colored toner particles, i.e. the complement of the color thereof, to produce a subtractive system. A detailed description of filter 42 may be found in U.S. Patent No. 3,775,006.

Preferably, screen member 22 includes a substantially transparent sheet made from a suitable plastic or glass. A plurality of spaced, opaque lines are disposed on the transparent sheet. Screen member 42 includes a plurality of lines printed on the transparent sheet by a suitable chemical etching or photographic technique. Preferably, the screen comprises a plurality of hard cross lines. The spacing between adjacent lines determines the quality of the resultant copy. A finer screen size generally results in a more natural or higher quality copy. Thus, while a coarse screen having 50 to 60 lines per inch will be useful for some purposes, finer screens such as those having anything from 100 to 400 or more lines per linear inch will form a copy having a nearly continuous tone appearance.

With finer screens, the screen pattern will be barely perceptible on the finished copy and the copy will have the appearance of a continuous tone photograph. Preferably, screen 22 has about 120 lines to the linear inch.

While the invention has been described in connection with a line screen, one skilled in the art will appreciate that the invention is not necesasrily so limited and that a dot screen may be employed in lieu thereof.

Preferably, the dot screen comprises a plurality of hard clear and opaque dots.

By way of example, a suitable dot screen has about 120 dots to the linear inch.

When a dot screen is employed, a flash illumination light source is utilized therewith.

In recapitulation, the electrophoto graphic printing machine depicted in Figure 1 is adapted to produce color opaque copies from color transparencies. The color transparency may be a conventional 35mm slide or any other type of microfilm. In this type of a printing machine, a light image of a screen pattern exposes the charged portion of the photoconductive surface and a light image of the color transparency is projected in registration thereon. Thus, a modulated electrostatic latent image is recorded on the photoconductive surface which readily lends itself to producing a photographic quality copy of the transparency. While the screen has been depicted as being located prior to the optical light path of the color transparency, one skilled in the art will appreciate that it may alternatively be located subsequent thereto.In the event that the screen is located after the formation of the transparency light image, the screen light pattern will be projected in superimposed registration with the electrostatic latent image of the transparency recorded on photoconductive surface 12. Thus, the resultant electrostatic latent image wil be modulated. Hence, a modulated electrostatic latent image of a color transparency is recorded on the photoconductive surface by locating the screen prior to or subsequent to the optical path of the transparency light image. This system employs a conventional scan lamp in a typical electrophotographic printing machine and does not require a high intensity illumination system. The foregoing is achieved by the utilization of an auxiliary light source in conjunction with the screen for projecting the screen pattern onto the photoconductive surface.This eliminates the requirements that the transparency light image pass through the screen.

WHAT WE CLAIM IS: - An electrophotographic printing machine for printing from a transparency, includ ing:- a photoconductive member; means for charging at least a portion of said photoconductive member to a substantially uniform level; means for forming a light image of the transparency on the charged portion of said photoconductive member to selectively dissipate the charge thereon, recording an electrostatic latent image of the transparency; a screen member positioned closely adjacent to said photoconductive member;; a light source positioned to transmit light rays through said screen member, forming a light image of the screen pattern which exposes the charged portion of said photoconductive member to record thereon an electrostatic latent image of the screen pattern in superimposed registration with the electrostatic latent image of the transparency; a transparent plate; a composition frame disposed on said platen; a field lens positioned on said composition frame; and means for exposing the charged portion of said photoconductive member to a light image of said composition frame, recording thereon a combined electrostatic latent image of the transparency and composition frame in superimposed registration with the electrostatic latent image of the screen pattern.

2. A printing machine as recited in Claim 1, including means for filtering the light image of the transparency to form a single color light image which exposes the charged portion of said photoconductive member to record thereon a single color electrostatic latent image.

3. A printing machine as recited in Claim 1 or Claim 2 wherein said forming means includes a slide projector mounted on the printing machine to project an image of the transparency through said receiving member.

4. A printing machine as recited in any one of claims 1 to 3, wherein said exposing means includes : -- a light source arranged to illuminate said composition frame disposed on said platen; and a lens positioned to receive the light rays from the combined image of the transparency and said composition frame.

5. A printing machine as recited in any one of claims 1 to 4, including: means for developing the latent image recorded on said photo conductive member with toner particles complementary in color to the single color light image; means for transferring the toner powder image from the electrostatic latent image recorded on said photoconductive member to a sheet of support material; and means for permanently affixing the toner powder image to the sheet of support material.

6. A printing machine as recited in any one of claims 1 to 5 including means for selectively energizing said light source associated with said screen member.

7. A printing machine as recited in any one of claims 1 to 6, wherein said screen member includes a transparent sheet having a plurality of spaced lines thereon.

8. A printing machine as recited in any one of claims I to 6, wherein said screen member includes a transparent sheet having a plurality of spaced dots thereon.

9. A printing machine as recited in any

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   graphic printing machine depicted in Figure 1 is adapted to produce color opaque copies from color transparencies. The color transparency may be a conventional 35mm slide or any other type of microfilm. In this type of a printing machine, a light image of a screen pattern exposes the charged portion of the photoconductive surface and a light image of the color transparency is projected in registration thereon. Thus, a modulated electrostatic latent image is recorded on the photoconductive surface which readily lends itself to producing a photographic quality copy of the transparency. While the screen has been depicted as being located prior to the optical light path of the color transparency, one skilled in the art will appreciate that it may alternatively be located subsequent thereto.In the event that the screen is located after the formation of the transparency light image, the screen light pattern will be projected in superimposed registration with the electrostatic latent image of the transparency recorded on photoconductive surface 12. Thus, the resultant electrostatic latent image wil be modulated. Hence, a modulated electrostatic latent image of a color transparency is recorded on the photoconductive surface by locating the screen prior to or subsequent to the optical path of the transparency light image. This system employs a conventional scan lamp in a typical electrophotographic printing machine and does not require a high intensity illumination system. The foregoing is achieved by the utilization of an auxiliary light source in conjunction with the screen for projecting the screen pattern onto the photoconductive surface.This eliminates the requirements that the transparency light image pass through the screen.

   WHAT WE CLAIM IS: - An electrophotographic printing machine for printing from a transparency, includ ing:- a photoconductive member; means for charging at least a portion of said photoconductive member to a substantially uniform level; means for forming a light image of the transparency on the charged portion of said photoconductive member to selectively dissipate the charge thereon, recording an electrostatic latent image of the transparency; a screen member positioned closely adjacent to said photoconductive member;; a light source positioned to transmit light rays through said screen member, forming a light image of the screen pattern which exposes the charged portion of said photoconductive member to record thereon an electrostatic latent image of the screen pattern in superimposed registration with the electrostatic latent image of the transparency; a transparent plate; a composition frame disposed on said platen; a field lens positioned on said composition frame; and means for exposing the charged portion of said photoconductive member to a light image of said composition frame, recording thereon a combined electrostatic latent image of the transparency and composition frame in superimposed registration with the electrostatic latent image of the screen pattern.
2. 2. A printing machine as recited in Claim 1, including means for filtering the light image of the transparency to form a single color light image which exposes the charged portion of said photoconductive member to record thereon a single color electrostatic latent image.
3. 3. A printing machine as recited in Claim 1 or Claim 2 wherein said forming means includes a slide projector mounted on the printing machine to project an image of the transparency through said receiving member.
4. 4. A printing machine as recited in any one of claims 1 to 3, wherein said exposing means includes : -- a light source arranged to illuminate said composition frame disposed on said platen; and a lens positioned to receive the light rays from the combined image of the transparency and said composition frame.
5. 5. A printing machine as recited in any one of claims 1 to 4, including: means for developing the latent image recorded on said photo conductive member with toner particles complementary in color to the single color light image; means for transferring the toner powder image from the electrostatic latent image recorded on said photoconductive member to a sheet of support material; and means for permanently affixing the toner powder image to the sheet of support material.
6. 6. A printing machine as recited in any one of claims 1 to 5 including means for selectively energizing said light source associated with said screen member.
7. 7. A printing machine as recited in any one of claims 1 to 6, wherein said screen member includes a transparent sheet having a plurality of spaced lines thereon.
8. 8. A printing machine as recited in any one of claims I to 6, wherein said screen member includes a transparent sheet having a plurality of spaced dots thereon.
9. 9. A printing machine as recited in any

   one of claims 1 to 8, wherein said field lens includes 200 gratings per inch.
10. 10. A printing machine as recited in Claim 2 or any Claim dependent thereon, wherein said filtering means includes.

    a red filter arranged to be interposed into the light image path to transmit a red light image therethrough; a blue filter arranged to be interposed into the light image path to transmit a blue light filter image therethrough; and a green filter arranged to be interposed into the light image path to transmit a green light image therethrough.
11. 11. An electrophotographic printing machine substantially as with reference to and as illustrated in the accompanying drawings.