LU82270A1 - COLORED ELECTROPHOTOGRAPHIC PRINTING METHOD AND APPARATUS - Google Patents

Description

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Methods and apparatuses are known for making color copies of color originals by electrostatic techniques consisting in optically projecting images of the original having undergone color separation onto a single charged electrophotographic element or onto several electrophotographic elements charged each corresponding to an image of a certain color to form corresponding latent electrostatic images, to develop each latent electrostatic image with its own color, then to fix the different images in superimposed condition. The images to be projected on the electrophotographic elements are obtained by projecting an image of the original through several color separation filters, a filter being provided for each color to be reproduced. Depending on the system used, the final composite image 15 is either formed directly on a single electrophotographic element, or transferred from one or more electrophotographic elements onto a sheet of support material, such as plain paper. Although many different types of electrostatic systems have been proposed or made, they have generally not been found to be satisfactory. These deficiencies have been explained by the fact that the resulting apparatuses are too large, are excessively complex in construction, costly to manufacture and use, unsafe to operate, and / or by the that they are not capable of producing images having a quality or resolution compatible with copies made by photographic and / or lithographic techniques. Furthermore, these systems do not allow modifications of color, dimensions or hue to be made to the final copy, when such modifications are either desirable or necessary, except by very delicate or costly means involving modifications. of the process.

At the present time, an electrophotographic film is available which has qualities and properties which make it superior to any other known electrophotographic film. This electrophotographic film has a photoconductive coating which is totally mineral, microcrystalline, of an anisotropic nature, which does not give rise to reciprocity or intermittence effects, which operates under low voltages, which has a very high sensitivity and which provides exceptionally high quality developed images from analog or digital information. This electrophoto-graphic film is well suited for making high resolution color copies of color originals by electrostatic techniques and, in fact, has properties that allow it to be used for this purpose. a way that had never been applied until now to other types of electrophotographic elements.

Due to the high response speed of said coating (which can be exposed in the order of a few nanoseconds), the film can be used with a very fast machine.

Among the proposals relating to the prior art, mention may be made of the following United States patents:

Our. 3,399,611, 3,690,756, 3,832,170, 4,095,879, 4,120,577 and 4,124,286.

The object of the invention is to remedy the drawbacks of known embodiments and it relates to a method of electrostatic color printing according to which the individual colors of a composite original are stored digitally in a computer and can be extracted separately for their purpose. writing or recording by laser on an electrophotographic element, method using a rotary electrophotographic drum and a transfer roller arranged to carry an element of receiving material which is applied against the rotary electrophotographic drum. loads the drum, exposes the loaded drum to an image of a color of the original, ensures the development of the image and transfers the developed image onto the element of receiving material, said method being characterized in what the exposure phase consists in ensuring the extraction and writing by laser of the image, called image, and in carrying out all of the abovementioned operations in a single revolution of the drum and for a single simultaneous revolution 35 of the transfer roller, said method being further characterized in that the loading, writing, development and transfer of each other color image of the composite original is repeated during each subsequent revolution of the drum and transfer roller up to that all the colors A-4 3 have been transferred in a condition superimposed on the element in a receiving manner, and in that this element of receiving material is removed from the transfer roller and is replaced by another element in order to allow a repeat of the pro-5 cessui on this new replacement element.

j. in addition, the invention relates to an apparatus for implementing the method according to the invention, for the execution of a | or multiple color copies of a color original with a | electrophotographic process, comprising: an electro- element | 10 rotary photographic, a drive mechanism for rotating: said electrophotographic element sequentially hung a cycle through a series of processing stations which is distributed along its periphery, said processing stations comprising in order: a charging station, an expedition station, a development station and an image transfer station, and means for applying a uniform electrostatic charge to a part of the electrophotographic element in the charging station, apparatus characterized in what it includes: A. these means for sequentially forming several latent electrostatic images on said electrophoto-graphic element in the exposure station during the rotation of said element, each of said electrostatic images corresponding to a different color component of the original in color and each image being formed during a respective cycle, B. a development device which can be d moved into the development station along a path which is oriented tangentially to said rotating electrophotographic element, said development device comprising a plurality of development units which are distributed in a row and which are arranged to pass in series into the development station, each unit development device comprising a developer, the color of which corresponds to the color component of one of the latent electrostatic images, 35 C. a drive mechanism for moving the development device in stages over its tangential path through said development station , in synchronization with the formation of the latent images of corresponding colors, and to bring the development units into a relation of developer application with respect to the electrophotographic element in series when each unit is located in said station, said mechanism training acting to advance 5 p step by step each development unit in said development station, then to stop it there for a sufficiently long pause period, then to take said development unit step by step out of said station while simultaneously ensuring movement of the next unit in said station, the part of the electrophotographic element which carries a latent color image corresponding to each development unit being completely moved through the development station during the break period when its development unit 15 respective is located in said station, and D. a transfer device placed in said transfer station to ensure the transfer of each developed image on a sheet of support material in an overlapping relationship when each developed image passes through the transfer station during its respective cycle, the number of cycles planned corresponding to the number of colors and the number of prints on each sheet corresponding to the number of cycles.

Other advantages and characteristics of the invention will be highlighted in the following description, given by way of nonlimiting example, with reference to. single appended drawing which is a partly perspective view and partly in block diagram of an apparatus for making color copies of color originals in accordance with the present invention.

In the drawing, there is shown an embodiment of an electrophotographic copying apparatus which is arranged in accordance with the present invention and which has been designated as a whole by the reference 11.

An original to be copied is placed on a flat bench analyzer 13 where the representation which it carries is quickly analyzed and converted into digital separation information in three or four colors. The flat bench analyzer 13 may include a white light source, an optical analysis unit, j / red, green and blue filtering units to form

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*, · * “5 -¾ Π the three color separations, and an analog-to-digital converter to convert analog information into digital data. The three or four color separations ii can be carried out simultaneously by passing images 5 of the original at the same time through the three filters.

| <i j A special system of analysis can be used for a black pigment; lysis or filtering.

j The digital data thus obtained are applied to one! computer 15 where they are stored, either permanently! _ 10 or temporarily, for further processing.

Ü This further processing consists in converting the digital data! II risks of red, green, blue and black in corresponding values - || laying respectively in the colors blue-green, lilac, yellow and black. Further processing can also include ï; 15 operations such as linear framing, cutting, density modification, color balancing, color inversion, titration and the like.

! A graphic display terminal 17, which is connected to the gold! dinateur 15 ,; allows you to examine the images stored in the or-; 20 dinator at any time appropriate.

A laser system 19 for writing or recording images using digital data is also connected to the computer 15. The laser system 19 may include an analysis prism, a laser and an acousto-optic modulator for modulating the laser output beam in accordance with j digital information. The laser system 19 is arranged for I; perform the analysis in a particular angle. Instead of having a single laser, the system * 19 can have several! lasers which are each arranged to analyze part of this particular angle.

| An electrophotographic element is used which is: in the form of a rotary electrophotographic drum 21 which <is mounted on a shaft 23 which can rotate on a support frame 25 in the direction indicated by the arrows. This support frame 25 35 has been shown in cutaway view, the bearings, the journals and the brackets not being indicated to simplify the drawing.

The drum 21 is driven by a motor 27, the output shaft of which is mechanically coupled, as indicated at 22, to the shaft I 23. The peripheral surface of the drum 21 comprises a coating I â.

I i / * 4 6 photoconductor placed on a conductive substrate. This conductive substrate may consist of a sleeve mounted on the drum 21, or it may form an integral part of the drum 21. Thus, it may comprise a metal substrate provided with a photoconductive coating on its surface, or else a sheet of film. insulating material comprising an ohmic layer which is placed between it and the photoconductive coating. In one or the other case, the metal substrate or the ohmic layer are necessary in order to be able to ensure the electrical connection with a> 10 charging circuit comprising a voltage source with corona effect.

The photoconductive coating allows the formation of latent electrostatic images by laser writing at very high speed, the images then being developed to form high quality and high resolution copies. An example of such a coating has been described in the aforementioned United States Patent No. 4,025,339.

It is provided on the path followed by the peripheral surface of the drum 21, and in the order indicated, a charging station 31, an exposure station 33, a development station 35, a transfer station 37 and a station cleaning 39 of the ultrasonic or other type. As shown in the figure, the development station 35 is placed just below the drum 21.

In the charging station 31, there is provided a charging device 41 for applying a uni-form electrostatic charge to the photoconductive surface of the drum 21. This charging device 41 may comprise one or more corona wires which are connected to a crown voltage source 42 via a suitable connection 40. The wire (s) (not visible) of the device 41 can be moved al-30 ternatively and / or in rotation to produce a uniform charge.

When the surface portion loaded in station 31 passes through exposure station 33, a latent electrostatic image corresponding to one of the four color components of the original (i.e. blue-green, lilac, yellow or black) is "written" on the surface by the laser beams 20 emitted by the system 19. (The beam (s) have been represented only symbolically in the drawing).

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When the latent electrostatic image is moved through the development station, it is developed using a corresponding color developer from a development device 43.

The development device 43 comprises four individual development units 45, 47, 49, 51 which are mounted in a row on a frame 53. Each development unit comprises a tray containing a certain quantity of a liquid developer, of a color different from the others, and a developer applicator roller 10 which is partially submerged in the corresponding tank. The color of the liquid developer in each tray corresponds to one of the four colors making up the original.

Consequently, the colors of the developers located in the four tanks are respectively: blue-green, lilac yellow and black. The chassis 53 is mounted on a rigid carriage 54 which is guided by slides 55 so as to move step by step and tangentially with respect to the drum 21 so as to pass development units 45, 47, 49 and in series. 51 in the development station 35. The chassis 53 and the carriage 20 54 are driven by a worm and nut mechanism, in which a programmed stepping motor 57 is provided, the shaft of which is coupled to the worm gear end 59 which is screwed into a suitable nut integral with the carriage 54. The nut may comprise a threaded support 61 which is directed downwards from the carriage 54. The motor 57 can be mounted on the carriage and the worm 59 can be rotatably mounted in a block 62 which is connected to the frame 25 .. The electrical connections have not been indicated in the drawing.

The development units 45, 47, 49 and 51 are arranged on the carriage 53 in the order in which it is desirable to transfer the four developed images to the receiving medium in the transfer station 37. Consequently, if the developed images are transferred in the order of the following colors: blue-green, lilac, yellow and black, there are the developers of 35 corresponding colors in the bins of the development units 45, 47, 49 and 51, assuming that the working stroke of the carriage 54 is directed to the left (refer to the double-headed arrow which indicates the directions of movement of the cha-j riot 53-54).

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In operation, when a multi-color original is to be reproduced, the apparatus is synchronized and programmed so that the carriage 53 moves step by step to the left by driving the developer applicator roller of the developing unit 45 to apply it against the lower surface of the electrophotographic drum 21 a short time before the arrival of the front edge of the first latent image which has been formed in the exposure station 33. This gives the applicator roller of the unit 45 a sufficient time to start picking up the color developer from its tray to produce good development. Alternatively, the applicator rollers can be rotated slowly and continuously to keep the developers flowing over the corresponding surfaces of the rollers. Friction drive means can be used to rotate the applicator rollers, the drive action of which can be appropriately controlled.

The carriage 53 keeps the applicator roller of the developing unit 45 in contact with the drum 21 for a certain period of processing until the latent image of a particular color corresponding to the unit 45 has been developed. The rotation of the drum causes or accompanies the rotation of the applicator roller. In the blank zone existing between latent images during a fraction of a revolution of the drum 21, the carriage 53 is advanced step by step to the left, looking at the figure, so as to now bring the applicator roller from the second development unit 47 in contact with the lower surface of the drum 21. The applicator roller of the development unit 45 is now released, after having been moved to the left of the development station. The developing unit 47 then applies the lilac color developer coming from its tank to the drum 21 in the development station in order to ensure the development of the second latent image formed by the laser system 19. It remains in position during a treatment period of the same duration as before. The first developed blue-green image is transported on the drum 21 to the transfer station 37 where it is transferred to the receiving sheet S carried by the transfer roller 65. Developer remaining on the surface of the drum 21 is removed in station 39 by a device? /> 9% positive cleaning 67, for example a collector operating by vacuum or else an ultrasonic device, so that the photoconductive coating situated on the drum 21 is ready to receive the next image to be produced during the next round. Consequently, when the frame 53 and the carriage 54 are moved one step to the left so as to bring the applicator roller of the developing unit 47 into contact with the lower part of the drum 21, there may still be a part of the previous developed image which is turning towards the transfer station 37 on the left side of the drum 21, and the following image can already be partially applied in latent form on the right side of the drum 21 and be moved towards the development station 35.

In this way, the frame 53 progresses step by step to the left and stops once each revolution of the drum 21 until the four development units 45, 47, 49 and 51 are brought into contact. from drum 21 and until four developed images have been transferred to sheet 20 of paper S.

It can be considered that a complete or global cycle is made up of four cycles of staggered advance and pause for the execution of a complete copy in multiple colors.

One revolution of the transfer roller 65 can be used for the removal of the receiving sheet S while the drum 21 rotates freely relative to any developing unit. During this period of time, the motor 57 can be programmed to rotate the worm 59 in the opposite direction in order to return the carriage 54 to its rest position, located on the right in the figure. This movement does not have to be done step by step. Preferably, contact and / or transfer of developer is avoided between the applicator rollers of the developing units 45, 47, 49 and 51 and the drum 21 during this return stroke. For example, the entire chassis 53 can be mounted on springs which themselves rest on the carriage 54 which is directly driven by the worm screw 59. A simple member such as a cam, a relay, a lever or the like can pull the chassis 53 /

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slightly down towards carriage 54 and hold it in position while carriage 54 is moving to the right to return to its rest position, release then taking place.

Alternatively, the drum 21 and the transfer roller 65 can be moved slightly upward during the return movement of the carriage.

In another variant, contact rollers are allowed with the drum 21 during the return movement 10 and means such as 63 are provided for cleaning the drum 21 from the developer which could have been transferred to the virgin part of the drum 21 during this movement.

In another variant, which is not as interesting, one could reverse the order of transfer of the color images 15 on alternate sheets of paper S. The laser system 19 would then be controlled by the computer 15 to reverse the writing order of the color images and the latent images would be developed in the order 51, 49, 47, 45, during the carriage return stroke. 54 and the frame 53 step by step from the left 20 to the right.

Anyway, the different components must be synchronized in movements and operations so that a particular color image is written by the laser system 19 on the drum 21, that it reaches the development station 25 35 at the moment. where the applicator roller of the developer unit corresponding to the same color is applied against the lower surface of the drum 21. As a result, each latent electrostatic image is developed using the correct color developer and in the correct sequence.

After the latent electrostatic image has been developed in the developing station, the excess developer is removed from the surface of the drum 21, when the developed image is moved to the transfer station 37, by a device 63 operating under vacuum and placed on the path followed by image 35 between the two stations. In the transfer station 37, the developed image is transferred to a sheet of support material S, for example plain paper from a source of sheets. designated by 64.

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A transfer roll is provided in transfer station 37! transfer 65 which is mounted so as to turn in the direc

tion of the arrows and which esc appropriately driven I at the same linear speed as the drum 21. A sheet S

j 5 is driven through guides 67 by a mechanism comprising | so many suction cups 68, the sheet coming into contact with the wheel! the transfer water 65. By a well known means, for example by electrostatic attraction, the sheet S is wound around the peripheral surface of the transfer roller 65 and hand-held tightly against it during its rotation.

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After each developed image has been transferred to the sheet S which is wrapped around the transfer roller 65, the surface of the drum 21 moves clockwise through the area which corresponds to the post 15 cleaning 39. In this zone, the excess developer i remaining on the surface of the drum 21 after transfer is removed by the cleaning device 67 which, as mentioned above, may be in the form of a collector operating under vacuum, or an ultrasonic device, which removes and / or dissipates the remaining developer.

The charging, imaging, development, transfer and cleaning phases are repeated for each of the color images. If there are three separate colors, the total number of images transferred to the receiving sheet is three; if the number of separate colors is four, the total number of transferred images is also four. These images must be brought into perfect coincidence, which can be achieved in a simple manner with the apparatus according to the invention. The mixing of the colors per-30 putting to achieve the reproduction by use of developers of different fundamental colors such as blue-green, lilac, yellow and black, must take into consideration their transparency and, possibly, other characteristics which are obviously very known to specialists. It goes without saying that the nature of the developer must be taken into consideration in order to obtain the best results.

When. The final composite image made up of the different individual color images is being formed on the receiving sheet by serial transfers of the colors to.

12 different constituting the final image, the rollers 21 and 65 rotate together at the same speed. These rollers have identical diameters; accordingly, the numbers of turns performed by each of them to produce a single color composite image on the receiving sheet S are equal and correspond to the number of colors to form the final composite image. Normally, this number is equal to four and the receiving sheet S is held in place on the periphery of the roll while the above operations take place, s. 10 When the composite image is finished and when all the colors constituting it have been transferred to the sheet S, the final image is constituted by a series of, for example, four developed but non-fixed images which are placed one on the other. At this moment of the operation of the machine, that is to say either before the sheet S is released from the transfer roller 65, or immediately afterwards, the developed composite image is fixed on the sheet by passing it through in front of a fixing device 69. This device can be constituted by a heating appliance or by another appropriate fixing means. For example, instead of or in addition to the application of heat, the device 69 can deposit, using a roller or a sprayer, a layer of a protective coating or a resinous varnish on the final composite image. There are many different forms of material which are transparent and relatively resistant to abrasion and which are used to protect inked or developed images. Preferably, it is desirable to use a glossy or vitrified finish to give the resulting image a certain background appearance. The final sheet S is transported to the left, looking at the drawing, 30 and it is deposited in an output bin 73.

After the development device 43 has been brought back to the right into its "rest" position, which is that shown in the drawing, the apparatus has completed its overall cycle and it is ready to make another composite copy, by extracting the same information from the computer memory or from different information contained in this memory.

It is possible to store in reservoirs 75, 77, 79 and 81 reserves of developers usable in the various development units J, said reservoirs being installed on the base 13 of the frame 25, which can be equipped with pumps and hoses in order to '' transfer the developers to the respective tanks of the development units.

Although the invention has been described with reference to the making of color copies of color originals, it is obvious that the apparatus can also be used, if necessary, to make copies in black and white , from black and white originals, or to make black and white copies of color originals.

When using the apparatus 11, the functions of the various components can be programmed by suitable programming means such as relays, shafts, cams and the like. Preferably, the operations are programmed by the computer using appropriate control and / or validation signals, which are transmitted via the lines 100 to the various motors, drive means, etc. The device.

To establish a coincidence of the images superimposed on the sheet of paper S, the construction and synchronization of the moving parts of the apparatus 11 is carried out with appropriate care, but it is also possible to make adjustments by means manually operated mechanical devices, automatic detection devices, laser operation adjusting means and / or a combination of said means.

In the claims, the term "cycle" generally designates a revolution of the drum 21 and the transfer roller 65, during which a color print is produced and transferred. For a composite original of four colors, provision must be made four "cycles", the overall cycle being completed after the sheet has been unloaded, after its composite image has been fixed and / or provided with a protective coating, has been deposited in the output bin, the developing device being returned to its rest position and the apparatus being ready to execute the new series of cycles 35 | or revolutions.

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Claims (20)

14 1. A method of electrostatic color printing in which the individual colors of a composite original are stored digitally in a computer and can be extracted separately for writing or recording by laser on an electrophotographic element, method in which using a rotating electrophotographic drum and a transfer roller arranged to carry a receiving material element which is applied against the rotating electrophotographic drum, loading the drum, exposing the loaded drum to a color image of the original , the image is developed and the developed image is transferred onto the element of receiving material, said method being characterized in that the exposure phase consists in ensuring the extraction and writing by laser of said image and to carry out all the aforementioned operations in a single revolution of the drum and for a single simultaneous turn of the transfer roller, ledi The method is further characterized in that the loading, writing, development and transfer of each other color image of the original composite is repeated during each subsequent revolution of the drum and the transfer roller up to that all the colors have been transferred in a condition superimposed on the receiving material element, and in that this receiving material element is removed from the transfer roller and is replaced by another element in order to allow a repetition of the process on this new replacement element. 2. Method according to claim 1, characterized in that each latent electrostatic image corresponding to one of the color components of the color original is formed during a revolution of the rotary element, in that each latent electrostatic image thus formed is developed with a material the color of which corresponds to the color component of the latent electrostatic image by moving several developing units each containing a material of different color in front of said electrophotographic element successively and in a synchronization sequence controlled in such a way that each development unit develops independently | a respective latent electrostatic image during its revolution and that each image is transferred in this condition developed sequentially onto a sheet of support material, in an overlapping relationship with the other images and by causing the rotary member to execute a number of 5 revolutions equal to the number of colors making up the original. 3 ^ - A method according to claim 1 or 2, characterized in that the various latent electrostatic images are formed by performing the charge of the electrophotographic element, then writing the latent electrostatic images 10 on said element, successively and using a laser modulated using digital information derived from the color original. 4. Method according to any one of claims 1 to 3f, characterized in that each of said latent electrostatic images is developed by applying a liquid developer on the corresponding latent electrostatic image. 5. Method according to claim 1, characterized in that said latent electrostatic images are at least three in number and they are each adapted to form a developed image of a color different from the others. 6. Apparatus for implementing the method according to any one of claims 1 to 5, for the execution of one or more color copies of a color original by an electrophotographic process, comprising: an electro- 25 rotary photographic, a driving mechanism for rotating said electrophotographic element sequentially during a cycle through a series of processing stations which are distributed along its periphery, said processing stations comprising in order: a station of charge, a post. 30 of exposure, a development station and an image transfer station, and means for applying a uniform electrostatic charge on a part of the electrophotographic element in the charging station, apparatus characterized in that it comprises: A. means for sequentially forming several latent electrostatic images on said electrophotographic element in the exposure station during the rotation of said element, each of said electrostatic images corresponding to a different color component of the color original and each image being formed during a respective cycle, B. a developing device movable in the developing station along a path which is oriented tangentially to said rotating electrophotographic element, said developing device comprising a plurality of developing units which are distributed in a row and which are arranged to pass in series in the station of development, each development unit comprising a developer, the color of which corresponds to the ~ 10 color component of one of the latent electrostatic images, C. a drive mechanism for moving the development device in stages over its tangential path to through said development station, in synchronization with the formation of the latent images of corresponding colors, and to bring the development units into a developer application relationship with respect to the electrophotographic element in series when each unit is located in said station, said driving mechanism acting so as to advance each development unit step by step in said development station, then to stop it therein for a sufficiently long pause period, then to bring out step by step not said development unit outside said station while simultaneously moving the next unit in said station, the part of the electrophotographic element which carries a latent image of color corresponding to each development unit being completely moved through the development station during the break period when its respective development unit is in said station , and D. a transfer device placed in said transfer station to ensure the transfer of each developed image on a sheet of support material in an overlapping relationship when each developed image passes through the transfer station during its respective cycle, the expected number of cycles corresponding to the number of colors and the I number of prints on each sheet corresponding to the J number of cycles, / * '17 7. Apparatus according to claim 6, characterized in that it comprises a coding converter ensuring the conversion of the original in color into digital information coded in correspondence with the colors and in that there is provided a laser whose beam outgoing is modulated in correspondence to said digital information in order to write each of said latent electrostatic images on said electrophotographic element. 8. -. Apparatus according to claim 6 or 7, characterized in that each developing unit comprises a container and an applicator placed in a developer transfer relationship with respect to the electrophotographic element and in that the developing material of which the color corresponds to the component of. Color of the latent electrostatic image is formed by a liquid developer placed in the tank and in contact with the applicator. 9. Apparatus according to claim 8, characterized in that the applicator is a roller. 10. Apparatus according to any one of claims 6 to 20 9, characterized in that there is provided at least three development units each corresponding to a different color. 11. Apparatus according to any one of claims 6 to 10, characterized in that the development device comprises a carriage mounted on a slide and in that a stepping motor is provided which is coupled to the carriage so to move it along the slide. 12. Apparatus according to claim 11, characterized in that the developing device is moved step by step in a direction along said tangential path while said cycles are being executed and in that said carriage is returned to a rest position in an opposite direction after completion of said cycles of execution of a fully developed image, so that the carriage is ready to execute again a stepwise movement in the first direction for the purpose of the execution of a following series of I cycles. L * r * 18 13. Apparatus according to any one of claims 6 to 12 / characterized in that said tangential path is rectilinear. 14. Apparatus according to any one of claims 1 to 5 13, characterized in that the transfer device comprises a rotary transfer drum. 15. Apparatus according to claim 14, characterized in that the transfer drum comprises means allowing selectively the retention and the release of the sheet of support material and its movement on a path away from said transfer drum. 16. Apparatus according to claim 14 or 15, characterized in that the rotary electropiiotographic element and the rotary transfer drum are in contact with each other by their surfaces along an axial line, have the same diameter and are driven at the same speed. 17. Apparatus according to any one of claims 6 to 16, characterized in that there is provided a cleaning station allowing the removal of the developer remaining on the electropiiotographic element 20 after the image developed on said element has passed through said image transfer station, said cleaning station also being placed along the periphery of said electropiiotographic element between said image transfer station and said exposure station. 18. - Apparatus according to claim 17, characterized in that said cleaning station comprises an ultrasonic cleaning device. 19. Apparatus according to claim 15, characterized in that * there is a fixing station arranged so as to fix the images developed on said sheet of support material after all the images developed in a complete series of prints have been applied to said sheet. 20. Apparatus according to claim 19, characterized in that the fixing station is placed in a position adjacent 35. to the path followed by the sheet after its release. JL, * 19 " 21, - Apparatus according to claim 19, characterized in that said fixing station comprises a coating device π for depositing a protective coating on said images; ; developed. 22. Apparatus according to claim 19, characterized in that a coating deposition station is placed in an area adjacent to the fixing station so as to apply a protective coating to said sheet after it has passed through the | fixing station. / I ^ k ~: ~ -cr / 'ï / 1 / y i