FR2589103A3 - Indirect electrostatic printer - Google Patents

Abstract

Indirect electrostatic printer in which an intermediate recording support film, intended to receive a latent electrostatic image of that which it is desired to print, and a final recording support medium, intended to receive the latent image revealed by inking and fixed to it by pressure, are employed. The printer is conventionally provided with an electrostatic printing head 8, with an inking device 9 and with a transfer and fixing unit 23, 24, the latter two having, in common, a roller 23 called a transfer roller. The arrangement of the paper-sheet loader or loaders 2, of the container 3 for receiving the printed sheets, of the inking device 9 of the electrostatic head 8, of a device 17, 18 for eliminating electrostatic charges and of the shafts 13, 14 carrying the intermediate recording support film 10 on either side of the transfer roller and of a pressure roller 24 which is parallel and tangential to it in the transfer unit, enables a compact structure to be obtained offering easy access to the internal members and to the film.

Description

Indirect electrostatic printer
The present invention relates to indirect electrostatic printers in which an intermediate recording medium film intended to receive a latent electrostatic image of what is to be printed is used and a final recording medium intended to receive the latent image revealed by inking and fixed on it by pressure.

 The intermediate recording medium which is flexible consists of a thin strip of dielectric film, for example polyester; this strip is stored in the form of a roll in the printer.

 The latent electrostatic image is composed of ions deposited on the intermediate recording medium by selective electrical discharge, at this level between printing, miniature, multiple electrodes and neighboring counter-electrodes. The electrodes are usually distributed over one or more parallel rows and the counter-electrodes are usually arranged either opposite the electrodes and on the other side of the intermediate support film, or even along the electrodes and on the same side as by compared to the intermediate support film, in the area where electric shocks occur.

 Inking, which reveals the latent image, is carried out using particles of electrically charged liquid ink or magnetic powder ink, both attracted by the electrostatic charges which the intermediate support of recording conveys.

 The moving intermediate recording medium is pressed against the final recording medium, in a transfer station, so as to transmit the ink particles which are fixed to this final recording medium by mechanical pressure leading to close contact between supports.

 The final recording medium is preferably a medium of current quality, for example a conventional uncoated paper.

 The image is formed with a very high speed, typically of the order of ten micro-seconds per point or series of points simultaneously formed.

 Insofar as such printers are intended to be able to be installed in very diverse and generally non-specialized premises and for example on a desk or on a table, it becomes preponderant to obtain compact designs which are easy to operate by users. very diverse and possibly clumsy.

 The present invention therefore provides an indirect electrostatic printer, therefore without impact, of small size, the structure of which allows easy access to the internal organs and in particular to the rolls of intermediate recording medium, the regular replacement of which is necessary.

 The indirect electrostatic printer according to the invention conventionally comprises an electrostatic writing head provided with a set of electrodes and counter-electrodes making it possible to create, on a dielectric film serving as an intermediate recording medium, an electrostatic image of what one wishes to print, a device for inking the electrostatic images created on the film, as well as a transfer unit for transferring and fixing on a final recording medium, such as a sheet of paper, the inked images carried by the film, in addition the inking device and the transfer unit have in cpmmun a transfer roller against which the film is pressed for inking and image transfer.

 According to a characteristic of the invention, said printer comprises, on either side of the transfer roller and of a pressure roller, of transfer unit, which is at least approximately parallel to it and which is pressed against it, at least one part of a removable sheet feeder partially penetrating one side of the printer body, as well as a short guide path consisting of at least one internal wall of the printer, leading from one end extraction of the feeder towards the contact zone between transfer roller and pressure roller, on the other hand, a tray for collecting printed sheets, located at the upper part of the body and connected by a short guide at the exit of the contact between transfer roller and pressure roller, the rest of the inking device, consisting of a magnetic brush and an ink tank, being positioned under the transfer roller that brushes against said magnetic brush, the electrostatic head that being placed near the transfer roller and said magnetic brush, on the same side as two shafts located under the tray of printed sheets and on which the film is stored in rolls, the emitting shaft which carries the film before printing, being located on the other side of the print head from which it is separated by at least one eraser for electrostatic charges, on the path of the film between emitting shaft and printing head, the receiving shaft which receives the film after use being located beyond the emitter shaft with respect to the print head and at a level higher than that of said emitter shaft from which it is separated by a movable conductive separating plate by one of its ends and bearing on the portion of film wound on the transmitting shaft.

 FIG. 1 shows an example of an indirect electrostatic printer according to the invention.

 Figure 2 shows a detail of a variant transfer unit according to the invention.

 Figures 3 and 4 show two variants of the writing head according to the invention seen from the side.

 Figures 5 and 6 show two views of the same additional variant of a writing head according to the invention.

 The indirect electrostatic printer, presented in FIG. 1, conventionally comprises a bodywork 1 mounted on a frame not shown which carries the constituent parts of the printer proper. The body 1 is open to allow the lateral introduction of at least one and here, for reasons of operating convenience, two loaders 2 of sheets of paper 50 intended to constitute the final recording media on which the prints are performed. The body 1 is also open to allow the output and collection of printed sheets, not shown, in a tray 3 which is located here on the top of this body 1.

 The sheet feeders 2 are for example conventional removable feeders each capable of receiving a stack of sheets 50 which a push plate 4 with spring 5 presses against a destacker roller 6 housed in the bodywork 1 above the opening by where comes the unstacking end of the magazine 2 considered. Each feeder 2 is mechanically jammed inside the bodywork 1 so that the stack of blank 50 sheets to be printed which are stored on the push plate comes to bear at one of its ends and by its upper sheet, against the periphery of the unstacker roller 6.Each unstacker roller 6 is controlled to rotate by known means when printing is requested on one of the sheets that it contains, it then collects, out of the feeder 2 that it serves, the upper sheet of the stack against which it rests, through an open extraction end of the corresponding charger 2.

 Each sheet extracted from a feeder 2 is sent to the printing arrangement proper, via a short guide path 7 constituted by at least one internal wall of the bodywork 1.

 The printing arrangement essentially comprises an electrostatic writing head 8, an inking device 9 and a transfer unit to which are added an auxiliary device for an intermediate recording medium film 10, of dielectric material, such as indicated above.

 The writing head 8 is intended to gradually create, on the film 10, a latent electrostatic image by discharge between the printing electrodes and the counter-electrodes associated therewith. This writing head 8 has for this purpose a fixed block 11 of insulating material housing the printing electrodes and possibly the counter-electrodes and a cylinder 12 pressing the film 10 against the aligned point ends of the printing electrodes as well as 'optionally against those of the counter-electrodes, the axis of rotation of the cylinder 12 being perpendicular to the direction of movement of said film.

 The writing head 8 is for example of the type described in European patent application 0091073 in which the cylinder 12 constitutes a rotary counter-electrode situated on the other side of the intermediate recording medium with respect to the printing electrodes that includes block 11.

 Other variants of writing head 8 adaptable to the present printer will be specified below in connection with FIGS. 3 to 6.

 Whatever the variant chosen, the film 10 must be arranged so as to be able to move against the assembly 11 in a movement perpendicular to the alignment of electrodes, for this purpose this film is conventionally wound on the one hand by a end around a transmitting shaft 13 where it is stored before use, on the other hand by another end around a receiving shaft 111 which receives it after use.

 In the embodiment, the two shafts are arranged on the same side of the writing head and in positions offset in height, the emitting shaft 13 being placed so that at full capacity the film roll 10 which it carries , the bottom of this roller adjoins the bottom of the body 1, or more precisely of its lower part 1A.

 The shafts 13 and 14, which are parallel and placed the first upstream of the electrostatic head 8 and the second downstream, are brought together, at a distance slightly greater than the value for which the portions of film roll 10 which they respectively carry would come into contact. A plate, conductive separator 15, movable around a fixed axis 16 situated at one of its ends, is brought to the ground potential of the printer, it comes to bear on the portion of film roll 10 wound on the the receiving shaft 14 in the region of this roller which is closest to the portion of film wound on the transmitting shaft 13, so as to always be inserted between these two portions of film wound on different trees. is provided to ensure an electrostatic discharge of the film 10 during its winding and protection against ink residues liable to fall from the receiving film 10, after use for printing. An electrostatic discharge as complete as possible before use is optionally carried out using an electrostatic charge eraser composed of at least one and preferably two erasing units then assigned each to one of the two sides of the film. 'erasing are for example each constituted by two conductive rollers 17, 18 parallel and quasi-tangent which are arranged transversely to the film 10 at the output of the reel formed around the emitting shaft, so as to apply to the width of the film on either side of this film, and which are subjected to a difference in high voltage alternating potential for example of the order of 1500 volts and from 1 to 150 kHz.

 One of the conductive rollers of each erasing unit, here the roller 18, is made of hard metallic material and good conductor, while the other is preferably made of flexible and conductive material of the elastomer or silicone type charged with conductive particles.

 As a variant, it is of course possible to use a conventional device with a Corona effect, knowing that this device is more fragile than the solution mentioned above and more delicate to use.

 The rollers 17 and 18 of the two erasing units are preferably arranged so as to force the film 10 to oblique twice in opposite direction between the coil formed around the emitting shaft 13 and the read head 8 which is also close thereto. as possible, so that this film is applied to a large area of the metal rollers 18.

 The inking device 9 is located near the writing head 8, it comprises for example, a magnetic brush 19 which constitutes a multipolar magnet intended to entrain in its field lines the crests of a magnetic powder which contains a tray 20, here filled with a removable cartridge 21, placed over the tray 20.

 The magnetic brush is rotatable around an axis 22, arranged transversely to the film at the outlet of the writing head, the film 10 being pressed at this point over its entire width against a peripheral zone of a so-called transfer roller 23 produced by example in non-magnetic, conductive, hard alloy, brought to the ground potential of the printer and rotatably mounted.

 The transfer roller 23 which forms a counter electrode is placed on the same side of the film as the roller 12 downstream of the latter. The magnetic brush 19 rotated by conventional motor means (not shown) comes close to the film 10 without touching it in the zone where this film is pressed against the transfer roller 23 and on the other side of the latter.

 The egrets of magnetic powder come in the vicinity of the face of the film 10, which has passed in front of the pressure electrodes of the read head 8 and which faces the magnetic brush 19.

 The magnetic powder which is conductive is charged by influence at a reverse polarity of the zone of the film in front of which it passes, when this zone has been electrostatically charged, during its passage through the writing head 8.

 If the electric charge is sufficient, the Coulomb force becomes greater than the magnetic force of attraction and the powder is deposited on the electrostatically charged places of the film 10 in motion.

 The film 10 is inked at the level of the magnetic brush 19 on its side opposite to that by which it rests on the transfer roller 23, it remains pressed against this conducting roller on, for example, practically a half-cylinder before arriving at the fixing transfer unit in which the image revealed by inking is fixed on its final recording medium, commonly constituted by a sheet of paper originating at the choice of one of the magazines 2 by one of the guide paths up to 'to be placed on the film 10-parallel to it, here practically at the top of the transfer roller 23.

 The transfer and fixing unit associates at least one pressure roller 24 with the roller 23 to ensure the transfer to the sheets of paper, constituting the final recording medium, inked latent images carried by the film 10 which appear progressively at the output. inking device 9.

 The pressure roller 24 is applied against the transfer roller 23 under very high pressure, conventionally by a mechanism 25 with springs, not shown, to ensure the transfer and the fixing of the inked particles carried by the film 10 on the successive sheets of paper with which it passes between these rollers 23 and 24.

 One of the rollers, such as 23 in FIG. 2, has a tiny recess 26 reducing its diameter over most of its length except for its ends, this recess 26 which has for example a depth of about fifty microns and a length slightly greater than the width of the film 10 is intended to allow the film 10 to circulate freely between the rollers 23 and 24 in the absence of a sheet of paper so as to be able to compensate for any lateral slippage.

 The recess 26 also makes it possible to reduce the drive torque at the time of the insertion of a sheet of paper between the rollers 23 and 24, the displacement of the pressure roller 24 against the springs of its pressure mechanism then being very weak.

 To limit the width of the longitudinal contact zone of the pressure roller 24 on a sheet of paper pressed against this contact zone on the film 10 which rests on the transfer roller 23 also at the right of said contact zone, 'endeavor to reduce the diameter of said pressure roller 24 which must however withstand a strong pressure and which therefore tends to flame. To avoid this buckling as much as possible, the pressure roller 24 is here flanked by two identical auxiliary rollers 27, 28 symmetrically disposed with respect to a longitudinal median plane passing through the axes of the rollers 23 and 24, so as to be both parallel and tangent to this pressure roller. It is the rollers 23 and 24 which receive the pressure from the springs of the mechanism 25 and which apply it symmetrically to the pressure roller 24 so that it is pressed against the transfer roller 23. This makes it possible to reduce the buckling of the pressure roller 24 and by Therefore improve the print quality accordingly.

 As a variant, it is possible to reduce the number of rollers involved in the operation of the transfer and fixing unit, for example by replacing the two auxiliary rollers 27, 28 with a single roller slightly offset from the pressure roller 24 on which it is slightly wound on either side of a midpoint under the pressure of the springs of the mechanism 25 which is applied at its ends. The pressure roller 24 can also be slightly offset from the transfer roller.

 The film 10 and the sheets of paper, which successively pass with it between the rollers 23 and 24, are separated after this simultaneous transit, the film remaining temporarily applied between the transfer roller 23 by the action of a flexible roller 29, while the sheet of paper is guided outwards by a short guide 30 formed by at least one internal wall of the printer which directs the outgoing sheet towards at least one and here two ejector rollers 31 positioned at the entrance to the tray 3 which opens at the upper part 1B of the bodywork for the output of the sheets.

 The film 10 is then directed by rollers 32, 33 under the tank 3 so as to come to form the reel which the receiving shaft 14 carries.

 According to a preferred embodiment according to the invention, the chassis (not shown) and the bodywork are provided divided into two parts which are divided at the dotted line referenced AB in FIG. 1. The part which comprises in particular the rollers 12, 23, 24, 27, 28 and the mechanism 25 are mounted on an upper part of the chassis rotating around an axis 34 mounted on the base of the chassis so as to allow the upper part of the chassis and the upper body part 1B associated therewith. , to tilt upwards relative to the base and to the lower fixed part 1B of the bodywork to give access to the rolls of film carried by the shafts 13, 14 and to the assembly 11 of the writing head which comprises the electrodes once the top has been tilted.

 In one embodiment, the mechanism 25 has a leaf spring at its upper part, this leaf is tensioned by means of a cam linked to the axis 34 so as to release the pressure of the springs of the mechanism 25 when the upper parts are tilted up to facilitate film changes after use, moreover not shown return springs spread the rollers to facilitate the insertion of the film.

 As indicated above, the writing head 8 can be produced according to various variants.

 In a variant presented in FIG. 3, the electrodes such as 35 and their counter-electrodes such as 36 and 37 of the writing head 8 are grouped in an assembly 11 ′ on the same side of the film 10 and a cylinder 12 ′, of circular section, ie, a roller, is used as the rotary coupling electrode.

 The cylinder 12 'is brought to a continuous potential V1 of the same polarity as the value control pulses + V / 2 applied to the counter-electrodes, so as to associate its action with theirs in the event of control.

 The continuous potential + V1 is chosen to have a value much lower than the value + V / 2 so as not to allow the triggering of an ionic discharge between the coupling electrode constituted by the cylinder 12 'and one of the electrodes of the assembly 11 ′, knowing that these electrodes, such as 35, which are normally at ground potential + OV like the counter-electrodes in the absence of a print command, are selectively brought to a negative high voltage potential -V / 2 per pulse and as needed during printing.

 In the embodiment shown in Figure 3, the roller 12 'consists of a tube 38 of flexible material having for example a hardness of about thirty shores and a diameter of about six centimeters.

 The flexible tube obtained is for example of an elastomeric material having a resistivity of the order of 106 to 107 ohm-centimeters; in the alternative embodiment presented here the flexible tube 38, mounted idly on an axis 39, is covered by an outer layer 40 of constant thickness, of a value for example between 0.1 and several millimeters, which has the required resistivity and which is connected to the potential + V1, for example by a ring system associated with the tube with fixed wiper, which is not reproduced here because of its classicism.

 The coupling electrode formed by the roller 12 'is mechanically pressed, for example by a spring system against the film 10 itself applied against the assembly formed by the electrodes, the counter-electrodes and the insulating block part 11' who contains them; this electrode is deformed under pressure so as to cover the ends of said electrodes and counter electrodes, projecting on either side.

 Since the film 10 is generally constituted by a very smooth thin film, a small air gap 41 is provided under the electrodes between them and the film, this gap is usually obtained by grooving the block 11 ′ in line with the electrodes E.

 The support which rubs against the coupling electrode formed by the roller 12 'during the recording of latent images, cracks this roller 12' usually mounted idly. It is of course conceivable to drive the coupling electrode in rotation by any conventional means to almost completely reduce the friction of the recording medium at its level.

 In an alternative embodiment presented in FIG. 4, the cylinder forming the coupling electrode 12 "consists of an endless band 42 of flexible resistive material, of the charged elastomer type, the resistivity of which is for example of the order of 106 to 10-7 ohm centimeter.

This strip electrode is wound freely around carrier pulleys 43 here three in number which allow its tension and for two of them its plating against the film 10 on and around the ends of the electrodes and counter-electrodes. The coupling electrode thus formed is brought to potential + V1, for example at one of its bearing pulleys by contact using means known in themselves, of the wiper type or connection by ring and wiper.

 In the variant presented in FIGS. 5 and 6, the counter-electrodes are dissociated from the electrodes, such as 35 "', which are enclosed alone in a set 11"' of external shape similar to that of the set 11 'mentioned above, in particular with regard to the groove creating an air gap 41 "'between the electrodes and the film.

 The counter-electrodes are here produced on a circular section cylinder or 12 "roller intended to replace the roller 12 provided on the printer shown diagrammatically in FIG. 1. To this end the 12" roller, mounted rotatably about its axis by means of end bearings, such as 42 (FIG. 6), comprises parallel conducting rings C1, C2 ... Cn delimiting the counter-electrodes facing the electrodes situated on the other side of the film 10 against which the roller 12 "'is applied so as to press this film 10 against the point end of said electrodes. The rings C1 to Cn are carried by a round and rigid tube 43, mounted on bearings 42, these rings are covered, as well as the tube 43, by a layer 44 of flexible resistive material of relatively small thickness for example ..., whose resistivity is of the order of 107 or 108 ohm / cm.

 Each layer portion 44 located between two successive rings, such as C1 and C2, defines a resistive zone constituting one of the counter-electrodes of the writing head considered.

The counter-electrodes thus formed are energized by means of conductive rods or pins P connected to the various rings C; these pins are two in number per ring in the variant shown, such as P11A and P11B for the ring C11, they pass through the tube 43 to be fixed on a printed circuit board 45 carrying at least part of the selective switching circuit voltages which is necessary for controlling the counter-electrodes, this circuit being here symbolized by resistors r11, r12 'n + l .. and diodes D11, D12 ... Dn + 1 respecti
rr and diodes D11, D12 n + 1 vely assigned to the different rings C11, C12 .... Cn + 1.

 In one embodiment, the printed circuit board 45 is disposed in a median longitudinal plane of the roller 12 "', between two semi-cylindrical shells of insulating material which adjusts one on the other to form the tube 43 .

 The rings C are placed for example in external circular grooves of the assembly formed by the two assembled half-shells.

 The pins P are flush with the outside of the half-shells for the connection of the rings to which they are for example welded. These pins P are here arranged in the plane of the rings they serve, and pass through the assembly formed by the half-shells assembled by not shown notches which are formed at the joint plane of these half-shells.

 The supply of the electronic voltage switching circuit carried by the printed circuit board 45 is carried out for example using a conventional ring device 46 secured to the rotating part, that is to say the tube 12 "', and with wipers 47 fixed connected to a connector 48 also fixed, by different control wires 49 of the electronic voltage switching circuit.

 As a variant, it is possible to make the roller 12 "'fixed or even to use only a fraction of the roller which is then immobile, the film 10 then rubbing against the external surface.

Claims (9)

1 / Indirect electrostatic printer, comprising an electrostatic writing head (8) provided with a set of printing electrodes and counter-electrodes making it possible to create, on a dielectric film (1Q) serving as an intermediate recording medium , an electrostatic image of what one wishes to print, also comprising an inking device (9) for the electrostatic images created on the film, as well as a transfer unit (23, 24) for transferring and fixing on a support recording medium (50), such as sheet paper, inked images carried by the film, the inking device and the transfer unit having in common a transfer roller (23) against which the film is plated for inking and image transfer, said printer being characterized in that it comprises, on either side of the transfer roller and a pressure roller (24) of the transfer unit and fixing which is at least approximately parallel to it and which is plated co ntre him, on the one hand at the input at least one detachable sheet paper (2) partially penetrating on one side of the body (1) of the printer, as well as a short guide path (7) constituted by at least one internal wall of the printer, leading from an extraction end of the feeder to the contact zone between transfer roller and pressure roller, on the other hand, of a tray (3) for collecting printed sheets , located at the top of the body - (1) and connected by a short guide (30) at the outlet of the contact area between transfer roller and pressure roller, the rest of the inking device (9), composed of '' a magnetic brush (19) and a tray (20) for the ink, being positioned under the transfer roller (23) which brushes against said magnetic brush, the electrostatic head (8) being placed near the transfer roller and of said magnetic brush on the same side as two shafts (13, 14) situated under the tray of printed sheets and on the esquels is stored in rolls the film, the emitting shaft (14) which carries the printing film, being located on the other side of the printing head (8) the receiving shaft which receives the film after use being located beyond the emitter shaft with respect to the print head and at a level higher than that of said emitter shaft from which it is separated by a conductive separating plate (15), movable by one of its ends and bearing on the portion of film wound on the emitting shaft. 2 / electrostatic printer according to claim 1, characterized in that it comprises an electrostatic charge eraser (18) located between the emitter shaft and the print head and provided with at least one erasing unit composed of two conductive rollers (17, 18) with circular section, parallel, one hard, the other flexible, which are arranged transversely to the film pressed between them and which are brought to a low frequency alternating potential. 3 / electrostatic printer according to claim 1, wherein the electrostatic printing head (8) comprises on the one hand a fixed insulating block (11) comprising at least the printing electrodes and a cylinder applying the film against the block fixed to the right of the point ends of the printing electrodes, characterized in that the cylinder (12 "') is of circular section and comprises annular counter-electrodes intended to face the electrodes of the fixed block and each constituted by an annular portion a layer of resistive material (44) delimited by two conductive rings (C) carried by an insulating tube (43), the various conductive rings which are regularly arranged in parallel on the insulating tube being covered just like the latter by the layer of resistive material (44) which applies the film (10) to the block (11) in line with the ends of the aligned electrodes. 4 / electrostatic printer according to claim 3, characterized in that the conductive rings C are electrically connected by pins (P) passing through the insulating tube (43) to a printed circuit board (45) immobilized in said insulating tube. 5 / electrostatic printer according to claim 1 wherein the electrostatic printing head (8) comprises on the one hand a fixed insulating block (11) containing in parallel the printing electrodes (35) and the counter-electrodes (36, 37) and on the other hand a rotary cylinder (12 ′ or 42) applying the film against the insulating block fixed to the right of the ends of the electrodes and counter-electrodes, characterized in that this rotary cylinder is made of conductive material and is brought to a medium voltage direct potential of the same polarity as the high control electrode pulses. 6 / electrostatic printer according to claim 5, characterized in that the cylinder (12 ') which is of circular section is formed at least externally by a layer (40) of conductive elastomeric material. 7 / electrostatic printer according to claim 5, characterized in that the cylinder (42 ') consists of an endless strip (42) of flexible and conductive material, mounted on rotating shafts (43) arranged transversely to the film ( 10) so that this strip comes to be pressed against this film in an area extending on either side and in line with the electrodes and counter-electrodes. 8 / electrostatic printer according to claim 1, characterized in that the transfer roller (23), against which the pressing roller (24) is supported in the transfer and fixing unit, has a slight recess (26) reducing its diameter over a central zone of a length slightly greater than the width of the film (10) to allow the free sliding of this film between said rollers and facilitate the insertion of the sheets of final recording medium. 9 / electrostatic printer according to claim 1, characterized in that the electrostatic print head (8) comprises a fixed insulating block (11) containing at least the printing electrodes and a cylindrical sector applying the film against the fixed block in line with the point ends of the printing electrodes, said sector comprising semi-annular counter-electrodes intended to face the electrodes of the fixed block and each consisting of a semi-annual portion of a layer of resistive material (44) delimited by two sections of conducting rings (C) carried by a sector of insulating tube (43), the various sections of conducting rings being regularly arranged in parallel on the sector of insulating tube and being covered like the latter by the layer of material resistive (44) which applies the film (10) to the block (11) in line with the ends of the aligned electrodes.