DE2023719A1 - Electrographic printing system - Google Patents

Description

Patent attorney

8 Munich 26, P.O. Box 4

My reference: P 925

Applicant: HONElWELL INC.

2701 Fourth Avenue South, Minneapolis, Minnesota, V. St. A.

Electrographic printing system

The invention is generally in the field of image reproduction} it relates in particular to an electrographic one Printing system in which / recording medium a Contains electrically conductive base carrier layer and a dielectric layer.

There are currently various special methods of image reproduction. Most processes work with electrostatic charge transfer. With electrographic copiers or Printing systems, including the invention Systems, is generally based on a dielectric medium creates a latent image. This is done by the fact that the Medium is brought into the field between two electrodes. Between the two opposing electrodes, which can have different shapes (round shape, square shape, character shape, etc.), lies a high electrical level Potential difference. This way it becomes the required Field generated. The generated latent charge image

ooeiu7 / im

has the shape of the electrode, that of the dielectric Surface facing the medium.

Most electrographic copier systems can with regard to of the electrode configurations essentially in two ' Groups are divided, one group of which includes systems which contain character-shaped electrodes, and the others Group contains systems that contain pen-shaped electrodes. In systems of the former type, for example, a platen is rotated at high speed and selected electrodes

ι are led downwards in pulses, if the required Sign facing the dielectric surface. In this way, a latent image is created on the medium in the Area created in which the drawing electrode was arranged » However, such systems have certain disadvantages. For example, it has been found necessary to have a Provide roller, which consists of individual, electrically isolated segments. It has also proven necessary Provide means for switching the segments of the rotating drawing drum. Therefore, with the rotating drum associated mechanical problems. It also needs to print at a reasonable speed

. to be able to work without the blurring of characters the duration of the selection pulses must be short, and finally the paper must stand still while it is being printed. This leads to a limitation of the printing speed in a system of this type,

For printing or copying systems in which a number of Using pen electrodes, various patterns or images, such as alphanumeric characters, can be reproduced thereby that certain electrodes are selected when

the recording medium passes these electrodes. Certain problems are also associated with such a system, that result in poor copy quality · Two

009847/1679

the most significant problems are the poor contrast density and the resolution of the copied or finally printed characters. The contrast (shadow) density can be used as Degree of darkness can be defined on the gray scale while resolution can be defined as a property of forming precisely shaped characters. Theoretically deliver printed or copied characters have a 100 # contrast, which means that the characters are completely black. The pen electrodes are gedc-ch at a minimal distance from each other to hold so that they can be operated selectively. is if this is not the case, the character printed in each case is characterized by poor density and poor resolution the end.

Another associated with a pen electrode system The problem arises from the manufacture of the electrode assembly itself. Usually the electrodes have one very small cross-section, and moreover they are arranged close together. The structure is therefore sensitive to damage and generally difficult to manufacture.

The cost of currently available electrographic Printing or copying systems are relatively high. An important factor leading to the high cost of such systems is the need for a control device for each electrode to be provided. In systems that require relatively high resolution and shadow density, the total number of electrodes on the order of 200 electrodes per 25.4 mm. If a separate high voltage control circuit is required for each electrode, the cost of the system increases unusually high.

The invention is therefore based on the object of an elec- * trographisch.es copier or printing system that

009847/1679

can be constructed particularly simply and inexpensively while avoiding the disadvantages indicated above.

The object indicated above is achieved by an electrographic copier or printing system in which on a recording medium latent images by applying a High voltage generated on this recording medium and by Toner are made visible «This printing system is according to the invention characterized in that an electrode structure containing a plurality of electrodes is provided is that an electrode control circuit is provided which comprises a character generator, a first and a second group of Contains high-voltage control circuits for feeding through the character generator and a selection matrix. That the selection matrix a first plurality of passive elements connected to the outputs of the first group of high voltage control circuits are connected, and a second plurality of passive elements connected to the outputs of the second group of high-voltage control circuits, that includes those connected to the first group of high-voltage control circuits connected elements are connected to one another at a common connection node, with a separate Element is connected to one of the high-voltage control circuits belonging to the second group, that an output line connects these nodes to one of the electrodes and that with the occurrence of an output signal of the character generator can selectively apply a high voltage to the corresponding electrode through each output line.

The invention is therefore an electrographic copier Provided a printing system in which a recording medium carries latent images which are produced on the recording medium by the fact that this recording medium has a high Potential is applied. The latent images are thereby through

009847/16 7-9

subsequent supply of! toner made visible. That The copying or printing system according to the invention also contains an electrode structure comprising a plurality of rows of electrodes, a character generator and a selection matrix. This selection matrix enables a smaller one to be used Number of high voltage control circuits than the total number of electrodes in the electrode structure.

The subject matter of the invention copying or printing system enables printing with increased resolution by eliminating the previously unattainable possibility of pressing between adjacent electrode areas is reached. According to the invention, a nested electrode structure is used, due to the printing processes with a much higher shadow density (up to 100 #) than before was possible. Further advantages of the invention result from the ability to manufacture the individual assemblies more cheaply to be able to.

The invention is explained in more detail below using individual exemplary embodiments with reference to drawings. Fig. 1 shows in a perspective view, partly in block form, part of a preferred embodiment according to the invention.

FIG. 2A shows a top view of that shown in FIG Electrode structure.

Figure 2B shows a segment of the recording medium, below Illustration of the latent charge image for the letter E.

3A to 3Ξ show different stages of manufacture a dual electrode structure.

4 shows the electrode structure in a block diagram and its associated control circuit.

Fig. 5 shows a circuit diagram of an embodiment of the Electrode control circuit.

009847/1879

Fig. 6 shows a schedule of in lig. 5 and 7 shown Control circuits.

Fig. 7 shows a circuit diagram of a second embodiment of the electrode control circuit »

Electrode structure

In Fig. 1 is in a perspective view, a part of a preferred copying or printing system according to the invention. An electrode structure 10 is illustrated here, a portion of which is cut away to expose the electrodes 12. In the illustrated embodiment, each has an electrode an almost square cross-section; it ends in a work surface 14k. This work surface 14 lies in a common area, in the immediate vicinity of an image recording medium 20. In a practical execution foria

ρ, the surface 14 has an area of approximately 0.04? mm (corresponding to 0.005 Zdtftt 0iK? di #), and the electrode series are just like neighboring electrodes within a row of electrodes by a distance d of about 0.13 mm (corresponding to 0.005 inches) apart.

In a preferred embodiment of the invention, two rows of electrodes 15 and 17 are used. Any work surface 14 (with the exception of those at the ends of the rows is to the Aligned the space between two work surfaces of the adjacent row. The space between two rows of electrodes depends on the paper speed and the time it takes to print one scan line.

A scanning line can in particular be an imaginary line on the recording medium having the width of an electrode as shown in Figure 2B. Is the ^ upper limit © of the speed at which a row of electrodes

009847/1679

for performing the printing of a latent image on the above the scan line can be fed, given is the minimum distance between the rows of electrodes determined by the paper speed and the completion of printing a single scan line. One of those The printing process must be completed before the scanning line moves over to the second row of electrodes.

Rolls 16 and 18 represent a device that the recording medium 20 moves past the electrode structure 10. Various other drive devices can be used here} all drive devices are located within the scope of the invention. The recording medium 20 can contain a conductive base backing, such as treated paper with a dielectric layer attached thereto certain thickness. Usually the dielectric layer is thinner than the base material. Which the dielectric layer, supporting the side of the recording medium 20 lies. of the roller 16 opposite, while the conductive side of the roller 18 is opposite.

As mentioned earlier, one is created (printed) latent image when a high potential on the recording medium is applied at a specific location on the recording medium. About that particular one Area (the area above the electrode surface 14) takes place an electrostatic charge transfer, wherein the Dielectric maintains this charge image for a sufficiently long period of time so that a toner is supplied and can be burned onto the recording medium. This happens in areas where the charge is still present. By supplying the toner, the respective latent Image visible.

In the system shown in Fig. 1, a high-voltage

009847/1679

source 19 is provided, which supplies the high voltage required to carry out a printing process. These High voltage is fed to the roller 18 via a commutation or power supply brush 21. With this brush it is an element that is capable of delivering the high voltage to the roller 18. Then the high voltage applied to the conductive side of the medium 20. If, yourself, that

Designate the storage medium in which is moved by the arrow J ^ / at a speed of, for example, 25.4 cm / sec, selected electrodes are grounded in pulses. This is done with the aid of the electrode control circuit 24. In this way, the dielectric surface of the Recording medium 20 generates a charge according to a certain pattern. A character generator 26 is connected to the electrode control circuit 24; he determines the form or the respective print image.

The generator 26 receives suitable electrical signal sequences (not shown), for example from a computer. These Signal sequences are characteristic of pictorial information, alphanumeric information or other information Information to be recorded. These signal sequences are converted into timed and appropriately distributed electrical pulses that are fed to circuit 24 will. Character generator 26 may be a typical function generator such as that disclosed in U.S. Patent 3,289,030.

For purposes of illustration, assume that a latent image is present in area 21 of recording medium 20 is printed. The part of the area 21 which has either passed over the electrode structure 10 or above this electrode structure is shown in gray. This is to indicate where the latent image is generated

0098A7 / 1679

has been. The dielectric surface of the recording media 20 actually retains the charge. For the purpose of illustration, however, the visible side of the recording medium 20 is tinted gray shown. As shown, the tooth-shaped latent image is present immediately above the electrode structure 10.

At one point during the operation of the system, the first row of electrodes 15 fed, while the second row of electrodes 17 is not yet fed. If only one row of electrodes is used to perform a printing process, thus provides the required minimum distance between neighboring ones Electrodes in a row of electrodes have a print density that is not higher than about 60 JIi. With the help of the in Pig. 1 shown nested dual electrode structure, however, a print density of up to $ 100 can be achieved. The usage this particular electrode structure also enables increased resolution, especially when curved alphanumeric characters can be printed. This increased resolution is mainly due to the fact that twice as a result of the nested electrode arrangement there are as many scans in the direction of paper travel as in the pail that a single row of electrodes is used will. In this way, then, through the invention a better sharpness achieved.

Print sample '

For the purpose of a better understanding of the printing system according to the invention, the Pig. 2A and 2B considered closer. Pig. 2A shows a front face of one nested dual electrode structure, while Pig. 2 B shows a segment of recording medium 20 on which a Character has been printed. The segment is divided into imaginary cells (elements) 30 which have the same dimensions.

0098 47 / I 879

like the electrode area 14 (e.g. about 0.13 mm square). The entire character segment consists of a group of cells contained in a 16 × 25 matrix. To the Achieving inter-character spacing defines a 13 x 16 cell matrix the usual character, which in the case of the example of FIG. 2B is an E-shaped character acts.

The one in Pig. 2A are designated by a Ms h for the electrode row 15 and by a 'to h ¹ for the electrode row 17. Corresponding designations are used in the scan line of FIG. 2B. It is assumed that the electrode structure 10 is stationary and that the segment of the medium 20 shown in FIG. 2B is moved over the electrodes in the direction of the arrow indicating the movement of the paper. The following processes occur. As determined by the character generator 26, for printing the character E in the event that the scanning line 1 lies above the first row of electrodes 15, the electrodes a to g are activated, while the electrode h is not activated. The cells marked a to g are electrostatically charged, but not the cell h. If the scanning line 2 is above the first row of electrodes 15, the same electrodes are activated (electrodes a to g). At the same time, the scanning line 1 lies over an intermediate electrode area 25 which is part of the aforementioned common area. The row of electrodes 17 is not yet activated at this point in time.

At a later point in time, that is to say at the point in time at which the scanning line 3 is moved directly over the first row of electrodes 15, only the electrode h is activated. At the same time, the scanning line 1 has been moved over the second row of electrodes 17. Now the electrodes a ¹ to f '

OQ9847 / 167 9

activated, but not electrodes g ¹ and h ¹ . This process is repeated in a corresponding manner to enable the printing of latent images in the shaded areas according to Fig. 2B. The character generator programs the control or supply sequence for the respective row of electrodes. In this way it is possible to print alphanumeric characters, special characters and basically any desired images.

Although only a segment of the recording medium 20 is shown in the drawing, practically one can Character Printing System 152 characters can be printed in the horizontal direction. With 25 possible samples for the complete formation of one character, 132 characters (one character line) can be printed every 25 scans. The number of electrodes required for this is as follows certainly. With 132 character positions and 16 cells per character position, there is a total of 2112 electrodes per scan line (1056 electrodes per row of electrodes) available. Consists

the desire to print 5000 lines of characters per minute at a paper speed of 25 _} 4 cm / sec (with a maximum character height of about 3.2 mm), then 12 milliseconds are required to print one line of characters (60 sec / min + 5OOO character lines / min). If 25 scan lines are used per character line, one scan line is printed every 0.48 milliseconds (12 milliseconds + 25 scan lines).

A print pulse width between 40 and 50 microseconds is required to achieve good quality print. The pulse width is mainly determined by the EG time constant of the electro graphic medium. At a minimum pulse width of 40 microseconds could be 12 print intervals can be provided to print one scan line (0.46 milliseconds + 40 microseconds). At a

009847/1679

A pulse width of 50 microseconds is only 9.6 print intervals j © Requires scan line. Will be a mean one. If a value of eleven intervals is selected, eleven intervals can be selected each of 12 character positions can be used. The pressure pulse : Vr in this particular example would be about 4-3.5 microseconds long.

In a practical embodiment of the invention, a scan line can thus contain 132 character positions, where 25 scanning lines are used to completely print the entire character line. The 132 character positions are in eleven Printed at intervals. During each such interval, 12 character positions are printed, i.e. 192 (12 χ 16) cells printed (corresponding to 192 electrodes). Each print interval thus lasts 43.5 microseconds, where a total of 12 milliseconds is required to print a full line of characters. Through the under Referring to Figure 2B, dual electrode row operation explained make up the 192 electrodes that are used to print the twelve Character positions are each fed, physically two rows with 96 electrodes each, which can be seen in FIG. 2A Are nested inside each other.

Electrode manufacture

The electrode structure according to the invention can be produced in various ways. The respective electrode cross-section ufi not be square, it can rather be rectangular, circular or otherwise shaped. In FIG. 3A there is now shown a part of a printed holding plate @ © 4Ό, which contains two conductive copper layers U-2 separated by an insulating layer 44 made of glass epoxy or the like material. These three layers are connected to one another by gluing or in some other suitable way «,

009847/1679

A special way of producing the electrode structure is to start with an etched printed circuit board with copper conductors on either side which in a preferred embodiment have a width of about 0.13 mm and about 0.13 mm are spaced from each other (see Fig. 3B). The one used to manufacture The processes leading to this etched circuit board are similar to the processes used to manufacture conventional ones printed circuits are applied. Due to the small width of the conductors (electrodes) and the small However, the distance between the conductors is a certain process control necessary.

The first manufacturing step in the course of manufacturing the electrode structure consists in applying a photoresist on both sides of the:; . Copper-glass-epoxy-copper layer structure applied will. After the plate has been suitably cleaned and dried, a negative becomes the coated layer structure (one negative on each side) and with exposed to ultraviolet light. The layer formed is then developed in a conventional developer. The last Step to achieve the structure according to Pig. 3B consists of the execution of a chemical etch. This is achieved in that the layer structure is in a warm, 40 # ige Solution of a weak acid is immersed. For this comes Iron-HI-Chloride in embossing. After washing off all traces of acid and drying, the layer structure or plate is ready for the next manufacturing step.

Then the spaces between the strips must be filled with epoxy. For this purpose, epoxy strips are used 50 applied to the strips 52 according to Pig »3G.

0 098 4 7/1673

• Glass epoxy layers 60 are brought up against the strips or layers 50 on the outside. Spacers determine the extent to which the layers 46 can be pressed against the layers 50. If the arrangement is heated and a pressure is exerted on the arrangement, as indicated by the arrows 54, the epoxy layers 50 melt and fill the cavities between the strips 52. After the structure has cooled, a grinding and polishing operation is carried out, then finally the Pig. To obtain electrode structures 57 shown in 3D. An end view of the structure shown in Figure JD is in Pig. JE shown along with rollers 56 and recording medium 58.

Electrode control circuit

As mentioned above, the previously known electro " graphic printing systems have a control circuit for each feeding electrode. Because high voltage levels are required for printing are (near 750 volts), so far is one Multiple use of high-voltage control circuits without Success has been tried.

Fig. 4 now shows an electrode control shell in a block diagram device 24 and an electrode structure 10. A preferred implementation of the circuit, which is used as an electrode control circuit 24 is shown in FIGS. 5, 6 and 7. The electrode control circuit 24 has position inputs 70 and data inputs 72. In the case of the following to be described in more detail practical embodiment of the In the invention, eleven position inputs - corresponding to the eleven pressure intervals - are provided, while the Bafcen input number (192) corresponds to the (192 ") activated or fed electrodes in order to print twelve character positions (see dos

0 9 8 4 7/1679

print example above). The output lines 74- connect " the electrode control circuit 24 with the electrode structure ■ 1Q. Eleven such connections are shown in the drawing. In actual implementation, each connection contains (192) lines ,. their corresponding segments of the electrode structure 10 are able to dine.

Fig. 5 shows an embodiment of a cable of the electrode control circuit 24. This circuit part contains drivers or control devices 76 * data inputs 72, position inputs 7P, outputs 74 and a resistor matrix. Wit.derstandspaare 8Ia ₅ 81b to 89a, 89b are each connected to a common connection point or node. These connection points or nodes are labeled 81 to 89. The output lines 74 leading to the outside are connected to these connection points or nodes 81 to 89. The others. Connections of the resistors 81a, 84a and 87a are jointly connected to a control device 76, while the other connections of the three resistors 82a, 85a, 88a or 83a, 86a, 89a or 81b, 82b, 83b or 84b, 85b, 86b or respectively 87b, 88b, 89b are each connected in common to the other drivers or control devices 76 according to FIG. 5. In this embodiment, all resistors have approximately the same resistance value More than one data driver can be activated at a time, and in most cases more than one data driver is actually activated at a time. Those drivers which receive signals from the position inputs 70 are each active.

The application of the in fig. 1 shown printing scheme in the Resistance mix according to Fig. 5 requires the electrode (Roller 18) on the conductive side of the recording medium

.00.0847 / 1679

is biased to a high voltage of e.g. 700 volts. The pin electrodes facing the dielectric side of the recording medium provide in the case of their grounding, the high voltage required for printing.

In the currently available electrographic printing systems insufficient charge is applied to the dielectric surface of the recording medium, to attract and hold the toner when the voltage applied across the dielectric is of the order of magnitude half of the normally used voltage of 700 volts. Thus, the 350 volt difference can be viewed as a threshold value below which successful printing does not occur.

As will become more apparent further below, this fact is advantageously used in the invention. The drivers shown in Figures 5, 6 and 7 provide a binary output of 900 volts for non-selection operation and a binary output signal of 0 volts for the select operation. The data drivers therefore give their Outputs voltages of 900 volts or 0 volts. Since there is only one position driver from a total of 11 drivers to one Time is controlled in operation, this driver emits an output signal of 0 volts, while the other drivers each emit an output signal of 900 volts. It should be seen that the position inputs 70 all Position drivers are fed by the character generator 26 one after the other.

In the following, FIG. 5 in particular is considered in more detail. It is assumed \ that the left Poßitions- »Tr @ iber 76 76 is selected together with the uppermost data driver. The outputs of these two drivers are therefore at ground potential

009847/1679

also at the connection point 81 is essentially ground potential. In a practically implemented embodiment, the is on the other side of the medium or recording medium lying — the electrode biased to -700 volts. The electrode associated with connection point 81 thus executes printing. The connection points 85, 86, 88 and 89 then carry a voltage of 900 volts, therefore no printing takes place here. (It is actually an inverse potential difference of 200 volts across that Recording medium available). .The remaining connection points 82, 83, 84, 8? carry a voltage of 450 volts, i.e. the Half of 900 volts. The potential difference across the recording medium in this pail is 250 volts (that is 700 volts - 450 volts). This potential difference is good below the threshold voltage of 350 volts. The connection point 83 is thus the only connection point that supplies the correct potential to aid printing.

It should be understood that the position inputs 70 for the drivers 76 are fed sequentially, namely according to the action of the character generator «26. D # e§ufsequence occurs the above-described effect one after the other, i.e. the Connection points are selected one after the other in groups of three, i.e. the connection points · 81-82-83 $ 84-85-86 and 87-88-89. In a corresponding way, »the output ·? 4 In accordance with the above sequence in the case of the troubled data singang selected one after the other.

In Pig. 6 shows a preferred circuit arrangement for the driver 76. There is a zero volt or +15 volt signal at the input terminal * 110. The input signal is normally 0 VOltf - ** increases to +15 full * with the appropriate selection (the, output 128 fills with earth potential). A diode 112 is ^r:; t their cathode to the

008847/1670

Input terminal 110 connected. The anode of the diode 112 is connected to the anode of a diode 116. A resistor 114 connects the anodes of the two diodes 112 and 116 to a voltage source + V _-1 . A parallel connection of a resistor 118 and a capacitor 119 connects the cathode of the diode 119 to the anode of a diode 120. The cathode of the diode 120 is connected to the base of a transistor 124. The base of the transistor 124 is also connected to a supply voltage source -V ^, via a resistor 122. closed. In addition to the transistor 124, a transistor is also provided. These transistors 124 and 126 are connected in series with their emitter-collector paths, the emitter of transistor 124 being grounded. The collector of. Transistor 124 is coupled to the emitter of the transistor 126, its collector connected to a high voltage source + V ₂ via a resistor 130 is "Further .The output terminal 128 connected to the collector of the transistor 126. A resistor 132 connects the base of the transistor. 126 to the high voltage source + Vg§ a resistor 134 connects, the base of transistor 126 to ground, and a capacitor 133 also connects the base of transistor 126 to ground.

If driver 76 is not selected during operation,

so the input aclearne 110 is at ground potential, and. a ! VorwÄrtwetroB from §t, v » 35.5« A flows through the diode 112 and dta resistor 114 · A kl »4.n» r ode? No 8troft at all flows through the diodes 116 htm * 120, and the safawach negative bias voltage at the base of the transistor 124, which is mainly determined by the resistor 122, keeps the transistor 12 * in the non-conductive state, the transistor 126, which is through the positive bias at its base can be converted into the conductive state (the resistors 132 and 134 were running, hem part of the positive bias) exists, ie transistor 124 is present

009847/1679

in the non-conductive state.

If the select is Treiber.76 _{i is} the voltage applied to the input terminal 110 is raised to about +15 volts. The diode 112 is then stressed in the reverse direction, while the diodes 116 and 120 are stressed in the forward direction. Now flows a current from the voltage source + V ^ via the resistor 114-, through the diode 116, the RC element 118, 119, the diode 120 and the resistor 122 to the voltage source -V, -. Based on the preselected values

of resistors 1 ^ 4-, 118 and 122 (the resistance of the Resistor 122 'is greater than the resistance of the Resistor 114- and resistor 118) becomes the base voltage of transistor 124- positive. This brings transistor 124-in the conductive state. This effect is due to the parallel resistance 118 and the capacitor 119 are still accelerated.

When the input signal goes positive, capacitor 119 instantly shorts resistor 118, and the Transistor 124- saturates quickly. This effect leads to the fact that the transistor 126 due to the positive base voltage enters the conductive state. The positive base voltage is provided by resistors 152 and 134- and formed by the capacitor 133. The output voltage occurring at terminal 128, which is around + V ^ (e.g. +900 volts) lag, now takes a value of 0 volts (slightly, positive at). This voltage is supplied via the output resistor 130.

Referring to Fig. 7, there is another embodiment of the electrode driver circuit shown. Corresponding reference symbols have been retained. As shown, includes the driver circuit 24 drivers 76, data inputs 72, position inputs 70, successively effective outputs 74 and a diode-resistor matrix. Diode pairs 91a, 91b to 99a, 99b are

009847/1679

202371

each formed by diodes connected to their cathodes. The connection points of the cathodes of the respective diodes are labeled 91 to 99. With the connection points 91 to 99 are ©: stars ₅ successively effective output lines? 4 connected »Furthermore, these connection points are each connected to one end of resistors 91c to 99e connected ο B_j, e other ends of the resistors 91c to 99c are grounded. The anodes of the diodes 91a, 9 ^ a and 97a are connected to a common driver 76, while the anodes of the diodes 92a, 95a, 98a and 93a, 96a, 99a, respectively or 91b, 92b, 93b or 9 ² I-Is 95b, 96b or 97b _s 98b, 99b are each jointly connected to one of the remaining drivers 7 © according to FIG. 7. Those drivers that receive data via the Baten inputs switch continuously with each new data scanning line displayed. »More than one data driver can be activated, and in most cases more than one data driver is activated. The drivers or data drivers that receive data via the position inputs 70 are activated in each case «,

With regard to the circuit arrangement according to FIG. 7, it is assumed that that the left position driver 76 together with the top one Data driver 76 is selected. The outputs of these two drivers (see Fig. 6) thus carry ground potential, and at the connection point 91. occurs essentially earth potential (the diodes 91a and 91b are biased in the reverse direction). Location the electrode on the other side of the recording medium a voltage of 700 volts, the electrode associated with the connection point 91 carries out a printing process. The connection points or nodes 95, 96, 98 and 99 carry a voltage of 900 volts, which is why there is no printing process here. In the practical execution, however, is actually the opposite Potential difference of 200 volts across the recording medium. The remaining connection points 92, 93, 94,

0098A7 / 1679

carry a tension of 450 yoIt or half of 900 volts. Me potential difference across the recording medium in this case is 250 volts (700 volts - 450 volts). This value is well below the threshold voltage of 550 volts. The .-., - connection point 91 is thus the only one Connection point that carries the correct potential to support the printing process.

The invention has been explained above with reference to certain illustrated embodiments. It should however, it should be understood that lying within the scope of the invention Modifications to the arrangement shown apply can. For example, more than two rows of electrodes could contain Electrode structures are used in an advantageous manner. For example, if three rows of electrodes were used, so could the individual electrodes in each row of electrodes be a little further apart. In addition, the voltage levels and polarities do not need to be chosen as this is the case in the example shown. A potential difference of 700 volts may be required for printing be. Furthermore, the roller could be held at ground potential and the pin electrodes could be selectively pulsed be applied to a high voltage, either with a positive or negative sign. Furthermore, the common Surface of the electrode frame different shapes accept.

From the above description it should be apparent that the invention provides an improved electrographic Printing system has been created. That from a multitude of Electrode structures consisting of nested rows of electrodes provide an improved resolution and create thus the possibility of achieving a 100% density of shadows. This is particularly useful when printing alphanumeric characters. The electrode control circuit brings

009847/1679

further advantages with sieve. * These advantages consist in the fact that fewer! "drivers are required ₅ than in currently available systems the Hesstellverfahren discussed above? wr producing the electrode structure is to be called.

009847/1679

Claims (1)

Pat ent a n sp r ehe Electrographic printing system with a recording medium on which latent images are generated with the aid of a high voltage, these latent images being made visible with the aid of toner, characterized in that an electrode structure (10) containing a plurality of electrodes is provided, that an electrode structure Control circuit (2U-) is provided which contains a character generator (26), first and second groups of high-voltage control circuits (76) fed by the character generator (26) and a selection matrix, the selection matrix having a first number of passive elements (81a to 89a), which are connected to the outputs of the first group of high-voltage control circuits (76), and a second number of passive elements (81b to 89b) which are connected to the outputs of the second group of high-voltage control circuits (76) contains that the passive elements ( 81a to 89a) are each connected to a passive element of the passive elements (81b to 89b) belonging to the second group, so that one of the electrodes of the electrode structure (19) is connected to the common connection points (81 to 89) of the passive elements connected to each other. is connected and that when an output signal from the character generator (26) occurs, a high voltage can be selectively applied to the respective electrode. Printing system according to claim 1, characterized in that that the electrode structure (10) a plurality of each other spaced rows (15,17) of electrodes contains that successive electrodes of the respective electrode row (15,17) are spaced from one another and 00984 7/1679 that the electrodes of the successive rows of electrodes (15, 17) are mutually offset * 3. Pressure sintering after. Claim 2, characterized in that that the distance between successive rows of electrodes is almost equal to the width of the respective electrodes in the transverse direction of the row " 4-. Printing system according to one of claims A to 3? characterized in that the electrodes end in a common area, that each electrode forms a working area with the common area, and that the working areas are aligned and dimensioned with corresponding gaps between the electrodes of successive rows (15, 17) so that they contain these gaps almost fill in " 5 · Printing system according to claim 4, characterized in that each work surface has a square shape. 6. Printing system according to one of claims 1 to 5 _5, characterized in that each passive element (81a, 81b to 89a, 89b) contains a resistor. 7. Printing system according to one of claims 1 to 5, characterized characterized in that each passive element includes a diode (91a, 91b to 99a, 99b) connected between the output the high-voltage control circuit and the common connection point is connected, the resistive is coupled to a reference voltage source. one of the ■ to ?: 8. Printing system according to / lnspruche1 _/ ^ a characterized by that each high voltage control circuit (76). an A * - contains an input terminal (110) and an output terminal (128) and further a first and second transistor (124,126), 009847/1679 that the first transistor (124) with its emitter grounded and connected with its base to the input (110) and that the second! transistor (126) with its emitter connected to the collector of the first transistor (124), with its base on a reference potential and its collector is connected to the output (128). Printing system according to one of Claims 1 to 8, characterized in that the electrode structure (10) contains two spaced-apart rows (15> 1?) Of electrodes, that each electrode of an electrode row (15 »17) TUi the space between the electrodes the respective other row of electrodes (17ji5) is aligned and. that the electrodes have the same dimensions in the longitudinal direction of the electrode rows. 10. Printing system according to claim 9, characterized in that the ^r,. '. ^s ro Working surfaces of the electrodes lie in a common plane / that the distance between the rows of electrodes (15,17) and between adjacent electrodes within a row of electrodes (15ji7) is almost equal to the side length of a working surface. 11. Printing system according to claim 10, characterized in that that the common plane is convexly curved. 009847/1679 Blank page