DE1772826B2 - Device for regulating the toner supply in electrophotographic printing devices - Google Patents

Description

The invention relates to a device for regulating ier toner supply for the development of electrostatic, Charges generated by a character generator in electrophotographic printing machines having an electromechanically actuated toner supply device.

In electrophotographic ones using powdered toner Devices is the main reason for a change in the quality of the print image or the Copy in that there are variations in the amount of toner deposited on the latent image a change the amount of toner supplied causes a change in color or intensity of the print image, the recognition can be made extremely difficult by blurring or insufficient contrast. It is therefore important to replenish the toner supply accordingly.

In most of the electrophotographic Process-working equipment is a powdery toner mixed with carrier particles, which are small glass spheres or the like. The toner can just as well be contained in a liquid as a dispersion. Since the toner depletes itself while the carrier particles are left behind and are used again, it is necessary to replenish the toner at sufficiently short intervals to achieve that proportion nis between toner and carrier particles almost constant remain.

Various methods of toner supply have heretofore been used. The manual is probably the most common Process by which the operator of the machine reviews the copies that come out of the machine and receives them from Hand toner refills as soon as the legibility falls below an understandably subjective threshold. If the filling is carried out by hand at long intervals, the result is due to the change in the Reserve a deterioration in the print image. However, manual feed will be used after short periods of time made, there is an unreasonable expenditure of time. Plus, it's relatively difficult to do determine how much toner has been used and how much toner has to be refilled. Additional to that, that handling powdered toner creates dust and pollution. In many cases it is Process of manual refilling and the subjective test of legibility completely sufficient. However, once the need for high output arises, the manual process is no more applicable.

In the German Auslegeschrift 12 49 690 a device is described in which the amount of The toner supplied is adapted to the ratio of black and white in the image to be reproduced. The method or the measuring device for determining this black-and-white ratio is not described.

U.S. Patent 3,013,703 describes a Apparatus for supplying toner, in which a container within the developing device is filled with toner its underside contains a continuously operating extraction device. By this measure However, a consistent quality of the copies cannot be achieved, since the toner requirement depends on the type and number of copies made per unit of time.

In the USA. Patent 32 33 781 is as a stand dor Technique mentions a method in which a constant amount of toner is added each time copying is performed. This method is of limited use as not every copy requires the same amount of toner. Go on in this patent specification is a method for directly measuring the toner concentration, that is the ratio from toner to carrier particles. It is a closed-loop control circuit with a Dead time element only contains a change in the very

Difficult to determine toner concentration causes a supply.

So far, no automatic method has been described in which the toner supply corresponds to the actual Toner consumption corresponds to instructions. the the Toner supply depending on paper consumption '' «on the number of blue stains or from the length of the output record carrier annoy, are unsatisfactory because the consumed Amount of toner varies from page to page or copy to copy. Other arrangements that the toner supply in Regulate as a function of the time are just as useless as the toner consumption as a function of time is not constant. Weight or fill level dependent arrangements are due to their long dead time also not applicable. The problem is also not due to the scanning of the degree of blackness of the copy solvable. For example, it is not just a change the toner concentration is responsible for a variation in legibility, but it can /. B. in one Copier can also change the contrast of the original so that a variation in legibility entry. Both when refilling manually as well as when scanning the degree of blackening and thus coupled refilling of the toner, a change in the original is not taken into account at all, as whether only the toner itself influences the quality of the displayed image.

Many printing devices, especially as output units for electronic computers, use non-mechanical see printing processes like electrophotographic Procedure. Toners are used to make the means to visualize latent electrostatic images generated by a character generator. There is a problem in replenishing the toner as it was used to print. So far it was An automatically working solution is known because of the high printing speed in a short time a lot of toner is consumed and on the other hand a certain and balanced mixing ratio between toner and carrier particles is required.

The object of the present invention is to provide a device of the type mentioned at the beginning which is the amount of toner supplied as well as the amount of toner required for development.

The solution according to the invention is characterized in the device mentioned at the beginning by a for character generation serving signals (character signals) integrating device, the output signal when a threshold value is reached with simultaneous actuation of the feed device again on the Initial value decreases. Advantageously, with the help of this solution, the immediately consumed Detected amount of toner and according to the requirements, d. H. the set threshold value, the Developing unit are supplied.

In non-mechanical printing processes, there are usually electrical signals for different «: functions available. You can turn on a switch for a light source such as a flash lamp, you can use a Control the cathode ray tube, or they can generate a high voltage pulse that the electrode an electrostatic printer. All of these processes produce latent images of characters, which have to be developed for visualization.

As set out with reference to an embodiment of the present invention, an electrical signal that is to a character, part of a character or a group of characters belongs to a corresponding counter counted until a sum of χ signals is reached. The output signal emitted by the counter controls an electromechanical actuation device for the toner supply. The toner is fed to the development unit of an electrophotographic high-speed printer in such an amount that is required to print the desired characters.It is useful to keep the size χ small in order to be able to use a simple counter and the mixing ratio between toner and carrier particles as a function of time to be kept as constant as possible. Too low a value of χ would, however, require an extremely fast response of the electromechanical device for the toner supply and a very short reset time of the counter. In addition, the smallest possible value of χ is a function of the information represented by the character signal. If the signal represents a complete character, the value * that is necessary to trigger the electromechanical feed device will be smaller than if this character signal only means a small part of a character consisting of several parts

Embodiments of the invention are described in more detail with reference to the drawings. It shows

F i g. t the block diagram of a device for Regulation of the toner supply.

F i g. FIG. 2 is a block diagram of a high-speed electrophotographic printer employing the methods shown in FIG. 1 shown Contains device.

K 1 g. 3 the schematic diagram of a high-speed printer equipped with a cathode ray tube with a second device for regulating the toner supply,

4 shows the detailed circuit of the circuit shown in FIG shown generator for the supply signal and

F i g. Fig. 5 shows a high-speed cathode ray tube printer incorporating another embodiment of the device according to the invention.

The block diagram of a device for regulating the toner supply is shown in FIG. 1 shown. The single ones, Time control signals entered via input 24 are counted by the counter 17, which as soon as a predetermined number of signals is reached, a Output signal to relay driver 18 forwards. This resets the counter 17 via line 2! 6 and switches the relay 19. which a circuit in the electromechanical actuator 2f closes. The actuating device 28 opens the measuring device 32 via the mechanical connection 29 whereby a predetermined amount of the toner 31 au; the container 30 can escape.

In Fig.2 the device shown in Fig.l is together with the principal details one; xerographic high-speed printer 23 is shown. The switching circuits 33 for printer control are schematic! shown. The output from the circuits 33! Character print signals are input to the counter 17. The toner dispenser 46 distributes the clay evenly over the printing device 47. The Toner-Behäl ter 30 is located above the distributor 46 in order to mi to load predetermined amounts as a function of the toner supply control 34.

As soon as a predetermined number of character signals is displayed by the counter 17, the drive will be 18 is applied and thus the counter 17 is reset and the relay 19 is actuated. The relay 19 supplies the electromechanical actuating device 28, ie

thereupon the mechanical connection 29, for example, pulls to the left against a spring tension. Through this one arrives; predetermined amount of toner from the measuring device 46. • ^: Fig. 3 shows an output device, for example for electronic computing systems, which works using a cathode ray tube. A conventional xerographic drum I, which has a photoconductive film applied to a conductive base on its surface, is mounted rotatably about the axis 2. In Fig. 3, as also in FIGS. 4 and 5, bearings, housings, supports and the like are not shown in order not to unnecessarily complicate the drawings. The cathode ray tube 3 in FIG. 3 describes the surface of the drum 1 with its beam 4. The photoconductive film located on the surface was previously charged to a uniform potential by means of a corona discharge unit 5. The light beam 4 emerging from the cathode ray tube 3 discharges the photoconductor at the points on the drum 1 it hits, thereby creating a latent electrostatic image on the drum. When the drum continues to rotate in the direction of the arrow, the latent image is made visible in the developing unit 6. For this purpose, with the aid of spoons 9 attached to an endless belt 8, the mixture of toner and carrier particles 7 is poured over the part of the drum 1 which contains the latent electrostatic image. When the amount of the existing toner falls below a certain level, the carrier particles which are thrown over the outer periphery of the drum 1 do not leave any toner on the charged surface parts, but often take up previously deposited toner. resulting in poor quality copies.

After passing through the developing unit 6, the developed image is fed into the by rotating the drum Transfer station IO moved, which includes a corona discharge unit 11. This discharge unit 11 charges the back of a paper web 12. so that the toner is conveyed from the drum 1 onto the paper web 12 will. Thereafter, the paper web 12 is passed through a heating unit 13, in which by the action of heat the toner is fixed on the paper. The paper can then be moved in the direction of arrow 14 can be removed. The drum I is now passed through a cleaning unit 15, which is a rotating Brush 16 for removing toner left on the drum 1 contains

The process just described is known. Therefore For details of the corona discharge units 5 and 11, the developing unit 6, the heating unit 13 and the cleaning unit 15 can be dispensed with. A use of the device is not only in connection with one designated as 6 in the figure Development unit possible, development units of another type, e.g. B. with a magnetic bear equipped, can be used. It is also possible to do it in a xerographic Printing device to use the invention in a device operating according to the electrofax method.

As in Fig. 3, the cathode ray tube 3 is supplied by a signal source 20 via the lines 21 and 22 controlled. The signal source 20 can be of any type and Represent the number of signal generators. For example, it can represent an electronic computer or a scanner for character recognition. The intcnsjtätsMgnal from the signal source 20. which via

lines 21 and 22 to the cathode ray tube is given, is also fed via line 24 'to a generator for a feed signal 25 (feed signal generator). This generator 25 receives also an on / off signal from the signal source 20 via the line 24 ″. The output of the generator 25 is Connected via the line 27 to the actuating device 28 for the toner supply, which is the latter mechanically coupled to the toner container 30, which is indicated by the line 29. There are numerous Ways of removing the toner 31 from the toner container 30 by means of the actuating device 28. One this method will be described in connection with FIG.

During operation, the signal coming from the signal source 20 via the lines 21 and 22 is used for Intensity modulation of the beam from the cathode ray tube 3. In addition, the intensity signal passes over Line 24 'to the feed signal generator 25. This generator 25 was at the beginning of the write process switched on via line 24 ". The intensity signal on line 24 'is integrated in generator 25 and as soon as the integral exceeds a predetermined value, an output signal is generated in generator 25, which via line 27 reaches the actuator 28 for the toner supply. The actuator 28 causes a predetermined amount of the im Toner 31 contained in the toner container 30 enters the developing unit 6. As soon as from the generator 25 a supply signal is given on line 27, the generator is reset itself so that the next Integration can take place. In this way the toner supply is directly proportional to the total too area to be printed or blackened.

In Fig. 4 shows the generator 25 in detail. It is an integrator for integrating the intensity signals that control the cathode ray tube and a threshold detector, which as soon as the absolute value of the integral exceeds a predetermined value Emits signal which is used to start the actuating device 28 and to reset the Integrator is used.

As in Fig. 4, the on / off signal of the signal source is fed via line 24 ″ to a relay driver 35 which, via line 36, carries the relay coil 37 with it Powered. When the relay with normally open contact is switched on, the contact arm 38 comes into contact brought to the fixed contact 39 so that the generator 25 is set in motion. The intensity signal of the signal source, the. As shown in Fig.3, the Cathode ray tube 3 is supplied, passes via line 24 'and the opposing land 40 in the capacitor 41, which stores it Resistor 40 and capacitor 41 determine the time constant of the Integrators. The charge of the capacitor 41 increases as long as pulses from the line 24 ' Arriving signal source The connection 42 is both with the capacitor 41 and via the line 43 connected to the fixed contact 44. Contact 44 is part of the relay 45 with normally open contact is normally the connection between the fixed contact 44 and the contact arm 61 is interrupted, as long as the capacitor 4t can be charged. Because of the high Input impedance of the insulation used Layer FekJeffekuransistor 50 becomes the capacitor 41 maintained its charge for a long time. The output of the field effect transistor SO is over Line 51 and a resistor 70 with #w n «« * w

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Transistor 52 and connected to a negative voltage source via an operating resistor%. As soon the charge in the capacitor 41 exceeds a certain threshold, whereby the potential of the line 51 is raised, the transistor 52 turns on. This transistor 52 is part of a bistable A circuit representing the multivibrator, another part is the transistor 53 with the collector resistor 73. The transistor 52 is switched off as long as the potential on line 51 it through the resistor 70 is supplied does not exceed a predetermined threshold value. During this time is the Transistor 53 is turned on, since at its base a positive potential passed through resistors 71 and 72 prevails. The collector of this transistor and thus the line 55 is almost at ground potential. As soon When transistor 52 turns on, transistor 53 will turn off, since its base is approached via resistor 72 Ground potential is supplied. At this point, the one appearing at the collector of transistor 53 will be Potential change from near mass to a positive amount. This means that as long as transistor 52 is switched off, the collector of the transistor 53 carries ground potential; however transistor 52 is on, the collector of the transistor 53 has a positive potential, that of the collector supply voltage is equivalent to. The pulses that occur in the collector circuit of the transistor 53 are transmitted via line 55 to the Lines 56 and 57 transferred. Line 56 is connected to a monostable multivibrator, which then emits a pulse on the line 59 to the relay driver 60 when the starting edge of the the pulse generated by the multivibrator arrives. This makes the normally open contact of the relay 45 with Connected to ground potential, the capacitor 41 discharged, whereby the integrator is reset, d. H. for one new integration is prepared. The same starting edge of the output from the collector of transistor 53 Impulse is transmitted via line 57 to a monostable multivibrator 62, which via Line 27 controls the actuator for the toner supply (see FIG. 3).

In Fig. 5 shows an arrangement in which means are provided to vary the threshold at which the bistable multivibrator responds, namely in Depending on the amount of toner that is present in the supply container. The reference numbers correspond those from Fig.l. 2 and 4. if available there, each supplemented by the preceding hundred digit.

The other details correspond to those in FIG. t and 2 arrangement shown. The signal source 120 is connected to the cathode ray tube 103 by means of the Cathode ray 104 is applied to the electrophotographic Drum 101 creates an electrostatic latent image. When rotating the drum 101 about the axis 102 is the latent image through the developing unit 106. Transition unit 110 with the corona discharge direction 111 led. The powder image transferred onto the paper web 112 in the transfer unit 110 is fixed in the heating unit 113 and can be removed in the direction of arrow 114. With continued The drum 101 rotates through the cleaning device 115, which is usually a rotating brush 116 contains. Thereafter, the drum 101 is by means of Corona discharge units 105 on one over the surface constant distributed potential charged. The signal transmitted to the cathode ray tube 103 becomes through resistor 140 and capacitor 141 integrated. The charge appearing on the capacitor 141 appears at the output of the insulating layer field effect transistor 150 at connection 199. This is through the resistance 1% with a voltage source which generates a negative bias voltage which is used to turn off transistor 152. Parallel to Resistance 1% is the potentiometer 195, which through the connection 200 also with the source for the negative bias is connected. If the

ίο Potentiometer tap 194 is moved upwards, engages it offs a smaller amount of negative voltage as a bias for transistor 152: it will against it moves down, the negative bias on the base of transistor 152 increases. This enlarged negative bias means that to switch the transistor 152 and thus the entire bistable Multivibrators the capacitor 141 must have reached a much larger charge.

In contrast, a small «means negative bias the base of the transistor 152, that is to say a tap 194 moved upwards, that already a lower one Charge capacitor 141 to turn on transistor 152 and the entire multivibrator sufficient.

5 also shows a storage container 130 for receiving the toner 131, which protrudes into the developing unit 106 with its lower end, which has the controllable outlet openings. The toner here forms a solid block 131 with the height H. As shown in the enlarged drawing. the mechanism for measuring the size H consists of a float or scanner 190 which is attached to an arm 191 which is movable about the joint 192. By means of the connection 193, the arm 191 moves the tap 194 of the potentiometer in this way. that as the size H decreases, the tap 194 is shifted upwards and thereby a less large negative bias voltage is applied to the base of the transistor 152. As a result, a smaller charge of the capacitor 141 is required when the supply of toner 131 decreases. This change in the threshold value serving to trigger the toner supply has the effect that the influence of the decreasing weight of the toner block 131 on the amount of toner scraped off by the scraping device 202 and discharged into the developing unit 106 is compensated. As long as the toner weight and thus the size H is large, the movement of the scraper device 202 will scrape off a much larger amount of toner than with a small toner weight. The arrangement just described avoids this disadvantage in that with increasing height H the threshold value defining the switching process is raised, while with a smaller height H this threshold value is lowered. d. That is, if the height H is high, the bistable multivibrator consisting of transistors 152 and 153 will require a higher charge of capacitor 141 in order to switch over and will therefore switch less often within a given line. In contrast, if the height H wire is small, the bistable multivibrator will switch significantly more often within the same time interval.

The output of the multivibrator at the collector of the transistor 153 is via the lines 1S5 and 15 ' fed to the monostable multivibrator 162. The voi this generated pulse reaches the actuating device 128 for the scraper device via the line 121 tion. This can be, for example, a plunger pulse system, which via the mechanical connection 129 dii

509 537 / 3C

Scraper device 202 actuated.

It goes without saying that an analogous application of the present invention is in an electrostatic one Image-forming device possible, which for example a liquid toner, or the dispersion of a toner applies in a liquid.

For this purpose 3 sheets of drawings

Claims (6)

Patent claims: 1. Device for regulating the toner supply for the development of electrostatic charge images generated by means of a character generator in electrophotographic printing devices with an electromechanically operated toner supply device, characterized by a device (17, 40, 41) which integrates the signals (character signals) used for character generation. the output signal of which returns to the initial value when a threshold value is reached with simultaneous actuation of the feed device (30, 130). 2. Device according to claim 1, characterized in that that an electromechanical actuator (28) via a mechanical connection (29) each dispensing a fixed amount of toner (31) from the toner container (30) Measuring device (32) is connected. 3. Apparatus according to claim I or 2. characterized. daU as an integrating institution for / calibration signals. which character parts, whole Characters or lines correspond to a counter (17) is provided. the. as soon as the sum of the Character signals has exceeded a predetermined threshold. over a counter (17) resetting relay driver (18) actuates a relay (19), which with the effecting the toner supply electromechanical actuator (28) is in communication. 4. Apparatus according to claim 1 or 2. characterized characterized in that as an integrating device, for character signals which have the intensity of a Control the cathode ray tube, an RC element (40, 41) is provided. that via a field effect transistor (50) a bistable multivibrator (52.53.71.72.73) controls whose output signal generated when the threshold value is exceeded, the actuation of the toner supply device causes. 5. Apparatus according to claim 4, characterized in that then at the output (55) of the bistable multivibrator (52, 53, 71, 72, 73) a monostable Multivibrator (58) is switched on. via a relay (44. 45. 61) the ÄC element (40. 41) to ground lays. 6. Apparatus according to claim 5, characterized in that the working resistance in the output circuit of the field effect transistor (150) is designed as a potentiometer (155) . whose tap (194), which is electrically connected to the input of the bistable multivibrator, is mechanically connected to one end of a HeM (191) . which is rotatable about a bearing (192 ) attached to the toner container (130) and at its other end carries a float (190) resting on the surface of the toner supply (131) , whereby the threshold value is dependent on the height of the filler land (H) of the toner container (130) is changeable.