EP0403523A1

EP0403523A1 - Electrophotographic printing device with regulated electrophotographic process.

Info

Publication number: EP0403523A1
Application number: EP89903096A
Authority: EP
Inventors: Hans Manzer; Rainer Koefferlein
Original assignee: Siemens AG
Current assignee: Canon Production Printing Germany GmbH and Co KG
Priority date: 1988-03-04
Filing date: 1989-03-03
Publication date: 1990-12-27
Anticipated expiration: 2009-03-03
Also published as: JP3162357B2; JPH03503575A; WO1989008283A1; DE58902832D1; US5124732A; EP0403523B1; DE3807121A1

Abstract

Un agencement d'impression électrophotographique comprend un dispositif de réglage à circuit fermé pour saisir et réguler les paramètres essentiels de fonctionnement du procédé électrophotographique. L'agencement comprend un premier étage de réglage qui stabilise le processus électrophotographique sur le photoconducteur (12) en régulant le potentiel de charge (18) et, l'éclairage de décharge (17) et en saisissant et contrôlant le potentiel résiduel (SL). Un deuxième étage de réglage sert à optimiser et à rendre plus fiable le développement et la mise en couleurs de l'image électronique de charge par le réglage de l'apport en toner à la zone de développement (14) et de l'encrage de l'image de charge. Un troisième étage de réglage optimise et rend plus fiable la duplication par la saisie des valeurs spécifiques du support d'enregistrement et par le réglage du dispositif à effet de couronne (UK).An electrophotographic printing arrangement includes a closed circuit adjuster for capturing and regulating essential operating parameters of the electrophotographic process. The arrangement includes a first adjustment stage which stabilizes the electrophotographic process on the photoconductor (12) by regulating the charge potential (18) and, the discharge lighting (17) and by capturing and controlling the residual potential (SL) . A second adjustment stage serves to optimize and make more reliable the development and the coloring of the electronic charge image by adjusting the supply of toner to the development zone (14) and the inking of the load image. A third adjustment stage optimizes and makes duplication more reliable by entering the specific values of the recording medium and by adjusting the crown effect device (UK).

Description

Electrophotographic printing device with controlled electrophotographic process.

The invention relates to an electrophotographic printing device according to the features of patent claim 1.

There is a significant difference between the acceptance by the operators of the copying result of electrophotographic copying devices and the printing result of printing devices working according to the principle of electrophotography: While in copying devices the copying result is measured on the copy template and the operator generally also accepts poorer copies , this is not the case with electrophotographic printing devices.

Electrophotographic printing devices are generally used in connection with EDP systems and the possibility of influencing the print quality is low or the operator expects the printer to deliver an optimal printing result under all conditions. This results in different demands on the quality of the electrophotographic process between printers and copiers.

In order to achieve this high requirement with regard to print quality in printers, it is necessary to minimize the tolerances in the electrophotographic process.

The quality of the consumables, such as toner and developer, and the manufacturing quality of the photoconductor are also of significant influence on the print quality. The printer manufacturer has less influence on the quality of these materials when operating the printing device.

In the case of copying machines, it is known to regulate the individual units involved in the electrophotographic process to predetermined standard values via control devices. So it is from Patent Abstracts of Japan, Volume 10, No. 288

(P-502) (2344) Sept. 30, 1986 and JP-A-61 105 578 to control the charging device for a photoconductor drum for a certain period of time during and after the switch-on phase in such a way that the fluctuations in the generated Surface potentials are compensated for by the switch-on process.

Furthermore, it is known from Patent Abstracts of Japan, Volume 7, No. 101 (P-194) (1246) April 28, 1983 JP-A-58 25 677 to determine the resistance value of the paper web with the aid of a multi-stage comparison device in front of the transfer station and, depending on this, to control the corona discharge of the transfer corona in the transfer printing station step by step.

In the patent abstracts of Japan, volume 7, No. 184 (P-216) (1329) August 13, 1983 and JP-A-58 86 562 a control method for an electrophotographic copier is described. The toner density and the residual charge on the surface of a photoconductor are scanned using a toner image generated using a standard image. The values detected and calculated in this way are compared with predetermined standard values and, depending on this, a developer circuit, an exposure circuit, a toner supply circuit and a developer sequence are controlled via a microcomputer circuit. Among others, a reflection density measuring device and a surface charge sensor are used as sensors.

With the known arrangement, a standard template is imaged on the photoconductor and the developer station is regulated depending on the values of the standard template. This means that mean norm values of the electrophotographic process are ensured via the norm template and, based on these norm values, different templates are copied with respect to these norm values.

This has the disadvantage that an adaptation to different templates is not possible. Bad templates are considered bad originals formed, regulation of the standard values even depending on the copying result is not provided.

The aim of the invention is to provide an electrophotographic printing device which, regardless of quality fluctuations in the consumables and independent of changing operating conditions, delivers optimum printing quality.

Another object of the invention is to design an electrophotographic printing device in such a way that the tolerances in the electrophotographic process can be significantly reduced in order to achieve maximum print quality. The entire process should run automatically if possible.

This object is achieved in an electrophotographic printing device in accordance with the features of patent claim 1.

Advantageous embodiments of the invention are characterized in the claims.

The process-controlled, multi-stage control arrangement for optimizing the electrophotographic process as a function of the process results and the process flow of the individual process steps results in a guaranteed constant print quality even when the process itself changes. First of all, the electrophotography is made via closed internal control loops ¬ fish process itself stabilized and then the operating parameters of the printing device, including the process parameters, are regulated for optimum print quality.

Can not affect consumption materials changes in operating conditions and fluctuations of Ver¬ ^widget. This increases the print quality and the entire printing device becomes more operational. Embodiments of the invention are shown in the drawings and are described in more detail below, for example.

Show it

1 shows a schematic sectional view of an electrophotographic printing device for single sheets with duplex and simplex printing

2 shows a schematic block diagram of a control arrangement for the printing device

3 shows a schematic block diagram of the main processor used in the control arrangement of FIG

4 shows a schematic diagram of the control circuit for regulating the charging potential

5 shows a schematic representation of the structure of the control arrangement for program-guided electrophotography

6 shows a schematic representation of an overall overview of the control concept

7 shows a schematic block diagram of the control arrangement for program-guided electrophotography and

8 shows a schematic illustration of the test marks and test patterns generated on the photoconductor.

A single sheet page printer shown schematically in FIG. 1 and working on the principle of electrophotography contains three paper storage containers VI, V2 and V3 with different capacities for holding single sheets. The paper supply containers VI, V2 and V3 are constructed in the usual way and are located above paper feed channels 11 with a pressure channel DK Druckeinrichtuπg in connection. The pressure channel DK contains the actual printing station DS with a photoconductor drum 12 which is driven by a motor and around which the individual units of the electrophotographic printing station are arranged. An aggregate is a character generator 13 with a character-dependent controllable LED comb with individual controllable lighting elements, not shown here, which can be constructed, for example, in accordance with US Pat. No. 4,780,731 and which is varied by varying the control voltage or the control current is adjustable in its light intensity. A charging sensor SL is connected to the exposure station 13, which measures the surface potential on the photoconductor drum and emits a signal as a function thereof. The charge image generated on the photoconductor with the character generator 13 depending on the character is colored with the aid of a developer station 14. The developer station 14 contains a toner reservoir TV for receiving toner and a metering device D in the form of a metering roller. Depending on the toner consumption, the metering roller D supplies the actual developer station with toner. The toner is mixed with the aid of two mixing screws MS and the developer mixture of ferromagnetic carrier particles and toner particles is then fed to a developer roller E. The developer roller E acts as a so-called magnetic brush roller and consists of a hollow roller with a magnetic strip arranged therein. The developer roller transports the developer mixture of ferromagnetic carrier particles and toner particles to the development gap ES between the photoconductor drum 12 and developer roller E. Excess developer is transported back to the developer station 14 via the developer roller E.

A toner mark scanner TA in the form of a reflection scanner is arranged immediately downstream of the developer station 14. This scanning device TA is described later and is used when scanning a test routine or to scan and color-colored test marks generated and colored automatically and regularly on the photoconductor and to evaluate these test patterns, for example with regard to coloring density and color saturation. The inked charge image is then transferred to a recording medium, in this case to single sheets, in a transfer printing station 15. For this purpose, the transfer printing station 15 has a transfer printing corona device UK. The U pressure corona device UK loosens the colored charge image on the photo conductor drum 12 so that it can be transferred to the recording medium (single sheet).

The single sheet is then transported via a suction table S to a fixing station F with electrically heated fixing rollers FX, which are driven by an electric motor, and the toner image on the recording medium is thermally fixed.

A cleaning station 16 follows in the direction of rotation of the photoconductor drum 12. The cleaning device 16 is constructed in a conventional manner and contains e.g. a stripping element RE, which removes the excess toner or the carrier particles from the photoconductor drum 12. This cleaning process is supported by a corona device KR.

The surface of the photoconductor drum 12 is then unloaded with the aid of an exposure device 17. This illuminating device contains a light source which is homogeneous over its entire spatial length and whose intensity can be controlled in a targeted manner.

Thereafter, the surface of the photoconductor drum discharged by the discharge exposure is uniformly recharged in a charging device 18 with a charging corotron arranged therein.

For transporting the single sheets through the printing channel, the printing channel DK contains paper transport elements in the form of a belt-shaped suction table S and paper transport rollers P.

To the pressure channel DK switched on and the output side to a paper-transport elements P in the form of motor-driven Walzenpaa ^'ren contained return channel RF. The return channel RF has a turning device W1, in which, in the so-called duplex mode, the front and back of the single sheets are described, the single sheets before being fed again

Pressure channel DK can be turned.

Controlled by a paper switch, the paper channel DK is followed by a paper transport channel system PK which feeds the single sheets, not shown here, in the Simplex or duplex process.

To determine the position of the continuous single sheets and to control the paper transport elements P, all paper channels have paper scanning sensors LS (shown as black triangles), which consist of light barriers. For reasons of clarity, only a few light barriers are shown here.

The page printer shown schematically in FIG. 1 is controlled with the aid of a control arrangement as shown in FIGS. 2 and 3.

control

The controller for the page printer is basically divided into a controller part C and the actual device control G. The controller C is principally in accordance with the US PS

4,593,407 built. It has the task of accepting the print data coming in from a computer H, preparing them page by page and controlling the character generator 13 of the printing station as a function of the characters to be displayed. The device control G in turn serves for the coordinated execution of all printer functions. It has a modular structure and consists of a main processor HP and various submodules SUB1 to SUB5, which ensure independent monitoring of the assigned printer units. Communication between the individual control parts takes place via a hardware / software interface that is uniform for all parts (network-like coupling, serial bus). Each submodule SUB1 to SUB5 is equipped with a equipped processor and can operate the associated unit of the printing device independently and is test-capable itself. This self-test capability means that independent test routines are carried out both when the device is switched on and when the main processor HP requests it. All control flat modules of the printer in the device control are registered with regard to their status in a non-volatile memory. The controller can access these values. In addition, the contents of the non-volatile memory can be printed out if necessary. There are also interfaces for additional devices.

2 and 3 show the basic structure of the device control in the form of a block diagram. 3 shows a block diagram of the structure of the main processor HP.

All submodules SUB1 to SUB5 and the main processor HP are connected to one another with a serial interface INT1, which is controlled via line drivers. The serial interface INT1 is controlled under the control of the main processor HP via a BIT bus. The interface protocol corresponds to the usual HDLC / SDLC description (fast data transmission). In order to relieve the load on the interface and to simplify the cable routing to the individual units, the units are controlled by the associated submodules SUB1 to SUB5 directly via power amplifiers (not shown here). The main processor HP checks the function of the individual submodules SUB1 to SUB5 at regular intervals. A monitoring circuit (hardware / watchdog) checks the process in the main processor. The sequence control is synchronized with the peripheral speed of the photoconductor drum 12 via the output signals of a rotary pulse generator DI. The output of this rotary pulse generator DI (FIG. 1) is connected to all submodules SUB1 to SUB5 and supplies a synchronizing signal F at cyclical intervals. 3, the main processor has the following structure:

A central processing unit CPU is connected to three memories SP1 to SP3 and an input / output unit EA. The memory SP1 is a read-write memory, in which

Memory SP2 by an electrically programmable read-only memory and by memory SP3 by a non-volatile data memory. The input / output unit EA detects, among other things, the synchronization pulse F.

In the non-volatile memory SP3, consumable metabolism, printed / fixed page, maintenance intervals, error statistics and deviations from guide values etc. entered by the operator are stored. The connection to controller C is made via a common interface INT2.

The main processor HP has the task of coordinating, checking for plausibility and forwarding all messages, commands and measurement data from the outdoor stations SUB1 to SUB4. Furthermore, he establishes the connection to controller C via the

Interface INT2 and the system bus BUS2. In the process, bidirectional commands and messages are transferred. The correct program sequence in the device control is continuously monitored via the monitoring circuit U (watchdog circuit).

As already explained, five submodules SUB1 to SUB5 independently monitor and control the aggregates assigned to them. The communication between the individual modules SUB1 to SUB5 and the main processor HP takes place via a hardware / software interface INT1 that is uniform for all parts. Each submodule has its own processor with an input buffer, which transmits the data supplied via input I to the processor, and power levels which drive the associated units via output 0. The submodules can be tested themselves, ie test routines are carried out independently when the device is switched on or when the main processor HP requests it. The submodule SUB1 monitors all sensors LS of the storage containers VI to V3, the feed channels 11 and the pressure channel DK and in particular the pressure start signal of the sensor LS SYN. The submodule SUB1 controls all units in this area. It detects and reports paper run errors.

The submodule SUB2 detects all sensors LS in the paper output area, i.e. in the area of the dispensing container and in the dispensing channel AK. Paper run errors are detected and reported to the main processor HP.

The submodule SUB3 monitors the sensors LS in the paper channel system and in the return channel RF. It controls the paper flow in these channels and detects paper flow errors.

The SUB4 submodule controls a control panel AZ on the printer. The control panel AZ contains a keyboard and a display device, the display showing the paper path in the printer or, in the event of a paper transport malfunction, the fault location.

The submodule SUB4 in connection with the control panels AZ represents the interface between the operator or maintenance technician and the printing device. All inputs by the operator and all information from the device are made via the control panel. This essentially consists of a display for displaying the information and a keyboard for entering various commands and parameters. In addition, it has some special controls and indicators.

The submodule SUB5 detects the sensors of the printing station DS and the fixing station FX. These sensors are, for example, the charge sensor SL for detecting the surface potential of the photoconductor 12, transport monitoring sensors in the developer station 14, temperature sensors and microswitches in the fixing station FX, the toner mark sensor TA between the developer station 14 and transfer printing station UK. The submodule SUB5 controls the aggregates, the fi xier lamps, motors, fans, charging corotrons etc. The errors that occur are communicated to the main processor HP.

The submodule SUB5 in connection with the main processor HP also contains the process-controlled control arrangement according to the invention for detecting and regulating the essential operating parameters of the electrophotographic process.

This control arrangement is a process-controlled control arrangement which is constructed in several stages and in principle consists of three blocks (control stages) CC1, CC2, CC3. According to the regulation strategy on which the regulation is based, the entire electrophotographic process is first divided into a sequence of process steps which take place or interlock, namely the photoconductor process, the development process and the transfer printing process. An attempt is now being made to regulate the individual process steps independently via individual control blocks, specifically on the basis of the result of the individual process step and the course of process 0 in the process step. The aim is to stabilize the individual process steps with regard to their operating parameters in order to build up the next process step on the continuous stabilized process step.

5 When optimizing the entire electrophotographic process, the results of the individual steps are therefore initially assumed. However, this can only serve as the basis for a first approximation optimization, because the three control blocks CC1, CC2, CC3 in turn form their own control system, for example ° a change in the light intensity of the character generator 13 has a direct influence on the residual potential of the surface charge of the Photoconductor 12, this in turn leads to a change in contrast during the coloring in the developer station 14. If a change to be regulated is found in the process step "development", it may be necessary to regulate parameters whose changes affect the process ¬ step "photoconductor" has. In the first control stage CC1, the electrophotographic parameters are stabilized as a prerequisite for optimizing the development process. The electrophotographic parameters are understood to mean in particular the variables influencing the charge balance on the photoconductor. In order to be able to safely regulate this charge balance in the photoconductor, the first regulating stage contains a control circuit shown in FIG. 4 for regulating the charging potential on the photoconductor.

Test runs and experience in operation have shown that, in particular, the tolerances of the charging of the photoconductor drum can greatly reduce quality and give rise to faults. Influencing variables are, in particular, drum specimen scatter, temperature and air humidity, photoconductor fatigue, state of aging of the toner, influence of the cleaning station, device adjustment and corotron state in the charging station 18. In order to become independent of these influencing variables, it is necessary that Regulate the charging potential of the photoconductor. For this purpose there is a charge sensor SL directly in front of the developer station, for example in the form of an electro-voltmeter, with which the charging potential of the photoconductor drum can be continuously detected. The output signal of this measuring probe is interrogated at defined intervals using a conventional interrogation arrangement AF. The interrogation arrangement AF compares the obtained measured values with stored reference measured values and corrects the charging current at the charging decorron 18. After a time delay of approximately 1 second, the output correction value is again detected by the measured value detection device AF in accordance with the speed of the photoconductor drum 12 . This cyclical detection enables an almost instantaneous correction of the charging current of the charging corotron 18. The regulation of the charging potential is of very great importance for the print quality. Fluctuations in the charging potential have a direct impact on the print quality. The constant automatic detection and correction of the charging potential enables safe operation within the permissible bandwidth. With the invention According to the control arrangement, it is possible to reduce the tolerance of the charging potential that occurs by a factor of 5, for example from absolutely 400 V to approximately 80 V. The remaining 80 V potential tolerances are mainly due to the non-adjustable charge fluctuations on the circumference of the photoconductor drum. An achievable reduction in tolerance from 400 V to 80 V already leads to considerable quality stabilization and assurance. For example, it is possible to increase the pretension at the developer station for better coloring of large areas and at the same time to ensure sufficient security against background coloring.

In a further control circuit assigned to the first control stage, the light output of the discharge lamps 17 is controlled in the exposure station. The light output of the discharge lamps strongly depends on the lamp age, the specimen scatter and the temperature. In order to become independent of these tolerances, the light output is e.g. detected by a photo sensor PS arranged in the light channel of the discharge lamp 17 and corrected by raising or lowering the lamp current. To the

To be able to regulate the light output better, a light source that is homogeneous over its entire length is used, the intensity of which can be controlled in a targeted manner.

The contrast or residual potential of the photoconductor drum 12 has a further significant influence on the print quality when it is discharged from, for example, a regulated charging potential with a defined exposure. Despite the regulated charging potential, there are very clear deviations in the residual potential or the ability to discharge over the photoconductor spectra spectrum. These tolerances correspond in part to deviations such as those which can arise with uncontrolled charging. In addition to the scatter of specimens of the photoconductor drum, the overall tolerance of the residual or contrast potential also depends on fluctuations in the power of the writing light and, under certain circumstances, also on the influences of the toner (developer mixture). This ensures a constant quality of the print result, in particular of full areas or not always guaranteed when printing bar codes.

Too high a residual potential leads to insufficient coloring of the large area.

However, it is difficult to regulate the residual potential. In addition, regulation is not without risk for e.g. printing quality possible. The residual potential can, however, be detected with the aid of a monitoring device.

This monitoring device uses two sensors, namely the charging sensor SL, which is also used to measure the charging potential, and the toner mark sensor TA.

The charging sensor SL and the toner mark sensor TA are located in the area of the photoconductor 12 on a single movement track. In this way, a test mark, preferably generated outside the actual writing area on the photoconductor, first reaches the area of the charge sensor SL and then the area of the toner mark sensor TA.

The charging sensor SL has several functions: first, it is used in the manner described for measuring the charging potential, wherein it detects the unexposed areas after charging.

It also serves to measure the residual charge of the residual charge potential. This takes place in that, according to the illustration in FIG. 8, an elongated full-area mark 31 is produced outside the writing area 29 by exposure at the edge of the photoconductor drum. All the LEDs of the character generator necessary for generating the full-area mark are activated with a predetermined light output, this light output being dependent on the type and temperature of the photoconductor. If the full-area mark 31 is generated by exposure but has not yet been colored, the charging sensor SL measures in the loading the residual potential of the full surface. The elongated

Full area mark is necessary, among other things, because the charge sensor SL has a certain inherent inertia and, as a result of the rotational speed of the photoconductor drum, a reliable measurement is only possible after a certain time and thus after a certain pass through the full area mark.

The optical scanner TA in the form of a reflection light barrier is located in the same movement track of the photoconductor 12, downstream of the developer station. The reflection light barrier is constructed in the usual way and consists of a light source and a photo transistor as a receiver. The output signal of the phototransistor depends on the degree of reflection of the toner mark applied to the photoconductor and now colored by the developer station and thus on the color saturation, i.e. the optical density of the applied mark and colored by the developer station (pattern). The wavelength of the reflection light barrier is selected so that the scanning light has no influence on the function of the photoconductor drum. This is necessary because the light barrier is constantly activated and thus also scans areas that have not been exposed.

To detect the residual potential, test routines for generating the described full-area markers are called up from time to time via test programs stored in the control arrangement. Then the residual potential is determined in the exposed and non-inked full-area mark via the charge sensor SL and this signal is compared with a limit value stored in the memory device and, depending on this comparison process, a warning signal is then triggered on the display device AZ if the residual potential is exceeded. The maintenance personnel can now stabilize the residual potential, for example, by changing the pretension at the developer station (BIAS voltage) or by other measures. However, this regulation can also be carried out automatically by the control arrangement. However, it is also possible to influence the residual potential by changing the light intensity of the character generator 13 and thus to regulate the residual potential. For this purpose, the intensity of the writing light of the character generator 13 is changed depending on the comparison process. This is done by changing the drive current or the drive voltage of the LED,

If a character generator with a laser beam is used instead of a character generator with activatable individual points (LED comb), it is necessary to change the intensity of the laser beam, this can e.g. also take place via filters or other measures.

The development device for securing and optimizing the development of the charge pattern is regulated with a second control stage CC2.

In order to regulate the conveyance of toner from the storage container TV via the metering device D to the developer station 14, a toner mark 30 is constantly generated on the photoconductor 12 outside the actual writing area in short time intervals using the character generator 13, specifically with a defined exposure intensity and this toner mark 30 via the Colored developer station. The colored toner mark 30 is then scanned on the photoconductor 12 with the aid of the optical scanning device TA and, depending on the degree of inking of this mark, the regulation of the conveyance of the toner from the storage container TV via the metering device D to the developer station 14 takes place. The developer supply in the developer station 14 becomes depleted is directly reflected in the color density of the toner marking. If the developer supply in the developer station is used up, the color density of the toner marking is greatly changed, this cannot be compensated for by additional funding. This state of consumption is recognized by the control arrangement and a warning signal is activated on the display device AZ. May consist in further longer time intervals which may for example by calling a test routine "Großflächeπeinfärbung" for example from the control panel, a test pattern are generated from an extending over the entire width of the recording medium Bai- ^'ken. This test pattern can also be scanned on the photoconductor via the optical scanning device TA. For this purpose, for example, several scanners can also be arranged side by side. However, this can also be accomplished by means of a single scanner if, for example, an elongated bar corresponding to the full-area mark 31 is used as the test pattern, which bar is arranged outside the actual writing zone, a continuous scanning being carried out when the test mark is passed through. However, this scanning can also take place in sections at short intervals. A value for the large area coloring can be derived from this. If the degree of coloring of the test pattern is too low, the coloring of the background areas on the photoconductor drum and / or on the paper must first be checked. If this is too high, this indicates a device malfunction or a very aged developer mix. Appropriate activities to compensate for this can then be undertaken.

In the case of a correct degree of coloring of the background area, an improvement of the large-area coloring can be achieved again by correcting the developer roller pretension or the operating point of the toner delivery control.

The background area of printed images can also be monitored via the scanning device TA. This background monitoring can be done continuously. If the background coloring exceeds a permissible level, the degree of coloring of the large area is first checked again. If this is within the permissible limits, it can be corrected as described for the measurement of the large area coloring.

Another possibility of checking the print quality is to record the raster reproduction. Due to the different discharge characteristics of the photosensitive recording material in the fine range, a defined raster reproduction can be impaired. For example, a very easily unloadable photoconductor layer changes a raster to higher or darker values, while a somewhat poorly unloadable photoconductor layer hinders raster printing. Since the human eye is very sensitive on this point and therefore high demands have to be made in this regard, it is necessary to correct this tolerance.

The pictorial representation with electrophotographic printers takes place in the dot pattern in different gray values, the gray value representation being carried out by corresponding configuration of the individual points having the same size.

In order to be able to check this gray value display, it is possible to generate a raster mark at certain time intervals by calling a test routine via the control arrangement. As shown in FIG. 8, the raster mark consists of a raster area which has a 50% optical density (black area), i.e. 50% black, 50% white. However, this can vary in a range from 25 to 75% area coverage. The raster mark is generated via the character generator 13 and colored via the developer station 14. It is then scanned in the manner described using the optical scanner TA.

The scanned value is compared with a stored target value and the light intensity of the character generator 13 is changed in accordance with the deviation, for example by increasing or decreasing the LED voltage. However, the stored setpoint can also be changed as a function of various machine parameters in order to achieve an adjustment depending on the recording medium used, the photoconductor drum used or the type of recording medium itself. For this purpose, the corresponding correction values or characteristic data can be entered via the display device AZ, or corresponding sensors independently detect these values. The transfer station is controlled in principle with a third control stage CC3 for securing and optimizing the transfer printing.

It has been found that the setting of an optimal transfer corotron current in the corona device UK of the transfer station 15 is strongly dependent on the paper weight class used and on the paper width, and also on the corotron contamination itself. In order to set the transfer corona device optimally can, the paper width and the paper thickness are entered via the control panel AZ with its keyboard-like input device, and the assigned optimum transfer corotron current determined from empirical values is set via the device software. This can also be accomplished automatically with a detection device, not shown here, which e.g. when leaving the individual sheets via the feed channels 11, the thickness and size of the paper are detected by an optoelectronic scanning device.

The three control levels record and stabilize all parameters that are important for print quality. This makes it possible to place the working points of the various parameters in optimal areas without considering the worst case conditions and thus to ensure the maximum achievable quality at all times.

Furthermore, the data recorded and ascertained in the course of the control processes can be used for testing and service purposes.

The structure of this control process, referred to as program-guided electrophotography, is listed in FIG. 5. An overall overview of the control concept can be seen in FIG. 6. The control loops shown in FIG. 6 are largely self-contained in order to rule out a clear and undefined control behavior. The individual control loops are influenced depending on the results of the individual process steps, for example changing a parameter. In summary, essential functions of the microprocessor-controlled control arrangement are the following:

Regulation of the charging potential of the photoconductor drum

In addition to a clear reduction in tolerance, the information about whether the conditions in the electrophotographic printing process are still regular is available via the setting value of the charging corotron current determined in the microprocessor for diagnostic purposes.

A strong reduction or increase in the charging capacity of the photoconductor drum, caused by external influences such as temperature, toner, etc., can be detected, evaluated and corrected.

Furthermore, various test programs can run routinely or on command for diagnostic and remote diagnosis purposes, gray fog test, background test.

Detection of the residual potential (discharge potential) or regulation of the residual potential e.g. about the light output of the drawing generator.

The information about the residual potential of the photoconductor drum provides valuable information about the current state of the electrophotographic printing unit. The residual potential can be regulated within limits via the light output of the character generator.

For example, the value of the residual potential can provide information as to whether the printing of sophisticated programs (barcode) or raster printing with high quality is possible. By scanning the raster marks, it is also possible to regulate the light output of the character generator. Is e.g. If the grid mark is too dark, the light output is reduced and the mark becomes brighter.

Furthermore, deterioration of the discharge ability caused by toner can be detected and monitored. Regulation of the coloring ability

In view of the relatively large fluctuations in the coloring of large areas, the information about the degree of coloring can be used to different parameters such as adjust the bias of the developer station within certain limits.

Claims

1. Electrophotographic printing device in which, as part of an electrophotographic process, charge images are generated in a sequence of process steps via a character generator (13) on a photo conductor (12), developed in a developer station (14) and in a transfer printing station (15) a record carrier are transmitted with the following features:

- A process-controlled, multi-stage control arrangement (SUB5) is provided for optimizing the electrophotographic process depending on the process results and the course of the process of the individual process steps;

- The control arrangement (SUB5) contains sensors (SL, TA, PS) for recording the essential operating parameters of the individual process steps and input means (AZ) for specific parameters of the process and

- The control arrangement has means to generate test marks and / or test patterns of process-relevant structures, the state of charge of which before development and / or, depending on the operating state of the printing device on the photoconductor (12), preferably outside the actual writing range, via the character generator (13) whose color density after development on the photoconductor (12) is detected by the sensors (SL, TA).

2. Electrophotographic printing device according to claim 1, characterized by a first control stage (CC1) for stabilizing the electrophotographic process on the photoconductor (12) by regulating and / or monitoring the operating parameters of the photoconductor (12) such as charging potential (18), discharge exposure ( 17) and residual potential (SL), a second control stage (CC2) for securing and optimizing the development of the charge pattern by regulating and / or monitoring the operating parameters of the developer station (14) such as nerzufuhr to the development area (ES), coloring the charge image, cleaning the photoconductor (12) and light intensity of the character generator (13) and a third control stage (CC3) for securing and optimizing the transfer printing by regulating and / or monitoring the operating parameters of the Transfer printing station (15) by recording the specific recording medium sizes and adapting the corona device (UK).

3. Electrophotographic printing device according to claim 1, characterized by a charge sensor (SL) arranged between the drawing generator (13) and the developer station (UK) and an optical scanner () arranged downstream of the developer station (UK) in the direction of movement of the photoconductor (12). TA), the charge sensor (SL) and optical scanner (TA) being arranged one behind the other in a movement track of the photoconductor (12).

4. Electrophotographic printing device according to claim 2, so that the optical scanner (TA) is designed as a reflection light barrier, the scanning light of which has a wavelength such that the scanning light does not photoelectrically influence the photoconductor (12).

5. Electrophotographic printing device according to claim 1, d a d u r c h g e k e n n z e i c h n e t that a toner test mark (30) is generated at regular time intervals, the ink density of which is scanned by the optical scanner (TA) and transmitted to the control arrangement which is in

Depending on the ink density, the toner supply to the development area (UK) is regulated and / or a warning device (AZ) is actuated.

6. Electrophotographic printing device according to claim 1, characterized in that after calling a test routine on the control arrangement first by loading a full-area test mark (31) is generated with an exposure intensity which, on the one hand, makes it possible to determine the residual charge potential via the charge sensor (SL) and, on the other hand, after the full-area mark (31) has been colored as required, a scanning of the coloration density via the optical scanner (TA) enables.

7. Electrophotographic printing device according to claim 1, characterized in that after calling up a test routine via the control arrangement, raster marks (32) are defined and the optical scanner (TA) are defined, and that the control arrangement is dependent on The light signal of the character generator preferably adjusts the output signal of the optical scanner (TA) in addition to other control parameters.

8. Electrophotographic printing device according to claim 2, g e k e n n z e i c h n e t by a control circuit which detects the charging potential of the photoconductor (12) via a charging sensor (SL) and controls a charging corotron (18) of the charging station as a function thereof.

9. Electrophotographic printing device according to claim 2, by means of a device for regulating the light output in the unloading station (17) with an exposure device which can be controlled in its intensity.

10. Electrophotographic printing device according to claim 2, provided by a device for regulating the transfer printing, which detects the specific parameters of the record carrier via an input device (AZ) and, depending on this, sets the corona device in the transfer printing station (UK).

11. Electrophotographic printing device according to one of claims 1 to 10, so that the character generator (13) is designed as a character generator (13) which can be controlled in terms of its light intensity.