Abstract:
In a method and apparatus for adjusting an electrographic printing or copying process, information to be printed is generated as a toner intermediate image on a support for intermediate images and is subsequently transmitted from a reprinting surface to a recording medium at a transfer printing zone. A toner mark is produced on an electrographic support for intermediate images. The toner mark is at least partially scanned on the support for intermediate images and is then removed from the support for intermediate images. The toner Ad concentration is adjusted in a developing station by means of a measured value based on scanning the toner mark. Transfer of the toner intermediate image from the reprinting surface to the recording medium at the transfer printing zone is at least temporarily prevented in the period between the production and the removal of the toner mark.

Description:
BACKGROUND OF THE INVENTION 
     The invention is directed to a method and to an apparatus for controlling an electrographic printing or copying process. The invention is particularly directed to a method and to a system for controlling the toner concentration in a toner/developer mixture. 
     EP 403 523 B1 discloses an electrographic process wherein a number of process parameters are monitored and regulated, including the toner concentration in a development station. It is provided for this purpose that a toner mark be generated on a photoconductor drum, that the mark be sensed on the photoconductor drum with a reflex light sensor, and the measured value be employed for the control of the toner resupply in the development station. The solid toner mark is thereby generated at the lateral edge of the photoconductor drum, so that it lies only in the region of the margin perforations with respect to the web-shaped, margin-perforated recording medium and thus does not lie in the actual writing region of the recording medium or of the photoconductor drum. A number of disadvantages result therefrom. 
     First, the toner mark can thus be only designed relatively small, as a result of which the sensing area and, thus, the measuring precision as well are limited, particularly transversely relative to the transport direction of the photoconductor drum or of the recording medium. Second, it is definitely meaningful for regulating various parameters of the electrographic process to also apply and sense a toner mark in the actual writing region of the photoconductor drum. Particularly when employing web-shaped recording media, for example what is referred to as continuous stock, however, spoilage then arises because the recording medium printed in this way is no longer available for being printed with other information. Conditioned by the process, third, edge effects, for example of the electrical field, arise at the edges of a photoconductor, as a result of which the expressiveness of a measurement in this region is diminished. Such edge effects superimpose all the more greatly the narrower a toner mark is. 
     WO 97/17635 A discloses an electrophotographic printer device that contains compensation elements, particularly rockers, springs and other prestressing elements, that are intended to avoid fluctuations in the position of the recording medium in the region of the transfer printing zone. This is particularly necessary in a duplex mode wherein the web-shaped recording medium is conducted twice through the same transfer printing station. However, nothing noteworthy can be derived from this publication with respect to the regulation of the electrographic process. 
     DE 198 01 521.6 (applicant&#39;s reference 980101DE) discloses a control method for the toner/developer mixture, what is referred to as a two-component development system, in an electrographic printer or copier device. in this method, a toner mark is sensed at least two places with respect to the transport direction of the photoconductor drum. In order to achieve an adequate sensing precision with this method, it is necessary that the toner mark be adequately broad. It would thereby be especially advantageous if the toner mark could also extend into the actual writing region of the photoconductor drum. 
     DE 197 49 651.2 (applicant&#39;s reference 971104DE) discloses an electrophotographic printer that can process both recording media with margin perforation as well as recording media without margin perforation. A unit with a friction drive is provided for this purpose and can be pivoted against and away from a photoconductor drum so precisely that the recording medium again comes to lie exactly at the original position with respect to the photoconductor drum after being pivoted away and back in. The components disclosed therein are designed therefor that the pivoting in and away occurs, for example, during the course of a service call. Such a printer, on the other hand, is suited for printing a recording medium without a margin perforation wider than a recording medium with a margin perforation. A recording medium free of margin perforations can then also be printed by the photoconductor drum in the region of the drum wherein the margin perforations are located given a margin-perforated recording medium. This advantage, however, is accompanied by the disadvantage that the toner mark must be transfer-printed onto the unperforated, web-shaped recording medium in its writing region and, thus, spoilage again arises. 
     U.S. Pat. No. 5,387,965 A and U.S. Pat. No. 4,468,112 A disclose electrographic processes wherein the toner concentration in a development station is identified and compared to a rated value. The rated value is dependent on a second measurement event in which a toner mark is interpreted. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to specify a method and an electrographic system wherein a monitoring of toner density can occur and wherein an optimally high printing width on the recording medium can be achieved at the same time. 
     This object is achieved by a method and system of the invention for regulating an electrographic printing or copying process wherein information to be printed are generated as an intermediate toner image on an intermediate image carrier and are later transferred from a transfer printing surface onto a recording medium in a transfer printing zone. A toner mark is generated on an intermediate image carrier such as an electrographic intermediate image carrier. The toner mark on the intermediate image carrier is sensed at least in regions and the toner mark is subsequently in turn removed from the intermediate image carrier. The toner concentration in a development station is regulated with a measured value such as a density value. The transfer of the intermediate toner image from the transfer printing surface onto the recording medium is at least temporarily prevented in the time span between the generation and the removal of the toner mark. 
     According to a first aspect of the invention, the information to be printed are generated as an intermediate toner image on an intermediate image carrier with a photoconductor drum and, in a transfer printing zone, are transferred later from a transfer printing surface, for example from the surface of the photoconductor drum or from a transfer printing tape, onto a recording medium. For regulating the toner density, a toner mark is generated on the electrographic intermediate image carrier, the toner mark on the intermediate image carrier is sensed at least in regions, and the toner mark is in turn removed from the intermediate image carrier later. In particular, the density is sensed at the toner mark. The toner concentration is then regulated with the measured value, particularly density value, in a development station such that the inking can be kept constant. A transfer of the intermediate toner image from the transfer printing surface onto the recording medium is at least temporarily prevented in the time span between the generation of the toner mark on the intermediate image carrier and the removal of the toner mark from the intermediate image carrier. This impeding transfer of the transfer printing is particularly prevented during a time span wherein the toner mark passes the transfer printing zone. The prevention of the transfer printing can, in particular, occur by separation/lift-off of the recording medium from the transfer printing surface. 
     In particular, the invention provides two operating states for the operation of an electrographic printer or copier device. In the first operating state, what is referred to as the measurement cycle, a toner mark is generated on the intermediate image carrier, the density of the toner mark is sensed, and the toner mark is then in turn removed from the intermediate image carrier. The sensed toner density value is employed for the regulation of the toner concentration in the development station and, in particular, has influence on a toner concentration rated value and/or on a control threshold. In the second operating state, information to be printed are generated on the intermediate image carrier as a toner image and are transfer-printed onto the recording medium later. In the second operating state, the toner concentration is, in particular, controlled with the toner concentration or regulation threshold determined from the first operating state. 
     Inventively, the recording medium is at least temporarily separated or lifted off from the transfer printing surface, particularly from the intermediate image carrier, in the first operating state. The invention is therefore suited for generating the toner mark on the intermediate image carrier in a region in which the information to be printed onto the recording medium are also output. The recording medium is, in particular, web-shaped and can, for example, be made of paper. 
     A photoconductor drum is particularly provided as an intermediate carrier on which the toner mark is generated. The recording medium is separated or lifted off from it for at least one revolution. In a further embodiment of the invention, a photoconductor tape is employed as a first intermediate image carrier and/or a transfer band is employed as a second intermediate image carrier. Information to be printed are thereby generated on the first intermediate image carrier, are subsequently transferred onto the transfer band and are finally transfer-printed from the transfer band onto the recording medium. 
     In particular, density values of several toner marks can be employed for determining the rated value in the regulation of the toner concentration. The various toner marks can derive from a plurality of measurement cycles that lie far apart in time or can be formed in a continuous measurement cycle, particularly with one or with several revolutions of the photoconductor drum. 
     A rapidly switchable, high-precision mechanical lift-off device can, in particular, be employed for separating the recording medium from the transfer printing surface. It is thereby particularly provided that the recording medium lies in nearly the same position with respect to the transfer printing station both in the conveying direction as well as transversely relative to the conveying direction before the lift-off and after being pivoted back in. Optionally, the recording medium can be moved or the transfer printing surface or the transfer printing element can be moved for separating the recording medium from the transfer printing surface. Instead of or in addition to the mechanical movement, an electrophotographic quantity in the region of the transfer printing station is modified in a further version for preventing the transfer printing such that a transfer printing is suppressed. For example, the electrical voltage at a transfer printing corotron can be reduced for this purpose. 
     As a result of the invention, two operating states of the device are created that are employed alternating in time. The operating state wherein the toner mark is generated and interpreted and no transfer printing onto the recording medium occurs is thereby temporally inserted between the other operating state wherein print information are transfer-printed onto the recording medium. 
     What is especially advantageous about the invention is that the toner mark can be designed very broad, up to the entire width of the intermediate image carrier, for example of a photoconductor drum. As a result thereof, the toner mark can be interpreted at a plurality of locations, particularly according to the method disclosed by DE 198 01 521.6. The content of this application and the WO Publication corresponding with this application is herewith incorporated into the present specification. 
     The toner mark can also be positioned at any arbitrary location within the printing width of the intermediate image carrier. As a result of these possibilities, not only is the measurement precision enhanced compared to narrow toner marks but the possibility is also created to apply various methods for the interpretation of the toner mark instead of an evaluation of the toner density. For example, an interpretation of the shape of the generated toner mark or the comparison thereof to a rated shape is also possible. This further enables the interpretation methods to be optimized for colored toner. Various interpretation methods can be combined to form an overall interpretation, for example various interpretation methods and/or color-specific properties of the toner mark sensor can be taken into consideration color-specifically with respect to the toner color. 
     The evaluation method of the toner mark can be designed due to the adaptability of the toner mark in view of its position, size and shape such that independence from the toner color can be achieved. This also particularly applies when an optoelectronic toner mark sensor works in a narrow light wavelength spectrum, for example in only one color, and its light has a direct influence on the reflection and absorption behavior of the toner-pigments. In this case, in particular, the shape recognition of a large-area mark can be advantageously utilized. 
     In a second aspect of the invention, toner marks in an electrographic process are cyclically generated and sensed only at relatively large page intervals, for example only after a few thousand printed pages. In the intervening printing intervals, the tone concentration is then implemented in some other way, for example based only on other measured quantities. One such other measured quantity can, for example, be the toner concentration, this being measured in the development station with a toner concentration sensor. A rated value, for example for the toner concentration or for a regulation threshold, is then defined from the measured value (toner density, toner mark shape, etc.) determined from the toner mark and the toner concentration is regulated therewith. This regulation of the toner concentration in a development station to be applied between the toner mark measurements can occur in a known way. 
     Corresponding to the second aspect of the invention, the toner replenishment is regulated in some other way over relatively large printing intervals (between the tone mark evaluation cycles). Instead of or in addition to the toner concentration control that has just been described, the toner consumption can also be identified on the basis of the printed information, particularly as a result of the total number of printed picture elements (pixels). This determination can also occur dependent on the contrast ratio set at the printer device, on a specific transfer printing efficiency, on the age of the toner/developer mixture, on the toner type and/or on other influencing variables. The delivery of toner into the development station from a toner reservoir can then be controlled with quantities defined in this way. 
     The second aspect of the invention achieves the object of being able to implement a largely independent regulation of the toner inking in an electrographic process in the intervals between the formation and measurement of the toner mark. 
    
    
     Exemplary embodiments of the invention are explained in greater detail below on the basis of some Figures. Further advantages and effects of the invention become clear therefrom. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic sectional view of an electrophotographic printer device; 
     FIG. 2 illustrates electronic components of the printer device; 
     FIGS. 3 a  and  3   b  illustrate a flowchart for printing and generating a toner mark; and 
     FIG. 4 is a second electrographic printer device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alternations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     FIG. 1 schematically shows a printer device  1  for web-shaped recording media working according to the principle of electrophotography. The web-shaped recording medium in the form of a paper web  2  is supplied to a photoconductor drum  4  by a drive unit  3  having a motor-driven friction drum  19 . Details of the drive unit  3  and other components can be derived from DE 197 49 651.2, the content thereof or of the corresponding patent in the USA being herewith incorporated by reference into the present specification. Additionally, the unit contains movable swivel elements  15  with which the paper web  2  can be pressed against the surface of the photoconductor drum or lifted off therefrom. For that purpose, they can be automatically moved by an electrical actuator  20 , for example a stepping motor or lifting magnet. Details about suitable swivel elements in the form of transfer printing rockers are known, for example, from WO 97/17635 A1. In particular, they can be designed like the rockers  40  and  44  shown in FIG. 5 of the WO publication and can be pivotably seated at shafts such that the paper web can be swivelled in and out in length-neutral fashion with respect to parts of the drive unit lying farther away. The content of WO 97/17635 A1 is herewith likewise incorporated by reference into the present specification. 
     Returning to FIG. 1, the paper web  2  is printed in a transfer printing zone  5 . For that purpose, the photoconductor drum  4  driven via a motor is charged with an intermediate toner image by various connected units, the intermediate toner image being transfer-printed onto the paper web  2  in the transfer printing zone  5 . A first unit is a character generator  6  that contains a comb of light-emitting diodes with individually derivable light-emitting elements that, for example, can be constructed according to WO 96/3782 A1. This publication is herewith incorporated by reference into the present specification. The light intensity of the character generator  6  can be regulated by variation of the drive voltage or drive current. An electronic control drives the individual light-emitting diodes according to the image information to be printed. The illumination station is followed by a charge sensor  7  that measures the surface potential on the photoconductor drum  4  and outputs a signal dependent thereon. The image (charge image) generated on the photoconductor drum  4  with the character generator  6  in character-dependent fashion is inked with the assistance of a development station  8 . The development station  8  contains a toner reservoir  9  for the acceptance of toner as well as a metering device  10  in the form of a metering drum. The metering drum  10  delivers toner to a mixing chamber  11  dependent on the toner consumption. A toner/developer mixture of ferromagnetic carrier particles and toner particles is located in the mixing chamber  11 . The toner mixture is supplied to a development drum  12 . The development drum  12  acts as what is referred to as a magnetic brush drum and comprises of a hollow drum with the magnetic ledges arranged therein. The development drum  12  transports the developer mixture to a development gap between the photoconductor drum  4  and the development drum  12 . Excess developer mixture is transported back into the mixing chamber via the development drum  12 . The development station  11  is followed by a toner mark sensor  14  with respect to the rotational sense B 1  of the photoconductor drum  4 . The toner mark sensor  14  is an optoelectronic sensor that, for example, can be designed as a reflected light barrier. It is composed of a light source and of a phototransistor as a receiver. The output signal of the phototransistor is dependent on the reflectivity of the information applied on the photoconductor drum  4  and inked via the development station. In particular, the sensor senses a toner mark that serves for the determination of the color saturation, i.e. of the applied optical density of the toner mark. The wavelength of the reflection light barrier is selected such that the scan light has no influence on the function of the photoconductor drum  4 . 
     The toner mark is started when a test routine is called or is regularly automatically started, for example after 2000 printed pages. The toner mark that is generated then is sensed, and the test pattern is evaluated, for example in view of inking density and/or color saturation. 
     During the running of the test routine or the generation of the toner mark, the paper web  2  is pivoted away from the photoconductor drum, so that it does not touch the surface  4   a  of the photoconductor drum  4  in the transfer printing zone  5 . The drive unit  3  or the pressure elements pressing the paper web  2  against the photoconductor drum  4  are then pivoted away from the photoconductor drum  4 . 
     A cleaning device  16  with which residual toner is removed from the photoconductor drum  4  that was not released from the photoconductor drum  4  or transfer-printed onto the paper  2  in the region of the transfer printing zone, and is situated following the transfer printing zone  5  as viewed in the rotational sense of the photoconductor drum  4 . The cleaning station  16  is built in the usual way and contains, for example, a stripper element  17  that strips the excess toner or the carrier particles from the photoconductor drum  4 . The cleaning process is supported by a corona device  18 . Moreover, further corona devices are provided in the printer device in a known way. These include, for example, a charging corotron that is provided between the cleaning device  16  and the character generator  6 . Illumination devices that serve the purpose of discharging the photoconductor drum  4  can also be arranged in the apparatus. Further details about the electrophotographic process and the devices required therefor are disclosed, for example, by EP 403 523 B1, the content thereof as well as the content of the corresponding patent in the USA being herewith incorporated by reference into the present specification. 
     FIG. 2 shows a device control  25  of the electrographic printer that is connected to all electronic components of the various units of the device, so that the executive sequences can be coordinated with one another. The device control  25  is connected, on the one hand, to a controller  26  to which print data to be printed are input and where converts into signals to drive point-by-point the light-emitting diodes of the character generator  6 . These signals are transmitted to the control  27  of the character generator. Further, the device control  25  is connected to a controller  28  that controls electrophotographic parameters such as the voltages of corotron wires. 
     The toner mark sensor  14  that senses the photoconductor drum  4  comprises toner mark sensor electronics  29  that are likewise in communication with the device control  25 . The controller  30  of the development station  8  bilaterally exchanges data with the device control  25 . The toner concentration sensor  21 , which measures the concentration of the toner in the toner/developer mixture in the mixing chamber  11  of the development station  21 , comprises toner concentration sensor electronics  31  that is likewise connected to the device control  25 . 
     Finally, the device control  25  is also connected to the electronic control  32  of the drive unit  3 . The control  32 , in particular, drives stepper motor electronics  33  of the stepping motor that moves the paper web  2  and also controls the electronic components that activates the stepping motor  20  or a corresponding lifting magnet for the pressure elements  15 . Of course, the various pressure elements  15  can also be equipped with their respectively own stepping motors or lifting magnets in order to thus be able to accomplish an individual pressing of the rockers. Further, the device control  25  is connected to toner transport electronics  35  that effects the toner transport from an external toner reservoir into the development station. A further electronics can be provided within the development station to control the metering of the toner from the toner reservoir  9  into the mixing chamber  11  with the metering drum  10 . 
     The executive sequence of the printing and of the toner concentration regulation shall now be described in greater detail on the basis of FIG.  3 . Method steps S 1  through S 5  show a first operating state wherein print data are transfer-printed onto the paper web  2 . A check is carried out in step S 1  to see whether print data are present. When this is not the case, the printer device switches into a standby condition in which various units like the photoconductor drum, transfer printing corotron, the transport unit, etc., are set to a low energy consumption. 
     As soon as the device control  25  receives a signal from the controller  26  that print data are present, this activates the participating units, the electrophotographically relevant units in step S 3  and the transport unit  3  in step S 4 . In particular, the actuator motor  20  with which the paper web  2  is swivelled against the surface of the photoconductor drum  4  is thereby activated. Further, the drive motor which drives the friction transport roller  19  for the transport of the paper web is activated. Subsequently, the print data to be output are written via the character generator  6  onto the photoconductor drum  4  as an intermediate toner image, the intermediate toner image on the photoconductor drum being applied onto the photoconductor drum  4  in the development gap  13  of the development station  8  and is transfer-printed onto the paper web  2  in the transfer printing zone. Later, the toner image that has been transfer-printed in this way is fixed on the recording medium  2  in a fixing device. During the normal printing phase (steps S 1  through S 5 ), the toner concentration in the development station  8  is monitored by a toner concentration control. The toner concentration in the development station  8  is thereby permanently acquired with the sensor  21 , and a constant toner/developer mixture is maintained in the mixing chamber  11  by means of an appropriate replenishment with the conveyor device  10 . 
     Alternatively to the regulation of the toner concentration with the toner concentration sensor  21 , it is also possible to control the toner quantity conveyed per time unit by the device  10  in that the transfer-printed, set picture elements (pixels) are counted in the controller  26  and/or other quantities are employed defining the toner consumption such as, for example, the contrast setting of the image, the temperature of the photoconductor drum or the like for defining the amount of toner conveyed. 
     In step S 6 , a check is carried out to see whether the end of the print job has been reached. When this is the case, then the printing procedure is ended. When not, then a check is carried out in step S 7  to see whether a page counter that counts successively with every printed page from an initial counter reading N 0 =2000 is equal to zero. When not, then the page counter is lowered by a value in step S 8  and the transfer printing of the next page can occur (step S 5 ). 
     When the page counter is N=0, the printer operations are ended in step S 11  and the second operating mode is started for generating a toner mark. At the same time, the page counter is reset in step S 10  to the initial value N 0 =2000. 
     After respectively 2000 pages, thus the normal printing process is interrupted and a check of the current development conditions is implemented on the basis of a toner mark. For that purpose, the paper web  2  is first pivoted away from the surface of the photoconductor drum  4  in the transfer printing zone  5  with the pressure elements  15 . The paper transport is thereby also arrested. 
     In step S 9 , the value of the page counter is deposited in a memory of the printer control  25 . 
     The steps S 12  through S 17  describe a second operating state wherein a toner mark is written onto the photoconductor  4  and interpreted for the modification of the toner conveying control, which occurs during the transfer printing phase (S 5 ) in the normal printing operation. 
     In step S 12 , one or more toner marks are successively written onto the photoconductor drum  4 . The toner marks can be generated during a revolution of the photoconductor drum or, alternatively, a plurality of toner marks can be generated over a plurality of revolutions of the photoconductor drum  4 . The toner marks are so wide that they proceed into the writing region of the photoconductor drum wherein print information are output in the normal printing operation (step S 5 ), these being normally transfer-printed onto the paper web  2 . As needed, the toner mark can even extend over the entire width of the photoconductor drum  4 . 
     Such marks are generated on the photoconductor drum  4  or the marks are sensed with the sensor  14  in step S 13  and interpreted in the control  25 . The interpretation can occur in view of the generated toner density and/or on view of the shape of the toner mark. Dependent on the type of toner employed (for example, different colors), the toner mark or, respectively, the toner marks can exhibit different densities, shapes and/or dimensions. A value is then derived from the values, this value being compared to a regulation threshold RS in step S 14 . When the toner density value OD of the toner marks lies in the interval [RS−Δ, . . . , RS+Δ], then the operating mode of the toner mark printing can be aborted in step S 17  and a switch can be made back to the normal print operation mode. 
     When, in contrast, the toner density OD lies outside the interval [RS−, . . . , RS+], then a toner transport is initiated in step S 15  and a further toner mark is generated according to step S 12 . This process (steps S 12  through S 15 ) is repeated until the inking OD of the toner mark lies in the required interval. Finally, at least one correction value is determined from the operating mode of toner mark generation in step S 16 , the regulation of the toner concentration in the normal printing phase (steps S 5  through S 8 ) being adapted therewith. In particular, a control threshold for the toner concentration is thereby modified. 
     The regulation of the toner concentration in the printing intervals that lie between the balanced operating states wherein toner marks are formed and interpreted can, for example, occur according to the methods disclosed by U.S. Pat. No. 4,468,112 A or U.S. Pat. No. 5,387,965 A. Their contents are herewith incorporated into the present specification by reference. In the balance operating states, a difference is thereby formed from the measured toner density and the rated value of the toner density, and the difference value is employed for the determination of a new rated toner concentration value or of a threshold for the toner concentration regulation. 
     In a somewhat modified toner concentration regulation, a factor for modifying a rated toner concentration value and/or a toner concentration control threshold is employed from the measured value. 
     In a somewhat simplified version of the adaptation of the toner concentration regulation wherein no toner concentration sensor is required (but it can nonetheless be helpful), the quantity of toner conveyed into the development station per time unit can also be adapted in step S 12 . Other quantities such as the sum of a set of, for example black pixels, the temperature of the photoconductor drum, or the image contrast that has been set can be additionally taken into consideration in the regulation of the toner transport during the normal printing process. 
     FIG. 4 shows a further printer device wherein at least one latent image is generated on a photoconductor band  122  by a first character generator  124  in a first printing unit  150 . One or more intermediate toner images are generated on the photoconductor band  122  in motion direction B using a plurality of development stations  126   a ,  126   b , . . .  126   e  that contain toner having different colors. 
     Correspondingly, a second character generator  138  and a plurality of development stations  140   a  through  140   e  in a second printing unit  152  generate latent images and intermediate toner images in various colors in motion direction D on a second photoconductor band  136 . This printer device is disclosed in greater detail in German Patent Application DE 198 561 45.8 of the assignee (internal reference 981101DE). The content of this German Patent Application or of the corresponding patent in the USA is herewith likewise incorporated by reference into the present specification. 
     At a first transfer printing location  128 , the intermediate toner images are transferred from the first photoconductor band  122  onto a first transfer band  130  running in direction C and, at a third transfer printing location  142 , are transferred from the second photoconductor band  136  onto a second transfer band  144  that moves in direction E. The transfer band  130 ,  144  respectively collect the intermediate toner images of the various color separations and then transfer-print the full-color image onto both sides of the web-shaped recording medium  114 , i.e. duplex, at a second transfer printing station  132  or, respectively, a fourth transfer printing station  146  at a transfer printing zone. In transport direction A, the recording medium  114  driven by the transport rollers  116  by friction then passes through a fixing station  118  for fixing the two toner images and is subsequently cooled in a cooling device  120 . 
     Given this device, too, an operating state corresponding to the exemplary embodiments described in FIGS. 1 through 3 is implemented with the present invention wherein the character generators  124  or, respectively,  138  and at least of the development stations  126   a  through  126   e  or, respectively,  140   a  through  140   e  generate a toner mark on at least one photoconductor band  122 ,  136 . The toner mark is then transfer-printed onto one of the transfer bands  130 ,  144 , is sensed on the latter by one of the optoelectronic sensors  154 ,  156  and is removed from the transfer band without being transfer-printed onto the paper web  114 . For that purpose, the two transfer bands  130  and  144  are lifted off from the paper web  114  in the region of the transfer printing stations at the transfer printing zone, so that the transfer printing onto the paper  114  can be prevented. 
     Alternatively to the sensing of the toner mark on the transfer bands  130 ,  144 , the toner mark on the photoconductor bands  122 ,  136  can also be sensed by corresponding sensors. Either the transfer printing onto the surfaces  130   a ,  144   a  of the transfer band  130 ,  144  or the transfer printing onto the paper web  114  is then prevented. For lifting the transfer bands  130 ,  144  off from the paper web  114  and/or the transfer bands  130 ,  144  off from the photoconductor bands  122 ,  136 , correspondingly fast switch units are provided in the region of the transfer printing zones  132 ,  146  and/or  128 ,  142 . 
     Although the invention was described in such a way that approximately 2000 printed pages of the second operating state lie between two evaluation cycles for the toner mark (i.e. between the automatic start of the first operating state), this plurality of printed pages can be varied dependent on the given stability of the toner concentration regulation, i.e. can be raised or lowered. In the second operating state, the inking is particularly defined only by the toner concentration regulation, whereby at least one of its regulating variables, for example the regulation threshold of the toner concentration, are determined by the first operating state, namely the generation of the toner mark. This version of the invention is therefore also to be considered a toner mark-guided toner concentration regulation. 
     Instead of being employed in a printer device for web-shaped recording media, the invention can also be employed in a device for single sheets. Preventing the transfer printing in the operating condition wherein a toner mark is formed and interpreted can thereby occur, for example, in such a way that the feed of a sheet-shaped recording medium to the transfer printing station is completely suppressed. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. 
     List of reference characters 
       1  printer device 
       2  recording medium (paper web) 
       3  drive unit 
       4  photoconductor drum 
       4   a  surface of the photoconductor drum 
       5  transfer printing zone 
       6  character generator 
       7  charge sensor 
       8  development station 
       9  toner reservoir 
       11  mixing chamber 
       12  development drum 
       13  development gap 
       14  toner mark sensor 
       15  pressure element 
       16  cleaning device 
       17  stripper element 
       18  corona device 
       19  drive roller 
       20  in-swivel actuator motor 
       21  toner concentration sensor 
       25  device control 
       26  controller 
       27  character generator control 
       28  electrophotography control 
       29  electronic of the toner mark sensor 
       30  control of the d-station 
       31  electronics of  21   
       32  electronics of  3   
       33  electronics of the motor 
       34  electronics of the actuators 
       35  electronics for toner transport 
       114  paper web 
       116  drive roller 
       118  fixing station 
       120  cooling device 
       122  first photoconductor tape 
       124  first character generator 
       126   a-e  development stations 
       128  first transfer printing location 
       130  first transfer tape 
       130   a  surface of the first transfer tape 
       132  second transfer printing location 
       136  second photoconductor tape 
       138  second character generator 
       140   a-e  development stations 
       142  third transfer printing location 
       144  second transfer tape 
       144   a  surface of the second transfer tape 
       146  fourth transfer printing location 
       150  first printing unit 
       152  second printing unit 
     A,A 1  paper transport direction 
     B motion direction of the first photoconductor tape 
     B 1  rotational sense of the photoconductor drum 
     C motion direction of the first transfer tape 
     D motion direction of the second photoconductor tape 
     C [sic] motion direction of the second transfer tape