Patent Publication Number: US-9835974-B2

Title: Method and developer station for adaptation of the inking of an image substrate of a toner-based digital printer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims priority to German Patent Application No. 102015107938.0, filed May 20, 2015, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The disclosure is directed to a toner-based digital printer (e.g., electrographic digital printer) configured to print to a recording medium with toner. 
     Given toner-based digital printers, for example, a latent charge image (given an electrographic printer) or a latent magnetic image (given a magnetographic printer) of an image substrate is inked with toner (for example liquid toner or dry toner). The toner image that is thus created is transferred directly from the image substrate or indirectly via a transfer station onto a recording medium. Even given the transfer of a plurality of identical toner images (i.e. given the creation of a plurality of identical print images), the inking or the color location of the different print images should thereby be kept constant in order to provide a uniformly high print quality. 
     A uniform inking of different print images requires a uniform inking of a toner image. In this context, DE102012103336A1 describes a method via which the concentration of toner particles in a liquid developer may be determined and adapted. It may thus be ensured that liquid toner with a defined quantity of toner particles is used in an electrophotographic digital printer. 
     However, the use of liquid toner with a defined quantity of toner particles typically still does not guarantee a uniform inking of toner images. In particular, a change to the inking of the toner image may occur via a change to the quantity of liquid toner which is provided by a developer station for inking of the toner image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the embodiments of the present disclosure and, together with the description, further serve to explain the principles of the embodiments and to enable a person skilled in the pertinent art to make and use the embodiments. 
         FIG. 1  illustrates an example digital printer; 
         FIG. 2  illustrates a schematic design of a print group of the digital printer according to  FIG. 1 ; 
         FIG. 3  illustrates a system configured to adjust the toner quantity in a developer station according to an exemplary embodiment of the present disclosure; 
         FIG. 4 a    illustrates a curve of an optical measurement signal with regard to the inking of a developer roller according to an exemplary embodiment of the present disclosure; 
         FIG. 4 b    illustrates a curve of the current through a developer layer on a developer roller according to an exemplary embodiment of the present disclosure; 
         FIG. 4 c    illustrates a curve of an optical measurement signal with regard to the inking of a recording medium according to an exemplary embodiment of the present disclosure; 
         FIG. 4 d    illustrates a control loop configured to adjust the thickness of a developer layer according to an exemplary embodiment of the present disclosure; and 
         FIG. 5  illustrates a workflow diagram of a method for the adaptation of a developer layer in a developer station according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. However, it will be apparent to those skilled in the art that the embodiments, including structures, systems, and methods, may be practiced without these specific details. The description and representation herein are the common means used by those experienced or skilled in the art to most effectively convey the substance of their work to others skilled in the art. In other instances, well-known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring embodiments of the disclosure. 
     An object of the present disclosure is to provide a method and a corresponding developer station via which a defined quantity of toner or of toner particles is precisely provided in order to ensure a uniform inking of toner images. 
     According to one aspect, a method is described for the adaptation of a developer layer on a developer element, wherein the developer element is set up to ink an image substrate of a toner-based digital printer with toner particles from the developer layer. The developer layer may also comprise a carrier fluid (a mineral oil, for example) in addition to toner particles. The developer layer may thus comprise a liquid developer. The method can include the application of a voltage between a measurement electrode and the developer element, wherein the measurement electrode is arranged such that a developer layer that has already been adapted for the inking of the image substrate is located between the measurement electrode and the developer element. The method can additionally include the determination (the detection, for example) of a current that flows between the measurement electrode and the developer element due to the voltage. Moreover, the method includes the adaptation of a developer layer (which is to be adapted for the inking of the image substrate) depending on the voltage and/or depending on the current. 
     According to a further aspect, a developer station for a print group of a toner-based digital printer is described. The developer station comprises a developer element that is set up to ink an image substrate of the print group with toner particles from a developer layer. The developer station additionally comprises a doser that is set up to apply a developer layer onto the developer element and/or to adapt a developer layer for the inking of the image substrate. Moreover, the developer station comprises a measurement electrode that is arranged such that a developer layer that has already been applied by the doser onto the developer element and/or that has already been adapted by the doser for the inking of the image substrate is located between the measurement electrode and the developer element. The developer station additionally comprises a voltage source that is set up to apply a voltage between the measurement electrode and the developer element. Furthermore, the developer station comprises a current measurement device that is set up to determine a current that flows between the measurement electrode and the developer element due to the voltage. Moreover, the developer station comprises a controller that is set up to induce the doser to adapt a developer layer that is to be applied onto the developer element and/or a developer layer that is to be adapted for the inking of the image substrate, depending on the voltage and/or on the current. 
     According to one aspect, a print group for a toner-based digital printer is described. The print group comprises the developer station described in this document. 
       FIG. 1  shows an example a digital printer  10  for printing to a recording medium  20 . The digital printer  10  can include one or more print groups  11   a - 11   d  and  12   a - 12   d  that print a toner image (print image  20 ′; see  FIG. 2 ) onto the recording medium  20 . As shown, a web-shaped recording medium  20  (as a recording medium  20 ) is unrolled from a roll  21  with the aid of a take-off  22  and is supplied to the first print group  11   a . The print image  20 ′ is fixed on the recording medium  20  in a fixer  30 . The recording medium  20  may subsequently be taken up on a roll  28  with the aid of a take-up  27 . Such a configuration is also designated as a roll-to-roll printer. Details regarding the example digital printer  10  are described in detail in German Patent Application DE 10 2013 201 549 B3, Japanese Patent Application JP 2014/149526 A, and U.S. Patent Application 2014/0212632, each of which is incorporated herein by reference in its entirety. 
     The principle design of a print group  11 ,  12  is depicted in  FIG. 2 . The print group depicted in  FIG. 2  is based on the electrophotographic principle, given which a photoelectric image substrate (in particular a photoconductor  101 ) is inked with the aid of a liquid developer with charged toner particles, and the toner image that is created in such a manner is transferred to the recording medium  20 . The print group  11 ,  12  is essentially comprised of an electrophotography station  100 , a developer station  110  and a transfer station  120 . 
     The core of the electrophotography station  100  is a photoelectric image substrate that has a photoelectric layer (what is known as a photoconductor) on its surface. The photoconductor here is designed as a roller (photoconductor roller  101 ) and has a hard surface. The photoconductor roller  101  rotates past the various elements to generate a print image  20 ′ (rotation in the arrow direction). 
     The electrophotography station  100  comprises a character generator  109  that generates a latent image on the photoconductor  101 . The latent image is inked with toner particles by the developer station  110  in order to generate an inked image (i.e. a toner image). For this, the developer station  110  has a rotating developer roller  111  that brings a layer of liquid developer onto the photoconductor  101 . 
     The inked image rotates with the photoconductor roller  101  up to a first transfer point, at which the inked image (i.e. the toner image) is essentially completely transferred onto a transfer roller  121 . The recording medium  20  travels in the transport direction  20 ″ between the transfer roller  121  and a counter-pressure roller  126 . The contact region (nip) represents a second transfer point in which the toner image is transferred onto the recording medium  20 . The recording medium  20  may be made of paper, paperboard, cardboard, metal, plastic and/or other suitable and printable materials. Additional details with regard to the example of a print group  11 ,  12  that is depicted in  FIG. 2  are described in German Patent Application DE 10 2013 201 549 B3, Japanese Patent Application JP 2014/149526 A, and U.S. Patent Application 2014/0212632. 
     In one or more exemplary embodiments, the quantity of toner that is applied onto a photoconductor roller  101  by a developer roller  111  is precisely adjusted in order to produce a uniform inking of the toner image onto the photoconductor roller  101  and a uniform inking of the print image  20 ′ onto the recording medium  20 . 
     In an exemplary embodiment, the provided quantity of toner is adjusted by measuring an inking and/or a color location optically with one or more optical sensors at a suitable point in the printing process. In an exemplary embodiment, the measurement of the inking and/or of the color location may already take place before the toner transfer to the recording medium  20  (for example at the developer roller  111 ) and/or after the toner transfer, and possibly after the fixing of the print image  20 ′ (on the recording medium  20 ). In an exemplary embodiment, the provided quantity of toner may then be adapted (in particular regulated) on the basis of one or more optical measurement signals with regard to the inking and/or the color location. 
     The regulation of the toner quantity provided onto the developer roller  111  is advantageous with regard to a fast reaction to disruptions, since the regulation is already undertaken before the creation of a toner image. On the other hand, problems may result due to the determination of the inking by means of an optical sensor. The determination of the inking using an optical sensor typically assumes that the surface of the roller (of the developer roller  111 , for example) on which the inking is measured by an optical measurement method has a high color contrast relative to the color of the toner. In particular, it may be necessary to use a roller with a white surface. Limitations with regard to the selection of materials that may be used for the roller result due to this condition. For example, these limitations may be disadvantageous to the effectiveness of the toner transfer from the developer roller  111  onto a photoconductor roller  101 . 
     An additional problem may result (for example after long use) due to a film formation on the roller due to the toner that is used. A reference calibration for the determination of the inking may be hindered by such a film formation. Furthermore, the contrast difference between a toner-free surface of the roller and a surface of the roller with developer layer is reduced due to a film formation, which may lead to a decrease in the precision of inking measurements. 
     Additional problems in the optical measurement may result from the fact that the layer thickness of a developer layer, which layer thickness is to be adjusted, is within the saturation range of an optical sensor, such that a precise regulation of the layer thickness (and therefore of the provided quantity of toner) is not possible on the basis of a provided measurement signal. Moreover, a contamination of the optical sensor (by aerosols, for example) may lead to a falsification of the measurement values. Furthermore, the use of optical sensors typically requires complicated and cost-intensive electronics. 
       FIG. 3  shows a system  300  according to an exemplary embodiment. The system  300  is configured to enable the quantity of toner on a developer roller  111  (e.g., the layer thickness of a developer layer  303  on the developer roller  111  and/or the toner quantity in a developer layer  303  on the developer roller  111 ) to be measured electrically. The aforementioned problems of an optical measurement of the inking may be avoided via the system  300  depicted in  FIG. 3 . 
     In an exemplary embodiment, the system  300  includes a doser  315  (which, for example, includes the electrode segment  114  and, if applicable, the dosing roller  115  of the print group  11  from  FIG. 2 ) that is configured to modify a property (for example a quantity of toner and/or a layer thickness) of the developer layer  303  on the developer roller  111 . In this example, the doser  315  can adjust the dose (e.g., quantity) of the toner. In particular, the doser  315  can be configured to modify the quantity of developer applied onto the developer roller  111  and/or the quantity of toner applied onto the developer roller  111 . For example, the doser  315  can be configured to change a toner application voltage between the doser  315  (in particular, the electrode segment  114 ) and the developer roller  111 . The toner quantity in the developer layer  303  may be increased by increasing the toner application voltage, and vice versa. The toner application voltage is thus one example of a toner control variable, i.e. of a control variable with which the properties (in particular the toner quantity) of a developer layer  303  may be adapted. 
     In an exemplary embodiment, the thickness or size of a nip between the dosing roller  115  and the developer roller  111  can be used as a toner control variable, via which the layer thickness of the developer layer  303  may be adapted. In an exemplary embodiment, the thickness or size of the nip between the dosing roller  115  and the developer roller  111  is dependent on the rotation speed of the dosing roller  115  and/or on the contact pressure force between dosing roller  115  and developer roller  111 . The size of the nip, or the rotation speed and/or the contact pressure force, are thus examples of toner control variables with which the properties (in particular the layer thickness) of a developer layer  303  may be adapted. 
     The developer layer  303  applied onto the developer roller  111  is brought to the photoconductor roller  101  by said developer roller  111  in order to develop a latent charge image on the photoconductor roller  101  with toner, and in order to thus generate a toner image on the photoconductor roller  101 . 
     On the transport path between doser  315  and photoconductor roller  101 , the developer layer  303  is directed past a measurement electrode  310  (for example past a measurement roller). In an exemplary embodiment, the measurement electrode  310  can be configured to apply an electrical field across the developer layer  303 . In an exemplary embodiment, an electrical voltage  301  (i.e. a potential difference) may be applied between the measurement electrode  310  and the developer roller  111  (for example the rotation axle of the developer roller  111 ) in order to generate an electrical field transversally through developer layer  303 . In an exemplary embodiment, the voltage  301  is produced by a voltage source  311  of the system  300 . In an exemplary embodiment, the measurement electrode  310  includes its own voltage source, in particular, if the measurement electrode  310  is additionally used for a conditioning (for a smoothing, for example) of the developer layer  303 . For example, in one embodiment, the dosing roller  115  may be used as a measurement electrode  310 . 
     In an exemplary embodiment, a current  302  through the developer layer  303  is produced by the applied voltage  301 . The strength of the current  302  may be measured by a current measurement device  312 . The amperage of the current through the developer layer  303  may be considered as an indication of the transversal electrical resistance of the developer layer  303 , of the thickness of the developer layer  303  and/or of the toner quantity in the developer layer  303 . In particular, a relatively high current  302  may be an indication of a relatively low transversal electrical resistance, of a relatively thin developer layer  303  and/or of a relatively low toner quantity in the developer layer  303  (and vice versa). 
     In an exemplary embodiment, the system  300  includes a controller  313  configured to control the doser  315 . The controller  313  can control the doser  315  based on the measured strength of the current  302 . Furthermore, the doser  315  may be controlled depending on a target specification  316  (for example depending on the nominal value  434  described further below). In particular, the doser  315  may be induced by the controller  313  to adapt the thickness of the developer layer  303  and/or the toner quantity within the developer layer  303  depending on the measured amperage of the current  302 , and possibly depending on a target specification  316 . For example, the controller  313  can be configured to control the doser  315  to adapt the toner application voltage between electrode segment  114  and developer roller  111  and/or the contact pressure force between dosing roller  115  and developer roller  111 . In an exemplary embodiment, the controller  313  includes processor circuitry configured to perform one or more functions of the controller  313 , including, for example, controlling the doser  315 . 
     In an exemplary embodiment, the system  300  is configured to apply an electrical field across the developer layer  303  via use off a conductive or partially conductive measurement roller  310  that is located in front of the inking nip (i.e., before the nip between developer roller  111  and photoconductor roller  101 ) such that a current  302  flows between the measurement roller  310  and the developer roller  111 . In an exemplary embodiment, the current  302  is dependent on the toner quantity or on the developer layer  303  that is located between the measurement roller  310  and the developer roller  111  at a specific measurement point in time. 
     In an exemplary embodiment, a direct correlation between the amperage of the current  302  and the toner quantity offered by the developer roller  111  results. A regulation of the toner quantity applied by the doser  315  onto the developer roller  111  may thus be implemented via the provision of a “toner quantity vs. current flow” or “toner control variable vs. amperage” characteristic curve. The measured amperage of the current  302  (given constant voltage  301 , for example) may thereby represent a controlled variable. 
     In an exemplary embodiment, the developer roller  111  has an elastomer coating. The electrical properties—in particular the electrical resistance—of the elastomer coating may vary with temperature. In an exemplary embodiment, the system  300  includes a temperature sensor (not shown) that configured to detect the temperature of the developer roller  111  (or the temperature of an environment of the developer roller  111 ). A characteristic curve which describes the correlation between current  302  and toner quantity, or between current  302  and toner control variable, may depend on the temperature. For example, a plurality of different characteristic lines for different temperatures may be provided. The controller  313  may then select a characteristic curve to be used depending on the measured temperature. 
     In an exemplary embodiment, the measurement electrode  310  is implemented via a component (roller, for example) already present in the print group  11 . For example, the smoothing roller or the dosing roller  115  of the developer station  110  may be used as a measurement roller  310 . For example, the toner application voltage between electrode segment  114  and developer roller  111  may then be used as a toner control variable. 
     In an exemplary embodiment, the already present component can be current-regulated (to a defined nominal current). In this case, a variation of the level of the voltage  301  that results from the current regulation may be used as an indicator of the transversal electrical resistance of the developer layer  303  and as an indicator of the toner quantity on the developer roller  111 . For this purpose, the value of the voltage  301  may be determined, which can be used to produce a defined (constant) nominal current. The value of the voltage  301  may then indicate (via a characteristic curve) the layer thickness of a developer layer  303  or the toner quantity in the developer layer  303 . 
       FIG. 4 a    shows an example of a curve  404  according to an exemplary embodiment. The curve  404  represents an optical measurement signal  403  of an optical sensor via which a degree of the inking of the developer roller  111  may be detected. The optical measurement signal  403  is depicted as a function of the toner application voltage  401  which is used by the doser  315  (in particular, by the electrode segment  114 ) in order to apply toner onto the developer roller  111 . In an exemplary embodiment, the toner quantity on the developer roller  111  increases with increases toner application voltage  401  (and vice versa). In an exemplary embodiment, the toner application voltage  401  may thus be used by the controller  313  or by the doser  315  as a toner control variable in order to modify the toner quantity applied on the developer roller  111 . From  FIG. 4 a    it is clear that the curve  404  becomes saturated with increasing layer thickness or toner quantity (i.e. with increasing toner application voltage  401 ). From  FIG. 4 a    it is thus clear that a precise adjustment of the layer thickness or toner quantity of the developer layer  303  is not possible using an optical sensor, in particular given relatively large layer thicknesses or toner quantities. 
       FIG. 4 c    shows a corresponding curve  405  of an optical measurement signal  403  according to an exemplary embodiment. The curve  405  corresponds to the inking of a recording medium  20  as a function of the toner application voltage  401 . 
       FIG. 4 b    shows an example of a curve  411  of the amperage  402  of the current  302  through a developer layer  303  according to an exemplary embodiment. The curve  411  illustrates the amperage  402  of the current  302  through a developer layer  303  as a function of the toner application voltage  401 . The toner application voltage  401  was thereby increased in stages. Furthermore,  FIG. 4 b    shows a smoothed curve  412  (a mean value, for example) of the amperage  402 .  FIG. 4 b    shows an approximately linear correlation between the amperage  402  and the toner application voltage  401 . The amperage  402  (in connection with the applied voltage  301 ) thus represents a precise indicator of the layer thickness of the developer layer  303  or of the toner quantity in the developer layer  303 .  FIG. 4 b    shows the curve  411  of the amperage  402  of the current  302  given a constant voltage  301 . Analogously, a characteristic line for the curve of the value of the voltage  301  may be determined and provided given a current  302  that is regulated to a constant nominal current. The value of the voltage  301  may then be used as an indicator of the layer thickness of the developer layer  303  or of the toner quantity in the developer layer  303 . In general, an indicator of the transversal electrical resistance of the developer layer  303  may be determined on the basis of the current  302  and on the basis of the voltage  301 , wherein the transversal electrical resistance of the developer layer  303  indicates the layer thickness of the developer layer  303  and/or the toner quantity in the developer layer  303 . 
       FIG. 4 d    shows an example of a control loop  420  configured to regulate the toner application voltage  401  according to an exemplary embodiment. The regulation of the toner application voltage  401  can depend on the amperage  402  of the current  302  through the developer layer  303 . Analogously, a regulation based on the voltage  301  may be provided. In an exemplary embodiment, a nominal value  434  for the toner application voltage  401  is provided as a command variable, via which a desired layer thickness of the developer layer  303  or a desired toner quantity in the developer layer  303  is produced. In the example depicted in  FIG. 4 d   , the real amperage  432  of the current  302  is the controlled variable. The real amperage  432  may be converted (e.g., using the characteristic curve  411  and/or the mean characteristic curve  412 , which may depend on the temperature  436  of the developer roller  111 ) into a real value  433  of the toner application voltage  401 . 
     In an exemplary embodiment, the real value  433  of the toner application voltage  401  is subtracted from the nominal value  434  of the toner application voltage  401  in order to determine a control error  435 . Using a controller  402  (for example a controller with P (proportional), I (integral) and/or D (differential) configurations), an adapted value  431  of the toner application voltage  401  can be determined as a control variable. In an exemplary embodiment, the adapted value  431  of the toner application voltage  401  may be adjusted at the doser  315  in order to adapt the properties (in particular the toner quantity) of the developer layer  303 . In an exemplary embodiment, the present amperage  432  of the current  432  is produced via the actual control path  422  (i.e. by the actual path between doser  315 , measurement roller  310  and developer roller  111 ), which present amperage  432  may then be used again for the further adaptation of the toner application voltage  401 . 
     A developer station  110  for a print group  11  of a toner-based digital printer  10 —for example of an electrographic (in particular electrophotographic) or magnetographic digital printer—will now be described. In an exemplary embodiment, the developer station  110  includes a developer element  111  that is set up to ink an image substrate  101  (for example a photoconductor, in the event of an electrographic digital printer) of the print group  11  with toner particles from the developer layer  303 . In particular, the developer element  111  may be set up to carry a developer layer  303  to the image substrate  101  for the inking of said image substrate  101  and for the creation of a toner image. For example, the developer element  111  may include a developer roller and the image substrate  101  may include an image substrate roller. In an exemplary embodiment, via rotation of the developer roller, the developer layer  303  may be carried to the image substrate roller and be transferred at least partially to the image substrate roller. 
     In an exemplary embodiment, the developer layer  303  includes toner particles. Furthermore, the developer layer  303  may include a carrier fluid for the toner particles. The developer layer  303  carried to the image substrate  101  may include specific properties which influence the inking of the image substrate  101 . In an exemplary embodiment, the developer layer  303  includes a specific toner quantity (per area unit of the developer layer  303 ), where a degree of the inking of the image substrate  101  typically increases by raising the toner quantity (and vice versa). 
     In an exemplary embodiment, the developer station  110  further includes a doser  315  that is configured to apply a developer layer  303  onto the developer element  111  and/or to adapt the developer layer  303  for the inking of the image substrate  101 . In particular, the doser  315  is configured to adapt the developer layer  303  based on a toner control variable  401 , such as the toner application voltage  401 . In an exemplary embodiment, one or more properties of the developer layer  303  (for example a thickness and/or a density and/or a toner quantity) may thereby be adapted to the developer layer  303 . In an exemplary embodiment, the doser  315  includes an electrode segment  114  and/or a dosing roller  115  for the application of the developer layer  303 . In particular, developer may be applied onto the developer element  111  via the electrode segment  114 . The layer thickness of the developer layer  303  may subsequently be adapted via the dosing roller  115 . The toner quantity within the developer layer  303  may be adapted via the toner application voltage  401  between the electrode segment  114  and the developer element  111 . 
     In an exemplary embodiment, the toner quantity within the developer layer  303  may be increased by increasing the toner application voltage  401  (and vice versa). The layer thickness of the developer layer  303  may be adapted via the contact pressure force between dosing roller  115  and developer element  111 . In particular, the layer thickness may be reduced by increasing the contact pressure force (and vice versa). 
     In an exemplary embodiment, the doser  315  includes the electrode segment  114  that is configured to apply the developer layer  303  onto the developer element  111 . In this example, the toner application voltage  401  between the electrode segment  114  and the developer element  111 , via which the toner quantity in the developer layer  303  may be adapted, serves as a toner control variable. 
     In an exemplary embodiment, the developer station  110  includes a measurement electrode  310  that is arranged such that a developer layer  303  that has already been applied by the doser  315  onto the developer element  111  and/or that has already been adapted by the doser  315  is located between the measurement electrode  310  and the developer element  111 . In other words, the measurement electrode  310  may be arranged such that a developer layer  303  that has already been applied by the doser  315  onto the developer element  111 , and/or that has already been adapted by the doser  315 , may be directed through a gap (a roller nip, for example) between the measurement electrode  310  and the developer element  111 . In other words again, given use of a developer roller  111  the measurement electrode  310  may be arranged after the doser  315  in the rotation direction of the developer roller  111  (and before a point at which the developer layer  303  is used to develop a toner image). In an exemplary embodiment, the measurement electrode  310  includes an electrically conductive measurement roller, for example. 
     In an exemplary embodiment, the developer station  110  includes a voltage source  311  that is configured to apply a voltage  301  (i.e. a potential difference) between the measurement electrode  310  and the developer element  111 . Moreover, the developer station  110  can include a current measurement device  312  that is configured to determine (for example, to detect) a current  302  that flows between the measurement electrode  310  and the developer element  111  due to the applied voltage  301 . 
     In an exemplary embodiment, the developer station  110  includes a controller  313  that is configured to induce/control the closer  315  to adapt the developer layer  303  to be applied onto the developer element  111 , and/or a developer layer  303  that is to be adapted for the inking of the image substrate  101 , depending on the current  302 . In an exemplary embodiment, the developer layer  303  may be adapted depending on the voltage  301  and depending on the current  302  (for example depending on a relative ratio between voltage  301  and current  302 ). The developer layer  303  may thus be precisely adapted by the developer station  110  in order to produce a homogeneous inking of the image substrate  101 . 
     In an exemplary embodiment, the measurement electrode  310  includes an element configured to smooth the developer layer  303  on the developer element  111 . For example, a measurement roller can include a smoothing roller that is already used for the smoothing of the developer layer  303  on the developer element  111 . The measurement electrode  310  may thus be provided in a cost-effective and space-efficient manner. For example, the smoothing roller may include the dosing roller  115  or correspond to the dosing roller  115 . The current between dosing roller  115  and developer element  111  may then be measured. Furthermore, the toner application voltage  401  between the electrode segment  114  and the developer element  111  may be adapted depending on the current  302  in order to adapt (for example regulate) the toner quantity in the developer layer  303 . 
       FIG. 5  shows a workflow diagram of a method  500  for the adaptation of a developer layer  303  on the developer element  111  according to an exemplary embodiment. The developer element  111  is set up to ink an image substrate  101  of a toner-based digital printer  10  with toner particles from the developer layer  303 . 
     In an exemplary embodiment, the method  500  includes the application  501  of a voltage  301  between a measurement electrode  310  and the developer element  111 . The measurement electrode  310  is thereby arranged such that a developer layer  303  that has already been applied onto the developer layer  111  and/or that has already been adapted for the inking of the image substrate  101  is located between the measurement electrode  310  and the developer layer  111  (for example in a roller nip between a measurement roller and a developer roller). In other words, the measurement electrode  310  may be arranged after a doser  315  via which the developer layer  303  is adapted for the inking of the image substrate  101 . 
     In an exemplary embodiment, the method  500  further includes the determination (detection, for example)  502  of a current  302  that flows between the measurement electrode  310  and the developer element  111  due to the voltage  301 . For example, the amperage  402  of the current  302  may be determined. 
     In an exemplary embodiment, the method  500  includes the adaptation  503  of a developer layer  303  to be applied onto the developer element  111  and/or to be adapted for the inking of the image substrate  101 , depending on the voltage  301  and/or depending on the current  302 . For example, the developer layer  303  can be adapted depending on the value of the applied voltage  301  and/or on the determined amperage  402  of the current  302 . In particular, the quantity of toner in the developer layer  303  and/or the thickness of the developer layer  303  may thereby be adapted. 
     In an exemplary embodiment, via the consideration of the current  302  and/or of the voltage  301 , the method  500  enables a precise adjustment of the quantity of toner applied onto the developer element  111  or of the thickness of the developer layer  303  applied onto the developer element  111 . In particular, a precise adjustment of the properties of the developer layer  303  may take place even given relatively high toner quantities or given a relatively thick developer layer  303 . The precise adjustment of the toner quantity or of the developer layer thickness in turn enables an inking of print images  20 ′ that is consistent over time. 
     In an exemplary embodiment, the developer layer  303  may be adapted via a toner control variable  401  (for example via a toner application voltage between electrode segment  114  and developer element  111 ). In an exemplary embodiment, the method  500  may additionally include the determination of a characteristic curve  411 ,  412  which indicates a correlation between the voltage  301  and/or the current  302  on the one hand and the toner control variable  401  on the other hand. In an exemplary embodiment, the characteristic curve  411 ,  412  may be based on a plurality of test measurements with different values of the toner control variable  401  and/or with different values of the current  302  and/or of the voltage  301 . Different characteristic curves  411 ,  412  may thereby be determined for different developer types (in particular for different color toners, for example of the colors C, M Y, K, O, V, and/or G). In an exemplary embodiment, the adaptation  503  of the developer layer  303  that is to be applied onto the developer element  111  may include the adaptation of the toner control variable  401  depending on the characteristic curve  411 ,  412 , wherein the characteristic curve  411 ,  412  typically depends on the developer types of the developer layer  303 . The precision of the adjustment of the toner quantity or of the thickness of the developer layer  303  may thus be further increased. 
     In an exemplary embodiment, the adaptation (in particular the regulation) of a property of the developer layer  303  (for example of the toner quantity in the developer layer  303 ) may take place using a characteristic curve  411 ,  412 . The developer layer  303  may thus be adapted (in particular regulated) depending on the voltage  301  and/or depending on the current  302 , as well as depending on the characteristic curve  411 ,  412 . In an exemplary embodiment, the current  302  (i.e. the measured amperage  402 ) is compared with the characteristic curve  411 ,  412  in order to adapt the developer layer  303 . For example, on the basis of the measured amperage  402  and the characteristic curve  411 ,  412  it may be determined whether the developer layer  303  that is used for the inking of the image substrate  101  comprises the desired toner quantity. If this is not the case, the toner control variable  401  (i.e. in particular the toner application voltage) may thus be adapted in order to adapt the toner quantity of the developer layer  303 . A consistent inking of the image substrate  101  may thus be produced. 
     In exemplary embodiments, the characteristic curve  411 ,  412  can indicate what concrete characteristic of the property of the developer layer  303  (for example what concrete toner quantity) corresponds to a specific measured amperage  402  of the current  302  and/or to a specific value of the voltage  301 . Alternatively or additionally, the characteristic curve  411 ,  412  may indicate what value of the toner control variable  401  (for example of the toner application voltage) corresponds to a specific measured amperage  402  of the current  302  and/or to a specific value of the voltage  301 . For example, the characteristic curve  411 ,  412  may be determined in that the amperages  402  and/or voltage values that result for specific values of the toner control variable  401  (and therefore for specific properties of the developer layer  303 ) are measured within the scope of test measurements. 
     In an exemplary embodiment, the amperage  402  and/or voltage value that results if no developer layer  303  is located on the developer element  111  can be determined using a reference measurement. A reference amperage (for a specific nominal voltage value) or a reference voltage value (for a specific nominal current value) may thus be determined. In an exemplary embodiment, the adaptation of the developer layer  303  may also take place depending on the reference amperage and/or on the reference voltage value. In particular, a characteristic curve  411 ,  412  may be adapted under consideration of the reference amperage and/or of the reference voltage value. For example, the characteristic curve  411 ,  412  may be shifted or “offset” depending on the reference amperage and/or the reference voltage value. In an exemplary embodiment, a measurement offset of the characteristic curve  411 ,  412  may thus be compensated, and the precision of the adjustment of the toner quantity or of the thickness of the developer layer  303  may be further increased. 
     In an exemplary embodiment, the method  500  may additionally include the determination of a temperature  436  of the developer element  111 . The toner control variable  401  may then (also) be adapted depending on the temperature  436  of the developer element  111 . For example, depending on the temperature  436  the characteristic curve  411 ,  412  may be adapted or a different characteristic curve  411 ,  412  may be selected from a plurality of temperature-dependent characteristic curves  411 ,  412 . In an exemplary embodiment, the precision of the adjustment of the toner quantity or of the thickness of the developer layer  303  may be further increased by taking the temperature  436  into account. 
     In an exemplary embodiment, the toner control variable  401  may be regulated to a nominal value  434  of the toner control variable  401  depending on the characteristic curve  411 ,  412  and depending on the voltage  301  and/or on the current  302 . In an exemplary embodiment, a control loop  420  with a controller  421  may be provided for this purpose. The precision of the adjustment of the toner quantity or of the thickness of the developer layer  303  may be further increased via the regulation of the toner control variable  401 . 
     In an exemplary embodiment, the method may include the determination, on the basis of, for example, the voltage  301  and/or on the basis of the current  302 , of an indicator of a transversal electrical resistance of the developer layer  111  that has already been applied onto the developer element  111  and/or that has already been adapted for the inking of the image substrate  101 . In an exemplary embodiment, an indicator of the transversal electrical resistance of the developer layer  111  may be determined on the basis of a ratio of the determined amperage  402  of the current  302  and the value of the set voltage  301 . The developer layer  303  that is to be applied onto the developer element  111  and/or that is to be adapted may then be adapted depending on the indicator of the transversal electrical resistance. 
     The method described in the exemplary embodiments and the developer station  110  described in the exemplary embodiments enable a precise adjustment of the provided toner quantity without the use of an optical sensor. The disadvantages described which result from the use of an optical sensor can be avoid. Moreover, a precise adjustment in a wide range of layer thicknesses or toner quantities is enabled. Furthermore, the method  500  and the developer station  110  may be implemented more cost-effectively, in particular, if a component (for example a smoothing roller) of a print group  11  that is already used otherwise is used as a measurement electrode  310 . 
     CONCLUSION 
     The aforementioned description of the specific embodiments will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, and without departing from the general concept of the present disclosure. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. 
     References in the specification to “one embodiment,” “an embodiment,” “an exemplary embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     The exemplary embodiments described herein are provided for illustrative purposes, and are not limiting. Other exemplary embodiments are possible, and modifications may be made to the exemplary embodiments. Therefore, the specification is not meant to limit the disclosure. Rather, the scope of the disclosure is defined only in accordance with the following claims and their equivalents. 
     Embodiments may be implemented in hardware (e.g., circuits), firmware, software, or any combination thereof. Embodiments may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact results from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc. Further, any of the implementation variations may be carried out by a general purpose computer. 
     For the purposes of this discussion, processor circuitry can include one or more circuits, one or more processors, logic, or a combination thereof. For example, a circuit can include an analog circuit, a digital circuit, state machine logic, other structural electronic hardware, or a combination thereof. A processor can include a microprocessor, a digital signal processor (DSP), or other hardware processor. In one or more exemplary embodiments, the processor can include a memory, and the processor can be “hard-coded” with instructions to perform corresponding function(s) according to embodiments described herein. In these examples, the hard-coded instructions can be stored on the memory. Alternatively or additionally, the processor can access an internal and/or external memory to retrieve instructions stored in the internal and/or external memory, which when executed by the processor, perform the corresponding function(s) associated with the processor, and/or one or more functions and/or operations related to the operation of a component having the processor included therein. 
     In one or more of the exemplary embodiments described herein, the memory can be any well-known volatile and/or non-volatile memory, including, for example, read-only memory (ROM), random access memory (RAM), flash memory, a magnetic storage media, an optical disc, erasable programmable read only memory (EPROM), and programmable read only memory (PROM). The memory can be non-removable, removable, or a combination of both. 
     REFERENCE LIST 
     
         
           10  digital printer 
           11 ,  11   a - 11   d  print group (front side) 
           12 ,  12   a - 12   d  print group (back side) 
           20  recording medium 
           20 ′ print image (toner) 
           20 ″ transport direction of the recording medium 
           21  roll (input) 
           22  take-off 
           23  conditioning group 
           24  turner 
           25  register 
           26  drawing group 
           27  take-up 
           28  roll (output) 
           30  fixer 
           40  climate control module 
           50  power supply 
           60  controller 
           70  fluid management 
           71  fluid controller 
           72  reservoir 
           100  electrophotography station 
           101  image substrate (photoconductor, photoconductor roller) 
           102  erasure light 
           103  cleaning device (photoconductor) 
           104  blade (photoconductor) 
           105  collection container (photoconductor) 
           106  charging device (corotron) 
           106 ′ wire 
           106 ″ shield 
           107  supply air channel (aeration) 
           108  exhaust air channel (ventilation) 
           109  character generator 
           110  developer station 
           111  developer element (developer roller) 
           112  storage chamber 
           112 ′ fluid supply 
           113  pre-chamber 
           114  electrode segment 
           115  dosing roller (developer roller) 
           116  blade (dosing roller) 
           117  cleaning roller (developer roller) 
           118  blade (cleaning roller of the developer roller) 
           119  collection container (liquid developer) 
           119 ′ fluid discharge 
           120  transfer station 
           121  transfer roller 
           122  cleaning unit (wet chamber) 
           123  cleaning brush (wet chamber) 
           123 ′ cleaning fluid discharge 
           124  cleaning roller (wet chamber) 
           124 ′ cleaning fluid discharge 
           125  blade 
           126  counter-pressure roller 
           127  cleaning unit (counter-pressure roller) 
           128  collection container (counter-pressure roller) 
           128 ′ fluid discharge 
           129  charging unit (corotron at transfer roller) 
           300  system for adaptation of the toner quantity 
           301  voltage 
           302  current 
           303  developer layer 
           310  measurement electrode (measurement roller) 
           311  power supply 
           312  current measurement device 
           313  controller 
           315  doser 
           316  target specification 
           401  toner application voltage 
           402  amperage (mA) 
           403  optical measurement signal 
           404 ,  405  curve of the optical measurement signal 
           411  curve of the amperage 
           412  smoothed curve of the amperage 
           420  control loop 
           421  controller 
           422  control path 
           431  adapted value of the toner application voltage 
           432  real amperage 
           433  real value of the toner application voltage 
           434  nominal value of the toner application voltage 
           345  control error 
           436  temperature 
           500  method to adjust the toner quantity 
           501 ,  502 ,  503  method steps