Patent Publication Number: US-6909856-B2

Title: Functionality switching for MICR printing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application Ser. No. 60/415,221 titled FUNCTIONALITY SWITCHING FOR MICR PRINTING filed Oct. 1, 2002 and which is incorporated herein in it&#39;s entirety by reference. 

   FIELD OF THE INVENTION 
   The present invention electrographic printers, and more particularly to electrographic printing machines operable in combination with an installed one of a plurality of developing, or toning, stations. 
   BACKGROUND OF THE INVENTION 
   This invention is in the field of electrographic printing, and is more specifically directed to the electrographic printing of documents suitable for reading by Magnetic Ink Character Recognition (MICR) technology. 
   Electrographic printing has become the prevalent technology for modem computer-driven printing of text and images, on a wide variety of hard copy media. This technology is also referred to as electrographic marking, electrostatographic printing or marking, and electrophotographic printing or marking. Conventional electrographic printers are well suited for high resolution and high speed printing, with resolutions of 600 dpi (dots per inch) and higher becoming available even at modest prices. As will be described below, at these resolutions, modem electrographic printers and copiers are well-suited to be digitally controlled and driven, and are thus highly compatible with computer graphics and imaging. 
   A typical electrographic printer includes a primary image forming photoconductor, which may be a moving belt in large scale printers, or a rotating drum in smaller laser printers and photocopiers. The photoconductor is initially sensitized or conditioned by the application of a uniform electrostatic charge at a primary charging station in the printer. An exposure station forms an image on the sensitized photoconductor by selectively exposing it with light according to the image or text to be printed. The exposure station may be implemented as a laser, an array of light emitting diodes (LEDs), or a spatial light modulator. In modem electrographic printing, a computer typically drives the exposure station in a raster scan manner according to a bit map of the image to be printed. The exposing light discharges selected pixel locations of the photoconductor, so that the pattern of localized voltages across the photoconductor corresponds to the image to be printed. 
   At a developing or toning station in the typical electrographic printer, a developer roller or brush is biased to a bias voltage roughly at the primary charging voltage of the sensitized photoconductor prior to exposure. The biased developer roller or brush is loaded with toner charged to the bias voltage. As the exposed photoconductor passes the developing station, toner is attracted to the discharged pixel locations of the photoconductor. As a result, a pattern of toner corresponding to the image to be printed appears on the photoconductor. 
   The typical electrographic printer transfers the pattern of toner from the photoconductor to the printed medium (e.g., paper) at a transfer station. The transfer station charges the medium to an opposing voltage, so that the toner on the photoconductor is attracted to the medium, as the medium is placed in proximity to the photoconductor. Heat is then applied to the medium to fuse the transferred toner, and the medium is discharged and ejected from the printer. The photoconductor is then cleaned of any residual toner, and is prepared for the next image. 
   Magnetic Ink Character Recognition (MICR) technologies have been used for many years for the automated reading and sorting of checks and negotiable payment instruments, as well as for other documents in need of high speed reading and sorting. As well known in the art, MICR toner is a mixture of a fine metallic powder with polyester resin and powdered dye and MICR documents are printed with characters in a special font (e.g., the E13-B MICR font in the United States, and the CMC-7 MICR standard in some other countries). Typically, MICR characters are used to indicate the payor financial institution, payor account number, and instrument number, on the payment instrument. In addition to the special font, MICR characters are printed with special inks or toners that include magnetizable substances, such as iron oxide, that can be magnetized in the reading process. The magnetized MICR characters present a magnetic signal of adequate readable strength to the reading and sorting equipment, to facilitate automated routing and clearing functions in the presentation and payment of these instruments. 
   The relatively heavy loading of iron oxide in conventional MICR toner for electrographic MICR printing has been observed to adversely affect the image quality of the printed characters, however. It is difficult to achieve and maintain an adequate dispersion of the heavy iron oxide particles in the toner resin. In addition, the toning and fusing efficiencies of MICR toners are poorer than normal (i.e., non-MICR) toners, because of the magnetic loadings present in the MICR toner. Accordingly, the image quality provided by MICR toner is often poorer than those formed by normal toner, unless the printing machine makes significant adjustments in its printing process. 
   Many documents having MICR characters also include printed features and characters that are not MICR characters. This of course requires either two printing passes (one pass for MICR printing using MICR toners and another pass for the non-MICR printing using normal toners), or the printing of both the MICR and non-MICR features with MICR toners. In some installations, the MICR printing volume is sufficient that one electrographic printer is dedicated to the printing of the MICR characters on all documents, with other printers used to print the non-MICR features on those documents. In other installations, the MICR encoded volume is less than the capacity of one printer. Some conventional electrographic printing systems permit the swapping of toning stations, so that the operator can switch between MICR and normal toners, for printing MICR and non-MICR documents, respectively. 
   As noted above, MICR characters are used for the printing of sensitive information such as financial institution routing numbers, and account numbers. Unauthorized use of these numbers on payment documents can facilitate fraud and theft. As such, MICR printing is preferably carried out in reasonably secure environments, by trusted human operators. 
   It has been observed, in connection with this invention, that the differences between MICR toners and normal toners, particularly in the developing or toning process of electrographic printing, require different operational settings for optimal image formation using MICR toners from the operational settings for optimal image formation using normal toners. Accordingly, the operator ought to change the operational settings of the electrographic printer as he or she swaps toning stations to change between MICR and normal toners. 
   BRIEF SUMMARY OF THE INVENTION 
   It is therefore an object of this invention to provide an electrographic printer and method of operating the same that automatically changes settings according to the type of toner currently in use. 
   It is a further object of this invention to provide such a printer and method in which the developer settings are automatically changed according to the type of toner used. 
   It is a further object of this invention to provide such a printer and method in which the type of toner is automatically sensed upon change of the developer station. 
   It is a further object of this invention to provide such a printer and method in which security features are automatically enabled upon use of a certain toner type, such as MICR toner. 
   Other objects and advantages of this invention will be apparent to those of ordinary skill in the art having reference to the following specification together with its drawings. 
   The present invention may be implemented into an electrographic printer capable of accepting different types of toner. The printer senses the insertion of a developing station using a certain type of toner, such as MICR toner. Upon sensing the toner type, the printer sets its operational parameters to optimal settings for that toner. According to another aspect of the invention, the printer enables certain security settings upon insertion of a toner type, such as MICR toner, that is used for secure printing. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a schematic diagram of an electrographic marking, or reproduction machine, such as an electrographic printing machine, constructed according to a preferred embodiment of this invention. 
       FIG. 2  is a cross-sectional schematic diagram of a toning station used in the printing machine of  FIG. 1 , and constructed according to the preferred embodiment of the invention. 
       FIG. 3  is a flow chart illustrating the operation of the printing machine of  FIG. 1 , according to the preferred embodiment of the invention. 
       FIG. 4  is an electrical diagram, in schematic form, illustrating the sensing of a toning station indicator in the process of  FIG. 3 , according to the preferred embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The preferred embodiment of this invention will now be described in connection with an electrographic printer, by way of example, because this invention is contemplated to be particularly beneficial in such an application. It will be appreciated by those skilled in the art having reference to this specification that this invention can also be used in any type of electrographic system, of any size or capacity. As such, this description is provided by way of example only, and is not intended or contemplated to limit the true scope of the invention as claimed. 
   Referring now to  FIG. 1 , printer machine  10  according to the preferred embodiments of the invention will now be described. The exemplary printing machine  10  is illustrated in a general schematic sense, to provide a general context for the preferred embodiments of the invention; it is contemplated that this invention will be applicable to a wide range of printing machines. An example of a preferred model of printing machine  10  into which the preferred embodiments of the invention can be implemented is the DIGIMASTER 9110 printer available from Heidelberg Americas, Inc. 
   In the example of electrographic printer machine  10  of  FIG. 1 , moving photoconductor  18 , in the form of a belt, is entrained about a plurality of rollers or other supports  21   a  through  21   g , one or more of which is driven by a motor to advance photoconductor  18 . By way of example, roller  21   a  is illustrated as being driven by motor  20 . Motor  20  preferably advances photoconductor  18  at a high speed, such as 15 inches per second or higher, in the direction indicated by arrow P, past a series of workstations of the printer machine  10 . Alternatively, photoconductor  18  may be wrapped and secured about a single drum, rather than the multiple supports shown in FIG.  1 . 
   Printer machine  10  includes logic and control unit (LCU)  24 , preferably a digital computer or microprocessor operating according to a stored program, for sequentially actuating the workstations within printer machine  10  and effecting overall control of printer machine  10  and its various subsystems. LCU  24  is also programmed to provide closed-loop control of printer machine  10  in response to signals from various sensors and encoders. According to the preferred embodiments of the invention, one such sensor senses the identity of a toning, or development, station installed into printing machine  10 , thus sensing the type of toner currently being used. Also, the identity of toning will effect the particular start up cycle which is initiated. In response to the identity of the toning station, printing machine  10  selects a set of process control parameters including fuser temperature, toning station bias, densitometer aim, transfer current, fuser heater cleaning web advance rate, and other process setpoints. The sensed identity of the toning station, and thus the toner, also controls whether certain security features are enabled, according to the preferred embodiment of the invention; examples of these security features include printing permission or authority levels, print settings such as controlled reprints, access to certain fonts, and the like. These operations will be described in further detail below. 
   Referring back to  FIG. 1 , primary charging station  28  in printer machine  10  sensitizes photoconductor  18  by applying a uniform electrostatic corona charge, from high-voltage charging wires at a predetermined primary voltage, over an image frame area of the surface  18   a  of photoconductor  18 . Preferably, photoconductor  18  is sufficiently long to have multiple image frames over its length, with interframe spaces between these image frames that are used for process control as described below. The primary charging voltage output by charging station  28  is regulated by programmable voltage controller  30 , which is in turn controlled by LCU  24 . This primary voltage is preferably adjusted by controlling the electrical potential of a grid, which controls movement of the corona charge as is well known. Other forms of chargers, including brush or roller chargers, may also be used. 
   Exposure station  34  in printer machine  10  projects light from writer  34   a  to photoconductor  18 . This light selectively dissipates the electrostatic charge on photoconductive photoconductor  18  to form a latent electrostatic image of the document to be copied or printed. Writer  34   a  is preferably constructed as an array of light emitting diodes (LEDs), or alternatively as another light source such as a laser or spatial light modulator. In any case, writer  34   a  exposes individual picture elements (pixels) of photoconductor  18  with light at a regulated intensity and exposure. According to this embodiment of the invention, image data to be printed is provided to writer  34   a  by data source  36 , which is contemplated to be a computer or microcontroller. The exposed image is stored as a bit map in the memory of data source  36 , or is received by data source  36  over a data network. Signals from data source  36 , in combination with control signals from LCU  24  generated according to this invention, are provided to writer interface  32 , to apply the pixel exposure pattern and also exposure correction parameters. 
   After exposure, the image frame of photoconductor  18  bearing the latent charge images travels to an installed one of multiple toning stations  38   a ,  38   b . According to the preferred embodiment of the invention, toning stations  38   a ,  38   b  are modular, so that each can be easily installed into and removed from printing machine  10  by a human operator. The multiple modular toning stations  38   a ,  38   b  each contain a different type of toner, according to this embodiment of the invention, so that the appropriate toner can be selected and installed for particular printing jobs simply by selecting and installing the corresponding toner station  38   a ,  38   b.    
   According to this preferred embodiment of the invention, toning station  38   a  contains Magnetic Ink Character Recognition (MICR) toner, as used for the printing of MICR encoded characters, such as bank routing numbers and account numbers on checks. Other documents that are commonly printed with at least some MICR encoded characters include airline tickets, vouchers, return receipts, and the like. Toning station  38   b  (available but not installed in the configuration shown in  FIG. 1 ) contains conventional toner, and is for conventional black-and-white printing by electrographic printer  10 . In general, the toner in each of the multiple toning stations  38   a ,  38   b  consists of a two component developer mix which comprises a dry mixture of toner and carrier particles. The carrier particles are typically high coercivity (hard magnetic) ferrite particles, which are generally quite large (e.g., on the order of 30μ in volume-weighted diameter), while the dry toner particles are substantially smaller (e.g., on the order of 6μ to 15μ in volume-weighted diameter). The specific composition of the developer mix will depend upon the desired characteristics for the particular printing job, as will be described in further detail below. 
   MICR toner, as contained in toning station  38   a , conventionally includes a heavy loading of iron oxide or another magnetic material, in its toner particles. When printed on a document, preferably in a MICR font, this magnetic material provides a sufficiently strong magnetic signal to a conventional MICR reader that the characters printed using the MICR toner can be magnetically read. In addition, as well known in the art, conventional MICR toner also contains a sufficient amount of carbon black or another dye as to be visible when printed on conventional paper or other media; in addition, the MICR font also resembles the alphanumeric characters sufficiently that MICR encoded text is human-readable. A preferred composition of a MICR toner is described in copending application U.S. Ser. No. 09/747,764, filed Dec. 26, 2000, published on Aug. 22, 2002 as U.S. Patent Application Publication No. US 2002/0115006 A1, commonly assigned herewith and incorporated herein by this reference. 
   Conventional toner, as contained in toning station  38   b , may be of a conventional type of toner or developer mixture as appropriate for non-coded printing, depending upon the particular printing task that is to be carried out with toning station  38   b  installed in printing machine  10 . The dye contained within this conventional toner will, of course, correspond to the desired color of printed output. 
   The generalized construction of toning station  38   a  according to an exemplary implementation of the preferred embodiments of the invention, will now be described relative to FIG.  2 . It is contemplated that the other toning stations suitable for use with printing machine  10 , such as toning station  38   b , will be similarly constructed as toning station  38   a , particularly in form factor and in its interfaces for coupling to printing machine  10 . As shown in  FIG. 2 , toning station  38   a  is constructed within housing  7 . Mixer  9  mixes the carrier and toner particles, and feed roller  11  moves the developer mixture toward applicator roller  13 . Applicator roller  13 , according to the preferred embodiment of the invention, has non-magnetic cylindrical shell or sleeve  15  surrounding rotatable magnetic core  17 . Motors (not shown) are provided to rotate mixers  9 , feed roller  11 , and rotatable magnetic core  17 . Shive blade  27  is disposed adjacent to applicator roller  13 , to clean the large carrier particles from its surface. As described in U.S. Pat. No. 4,473,029, incorporated herein by this reference, the relative rotation of the core and shell moves the developer mixture through a development zone in the presence of an electrical field. As known in the art, applicator  13  is biased by variable power supply  19  to DC potential V B , within programmable controller  40  (FIG.  1 ), in response to control signals from LCU  24 , to control the toning or development process. 
   This construction of toning station  38  is described in a somewhat generic sense, as including a mixer, a feeder (e.g., a feed roller), and a core-and-shell applicator. Various alternative constructions of toning station  38  will be apparent to those skilled in the art having reference to this specification. One example of such an alternative construction of toning station  38  includes a magnetic brush in juxtaposition to, but spaced from, the travel path of photoconductor  18 . Magnetic brush toning, or development, stations are well known in the art, and are preferred in many applications; alternatively, other known types of toning stations or devices may be used. 
   Each of toning stations  38   a ,  38   b  include an indicator  50 , for communicating the identity of its toning station  38   a ,  38   b  to LCU  24 , when installed in printing machine  10 . According to an exemplary embodiment of the preferred embodiment of the invention, as shown in  FIG. 2 , indicator  50  is a resistor having a selected value that distinguishes its toning station  38  from the other available toning stations  38 , connected to external terminals that mate with printing machine  10  when toning station  38  is installed. Alternatively, other types of identifiers may be used as indicator  50 , including an externally readable digital code (for example in a read-only-memory), an optical indicator such as a bar code, or a mechanical indicator such as a code of tabs or openings. It is contemplated that other types of identifiers will be readily apparent to those skilled in the art having reference to this specification. The detection of the installed one of toning stations  38   a ,  38   b , and the subsequent operation of printing machine  10  in response to the result of that detection, according to the preferred embodiment of the invention, will be described in further detail below. 
   In operation, referring back to  FIG. 1 , roller  39  applies pressure to bias photoconductor  18  toward applicator roller  13  of toning station  38   a . The charged toner particles at applicator roller  13  are selectively attracted to the latent image patterns defined by the exposed locations of photoconductor  18  and adhere to these exposed locations of photoconductor  18 , thus developing the electrostatic images onto photoconductor  18  according to the exposure pattern. The carrier material remains at toning station  38 . As the toner particles are depleted from the developer mixture as images are developed, additional toner is periodically introduced by a conventional toner auger (not shown), for mixture with the carrier particles to maintain a uniform amount of development mixture. This development mixture is controlled in accordance with various development control processes, which are well known in the art. 
   Transfer station  46  in printing machine  10 , as is well known, moves receiver sheet S into engagement with photoconductor  18 , in registration with the developed image, to transfer this developed image to receiver sheet S. Receiver sheet S may be plain or coated paper, plastic, or another medium capable of being handled by printer machine  10 . Typically, transfer station  46  includes a charging device for electrostatically biasing movement of the toner particles from photoconductor  18  to receiver sheet S. In this example, the biasing device is roller  46   b , which engages the back of sheet S and which is connected to programmable voltage controller  46   a  that operates in a constant current mode during transfer. Alternatively, an intermediate member may have the image transferred to it and the image may then be transferred to receiver sheet S. After transfer of the toner image, sheet S is detacked from photoconductor  18  and transported to fuser station  49  where the image is fixed onto sheet S, typically by the application of heat. Alternatively, the image may be fixed to sheet S at the time of transfer. 
   Cleaning station  48 , such as a brush, blade, or web as is well known, is also located behind transfer station  46 , and removes residual toner from the image frame of photoconductor  18 . A pre-clean charger (not shown) may be located before or at cleaning station  48  to assist in this cleaning. After cleaning, the portion of photoconductor  18  corresponding to the printed image frame is then ready for recharging and re-exposure. Of course, other image frames of photoconductor  18  are simultaneously located at the various workstations of printing machine  10 , so that the printing process is carried out in a substantially continuous manner. 
   As mentioned above, LCU  24  provides overall control of the apparatus and its various subsystems as is well known. LCU  24  will typically include temporary data storage memory, a central processing unit, timing and cycle control unit, and stored program control. Data input and output is performed sequentially through or under program control. Input data can be applied through input signal buffers to an input data processor, or through an interrupt signal processor, and include input signals from various switches, sensors, and analog-to-digital converters internal to printing machine  10 , or received from sources external to printing machine  10 , such as from as a human user or a network control. The output data and control signals from LCU  24  are applied directly or through storage latches to suitable output drivers and in turn to the appropriate subsystems within printing machine  10 . 
   Process control strategies generally utilize various sensors to provide real-time closed-loop control of the electrographic process so that printing machine  10  generates “constant” image quality output, from the user&#39;s perspective. One of such sensors may be densitometer  76 , which monitors test patches that are exposed and developed in non-image areas of photoconductive photoconductor  18  under the control of LCU  24 , as described in U.S. Pat. No. 6,121,986. Densitometer  76  may include a light emitter, such as infrared or visible light LED, and a light collector such as a photodiode. A preferred construction of densitometer  76  is described in International Publication Number WO 02/14957 A1, commonly assigned herewith and incorporated herein by this reference. Depending on the arrangement of densitometer  76 , light from the light emitter either shines through the belt or is reflected by the belt onto the light collector, and the intensity is converted to an electrical signal representative of the reflected or transmitted light. As described in U.S. Pat. No. 6,121,986 and in International Publication WO 02/10860, the toned test patches are preferably formed to varying toner density levels, to provide improved accuracy in the process control of printing machine  10 . Because the toned test patches are formed in the interframe area of photoconductor  18 , this process control can be carried out in real time without reducing the printed output throughput. 
   Another sensor useful for monitoring process parameters in printer machine  10  is electrometer probe  50 , mounted downstream of the corona charging station  28  relative to direction P of the movement of photoconductor  18 . An example of an electrometer is described in U.S. Pat. No. 5,956,544. Electrometer probe  50  provides a measurement of the reading of the actual voltage at photoconductor  18 , for use in calculating the efficiency of primary charger  28 , as described in U.S. Pat. No. 6,121,986. 
   Certain process control parameters have been observed, in connection with this invention, to be dependent upon the type of toner used. More specifically, it has been observed that MICR toners and conventional normal toners require different process control parameter setpoints for optimal printing. One such setting is the adjustment of primary charging voltage and exposure according to the aim densitometer  76  output voltage, which preferably differs between MICR and other toners. In addition, the fusing temperature applied by fuser station  49  is preferably set to different temperatures for MICR toners (e.g., on the order of 190° C.) than for normal toners (e.g., on the order of 180° C.). Other process parameters that preferably differ for MICR and normal toners include fuser heater cleaning web advance rate, the transfer current applied by transfer station  46 , and the toning station bias voltage VB applied by variable power supply  19  under the control of programmable controller  40 . It is contemplated that those skilled in the art having reference to this specification will recognize other process parameters that have different optimal settings for use in connection with different types of toners, including MICR toners. 
   As mentioned above, MICR encoded characters are often used for financial instruments, or for documents that are associated with significant monetary value (e.g., airline tickets, vouchers, etc.). The financial value of these types of documents often make it prudent to incorporate security functions for the printing of MICR encoded documents. These security functions of course are often not necessary for documents that are not MICR encoded, or for the printing of the non-MICR encoded portions of documents that will eventually be MICR encoded. 
   Referring now to  FIG. 3 , the operation of printing machine  10  according to the preferred embodiment of the invention will now be described in detail. Of course, alternatives to the specific operations and steps of this exemplary process will be apparent to those skilled in the art having reference to this specification, it being understood that such alternatives are within the scope of this invention as claimed. In addition, while this process will be described in connection with two available toning stations  38   a ,  38   b , with toning station  38   a  associated with MICR toner, it is of course contemplated that more than two toning stations  38  may be available, each with their own associated optimal printing and process conditions; it is further contemplated that these toning stations  38  may not necessarily include a toning station  38   a  having MICR toner. This description is based on toning station  38   a  having such MICR toner, however, because it is contemplated that this invention is particularly advantageous when applied to MICR encoded printing. 
   In process  60 , toning station  38  is installed into printing machine  10 , in advance of the printing of documents or other output using the toner in that toning station. As noted above, the available toning stations  38   a ,  38   b , etc. are constructed to have a common form factor and interface capability, so as to be interchangeable within printing machine  10 . Process  60  may also be initiated upon the power-up of printing machine  10 , without the installation of a different toning station  38 . 
   In process  62 , printing machine  10  senses the identity of the installed toning station  38 , by sensing indicator  50  associated with that installed toning station. According to an exemplary implementation of the preferred embodiment of the invention, sensing process  62  is carried out by LCU  24  measuring a voltage drop across a resistor value in indicator  50 , as will now be described relative to FIG.  4 . 
   As mentioned above, according to an exemplary embodiment of the invention, indicator  50  is constructed as a resistor, with external terminals that interface with printing machine  10 .  FIG. 4  schematically illustrates the operation of LCU  24  in measuring the voltage across a resistor network including indicator  50 . In this implementation, LCU  24  is in electrical connection with the external terminals of indicator  50 , such that indicator  50  is placed in series with test resistor  54  (either in LCU  24  or external thereto). Indicator  50  thus becomes part of a voltage divider, measurable by LCU  24 . In sensing process  62 , LCU  24  applies a test voltage V test  across the voltage divider, between one terminal of indicator  50  and test resistor  54 , resulting in a test current I test . LCU  24  then measures the voltage V div  at a second terminal of indicator  50 , which is at the point between indicator  50  and test resistor  54 . The voltage V div  will of course depend on the resistance value of indicator  50  (test resistor  54  being constant for all toning stations  38 ). A comparison of voltage V div  against preselected voltage ranges for identifying the various toning stations  38  thus indicates the identity of the installed toning station  38  as the result of process  62 . 
   Alternatively, LCU  24  could sense the resistance value of indicator  50 , by measuring current I test  and dividing it into applied voltage V test . Further in the alternative, the entire voltage divider (i.e., both the resistor of indicator  50  and also resistor  54 ) could be incorporated within indicator  50 , so that indicator  50  would present a three-terminal interface to LCU  24  (two bias terminals, and the measurement terminal between the two resistors). It is contemplated that these and other alternative realizations of a passive electrical indicator may be used to implement indicator  50  and its sensing by LCU  24 . 
   As mentioned above, alternative identification techniques are also contemplated. One example of such an alternative techniques include the incorporation of a digital identifier  50  within toning station  38 , such as by way of an addressable memory location. Mechanical indicators, such as the placement of movable lugs into selected locations of an array of holes in toning station  38 , may also be used. Optical indicators may also be utilized according to this invention. It is contemplated that those skilled in the art having reference to this specification will readily recognize other alternative identification schemes, each of which are contemplated to be within the scope of this invention. It is contemplated, however, that the simple voltage divider technique described relative to  FIG. 4  is particularly advantageous because of its simplicity and its compatibility with conventional logic units serving as LCU  24 . 
   In this preferred embodiment of the invention, LCU  24  executes decision  63  based on the results of sensing process  62 , to determine whether MICR toning station  38   a  was installed in printing machine  10 . If not (decision  63  is NO), printing machine  10  selects a set of process parameter setpoints associated with normal toner printing, in process  78 . A startup exercise cycle for printing machine  10 , for normal printing, is then executed in process  79 , carrying out an auto set-up routine, for example as described in U.S. Pat. No. 6,121,986, incorporated herein by this reference. These functions include adding toner, warming and charging the developer mix in toning station  38   b , retrieving from memory the set of electrographic printing setpoint values and operating parameters selected in process  78 , recalculating additional electrographic printing setpoints as appropriate to begin printing. Other functions include the synchronization of system timing is synchronized, measurement of bare film densitometer readings for toner density process control as described in International Publication Number WO 02/14957 A1, incorporated herein by this reference, and the derivation of bias voltages for primary charging station  28 , developing station  38   b , and exposure station  34 . The electrographic printing setpoints are then adjusted for the current ambient conditions by way of the exposure and development of test toner patches on photoconductor  18 . Printing machine  10  then begins the printing of documents in process  80 , preferably under real-time process control, for example in the manner described in U.S. Pat. No. 6,121,986. 
   On the other hand, if LCU  24  determines that MICR toning station  38   a  is installed in printing machine  10  (decision  63  is YES), LCU  24  carries out a series of processes to enable, set up, and carry out MICR printing by printing machine  10 . In process  64 , LCU  24  selects a set of process parameters and setpoints for printing using the MICR toner in toning station  38   a . As mentioned above, these parameters and setpoints include the aim of onboard densitometer  76 , the fusing temperature applied by fuser station  49 , the fuser heater cleaning web advance rate, the transfer current applied by transfer station  46 , and the toning station bias voltage VB applied by variable power supply  19  under the control of programmable controller  40 . In process  66 , LCU  24  then executes the startup exercise cycle of printing machine  10  for MICR printing. As discussed above for normal printing, this startup routine includes an auto set-up routine, for example as described in U.S. Pat. No. 6,121,986; adding toner; warming and charging the developer mix in toning station  38   a ; retrieving the set of electrographic printing setpoint values and operating parameters selected in process  64 ; recalculating additional electrographic printing setpoints as appropriate to begin printing; synchronizing system timing; measuring bare film densitometer readings for toner density process control as described in International Publication Number WO 02/14957 A1; deriving bias voltages for primary charging station  28 , developing station  38   b , and exposure station  34 ; and adjusting the electrographic printing setpoints for the current ambient conditions via test toner patches. 
   According to this embodiment of the invention, beginning with process  68 , LCU  24  carries out a series of security functions that are suitable for MICR printing. In process  68 , LCU  24  receives an operator security ID from the human operator, for example by the operator entering a password or identifier at a keypad of printing machine, or by printing machine  10  reading a magnetic or optical identifier from the operator&#39;s badge. In decision  69 , LCU  24  determines whether the identified operator has sufficient authority to perform MICR printing, for example by matching the operator ID to a look-up table of assigned authority levels. If not (decision  69  is NO), printing machine  10  is locked out in process  70 , until a non-MICR toning station  38   b  is installed or until intervention by a supervisor or superuser of printing machine  10 . 
   If the operator is identified as having adequate authority for MICR printing (decision  69  is YES), the appropriate permissions are then granted by LCU  24  to this operator. According to this embodiment of the invention, tuned MICR fonts (e.g., the E13-B MICR font in the United States, and the CMC-7 MICR standard in some other countries) are enabled for use in process  72 , and printing machine  10  enables access to secure MICR files for printing, in process  74 . Other security functions may also be enabled at this time. In this example, automatic reprints of pages are blocked in process  76 . It is contemplated that those skilled in the art having reference to this specification will readily recognize that other security functions and permissions, as well as the implementation of a range of authority or permission levels, may similarly be added or substituted for those described in this exemplary implementation of the preferred embodiment of this invention. 
   Following the startup exercise cycle (process  66 ) and the enabling and setting of the appropriate security functions (processes  72 ,  74 ,  76 ), printing machine  10  then begins the printing of documents in process  80 . As in the normal toner case, the printing of process  80  is preferably carried out under real-time process control, for example in the manner described in U.S. Pat. No. 6,121,986, but of course with the settings corresponding to those for MICR printing. 
   The printing and setup of printing machine  10  continues until the printer is turned off, or until a different toning station  38  is installed. Following each of these events, the process of  FIG. 3  will again be carried out to sense the identity of the installed toning station  38 , and to control printing machine  10  accordingly. 
   This invention provides several important benefits to electrographic printing. By sensing the identity of the installed toning system, the electrographic printer is able to automatically select its operating parameters and functionality, without requiring a human operator to manually carry out an involved set up process. This automatic sensing and control is especially important for electrographic printing machines capable of use with different types of toners that have significant differences in their optimal printing parameters. As a result of this invention, optimized printed output using any one of a number of toner types can be obtained, with a minimal amount of human intervention. In addition, the use of toner types, such as MICR toner, can be minimized according to this invention, because the automated setting of the printing machine facilitates the switching of toner types for different printing jobs. In addition, this invention enables the use of automated security functions for toning stations used for secure or financially sensitive documents, such as MICR toner for financial documents. 
   While the present invention has been described according to its preferred embodiments, it is of course contemplated that modifications of, and alternatives to, these embodiments, such modifications and alternatives obtaining the advantages and benefits of this invention, will be apparent to those of ordinary skill in the art having reference to this specification and its drawings. It is contemplated that such modifications and alternatives are within the scope of this invention as subsequently claimed herein.