Abstract:
A specific magnet roll design for high speed semi-conductive magnetic brush (SCMB) development systems for magnetic image character recognition (MICR) printing is provided. The resulting magnetic field distributions include a more uniform radial field and enhance solid area development and halftone graininess without or substantially without bead carryout issues. In addition, this enhancement of solid area development enables magnetic toner in these hill speed SCMB systems that normally would not provide sufficient development latitude for MICR.

Description:
BACKGROUND 
       [0001]    The exemplary embodiments generally relate to xerographic marking and devices, and specifically relates to semi-conductive magnetic brush (SCMB) development systems, emulsion aggregation-SCMB based systems and magnetic image character recognition (MICR) printing. 
         [0002]    Pending U.S. patent application Ser. No. 11/262,575, filed Oct. 31, 2005, by Michael D. Thompson et al., entitled “Xerographic Developer Unit Having Multiple Magnetic Brush Rohls Rotating Against the Photoreceptor,” Attorney Docket No.: 20031548-US-NP, describes how in the process of electrophotographic printing, a charge-retentive surface, also known as a photoreceptor, is charged to a substantially uniform potential, so as to sensitize the surface of the photoreceptor. The charged portion of the photoconductive surface is exposed to a light image of an original document being reproduced, or else a scanned laser image created by the action of digital image data acting on a laser source. The scanning or exposing step records an electrostatic latent image on the photoreceptor corresponding to the informational areas in the document to be printed or copied. After the latent image is recorded on the photoreceptor, the latent image is developed by causing toner particles to adhere electrostatically to the charged areas forming the latent image. This developed image on the photoreceptor is subsequently transferred to a sheet on which the desired image is to be printed. Finally, the toner on the sheet is heated to permanently fuse the toner image to the sheet. 
         [0003]    U.S. Pat. No. 4,901,114 discloses an electronic printer employing tri-level xerography to superimpose two images with perfect registration during the single pass of a charge retentive member past the processing stations of the printer. One part of the composite image is formed using MICR toner, while the other part of the image is printed with less expensive black, or color toner. For example, the magnetically readable information on a check is printed with MICR toner and the rest of the check is printed in color or in black toner that is not magnetically readable. 
         [0004]    Magnetic image character recognition (MICR) when used in laser printing systems is an important technology for check printing, especially for variable data check applications. Using MICR toners in SCMB-based printers may require more electric bias for the development system (with an attendant modification of the controls system) as well as special toner additives and sometimes carrier conductivity modification to overcome the additional magnetic forces in development. These modifications to the base non-MICR system and developer material add significant cost to the MICR printing process. The magnetic fields used for SCMB systems are typically very high, exacerbating the problem. This added bias limits the print process latitude and can decrease the reliability of the print engine. There is also undesirable structure in the images with MICR toners that precludes their use for both MICR characters and high quality images on checks. 
         [0005]    Graininess and mottle in xerographic SCMB images has a component contributed by the magnetic brush structure. This structure comes from the physical structure of the magnetic brush, which causes fluctuations in the electric field during the development process and, although it may be a fairly small effect, it may be a barrier to SCMB systems being used in high quality printing applications. 
       SUMMARY 
       [0006]    Exemplary embodiments include various aspects of a specific magnet roll design for high speed semi-conductive magnetic brush (SCMB) development systems for magnetic image character recognition (MICR) printing is provided. The resulting magnetic field distributions include a more uniform radial field and enhanced solid area development and halftone graininess without or substantially without bead carryout issues. In addition, this enhancement of solid area development enables magnetic toner in these high speed SCMB systems that normally would not provide sufficient development latitude for MICR. 
         [0007]    One aspect is a development system for a printing machine that uses MICR toner particles, including a developer housing, at least one magnetic roll, and a motor. The developer housing retains a quantity of developer. The magnetic roll has a stationary core with at least one magnet and at least one sleeve that rotates about the stationary core of the magnetic roll. The motor is coupled to the magnetic roll to drive the rotating sleeve of the magnetic roll in a direction toward a photoreceptor. The magnetic roll carries the developer through a development zone in a maimer that lowers the magnetic field in a portion of the development zone, facilitating developer transport onto the photoreceptor. The shape of the magnet may be used to lower the magnetic field in the portion of the development zone. A halftone image may be produced. The magnetic field may be lowered substantially at a center of the development zone. A spaced geometry may be used. 
         [0008]    Another aspect is a method, wherein quantity of developer is retained having MICR toner particles in a developer housing. At least one sleeve is rotated about a stationary core of at least one magnetic roll. The stationary core has at least one magnet. The rotating sleeve of the magnetic roll is driven by a motor coupled to the magnetic roll in a direction toward a photoreceptor. The magnetic roll carries the developer through a development zone in a manner that lowers the magnetic field in a portion of the development zone, facilitating developer transport onto the photoreceptor. The shape of the magnet may be used to lower the magnetic field in the portion of the development zone. A halftone image may be produced. The magnetic field may be lowered substantially at a center of the development zone. A spaced geometry may be used. 
         [0009]    Yet another aspect is a xerographic system, including a feeding unit, a printer unit, an output unit, a developer housing, at least one magnetic roll, and a motor. The feeding unit supplies a plurality of sheets. The printer unit is coupled to the feeding unit and receives the sheets and transfers images onto the sheets. The output unit is coupled to the printer unit and receives the sheets with images. The developer housing in the printer unit retains a quantity of developer having MICR toner particles. The magnetic roll has a stationary core with at least one magnet and at least one sleeve that rotates about the stationary core of the magnetic roll. The motor is coupled to the magnetic roll to drive the rotating sleeve of the magnetic roll in a direction toward a photoreceptor. The magnetic roll carries the developer through a development zone in a manner that lowers the magnetic field in a portion of the development zone, facilitating developer transport onto the photoreceptor. The shape of the magnet may be used to lower the magnetic field in the portion of the development zone. A halftone image may be produced. The magnetic field may be lowered substantially at a center of the development zone. A spaced geometry may be used. A region pre- and post-development zone may maintain material transport. A halftone dot size may be normalized around a predetermined area. The visual noise may be below a predetermined threshold. The portion of the magnetic field may be about 50 degrees of rotational position or about 25 degrees clockwise to about 25 degrees counterclockwise relative to a line defining a center of the development zone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates an elevational view of an electrostatographic printing apparatus in the related art; 
           [0011]      FIG. 2  illustrates the overall function of a developer unit in the related art; 
           [0012]      FIG. 3  illustrates a schematic of various components of an electrophotographic printing machine in the related art; 
           [0013]      FIG. 4  illustrates a typical response when a MICR toner is used with a standard SCMB development system; 
           [0014]      FIG. 5  illustrates MICR development behavior according to exemplary embodiments; 
           [0015]      FIGS. 6A and 6B  illustrate differences between MICR and non-MICR toners; 
           [0016]      FIGS. 7A and 7B  illustrate halftone dot size distribution with and without exemplary embodiments; 
           [0017]      FIG. 8  illustrates visual noise reduction achieved in experimental testing with exemplary embodiments; and 
           [0018]      FIGS. 9A and 9B  illustrate a tangential magnetic field and a radial magnetic field in a development zone for exemplary embodiments. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0019]      FIG. 1  is an elevational view of an electrostatographic printing apparatus  10  in the related art, such as a printer or copier, having a development subsystem that uses two magnetic rolls for developing toner particles that are carried on semiconductive carrier particles. Such toner particles and carrier particles are one type of developer material among many types. One embodiment includes single component developers in which there is no carrier, where the toner itself is magnetic and is transported similarly to two component systems. One embodiment includes semi-conductive magnetic brush development (a two component technology while another embodiment includes single component technology. 
         [0020]    One related art type of development of an electrostatic image is called “two-component development”. Two-component developer material generally includes toner particles interspersed with carrier particles. The carrier particles are magnetically attractable, and the toner particles are caused to adhere triboelectrically to the carrier particles. This two-component developer can be conveyed, by means such as a “magnetic roll,” to the electrostatic latent image, where toner particles become detached from the carrier particles and adhere to the electrostatic latent image. 
         [0021]    In magnetic roll development systems, the carrier particles with the triboelectrically adhered toner particles are transported by the magnetic rolls through a development zone. The development zone is the area between the outside surface of a magnetic roll and the photoreceptor surface on which a latent image has been formed. Because the carrier particles are attracted to the magnetic roll, some of the toner particles are interposed between a carrier particle and the latent image on the photoreceptor. These toner particles are attracted to the latent image and transfer from the carrier particles to the latent image. The carrier particles are removed from the development zone as they continue to follow the rotating surface of the magnetic roll. The carrier particles then fall from the magnetic roll and return to the developer supply where they attract more toner particles and are reused in the development process. The carrier particles fall from the magnetic roll under the effects of gravity or are directed away from the roller surface by a magnetic field. 
         [0022]    Different types of carrier particles can be used to enhance the development of toner from two-component developer with magnetic roll development systems. One type of carrier particle is a very electrically insulated carrier and development systems using developer having these carrier particles typically develop lines and fine detail with high fidelity. Development efficiency for solid areas, however, is increased through low magnetic field agitation in the development zone along with close spacing to the latent image and elongation of the development zone. The magnetic field agitation helps reduce or prevent electric field collapse caused by toner countercharge in the development zone. The close spacing increases the effective electric field for a potential difference and the longer development zone provides more time for toner development. 
         [0023]    Another type of carrier particle used in two-component developers is an electrically conductive carrier particle. Developers using this type of carrier particle are capable of being used in magnetic roll systems that produce toner bearing substrates at speeds of up to approximately  100  pages per minute (ppm). These developers typically recruit toner for the latent electrostatic image from areas near the tip of the developer magnetic brush that are proximate the surface of the photoconductor because the electric fields are high in this region. The electrical conductivity of the carrier particles serves to reduce or prevent development field collapse caused by the retention of toner countercharge and thereby allows high efficiency development, especially of solid area latent images. 
         [0024]    Another type of carrier particle used in two-component developers is the semiconductive carrier particle. Developers using this type of carrier particle are also capable of being used in magnetic roll systems that produce toner bearing substrates at speeds of up to approximately 200 pages per minute (ppm). Developers having semiconductive carrier particles use a relatively thin layer of developer on the magnetic roll in the development zone. This feature allows more of the toner to be recruited during development than thick brush conductive developers allow. In these systems, an AC electric waveform is typically applied to the magnetic roller to cause the developer to become electrically conductive during the development process. The electrically conductive developer increases the efficiency of development by reducing or preventing development field collapse due to countercharge left in the magnetic brush by the developed toner. A typical waveform applied to these systems is, for example, a square wave at a peak to peak amplitude of 1000 Volts and a frequency of 9 KHz. This waveform controls both the toner movement and the electric fields in the development zone. 
         [0025]    The electrostatographic printing apparatus  10  of  FIG. 1  has a development subsystem that uses two magnetic rolls for developing toner particles that are carried on semiconductive carrier particles. The machine  10  includes a feeder unit  14 , a printing unit  18 , and an output unit  20 . The feeder unit  14  houses supplies of media sheets and substrates onto which document images are transferred by the printing unit  18 . Sheets to which images have been fixed are delivered to the output unit  20  for correlating and/or stacking in trays for pickup. 
         [0026]    The printing unit  18  includes an operator console  24  where job tickets may be reviewed and/,or modified for print jobs performed by the machine  10 . The pages to be printed during a print job may be scanned by the printing machine  10  or received over an electrical communication link. The page images are used to generate bit data that are provided to a raster output scanner (ROS)  30  for forming a latent image on the photoreceptor  28 . Photoreceptor  28  continuously travels the circuit depicted in  FIG. 1  in the direction indicated by the arrow. The development subsystem  34  develops toner on the photoreceptor  28 . At the transfer station  38 , the toner conforming to the latent image is transferred to the substrate by electric fields generated by the transfer station. The substrate bearing the toner image travels to the fuser station  44  where the toner image is fixed to the substrate. The substrate is then carried to the output unit  20 . 
         [0027]      FIG. 2  shows the overall function of a developer unit  200 , which is to apply marking material, such as toner, onto suitably-charged areas forming a latent image on an image receptor such as the photoreceptor  228 , in a manner generally known in the art. The developer unit  200 , however, provides a longer development zone while maintaining an adequate supply of developer having semiconductive carrier particles than many other development systems. Various types of printers can include multiple such developer units  200 , such as one for each primary color or other purpose. For example, MICR development may be performed in tandem with color development, 
         [0028]    Among the elements of the developer unit  200 , which is shown in  FIG. 2 , are a housing  212 , which functions generally to hold a supply of developer material having semiconductive carrier particles, as well as augers, such as  230 ,  232 ,  234 , which variously mix and convey the developer material, and magnetic rolls  236 ,  238 , which in this embodiment form magnetic brushes to apply developer material to the photoreceptor  228 . Other types of features for development of latent images, such as donor rolls, paddles, scavengeless-development electrodes, commutators, etc., are known in the art.  FIG. 2  also shows air manifolds  240 ,  242 , attached to vacuum sources (not shown) for removing dirt and excess particles from the transfer zone near photoreceptor  228 . As mentioned above, a two-component developer material is comprised of toner and carrier. The carrier particles in a two-component developer are generally not applied to the photoreceptor  228 , but rather remain circulating within the housing  212 . The augers  230 ,  232 , and  234  are configured and cooperate in a manner described in U.S. patent application Ser. No. 11/263,370 filed Oct. 31, 2005 by Steven C. Hart et al, entitled “Variable Pitch Auger To Improve Pickup Latitude In Developer Housing,” Attorney Docket No. 20041346, and U.S. patent application Ser. No. 11/263,371 filed Oct. 31, 2005 by Steven C. Hart et al., entitled “Developer Housing Design With Improved Sump Mass Variation Latitude,” Attorney Docket No. 20041120. 
         [0029]      FIG. 3  schematically depicts the various components of an illustrative electrophotographic printing machine disclosed in U.S. Pat. No. 4,901,114. As shown in  FIG. 3 , the printing machine utilizes a photoconductive belt  310 , which includes of a photoconductive surface and an electrically conductive substrate. Belt  310  moves in the direction of arrow  316  to advance successive portions thereof sequentially through the various processing stations disposed about the path of movement thereof. Belt  310  is entrained about a plurality of rollers  318 ,  320  and  322 , the former of which can be used as a drive roller and the latter of which can be used to provide suitable tensioning of the photoreceptor belt  310 . Motor  324  rotates roller  318  to advance belt  310  in the direction of arrow  316 . Roller  318  is coupled to motor  324  by suitable means, such as a belt drive. 
         [0030]    As can be seen by further reference to  FIG. 3 , initially a portion of belt  310  passes through charging station A. At charging station A, a corona discharge device such as a scorotron or corotron indicated generally by the reference numeral  325 , charges the belt  310  to a selectively high uniform positive or negative potential, 
         [0031]    Next, the charged portion of the photoreceptor surface is advanced through exposure station B. At exposure station B, the uniformly charged photoreceptor or charge retentive surface  310  is exposed to a laser based input and/or output scanning device  312 , which causes the charge retentive surface to be discharged in accordance with the output from the scanning device. Preferably, the scanning device is a three level raster output scanning device. 
         [0032]    The photoreceptor  310  which is initially charged to a voltage V 0 , undergoes dark decay to a level V ddp . When exposed at the exposure station B it is discharged to V w  imagewise in the background (white) image areas and to V c  which is near zero or ground potential in the highlight (i.e. color other than black) color parts of the image. 
         [0033]    At development station C, a magnetic brush development system, indicated generally by the reference numeral  330  advances developer materials into contact with the electrostatic latent images. The development system  330  includes first and second developer housings  332  and  334 . Preferably, each magnetic brush development housing includes a pair of magnetic brush developer rollers. Thus, the housing  332  contains a pair of rollers  335 ,  336  while the housing  334  contains a pair of magnetic brush rollers  337 ,  338 . Each pair of rollers advances its respective developer material into contact with the latent image. Each developer roller pair forms brush structure comprising toner particles which are attracted by the latent images on the photoreceptor. 
         [0034]    Color discrimination in the development of the electrostatic latent image is achieved by passing the photoreceptor past the two developer housings in a single pass with the magnetic brush rolls electrically biased to voltages which are offset from the background voltage V w , the direction of offset depending on the toner in the housing. One housing, e.g.  332  (for the sake of illustration, the first), contains developer with black toner  340  having triboelectric properties such that the toner is driven to the most highly charged (V ddp ) areas of the latent image by the electrostatic field (development field) between the photoreceptor and the development rolls biased at V bb1  and V bb2  (V black biases). Conversely, the triboelectric charge on colored toner  342  in the second housing is chosen so that the toner is urged towards parts of the latent image at residual potential, V c  by the electrostatic field (development field) existing between the photoreceptor and the development rolls in the second housing at bias voltages V cb1  and V cb2  (V color biases). 
         [0035]    In prior art or related art tri-level xerography, the entire photoreceptor voltage difference (|V ddp −V c |) is shared equally between the charged area development (CAD) and the discharged area development (DAD). This corresponds to apprxeq 600 volts (if a realistic photoreceptor value for V ddp  of 700 volts and a residual discharge voltage of 100 volts are assumed). Allowing an additional 100 volts for the cleaning field in each development housing (|V bb −V white | or |V white −V cb |) means an actual development contrast voltage for CAD of approximately 200 volts and an approximrately equal amount for DAD. In the foregoing case, the 200 volts of contrast voltage is provided by electrically biasing the first developer housing to a voltage level of approximately 500 volts and the second developer housings to a voltage level of 300 volts. Although 200 volts contrast is generally sufficient, 250 volts is more desirable in practice to assure adequate system latitude as the developers age. 
         [0036]    Accordingly, a more desirable development field is provided with the first developer housing by biasing the roller  335  to a voltage level (V bb1 ) equal to 450 volts which provides 250 (|V adp −V bb |) or (700−450=250) volts for the development field. An added advantage of this increased development field is that the reverse development field is reduced by the magnitude of such increase, therefore, there is less tendency for induction charging to reverse the polarity of the charge on the black toner and cause it to be attracted to the red latent image. The reverse development field is that field which is established between the developer rollers and the colored image areas. The bias on the roller  36  in the first housing is 500 volts, consequently, the increased development seen with the roller  335  is not present with the roller  336 . However, the cleaning field (|V bb2 −V w ) is twice that of the field established between roller  335  and the photoreceptor in the V w  areas. The bias, V cb1  on the roller  336  is 350 volts thereby providing 250 volts for the development field between the roller  337  and the colored image areas of the photoreceptor. The bias, V cb2  on the roller  338  is 300 volts thereby providing only a 200 volt development field but a larger cleaning as in the case of the roller  36 . 
         [0037]    The foregoing developer biases are provided by power supplies  341  and  343 . These power supplies are each provided with suitable resistor pairs  344  and  346  for providing the different biases to the rolls  335 ,  336 ,  337  and  338 . 
         [0038]    In  FIG. 3 , the housing  332  contains black MICR type developer. The housing  334  preferably contains a magnetic developer whose magnetic component is reduced such that it is not readable by MICR devices. Alternatively, the developer in the housing  334  may be non-magnetic. While the developers in  FIG. 3  are different colors, they may also be the same color. 
         [0039]    A sheet of support material  358  is moved into contact with the toner image at transfer station D). The sheet of support material is advanced to transfer station D by conventional sheet feeding apparatus, not shown. Preferably, sheet feeding apparatus includes a feed roll contacting the uppermost sheet of a stack copy sheets. Feed rolls rotate so as to advance the uppermost sheet from stack into a chute which directs the advancing sheet of support material into contact with photoconductive surface of belt  310  in a timed sequence so that the toner powder image developed thereon contacts the advancing sheet of support material at transfer station D. 
         [0040]    Because the composite image developed on the photoreceptor consists of both positive and negative toner, a pre-transfer corona discharge member  356  is provided to condition the toner for effective transfer to a substrate using corona discharge. 
         [0041]    Transfer station D includes a corona generating device  360  which sprays ions of a suitable polarity onto the backside of sheet  358 . This attracts the charged toner powder images from the belt  310  to sheet  358 . After transfer, the sheet continues to move, in the direction of arrow  362 , onto a conveyor (not shown), which advances the sheet to fusing station E. 
         [0042]    Fusing station E includes a fuser assembly, indicated generally by the reference numeral  364 , which permanently affixes the transferred powder image to sheet  358 . Preferably, fuser assembly  364  comprises a heated fuser roller  366  and a back-up roller  368 . Sheet  358  passes between fuser roller  366  and back-up roller  368  with the toner powder image contacting f-user roller  366 . In this manner, the toner powder image is permanently affixed to sheet  358 . After fusing, a chute, not shown, guides the advancing sheet  358  to a catch tray, also not shown, for subsequent removal from the printing machine by the operator. 
         [0043]    After the sheet of support material is separated from photoconductive surface of belt  310 , the residual toner particles carried by the non-image areas on the photoconductive surface are removed therefrom. These particles are removed at cleaning station F. 
         [0044]    Subsequent to cleaning, a discharge lamp (not shown) floods the photoconductive surface with light to dissipate any residual electrostatic charge remaining prior to the charging thereof for the successive imaging cycle. 
         [0045]    Turning now to the present invention, exemplary embodiments include tailoring a magnetic field in a development zone of a modern SCMB magnetic brush development system such that the structure of the brush is changed in such a way as to preserve the normal transport characteristics of the magnetic developer material and, at the same time, to reduce the magnetically induced structure in the development zone. Exemplary embodiments include a special magnetic field patterning in the development zone for a SCMB system. This magnetic field patterning reduces magnetic brush induced image noise for standard and MICR toners as well as reducing the magnetic holding forces in the nip for MICR toners thereby allowing MICR toners to develop at reduced electric fields, increasing the latitude of the system and reducing or eliminating the necessity for drastic changes in developer material for MICR electrophotographic printing systems compared to non-MICR systems. 
         [0046]    Typical contemporary SCMB-based development systems are at the heart of many color electrophotographic systems. These systems are characterized by a magnetic development roll with high magnetic fields, typically 800-1200 g at the roll surface in the development zone. The solid area development response is relevant to the behavior of the system and for the control system design. Magnetic brash development needs a certain electrostatic field to strip toner from the developer beads and present the toner to a latent electrostatic image, as indicated in  FIG. 4 . 
         [0047]      FIG. 4  shows a typical response when a MICR toner is used with a standard SCMB development system, i.e., reduced development response for equivalent development electric field. The source of this problem is illustrated in  FIGS. 6A and 6B , which show the increased adhesion of MICR toner to magnetic carrier in an external magnetic field. 
         [0048]      FIG. 5  shows results produced by one exemplary embodiment, which increase the development response for MICR toner and makes the performance similar to that of standard toner for similar toner charge to mass ratios, reducing the need for special charging additives and conductivity modification of MICR developer. 
         [0049]    Graininess and mottle in xerographic SCMB images has a component contributed by the magnetic brush structure. This structure comes from fluctuations in the electric field during the development process and, although it may be a fairly small effect, it may be a barrier to these systems being used in high quality printing applications. The approach used in exemplary embodiments for enhancing MICR capability with SCMB also improves development with standard toners by reducing magnetic brash structure in the development zone 
         [0050]      FIGS. 6A and 6B  show differences between MICR and non-MICR toners.  FIG. 6A  shows an exemplary non-MICR toner, while  FIG. 6B  shows an exemplary MICR toner. 
         [0051]    With the normal SCMB development of  FIG. 6A , development brush electrostatic forces and short range adhesion forces exist between the carrier beads  600  and toners  602 . 
         [0052]    With the MICR SCMB development of  FIG. 6B , brush electrostatic forces and short range adhesion forces exist between the carrier beads  604  and toners  606  plus an added magnetic adhesion force  608 . This added magnetic adhesion force may be expressed as the following equation. 
         [0000]        {dot over (F)}   m ∝∇( m   t   ·{dot over (B)})   
         [0000]    where F m  is the magnetic force between the toners  606  and carriers  604 , m t  is the magnetic moment of toner, and B is the field around the carrier bead  604  caused by the response of beads  604  to external magnetic field H. Because MICR toners have magnetic material in them and the magnetic brush already has a magnetic field in it, the toner tends to stick tighter to the carrier so that the movement of the toner toward the photoreceptor is more difficult. 
         [0053]    In  FIG. 6A , carrier  600  and toner  602  particles are on top of a magnetic brush or roller (not shown) moving towards a photoreceptor  610 . A magnetic component (H)  612  holds the carrier particles  600  with electrostatically attached toner particles  602 , to the roll surface as they move into the vicinity of the photoreceptor  610 . 
         [0054]    In  FIG. 6B , carrier  604  and MICR toner  606  particles are on top of a magnetic brush or roller (not shown) moving towards a photoreceptor  610 . A magnetic field (H)  614  holds the carrier particles  604  with electrostatically and magnetostatically attached MICR toner particles  606 , to the roll surface as they move into the vicinity of the photoreceptor  610 . The MICR toner  606  and carrier particles  604  have both electrostatic and magnetic forces adhering them together because the toner  606  is magnetic. Thus, it is harder for the particles to move off the magnetic brush and onto the photoreceptor  610 . Exemplary embodiments reduce the magnetic field to allow this to occur more easily. Exemplary embodiments change the magnetic field in a way according to  FIGS. 9A and 9B  by, for example, changing the shape of at least one magnet. Other embodiments include lowering the magnetic field in other ways, such as using a different magnet material in the appropriate region. More electrostatic bias is needed to break apart the particles, if the force increases between the toner and the carrier beads. Lowering the magnetic field in a portion of the development zone in the way indicated in  FIGS. 9A and 9B  not only reduces the stickiness of the particles for MICR toner in  FIG. 6B , but also improves image quality by reducing graininess and noise for non-MICR toner. 
         [0055]      FIGS. 7A ,  7 B and  8  show enhancements in the halftone dot size variation and image noise with exemplary embodiments compared to related art.  FIGS. 7A and 7B  show that the effect of the modified magnet is to lowers the magnetic field and thereby to enhance development as well as enhance halftone image quality.  FIG. 8  shows a reduction in image noise using the modified magnetics. 
         [0056]      FIGS. 9A and 9B  illustrate an exemplary embodiment of a magnetic field pattern.  FIG. 9A  shows the tangential magnetic field, while  FIG. 9B  shows the radial magnetic field. The tangential magnetic field of  FIG. 9A  defines a maximum position of the change. The radial position only shows a change from −15 to +15 degrees, but consider the sum of the radial and tangential magnetic fields. Both figures show curves for a standard magnet and a magnet modified according to exemplary embodiments. The lobes in the radial field ( FIG. 9B ) and slight twist in the tangential field ( FIG. 9A ) allow developer transport through the development zone. The lower magnetic field of the modified magnet reduces magnetic forces between MICR toner and carrier in the development zone. Simply lowering the magnetic field throughout the development zone would not be sufficient in a spaced development zone configuration, such as that in  FIGS. 9A and 9B  because the developer would not move through the development zone correctly. 
         [0057]    Together  FIGS. 9A and 9B  illustrate the altered magnetic field vector (i.e., magnitude and direction). The special magnetic field patterning in these figures provides enhanced development and enhanced halftone image quality. The curve for the modified magnet in the development zone (i.e., from about −40 degrees to about 40 degrees in this example) is altered. 
         [0058]    A magnet at the center of the development zone is modified in exemplary embodiments, leaving two regions pre- and post-nip to maintain material transport. This is different from Haze-type development (i.e., low magnetic field zones; see U.S. Pat. No. 4,394,429) in that exemplary embodiments modify the field in only a portion of the development zone and rely on a wrapped geometry to contain the developer particles. This approach used here enables the use of a spaced geometry that is typical for SCMB systems. Prior testing demonstrated the need for two rollers with MICR in SCMB; however, exemplary embodiments may allow a single developer roll for high speed applications. Experimental testing demonstrated low noise and that MICR toners need more development potential applied with SCMB. Thus, MICR printers may print pictorials that require low noise. One exemplary embodiment is a machine using MICR in a print engine that uses SCMB. Another exemplary embodiment is a method for allowing small engines to print high quality output and use MICR. 
         [0059]    It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also, various presently unforeseen or subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.