Abstract:
This disclosure is directed to systems and methods for calibrating, to a higher level of precision, the timing of operation of a bias transfer element in an image forming device. Specifically, the systems and methods are directed to calibrating the timing of forward and reverse biasing in a document processing apparatus to account for myriad mechanical and environmental disturbances.

Description:
BACKGROUND 
       [0001]    This disclosure is directed to systems and methods for recalibrating the timing of operation of a bias transfer element in an image forming device. Specifically, the systems and methods are directed to calibrating the timing of forward and reverse biasing in a document processing apparatus. 
         [0002]    Bias transfer elements directly support the transfer of a developed toner powder image from a photoconductive member. A bias transfer element is an element that uses electric charge to attract or repel a substance. Bias transfer elements may transfer a developed toner powder image from a photoconductive member by creating a charge that attracts the toner from the photoconductive member onto a substrate. The process of attracting a substance toward the bias transfer element may be referred to as forward biasing. Similarly, the process of repelling a substance from the bias transfer element may be referred to as reverse biasing. Forward and reverse biasing the bias transfer element are examples of activating the bias transfer element. Bias transfer elements may include bias transfer rolls (BTRs) and bias transfer belts (BTBs). 
         [0003]    Due to varying electrostatic forces involved with the transfer process, stray toner and debris particles may adhere to the surface of the transfer support member. Consequently, image quality deteriorates. There is a need, therefore, to clean the surface of the transfer support member to prevent degradation of the quality of subsequent copies and/or to prevent toner particles from being fused to, for example, the backside of the final support sheet. Typical cleaning methods include wiping with a brush, a web, a blade, a magnetic brush, or using an airflow, or a combination of these. 
         [0004]    In order to deliver a lower unit manufacturing cost and reduce complexity for office and production markets, cleaning implementation for the bias transfer element may include reverse biasing while using the intermediate transfer belt or photoreceptor belt cleaner to remove toner or contamination. Intermediate transfer belts, photoreceptor belts and photoconductive belts in general are examples of “the belt” described throughout the remainder of this application. One problem associated with the use of reverse biasing in conjunction with the belt cleaner is that the use of reverse biasing involves sensitive timing to reverse bias the belt in inter-document zones, i.e. zones of the belt between transfer regions of the belt, which are those areas designated for image transfer. The reverse bias is applied in the inter-document zones to avoid contamination. The timing is critical to effect cleaning while ensuring that the bias transfer element correctly biases in the transfer regions for transfer of an image to a substrate. With advancing technology, the size of these inter-document zone is decreasing and the speed of the belt is increasing. For example, certain current xerographic image forming systems have inter-document zones of less than 40 mm, with photoreceptor belt or drum speeds of 600 mm per second and higher. As the size of the inter-document zone decreases and the speed of the belt increases, the difficulty with precisely timing the forward and reverse biasing of the bias transfer element to accomplish cleaning becomes particularly acute. 
         [0005]    The changing of an attribute of the belt, or a substrate on the belt, caused by close proximity between an activated bias transfer element and the belt may be referred to as engagement between the bias transfer element and the belt. For example, engagement between the bias transfer element and the belt may cause a change in an amount of charge or toner on the belt. 
         [0006]    Problems associated with the difficulty of precisely timing the forward and reverse biasing of the bias transfer element can be generated from a number of sources. For example, over the life of the image forming device, various mechanical disturbances and other changes due to, for example, normal wear and tear of the machine, may introduce imprecisions and inaccuracies in the timing of activation of forward and reverse biasing. Environmental factors in the vicinity of the image forming device, such as changes in relative humidity and temperature, may separately introduce, or otherwise add to, such imprecisions and inaccuracies in the timing of activation of forward and reverse biasing. Variations in the composition and characteristics of the transfer substrate, such as, for example, noise attributed to paper type, resistivity or flatness, can also introduce or increase errors. The dimensional stability of the various mechanical components of the device, as well as the electrostatic effects of the device, can be adversely affected. As these errors creep into the device&#39;s operation, and the timing of forwarding and reverse biasing begins to drift away from nominal, desired or acceptable values, there is a need to correct or compensate for these errors by recalibrating, to a higher level of precision, the timing of activation of forward and reverse biasing. 
       SUMMARY 
       [0007]    In view of the above shortfalls, it would be advantageous to provide a capability by which a document processing apparatus could automatically detect, with precision, the location on the belt where biasing by the bias transfer element has been applied. The document processing apparatus may then automatically recalibrate the timing of forward and reverse biasing based on the detected previous timing. 
         [0008]    It would be advantageous to have a system and method to allow a document processing apparatus to determine the timing at which the forward and reverse biasing of a bias transfer element is being applied to a belt. It may be desirable to determine the timing for engaging the bias transfer element with or without a substrate for producing a user-requested image. Determining the timing without engaging the bias transfer element with the substrate avoids the unnecessary waste of a substrate, and may also present advantages in terms of more easily detecting the engagement between the bias transfer element and the belt. It is also desirable that the document processing apparatus be able to recalibrate the timing of activating the bias transfer element in real time without halting movement of the belt. 
         [0009]    In various exemplary embodiments, the systems and methods according to this disclosure may provide a capability by which a forward bias is applied by a bias transfer element to a belt. Once the activated bias transfer element is engaged with the belt, an effect caused by the engagement may be analyzed. The effect may be, for example, an edge in a toner patch indicating the change from the drawn toner patch to an approximately bare belt caused by the forward biasing. A timing of the engagement between the bias transfer element and the belt may then be determined based on the analysis. An objective is to learn the timing of engagement between the bias transfer element and the belt, and to then recalibrate the system to a higher level of precision for future timing of activating forward biasing when substrates pass the bias transfer element. 
         [0010]    In various exemplary embodiments, the forward bias may be activated when the bias transfer element is in close proximity to the belt. The activation of forward bias may occur in an inter-document zone or in a transfer zone. The bias transfer element may reverse bias before and after the application of forward bias in order to clean the bias transfer element as discussed below. 
         [0011]    In various exemplary embodiments, toner may be pulled from a belt onto a substrate by forward and reverse biasing the bias transfer element in a transfer zone. An edge at which an amount of toner on the substrate changes may then be sensed. The timing of the engagement between the bias transfer element and the belt may then be determined based on the location of the sensed edge. In this manner, the various error producing effects can be accounted for. Engagement with the bias transfer element may be adjusted to account for, for example, noise associated with paper type, resistivity and/or flatness. 
         [0012]    In various exemplary embodiments, a toner patch may be drawn on a belt in an inter-document zone. An edge may then be sensed at which an amount of toner in the toner patch changes. The timing of the engagement between the bias transfer element and the belt may then be determined based on the location of the sensed edge. 
         [0013]    In various exemplary embodiments, an edge may be sensed at which an amount of charge on the belt changes. The timing of the engagement between the bias transfer element and the belt may then be determined based on the location of the sensed edge. 
         [0014]    These and other features and advantages of the disclosed systems and methods, are described in, or apparent from, the following detailed description of various exemplary embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Various exemplary embodiments of disclosed systems and methods for automatic recalibration, to a higher level of precision, of timing for activation of a bias transfer element will be described, in detail, with reference to the following drawings wherein: 
           [0016]      FIG. 1  illustrates an exemplary document processing apparatus according to this disclosure; 
           [0017]      FIG. 2  illustrates an exemplary engagement between a bias transfer element and a belt; 
           [0018]      FIG. 3  illustrates a first exemplary detection result, including two detected dips, by a sensor system; 
           [0019]      FIG. 4  illustrates a second exemplary detection result, including a first detected dip, by a sensor system; 
           [0020]      FIG. 5  illustrates a third exemplary detection result, including a second detected dip, by a sensor system; 
           [0021]      FIG. 6  illustrates a flowchart of a first exemplary method for recalibrating, to a higher level of precision, a timing for activation of a bias transfer element according to this disclosure; 
           [0022]      FIG. 7  illustrates a flowchart of a second exemplary method for recalibrating, to a higher level of precision, a timing for activation of a bias transfer element according to this disclosure; and 
           [0023]      FIG. 8  illustrates a flowchart of a third exemplary method for recalibrating, to a higher level of precision, a timing for activation of a bias transfer element according to this disclosure. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0024]    The following embodiments illustrate examples of systems and methods for recalibrating the timing of activating a bias transfer element in a document processing apparatus by detecting the timing of engagement between the bias transfer element and a belt. The following description of various exemplary embodiments may refer to one specific type of image forming device, such as, for example, an electrostatic or xerographic image forming device, and discuss various terms related to image production within such an image forming device, for the sake of clarity, and ease of depiction and description. It should be appreciated, however, that, although the systems and methods according to this disclosure may be applicable to such a specific application, the depictions and/or descriptions included in this disclosure are not intended to be limited to any specific application. 
         [0025]    In referring to, for example, image forming devices as this term is to be interpreted in this disclosure, such devices may include, but are not limited to, copiers, printers, scanners, facsimile machines and/or xerographic image forming devices. 
         [0026]      FIG. 1  illustrates an exemplary bias transfer element within a copy transfer section of an electrostatographic imaging device. As noted above, many varieties of bias transfer elements are possible, and this embodiment is exemplary only, Copy substrate  14  is pressed against photoreceptor belt (PR)  10 . Bias transfer roll (BTR)  54  charges the copy substrate sufficiently to urge toner particles to transfer from PR  10  to copy substrate  14 , as discussed below. Upon exiting the transfer section, corotron  56  provides an opposite charge, thereby aiding the detacking of copy substrate  14  from PR  10 . 
         [0027]    PR  10  can alternatively be any charged imaging surface useful in electrostatographic imaging, including such surfaces as photoreceptor drums or electrostatic dielectric surfaces. 
         [0028]    BTR  54  is a bias transfer element, as described above, in the form of a roll. The BTR  54  is positioned in close proximity to the PR  10  so that the copy substrate  14  may pass through a nip formed between the BTR  54  and the PR  10 . As the copy substrate  14  passes the BTR  54 , the BTR  54  may be forward biased to attract a developed toner powder image from the PR  10  onto the copy substrate  14 . At other times, the BTR  54  may be reverse biased to repel any toner or contamination from the BTR  54  onto the PR  10 . The repelled toner or contamination may then be removed by a cleaning mechanism, including cleaning blade  57 . 
         [0029]    Prior to arrival at the BTR  54 , a half-tone image may be developed in a region  11  of PR  10 . The half-tone image may be in any pattern and in any percentage of coverage sufficient for subsequent detection of toner removal when the developed area is subject to forward bias by the BTR  54 , as described below. Area coverage of between about 20 and about 80% would typically be used, and, preferably, area coverage between about 40 and about 60%. 
         [0030]    Region  11  may be placed in any region of PR  10  that is not reserved for transferring an image to a copy substrate. These regions may include inter-document zones, which may be located between document pitches, in skipped pitch areas, or anywhere during PR  10  rotation sequences when no copy output is intended. A preferred area for placement of region  11  is in the seam area of PR  10  since such a seam area is typically not used for imaging purposes due to unreliability of images across the seam. 
         [0031]    An area coverage sensor system  23  may also be provided. For a typical monochrome sensor, this sensor system  23  may be an electronic toner area coverage sensor (ETAC). Such an ETAC will be discussed as an example of sensor system  23 . As shown in  FIG. 1 , sensor system  23  is typically disposed between the corotron station  56  and cleaning blade  57 . ETACs are used in modern printers and copiers to monitor and correct image quality issues by measuring toner darkness at various percentages of imaged coverage. For instance, a printing system may periodically check image quality by developing on the PR  10  half-tone images in inter-document zones at such intensities as 0, 12, 50, 88 and 100% half-tone coverage. Since such half-tone regions occur in inter-document zones, no transfer to copy substrates occurs, and the developed image proceeds on PR  10  past sensor system  23  until removed from PR  10  by cleaning blade (or brush)  57 . 
         [0032]    The exemplary sensor system  23  shown in  FIG. 1  comprises a light source  23   a  and a sensor array  23   b  for detecting light reflected off of the underlying substrate. The wavelength emitted by light source  23   a  is generally selected for optical reflection (or absorption) by the toner being measured. The greater the area of toner coverage, the greater (or lesser) the reflection detected by sensor  23   b.  In the exemplary embodiment shown, sensor  23   b  detects reflected photons by emitting one or more electrons for each photon received. The result is a variable voltage signal with an increase (or decrease) in voltage signifying more (or less) reflected light, which, in turn, indicates greater (or lesser) area coverage by toner. By comparing the actual voltage signal to the signal predicted in response to the percentage of half-tone coverage, processor  221  may be used to determine if the amount of toner actually developed is less than or greater than predicted amounts. The processor  221  may include a memory  222  for storing program instructions for executing all or part of the methods disclosed in this application. In response to variations outside of specified amounts, corrective measures may be undertaken to bring the amount of the developed image within specifications. 
         [0033]    The system of  FIG. 1  may operate in the following manner to provide the recalibration, to a high level of precision, of the timing of BTR activation according to one exemplary embodiment (methods of operation according to this disclosure are also described in detail below with respect to  FIGS. 6-8 ). The system of  FIG. 1  may develop region  11  at a position on PR  10  that is not reserved for transfer of an image to a copy substrate. The system may save information indicating the precise location of the region  11  on the PR  10 . The region  11  may serve as a surrogate for a copy substrate, as discussed below. Prior to the region  11  passing the BTR  54 , the BTR  54  may be reverse biased to repel toner and contamination from the BTR  54  to the PR  10 , thereby cleaning the BTR  54 . The system of  FIG. 1  may estimate the time at which the region  11  will begin to pass the BTR  54 . At the estimated time, the system may control the BTR  54  to stop activation of reverse bias and to begin activation of forward bias. The activation of forward bias will attract toner from the region  11  onto the BTR  54 . When the region  11  completely passes the BTR  54 , toner will cease to be attracted from the region  11  onto the BTR  54 . Thus, if the length of region  11  on the PR  10  is greater than the length of the area on the PR  10  engaging with the BTR  54 , a portion of the toner inside of the region  11  will be removed. 
         [0034]    After passing the BTR  54 , the region  11  may proceed toward the sensor system  23 . The sensor system  23  may detect an amount of toner on the PR  10 . Thus, when the region  11  passes the sensor system  23 , the sensor system  23  may detect a first edge, indicating a change from the bare belt on the PR  10  to the beginning of the region  11 . The sensor system  23  will continue to detect the toner on the region  11  until meeting a second edge, which indicates the point at which the BTR  54  had begun to engage with the PR  10 , thereby removing toner from the region  11 . Thus, the sensor system  23  may detect a second edge indicating a change from toner in the region  11  back to an approximately bare belt. As the region  11  continues to pass the sensor system  23 , the sensor system  23  will continue to detect the approximately bare belt for the length on the PR  10  where the BTR  54  engaged with the PR  10 . At the end of that period, the sensor system  23  may detect a third edge, indicating a return from the approximately bare belt to an indication of toner on the PR  10 . This second indication of toner corresponds to the other end of the region  11  outside of the portion, within the region  11 , where the BTR  54  engaged with the PR  10 . The sensor system  23  will continue to detect toner from the region  11  until detecting a fourth edge, indicating a change from toner to the bare belt. The fourth edge indicates the end of the region  11 . In this manner, the sensor system  23  measures a signal on the PR  10  when running without and with substrates present. Separately, there may be a sensor  21  used in the paper path from which an inverse signal may be measured from the substrate when present. There may also be instances when an entire image (region  11 ) is transferred to BTR  54  and then in absence of substrate subsequently passed through a transfer nip again in contact with PR  10  with reverse biasing pulsed at different levels to push toner back onto PR  10  for analysis with an ETACS sensor. In this way, timing necessary for reverse biasing can potentially be ensured across BTR  54  length variation to ensure timing for a cleaning cycle to be completed, or otherwise to evaluate timing of pushing toner off the BTR  54  for comparison against analysis of instances when toner is pushed off the PR  10 . 
         [0035]    The above discussed operation of the system of  FIG. 1  allows the system to recalibrate, to a higher level of precision, the timing of activation of the BTR  54 , in the following manner. The system of  FIG. 1  may use the region  11  as a surrogate for a copy substrate. By detecting the precise timing at which the BTR  54  engages with the region  11 , the system may calculate the timing at which the BTR  54  would engage with a copy substrate corresponding to the region  11 . The system may then analyze the edges detected by the sensor system  23  to determine whether those edges are within specifications. The specifications may be formed to ensure that the BTR  54  would be forward biased only while a copy substrate passes the BTR  54 , and not when a copy substrate is not present beneath the BTR  54 . Similarly, the specifications may ensure that the BTR  54  would only be reverse biased when a copy substrate is not present beneath the BTR  54 . By ensuring that the BTR  54  only applies forward bias when the copy substrate is present, the system can ensure that the BTR  54  does not attract excess or unnecessary toner or contamination from the PR  10  onto the BTR  54 . Similarly, by ensuring that the BTR  54  only applies reverse bias when a copy substrate is not present beneath the BTR  54 , the system can ensure that no toner or contamination is repelled onto the backside of a copy substrate. 
         [0036]    The specifications indicating that the edges detected by the sensor system are desirable, or within acceptable values, may be based on testing a machine operating within acceptable conditions. The machine operating within acceptable conditions may be used to draw and analyze a region, such as region  11 , as discussed above, and also to draw an image on a copy substrate. The system may correlate the detected edges in the region with the timing of activating the BTR  54 . The specifications may indicate acceptable values for the detected edges in the region correlating with acceptable image output on the copy substrate. For example, if the image drawn on the copy substrate is shifted slightly from a desirable location, then the edges detected by the sensor system  23  may be correspondingly shifted to determine the specification values. It should be noted that the specific parameter measured may be dependent on the type and placement of the sensor. As a non-limiting example, measuring substrate shift may be accomplished when monitoring PR  10  with sensor system  23 . Differently, for substrate monitoring with sensor  21  along the paper path, it may be more appropriate or advantageous to measure size of a transferred zone. 
         [0037]    During operation, the timing of operation of the BTR  54  may gradually, or otherwise, decrease in precision and accuracy. Accordingly, the system may, in real time or otherwise, develop a region  11  and pass the region  11  past the BTR  54  and sensor system  23 , as discussed above, detecting edges corresponding to engagement between the BTR  54  and the belt. The system may then recalibrate, to a higher level of precision, the timing of activation of the BTR  54  based on the detected edges. 
         [0038]      FIG. 2  illustrates how the region  11  may pass under the BTR  54  as the PR  10  moves toward the area coverage sensor system  23 . As the region  11  passes the BTR  54 , processor  221  instructs the BTR  54  to activate forward bias, thereby attracting toner from the region  11  onto the BTR  54 . Before and after activating the forward bias as the region  11  passes the BTR  54 , processor  221  may instruct the BTR  54  to activate reverse bias. The reverse bias cleans the BTR  54  by repelling toner back from the BTR  54  onto the PR  10  so that toner or contamination repelled from the BTR  54  to the PR  10  may then be removed from the PR  10  by the cleaning blade  57 , or any other cleaning mechanism for the PR  10 . 
         [0039]    The region  11  may be larger than a region of the PR  10  over which the BTR  54  engages with the PR  10 . By using a larger region  11 , processor  221  may detect both the beginning and the end of the engagement, within the region  11 , between the BTR  54  and the PR  10 . 
         [0040]      FIG. 3  illustrates an ETAC voltage signal corresponding to the engagement between the forward biased BTR  54  and the PR  10 . The ETAC voltage is graphed versus time. The time dimension, in turn, corresponds to the distance of travel of PR  10  when the PR  10  is in motion at a constant rate as it is during imaging cycles. It should be noted that  FIGS. 3 ,  4  and  5  are idealized graphs because actual measurements show continually varying voltages with steep slopes conforming to the step functions indicated in the idealized graphs. 
         [0041]    The ETAC curve in  FIG. 3  shows how the influence of the BTR  54  is detected in the middle of the region  11 . Before time T 1 , the sensor system  23  detects a value of V1 volts, which corresponds to a bare belt. At T 1 , the sensor system  23  detects approximately V2 volts because the beginning of the region  11  begins to pass the sensor system  23 . The sensor system  23  detects approximately V2 volts until the time T 2 , at which point the sensor system  23  detects approximately V1 volts again. The sensor system  23  begins to detect about V1 volts again at time T 2 , indicating the beginning of the engagement between the BTR  54  and the PR  10 . The sensor system  23  detects about V1 volts at time T 2 , because the forward biased BTR  54  removed substantially all of the toner from that portion of the region  11 , so that the portion of the region  11  returned to an approximately bare belt state. The sensor system  23  may not detect the full V1 volts between the times T 2  and T 3 , however, as in times before T 1  and after T 4 , because the BTR  54  may fail to remove 100% of the toner from the patch  11 . Accordingly, the sensor system  23  may only detect approximately V1 volts, or a similar value lower than V1, between T 2  and T 3 . 
         [0042]    The value V1 may be about 3.5 volts and the value V2 may be about 1.5 volts, but the disclosed system is not limited to systems detecting those values. Rather, the disclosed system may recalibrate timing of activation of forward bias by the BTR  54 , if the processor  221  can detect any significant difference between the portions of the region  11  where the BTR  54  engages with the PR  10  (e.g., between T 2  and T 3 ) and portions of the region  11  where the BTR  54  does not engage with the PR  10  (e.g., between T 1  and T 2  and between T 3  and T 4 ). 
         [0043]    Between T 2  and T 3 , the sensor system  23  continues to detect approximately V1 volts. That period between T 2  and T 3  corresponds to the engagement between the BTR  54  and the PR  10 . At T 3 , sensor system  23  detects about V2 volts again, indicating the end of engagement between the BTR  54  and the PR  10 . The sensor system  23  continues to detect about V2 volts, indicating the toner patch drawn in the region  11 , until the end of the region  11  arrives at T 4 . At T 4 , the entire region  11  has passed the sensor system  23 . The sensor system  23  then detects about V1 volts corresponding to the bare belt. 
         [0044]      FIG. 4  shows how the sensor system  23  may detect a beginning, but not an end, of the engagement between the BTR  54  and the PR  10 . As in  FIG. 3 , the sensor system  23  in  FIG. 4  detects a dip between times T 1  and T 2 . At T 1 , the sensor system  23  ceases to detect the bare belt at V1 volts and begins to detect the toner patch drawn in the region  11 . At T 2 , the sensor system  23  ceases to detect the toner in the region  11 , and begins to detect an approximately bare belt at about V1 volts, because the BTR  54  has begun to remove the toner from the region  11 . 
         [0045]    Unlike the situation in  FIG. 3 , however, the end of the region  11  at T 3  does not occur after the end of engagement between the BTR  54  and the PR  10 . The BTR  54  continues to be forward biased, thereby removing any toner from the PR  10 , including toner in the region  11 , up to T 4 . Because toner was only drawn in the region  11 , which ends at T 3 , no second dip is detected in  FIG. 4 , as was detected between times T 3  and T 4  in  FIG. 3 . Thus, the sensor system  23  does not detect the end of the engagement between the BTR  54  and the PR  10 . 
         [0046]      FIG. 5  shows a situation similar to that shown in  FIG. 4 , except that in  FIG. 5 , the sensor system  23  does not detect the beginning of the engagement between the BTR  54  and the PR  10 . The sensor system  23  only detects the second dip between times T 3  and T 4 , but does not detect any first dip between times T 1  and T 2 , for reasons similar to those discussed with respect to  FIG. 4 . Because the situation in  FIG. 5  is similar to that shown in  FIG. 4 , but in reverse, further description is omitted. 
         [0047]    Referring again to  FIG. 1 , signals from sensor system  23  are typically analog voltage signals. In order to be read by many computers, such signals are first converted to digital signals by an analog-to-digital converter  24 . Even if sensor system  23  signals are digital, some data conversion device may be used to convert the signals into a form readable by processor  221 . Once converted, signals are sent to processor  221 . Processor  221  also receives data from drive device  220  indicating the timing of activation and deactivation signals. Using signals such as those shown in  FIGS. 3-5 , processor  221  can determine the relationship between the timing of activation and deactivation signals given to drive device  220  and the timing of BTR  54  engagement with and disengagement from PR  10 . One embodiment for determining such relationships and making appropriate adjustments to the timing of activation and deactivation signals is shown in  FIG. 6 . 
         [0048]    As shown in  FIG. 6 , operation of the method commences at step S 600  upon the occurrence of an event. The event may be based on a lapsed machine run time, number of imaging cycles, calendar time, or any similarly counted event. Commencement of the method may also be initiated by detected events related to machine performance or maintenance such as replacement of the BTR, photoreceptor or other component affecting BTR timing or by detection of imaging defects, including defects caused by faulty timing of BTR engagement or disengagement. Regardless of how the sequence commences, operation of the method proceeds to step S 605 . 
         [0049]    In step S 605 , the system is directed to draw a half-tone selected region, such as region  11 , on a PR. After drawing the toner patch on the region, operation of the method proceeds to step S 610 . 
         [0050]    In step S 610 , the BTR is activated at an estimated time for engagement with the region. The BTR may be activated by providing a signal to activate the drive device  220 . The signal may be given by the processor  221  or by another processor. Operation of the method proceeds to step S 615 . 
         [0051]    In step S 615 , a sensor system detects the amount of toner in the region on the PR. Operation of the method proceeds to step S 620 . 
         [0052]    In step S 620 , a processor determines the width of the region based on an analysis of the detection signal from the sensor system. Operation of the method proceeds to step S 625 . 
         [0053]    Step S 625  is a determination step in which a determination is made whether the detection signal from the sensor system shows that the BTR engagement with the PR is within specifications. 
         [0054]    If in step S 625  it is determined that BTR engagement is not within specifications, operation of the method proceeds to step S 630 . 
         [0055]    In step S 630 , the timing of BTR activation is recalibrated based on the detection signal from the sensor system. For example, if the sensor system detects edges in the region that are shifted from nominal, desired or acceptable positions, the system may accordingly shift the timing of activation of forward bias by the BTR so that, in future operations, the edges will be within specifications. Operation of the method proceeds to step S 635 . 
         [0056]    In step S 635 , the BTR may be cleaned. From step S 635 , the method returns to step S 605 . The method may return to step S 605  to run another region past the BTR and the sensor system to confirm that the system is now operating within specifications. Alternatively, if the recalibration process is sufficiently accurate, the recalibration process may be performed once with confidence, without returning to step S 605  to confirm that the system is now operating within specifications. That is, the system can return from step S 630  to step S 640 , thereby assuming that the system is now operating within specifications. 
         [0057]    If in step S 625  it is determined that the BTR engagement is within specifications, operation of the method proceeds to step S 640 . 
         [0058]    In step S 640 , the BTR is cleaned. The BTR may be cleaned by having the BTR engage in reverse biasing, which repels any toner or contamination from the BTR to the PR. Operation of the method proceeds to step S 645  where operation of the method ceases. 
         [0059]      FIG. 7  shows another exemplary embodiment for recalibrating the timing of BTR activation. Like the method shown in  FIG. 6 , the method in  FIG. 7  may measure an effect of engaging the BTR in a region on the PR within an inter-document zone. Unlike the method in  FIG. 6 , however, the method in  FIG. 7  may not draw a toner patch in the region  11 . Rather, the method in  FIG. 7  detects a change in charge in the region on the PR caused by the BTR. Accordingly, the method of  FIG. 7  uses an electrostatic voltage sensor (ESV)  25 , as shown in  FIG. 1 , to detect the change in charge in the region on the PR. Operation of a corotron station, such as corotron station  56 , may be halted as the region passes from the BTR toward the ESV, so to not interfere with the detection of the charge on the PR. 
         [0060]    The method shown in  FIG. 7  is similar to the method shown in  FIG. 6  so that elements in  FIG. 7  correspond to like elements in  FIG. 6  (e.g., element S 700  in  FIG. 7  corresponds to element S 600  in  FIG. 6 ). Unlike  FIG. 6 , however, the method in  FIG. 7  does not include a step S 705  of drawing the toner patch in the region  11 . Accordingly, the method of  FIG. 7  also does not include steps of cleaning the BTR  54  after forward biasing, as in steps S 635  and S 640  of  FIG. 6 . Further, because the system of  FIG. 7  is based on the ESV sensor  25 , and not an ETAC sensor, step S 715 , S 720 , S 725  and S 730  are based on ESV sensor  25  and not an ETAC sensor. 
         [0061]    As shown in  FIG. 7 , operation of the method commences at step S 700  upon the occurrence of an event. The event may be based on a lapsed machine run time, number of imaging cycles, calendar time, or any similarly counted event, as discussed above regarding  FIG. 6 . Regardless of how the sequence commences, operation of the method proceeds to step S 710 . 
         [0062]    In step S 710 , the BTR is activated at an estimated time for engagement with the region. The BTR may be activated by providing a signal to activate the drive device  220 . The signal may be given by the processor  221  or by another processor. Operation of the method proceeds to step S 715 . 
         [0063]    In step S 715 , an ESV detects the amount of charge in the region on the PR. Operation of the method proceeds to step S 720 . 
         [0064]    In step S 720 , a processor determines the width of the region based on an analysis of the detection signal from the ESV. The determination may be made by detecting a change in charge on the PR from a portion of the PR where the BTR did not engage with the PR to a portion of the PR where the BTR did engage with the BTR (and/or vice-versa). Operation of the method proceeds to step S 725 . 
         [0065]    Step S 725  is a determination step in which a determination is made whether the detection signal from the ESV shows that the BTR engagement with the PR is within specifications. 
         [0066]    If in step S 725  it is determined that BTR engagement is not within specifications, operation of the method proceeds to step S 730 . 
         [0067]    In step S 730 , the timing of BTR activation is recalibrated based on the detection signal from the ESV. For example, if the ESV detects edges in the region that are shifted from nominal, desired or acceptable positions, the system may accordingly shift the timing of activation of forward bias by the BTR so that, in future operation, the edges will be within specifications. Operation of the method proceeds to step S 710 . 
         [0068]    If in step S 725  it is determined that the BTR engagement is within specifications, operation of the method proceeds to step S 745 , where operation of the method ceases. 
         [0069]      FIG. 8  shows another exemplary embodiment of recalibrating the timing of BTR activation. The method of  FIG. 8  is similar to the method in  FIG. 6 , so that elements in  FIG. 8  correspond to like elements in  FIG. 6 . Unlike the system in  FIG. 6 , however, the system of  FIG. 8  is based on detection of toner drawn on a substrate (e.g., paper) in a transfer zone, rather than based on detection of an amount of toner drawn on a region of the PR in an inter-document zone. The system may use the sensor system  21  shown in  FIG. 1 . The sensor may be placed anywhere along the paper path where the substrate passes after engagement with the BTR. Accordingly, the detection referenced in steps S 815 , S 820 , S 825  and S 830  may occur using the sensor system  21 . 
         [0070]    As shown in  FIG. 8 , operation of the method commences at step S 800  upon the occurrence of an event. The event may be based on a lapsed machine run time, number of imaging cycles, calendar time, or any similarly counted event, as discussed above regarding  FIGS. 6 and 7 . Regardless of how the sequence commences, operation of the method proceeds to step S 805 . 
         [0071]    In step S 805 , the system is directed to draw a half-tone selected region on a substrate such a paper. After drawing the toner patch on the region of the substrate, operation of the method proceeds to step S 810 . 
         [0072]    In step S 810 , the BTR is activated at an estimated time for engagement with the region. The BTR may be activated by providing a signal to activate the drive device  220 . The signal may be given by the processor  221  or by another processor. Operation of the method proceeds to step S 815 . 
         [0073]    In step S 815 , a sensor system detects the amount of toner in the region on the substrate. Operation of the method proceeds to step S 820 . 
         [0074]    In step S 820 , a processor determines the width of the region based on an analysis of the detection signal from the sensor system. Operation of the method proceeds to step S 825 . 
         [0075]    Step S 825  is a determination step in which a determination is made whether the detection signal from the sensor system shows that the BTR  54  engagement with the PR  10  is within specifications. 
         [0076]    If in step S 825  it is determined that BTR engagement is not within specifications, operation of the method proceeds to step S 830 . 
         [0077]    In step S 830 , the timing of BTR activation is recalibrated based on the detection signal from the sensor system. For example, if the sensor system detects edges in the region that are shifted from nominal, desired or acceptable positions, the system may accordingly shift the timing of activation of forward bias by the BTR so that, in future operation, the edges will be within specifications. Operation of the method proceeds to step S 835 . 
         [0078]    In step S 835 , the BTR may be cleaned. From step S 835 , the method returns to step S 805 . Alternatively, the method may proceed to step S 840 , thereby assuming that the system is now operating within specifications, as discussed above regarding  FIG. 6 . 
         [0079]    If in step S 825  it is determined that the BTR engagement is within specifications, operation of the method proceeds to step S 840 . 
         [0080]    In step S 840 , the BTR is cleaned. The BTR may be cleaned by having the BTR engage in reverse biasing, which repels any toner or contamination from the BTR to the PR. Operation of the method proceeds to step S 845  where operation of the method ceases. 
         [0081]    It should be appreciated that although depicted as the PR  10  in  FIG. 1 , this disclosure contemplates systems in which, instead of, or in addition to, the PR  10 , any photoconductor for transporting an image, including an intermediate transfer belt, may be used. Further, although depicted as the BTR  54  in  FIG. 1 , any biasing element that may attract toner by forward biasing and/or repel toner by reverse biasing may be used, including a bias transfer belt. Further, although the system of  FIG. 1  shows engagement between the PR  10  and BTR  54  where an image may be transferred to a substrate, it is not necessary that the interaction occur along a path where a substrate passes. Rather, the interaction between the belt and bias transfer element may occur at a point where an image transfers from one belt to another belt, without the use of a substrate (e.g., from the PR  10  to an intermediate transfer belt). 
         [0082]    Any of the data or programs depicted, or alternately described above, including those stored in memory  222 , may be implemented using an appropriate combination of alterable, volatile or non-volatile memory, or non-alterable, or fixed, memory. The alterable memory, whether volatile or non-volatile, may be implemented using one or more of static or dynamic RAM, or for example, any computer-readable type media and compatible media reader, a hard drive, a flash memory, or any other like memory medium and/or device. Similarly, the non-alterable or fixed memory may be implemented using any one or more of ROM, PROM, EPROM, EEPROM, optical or OM disk such as, for example, CD ROM, DVD ROM, or other disk-type media and compatible disk drive, or any other like memory storage medium and/or device. 
         [0083]    It should be appreciated that, given the appropriate inputs, including, but not be limited to, appropriate memories, as generally described above, and/or inputs regarding control of the various elements in the system of  FIG. 1  by the processor  221 , software algorithms, hardware/firmware circuits, or any combination of software, hardware, and/or firmware control elements may be used to implement the methods shown in  FIGS. 6-8 , for example. 
         [0084]    The computations for establishing the timing of when the bias transfer element engages with the belt and for recalibrating timing of activating the bias transfer element based on the determined timing of the engagement, may be implemented with a circuit in an image processing apparatus itself. Alternatively, such computations may be performed on a programmable general purpose computer, a special purpose computer, a programmed microprocessor or microcontroller, or some form of digital signal processor, peripheral integrated circuit element ASIC or other integrated circuit, or hard-wired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FGPA or PAL or the like, or may even be manipulated through manual adjustment of one or more of the operating parameters, or coefficients that may be associated with one or more of the operating parameters. 
         [0085]    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 unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, and are also intended to be encompassed by the following claims.