Abstract:
A method increases the ability of a controller in a printer to detect weak or missing inkjets in the printer. The method includes generating a test pattern having at least twice as much ink as a typical test pattern used to detect weak or missing inkjets. The increased ink appropriately stresses inkjets to facilitate detection of weak or missing inkjets and the test pattern is transferred to media and removed from the printer to preserve the capacity of a drum maintenance unit to store residual ink removed from an imaging drum or belt.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to devices that produce ink images on media, and more particularly, to devices that that eject ink from inkjets to form ink images. 
       BACKGROUND 
       [0002]    Inkjet imaging devices eject liquid ink from printheads to form images on an image receiving member. The printheads include a plurality of inkjets that are arranged in some type of array. Each inkjet has a thermal or piezoelectric actuator that is coupled to a printhead controller. The printhead controller generates firing signals that correspond to digital data for images. The frequency and amplitude of the firing signals correspond to the selective activation of the printhead actuators. The printhead actuators respond to the firing signals by ejecting ink drops onto an image receiving member to form an ink image that corresponds to the digital image used to generate the firing signals. 
         [0003]    Throughout the life cycle of these inkjet imaging devices, the image generating ability of the device requires evaluation and, if the images contain detectable errors, correction. Missing inkjets or weak inkjets are an error condition that affects ink image quality. A missing inkjet is an inkjet that does not eject an ink drop in response to a firing signal. A weak inkjet is an inkjet that responds intermittently to a firing signal or that responds by ejecting ink drops having a mass that is less than the ink drop mass corresponding to the characteristics of the firing signal for the inkjet. Systems and methods have been developed that compensate for missing or weak inkjets, but the missing or weak inkjets must be detected before these systems and methods can be activated. 
         [0004]    Current detection methods include a test pattern being formed on an image receiving member and then digital data of the test pattern on the surface are generated. In an offset imaging device, the image receiving member is a rotating drum or belt. The digital data are produced by illuminating the drum or belt surface and generating an electrical signal that corresponds to the intensity of the light reflected from the surface. The signal is generated by an electro-optical sensor that is positioned to receive light reflected from a small portion of the drum or belt surface. By arranging a plurality of electro-optical sensors across the width of the drum or belt, the entire width can be used to generate reflected light received by the electro-optical sensors. The responses of the electro-optical sensors produce a digital image corresponding to the ink image on the drum or belt. The ink drops on the surface reflect light at an intensity that is different than the positions on the surface that do not have ink. 
         [0005]    Evaluating a digital image produced by illuminating an image drum or belt can be difficult because the surface may generate noise in the digital image. Detecting the portion of the image data corresponding to ink on the drum or belt is made more difficult by the amount of ink in the test pattern. The amount of ink in test patterns is deliberately kept small since the test pattern is wiped from the drum or belt and the ink is collected by a drum maintenance unit. The drum maintenance unit includes a supply of release agent, an applicator, and a wiper. The wiper is selectively moved into and out of engagement with the image drum or belt to remove residual ink and other debris from the drum surface. The removed release agent, ink, and debris are directed to a sump within the drum maintenance unit. Because the capacity of the sump in the drum maintenance unit is relatively small, test patterns are printed with small amounts of ink. Testing has shown, however, that certain jetting failure mechanisms can only be seen repeatedly when a larger amount of ink is flowed through the failed inkjet. For example, some internal contamination particles can be suspended in the ink within the inkjet. Sometimes, a larger amount of ink must flow through the inkjet to move these suspended particles into the aperture to block the flow. Other mechanisms may be more complex, such as contaminates partially hanging out of a jet, physical aperture defects, and/or insufficient anti-wetting coatings. These mechanisms can exhibit the same behavior in that the inkjet can work correctly when a small amount of ink is ejected, but can fail when used at a higher duty cycle with a larger amount of jetted ink mass. Consequently, the failed inkjet ejection process and/or the image processing required for detection of the actual number of failed inkjets can be significant and still be susceptible to error. Improving the ability of inkjet imaging systems to detect missing and weak inkjets in an inkjet imaging system remains important to such systems. 
       SUMMARY 
       [0006]    A method improves the detection of weak or missing inkjets in an inkjet printer. The method includes detecting a first number of missing inkjets identified with reference to a first test pattern is less than an actual number of missing inkjets in the inkjet printer, operating each inkjet in at least one printhead in the printer at a frequency to generate a second test pattern in a process direction on a rotating image receiving member with each inkjet being operated to eject at least twice as much ink in the second test pattern than each inkjet ejected to form the first test pattern, generating a digital image of the second test pattern on the image receiving member from light reflected by the second test pattern and the image receiving member to a plurality of light sensors linearly arranged on a first support member that is transverse to the process direction, detecting a second number of missing inkjets with reference to the generated digital image of the second test pattern, and storing an identification of the missing inkjets in the second number of missing inkjets that are not in the first number of missing inkjets detected with reference to the first test pattern to enable a controller to distribute image data corresponding to the missing inkjets in the second number of missing inkjets to operable inkjets in the printer. 
         [0007]    Another method improves the detection of weak or missing inkjets in an inkjet printer. The other method includes operating each inkjet in at least one printhead in the printer at a frequency to generate a second test pattern in a process direction on a rotating image receiving member with each inkjet being operated to eject at least twice as much ink in the second test pattern than each inkjet ejected in a first test pattern, generating a digital image of the second test pattern on the image receiving member from light reflected by the second test pattern and the image receiving member to a plurality of light sensors linearly arranged on a support member that is transverse to the process direction, transferring the second test pattern from the rotating image receiving member to a media sheet, and operating a media transport to deliver the media sheet to a discharge area. 
         [0008]    A printer implements the method to improve detection of missing and weak inkjets in an inkjet printer. The printer includes an image generator having a plurality of light sensors linearly arranged along a first support member that is transverse to a process direction of a rotating image receiving member, the plurality of light sensors configured to generate a digital image of ink images on the rotating image receiving member from light reflected by the ink images on the rotating image receiving member, a plurality of printheads operatively connected to a second support member to position the printheads in the plurality of printheads across a width of the rotating image receiving member, an actuator coupled to the second support member, the actuator being configured to move the second support member transversely to the process direction to move the printheads in a cross-process direction across the width of the rotating image receiving member, and a controller operatively connected to the image generator, the plurality of printheads, and the actuator, the controller configured to operate the printheads in the plurality of printheads to form a first test pattern on the rotating image receiving member and to operate the printheads in the plurality of printheads to form a second test pattern on the rotating image receiving member, the second test pattern having at least twice as much ink as the first test pattern. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The foregoing aspects and other features of a system and method that improve detection of missing and weak inkjets in inkjet printers are explained in the following description, taken in connection with the accompanying drawings. 
           [0010]      FIG. 1  is a test pattern for use with an improved missing inkjet detection method as disclosed herein. 
           [0011]      FIG. 2  is another test pattern for use with the improved missing inkjet detection method. 
           [0012]      FIG. 3  is a flow diagram of the improved process for detecting missing inkjets from digital images of test patterns on image receiving members. 
           [0013]      FIG. 4  is a block diagram of a prior art inkjet printing system in which the improved missing inkjet detection method may be used. 
           [0014]      FIG. 5  is a schematic diagram of a printer depicting the components operated by a controller to improve identification of missing inkjets from digital images of test patterns on image receiving members. 
           [0015]      FIG. 6  is a portion of a test pattern useful for detecting missing inkjets. 
           [0016]      FIG. 7A  is a portion of a digital image of a test pattern having evidence of a weak inkjet. 
           [0017]      FIG. 7B  is a profile of the data shown in the image of  FIG. 7A . 
           [0018]      FIG. 8A  is a portion of a digital image of a test pattern having evidence of a missing inkjet. 
           [0019]      FIG. 8B  is a profile of the data shown in the image of  FIG. 8A . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. As used herein, the word “printer” encompasses any apparatus that produces ink images on media, such as a digital copier, bookmaking machine, facsimile machine, a multi-function machine, or the like. As used herein, the term “process direction” refers to a direction of travel of an image receiving member, such as an imaging drum or print medium, and the term “cross-process direction” is a direction that is perpendicular to the process direction along the surface of the image receiving member. Also, the description presented below is directed to a system for operating an inkjet printer to print test patterns on an image drum or belt that more reliably enable missing inkjet detection. The reader should also appreciate that the principles set forth in this description are applicable to similar test pattern generators and digital image analyzers that may be adapted for use in any imaging device that generates images with dots of marking material. 
         [0021]    As shown in  FIG. 4 , a particular printer  10  includes a frame  11  to which are mounted directly or indirectly all of the operating subsystems and components of the printer  10 , as described below. The printer  10  further includes a rotating intermediate image receiving member  12  that has an imaging surface  14  movable in the direction  16 , and on which phase change ink images are formed. A transfix roller  19  rotatable in the direction  17  is loaded against the surface  14  of image receiving member  12  to form a nip  18 , within which ink images formed on the surface  14  are transfixed onto a heated media sheet  49 . 
         [0022]    The printer  10  also includes a phase change ink delivery system  20  that has at least one source  22  of one color phase change ink in solid form. The printer  10  shown is a multicolor image producing machine. The ink delivery system  20  includes four (4) sources  22 ,  24 ,  26 ,  28 , representing four (4) different colors CMYK (cyan, magenta, yellow, black) of phase change inks. The ink delivery system  20  also includes a melting and control apparatus (not shown) for melting or phase changing the solid form of the phase change ink into a liquid form. The phase change ink delivery system is suitable for supplying the liquid form to a printhead system  30  including at least one printhead assembly  32 . The printer  10  shown is a wide format high-speed, or high throughput, multicolor image producing machine. The printhead system  30  includes multiple multicolor ink printhead assemblies  32 ,  34 . In the embodiment illustrated, each printhead assembly includes a plurality of independent printheads. 
         [0023]    As further shown, the printer  10  includes a substrate supply and handling system  40 . The substrate supply and handling system  40 , for example, can include sheet or substrate supply sources  42 ,  44 ,  48 , of which supply source  48 , for example, is a high capacity paper supply or feeder for storing and supplying image receiving substrates in the form of cut media sheets  49 , for example. The substrate supply and handling system  40  also includes a substrate handling and treatment system  50  that has a substrate heater or pre-heater assembly  52 . The substrate supply and handling system  40  further includes a media transport  54 , such as media transport rollers, for moving media  49  through the printer  10  from the supply sources  42 ,  44 ,  48  to a discharge area  56 . The printer  10  as shown can also include an original document feeder  70  that has a document holding tray  72 , document sheet feeding and retrieval devices  74 , and a document exposure and scanning system  76 . 
         [0024]    Operation and control of the various subsystems, components, and functions of the printer  10  are performed with the aid of a controller  80 . The controller  80 , for example, is a self-contained, dedicated mini-computer having a central processor unit (CPU)  82  with electronic storage  84 , and a display or user interface (UI)  86 . The controller  80 , for example, includes a sensor input and control circuit  88  as well as a pixel placement and control circuit  89 . In addition, the CPU  82  reads, captures, prepares, and manages the image data flow between image input sources, such as the scanning system  76 , or an online or a work station connection  90 , and the printhead assemblies  32 ,  34 . As such, the controller  80  is the main multi-tasking processor for operating and controlling all of the other printer subsystems and functions. 
         [0025]    The printer controller  80  further includes memory storage for data and programmed instructions. The controller  80  may be implemented with general or specialized programmable processors that execute programmed instructions. The instructions and data required to perform the programmed functions can be stored in memory associated with the processors or controllers. The processors, their memories, and interface circuitry configure the controllers to perform the functions, such as the test pattern generation and the digital image analysis, described more fully below. These components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits may be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in VLSI circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits. 
         [0026]    Referring to  FIG. 5 , a schematic diagram of the printer  10  depicting the components operated by the controller  80  to identify missing and weak inkjets from a test pattern image on the image receiving member  12  is shown. The printhead assembly  32  includes four printheads  35 ,  36 ,  37 ,  38 . Typically, each of these printheads ejects ink, indicated by arrow  43 , to form an image on the image receiving member  12 . The four printheads are arranged in a two by two matrix with the printheads in one row being staggered with reference to the printheads in the other row. Although the embodiment shown depicts a printhead assembly having four printheads, solid ink printers can have one or any number of any size printheads arranged in any practical manner. 
         [0027]    Referring to  FIGS. 4 and 5 , the printheads  35 ,  36 ,  37 ,  38  of the printhead assembly  32  are operatively connected to a second support member  33  to position the printheads across a width of the image receiving member  12  that extends in the cross-process direction. To permit movement of the printheads  35 ,  36 ,  37 ,  38  across the image receiving member  12 , the printer  10  further includes a second actuator  41  coupled to the second support member  33 . The second actuator  41  is configured to move the second support member  33  transversely to the process direction to move the printheads in a cross-process direction across the width of the image receiving member  12 . 
         [0028]    The rotating intermediate image receiving member  12  can be a rotating drum, as shown in the figures, belt, or other substrate for receiving ink ejected from the printheads. Alternatively, the printheads can eject ink onto cut or continuous media  49  moving along a path adjacent to the printheads. To rotate or otherwise move the image receiving member  12 , the printer  10  further includes an actuator  96  coupled to the image receiving member  12 . Controlled firing of the inkjets in the printheads  35 ,  36 ,  37 ,  38  in synchronization with the rotation of the image receiving member  12  enables the formation of a single continuous horizontal bar across the width of the image receiving member  12 . When occurring in synchronization with multiple consecutive rotations of the image receiving member  12 , controlled firing of the inkjets and controlled actuation of the printhead assembly  32  in the cross-process direction enable a single inkjet to form a single continuous horizontal bar over different portions of the image receiving member  12 . Similarly, controlled firing of the inkjets at a given frequency without actuation of the printhead assembly  32  enables a single inkjet to form a single continuous vertical bar extending in the process direction. Depending on the rotational speed of the image receiving member  12  and the firing frequency capability of the printheads, the vertical line can be formed in a single rotation of the image receiving member  12  or in multiple consecutive rotations of the image receiving member  12 . 
         [0029]    Referring still to  FIGS. 4 and 5 , the printer  10  also includes an image generator  94  to form a digital image of the ink image on the image receiving member  12 . The image generator  94  includes a light source  58  for illuminating the image receiving member  12  and a plurality of electro-optical sensors  59 . Each sensor  59  generates an electrical signal having an amplitude that corresponds to the intensity of the reflected light received by the sensor  59 . These signals form the digital image of the ink image on the image receiving member  12 . In one embodiment, the electro-optical sensors  59  are implemented in an integrated circuit. Each integrated circuit provides 432 electro-optical sensors  59 . The image generator  94  has twelve integrated circuits that are linearly arranged in the cross-process direction to generate the digital image of the imaging member. 
         [0030]    The light source  58  and electro-optical sensors  59  of the image generator  94  are operatively mounted to a first support member  60 . In one embodiment, the first support member  60  is mounted on a bar  64  for reciprocating movement across the image receiving member  12  in the cross-process direction. In this embodiment, a first actuator  68 , such as an electrical motor, is coupled to the first support member  60 , through gear trains, translational, or rotational linkages or the like to move the first support member of the image generator  94  across the image receiving member  12  in response to a signal from the controller  80 . The first actuator  68  is configured to respond to signals from the controller  50 . Although the first support member  60  of this embodiment is configured for reciprocating movement across the image receiving member  12 , other embodiments may use a fixed first support member. 
         [0031]    Referring to  FIG. 5 , the controller  80  is coupled to the printhead assembly  32 , the image receiving member  12 , and the image generator  94  to synchronize the operation of these subsystems. To generate an image, the controller renders a digital image in a memory and generates inkjet firing signals and printhead actuation profiles from the digital image. The firing signals are delivered to the printheads  35 ,  36 ,  37 ,  38  in the assembly  32  to operate the inkjets to eject ink selectively. The actuation profiles are delivered to the second actuator  41  to control movement of the printhead assembly  32  in the cross-process direction. The controller  80  is coupled to the image receiving member  12  to control the rate and direction of rotation of the image receiving member  12 . The controller  80  also generates signals to activate the image generator  94  for illumination of the image receiving member  12  and generation of a digital image that corresponds to the image on the member  12 . The digital image is received by the controller  80  for storage and processing. A portion of the instructions executed by the controller  80  implement an image evaluator  92  that processes digital images of test patterns on the image receiving member  12  to detect weak and/or missing inkjets. 
         [0032]    To improve the evaluation of the images being generated in one embodiment, the controller  80  executes programmed instructions that enable the printer  10  to operate the printheads  35 ,  36 ,  37 ,  38  and form an ink image with a substantially larger amount of ink than otherwise used for similar missing and/or weak inkjet detecting techniques. Because a larger amount of ink is used to form the test pattern, the controller  80  also executes the programmed instructions to transfer the test pattern to media, such as the media sheets  49 , which are subsequently ejected from the printer  10  for disposal. The larger amount of ink in the test pattern enables missing inkjets to be detected more easily and the removal of the test pattern from the printer preserves the operational life of the drum maintenance unit. The processing of the scanned test pattern image enables the detection of missing and/or weak inkjets and the positioning of the electro-optical sensors  59  to image the test pattern for better analysis. 
         [0033]    A process for detecting missing and/or weak inkjets in a digital image of a test pattern is now described with reference to  FIG. 6 ,  FIGS. 7A and 7B , and  FIGS. 8A and 8B .  FIG. 6  shows a portion of a test pattern useful for detecting missing and/or weak inkjets. The test pattern  604  is comprised of a series of vertical dashes  608 . Each dash is generated by a single inkjet ejecting a series of ink drops as the image receiving member  12  is rotated past a printhead. Thus, the portion of the test pattern  604  shown in  FIG. 6  is generated by twenty-two inkjets. The amount of ink in typical test patterns, such as test pattern  604 , is deliberately kept small since the test pattern is wiped from the image receiving member  12  and the ink is collected by a drum maintenance unit ( 98 ,  FIG. 4 ). 
         [0034]    In  FIG. 7A , a portion of a test pattern  304  is shown with the dashes  308  in the pattern being generated by a weak inkjet. A “weak” inkjet is an inkjet that responds intermittently to a firing signal or that responds by ejecting ink drops having a mass that is less than the ink drop mass corresponding to the characteristics of the firing signal for the inkjet. The ink in the dashes  308  causes the image generator  94  to generate an electrical signal that has an amplitude that is closer to the amplitude for the signals generated for the areas of the image receiving member that do not have ink on them than the amplitudes for the signals generated for the other dashes  310 . The amplitude differences and similarities of a digital image across test pattern  304  are shown in  FIG. 7B . Similarly, the portion of the test pattern  404  shown in  FIG. 8A  has area  408  being generated by a missing inkjet where little or no ink was ejected by the inkjet. A “missing” inkjet is an inkjet that does not eject an ink drop or that ejects an essentially imperceptible amount of ink in response to a firing signal. A digital image across test pattern  404  yields the amplitude profile shown in  FIG. 8B . As further used herein, a “missing” inkjet is an inkjet that has one or more of the characteristics of “weak” or “missing” inkjets as described above. An operable inkjet is an inkjet that does not exhibit any of the characteristics of a missing inkjet as now defined. 
         [0035]    The amplitude profiles generated by the image generator  94 , such as those shown in  FIGS. 7B and 8B , are used by the image evaluator  92  to detect missing inkjets. In one evaluation method, the amplitude of a profile curve for an inkjet is compared to a predetermined amplitude threshold to identify a missing inkjet from a test pattern. In another evaluation method, an area under a profile curve for an inkjet is integrated and compared to a predetermined area threshold to identify a missing inkjet from a test pattern. In yet another evaluation method, the amplitudes of the profiles and the areas under the profile curves are computed and compared to predetermined thresholds. In this method, both the amplitude and integration result must be greater than the predetermined thresholds before the inkjet is identified as being missing. Although the inkjet evaluation methods have been described with reference to amplitude and area comparisons, other evaluation methods and combinations of methods are possible. 
         [0036]    Exemplary test patterns for use with the improved missing inkjet detection method are shown in  FIGS. 1 and 2 .  FIG. 1  shows a test pattern  100  useful for improving the reliability of detecting missing inkjets. The test pattern  100  includes a plurality of solid lines  102  with each line  102  having a mud portion  104  and a measurement portion  106 . Each line  102  is formed on the image receiving member  12  by a single inkjet of a single printhead ejecting ink at the maximum frequency capability of the printhead. For example, the lines  102  of test pattern  100  are formed by twenty-three inkjets. The mud portion  104  is formed over multiple consecutive revolutions for a given length. The function of the mud portion is to eject a larger amount of ink than the amount of ink ejected in a typical detection pattern, such as the test pattern  604  shown in  FIG. 6 , and to stress the inkjets and exacerbate a missing inkjet failure condition. The measurement portion  106  is formed over one revolution of the image receiving member  12  with a length that extends past the mud portion  104 . This measurement portion typically is formed on the last revolution on the trailing edge of the mud portion of the print in order to exercise the inkjet to the fullest extent. The image generator  94  generates digital image amplitude profiles of the measurement portion  106  for further processing by the controller  80  and the image evaluator  92 . In one embodiment, the lines  102  of the test pattern  100  extend the entire length of a media sheet  49  for disposal of the ink after imaging. In another embodiment, the test pattern  100  extends for only a portion of the length of the media sheet  49 . 
         [0037]      FIG. 2  shows another test pattern  200  useful for improving the reliability of detecting missing inkjets on one or more printheads. To detect missing inkjets on multiple printheads, each printhead forms the test pattern  200  on a different portion of the image receiving member  12 . To detect missing inkjets on a single printhead, the printhead can repeat the test pattern  200  on different portions of the image receiving member  12 . The test pattern  200  includes a plurality of lines  202  with each line  202  having a mud portion  204  and a measurement portion  206 . The mud portions  204  and measurement portions  206  are formed in a similar manner to the mud portions  104  and measurement portions  106  in test pattern  100 ; however, the mud portions  204  of the test pattern  200  are adjacent, giving the appearance of a single, continuous mud portion across the test pattern. The layout of the test pattern  200  enables generation of a plurality of lines  212 ,  222 ,  232  for each printhead in a printhead assembly. In the embodiment shown, the total length of the lines  202 ,  212 ,  222 ,  232  extends the entire length of a media sheet  49  for disposal of the ink after imaging. 
         [0038]    A process  500  for improving the detection of missing inkjets is shown in  FIG. 3 . The controller configured to execute the programmed instructions to implement the process  500  begins by monitoring the printer for one or more process initiation states (block  502 ), such as an operator-initiated request for an advanced recovery process or an operation of a normal recovery process. In the normal recovery process, the printer controller is configured with programmed instructions to print a first test pattern, such as pattern  604  as shown in  FIG. 6 , on the image receiving member. The instructions enable the image generator to generate digital images of the first test pattern and enable the image evaluator to analyze the digital images of the first test pattern to identify missing inkjets. During the life of the printer, the controller generates and images the first test pattern for analysis and detection of missing inkjets in accordance with a schedule or in response to manual activation by a user or a customer service technician. In the advanced recovery process, the printer controller is configured in the same manner as the normal recovery process, except that the programmed instructions direct the printer to print a second test pattern, such as the patterns  100  and  200  as shown in  FIGS. 1 and 2 . The operator-initiated request is a direct, manual activation of the advanced recovery process by the user or the customer service technician. 
         [0039]    If the one or more process initiation states are detected, the controller configured to execute the programmed instructions to implement the process  500  determines whether the initiation state is an operator-initiated request or an operation of the normal recovery process (block  504 ). If the detected initiation state is an operator-initiated request for the advanced recovery process, the controller implementing the process  500  initiates the advanced recovery process (block  522 ). If the detected initiation state is not an operator-initiated request for the advanced recovery process, the initiation state is identified as the normal recovery process that uses the first test pattern to detect missing inkjets. Although the one or more process initiation states have been described with reference to an operator-initiated request for the advanced recover process or an operation of the normal recovery process, the process may monitor for other initiation states. 
         [0040]    If the controller initiates the process  500  by operation of the normal recovery process, the controller configured to execute the programmed instructions to implement the process  500  continues by detecting that a first number of missing inkjets identified with reference to the first test pattern process is less than an actual number of missing inkjets in the printer (block  508 ). The detection of whether the first number of missing inkjets is less than the actual number of missing inkjets is accomplished by using one or more criteria to estimate the accuracy of the first number of missing inkjets as compared to the actual number of missing jets. The criteria selected to estimate the accuracy of the first number of missing inkjets are any criteria that indicate that the first number of missing inkjets is less than the actual number of missing inkjets. In one accuracy estimation method, repeated purges of at least one printhead are counted and stored in memory. If the purges counted within a predetermined period of time exceed a predetermined purge count threshold, the first number of missing inkjets detected with reference to the first test pattern is less than the actual number of missing inkjets (block  510 ). In another accuracy estimation method, the printer waits for the operation of the normal recovery process and monitors the printer for a signal requesting generation of the second test pattern of the advanced recovery process. The signal can be the result of a printer-initiated request for the advanced recovery process in response to a detected fault state within the printer or from an input from a customer or service technician possibly based on the quality of a printed (or reprinted) image. For instance, input can be required in response to a question generated and displayed by the printer. If after operation of the normal recovery process, the signal requesting generation of the advanced recovery process is detected, the first number of missing inkjets detected with reference to the first test pattern is less than the actual number of missing inkjets (block  512 ). 
         [0041]    In yet another accuracy estimation method, the passage of time since a last generation of the second pattern of the advanced recovery process is monitored. If the passage of time since the last advanced recovery process exceeds a predetermined period of time, the first number of missing inkjets detected with reference to the first test pattern is less than the actual number of missing inkjets (block  514 ). In yet another accuracy estimation method, pages printed since a last generation of the second pattern of the advanced recovery process are counted. If the pages counted since the last advanced recovery process exceed a predetermined page count threshold, the first number of missing inkjets detected with reference to the first test pattern is less than the actual number of missing inkjets (block  516 ). If none of the criteria in the accuracy estimation methods are met, the controller configured to execute the programmed instructions to implement the process  500  continues to monitor for the one or more process initiation states (block  502 ). If any of the criteria in the accuracy estimation methods are met, the controller performing the process  500  initiates the advanced recovery process (block  522 ). 
         [0042]    Process  500  is continued by operating the advanced recovery process to generate the second test pattern (block  524 ). The second test pattern is used to generate firing signals for the ejection of ink onto the image receiving member. The amount of ink ejected by inkjets onto the image receiving member during operation of the advanced recovery process is at least twice as much ink than each inkjet ejected to form the first test pattern of the normal recovery process. Moreover, printheads that are operated to form the second test pattern are operated at a frequency that could be greater than the frequency at which each inkjet operated to form the first test pattern of the normal recovery process (up to the maximum operational frequency of the print head). 
         [0043]    The controller configured to execute the programmed instructions to implement the process  500  then detects a second number of missing inkjets with reference to a digital image of the second test pattern (block  526 ). To accomplish this detection, the image generator captures a digital image of the second test pattern on the image receiving member. The image evaluator generates an amplitude measurement, an area under a curve from the profile curve, or both for each inkjet in the digital image. The results are compared to appropriate predetermined thresholds for missing inkjets to determine whether the results indicate the inkjets are missing. If the results are less than the thresholds, the inkjets are identified as being missing inkjets and the process determines whether more results are to be processed. If the results for other inkjets have not been processed, then the process selects the next inkjet and generates the measurements from the inkjet profile. Once the results for all inkjets in the second test pattern are compared to the appropriate predetermined thresholds, the resulting missing inkjet identifications from the second test pattern are compared to the missing inkjet identifications from the first test pattern. Any missing inkjet identifications from the second test pattern that were not identified from the first test pattern are stored for additional processing (block  528 ). 
         [0044]    To dispose of the ink ejected onto the image receiving member during operation of the advanced recovery process, the ink from the second test pattern is transferred to the media sheet (block  530 ). The controller operates a media transport to deliver a media sheet to a nip formed between the rotating image receiving member and a transfix roller to transfer the second test pattern from the rotating image receiving member to the media sheet. The controller continues to operate the media transport to deliver the media sheet with the transferred ink image of the second test pattern to a discharge area for disposal of the ink (block  532 ). After the media sheet is delivered to the discharge area, the process returns to monitor for the one or more process initiation states (block  502 ). The reader should note that the process described above can be used in an offset inkjet printer and in an inkjet printer that ejects ink directly onto cut media or onto continuous media. 
         [0045]    It will be appreciated that variants of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.