Abstract:
Methods and apparatus provide for automatic fluid ejector alignment and performance evaluation and modification in one or multiple planes. A fluid ejector fires a drop through a drop detection module. A signal indicating drop presence or absence is sent to a computer. The computer analyzes the data, and makes a compensation determination of a preferred method of using the fluid ejector. The compensation determination may include electronically modifying the image data to be printed, physically manipulating the fluid ejector, completely skipping the fluid ejector during printing operations, or in some other way modifying the fluid ejector or image data such that apparent printed image error due to fluid ejector alignment or performance error is reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to methods and apparatus for an automatic fluid ejector alignment and performance system that has the ability to determine alignment and operation of at least one fluid ejector, and can provide various implementation methods to modify defects or errors in operation. 
     2. Description of Related Art 
     Fluid ejector systems, such as drop-on-demand liquid ink printers, including piezoelectric, acoustic, phase change wax-based or thermal printers, have at least one fluid ejector from which drops of fluid are ejected towards a receiving sheet. Within the fluid ejector, the fluid is contained in a plurality of channels. Power pulses cause the droplets of fluid to be expelled as required from orifices or nozzles at the end of the channels. 
     When the fluid ejector is an ink jet printhead, the fluid ejector may be incorporated into for example, a carriage-type printer, a partial width array-type printer, or a page-width type printer. The carriage-type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be functionally attached to a disposable ink supply cartridge. The combined printhead and cartridge assembly is attached to a carriage that is reciprocated to print one swath of information at a time, on a stationary receiving medium, such as paper or transparencies, where each swath of information is equal to the length of a column of nozzles. 
     Conventional printing systems step the receiving medium a distance generally equal to or less than the height of the swath to be printed, so that the next printed swath is contiguous or overlaps with the previously printed swath. When there is no data to print in large blocks, the receiving medium may be stepped a larger amount. This procedure is repeated until the entire image is printed. 
     Optimal performance of a fluid ejector requires the nozzles be properly aligned. When the fluid ejector is a color ink jet printhead, such as a four color printhead (CMYK), proper alignment of the various color heads is necessary and printed test patterns are generally used. Each alignment procedure, including vertical head to head alignment, horizontal head to head alignment, bi-directional alignment, and tilt alignment, requires four test pattern sets to be run for a four printhead printer. Furthermore, if the printhead carriage operates at multiple speeds, such as draft and normal, test pattern sets for some alignment procedures must be run for each speed. Manual procedures for correcting alignment require considerable user labor and are prone to user error. These procedures require the user to run the test pattern sets, visually observe the test pattern sets, visually judge the optimal test pattern set among various alternatives, and choose an adjustment value. 
     Automatic alignment procedures are also known. U.S. Pat. No. 6,609,777 B2 to Endo, the disclosure of which is incorporated herein by reference in its entirety, discloses technology for printing and determination of an adjustment value for correcting bi-directional misalignment of the dot recording positions. The printing apparatus includes an inspection unit that optically detects the passage of a continuous stream of ink droplets ejected from a printer nozzle. An adjustment value is determined based on the results of the performance of a forward pass test and a reverse pass test, and bi-directional misalignment can be determined without need for human observation. 
     Fluid ejector system&#39;s performance will also be impacted by a fluid ejector&#39;s nozzle performance. When the fluid ejector is in an ink jet printhead, fluid ejector performance may be impacted where particle contamination clogs the nozzle, where kogation of the heaters decreases drop velocity, or where damage occurs to the nozzle, such as due to resistor burn-out, or where the printhead brushes against the print medium, or where the nozzle plate becomes worn due to frequent servicing. Other factors may also impact nozzle performance. Fluid ejector performance is often determined by printing a test pattern and visually inspecting the test pattern results. 
     Automatic methods for detecting fluid ejector performance are also known. U.S. Pat. No. 6,454,380 B1 to Endo, the disclosure of which is incorporated herein by reference in its entirety, discloses a system for inspecting nozzles requiring the jetting of a continuous stream of ink droplets for detecting the clogging of nozzles in a printer wherein timings for printing operations for conducting the inspection are preset with respect to at least two print modes. Similarly, U.S. Pat. No. 6,585,346 B2 to Endo, the disclosure of which is incorporated herein by reference in its entirety, discloses a technique for detecting the presence or absence of inoperative nozzles by comparing a specific threshold with a time interval between successive detection pulses. Similarly, U.S. Pat. No. 6,604,807 to Murcia, the disclosure of which is incorporated herein by reference in its entirety, discloses a method for determining anomalous nozzles in an ink jet printing device. 
     SUMMARY OF THE INVENTION 
     Current fluid ejector alignment and performance techniques for determining and modifying fluid ejector alignment and performance have significant disadvantages. For example, a large number of test pattern sets are required to be printed. The user then visually analyzes the test pattern sets and manually enters a value into a computer to modify the fluid ejector alignment or performance. Because of the user involvement, the method is onerous, time-consuming, and prone to error. Thus, the conventional method often has inconsistent results in both determining and modifying fluid ejector alignment and performance. 
     The methods and apparatus of this invention provide for automatic fluid ejector alignment and performance evaluation and modification in one or multiple planes. 
     The methods and apparatus of this invention separately provide an automatic fluid ejector alignment and performance evaluation that can determine properties on an individual nozzle basis. 
     In various exemplary embodiments, a fluid ejector fires a fluid drop through a laser beam emitted from a drop detection module&#39;s laser. A shadow is created on the drop detection module&#39;s photodiode if the fluid drop impinges the laser beam. A shadow is not created if the firing of the drop either fails to eject a fluid drop, or the fluid drop fails to impinge the laser beam. The shadow or lack of shadow signal is focused by a microscope through an aperture onto a photodiode. The microscope is not essential to the invention and the removal of the microscope will result in a simpler apparatus. 
     In various exemplary embodiments, the focus of the shadow or lack of shadow on the photodiode is amplified by an amplifier and converted into a signal. The signal is sent to a computer as data. After analyzing the data, the computer makes a compensation determination which may then be applied to the fluid ejector to electronically modify the image data to be printed, physically manipulate the fluid ejector nozzle, completely skip the fluid ejector during printing operations or in some other way modify the fluid ejector or image data such that error in the printed image due to fluid ejector mis-alignment or performance error is reduced. 
     Throughout this application, the decision by the computer on how to modify the fluid ejector such that error induced by the fluid ejector on the printed image is reduced, will be referenced to collectively as the compensation determination. Among other determinations, the computer may make a compensation determination to modify the image data to be printed, to physically manipulate a fluid ejector, or to completely skip a fluid ejector during the printing process. 
     The compensation determination determines the preferred method of using the selected fluid ejectors to create the printed image. An example of a compensation determination to modify an image to be printed in order to correct for fluid ejector alignment or performance errors may include rotating an image. Similarly, a determination to physically manipulate a fluid ejector in order to compensate for error may include wiping or priming a fluid ejector, or changing the voltage to a fluid ejector. 
     In various exemplary embodiments, the compensation determination may be made by an on-board diagnostic tool, such as a controller, that allows the apparatus to self-check and modify fluid ejector metrics on a regular basis. 
     Other objects, advantages and features of the invention will become apparent from the following detailed description taken in conjunction with the attached drawings, which disclose exemplary embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the following drawings in which like reference numerals refer to like elements and wherein: 
         FIG. 1  illustrates one exemplary embodiment of a fluid ejector system drop detection module according to the invention; 
         FIG. 2  illustrates one exemplary embodiment of a fluid ejector device usable with various exemplary systems and methods according to this invention; 
         FIG. 3  is a view of a fluid ejector device from a first direction; 
         FIG. 4  is a view of a fluid ejector device from a second direction; 
         FIG. 5  is a graph showing an output drop signal from a photodiode over time; 
         FIG. 6  is a block diagram of an exemplary fluid ejector alignment and performance system according to the invention; 
         FIG. 7  is a flowchart outlining one exemplary embodiment of a method for automatically determining fluid ejector alignment and performance according to the invention; 
         FIG. 8  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, modify fluid ejector alignment and performance according to the invention; 
         FIG. 9  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, electronically compensate, horizontal printhead alignment according to the invention; 
         FIG. 10  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, electronically compensate, vertical printhead alignment according to the invention; 
         FIG. 11  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, electronically compensate, printhead tilt according to the invention; 
         FIG. 12  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, electronically compensate, bi-directional alignment according to the invention; 
         FIG. 13  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, modify fluid ejector performance for ejector problems, such as blocked or non-firing jets according to the invention; and 
         FIG. 14  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, modify fluid ejector performance for ejector problems such as kogation, re-fill, and maximum frequency problems, according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following detailed description of various exemplary embodiments of the fluid ejection systems according to this invention may refer to one specific type of fluid ejection system, an ink jet printer, for sake of clarity and familiarity. However, it should be appreciated that the principles of this invention, as outlined and/or discussed below, can be equally applied to any known or later developed fluid ejection systems, beyond the ink jet printer specifically discussed herein. 
       FIG. 1  shows an exemplary embodiment of a fluid ejector system drop detection module  200  that incorporates the systems and methods of the invention. A fluid ejector or emitter  305  is housed in a printhead  300 . A computer  400  signals the laser  205  to fire a drop detection module laser beam  210 . The computer  400  may also signal the printhead  300  to fire a drop  310  from fluid ejector  305 . A microscope  215  captures the laser beam  210  and focuses the laser beam  210  through an aperture  220  onto a photodiode  225 . The signal from the photodiode  225  may be amplified by amplifier  230  and sent to the computer  400 . The drop detection module  200  and its components are provided to detect the passage of individual drops  310  from emitter  305  for purposes of alignment and/or performance monitoring. 
     For simplicity and clarification, the operating principles and design factors of various exemplary embodiments of the systems and methods according to this invention are explained with reference to one exemplary embodiment of a carriage-type ink jet printer  100 , as shown in  FIG. 2 , and one exemplary embodiment of a printhead  300  as shown in  FIGS. 1–3 . The basic explanation of the operation of the ink jet printer  100  and the printhead  300  is applicable for the understanding and design of any fluid ejection system that incorporates this invention. Although the systems and methods of this invention are described in conjunction with the ink jet printer  100  and the printhead  300 , the systems and methods according to this invention can be used with any other known or later-developed fluid ejection system. 
       FIG. 2  shows a carriage-type thermal ink jet printing device  100 . A linear array of droplet producing channels is housed in a printhead  300  mounted on a reciprocal carriage assembly  105 . A number of ink droplets  310  are propelled towards a receiving medium  110 , such as a sheet of paper, that is stepped by a motor  115  a preselected distance in a process direction, indicated by the arrow  120 , each time the printhead  300  traverses across the receiving medium  110  along the scan axis perpendicular to the process direction. The receiving medium  110  can be stored on a supply roll  125  and stepped onto a take up roll  130  by the motor  115  or other means well known to those skilled in the art. For example, the receiving medium may be individual sheets of paper indexed in process direction  120 . 
     In the exemplary embodiment shown in  FIG. 2  droplets  310  are fired horizontally from the printhead  300  toward the receiving medium  110 . However, the droplets  310  may also be propelled vertically or diagonally. Thus, although the systems and methods of this invention, as shown in exemplary embodiment  FIG. 2 , are described with reference to droplets  310  being fired horizontally, the systems and methods according to this invention can include droplets  310  being fired vertically or diagonally. 
     The printhead  300  is fixedly mounted on a support base  135  of the carriage assembly  105 , which reciprocally moves along two parallel guide rails  145 . The printhead  300  may be reciprocally moved by a cable or endless belt  150  and a pair of pulleys  155 , one of which is powered by a reversible motor  160 . The printhead  300  is generally moved across the receiving medium  110  perpendicular to the direction that the receiving medium  110  is moved by the motor  115 . Of course, any other known or later-developed structure usable to move the carriage assembly  105  can be used in the ink jet printing device  100 . 
     Alternatively, the linear array of droplet producing channels may extend across the entire width of the receiving medium  110 , as is well known to those of skill in the art. This is typically referred to as a full-width array. See, for example, U.S. Pat. No. 5,160,403 to Fisher et al. and U.S. Pat. No. 4,463,359 to Ayata et al., each of which is incorporated herein by reference in its entirety. 
     An encoder  165  is located such that the location or position of the printhead  300  can be determined with respect to the carriage assembly and/or ink jet printing device  100 . Exemplary encoders  165  may include a linear strip encoder or a rotary encoder. However, any known or later-developed structure usable to determine the position of the printhead  300  or fluid ejectors  305  can be used in the ink jet printing device  100 . 
     In various exemplary embodiments, two drop detection modules  200  are located within the ink jet printing device  100 , each preferably being provided to detect fluid droplets in a different plane. For example, in the embodiment illustrated, one is vertically aligned and one is horizontally aligned. However, the present invention is not limited to this. Moreover, while two modules are shown, only one drop detection module  200  is necessary for some embodiments of the present invention. The drop detection module  200  includes a laser  205 , microscope  215 , aperture  220 , photodiode  225 , and amplifier  230 . As shown in  FIG. 2 , it is preferable that at least one drop detection module  200  is capable of movement in at least one plane. 
     In the exemplary embodiment, movable drop detection modules  200  may have the laser  205  mounted on a reciprocal carriage assembly  235  and the photodiode  225  and amplifier  230  mounted on a reciprocal carriage assembly  240 . The reciprocal carriages  235 ,  240  may move along two parallel guide rails  245 ,  250 , respectively. The reciprocal carriages  235 ,  240  may be moved by a cable  255 ,  260 , respectively; and a pair of pulleys  265 ,  270 , respectively. The reciprocal carriages may be powered by a reversible motor  275 ,  280 , respectively. It is preferable that the movable drop detection module  200  is moved across the printhead  300  in a direction parallel to the direction that the receiving medium  110  is moved by motor  115 . However, in some embodiments, one or more drop detection modules may be moved in a different direction, such as a direction perpendicular to the direction that the receiving medium  110  is moved by motor  115 . Furthermore, in some embodiments, the drop detection module&#39;s laser may be capable of rotation and the photodiode capable of movement. With respect to the drop detection module&#39;s movement, and the rotation of the laser and the movement of the photodiode, any known or later-developed structure usable to move the drop detection module  200 , or similarly, rotate the laser and move the photodiode may be used in the ink jet printing device  100 . 
     In the exemplary embodiment, a second drop detection module  200  includes a laser  205  fixedly mounted on the ink jet printer  100 , and a corresponding photodiode  225  and amplifier  230  also fixedly mounted on the ink jet printing device  100 . In the exemplary embodiment shown in  FIG. 2 , this second drop detection module  200  is placed outside the paper path along the side of the paper, where generally there is more space. However, the drop detection module  200  may also be placed off the face of paper, and directly between the face of the paper and the printhead. 
     Each drop detection module  200  is oriented in a plane such that laser beam may be fired by laser  205  across printhead  300  and received by a corresponding photodiode  225  and, thus provide an indication of whether droplets  310  are ejected from individual nozzles of the printhead  300 . 
       FIG. 3  shows one exemplary embodiment of four printheads  300  each including an array of fluid ejectors  305 . A plurality of such ejectors  305  are found in a typical ink jet printhead  300 . The systems, methods and architectures according to this invention may be used with side-shooter type ejectors, roof-shooter type ejectors, or other ejectors. 
       FIG. 3  is a view from a first direction showing a front face  315  of four exemplary printheads  300 . In this exemplary embodiment, each printhead  300  is shown for illustrative purposes with seven rows of ejectors  305  and two columns of ejectors  305  on the face  315 . In an exemplary embodiment, the ejectors  305  are sized and arranged in linear arrays of 300 to 1200 or more of the ejectors per inch. Other arrangements and dimensions can be used in other exemplary embodiments, as known to those skilled in the art. Of course, fluid ejectors need not be structured on the printhead in rows or columns or include multiple ejectors. 
     The face of the printhead may include a single printhead color, or may contain multiple color nozzles, such as a four color printhead (CMYK), including a cyan ink ejector group, a magenta ink ejector group, a yellow ink ejector group, and a black ink ejector group. 
     The printheads  300  may be capable of movement in the scanning direction. The scanning direction is perpendicular to the process direction. Similarly, at least one drop detection module  200  may be capable of movement in a direction other than the scanning direction. Furthermore, as in the exemplary embodiment shown, at least one other drop detection module  200  may be fixedly attached to the ink jet printing device  100 . In the illustrative embodiment, one drop detection module is oriented horizontally while a second drop detection module is oriented vertically. 
       FIG. 4  is a view of a fluid ejector device from a second direction, perpendicular to the view of  FIG. 3 . In use fluid, such as a drop (not shown), is emitted from ejectors  305 . The fluid travels generally perpendicular to beam  210  toward recording medium  110 . The individual droplets are then sensed by the drop detection module  200 . 
       FIG. 5  is a graph showing two plots. Plot  421  is a plot showing an output drop signal from a photodiode  225  over time using the printhead  300  and drop detection modules  200  of  FIGS. 2–4 . Plot  422  is a plot of the current sent to a heater of a fluid ejector  305 , in order for a fluid ejector  305  to fire a drop. 
     In general, the graph shown in  FIG. 5  may be generated as follows. A controller signals a fluid ejector  305  on a printhead  300  to fire at least one drop  310  such as by sending a current burst or pulse  422  to the heater of a fluid ejector  305 . If the drop  310 , fired by the fluid ejector, impinges laser beam  210 , fired by drop detection module  200 , a shadow is created. The shadow signifies the failure of the photodiode  225  to receive the laser beam  210 . The shadow is focused by the microscope  215  through the aperture  220  onto the photodiode  225 . The microscope  215  is not essential to the present invention, however it may increase the spatial resolution of the drop detection module  200 . The shadow or lack of shadow signal  421  once received by the photodiode  225  may be amplified by an amplifier  230  and transmitted to the computer  400 . The amplifier is not essential to the present invention, however it strengthens the signal  421  transmitted to the computer  400 . 
     The signal  421 , from the photodiode  225 , is plotted on the graph shown in  FIG. 5 . The spikes in the plot  421  coincide with individual drops  310  that impinged the laser beam  210 . Coincidentally, the spikes in plot  422  coincide with where a current burst was sent to a fluid ejector as the signal to fire a drop. Thus, by monitoring the drop signal  421  and selectively ejecting fluid from each of the ejectors  305 , it is possible to detect the firing of very small quantities of liquid from individual ejectors. In fact, by use of the laser/photodiode arrangement, determination of droplets as small as 1 picoliter can be detected and resolved. 
     In the exemplary embodiment shown in  FIG. 5 , the drop signal (y value) ranges in voltage (V) from 0 to 8 and the time signal (x-value) ranges in seconds (s) from 0 to 277.8×10 −6 . However, other values and ranges for current and time may also be used in the systems and methods according to this invention. 
       FIG. 6  shows one exemplary embodiment of a fluid ejector alignment and performance system  410  that controls fluid ejector alignment and performance according to this invention. This system may be housed in computer  400 . As shown in  FIG. 6 , the fluid ejector alignment and performance system  410  includes an input/output interface  415 , a controller  420 , a memory  425 , an alignment and performance determining circuit, routine or application  430 , a position determining circuit, routine or application  445 , an alignment and performance modifying circuit, routine or application  450 , a position modifying circuit, routine or application  460 , a timer  465 , and a counter  470  interconnected by one or more control and/or data busses and/or application programming interfaces  475 . I/ 0  interface  415  may receive data signals, such as an image signal as an input for ejector firing, from a datasource (DS)  500 . 
     As shown in  FIG. 6 , the fluid ejector alignment and performance system  410  is, in various exemplary embodiments, implemented on a programmed general purpose computer. However, the fluid ejector alignment and performance system can also be implemented on a special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an ASIC or other integrated circuit, a digital signal processor, a hardwired electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA or PAL, or the like. In general, any device, capable of implementing a finite state machine that is in turn capable of implementing the flowchart shown in  FIGS. 7–15 , can be used to implement the fluid ejector alignment and performance system. 
     In  FIG. 6 , alterable portions of the memory  425  are, in various exemplary embodiments, implemented using static or dynamic RAM. However, the memory  425  can also be implemented using a floppy disk and disk drive, a writable optical disk and disk drive, a hard drive, flash memory or the like. In  FIG. 6 , the generally static portions of the memory  425  are, in various exemplary embodiments, implemented using ROM. However, the static portions can also be implemented using other non-volatile memory, such as PROM, EPROM, EEPROM, an optical ROM disk, such as a CD-ROM or DVD ROM, and disk drive, flash memory or other alterable memory, as indicated above, or the like. 
     As shown in  FIG. 6 , the memory  425  can be implemented using any appropriate combination of alterable, volatile or non-volatile memory or non-alterable, or fixed, memory. The alterable memory, whether volatile or non-volatile, can be implemented using any one or more of static or dynamic RAM, a floppy disk and disk drive, a writable or re-rewritable optical disk and disk drive, a hard drive, flash memory or the like. Similarly, the non-alterable or fixed memory can be implemented using any one or more of ROM, PROM, EPROM, EEPROM, an optical ROM disk, such as a CD-ROM or DVD-ROM disk, and disk drive or the like. 
     It should be understood that each of the various embodiments of the fluid ejector alignment and performance system  410  can be implemented as software executing on a programmed general purpose computer, a special purpose computer, a microprocessor or the like. It should also be understood that each of the circuits, routines, applications, objects or managers shown in  FIG. 6  can be implemented as portions of a suitably programmed general-purpose computer. Alternatively, each of the circuits, routines, applications, objects or managers shown in  FIG. 6  can be implemented as physically distinct hardware circuits within an ASIC, using a digital signal processor (DSP), using a FPGA, a PLD, a PLA and/or a PAL, or using discrete logic elements or discrete circuit elements. The particular form of the circuits, routines, applications, objects or managers shown in  FIG. 6  will take is a design choice and will be obvious and predictable to those skilled in the art. It should be appreciated that the circuits, routines, applications, objects or managers shown in  FIG. 6  do not need to be of the same design. 
     Further, it should be appreciated that the programming interfaces  475  connecting the memory  425  to the computer  400  can be a wired or wireless link to a network. The network can be a local area network, a wide area network, an intranet, the Internet, or any other distributed processing and storage network. 
     The fluid ejector alignment and performance system may not only be run to check alignment and/or performance manually, it may also be run automatically. If the system is manually operated, the user inputs a request to start the system. If the system is set to automatically run, the system is set to run by the controller  420 . If the fluid ejector alignment and performance system is automatically run, various exemplary embodiments of the present invention may allow the system to be run based on either a print count counter  470  or a timer  465 . For example, it could be run at start up, after a predetermined number of print jobs, or after replacement of any of the printheads. Of course, any other know or later developed method to automatically run the fluid ejector alignment and performance system may be employed in the present invention. 
     If the fluid ejector alignment and performance system is automatically run, the controller  420  selects the at least one fluid ejector to be tested and, if necessary, modified. Alternatively, a routine may be implemented to select multiple fluid ejectors. For example, a routine may be selected to select multiple fluid ejectors, such that the drop detection module may ripple through each fluid ejector in a column or row of the printhead, until all ejectors have been fired and tested. 
     A particular fluid ejector or group of fluid ejectors may be automatically selected based on the results determined by the use of a drop detection module to determine a fluid ejector&#39;s operating properties in a different plane. Other automatic methods for selecting fluid ejectors may include a routine that selects an arbitrary fluid ejector based on the image or type of image to be printed, fluid ejectors selected based on a timer  465 , or fluid ejectors selected based on a print count counter  470 . Of course, any other known or later developed method of selecting a fluid ejector may be employed in this invention. 
     If timer  465  is used to control the running of the fluid ejector alignment and performance system, controller  420  automatically selects fluid ejectors for alignment and performance testing and, if necessary, modification, based on an internal clock. 
     Similarly, if a print count counter  470  is used to control the running of the fluid ejector alignment and performance system, controller  420  may automatically select fluid ejectors for alignment and performance testing and, if necessary, modification, based on a print count of the selected fluid ejector. 
     Once the group or set of fluid ejectors to be tested has been selected, a first fluid ejector of the set is selected for determining alignment and/or performance operating properties and, if necessary, modification. 
     The alignment and/or performance determining control, routine, or application  430  employs at least one drop detection module to determine an operating alignment and/or performance property of a selected fluid ejector. 
     The alignment and/or performance modifying control, routine, or application  450  may employ various methods, to make compensation determinations. These compensation determinations may then be applied to a fluid ejector or otherwise used to modify the alignment or performance properties of a selected fluid ejector. 
       FIG. 7  is a flowchart outlining one exemplary embodiment of a method for automatically determining fluid ejector alignment and performance. In step S 1000 , the routine begins. The routine continues to step S 6000 . 
     In step S 2000 , a fluid ejector or set of fluid ejectors is selected to be tested for either or both alignment and performance. This fluid ejector&#39;s alignment and/or performance may also be modified in this routine. 
     After at least one fluid ejector has been selected, the control routine continues to step S 3000 . 
     In step S 3000 , the control routine applies an increment counter to count which fluid ejectors of a selected set have been tested. 
     In step S 4000 , the drop detection module control routine is run. In this step, a method for using at least one drop detection module to determine fluid ejector alignment and performance is applied to the selected fluid ejector. Furthermore, in this step, the fluid ejector alignment and performance may be modified by applying an alignment and/or performance determining and modifying control, routine, or application to the selected fluid ejector. Various exemplary modes for using the drop detection module for determining fluid ejector alignment and performance are possible and several exemplary modes will be described later in the specification in more detail. 
     After step S 4000  has been applied to a selected fluid ejector, the control routine continues to step S 5000 . In step S 5000 , a determination as to whether all of the selected fluid ejectors have been tested is made. If the determination in step S 5000  is that all selected fluid ejectors have been tested, the routine continues to step S 6000  where the routine ends. If the determination in step S 5000  is that not all of the selected fluid ejectors have been tested, the routine returns to step S 2000  where a next fluid ejector is selected. Accordingly, the routine continues from step S 2000  through step S 5000  until all fluid ejectors have been tested. 
       FIG. 8  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, modify fluid ejector alignment and performance. In step S 4005 , the routine begins. 
     In step S 4010 , a first drop detection module is set in a first plane. In step S 4015 , a second drop detection module is set in a second plane, wherein the second plane is different from the first plane. 
     In various exemplary embodiments, the drop detection module may be set in planes different than the planes described in the specification or shown in the drawings. The plane within which the drop detection module is positioned determines the fluid ejector alignment the module may test for. For example, for fluid ejector alignment in one plane, such as vertical or horizontal alignment with respect to the scanning direction (face of the printhead), a drop detection module may be positioned in a plane parallel or perpendicular to the scanning direction, respectively. 
     After the drop detection modules are set, the routine continues to step S 4020  where the lasers on the drop detection modules are fired. The lasers need not be fired simultaneously. The lasers are fired with respect to the plane in which fluid ejector alignment or performance information is desired to be obtained. In various exemplary embodiments, a light emitter, such as an LED, may be substituted for a laser. 
     In step S 4025 , a position determining control, routine, or application is applied to the selected fluid ejector to determine the fluid ejector&#39;s position relative to a fiducia on the ink jet printing device. 
     The fluid ejector offset can also be determined from the position determining control, routine, or application. The position determining control, routine, or application may use the drop detection module to determine the position of a fluid ejector based on when a drop fired by a fluid ejector impinges the laser beam. 
     In step S 4030 , the selected fluid ejector fires a drop. 
     After the drop has been fired, the routine continues to step S 4035  where a determination is made whether the drop impinged the laser beam of one or more of the respective drop detection modules operating in the routine. If the drop impinged the laser beam, the routine continues to step S 4050  where the routine ends. However, if a determination is made that the drop did not appear to impinge at least one laser beam, the routine continues to step S 4040 . 
     In step S 4040 , the compensation determination is calculated automatically by the alignment and/or performance modifying control, routine, or application. A compensation determination is calculated for the fluid ejector nozzles that fail to have at least one drop impinge the laser beam. This compensation can be performed after individual nozzle firing, or after completion of an array of nozzle firings. 
     After the compensation determination, the routine continues to step S 4045 . In step S 4045 , the selected fluid ejector is modified in accordance with the compensation determination made by the alignment and/or performance modifying control, routine, or application. The compensation determination can then be applied by the alignment and/or performance modifying control, routine, or application to modify the fluid ejector alignment and/or performance electronically. Where a fluid ejector cannot be adequately modified electronically, a different compensation determination, such as compensation value, may be calculated and applied to the image data. This value is applied to the image data to modify the image data such that the printed product does not reflect the apparent fluid ejector alignment or performance error. Other methods for modifying fluid ejector alignment and performance will be discussed further in the specification. 
     After step S 4045 , the control routine continues to step S 4050  where the control routine ends. In various exemplary embodiments, step S 4050  may also contain a further routine where steps, including steps S 4010  through step S 4050 , are re-applied to the selected fluid ejector to determine whether the alignment and/or performance control, routine, or application has sufficiently modified the selected fluid ejector. 
     As discussed above, the plane within which the drop detection module is positioned determines the fluid ejector alignment the module may test for. For example,  FIG. 9  and  FIG. 10  show two exemplary embodiments of a method to determine horizontal alignment and vertical alignment, respectively. 
       FIG. 9  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine, and if necessary, modify fluid ejector horizontal head alignment and performance. In step S 4105 , the routine begins. 
     In step S 4110 , a drop detection module is set in a plane perpendicular to the carriage motion. 
     In step S 4115 , one or more selected fluid ejectors fire a drop from the printhead. This may, for example, be a middle ejector in the array. After the drop has been fired, the control routine continues to step S 4120  where the signal generated by the photodiode is monitored. After step S 4120  the control routine continues to step S 4125 . 
     In step S 4125 , a determination is made as to whether the column of ejectors selected has been detected. If the determination is that the column of selected fluid ejectors has not been detected, the control routine proceeds to step S 4130 . In step S 4130 , the printhead carriage incrementally moves across the laser beam and steps S 4115 , S 4120 , and S 4125  are repeated until the column of selected fluid ejectors is detected. Alternatively, drop module  200  may be incremented while the printhead remains fixed. 
     If a determination is made that the column of selected fluid ejectors has been detected, the control routine continues to step S 4135  where the horizontal offset of this printhead and/or column of ejectors is determined from the position of the carriage when a drop impinged the laser beam. The horizontal offset of each printhead and/or column of ejectors may be a relative or absolute offset amount. It may be based on the determination of the position of the carriage relative to drop module when the fluid ejector drops impinge the laser beam and/or based on known distances between nozzles. After step S 4135  has been completed, the control routine continues to step S 4140 . 
     In step S 4140 , a determination is made as to whether each column of ejectors has completed steps S 4115  through S 4135 . If the determination is that a column has not completed steps S 4115  through S 4135  the control routine returns to S 4115  where the next column completes the steps S 4115  through S 4135 . Otherwise, the control routine continues to step S 4145 . 
     In step S 4145 , error due to the horizontal offset of each printhead nozzle can be compensated for electronically by known or subsequently developed methods, such as delayed firing, print mask compensation, etc. 
     After step S 4145 , the control routine continues to step S 4150  where the control routine ends. In various exemplary embodiments, step S 4150  may also contain a further routine where steps, including step S 4110  through step S 4145 , are re-applied to the selected fluid ejector to determine whether the alignment and/or performance control, routine, or application has sufficiently modified the selected fluid ejector. 
     Similarly,  FIG. 10  is a flowchart outlining one exemplary embodiment of a method for using a drop detection module to determine and, if necessary, modify fluid ejector vertical head alignment and performance. In step S 4205 , the routine begins. 
     In step S 4210 , a drop detection module is set in a plane such that the laser beam is parallel to the carriage motion. 
     After the drop detection module is set, the routine continues to step S 4220  where the control routine selectively fires one, some, or all of the fluid ejectors. After step S 4220 , the control routine continues to step S 4225 . 
     In step S 4225 , the control routine monitors the drop output signal generated by the photodiode. This step includes the photodiode alerting the controller when a drop either impinges or fails to impinge the laser beam. After step S 4225  has been completed, the control routine continues to step S 4230 . 
     In step S 4230 , a determination is made of whether at least one ejector from each column and/or printhead has been detected. If ejectors from all columns and/or printheads have not been detected, the control routine returns to step S 4220 , where steps S 4220  through step S 4230  are re-applied after selecting different ejectors and/or moving the drop detection module with respect to the printhead. If a determination is made that ejectors from all columns and/or printheads have been detected, the control routine continues to step S 4235  where the vertical offset of each column and/or printhead is determined by analysis of which of the fluid ejector&#39;s drops impinged the laser. 
     After step S 4235  is completed, the control routine continues to step S 4240 . In step S 4240  the vertical offset of each printhead can be compensated for electronically. 
     After step S 4240 , the control routine continues to step S 4245  where the control routine ends. In various exemplary embodiments, step S 4245  may also contain a further routine where steps, including steps S 4210  through step S 4240 , are re-applied to the selected fluid ejector to determine whether the alignment and/or performance control, routine, or application has sufficiently modified the selected fluid ejector. 
     Besides fluid ejector alignment in the vertical or horizontal direction with respect to the face of the printhead, fluid ejector tilt alignment and bi-directional alignment may also be determined and modified, if necessary, by using at least one drop detection module with the alignment determining and modifying control, routine, or application. 
     To determine tilt alignment, at least two fluid ejectors are tested and the drop detection module is positioned such that the position of at least two fluid ejectors can be determined. It is preferred that the fluid ejectors selected be at opposite ends of the printhead. Each fluid ejector separately fires a drop and the drop detection module separately records the signal generated by each respective drop. Once the drop detection module has sent each respective signal to the computer, the fluid ejector offset for each fluid ejector can be determined from the position determining control, routine, or application. 
     Next, a compensation determination can be generated by the alignment and/or performance routine or application. A compensation value to be applied to the image data can be generated and applied to modify the image data prior to printing. Thus, once the image data is printed, the apparent error due the printhead tilt offset is reduced because of the compensation value applied to modify the image data. Generally, compensation values can be generated to modify printhead tilt offsets of greater than one pixel. 
       FIG. 11  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, modify fluid ejector tilt alignment and performance. In step S 4305 , the routine begins. 
     In step S 4310 , drop detection module is provided such that the laser beam fired from the drop detection module is in a plane perpendicular to the carriage motion. 
     After the drop detection module is set, the routine continues to step S 4315  where a first selected fluid ejector fires a drop. After step S 4315 , the control routine continues to step S 4320 . 
     In step S 4320  the output signal generated by the photodiode is monitored to determine whether the drop fired impinged the laser beam. After step S 4320 , the control routine continues to step S 4325 . 
     In step S 4325 , a determination is made of whether at least two fluid ejectors have been tested. If the selected number of fluid ejectors has not been tested, the control routine returns to step S 4315  where the next fluid ejector is fired. Preferably, the selected ejectors span the entire column of drop ejectors being aligned for improved accuracy. As such, steps S 4315  through step S 4325  are applied to the next fluid ejector. If instead, in step S 4325  a determination is made that the selected number of ejectors has been tested, the control routine continues to step S 4330  where the printhead tilt is determined. 
     Once the printhead tilt has been determined, the control routine continues to step S 4335  where a compensation value can be determined and applied to the image data to compensate for printhead tilt. 
     After step S 4335 , the control routine continues to step S 4340  where the control routine ends. In various exemplary embodiments, step S 4340  may also contain a further routine where steps, including steps S 4310  through step S 4335 , are re-applied to the printhead to determine whether the alignment and/or performance control, routine, or application has sufficiently modified the image data appropriately. 
     Fluid ejector bi-directional alignment may also be determined and modified in a similar manner.  FIG. 12  is a flowchart outlining one exemplary embodiment of a method for using a drop detection module to determine and, if necessary modify fluid ejector alignment and performance. In step S 4405 , the control routine begins. 
     In the exemplary embodiment shown in  FIG. 12 , in step S 4410  a drop detection module is provided perpendicular to carriage motion. Next, in step S 4415 , the drop detection module is set at, or close to the paper plane. The drop detection module does not have to be above the paper itself, but may be placed outside the paper path. The drop detection module should be located such that the laser beam is perpendicular to the carriage motion. The drop detection module should also be positioned with respect to a fiducia, such that the drop detection module position is known relative to both the paper and printhead. 
     After step S 4415  has been completed, the control routine continues to step S 4420  where a timer is set. After the timer has been set, the control routines continues to step S 4425 . In step S 4425 , the laser on the drop detection module is fired. The printhead is then moved in the scanning direction and the fluid ejector&#39;s position is determined relative to a fiducia on the ink jet printing device. While the printhead is moving, a selected fluid ejector fires a drop and, simultaneously, a timer controlled by a controller is activated. 
     After the fluid ejector fires a drop and the timer is activated, in step S 4430  the timer is stopped when the drop impinges the laser beam. 
     Once the drop has impinged the laser beam, the routine continues to step S 4435  where the drop transit time from drop ejection until when the drop impinged the laser beam is calculated. 
     After step S 4435  has been completed, the control routine continues to step S 4440  where the fluid ejector velocity due to printhead movement in the scanning direction, while the drop was in transit between the nozzle and impingement of the laser beam, is calculated. This information may be calculated using signals from position encoder. 
     Next, in step S 4445 , the drop offset from the position the drop was projected to impact the paper is determined based on the transit time and printhead velocity. After the offset and drop position have been calculated, the control routine continues to step S 4450 . 
     In step S 4450 , steps S 4420  to S 4445  are repeated with the printhead moved in the direction opposite to the direction the printhead was initially moved. The printhead was initially moved in step S 4425 . 
     In step S 4455 , a compensation value can be determined to control the firing times of the fluid ejectors, or the image data can be modified so that errors in image quality, due to bi-directional alignment error, can be reduced or, at least, be visually less apparent. 
     Next, as shown in step S 4455 , the compensation value can be applied to the image data to electronically compensate for bi-direction alignment error. 
     After step S 4455 , the control routine continues to step S 4460  where the control routine ends. 
     When determining and modifying bi-directional alignment, it is important that the drop detection module be adequately located with respect to the printhead and paper. If positioning of the drop detection module is difficult, such that the transit time of the drop to he paper cannot be directly measured, then an additional step may be added to the bi-directional alignment routine. 
     In this step, the transit time of drops from the same fluid ejector is determined at two different distances from the printhead. This requires that the drop detection module or portions thereof be moved a known distance between printhead and paper. The drop detection module or portions thereof can be moved with a motor. The approximate drop speed can be determined from the change in transit time and the change in distance. Then, knowing the nominal distance between printhead and paper allows the approximate determination of the transit time of the drop to the paper. 
     As discussed above, the alignment and performance modifying control, routine, or application calculates the preferred method of using the selected fluid ejectors to create the printed image. For example, among other compensation determinations, the routine may result in the calculation of a compensation value by which to rotate or stretch an image, or result in a decision to wipe or prime a selected fluid ejector, change the voltage to a selected fluid ejector, or skip a fluid ejector during the printing process. Automatic modification of a fluid ejector for either alignment and/or performance may also include any other known or later developed method for modifying a fluid ejector. 
     For instance, as shown in  FIG. 13 , various exemplary embodiments of the present invention may include the detection and modification of a fluid ejector whose performance has deteriorated due to extended idle times. In the exemplary embodiment shown in  FIG. 13 , the recovery modification procedure can be employed after a selected fluid ejector has been exposed to an extended idle time. The recovery modification procedure may include modification techniques for modifying a fluid ejector, such as firing fluid through the ejector into a waste container, priming the fluid ejector, wiping the fluid ejector, heating the fluid ejector, or other methods familiar to those skilled in the art. After the recovery modification procedure, the fluid ejector may again be tested for alignment and/or performance. 
       FIG. 13  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to modify a fluid ejector. In step S 4505  the control routine begins. 
     In step S 4510  a determination is made as to whether there was an extended idle time for a fluid ejector or printhead. If the determination is that there was, the control routine continues to S 4515 , otherwise the control routine continues to step S 4545  where the control routine ends. 
     In step S 4515 , a drop detection module is set in a first plane such that the laser on the drop detection module may scan across selected fluid ejectors. After the drop detection module is set, the routine continues to step S 4520  where the selected fluid ejector fires a drop. 
     In step S 4525 , a determination is made of whether the fluid ejector drop impinged the laser beam of the drop detection module. If the drop impinged the laser beam, the routine continues to step S 4540 . However, if a determination is made that the drop did not appear to impinge the laser beam, the routine continues to step S 4530 . 
     In step S 4530 , a determination is made of a modification method to be applied to the selected fluid ejector. As discussed above, the modification method may include wiping or priming the fluid ejector or any other modification method known to those skilled in the art. 
     After a modification method has been determined, the routine continues to step S 4535  where the modification method is applied to the selected fluid ejector. 
     After step S 4535 , the routine continues to step S 4540  where a determination is made as to whether all fluid ejectors have been tested. If so, the control routine continues to step S 4545  where the routine ends. If a determination is made that not all fluid ejectors have been tested, the control routine returns to step S 4520  and repeats steps S 4520  through step S 4540  until all fluid ejectors have been tested. 
     In various exemplary embodiments, step S 4545  may also contain a further routine where steps, including steps S 4510  through step S 4540 , are re-applied to the selected fluid ejector to determine whether the alignment and/or performance control, routine, or application has sufficiently modified the selected fluid ejector. 
     As discussed above, many modification procedures may be used with the present invention. For instance, modification procedures may be employed to correct kogation, refill problems and frequency problems. If the fluid ejector has kogation or threshold voltage variation problems, drop speed variations may be adjusted with different enable trains or main pulse length. After a modification procedure has adjusted an enable train or main pulse length, the fluid ejector can be re-tested and the enable train re-modified until the fluid ejector drop speed is within acceptable tolerances. 
     Other problems with fluid ejectors such as refill problems and maximum frequency problems may also be confronted by modification procedures. For instance, if a filter clogs causing firing before re-fill and/or exceedingly fast drops such as spears occur, the fluid ejector and printer can be modified for lower frequency jetting to modify the problem. 
       FIG. 14  is a flowchart outlining one exemplary embodiment of a method for using the drop detection module to determine and, if necessary, modify fluid ejector alignment and performance. In step S 4605 , the routine begins. 
     In step S 4610 , a drop detection module is set in a first plane to scan selected fluid ejectors. 
     After the drop detection module is set, the routine continues to a step S 4615  where a timer is set. After the timer has been set, the control routine continues to step S 4620  where a first fluid ejector fires a drop. Simultaneously, the timer is activated. 
     After the drop has been fired and the timer activated the routine continues to step S 4625  where the drop speed is analyzed. The transit time of drops from the same fluid ejector is determined at two different distances from the printhead. This requires that the drop detection module or portions thereof be moved a known distance between the printhead and paper. The drop detection module or portions thereof can be moved with a motor or the like. The approximate drop speed can be determined from the change in transit time and the change in distance. 
     After step S 4625  has been completed, the routine continues to step S 4630  where a determination is made of whether the drop speed is within acceptable product tolerances. If the drop speed is determined to be outside specific product tolerances, the routine continues to step S 4635  where an electronic compensation can be determined and applied to a selected fluid ejector to compensate for drop speed. This compensation may include adjusting with different enable trains or adjusting the frequency of jetting. Once an electronic compensation has been applied to a selected fluid ejector, the routine continues to a step S 4640 . 
     However, if it is determined in step S 4630  that drop speed is within acceptable product tolerances, the routine continues from step S 4630  to step S 4640 . 
     In step S 4640  a determination is made as to whether all fluid ejectors have been tested. If so, the control routine continues to step S 4645  where the control routine ends. If, on the other hand, a determination is made that not all fluid ejectors have been tested, the control routine returns to step S 4615 , and repeats steps S 4615  through step S 4640  until all fluid ejectors have been tested. 
     Of course, in various exemplary embodiments, step S 4645  may also contain a further routine where steps, including steps S 4610  through step S 4640 , are re-applied to the selected fluid ejector to determine whether the alignment and/or performance control, routine, or application has sufficiently modified the selected fluid ejector. 
     In various exemplary embodiments, the apparatus of the invention may also include a modifying device. The modifying device may be used for wiping the fluid ejector&#39;s nozzle or other manipulation of the fluid ejector in order to modify the performance or alignment of the fluid ejector. 
     Alternatively, or in the event modification fails to adequately modify the fluid ejector&#39;s alignment or performance, defects in the image printed can be avoided through smart image processing or alternative print modes. Furthermore, if the modification process fails to adequately modify a selected fluid ejector the fluid ejector may be skipped during image processing. 
     While the invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications, and variations, will be apparent to those skilled in the art. For instance, while one skilled in the art of printing will apply the systems and methods to printing with ink, it is noted that the systems and methods of the invention apply to fluids other than ink. Accordingly, the exemplary embodiments of the invention as set forth above are intended to be illustrative and not limiting. Various changes may be made without departing from the spirit and scope of the invention as described herein.