Patent Publication Number: US-7914110-B2

Title: Purging fluid from fluid-ejection nozzles by performing spit-wipe operations

Description:
BACKGROUND 
     A common way to form images on media, such as paper, is to use a fluid-ejection device, such as an inkjet-printing device. An inkjet-printing device has a number of inkjet nozzles that eject ink, such as differently colored ink, in such a way as to form a desired image on the media. Many inks are dye-based, whereas other inks are pigment-based. In some formulations, these inks may be or may become relatively viscous. 
     Such viscous inks can form viscous sludge inside the inkjet nozzles. This sludge can affect typical testing, such as single drop detect testing, to determine whether the inkjet nozzles properly eject the ink. For instance, the performance of a single drop detect test may result in an inkjet nozzle using a pigment-based ink being seemingly OK to properly eject ink, only to fail to eject ink thereafter. 
     When an inkjet nozzle has failed a test to determine whether it is properly ejecting ink, generally the nozzles undergo servicing so that they can indeed properly eject ink. Typically, the nozzles undergo servicing such that a least-severe servicing event is performed first. The least-severe servicing event causes less ink to be ejected than more-severe servicing events. However, this conventional approach of servicing can greatly lengthen the time it takes to service an inkjet nozzle for pigment-based inks. 
     So-called “spitting,” or ejecting, of ink from an inkjet nozzle has been found to be an efficient way to remove large volumes of ink from an inkjet mechanism, such as an inkjet printhead, including the nozzle, when needed. However, in the case of pigment-based inks, such spitting can result in viscous sludge forming on the inkjet mechanism. This conventional ink spitting is thus disadvantageous as well. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a representative inkjet-printing device, according to an embodiment of the invention. 
         FIGS. 2A and 2B  are diagrams of inkjet cartridges and how they are inserted into an inkjet-printing device, according to an embodiment of the invention. 
         FIGS. 3A and 3B  are diagrams of inkjet printheads and how they are inserted into an inkjet-printing device, according to an embodiment of the invention. 
         FIG. 4  is a diagram of an inkjet printhead having a number of inkjet nozzles, according to an embodiment of the invention. 
         FIGS. 5A ,  5 B, and  5 C are flowcharts of a method for servicing an inkjet printhead, according to an embodiment of the invention. 
         FIG. 6  is a diagram depicting a representative drop detect test, according to an embodiment of the invention. 
         FIG. 7  is a diagram depicting a representative spit operation, according to an embodiment of the invention. 
         FIG. 8  is a diagram depicting a representative wipe operation, according to an embodiment of the invention. 
         FIG. 9  is a diagram depicting a representative prime operation, according to an embodiment of the invention. 
         FIG. 10  is a rudimentary block diagram of an inkjet-printing device, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Representative Fluid-Ejection Device 
       FIG. 1  shows a representative inkjet-printing device  100 , according to an embodiment of the invention. The inkjet-printing device  100  is a device, such as a printer, that ejects ink onto media, such as paper, to form images, which can include text, on the media. The inkjet-printing device  100  is more generally a fluid-ejection device that ejects fluid, such as ink. 
     The inkjet-printing device  100  may eject pigment-based ink, dye-based ink, or another type of ink. The inkjet-printing device  100  includes at least two access doors: an access door  102 , and an access door  104 . The access door  104  is opened to permit a user to remove and insert ink cartridges into and from the inkjet printing device  100 . The access door  102  is opened to permit a user to remove and insert inkjet printheads into and from the inkjet printing device  100 . 
       FIG. 2A  shows a number of ink cartridges  202  that may be inserted into the inkjet-printing device  100 , according to an embodiment of the invention. In one embodiment, there may be eight such ink cartridges  202 . These ink cartridges  202  may include photo black pigment-based ink cartridge, a light gray pigment-based ink cartridge, and a matte black pigment-based ink cartridge. These ink cartridges  202  may further include a cyan pigment-based ink cartridge, a magenta pigment-based ink cartridge, a yellow pigment-based ink cartridge, a light magenta pigment-based ink cartridge, and a light cyan pigment-based ink cartridge. Having eight such ink cartridges  202  enables the inkjet-printing device  100  to print photorealistic full-color images on media. 
     In another embodiment, however, there may be just four ink cartridges  202 . The ink cartridges  202  in this embodiment may include black, cyan, magenta, and yellow ink cartridges. Having four such ink cartridges enables the inkjet-printing device  100  to print full-color images on media, but generally not as photorealistic as when there are eight ink cartridges  202 . In still another embodiment, there may be just a single black ink cartridge  202 . In this embodiment, the inkjet-printing device  100  can print black-and-white and grayscale images on media, but not color images. 
       FIG. 2B  shows how the ink cartridges  202  may be inserted into the inkjet-printing device  100 , according to an embodiment of the invention. The access door  104  is opened downwards. Opening the access door  104  reveals a number of slots. The ink cartridges  202  can be inserted into and removed from these slots of the inkjet-printing device  100 . The ink cartridges  202  supply the differently colored ink by which the inkjet-printing device  100  forms images on media. The inkjet cartridges  202  are more generally fluid supplies, such as supplies of ink. 
       FIG. 3A  shows a number of inkjet printheads  302  that may be inserted into the inkjet-printing device  100 , according to an embodiment of the invention. The inkjet printheads  302  are more generally fluid-ejection mechanisms, in that they are the actual mechanisms that eject fluid, such as ink, onto media to form images on the media. There may be four such inkjet printheads  302  in one embodiment of the invention. One inkjet printhead may be responsible for ejecting photo black and light gray ink. Another inkjet printhead may be responsible for ejecting matte black and cyan ink. A third inkjet printhead may be responsible for ejecting magenta and yellow ink. The last inkjet printhead may be responsible for ejecting light magenta and light cyan ink. 
     In another embodiment, however, there may be just two inkjet printheads  302 , in the case where there are just four differently colored inks, cyan, magenta, yellow, and black. One of these inkjet printheads may be responsible for ejecting black ink, whereas the other printhead may be responsible for ejecting cyan, magenta, and yellow ink. In still another embodiment, there may be just a single inkjet printhead, in the case where there is just black ink, such that the single inkjet printhead ejects this black ink. 
       FIG. 3B  shows how the inkjet printheads  302  may be inserted into the inkjet-printing device  100 , according to an embodiment of the invention. The access door  102  is opened upwards. Opening the access door  102  reveals a number of slots. The inkjet printheads  302  can be inserted into and removed from these slots of the inkjet-printing device  100 . The inkjet printheads  302  thus eject the ink supplied by the ink cartridges  202  to form images on media. 
     The embodiments of the invention that have been described in relation to  FIGS. 2A ,  2 B,  3 A, and  3 B employ ink supplies—the ink cartridges  202 —that are separate from the inkjet printheads  302 . However, in another embodiment, the inkjet cartridges  202  may be integrated within the inkjet printheads  302 . That is, the inkjet printheads  302  may themselves include supplies of ink, such that there are no separate inkjet cartridges  202  per se to be inserted into and removed from the inkjet-printing device  100 . 
       FIG. 4  shows a detailed view of an inkjet printhead  402 , according to an embodiment of the invention. The inkjet printhead  402  exemplifies each of the inkjet printheads  302  that have been described. The side of the inkjet printhead  402  from which ink is actually ejected is specifically depicted in  FIG. 4 . 
     The inkjet printhead  402  includes a number of inkjet nozzles  404 , which may more generally be referred to as fluid-ejection nozzles. The inkjet nozzles  404  are organized over a number of columns  406 A,  406 B, . . . ,  406 M, collectively referred to as the columns  406 , and a number of rows  408 A,  408 B, . . . ,  408 N, collectively referred to as the rows  408 . In one embodiment, for example, there may be four columns  406  and  528  rows  408 , for a total of 2,112 of inkjet nozzles  404 . It is noted that the inkjet nozzles  404  are organized in aligned columns  406  in the example of  FIG. 4 . However, in another embodiment, the inkjet nozzles  404  may be organized in columns  406  such that adjacent columns are staggered relative to one another. 
     The inkjet nozzles  404  are the orifices from which ink, or fluid, is ejected out of the inkjet printhead  402 . The surface of the inkjet printhead  402  shown in  FIG. 4  may be referred to as the orifice plate, which comes into close contact with the media so that ink can be precisely ejected from the inkjet nozzles  404  onto the media in a desired manner. The inkjet nozzles  404 , especially in the case where the ink is a pigment-based ink, are susceptible to clogging, however. 
     That is, as described in the background section, pigment-based ink can form sludge on the orifice plate and/or on or within the inkjet nozzles  404 , impeding the ability of the inkjet nozzles  404  to properly eject ink onto the media to form desired images on the media, where such images may also include text in addition to graphics. Embodiments of the invention are thus concerned with detecting whether the inkjet nozzles  404  of the inkjet printhead  402  are able to properly eject ink. Embodiments of the invention are further concerned with detecting whether servicing the inkjet nozzles  404  of the inkjet printhead  402  when they are unable to properly eject ink. 
     Servicing Process 
       FIGS. 5A ,  5 B, and  5 C show a method  500  for servicing the inkjet printhead  402  of the inkjet-printing device  100 , according to an embodiment of the invention. The method  500  may be performed when the inkjet printhead  402  has been newly installed within the inkjet-printing device  100 . The method  500  may further be performed at periodic cleaning or servicing intervals, or may be initiated by the user when printing quality has degraded. 
     Referring first to  FIG. 5A , a counter is reset to zero ( 502 ). Thereafter, a first drop detect test is performed ( 504 ). A drop detect test determines which and how many of the inkjet nozzles  404  of the inkjet printhead  402  are properly ejecting ink, as opposed to, for instance, being clogged. Drop detect tests include electrostatic drop detect tests and optical drop detect tests, among other types of drop detect tests. An electrostatic drop detect test detects the charge of an ink drop that is induced upon the ink drop by an electrostatic drop detect target. The amount of charge that is detected is related to the amount of ink that is deposited on the target. By comparison, an optical drop detect test optically determines whether and how much ink has been deposited on a target. 
     Thus, the first drop detect test can be performed in one embodiment as follows. First, the inkjet printhead  402  is moved so that it is aimed against a drop detector ( 506 ), which is another term for a drop detect target. The inkjet nozzles  404  of the inkjet printhead  402  are then fired ( 508 ). Based on where and how much ink is deposited on the drop detect target, it can be determined which and how many of the inkjet nozzles  404  successfully (and actually) ejected ink ( 510 ). 
       FIG. 6  illustratively shows a drop detect test, according to an embodiment of the invention. Just three inkjet nozzles  404 A,  404 B, and  404 C of the inkjet printhead  402  are depicted in  FIG. 6  for illustrative convenience. The inkjet printhead  402  is aimed against a drop detector  602 , which may also be referred to as a drop detect target. The inkjet nozzles  404 A,  404 B, and  404 C are then fired to cause them to eject ink. 
     As indicated by the arrows  604 A and  604 C, the inkjet nozzles  404 A and  404 C ejected ink  606 A and  606 C, respectively, against the drop detector  602 . The drop detector  602  is able to detect this ink  606 A and  606 C, and correspond the ink  606 A and  606 C to the inkjet nozzles  404 A and  404 C, so that it can be concluded that the inkjet nozzles  404 A and  404 C properly ejected ink. By comparison, however, dried ink  608 , or sludge, has formed over the inkjet nozzle  404 B. As a result, the inkjet nozzle  404 B did not successfully and properly eject ink, such that the drop detector  602  did not detect any ink being deposited thereon as a result of the inkjet nozzle  404 B firing. 
     Referring back to  FIG. 5A , after the first drop detect test is performed, a second drop detect test is performed ( 512 ). The second drop detect test may be performed in the same manner in which the first drop detect test has been performed, as has been described. More generally, more than one drop detect test is performed. The method  500  determines whether the results of the second drop detect test in the embodiment of  FIG. 5A  has failed a criterion ( 514 ). More generally, the method  500  determines whether the results of the last drop detect test has failed the criterion. Thus, in the embodiment of  FIG. 5A , the results of the first drop detect test are discounted and not used or compared against a criterion, and just the results of the second drop detect test are used. More generally, just the results of the last drop detect test are used and compared against the criterion. 
     It has been found, for instance, that where a single drop detect test is performed and indicates that the inkjet nozzles of an inkjet printhead are properly ejecting ink, the inkjet printhead may nevertheless may have residual clogs or sludge that did not prevent the single drop detect test from succeeding, but that will soon affect ink ejection by the nozzles. Therefore, this is why two drop detect tests are performed in the embodiment of  FIG. 5A . More generally, it has been found that where more than one drop detect test is performed, the results of the last drop detect test more accurately reflect whether the inkjet nozzles of the inkjet printhead are properly ejecting ink, and are not affected by any residual clogs or sludge that would otherwise soon affect ink ejection. 
     It is noted that performing more than one drop detect test does not have to be performed for all colors of ink. Rather, just one drop detect test may be performed for some of the differently colored inks, and more than one drop detect may be performed for other of the differently colored inks. In one embodiment, for instance, more than one drop detect test is performed just for matte black ink. Empirical testing can be performed, as can be appreciated by those of ordinary skill within the art, to determine whether one or more than one drop detect test should be performed for a given color of ink. 
     In one embodiment, the criterion against which the results of the second (i.e., last) drop detect test are compared is a number of the inkjet nozzles  404  of the inkjet printhead  402  that did not successfully eject ink, as detected by the drop detect target. For instance, this criterion may be twenty nozzles. If more than twenty nozzles did not eject ink during the drop detect test, then the drop detect test is considered as having failed the criterion. If twenty or less nozzles did not eject ink during the drop detect test, then the drop detect test is considered as having passed the criterion, by comparison. 
     Assuming that the results of the second drop detect test in the embodiment of  FIG. 5A  failed the criterion ( 514 ), then a servicing event is performed ( 516 ) in order to clear the clogged or sludged-over nozzles. A different servicing event is performed based on the current value of the counter. In particular, however, the servicing event that is performed first (i.e., corresponding to a counter value of zero) is a most-severe servicing event. Servicing event severity can denote the amount of ink that is removed from an inkjet nozzle. Thus, a more severe servicing event is one that removes more ink than a less severe servicing event. 
     The severity of a servicing event is thus dependent on which operations are performed as part of the servicing event. For example, as will be described in more detail, a servicing event can include one or more spit operations, one or more wipe operations, and/or one or more prime operations designed to unclog any clogged of the inkjet nozzles  404  of the inkjet printhead  402 . A spit operation is specifically an operation in which a predetermined amount of ink is ejected from an inkjet nozzle. The inkjet nozzle may be fired a number of times at high frequency to eject this predetermined amount of ink. A wipe operation is an operation in which a wiper is moved in relation to the inkjet nozzle, to clean any ink on or around the nozzle. A prime operation is specifically an operation in which ink is removed from an inkjet nozzle by using suction. Examples of spit and wipe operations are described in more detail later in the detailed description. The amount of ink removed from an inkjet nozzle by all the various operations of a given servicing event in total thus is indicative of the severity of this servicing event. 
     In one embodiment, one of three servicing events, corresponding to counter values of zero, one, and two, is performed in part  516  of the method  500 . As has been noted, the first servicing event is most severe, and may include performing heavy prime, light prime, spit, and wipe operations. The second servicing event is less severe, and may include performing heavy prime, spit, and wipe operations. The third servicing event is least severe, and may include performing light prime, spit, and wipe operations. 
     It is noted that performing the most-severe servicing event first is unlike the prior art, and indeed is somewhat counterintuitive. Conventionally, the least-severe servicing event is performed first, and any other servicing events are performed in order in increasing degrees of severity, such that the most-severe servicing event is performed last. The motivation behind doing so is to decrease servicing time, insofar as the greater the severity of a servicing event, the longer it takes to perform the servicing event. 
     However, what has been found is that with pigment-based inks in particular, the least-severe servicing event either does not usually clear the clogged inkjet nozzles for at least certain colors of ink such as matte black ink, and/or clears the clogged inkjet nozzles but not enough to prevent image formation degradation from occurring soon thereafter. Therefore, performing the most-severe servicing event first is accomplished so that image formation degradation does not occur soon after servicing is performed, and to ensure that the clogged inkjet nozzles are more likely to be cleared the first time a servicing event is performed. This will become more apparent as the remainder of  FIG. 5A  is described. 
     Once the servicing event has been performed, the counter is incremented ( 518 ). The counter is then compared against a predetermined threshold ( 520 ). In one embodiment, this threshold is three. Thus, if the value of the counter is less than three, then the method  500  repeats at part  504 . Otherwise, once the value of the counter has reached three, then the method  500  proceeds to part  522  in  FIG. 5B . The method  500  also proceeds to part  522  in  FIG. 5B  where the results of the second drop detect test do not fail the criterion in part  514 . 
     Where the threshold against which the counter is compared is three, this means that at most three different servicing events are performed in the various iterations of part  516 . In the first iteration of part  516 , the most-severe servicing event is performed. Performing the most-severe servicing event takes longer than performing less-severe servicing events. However, the likelihood that performing the most-severe servicing event will clear the clogged nozzles  404  of the inkjet printhead  402  is greater than if less-severe servicing events were instead performed. Thus, the likelihood that the second drop detect test (in the embodiment of  FIG. 5A ) will again fail is less after performing the most-severe servicing event than if a less-severe servicing event were performed first. 
     That is, what has been found in relation to pigment-based inks in particular is that performing servicing events in order from least-severe to most-severe during successive iterations still results in the most-severe servicing event more often than not having to be performed to clear the clogged inkjet nozzles  404 . Therefore, while intuition would suggest that the least-severe servicing event be performed first, since it takes less time to complete such that servicing time may be minimized if performance of this servicing event yields cleared nozzles, it has been found in actuality that least-severe servicing event does not often clear the clogged inkjet nozzles  404  when performed first. Instead, performing the most-severe servicing event first, even though taking more time, is more likely to clear the clogged nozzles  404 , so that less-severe servicing events do not have to be performed. 
     Referring next to  FIG. 5B , the method  500  continues from part  514  or from part  520  by performing a sustainability purge operation ( 522 ). Performing a sustainability purge operation for the inkjet nozzles  404  of the inkjet printhead  402  adds extra assurance that the inkjet nozzles  404  will remain clear of clogs during subsequent printing, or image-formation, operations. That is, the sustainability purge operation purges additional ink from the inkjet nozzles  404 , to ensure that the inkjet nozzles  404  can in a sustained manner eject ink properly. 
     In one embodiment, the sustainability purge operation is performed by performing parts  524  and  530 . A first series of spit-wipe operations is performed ( 526 ). Such a series of spit-wipe operations includes performing one or more spit operations ( 526 ), substantially interleaved with performing one or more wipe operations ( 528 ). A spit operation ejects a predetermined amount of ink from the inkjet nozzles  404  by firing the inkjet nozzles  404  a number of times at high frequency. A wipe operation cleans the nozzles  404  by moving the nozzles  404  against a stationary wiper, or by moving a wiper against the nozzles  404  as they remain stationary. A second series of spit-wipe operations is performed ( 530 ) after the first series of spit-wipe operations is performed. 
       FIG. 7  illustratively shows a spit operation, according to an embodiment of the invention. Just a single inkjet nozzle  404 A of the inkjet printhead  402  is depicted in  FIG. 7  for illustrative clarity and convenience. The inkjet nozzle  404 A is fired multiple times at a given frequency, such as twelve kilohertz, where each time the inkjet nozzle  404 A is fired, desirably one of the ink droplets  704 A,  704 B, . . . ,  704 N, collectively referred to as the ink droplets  704 , is ejected from the nozzle  404 A. The total volume of the ink droplets  704  is the amount of ink ejected by the nozzle  404 A during the spit operation. The ink droplets  704  are collected within a spittoon  702 , and may later evaporate, or the spittoon  704  may be periodically emptied. 
       FIG. 8  illustratively shows a wipe operation, according to an embodiment of the invention. Just a single inkjet nozzle  404 A of the inkjet printhead  402  is depicted in  FIG. 8  for illustrative clarity and convenience. In one embodiment, the inkjet printhead  402  is moved back and forth as indicated by arrows  804 A and  804 B so that the inkjet nozzle  404 A is moved back and forth against a stationary wiper  802 . The wiper  802  may be a polymer tab, or another type of wiper. In another embodiment, the inkjet printhead  402  remains stationary, and the wiper  802  is moved back and forth against the inkjet nozzle  404 A, as indicated by arrows  806 A and  806 B. 
     It is noted that in at least one embodiment, the sustainability purge operation of part  522  of  FIG. 5B  does not include performance of any prime operations, but just spit and wipe operations. However,  FIG. 9  illustratively shows a prime operation, according to an embodiment of the invention. The prime operation depicted in  FIG. 9  may be that which is performed as part of the servicing event that may be performed in at least some iterations of part  516 . Just a single inkjet nozzle  404 A of the inkjet printhead  402  is depicted in  FIG. 9  for illustrative clarity and convenience. A cap, or primer,  902  seals around the inkjet nozzles, including the inkjet nozzle  404 A. Negative air pressure around the inkjet nozzle  404 A is then created by a suction or vacuum effect, as indicated by the arrow  904 . As a result, ink, as denoted by the ink droplet  906 , is removed from the inkjet nozzle  404 A, and the area surrounding the inkjet nozzle  404 A. A heavy servicing operation may create greater suction and/or apply suction for a longer period of time, than a light servicing operation. 
     Referring back to  FIG. 5B , in one embodiment of the invention, each of the first and the second series of spit-wipe operations is a predetermined sequence of spit and wipe operations. One such sequence may include two sub-sequences. The first sub-sequence may include a first spit operation, followed by a second spit operation, a third spit operation, a wipe operation, and a fourth spit operation. The second sub-sequence may include a first spit operation, followed by a first wipe operation, a second spit operation, a third spit operation, a second wipe operation, and a fourth spit operation. The predetermined sequence may thus include performing one iteration of the first sub-sequence, followed by three iterations of the second sub-sequence. Each of the first and the second series of spit-wipe operations denoted in  FIG. 5B  may be this predetermined sequence of spit and wipe operations. 
     The performance of both spit and wipe operations in a sustainability purge of the inkjet nozzles  404  of the inkjet printhead  402  differs from the prior art, and is somewhat counterintuitive. Conventional sustainability purges, for instance, typically just involve a number of spit operations, since the motivation is to clear the inkjet nozzles as much as possible. However, what has been found is that such conventional sustainability purges can result in undesired sludge buildup on the inkjet nozzles  404  where pigment-based inks are used, resulting in later image formation or printing problems. Therefore, although performing one or more wipe operations is not intuitively performed during a purge operation, embodiments of the invention nevertheless perform such wipe operations to clean the sludge buildup on the inkjet nozzles  404  resulting from the spit operations. 
     After the sustainability purge operation has been performed, an alignment operation of the inkjet nozzles  404  of the inkjet printhead  402  may be performed ( 532 ). This operation is performed to align the ink droplets ejected by the nozzles  404  relative to one another, and as such adjusts the relative positioning of the ink droplets. Such an alignment operation may be performed as is conventional, as can be appreciated by those of ordinary skill within the art. 
     Likewise, a color calibration operation of the inkjet nozzles  404  of the inkjet printhead  402  may be performed ( 534 ). This operation is performed to ensure that the colors that are formed by ejecting differently colored of the inks match predetermined profiles or other criteria. This operation adjusts how much of each ink is ejected to ensure a given color results. Such a color calibration operation may be performed as is conventional, as can be appreciated by those of ordinary skill within the art. Finally, the most-severe servicing event is again performed ( 536 ), to potentially clear any of the nozzles  404  that may have been clogged, or that may soon clog when normal image formation or printing commences, as a result of the operations of parts  532  and  534 . 
     Referring finally to  FIG. 5C , another counter is reset ( 538 ). The first drop detect test is performed again ( 540 ), as is the second drop detect test ( 542 ). Where the results of the second drop detect test failed the criterion ( 544 ), then a servicing event corresponding to the current value of the counter is performed ( 546 ). In one embodiment, one of four servicing events, corresponding to counter values of zero, one, two, and three, is performed in part  546  of the method  500 . 
     The first servicing event may include performing heavy prime, spit, and wipe operations. The second servicing event is less severe than the first servicing event, and may include performing light prime, spit, and wipe operations. The third servicing event is more severe than the first servicing event, and may include performing scrub, spit, and wipe operations. A scrub operation is similar to a wipe operation. However, where a wipe operation moves the wiper in relation to the printhead back and forth in smooth motions, a scrub operation moves the wiper in relation to the printhead back and forth in jerky motions. As such, a scrub operation may be considered a mechanically agitated wipe operation. The fourth servicing event is identical to the first servicing event. Thus, in part  546 , unlike in part  516 , the first servicing event performed is not the most-severe servicing event. 
     The counter is then incremented ( 548 ), and where the current value of the current is less then a predetermined threshold, such as four, the method  500  repeats at part  540  ( 550 ). Therefore, at most four servicing events are performed in various iterations of part  548 , depending on whether the second drop detect test fails the criterion in part  544 , which may, as before, be whether more than twenty of the inkjet nozzles  404  of the inkjet printhead  402  failed to eject ink. Where the second drop detect test satisfies the criterion in part  544 , or once the counter has reached the predetermined threshold in part  550 , the method  500  is finished ( 552 ). As such, the inkjet-printing device  100  is ready to form images on media by ejecting ink. 
     Concluding Block Diagram of Fluid-Ejection Device 
     In conclusion,  FIG. 10  shows a block diagram of the inkjet-printing device  100 , according to an embodiment of the invention. As has been noted, the inkjet-printing device  100  is more generally a fluid-ejection device. The inkjet-printing device  100  is depicted in  FIG. 10  as including the inkjet printhead  402  and logic  1002 . As can be appreciated by those of ordinary skill within the art, the inkjet-printing device  100  may include other components, in addition to and/or in lieu of those depicted in  FIG. 10 . For example, the inkjet-printing device  100  may include the drop detector  602  of  FIG. 6  that has been described, as well as various motors, carriages, and so on, to properly move the inkjet printhead  402  and/or the media on which the printhead  402  forms an image. 
     The inkjet printhead  402  is depicted as part of the inkjet-printing device  100  in  FIG. 10  to denote that the inkjet-printing device  100  can include one or more of the inkjet printheads  302  that have been described. The inkjet printhead  402  is more generally an inkjet-printing mechanism, and is most generally a fluid-ejection mechanism. The inkjet printhead  402  includes a number of inkjet nozzles  404  from which ink is actually ejected. The inkjet nozzles  404  are more generally fluid-ejection nozzles that eject fluid, such as dye-based ink, pigment-based ink, or another type of ink. 
     The logic  1002  may be implemented in software, hardware, or a combination of software and hardware, and may be considered the means that performs various functionality. The logic  1002  can perform, or cause the inkjet printhead  402  to perform, the method  500  of  FIGS. 5A ,  5 B, and  5 C that has been described. Thus, the logic  1002  can cause the inkjet printhead  402  to perform more than one drop detect tests before determining whether to service the inkjet printhead  402  so that ink is properly ejected. 
     As another example, the logic  1002  can cause the inkjet printhead  402  to be serviced by performing one or more servicing events, where the most-severe servicing event is performed first, as has been described. As a final example, the logic  1002  can cause ink to be purged from the inkjet nozzles  404  by performing a number of series of spit-wipe operations, where both spit operations and wipe operations are performed. Thus, the logic  1002  can determine whether servicing has to be performed, and cause such servicing to be performed if needed.