Patent Publication Number: US-6698864-B2

Title: Ink drop detector waste ink removal system

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation of application Ser. No. 09/933,688 filed on Aug. 20, 2001, now U.S. Pat. No. 6,491,366, which is hereby incorporated by reference herein. 
    
    
     INTRODUCTION 
     Printing mechanisms, such as inkjet printers or plotters, often include an inkjet printhead which is capable of forming an image on many different types of media. The inkjet printhead ejects droplets of colored ink through a plurality of orifices and onto a given media as the media is advanced through a printzone. The printzone is defined by the plane created by the printhead orifices and any scanning or reciprocating movement the printhead may have back-and-forth and perpendicular to the movement of the media. Conventional methods for expelling ink from the printhead orifices, or nozzles, include piezo-electric and thermal techniques which are well-known to those skilled in the art. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, the Hewlett-Packard Company. 
     In a thermal inkjet system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains columnar arrays of heater elements, such as resistors, which are individually addressable and energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. The inkjet printhead nozzles are typically aligned in one or more columnar arrays substantially parallel to the motion of the print media as the media travels through the printzone. The length of the columnar nozzle arrays defines the maximum height, or “swath” height of an imaged bar that would be printed in a single pass of the printhead across the media if all of the nozzles were fired simultaneously and continuously as the printhead was moved through the printzone above the media. 
     Typically, the print media is advanced under the inkjet printhead and held stationary while the printhead passes along the width of the media, firing its nozzles as determined by a controller to form a desired image on an individual swath, or pass. The print media is usually advanced between passes of the reciprocating inkjet printhead in order to avoid uncertainty in the placement of the fired ink droplets. If the entire printable data for a given swath is printed in one pass of the printhead, and the media is advanced a distance equal to the maximum swath height in-between printhead passes, then the printing mechanism will achieve its maximum throughput. 
     Often, however, it is desirable to print only a portion of the data for a given swath, utilizing a fraction of the available nozzles and advancing the media a distance smaller than the maximum swath height so that the same or a different fraction of nozzles may fill in the gaps in the desired printed image which were intentionally left on the first pass. This process of separating the printable data into multiple passes utilizing subsets of the available nozzles is referred to by those skilled in the art as “shingling,” “masking,” or using “print masks.” While the use of print masks does lower the throughput of a printing system, it can provide offsetting benefits when image quality needs to be balanced against speed. For example, the use of print masks allows large solid color areas to be filled in gradually, on multiple passes, allowing the ink to dry in parts and avoiding the large-area soaking and resulting ripples, or “cockle,” in the print media that a single pass swath would cause. 
     A printing mechanism may have one or more inkjet printheads, corresponding to one or more colors, or “process colors” as they are referred to in the art. For example, a typical inkjet printing system may have a single printhead with only black ink; or the system may have four printheads, one each with black, cyan, magenta, and yellow inks; or the system may have three printheads, one each with cyan, magenta, and yellow inks. Of course, there are many more combinations and quantities of possible printheads in inkjet printing systems, including seven and eight ink/printhead systems. 
     Each process color ink is ejected onto the print media in such a way that the drop size, relative position of the ink drops, and color of a small, discreet number of process inks are integrated by the naturally occurring visual response of the human eye to produce the effect of a large colorspace with millions of discernable colors and the effect of a nearly continuous tone. In fact, when these imaging techniques are performed properly by those skilled in the art, near-photographic quality images can be obtained on a variety of print media using only three to eight colors of ink. 
     This high level of image quality depends on many factors, several of which include: consistent and small ink drop size, consistent ink drop trajectory from the printhead nozzle to the print media, and extremely reliable inkjet printhead nozzles which do not clog. 
     To this end, many inkjet printing mechanisms contain a service station for the maintenance of the inkjet printheads. These service stations may include scrapers, ink-solvent applicators, primers, and caps to help keep the nozzles from drying out during periods of inactivity. Additionally, inkjet printing mechanisms often contain service routines which are designed to fire ink out of each of the nozzles and into a waste spittoon in order to prevent nozzle clogging. 
     Despite these preventative measures, however, there are many factors at work within the typical inkjet printing mechanism which may clog the inkjet nozzles, and inkjet nozzle failures may occur. For example, paper dust may collect on the nozzles and eventually clog them. Ink residue from ink aerosol or partially clogged nozzles may be spread by service station printhead scrapers into open nozzles, causing them to be clogged. Accumulated precipitates from the ink inside of the printhead may also occlude the ink channels and the nozzles. Additionally, the heater elements in a thermal inkjet printhead may fail to energize, despite the lack of an associated clogged nozzle, thereby causing the nozzle to fail. 
     Clogged or failed printhead nozzles result in objectionable and easily noticeable print quality defects such as banding (visible bands of different hues or colors in what would otherwise be a uniformly colored area) or voids in the image. In fact, inkjet printing systems are so sensitive to clogged nozzles, that a single clogged nozzle out of hundreds of nozzles is often noticeable and objectionable in the printed output. 
     It is possible, however, for an inkjet printing system to compensate for a missing nozzle by removing it from the printing mask and replacing it with an unused nozzle or a used nozzle on a later, overlapping pass, provided the inkjet system has a way to tell when a particular nozzle is not functioning. In order to detect whether an inkjet printhead nozzle is firing, a printing mechanism may be equipped with a number of different ink drop detector systems. 
     One type of ink drop detector system utilizes a piezoelectric target surface that produces a measurable signal when ink droplets contact the target surface. Unfortunately, however, this type of technology is expensive and often is unable to detect the extremely small drops of ink used in inkjet printing systems with photographic image quality. 
     Another type of ink drop detector utilizes an optical sensor which forms a measurable signal when an ink droplet passes through a light beam from a sensory circuit. Unfortunately, this method is subject to extremely tight alignment tolerances which are difficult and expensive to setup and maintain. Additionally, an optical ink drop detection system is susceptible to the ink aerosol which results from the firing of the inkjet printhead inside of the printing mechanism. The aerosol coats the optical sensor over time, degrading the optical sensor signal and eventually preventing the optical sensor from functioning. 
     A more effective solution for ink drop detection is to use a low cost ink drop detection system, such as the one described in U.S. Pat. No. 6,086,190 assigned to the present assignee, Hewlett-Packard Company. This drop detection system utilizes an electrostatic sensing element which is imparted with an electrical stimulus when struck by a series of ink drop bursts ejected from an inkjet printhead. The electrostatic sensing element may be made sufficiently large so that printhead alignment is not critical, and the sensing element may function with amounts of ink or aerosol on the sensing element surface which would incapacitate other types of drop detection sensors. 
     In practical implementation, however, this electrostatic sensing element has some limitations. First, successive drops of ink, drying on top of one another quickly form stalagmites of dried ink which may grow toward the printhead. Since it is preferable to have the electrostatic sensing element very close to the printhead for more accurate readings, these stalagmites may eventually interfere with or permanently damage the printhead, adversely affecting print quality. Second, as the ink residue dries, it remains conductive and may short out the drop detector electronics as the ink residue grows and spreads. Thus, this dried residue may impair the ability of the sensor to measure the presence of drops properly. 
     Therefore, it is desirable to have a method and mechanism for effectively removing the waste ink residue from an electrostatic ink drop detector in an inkjet printing mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmented perspective view of one form of an inkjet printing mechanism, here including a service station having an electrostatic ink drop detector and illustrating an embodiment of an electrostatic ink drop detector waste ink removal system. 
     FIG. 2 is an enlarged perspective view of the service station of FIG. 1 
     FIG. 3 is an enlarged side elevational view of the service station of FIG. 1 shown with an inkjet printhead firing ink onto the electrostatic ink drop detector. 
     FIG. 4 is an enlarged side elevational view of the service station of FIG. 1, showing the electrostatic ink drop detector being cleaned by an embodiment of a waste ink removal system. 
     FIGS. 5-7 are cross-sectional partial perspective views of separate embodiments illustrating capillary drain surfaces. 
     FIG. 8 is a cross-sectional view of the embodiment of a capillary drain surface illustrated in FIG. 9, taken along the lines indicated in FIG.  9 . 
     FIGS. 9-14 are partial plan views from the top of separate embodiments illustrating capillary drain surfaces. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an embodiment of a printing mechanism, here shown as an inkjet printer  20 , constructed in accordance with the present invention, which may be used for printing on a variety of media, such as paper, transparencies, coated media, cardstock, photo quality papers, and envelopes in an industrial, office, home or other environment. A variety of inkjet printing mechanisms are commercially available. For instance, some of the printing mechanisms that may embody the concepts described herein include desk top printers, portable printing units, wide-format printers, hybrid electrophotographic-inkjet printers, copiers, cameras, video printers, and facsimile machines, to name a few. For convenience the concepts introduced herein are described in the environment of an inkjet printer  20 . 
     While it is apparent that the printer components may vary from model to model, the typical inkjet printer  20  includes a chassis  22  surrounded by a frame or casing enclosure  24 , typically of a plastic material. The printer  20  also has a printer controller, illustrated schematically as a microprocessor  26 , that receives instructions from a host device, such as a computer or personal digital assistant (PDA) (not shown). A screen coupled to the host device may also be used to display visual information to an operator, such as the printer status or a particular program being run on the host device. Printer host devices, such as computers and PDA&#39;s, their input devices, such as a keyboards, mouse devices, stylus devices, and output devices such as liquid crystal display screens and monitors are all well known to those skilled in the art. 
     A conventional print media handling system (not shown) may be used to advance a sheet of print media (not shown) from the media input tray  28  through a printzone  30  and to an output tray  31 . A carriage guide rod  32  is mounted to the chassis  22  to define a scanning axis  34 , with the guide rod  32  slidably supporting an inkjet carriage  36  for travel back and forth, reciprocally, across the printzone  30 . A conventional carriage drive motor (not shown) may be used to propel the carriage  36  in response to a control signal received from the controller  26 . To provide carriage positional feedback information to controller  26 , a conventional encoder strip (not shown) may be extended along the length of the printzone  30  and over a servicing region  38 . A conventional optical encoder reader may be mounted on the back surface of printhead carriage  36  to read positional information provided by the encoder strip, for example, as described in U.S. Pat. No. 5,276,970, also assigned to the Hewlett-Packard Company, the present assignee. The manner of providing positional feedback information via the encoder strip reader may also be accomplished in a variety of ways known to those skilled in the art. 
     In the printzone  30 , the media sheet receives ink from an inkjet cartridge, such as a black ink cartridge  40  and a color inkjet cartridge  42 . The black ink cartridge  40  is illustrated herein as containing a pigment-based ink. For the purposes of illustration, color cartridge  42  is described as containing three separate dye-based inks which are colored cyan, magenta, and yellow, although it is apparent that the color cartridge  42  may also contain pigment-based inks in some implementations. It is apparent that other types of inks may also be used in the cartridges  40  and  42 , such as paraffin-based inks, as well as hybrid or composite inks having both dye and pigment characteristics. The illustrated printer  20  uses replaceable printhead cartridges where each cartridge has a reservoir that carries the entire ink supply as the printhead reciprocates over the printzone  30 . As used herein, the term “cartridge” may also refer to an “off-axis” ink delivery system, having main stationary reservoirs (not shown) for each ink (black, cyan, magenta, yellow, or other colors depending on the number of inks in the system) located in an ink supply region. In an off-axis system, the cartridges may be replenished by ink conveyed through a conventional flexible tubing system from the stationary main reservoirs which are located “off-axis” from the path of printhead travel, so only a small ink supply is propelled by carriage  36  across the printzone  30 . Other ink delivery or fluid delivery systems may also employ the systems described herein, such as replaceable ink supply cartridges which attach onto print cartridges having permanent or semi-permanent print heads. 
     The illustrated black cartridge  40  has a printhead  44 , and color cartridge  42  has a tri-color printhead  46  which ejects cyan, magenta, and yellow inks. The printheads  44 ,  46  selectively eject ink to form an image on a sheet of media when in the printzone  30 . The printheads  44 ,  46  each have an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The nozzles of each printhead  44 ,  46  are typically formed in at least one, but typically two columnar arrays along the orifice plate. Thus, the term “columnar” as used herein may be interpreted as “nearly columnar” or substantially columnar, and may include nozzle arrangements slightly offset from one another, for example, in a zigzag arrangement. Each columnar array is typically aligned in a longitudinal direction perpendicular to the scanning axis  34 , with the length of each array determining the maximum image swath for a single pass of the printhead. The printheads  44 ,  46  are illustrated as thermal inkjet printheads, although other types of printheads, or ink drop generators may be used, such as piezoelectric printheads. The thermal printheads  44 ,  46  typically include a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed which ejects a droplet of ink from the nozzle and onto the print media when in the printzone  30  under the nozzle. The printhead resistors are selectively energized in response to firing command control signals delivered from the controller  26  to the printhead carriage  36 . 
     Between print jobs, the inkjet carriage  36  moves along the carriage guide rod  32  to the servicing region  38  where a service station  48  may perform various servicing functions known to those in the art, such as, priming, scraping, and capping for storage during periods of non-use to prevent ink from drying and clogging the inkjet printhead nozzles. 
     FIG. 2 shows the service station  48  in detail. A service station frame  50  is mounted to the chassis  22 , and houses a moveable pallet  52 . The moveable pallet  52  may be driven by a motor (not shown) to move in the frame  50  in the positive and negative Y-axis directions. The moveable pallet  52  may be driven by a rack and pinion gear powered by the service station motor in response to the microprocessor  26  according to methods known by those skilled in the art. An example of such a rack and pinion system in an inkjet cleaning service station can be found in U.S. Pat. No. 5,980,018, assigned to the Hewlett-Packard Company, also the current assignee. The end result is that pallet  52  may be moved in the positive Y-axis direction to a servicing position and in the negative Y-axis direction to an uncapped position. The pallet  52  supports a black printhead cap  54  and a tricolor printhead cap  56  to seal the printheads  44  and  46 , respectively, when the moveable pallet  52  is in the servicing position, here a capping position. 
     FIG. 2 also shows an ink drop detector system  58  supported by the service station frame  50 . Clearly, the ink drop detector system  58  could be mounted in other locations along the printhead scanning axis  34 , including the right side of the service station frame  50 , inside the service station  48 , or the opposite end of the printer from the service station  48 , for example. However, the illustrated location of the ink drop detector  58  is the preferred location, and will be used to illustrate the preferred principles of manufacture and operation, although other locations may be more suitable in other implementations. 
     The ink drop detector system  58  has a printed circuitboard assembly (PCA)  60  which is supported by the service station frame  50 . The PCA  60  has a conductive electrostatic sensing element  62 , or “target” on the upper forward end onto which ink droplets may be fired and detected according to the apparatus and method described in U.S. Pat. No. 6,086,190, assigned to the Hewlett-Packard Company, the present assignee. The target  62  is preferably constructed of gold. The PCA  60  contains various electronics (not shown) for filtering and amplification of drop detection signals received from the target  62 . An electrical conductor  64  links the ink drop detector  58  to controller  26  for drop detection signal processing. The ink drop detector system  58  also has a waste ink removal system  65 . 
     Attached to the PCA  60  is a stationary slider cover  66  which acts as a guide for the movement of a scraper slider  68 . The slider cover  66  may also be designed to shield electrical components on the ink drop detector  58  from ink aerosol generated from the printheads  44 ,  46 . The scraper slider  68  is capable of being moved in the positive and negative Y-axis directions, and is biased towards the rear of the service station  48  (negative Y-axis direction) by a biasing member, such as a tension spring or return spring  70 , which is connected between the scraper slider  68  and a post projecting from the service station frame  50 . The scraper slider  68  has a scraper  72  attached or preferably overmolded onto a front end of the slider  68 . The front edge  74  of scraper  72  may be angled back (in the negative Y-axis and negative X-axis directions) towards the service station  48  as illustrated in FIG.  2 . This angled front edge  74  of the wiper helps to push ink and ink residue into the service station as well as providing a smooth transition while traveling over a capillary drain surface  76  which will be discussed shortly. The width of scraper  72  is sufficient to scrape the entire width of the target  62 . The scraper  72  is preferably constructed of an elastomer, such as a thermoplastic elastomer (TPE) which is overmolded onto the slider  68 . The scraper  72  may also be constructed of a non-overmolded, rigid one-piece plastic. Additionally, the scraper  72  may be pressed onto the slider  68  as a separate part. Other methods of coupling a scraper  72  to the slider  68  will readily be apparent to those skilled in the art, and those methods are intended to be covered by the scope of this specification. The return spring  70  is preferably mounted at an angle above the slider  68  in order to impart a minimal downward scraping force to scraper  72 , thereby minimizing the wear of target  62 . The ink drop detector  58  also includes a capillary drain surface  76  which may be molded as part of frame  50  or coupled to frame  50 . The capillary drain surface  76  is a reservoir configured to receive ink scraped from the electrostatic sensing element  62  when the scraper  72  is moved in the positive Y-axis direction across the sensing element  62  and over the capillary drain surface  76 . Capillary drain surface  76  has channels  77  formed in the top of the capillary drain surface  76 . The channels  77  may vary in cross-sectional shape, depth, and spacing. Each channel  77  leads to and may be fluidically coupled to the service station  48 . 
     Movement is preferably imparted to the scraper slider  68  through movement of the moveable pallet  52  as the pallet  52  moves from the uncapped position shown in FIG. 3 to the capped position shown in FIG.  4 . FIGS. 3 and 4 also show a moveable pallet tower  78  which protrudes upwardly from the moveable pallet  52  on the side of the moveable pallet  52  adjacent to the scraper slider  68 . A scraper slider leg  80 , which is integral to the scraper slider  68 , protrudes inwardly and downwardly towards the moveable pallet  52 . The moveable pallet tower  78  is sized and positioned to engage the scraper slider leg  80  as the moveable pallet  52  is moved from the uncapped position of FIG.  3 . to the capped position of FIG.  4 . The force exerted by the moveable pallet tower  78  on the scraper slider leg  80  is greater than the opposing force of the return spring  70 , and moving the moveable pallet  52  causes the scraper slider  68  to move from the fully retracted position shown in FIG. 3 to the fully engaged position of FIG.  4 . As the scraper slider  68  moves to the engaged position, the scraper  72  is scraped across the electrostatic target  62  and over the capillary drain surface  76 , as shown in FIG.  4 . The scraper  72  remains over the capillary drain surface  76  while the moveable pallet  52  is in the capped position. The capillary drain surface  76  may be designed so that it either contacts the scraper  72  or so that it does not contact scraper  72 . In either case, ink will be scraped off of the target  62  and deposited onto the capillary drain surface  76  for further removal. When the moveable pallet  52  is returned to the uncapped position, the scraper slider  68  is also retracted due to the force of return spring  70 . As moveable pallet  52  retracts, scraper  72  slides from the position shown in FIG. 4 over the capillary drain surface  76 , back across the target  62 , and into the retracted position shown in FIG.  3 . 
     While the preferred method of actuating the scraper  72  is through the above-described movement of moveable pallet  52 , it should be apparent that other mechanisms may be substituted to act as the actuator for the scraper  72 , including, for example, a solenoid or a motor which operate in response to the controller  26 . 
     While the moveable pallet  52  is in the uncapped position and the scraper  72  is in the retracted position, as shown in FIG. 3, the inkjet carriage  36  may be moved along the carriage guide rod  32  until one or more of the printheads  44 ,  46  are positioned directly over the electrostatic sensing target  62 . For illustration purposes, the tri-color printhead  46  is shown positioned over target  62  in FIG. 3, although it is apparent that either of the printheads  44 ,  46  may be positioned over the target  62  either one at a time or in various simultaneous combinations if allowed by the size of the target  62 , the size of each printhead, and the spacing between the printheads. 
     The preferred spacing between the printheads  44 ,  46  and the target  62  is on the order of two millimeters. Once the printhead  46  is properly aligned with the target  62 , the controller  26  causes ink droplets  82  to be fired from printhead  46  onto the target  62 . An electrical drop detect signal is generated by the ink droplets  82  as they contact the target  62 , and this signal is captured by the electronics of PCA  60 . The drop detect signal is then analyzed by controller  26  to determine whether or not various nozzles of printhead  46  are spitting ink properly or whether they are clogged. A preferred method of analyzing signals from an electrostatic target ink drop detector is shown in U.S. Pat. No. 6,086,190, also assigned to the present assignee, the Hewlett-Packard Company. Based on the determination made by the controller  26  as to whether each nozzle is functioning properly, the controller  26  may adjust the print masks to substitute functioning nozzles for any malfunctioning nozzles to provide consistent high-quality printed output while still using a printhead with permanently clogged nozzles. 
     In order to ensure that a reliable measurement may be made by the ink drop detector  58 , it is desirable to remove ink residue from the target  62  after a measurement or series of measurements have been made to prevent excessive deposits of dried ink from accumulating on the surface of target  62 . Dried ink deposits may short out the electrostatic sensing target  62 , degrading the ability of the ink drop detector system  58  to make measurements. Additionally, dried ink deposits may accumulate over time to form stalagmites which may eventually grow to interfere with the printheads  44 ,  46 , possibly damaging nozzles which hit the stalagmites, a process known as “stalagmite crashes.” 
     Accordingly, the scraper  72  is scraped across the target  62  every time the moveable pallet  52  is moved to the capping position to seal the printheads  44 - 46  as described above. Prior to moving the pallet  52 , the inkjet carriage  36  is preferably moved past the ink drop detector  58  and over the servicing region  38  until black printhead cap  54  aligns with black printhead  44 , and tri-color printhead cap  56  aligns with tri-color printhead  46 . When the printheads  44 ,  46  are aligned with the caps  54 ,  56  the scraper slider  68  and the scraper  72  are free to move without interference from the cartridges  40 ,  42  or the carriage  36 . 
     The previously described motion of the scraper  72 , as it traverses across the target  62  into the engaged position over the capillary drain surface  76 , forces the wet ink from the target  62  onto the capillary drain surface  76  while also pushing away any built-up deposits of dried ink on the target  62  which might otherwise have begun to form stalagmites. 
     FIGS. 5-7 illustrate example embodiments of the channels  77  which may be formed in the capillary drain surface  76 . FIG. 5 illustrates channels  77  which are triangular in a cross-section taken parallel to the plane defined by the Z-axis and the Y-axis. FIG. 6 illustrates channels  77  which are rectangular in a cross-section taken parallel to the plane defined by the Z-axis and the Y-axis. FIG. 8 illustrates channels  77  which are arcuate in a cross-section taken parallel to the plane defined by the Z-axis and the Y-axis. Of course, many other cross-sectional shapes are possible, including cross-sectional shapes which vary in any given channel. The channels  77  illustrated in FIGS. 5-7 are exaggerated to show detail, but in practice, the dimensions of the channels  77  may be much smaller to facilitate the formation of a capillary drain  84  at the base of the channel  77 , running the length of the channel  77 . Channels  77  which come to a substantial point, such as the channels  77  illustrated in FIG. 5, may be rather large compared to the capillary drain  84  which will naturally form at the narrowed point of the triangular channel  77  cross-section taken parallel to the plane defined by the Z-axis and the Y-axis. It should also be noted that the cross-sections in FIGS. 5-7 are substantially orthogonal to the path fluid will follow, or “fluid path”, in the capillary drains  84 . 
     FIG. 8 is a cross-sectional view of an alternate embodiment of the capillary drain surface  76 , taken along the lines indicated in FIG.  9 . FIG. 8 illustrates that it may also be desirable to form the capillary drains  84  in the channels  77  with a slope which leads downward to the service station  48 . Capillary drains  84  employing a slope similar to the embodiment of FIG. 8 will have the force of gravity to help ink to flow towards the service station  48  in addition to capillary forces, although capillary forces alone should be sufficient to remove the ink residue. 
     When the scraper  72  travels over the capillary drain surface  76 , the scraper  72  may contact peak areas  86 . It is also possible to design the peak areas  86  such that the scraper  72  does not contact the peak areas  86  when the scraper  72  is traveling over the capillary drain surface  76 . The peak areas  86  lie between the channels  77 , and form a plane which is substantially parallel with the plane target  62  lies in. Preferably, the peak areas  86  lie in substantially the same plane as target  62 . The size of the peak areas  86  will vary depending on the size, cross-sectional shape, and spacing of the channels  77 . As the moveable pallet  52  moves from the uncapped position in FIG. 3 to the capped position in FIG. 4, the scraper  72  is moved across the target  62  and over the capillary drain surface  76  as described above. Ink residue scraped by the scraper  72  is deposited into the channels  77 . The liquid ink residue flows into the capillary drains  84  formed in the bottom of the channels  77  and flows through capillary force and gravity to the service station  48  where it can conveniently be stored. Other receptacles, besides the service station  48  may also be used to receive the ink from the capillary drains  84 , such as a separate or stand-alone spittoon or receptacle. A separate spittoon or receptacle may also be used to separate the ink residue resultant from ink drop measurements from the ink residue which may otherwise be present in the service station  48 . Solid ink residue is pushed by the scraper  72  onto the peak areas  86  of the capillary drain surface  76 , and depending on the size of the solid ink residue with respect to the size of the channels  77 , the solid ink residue may be partially pushed into the channels  77 . The angled design of front edge  74  of scraper  72  will tend to sweep the solid ink residue off of the peak areas  86  and into the service station  48 . 
     FIGS. 9-14 are a partial plan view from the top of the wiper  72 , the target  62 , the capillary drain surface  76 , and illustrating several examples of patterns in which the channels  77  may be laid out. In FIGS. 9-14, the channels  77  are simplified by illustrating them as solid lines. There are numerous configurations of channels  77  which may be employed in a particular design for a capillary drain surface  76 . For example, FIG. 9 illustrates channels  77 , defined by the capillary drain surface  76 , which are parallel. The channels  77  defined by the capillary drain surface  76  in FIG. 10 radiate outwardly from a single point. The channels  77  in FIG. 11 include a plurality of parallel sets of channels  77  defined by the capillary drain surface  76 . The channels  77  in FIG. 12 include a plurality of parallel sets of channels  77  which intersect one another. The intersecting channels  77  of FIG. 12 provide alternate capillary paths for liquid ink in the event that one part of a channel  77  is blocked in some way. The embodiment of a capillary drain surface  76  illustrated in FIG. 13 includes manifold slots  88 . The manifold slots  88  intersect the channels  77  and provide a place for the liquid ink residue to accumulate before being removed by channels  77 . The manifold slots  88  also provide a means for the liquid ink to bypass channels  77 , which may be blocked, by providing many channels  77  for the ink to contact in a given manifold slot  88 . FIG. 14 illustrates channels  77  which are not linear. The channels of FIG. 14 are also not all parallel, and they intersect to allow a means to bypass portions of channels  77  which are blocked. Of course, there are many more configurations of channels  77  which may be formed in the capillary drain surface  76 . The spacing between channels  77  may be varied from one capillary drain surface  76  to another, or the spacing may even be varied between individual channels  77  on the same capillary drain surface  76 . 
     A printer control routine used by controller  26  is ideally adjusted to perform ink drop detection measurements just prior to capping. The immediately following process of moving the pallet  52  into the capping position activates the scraper  72 , and the scraper  72  removes the ink from the target  62  while the ink is still wet, thereby minimizing the possibility that stalagmites or dried ink are forming on the target  62  and allowing the liquid ink residue to be removed by the capillary action of the capillary drains  84  which are formed in the channels  77  on the capillary drain surface  76 . 
     When the moveable pallet  52  is moved to the uncapped position, scraper  72  is retracted by return spring  70 , providing clearance for the inkjet carriage  36  to move along carriage guide rod  32  and into the printzone  30  for printing. Using information from the ink drop detector measurements, print masks may be adjusted to replace clogged nozzles for optimum image quality. 
     A waste ink removal system  65 , used in conjunction with an electrostatic ink drop detector system  58 , provides the ability to remove wet ink from the target  62  to the service station  48  before it dries. A waste ink removal system  65  also provides the ability to remove dried-ink buildup before it has a chance to form stalagmites, thereby preventing damage to the printheads  44 ,  46 . Therefore, a waste ink removal system enables a printing mechanism to reliably use ink drop detection readings to provide users with consistent, high-quality, and economical inkjet output despite printheads  44 ,  46  which may clog over time. In discussing various components of the ink drop detector  58  and the service station  48 , various benefits have been noted above. 
     It is apparent that a variety of other structurally equivalent modifications and substitutions may be made to construct an ink drop detector waste ink removal system according to the concepts covered herein depending upon the particular implementation, while still falling within the scope of the claims below.