Abstract:
Disclosed herein is a method of placing fluid droplets onto an object. The method includes moving a fluid ejection device in a first direction, reducing air flow between the fluid ejection device and the object with a member leading the fluid ejection device, and ejecting the fluid droplets onto the object.

Description:
BACKGROUND 
     Inkjet printers are of various types including those on which one or more inkjet printheads, also known as pens, are mounted on a reciprocally moving so called scanning carriage, and others in which the pens may be mounted in a stationary position on a frame for so-called page wide printing. Scanning inkjet printers ordinarily have a pen servicing station located at some point on the path of travel of the pen carriage, typically to one side or the other of the print area, so that the scanning carriage and associated pens thereon can be moved to the service station for purging or “spitting”, priming, wiping, capping or otherwise servicing the pen orifices. The servicing station may include pen wipers, a source of pen servicing fluid and pen caps, some or all of which may be mounted in a stationary position or on a sled or other moveable support to bring the pens to be serviced and the service station into and out of operating proximity to each other for servicing. Inkjet printers with stationary printheads or pens which also may require periodic servicing may employ such a sled or moveable support to bring the service station to the stationary pens when servicing of the pen orifices is required. 
     Particularly in high speed printing using large format printer/plotters, the pen carriage and associated pens may be moved at speeds of 30-60 inches per second or even higher. Close control of the pen to paper or other media spacing (PPS) can improve print quality. Swath height error (SHE) is the variation (i.e., in the Y-direction in FIG. 1) in the swath of ink that the pen prints onto the media. Variation in the swath height directly impacts print quality and is responsible for swath boundary banding print defects. Single pass printing is especially sensitive to boundary banding because errors cannot be corrected with shingling or masking techniques as carriage speeds have increased. Dynamic swath height errors due to aerodynamic effects have therefore become an increasing problem, especially during single pass bi-directional printing. Single pass printing and rapid carriage speeds are therefore used for rapid printing. The leading and trailing pens on the carriage are most affected by this aerodynamic phenomenon. 
     SUMMARY 
     Disclosed herein is a method of placing fluid droplets onto an object. The method includes moving a fluid ejection device in a first direction, reducing air flow between the fluid ejection device and the object with a member leading the fluid ejection device, and ejecting the fluid droplets onto the object. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a wide format scanning inkjet printer/plotter as one example of a fluid ejection device in which an embodiment of the present invention may be used. 
     FIG. 2 is a perspective view of one form of a carriage which may be used to support one or more inkjet ink-ejecting pens, here shown with a service station capping or sealing the pens during a period of printing inactivity. 
     FIG. 3 is front elevation view of the carriage of FIG.  3 . 
     FIG. 4 is a side elevation view of the carriage of FIG.  3 . 
     FIG. 5 is a perspective view of one form of a fluid ejection device, here shown as a pen cartridge. 
     FIG. 6 is a schematic perspective of a carriage with an alternative embodiment of an airflow deflecting mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention has broad application to various types of fluid ejection devices such as inkjet pens and may also find application to medical devices, fuel injectors and other equipment in which droplets are to be forcefully ejected from a device such as a piezo-electric, thermal or any other fluid droplet ejector under controlled conditions. For convenience an embodiment of the invention will be described with reference to inkjet printers which typically use thermal or piezo-electric means to eject ink droplets through orifices of a pen nozzle onto media, such as paper or fabric, on which printing is to take place. 
     FIG. 1 is a perspective view of one form of an apparatus using fluid ejection technology, here shown as an inkjet printer/plotter mechanism having a chassis  2  supported by a pair of spaced apart legs  4  and a housing which includes an upper casing  5  and a generally arcuate cover  6  for containing a roll of print medium such as paper, velum, fabric or film. Although a large format printer/plotter is depicted in FIG. 1 by way of example, those skilled in the art will understand that this disclosure is applicable to other types of printers as well, such as desk top size printers, along with other fluid ejection devices such as medical devices, fuel injectors and other equipment in which droplets are forcefully ejected from a device. A printzone  10 , extends transversely across the printer/plotter in the X-direction and has a reach extending in the Y-direction a relatively short distance usually about 2 ½-7cm (about 1-3 inches) although this length is technically unlimited. 
     Referring to FIGS. 2-4, a carriage  20 , which supports a plurality of ink ejecting cartridges or pens  22   a - 22   d  (only four are shown in the illustrated embodiment), is supported on the printer/plotter chassis  2  by guides  24 ,  26  shown in dashed lines in FIG. 4 which, in the illustrated embodiment, comprise a front guide rail  24  which engages a front carriage support  28  and a rear guide  26  shown in the form of a rod which engages a rear carriage support depicted in the illustrated embodiment as a bushing  30 . The carriage is driven back and forth in the X-direction to print onto media intermittently moveable in the Y direction which is supported on a flat or curved platen  12  extending through the print zone  10 . As seen in FIGS. 3 and 4, the spacing in the Z direction from the orifice nozzles of the pens  22  to paper or other media laying on the platen  12  labeled as the dimension “PPS”. (PPS) is preferably closely controlled to optimize printing resolution. 
     In the exemplary type of printer depicted in FIG. 1, a pen service station  32  may be positioned laterally to one side or the other of the media path (at the right side of the printer  1  as shown) and a so-called offboard or “off-axis” ink supply station  34  may be provided at the other (left) side containing relatively large supplies of ink for replenishing ink used during printing from ink chambers in the carriage borne pens  22   a - 22   d . The carriage  20  and pens mounted thereon therefore may be parked at the service station  32  so that fluid ejection orifices in the pen nozzles can be serviced by wiping, cleaning, spitting or priming as desired. Pen servicing equipment such as wipers (not shown) and caps  36  may be mounted on a moveable support sled  38  depicted partially in FIGS. 2 and 3 at the service station  32  so that the sled and servicing equipment may be moved toward and away from the carriage  20  and pens  22   a - 22   d  when parked for servicing and/or maintaining the pens in a moist condition during periods when the printer is not engaged in printing. 
     The carriage  20  as depicted in FIGS. 3 and 4 is preferably fabricated of plastic with a bottom portion preferably in the form of a frame  40  having separate apertures therein for reception of nozzle ends  42   a - 42   d  of the respective pens  22   a - 22   d . Each of the nozzle ends  42   a - 42   d , referred to herein generically by item number  42 , comprises a series of fluid ejection nozzles  45  (see FIG. 6 in which the nozzles  45  are shown to a greatly enlarged scale) often arranged in a pair of linear arrays as shown. The pens  22   a - 22   d  may be positioned in individual stalls or receptacles in the carriage  20 . The carriage  20  includes spaced sides  46 ,  48  (FIG. 3) and front and rear portions  50 ,  52  (FIG. 4) comprised of beams, walls or other structural members, the configuration of which will be varied as necessary from printer to printer. 
     Airflow reducing members, depicted in the form of deflectors  56 ,  58  to deflect and thus partially reduce the flow of air between the fluid ejection nozzles  45  and media or other target object, are provided preferably on the carriage  20  or other holder on which the fluid ejectors are supported, although it is possible that appropriately configured deflectors might be provided alternatively or additionally on the fluid ejectors themselves so long as spacing is provided between the deflectors  56 ,  58  and nozzles  45  to allow for capping or other servicing as necessary. The deflectors  56 ,  58  or other airflow reducing means may be separately fabricated parts suitably affixed to the frame  40  such as through bonding or various fasteners, or they may comprise tabs or other fairing configurations molded as integral parts of the carriage  20 . In the depicted embodiment, the carriage includes a pair of holders  54  which space the deflectors  56 ,  58  outwardly in the X-direction from the sides  46 ,  48  of the carriage, and away from the outboard pens  22   a ,  22   d . Accordingly, the fluid ejection nozzles  45  travel through a print zone during movement of said carriage, one of said deflectors  56 ,  58  being outside the print zone, i.e., located to one side of the print zone, when the carriage  20  reaches an end of its reciprocal movement. The deflectors  56 ,  58  are thus positioned so that the carriage  20  and pens mounted thereon can be moved for servicing into the service station  32  without interference with the various servicing modules such as pen caps and wipers when desired. The pens  22  are generally sealed by caps  36  when the printer is not being used, which prevents drying of the ink and clogging of the orifices in the nozzles  45 . Other servicing modules (not shown) may also be present at the service station including pen wipers, primers and receptacles or “spittoons” for receiving ink purposely ejected or “spit” from the pens  22  at the service station to clean the nozzles. 
     The servicing modules present at the servicing station  32  may be mounted on a moveable frame and include the caps  36  as well as other servicing equipment previously described but not shown. FIG. 3 schematically shows part of the service station  32  which includes a frame for holding servicing components mounted for movement toward and away from the pens  22  when the carriage  20  is parked in the service station so that the caps  36  may engage the orifice plate and surround the nozzles  45  to create a humid sealing chamber around the nozzles  45 . As seen in FIG. 3, adequate clearance space is provided between the deflectors  56 ,  58  and the outboard pens  22   a ,  22   d  for the service station frame to have when the caps  36  cover the pen nozzles  45 . 
     The deflectors  56 ,  58  are positioned on the carriage  20  preferably about one pen width (in the X-direction) outwardly away from the fluid ejection nozzles  45  of the outer pens  22   a  and  22   d  to ensure that the deflectors  56 ,  58  effectively reduce airflow near the pens  22  as the carriage travels through the printzone  10 . Airflow reduction will of course be realized by other spacing of the deflectors  56 ,  58  from the nozzles  45 . As seen in FIGS. 3 and 4, the nozzles  45  of the pens  22  typically occupy a common plane P and the deflectors  56 ,  58  preferably extend to and terminate in or near the same plane P, although in other implementations, the deflectors,  56 ,  58  may extend to terminate beyond or before plane P. 
     Although the individual pens  22  need take no special configuration for use, one suitable embodiment of an inkjet pen  22  is shown in FIG. 5 in the form of a disposable inkjet cartridge having an ink reservoir  70 , a nozzle end  42 , a finger grip  72  for removing the cartridge from its individual receptacle in the carriage  20 , an electrical interconnect  74  and various datum surfaces such as  75 ,  76 ,  78  and  80  for accurately positioning the pen  22  in its carriage receptacle. In larger scale printer/plotters in which a considerable amount of ink is used during the printing process, the individual pens  22  may include a refill port  82  which, during use of the printer, is used to intermittently or regularly refill the cartridge with ink from larger so-called off-board or “off-axis” ink supplies located at the ink supply station  34  (shown schematically in FIG. 5) via fluid conduits such as flexible plastic tubing  84 . In smaller printer applications, the pens  22  comprise cartridges each containing sufficient ink for relatively long use and may not have a refill port  74 . Such cartridges are usually disposed after use. 
     The deflectors  56 ,  58  are designed to reduce the detrimental aerodynamic effects on print quality, particularly swath height errors (SHE). The size, position and configuration of the deflectors  56 ,  58  will vary with the specific construction of the carriage  20  and pens  22 . 
     The deflectors  56 ,  58  are therefore appropriately sized, configured and positioned in a particular implementation to effectively deflect and reduce airflow which adversely affects the trajectory of ink droplets ejected from the fluid ejection device toward the media or other target onto which the droplets are to be precisely positioned. The deflectors  56 ,  58  may be angled or pointed in the direction of movement to function as a plow and deflect air away from the leading one of the moving pens  22 . The deflectors  56 ,  58 , thus enhance the performance of fluid ejection devices comprised of one or more separate ejectors such as individual inkjet pens  22  which may be aligned in the X-direction of carriage movement. 
     Lower edges  59  of the deflectors  56 ,  58  extend (downwardly as shown in FIG. 3) to a position closely spaced from the media support platen  12  or other object onto which fluid droplets are to be ejected. As seen in FIG. 4, the lower boundary or edge of the deflectors  56 ,  58  is depicted as straight in the Y-direction although it will be appreciated that this is not essential since the platen  12  over which the media passes for printing may be curved instead of straight, so curved boundary edges for the deflectors  56 ,  58  might be preferable in this instance. Also, the lower edges  59  of the deflectors  56 ,  58  may be generally flat in the X-direction as seen in FIG. 3 or the edges  59  may be tapered, sharpened or rounded to minimize the adherence of ink or debris thereto, and to enhance their aerodynamic effect in reducing airflow between the fluid ejection device and the object onto which droplets are to be projected. Furthermore, while the illustrated deflectors  56 ,  58  are shown as having generally planar outboard surfaces, in other implementations it may be preferable to configure a leading, outboard, exterior surface with an air-piercing contour to minimize drag from air-induced friction. Additionally, the deflectors  56 ,  58  may be rigid or may be purposely designed of resilient materials such as an elastomer to flex slightly during operation. Ink compatible elastomers such as those used to construct resilient components of the service station  32  such as the caps  36  may be used for this purpose. 
     Although the airflow deflecting means are depicted in the preferred embodiments illustrated in FIGS. 2-4 as generally rectangular deflectors  56 ,  58 , various other configurations of airflow deflectors can be readily envisioned including, for example, a fixed carriage skirt  90  as depicted schematically in FIG. 6 in a rectangular configuration. This and some other configurations may, however, undesirably enlarge the dimensions and weight of the carriage  20  and may physically interfere with the frame of the service station  32 , caps  36 , the chassis, the exterior casing  5  or with other service components. As compared with the broad surface area of the skirt  90  depicted in FIG. 6, it will be noted that the surface areas of the edges  59  of the deflectors  56 ,  58  of FIGS. 2-4 which extend generally parallel to the platen  12  are very small and thus accumulation of ink and fiber on the ends of the deflectors  56 ,  58  is minimized to reduce or completely eliminate the necessity to occasionally wipe or otherwise clean them. 
     It will be appreciated that although the edges  59  of the deflectors  56 ,  58  are depicted in the same plane as the nozzles of the pens, this also is not essential. Typically, the PPS is only about  1  mm and it is therefore presently believed that the edges  59  of the deflectors  56 ,  58  should be spaced approximately the same distance from the platen  12  as are the fluid ejection nozzles  45  of the pens  22 . 
     In its broadest sense, the provision of deflectors to deflect and reduce airflow effects on droplet placement in inkjet printers is applicable not only to the bi-directional scanning printers having a moving carriage as described above, but is also applicable to rotary printers and other types of printers in which media is supported on a rapidly rotating drum or belt as it moves relative to inkjet pens and to other applications in which fluid droplets must be accurately positioned on an object moving relative to the fluid ejector or ejectors. 
     Persons skilled in the art will also appreciate that various additional modifications can be made in the preferred embodiments shown and described above and that the scope of protection is limited only by the scope of the claims which follow.