Abstract:
A printhead and method of printing are provided. The printhead has a body with portions of the body defining a fluid chamber and a nozzle orifice. The nozzle orifice is in fluid communication with the fluid chamber. A drop forming mechanism is operatively associated with the nozzle orifice of the body. A plate is removably positioned over the body and has at least one orifice with the at least one orifice being in fluid communication with the nozzle orifice of the body.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled printing devices, and in particular to the printhead portion of these devices. 
     BACKGROUND OF THE INVENTION 
     Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing. Ink jet printing mechanisms can be categorized by technology, as either drop on demand ink jet or continuous ink jet. 
     The first technology, drop-on-demand ink jet printing, typically provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of an ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. With thermal actuators, a heater, located at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble. This increases the internal ink pressure sufficiently for an ink droplet to be expelled. The bubble then collapses as the heating element cools, and the resulting vacuum draws fluid from a reservoir to replace ink that was ejected from the nozzle. 
     The second technology, commonly referred to as “continuous stream” or “continuous” ink jet printing, uses a pressurized ink source that produces a continuous stream of ink droplets. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of ink breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes. When no print is desired, the ink droplets are directed into an ink-capturing mechanism (often referred to as catcher, interceptor, or gutter). When print is desired, the ink droplets are directed to strike a print medium. 
     A number of different nozzle arrangements are used with various types of printers described above. While,  FIGS. 1   a - 1   d  show representative nozzle architectures for drop-on-demand printhead, the thermal and piezoelectric actuators described below, can also be found in nozzle architectures for continuous printheads. 
       FIG. 1   a  shows, in cross-sectional side view, the basic arrangement of an ejector  10  for one type of drop-on-demand ink jet printer, commonly termed a “roof-shooter device,” and disclosed, for example, in U.S. Pat. No. 6,582,060 issued to Kitakami, et al. on Jun. 24, 2003. A bubble-jet heater provides a drop-forming mechanism  12  for ejecting ink from a nozzle orifice  14  of a fluid chamber  16  formed on a body  38  from a polymer material. The vapor bubble expands in the same direction as the direction of the ejected drop. With this arrangement, nozzle orifice  14  is part of a structure that is permanently bonded to a substrate  18  in the location of arrows  17 . 
       FIG. 1   b  shows a schematic cross-sectional side view of an alternate ejector  10  arrangement in a drop-on-demand ink jet printer utilizing a thermal microactuator device, such as that disclosed in U.S. Pat. No. 6,631,979, issued to Lebens et al. on Oct. 14, 2003, and U.S. Pat. No. 6,598,960 issued to Cabal et al. on Jul. 29, 2003, as drop-forming mechanism  12  for ejecting ink from a nozzle orifice  14  of an fluid chamber  16 . As with the  FIG. 1   a  configuration, nozzle orifice  14  is permanently fixed in size and position as part of a structure bonded to substrate  18  in the location of arrows  17 . 
       FIG. 1   c  shows a cross-sectional side view of another alternate ejector  10  arrangement in a drop-on-demand ink jet printer utilizing a piezoelectric actuator as drop-forming mechanism  12 , and disclosed, for example, in U.S. Pat. No. 6,609,778 issued to Ingham, et al. on Aug. 26, 2003. Here, nozzle orifice  14  is provided by a nozzle plate  19  that is permanently bonded to fluid chamber  16  in the location of arrows  17 . 
       FIG. 1   d  shows a cross-sectional side view of ejector  10  components in another type of drop-on-demand printer, commonly termed a “back-shooter device” type, and disclosed, for example, in U.S. Pat. No. 6,561,626, issued to Min et al. on May 13, 2003, using a thermal bubble-jet heater as drop-forming mechanism  12 . The vapor bubble expands in a direction opposite the direction of the ejected drop. With this arrangement, nozzle plate  19 , permanently bonded to substrate  18 , forms part of the enclosing structure for fluid chamber  16  along with body  38  in the location of arrows  17 . 
     In conventional continuous and drop-on-demand printhead design, nozzle plates are permanently bonded to the body of the printhead using various manufacturing techniques. For example, U.S. Pat. No. 6,644,789, issued to Toews, III on Nov. 11, 2003 discloses an arrangement using a photoresist layer having nozzle apertures laminated to another photoresist layer on the body of the printhead. U.S. Pat. No. 5,900,892 issued to Mantell et al. on May 4, 1999 discloses a nozzle plate fabricated using a photolithographic process, permanently bonded to the body of a printhead. 
     Additionally, and referring back to  FIGS. 1   a - 1   d , printheads are conventionally fabricated with a fixed diameter for nozzle orifice  14 . The dimensions of nozzle orifice  14  are tailored to the viscosity and related drop-forming characteristics of a particular ink. While this arrangement may be expedient for many types of applications, this relatively inflexible dimensional constraint has some drawbacks. For example, by using a fixed diameter for nozzle orifice  14 , a printing apparatus can be constrained to using only a narrow range of inks having a narrow range of viscosity or surface tension. Fixed nozzle orifice  14  dimensions also constrain possible droplet volumes to within a narrow range. Additionally, while it would be desirable to be able to vary the nozzle size of a given printhead instead of constructing a new printhead, no such technology has been commercialized. 
     Another disadvantage of conventional ejector  10  designs relates to cleaning. Numerous types of devices are employed for cleaning ink jet nozzles  10 , both automatically and by hand. Using permanently bonded structures for nozzles  10  complicates the task of cleaning and refurbishing an ink jet printhead. A clogged nozzle plate, if bonded to the printhead using permanent adhesives such as epoxies, may render it economically impractical to clean the printhead, necessitating replacement of the complete printhead as a unit. 
     Thus, it can be appreciated that a more flexible ink jet nozzle plate design could provide substantial benefits for ease of use, equipment maintenance, and overall versatility of a printing apparatus. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a printhead includes a body with portions of the body defining an fluid chamber and a nozzle orifice. The nozzle orifice is in fluid communication with the fluid chamber. A drop forming mechanism is operatively associated with the nozzle orifice of the body. A plate is removably positioned over the body. The plate has at least one orifice in fluid communication with the nozzle orifice of the body. 
     According to another aspect of the present invention, a method of printing includes ejecting fluid drops through a body nozzle orifice and then through a plate nozzle orifice, the plate nozzle orifice being in fluid communication with the body nozzle orifice; removing the plate; replacing the plate with a second plate having a nozzle orifice; and ejecting fluid drops through the body nozzle orifice and then through the second plate nozzle orifice, the second plate nozzle orifice being in fluid communication with the body nozzle orifice. 
     According to another aspect of the present invention, a method of printing includes ejecting fluid drops through a body nozzle orifice and then through a plate nozzle orifice of a plate, the plate nozzle orifice being in fluid communication with the body nozzle orifice; manipulating the plate; repositioning the plate; and ejecting fluid drops through the body nozzle orifice and then through the plate nozzle orifice, the plate nozzle orifice being in fluid communication with the body nozzle orifice. 
     According to another aspect of the present invention, a printhead includes a body with portions of the body defining an fluid chamber. A drop forming mechanism is operatively associated with the fluid chamber. A removable plate has a first position over the body and a second position removed from the body. The plate has at least plate one orifice with the at least one plate orifice being in fluid communication with the fluid chamber of the body when the plate is located in the first position over the body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
         FIGS. 1   a ,  1   b ,  1   c , and  1   d  are cross-sectional side views showing various prior art arrangements of printheads with associated droplet formation components; 
         FIGS. 2   a  and  2   b  are cross-sectional side views showing a drop-on-demand ink jet nozzle using a piezoelectric actuator, adapted with a removable nozzle plate according to the present invention, showing component arrangement and operation, respectively; 
         FIGS. 3   a  and  3   b  are cross-sectional side views showing a drop-on-demand ink jet nozzle of the thermal backshooter type using a heater for droplet formation, adapted with a removable nozzle plate according to the present invention, showing component arrangement and operation, respectively; 
         FIGS. 4   a  and  4   b  are cross-sectional side views showing a drop-on-demand ink jet nozzle of the thermal roofshooter type using a heater for droplet formation, adapted with a removable nozzle plate according to the present invention, showing component arrangement and operation, respectively; 
         FIGS. 5   a  and  5   b  are cross-sectional side views showing a continuous ink jet nozzle using a heater for droplet formation, adapted with a removable nozzle plate according to the present invention, showing component arrangement and operation, respectively; 
         FIG. 6   a - 6   d  are cross-sectional side views showing the inkjet nozzles of  FIGS. 2   a  and  2   b ,  3   a  and  3   b ,  4   a  and  4   b , and  5   a  and  5   b  respectively, having the removable nozzle plate removed to a second position. 
         FIG. 7  shows a top view of one arrangement wherein multiple smaller plate orifices are provided for a single nozzle orifice; 
         FIGS. 8   a ,  8   b , and  8   c  show top views of a removable nozzle plate of the present invention, in various clamping arrangements; 
         FIG. 8   d  shows a side view of the clamping arrangement of  FIG. 8   c;    
         FIGS. 8   e ,  8   f , and  8   g  show top views of a removable nozzle plate of the present invention having various arrangements of plate orifices; 
         FIG. 9  is a cross-sectional side view showing an ink jet nozzle outfitted with the nozzle plate of the present invention, retained by a spring clamping mechanism; 
         FIG. 10  is a cross-sectional side view showing an ink jet nozzle outfitted with the nozzle plate of the present invention, retained by an applied electromagnetic force; 
         FIG. 11  is a cross-sectional side view showing an ink jet nozzle outfitted with the nozzle plate of the present invention, retained by applied pressure or vacuum; 
         FIGS. 12   a  and  12   b  are cross-sectional side views showing an ink jet nozzle outfitted with the nozzle plate of the present invention, wherein the position of the nozzle plate orifice can be adjusted by adjusting the clamping mechanism; 
         FIG. 13  is a cross-sectional side view showing an ink jet nozzle outfitted with the nozzle plate of the present invention, with a liquid film providing attractive force to retain the nozzle plate against the printhead body; 
         FIG. 14  is a cross-sectional side view showing an ink jet nozzle outfitted with the nozzle plate of the present invention, with an additional heat-conductive element for improved energy delivery; 
         FIGS. 15   a  and  15   b  are side and top views respectively of an arrangement of an ink jet nozzle using an additional heat-conductive element; 
         FIG. 16  is a top view showing an arrangement of heater elements and electrical contacts for an alternate embodiment of the nozzle plate of the present invention; 
         FIGS. 17   a  and  17   b  are side and top views respectively of an alternate arrangement of heater elements and electrical contacts for an alternate embodiment of the nozzle plate of the present invention; 
         FIGS. 18   a  and  18   b  are cross-sectional side views showing an ink jet nozzle outfitted with the nozzle plate of the present invention, showing specific dimensions of interest for implementing the method of the present invention; and, 
         FIGS. 19   a ,  19   b , and  19   c  are cross-sectional side views of an ink jet nozzle according to the present invention, showing the basic sequence for removal, cleaning, and reassembly of a printhead. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
       FIGS. 2   a  and  2   b  show cross-sectional side views of ejector  10  in accordance with one embodiment of the present invention. In  FIG. 2   a , within body  38 , a piezoelectric actuator having a piezoelectric crystal  48  on a piezoelectric mount  50  serves as drop-forming mechanism  12  for ejecting ink droplets from nozzle orifice  14  of fluid chamber  16 .  FIG. 2   a  depicts the structure of ejector  10 , particularly showing a removable nozzle plate  20  and a plate orifice  22  of removable nozzle plate  20  as well as a clamping mechanism  24  which holds removable nozzle plate  20  to body  38  of ejector  10 , while  FIG. 2   b  depicts the ejection of a fluid  15  from fluid chamber  16 , particularly showing fluid  15  as it is ejected through plate orifice  22 . 
     Fluid  15  is ejected through plate orifice  22  in a manner similar to the way fluid  15  would be ejected through nozzle orifice  14  in the absence of removable plate  20 , as discussed later, in the sense that piezoelectric crystal  48  generates a pressure pulse within fluid chamber  16  which forces fluid  15  out of plate orifice  22 , subsequently resulting in formation of a fluid droplet  13 , as is well known in the art of inkjet printing. Plate orifice  22  is preferably smaller than nozzle orifice  14  and hence the ejected fluid droplets  13  of the present invention are preferably somewhat smaller than droplets  13  which would be ejected through nozzle orifice  14  in the absence of removable plate  20 . Typically, although not necessarily, nozzle orifice  14  is smaller in diameter than fluid chamber  16 . Plate orifice  22  is usually centered within nozzle orifice  14 , although this is not required in every application. Typically, although not necessarily, plate orifice  22  and nozzle orifice  14  are round. 
     Referring to  FIGS. 3   a  and  3   b , there is shown schematically a second embodiment of ejector  10  according to the present invention. Here, a drop-on-demand ink jet printhead of the thermal backshooter device type, disclosed, for example, in U.S. Pat. No. 6,561,626 is adapted with a removable nozzle plate  20 , held in place against body  38  by clamping mechanism  24 . Plate orifice  22  in nozzle plate  20  is held in place over nozzle orifice  14  of the printhead. Removal of removable nozzle plate  20  and of clamping mechanism  24  is possible, in which case fluid  15  would then be ejected from nozzle orifice  14  as in U.S. Pat. No. 6,561,626.  FIG. 3   a  depicts the structure of ejector  10 , particularly showing removable nozzle plate  20  and plate orifice  22  of removable nozzle plate  20 , while  FIG. 3   b  depicts the ejection of fluid  15  from fluid chamber  16 , particularly showing fluid  15  as it is ejected through plate orifice  22 . 
     Fluid  15  is ejected through plate orifice  22  to form fluid droplet  13  in a manner similar to the way fluid  15  would be ejected through nozzle orifice  14  in the absence of removable plate  20 , as discussed later, in the sense that the bubble formed by the thermal backshooter shown in  FIG. 3   b  forces fluid  15  out of plate orifice  22 , subsequently resulting in formation of fluid droplet  13 , as is well known in the art of inkjet printing. Plate orifice  22  is preferably smaller than nozzle orifice  14  and hence ejected fluid droplets  13  of the present invention are preferably somewhat smaller than fluid droplets  13  which would be ejected through nozzle orifice  14  in the absence of removable plate  20 . Typically, although not necessarily, the diameter of nozzle orifice  14  is smaller than fluid chamber  16 . Plate orifice  22  is usually centered within nozzle orifice  14 , although this is not required in every application. Typically, although not necessarily, plate orifice  22  and nozzle orifice  14  are round. As described in more detail below, using plate orifice  22 , the dimensions of the ejecting orifice can be changed, affecting the dimensions of ejected fluid droplet  13 . 
     Referring to  FIGS. 4   a  and  4   b , there is shown another embodiment of the present invention, applied to a thermal roof-shooter device drop-on-demand printhead using a heater element  54  as drop forming mechanism  12 , as disclosed, for example, in U.S. Pat. No. 6,582,060. Again, removable nozzle plate  20 , held in place by clamping mechanism  24 , positions plate orifice  22  over nozzle orifice  14 . As  FIG. 4   b  shows, a heat-generated bubble  44  or other disturbance is generated to eject the ink stream from plate orifice  22 . Removal of removable nozzle plate  20  and of clamping mechanism  24  is possible, in which case ink would then be ejected from nozzle orifice  14  as in U.S. Pat. No. 6,582,060.  FIG. 4   a  depicts the structure of ejector  10 , particularly showing removable nozzle plate  20  and plate orifice  22  of removable nozzle plate  20 , while  FIG. 4   b  depicts the ejection of fluid  15  from fluid chamber  16 , particularly showing fluid  15  as it is ejected through plate orifice  22 . 
     Fluid  15  is ejected through plate orifice  22  in a manner similar to the way fluid  15  would be ejected through nozzle orifice  14  in the absence of removable plate  20 , as discussed later, in the sense that the bubble formed by the thermal roof-shooter shown in  FIG. 4   b  forces fluid out plate orifice  22 , subsequently resulting in formation of fluid droplet  13 , as is well known in the art of inkjet printing. Plate orifice  22  is preferably smaller than nozzle orifice  14  and hence ejected droplets  13  of the present invention are preferably somewhat smaller than droplets  13  which would be ejected through nozzle orifice  14  in the absence of removable plate  20 . Preferably, although not necessarily, nozzle orifice  14  is smaller in diameter than fluid chamber  16 . Typically, although not necessarily, plate orifice  22  is centered within nozzle orifice  14 . Usually, although not necessarily, plate orifice  22  and nozzle orifice  14  are round. As described in more detail below, using plate orifice  22 , the dimensions of the ejecting orifice could be changed, affecting the dimensions of ejected fluid droplet  13 . 
     Referring to  FIGS. 5   a  and  5   b , there is shown another embodiment of the present invention, applied to a continuous inkjet ejector  10  whose drop formation means is thermal, as disclosed, for example, in U.S. Pat. No. 6,254,225. Again, removable nozzle plate  20 , held in place by clamping mechanism  24 , positions plate orifice  22  over nozzle orifice  14 . As  FIG. 5   b  shows, activation of a heater causes the ejected stream from plate orifice  22  to break up into discrete fluid droplets  13 . 
       FIG. 5   a  depicts the structure of ejector  10 , particularly showing removable nozzle plate  20  and plate orifice  22  of removable nozzle plate  20 , while  FIG. 5   b  depicts the ejection of fluid  15  from fluid chamber  16 , particularly showing fluid  15  as it is ejected through plate orifice  22 . 
     Fluid  15  is ejected through plate orifice  22  in a manner similar to the way fluid  15  would be ejected through nozzle orifice  14  in the absence of removable plate  20 , as discussed later, in the sense that fluid droplets  13  are formed by the continuous inkjet droplet ejector in accordance with the teachings of U.S. Pat. No. 6,254,225. Plate orifice  22  is preferably smaller in diameter than nozzle orifice  14  and hence ejected fluid droplets  13  of the present invention are preferably somewhat smaller than droplets  13  which would be ejected through nozzle orifice  14  in the absence of removable plate  20 . Typically, although not necessarily, nozzle orifice  14  is smaller in diameter than fluid chamber  16 . Typically, although not necessarily, plate orifice  22  is centered within nozzle orifice  14 . Usually, although not necessarily, plate orifice  22  and nozzle orifice  14  are round. As described in more detail below, using plate orifice  22 , the dimensions of the ejecting orifice could be changed, affecting the dimensions of the ejected ink stream and of fluid droplets  13  formed therefrom. 
     Referring to  FIGS. 6   a - 6   d , corresponding, respectively, to  FIGS. 2   b ,  3   b ,  4   b , and  5   b , ejectors  10  are shown having their respective removable nozzle plates  20  in a removed or second position, and preferably ejecting fluid  15  in a manner similar to the way fluid  15  would be ejected in prior art devices, although the ejection efficiency of such devices having their respective removable nozzle plates  20  in a removed or second position would not necessarily be optimal. As would be appreciated by one skilled in the art of inkjet ejector design, if the diameter of nozzle orifice  19  is close to or greater than that of fluid chamber  16 , droplet  13  ejection might not be possible at all when removable nozzle plate  20  is in a removed or second position. 
     Arrangement and Clamping of Nozzle Plate  20   
     Referring to  FIG. 7 , there is shown a top view of a single ejector  10  of removable nozzle plate  20  in an alternate embodiment. Here, there are multiple plate orifices  22  for a single nozzle orifice  14 . This enables ink ejection from multiple ports, which may have advantages for fluid droplet  13  formation in some applications. Contrast this top view with the top view of  FIG. 8   a , in which a single plate orifice  22  is centered over each nozzle orifice  14 . Although the plate orifices in  FIGS. 7 and 8   a - 8   g  are shown round, other shapes are possible, for example triangular or rectangular shapes, which may be beneficial in controlling droplet  13  trajectories and improving fluid droplet  13  ejection efficiency. 
     Referring to  FIGS. 8   a ,  8   b ,  8   c , and  8   d , there are shown a few of the many possible embodiments of removable nozzle plate  20  and clamping mechanism  24 . In the embodiment of  FIG. 8   a , removable nozzle plate  20  is affixed to body  38  of the printhead using a removable or reusable bonding agent or adhesive. This is to be distinguished from the use of a permanent bonding agent, such as epoxy or similar adhesive substance. For removability, only a small force should be required for peeling removable nozzle plate  20  from base  38 . As a guideline, this removal force, or peeling force, should not exceed about 100 g/cm applied to an edge of removable nozzle plate  20  in a direction perpendicular to the plane of removable nozzle plate  20 . 
     A reusable bonding agent or adhesive retains nozzle plate  20  in place with sufficient strength for printing, but allows disassembly of a printhead for cleaning, for indexing of removable nozzle plate  20  to some other position, for replacement of removable nozzle plate  20 , etc. Reusable bonding agents can include any of a number of types of adhesives, including paraffin or a suitable adhesive wax. Wax substances are particularly advantaged due to their hydrophobic properties. Use of a wax substance allows heat to be used for removal of nozzle plate  20 . However, the melting temperature of the wax substance should be higher than the temperature experienced by the printhead during operation. The wax substance can be vacuum-deposited or applied as a melt or a liquid in a solvent. 
     In the embodiment of  FIG. 8   b , clamping mechanism  24  in the form of a sheet clamp  26  is provided for retaining removable nozzle plate  20  in place against body  38 , using an arrangement of fasteners  62  such as screws or other free or captive mechanisms, for example. Such a sheet clamp  26  could be fabricated from a thin, stiff membrane made, for example, by semiconductor fabrication techniques well known in the art of Micro Electromechanical Systems (MEMS) fabrication. 
     In the embodiment shown in the top view of  FIG. 8   c  and in its corresponding side view in  FIG. 8   d , a wire clamp  28  is employed as clamping mechanism  24  for retaining removable nozzle plate  20 , preferably applying some amount of spring force for maintaining good contact and stable positioning. In one embodiment, electro-formed nickel is used to provide wire clamp  28  having a spring force, made, for example, by MEMS fabrication methods. 
     Referring to  FIG. 8   e - 8   g , other configurations of plate orifices  22  are useful in accordance with the present invention. For example,  FIG. 8   e  shows the case in which not all nozzle orifices  14  are associated with a plate orifice  22 , in other words some plate orifices  22  have been omitted. Since no fluid droplets  13  are ejected in the absence of a plate orifice  22 , this embodiment allows for a controlled reduction in the density of fluid droplet  13  ejectors. In  FIG. 8   f , plate orifices  22  and  22 ′ having different sizes are interspersed on an array of nozzle orifices  14 , which allows for multiple sizes of ejected fluid droplets  13 . 
     In yet another embodiment, shown in  FIG. 8   g , plate orifices  22  are shown located in more than one array. In this case, removable nozzle plate  20  can be positioned or indexed, for example by sliding or by removal and repositioning, so that a different group of plate orifices  22  are positioned over nozzle orifices  14 , so as to provide a redundancy of plate nozzles, for example, should a portion of those initially positioned over nozzle orifices  14  be damaged. 
     It is also contemplated, although not shown, that certain nozzle orifices could  14  be omitted, so that the number of plate orifices  22  is larger than the number of nozzle orifices  14 . For example, every other nozzle orifice  14  might be omitted in  FIG. 8   a , for example. Again, in this case, removable nozzle plate  20  can be positioned, for example by sliding or by removal and repositioning, so that a different group of plate orifices  22  is positioned over nozzle orifices  14 , so as to provide a redundancy of plate orifices  22  should a portion of those initially positioned over nozzle orifices  14  be damaged. 
     Referring to  FIG. 9 , there is shown another mechanism for retaining removable nozzle plate  20  against body  38 . Here, removable nozzle plate  20  is formed from a flexible material that allows it, over a flexible portion  30 , to be bent around edges of body  38  and to be held in place by a clamping force f from a spring and a spring clamp mechanism of some type (as represented by clamping mechanism  24  in  FIG. 9 ). Retaining force f can be provided by others sources. For example, a retaining force f can be applied by a solenoid activated electrically. 
     Referring to  FIGS. 12   a  and  12   b , it can be observed that, by making removable nozzle plate  20  of some flexible material and by varying the retaining force f 1 , f 2  applied, plate nozzle  22  can be shifted from a position A (shown in  FIG. 12   a ) to a slightly different position B (shown in  FIG. 12   b ). This arrangement allows adjustment of plate nozzle  22  position for some portion of the printhead or for the complete printhead. By proper selection of materials and positioning of clamping mechanism  24  components, individual plate nozzle  22  positioning can be performed. This allows, for example, nozzle-to-nozzle correction, can be useful for compensating for performance or mechanical tolerance variations across the printhead, providing nozzle plate  20  were an elastic material such as silicone or poly dimethyl silane (PDMS). 
     Referring to  FIG. 10 , an electrostatic clamping mechanism  32  is shown for retaining removable nozzle plate  20  in place. In this embodiment, a voltage V 1  is applied between a metallized plate  46  and body  38 , thereby clamping removable nozzle plate  20  in place. For the embodiment of  FIG. 10 , removable nozzle plate  20  is a non-conductive material. Metallized plate  46  can be an aluminum-coated mylar plate, for example, and voltage V 1  can be in the range of several tens to hundreds of volts. Magnetic or electromagnetic retaining mechanisms can similarly be employed if removable nozzle plate  20  or clamping sheet  26  is made of magnetic material which can be attracted toward body  38  by magnetic forces, either from body  38  itself or associated permanent or electromagnets (not shown), as can be appreciated by one skilled in electromechanical design. 
     Another method for retaining removable nozzle plate  20  on body  38  is using vacuum pressure, as is shown in the cross-sectional view of  FIG. 11 . Negative vacuum pressure P is applied through passages  66  to hold removable nozzle plate  20  securely in place. 
     Yet another method for retaining removable nozzle plate  20  on body  38  is shown in  FIG. 13 . Here, a liquid film  58  is used to retain removable nozzle plate  20 , rather than a bonding agent. For example, films of water or oil can be employed as well as highly viscous films such as greases. The adhesive energy of these liquid films  58  to body  38  and nozzle plate  20  is advantageously chosen to be high in these cases. 
     Embodiments using Heat-Conductive Elements for Droplet Formation 
     Adding removable nozzle plate  20  over nozzle orifice  14  may cause subtle changes in fluid droplet  13  formation where a heating mechanism is used, particularly in the continuous type ejector shown in  FIG. 5   a . Referring to  FIG. 14 , there is shown yet another embodiment of the present invention in which heater element  54  provides fluid droplet  13  formation. An additional heat-conductive element  52  is also provided in order to transport heat generated from heater element  54  more effectively to plate orifice  22 . 
     As is shown in  FIG. 15   a , heat-conductive element  52  can be spaced back, by some distance x 1 , from the perimeter of plate orifice  22 , where each fluid droplet  13  is formed. Distance x 1  is preferably within at least about 2 microns from the perimeter of nozzle orifice  22  in a preferred embodiment. As is shown in the top view of this embodiment of  FIG. 15   b , heater element  54  is itself spaced back from the perimeter of plate orifice  22 . In one embodiment, the inner diameter of heater element  54  is sized and positioned so that the distance from the center of plate orifice  22  to the inner edge of heater element  54  is no more than about 200 microns. 
     By adding heat-conductive element  52  against or attached to removable nozzle plate  20 , droplet-forming heat energy is transferred more closely to the plate orifice  22 . Thus, the arrangement of  FIGS. 14 and 15   a  stabilize the response of ejector  10  and provide an even distribution of heat around plate orifice  22 . Heat-conductive element  52  is shown against the lower surface of removable nozzle plate  20  in the embodiment of  FIG. 14 . However, other arrangements are possible, including forming heat-conductive element  52  as an integral part of removable nozzle plate  20  or applying heat-conductive element  52  to the top surface of removable nozzle plate  20 . Heat-conductive element  52  could be any of a number of suitable materials, including copper, for example. 
     Referring to the top view of  FIG. 16 , there is shown an alternate embodiment in which heat energy is provided by a plurality of independent segmented heater elements  54   a ,  54   b ,  54   c , and  54   d , each of which is capable of independently providing heat to a corresponding heat-conductive element  52   a ,  52   b ,  52   c , and  52   d . Thus, by adding heat-conductive elements  52   a - 52   d  against or attached to removable nozzle plate  20 , droplet-forming heat energy from a plurality of heater elements is transferred more closely to plate orifice  22 . In this way, the trajectory of ejected fluid droplets  13  can be controlled to some extent by providing heat asymmetrically to the ejecting orifice, as disclosed, for example, in U.S. Pat. No. 6,254,225. 
     In yet another embodiment, one or more heater elements  54  may be an integral part of removable nozzle plate  20 . As is shown in the side and top views of  FIGS. 17   a  and  17   b , respectively, electrical contacts  56  are provided on body  38  for conducting current through heater elements  54  that are part of removable nozzle plate  20 , in order that heat be generated near to plate orifice  22 . Also in the case of more than one heater element  54 , the trajectory direction of ejected fluid droplets  13  can be controlled to some extent by providing heat asymmetrically to the ejecting orifice, as disclosed, for example, in U.S. Pat. No. 6,079,821. 
     Referring to dimensions as labeled in  FIG. 18   a , diameter dimension d 1  of plate orifice  22  can be different from diameter dimension d 2  of nozzle orifice  14 . Plate orifice  22  can be centered over nozzle orifice  14  or offset from this center position. As is shown in  FIG. 18   b , thickness t 1  of removable nozzle plate  20  and t 2  of the existing nozzle orifice  14  may be selected to optimize fluid droplet  13  formation characteristics of the printhead. In a preferred embodiment, thickness t 1  is also related to diameter dimension d 2 , such that the ratio of thickness t 1  to diameter dimension d 2  is less than about 0.20. 
     Cleaning of the Printhead 
     One advantage of the apparatus of the present invention relates to ease of cleaning of the printhead. Referring to  FIG. 19   a , there is shown a side view of ejector  10  with an obstruction  60  blocking plate orifice  22 .  FIG. 19   b  shows the printhead disassembled, with clamping mechanism  24  removed to free removable nozzle plate  20  from body  38 . Removable nozzle plate  20  can be thoroughly cleaned or, if necessary, replaced to eliminate the problem caused by obstruction  60 , then reassembled, as is shown in  FIG. 19   c.    
     Other Alternative Embodiments and Materials 
     The apparatus and method of the present invention allows for a range of alternative embodiments and the use of a variety of possible materials and configurations for removable nozzle plate  20 . As described above, a wide range of clamping mechanisms  24  can be employed. Additionally, examples shown illustrate the use of removable nozzle plate  20  with a continuous flow printhead, or with a drop-on-demand printhead. 
     Removable nozzle plate  20  can be fabricated from a number of different types of materials, including any of a number of types of plastics, such as mylar, for example. The material used can be solid or a composite, laminated as layers onto a substrate. Various types of coatings can be applied to the surfaces of removable nozzle plate  20  for optimizing ink droplet ejection, such as hydrophobic coatings. Coatings can be applied to allow separation of removable nozzle plate  20  without causing damage. Such coatings can be formulated, for example, from self-assembled monolayers such as FDS or fluorinated siloxanes. Removable nozzle plate  20  can be formed from a number of elastic materials to allow stretching and repositioning of plate orifice  22  as shown in  FIGS. 12   a  and  12   b . Plate orifices  22  can be formed using any of a number of lithographic techniques or other fabrication techniques, as are well known in the art. 
     The removable nozzle plate  20 , described above, helps provide at least one of, simplified cleaning, nozzle refurbishing and replacement, and/or re-sizing of orifice diameters as needed for various ink viscosities and fluid droplet  13  characteristics when compared to current printhead designs. Additionally, the removable nozzle plate  20  allows different arrangements of nozzle orifices without requiring complete printhead redesign. The removable nozzle plate  20  can be adapted to allow the use of different nozzle orifice designs suited to a wide variety of liquid types and/or print conditions. As such, the printhead described herein is not limited to the field of inkjet printing. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
     
         
           10 . Ejector 
           12 . Drop-forming mechanism 
           13 . Droplet 
           14 . Nozzle orifice 
           15 . Fluid 
           16 . Fluid chamber 
           17 . Arrows 
           18 . Substrate 
           19 . Nozzle plate 
           20 . Removable nozzle plate 
           22 ,  22 ′. Plate orifice 
           24 . Clamping mechanism 
           26 . Sheet clamp 
           28 . Wire clamp 
           30 . Flexible portion 
           32 . Electrostatic clamping mechanism 
           34 . Vacuum 
           36 . Force-adjustable clamping mechanism 
           38 . Body 
           40 . Printhead 
           44 . Bubble 
           46 . Metallized plate 
           48 . Piezoelectric crystal 
           50 . Piezoelectric mount 
           52 ,  52   a ,  52   b ,  52   c ,  52   d . Heat-conductive element 
           54 ,  54   a ,  54   b ,  54   c ,  54   d . Heater element 
           56 . Contacts 
           58 . Liquid film 
           60 . Obstruction 
           62 . Fasteners 
           64 . Opening 
           66 . Passage 
         A, B. Positions 
         d 1 , d 2 . Diameter dimension 
         f, f 1 , f 2 . Retaining force 
         P. Pressure 
         t 1 , t 2 . Thickness 
         V 1 . Voltage 
         x 1 . Distance