Abstract:
A continuous stream ink jet printer is provided having an ink droplet forming mechanism for ejecting a stream of ink droplets having a selected one of at least two different volumes toward a print medium and a droplet deflector and ink conduit which are integrally formed to the printhead for producing a flow of gas that interacts with the ink droplet stream to separate droplets having different volumes and collects all droplets not used for printing. The provision of integrally forming the gutter system with the droplet forming mechanism eliminates the requirement to align an external gutter system upon full print engine assembly.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled continuous ink jet printing devices, and in particular to continuous ink jet printers in which selected droplets are deflected by a transverse flow of air or gas. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 6,079,821 issued to Chwalek et al. discloses a continuous ink jet printhead in which deflection of selected droplets is accomplished by asymmetric heating of the jet exiting the orifice. 
     U.S. Pat. No. 6,554,410 by Jeanmaire et al. teaches an improved method of deflecting the selected droplets. This method involves breaking up each jet into small and large drops and creating an air or gas cross flow relative to the direction of the flight of the drops that causes the small drops to deflect into a gutter or ink catcher while the large ones bypass it and land on the medium to write the desired image or the reverse, that is, the large drops are caught by the gutter and the small ones reach the medium. 
     U.S. Pat. No. 6,450,619 to Anagnostopoulos et al. discloses a method of fabricating nozzle plates, using CMOS and MEMS technologies which can be used in the above printhead. Further, in U.S. Pat. No. 6,663,221, issued to Anagnostopoulos et al., methods are disclosed of fabricating page wide nozzle plates, whereby page wide means nozzle plates that are about 4″ long and longer. A nozzle plate, as defined here, consists of an array of nozzles and each nozzle has an exit orifice around which, and in close proximity, is a heater. Logic circuits addressing each heater and drivers to provide current to the heater may be located on the same substrate as the heater or may be external to it. 
     For a complete continuous ink jet printhead, besides the nozzle plate and its associated electronics, a means to deflect the selected droplets is required, an ink gutter or catcher to collect the unselected droplets, an ink recirculation or disposal system, various air and ink filters, ink and air supply means and other mounting and aligning hardware are needed. 
     In these continuous ink jet printheads the nozzles in the nozzle plates are arranged in a straight line, they are between about 150 to 2400 per inch and, depending on the exit orifice diameter, can produce droplets as large as about 100 Pico liters and as small as 1 Pico liter. 
     As already mentioned, all continuous ink jet printheads, including those that depend on electrostatic deflection of the selected droplets (see for example U.S. Pat. No. 5,475,409 issued to Simon et al), an ink gutter or catcher  10  is needed to collect the unselected droplets. Such a gutter has to be carefully aligned relative to the nozzle array since the angular separation between the selected and unselected droplets is, typically, only a few degrees. The alignment process is typically a very laborious procedure and increases substantially the cost of the printhead. The printhead cost is also increased because each gutter must be aligned to its corresponding nozzle plate individually and one at a time. 
     The gutter or catcher may contain a knife-edge or some other type of edge to collect the unselected droplets, and that edge has to be straight to within a few tens of microns from one end to the other. Gutters are typically made of materials that are different from the nozzle plate and as such they have different thermal coefficients of expansion so that if the ambient temperature changes the gutter and nozzle array can be in enough misalignment to cause the printhead to fail. Since the gutter is typically attached to some frame using alignment screws, the alignment can be lost if the printhead assembly is subjected to shock as can happen during shipment. If the gutter is attached to the frame using an adhesive, misalignment can occur during the curing of the glue as it hardens, resulting in yield loss of printheads during their assembly. 
     These problems of alignment and assembly are exacerbated as the printhead lengths are increased from an inch or less to page wide which could be tens of inches long. 
     A need therefore exists for an assembly free and self-aligned ink gutter or catcher for page wide nozzle arrays that is free of misalignment due to changes in the ambient or operating temperature. Furthermore, a need exists for an ink gutter or catcher that is assembly free and self aligned to smaller nozzle arrays, which may then be arranged in a staggered or tiled configuration to form page wide continuous ink jet printheads. Finally, a need exists to reduce the cost of the printheads by eliminating the labor-intensive alignment procedure and the one at a time alignment process of each nozzle plate to its corresponding gutter. 
     SUMMARY OF THE INVENTION 
     The invention is directed to an ink jet printing apparatus and method of fabrication that solves or at least ameliorates some or all of the aforementioned problems associated with the prior art. 
     In accordance with one aspect of the present invention there is provided an ink jet printing apparatus comprising an ink droplet forming mechanism for ejecting a stream of ink droplets having a selected one of at least two different volumes toward a print medium and an integral deflector gutter structure which is integrally formed to the printhead for providing a flow of gas that interacts with the ink droplet stream to separate ink droplets having the different volumes from one another and captures excess ink from one of the at least two different volumes of the ink droplets. 
     In accordance with another aspect of the present invention there is provided a method of making an ink-jet printhead having an integral gutter, comprising the steps of: 
     a. providing a support substrate on which an ink jet printhead is integrally formed, the printhead ejecting a stream of ink droplets having a selected one of at least two different volumes toward a print medium; 
     b. forming a deflector gutter structure integrally on the support substrate, the deflector gutter structure having at least one passage for directing a stream of gas against the stream of ink droplets for deflecting the stream of ink droplets and at least one passageway for capturing one of the at least two different volumes of the ink droplets. 
     In accordance with another aspect of the invention there is provided an ink-jet printing apparatus comprising a plurality of ink-jet print assemblies positioned with respect to each other so as to form a single line of print on a media, each of said ink-jet print assemblies having an ink droplet forming mechanism for ejecting a stream of ink droplets having a selected one of at least two different volumes toward a print medium and an integral deflector gutter structure which is integrally formed to each of the printheads for providing a flow of gas that interacts with said ink droplet stream to separate ink droplets having said different volumes from one another and captures excess ink from said at least two different volumes of said ink droplets. 
     These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims and by reference to the accompanying drawings. 
    
    
     
       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: 
         FIG. 1  is a schematic plan view of a printhead/nozzle array made in accordance with a preferred embodiment of the present invention; 
         FIGS. 2A-F  illustrates the relationship between the switching frequency of the heaters of the nozzle array and the volume of ink droplets produced by the nozzles adjacent to the heaters; 
         FIG. 3  is an enlarged schematic side view of the operation of a nozzle array made in accordance with the preferred embodiment of the present invention illustrating how the droplet deflector deflects smaller volume droplets from larger volume droplets; 
         FIG. 4  is schematic side view of an ink jet printer made in accordance with a preferred embodiment of the present invention; 
         FIG. 5  is a schematic side view of a nozzle array and integral gutter system made in accordance with a preferred embodiment of the present invention; 
         FIG. 6  is a schematic top view of a nozzle plate wafer prior to singulation with integral gutter system made in accordance with a preferred embodiment of the present invention; 
         FIG. 7  illustrates an ink jet printhead assembly comprising a plurality of printhead and integral gutter made in accordance with the present invention; and 
         FIG. 8  illustrates a modified ink jet nozzle plate structure made in accordance with the present invention. 
     
    
    
     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 of ordinary skill in the art. 
     With reference to  FIGS. 1 and 4 , wherein like reference numerals designate like components throughout all of the several figures, the continuous stream printer  10  of the invention generally comprises an ink droplet forming mechanism in the form of a nozzle array  12 . In the embodiment illustrated the ink droplet forming mechanism comprises an ink jet printhead for use in an ink jet printer. 
     Referring in particular to  FIG. 1 , there is illustrated a plurality of annular heaters  13  which are at least partially formed or positioned on a silicon substrate  16  of nozzle array/printhead  12  around each corresponding nozzle  17 . Although each heater  13  may be disposed in various ways about each nozzle, such as in the neck of the nozzle  17  or at the bottom of it, the heaters  13  are preferably disposed close to corresponding nozzles  17  in a concentric manner. In a preferred embodiment, heaters  13  are formed in a substantially circular or ring shape. However, it is specifically contemplated that heaters  13  may be formed in a partial ring, square, or other shape adjacent to the nozzles  17 . Each heater  13  in a preferred embodiment is principally comprised of a resistive heating element electrically connected to contact pads  21  via conductors  28 . Each nozzle  17  is in fluid communication with ink supply  24  through an ink passage (not shown) formed in the substrate  16  of the nozzle array  12 . It is specifically contemplated that nozzle array  12  may incorporate additional ink supplies in the same manner as supply  24  as well as additional corresponding nozzles  17  in order to provide color printing using three or more ink colors. Additionally, black and white or single color printing may be accomplished using a single ink supply  24  and nozzle  17 . 
     Conductors  28  and electrical contact pads  21  may be at least partially formed or positioned on the nozzle array substrate  12  and provide an electrical connection between a controller  23  and the heaters  13 . Alternatively, the electrical connection between the controller  23  and heater  13  may be accomplished in any well-known manner. Controller  23  may be a relatively simple device (a switchable power supply for heater  13 , etc.) or a relatively complex device (a logic controller or programmable microprocessor in combination with a power supply) operable to control many other components of the printer in a desired manner. 
     In  FIGS. 2A-F , examples of the electrical activation waveforms provided by controller  23  to the heaters  13  are shown and their associated ink droplet size produced by the waveforms. Generally, a high frequency of activation of heater  13  results in small volume droplets  33  as shown in  FIGS. 2C and 2D , while a low frequency of activation results in large volume droplets  31  as illustrated in  FIGS. 2A and 2B . In the preferred embodiment, large ink droplets are to be used for marking the print medium, while smaller droplets are captured for ink recycling. It must be understood, however, that this could be reversed in operation (depending on imaging requirements), where the smaller droplets are used for printing, and the larger drops recycled. Also in this example, only one printing droplet is provided for per image pixel, thus there are two states of heater actuation, printing or non-printing. The electrical waveform of heater  13  actuation for large ink droplets  31  is presented schematically as  FIG. 2A . The individual large ink drops  31  produced from the jetting of ink from nozzle  17  as a result of low frequency heater actuation are shown schematically in  FIG. 2B . Heater actuation time  25  is typically 0.1 to 5 microseconds in duration, and in this example is 1.0 microsecond. The delay time  38  between subsequent heater actuation is 42 microseconds. The electrical waveform of heater  13  actuation for the non-printing case is given schematically as  FIG. 2C . Electrical pulse  35  is 1.0 microsecond in duration, and the time delay  42  between activation pulses is 6.0 microseconds. The small droplets  23 , as illustrated in  FIG. 2D , are the result of the activation of heater  13  with this non-printing waveform. 
       FIG. 2E  is a schematic representation of an electrical waveform of heater activation for mixed image data where a transition is shown from the non-printing state to the printing state, and back to the non-printing state. Schematic representation in  FIG. 2F  is the resultant droplet stream formed. It is apparent that heater activation may be controlled independently based on the ink color required and ejected through corresponding nozzles  17 , the movement of nozzle array  12  relative to a print media W, and an image to be printed. It is specifically contemplated that the absolute volume of the small droplets  2   3  and the large droplets  27  may be adjusted based upon specific printing requirements such as ink and media type or image format and size. 
     With reference now to  FIG. 3 , the operation of nozzle array  12  in a manner such as to provide an image-wise modulation of droplets, as described above, is coupled with a droplet deflector  45  of integral gutter structure  61  (as later described in detail and illustrated by  FIG. 5 ). The deflector  45  separates the droplets into printing or non-printing paths according to drop volume by means of a transversely disposed gas flow  47 . Ink is ejected through nozzle  17  in nozzle array  12 , creating a filament of working fluid  96  moving substantially perpendicular to nozzle array  12  along axis X. The physical region over which the filament of working fluid is intact is designated as r 1 . Heater  13  is selectively actuated at various frequencies according to image data, causing filament of working fluid  96  to break up into a stream of individual ink droplets. Some coalescence of droplets often occurs in forming non-printing drops  31 . This region of jet break-up and drop coalescence is designated as r 2 . Following region r 2 , drop formation is complete in region r 3 , such that at the distance from the nozzle array  12  that the gas flow from the deflector  45  is applied, droplets are substantially in two size classes: small, printing drops  33  and large, non-printing drops  31 . In the preferred implementation, the force  46  provided by the gas flow  47  is perpendicular to axis X. The force  46  acts across distance L, which is less than or equal to distance r 3 . Because area increases with the square of the radius of a sphere while mass increases with the cube of the radius, large, non-printing droplets  31  have a greater mass and more momentum than small volume droplets  33  which more than offsets the greater force applied to them by the gas flow as a result of their layer area. As gas force  46  interacts with the stream of ink droplets, the individual ink droplets separate depending on each droplet&#39;s volume and mass. Accordingly, the gas flow rate can be adjusted to create a sufficient differentiation angle D in the small droplet path S from the large droplet path K, permitting large droplets  31  to strike print media M while small, non-printing droplets  33  are captured by an ink guttering structure  60  described in more detail in the apparatus below. 
     An amount of separation D between the large, non-printing droplets  31  and the small, printing droplets  33  will not only depend on their relative size but also the velocity, density, and viscosity of the gas flow producing force  46 , the velocity and density of the large printing droplets  31  and small, non-printing droplets  33 , and the interaction distance (shown as L in  FIG. 3 ) over which the large printing droplet  31  and the small, non-printing droplets  33  interact with the gas flow  47 . Gases, including air, nitrogen, etc., having different densities and viscosities can also be used with similar results. 
     Referring to  FIGS. 3 ,  4  and  5 , a printing apparatus (typically, an ink jet printer or printhead) used in a preferred implementation of the current invention is shown schematically. The printer  10  includes an integral deflector gutter structure  60  that has been integrally formed as a part of the ink-jet nozzle array  12 . Large volume ink droplets  31  and small volume ink droplets  33  are formed from ink ejected from the ink droplet forming mechanism/printhead  12  substantially along ejection path X in a stream. The integral deflector gutter structure  60  includes an inlet plenum  50  and an outlet plenum  40  for directing a gas through integral deflector gutter structure  60  and against the ink droplets for separating the different size ink droplets. The integral deflector gutter structure  60  also includes a droplet deflector  62  that is positioned adjacent to an outlet plenum  40 . The purpose of deflector  62  is to intercept the displaced small droplets  23 , while allowing large ink droplets  31  traveling along small droplet path S to continue on to the recording media M carried by print drum  80 . Plenums  40 ,  50  include baffles  48  which facilitates a laminar flow of gas. Vacuum pump  150  communicates with plenum  40  and provides a sink for the gas flow  47 . In the center of the droplet deflector  62  is positioned proximate path X. The application of force  46  due to gas flow  47  separates the ink droplets into small-drop path S and large-drop path K. Pump  220  draws in air, while filter  210  removes dust and dirt particles. In the preferred embodiment, the flow distance F of the upper plenum  50  is of sufficient length to allow full formation of a laminar airflow. As previously discussed, baffles  48  in plenums  40 ,  50  in the integral deflector gutter structure  60  facilitate increased gas flow  47  velocity while maintaining laminar flow. 
     An ink recovery conduit/passageway  70  is connected to outlet plenum  40  of integral deflector gutter structure  60  for receiving droplets recovered by deflector  62 . Ink recovery conduit  70  communicates with ink recovery reservoir  90  to facilitate recovery of non-printed ink droplets by an ink return line  100  for subsequent reuse. Ink recovery reservoir contains open-cell sponge or foam  135 , which prevents ink sloshing in applications where the nozzle array  12  is rapidly scanned. A vacuum conduit  110 , coupled to a negative pressure source, can communicate with ink recovery reservoir  90  to create a negative pressure in ink recovery conduit  70  improving ink droplet separation and ink droplet removal. The gas flow rate in ink recovery conduit  70 , however, is chosen so as to not significantly perturb large droplet path K. Lower plenum  40  is fitted with filter  140  and drain  130  to capture any ink fluid resulting from ink misting, or misdirected jets which has been captured by the air flow in plenum  40 . Captured ink is then returned to recovery reservoir  90 . 
     Additionally, a portion of plenum  50  diverts a small fraction of the gas flow from pump  220  and conditioning chamber  190  to provide a source for the gas which is drawn into ink recovery conduit  70 . The gas pressure at gutter deflector  62  and in ink recovery conduit  70  are adjusted in combination with the design of ink recovery conduit  70  and plenum  50  so that the gas pressure in the printhead assembly near integral deflector gutter structure  60  is positive with respect to the ambient air pressure near print drum  80 . Environmental dust and paper fibers are thusly discouraged from approaching and adhering to integral deflector gutter structure  60  and are additionally excluded from entering ink recovery conduit  70 . 
     In operation, a recording medium M is transported in a direction transverse to axis X by print drum  80  in a known manner. Transport of recording medium M is coordinated with movement of printhead/nozzle array mechanism, not shown, for movement of nozzle array  12 . This can be accomplished using controller  13  in a known manner. Recording media M may be selected from a wide variety of materials including paper, vinyl, cloth, other fibrous materials, etc. 
     The recovery air plenums  40 ,  50  of integral deflector gutter structure  60  is integrally formed on nozzle array  12 . In the preferred embodiment, an orifice cleaning system  240  may also be incorporated into integral deflector gutter structure  60 . Cleaning would be accomplished by flooding the nozzle array  12  with solvent injected through the input port  241 . Used solvent is removed by drawing vacuum on the cleaning solvent through output port  242 . 
     In the present invention the guttering structure is integrally formed with nozzle array  12 . This is done in order to maintain accuracy between the ink jet nozzles  17  and the deflector  62 . In a preferred embodiment of the present invention, nozzle array  12  is formed from a semiconductor material (silicon, etc.) using known semiconductor fabrication techniques (CMOS circuit fabrication techniques, micro-electro mechanical structure (MEMS) fabrication techniques, etc.). Such techniques are illustrated in U.S. Pat. Nos. 6,663,221 and 6,450,619 which are hereby incorporated by reference in their entirety. However, it is specifically contemplated and therefore within the scope of this disclosure that nozzle array  12  may be integrally formed with the gutter structure from any materials using any fabrication techniques conventionally known in the art. 
     Referring to  FIG. 6  there is illustrated a wafer  250  incorporating a plurality of integrally formed ink-jet printhead  12  and integral deflector gutter structure  60  of  FIG. 5 . In the construction of wafer  250  having a plurality of integral printheads and gutter structure, a first layer is constructed which incorporates ink-jet printhead  12 . After the first layer has been formed, then integral deflector gutter structure  60  is formed directly thereon using normal photolithographic techniques until integral deflector gutter structure  60  is formed on each of the respective printheads  12 . The photolithographic techniques allows for precise positioning of the orifices  17  with respect to the deflector  62 . Once formed the individual printheads  12  and integral deflector gutter structure  60  are separated. Then a plurality of integral printheads  15  and deflector gutter structures  60  may be combined together as illustrated by  FIG. 7  to form a long continuous printhead  110  that can print along the entire with of a media. The individual integral printheads  12  can be simply positioned so that the printing nozzles  17  of all the printheads  12  are aligned for printing along a straight line. Since the individual nozzles  17  of each of the printheads are aligned with its respect deflector  62 , mis-spraying will be avoided. Using this technique, ink-jet printhead assemblies for continuous ink-jet printers can be made in lengths of up to 36 inches or greater, as desired. 
     Referring to  FIG. 8  there is illustrated a modified integral ink-jet printhead  12  and gutter structures also made in accordance with the present invention; like numerals indicating like parts and operation as previously discussed. In this embodiment, the integral deflector gutter structure  160  is composed of a plurality of laminated sub-layers  161  of a photoimageable material (such as polyimide) bonded to stiffening material (such as stainless steel). The sub-layers are patterned and selectively etched with functional and alignment features. The sub-layers are then stacked and cured under heat and vacuum to form multiple integral deflector gutter structure  160  that correspond to printheads on the printhead wafer  150 . This structure is aligned and bonded to the wafer  150 , which is then singulated into individual printheads  12 . A description of materials and processes for fabricating laminated ink jet structures can be found in U.S. Pat. No. 6,463,656. 
     It is specifically contemplated that integral deflector gutter structure  160  or  150  may be formed from any materials using any fabrication techniques conventionally known in the art, including high aspect photo resist, such as SU-8 so long as the integral deflector gutter structure in integrally. The structure may be attached prior to or following printhead singulation. 
     While the foregoing description includes many details and specificities, it is to be understood that these have been included for purposes of explanation only, and are not to be interpreted as limitations of the present invention. Many modifications to the embodiments described above can be made without departing from the scope of the invention, as is intended to be encompassed by the following claims and their legal equivalents. 
     PARTS LIST 
     
         
           10  printer 
           12  printhead/nozzle array 
           13  controller 
           13  Heater 
           16  silicon substrate 
           17  Nozzle 
           21  contact pad 
           23  small droplets 
           23  controller 
           24  ink supply 
           25  actuation time 
           27  large droplets 
           28  conductor 
           31  large drop 
           33  small drop 
           35  electrical pulse time 
           38  delay time 
           40  exit plenum 
           41  pixel time 
           42  delay time 
           45  droplet deflector 
           46  force 
           47  gas flow 
           48  baffles 
           50  Entry plenum 
           60  guttering structure 
           61  gutter structure 
           62  droplet deflector 
           70  ink recovery conduit 
           80  print drum 
           90  ink recovery reservoir 
           96  working fluid 
           100  ink return line 
           102  first layer 
           110  vacuum conduit 
           130  ink return line 
           135  foam 
           140  filter 
           150  vacuum pump 
           150  printhead wafer 
           160  gutter structure 
           161  sub-layers 
           170  gas recycling line 
           190  conditioning chamber 
           210  intake filter 
           220  pressure pump 
           230  integral gutter structure 
           231  integral gutter sub-layer 
           240  orifice cleaning system 
           241  solvent inlet port 
           242  solvent evacuation port 
           250  printhead wafer 
         D separation distance 
         F air flow distance 
         K Large droplet path 
         L interaction distance 
         M pint media 
         S small droplet path 
         W print media 
         X ejection path