Abstract:
An apparatus for printing an image is provided. The apparatus includes a print head with nozzles of differing diameters. This allows multiple printing drop sizes for multi-level printing, thus achieving higher print quality at the same resolution. Additionally, each nozzle is operable to selectively create a stream of ink droplets having a plurality of volumes. The apparatus also includes a droplet deflector having a gas source. The gas source is positioned at an angle with respect to the stream of ink droplets and is operable to interact with the stream of ink droplets thereby separating ink droplets into printing and non-printing paths.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned, co-pending U.S. patent applications Ser. No. 09/750,946, entitled “printhead having gas flow ink droplet separation and method of diverging ink droplets” filed in the names of D. L. Jeanmaire et al. on Dec. 28, 2000, and Ser. No. 09/861,692, entitled “continuous ink-jet printing method and apparatus with nozzle clusters ” filed in the name of D. L. Jeanmaire on May 21, 2001. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous ink jet printers in which a liquid ink stream breaks into droplets, some of which are selectively deflected. 
     BACKGROUND OF THE INVENTION 
     Traditionally, digitally controlled color ink jet printing capability is accomplished by one of two technologies. Both require independent ink supplies for each of the colors of ink provided. Ink is fed through channels formed in the print head. Each channel includes a nozzle from which droplets of ink are selectively extruded and deposited upon a receiving medium. Typically, each technology requires separate ink delivery systems for each ink color used in printing. Ordinarily, the three primary subtractive colors, i.e. cyan, yellow and magenta, are used because these colors can produce, in general, up to several million perceived color combinations. 
     The first technology, commonly referred to as “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 a flying ink droplet that crosses the space between the print head 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. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle, thus helping to keep the nozzle clean. 
     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. 
     Piezoelectric actuators, such as that disclosed in U.S. Pat. No. 5,224,843, issued to vanLintel, on Jul. 6, 1993, have a piezoelectric crystal in an ink fluid channel that flexes when an electric current flows through it forcing an ink droplet out of a nozzle. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. 
     In U.S. Pat. No. 4,914,522, which issued to Duffield et al. on Apr. 3, 1990, a drop-on-demand ink jet printer utilizes air pressure to produce a desired color density in a printed image. Ink in a reservoir travels through a conduit and forms a meniscus at an end of an ink nozzle. An air nozzle, positioned so that a stream of air flows across the meniscus at the end of the nozzle, causes the ink to be extracted from the nozzle and atomized into a fine spray. The stream of air is applied for controllable time periods at a constant pressure through a conduit to a control valve. The ink dot size on the image remains constant while the desired color density of the ink dot is varied depending on the pulse width of the air stream. 
     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 media. 
     Typically, continuous ink jet printing devices are faster than drop-on-demand devices and produce higher quality printed images and graphics. However, each color printed requires an individual droplet formation, deflection, and capturing system. 
     U.S. Pat. No. 1,941,001, issued to Hansell on Dec. 26, 1933, and U.S. Pat. No. 3,373,437 issued to Sweet et al. on Mar. 12, 1968, each disclose an array of continuous ink jet nozzles wherein ink droplets to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous ink jet. 
     U.S. Pat. No. 3,416,153, issued to Hertz et al. on Oct. 6, 1963, discloses a method of achieving variable optical density of printed spots in continuous ink jet printing using the electrostatic dispersion of a charged droplet stream to modulate the number of droplets which pass through a small aperture. 
     U.S. Pat. No. 3,878,519, issued to Eaton on Apr. 15, 1975, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates. 
     U.S. Pat. No. 4,346,387, issued to Hertz on Aug. 24, 1982, discloses a method and apparatus for controlling the electric charge on droplets formed by the breaking up of a pressurized liquid stream at a droplet formation point located within the electric field having an electric potential gradient. Droplet formation is effected at a point in the field corresponding to the desired predetermined charge to be placed on the droplets at the point of their formation. In addition to charging tunnels, deflection plates are used to actually deflect droplets. 
     U.S. Pat. No. 4,638,382, issued to Drake et al. on Jan. 20, 1987, discloses a continuous ink jet print head that utilizes constant thermal pulses to agitate ink streams admitted through a plurality of nozzles in order to break up the ink streams into droplets at a fixed distance from the nozzles. At is point, the droplets are individually charged by a charging electrode and then deflected using deflection plates positioned the droplet path. 
     As conventional continuous ink jet printers utilize electrostatic charging devices and deflector plates, they require many components and large spatial volumes in which to operate. This results in continuous ink jet print heads and printers that are complicated, have high energy requirements, are difficult to manufacture, and are difficult to control. 
     U.S. Pat. No. 3,709,432, issued to Robertson on Jan. 9, 1973, discloses a method and apparatus for stimulating a filament of working fluid causing the working fluid to break up into uniformly spaced ink droplets through the use of transducers. The lengths of the filaments before they break up into ink droplets are regulated by controlling the stimulation energy supplied to the transducers, with high amplitude stimulation resulting in short filaments and low amplitude stimulations resulting in longer filaments. A flow of air is generated across the paths of the fluid at a point intermediate to the ends of the long and short filaments. The air flow affects the trajectories of the filaments before they break up into droplets more than it affects the trajectories of the ink droplets themselves. By controlling the lengths of the filaments, the trajectories of the ink droplets can be controlled, or switched from one path to another. As such, some ink droplets may be directed into a catcher while allowing other ink droplets to be applied to a receiving member. 
     While this method does not rely on electrostatic means to affect the trajectory of droplets, it does rely on the precise control of the break up points of the filaments and the placement of the air flow intermediate to these break up points. Such a system is difficult to control and to manufacture. Furthermore, the physical separation or amount of discrimination between the two droplet paths is small, further adding to the difficulty of control and manufacture. 
     U.S. Pat. No. 4,190,844, issued to Taylor on Feb. 26, 1980, discloses a continuous ink jet printer having a first pneumatic deflector for deflecting non-printed ink droplets to a catcher and a second pneumatic deflector for oscillating printed ink droplets. A print head supplies a filament of working fluid that breaks into individual ink droplets. The ink droplets are then selectively deflected by a first pneumatic deflector, a second pneumatic deflector, or both. The first pneumatic deflector is an “on/off” type having a diaphragm that either opens or closes a nozzle depending on one of two distinct electrical signals received from a central control unit. This determines whether the ink droplet is to be printed or non-printed The second pneumatic deflector is a continuous type having a diaphragm that varies the amount that a nozzle is open, depending on a varying electrical signal received the central control unit. This oscillates printed ink droplets so that characters may be printed one character at a time. If only the first pneumatic deflector is used, characters are created one line at a time, being built up by repeated traverses of the print head. 
     While this method does not rely on electrostatic means to affect the trajectory of droplets, it does rely on the precise control and timing of the first (“ON/OFF”) pneumatic deflector to create printed and nonprinted ink droplets. Such a system is difficult to manufacture and accurately control, resulting in at least the ink droplet build up discussed above. Furthermore, the physical separation or amount of discrimination between the two droplet paths is erratic due to the precise timing requirements, increasing the difficulty of controlling printed and non-printed ink droplets and resulting in poor ink droplet trajectory control. 
     Additionally, using two pneumatic deflectors complicates construction of the print head and requires more components. The additional components and complicated structure require large spatial volumes between the print head and the media, increasing the ink droplet trajectory distance. Increasing the distance of the droplet trajectory decreases droplet placement accuracy and affects the print image quality. Again, there is a need to minimize the distance that the droplet must travel before striking the print media in order to insure high quality images. 
     U.S. Pat. No. 6,079,821, issued to Chwalek et al. on Jun. 27, 2000, discloses a continuous ink jet printer that uses actuation of asymmetric heaters to create individual ink droplets from a filament of working fluid and to deflect those ink droplets. A print head includes a pressurized ink source and an asymmetric heater operable to form printed ink droplets and non-printed ink droplets. Printed ink droplets flow along a printed ink droplet path ultimately striking a receiving medium, while non-printed ink droplets flow along a non-printed ink droplet path ultimately striking a catcher surface. Non-printed ink droplets are recycled or disposed of through an ink removal channel formed in the catcher. While the ink jet printer disclosed in Chwalek et al. works extremely well for its intended purpose, it is best adapted for use with inks that have a large viscosity change with temperature. 
     Each of the above-described ink jet printing systems has advantages and disadvantages. However, print heads which are low-power and low-voltage in operation will be advantaged in the marketplace, especially in page-width arrays. U.S. patent application Ser. No. 09/750,946, filed in the names of D. L. Jeanmaire et al. on Dec. 28, 2000, discloses continuous-jet printing wherein nozzle heaters are selectively actuated at a plurality of frequencies to create the stream of ink droplets having the plurality of volumes. A gas stream provides a force separating droplets into printing and non-printing paths according to drop volume. While this process consumes little power, and is suitable for printing with a wide range of inks, the apparatus described does not easily create ink drops of variable size where the size is varied image-wise on a pixel-by-pixel basis. 
     Often it is desirable to print with multiple drop sizes to achieve multi-level printing, allowing higher print quality at the same resolution. One solution to this problem is the use of multiple rows of nozzles on the print head as disclosed in U.S. Pat. No. 5,892,524, which issued to Silverbrook in 1999, for a drop-on-demand print head. The concept of multiple rows of nozzles has not been implemented, however, in a continuous ink jet printer, due to the difficulty of dealing with small deflection angles, multiple separation fields, and the resultant need for multiple droplet catchers required for continuous systems. An example of this can be seen in a printing apparatus described in U.S. Pat. No. 3,701,998, which issued to Mathis in 1972, and discloses two rows of nozzles and multiple ink catcher structures. 
     It can be seen that there is an opportunity to provide an improvement to continuous ink jet printers. The features of low-power and low-voltage print head operation are desirable to retain, while providing for multi-level printing, without the complexity of structure replication. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide for multi-level printing in printers with print heads in which heat pulses are used to break up fluid into drops having a plurality of volumes, and which use a gas flow to separate the drops along printing and non-printing paths. This introduction of multi-level printing improves the quality of the image on the receiver media. 
     According to a feature of the present invention, an apparatus for printing an image comprises a print head having a first group of nozzles from which a stream ink droplets of a first volume are emitted, and a second group of nozzles from which a stream of ink droplets of a second volume are emitted. The said second volume is less than the first volume. A mechanism is associated with each group of nozzles and is adapted to independently adjust the volume of the ink droplets emitted by the nozzles. The mechanism has a first state, wherein the volumes of the droplets emitted from the first and second groups are of the first and second volume, respectively, and a second state wherein the volumes of the droplets emitted from the first and second groups are of a third and forth volume, respectively; the third and forth volumes being smaller than said first and second volumes. A droplet deflector is adapted to produce a force on the emitted droplets, said force being applied to the droplets at an angle with respect to the stream of ink droplets to cause ink droplets having either of the first and second volumes to move along a first set of paths, and ink droplets having either of the third and forth volumes to move along a second set of paths. An ink catcher is positioned to allow drops moving along one of the first and second sets of paths to move unobstructed past the catcher, while intercepting drops moving along the other of said first and second sets of paths. 
     According to another feature of the present invention, an ink droplet forming mechanism has two rows of nozzles operable to selectively create streams of ink droplets having a plurality of volumes. Additionally, a droplet deflector having a gas source is positioned at an angle with respect to the stream of ink droplets and is operable to interact with the stream of ink droplets. The interaction separates ink droplets having one volume from ink droplets having other volumes. The large separation angles between printing and non-printing droplet paths that can be obtained using this printing method (as opposed to electrostatic means of droplet separation common in the prior art) enables the use of a single gas flow and ink catcher assembly, thereby simplifying the apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the present invention will become apparent from the following description of the preferred embodiments of the invention and the accompanying drawings, wherein: 
     FIG. 1 is a schematic plan view of a print head made in accordance with a preferred embodiment of the present invention; 
     FIG. 2 is a diagram illustrating a frequency control of a heater used in the preferred embodiment FIG. 1; 
     FIG. 3 is a cross-sectional view of an ink jet print head made in accordance with the preferred embodiment of the present invention; 
     FIG. 4 is a schematic view of an ink jet printer made in accordance with a preferred embodiment of the present invention; 
     FIG. 5 consists of diagrams illustrating a frequency control of a heater used in an alternate embodiment of the present invention; and 
     FIG. 6 is a schematic view of an ink jet printer made in accordance with another embodiment of 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 skilled in the art. 
     FIG. 1 shows an ink droplet forming mechanism  10  of a preferred embodiment of the present invention, including a print head  20 , at least one ink supply  30 , and a controller  40 . Although ink droplet forming mechanism  10  is illustrated schematically and not to scale for the sake of clarity, one of ordinary skill in the art will be able to readily determine the specific size and interconnections of the elements of a practical apparatus according to a specific desired application. 
     In a preferred embodiment of the present invention, print head  20  is formed from a semiconductor material, such as for example silicon, using known semiconductor fabrication techniques (CMOS circuit fabrication techniques, micro-electro mechanical structure (MEMS) fabrication techniques, etc.). However, print head  20  may be formed from any materials using any fabrication techniques conventionally known in the art. 
     As illustrated in FIG. 1, at least two rows of nozzles (n 1  and n 2 ) of at least one nozzle each are formed on print head  20  and are separated by distance H, which distance H can range from about 20 micrometers to about 10 mm. In a preferred embodiment, H is preferably about 50 micrometers to about 150 micrometers. The nozzles in row n 2 , designated by reference numeral  35 , have diameters equal to or larger than the nozzles in row n 1 , designated by reference numeral  25 . For example, nozzles  25  may be, say, 9 micrometers in diameter and nozzles  35  may be, say, 16 micrometers in diameter. Nozzles  25  and nozzles  35  are in fluid communication with ink supply  30  through ink passage  50 , also formed in print head  20 . Single color printing, such as so-called black and white, may be accomplished using a single ink supply  30  and single sets of nozzles  25  and  35 . In order to provide color printing using two or more ink colors, print head  20  may incorporate additional ink supplies in the manner of supply  30  and corresponding sets of nozzles  25  and  35 . 
     A set of heaters  60  are at least partially formed or positioned on print head  20  around corresponding nozzles  25  and  35 . Although heaters  60  may be disposed radially away from the edge of corresponding nozzles  25  and  35 , they are preferably disposed close to corresponding nozzles  25  and  35  in a concentric manner. In a preferred embodiment, heaters  60  are formed in a substantially circular or ring shape. However, heaters  60  may be formed in a partial ring, square, etc. Heaters  60  in a preferred embodiment consist principally of an electric resistive heating element electrically connected to electrical contact pads  55  via conductors  45 . 
     Conductors  45  and electrical contact pads  55  may be at least partially formed or positioned on print head  20  to provide an electrical connection between controller  40  and heaters  60 . Alternatively, the electrical connection between controller  40  and heaters  60  may be accomplished in any well-known manner. Controller  40  is typically a logic controller, programmable microprocessor, etc. operable to control many components (heaters  60 , ink droplet forming mechanism  10 , etc.) in a desired manner. 
     FIG. 2 is a schematic example of the electrical activation waveform provided by controller  40  to heaters  60 . A similar method is used to operate both rows of nozzles n 1  and n 2 . In general, rapid pulsing of heaters  60  forms small ink droplets, while slower pulsing creates larger drops. In the first example presented here, small ink droplets are to be used for marking the image receiver, while larger, non-printing droplets are captured for ink recycling. 
     In a preferred implementation, multiple drops per nozzle per image pixel are created. Periods P 0 , P 1 , P 2 , etc. are the times associated with the printing of associated image pixels, the subscripts indicating the number of printing drops to be created during the pixel time. The schematic illustration shows the drops that are created as a result of the application of the various waveforms. A maximum of two small printing drops is shown for simplicity of illustration, however, it will be understood that the reservation of more time for a larger count of printing drops is within the scope of this invention. 
     In the drop formation for each image pixel, a non-printing large drop  95 ,  105 , or  110  is always created, in addition to a selectable number of small, printing drops. The waveform of activation of heater  60  for every image pixel begins with electrical pulse time  65 , typically from about 0.1 microsecond to about 10 microseconds in duration, and more preferentially about 0.5 microsecond to about 1.5 microseconds. The further (optional) activation of heater  60 , after delay time  83 , with an electrical pulse  70  is conducted in accordance with image data wherein at least one printing drop  100  is required as shown for interval P 1 . For cases where the image data requires that still another printing drop be created as in interval P 2 , heater  60  is again activated after delay  83 , with a pulse  75 . Heater activation electrical pulse times  65 ,  70 , and  75  are substantially similar, as are all delay times  83 . Delay time  83  is typically about 1 microsecond to about 100 microseconds, and more preferentially, from about 3 microseconds to about 6 microseconds. Delay times  80 ,  85 , and  90  are the remaining times after pulsing is over in a pixel time interval P and the start of the next image pixel. All small, printing drops  100  are the same volume. However, the volume of the larger, non-printing drops  95 ,  105  and  110 , varies depending on the number of small drops  100  created in the pixel time interval P; as the creation of small drops takes mass away from the large drop during the pixel time interval P. The delay time  90  is preferably chosen to be significantly larger than the delay time  83 , so that the volume ratio of large non-printing-drops  110  to small printing-drops  100  is a factor of about 4 or greater. 
     Referring to FIG. 3, the operation of print head  20  in a manner such as to provide an image-wise modulation of drop volumes, as described above, is coupled with an gas-flow discrimination means which separates droplets into printing or non-printing paths according to drop volume. Ink is ejected through nozzles  25  and  35  in print head  20 , creating a filament of working fluid  120  moving substantially perpendicular to print head  20  along axes X 1  and X 2 , respectively. The physical region over which the filament of working fluid is intact is designated as r 1 . Heaters  60  are selectively activated at various frequencies according to image data, causing filaments of working fluid  120  to break up into streams of individual ink droplets. Coalescence of drops often occurs in forming non-printing drops  95 ,  105  and  110 . 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 , and small printing drops and large non-printing drops are spatially separated. Beyond this region in r 4 , aerodynamic effects can cause merging of adjacent small and large drops, with concomitant loss of imaging information. A discrimination force  130  is provided by a gas flow at a non-zero angle with respect to axes X 1  and X 2 . For example, the gas flow may be perpendicular to axes X 1  and X 2 . Discrimination force  130  acts over distance L, which is less than or equal to distance r 3 . Large, non-printing drops  95 ,  105 , and  110  have greater masses and more momentum than small volume drops  100 . As gas force  130  interacts with the stream of ink droplets, the individual ink droplets separate, depending on individual volume and mass. The gas flow rate can be adjusted to provide sufficient deviation D 1  or D 2  between the small droplet paths S 1  and S 2  and the large droplet paths K 1  and K 2 , thereby permitting small drops  100  to strike print media W while large, non-printing drops  95 ,  105 , and  110  are captured by a ink guttering structure described below. 
     Referring to FIG. 4, a printing apparatus (typically, an ink jet printer or print head) used in a preferred implementation of the current invention is shown schematically. The print head here contains two rows of nozzles. The larger-nozzle row is the higher in the drawing. Large volume ink drops  95 ,  105  and  110  (FIG. 2) and small volume ink drops  100  (also FIG. 2) are formed from ink ejected in streams from print head  20  substantially along ejection paths X 1  and X 2 . A droplet deflector  140  contains upper plenum  230  and lower plenum  220  which facilitate a laminar flow of gas in droplet deflector  140 . Pressurized air from pump  150  enters upper plenum  230  which is disposed opposite plenum  220  and promotes laminar gas flow while protecting the droplet stream moving along paths X 1  and X 2  from external air disturbances. The application of force  130  due to gas flow separates the ink droplets into small-drop paths S 1  and S 2  and large-drop paths K 1  and K 2 . 
     An ink collection structure  165 , disposed adjacent to plenum  220  near paths X 1  and X 2 , intercepts both paths K 1  and K 2  of large drops  95 ,  105 , and  110 , while allowing small ink drops  100  traveling along small droplet paths S 1  and S 2  to continue on to the recording media W carried by print drum  200 . Since paths S 1  and S 2  do not necessarily intersect at the surface of the recording media W, and the droplets moving on paths S 1  and S 2  may not have the same velocity, printing of a pixel may not involve the simultaneous arrival of drops originating from nozzles  25  and  35 . Controller  40  therefore, provides a compensating delay function so that proper registration of drops will occur. 
     Large, non-printing ink drops  95 ,  105 , and  110  strike ink catcher  240  in ink collection structure  165 . Ink recovery conduit  210  communicates with recovery reservoir  160  to facilitate recovery of non-printed ink droplets by an ink return line  170  for subsequent reuse. A vacuum conduit  175 , coupled to negative pressure source  180  can communicate with ink recovery reservoir  160  to create a negative pressure in ink recovery conduit  210  improving ink droplet separation and ink droplet removal as discussed above. The pressure reduction in conduit  210  is sufficient to draw in recovered ink, however it is not large enough to cause significant air flow to substantially alter drop paths S 1  and S 2 . Ink recovery reservoir contains open-cell sponge or foam  155 , which prevents ink sloshing in applications where the print head  20  is rapidly scanned. 
     A small portion of the gas flowing through upper plenum  230  is re-directed by plenum  190  to the entrance of ink recovery conduit  210 . The gas pressure in droplet deflector  140  is adjusted in combination with the design of plenum  220  and  230  so that the gas pressure in the print head assembly near ink catcher  240  is positive with respect to the ambient air pressure near print drum  200 . Environmental dust and paper fibers are thusly discouraged from approaching and adhering to ink catcher  240  and are additionally excluded from entering ink recovery conduit  210 . 
     In operation, a recording media W is transported in a direction transverse to axes X 1  and X 2  by print drum  200  in a known manner. Transport of recording media W is coordinated with movement of print mechanism  10  and/or movement of print head  20 . This can be accomplished using controller  40  in a known manner. Recording media W may be selected from a wide variety of materials including paper, vinyl, cloth, other fibrous materials, etc. 
     It will be understood that the principle of the printing operation can be reversed (depending on imaging requirements), where the larger droplets are used for printing, and the smaller drops recycled. An example of this mode is presented in FIG.  5 . In this example, only one printing drop is provided for per image pixel, thus there are two states of heater  60  actuation, printing or non-printing. The electrical waveform of heater  60  actuation for the printing case is presented schematically in line (a) of FIG.  5 . The individual large ink drops  95  resulting from the jetting of ink from nozzles  25  and  35 , in combination with this heater actuation, are shown schematically in line (b) of FIG.  5 . Heater  60  activation time  65  is typically about 0.1 to about 5 microseconds in duration, and in this example is 1.0 microsecond. The delay time  80  between heater  60  actuations is  42  microseconds in the illustrative embodiment. The electrical waveform of heater  60  activation for the non-printing case is given schematically in line (c) of FIG.  5 . Electrical pulse  65  is 1.0 microsecond in duration, and the time delay  83  between activation pulses is 6.0 microseconds in the illustrative example. Small drops  100 , as diagrammed in line (d) of FIG. 5, are the result of the activation of heater  60  with this non-printing waveform. 
     Line (e) of FIG. 5 schematically represents the electrical waveform of heater  60  activation for mixed image data where a transition is shown for the non-printing state, to the printing state, and back to the non-printing state. Schematic representation in line (f) of FIG. 5 is the resultant droplet stream formed. It is apparent that heater  60  activation may be controlled independently based on the ink color required and ejected through corresponding nozzles  25  and  35 , movement of print head  20  relative to a print media W, and an image to be printed 
     Referring to FIG. 6, an alternative embodiment of the present invention is shown with like elements being described using like reference signs. As in the preceding example, the print head contains two rows of nozzles. However, in this implementation the smaller-nozzle row is the higher in the drawing. Large volume ink drops  95  and small volume ink drops  100  are formed from ink ejected from print head  20  substantially along ejection paths X 1  and X 2  in streams. A droplet deflector  140  contains upper plenum  230  and lower plenum  220  which facilitate a laminar flow of gas in droplet deflector  140 . Pressurized air from pump  150  enters upper plenum  230  which is disposed opposite plenum  220  and promotes laminar gas flow while protecting the droplet streams moving along paths X 1  and X 2  from external air disturbances. Negative pressure source  180  communicates with plenum  220  and provides a sink for gas flow. In the center of droplet deflector  140  is positioned proximate paths X 1  and X 2 . The application of force  130 , due to gas flow, separates the ink droplets into small-drop paths S 1  and S 2  and large-drop paths K 1  and K 2 . 
     An ink collection structure  165 , adjacent to plenum  220 , near paths X 1  and X 2 , intercepts the path of small drops  100  moving along paths S 1  and S 2 , while allowing large ink drops  95  traveling along large droplet paths K 1  and K 2  to continue on to the recording media W carried by print drum  200 . Small ink drops  100  strike ink catcher  240  in ink collection structure  165 . Ink recovery conduit  210  communicates with recovery reservoir  160  to facilitate recovery of non-printed ink droplets by an ink return line  170  for subsequent reuse. A vacuum conduit  175 , coupled to negative pressure source  180  can communicate with ink recovery reservoir  160  to create a negative pressure in ink recovery conduit  210  improving ink droplet separation and ink droplet removal as discussed above. The pressure reduction in conduit  210  is sufficient to draw in recovered ink. However it is not large enough to cause significant air flow to substantially alter drop paths K 1  and K 2 . Ink captured by element  150  to move downward, largely through the interior of element  150 , and enter into ink recovery reservoir  90 . Ink is then removed from reservoir  90  through line  100  for reuse. 
     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 spirit and scope of the invention, as is intended to be encompassed by the following claims and their legal equivalents.