Abstract:
An inkjet printhead, that includes a plurality of nozzle bores from which streams of ink droplets having selectable first and second volumes are emitted; a droplet deflector for deflecting the ink droplets having first and second volumes into first and second paths respectively, the droplet deflector producing a corresponding plurality of physically separate streams of gas, each stream of gas directed on a corresponding one of the streams of ink droplets; and an ink gutter positioned to catch the ink droplets moving along one of the first or second paths. In addition to a method for selectively controlling the ink droplets with the aforementioned inkjet printhead.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned, co-pending U.S. patent application Ser. No. 09/751,232, filed Dec. 28, 2000, titled “A Continuous Ink-Jet Printing Method And Apparatus,” by D. L. Jeanmaire, et al., U.S. patent application Ser. No. 09/750,946, filed Dec. 28, 2000, titled “Printhead Having Gas Flow Ink Droplet Separation And Method Of Diverging Ink Droplets,” by D. L. Jeanmaire, et al., and U.S. patent applications Ser. No. 10/100,376, filed Mar. 18, 2002, titled “A Continuous Ink Jet Printing Apparatus With Improved Drop Placement,” by D. L. Jeanmaire. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous inkjet printers wherein a liquid ink stream breaks into droplets, some of which are selectively deflected. 
     BACKGROUND OF THE INVENTION 
     Continuous inkjet printing, uses a pressurized ink source that produces a continuous stream of ink droplets. Conventional continuous inkjet 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 printing is desired, the ink droplets are directed into an ink-capturing mechanism (often referred to as a catcher, interceptor, or gutter). When printing is desired, the ink droplets are directed to strike a print media. 
     Typically, continuous inkjet 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 inkjet nozzles wherein ink droplets to be printed are selectively charged and deflected towards the recording medium. This technique is known as binary deflection continuous inkjet. 
     U.S. Pat. No. 3,416,153, issued to Hertz et al. on Dec. 10, 1968, discloses a method of achieving variable optical density of printed spots in continuous inkjet 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. 4,638,328, issued to Drake et al. on Jan. 20, 1987, discloses a continuous inkjet printhead 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 this point, the droplets are individually charged by a charging electrode, and subsequently deflected using deflection plates positioned in the droplet path. 
     As conventional continuous inkjet printers utilize electrostatic charging devices and deflector plates, they require many components and large spatial volumes to operate. This results in continuous inkjet printheads 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 uniform 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. High amplitude stimulation causes short filaments and low amplitude stimulations causes 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 inkjet 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 printhead 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 printed or not 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 by the central control unit. This second pneumatic deflector 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, as a result of repeated traverses of the printhead and ink build up. 
     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 non-printed ink droplets. Such a system is difficult to manufacture and accurately control, resulting in at least a similar ink droplet build up as discussed above. Furthermore, the physical separation or amount of discrimination between the two droplet paths is erratic, due to the precise timing requirements, therefore, 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 printhead and requires more components. The additional components and complicated structure require large spatial volumes between the printhead and the media, thereby, 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 inkjet 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 printhead 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 inkjet 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 inkjet printing systems has advantages and disadvantages. However, printheads 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 Dec. 28, 2000 by D. L. Jeanmaire et al. and U.S. patent application Ser. No. 09/751,232, filed Dec. 28, 2000 by D. L. Jeanmaire et al., disclose continuous inkjet 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 droplet volume. While this process consumes little power, and is suitable for printing with a wide range of inks, when implemented in a page-width array, a correspondingly wide laminar gas flow is required. The wide laminar gas flow is often difficult to obtain due to the mechanical tolerances involved in the gas flow plenum, with the result that the gas velocity varies somewhat across the printhead, and turbulent flow regions may exist. Non-uniform gas flow has an adverse effect upon droplet placement on the print medium, and therefore image quality is compromised. 
     It can be seen that there is a need to improve gas-flow uniformity in the design of large nozzle-count printheads such as those used in inkjet printers having page-width arrays. 
     SUMMARY OF THE INVENTION 
     The above need is met according to the present invention by providing an inkjet printhead, that includes a plurality of nozzle bores from which streams of ink droplets having selectable first and second volumes are emitted; a droplet deflector for deflecting the ink droplets having first and second volumes into first and second paths respectively, the droplet deflector producing a corresponding plurality of physically separate streams of gas, each stream of gas directed on a corresponding one of the streams of ink droplets; and an ink gutter positioned to catch the ink droplets moving along one of the first or second paths. 
     Additionally, the present invention provides a method for selectively controlling ink droplets in an inkjet printhead, which includes the steps of: emitting streams of ink droplets having selectable first and second volumes; deflecting the ink droplets having first and second volumes into first and second paths, respectively; providing a plurality of separate streams of gas; directing each of the plurality of separate streams of gas at a corresponding one of the streams of ink droplets to move the streams of ink droplets along the first and second paths; and catching the ink droplets moving along one of the first or second paths in an ink gutter. 
    
    
     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 prior art schematic diagram of a printing apparatus incorporating a page-width printhead; 
     FIG. 2 is a top view of a printhead having a droplet forming mechanism incorporating the present invention; 
     FIG. 3 is a schematic example of the electrical activation waveform provided by the present invention; 
     FIG. 4 is a schematic example of the operation of an inkjet printhead according to the present invention; 
     FIG. 5 is an isometric view of a gas discriminator according to the present invention; 
     FIG. 6 is a schematic view showing droplet streams ejected from a printhead incorporating the present invention; 
     FIGS. 7 a - 7   f  are schematic representations of the electrical waveform of a heater in the present invention; 
     FIG. 8 is an isometric view of an aperture plate according to the present invention; 
     FIG. 9 is a cross-sectional view of the aperture plate in FIG. 8; 
     FIG. 10 is an isometric view of the printhead assembly as droplet streams are emitted according to the present invention; 
     FIG. 11 shows an alternate embodiment of the present invention; and 
     FIG. 12 shows still another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be directed in particular to elements forming part of, or cooperating more directly with the present invention. It is to be understood that elements not specifically shown or described may take various forms that are well known to those skilled in the art. 
     Referring to FIG. 1, a prior art continuous inkjet printer system  5  is shown. The continuous inkjet printer system  5  includes an image source  10  such as a scanner or computer which provides raster image data, outline image data in the form of a page description language, or other forms of digital image data. This digital image data is converted to half-toned bitmap image data by an image processing unit  12 , which also stores the digital image data in image memory  13 . A heater control circuit  14  reads data from the image memory  13  and applies electrical pulses to a heater  32  that is part of a printhead  16 . These pulses are applied at an appropriate time, so that droplets formed from a continuous inkjet stream will print spots on a recording medium  18 , in the appropriate position, designated by the data in the image memory  13 . The printhead  16 , shown in FIG. 1, is commonly referred to as a page-width printhead. 
     Recording medium  18  is moved relative to printhead  16  by a recording medium transport system  20  which is electronically controlled by a recording medium transport control system  22 , and which in turn is controlled by a micro-controller  24 . The recording medium transport system  20  shown in FIG. 1 is a schematic only, and many different mechanical configurations are possible. For example, a transfer roller could be used as recording medium transport system  20  to facilitate transfer of the ink droplets to recording medium  18 . Such transfer roller technology is well known in the art. In the case of page-width printheads  16 , it is most convenient to move recording medium  18  past a stationary printhead  16 . 
     Ink is contained in an ink reservoir  28  under pressure. In the nonprinting state, continuous inkjet droplet streams are unable to reach recording medium  18  due to an ink gutter  34  that blocks the stream and which may allow a portion of the ink to be recycled by an ink recycling unit  36 . The ink recycling unit  36  reconditions the ink and feeds it back to ink reservoir  28 . Such ink recycling units  36  are well known in the art. The ink pressure suitable for optimal operation will depend on a number of factors, including geometry and thermal properties of the nozzle bores  42  (shown in FIG. 2) and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to ink reservoir  28  under the control of ink pressure regulator  26 . 
     Continuous inkjet printers system  5  can incorporate additional ink reservoirs  28  in order to facilitate color printing. When operated in this fashion, ink collected by ink gutter  34  is typically collected and disposed. 
     The ink is distributed to the back surface of printhead  16  by an ink channel  30 . The ink, preferably, flows through slots and/or holes etched through a silicon substrate of printhead  16  to its front surface where a plurality of nozzles and heaters are situated. With printhead  16  fabricated from silicon, it is possible to integrate heater control circuits  14  with the printhead  16 . Printhead  16  can be formed using known semiconductor fabrication techniques (including CMOS circuit fabrication techniques, micro-electro mechanical structure MEMS fabrication techniques, etc.). Printhead  16  can also be formed from semiconductor materials other than silicon, for example, glass, ceramic, or plastic. 
     Referring to FIG. 2, printhead  16  is shown in more detail. Printhead  16  includes a droplet forming mechanism  38 . Droplet forming mechanism  38  can include a plurality of heaters  40  positioned on printhead  16  around a plurality of nozzle bores  42  formed in printhead  16 . Although each heater  40  may be radially disposed away from an edge of a corresponding nozzle bore  42 , heaters  40  are, preferably, disposed close to corresponding nozzle bores  42  in a concentric manner. Typically, heaters  40  are formed in a substantially circular or ring shape. However, heaters  40  can be formed in other shapes. Conventionally, each heater  40  has a resistive heating element  44  electrically connected to a contact pad  46  via a conductor  48 . A passivation layer (not shown), formed from silicon nitride is normally placed over the resistive heating elements  44  and conductors  48  to provide electrical insulation relative to the ink. Contact pads  46  and conductors  48  form a portion of the heater control circuits  14  which are connected to micro-controller  24 . Alternatively, other types of heaters can be used with similar results. 
     Heaters  40  are selectively actuated to from droplets. The volume of the formed droplets is a function of the rate of ink flow through the nozzle bore  42  and the rate of heater activation, but is independent of the amount of energy dissipated in the heaters. FIG. 3 is a schematic example of the electrical activation waveform provided by micro-controller  24  to heaters  40 . In general, rapid pulsing of heaters  40  forms small ink droplets, while slower pulsing creates larger droplets. In the example presented herein, small ink droplets are to be used for marking the recording medium  18 , while larger, non-printable droplets are captured for ink recycling. 
     Consequently, multiple droplets 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 indicate the number of printing droplets created during the pixel time. The schematic illustration shows the droplets that are created as a result of the application of the various waveforms. A maximum of two small printing droplets is shown for simplicity of illustration, however, the concept can be readily extended to permit a higher maximum count of printing droplets. 
     In the droplet formation for each image pixel, a non-printable large droplet  95 ,  105 , or  110  is always created, in addition to a select number of small, printable droplets  100 . The waveform of activation for heater  40 , for every image pixel, begins with an electrical pulse time  65 . The further (optional) activation of heater  40 , after delay time  83 , with an electrical pulse  70 , is conducted in accordance with image data, wherein at least one printable droplet  100  is required as shown for interval P 1 . For cases where the image data requires that still another printable droplet  100  be created as in interval P 2 , heater  40  is again activated, after delay  84 , with a pulse  75 . Heater activation. electrical pulse times  65 ,  70 , and  75  are substantially similar, as are all delay times  83  and  84 . 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 printable droplets  100  are the same volume. However, the volume of the larger, non-printable droplets  95 ,  105  and  110  varies depending on the number of small printable droplets  100  created in the preceding pixel time interval P as the creation of small droplets takes mass away from large droplets during the pixel time interval P. The delay time  90  is preferably chosen to be significantly larger than the delay times  83 ,  84 , so that the volume ratio of large non-printable-droplets  110  to small printable droplets  100  is a factor of 4 or greater. 
     FIG. 4 is a schematic example of the operation of printhead  16  in a manner that provides one printing droplet per pixel. Printhead  16  is coupled with a gas-flow discriminator  130  which separates droplets into printing or non-printing paths, according to droplet volume. Ink is ejected through nozzle bores  42  in printhead  16 , thus creating a filament of working fluid  62  that moves substantially perpendicular to printhead  16  along axis X. Heaters  40  are selectively activated at various frequencies according to image data, causing filaments of working fluid  62  to break up into streams of individual ink droplets. Coalescencing of droplets often occurs when forming non-printable droplets  105 . The gas flow discriminator  130  is provided by a gas flowing at a non-zero angle with respect to axis X. As one example, the gas flow may be perpendicular to axis X. Gas flow discriminator  130  acts over distance L, and as a gaseous force from gas flow discriminator  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 between the small droplet path S and the large droplet paths K, thereby permitting small printable droplets  100  to strike print media W, while large non-printable droplets  105  are captured by an ink guttering structure  240 . 
     In one embodiment of the present invention, a gas flow discriminator  130  is shaped by a plenum (not shown) fitted with an exit aperture plate  200  or cap as shown in FIG.  5 . This plate is a structure with holes or slits  210  that serve to channel gas flow into individual jets, where the pitch of the openings is essentially the same as the nozzle pitch on the printhead. In this manner, each ink droplet stream has an associated gas flow stream. Exit aperture plate  200  is formed from silicon, using known semiconductor fabrication techniques (such as, micro-electro mechanical structure (MEMS) fabrication techniques, etc.). However, exit aperture plate  200  may be formed from any materials (e.g. plastics, ceramics, metal, etc.) using any fabrication techniques conventionally known in the art. Due to the fact that the total area of exit slits  210  is less than the cross-sectional area of the plenum, a pressure droplet is created across the exit aperture plate  200 . This serves to increase the uniformity in the velocity of gas flow across the exit aperture plate  200  from slit-to-slit, as well as reduce gas-flow turbulence. 
     Referring now to FIG. 6, which is a schematic view incorporating an embodiment of the current invention, droplet streams are ejected from printhead  16 . As discussed earlier with reference to FIG. 3, but not shown herein, droplet forming mechanism  38  is actuated such that droplets of ink having a plurality of volumes  95 ,  100 ,  105  and  110  (as shown in FIG. 3) traveling along paths X (FIG. 6) are formed. A gas flow discriminator  130  supplied from a droplet deflector system  56 , including a gas flow source  58  (not shown), plenum  220 , and exit aperture plate  200 , is continuously applied to droplets  95 ,  100 ,  105  and  110  over an interaction distance L. Because droplets  95 ,  105  and  110  have a larger volume (in addition to more momentum and greater mass) than droplets  100 , droplets  100  deviate from path X and begin traveling along path S; while droplets  95 ,  105  and  110  remain traveling, substantially, along path X or deviate slightly from path X and begin traveling along path K. With appropriate adjustment of gas flow discriminator  130 , and appropriate positioning of the ink guttering structure  240 , droplets  100  contact print media W at location  250 , while droplets  95 ,  105  and  110  are collected by ink guttering structure  240 . 
     In another embodiment of the current invention, the principle of the printing operation is reversed, where the larger droplets are used for printing, and the smaller droplets recycled. An example of this mode is presented here. In this example, only one printing droplet is provided for per image pixel, thus there are two states of heater  40  actuation, printing or non-printing. The electrical waveform of heater  40  actuation for the printing case is presented schematically as FIG. 7 a . The individual large non-printable droplets  95  resulting from the jetting of ink from nozzle bores  42 , in combination with this electrical pulse time  65  and delay times  80 , are shown schematically as FIG. 7 b . The electrical waveform of heater  40  activation for the non-printing case is given schematically as FIG. 7 c . Electrical pulse time  65  duration remains unchanged from FIG. 7 a , however, time delay  83  between activation pulses is a factor of  4  and shorter than delay time  80 . The small droplets  100 , as diagrammed in FIG. 7 d , are the result of the activation of heater  40  with this non-printing waveform. 
     FIG. 7 e  is a schematic representation of the electrical waveform of heater  40 &#39;s activation for mixed image data. A transition from the non-printing state to the printing state, and back again to the non-printing state is shown. A schematic representation is shown of the resultant formed droplet stream, FIG. 7 f . Heater  40 &#39;s activation may be independently controlled, based on a required ink color, and ejecting the desired ink through corresponding nozzle bores  42 ; or moving printhead  16  relative to a print media W. In one embodiment of this invention, the function of droplet deflection is combined physically with that of ink guttering. This combined assembly allows for a more compact physical implementation, and thus the printhead  16  can be closer to the print media W for improved droplet placement. Referring to FIG. 8, in this configuration, vacuum aperture plate  260  consists of holes or slots  270  to permit the entry of gas into a plenum (not shown). The air pressure in the plenum is below ambient, such that air flows from the external environment into vacuum aperture plate  260 . Slots  270  are spaced at the same pitch as the nozzles on printhead  16 . Vacuum aperture plate  260  also contains guttering ribs  280  and relief channel  290  whose functions will become more clear from the following discussion. 
     FIG. 9 is an end-on cross-sectional view of vacuum aperture plate  260  taken through the center of a slot  270 . As an example here, vacuum aperture plate  260  is fabricated from silicon, and was constructed by bonding wafers  300  and  310  together, after etching steps were completed. Vacuum aperture plate  260  is then adhesively joined to the end of plenum  220 . Droplet streams ejected from printhead  16  consisting of large non-printable droplets  95  and small printable droplets  100  initially pass over droplet deflection system  56  and interact with gas flow discriminator  130 . Small printable droplets  100  are deflected into slot  270  and strike guttering rib  280  before being drawn down into plenum  220 . Guttering rib  280  has a top plate which overhangs slot  270  to prevent ink from splattering over guttering rib  280  and down the outside of droplet deflection system  56 . Large non-printable droplets  95  pass over guttering rib  280  and are allowed to strike print media W. Relief channel  290  provides clearance for large non-printable droplets  95 , so that they do not strike the top of vacuum aperture plate  260 . 
     An overall view of a printhead assembly using this embodiment is given in FIG.  10 . As droplet streams are emitted from printhead  16 , they pass over droplet deflector system  56 . Small ink droplets  100  are deflected from initial path X, and are drawn into plenum  220 . Large droplets  95  are only slightly deflected onto path K which clears the guttering elements of vacuum aperture plate  260 , and the droplets then strike print media W at locations  250 . 
     An alternate embodiment of this invention for the design of a droplet deflector  430  involves the formation of gas-flow channels  410  in a substrate  400  as shown in FIG.  11 . The substrate  400  may be ceramic, metal, plastic, etc. however, silicon is preferred. A cover plate  420  is adhesively bonded to substrate  400 , thereby forming one side of the gas-flow channels  410 . As in the previous embodiment, there is a one-to-one correspondence between gas-flow channels  410  and individual jets (not shown) on the printhead  16 . A manifold (not shown) couples a gas source (or vacuum) into the gas-flow channels  410 . An advantage of this embodiment is that the droplet deflector system  56  is a more mechanically durable structure, however, the structure is more expensive due to increased silicon consumption. 
     A modification of droplet deflector  430  is envisioned wherein cover plate  420  is manufactured with plural thermal-bend-actuators  440  disposed on the surface as shown in FIG.  12 . The thermal-bend-actuators may be formed from a bi-layer of TiAl and SiN, for example. They are positioned such that when cover plate  420  is bonded to substrate  400 , there is a thermal-bend-actuator in each of the gas-flow channels  410 . In the rest or non-activated state, the thermal-bend-actuators lie flat against cover plate  420 , and thus do not impede gas flow in gas -flow channels  410 . When the thermal-bend-actuators  440  experience resistive heating due to the passage of electrical current as directed by micro-controller  24 , they bend away from cover plate  420  and restrict gas flow. Generally, larger electrical currents produce larger actuator bending, so that the gas flow may be individually regulated in each gas-flow channel  410 . This control of gas flow allows the deflection of each individual jet on the printhead to be balanced for optimum operation. 
     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. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 PARTS LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 5 
                 continuous inkjet printer system 
               
               
                 10 
                 image source 
               
               
                 12 
                 image processing unit 
               
               
                 13 
                 image memory 
               
               
                 14 
                 heater control circuit 
               
               
                 16 
                 printhead 
               
               
                 18 
                 recording medium 
               
               
                 20 
                 recording medium transport system 
               
               
                 22 
                 recording medium transport control system 
               
               
                 24 
                 micro-controller 
               
               
                 26 
                 ink pressure regulator 
               
               
                 28 
                 ink reservoir 
               
               
                 30 
                 ink channel 
               
               
                 32 
                 heater 
               
               
                 34 
                 ink gutter 
               
               
                 36 
                 ink recycling unit 
               
               
                 38 
                 droplet forming mechanism 
               
               
                 40 
                 heater 
               
               
                 42 
                 nozzle bore 
               
               
                 44 
                 resistive heating element 
               
               
                 46 
                 contact pad 
               
               
                 48 
                 conductor 
               
               
                 56 
                 droplet deflector system 
               
               
                 58 
                 gas flow source 
               
               
                 62 
                 filament of working fluid 
               
               
                 65 
                 electrical pulse time 
               
               
                 70 
                 electrical pulse time 
               
               
                 75 
                 electrical pulse time 
               
               
                 80 
                 delay time 
               
               
                 83 
                 delay time 
               
               
                 84 
                 delay time 
               
               
                 85 
                 delay time 
               
               
                 90 
                 delay time 
               
               
                 95 
                 large non-printable droplets 
               
               
                 100 
                 small printable droplets 
               
               
                 105 
                 large non-printable droplets 
               
               
                 110 
                 large non-printable droplets 
               
               
                 130 
                 gas flow discriminator 
               
               
                 200 
                 exit aperture plate 
               
               
                 210 
                 exit slits 
               
               
                 220 
                 plenum 
               
               
                 240 
                 ink guttering structure 
               
               
                 250 
                 location of print media 
               
               
                 260 
                 vacuum aperture plate 
               
               
                 270 
                 slots 
               
               
                 280 
                 guttering ribs 
               
               
                 290 
                 relief channel 
               
               
                 300 
                 bonding wafer 
               
               
                 310 
                 bonding wafer 
               
               
                 400 
                 substrate 
               
               
                 410 
                 gas-flow channels 
               
               
                 420 
                 cover plate 
               
               
                 430 
                 droplet deflector 
               
               
                 440 
                 thermal-bend-actuators