Patent Publication Number: US-2022212468-A1

Title: Binary array inkjet printhead

Description:
BACKGROUND 
     The present disclosure relates to an electrode assembly for a continuous stream ink jet printhead, particularly for a binary array printhead. 
     Continuous ink jet (CIJ) is a form of ink jet that operates on the theory of selectively charging and deflecting drops in flight. Drops are continuously generated at the nozzle by inducing break-off from a pressurized continuous stream of ink in the presence of a variable electrostatic field created by a charging electrode that places a discrete charge on selected drops. Drops subsequently pass through an electrostatic field wherein the field potential induces deflection on the charged drops in order to direct them to print or direct them into an ink catcher to be reused in the ink system. This same mechanism is often used in binary array CIJ printing which is a type of inkjet that includes an array of jets and that can print at relatively high resolutions of at least 128 by 128 dots per inch (dpi). 
     Binary array printheads use actuators to vibrate ink and eject droplets thereof from the printhead. The actuators need to be precisely situated for the printhead to work properly. Binary array printheads also use a charge electrode assembly to charge droplets that are meant to be printed and not charge droplets that are to be collected in a gutter. A problem with prior charge electrode assemblies is that, because the printhead driver electronics are located far from the charge electrodes, given the number of electrodes, they require large number of electrical connections between the printhead drivers and the charge electrode assembly, which is bulky and cumbersome. 
     BRIEF SUMMARY 
     The present disclosure provides a charge electrode assembly for a binary array inkjet printhead. The charge electrode assembly includes a compact design with electrode electronics disposed behind the face of the charge electrode. The disclosed design provides smaller interconnect path than previous designs and eliminates the need for a bulky flexible connection between a printhead or print module and the rest of the printer. It provides a more compact electrode assembly and movement of the electronics closer to the jet array. 
     In one aspect, a binary array ink jet printhead includes a cavity for containing ink, nozzle orifices in fluid communication with the cavity for passing the ink from the cavity to form droplets, the nozzle orifices extending along a length of the cavity, and an electrode assembly. The electrode assembly includes a front face configured to be disposed generally parallel to a plurality of droplet paths of droplets from the nozzle orifices. A plurality of charge electrodes are disposed on the front face, each charge electrode corresponding to a droplet path and disposed parallel to the droplet path. At least one sensor electrode is disposed on the front face and oriented perpendicular to the droplet paths. Circuitry is disposed on a back portion of the electrode assembly opposite from the front face, wherein each electrode is electrically connected to the circuitry. The circuitry is further in electrical connection to a connector for connecting the electrode assembly to a controller for the printhead. 
     In another aspect, a method of operating a print assembly includes ejecting ink droplets from the nozzle orifices, generating drive signals for the plurality of charge electrodes in circuitry disposed in the print module, using the charge electrodes to charge drops not to be printed, not charging drops used for printing, collecting unprinted drops in a gutter, and printing an image on a substrate with the uncharged drops. 
     In another aspect, a print assembly for a binary array printer includes a printhead. The printhead includes a controller, a plurality of fluid connectors providing fluid communication to fluid sources, and at least one electrical connector in electrical communication with the controller. A print module is configured for releasable connection to the printhead, the print module including at least one electrical connector for connection to the at least one electrical connector of the printhead, a plurality of fluid connectors for connection to the plurality of fluid connectors of the print module, an actuator assembly, a charge electrode assembly disposed adjacent the actuator assembly for charging droplets ejected from the actuator assembly, a deflection electrode assembly for deflecting charged droplets, and a gutter for collecting charged droplets. The print module is easily removable from the printhead in a single step. 
     The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view of a printhead assembly. 
         FIG. 1B  is a side view of the printhead assembly of  FIG. 1  with the print module detached. 
         FIG. 2  is a view of the printhead with the print module removed. 
         FIG. 3  is a front view of a print module. 
         FIG. 4  is a rear view of the print module of  FIG. 3 . 
         FIG. 5  is a bottom view of the print module of  FIG. 3 . 
         FIG. 6  is a sectional view of an embodiment of the print module of  FIG. 3  with the outer cover transparent. 
         FIG. 6A  is an enlarged view of a portion of  FIG. 6   
         FIG. 7  is a front view of an embodiment of a charge electrode. 
         FIG. 7A  is an enlarged view of a portion of  FIG. 7   
         FIG. 8  is a top view of the charge electrode of  FIG. 7 . 
         FIG. 9  is a side view of the charge electrode of  FIG. 7  with the ceramic carrier removed. 
         FIG. 10  shows the charge electrode of  FIG. 8  with most of the ceramic carrier transparent to show the embedded electronics. 
         FIG. 11  is a top view showing two printheads disposed in a serial configuration. 
         FIG. 12  is a top view showing two printheads disposed in a parallel configuration. 
     
    
    
     DETAILED DESCRIPTION 
     The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and functioning of the various elements of this invention are better understood by the following detailed description. However, the embodiments of this invention as described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings. 
     In one aspect, the present disclosure provides a charge electrode assembly for a binary array ink jet printhead. The charge electrode assembly includes a compact design with electrode electronics disposed behind the face of the charge electrode. The disclosed design provides a smaller interconnect path than previous designs and eliminates the need for a bulky flexible connection between a printhead or print module and the rest of the printer. The design provides a more compact electrode assembly and movement of the electronics closer to the jet array. 
     Existing binary array designs create the drive signals for driving the electrodes remote from the charge electrode assembly, and thus require an approximately 300 mm long flexible circuit between the driver circuitry and the charge electrode ceramic block, where a further 20 mm of exposed tracking (separated by &lt;100 um) leads to the active charge pad. As a result, capacitive coupling introduces up to 10% cross-talk on adjacent channels. The disclosed design positions the driver circuitry in the print module very close to the charge electrodes; this configuration reduces the total length between the driver circuitry and the charge electrodes to a few millimeters, thus greatly reducing this cross-talk and reduces capacitive coupling from track to track. 
     The disclosed design also moves the serial to parallel signal conversion closer to the jet array. Prior systems with 256 jets require at least 256 electrical interconnects between the printhead electronics and the sub assembly containing the jet array. The present design reduces the number of electrical interconnects below 100 for 512 jets and enables quick disconnection of the print module from the system, leading to a modular design of printhead and print module. Consequently the user experience is improved as the print module can be replaced in a manner similar to that found in desk top style printers. 
     The disclosed design also provides a significant reduction in footprint for the electronics. Prior art designs require two driver electronics printed circuit boards (PCB&#39;s), each with an approximate area 100 mm×80 mm. The disclosed design integrates the same functionality into the charge electrode tile having area of 130 mm×21 mm. 
       FIG. 1A  is a side view of a printhead assembly  10 . The printhead assembly  10  includes a printhead  12  and a removable print module  20 . Print module  20  is releasably connectable to the printhead  12 . The printhead  12  may include such components as a controller printed circuit board, fluid and electrical connections, pressure, vacuum and ink temperature sensors, and other electronics. The controller (not shown) may be any conventional controller known in the art and will generally include a CPU and memory. The controller is in electrical communication with the print module through the electrical connections described below. The print module  20  includes components such as the actuator assembly, charge electrode, deflection electrode, gutter, and related components. In one embodiment, the print module  20  includes all the structures in the printhead assembly  10  for ejecting ink, and the printhead  12  itself does not include any such structures like the actuator assembly, charge electrode, deflection electrode, and gutter. Because all the ink ejection features are in the print module itself, there is no issue of difficulties in alignment of different structures to each other during replacement of the module, such as the nozzles and the charge electrodes, since they are pre-aligned in the module. The print module  20  (disclosed further below) is designed to be easily detachable from the printhead  12 .  FIG. 1B  is a side view of the printhead assembly of  FIG. 1  with the print module  20  detached. The print module  20  is connected to the printhead by a variety of fluid and electronic connections, which will be described in more detail below. 
       FIG. 2  is a view of the printhead with the print module detached.  FIG. 3  is a front view of the print module  20 .  FIG. 4  is a rear view of the print module  20 .  FIG. 5  is a bottom view of the print module  20 . The print module  20  may be in the general shape of a rectangular solid. In one embodiment, the print module  20  is about 5 inches wide, 2 inches high, and 2 inches deep. The print module  20  includes a front wall  21 , back wall  22 , side walls  23 ,  24 , top wall  25 , and bottom wall  26 . Extending from back wall  22  are various connectors, including electrical connector  31 , mechanical connectors  35 , and various fluid connectors which may include ink feed  27 , ink purge  28 , gutter lines  29 , and cleaning channels  33 . Printhead  12  includes complementary connectors for connecting the electrical and fluid connections of the print module to the printhead. For example, if the print module includes extending spigots for fluid transfer, the printhead will include openings  14  for accommodating the spigots and providing a secure fluid connection thereto. Likewise, printhead  12  will provide an electrical connector  16  for connecting to print module connector  31 . It will be apparent that other electrical, fluid, and mechanical connections are possible. These connections allow the print module  20  to be quickly and easily removed from the printhead  12 . In particular, the electrical and fluid connections between the print module  20  and the printhead  12  can be disconnected in a single step. In one embodiment, all of the electrical and fluid connections between the print module  20  and the printhead  12  are provided on a single face of the print module. This configuration helps provide an easy connection, without the need for any difficult alignment. Ink is ejected from the bottom wall  26  of the print module; in particular, from slot  64  disposed on the bottom wall  26  of the print module. 
       FIG. 6  is a sectional view of an embodiment of a print module  20 , with the cover shown as transparent for clarity of view. The technology used in the printhead and print module  20  is known as a binary array printhead. In binary array printing, an array of jets is ejected and modulated to produce droplets, wherein each droplet is either printed or recycled by a gutter, based on the image being printed.  FIG. 6A  is an enlarged view of a portion of  FIG. 6  showing the components in more detail. The print module  20  includes a droplet generator  30 , charging electrode and deflection electrode assembly  40 , and gutter  32 . The gutter  32  is disposed “downstream” of the charging electrode and deflection electrode assembly  40 . Ink droplets are ejected from orifices  43 . Droplets to be printed are not charged, while non-printed droplets are charged. The charged droplets are deflected by the electric field generated by the deflection electrode and collected by the gutter  32 . The print module  20  includes a cavity  41  for containing ink (particularly organic solvent-based ink) and an array of nozzle orifices  43  in fluid communication with the cavity for passing the ink from the cavity to form droplets, the nozzle orifices extending along a length of the cavity. The droplet generator may be of the design disclosed in PCT publication WO2015031485A1, assigned to the same applicant of the present application, Videojet Technologies Inc., the contents of which are incorporated by reference herein. 
       FIG. 7  is a front view of an embodiment of a charge electrode.  FIG. 8  is a top view of the charge electrode of  FIG. 7 . The electrode assembly  40  includes a front face  42  configured to be disposed generally parallel to a plurality of droplet paths of droplets from the nozzle orifices. Thus, the face  42  of the electrode assembly is disposed along the width of the array of nozzle orifices  43 . As best seen in  FIG. 7A , a plurality of charge electrodes or tracks  44  are disposed on the front face  42 . The electrodes include conductive material disposed on and between insulating materials such as ceramic. The electrode tracks are each about 100 micron to 200 micron wide, preferably between 100 and 150 micron wide, most preferably about 135 micron wide. Each charge electrode  44  corresponds to a droplet path from the nozzle array and is oriented generally parallel to the droplet path. The charge electrodes may be generally flat, or may include grooves like the designs shown in U.S. Pat. No. 5,561,452, the contents of which are incorporated by reference. The front face  42  further includes one or more sensor electrodes disposed on the front face  42  and oriented generally perpendicular to the droplet paths. As shown in  FIG. 7A , in one embodiment the electrode assembly includes four sensor electrodes  45 ,  46 ,  47 ,  48 , and deflection electrode  36  disposed laterally across the droplet paths. Sensors  45 ,  46 ,  47 ,  48  may be used to measure the phase and/or velocity of the droplets. The electrode assembly may include at least two sensors for detecting velocity and/or phase of the droplets. In one embodiment, the deflection electrode  36  is disposed between pairs of the sensor electrodes, with sensor electrodes  45 ,  46  disposed upstream of the deflection electrode  36  and sensors  47 ,  48  disposed downstream of deflection electrode  36 . 
       FIG. 9  is a side view of the charge electrode of  FIG. 7  and associated components. It can be seen that the charge electrode assembly  40  includes a generally planar charge electrode block portion  50  disposed between the droplet generator  30  and the gutter  32 , circuitry  70  disposed on block portion  50 , a flexible connector circuit  52 , and a portion  54  including connector  31  and modulation signal connectors  56 . Of course, other configurations are possible. Block portion  50  includes insulator plate  60  and cleaning fluid channel  62  on the top portion, as best seen in  FIG. 8 . Thus, in one embodiment, the driver circuits are disposed in the print module  20  on the block portion  50  near the charge electrode assembly  40 , and not remote from the charge electrode assembly, as disclosed in the prior art. 
       FIG. 10  shows the charge electrode of  FIG. 8  with most of the ceramic carrier removed to show the embedded electronics. As shown in  FIG. 10 , circuitry  70  is disposed on a planar portion of the electrode assembly behind the front face  42 . In prior art designs, the circuitry for the charge electrode is disposed remote from the charge electrode rather than adjacent to it. Circuitry  70  is preferably disposed within 10 mm of the charge electrode assembly. In one embodiment, circuitry  70  is disposed less than 20 mm, less than 15 mm, less than 10 mm, or less than 5 mm from the charge electrode assembly. Circuitry  70  generally includes a PCB with integrated circuits and discrete components. The circuitry provides the drive signals to apply drop charging pulses to the electrodes  44 , at the correct timing relative to the drop generation clock. In essence, the circuitry  70  provides the switches to determine which electrode  44  is to be charged at a given time. The circuitry  70  also provides a conversion between the serial connection of connector  31  to a parallel connection. Thus, in one embodiment, the conversion between a serial to a parallel connection occurs less than 20 mm, less than 15 mm, less than 10 mm, or less than 5 mm from the charge electrode assembly. Each electrode  44 ,  45 ,  46 ,  47 ,  48 , is electrically connected to the circuitry  70 . The circuitry  70  is further in electrical connection to connector  31  for further connecting the electrode assembly  40  to a controller for the printhead. Connector  31  may be an appropriate connector, such as a card edge serial connector. 
     The connector  31  for connecting the electrode assembly  40  to a controller for the printhead includes electrical connections for providing print data, power, sensors, ground, and modulation signals. In one embodiment, the connector and the circuitry comprise less than 100 separate electrical connections or channels to provide for 512 charge electrodes. Thus, the number of distinct electrical connections in connector  31  is less than the number of charge electrodes. In one embodiment, the number of distinct electrical connections between the print module and the printhead is less than 50%, less than 40%, less than 25%, or less than 20% of the number of charge electrodes. 
     In one embodiment, the plurality of charge electrodes  44  includes at least 256 charge electrodes. In another embodiment, the plurality of charge electrodes  44  includes at least 512 charge electrodes. Disposed over 4 inches of the electrode, 512 charge electrodes provides 128 dpi printing resolution. In further embodiments, the printhead includes less than 256 electrodes and/or prints at less than 128 dpi, such as between 80 and 100 dpi. 
     The print module  20  is easily replaceable in the field, such as if the module wears out, malfunctions, needs to be cleaned, or otherwise needs to be replaced. The print module  20  is easily disconnected from the printhead  12  in a single step. In addition to the fluid and electrical connections, the module is mechanically connected to the printhead by one or more posts  35 . In one embodiment, these post features have threaded bores that accept screws which are captive in the printhead. The screws are tightened to secure the module  20  and undone to release the module  20  from the printhead  12 . Once the screws are released, the module  20  can be removed and replaced by hand in a single motion, since all the connections are on a single face. 
     The electrodes in the charge electrode assembly  40  may be manufactured by any suitable method. In one embodiment, a conductive material is disposed on an insulating substrate and laser trimming is used to remove the metallic layer to provide the desired electrode tracks. In a more specific embodiment, three sputter coated layers of titanium, platinum, and gold are applied to create the conductive coating, then laser ablation is used to selectively remove and create the tracks. 
     The disclosed electrode and printhead design are especially suitable for printing graphic images. A feature of the printhead is that it is capable of printing at on high speed substrates and is very reliable. In particular, in one embodiment the binary array printer can print on a substrate travelling 2000 feet/min and provides at least 99% uptime. By uptime is meant that the printer is available for printing at least 99% of the time, the other 1% or less being required maintenance, such as cleaning, parts replacement, and the like. Higher uptime results from a robust design that does not include many unplanned operational failures. In one embodiment the binary array printer can print on a substrate travelling at least 1000 feet/min, 1500 feet/min, or 2000 feet/min. In one embodiment the binary array printer provides at least 96%, at least 98%, at least 99%, or at least 99.5% uptime. 
     The disclosed design includes the option of using multiple print modules in series or parallel. For example, by putting print modules and/or printheads in series, multiple colors can be printed. By putting modules in parallel, an image of greater width can be printed.  FIG. 11  shows printheads disposed in series on a production line  65 . The printheads are controlled by a common controller. First printhead  66  prints an image in a first color, while second printhead  68  prints an image in a second color. As shown, substrate  70  includes a first image  72  of a circle in one color (printed by printhead  66 ), encircling a second image  74  of a star in a second color (printed by printhead  68 ). It will be apparent that any number of different colors can be printed using this method.  FIG. 12  shows printheads disposed in parallel. This arrangement allows images of a wider width to be printed. The printheads are controlled by a common controller. First printhead  76  prints a first portion of the image  80  (such as the left side) on one part of the substrate  70 , and second printhead  78  prints a second portion of the image  80  (such as the right side) on a second part of the substrate  70 . Thus, if an individual printhead is capable of printing an image 4 inches wide, two printheads disposed in parallel can print an image 8 inches wide. The printheads  76 ,  78  are controlled to provide a single image  80  with no visible seams between the two component images. 
     The system is particularly useful for printing with organic solvent-based inks, such as those using acetone, methyl ethyl ketone, and ethanol. The ink is supplied to the printhead assembly  10  and contained within the print module in ink cavity  41 . Thus, the components of the printhead assembly that are in contact with the ink are resistant to organic solvents. The system is suitable for printing inks containing an organic solvent selected from C 1 -C 4  alcohols, C 3 -C 6  ketones, C 3 -C 6  esters, C 4 -C 8  ethers, and mixtures thereof, in an amount 50% or more by weight of the ink composition. Organic solvents that are contemplated for use with the printing system include ketones, especially methyl-ethyl ketone, acetone, and cyclohexanone; alcohols, especially ethanol; esters; ethers; polar aprotic solvents, and combinations thereof. Examples of C 1 -C 4  alcohols include methanol, ethanol, 1-propanol, and 2-propanol. Examples of C 3 -C 6  ketones include acetone, methyl ethyl ketone, methyl n-propyl ketone, and cyclohexanone. Examples of C 4 -C 8  ethers include diethyl ether, dipropyl ether, dibutyl ether and tetrahydrofuran. Examples of C 3 -C 6  esters include methyl acetate, ethyl acetate and n-butyl acetate. 
     The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the scope of the inventions as defined in the claims are desired to be protected. It should be understood that while the use of words such as “preferable”, “preferably”, “preferred” or “more preferred” in the description suggest that a feature so described may be desirable, it may nevertheless not be necessary and embodiments lacking such a feature may be contemplated as within the scope of the invention as defined in the appended claims. In relation to the claims, it is intended that when words such as “a,” “an,” “at least one,” or “at least one portion” are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim. When the language “at least a portion” and/or “a portion” is used the item can include a portion and/or the entire item unless specifically stated to the contrary.