Abstract:
A fluid ejection including a substrate having at least one fluid ejecting element adapted to eject a fluid, a flow feature layer disposed over the substrate, the flow feature layer including a plurality of flow features, a nozzle plate layer disposed over the flow feature layer, the nozzle plate layer including one or more nozzle arrays, each nozzle in each of the one or more nozzle arrays being in fluid communication with a corresponding flow feature of the plurality of flow features and a corresponding fluid ejecting element of the at least one fluid ejecting elements, at least one intake via through which fluid flows into the plurality of flow features, and at least one output via through which fluid flows out of the plurality of flow features.

Description:
FIELD 
       [0001]    The present invention related generally to inkjet printers, and more particularly, to ejection devices for inkjet printers. 
       BACKGROUND 
       [0002]    Thermal inkjet printheads have two major issues that are generally lumped in the category called printhead maintenance. The two issues are coined “startup” and “idle time.” When a printer is not in use for any time period from a few minutes to a few weeks, the printhead is generally capped to prevent excessive drying of ink in the nozzles which are exposed to the air. Evaporation of water from the ink in the nozzles causes the viscosity to increase significantly. Still, no cap can provide a perfect seal, and drying occurs either due to leakage in the seal, or diffusion through the capping materials. For typical extended capping periods in the range of a weekend, the drying can be excessive enough to require large amounts of waste “spits” before starting up the first printing job. Even worse, at times a pump must be employed to pull ink through the nozzles to eliminate the dried ink. This is the essence of the “startup” problem. To get a nozzle with dried ink to startup, a certain amount of ink must be wasted prior to the nozzles first print on the page. In addition to the wasted ink, these startup algorithms are often noisy, and can take significant time—sometimes several minutes—which is undesirable to the customer, because it increases the time to first print. 
         [0003]    While printing, and depending on the images being printed, many nozzles may not be called upon to produce a dot. In this case, idle nozzles aren&#39;t capped, but rather they are in open air and they experience forced convection due to the movement of the printhead carrier. If a nozzle hasn&#39;t been used for as little as a few seconds during a print job, then the ink in the nozzle can dry, and the viscosity can increase enough to compromise the quality of the next few ejected drops from that nozzle. To avoid noticeable print quality issues due to idle time, typically the printhead returns to the maintenance station to spit all nozzles at a required interval. Again, this wastes ink, passing undesirable added cost to the customer. Since nozzles that are uncapped and on a moving printhead become unacceptably dry in a matter of a few seconds, idle time spits can have a significant, adverse effect on print speed. 
         [0004]    Waste ink generated by idle time and startup spits increases linearly with the number of nozzles present in the inkjet printhead. Thus, as heater chips continue to grow in length to increase print speed the waste ink amount grows to uneconomical volumes, in some cases equaling or even exceeding the amount of usable ink in the system. In the case of a page-wide printhead, it is extremely so. Also, for specialty inks with higher solid content in the commercial/industrial printing markets, such as a latex ink or ink with binder, this problem gets increasingly worse. In applications where maintenance stations do not exist, such as in many industrial printing applications, there is also a need for the printhead to startup without any maintenance spits. 
         [0005]    Other solutions to these two problems involve re-circulating ink upstream of the ejector, or often even upstream of the filter. However, to truly keep nozzles fresh and ready to fire, recirculation must happen at the ejector level. Another conventional solution is to recycle ink that has been primed through the nozzles for the purpose of enabling a quality startup. Although this technique avoids wasting ink, in a multi-color printer it requires a separate seal for each color thereby rendering the technique nearly impossible to use with a multi-color heater chip. Also, this technique can be used to reclaim ink from mid-print job spits for idle time, but it is not helpful for increasing the time interval required between spits. Thus, the print speed reduction due to idle time spits is not reduced. 
         [0006]    Other conventional art includes United States Patent Application US2012/07921A1. Here, an extra heater positioned at the end of the heater array is used to pump ink from the via, along the array, through the ejectors and back into the via. This embodiment has a significant drawback in that a pressure drop occurs across each ejector resulting in minimal flow rate toward the center of an array of ejectors. 
         [0007]    A solution is needed for the startup and idle time problems that doesn&#39;t waste ink, works for a multi-color heater chip, and does not slow down print speed. 
       SUMMARY OF THE INVENTION 
       [0008]    A fluid ejection device according to an exemplary embodiment of the present invention comprises: a substrate comprising at least one fluid ejecting element adapted to eject a fluid; a flow feature layer disposed over the substrate, the flow feature layer comprising a plurality of flow features; a nozzle plate layer disposed over the flow feature layer, the nozzle plate layer comprising one or more nozzle arrays, each nozzle in each of the one or more nozzle arrays being in fluid communication with a corresponding flow feature of the plurality of flow features and a corresponding fluid ejecting element of the at least one fluid ejecting elements; at least one intake via through which fluid flows into the plurality of flow features; and at least one output via through which fluid flows out of the plurality of flow features. 
         [0009]    According to at least one embodiment, the one or more nozzle arrays comprise a plurality of nozzle arrays. 
         [0010]    According to at least one embodiment, the plurality of nozzle arrays are in fluid communication with one another so as to form a plurality of fluid flow paths, each fluid flow path extending from the at least one intake via, across at least one nozzle of each of the plurality of nozzle arrays, and to the at least one output via. 
         [0011]    According to at least one embodiment, the plurality of fluid flow paths are in fluid communication with one another between the plurality of nozzle arrays. 
         [0012]    According to at least one embodiment, the plurality of fluid flow paths are not in fluid communication with one another between the plurality of nozzle arrays. 
         [0013]    According to at least one embodiment, the nozzle plate layer further comprises an array of priming orifices. 
         [0014]    According to at least one embodiment, the substrate is made of silicon. 
         [0015]    According to at least one embodiment, the at least one fluid ejecting element is a resistor element. 
         [0016]    According to at least one embodiment, the at least one fluid ejecting element is a piezoelectric element. 
         [0017]    Other features and advantages of embodiments of the invention will become readily apparent from the following detailed description, the accompanying drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The features and advantages of exemplary embodiments of the present invention will be more fully understood with reference to the following, detailed description when taken in conjunction with the accompanying figures, wherein: 
           [0019]      FIG. 1  is a plan view of an inkjet printhead according to an exemplary embodiment of the invention; 
           [0020]      FIG. 2  is a cross-sectional view of an inkjet printhead according to an exemplary embodiment of the invention; 
           [0021]      FIG. 3  is a cross-sectional view of an inkjet printhead according to another exemplary embodiment of the invention; 
           [0022]      FIG. 4A  is a plan view of an inkjet printhead according to an exemplary embodiment of the invention; 
           [0023]      FIG. 4B  is a plan view of an inkjet printhead according to an exemplary embodiment of the invention; 
           [0024]      FIG. 5  is a cross-sectional view of an inkjet printhead according to another exemplary embodiment of the invention; 
           [0025]      FIG. 6A  is a plan view of an inkjet printhead according to an exemplary embodiment of the invention; 
           [0026]      FIG. 6B  is a plan view of an inkjet printhead according to an exemplary embodiment of the invention; 
           [0027]      FIG. 7  is a photograph of an exemplary inkjet printhead according to an exemplary embodiment of the invention; and 
           [0028]      FIG. 8  is a graph showing a comparison of test patterns generated by an inkjet printhead according to an exemplary embodiment of the present invention and a conventional inkjet printhead. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claims. As used throughout this application, the words “may” and “can” are used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include,” “including,” and “includes” mean including but not limited to. To facilitate understanding, like reference numerals have been used, where possible, to designate like elements common to the figures. 
         [0030]    An inkjet printhead according to an exemplary embodiment of the present invention includes a flow-through ejector, multiple vias per color and a pump to re-circulate the ink. A flow-through ejector is an ejector that allows ink to flow through it. For example,  FIG. 1  is a plan view and  FIG. 2  is a partial cross-sectional view of an inkjet printhead, generally designated by reference number  1 . The inkjet printhead  1  includes a substrate  10  including actuators, flow-feature layer  12 , a nozzle plate layer  14 , an array of nozzles  16 , an input-side ink via  18  and a output-side ink via  20 . As is known in the art, the substrate may be made of silicon, and the actuators may be resistors or piezoelectric elements. A pump (not shown) is used upstream in the fluidic path, to generate flow of bulk ink to the input-side ink via  18 , across the nozzles  16 , and exiting through the output-side ink via  20 , as shown in  FIG. 2 . This arrangement preserves the bulk water concentration of the ink all the way up to the bottom of the nozzles  16 . Of course, water can still evaporate from the nozzles  16 , causing drying and increased viscosity. However, the viscosity increase can not advance past the flow of ink in the flow feature layer  12 . 
         [0031]    In another implementation of the present embodiment, the pump is turned off, and an increased viscosity front advances past the bottom of the nozzles  16  and into the flow feature layer  12  and perhaps beyond. The pump can then be turned on in regular intervals to clear the high viscosity ink, mixing it into the bulk ink supply. Depending on many factors, such as ink composition and environmental conditions, the pump can be ran periodically, such as hourly, daily, or only immediately prior to printing, or in extreme cases, continuously. The duration of each pump run may depend on the same factors used to determine periodicity. This eliminates, or significantly reduces the need to spit and/or prime nozzles after long periods of disuse. Since the fluid never leaves the printhead, no ink is wasted. 
         [0032]    For the idle time problem, the pump may be ran while printing, maintaining fresh ink in all nozzles, even if some nozzles are not used. This eliminates the need to stop printing, return to the maintenance station and spit waste ink. While printing, it is estimated that the high viscosity front can move through the bottom of the nozzle at a velocity of about 10 μm/s. Thus, the fluid velocity may be at least 10 μm/s to adequately keep nozzles fresh. This estimate assumes standard environmental conditions and a typical commercialized aqueous based pigment ink. 
         [0033]    Since the flow advances through all ejectors in parallel, the present invention solves the pressure drop problem associated with the structure disclosed in application US2012/0007921A1. 
         [0034]    In various exemplary embodiments of the present invention, two ink vias may be needed for each ink color integrated into the chip. For example, for a one color chip, two vias would be needed, and for a three color chip, six vias would be needed. However, during high coverage printing, when flow rate demands are high, the pump may be turned off, allowing both vias to supply the ejector. In a high coverage print, all nozzles are usually needed and idle time is rarely an issue, so the pump would likely not need to run during printing. Therefore, the vias could be smaller than the typical one via per array design and still provide the necessary flow rate without a significant pressure drop across the via. Firmware algorithms may be used to determine high coverage printing situations where the pump would not be needed. 
         [0035]      FIG. 3  is a cross-sectional view of an inkjet printhead, generally designated by reference number  100 , according to another exemplary embodiment of the present invention. This embodiment differs from the previous embodiment in that more than one array of ejectors may correspond to each via, thereby increasing ejector density and better utilizing valuable silicon space. The inkjet printhead  100  includes a substrate  110  including actuators, flow-feature layer  112 , a nozzle plate layer  114 , a first array of nozzles  116 , a second array of nozzles  117 , an input-side ink via  118  and a output-side ink via  120 . As shown by the arrows, ink flows by action of a pump (not shown) from input-side ink via  118 , through flow features in flow feature layer  112 , across and through active nozzles in the nozzle arrays  116 ,  117 , and to output-side ink via  120 . 
         [0036]    There are many different possible ways to provide fluid communication from via to via and across the ejectors.  FIGS. 4A and 4B  are plan views showing two possible designs of an inkjet printhead according to exemplary embodiments of the present invention in which more than one nozzle array corresponds to each via. In both layouts, flow feature layer material  113  may be left between vias  118 ,  120  to prevent the nozzle plate layer  114  from touching the heater chip (substrate  110 ). Depending on the manufacturing process method used to make these structures, these spacer features may or may not be needed. As shown in  FIG. 4B , nozzles  116 ,  117  may be kept substantially isolated from each other fluidically, to avoid crosstalk. Priming orifices  124  may be provided to more easily evacuate air during the initial prime of the printhead  100 . It may be advantageous to add additional ejectors on the outboard side of each via, as opposed to only between vias, as shown. For example,  FIG. 7  shows an embodiment including two vias, two arrays of flow-thru ejectors between the two vias, and two additional arrays of ejectors outboard of each of the two vias. 
         [0037]    Depending on the electrical and fluidic constraints of the device, an inkjet printhead according to another exemplary embodiment of the present invention may include one or more ejector arrays between the two arrays adjacent to the vias. For example,  FIG. 5  shows an inkjet printhead  200  including a substrate  210  including actuators, flow-feature layer  212 , a nozzle plate layer  214 , a first array of nozzles  215 , a second array of nozzles  216 , a third array of nozzles  217 , an input-side ink via  218  and a output-side ink via  220 . As shown by the arrows in  FIG. 5 , ink flows by action of a pump (not shown) from input-side ink via  218 , through flow features in flow feature layer  212 , across and through active nozzles in the nozzle arrays  215 ,  216 ,  217 , and to output-side ink via  220 . 
         [0038]      FIGS. 6A and 6B  show two possible layouts of the inkjet printhead according to an exemplary embodiment of the present invention in which three nozzle arrays are arranged between each via with flow feature layer material  213  left between vias  218 ,  220 . The arrangement shown in  FIG. 6A  is similar to that shown in  FIG. 4A  in that ink flow is combined between nozzle arrays. The arrangement shown in  FIG. 6B  is similar to that shown in  FIG. 6A  except for the absence of “spacers” to ensure the nozzle layer does not sag down and touch the substrate. In both embodiments shown in  FIGS. 6A and 6B , priming orifices  224  may be provided to evacuate air during the initial prime of the printhead  200 . 
         [0039]    According to another exemplary embodiment of the present invention, an inkjet printhead is provided having an edge-feed design, where ink is fed from the sides of the chip to ejectors that are also located along the sides. Flow-through ejectors are employed to provide a recirculation path from one side of the chip to the other. 
         [0040]    An issue surrounding this invention is the quality of the ejected droplets. The ejectors are placed in a channel instead of the conventional approach of having a bubble chamber walled on three sides. A concern is that the energy imparted by the bubble onto the ink will be less directed toward the nozzle, and more directed in both the positive and negative axial directions of the channel. In this regard, the effect has been measured, and the resulting droplet quality is quite acceptable. A conventional ejector delivers 2.9 ng, 490 in/s droplets with a given ink and optimized electrical pulse input. With identical ink, and electrical input; with identical physical geometry, except the back of the chamber is opened to a filter pillar, then to an open area between vias as in the embodiment shown in  FIG. 6A , the flow-through ejector delivers 2.4 ng, 400 in/s droplets. The peak frequency of the flow-through ejectors was increased from 28 kHz to about 36 kHz. These parameters, though different, are generally either acceptable, as in the case of the velocity, or can be adjusted with minor design changes, as in the case of the drop mass and peak frequency. 
         [0041]    In order to illustrate various advantages of the present invention, the following experiments were performed: 
         [0042]    Accelerated Startup: The printhead is left uncapped and in normal carrier motion for 33 minutes. By putting the printhead in motion, and leaving the printhead uncapped, the drying mechanism for startup is accelerated. 
         [0043]    Idle Time Test: Idle time is measured by idling the printhead while uncapped, and swathing for zero to five seconds, in one second increments. Drops are printed before and after idling, and the resulting misdirection is measured as a function of the time idled. When the misdirection exceeds 84 μm, this is determined to be the minimum acceptable idle time. 
       EXAMPLE 1 
       [0044]    An inkjet printhead having a layout similar to that shown in  FIG. 6A  is provided. The inkjet printhead includes four ejector arrays per two vias, per one color. A pressure drop of 47 cmwc from via to via produced a fluid velocity of about 5 mm/s within each flow channel. A photograph of the experimental test vehicle is shown in  FIG. 7 . Accelerated Startup was then measured for this printhead. With a conventional ejector, it takes an average of  26  fires to begin jetting and  59  fires to jet in a high quality manner. With the provided flow-through ejectors, it took zero fires to begin jetting and nine fires to jet in a high quality manner.  FIG. 8  shows a comparison of the two test patterns. 
         [0045]    An idle time test was also run with the same test vehicles. The idle time for conventional ejectors at ambient environmental conditions ranged from 2.5 to 2.9 seconds, as expected. The misdirection due to idle time up to five seconds for the flow-through ejectors never exceeded 84 μm. 
         [0046]    While particular embodiments of the invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications may be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.