Abstract:
A printhead having a drop generator for creating print and non-print drops and a drop deflector for causing the trajectories of the print drops and the non-print drops to diverge includes a liquid extraction channel for removing liquid from the gas flow duct; the liquid extraction channel having an entrance which opens off from the gas flow duct; an outlet; a catcher for collecting the non-print drops wherein the catcher has an ink return channel; at least one via connecting the ink return channel to the liquid extraction channel; and wherein a portion of the liquid passing through the ink return channel of the catcher flows through the at least one via into the liquid extraction channel and from the liquid extraction channel out the outlet.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled printing devices, and in particular to continuous printing systems in which a liquid stream breaks into droplets that are deflected by a gas flow. 
     BACKGROUND OF THE INVENTION 
     Continuous stream inkjet printing uses a pressurized ink source to supply ink to one or more nozzles to produce a continuous stream of ink from each of the nozzles. Stimulation devices, such as heaters positioned around the nozzle, stimulate the streams of ink to break up into drops with either relatively large volumes or relatively small volumes. These drops are then directed by one of several systems including, for example, electrostatic deflection or gas flow deflection devices. 
     In printheads that include gas flow deflection systems, the drop deflecting gas flow is produced at least in part by a gas, typically air, drawn laterally across the drop trajectories into a negative gas flow duct as a result of vacuum applied to the duct. Drops of a predetermined small volume are deflected more than drops of a predetermined large volume. This allows for the small drops to be deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) where they are either recycled or discarded. The large drops are allowed to strike the print medium. Alternatively, the small drops may be allowed to strike the print medium while the larger drops are collected in the ink capturing mechanism. 
     It has been determined that while small drops are deflected by the lateral airflow more than large drops, not all small drops follow the same trajectory. Some of these drops can be deflected sufficiently by the air flow such that they enter the gas flow duct, causing ink puddles to form. Ink puddles in the gas flow duct can also be formed during startup and shutdown of the printhead, caused by ink dripping off the upper wall of the gas flow duct and landing on the lower wall of the gas flow duct. Additionally, ink puddles can be formed due to a crooked jet which causes ink to be directed into the gas flow duct. Ink from the puddles of ink in the gas flow duct can be dragged by the gas flow up into the vacuum source that is attached to the gas flow duct, possibly damaging the vacuum source. If the ink puddles remain close to the entrance to the duct, these puddles can affect the uniformity of the air flow across the width of the jet array. Ink puddles can induce oscillations in the gas flow that can produce a modulation in the print drop trajectories that adversely affect print quality. 
     U.S. Pat. No. 8,091,991 (Hanchak et al.) described a drain for removing such ink from the negative gas flow duct and also a method for cleaning the negative gas flow duct. While the drain is effective at removing such ink from the negative gas flow duct, it has been found that under some conditions the amount of ink that enters the negative gas flow duct and is extracted through the drain can be quite low. Under such conditions some of the ink extracted through the drain can dry in the drain line before reaching the ink reservoir or waste tank. Eventually sufficient ink can dry in the drain line that it begins to clog the drain line. When this occurs ink can begin to build up in the negative gas flow duct, with the problems discussed above. 
     Accordingly, a need exists to improve the removal of such ink deposits from the interior of the negative gas flow duct of the printhead. 
     SUMMARY OF THE INVENTION 
     Briefly, according to one aspect of the present invention a printhead having a drop generator for creating print and non-print drops and a drop deflector for causing the trajectories of the print drops and the non-print drops to diverge includes a liquid extraction channel for removing liquid from the gas flow duct; the liquid extraction channel having an entrance which opens off from the gas flow duct; an outlet; a catcher for collecting the non-print drops wherein the catcher has an ink return channel; at least one via connecting the ink return channel to the liquid extraction channel; and wherein a portion of the liquid passing through the ink return channel of the catcher flows through the at least one via into the liquid extraction channel and from the liquid extraction channel out the outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
         FIG. 1  shows a simplified schematic block diagram of an example embodiment of a printing system made in accordance with the present invention; 
         FIG. 2  is a schematic view of an example embodiment of a continuous printhead made in accordance with the present invention; 
         FIG. 3  is a schematic view of an example embodiment of a continuous printhead made in accordance with the present invention; 
         FIG. 4  is a schematic cross-sectional view of a continuous inkjet printhead, showing the gas flow ducts; 
         FIG. 5  is a prior art schematic cross-sectional view of a continuous inkjet printhead, showing a portion of the negative gas flow duct and a prior art liquid extraction channel; 
         FIG. 6  is a schematic cross-sectional view of a continuous inkjet printhead, showing a portion of the negative gas flow duct, the liquid extraction channel and the liquid return duct of the catcher, made in accordance with the present invention; 
         FIG. 7  is a schematic top section view of a continuous inkjet printhead, showing the negative gas flow duct, the liquid extraction channel and the liquid return duct of the catcher, made in accordance with the present invention; and 
         FIG. 8  is a schematic isometric view of a continuous inkjet printhead, showing the negative gas flow, the liquid extraction channel and the liquid return duct of the catcher, made in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. In the following description and drawings, identical reference numerals have been used, where possible, to designate identical elements. 
     The example embodiments of the present invention are illustrated schematically and not to scale for the sake of clarity. One of the ordinary skills in the art will be able to readily determine the specific size and interconnections of the elements of the example embodiments of the present invention. 
     As described herein, the example embodiments of the present invention provide a printhead or printhead components typically used in inkjet printing systems. However, many other applications are emerging which use inkjet printheads to emit liquids (other than inks) that need to be finely metered and deposited with high spatial precision. As such, as described herein, the terms “liquid” and “ink” refer to any material that can be ejected by the printhead or printhead components described below. 
     Referring to  FIG. 1 , a continuous printing system  20  includes an image source  22  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 image data is converted to bitmap image data by an image processing unit  24  which also stores the image data in memory. A plurality of drop forming mechanism control circuits  26  read data from the image memory and apply time-varying electrical pulses to a drop forming device(s)  28  that are associated with one or more nozzles of a printhead  30 . These pulses are applied at an appropriate time, and to the appropriate nozzle, so that drops formed from a continuous ink jet stream will form spots on a recording medium  32  in the appropriate position designated by the data in the image memory. 
     Recording medium  32  is moved relative to printhead  30  by a recording medium transport system  34 , which is electronically controlled by a recording medium transport control system  36 , and which in turn is controlled by a micro-controller  38 . The recording medium transport system 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  34  to facilitate transfer of the ink drops to recording medium  32 . Such transfer roller technology is well known in the art. In the case of page width printheads, it is most convenient to move recording medium  32  past a stationary printhead. However, in the case of scanning print systems, it is usually most convenient to move the printhead along one axis (the sub-scanning direction) and the recording medium along an orthogonal axis (the main scanning direction) in a relative raster motion. 
     Ink is contained in an ink reservoir  40  under pressure. When the image data does not call for printing a drop on the recording medium, continuous ink jet drop streams are unable to reach recording medium  32  due to an ink catcher  42  that blocks the stream and which may allow a portion of the ink to be recycled by an ink recycling unit  44 . The ink recycling unit reconditions the ink and feeds it back to reservoir  40 . Such ink recycling units 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 nozzles and thermal properties of the ink. A constant ink pressure can be achieved by applying pressure to ink reservoir  40  under the control of ink pressure regulator  46 . Alternatively, the ink reservoir can be left unpressurized, or even under a reduced pressure (vacuum), and a pump is employed to deliver ink from the ink reservoir under pressure to the printhead  30 . In such an embodiment, the ink pressure regulator  46  can comprise an ink pump control system. As shown in  FIG. 1 , catcher  42  is a type of catcher commonly referred to as a “knife edge” catcher. 
     The ink is distributed to printhead  30  through an ink channel  47 . The ink preferably flows through slots or holes etched through a silicon substrate of printhead  30  to its front surface, where a plurality of nozzles and drop forming mechanisms, for example, heaters, are situated. When printhead  30  is fabricated from silicon, drop forming mechanism control circuits  26  can be integrated with the printhead. Printhead  30  also includes a deflection mechanism (not shown in  FIG. 1 ), which is described in more detail below with reference to  FIGS. 2 and 3 . 
     Referring to  FIG. 2 , a schematic view of continuous liquid printhead  30  is shown. A jetting module  48  of printhead  30  includes an array or a plurality of nozzles  50  formed in a nozzle plate  49 . In  FIG. 2 , nozzle plate  49  is affixed to jetting module  48 . However, as shown in  FIG. 3 , nozzle plate  49  can be integrally formed with jetting module  48 . 
     Liquid, for example, ink, is emitted under pressure through each nozzle  50  of the array to form filaments of liquid  52 . In  FIGS. 2-5 , the array or plurality of nozzles extends into and out of the figure. 
     Jetting module  48  is operable to form liquid drops having a first size or volume and liquid drops having a second size or volume through each nozzle. To accomplish this, jetting module  48  includes a drop stimulation or drop forming device  28 , for example, a heater or a piezoelectric actuator, that, when selectively activated, perturbs each filament of liquid  52 , for example, ink, to induce portions of each filament to break off from the filament and coalesce to form drops  54 ,  56 . 
     In  FIG. 2 , drop forming device  28  is a heater  51 , for example, an asymmetric heater or a ring heater (either segmented or not segmented), located in a nozzle plate  49  on one or both sides of nozzle  50 . This type of drop formation is known and has been described in, for example, U.S. Pat. No. 6,457,807 (Hawkins et al.); U.S. Pat. No. 6,491,362 (Jeanmaire); U.S. Pat. No. 6,505,921 (Chwalek et al.); U.S. Pat. No. 6,554,410 (Jeanmaire et al.); U.S. Pat. No. 6,575,566 (Jeanmaire et al.); U.S. Pat. No. 6,588,888 (Jeanmaire et al.); U.S. Pat. No. 6,793,328 (Jeanmaire); U.S. Pat. No. 6,827,429 (Jeanmaire et al.); and U.S. Pat. No. 6,851,796 (Jeanmaire et al.). 
     Typically, one drop forming device  28  is associated with each nozzle  50  of the nozzle array. However, a drop forming device  28  can be associated with groups of nozzles  50  or all of nozzles  50  of the nozzle array. 
     When printhead  30  is in operation, drops  54 ,  56  are typically created in a plurality of sizes or volumes, for example, in the form of large drops  56 , a first size or volume, and small drops  54 , a second size or volume. The ratio of the mass of the large drops  56  to the mass of the small drops  54  is typically approximately an integer between 2 and 10. A drop stream  58  including drops  54 ,  56  follows a drop path or trajectory  57 . 
     Printhead  30  also includes a gas flow deflection mechanism  60  that directs a flow of gas  62 , for example, air, past a portion of the drop trajectory  57 . This portion of the drop trajectory is called the deflection zone  64 . As the flow of gas  62  interacts with drops  54 ,  56  in deflection zone  64 , it alters the drop trajectories. As the drop trajectories pass out of the deflection zone  64 , they are traveling at an angle, called a deflection angle, relative to the undeflected drop trajectory  57 . 
     Small drops  54  are more affected by the flow of gas than are large drops  56  so that the small drop trajectory  66  diverges from the large drop trajectory  68 . That is, the deflection angle for small drops  54  is larger than for large drops  56 . The flow of gas  62  provides sufficient drop deflection and therefore sufficient divergence of the small and large drop trajectories so that catcher  42  (shown in  FIGS. 1 and 3 ) can be positioned to intercept one of the small drop trajectory  66  and the large drop trajectory  68  so that drops following the trajectory are collected by catcher  42  while drops following the other trajectory bypass the catcher and impinge a recording medium  32  (shown in  FIGS. 1 and 3 ). 
     When catcher  42  is positioned to intercept large drop trajectory  68 , small drops  54  are deflected sufficiently to avoid contact with catcher  42  and strike the print media. As the small drops are printed, this is called small drop print mode. When catcher  42  is positioned to intercept small drop trajectory  66 , large drops  56  are the drops that print. This is referred to as large drop print mode. 
     Referring to  FIG. 3 , jetting module  48  includes an array or a plurality of nozzles  50 . Liquid, for example, ink, supplied through channel  47 , is emitted under pressure through each nozzle  50  of the array to form filaments of liquid  52 . In  FIG. 3 , the array or plurality of nozzles  50  extends into and out of the figure. 
     Drop stimulation or drop forming device  28  (shown in  FIGS. 1 and 2 ) associated with jetting module  48  is selectively actuated to perturb the filament of liquid  52  to induce portions of the filament to break off from the filament to form drops. In this way, drops are selectively created in the form of large drops and small drops that travel toward a recording medium  32 . 
     Positive pressure gas flow structure  61  of gas flow deflection mechanism  60  is located on a first side of drop trajectory  57 . Positive pressure gas flow structure  61  includes positive gas flow duct  72  that includes a lower wall  74  and an upper wall  76 . Gas flow duct  72  directs gas flow  62  supplied from a positive pressure source  92  at downward angle θ of approximately a 45° relative to liquid filament  52  toward drop deflection zone  64  (also shown in  FIG. 2 ). An optional seal(s)  84  provides an gas seal between jetting module  48  and upper wall  76  of positive gas flow duct  72 . 
     Upper wall  76  of positive gas flow duct  72  does not need to extend to drop deflection zone  64  (as shown in  FIG. 2 ). In  FIG. 3 , upper wall  76  ends at a wall  96  of jetting module  48 . Wall  96  of jetting module  48  serves as a portion of upper wall  76  ending at drop deflection zone  64 . 
     Negative pressure gas flow structure  63  of gas flow deflection mechanism  60  is located on a second side of drop trajectory  57 . Negative pressure gas flow structure includes a negative gas flow duct  78  located between catcher  42  and an upper wall  82  that exhausts gas flow from deflection zone  64 . The negative gas flow duct  78  is connected to a negative pressure source  94  that is used to help remove gas flowing through second duct  78 . An optional seal(s)  84  provides an gas seal between jetting module  48  and upper wall  82 . 
     As shown in  FIG. 3 , gas flow deflection mechanism  60  includes positive pressure source  92  and negative pressure source  94 . However, depending on the specific application contemplated, gas flow deflection mechanism  60  can include only one of positive pressure source  92  and negative pressure source  94 . 
     Gas supplied by positive gas flow duct  72  is directed into the drop deflection zone  64 , where it causes large drops  56  to follow large drop trajectory  68  and small drops  54  to follow small drop trajectory  66 . As shown in  FIG. 3 , small drop trajectory  66  is intercepted by a front face  90  of catcher  42 . Small drops  54  contact face  90  and flow down face  90  and into a liquid return duct  86  located or formed between catcher  42  and a plate  88 . Collected liquid is either recycled and returned to ink reservoir  40  (shown in  FIG. 1 ) for reuse or discarded. Large drops  56  bypass catcher  42  and travel on to recording medium  32 . Alternatively, catcher  42  can be positioned to intercept large drop trajectory  68 . Large drops  56  contact catcher  42  and flow into a liquid return duct located or formed in catcher  42 . Collected liquid is either recycled for reuse or discarded. Small drops  54  bypass catcher  42  and travel on to recording medium  32 . 
       FIG. 4  provides a broader cross section view of a printhead  30  than that of  FIG. 3  to show more of the gas flow ducts. From the plurality of nozzles of the jetting module  48 , streams of drops  58  are created. A gas flow deflection mechanism  60  made up of a positive pressure gas flow structure  61  and a negative pressure gas flow structure  63  directs a flow of gas across the trajectories of the drop streams  58 . The positive pressure gas flow structure  61  includes a positive pressure source  92  that produces a flow of gas through the positive gas flow duct  72 , directed toward the trajectories of the drop streams. The positive pressure gas flow structure  61  can also include a first gas flow meter  98  to monitor the flow rate of the supplied gas flow. The negative gas flow structure  63  includes a negative pressure source  94  that draws a flow of gas through the negative gas flow duct  78 . A second gas flow meter  99  can be included to monitor the flow rate of the gas through the negative gas flow duct  78 . The micro-controller  38  can make use of the output from the first and second gas flow meters  98 ,  99  as feedback in its control of the positive and negative pressure sources  92 ,  94 . 
     Under some conditions, ink can enter the negative gas flow duct  78 . This can occur during one or more of the startup sequence steps, as well as during the printing process. U.S. Pat. No. 8,091,991 disclosed the use of a liquid extraction channel for extracting such ink from the negative gas flow duct. In an embodiment of that invention, shown in  FIG. 5 , the negative gas flow duct  78  changes direction between a first portion  96  and a second portion  98  of the duct. The entrance  100  of the liquid extraction channel  102  is located along the lower wall  83  of the negative gas flow duct at the transition between the first portion  96  and the second portion  98 . The liquid extraction channel  102  can be fabricated in the wall of the duct at the seam between the catcher and the structure  104  that forms the upward sloping lower wall of the negative gas flow duct  78 . Ink that strikes the lower wall of the negative gas flow duct  78  is entrained by the gas flow through the duct until it reaches the entrance of the liquid extraction channel. Vacuum applied to the outlet of the liquid extraction channel via a drain line  106  can then pull the ink through the liquid extraction channel. The ink extracted in this manner can be returned through the drain line  106  to the ink reservoir  40  ( FIG. 1 ) or directed to a waste tank (not shown). 
     It has been found that during normal operation the amount of ink entering the negative gas flow duct and extracted in this manner can be quite low. At such low flow rates of ink through the drain line  106 , ink can dry in the drain line  106 . Over time sufficient ink can dry in the drain line to obstruct the drain line. If the drain line becomes obstructed then ink that enters the negative gas flow duct can begin to build up in the negative gas flow duct  78 , which can lead to a printhead failure. 
     The invention prevents the drying of ink in the drain line  106  by providing sufficient flow of ink through the drain line to prevent drying. Ink is obtained for this purpose from the liquid return duct  86  of the catcher. One or more vias  108  are formed through the catcher  42  to provide fluid communication between the liquid return duct  86  of the catcher  42  and the liquid extraction channel  102  of the negative gas flow duct  78 , as shown in  FIG. 6-8 . During normal operation of the printer, the liquid return duct  86  of the catcher is essentially filled with ink from the non-print drop caught by the catcher. The vacuum provided to the liquid extraction channel  102  by means of the drain line  106  is sufficient to suck from some ink through the one or more via  108  from the liquid return duct  86  into the liquid extraction channel  102 . The flow of ink into the liquid extraction channel  102  is sufficient to keep ink from drying in the drain line  106 , but is not so much that it interferes with the extraction of ink from the negative gas flow duct  78 . 
     In a preferred embodiment, the liquid return duct  86  of the catcher includes at least one small flow channel  110  that branches off from an outer one of the primary flow channels  112  of the liquid return duct and that connects with a via  108 . The small flow channel  110  branches off from the primary flow channel at a branching point  114 , which is located in the distance range of 0.1 inch to 1 inch from the entrance to the liquid return duct. More preferably the branching point  114  is in the distance range of 0.3-0.7 inches from the entrance to the liquid return duct. It has been found that branching off from the primary flow channel at too large a distance from the entrance can result in the vacuum of the catcher return line applying excessive vacuum to the small flow channel and the via, which inhibits the flow of ink through the via from the liquid return duct of the catcher to the liquid extraction channel of the negative gas flow duct. Placing the branching off point  114  of the small flow channel  110  too close to the entrance of the liquid return duct  86  can result in drawing excessive amounts of air through the vias  108 . 
     Preferably the entrance region of the liquid extraction channel includes an expansion region  116  in which the thickness of the liquid extraction channel increases. see  FIG. 6 . The increased height of the liquid extraction channel reduces the flow impedance of the liquid extraction channel, and reduces the capillary forces that can retain ink in the liquid extraction channel. The reduced height of the liquid extraction channel  102  right at the entrance  100  provides an increased pressure drop at the entrance to the liquid extraction channel. This increased pressure drop at the entrance reduces the relative flow impedance variations across the width of the liquid extraction channel to improve the uniformity of ink extraction across the liquid extraction channel. The increased pressure drop at the entrance  100  to the liquid extraction channel  102  also helps to provide sufficient vacuum at the vias  108  to draw ink through the vias into the liquid extraction channel. Downstream of the expansion region, the liquid extraction channel includes a funnel region  118  in which the liquid extraction channel, as viewed from the top in  FIG. 8 , converges into two funnels  124 . The funnels  124  funnel the liquid and gas flow in the liquid extraction channel toward two approximately uniform cross-sectional channels  120 . The two channels  120  converge to direct the flow to the drain line  106 . Preferably the flow impedance of each of the two uniform cross-sectional channels  120  are matched to each other to ensure uniform ink extraction across the width of the liquid extraction channel  102 . It has been found that having the funnel region converge to two uniform cross sectional channels instead of a single outlet channel produces more uniform ink extraction across the width of the liquid extraction channel and the width of the negative gas flow duct  78 . This reduces the risk of ink getting trapped in low flow regions of the liquid extraction channel. 
     Preferably the exit of the vias  108  is located near the midpoint of the funnel region  118  between the entrance  100  of the liquid extraction channel and the uniform cross-sectional channels  120 . Placement of the vias too far to the rear of the funnel region  118  can limit how much of the liquid extraction channel can be moistened by the flow of ink from the vias, and it can also result in in a higher vacuum level at the vias contributing to an excessive flow of ink through the vias  108  from the catcher liquid return duct. Placement of the via  108  too close to the entrance of the liquid extraction channel can result in too low of a vacuum level at the via which can produce insufficient flow of ink through the vias. 
     Preferably the vias  108  each have a diameter of approximately 1.6 mm. To small of via can increase the risk that the vias could get clogged with ink, and too large of a via diameter can result in excessive flow of ink into the liquid extraction channel. The via can be formed through the catcher  42  normal to the surface of the catcher  42 , or it can be formed at an angle which reduces the flow energy losses as the fluid flow makes the turn from the small channel  110  into the via  108 . 
     U.S. Pat. No. 8,091,991 described a process for cleaning of the negative gas flow duct in which a cleaning liquid is pumped to the negative gas flow duct  78  through the drain line  106 . The same cleaning process can be employed with the present invention during shutdown or special cleaning operations of the printing system. Cleaning liquid pumped into the liquid extraction channel  102  through the duct drain  106  can flow out the entrance  100  of the liquid extraction channel into the negative gas flow duct  78 . It can then flow out of the negative gas flow duct  78 , down the front face  90  of the catcher  42 , and into the liquid return duct  86  of the catcher from which it is extracted by vacuum applied to the outlet  122  of the liquid return duct  86 . Some of the supplied cleaning liquid can flow directly from the liquid extraction channel  102  to the liquid return duct  86  of the catcher through the vias  108  to help clean the vias and the small flow channels  110  of the catcher. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           20  continuous printer system 
           22  image source 
           24  image processing unit 
           26  mechanism control circuits 
           28  drop forming device 
           30  printhead 
           32  recording medium 
           34  recording medium transport system 
           36  recording medium transport control system 
           38  micro-controller 
           40  reservoir 
           42  catcher 
           44  recycling unit 
           46  pressure regulator 
           47  channel 
           48  jetting module 
           49  nozzle plate 
           50  plurality of nozzles 
           51  heater 
           52  liquid 
           54  drops 
           56  drops 
           57  trajectory 
           58  drop stream 
           60  gas flow deflection mechanism 
           61  positive pressure gas flow structure 
           62  gas flow 
           63  negative pressure gas flow structure 
           64  deflection zone 
           66  small drop trajectory 
           68  large drop trajectory 
           72  positive gas flow duct 
           74  lower wall 
           76  upper wall 
           78  negative gas flow duct 
           82  upper wall 
           83  lower wall 
           84  seal 
           86  liquid return duct 
           88  plate 
           90  front face 
           92  positive pressure source 
           94  negative pressure source 
           96  wall 
           98  first gas flow meter 
           99  second gas flow meter 
           100  entrance 
           102  liquid extraction channel 
           104  structure 
           106  drain line 
           108  via 
           110  small flow channel 
           112  primary flow channel 
           114  branching point 
           116  expansion region 
           118  funnel region 
           120  uniform cross-sectional channels 
           122  outlet 
           124  funnel