Patent Publication Number: US-8523327-B2

Title: Printhead including port after filter

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned, U.S. patent application Ser. No. 12/712,256, entitled “REINFORCED MEMBRANE FILTER FOR PRINTHEAD” and Ser. No. 12/712,261, entitled “METHOD OF MANUFACTURING FILTER FOR PRINTHEAD”, both filed concurrently herewith. 
     FIELD OF THE INVENTION 
     This invention relates generally to the field of digitally controlled printing systems and, in particular, to the filtering of liquids that are subsequently emitted by a printhead of the printing system. 
     BACKGROUND OF THE INVENTION 
     The use of inkjet printers for printing information on recording media is well established. Printers employed for this purpose can include continuous printing systems which emit a continuous stream of drops from which specific drops are selected for printing in accordance with print data. Other printers can include drop-on-demand printing systems that selectively form and emit printing drops only when specifically required by print data information. 
     Continuous printer systems typically include a printhead that incorporates a liquid supply system and a nozzle plate having a plurality of nozzles fed by the liquid supply system. The liquid supply system provides the liquid to the nozzles with a pressure sufficient to jet an individual stream of the liquid from each of the nozzles. The fluid pressures required to form the liquid jets are typically much greater than the fluid pressures employed in drop-on-demand printer systems. 
     Different methods known in the art have been used to produce various components within a printer system. Some techniques that have been employed to form micro-electro-mechanical systems (MEMS) have also been employed to form various printhead components. MEMS processes typically include modified semiconductor device fabrication technologies. Various MEMS processes typically combine photo-imaging techniques with etching techniques to form various features in a substrate. The photo-imaging techniques are employed to define regions of a substrate that are to be preferentially etched from other regions of the substrate that should not to be etched. MEMS processes can be applied to single layer substrates or to substrates made up of multiple layers of materials having different material properties. MEMS processes have been employed to produce nozzle plates along with other printhead structures such as ink feed channels, ink reservoirs, electrical conductors, electrodes and various insulator and dielectric components. 
     Particulate contamination in a printing system can adversely affect quality and performance, especially in printing systems that include printheads with small diameter nozzles. Particulates present in the liquid can either cause a complete blockage or partial blockage in one or more nozzles. Some blockages reduce or even prevent liquid from being emitted from printhead nozzles while other blockages can cause a stream of liquid jetted from printhead nozzles to be randomly directed away from its desired trajectory. Regardless of the type of blockage, nozzle blockage is deleterious to high quality printing and can adversely affect printhead reliability. This becomes even more important when using a page wide printing system that accomplishes printing in a single pass. During a single pass printing operation, usually all of the printing nozzles of a printhead are operational in order to achieve a desired image quality. As the printing system has only one opportunity to print a given section of media, image artifacts can result when one or more nozzles are blocked or otherwise not working properly. 
     Conventional printheads have included one or more filters positioned at various locations in the fluid path to reduce problems associated with particulate contamination. Even so, there is an ongoing need to reduce particulate contamination in printheads and printing systems and an ongoing need for printhead filters that provide adequate filtration with acceptable levels of pressure loss across the filter. There is also an ongoing need for effective and practical methods for forming printhead filters using MEMS fabrication techniques. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a printhead includes a liquid source, a first substrate, a filter, and a liquid chamber. Portions of the first substrate define a nozzle adapted to emit liquid from the liquid source. The liquid chamber includes a port. The liquid chamber is in fluid communication with the nozzle and the filter and is positioned between the first substrate and the filter. 
    
    
     
       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  is 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. 4A  is a schematic cross sectional view of a jetting module including an example embodiment of the present invention; 
         FIG. 4B  is a schematic perspective view of a jetting module including another example embodiment of the present invention; 
         FIG. 5  is flow chart describing a method of manufacturing a filter suitable for use in a jetting module including an example embodiment of the invention; 
         FIGS. 6A through 6G  show stages of formation of a filter manufactured using the method described in  FIG. 5 ; and 
         FIGS. 7 through 9  are schematic diagrams of example embodiments of printing system fluid systems made in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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  FIGS. 1 through 3 , example embodiments of a printing system and a continuous printhead are shown that include the present invention described below. It is contemplated that the present invention also finds application in other types of printheads or jetting modules including, for example, drop on demand printheads and other types of continuous printheads. 
     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 half-toned 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 mechanism(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 transfer system  34 , which is electronically controlled by a recording medium transfer control system  36 , and which in turn is controlled by a micro-controller  38 . The recording medium transfer 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 transfer 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. In the non-printing state, continuous inkjet 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 manifold  47  which is sometimes referred to as a channel. 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 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 an integral portion of the jetting module  48 . 
     Liquid, for example, ink, is emitted under pressure through each nozzle  50  of the array to form streams, commonly referred to as jets or filaments, of liquid  52 . In  FIG. 2 , the array or plurality of nozzles extends into and out of the figure. Typically, the orifice size of nozzle  50  is from about 5 μm to about 25 μm. 
     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, a piezoelectric actuator, or an electrohydrodynamic stimulator that, when selectively activated, perturbs each jet of liquid  52 , for example, ink, to induce portions of each jet to break-off from the jet 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 with certain aspects having been described in, for example, one or more of U.S. Pat. No. 6,457,807 B1, issued to Hawkins et al., on Oct. 1, 2002; U.S. Pat. No. 6,491,362 B1, issued to Jeanmaire, on Dec. 10, 2002; U.S. Pat. No. 6,505,921 B2, issued to Chwalek et al., on Jan. 14, 2003; U.S. Pat. No. 6,554,410 B2, issued to Jeanmaire et al., on Apr. 29, 2003; U.S. Pat. No. 6,575,566 B1, issued to Jeanmaire et al., on Jun. 10, 2003; U.S. Pat. No. 6,588,888 B2, issued to Jeanmaire et al., on Jul. 8, 2003; U.S. Pat. No. 6,793,328 B2, issued to Jeanmaire, on Sep. 21, 2004; U.S. Pat. No. 6,827,429 B2, issued to Jeanmaire et al., on Dec. 7, 2004; and U.S. Pat. No. 6,851,796 B2, issued to Jeanmaire et al., on Feb. 8, 2005. 
     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  having a first size or volume, and small drops  54  having 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 . Typically, drop sizes are from about 1 pL to about 20 pL. 
     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 un-deflected 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 recording medium  32 . 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  (shown in  FIG. 2 ), is emitted under pressure through each nozzle  50  of the array to form jets 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 jet of liquid  52  to induce portions of the jet to break off from the jet 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 first 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 45° relative to the stream of liquid  52  toward drop deflection zone  64  (also shown in  FIG. 2 ). Optional seal(s)  84  provides an air seal between jetting module  48  and upper wall  76  of gas flow duct  72 . 
     Upper wall  76  of 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 second gas flow duct  78  located between catcher  42  and an upper wall  82  that exhausts gas flow from deflection zone  64 . Second duct  78  is connected to a negative pressure source  94  that is used to help remove gas flowing through second duct  78 . Optional seal(s)  84  provides an air 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 first 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 . 
     Alternatively, deflection can be accomplished by applying heat asymmetrically to a jet of liquid  52  using an asymmetric heater  51 . When used in this capacity, asymmetric heater  51  typically operates as the drop forming mechanism in addition to the deflection mechanism. This type of drop formation and deflection is known having been described in, for example, U.S. Pat. No. 6,079,821, issued to Chwalek et al., on Jun. 27, 2000. Deflection can also be accomplished using an electrostatic deflection mechanism. Typically, the electrostatic deflection mechanism either incorporates drop charging and drop deflection in a single electrode, like the one described in U.S. Pat. No. 4,636,808, or includes separate drop charging and drop deflection electrodes. 
     As shown in  FIG. 3 , catcher  42  is a type of catcher commonly referred to as a “Coanda” catcher. However, the “knife edge” catcher shown in  FIG. 1  and the “Coanda” catcher shown in  FIG. 3  are interchangeable and either can be implemented. Alternatively, catcher  42  can be of any suitable design including, but not limited to, a porous face catcher, a delimited edge catcher, or combinations of any of those described above. 
     Referring to  FIG. 4A , a cross-sectional view of jetting module  48  of printhead  30  including an example embodiment of the present invention is shown. Printhead  30  includes a source of liquid  260  in fluid communication with at least one nozzle  250  of jetting module  48 . Portions of a first substrate  249 , sometimes referred to as a nozzle plate, define nozzle(s)  250  which is adapted to emit liquid supplied from the source of liquid  260 . Jetting module  48  includes a filter  270 . A liquid chamber  252  is in fluid communication with each of the at least one nozzles  250  and filter  270 . Liquid chamber  252  is located between the at least one nozzle  250  defined by corresponding portions of first substrate  249  and filter  270 . Liquid chamber  252  includes a port  150 . Port  150  is located downstream relative to filter  270 . 
     As shown in  FIG. 4A , the source of liquid  260  includes liquid manifold  47  although other configurations of liquid source  260  are permitted. Liquid manifold  47  is connected in fluid communication to liquid reservoir  40  (shown in  FIG. 1 ) through a port  122  located in manifold  47 . Port  122  is upstream relative to filter  270 . Liquid is provided to nozzles  250  from manifold  47  under pressure sufficient to form liquid jets  253 . Liquid manifold  47  is often referred to as a second liquid chamber with liquid chamber  252  being referred to as a first liquid chamber. 
     Typically, port  150  functions as an outlet port for liquid while port  122  functions as an inlet port. In alternative embodiments of the present invention, jetting module  48  can include more ports, described in more detail below. The functions of ports  150  and  122  as well as any additional ports can also change. This is also described in more detail below. 
     As shown in  FIG. 4A , filter  270  is a separately formed printhead component and is assembled between substrate  249  and liquid supply manifold  47 . Provided to filter various particulates (not shown) in the liquid, filter  270  is shared by nozzles  250  such that filtered liquid can be provided to any or all of the nozzles  250  from one or more portions of filter  270 . Filter  270  includes a plurality of pores  280  adapted to filter the particulate matter from the liquid. Each pore  280  is appropriately sized and shaped to filter a desired size of particulate matter as the liquid flows through pores  280 . For example, the cross sectional area of each pore  280 , or diameter depending on the shape of each pore  280 , is selected such that a desired size of particulate matter is effectively filtered from the liquid without creating an undesired level of pressure loss or pressure drop across the filter between the upstream and downstream sides of the filter. The number, size, shape and spacing of the pores  280  is also selected such that the structural robustness of filter  270  is sufficient for the operating environment contemplated. The height (or thickness) of filter  270  is also selected to provide structural robustness and to effectively filter from the liquid without creating an unacceptably large loss in pressure across the filter  270 . 
     Filter  270  is a sieve type filter including pores that are through holes in a single layer of material. Such filters are preferred because it has been determined that particle filtering tolerances can be more easily maintained and adhered to when compared to filter pores  280  that include tortuous paths. Pores  280  can be columnar or pores  280  can include sloped or tapered walls, so that the pore entrance size differs from the pore exit size; the smaller of the pore entrance and pore exit size determining the size of particle blocked by the filter pore. Pores  280  can be oriented perpendicular the surface of the filter or the pores  280  can be angled, for example, relative to a surface of the filter. Filter  270  can include more than one material layer. Additionally, the overall size of filter  270 , usually expressed in terms of height or thickness, can be smaller when compared to filter pores  280  that include tortuous paths. Filters including pores  280  with tortuous paths do provide sufficient filtering in some applications, for example, applications in which the size of particle to be filtered is large enough to be consistently trapped by such filters  270 . Usually, pores  280  are arranged in a two dimensional pattern in which the pores  280  are positioned in either an ordered manner relative to each other or a random manner relative to each other. Pores  280  can also be grouped together with non-porous segments positioned between pore groups. Typically, pore  280  sizes are from 1 to 10 μm, and more preferably from 1 to 5 μm. While filter  270  is shown as a planar structure, corrugated or pleated filters can also be used. These filters can have increased filter capacity to trap more debris before becoming overloaded. 
     Pores  280  can include various sectional shapes suitable for filtering the liquid  52 . For example, pores  110  can have triangular, square, oval, or rectangular cross sectional shapes. When pores  280  include corners, the corners should be rounded. Sharp corners are undesirable from a mechanical robustness standpoint. The size of pores  280  can vary in accordance with a measured or anticipated size of particulate manner within liquid  52 . For example, when circular shaped pores  280  are used, diameters are on the order of 4 μm. When triangular shaped pores  280  are used, side dimensions are on the order of 5 μm. Pores  280  can also have a “honeycombed” or cellular composition with cell sizes on the order of 1 μm. Pores  280  can also have a uniform shape and vary in size. For example, pores  280  can be round in shape but individual pores  280  can have different diameters when compared to each other. However, as both the pressure drop for fluid passing through a pore and the particle removing capability of the filter  270  are related to pore size, it is preferable that each pore of the plurality of pores  280  has a substantially uniform size when compared to other pores of the plurality of pores  280  to provide effective filtering and predictable pressure drop across filter  270 . Pores  280  are through holes arranged in a two dimensional pattern in which the pores  280  are positioned in an ordered manner relative to each other. 
     Filter  270  can be made from a stainless steel material, a ceramic material, a polymer material, including for example, track etched polymer membranes, or other metals such as electroformed metals, and etched metals. When filter  270  is electro-formed, suitable metals include, for example, Ni, Pd, and combinations thereof. When filter  270  includes a tortuous path, it is usually made from a woven mesh, a fibrous mat, a foam material, or another material that lends itself to providing a tortuous path. 
     Referring to  FIG. 4B , a cross-sectional view of jetting module  48  of printhead  30  including another example embodiment of the present invention is shown. Nozzle plate  49  is formed from a substrate  85  with portions of substrate  85  defining a plurality of nozzles  50 . Manifold  47  is formed from a substrate  87 . Jetting module  48  also includes a filter  100  adapted to filter particulate matter from liquid flowing through jetting module  48 . Filter  100  is formed in a substrate  97 . In this example embodiment of the present invention, filter  100  includes a filter membrane  102  and a rib structure  137 . Nozzles  50  and filter  100  are spaced apart relative to each other such that a liquid chamber  53  is located between nozzles  50  and filter  100 . Liquid chamber  53  is common to filter  100  and any or all of nozzles  50 . Liquid manifold  47  is often referred to as a second liquid chamber with liquid chamber  53  being referred to as a first liquid chamber. In  FIG. 4B , typically liquid flow directions within jetting module  48  are shown using arrows “→”. 
     Liquid chamber  53  includes a port  150 . Port  150  is located downstream relative to filter  270 . Liquid manifold  47  includes port  122  which is positioned upstream from filter  100 . Nozzle plate  49 , filter  100 , and manifold  47  are typically formed as separate components and assembled to form jetting module  48 . Typically, port  150  functions as an outlet port for liquid while port  122  functions as an inlet port. In alternative embodiments of the present invention, jetting module  48  can include more ports, described in more detail below. The functions of ports  150  and  122  as well as any additional ports can also change. This is also described in more detail below. 
     As shown in  FIG. 4B , filter membrane  102  includes pores  110  that are columnar, are uniformly round in shape, have a uniform diameter, and are sized to effectively filter particles that may obstruct, in whole or in part, or otherwise adversely affect nozzle orifice having sizes of from 1 μm to 20 μm. Pores  110  are arranged in a two dimensional pattern in which the pores  280  are positioned in an ordered manner relative to each other. Pores  110  are also grouped together with non-porous segments positioned between pore groups. Rib structures  137  are located in these non-porous segments. Alternative embodiments of filter  100  are permitted and include, for example, those alternatives discussed with reference to  FIG. 4A . 
     Liquid chamber  53  is formed in or with one or more of the components that make up jetting module  48 . This includes, for example, all or portions of one or more of substrate  85 , substrate  97 , and a substrate  95  positioned between filter  100  (substrate  97 ) and nozzle plate  49  (substrate  85 ). 
     Although shown in  FIG. 4B  as being made from one substrate, liquid chamber  53  and other printhead components such as nozzle plate  49 , filter  100 , and manifold  47  can each be formed using more than one substrate. Each substrate can include a single material layer or a plurality of material layers. One or more of each substrate can include at least one material layer formed by a deposition process or at least one material layer applied by a lamination process or combinations thereof. An additional adhesive can be used in some example embodiments to adhere one substrate to another substrate while no additional adhesive is used to adhere substrates to each other in other example embodiments. Liquid chamber  53  and other printhead components such as nozzle plate  49 , filter  100 , and manifold  47  can each be made from various materials including, for example, ceramic, polymer, semiconductor materials such as silicon, stainless steel, and other metal materials. When a metal material is selected for the filter  100 , the metal can be of the type that is deposited by electro-deposition, for example, Ni, Pd, and combinations thereof. 
     In  FIG. 4B , filter  100  includes a planar membrane  102  positioned to span across or “bridge” liquid chamber  53 . As such, portions of liquid chamber  53  are defined by filter membrane  102 , portions of substrate  85 , and portions of substrate  95 . Liquid chamber  53  is in fluid communication with at least one of the pores  110  and at least one of the nozzles  50 . As shown, liquid in liquid chamber  53  is provided to each of nozzles  50 . Liquid chamber  53  allows liquid pressure and flow characteristics to normalize across the array of nozzles  50  after the liquid passes through pores  110  located in filter membrane  102  and before the liquid is directed toward nozzles  50 . 
     As shown in  FIG. 4B , each nozzle  50  includes a liquid flow channel  50 B in fluid communication with a nozzle orifice  50 A, commonly referred to as a nozzle bore. Also in fluid communication with liquid chamber  53 , each flow channel  50 B provides a portion of the liquid in liquid chamber  53  to a corresponding orifice  50 A. Each flow channel  50 B is formed in substrate  85 . Flow channels  50 B help to condition flow turbulence in the liquid as the liquid enters nozzles  50  as described U.S. Pat. No. 7,607,766 B2, which is incorporated by reference herein. As shown, flow channels  50 B are rectangular in shape. Flow channels  50 B can include other shapes and provide other functions. For example, one or more of flow channels  5013  can have circular or elliptical cross sections. The walls of the flow channels  50 B can be substantially perpendicular to the plane of the nozzle plate  49  or alternatively the walls can converge as they extend toward a corresponding nozzle orifice  50 A in order to better direct liquid flow through nozzle  50 . 
     Outlet port  150  is positioned in jetting module  48  at a location downstream from filter  100 . Outlet port  150  provides an alternate fluid path for directing liquid away from nozzles  50  and out of jetting module  48  after the liquid passes through filter  100 . Outlet port  150  can include a valve to control flow of fluid passing through this port. Liquid chamber  53  can include one or more outlet ports  150 . As shown in  FIG. 4B , jetting module includes outlet port  150 A and outlet port  150 B although other example embodiments include less or more. Outlet port  150 A, located on one side of liquid chamber  53  in jetting module  48 , provides a liquid flow path away from nozzles  50 . Outlet port  150 B is located in a side of liquid chamber  53  that is opposite outlet port  150 A. Outlet port  150 B is typically used to achieve better flow profile characteristics during a jetting module cross-flushing operation. Outlet ports  150 A and  150 B are appropriately sized to provide a desired fluid flow through liquid chamber  53  during the cross-flush operation. 
     As shown in  FIG. 4B , manifold  47  optionally includes an outlet port  124  in addition to inlet port  122 . Outlet port  124  is positioned upstream of filter  100  and is used during a cross-flushing operation to help remove particulate matter that has accumulated in manifold  47  or on filter  100  during jetting module  48  operation. This type of cross-flushing operation includes establishing a flow across an upstream surface of filter  100  in manifold  47  from inlet port  122  to outlet port  124 . As this cross-flushing process helps to remove particulate matter that has accumulated on filter  100  during jetting module  48  operation, variations in pressure drop, commonly referred to as loss, created by the accumulation of particulate matter on an upstream surface of filter  100  are reduced. Periodically removing particulate material from the upstream surface of filter  100  using a cross-flush operation can help maintain pressure drop across filter  100  at tolerable levels. 
     Whereas outlet port  124  is located in manifold  47  upstream relative to filter  100  to allow particles to be flushed from manifold  47 , outlet port  150 A or outlet port  150 B is positioned in liquid chamber  53  positioned downstream relative to filter  100  to allow particles to be flushed from liquid chamber  53 . The cross-flushing action provided by outlet port  150 A or outlet port  150 B allows for some of the liquid to flow across and away from inlets of flow channels  50 B. 
     Advantageously, incorporation of one or both of outlet port  150 A or outlet port  150 B in the example embodiments of the present invention as described herein helps increase printhead reliability and print quality by cross-flushing particulate matter present in liquid located downstream of filter  100 . Particulate matter may still be present in the liquid even though the liquid has already been filtered by filter  100 . For example, if filter  100  and nozzle plate  49  are separately formed components which are subsequently assembled to form jetting module  48 , undesired particulate matter that may partially or fully occlude each one or more of nozzles  50  can be generated during the assembly process. Also, when printhead  30  has not been used for a period of time, obstructions in one or more of nozzles  50  may develop from a congealing action associated with liquid. For example, some pigment-based inks can form relatively soil plugs in nozzles  50  when printhead  30  is not operated for some time. The use of outlet port  150 A or outlet port  150 B can be used to generate a cross-flushing action to assist in the removal of the aforementioned particulate matter and obstructions. 
     Outlet port  150 A or outlet port  150 B can be used to cross-flush liquid away from nozzles  50  at various times. For example, cross-flushing can be performed at the point of manufacture as part of an assembly test. Alternatively, the printing system can be configured so that cross-flushing can also be used in the field. Cross-flushing examples are discussed in more detail below. In some example embodiments, outlet port  150 A or outlet port  150 B is used to cross-flush printhead  30  on a predetermined schedule. In some example embodiments, outlet port  150 A or outlet port  150 B is used to cross-flush printhead  30  automatically while in other example embodiments, outlet port  150 A or outlet port  150 B is used to cross-flush printhead  30  as a result of operator intervention. In some example embodiments, outlet port  150 A or outlet port  150 B is used to cross-flush printhead  30  each time printhead  30  is started up. In some example embodiments, outlet port  150 A or outlet port  150 B is used to cross-flush printhead  30  as part of a corrective action undertaken to alleviate a print defect caused by, for example, a misaligned or missing jet of liquid. It is understood that outlet port  150 A or outlet port  150 B can be operated to cross-flush printhead  30  with liquids other than ink. For example, various suitable cleaning agents may be employed. In some example embodiments, liquid chamber  53  is also provided with an inlet port that is distinct from pores  110  of filter  100  that can be used to provide a liquid other than ink to liquid chamber  53 . 
     In the example embodiments described above with reference to  FIGS. 4A and 4B , fluid flow associated with any or all of ports  122 ,  124 ,  150 A, or  150 B can be selectively occluded by a corresponding valve  160 . Each valve  160  can be operated to selectively redirect a flow of a portion of liquid either toward or away from at least one of nozzles  50 . In some example embodiments, valve  160  is manually operated while in other example embodiments, valve  160  is operated under the influence of micro-controller  38  (shown in  FIG. 1 ). Valve  160  can be operated from a fully closed position in which no fluid flow occurs to a partially open or fully open position in which varying degrees of fluid flow occur. Valves  160  can be any suitable valve that accommodates contemplated liquid operating pressures and flow rates. The selection of a valve  160  can be motivated by its particular compatibility with various material characteristics of liquid or by the design characteristics of valve  160  that reduce the likelihood of particle generation during printhead operation. Valves  160  can be external to jetting module  48 . Alternatively, valve  160  can be a MEMS valve which can be advantageous when other components of printhead  30  are fabricated using MEMS processes. 
     Optionally, the cross-flushing operation to remove particulates from chamber  47  and the upstream surface of filter membrane  100  can be enhanced by ultrasonically vibrating jetting module  48  or the liquid in jetting module  48 . Such vibrations can dislodge the particulate material from the surfaces of the chamber and the upstream surface of the filter membrane  100  so that they can be swept out of the jetting module. Piezoelectric elements or actuators bonded to the exterior of the jetting module may be employed to generator the desired ultrasonic vibrations. Optionally the piezoelectric actuators are driven at a plurality of frequencies to further enhance the effectiveness of the cross-flush as described in, for example, European Patent EP 1 095 776. 
     In the example embodiment shown in  FIG. 4B , the components of jetting module  48  can be separate parts that are assembled to form jetting module  48 . One or more of these components can also be formed and assembled using MEMS fabrication techniques as described below. 
     Jetting module  48  includes a plurality of stacked planar substrates with nozzles  50 , liquid chamber  53  and filter  100  being formed in one or more of these planar substrates. This configuration lends itself to MEMS fabrication. Accordingly, in this example embodiment of the present invention, one or more of the features of jetting module  48 , for example, nozzles  50 , liquid chamber  53 , or filter  100 , are formed using MEMS fabrication techniques. 
     MEMS fabrication techniques are preferentially employed to form various components having various combinations of conductive, semi-conductive, and insulator material layers, some or all of these layers having features formed therein by various material deposition and etching processes commonly controlled by a patterned mask layer. As previously described, nozzles  50  can be formed in substrate  85  using MEMS processes. MEMS processes can also be used to form filter  100  from substrate  97 . In this example embodiment substrate  97  includes a semi-conductor material. Semi-conductor materials such as silicon are readily processed using MEMS fabrication techniques. 
     Substrate  97  is patterned and etched to remove various portions of the semi-conductor material, for example, silicon, to form rib structures  137  and filter membrane  102 . Pores  110  are formed in filter membrane  102  of substrate  97 . As shown in  FIG. 4B , pores  110  are arranged in pore groups  120  although other configurations are permitted. Pores  110  are formed using additional patterning and etching processes. Adjacent rib structures  137  are spaced apart from each other by one of the pore groups  120  formed in filter membrane  102 . A typical rib structure  137  has a thickness of at least 10 μm to about 450 μm thick. A typical filter membrane  102  has a thickness of about 2 μm to about 10 μm. As shown in  FIG. 4B , rib structures  137  bracket a pore group  120  on two sides. In other example embodiments, one or more pore groups  120  can be surrounded by one or more rib structures  137 . For example, rib structures  137  can be arranged in a two-dimensionally grid relative to filter membrane  102 . 
     Rib structures  137  are integrally formed with filter membrane  102 . Rib structures  137  help to reinforce filter membrane  102  which allows filter membrane  102  to be thinner than would be otherwise possible. It is desired that a pressure drop, commonly referred to as loss, associated with the liquid as it flows through pore groups  120  be reduced as much as possible. Thinner filter membranes  102  reduce the loss across filter  100  when compared to thicker filter membranes  102 . As such, operating pressures can be lowered when a thinner filter membrane  102  is used. Typically, it is desirable to keep operating pressures as low as possible in order to maintain reliable system operation. Increased operating pressures put unwanted stress on the system. Additionally, when operating pressures are increased, equipment costs can also increase. For example, pumps have to be sized appropriately, which adds cost to the system. 
     In some example embodiments, a loss across filter  100  of no more than 10 psi is desired. In other example embodiments, a loss across filter  100  of no more than 5 psi is desired. In other example embodiments, a loss across filter  100  of no more than 3 psi is desired. A loss across filter  100  can vary as a function of liquid flow rate with higher flow rates experiencing higher pressure drops. The pressure drop across filter  100  can also be dependant on factors such as the size of pores  110 , the number of pores  110  and the thickness of filter membrane  102 . Pores  110  are typically sized to trap a predicted or measured size of particulate mater within the liquid. Generally stated, the effective diameter of the pore should be less than ½, and preferably less than ⅓ of the effective diameter of the orifice  50 A of the nozzle  50 . The effective diameter of an opening, such as a nozzle or pore, is equal to two times the square root of the opening area divided by π. For example, each nozzle  50  of printhead  30  has an effective diameter when viewed in a direction of fluid flow through the nozzle  50  and each pore  110  has an effective diameter when viewed along the direction of fluid flow through the pores  110 . The effective diameter of the pore  110  is less than half the area of the nozzle  50 . 
     In some example embodiments, the number of pores  110  is increased to help reduce an expected pressure drop as liquid flows through filter  100 . In other example embodiments, the thickness of filter membrane  102  is controlled reduce an expected pressure drop across filter  100 . Accordingly, very thin filter membranes  102  may be required. In some instances, filter membranes  102  including very thin thicknesses may be prone to handling damage when filter  100  is assembled into printhead  30 . Filter membranes  102  including these thicknesses may not be well suited for withstanding the effects of the pressure differential created by liquid  52  across filter membranes  102 . Rib structures  137  formed in accordance with the present invention advantageously reinforce filter membranes  102  thereby reducing the potential for damage to their delicate structures. Unlike conventional printhead filter systems including relatively thick membranes with corresponding large pressure drops, the formation of rib structures  137  advantageously allows for the formation reinforced filter membranes  102  that are capable of resisting damage while not adversely increasing the pressure drop across filter membrane  100 . Typically, the thickness of filter membranes  102  is &lt;10 μm, preferably &lt;5 μm, and more preferable &lt;2 μm. 
     Referring to FIGS.  5  and  6 A- 6 G, a flow chart representing a method  300  for manufacturing a portion of filter membrane  100  in accordance with an example embodiment of the invention is shown. Various processes steps associated with the method represented by the flow chart in  FIG. 5  are also illustrated in  FIGS. 6A ,  6 B,  6 C,  6 D,  6 E,  6 F, and  6 G. In step  310 , a first substrate  140  is provided, the first substrate  140  having a first surface  141  and a second surface  142 . In this example embodiment, first substrate  140  includes a semi-conductor material, for example, silicon. In step  315 , a material layer  155  is provided over first surface  141  as illustrated in  FIG. 6A . In this example embodiment, material layer  155  is a silicon dioxide layer formed by coating first surface  141  with silicon dioxide. Other materials can be used, for example, tetraethyl orthosilicate (TEOS), silicon nitride, silicon oxynitride, and silicon carbide. In some example embodiments, one or more additional layers, for example, a silicon nitride (SiN), silicon oxynitride, or silicon carbide layer is also provided. 
     In step  320 , a plurality of pore groups  120  are formed in material layer  155 . In this example embodiment, a first mask layer  156 , for example, a photo-resist is deposited and patterned on a surface of material layer  155  as shown in  FIG. 6B . An etchant is then used to etch the material layer  155  exposed through the patterned first mask layer  156  to form the plurality of pore groups  120  as shown in  FIG. 6C . First mask layer  156  can be removed at this point or at a latter point in time if so desired. In this example embodiment, material layer  155  includes a thickness selected to reduce expected pressure drops when a desired liquid is subsequently made to flow through a printhead  30  that incorporates the formed filter membrane  102 . 
     In step  325 , a plurality of rib structures  137  is formed in first substrate  140 . In this example embodiment, a second mask layer  157 , for example, a photo-resist is deposited and patterned on second surface  142  of first substrate  140  as shown in  FIG. 6D . An etchant is then used to etch portions of first substrate  140  that are exposed through the patterned second mask layer  157  to form a plurality of rib structures  137  in first substrate  140  as shown in  FIG. 6E . The rib structures  137  are positioned such that a rib structure  137  is located between consecutive pore groups  120 . In this example embodiment of the invention, rib structures  137  are formed to reinforce portions of material layer  155  proximate to a pore group  120 . Second mask layer  157  is shown removed in  FIG. 6E . In one example embodiment, an aspect ratio of the pore groups  120  is 4 to 1 while the size of rib structures  137  is approximately 20 μm but these values can vary depending on material type and thickness. Preferably, the spacing between ribs  137  for the pore groups  120  is no greater than 200 times the thickness of the filter membrane  102 , and more preferably no greater than 75 times the filter membrane  102  thickness to reduce the potential for damage to filter membrane  102  structures. 
     In step  330 , a second substrate  170  is provided, the second substrate  170  including a first surface  171  and a second surface  172 . In step  330  a liquid chamber  53  is formed in second substrate  170 . In this example embodiment, a third mask layer  158 , for example, a photo-resist is deposited and patterned on first surface  171  of second substrate  170  as shown in  FIG. 6F . In step  335 , a liquid chamber  53  is formed in second substrate  170  by using an etchant to etch portions of second substrate  170  that are exposed through the patterned third mask layer  158  as shown in  FIG. 6G . Liquid chamber  53  is positioned to allow for fluid communication with at least one of the pore groups  120 . The third mask layer  158  is shown removed in  FIG. 6G . Liquid chamber  53  is combined with one filter  100  and one or more additional substrates, for example, nozzle plate  49 , to form printhead  30 . 
     In some embodiments in which liquid chamber  53  includes an outlet port  150 , the port geometry can be created using this same process by inclusion of the desired port features in one or more of the masks used to define the etched regions of substrate  170 , substrate  140 , and material layer  155 . The port can be formed through the side of substrate  170 , or alternatively, the port can pass through substrate  140  and material layer  155 . The portions of the flow channel(s) formed in layer  95  and layer  97 , shown in  FIG. 4B , (which along with the portion of the flow channel formed in substrate  87  form port  150 ) can be formed in this manner. 
     In some example embodiments, the second surface  142  of first substrate  140  is adhered to one of the first surface  171  and the second surface  172  of the second substrate  170  with an additional adhesive. In some example embodiments, an additional adhesive is not used to adhere first substrate  140  to second substrate  170 . In some example embodiments, first substrate  140  and second substrate  170  are integrated into a third substrate, referred to as an integrated substrate, that includes an etch stop layer positioned between the first substrate  140  and second substrate  170 . One example of such an integrated substrate is a silicon-on-insulator substrate (SOI). Alternatively, a timed etch without an etch stop layer can also form a suitable structure. 
     Manufacturing method  300  can be modified in various manners to process integrated substrates such SOI substrates. For example, liquid chamber  53  can formed by etching second substrate  170  exposed by the patterned third mask layer  158  through to the etch stop layer. Rib structures  137  can be formed in first substrate  140  by a process that includes etching regions of the etch stop layer that are exposed after the removal of various regions of second substrate  170 . The steps illustrated in manufacturing method  300  are provided by way of example only. Additional or alternate steps or sequences of steps are within the scope of the present invention. 
     Referring to  FIGS. 7 through 9 , example embodiments of fluid systems are shown that are suitable for use with printheads  30  or jetting modules  48  including the present invention. These fluid systems can be used to accomplish the cross flushing of jetting module  48  describe above. Broadly described, cross flushing includes moving the fluid through the chambers to remove trapped particles or accumulated debris from the jetting module through one of ports. Referring to  FIG. 7 , fluid from fluid reservoir  40  is pumped by pump  46 A through filter  350  and into inlet port  122  of jetting module  48  when valve  380  is open. It flows from the inlet port into fluid chamber or manifold  47  that is located upstream of filter  100 ;  270 . The fluid passes through filter  100 ;  270  that is either integrated with or integral to jetting module  48  and enters fluid chamber  53 . When valve  360  is closed, the fluid pressure rises to cause the fluid to be jetted from the plurality of nozzles  50  that are in fluid communication with fluid chamber  53 . When valve  360  is open, the fluid is drawn out of the fluid chamber  53  through port  150 B and is returned to fluid reservoir  40 . A vacuum, applied to fluid reservoir  40  by vacuum pump  370  assists the flow of fluid from port  150 B back to fluid reservoir  40 . The flow of fluid from port  122  through fluid chamber  53  and out through port  150 B enables the removal of particles from fluid chamber  53 . 
       FIG. 8  illustrates another embodiment of a fluid system. Like the fluid system described with reference to  FIG. 7 , fluid is supplied to fluid chamber or manifold  47  of the jetting module  48  through inlet port  122  located upstream of filter  100 ;  270 . Fluid chamber  53 , located downstream from filter  100 ;  270 , includes a first port  150 A and a second port  150 B. Valves  360  and  390  associated with ports  150 A and  150 B are used to control the fluid flow through ports  150 A and  150 B. If both valves  360  and  390  are closed, the fluid pressure rises to cause the fluid to be jetted from the plurality of nozzles  50  that are in fluid communication with fluid chamber  53 . If one or both of valves  360 ,  390  are open, fluid will flow through the corresponding port  150 B,  150 A and be returned to fluid reservoir  40 . This allows particles to be removed from fluid chamber  53  through either or both of ports  150 A,  150 B. In one embodiment, valves  360  and  390 , associated with both first ports  150 A and second port  150 B are open concurrently to enable fluid to flush out from fluid chamber  53  quickly. In another embodiment, one valve  360  or  390  is open at a time, to sequentially allow liquid to flush from first one end of fluid chamber  53  and then the other end of fluid chamber  53 . This enables higher flow rates to be achieved through port  150 A or  150 B that is open thereby providing more effective flushing of the corresponding end portion of fluid chamber  53 . 
     Referring to  FIG. 9 , in another embodiment of the fluid system, jetting module  48  includes four ports, two ports  122  and  124  upstream of filter  100 ;  270  and two ports  150 A and  150 B located downstream of filter  100 ;  270 . The fluid system shown in  FIG. 9  provides a greater number of options for flushing fluid chambers  53  and  47  of jetting module  48 . For example, if valves  380  and  400  are open, while valves  360 ,  390 , and  410  are closed, fluid can flush particles out of the fluid chamber provided by manifold  47 . This can serve to flush particles off the upstream face of filter  100 ;  270  which helps to keep the pressure drop across filter  100 ;  270  at acceptable levels. Opening valves  410  and  360 , while valves  390 ,  400 , and  380  are closed causes liquid to cross flush fluid chamber  53  to aid in removal of particles in that chamber. A filter  420  is located in the line supplying fluid directly to liquid chamber  53 , downstream of filter  100 ;  270  via port  150 A to minimize the risk of carrying particles from the fluid system directly into fluid chamber  53 . While  FIG. 9  shows an embodiment in which fluid supplied for cross-flushing fluid chamber  53  is the same fluid that is supplied to manifold  47 , it is contemplated that a second fluid can be supplied from a second fluid reservoir for the cross-flushing of fluid chamber  53 . 
     Alternatively, valves  380 ,  400 ,  390 , and  360  can be opened, with valve  410  closed to concurrently cross-flush both the first and second fluid chambers. Filter  100 ;  270  can be back-flushed by supplying fluid to fluid chamber  53  through valve  410  and port  150 A while withdrawing the fluid from manifold  47  through port  124  and valve  400 . Valves  380 ,  390 , and  360  are closed during this cross-flushing operation. Prior to introducing fluid into the second fluid chamber via port  150 A for any of the flushing processes described above, it can be desirable to first flush the fluid through filter  420  and the corresponding fluid line with valves  380 ,  390 , and  410  open and valves  360  and  400  closed for a period of time. This operation helps reduce the risk that particles will be injected into the second fluid chamber through port  150 A. 
     Optionally, the various flushing operation to remove particulates from the surface or surfaces of manifold  47 , chamber  53 , filter  100 ;  270  and nozzle plate  49  can be enhanced by ultrasonically vibrating at least one of or a portion of the filter  100 ;  270 , nozzle plate  49 , and the interior surfaces of the first liquid chamber  53  and the manifold (second liquid chamber)  47 . Such vibration can dislodge the particulate material from these surfaces so that the particles can be flushed out of jetting module  48 . Piezoelectric elements or actuators bonded to the exterior of jetting module  48  can be used to generate the desired ultrasonic vibrations. Optionally the piezoelectric actuators can be driven at a plurality of frequencies to further enhance the effectiveness of the cross-flush as described in EP 1 095 776. As described above, filter  100 ;  270  preferably includes a sheet of material having straight pores through it as opposed to pores having torturous paths to allow more effective particle removal flushing operations. 
     The invention has been described in detail with particular reference to certain example embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
     
         
         
           
               20  continuous printing system 
               22  image source 
               24  image processing unit 
               26  mechanism control circuits 
               28  device 
               30  printhead 
               32  recording medium 
               34  recording medium transfer system 
               36  recording medium transfer control system 
               38  micro-controller 
               40  reservoir 
               42  catcher 
               44  recycling unit 
               46  pressure regulator 
               46 A pump 
               47  manifold 
               48  jetting module 
               49  nozzle plate 
               50  nozzles 
               50 A nozzle orifice 
               50 B liquid flow channel 
               51  heater 
               52  liquid 
               53  liquid chamber 
               54  drops 
               56  drops 
               57  trajectory 
               58  drop stream 
               60  gas flow deflection mechanism 
               61  positive pressure gas flow structure 
               62  gas 
               63  negative pressure gas flow structure 
               64  deflection zone 
               66  small drop trajectory 
               68  large drop trajectory 
               72  first gas flow duct 
               74  lower wall 
               76  upper wall 
               78  second gas flow duct 
               82  upper wall 
               85  substrate 
               86  liquid return duct 
               87  substrate 
               88  plate 
               90  front face 
               92  positive pressure source 
               94  negative pressure source 
               95  substrate 
               96  wall 
               97  substrate 
               100  filter 
               102  filter membrane 
               110  pores 
               120  pore groups 
               122  port 
               124  port 
               137  rib structure 
               140  first substrate 
               141  first surface 
               142  second surface 
               150  port 
               150 A port 
               150 B port 
               155  material layer 
               156  first mask layer 
               157  second mask layer 
               158  third mask layer 
               160  valve 
               170  second substrate 
               171  first surface 
               172  second surface 
               249  first substrate 
               250  nozzle 
               252  liquid chamber 
               253  liquid jets 
               260  source of liquid 
               270  filter 
               280  pores 
               300  method 
               310  step 
               315  step 
               320  step 
               325  step 
               330  step 
               335  step 
               350  filter 
               360  valve 
               370  vacuum pump 
               380  valve 
               390  valve 
               400  valve 
               410  valve 
               420  filter