Patent Application
20110205319
Reference is made to commonly-assigned, U.S. patent application Ser. No. ______ (Docket 96122), entitled “REINFORCED MEMBRANE FILTER FOR PRINTHEAD” and Ser. No. ______ (Docket 96123), entitled “METHOD OF MANUFACTURING FILTER FOR PRINTHEAD”, both filed concurrently herewith.
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.
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.
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.
In the detailed description of the example embodiments of the invention presented below, reference is made to the accompanying drawings, in which:
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
Referring to
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
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
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
Referring to
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
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
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
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
Drop stimulation or drop forming device 28 (shown in
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
Upper wall 76 of gas flow duct 72 does not need to extend to drop deflection zone 64 (as shown in
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
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
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
Referring to
As shown in
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
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
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
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
In
As shown in
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
As shown in
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 150A or outlet port 150B 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 150A or outlet port 150B allows for some of the liquid to flow across and away from inlets of flow channels 50B.
Advantageously, incorporation of one or both of outlet port 150A or outlet port 150B 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 150A or outlet port 150B can be used to generate a cross-flushing action to assist in the removal of the aforementioned particulate matter and obstructions.
Outlet port 150A or outlet port 150B 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 150A or outlet port 150B is used to cross-flush printhead 30 on a predetermined schedule. In some example embodiments, outlet port 150A or outlet port 150B is used to cross-flush printhead 30 automatically while in other example embodiments, outlet port 150A or outlet port 150B is used to cross-flush printhead 30 as a result of operator intervention. In some example embodiments, outlet port 150A or outlet port 150B is used to cross-flush printhead 30 each time printhead 30 is started up. In some example embodiments, outlet port 150A or outlet port 150B 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 150A or outlet port 150B 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
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
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
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 50A 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 <10 μm, preferably <5 μm, and more preferable <2 μm.
Referring to FIGS. 5 and 6A-6G, 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
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
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
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
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
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
Referring to
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 150A 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 150A 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 150A.
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.
