Patent Publication Number: US-6702436-B2

Title: Fluid ejection cartridge including a compliant filter

Description:
BACKGROUND 
     DESCRIPTION OF THE ART 
     Over the past decade, substantial developments have been made in the micro-manipulation of fluids in fields such as electronic printing technology using inkjet printers. As the volume of fluid manipulated or ejected decreases the susceptibility to clogging of fluid channels and nozzles has increased. Fluid ejection cartridges provide a good example of the problems facing the practitioner in preventing the clogging of microfluidic channels and nozzles due to particulates. 
     Fluid ejection cartridges typically include a fluid reservoir that is fluidically coupled to a substrate that is attached to the back of a nozzle layer containing one or more nozzles through which fluid is ejected. The substrate normally contains an energy-generating element that generates the force necessary for ejecting the fluid held in the reservoir. Two widely used energy generating elements are thermal resistors and piezoelectric elements. The former rapidly heats a component in the fluid above its boiling point causing ejection of a drop of the fluid. The latter utilizes a voltage pulse to generate a compressive force on the fluid resulting in ejection of a drop of the fluid. 
     Currently there is a wide variety of highly-efficient inkjet printing systems in use, which are capable of dispensing ink in a rapid and accurate manner. However, there is a demand by consumers for ever-increasing improvements in speed and image quality. To improve image quality, the size or diameter of each nozzle typically decreases. For example, today printers generally have 300 to 600 dpi (dots per inch). In order to improve print speed the number of nozzles necessarily increases. Thus, improvements in both image quality and speed have led to a decrease in the size of the nozzles as well as an increase in the number of nozzles on a printhead. This utilization of a greater number of smaller nozzles has created a greater degree of susceptibility to plugging from particulates in the ink supply. The plugging of a nozzle results in serious degradation of the image or print quality of the printer system. 
     In order to prevent the nozzle system from becoming clogged with particulate matter, a mechanical filter element is typically disposed in the ink jet print cartridge such that the ink is filtered before it is supplied to the nozzle system. If the ink is not filtered it would tend to clog or block the nozzles. These mechanical filters are generally screens and typically made of stainless steel woven mesh. They are attached to what is generally referred to as a standpipe. The standpipe provides fluid communication between the ink reservoir of the print cartridge and the fluid ejectors. This mesh is typically rigidly secured around the edges to the standpipe to prevent leakage of ink around the filter element. 
     In addition, in an effort to reduce the cost and size of ink jet printers and to reduce the cost per printed page, printers have been developed having small, moving printheads that are connected to large stationary ink supplies. This development is called “off-axis” printing and has allowed the large ink supplies to be replaced as it is consumed without requiring the frequent replacement of the costly printhead containing the fluid ejectors and nozzle system. However, the typical “off-axis” system requires numerous flow restrictions between the ink supply and the printhead, such as additional orifices, long narrow conduits, and shut off valves. To overcome these flow restrictions and to also provide ink over a wide range of printing speeds, ink is now transported to the printhead at an elevated pressure. A pressure regulator is typically added to deliver the ink to the printhead at the optimum backpressure. 
     Further, an “off-axis” printing system strives to maintain the back pressure of the ink within the printhead to within as small a range as possible. Changes in back pressure greatly affect print density as well as print and image quality. In addition changes in back pressure can cause either the ink to drool out of the nozzles or to deprime the printhead. As consumer demands push the technology to ever smaller nozzles it becomes necessary to filter ever smaller particles from the ink. However, mechanical filter elements capable of filtering smaller particles typically require a larger pressure drop across the filter medium to generate the same flow rate as a larger particle filter. Thus, the requirement to filter smaller particles yet maintain the back pressure of the ink within the printhead to within as small a range as possible has produced a problem in inkjet technology development. 
     SUMMARY OF THE INVENTION 
     A fluid ejection cartridge includes a fluid container that has both a fluid inlet and a fluid outlet. The fluid ejection cartridge has one or more fluid ejectors fluidically coupled to the fluid container outlet and a fluid valve fluidically coupled to the fluid container inlet. The fluid ejection cartridge has a filter assembly having a compliant portion with an internal volume fluidically coupled to the fluid container outlet such that the internal volume changes when fluid flows into the fluid container. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a fluid ejection cartridge according to an embodiment of the present invention; 
     FIG. 2 a  is graph of pressure as a function of time in a fluid ejection cartridge according to an embodiment of the present invention; 
     FIG. 2 b  is graph of pressure as a function of time in a fluid ejection cartridge according to an embodiment of the present invention; 
     FIG. 3 a  is a perspective view of a fluid ejection cartridge according to an embodiment of the present invention; 
     FIG. 3 b  is a plan view of a filter assembly according to an embodiment of the present invention; 
     FIG. 3 c  is a cross-sectional view of a filter assembly according to an embodiment of the present invention; 
     FIG. 3 d  is a cross-sectional view of a filter assembly according to an embodiment of the present invention; 
     FIG. 4 is a perspective view of a fluid ejection system according to an embodiment of the present invention; 
     FIG. 5 a  is a cross-sectional view of a fluid ejection cartridge according to an embodiment of the present invention; 
     FIG. 5 b  is a cross-sectional view of a fluid ejection cartridge according to an embodiment of the present invention; 
     FIG. 6 a  is a cross-sectional view of a filter assembly according to an embodiment of the present invention; 
     FIG. 6 b  is a cross-sectional view of a filter assembly according to an embodiment of the present invention; 
     FIG. 7 a  is a cross-sectional view of a filter assembly according to an embodiment of the present invention; 
     FIG. 7 b  is a cross-sectional view of a filter assembly according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an embodiment of fluid ejection cartridge  100  of the present invention in a simplified block diagram is shown. In this embodiment, filter assembly  120  includes compliant portion  140  and non-complaint portion  130  disposed in fluid container  110 . However, depending on the particular application in which fluid ejection cartridge  110  will be used, filter assembly  120  may also be located outside of fluid container  110 , such as between fluid container  110  and fluid outlet  154 . Fluid inlet  150  is fluidically coupled to fluid container  110  so that when fluid regulator  152  or regulator is in an open state fluid can flow from a fluid supply (not shown) into fluid container  110 . Fluid in container  110  flows through filter assembly  120  through fluid outlet  154  to fluid ejector  156 , as fluid is ejected from fluid ejection cartridge  100  through one or more nozzles (not shown) by activating fluid ejector  156 . When fluid regulator  152  causes additional fluid to flow into fluid container  110 , compliant portion  140  of filter assembly  120  responds to changes in pressure, thereby dampening pressure transients created by the opening of the valve typical of most valves used as fluid regulator  152 . 
     Many fluid ejection delivery systems strive to keep the pressure of the fluid within fluid ejection cartridge  100  constant. Fluid flow is generally controlled by a fluid delivery system. The fluid delivery system regulates the pressure of the local fluid supply within fluid ejection cartridge  100  to a pressure less than ambient, which is generally referred to as backpressure. The backpressure range is controlled to keep the backpressure from affecting the ejecting frequency and amount of fluid ejected out of fluid ejection cartridge  100 . If the backpressure is equal to or greater than ambient pressure, fluid will leak or drool out of the one or more nozzles. If the backpressure is much less than ambient pressure, the nozzles and area around fluid ejector  156  will not properly refill. Typical fluid ejection cartridges utilize a regulator to control the backpressure over a range of fluid flow rates. The particular pressure and flow rates depend on the particular application of the fluid ejection cartridge. 
     The transient pressure response at a fixed flow rate for a typical regulator coupled to a fluid ejection cartridge having a non-compliant filter is shown graphically in FIG. 2 a . The bottom curve represents the transient pressure response of the filter, where the rising edge at the left side signifies the fluid ejector turning on and the peak indicates the start of fluid flow into the fluid container. The falling edge at the right side signifies the fluid ejector shutting off stopping fluid flow. The middle curve represents the transient pressure response of fluid container  110 , where the peak on the left side indicates that the backpressure within fluid container  110  exceeds the steady state pressure for a short period of time. When fluid stops flowing as depicted on the right side of the middle curve the backpressure undershoots the steady state pressure of fluid ejection cartridge  100 . The top curve represents the transient pressure response in the vicinity of fluid ejector  156  where the peak on the left side indicates that the backpressure exceeds the steady state backpressure for a short period of time at fluid ejector  156  resulting in a pressure spike. Thus, the fluid ejector pressure represents, for a system utilizing a non-compliant filter, the combined effect of the transient pressure response of the filter and the fluid container  110 . In the interval while the backpressure at fluid ejector  156  exceeds a predetermined value the drop size or amount of the fluid ejected will vary from its steady state value. 
     The transient pressure response at a fixed flow rate for a typical regulator coupled to a fluid ejection cartridge having a compliant filter portion is shown graphically in FIG. 2 b . The bottom curve represents the transient pressure response of the filter, where the rising edge on the left side, again signifies the fluid ejector turning on starting fluid flow. However, unlike a non-complaint filter, the internal volume of compliant portion  140  of filter assembly  120  decreases, in response to the flow transient, providing a more gradual rise in pressure. When the fluid ejector turns off, stopping fluid flow, the internal volume of compliant portion  140  increases eventually returning to substantially the same volume before filling started. This increase in volume provides a more gradual decrease in pressure as shown on the right side of the bottom curve when compared to a non-compliant filter. The middle curve represents the transient pressure response of fluid container  110 , and is substantially the same as that shown in FIG. 2 a  for a non-compliant filter. The top curve again represents the transient pressure response in the vicinity of fluid ejector  156 . The fluid ejector pressure, again, represents the combined effect of the transient pressure response of filter assembly  120  and fluid container  110 . By utilizing compliant portion  140 , the pressure spike observed using a non-compliant filter has been attenuated. Such attenuation provides a more uniform drop size during refill. 
     Referring to FIG. 3 a  an exemplary embodiment of the present invention is shown in perspective view. In this embodiment, pen body  360  forms the walls of fluid container  310  for fluid ejection cartridge  300 . Fluid ejector head  370  includes one or more fluid ejectors disposed on substrate  372 . Preferably, substrate  372 , nozzle layer  374 , nozzles (not shown), and a chamber layer (not shown) form what is generally referred to as an ejector head. However, depending on the particular application and fluid ejection properties desired, other embodiments may utilize nozzle layer  374  with flexible circuit  375  integrated to form one part. Nozzle layer  374  contains one or more nozzles (not shown) through which fluid is ejected. Flexible circuit  375  of the exemplary embodiment is a polymer film and includes electrical traces (not shown) connected to electrical contacts (not shown). The electrical traces and contacts to bond pads (not shown) on substrate  372  provide electrical connection for fluid ejection cartridge  300 . Preferably the one or more fluid ejectors are deposited onto substrate  372  using conventional semiconductor processing equipment to create the various thin films utilized in forming the fluid ejectors. 
     Located within pen body  360  is filter assembly  320  that is fluidically coupled to standpipe  378  via filter fitment  334 . Filter assembly  320  is shown in plan view in FIG. 3 b . Filter assembly  320  includes filter frame  332  that forms non-complaint portion  330 . In addition, a portion of filter frame  332  forms filter fitment  334  that is, preferably, press-fit into a mating structure in standpipe  378 . Compliant portion  340  includes filter material  342  that is, preferably, heat staked to filter frame  332  so that outer surface  341  of filter material  342  and  344  forms a convex shape. However, depending on the particular materials utilized for filter material  342  and filter frame  332 , adhesives and other mechanical fastening methods may also be utilized to attach filter material  342  to filter frame  332 . 
     Filter material  342  can be any of the filter materials well known in the art. The actual filter material utilized will depend both, on the particular application in which fluid ejection cartridge  300  will be utilized, as well as on characteristics or criteria of the filter material such as filtration efficiency, pressure drop, and chemical and thermal robustness to name a few. Preferably, the filter material is a polymer. However, materials woven from fibers of metal, ceramic, or glass can also be utilized. More preferably filter material  342  is a porous membrane such as polysulfone or polytetrafluoroethylene. 
     An exemplary filter material is a polyester/polysulfone/polyester three-layer film. The mean pore size of filter material  342  can range from about 1 micron to about 50 microns, preferably ranging from about 2 microns to about 10 microns. Typically the mean pore size is about one third the size of the smallest feature that the fluid flows through. In addition, filter material  342  exhibits a flow rate of between about 20 milliliters per min (ml/min.) to about 300 ml/min. at a pressure less than about 8 inches of water (in. H 2 O) at a viscosity of less than about 25 centipoise (cp). However, filter material  342 , preferably, exhibits flow rates of between about 40 ml/min. to about 100 ml/min. at a pressure less than about 5 in. H 2 O at a viscosity of less than about 15 cp. More preferably, filter material  342  exhibits flow rates of between about 45 ml/min. to about 55 ml/min. at a pressure less than about 2 in. H 2 O at a viscosity of less than about 5 cp. 
     Filter frame  332  can be formed from any of the metal, polymer or ceramic materials well known in the art. The actual frame material utilized will depend both, on the particular application in which fluid ejection cartridge  300  will be utilized, as well as on characteristics of the filter material such as the materials chemical and thermal robustness. Preferably, the frame material is a thermoplastic polymer, and more preferably an injection moldable thermoplastic polymer such as polyethylene, polypropylene or polyester to name a few. 
     Also located within pen body  360  is regulator  366  that includes pressure regulator lever  362 , accumulator lever  364 , and flexible bag  365  as shown in FIG. 3 a . Flexible bag  365  is illustrated as fully inflated in FIG. 3 a . Pressure regulator lever  362  and accumulator lever  364  are urged together by a spring (not shown). In opposition to the spring, flexible bag  365  spreads the two levers ( 362 ,  364 ) apart as it inflates outward. Flexible bag  365  is staked to fitment  367  that is preferably press-fit into crown  361 . Preferably pen body  360  and crown  361  are made from a thermoplastic polymer utilizing conventional injection molding equipment. Fitment  367  includes vent  369  to ambient pressure in the shape of a helical, labyrinth path. Vent  369  connects to, and is in fluid communication with, the inside of flexible bag  365 , so that flexible bag  365  is maintained at a reference pressure. The helical path reduces the diffusion of fluid out of fluid container  310  via diffusion through flexible bag  365 . 
     Regulator lever  362  rotates about two opposed axles (not shown) that form the axis of rotation of regulator lever  362 . When regulator lever  362  engages filter assembly  320  the rotation of the lever is stopped. Approximately perpendicular to the plane of regulator lever  362  is a valve seat (not shown) that is formed of a resilient material. In response to the expansion or contraction of flexible bag  365 , regulator lever  362  rotates about the axles (not shown) causing the valve seat (not shown) to open and close against a mating surface on crown  361 . This rotational motion of regulator lever  362  regulates the flow of fluid into fluid container  310  via septum  351 . Accumulator lever  364  and flexible bag  365  operate together, in a similar manner as that described for regulator lever  362 , to accommodate changes in volume due to any air that may be entrapped in fluid ejection cartridge  300 , as well as due to other pressure changes, such as a change in altitude. For a more detailed description of the structure and operation of such a regulator as depicted in FIG. 3 a , see U.S. Pat. No. 5,872,584. 
     When regulator lever  362  rotates causing the valve seat to open fluid will flow through septum  351  into fluid container  310  applying a force (i.e. the back pressure of a fluid delivery system) to compliant portion  340  that includes filter material  342 . This applied force or pressure changes the substantially convex shape of outer surface  341  of filter material  342  as shown in FIG. 3 c  to a substantially concave shape as shown in FIG. 3 d  with a corresponding decrease in internal volume  346  of compliant portion  340 . This change in internal volume  346  of compliant portion  340  acts to provide a more gradual rise in pressure observed in the vicinity of the one or more fluid ejectors disposed on substrate  372  of fluid ejector head  370 . As fluid ejection cartridge fills with fluid, flexible bag  365  deflates urging regulator lever  362  to rotate in the opposite direction causing the valve seat to close, thereby decreasing the force or pressure of the fluid delivery system on compliant portion  340 . This decrease in pressure allows compliant portion  340  to change, from the substantially concave shape as shown in FIG. 3 d , to a substantially convex shape as shown in FIG. 3 c , with a corresponding increase in internal volume  346  of compliant portion  340 . This increase in internal volume  346  acts to provide a more gradual decrease in pressure observed in the vicinity of the fluid ejectors on substrate  372 . 
     FIGS. 3 a-   3   d  illustrate an exemplary embodiment where fluid flows from the outside of filter assembly  320  through filter material  342  into internal volume  346  and then through filter fitment  334  to standpipe  378 . However, fluid ejection cartridge  300  may also be constructed such that filter fitment  334  is fluidically coupled, for example, to septum  351  such that fluid flows into internal volume  346  through filter material  342  to the outside of filter assembly  320  to standpipe  378 . In the latter case filter material  342  is formed so that the applied force of the fluid flow is against the substantially convex shape of inner surface  343  of filter material  342 . In addition, the amount of deflection will depend on the elasticity of filter material  342 . To obtain a particular amount of deflection for a given applied force both the thickness as well as the height and width of filter frame  332 , to which filter material  342  is attached, may be modified. The amount of tension, including no tension, applied to filter material  342  may also be varied to further optimize the amount of deflection for a given applied force. By controlling these variables a wide variety of filter materials having a range of elasticities may be utilized. For example, compliant portion  340  may include an elastic filter material such as a woven nylon mesh. 
     Referring to FIG. 4, a perspective view is shown of an exemplary embodiment of a fluid ejection system of the present invention in. As shown printer  480  includes fluid or ink supply  486 , including one or more secondary fluid or ink reservoirs  488  that provide fluid to one or more fluid ejection cartridges  400  commonly referred to as print cartridges. Preferably, print cartridges  400  are similar to fluid ejection cartridge  300  as shown in FIG. 3 a , however, other fluid ejection cartridges may also be utilized. Secondary fluid reservoirs  488  are fluidically coupled to fluid ejection cartridges via flexible conduit  495 . Fluid ejection cartridges  400  may be semi-permanently or removably mounted to carriage  490 . In this embodiment, a platen or sheet advancer (not shown) to which print media  484 , such as paper, is transported by mechanisms that are known in the art. Carriage  490  is typically supported by slide bar  494  or similar mechanism within fluid ejection system  480  and physically propelled along slide bar  494  to allow carriage  490  to be translationally reciprocated or scanned back and forth across sheet  484 . Printer  480  may also employ coded strip  492 , which may be optically detected by a photodector (not shown) in carriage  490  for precise positioning of the carriage. Carriage  490  may be translated, preferably, using a stepper motor (not shown), however other drive mechanism may also be utilized. In addition, the motor may be connected to carriage  490  by a drive belt, screw drive, or other suitable mechanism. 
     When a printing operation is initiated, print media  484  in tray  482  is fed into a printing area (not shown) of printer  480 . Once print media  484  is properly positioned, carriage  490  may traverse print media  484  such that one or more print cartridges  400  may eject ink onto print media  484  in the proper position. Print media  484  may then be moved incrementally, so that carriage  490  may again traverse print media  484 , allowing the one or more print cartridges  400  to eject ink onto a new position on print media  484 . Typically the drops are ejected to form predetermined dot matrix patterns, forming for example images or alphanumeric characters. 
     Rasterization of the data can occur in a host computer such as a personal computer or PC (not shown) prior to the rasterized data being sent, along with the system control commands, to the system, although other system configurations or system architectures for the rasterization of data are possible. This operation is under control of system driver software resident in the system&#39;s computer. The system interprets the commands and rasterized data to determine which drop ejectors to fire. Thus, when a swath of ink deposited onto print media  484  has been completed, print media  484  is moved an appropriate distance, in preparation for the next swath. This invention is also applicable to fluid dispensing systems employing alternative means of imparting relative motion between the fluid ejection cartridges and the print media, such as those that have fixed fluid ejection cartridges and move the print media in one or more directions, and those that have fixed print media and move the fluid ejection cartridges in one or more directions. 
     Referring to FIG. 5 a  an alternate embodiment of the present invention is shown in a simplified cross-sectional view. The fluid has been omitted from FIG. 5 a  to better provide a clear view of the drawing. In this embodiment, the filter assembly includes filter material  542  formed substantially as a bag acting as compliant portion  540 , and sealed to non-compliant portion  530  inside fluid container  510 . Filter spring  548  acts to return filter material  542  to an expanded form as fluid flow decreases or stops. Non-compliant portion  530  forms fluid outlet  554  that is fluidically coupled to standpipe  578  which provides a fluid path for fluid flowing to fluid ejector  556 . Ejector head  570  is formed by substrate  572 , fluid ejector  556 , nozzle layer  574 , nozzle  558 , and chamber layer  571 , which defines the side walls of an ejector chamber. Fluid inlet  550  includes septum  551  and is fluidically coupled to fluid container  510 . One end of regulator lever  562  forms valve  552  having a valve seat that mates with valve seat  554 . Flexible bag  565  and vent  569  perform similar functions as described above, and as shown in FIG. 3 a.    
     When regulator lever  562  rotates causing valve  552  to open fluid will flow through septum  551  into fluid container  510  applying a force (i.e. the back pressure of a fluid delivery system) to compliant portion  540  that includes filter material  542 . This applied force or pressure causes filter material  542  to deflate as shown in FIG. 3 b  with a corresponding decrease in internal volume  546  of compliant portion  540 . The decrease in internal volume  546  compresses filter spring  548 . In addition, this decrease in internal volume  546  of compliant portion  540  provides a more gradual rise in pressure observed in the vicinity of the one or more fluid ejectors disposed on substrate  572  of fluid ejector head  570 . As fluid ejection cartridge  500  fills with fluid, flexible bag  565  deflates causing valve seat  552  to close decreasing the force or pressure of the fluid delivery system on compliant portion  540 . This decrease in pressure causes filter material  542  to expand, via the force exerted by compressed filter spring  548 , with a corresponding increase in internal volume  546  of compliant portion  540 . The increase in internal volume  546  acts to provide a more gradual decrease in pressure observed in the vicinity of the fluid ejectors on substrate  572 . 
     Although this embodiment, depicts fluid flowing from the outside of the bag formed by filter material  542  it is also possible to form the filter assembly whereby fluid would flow from the inside of the bag to the outside. In such an assembly the bag expands when fluid flows out of the bag placing filter spring  548  in tension producing an increase in internal volume  546 . Then as the fluid flow decreases the bag deflates relieving the tension on filter spring  548 . 
     Referring to FIG. 6 a  an alternate embodiment of the present invention is shown in a simplified cross-sectional view. The fluid has been omitted from FIG. 6 a  to better provide a clear view of the drawing. In this embodiment, filter assembly  620  includes filter frame  632  that is compliant and forms compliant portion  640 . Filter material  642  and  644  formed in a substantially rigid manner forms non-compliant portion  630 , and is sealed to compliant portion  640  disposed inside of fluid container  610 . Filter frame  632 , preferably, is heat staked to filter material  642  and  644 . However, depending on the particular materials utilized for filter material  642  and  644  and filter frame  632 , adhesives and other mechanical fastening methods may also be utilized to attach filter material  642  and  644  to filter frame  632 . 
     In this embodiment when fluid flows from the outside of filter assembly  620  through filter material  642  and  644  into internal volume  646  filter frame  632  flexes or deforms providing the change in internal volume  646  that provides a more gradual rise in pressure observed in the vicinity of the one or more fluid ejectors. Whether internal volume increases or decreases depends both on the dimensions of filter frame  632  as well as on the elastic properties of the material used to form filter frame  632 . Filter frame  632  can be formed from any of the metal or polymer well known in the art. The actual frame material utilized depends both, on the particular application in which the fluid ejection cartridge will be utilized, as well as on characteristics of the filter material such as the materials chemical and thermal robustness. Preferably, the frame material is a thermoplastic polymer, and more preferably an injection moldable thermoplastic polymer such as polyethylene, polypropylene or polyester to name a few. Although FIGS. 6 a  and  6   b  depict a filter assembly utilizing fluid flow from outside the assembly to the internal volume inside the assembly other structures where fluid flows from inside the filter assembly to the outside may also be utilized. 
     Referring to FIG. 7 a  an alternate embodiment of the present invention is shown in a simplified cross-sectional view. The fluid has been omitted from FIG. 5 a  to better provide a clear view of the drawing. In this embodiment, filter assembly  720  includes pleated portion  748  attached between filter frame  732  and filter material  742  and  744 . Pleated portion  748  forms compliant portion  740  and filter frame  732  and filter material  742  and  744  form non-compliant portion  730 . However, filter material  742  and  744  may each be attached to a first and a second filter frame respectively with pleated portion  748  attached to first and second filter frames. In this embodiment, when fluid flows from the outside of filter assembly  720  through filter material  742  and  744  into internal volume  746  pleated portion  748  contracts as shown in FIG. 7 b . This contraction provides a decrease in internal volume  746  that results in a more gradual rise in pressure observed in the vicinity of the one or more fluid ejectors. As the fluid ejection cartridge fills with fluid, pleated portion  748  expands with a corresponding increase in internal volume  746 . 
     Filter frame  732  and pleated portion  748  can be formed from either metal or polymer or some combination thereof. The actual frame material and pleat material utilized depends both, on the particular application in which the fluid ejection cartridge will be utilized, as well as on characteristics such as the materials mechanical properties and chemical robustness. Preferably, the frame and pleat material is a thermoplastic polymer, and more preferably an injection moldable thermoplastic polymer such as polyethylene, polypropylene or polyester to name a few. 
     While the present invention has been particularly shown and described with reference to the foregoing preferred and alternative embodiments, many variations may be made therein without departing from the spirit and scope of the invention as defined in the following claims. For example, FIGS. 3 a - 3   d  depict an embodiment where the filter frame is rigid and the filter material is compliant, whereas the embodiment shown in FIGS. 6 a - 6   b  depicts the filter frame as complaint and the filter material as rigid. Embodiments having attributes of both may also be utilized in the present invention where the filter frame and the filter material have some degree of compliance. Thus, the foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed.