Patent Publication Number: US-7914125-B2

Title: Fluid ejection device with deflective flexible membrane

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 11/520,876, filed on even date herewith, assigned to the assignee of the present invention, and incorporated herein by reference, and is related to U.S. patent application Ser. No. 11/520,883, filed on even date herewith, assigned to the assignee of the present invention, and incorporated herein by reference. 
     BACKGROUND 
     An inkjet printing system, as one embodiment of a fluid ejection system, may include a printhead, an ink supply which supplies liquid ink to the printhead, and an electronic controller which controls the printhead. The printhead, as one embodiment of a fluid ejection device, ejects drops of ink through a plurality of nozzles or orifices and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more columns or arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other. 
     One type of printhead includes a piezo-actuated printhead. The piezo-actuated printhead includes a substrate defining a fluid chamber, a flexible membrane supported by the substrate over the fluid chamber, and an actuator provided on the flexible membrane. In one arrangement, the actuator includes a piezoelectric material which deforms when an electrical voltage is applied. As such, when the piezoelectric material deforms, the flexible membrane deflects thereby causing ejection of fluid from the fluid chamber and through an orifice communicated with the fluid chamber. Fabrication and operation of such printheads present various challenges. For these and other reasons, there is a need for the present invention. 
     SUMMARY 
     One aspect of the present invention provides a fluid ejection device. The fluid ejection device includes a substrate having a fluid channel including a fluid inlet and a fluid outlet, a flexible membrane supported by the substrate and extended a length of the fluid channel, an actuator provided on the flexible membrane, and a constriction provided within the fluid channel between the fluid inlet and the fluid outlet, such that the actuator is adapted to deflect the flexible membrane relative to the fluid channel, and the constriction supports the flexible membrane between the fluid inlet and the fluid outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is block diagram illustrating one embodiment of an inkjet printing system according to the present invention. 
         FIG. 2  is a schematic view illustrating one embodiment of a portion of a printhead assembly according to the present invention. 
         FIG. 3  is a schematic cross-sectional view illustrating one embodiment of a portion of the printhead assembly of  FIG. 2 . 
         FIG. 4  is a schematic, exploded perspective view illustrating one embodiment of a portion of a printhead assembly according to the present invention. 
         FIG. 5  is schematic view illustrating one embodiment of a portion of a printhead assembly according to the present invention. 
         FIG. 6  is a schematic cross-sectional view illustrating one embodiment of a portion of the printhead assembly of  FIG. 5 . 
         FIGS. 7A-7C  are schematic cross-sectional views illustrating one embodiment of operation of a printhead assembly according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
       FIG. 1  illustrates one embodiment of an inkjet printing system  10  according to the present invention. Inkjet printing system  10  constitutes one embodiment of a fluid ejection system which includes a fluid ejection device, such as a printhead assembly  12 , and a fluid supply, such as an ink supply assembly  14 . In the illustrated embodiment, inkjet printing system  10  also includes a mounting assembly  16 , a media transport assembly  18 , and an electronic controller  20 . 
     Printhead assembly  12 , as one embodiment of a fluid ejection device, is formed according to an embodiment of the present invention and ejects drops of ink, including one or more colored inks, through a plurality of orifices or nozzles  13 . While the following description refers to the ejection of ink from printhead assembly  12 , it is understood that other liquids, fluids, or flowable materials may be ejected from printhead assembly  12 . 
     In one embodiment, the drops are directed toward a medium, such as print media  19 , so as to print onto print media  19 . Typically, nozzles  13  are arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  13  causes, in one embodiment, characters, symbols, and/or other graphics or images to be printed upon print media  19  as printhead assembly  12  and print media  19  are moved relative to each other. 
     Print media  19  includes, for example, paper, card stock, envelopes, labels, transparent film, cardboard, rigid panels, and the like. In one embodiment, print media  19  is a continuous form or continuous web print media  19 . As such, print media  19  may include a continuous roll of unprinted paper. 
     Ink supply assembly  14 , as one embodiment of a fluid supply, supplies ink to printhead assembly  12  and includes a reservoir  15  for storing ink. As such, ink flows from reservoir  15  to printhead assembly  12 . In one embodiment, ink supply assembly  14  and printhead assembly  12  form a recirculating ink delivery system. As such, ink flows back to reservoir  15  from printhead assembly  12 . In one embodiment, printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet or fluidjet cartridge or pen. In another embodiment, ink supply assembly  14  is separate from printhead assembly  12  and supplies ink to printhead assembly  12  through an interface connection, such as a supply tube (not shown). 
     Mounting assembly  16  positions printhead assembly  12  relative to media transport assembly  18 , and media transport assembly  18  positions print media  19  relative to printhead assembly  12 . As such, a print zone  17  within which printhead assembly  12  deposits ink drops is defined adjacent to nozzles  13  in an area between printhead assembly  12  and print media  19 . Print media  19  is advanced through print zone  17  during printing by media transport assembly  18 . 
     In one embodiment, printhead assembly  12  is a scanning type printhead assembly, and mounting assembly  16  moves printhead assembly  12  relative to media transport assembly  18  and print media  19  during printing of a swath on print media  19 . In another embodiment, printhead assembly  12  is a non-scanning type printhead assembly, and mounting assembly  16  fixes printhead assembly  12  at a prescribed position relative to media transport assembly  18  during printing of a swath on print media  19  as media transport assembly  18  advances print media  19  past the prescribed position. 
     Electronic controller  20  communicates with printhead assembly  12 , mounting assembly  16 , and media transport assembly  18 . Electronic controller  20  receives data  21  from a host system, such as a computer, and includes memory for temporarily storing data  21 . Typically, data  21  is sent to inkjet printing system  10  along an electronic, infrared, optical or other information transfer path. Data  21  represents, for example, a document and/or file to be printed. As such, data  21  forms a print job for inkjet printing system  10  and includes one or more print job commands and/or command parameters. 
     In one embodiment, electronic controller  20  provides control of printhead assembly  12  including timing control for ejection of ink drops from nozzles  13 . As such, electronic controller  20  defines a pattern of ejected ink drops which form characters, symbols, and/or other graphics or images on print media  19 . Timing control and, therefore, the pattern of ejected ink drops, is determined by the print job commands and/or command parameters. In one embodiment, logic and drive circuitry forming a portion of electronic controller  20  is located on printhead assembly  12 . In another embodiment, logic and drive circuitry forming a portion of electronic controller  20  is located off printhead assembly  12 . 
       FIGS. 2-4  illustrate one embodiment of a portion of printhead assembly  12 . Printhead assembly  12 , as one embodiment of a fluid ejection device, includes a substrate  120 , a flexible membrane  130 , actuators  140 , and a reinforcement member  150 . Substrate  120 , flexible membrane  130 , actuators  140 , and reinforcement member  150  are arranged and interact, as described below, to eject drops of fluid from printhead assembly  12 . 
     In one embodiment, substrate  120  has a plurality of fluid channels  160  defined therein. Fluid channels  160  communicate with a supply of fluid and, in one embodiment, each include a fluid inlet  162 , a fluid plenum  164 , a fluid ejection chamber  166 , and a fluid outlet  168 . As such, fluid plenum  164  communicates with fluid inlet  162 , fluid ejection chamber  166  communicates with fluid plenum  164 , and fluid outlet  168  communicates with fluid ejection chamber  166 . In one embodiment, fluid inlet  162 , fluid plenum  164 , fluid ejection chamber  166 , and fluid outlet  168  are coaxial. In embodiment, fluid channels  160  have a substantially rectangular profile with fluid plenum  164  and fluid ejection chamber  166  each being formed by parallel sidewalls. 
     In one embodiment, substrate  120  is silicon substrate and fluid channels  160  are formed in substrate  120  using photolithography and etching techniques. 
     In one embodiment, a supply of fluid is distributed to and communicated with fluid inlet  162  of each fluid channel  160  via a fluid supply passage  170 . In one embodiment, fluid supply passage  170  is a single or common fluid supply passage communicated with fluid inlet  162  of each fluid channel  160 . As such, fluid is distributed from fluid supply passage  170  through fluid inlet  162  to plenum  164 , and through fluid plenum  164  to fluid ejection chamber  166  of each fluid channel  160 . In one embodiment, fluid outlet  168  of each fluid channel  160  forms a fluid nozzle or orifice of printhead assembly  12  such that fluid is ejected from fluid ejection chamber  166  through fluid outlet/nozzle  168 , as described below. 
     In one embodiment, fluid channels  160  each include a constriction  165 . In one embodiment, constriction  165  is formed by a narrowing of each fluid channel  160  between fluid plenum  164  and fluid ejection chamber  166 . More specifically, in one embodiment, a width of fluid channel  160  at constriction  165  is less than a width of fluid channel  160  along fluid plenum  164  and along fluid ejection chamber  166 . Thus, in one embodiment, constriction  165  forms a neck in each fluid channel  160  between fluid plenum  164  and fluid ejection chamber  166 . 
     In one embodiment, constriction  165  of each fluid channel  160  is formed by a pair of opposing projections  169  projecting into each fluid channel  160 . In one embodiment, a height of projections  169  is substantially equal to a depth of fluid channels  160 . Thus, in one embodiment, as described below, projections  169  and, therefore, constriction  165  contact flexible membrane  130  and provide support for flexible membrane  130  between fluid plenum  164  and fluid ejection chamber  166 . The shape and size of projections  169  can vary, for example, from an arcuate-like shape, such as that illustrated, to a trapezoid-like shape or other hydrodynamic favorable shape providing sufficient mechanical support for flexible membrane  130 . 
     In one embodiment, a width of constriction  165  and, therefore, a width of projections  169 , is selected so as to not substantially affect characteristics such as drop velocity and drop size of drops ejected from fluid channels  160 . In one exemplary embodiment, a depth of fluid channels  160  is approximately 90 microns, a width of fluid channels  160  is in a range of approximately 300 microns to approximately 600 microns, and a width of each projection  169  (measured perpendicular to a sidewall of fluid channels  160 ) is approximately 100 microns. 
     In one embodiment, fluid channels  160  each include a convergence  167 . In one embodiment, convergence  167  is provided between fluid ejection chamber  166  and fluid outlet  168 . As such, convergence  167  directs fluid from fluid ejection chamber  166  to fluid outlet  168 . Convergence  167 , therefore, forms a fluid or flow converging structure. During operation of printhead assembly  12 , convergence  167  reduces potential turbulence which may be generated if fluid channels  160  were formed only by right angles. In addition, convergence  167  prevents air ingestion into fluid outlet  168 . 
     In one embodiment, as illustrated in  FIG. 2 , convergence  167  is formed by two facets each extending at an angle of approximately 45 degrees from sidewalls of fluid ejection chamber  166  and converging towards fluid outlet  168 . In another embodiment, as illustrated in  FIG. 4 , convergence  167  is formed by arcuate sections extending from sidewalls of fluid ejection chamber  166  towards fluid outlet  168 . 
     As illustrated in the embodiments of  FIGS. 2-4 , flexible membrane  130  is supported by substrate  120  and extends over fluid channels  160 . In one embodiment, flexible membrane  130  is a single membrane extended over multiple fluid channels  160 . In one embodiment, flexible membrane  130  extends a length of fluid channels  160 . As such, flexible membrane  130  extends from fluid inlet  162  to fluid outlet  168  of each fluid channel  160 . 
     In one embodiment, flexible membrane  130  includes flexible membrane portions  132  each defined over one fluid channel  160 . In one embodiment, each flexible membrane portion  132  extends a length of a respective fluid channel  160 . As such, each flexible membrane portion  132  includes a first portion  134  extended over fluid ejection chamber  166  and a second portion  136  extended over fluid plenum  164 . Thus, first portion  134  of flexible membrane portions  132  extends in a first direction from constriction  165  of fluid channels  160 , and second portion  136  of flexible membrane portions  132  extends in a second direction opposite the first direction from constriction  165  of fluid channels  160 . 
     In one embodiment, with flexible membrane portions  132  each extending a length of a respective fluid channel  160 , flexible membrane portions  132  are each supported along a respective fluid channel  160  at a first location adjacent fluid outlet  168  and at a second location between or intermediate of fluid inlet  162  and fluid outlet  168 . For example, as described above, flexible membrane portions  132  are each supported between fluid inlet  162  and fluid outlet  168  by constriction  165 . More specifically, flexible membrane portions  132  are each supported by constriction  165  provided between fluid plenum  164  and fluid ejection chamber  166  of a respective fluid channel  160 . Constriction  165 , therefore, supports flexible membrane portions  132  between fluid plenum  164  and fluid ejection chamber  166 . 
     In one embodiment, flexible membrane  130  is formed of a flexible material such as, for example, a flexible thin film of silicon nitride or silicon carbide, or a flexible thin layer of silicon. In one exemplary embodiment, flexible membrane  130  is formed of glass. In one embodiment, flexible membrane  130  is attached to substrate  120  by anodic bonding or similar techniques. 
     As illustrated in the embodiments of  FIGS. 2-4 , actuators  140  are provided on flexible membrane  130 . More specifically, each actuator  140  is provided on first portion  134  of a respective flexible membrane portion  132 . In one embodiment, actuators  140  are provided or formed on a side of flexible membrane  130  opposite fluid channels  160 . As such, actuators  140  are not in direct contact with fluid contained within fluid channels  160 . Thus, potential affects of fluid contacting actuators  140 , such as corrosion or electrical shorting, are reduced. 
     In one embodiment, actuators  140  include a piezoelectric material which changes shape, for example, expands and/or contracts, in response to an electrical signal. Thus, in response to the electrical signal, actuators  140  apply a force to respective flexible membrane portions  132  which cause flexible membrane portions  132  and, more specifically, first portion  134  of flexible membrane portions  132  to deflect. Examples of a piezoelectric material include zinc oxide or a piezoceramic material such as barium titanate, lead zirconium titanate (PZT), or lead lanthanum zirconium titanate (PLZT). It is understood that actuators  140  may include any type of device which causes movement or deflection of flexible membrane portions  132  including an electrostatic, magnetostatic, and/or thermal expansion actuator. 
     In one embodiment, as illustrated in  FIG. 4 , actuators  140  are formed from a single or common piezoelectric material. More specifically, the single or common piezoelectric material is provided on flexible membrane  130 , and selective portions of the piezoelectric material are removed such that the remaining portions of the piezoelectric material define actuators  140 . 
     In one embodiment, as described below, actuators  140  deflect flexible membrane portions  132  and, more specifically, first portion  134  of flexible membrane portions  132 . Thus, when flexible membrane portions  132  of flexible membrane  130  deflect, droplets of fluid are ejected from a respective fluid outlet  168 . 
     As illustrated in the embodiments of  FIGS. 2 and 3 , reinforcement member  150  is provided on flexible membrane  130  and extends over fluid channels  160 . More specifically, reinforcement member  150  is provided on second portion  136  of flexible membrane portions  132  and extends over fluid plenum  164  of fluid channels  160 . In one embodiment, reinforcement member  150  is provided on a side of flexible membrane  130  opposite of fluid channels  160 . As such, reinforcement member  150  supports second portion  136  of flexible membrane portions  132  over fluid plenum  164  of fluid channels  160 . More specifically, reinforcement member  150  supports or stiffens second portion  136  of flexible membrane portions  132  such that deflection or oscillation of second portion  136  of flexible membrane  130  is reduced or prevented during operation of printhead assembly  12 . 
     In one embodiment, reinforcement member  150  extends beyond flexible membrane  130  and beyond fluid inlet  162  of fluid channels  160 . As such, reinforcement member  150  extends over fluid supply passage  170 . Thus, in one embodiment, reinforcement member  150  forms or defines a portion or boundary of fluid supply passage  170 . In one embodiment, reinforcement member  150  is a single member supporting second portions  136  of multiple flexible membrane portions  132 . 
       FIGS. 5 and 6  illustrate another embodiment of printhead assembly  12 . In the embodiment of  FIGS. 5 and 6 , printhead assembly  12 ′ includes substrate  120 ′, flexible membranes  130  provided on opposite sides of substrate  120 ′, actuators  140  provided on flexible membranes  130 , reinforcement members  150  provided on flexible membranes  130 , and fluid supply passage  170  defined in a supporting structure  180 . 
     Substrate  120 ′ includes fluid channels similar to fluid channels  160 , as illustrated and described above, which are formed on a first side and a second side, and which communicate with fluid supply passage  170 . In addition, flexible membranes  130  are provided on and supported by the first side and the second side of substrate  120 ′, similar to that illustrated and described above with reference to flexible membranes  130  and substrate  120 . Furthermore, actuators  140  are provided on flexible membranes  130 , as illustrated and described above, and reinforcement members  150  are provided on flexible membranes  130 , as illustrated and described above. 
     In one embodiment, substrate  120 ′, flexible membranes  130 , actuators  140 , and reinforcement members  150  are joined to supporting structure  180  at reinforcement members  150  so as to communicate with and, in one embodiment, further define fluid supply passage  170 . Thus, reinforcement members  150  facilitate attachment to supporting structure  180 . As such, the arrangement of printhead assembly  12 ′ provides two columns of fluid nozzles or orifices for ejection of fluid. 
       FIGS. 7A-7C  illustrate one embodiment of operation of printhead assembly  12  (including printhead assembly  12 ′). In one embodiment, as illustrated in  FIG. 7A , for operation of printhead assembly  12 , flexible membrane  130  is initially in a deflected state. More specifically, first portion  134  of flexible membrane  130  is deflected inward toward fluid channel  160 . In one embodiment, as described above, deflection of flexible membrane  130  results from the application of an electrical signal to actuator  140 . In one embodiment, as described above, with reinforcement member  150  provided on second portion  136  of flexible membrane  130 , deflection of second portion  136  of flexible membrane  130  is reduced or prevented during operation of printhead assembly  12 . 
     Next, as illustrated in the embodiment of  FIG. 7B , operation of printhead assembly  12  includes establishing a non-deflected state of flexible membrane  130 . In one embodiment, discontinuing application of the electrical signal to actuator  140  produces the non-deflected state of flexible membrane  130 . In one embodiment, as flexible membrane  130  returns to the non-deflected state, a negative pressure pulse (i.e., vacuum) is generated within fluid ejection chamber  166 . As such, a negative pressure wave propagates through fluid channel  160  such that fluid is drawn into fluid channel  160  from fluid inlet  162  when the negative pressure wave reaches fluid inlet  162 . Thus, printhead assembly  12  operates in a fill-before-fire mode. In one embodiment, the negative pressure wave is reflected from fluid inlet  162  thereby producing a reflected positive pressure wave within fluid channel  160 . 
     Next, as illustrated in the embodiment of  FIG. 7C , operation of printhead assembly  12  continues by establishing a second deflected state of flexible membrane  130 . More specifically, first portion  134  of flexible membrane  130  is deflected inward toward fluid channel  160 . In one embodiment, as described above, application of an electrical signal to actuator  140  produces the deflected state of flexible membrane  130 . As flexible membrane  130  assumes or establishes the deflected state, a positive pressure pulse is generated within fluid ejection chamber  166 . As such, a positive pressure wave propagates through fluid channel  160 . 
     In one embodiment, timing of the positive pressure pulse is such that the positive pressure wave combines with the previously generated reflected positive pressure wave (initiated when the flexible membrane returned to the non-deflected state) to produce a combined positive pressure wave within fluid ejection chamber  166 . Thus, the combined positive pressure wave propagates through fluid ejection chamber  166  such that when the combined positive pressure wave reaches fluid outlet  168 , a drop of fluid is ejected from fluid outlet  168 . It is understood that the extent of deflection of flexible membrane  130  illustrated in the embodiments of  FIGS. 7A and 7C  has been exaggerated for clarity of the invention. 
     By providing reinforcement member  150  on second portion  136  of flexible membrane portions  132 , reinforcement member  150  prevents flexible membrane  130  from oscillating over fluid plenum  164 , and ensures that the positive reflection occurs at the interface of fluid inlet  162  to fluid supply passage  170 . Furthermore, providing reinforcement member  150  on second portion  136  of flexible membrane portions  132  also ensures that no compliance exists to dampen the negative pressure pulse or the reflected positive pressure pulse. 
     In addition to preventing flexible membrane  130  from oscillating over fluid plenum  164 , reinforcement member  150  also provides an intermediary material to accommodate the differing materials (and, therefore, differing coefficients of thermal expansion) of a sub-assembly including substrate  120 , flexible membrane  130 , and actuators  140 , and supporting structure  180  ( FIGS. 5 and 6 ) for the sub-assembly when the sub-assembly and the supporting structure are joined together. For example, as described above, substrate  120  and flexible membrane  130  may be formed of silicon and/or glass, while supporting structure  180  may be formed of plastic. Thus, when the sub-assembly and the supporting structure are joined together, for example, by bonding under a temperature load, the plastic of the supporting structure may deform differently than the silicon and/or glass of substrate  120  and flexible membrane  130  thereby inducing stress in the silicon and/or glass. Accordingly, in one embodiment, reinforcement member  150  placed between the silicon and/or glass of substrate  120  and flexible membrane  130 , and the plastic of the supporting structure helps to absorb this stress. 
     The architecture of fluid channels  160 , as illustrated and described herein, produces low fluidic resistance and relatively even fluid flow whereby the fluid flow does not create hydraulic reflections that may impede the regular flow of fluid. As such, higher operating and drop ejection frequencies are enabled. In addition, the architecture of fluid channels  160 , as illustrated and described herein, reduces crosstalk between neighboring fluid channels. Furthermore, the support of flexible membrane  130  by, for example, constriction  165 , as illustrated and described herein, reduces failures caused by membrane cracking since such support reduces the stress applied to a particular, non-supported section. As such, production yield of printhead assembly  12  is increased. In addition, the fabrication of printhead assembly  12 , as illustrated and described herein, allows for reduced piezo drive voltages during operation. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.