Patent Publication Number: US-11027545-B2

Title: Fluid ejection device

Description:
BACKGROUND 
     Fluid ejection devices, such as printheads in inkjet printing systems, may use thermal resistors or piezoelectric material membranes as actuators within fluidic chambers to eject fluid drops (e.g., ink) from nozzles, such that properly sequenced ejection of ink drops from the nozzles causes characters or other images to be printed on a print medium as the printhead and the print medium move relative to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating one example of an inkjet printing system including an example of a fluid ejection device. 
         FIG. 2  is a schematic plan view illustrating an example of a portion of a fluid ejection device. 
         FIG. 3  is a schematic plan view illustrating an example of a portion of a fluid ejection device. 
         FIG. 4  is a schematic plan view illustrating an example of a portion of a fluid ejection device. 
         FIG. 5  is a flow diagram illustrating an example of a method of operating a fluid ejection device. 
     
    
    
     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 examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. 
       FIG. 1  illustrates one example of an inkjet printing system as an example of a fluid ejection device with fluid mixing, as disclosed herein. Inkjet printing system  100  includes a printhead assembly  102 , an ink supply assembly  104 , a mounting assembly  106 , a media transport assembly  108 , an electronic controller  110 , and at least one power supply  112  that provides power to the various electrical components of inkjet printing system  100 . Printhead assembly  102  includes at least one fluid ejection assembly  114  (printhead  114 ) that ejects drops of ink through a plurality of orifices or nozzles  116  toward a print medium  118  so as to print on print media  118 . 
     Print media  118  can be any type of suitable sheet or roll material, such as paper, card stock, transparencies, Mylar, and the like, and may include rigid or semi-rigid material, such as cardboard or other panels. Nozzles  116  are typically arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  116  causes characters, symbols, and/or other graphics or images to be printed on print media  118  as printhead assembly  102  and print media  118  are moved relative to each other. 
     Ink supply assembly  104  supplies fluid ink to printhead assembly  102  and, in one example, includes a reservoir  120  for storing ink such that ink flows from reservoir  120  to printhead assembly  102 . Ink supply assembly  104  and printhead assembly  102  can form a one-way ink delivery system or a recirculating ink delivery system. In a one-way ink delivery system, substantially all of the ink supplied to printhead assembly  102  is consumed during printing. In a recirculating ink delivery system, only a portion of the ink supplied to printhead assembly  102  is consumed during printing. Ink not consumed during printing is returned to ink supply assembly  104 . 
     In one example, printhead assembly  102  and ink supply assembly  104  are housed together in an inkjet cartridge or pen. In another example, ink supply assembly  104  is separate from printhead assembly  102  and supplies ink to printhead assembly  102  through an interface connection, such as a supply tube. In either example, reservoir  120  of ink supply assembly  104  may be removed, replaced, and/or refilled. Where printhead assembly  102  and ink supply assembly  104  are housed together in an inkjet cartridge, reservoir  120  includes a local reservoir located within the cartridge as well as a larger reservoir located separately from the cartridge. The separate, larger reservoir serves to refill the local reservoir. Accordingly, the separate, larger reservoir and/or the local reservoir may be removed, replaced, and/or refilled. 
     Mounting assembly  106  positions printhead assembly  102  relative to media transport assembly  108 , and media transport assembly  108  positions print media  118  relative to printhead assembly  102 . Thus, a print zone  122  is defined adjacent to nozzles  116  in an area between printhead assembly  102  and print media  118 . In one example, printhead assembly  102  is a scanning type printhead assembly. As such, mounting assembly  106  includes a carriage for moving printhead assembly  102  relative to media transport assembly  108  to scan print media  118 . In another example, printhead assembly  102  is a non-scanning type printhead assembly. As such, mounting assembly  106  fixes printhead assembly  102  at a prescribed position relative to media transport assembly  108 . Thus, media transport assembly  108  positions print media  118  relative to printhead assembly  102 . 
     Electronic controller  110  typically includes a processor, firmware, software, one or more memory components including volatile and non-volatile memory components, and other printer electronics for communicating with and controlling printhead assembly  102 , mounting assembly  106 , and media transport assembly  108 . Electronic controller  110  receives data  124  from a host system, such as a computer, and temporarily stores data  124  in a memory. Typically, data  124  is sent to inkjet printing system  100  along an electronic, infrared, optical, or other information transfer path. Data  124  represents, for example, a document and/or file to be printed. As such, data  124  forms a print job for inkjet printing system  100  and includes one or more print job commands and/or command parameters. 
     In one example, electronic controller  110  controls printhead assembly  102  for ejection of ink drops from nozzles  116 . Thus, electronic controller  110  defines a pattern of ejected ink drops which form characters, symbols, and/or other graphics or images on print media  118 . The pattern of ejected ink drops is determined by the print job commands and/or command parameters. 
     Printhead assembly  102  includes one or more printheads  114 . In one example, printhead assembly  102  is a wide-array or multi-head printhead assembly. In one implementation of a wide-array assembly, printhead assembly  102  includes a carrier that carries a plurality of printheads  114 , provides electrical communication between printheads  114  and electronic controller  110 , and provides fluidic communication between printheads  114  and ink supply assembly  104 . 
     In one example, inkjet printing system  100  is a drop-on-demand thermal inkjet printing system wherein printhead  114  is a thermal inkjet (TIJ) printhead. The thermal inkjet printhead implements a thermal resistor ejection element in an ink chamber to vaporize ink and create bubbles that force ink or other fluid drops out of nozzles  116 . In another example, inkjet printing system  100  is a drop-on-demand piezoelectric inkjet printing system wherein printhead  114  is a piezoelectric inkjet (PIJ) printhead that implements a piezoelectric material actuator as an ejection element to generate pressure pulses that force ink drops out of nozzles  116 . 
     In one example, electronic controller  110  includes a fluid mixing module  126  stored in a memory of controller  110 . Fluid mixing module  126  executes on electronic controller  110  (i.e., a processor of controller  110 ) to control the operation of one or more fluid actuators integrated as pump elements within printhead assembly  102  to control mixing of fluid within printhead assembly  102 .  FIG. 2  is a schematic plan view illustrating an example of a portion of a fluid ejection device  200 . In one example, fluid ejection device  200  includes an array of fluid ejection devices, such as fluid ejection devices  201 ,  202 ,  203 . 
     In one implementation, fluid ejection device  200 , including, more specifically, each of fluid ejection devices  201 ,  202 ,  203 , includes a fluid ejection chamber  210  with a corresponding drop ejecting element  212  formed in, provided within, or communicated with fluid ejection chamber  210 , a first fluid channel  230  communicated with fluid ejection chamber  210 , and a second fluid channel  240  communicated with fluid ejection chamber  210 . 
     In one example, fluid ejection chamber  210  and corresponding drop ejecting element  212  are formed on a substrate  206 . Substrate  206  may be formed, for example, of silicon, glass, or a stable polymer. 
     In one example, substrate  206  has a first fluid feed opening  207  formed therein and a second fluid feed opening  208  formed therein such that first fluid feed opening  207  provides a supply of a first fluid (or ink) to fluid ejection chamber  210  and corresponding drop ejecting element  212  via first fluid channel  230 , and second fluid feed opening  208  provides a supply of a second fluid (or ink) to fluid ejection chamber  210  and corresponding drop ejecting element  212  via second fluid channel  240 . First fluid feed opening  207  and second fluid feed opening  208  each include, for example, a hole, slot, passage, convex geometry or other fluidic architecture formed in or through substrate  206  by which or through which fluid is supplied to fluid ejection chamber  210 . First fluid feed opening  207  and second fluid feed opening  208  each may include one (i.e., a single) or more than one (e.g., a series of) such hole, slot, passage, convex geometry or other fluidic architecture that communicates fluid with one (i.e., a single) or more than one fluid ejection chamber, and may be of circular, non-circular, or other shape. 
     In one example, fluid ejection chamber  210  is formed in or defined by a barrier layer (not shown) provided on substrate  206 , such that fluid ejection chamber  210  provides a “well” in the barrier layer. The barrier layer may be formed, for example, of a photoimageable epoxy resin, such as SU8. In one example, a nozzle or orifice layer (not shown) is formed or extended over the barrier layer such that a nozzle opening or orifice  214  formed in the orifice layer communicates with respective fluid ejection chamber  210 . Nozzle opening or orifice  214  may be of a circular, non-circular, or other shape. 
     Drop ejecting element  212  can be any device capable of ejecting fluid drops through corresponding nozzle opening or orifice  214 . Examples of drop ejecting element  212  include a thermal resistor or a piezoelectric actuator. A thermal resistor, as an example of a drop ejecting element, may be formed on a surface of a substrate (substrate  206 ), and may include a thin-film stack including an oxide layer, a metal layer, and a passivation layer such that, when activated, heat from the thermal resistor vaporizes fluid in corresponding fluid ejection chamber  210 , thereby causing a bubble that ejects a drop of fluid through corresponding nozzle opening or orifice  214 . A piezoelectric actuator, as an example of a drop ejecting element, generally includes a piezoelectric material provided on a moveable membrane communicated with corresponding fluid ejection chamber  210  such that, when activated, the piezoelectric material causes deflection of the membrane relative to corresponding fluid ejection chamber  210 , thereby generating a pressure pulse that ejects a drop of fluid through corresponding nozzle opening or orifice  214 . Although illustrated as being of a rectangular shape, drop ejecting element  212  and corresponding fluid ejection chamber  210  each may be of a different shape and a different size. 
     As illustrated in the example of  FIG. 2 , fluid ejection device  200 , including, more specifically, each of fluid ejection devices  201 ,  202 ,  203 , includes a fluid pumping element  250  formed in, provided within, or communicated with first fluid channel  230 . More specifically, fluid pumping element  250  is formed on, provided on, or integrated with substrate  206 . 
     Fluid pumping element  250  forms or represents an actuator to pump fluid through first fluid channel  230 . As such, fluid from first fluid feed opening  207  is forced or moved through first fluid channel  230  to fluid ejection chamber  210  based on flow induced by fluid pumping element  250 . 
     In the example illustrated in  FIG. 2 , drop ejecting element  212  and fluid pumping element  250  are each thermal resistors. Each of the thermal resistors may include, for example, a single resistor, a split resistor, a comb resistor, or multiple resistors. A variety of other devices, however, can also be used to implement drop ejecting element  212  and fluid pumping element  250  including, for example, a piezoelectric actuator, an electrostatic (MEMS) membrane, a mechanical/impact driven membrane, a voice coil, and a magneto-strictive drive. As illustrated in the example of  FIG. 2 , first fluid channel  230  communicates with a first fluid (or ink), as represented by hatching  297 , and second fluid channel  240  communicates with a second fluid (or ink), as represented by hatching  298 . More specifically, in one implementation, first fluid channel  230  communicates with first fluid feed opening  207  to supply the first fluid (or ink) to fluid ejection chamber  210 , and second fluid channel  240  communicates with second fluid feed opening  208  to supply the second fluid (or ink) to fluid ejection chamber  210 . 
     In one implementation, fluid pumping element  250  may be operated to pump or move the first fluid toward, to (including into), and/or through fluid ejection chamber  210 , as represented by arrows  251 ,  252 ,  253 . In the illustrated example, a length of arrows  251 ,  252 ,  253  represents an example of a respective driving force of fluid pumping element  250  and, therefore, an example of a respective net result of fluid pumped and/or moved toward, to (including into), and/or through fluid ejection chamber  210 . 
     As illustrated in the example of  FIG. 2 , a mixture or combination of the first fluid and the second fluid, including different ratios or concentrations of the first fluid and the second fluid, may be formed or created, as represented by combined hatching  299 . In one example, a mixing zone  270 , in which a mixture or combination of the first fluid and the second fluid may be formed or created, is provided or established between fluid pumping element  250  and fluid ejection chamber  210 . In one implementation, mixing zone  270  includes fluid ejection chamber  210 . Thus, with mixing zone  270 , a mixture or combination of the first fluid and the second fluid is created or formed on substrate  206  of fluid ejection device  200 . 
     As such, based on operation of fluid pumping element  250 , fluid ejection device  200 , including, more specifically, fluid ejection devices  201 ,  202 ,  203 , may be operated to selectively or separately eject drops of the first fluid, drops of the second fluid, and drops of a combination or mixture of the first fluid and the second fluid, including different ratios or concentrations of the first fluid and the second fluid, from fluid ejection chamber  210 . 
     In one example, as illustrated with fluid ejection device  201 , a lesser amount of the first fluid, as represented by hatching  297 , is pumped or moved toward fluid ejection chamber  210 . As such, the second fluid, as represented by hatching  298 , may be ejected from fluid ejection chamber  210 . 
     In one example, as illustrated with fluid ejection device  202 , the first fluid is pumped or moved toward and/or to fluid ejection chamber  210  such that the first fluid, as represented by hatching  297 , and the second fluid, as represented by hatching  298 , mix or combine in mixing zone  270 , including in fluid ejection chamber  210 . As such, a combination or mixture of the first fluid and the second fluid, as represented by combined hatching  299 , may be ejected from fluid ejection chamber  210 . 
     In one example, as illustrated with fluid ejection device  203 , a greater amount of the first fluid, as represented by hatching  297 , is pumped or moved to and/or through fluid ejection chamber  210 . As such, the first fluid may be ejected from fluid ejection chamber  210 . 
     Further to the illustrated example of  FIG. 2 , first fluid channel  230  and second fluid channel  240 , including portions, sections, segments or regions thereof, may be of different or varying widths, and may be of different or varying lengths. 
       FIG. 3  is a schematic plan view illustrating an example of a portion of a fluid ejection device  300 . In one example, fluid ejection device  300  includes an array of fluid ejection devices, such as fluid ejection devices  301 ,  302 ,  303 ,  304 . 
     In one implementation, fluid ejection device  300 , including, more specifically, each of fluid ejection devices  301 ,  302 ,  303 ,  304 , includes a first fluid ejection chamber  310  with a corresponding drop ejecting element  312  formed in, provided within, or communicated with fluid ejection chamber  310 , a second fluid ejection chamber  320  with a corresponding drop ejecting element  322  formed in, provided within, or communicated with fluid ejection chamber  320 , a first fluid channel  330  communicated with fluid ejection chamber  310 , and a second fluid channel  340  communicated with fluid ejection chamber  320 . 
     In one example, fluid ejection chambers  310  and  320  and corresponding drop ejecting elements  312  and  322  are formed on a substrate  306 . Substrate  306  may be formed, for example, of silicon, glass, or a stable polymer. 
     In one example, substrate  306  has a first fluid feed opening  307  formed therein and a second fluid feed opening  308  formed therein such that first fluid feed opening  307  provides a supply of a first fluid (or ink) to fluid ejection chamber  310  and corresponding drop ejecting element  312  via first fluid channel  330 , and second fluid feed opening  308  provides a supply of a second fluid (or ink) to fluid ejection chamber  320  and corresponding drop ejecting element  322  via second fluid channel  340 . First fluid feed opening  307  and second fluid feed opening  308  each include, for example, a hole, slot, passage, convex geometry or other fluidic architecture formed in or through substrate  306  by which or through which fluid is supplied to fluid ejection chambers  310  and  320 . First fluid feed opening  307  and second fluid feed opening  308  each may include one (i.e., a single) or more than one (e.g., a series of) such hole, slot, passage, convex geometry or other fluidic architecture that communicates fluid with one (i.e., a single) or more than one fluid ejection chamber, and may be of circular, non-circular, or other shape. 
     In one example, fluid ejection chambers  310  and  320  are formed in or defined by a barrier layer (not shown) provided on substrate  306 , such that fluid ejection chambers  310  and  320  each provide a “well” in the barrier layer. The barrier layer may be formed, for example, of a photoimageable epoxy resin, such as SU8. In one example, a nozzle or orifice layer (not shown) is formed or extended over the barrier layer such that nozzle openings or orifices  314  and  324  formed in the orifice layer communicate with respective fluid ejection chambers  310  and  320 . Nozzle openings or orifices  314  and  324  may be of a circular, non-circular, or other shape. 
     Drop ejecting elements  312  and  322  can be any device capable of ejecting fluid drops through corresponding nozzle openings or orifices  314  and  324 . Examples of drop ejecting elements  312  and  322  include a thermal resistor or a piezoelectric actuator. A thermal resistor, as an example of a drop ejecting element, may be formed on a surface of a substrate (substrate  306 ), and may include a thin-film stack including an oxide layer, a metal layer, and a passivation layer such that, when activated, heat from the thermal resistor vaporizes fluid in corresponding fluid ejection chamber  310  or  320 , thereby causing a bubble that ejects a drop of fluid through corresponding nozzle opening or orifice  314  or  324 . A piezoelectric actuator, as an example of a drop ejecting element, generally includes a piezoelectric material provided on a moveable membrane communicated with corresponding fluid ejection chamber  310  or  320  such that, when activated, the piezoelectric material causes deflection of the membrane relative to corresponding fluid ejection chamber  310  or  320 , thereby generating a pressure pulse that ejects a drop of fluid through corresponding nozzle opening or orifice  314  or  324 . Although illustrated as being of a rectangular shape, drop ejecting elements  312  and  322  and corresponding fluid ejection chambers  310  and  320  each may be of a different shape and a different size. 
     As illustrated in the example of  FIG. 3 , fluid ejection device  300 , including, more specifically, each of fluid ejection devices  301 ,  302 ,  303 ,  304 , includes a first fluid pumping element  350  formed in, provided within, or communicated with first fluid channel  330 , and a second fluid pumping element  360  formed in, provided within, or communicated with second fluid channel  340 . More specifically, fluid pumping element  350  and fluid pumping element  360  are each formed on, provided on, or integrated with substrate  306 . 
     Fluid pumping element  350  forms or represents an actuator to pump fluid through first fluid channel  330 , and fluid pumping element  360  forms or represents an actuator to pump fluid through second fluid channel  340 . As such, fluid from first fluid feed opening  307  is forced or moved through first fluid channel  330  to fluid ejection chamber  310  based on flow induced by fluid pumping element  350 , and fluid from second fluid feed opening  308  is forced or moved through second fluid channel  340  to fluid ejection chamber  320  based on flow induced by fluid pumping element  360 . 
     In the example illustrated in  FIG. 3 , drop ejecting elements  312  and  322  and fluid pumping elements  350  and  360  are each thermal resistors. Each of the thermal resistors may include, for example, a single resistor, a split resistor, a comb resistor, or multiple resistors. A variety of other devices, however, can also be used to implement drop ejecting elements  312  and  322  and fluid pumping elements  350  and  360  including, for example, a piezoelectric actuator, an electrostatic (MEMS) membrane, a mechanical/impact driven membrane, a voice coil, and a magneto-strictive drive. 
     As illustrated in the example of  FIG. 3 , first fluid channel  330  communicates with a first fluid (or ink), as represented by hatching  397 , and second fluid channel  340  communicates with a second fluid (or ink), as represented by hatching  398 . More specifically, in one implementation, first fluid channel  330  communicates with first fluid feed opening  307  to supply the first fluid (or ink) to fluid ejection chamber  310 , and second fluid channel  340  communicates with second fluid feed opening  308  to supply the second fluid (or ink) to fluid ejection chamber  320 . 
     In one implementation, fluid pumping element  350  may be operated to pump or move the first fluid toward, to (including into), and/or through fluid ejection chamber  310 , as represented by arrows  351 ,  352 ,  353 , and fluid pumping element  360  may be operated to pump or move the second fluid toward, to (including into), and/or through fluid ejection chamber  320 , as represented by arrows  361 ,  362 ,  363 ,  364 . In the illustrated example, a length of arrows  351 ,  352 ,  353  and  361 ,  362 ,  363 ,  364  represents an example of a respective driving force of fluid pumping element  350  and fluid pumping element  360  and, therefore, an example of a respective net result of fluid pumped and/or moved toward, to (including into), and/or through fluid ejection chamber  310  and fluid ejection chamber  320 . 
     In one implementation, fluid pumping element  350  may be operated to pump or move the first fluid toward, to (including into), and/or through fluid ejection chamber  320 , and fluid pumping element  360  may be operated to pump or move the second fluid toward, to (including into), and/or through fluid ejection chamber  310 . As such, as illustrated in the example of  FIG. 3 , a mixture or combination of the first fluid and the second fluid, including different ratios or concentrations of the first fluid and the second fluid, may be formed or created, as represented by combined hatching  399 . 
     In one example, a mixing zone  370 , in which a mixture or combination of the first fluid and the second fluid may be formed or created, is provided or established between fluid pumping element  350  and fluid pumping element  360 , including, more specifically, between fluid pumping element  350  and fluid ejection chamber  320 , between fluid pumping element  360  and fluid ejection chamber  310 , and, therefore, between fluid ejection chamber  310  and fluid ejection chamber  320 . In one implementation, mixing zone  370  includes fluid ejection chamber  310  and/or fluid ejection chamber  320 . Thus, with mixing zone  370 , a mixture or combination of the first fluid and the second fluid is created or formed on substrate  306  of fluid ejection device  300 . 
     As such, based on operation of fluid pumping element  350  and/or fluid pumping element  360 , fluid ejection device  300 , including, more specifically, fluid ejection devices  301 ,  302 ,  303 ,  304 , may be operated to selectively or separately eject drops of the first fluid, drops of the second fluid, and drops of a combination or mixture of the first fluid and the second fluid, including different ratios or concentrations of the first fluid and the second fluid, from fluid ejection chamber  310  and/or fluid ejection chamber  320 . 
     In one example, as illustrated with fluid ejection device  301 , the first fluid, as represented by hatching  397 , is pumped or moved to and/or through fluid ejection chamber  310 , and the second fluid, as represented by hatching  398 , is pumped or moved to and/or through fluid ejection chamber  320 . As such, the first fluid may be ejected from fluid ejection chamber  310 , and the second fluid may be ejected from fluid ejection chamber  320 . 
     In one example, as illustrated with fluid ejection device  302 , a greater amount of the first fluid, as represented by hatching  397 , is pumped or moved through fluid ejection chamber  310  and toward and/or to fluid ejection chamber  320 , and a lesser amount of the second fluid, as represented by hatching  398 , is pumped or moved toward and/or to fluid ejection chamber  320  such that the first fluid and the second fluid mix or combine in mixing zone  370 , including in fluid ejection chamber  320 . As such, the first fluid may be ejected from fluid ejection chamber  310 , and a combination or mixture of the first fluid and the second fluid, as represented by combined hatching  399 , may be ejected from fluid ejection chamber  320 . 
     In one example, as illustrated with fluid ejection device  303 , a lesser amount of the first fluid, as represented by hatching  397 , is pumped or moved toward and/or to fluid ejection chamber  310 , and a greater amount of the second fluid, as represented by hatching  398 , is pumped or moved through fluid ejection chamber  320  and toward and/or to fluid ejection chamber  310  such that the first fluid and the second fluid mix or combine in mixing zone  370 , including in fluid ejection chamber  310 . As such, the second fluid may be ejected from fluid ejection chamber  320 , and a combination or mixture of the first fluid and the second fluid, as represented by combined hatching  399 , may be ejected from fluid ejection chamber  310 . 
     In one example, as illustrated with fluid ejection device  304 , the second fluid, as represented by hatching  398 , is pumped or moved through fluid ejection chamber  320  and to and/or through fluid ejection chamber  310 . As such, the second fluid may be ejected from fluid ejection chamber  320  and/or fluid ejection chamber  310 . In other examples, the first fluid may pumped or moved through fluid ejection chamber  310  and to and/or through fluid ejection chamber  320  such that the first fluid may be ejected from fluid ejection chamber  310  and/or fluid ejection chamber  320 . 
     Further to the illustrated example of  FIG. 3 , first fluid channel  330  and second fluid channel  340 , including portions, sections, segments or regions thereof, may be of different or varying widths, and may be of different or varying lengths. 
       FIG. 4  is a schematic plan view illustrating an example of a portion of a fluid ejection device  400 . In one example, fluid ejection device  400  includes an array of fluid ejection devices, such as fluid ejection devices  401 ,  402 ,  403 ,  404 . 
     In one implementation, fluid ejection device  400 , including, more specifically, each of fluid ejection devices  401 ,  402 ,  403 ,  404 , includes a first fluid ejection chamber  410  with a corresponding drop ejecting element  412  formed in, provided within, or communicated with fluid ejection chamber  410 , a second fluid ejection chamber  420  with a corresponding drop ejecting element  422  formed in, provided within, or communicated with fluid ejection chamber  420 , a first fluid channel  430  communicated with fluid ejection chamber  410 , and a second fluid channel  440  communicated with fluid ejection chamber  420 . 
     In one example, fluid ejection chambers  410  and  420  and corresponding drop ejecting elements  412  and  422  are formed on a substrate  406 . Substrate  406  may be formed, for example, of silicon, glass, or a stable polymer. 
     In one example, substrate  406  has a first fluid feed opening  407  formed therein and a second fluid feed opening  408  formed therein such that first fluid feed opening  407  provides a supply of a first fluid (or ink) to fluid ejection chamber  410  and corresponding drop ejecting element  412  via first fluid channel  430 , and second fluid feed opening  408  provides a supply of a second fluid (or ink) to fluid ejection chamber  420  and corresponding drop ejecting element  422  via second fluid channel  440 . First fluid feed opening  407  and second fluid feed opening  408  each include, for example, a hole, slot, passage, convex geometry or other fluidic architecture formed in or through substrate  406  by which or through which fluid is supplied to fluid ejection chambers  410  and  420 . First fluid feed opening  407  and second fluid feed opening  408  each may include one (i.e., a single) or more than one (e.g., a series of) such hole, slot, passage, convex geometry or other fluidic architecture that communicates fluid with one (i.e., a single) or more than one fluid ejection chamber, and may be of circular, non-circular, or other shape. 
     In one example, fluid ejection chambers  410  and  420  are formed in or defined by a barrier layer (not shown) provided on substrate  406 , such that fluid ejection chambers  410  and  420  each provide a “well” in the barrier layer. The barrier layer may be formed, for example, of a photoimageable epoxy resin, such as SU8. In one example, a nozzle or orifice layer (not shown) is formed or extended over the barrier layer such that nozzle openings or orifices  414  and  424  formed in the orifice layer communicate with respective fluid ejection chambers  410  and  420 . Nozzle openings or orifices  414  and  424  may be of a circular, non-circular, or other shape. 
     Drop ejecting elements  412  and  422  can be any device capable of ejecting fluid drops through corresponding nozzle openings or orifices  414  and  424 . Examples of drop ejecting elements  412  and  422  include a thermal resistor or a piezoelectric actuator. A thermal resistor, as an example of a drop ejecting element, may be formed on a surface of a substrate (substrate  406 ), and may include a thin-film stack including an oxide layer, a metal layer, and a passivation layer such that, when activated, heat from the thermal resistor vaporizes fluid in corresponding fluid ejection chamber  410  or  420 , thereby causing a bubble that ejects a drop of fluid through corresponding nozzle opening or orifice  414  or  424 . A piezoelectric actuator, as an example of a drop ejecting element, generally includes a piezoelectric material provided on a moveable membrane communicated with corresponding fluid ejection chamber  410  or  420  such that, when activated, the piezoelectric material causes deflection of the membrane relative to corresponding fluid ejection chamber  410  or  420 , thereby generating a pressure pulse that ejects a drop of fluid through corresponding nozzle opening or orifice  414  or  424 . Although illustrated as being of a rectangular shape, drop ejecting elements  412  and  422  and corresponding fluid ejection chambers  410  and  420  each may be of a different shape and a different size. 
     As illustrated in the example of  FIG. 4 , fluid ejection device  400 , including, more specifically, each of fluid ejection devices  401 ,  402 ,  403 ,  404 , includes a first fluid pumping element  450  formed in, provided within, or communicated with first fluid channel  430 , and a second fluid pumping element  460  formed in, provided within, or communicated with second fluid channel  440 . More specifically, fluid pumping element  450  and fluid pumping element  460  are each formed on, provided on, or integrated with substrate  406 . 
     Fluid pumping element  450  forms or represents an actuator to pump fluid through first fluid channel  430 , and fluid pumping element  460  forms or represents an actuator to pump fluid through second fluid channel  440 . As such, fluid from first fluid feed opening  407  is forced or moved through first fluid channel  430  to fluid ejection chamber  410  based on flow induced by fluid pumping element  450 , and fluid from second fluid feed opening  408  is forced or moved through second fluid channel  440  to fluid ejection chamber  420  based on flow induced by fluid pumping element  460 . 
     In the example illustrated in  FIG. 4 , drop ejecting elements  412  and  422  and fluid pumping elements  450  and  460  are each thermal resistors. Each of the thermal resistors may include, for example, a single resistor, a split resistor, a comb resistor, or multiple resistors. A variety of other devices, however, can also be used to implement drop ejecting elements  412  and  422  and fluid pumping elements  450  and  460  including, for example, a piezoelectric actuator, an electrostatic (MEMS) membrane, a mechanical/impact driven membrane, a voice coil, and a magneto-strictive drive. 
     As illustrated in the example of  FIG. 4 , first fluid channel  430  communicates with a first fluid (or ink), as represented by hatching  497 , and second fluid channel  440  communicates with a second fluid (or ink), as represented by hatching  498 . More specifically, in one implementation, first fluid channel  430  communicates with first fluid feed opening  407  to supply the first fluid (or ink) to fluid ejection chamber  410 , and second fluid channel  440  communicates with second fluid feed opening  408  to supply the second fluid (or ink) to fluid ejection chamber  420 . 
     In one example, first fluid channel  430  includes a path or channel portion  432  communicated with fluid feed opening  407 , a path or channel portion  434  communicated with fluid ejection chamber  410 , and a channel loop  433  extended between channel portion  432  and channel portion  434 . In addition, second fluid channel  440  includes a path or channel portion  442  communicated with fluid feed opening  408 , a path or channel portion  444  communicated with fluid ejection chamber  420 , and a channel loop  443  extended between channel portion  442  and channel portion  444 . 
     In one example, channel loop  433  and channel loop  443  each include a U-shaped portion such that a length (or portion) of channel portion  432  and a length (or portion) of channel portion  434  are spaced from and oriented substantially parallel with each other, and a length (or portion) of channel portion  442  and a length (or portion) of channel portion  444  are spaced from and oriented substantially parallel with each other. As such, in one example, channel portion  432  directs fluid in a first direction (arrow  432   a ) between fluid feed opening  407  and channel loop  433 , and channel portion  434  directs fluid in a second direction (arrow  434   b ) opposite the first direction between channel loop  433  and fluid ejection chamber  410 . In addition, channel portion  442  directs fluid in a first direction (arrow  442   a ) between fluid feed opening  408  and channel loop  443 , and channel portion  444  directs fluid in a second direction (arrow  444   b ) opposite the first direction between channel loop  443  and fluid ejection chamber  420 . 
     In one example, fluid pumping element  450  is formed in, provided within, or communicated with channel portion  432  of first fluid channel  430 , and fluid pumping element  460  is formed in, provided within, or communicated with channel portion  442  of second fluid channel  440 . As such, fluid pumping element  450  forms an asymmetry to first fluid channel  430  and fluid pumping element  460  forms an asymmetry to second fluid channel  440  whereby a fluid flow distance between fluid pumping element  450  and fluid feed opening  407  is less than a fluid flow distance between fluid pumping element  450  and fluid ejection chamber  410 , and a fluid flow distance between fluid pumping element  460  and fluid feed opening  408  is less than a fluid flow distance between fluid pumping element  460  and fluid ejection chamber  420 . 
     In one implementation, fluid pumping element  450  may be operated to pump or move the first fluid toward, to (including into), and/or through fluid ejection chamber  410 , as represented by arrows  451 ,  452 ,  453 ,  454 , and fluid pumping element  460  may be operated to pump or move the second fluid toward, to (including into), and/or through fluid ejection chamber  420 , as represented by arrows  461 ,  462 ,  463 ,  464 . In the illustrated example, a length of arrows  451 ,  452 ,  453 ,  454  and  461 ,  462 ,  463 ,  464  represents an example of a respective driving force of fluid pumping element  450  and fluid pumping element  460  and, therefore, an example of a respective net result of fluid pumped and/or moved toward, to (including into), and/or through fluid ejection chamber  410  and fluid ejection chamber  420 . 
     In one implementation, fluid pumping element  450  may be operated to pump or move the first fluid toward, to (including into), and/or through fluid ejection chamber  420 , and fluid pumping element  460  may be operated to pump or move the second fluid toward, to (including into), and/or through fluid ejection chamber  410 . As such, as illustrated in the example of  FIG. 4 , a mixture or combination of the first fluid and the second fluid, including different ratios or concentrations of the first fluid and the second fluid, may be formed or created, as represented by combined hatching  499 . 
     In one example, a mixing zone  470 , in which a mixture or combination of the first fluid and the second fluid may be formed or created, is provided or established between fluid pumping element  450  and fluid pumping element  460 , including, more specifically, between fluid pumping element  450  and fluid ejection chamber  420 , between fluid pumping element  460  and fluid ejection chamber  410 , and, therefore, between fluid ejection chamber  410  and fluid ejection chamber  420 . In one implementation, mixing zone  470  includes fluid ejection chamber  410  and/or fluid ejection chamber  420 . Thus, with mixing zone  470 , a mixture or combination of the first fluid and the second fluid is created or formed on substrate  406  of fluid ejection device  400 . 
     As such, based on operation of fluid pumping element  450  and/or fluid pumping element  460 , fluid ejection device  400 , including, more specifically, fluid ejection devices  401 ,  402 ,  403 ,  404 , may be operated to selectively or separately eject drops of the first fluid, drops of the second fluid, and drops of a combination or mixture of the first fluid and the second fluid, including different ratios or concentrations of the first fluid and the second fluid, from fluid ejection chamber  410  and/or fluid ejection chamber  420 . 
     In one example, as illustrated with fluid ejection device  401 , the first fluid, as represented by hatching  497 , is pumped or moved to and/or through fluid ejection chamber  410 , and the second fluid, as represented by hatching  498 , is pumped or moved to and/or through fluid ejection chamber  420 . As such, the first fluid may be ejected from fluid ejection chamber  410 , and the second fluid may be ejected from fluid ejection chamber  420 . 
     In one example, as illustrated with fluid ejection device  402 , a greater amount of the first fluid, as represented by hatching  497 , is pumped or moved through fluid ejection chamber  410  and toward and/or to fluid ejection chamber  420 , and a lesser amount of the second fluid, as represented by hatching  498 , is pumped or moved toward and/or to fluid ejection chamber  420  such that the first fluid and the second fluid mix or combine in mixing zone  470 , including in fluid ejection chamber  420 . As such, the first fluid may be ejected from fluid ejection chamber  410 , and a combination or mixture of the first fluid and the second fluid, as represented by combined hatching  499 , may be ejected from fluid ejection chamber  420 . 
     In one example, as illustrated with fluid ejection device  403 , a lesser amount of the first fluid, as represented by hatching  497 , is pumped or moved toward and/or to fluid ejection chamber  410 , and a greater amount of the second fluid, as represented by hatching  498 , is pumped or moved through fluid ejection chamber  420  and toward and/or to fluid ejection chamber  410  such that the first fluid and the second fluid mix or combine in mixing zone  470 , including in fluid ejection chamber  410 . As such, the second fluid may be ejected from fluid ejection chamber  420 , and a combination or mixture of the first fluid and the second fluid, as represented by combined hatching  499 , may be ejected from fluid ejection chamber  410 . 
     In one example, as illustrated with fluid ejection device  404 , the second fluid, as represented by hatching  498 , is pumped or moved through fluid ejection chamber  420  and to and/or through fluid ejection chamber  410 . As such, the second fluid may be ejected from fluid ejection chamber  420  and/or fluid ejection chamber  410 . In other examples, the first fluid may pumped or moved through fluid ejection chamber  410  and to and/or through fluid ejection chamber  420  such that the first fluid may be ejected from fluid ejection chamber  410  and/or fluid ejection chamber  420 . 
     Further to the illustrated example of  FIG. 4 , first fluid channel  430  and second fluid channel  440 , including portions, sections, segments or regions thereof, may be of different or varying widths, and may be of different or varying lengths. 
       FIG. 5  is a flow diagram illustrating an example of a method  500  of operating a fluid ejection device, such as fluid ejection devices  200 ,  300 ,  400 , as illustrated in the respective examples of  FIGS. 2, 3, 4 . 
     At  502 , method  500  includes communicating a first fluid with a fluid ejection chamber, such as a first fluid, as represented by hatching  297 , and as included, for example, in a combination or mixture of the first fluid and a second fluid, as represented by combined hatching  299 , communicated with fluid ejection chamber  210 , a first fluid, as represented by hatching  397 , and as included, for example, in a combination or mixture of the first fluid and a second fluid, as represented by combined hatching  399 , communicated with fluid ejection chamber  310 , and a first fluid, as represented by hatching  497 , and as included, for example, in a combination or mixture of the first fluid and a second fluid, as represented by combined hatching  499 , communicated with fluid ejection chamber  410 . 
     At  504 , method  500  includes communicating a second fluid different than the first fluid with the fluid ejection chamber, such as a second fluid, as represented by hatching  298 , and as included, for example, in a combination or mixture of a first fluid and the second fluid, as represented by combined hatching  299 , communicated with fluid ejection chamber  210 , a second fluid, as represented by hatching  398 , and as included, for example, in a combination or mixture of a first fluid and the second fluid, as represented by combined hatching  399 , communicated with fluid ejection chamber  310 , and a second fluid, as represented by hatching  498 , and as included, for example, in a combination or mixture of a first fluid and the second fluid, as represented by combined hatching  499 , communicated with fluid ejection chamber  410 . 
     At  506 , method  500  includes selectively ejecting drops of the first fluid, the second fluid, and a combination of the first fluid and the second fluid from the fluid ejection chamber, such as drops of a first fluid, as represented by hatching  297 ,  397 ,  497 , ejected from respective fluid ejection chambers  210 ,  310 ,  410 , drops of a second fluid, as represented by hatching  298 ,  398 ,  498 , ejected from respective fluid ejection chambers  210 ,  310 ,  410 , and a combination of a first fluid and a second fluid, as represented by combined hatching  299 ,  399 ,  499 , ejected from respective fluid ejection chambers  210 ,  310 ,  410 . 
     Although illustrated and described as separate and/or sequential steps, the method may include a different order or sequence of steps, and may combine one or more steps or perform one or more steps concurrently, partially or wholly. 
     With a fluid ejection device as disclosed herein, drops of a first fluid, drops of a second fluid (different than the first fluid), and drops of a mixture or combination of the first fluid and the second fluid, including different ratios or concentrations of the first fluid and the second fluid, may be selectively or separately ejected. More specifically, a mixture or combination of a first fluid and a second fluid may be created or formed on a substrate of the fluid ejection device prior to ejection. 
     In examples, the first fluid and the second fluid are or include different dyes, pigments, constituents, substances, agents, reactants or reagents. As such, a fluid ejection device as disclosed herein provides for blending the different dyes, pigments, constituents, substances, agents, reactants or reagents on the substrate. Thus, a fluid ejection device as disclosed herein provides for blending different dyes, pigments, constituents, substances, agents, reactants or reagents prior to ejection. 
     In examples, the first fluid and the second fluid are fluids of different colors (i.e., native colors). As such, a fluid ejection device as disclosed herein provides for creating various combinations of the native colors on the substrate. Thus, a fluid ejection device as disclosed herein provides for creating various combinations of native colors prior to ejection. In addition, a fluid ejection device as disclosed herein provides for color mixing on-demand. 
     Although specific examples 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 examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein.