Abstract:
Briefly described, embodiments of this disclosure include systems and methods for ejecting fluid from a fluid ejection system. One exemplary method, among others, includes: heating a fluid to a lower threshold using an electric heating layer; heating the fluid to an upper threshold using laser energy; and ejecting a volume of fluid.

Description:
BACKGROUND  
       [0001]     An inkjet printing system, as one embodiment of a fluid ejection system, may include a printhead assembly, an ink supply which supplies liquid ink to the printhead assembly, and an electronic controller which controls the printhead assembly. The printhead assembly, as one embodiment of a fluid ejection assembly, ejects ink drops through a plurality of orifices or nozzles 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 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 assembly and the print medium are moved relative to each other.  
         [0002]     Typically, the printhead assembly ejects the ink drops through the nozzles by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as thin film resistors, often referred to as firing resistors. Heating the ink causes the ink to vaporize and be ejected from the nozzles. Typically, for one dot of ink, a remote printhead assembly controller typically located as part of the processing electronics of a printer, controls activation of an electrical current from a power supply external to the printhead assembly. The electrical current is passed through a selected firing resistor to heat the ink in a corresponding selected vaporization chamber.  
         [0003]     One method of controlling the application of the electrical current through the selected firing resistor is to couple a switching device, such as a field effect transistor (FET), to each firing resistor. In one printhead arrangement, the firing resistors are grouped together in primitives, with a single power lead providing power to the source or drain of each FET for each firing resistor in a primitive. Each FET in a primitive has a separately energizable address lead coupled to its gate, with each address lead coupled to its gate, with each address lead shared by multiple primitives. In a typical printing operation, the address leads are controlled so that only a single firing resistor in a primitive is activated at a given time.  
         [0004]     In one arrangement, the address lead coupled to the gate of each FET is controlled by a combination of nozzle data, nozzle addresses, and a fire pulse. The nozzle data is typically provided by the electronic controller of the printer and represents the actual data to be printed. The fire pulse controls the timing of the activation of the electrical current through the selected firing resistor. Typical conventional inkjet printing systems employ the electronic controller to control the timing related to the fire pulse. The nozzle address is cycled through all nozzle addresses to control the nozzle firing order so that all nozzles can be fired, but only a single nozzle in a primitive is fired at a given time.  
         [0005]     While such arrangements are effective in controlling nozzle firing, connections between remote elements and the printhead assembly and between elements on the printhead assembly itself can become complex, especially as the number of nozzles on the print head area increase. An example of such a complex system is referred to as a wide-array inkjet printing system. A page-wide array printhead spans the width of an entire page of media (e.g., 8.5 inches for paper utilized in the United States) and is fixed relative to the media path. A page-wide array printhead assembly includes a page-wide array printhead with thousands of nozzles that span the entire page width. The page-wide array printhead assembly is typically oriented orthogonal to the paper path. During operation, the page-wide array printhead assembly is fixed, while the media is moved under the assembly. The page-wide array printhead assembly prints one or more lines at a time as the page moves relative to the assembly.  
         [0006]     A problem with page-wide array printing includes maintaining accurate drop weights while at the same time increasing operating speeds of a page wide array printhead. Another problem with page-wide array printing includes the large amounts of energy required to cause ink drop ejection.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Many aspects of this disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.  
         [0008]      FIG. 1  illustrates an embodiment of a fluid ejection system.  
         [0009]      FIG. 2A  illustrates an embodiment of a page-wide array printhead assembly, while  FIG. 2B  illustrates a cross-section of a representative nozzle system (cross section A-A of  FIG. 2A ).  
         [0010]      FIG. 3  is a graph illustrating an embodiment of an energy curve for ejecting a fluid drop from a thermal inkjet.  
         [0011]      FIG. 4  includes a graph illustrating embodiments of representative heating waveforms. 
     
    
     DETAILED DESCRIPTION  
       [0012]     Fluid ejection systems and methods of use thereof are provided. In particular, the embodiments relate to laser driven thermal fluid ejection systems. In one embodiment, the fluid ejection system uses a two-part heating process to emit or eject fluid (e.g., pigment-based inkjet inks and/or dye-based inkjet inks) from a page-wide array printhead assembly. In particular, energy from a first heating source (e.g., a resistor) in a page-wide array printhead assembly initially heats the fluid to a first threshold. In addition, energy from a second heating source (e.g., a laser system) heats the fluid from the first threshold to a second threshold, which causes a volume of fluid (e.g., a drop) to be ejected from the page-wide array printhead assembly onto a media (e.g., paper or transparency).  
         [0013]      FIG. 1  illustrates a block diagram of a representative fluid ejection system  10  (i.e., page-wide array printer system  10 ) that includes a computer control system  12  and a printer  14 , which is one embodiment of a fluid ejection system  10 . The computer control system  12  includes a print control system  16 . The printer  14  includes a page-wide array  18  and a laser system  20 , which is one embodiment of a fluid ejection system  10 . The print control system  16  is operative to control the printing process of the printer  14 .  
         [0014]     The page-wide array  18  includes, but is not limited to, a page-wide array printhead assembly  30 , which is illustrated in  FIG. 2A . The page-wide array printhead assembly  30  includes a first end  32  and a second end  34 . In addition, the page-wide array printhead assembly  30  includes a plurality of areas  36 A . . .  36 H located from the first end  32  to the second end  34  of the page-wide array printhead assembly  30 . Each area  36 A . . .  36 H includes a portion of a heating layer  38 A . . .  38 H and a plurality of nozzles systems  40  ( FIG. 2B ). A subset of the plurality of nozzles are disposed within each heating layer  38 A . . .  38 H. Although the page-wide array printhead assembly  30  is depicted as being divided into eight areas in  FIG. 2A , page-wide array printhead assemblies  30  can be divided into any number of desired areas (e.g., 48 to 100 areas). In addition, although each area  36 A . . .  36 H is depicted as including six nozzle systems  40 , each area can include any number of desired nozzles (e.g., from about 50 to 100 nozzle systems  40 ). In one embodiment, the page-wide array  18  includes about 2000 to 8000 nozzle systems. In other embodiments, the number of nozzle systems may vary depending on the requirements of the system (e.g., resolution and/or speed).  
         [0015]     Heating layers  38 A . . .  38 H include, but are not limited to, one or more electronic heating layer(s) and a plurality of photon absorbing layers. In one embodiment, the one or more electronic heating layers include a resistive layer and a conductive layer (e.g., a heating resistor). In addition, electronic heating layers may be coupled contacts located on the page-wide array  18  via conductive paths or electrodes as are well known in the art. The contacts can then be coupled to the printer  14  to provide energy to the electronic heating layers. In one embodiment, the resistive layer and conductive layer can be formed using materials such as tantalum and aluminum. In one embodiment, the photon absorbing layer includes materials such as tantalum nitride.  
         [0016]     In certain embodiments, the one or more electronic heating layers are separated from the photon absorbing layer via electrically insulating layers. In other embodiments, electrically insulating layers are not utilized. In further embodiments, one or more of the photon absorbing layers and electronic heating layers are substantially coplanar but located at different positions in a single layer. In additional embodiments, electronic heating layers are located proximate to fluid (ink) chamber  46 , while photon absorbing layers are located proximate transparent substrate  50 . ( FIG. 2B )  
         [0017]     In one embodiment, the heating layer  38 A . . .  38 H is a single layer, where the electronic heating layer and the photon absorbing layer are formed of the same material. In another embodiment, the heating layer  38 A . . .  38 H includes at least two layers, where at least one layer is the electronic heating layer and at least one layer is the photon absorbing layer.  
         [0018]     Each nozzle system  40  includes, but is not limited to, an orifice  42 , an orifice layer  44 , a fluid (ink) chamber  46 , a barrier layer  48 , a transparent substrate  50 , and the heating layer  38 A . . .  38 H. A portion of one of the heating layers  38 A . . .  38 H is positioned adjacent the ink chamber  36 . In particular, a portion of the electric heating layer is disposed in each nozzle system  40 , while each nozzle system  40  has a photon absorbing layer that can be activated independently of the photon absorbing layers for other nozzle systems  40 .  
         [0019]     The ink chamber  36  is capable of holding a volume of fluid (for example, ink) (not shown) such as, but not limited to, pigment-based inkjet inks and/or dye-based inkjet inks. These can include black ink and inks having a plurality of colors such as, but not limited to, cyan, yellow, and magenta. The barrier layer  48  functions to separate the ink flow so that ink can be individually provided to each nozzle system  40 . In one embodiment, barrier layer  48  can be made of materials such as, but not limited to, Kapton™, Upilex™, (3M Corp), or like material. The transparent substrate  50  is transparent to the laser energy  58  emitted by the laser system  20 . In one embodiment, the transparent substrate  50  can be made of material such as, but not limited to, glass, quartz or like material.  
         [0020]     When the heating layers  38 A . . .  38 H are activated (e.g., turned on electronically and/or through absorption of laser energy), the heating layers  38 A . . .  38 H input energy (i.e., heat) to cause the ink to increase in temperature. In particular, the electronic heating layer is capable, upon electrical activation, of heating the ink in the ink chamber  46  for a specific area  36 A . . .  36 H. The photon absorbing layer is capable, upon activation by laser energy, of heating the ink in the ink chamber  46  for a specific nozzle system  40  located in a specific area  36 A . . .  36 H.  
         [0021]     The electronic heating layers of the heating layers  38 A . . .  38 H are positioned so that each electronic heating layer overlaps a portion of the adjacent area. For example, the electronic heating layer in heating layer  38 A overlaps a portion of area  36 B. Thus, activating the electronic heating layer of heating layer  38 A causes the ink in area  36 A to be heated, while also heating the ink in the overlapped portion of area  36 B. In particular, the ink in the nozzle systems  40  in the portion of the overlapped area  36 B is heated. Heating the ink in this manner allows portions of the ink to be heated instead of heating the entire volume of ink. Also, the overlapping scheme of the electronic heating layers assists in generating a continuous thermal wave to proceed from area to area (i.e., from area  36 A to  36 B and so on).  
         [0022]     The electronic heating layer in the heating layer  38  in each area  36 A . . .  36 H can be activated by the print control system  16  in accordance with print information corresponding to the information to be printed onto the media. The electronic heating layers of the heating layers  38 A . . .  38 H may be heated in a sequential or non-sequential manner, depending on the nozzle systems that are to eject ink on the media at the give time, from the first end  32  to the second end  34  of the page-wide array printhead assembly  30 . In particular, the print control system  16  activates the electronic heating layer in heating layer  38 A, then activates the electronic heating layer in heating layer  38 B, and so on, in a sequential manner across the page-wide array printhead assembly  30 . As subsequent electronic heating layers in heating layers  38 A . . .  38 H are activated, the previously activated electronic heating layer is deactivated (i.e., turned off). In other words, a thermal wave moves through the ink from the first end  32  to the second end  34  of the page-wide array printhead assembly  30 , as opposed to heating the entire volume of ink in the page-wide array printhead assembly  30 .  
         [0023]     The page-wide array printhead assembly  30  is disposed adjacent the laser system  20 . The laser system  20  is operatively scanned or stepped across the page-wide array printhead assembly  30  and transmits laser energy  58  to the photon absorption layer of the heating layers  38 A . . .  38 H of selected nozzle systems  40  in accordance with the print information. As discussed above, the photon absorption layer absorbs the laser energy and converts the laser energy into heat, which is used to heat the ink in the ink chamber  46 .  
         [0024]     The print control system  16  controls the laser system  20  and synchronizes the scan of the laser system  16  with the sequential activation of the electronic heating layers of the heating layers  38 A . . .  38 H across the page-wide array printhead assembly  30  in accordance with the printing information. The synchronization includes timing the scan of the laser system  20  to follow the activation of the electronic heating layers across the page-wide array printhead assembly  30 . The print information indicates which nozzle systems  40  (i.e., selected nozzle systems) to pulse with the laser system  20  as it scans the page-wide array printhead assembly  30 . The print information includes information describing print indicia that are to be formed on the media. The print indicia include, but are not limited to, characters, graphics, and photographs. The page-wide array printhead assembly forms the print indicia in a sequential manner as the media moves relative to the page-wide array printhead assembly  30  and as the laser system  20  scans the page-wide array printhead assembly  30 .  
         [0025]     It should be noted, that in other embodiments, a page wide array  18  may move with respect to the media. In such embodiments, either or both the page wide array  18  and the media may move with respect to each other.  
         [0026]     The graph in  FIG. 3  illustrates a representative energy curve  62  for ejecting ink from a thermal inkjet device. The graph plots energy input (heating) into a volume of ink in a thermal inkjet device as a function of drop volume ejected. The energy curve  62  shows a lower knee  64  (lower threshold) and an upper knee  66  (upper threshold). The lower knee  64  is the area of the energy curve just before the energy curve  62  curves up, while the upper knee  66  is the area of the energy curve where it flattens out. Movement along the energy curve from the lower knee to the upper knee indicates that the energy inputted into the ink volume causes a volume of ink to be ejected from the thermal inkjet device. The ratio  68  of the lower knee  64  and the upper knee  66  is about 1 to 1.2. The advantage of heating to about the lower knee, is that a small amount of energy can then be utilized to heat the ink or fluid to the upper knee. This reduction in energy allows for heating to occur faster and with less energy than with traditional ink ejection systems that utilize optical or laser energy to heat ink or fluid for ejection.  
         [0027]     The information from the energy curve can be used in the design of the page-wide array print system  10 . In general, the ink in the ink chamber  46  can be heated to a lower knee threshold by the electronic heating layers of the heating layers  38 A . . .  38 H of the nozzle systems  40 . The lower knee threshold represents a position on the energy curve near the lower knee  64 . The lower knee threshold can be defined, for example, as sufficient energy to be about 50% to 99%, about 70% to 99%, about 80% to 99%, about 90% to 99%, or about 90% of the inputted energy to reach the lower knee.  
         [0028]     Then, the laser system  20  emits laser energy  58  at the photon absorbing layer of selected nozzle systems  40 , which absorbs the laser energy  58 . The laser energy  58  from the laser system  20  is sufficient to heat the ink to an upper knee threshold. A known volume of ink is ejected from the orifice  42  of selected nozzle system  40  when the energy inputted into the ink reaches the upper knee threshold. The upper knee threshold represents a position on the energy curve near the lower knee  64 . The upper knee threshold can be defined as about 101% to 150%, about 101% to 130%, about 101% to 125%, or about 120% of the upper knee.  
         [0029]     In other words, the electrical heating layers of the heating layers  38 A . . .  38 H heat the ink to a first level on the energy curve and the laser system  20  heats the ink from the first level to a second level on the energy curve. Using a two-part heating process with heating layers  38 A . . .  38 H and the laser system  20  results in the laser system  20  having to input less total energy to eject the ink drop than if the laser system  20  is used without the assistance of the electric heating layer. This is in contrast to other laser driven systems that use the laser system to provide all of the energy to eject the ink drop.  
         [0030]     As indicated above, the print control system  16  synchronizes the scan of the laser system  20  across the page-wide array printhead assembly  30  with sequential activation of the electrical heating layers of the heating layers  38 A . . .  38 H across the page-wide array printhead assembly  30 . For example, the electrical heating layer in heating layer  38 A of area  36 A is activated by the print control system  16  to heat the ink in each nozzle system  40  in area  36 A to the lower knee threshold. Once the ink in each nozzle system  40  is heated to the lower knee threshold, the print control system  16  instructs the laser system  20  to emit laser energy at selected nozzle systems  20  as the laser system  20  scans across area  36 A. The photon absorbing layers of the selected nozzle systems  20  absorb the laser energy and the energy is transferred into the ink, which inputs sufficient energy to reach the upper knee threshold. As a result of the ink having sufficient energy to reach the upper knee threshold, a known volume of ink is ejected from the selected nozzle system  20 . The same process occurs for each of the selected nozzle systems  20  in area  36 A as the laser system  20  scans across area  36 A. Once the laser system scan completes emitting laser energy at the selected nozzle systems  20  in area  36 A, the electrical heating layer in heating layer  38 A is deactivated and the ink in the nozzle systems  40  of area  36 A is allowed to cool.  
         [0031]     Next, the print control system  16  activates the electrical heating layer in heating layer  38 B of area  36 B to heat the ink in each of the nozzle systems  40  in area  36 B. The electrical heating layer is activated once the laser system scan of area  36 A is nearly complete. It should be noted that the electrical heating layer in heating layer  38 A heats a portion of area  36 B. Once the ink in each nozzle system  40  of area  36 B is heated to the lower knee threshold, the print control system  16  instructs the laser system  20  to transmit laser energy at selected nozzle systems  40  in area  36 B as the laser system  20  scans across area  36 B. The photon absorbing layers of the selected nozzle systems  40  absorb the laser energy and the energy is transferred into the ink, which inputs sufficient energy to reach the upper knee threshold. As a result of the ink having sufficient energy to reach the upper knee threshold, a known volume of ink is ejected from the selected nozzle systems  20 . The same process occurs for each of the selected nozzle systems  40  in area  36 B. Once the laser system scan completes emitting laser energy at the selected nozzle systems  40 , the electrical heating layer in heating layer  38 B is deactivated and the ink in the nozzle systems  40  of area  36 B is allowed to cool.  
         [0032]     The same process occurs for each area  36 C . . .  36 H so that the ink in the selected nozzle systems  40  is heated to the lower knee threshold by the electrical heating layer in heating layers  36 C . . .  36 H. Subsequently, the ink in the selected nozzle systems  40  is heated from the lower knee threshold to the upper knee threshold, so that a volume of ink is ejected from the selected nozzle systems  40 . The print control system repeats this process until the printing information is converted into print indicia on the printing material.  
         [0033]     The areas  36 A . . .  36 H are individually activated so that the ink in the nozzle systems  40  in each area  36 A . . .  36 H is not at an elevated temperature for a significant length of time. This reduces the likelihood of spitting or drooling of the ink in the page-wide array printhead assembly  30 . In addition, each area  36 A . . .  36 H is heated to the lower knee threshold to limit the amount of energy used by the laser system  20  to raise the ink to the upper knee threshold, which is more energy efficient than currently used techniques.  
         [0034]      FIG. 4  is a graph of representative waveforms A . . . H for activating the electrical heating layers in heating layers  38 A . . .  38 H, respectively. Waveforms A . . . H indicate when the electrical heating layers in heating layers  38 A . . .  38 H are activated and then deactivated. Activation of the electrical heating layers in heating layers  38 A . . .  38 H according to the waveforms A . . . H causes a thermal wave to proceed from the first end  32  to the second end  34  of the page-wide array printhead assembly  30 . The activation of the electrical heating layers in heating layers  38 A . . .  38 H precedes the scan of the laser system  20  to allow the ink in the nozzle systems  40  in each area to be heated to the lower knee threshold.  
         [0035]     Thus, activating the electrical heating layers in heating layers  38 A . . .  38 H immediately prior to scanning laser system  20  across the page-wide array printhead assembly  30  enables the page-wide array print system  10  to eject ink drops in a controlled energy efficient manner.  
         [0036]     Many variations and modifications may be made to the above-described embodiments. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.