Inkjet-printing devices, such as inkjet printers, are devices that are able to form images on sheets of media like paper by ejecting ink onto the media sheets. Drop-on-demand inkjet-printing devices primarily include actuation mechanisms based on heat generation, piezoelectric work, or electrostatic attraction. A thermal inkjet printing device ejects ink by heating the ink, which causes formation of a bubble within the ink and results in ink to be ejected. A piezoelectric inkjet printing device ejects ink by deforming a piezoelectric plate, which forces ink to be ejected. An electrostatic inkjet-printing device operates by deforming a membrane with an electrostatic charge between two electrodes. When the electrostatic charge is released, the membrane forcibly ejects ink from the device.
The membrane layer 102 can be fabricated from tantalum-aluminum, and in one embodiment is 0.1 microns in thickness. The membrane layer 102 may also be referred to as simply a membrane, and is flexible. The deformable beam layer 104 can also be fabricated from tantalum-aluminum, and in one embodiment is 3.0 microns in thickness. The frame layer 106 can be fabricated from silicon.
The deformable beam layer 104 includes a single deformable beam 110 in the embodiment of
The frame layer 106 includes a frame 108. The frame 108 has a left side 304A and a right side 304B, collectively referred to as the sides 304. The frame 108 further has a number of cross members 306; in the embodiment of
The deformable beam 110 defines slits 112 and 114, where the slit 112 is adjacent to the side 304B of the frame 108, and the slit 114 is adjacent to the side 304A of the frame 108. The slits 112 and 114 are depicted in
Liquid in the liquid chamber 502 is separated from the deformable beam 110 via the membrane layer 102. The liquid chamber 502 includes a liquid-ejection nozzle 504, and also a liquid inlet 514. When the deformable beam 110 deforms responsive to an electrostatic charge, additional liquid is drawn into the liquid chamber 502 via the liquid inlet 514. When the electrostatic charge is released, the deformable beam 110 reverts to its configuration depicted in
In this respect, as has been noted above, the deformable beam 110 serves as one electrode of the electrostatic liquid-ejection actuation mechanism 100. The actuation mechanism 100 also includes an additional electrode 506 and a dielectric 512 such as silicon nitride or tantalum pentoxide. An electrostatic gap 508 is defined between the beam 110 and the electrode 506, and thus encompasses the dielectric 512 and an air space between the dielectric 512 and the beam 110. The electrostatic gap 508 may be 0.6 microns in thickness. The dielectric 512 may have a thickness of 0.4 microns and a dielectric constant between 3 and 28.
It is noted that in
The width of the deformable beam 110 is independent of the width between the sides 304 of the frame 108, and thus is independent of the width of the area 302 defined by the frame 108 as depicted in
Having the width of the deformable beam 110 being independent of other widths within the electrostatic liquid-ejection actuation mechanism 100 is advantageous. Electrostatic liquid-ejection actuation using a deformable beam 110 as in
However, the width of the deformable beam 110 is not typically an independent variable, but is rather usually dependent on the width of the area 302 between the sides 304 of the frame 108 and/or on the width of the liquid chamber 502. One of the inventors' inventive insights is that the dependence of the width of the deformable beam 110 on the width of the area 302 and/or on the width of the liquid chamber 502 should be divorced. As such, the inventors inventively added the slits 112 and 114 to the sides of the deformable beam 110. Because the slits 112 and 114 can be made larger or smaller as desired, the width of the deformable beam 110 is no longer dependent on the width of the area 302 and/or on the width of the liquid chamber 502. Advantageously, this added independence of the width of the deformable beam 110 provides for more control of the characteristics of the deformation of the beam 110, and thus more control over the ejection of liquid droplets from the liquid chamber 502 via the liquid-ejection nozzle 504.
Therefore, in this respect, the inventors' inventive contributions are at least two-fold. First, the inventors recognized that the dependence of the width of the deformable beam 110 on the width of the area 302 and/or on the width of the liquid chamber 502 unduly constricts the characteristics of the deformation of the deformable beam 110 and thus how liquid droplets are ejected from the liquid chamber 502. Second, the inventors novelly invented a specific approach to making the width of the deformable beam 110 independent of the width of the area 302 and/or of the width of the liquid chamber 502, via introduction of the slits 112 and 114 to either side of the deformable beam 110.
Furthermore, the electrostatic liquid-ejection actuation mechanism 100 is inventive in at least a number of other respects. For instance, one such advantage relates to the usage of the deformable beam 110 along with the membrane layer 102 as an actuator, as opposed to just a single uniformly thick layer that is not divided into a beam 110 and a membrane layer 102. All other things being equal—chamber dimensions, gap dimensions, applied voltage, and so on—the volume displaced by a deformable beam 110 and a membrane layer 102 as compared to the volume displayed by a single uniformly thick layer not divided into a beam 110 and a membrane layer 102 can be the same. However, to achieve this, the thickness of the single uniformly thick layer has to be considerably thinner than the thickness of the deformable beam 110.
As a result, the mechanical frequency of oscillation of an actuator made up of a deformable beam 110 and a membrane layer 102 is higher than the mechanical frequency of oscillation of an actuator made up of a single uniformly thick layer. This is advantageous, because the actuator can return to an unstressed (i.e., unactuated) state more quickly when the electrostatic charge has been drained. Therefore, the actuator can be used again sooner to eject additional liquid. As a result, the time between ejected liquid drops is reduced, providing for higher liquid-ejection rates.
Furthermore, the pressure profile for an actuator made up of a deformable beam 110 and a membrane layer 102 is the same or narrower than it is for an actuator made up of a single uniformly thick layer. This is because the actuator made up of a deformable beam 110 and a membrane layer 102 reverts more quickly to the uncharged state. In addition, instead of optimizing the design of the deformable beam 110 for higher frequency, as noted in the previous paragraph, the design can instead be optimized for a lower voltage to build up the electrostatic charge (which would reduce the mechanical frequency of oscillation).
Therefore, when an electrostatic charge is established between the deformable beam 110 and the electrode 506, the beam 110 deforms from a first configuration as depicted in
It is noted that snap-down occurs at a point where the electric field strength becomes sufficiently strong to overcome the spring strength of the beam and membrane. The spacing between the beam 110 and the dielectric 512 becomes zero, with the surface of the beam touching the surface of the opposing electrode. The touching portion of the beam is then flat. The shape of the deformable beam 110 depicted in
It is further noted that as has been described thus far, there are two cross members 306 within the frame 108 of the frame layer 106, as in
As before, the actuation mechanism 100 includes a membrane layer 102, a deformable beam layer 104, and a frame layer 106. The deformable beam layer 104 includes two deformable beams 110A and 1108, collectively referred to as the deformable beams 110, in this embodiment. The frame 108 of the frame layer 106 has three cross members 306: the cross member 306C, in addition to the cross members 306A and 306B. The cross members 306A and 306B are top and bottom cross members, respectively, whereas the cross member 306C is a middle cross member.
The frame 108 defines two areas 302: an area 302B surrounded by the left and right sides of the frame 108 and by the cross members 306B and 306C, and an area 302A surrounded by the left and right sides of the frame 108 and by the cross members 306A and 306C. The areas 302A and 302B correspond to two liquid chambers 502A and 502B, respectively, of the electrostatic liquid-ejection actuation mechanism 100, and which are collectively referred to as the liquid chamber 502. It can be said that the number of the areas 302 and the number of the corresponding liquid chambers 502 are equal to the number of middle cross members, plus one.
The deformable beams 110 define four slits 112A, 112B, 114A, and 114B, collectively referred to as the slits 112 and 114. The slits 112 are adjacent to the right side of the frame 108, whereas the slits 114 are adjacent to the left side of the frame 108. The width of the beam 110A is control by the width of the slits 112A and 114A, and the width of the beam 110B is controlled by the width of the slits 112B and 114B. The left and the right sides of each of the deformable beams 110 are not attached to the frame 108. The number of deformable beams 110 is thus equal to the number of areas 302 defined by the frame 108, and thus equal to the number of liquid chambers 502.
Each of the deformable beams 110 acts as an electrode. An electrostatic charge is maintained over an electrostatic gap between a given deformable beam 110 and another electrode. For example, in
Having two deformable beams 110 and two liquid chambers 502 in the embodiment of
For instance, assume the case where there are N liquid chambers 502, where N is greater than one, and where each liquid chamber 502 can provide for a volume V of liquid. By firing M of the N liquid chambers 502, where M is less than or equal to N, in one embodiment a liquid droplet having a volume of liquid equal to K times V times M can be ejected (assuming that a minimum threshold of volume for liquid ejection has been exceeded), where K is the percentage of liquid displaced by a given actuator mechanism. Since M can be varied, this means that the volume of the liquid droplet that is ejected can be controlled in increments of K times V. As such, larger liquid droplets can be ejected when needed, as well as smaller liquid droplets can be ejected when needed.
It is noted that this scenario is different than simply having different liquid chambers that are to eject different droplets out of different liquid-ejection nozzles. In such instance, each liquid chamber ejects its own droplet. By comparison, in the situation that has been described, the liquid chambers 502 are used in unison to eject liquid from the same liquid-ejection nozzle 504. By increasing the number of deformable beams 110 that are deformed, the amount of liquid that is ejected from the same liquid-ejection nozzle 504 within the same liquid droplet is increased.
Furthermore, this is advantageous because no other changes, besides the number of deformable beams 110 that are to be deformed, have to be made. That is, the electrostatic charge placed on each deformable beam 110, and other variables controlling the deformation of each deformable beam 110, do not have to be modified based on the number of deformable beams 110 that are to be deformed. As such, this embodiment provides an elegant way in which to control, or tune, the size of a liquid droplet ejected from the liquid-ejection nozzle 504 to which all the liquid chambers 502 are fluidically coupled. Having multiple liquid chambers 502 operating in the appropriate sequence, and multiple deformable beams 110, can also prevent liquid breakup during liquid ejection, among other advantages.
Another such advantage is that larger drop volumes can be achieved at a higher frequency than with a chamber of comparable dimensions having a single layer actuator mechanism. That is, having multiple deformable beams 110 permits tuning the resulting actuator to achieve desired drop size and drop velocity, at a desired frequency. Furthermore, the individual actuators (i.e., the individual deformable beams 110) need not be dimensionally identical. In addition, the individual liquid chambers 502 do not have to be dimensionally identical, either.
In conclusion,
The liquid-ejection device 800 may be an inkjet-printing device, which is a device, such as a printer, that ejects ink onto media, such as paper, to form images, which can include text, on the media. The liquid-ejection device 800 is more generally a liquid-jet precision-dispensing device that precisely dispenses liquid, such as ink. The liquid-ejection device 800 may eject pigment-based ink, dye-based ink, another type of ink, or another type of liquid. Embodiments of the present disclosure can thus pertain to any type of liquid-jet precision-dispensing device that dispenses a liquid.
The liquid-jet precision-dispensing device precisely prints or dispenses a liquid in that gases such as air are not primarily or substantially ejected. The terminology liquid encompasses liquids that are at least substantially liquid, but which may include some solid matter, such as pigments, and so on. Examples of such liquids include inks in the case of inkjet-printing devices. Other examples of liquids include drugs, cellular products, organisms, fuel, and so on.
The liquid supplies 802 include the liquid that is ejected by the liquid-ejection device 800. In varying embodiments, there may be just one liquid supply 802, or more than one liquid supply 802. The electrostatic liquid-ejection actuation mechanisms 100 are implemented as has been described. In varying embodiments, there may be just one electrostatic liquid-ejection actuation mechanism 100, or more than one electrostatic liquid-ejection actuation mechanism 100. The liquid supplies 802 are fluidically coupled to the liquid-ejection actuation mechanisms 100, as indicated by the dotted line in
In conclusion, one specific exemplary embodiment of the present disclosure is provided. In this embodiment, there are ten actuators (i.e., ten electrostatic liquid-ejection actuation mechanisms). The liquid-ejection nozzle radius is ten microns, and the nozzle depth is twenty microns. There are further two liquid inlets, each being 20 microns in width, 26 microns in depth, and 300 microns in length. The viscosity of the liquid (e.g., ink) is 10 centipoise. The liquid chamber itself is 26 microns deep, by 1850 microns long, by 100 microns wide.
This specific exemplary embodiment provides for the following performance characteristics. Liquid drops ejected from the liquid-ejection nozzles are each 3.3 picoliters in volume, and have a speed of 8.8 meters/second. The drop emission frequency, for constant drop speed, can be zero to fifteen kilohertz. Finally, the fluidic natural resonant frequency of this embodiment of the disclosure is 70 kilohertz.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2008/082144 | 10/31/2008 | WO | 00 | 3/17/2011 |