Fluid sprinkling – spraying – and diffusing – With means to vibrate or jiggle discharge
Reexamination Certificate
2000-10-17
2002-05-28
Yuen, Henry C. (Department: 3752)
Fluid sprinkling, spraying, and diffusing
With means to vibrate or jiggle discharge
C239S102200, C239S553300
Reexamination Certificate
active
06394363
ABSTRACT:
The present invention relates to liquid projection apparatus in the form of what is known as a ‘face-shooter’ array.
In the ink-jet art there are many liquid projection devices that utilize the acoustic resonance of capillary channels or chambers, hereinafter collectively termed ‘cells’, associated with nozzles to provide a pressure wave to cause liquid to be expelled from those nozzles. These technologies are limited in their maximum frequency of operation by the liquid acoustic resonant frequency of these cells. In addition to this, the cells act as a restriction to flow causing pressure to be developed within the cells which effects drop ejection. Flow through the cells is therefore limited by the refill rate, causing a further upper limit to the operational frequencies of such devices. Moreover, the cells act as a trap for air bubbles and contaminant particles that severely disrupt operation and which are problematic to remove. Structures employing cells are also thereby restricted to handling liquids of particular rheology, high purity and stability. For example, unstable suspensions that are used to form white, gold and silver inks cannot be applied reliably with devices employing cells.
Further technologies described in the art provide excitational members in the bulk liquid in close proximity to the rear of a separate nozzle-plate. This configuration has the advantage of allowing bubbles to escape, but the method is intrinsically inefficient in use of energy and prone to crosstalk.
A further difficulty associated with printheads known in the art is that their construction is based on sub-assembly onto a three dimensional structure rather than onto a substantially two dimensional workpiece. This has the consequences of increasing the variability of the product and decreasing the manufacturing yield.
In the ink-jet industry, there is an unfulfilled requirement for printheads that can be fabricated with a sufficient number of ejection sites on a single printhead to constitute a page-wide array. The problem of producing such a printhead is the requirement that the fabrication processes must provide a structure with a high degree of consistency between thousands of ejection sites. Predominantly in the prior art, for example EP0728583A2, constructions are taught wherein there is a requirement to locate a number of components in three dimensions to form a linear drop on demand ink-jet printhead. This construction does not achieve the integration of the transducer means into a substantially planar form. It is the belief of the authors of the current invention that this lack of integration is the prime limitation on the width of the array that can be constructed by methods in the prior art.
The same construction difficulty arises in WO-A-94/22592 wherein excitation means are bonded to, but not integrated with, a material layer in which nozzles are formed. This prior art also requires an extended structure behind the nozzle-plate to provide the acoustic energy to enable drop production. The fabrication of this prior art must also proceed by fabrication in three dimensions, again introducing problems of component alignment.
As stated above, the inventors believe the solution to this problem is to understand that the extended construction can be achieved by integrating the transduction means to the surface. In practice, achieving this is not a trivial problem to overcome.
For example, if the structures disclosed in WO-A-94/22592 are reduced in height to achieve the substantially planar condition, a contradiction results. Firstly, the motional action of the PZT (piezoelectric lead zirconate titanate ceramic) as configured, reduces markedly with PZT height reduction. Secondly, the structure requires the surface to flex, but the PZT must remain rigidly bonded to a further surface. The structure cannot be reduced to a layer.
A second approach is to apply an annular ring geometry, such as is described in our EP-A-0615470, to form a surface array of such devices. If the flexural rings are set out and connected in an array there is first a problem of scale; the separation of nozzles on the array will be determined by the minimum achievable PZT ring outer diameter that will produce droplets at an acceptable drive voltage. This will be too large to form a high resolution linear array (such as 150 nozzles per inch, as is required, for example, in many printing applications). An attempt to apply the vibration of a surface (bimorph) flexural ring is disclosed in JP 09-226111. However in this case the rings being bonded to, or formed in, a material layer are unavoidably coupled around the outer circumference to the material layer as a whole, inducing undesirable crosstalk between rings.
An alternative form of excitation, from a similar physical structure to JP 09-226111, is shown in JP 10-58672. In this patent application, the radial vibration of a surface ring is apparent. Again, however, the rings are unavoidably coupled around their outer circumference to the material layer as a whole, inducing undesirable crosstalk.
A subsequent patent application, JP 10-58673, also discloses an annular ring geometry employed to produce a surface meniscus resonant wave. The inventors of JP 10-58673 seek to improve fluid coupling by introducing a further structure at a defined depth of ink beneath the nozzle, forming a flow constriction which effectively defines a resonant cell structure, and thereby the substantially planar condition of construction is lost.
In the prior constructions taught in JP 09-226111, JP 10-58672, JP 10-58673, the droplet formed is small compared to the ‘nozzle’ opening of the substrate. The relatively large nozzle is correspondingly more sensitive to undesirable wetting of the front face of the printhead than the constructions in which an issuing jet fills the nozzle to produce a droplet of similar size, for example under conditions of ink having low surface tension or physical shock to the printhead. This sensitivity arises from the lower pressure differences that the relatively larger diameter meniscus within the larger ‘nozzle’ can sustain.
According to the present invention there is provided a device for projecting liquid as jets or droplets from multiple nozzles, the device comprising;
a plurality of transducers oriented substantially parallel to one another and each having an inner face and an outer face opposite said inner face, the transducers being arranged in a substantially planar array;
a plurality of nozzles, each nozzle being associated with a respective transducer which is excitable to cause movement of the associated nozzle in a direction substantially aligned with the nozzle axis, to project liquid therefrom;
liquid supply means for supplying a liquid to said inner face of said nozzles;
means for selectively exciting transducers as required, thereby to project liquid as jets or droplets from the respective outer face by movement of the liquid through the nozzle in response to the movement of the nozzle.
Thus, in such a device, the transducers are all aligned in the same direction and, where the transducers are rectilinear, they all have a major axis parallel with that of the other transducers. Even where the transducers are not rectilinear, as long as they are congruent, they will have at least one edge in parallel with the same edges of other transducers in the array.
By the term “transducer” is meant a local region of the liquid projection device that can be stimulated into motion by an associated individually-addressable excitation means. By the term “substantially planar” it is meant that the height of the components is small with respect to the lateral extent of the array of individual components.
The inventors believe the key to achieving a page-wide array is making the array in layers which may be aligned optically using surface processing techniques.
The transducer components may be formed in one piece comprising, for example, a piezoelectric or similar excitation means. The transducers may also be formed as a composite component in which an excitation mea
Arnott Michael George
Humberstone Victor Carey
Johnson Simon Roger
van Rensburg Richard Wilhelm Janse
Dykame Gossett PLLC
Hwu Davis
The Technology Partnership PLC
Yuen Henry C.
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