Fluid dispensing method and apparatus employing piezoelectric transducer

A fluid dispensing apparatus, for use in fluid dispensing systems for the controlled application, metering, and/or dispensing of fluid from a plurality of orifices. The apparatus comprises a body having at least one cavity, at least one fluid inlet for introducing the fluid into the cavity, and at least one fluid outlet for discharging the fluid from the cavity. A plurality of orifices are in communication with the fluid outlet and at least one piezoelectric actuator is selectively coupled to the body and operable to pressurize the fluid within the cavity and permit the controlled discharge of the fluid through the plurality of orifices onto a substrate.

DETAILED DESCRIPTION Reference will now be made in detail to various embodiments of the present invention, examples of which are illustrated in the accompanying drawings wherein like numerals indicate the corresponding structure throughout the views. As will be understood hereafter, various embodiments of the present invention relate to improved fluid dispensing apparatus for the controlled application, metering, and/or dispensing of fluid droplets from a plurality of orifices. While the present invention is described hereafter with respect to fluid jet printheads for applying developer to a photographic element, it should be understood that the present invention can be adapted for other uses and applications of dispensing. For example, the fluid dispensing apparatus of the present invention might also be suitable for, inter alia, dispensing of drugs for pulmonary, nasal, or topical delivery; dispensing of odorants, pheromones, or other airborne chemicals to be detected by humans, animals, or instruments; application of adhesives and/or coating materials; and application of light emitting materials for display manufacturing. In one embodiment as shown in FIG. 1, a fluid dispensing apparatus comprises a fluid jet printhead 10 which employs an actuator driving a plurality of orifices. The fluid jet printhead 10 includes a body 15 , at least one fluid inlet 25 and at least one fluid outlet 30 (shown in phantom), a plurality of orifices 35 , and at least one piezoelectric actuator 45 . In a preferred embodiment, the body 15 is formed of stainless steel. Examples of other suitable materials include, but are not limited to, titanium, molybdenum, and nickel. In addition, rigid plastics, such as Ryton® may be used. The body 15 has at least one cavity 20 (shown in phantom) therein where fluid is held. The cavity 20 is typically an elongated oval shape in cross section into which fluid is introduced through the at least one fluid inlet 25 and from which fluid is discharged through the at least one fluid outlet 30 (shown in phantom). However, any suitable shape can be used for the cavity 20 . For example, a rectangular, triangular, or other cross-sectional shaped cavity 20 may be used. The fluid may be supplied to the cavity 20 by a pump, by gravity-feed, or by other known methods of supplying quantities of fluid to a fluid jet printhead. In addition, a fluid may be supplied to the cavity 20 via the fluid inlets 25 located at one or both ends, or at some intermediate point along the length of the cavity 20 . However, as further shown in FIG. 1 , the fluid jet printhead 10 preferably comprises two fluid inlets 25 located at opposite ends of the cavity 20 . The plurality of orifices 35 are formed in an orifice plate 40 and are in communication with the fluid outlet 30 . Preferably, the orifice plate 40 is formed from polymers, metal, or like materials. Preferred materials for use in forming the orifice plate include excimer laser machined polymers, such as polyamide, or electroformed nickel. However, one skilled in the art will recognize that any suitable type of precision orifice plate manufacturing method and material may be utilized to provide an appropriate orifice plate. In the embodiment shown in FIG. 1 , the plurality of orifices 35 are arranged to conform to the fluid outlet 30 . While any suitable fluid outlet shape may be used, the fluid outlet 30 preferably has an opening in the shape of a slot so that the plurality of orifices 35 are distributed in a linear array. Examples of alternative configurations for orifice arrays are shown in FIGS. 3 and 4 . In FIG. 3 , the orifice array is distributed across a flat, circular plate while in FIG. 4 the orifice array is distributed across a curved, cylindrical plate. The configurations shown in FIGS. 3 and 4 are preferable for the controlled dispensing of fluid droplets into the air. Referring again to FIG. 1 , the number of orifices 35 formed in the orifice plate 40 preferably is in the range of from about 20 to about 200, and even more preferably from about 50 to about 150. In addition, the orifices 35 are sized to produce fluid droplets preferably in the 5 &mgr;m to 250 &mgr;m range, more preferably in the 10 &mgr;m to 200 &mgr;m range, and even more preferably in the 25 &mgr;m to 100 &mgr;m range. While round orifices are preferred, orifices of other shapes, such as oval, triangular, and pentagonal, may be used, if desired. Preferably, orifices are sized to produce droplets having the above-mentioned preferred diameters. It should be noted that while the preferred location, configuration, number and size of the orifices have been described above, these arrangements may be varied depending on the desired application. Also, it should be further noted that the size and number of orifices are limited by actuator and electronic driver considerations. The at least one piezoelectric actuator 45 is selectively coupled to the body 15 and operable in order to pressurize the fluid within the cavity 20 and permit the controlled discharge of the fluid through the plurality of orifices 35 . As shown in FIG. 1 , the piezoelectric actuator 45 is a bend-mode piezoelectrically driven type actuator. However, one skilled in the art would recognize that additional actuators could also be used with equal facility, such as squeeze-tube actuators, push-mode actuators, and shear-mode actuators. Preferably, the piezoelectric actuator 45 is comprised of a piezoelectric material 50 bonded to a diaphragm 55 . The diaphragm may suitably be formed of metal. Additionally, it is preferable that the diaphragm 55 is comprised of stainless steel. Examples of other suitable metals include, but are not limited to, aluminum, titanium, molybdenum, and nickel. Typically, the diaphragm 55 has a thickness of from about 100 &mgr;m to about 500 &mgr;m and a width of from about 3 mm to about 15 mm. In a preferred embodiment as shown in FIG. 1 , the piezoelectric material 50 is a lead-zirconium-titanium oxide, for example, lead zirconate titanate or PZT. In further embodiments, the piezoelectric material 50 may be comprised of, for example, electrorestrictive materials, such as lead metaniobate or magnitostrictive materials, such as Terphanol. Typically, the piezoelectric material 50 has a thickness of from about 50 &mgr;m to about 250 &mgr;m. Also, the piezoelectric material 50 is metalized on both sides. As such, when a voltage pulse is applied across the piezoelectric material 50 via an electronic driver (not shown), the piezoelectric material 50 will readily bend or deform. In addition, the piezoelectric material 50 is preferably sized so that the actuator 45 is approximately as long as orifice plate 40 . In operation, fluid dispensing apparatus or fluid jet printhead 10 , as shown in FIG. 1 , is supplied with fluid from a fluid supply or reservoir (not shown). An electronic drive circuit (not shown) applies a voltage pulse via leads 60 to the piezoelectric actuator 45 . In response, the piezoelectric material 50 of the actuator 45 will tend to increase in thickness and decrease in width. Because piezoelectric material 50 is constrained by diaphragm 55 , the actuator 45 is displaced in a manner that reduces the volume in the cavity 20 and consequently increases the pressure of the fluid contained within cavity 20 . The fluid in cavity 20 receives the energy from actuator 45 and is transmitted to the fluid outlet 30 in the form of pressure waves, such that a droplet of fluid is forcibly discharged from the plurality of orifices 35 . However, because the direction of travel of these pressure waves does not determine the direction of travel of the droplets that are eventually formed, the actuator 45 can be located relative to the cavity 20 in various manners. In the preferred embodiment illustrated in FIG. 1 , the direction of motion of actuator 45 is substantially parallel to the plane of orifice plate 40 . This embodiment minimizes the size of the fluid jet printhead 10 in the direction parallel to the flight path of the fluid droplets. In another embodiment schematically illustrated in FIG. 2 , the fluid jet printhead 10 includes a body 15 , at least one fluid inlet (not shown), at least one fluid outlet 30 , a plurality of orifices 35 , orifice plate 40 , and at least one piezoelectric actuator 45 . Additionally, the piezoelectric actuator 45 illustrated in FIG. 2 is comprised of a piezoelectric material 50 bonded to a diaphragm 55 . In the embodiment shown in FIG. 2 , the direction of motion of the actuator 45 is substantially normal to the plane of the orifice plate 40 . As a result, the size of the fluid jet printhead 10 is minimized in the direction normal to the flight path of the fluid droplets. The embodiments illustrated in FIGS. 1 and 2 are preferable for the controlled application of fluid onto substrates. For example, it has been found that a particular application of the fluid dispensing apparatus or fluid jet head 10 such as illustrated in FIGS. 1 and 2 , can deliver temporal control of greater than or equal to about 5 &mgr;s, preferably greater than about 10 &mgr;s, at flow rates of less than or equal to about 200 &mgr;l/s, preferably less than 100 &mgr;l/s, while still maintaining linear coverage up to about 100 mm for a single printhead. Linear coverage describes the formation of a uniform line of fluid on a substrate. Examples of suitable substrates include, but are not limited to, paper, polymer, and metal substrates. The substrate may be in sheet or film form, or may comprise a more diverse shape. In a preferred embodiment, the substrate comprises a recording medium such as paper, film, or other light sensitive media. In alternative embodiments of the fluid dispensing apparatus or fluid jet printhead, the body comprises a plurality of the cavities and a plurality of the piezoelectric actuators, wherein at least one of the plurality of actuators is selectively coupled to the body and operable to pressurize the fluid within each cavity. In such embodiments, multiple fluids, for example developers, modifiers, inks, adhesives, antibodies, DNA, albumin, polymers, conductive polymers, nanoparticle suspensions, and optical filter materials, could be dispensed from a single apparatus during multiple passes. As shown in FIG. 1, a preferred method according to the invention is directed to application of developer to a photographic element. A source of developer fluid, a fluid cavity 20 , a plurality of orifices 35 , and at least one piezoelectric actuator 45 are provided. The cavity 20 is in communication with the fluid source, the plurality of orifices 35 are in communication with the cavity 20 . An electronic drive circuit selectively applies a voltage pulse via leads 60 to the actuator 45 to pressurize a developer within the cavity 20 whereby droplets of developer are forcibly discharged from the plurality of orifices 35 . Finally, the droplets exiting the plurality of orifices 35 are deposited onto a photographic element 65 , such as film, paper, or other light sensitive media. Having shown and described the preferred embodiments of the present invention, further adaptations of the methods and apparatus described herein can be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the present invention. Several of such potential modifications have been mentioned, and others will be apparent to those skilled in the art. Accordingly, the scope of the present invention should be considered in terms of the following claims and is understood not to be limited to the details of structure and operation shown and described in the specification and drawings.