Abstract:
This invention relates to an improved acoustic fluid emission head, e.g. an acoustic ink printhead, and a method of forming or assembling same. More particularly, the invention is directed to an acoustic ink printhead that advantageously incorporates elastomer gaskets to replace all epoxy joints in the printhead and a corrugated spacer to provide focal gap control in the printhead. A related method for manufacturing the printhead includes folding and spot welding the aperture plate of the printhead to maintain the elastomer gaskets in place and, consequently, control the focal gap.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an improved acoustic fluid emission head, e.g. an acoustic ink printhead, and a method of forming or assembling same. More particularly, the invention is directed to an acoustic ink printhead that advantageously incorporates elastomer gaskets to replace epoxy joints in the printhead and a corrugated spacer to provide focal gap control in the printhead. A related method for forming the printhead includes folding and spot-welding the aperture plate of the printhead to maintain the elastomer gaskets in place and, consequently, control the focal gap. 
     While the invention is particularly directed to the art of acoustic ink printing, and will be thus described with specific reference thereto, it will be appreciated that the invention may have usefulness in other fields and applications. For example, the invention may be used in any application where acoustic emitters are used. 
     By way of background, acoustic ink printing involves the emission of a droplet of ink from a pool of ink toward a print medium. Sound waves are generated and focussed toward the surface of the ink pool to emit the droplet therefrom. While acoustic ink printing elements may take various forms, such elements typically include a piezoelectric transducer, a lens, a cover plate having apertures formed therein to allow emission of the ink, and corresponding wiring. It is to be appreciated that approximately one thousand (1,000) or more of these elements may be disposed on a single printhead. It should also be appreciated that other fluids may be emitted such as molten metal, etc. rather than ink. 
     More particularly, as shown in FIG. 1, a single acoustic element  10  includes a glass layer  12  having an electrode layer  14  disposed thereon. A piezoelectric layer  16 , preferably formed of zinc oxide, is positioned on the electrode layer  14  and an electrode  18  is disposed on the piezoelectric layer  16 . Electrode layer  14  and electrode  18  are connected through a surface wiring pattern representatively shown at  20  and cables  22  to a radio frequency (RF) power source  24  which generates power that is transferred to the electrodes  14  and  18 . On a side opposite the electrode layer  14 , a lens  26 , preferably a concentric Fresnel lens, is formed. Spaced from the lens  26  is a liquid level control plate  28 , having an aperture  30  formed therein. Ink, or fluid,  32  is retained between the liquid level control plate  28  and the glass layer  12 , and the aperture  30  is aligned with the lens  26  to facilitate emission of a droplet  34  from surface  36 . The surface  36  is, of course, exposed by the aperture  30 . 
     The lens  26 , the electrode layer  14 , the piezoelectric layer  16 , and the electrode  18  are formed on the glass layer  12  through known photolithographic techniques. The liquid level control plate  28  is subsequently positioned to be spaced from the glass layer  12  to establish a focal gap. The ink  32  is fed into the space between the plate  28  and the glass layer  12 , e.g. the focal gap space, from an ink supply (not shown). 
     Acoustic ink printheads of the type incorporating emitting elements as described above typically have components that are bonded together with epoxy material. Epoxy bonded heads have the disadvantages of 1) experiencing epoxy delamination by the ink and 2) requiring increased manufacturing time resulting from the excessive cure time inherent in use of epoxy materials. Moreover, many types of epoxy materials are simply not compatible with the types of ink used in acoustic ink printing. Another disadvantage of the heretofore known types of acoustic emission heads is that, in such heads, it is difficult to maintain a uniform focal gap, i.e. the gap between the control plate  28  and the glass layer  12  shown in FIG. 1, across the entire emitting surface of the head. Controlling the focal gap is important for purposes of precision in emitting fluid. 
     It would, therefore, be advantageous to provide a head that is assembled without the use of epoxy. Such a head would be easier to assemble and would avoid the problems associated with the lack of compatibility of certain epoxy materials and the ink. It would also be advantageous to provide a head with improved focal gap control. 
     The present invention contemplates a new guleless acoustic ink printhead and a method of assembling the printhead that resolves the above-referenced difficulties and others. 
     SUMMARY OF THE INVENTION 
     A method and apparatus relating to an improved acoustic fluid emitting head, e.g. an acoustic ink printhead, are provided. 
     In one aspect of the invention, the apparatus comprises a glass substrate having lenses with emitters positioned thereon, a first frame positioned to support the glass substrate—the first frame having a flange extending therefrom, a first plate having a first portion with apertures defined therein, a second portion and a third portion—the apertures being positioned in alignment with the lenses of the glass substrate and separated from the lenses by a predetermined distance to establish a focal gap, a second frame positioned to support the first plate, a first sealing member disposed between the first plate and the second frame, a second sealing member disposed between the flange of the first frame and the second frame, a second plate positioned between the second portion of the first plate and the glass substrate—the second plate having corrugations defined therein, wherein the third portion of the first plate is disposed at an angle relative to the first and second portions and is connected to the second frame, and further wherein the flange of the first frame is connected to the second frame such that the glass substrate is maintained in a position between the first frame and the first plate. 
     In another aspect of the invention, the apparatus comprises an elastomer cushion and seal member positioned between the first frame and the glass substrate. 
     In another aspect of the invention, the flange is a deformable spring plate. 
     In another aspect of the invention, the apparatus comprises a fold between the second and third portions of the first plate. 
     In another aspect of the invention, the first sealing member is an elastomer gasket. 
     In another aspect of the invention, the second sealing member is an elastomer gasket. 
     In another aspect of the invention, the second frame includes a recess into which the elastomer gasket is disposed. 
     In another aspect of the invention, the second frame includes a recess into which the elastomer gasket is disposed. 
     In another aspect of the invention, the corrugations of the second plate are disposed to facilitate fluid flow. 
     In another aspect of the invention, the apparatus comprises a spot weld to connect the third portion of the first plate to the second frame. 
     In another aspect of the invention, the apparatus comprises a spot weld to connect the flange of the first frame to the second frame. 
     In another aspect of the invention, the apparatus comprises a fluid path extending between the first and second frames and through the corrugations of the second plate and the focal gap. 
     In another aspect of the invention, the apparatus comprises a tab positioned to align the glass substrate on the first frame. 
     In another aspect of the invention, the method comprises steps of folding the first plate such that a fold demarcates the second portion from the third portion, positioning the first sealing member in the first recess of the second frame, connecting the first plate to the second frame such that the first sealing member is compressed between the third portion of the first plate and the second frame, positioning the glass substrate to be supported by the first frame, maintaining the position of the glass substrate relative to the first frame with tabs extending from the first frame, positioning the second sealing member in the second recess of the second frame, positioning the second plate on a second portion of the glass substrate, positioning the first plate over the glass substrate and the second plate such that the first portion of the first plate is in alignment with the first portion of the glass substrate such that a focal gap is established between the first portion of the first plate and the first portion of the glass substrate and such that the second plate is positioned between the second portion of the first plate and the second portion of the glass substrate and connecting the flange of the first frame to the second frame such that the second sealing member is compressed between the flange of the first frame and the second frame. 
     In another aspect of the invention, the connecting of the first plate to the second frame comprises spot welding. 
     In another aspect of the invention, the connecting of the flange and the second frame comprises spot welding. 
     In another aspect of the invention, the apparatus comprises a glass substrate having lenses of acoustic emitters positioned thereon, a first frame positioned to support the glass substrate, a plate with apertures defined therein that are aligned with the lenses, a second frame positioned to support the plate, a first sealing member disposed between the plate and the second frame, a second sealing member disposed between the first frame and the second frame and a spacer positioned between the plate and the glass substrate, wherein the plate is connected to the second frame such that first sealing member is compressed, and further wherein the first frame is connected to the second frame such that the second sealing member is compressed and the glass substrate is maintained in a position between the first frame and the spacer and the plate whereby a focal gap is maintained between the glass substrate and the spacer. 
     In another aspect of the invention, the spacer has corrugations defined therein. 
     In another aspect of the invention, the apparatus comprises a spot weld to connect the first plate to the second frame. 
     In another aspect of the invention, the apparatus comprises a spot weld to connect the first frame to the second frame. 
     Further scope of the applicability of the present invention will become apparent from the detailed description provided below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The present invention exists in the construction, arrangement, in combination of the various parts of the device, and steps of the method, whereby the objects contemplated are attained as hereinafter more fully set forth, specifically pointed out in the claims, and illustrated in the accompanying drawings in which: 
     FIG. 1 is an illustration of an acoustic fluid emitting element; 
     FIG. 2 is an illustration of a preferred embodiment of an acoustic fluid emitting head according to the present invention; 
     FIG. 3 is a cross-sectional view of a portion of the head of FIG. 2; 
     FIG. 4 is a side view of a portion of the spacer plate of FIG. 3; and, 
     FIG. 5 is a flowchart illustrating a preferred assembly operation for the head shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring back now to the drawings wherein the showings are for purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same, FIG. 2 provides a view of the overall preferred apparatus according to the present invention. As shown in representative form, an acoustic fluid emission head, e.g. an acoustic ink printhead,  110  has a base portion  112  and an emitting portion  114 . End portions of the head (one of which is shown in simplified form) may take a variety of forms as a function of the precise head configuration, which may vary. 
     The base portion  112  has included therein a variety of components well known to those versed in the field of acoustic fluid emission. For example, the base portion  112  may include electronics for controlling the operation of the head and fluid delivery components, e.g. manifolds, for facilitating proper delivery of fluid to the emitting portion of the head. 
     The emitting portion  114  includes an aperture plate  116  disposed thereon. The plate  116  has a first portion  118  that has an aperture array positioned therein, second portions  120  adjacent the first portion, and a third portion  122  that is delineated from the second portion by a fold  124 . It is to be appreciated that the apertures of the aperture array align with emitters having lenses as shown in, for example, FIG.  1 . 
     Also shown in FIG. 2 is a frame  126  (preferably formed of metal) positioned to support the aperture plate  116 . The frame  126  may take a variety of forms to achieve this objective as well as facilitate proper sealing of the printhead. The frame  126  preferably is disposed around the periphery of the printhead and, at its ends, generally conforms to the shape of the angled aperture plate, as will be apparent from the representative view shown in FIG.  2 . It should be appreciated that the frame  126  may be unitary or may be comprised of a number of components suitably joined and/or scaled. 
     Significantly, the aperture plate  116  is connected to the frame  126  by connections representatively shown at  128 . The connections are shown as being disposed along the bottom, generally straight edge of the aperture plate but it may be desirable in some circumstances to provide connections elsewhere, such as along the angled side edges of the plate. While the preferred form of the invention uses a plurality of spot welds as the connectors  128 , as will be further described below, any suitable connection devices or techniques that accommodate the features of the present invention will suffice. For example, screws, pins or rivets could be suitably used in place of or in conjunction with the spot welds. It will be further appreciated by those skilled in the art that the left side of the head that is partially obscured in the figure includes components substantially identical to those shown on the right side that is in view. 
     Referring now to FIG. 3 wherein a cross-sectional view of a portion of the head  110  is depicted, it will be seen that a glass substrate  150  is supported by a frame  152 . The glass substrate  150  extends along the length of the printhead and has positioned thereon lenses, representatively shown at  151 , aligned with the apertures of the aperture array of the first portion  118  of the plate  116 . Of course, those of skill in the art will appreciate that, although not shown for simplicity, other elements of the acoustic emitters (such as those shown in FIG.  1 —e.g. electrodes, piezoelectric layers, etc.) cooperate with the lenses and apertures to emit fluid from the device, as illustrated and described in connection with FIG.  1 . In addition, it should be recognized that significant portions of the right side of the head as shown in FIG. 3 are not shown but are identical and complementary to those illustrated on the left side. 
     The frame  152 , preferably formed of metal, may vary in configuration but, as described herein, extends around an inner periphery of the printhead and is sized and configured to support the substrate  150 . For example, the frame  152  preferably is generally rectangular in shape. The frame  152  may be comprised of a unitary structure or a number of components suitably joined and/or sealed. The frame  152  has connected thereto tabs representatively shown at  154  that are suitably positioned to maintain the glass substrate  150  in position. These tabs may vary in number and location and may be connected to the frame  152  in a variety of known manners. A cushion and seal member  156  is also disposed between the glass layer  150  and the frame  152 . The member  156  may take a variety of forms but preferably is formed of an elastomer or foam material and is disposed along the periphery or a top portion of the frame  152 . 
     In addition, the frame  152  includes a flange portion  158  that extends along a bottom portion thereof to act as a deformable spring plate. The flange  158  is connected to the frame  126  via a connection  160 . As with the connection represented at  128 , the connections at  160  may take a variety of forms including but not limited to spot welds, screws, pins, or rivets. 
     A sealing member  162  is disposed between the flange  158  and the frame  126  around the circumference or periphery of the head. As such, the sealing member  162  lies generally in a single plane. In this regard, a recess  166  is preferably provided in the frame  126  to accommodate the sealing member  162 . 
     In addition, a sealing member  164  is provided between the frame  126  and the third portions  122  of the plate  116  along the length of the head and substantially along the angled edge of plate  116 . In this regard, the sealing member  164  is not disposed in a single plane but follows the shape of the plate  116 , which is angled as shown in FIG. 2 and 3. Similarly, a recess  168  is provided to accommodate the sealing member  164 . 
     It should be recognized that the sealing members  162  and  164  are preferably gaskets formed of an elastomer material. The gaskets may be shaped as o-rings or may be rectangular in form. In any configuration, the gaskets are preferably sized and configured to conform to the recess or desired shape to accomplish sealing. The recesses should be formed to suitably house these gaskets, maintain the position of the gaskets and allow for sufficient protrusion of the gaskets from the recesses to effect sealing. However, it should be appreciated that various sealing techniques could be used to attain the objectives of the invention, not all of which would require gaskets and/or recesses. 
     Further, a spacer plate, or spacer,  170  is provided between the plate  116  and the glass substrate  150  on both sides of the printhead. Preferably, spacer plates  170  are positioned between the second portions  120  of the plate  116  and portions of the glass substrate that do not have lenses formed thereon. The spacer plates  170  each preferably has corrugations defined therein. In this regard, a spacer plate  170  preferably is formed of 3×125 mil stainless steel ribbon and is corrugated to a dimension to provide a focal gap f between the first portion  118  of plate  116  and the glass substrate  150 . The corrugations are aligned across the width of the head (left to right in FIG. 3) to accommodate the fluid flow indicated by the arrows in FIG.  3 . Preferably, the corrugations provide about 75% transparency to minimize impedance to lateral fluid flow, and the fine pitch assures even fluid flow across the head. In addition, the spacer plate is preferably extremely stiff and experiences negligible compression under the force necessary to maintain the focal gap. Of course, it is to be recognized that the spacer may take a variety of forms provided that the spacer is of a configuration and positioned to maintain the focal gap f and fluid flow. 
     Referring now to FIG. 4, a side view of a preferred spacer plate  170  is shown. The plate  170  has formed therein corrugations  172  that define an effective thickness of the plate  170  to substantially correspond to the focal gap f, also shown in FIG.  3 . It should be appreciated that the corrugations  172  may be formed by any suitable techniques including those that are well known in the metal and wire bending field—provided that the resultant plate achieves the objectives of the invention. 
     To obtain the configuration shown in FIGS. 2-4, the aperture plate  116  (preferably approximately 100 micrometers thick) is first folded to approximately 55° (shown for example at  124  after connection) and spot welded to the frame  126  (shown for example at  128 ) near its outer edges. The frame  126  is beveled at approximately 45° and has the sealing member  164  positioned in the recess  168 . The angle discrepancy between the fold of the plate  116  and the frame  126  gives the aperture plate  116  a downward bow to be counteracted by the upward force of the spacer plate(s)  170 . Meanwhile, the glass substrate  150  containing the Fresnel lenses  151  and the elastomer cushion and seal member  156  are captured firmly by the tabs  154  of the frame  152 . The bottom outer flange  158  of the frame  152  is preferably thin enough to deflect when the frame  152  and glass  150  are pressed up into the spacer(s)  170  and aperture plate  116 . This ensures constant pressure against the spacer  170  over printhead life even if the cushion and seal member  156  takes a “set”. The connection  160 , e.g. a second set of spot welds which are suitably placed, substantially completes printhead assembly, with the exception of, for example, ink manifold and circuitry attachment. Ink entry and exit holes are not shown. 
     More specifically, referring now to FIG. 5, a method  500  of assembling the head  110  is illustrated in flowchart form. It is to be appreciated, however, that the particular order of the recited steps of this method may vary as a function of, for example, the preferences of the assembler or the equipment available in the assembly process. The steps themselves may also likewise vary. An important consideration in the assembly process, however, is that sufficient compression should be applied to the components of the head when it is being assembled so that, once the connections are made to complete assembly, the components maintain their position and the focal gap is maintained. 
     Initially, the plate  116  is folded such that a fold  124  demarcates the second portion  120  from the third portion  122  of the plate  116  on each side of the print head, of course (step  502 ). The sealing member  164  is advantageously positioned in the recess  168  of the frame  126  (step  504 ). The plate  116 , i.e. portion  122 , is connected to the frame  126  (on both sides of the plate/printhead) such that the first member  164  is compressed between the third portions  122  of the plate  116  and the frame  126  (step  506 ). The sealing member will also be compressed along the angled edge of the plate  116 . Because of the differences in the angles of the fold and the bevel of the frame  126  as noted above, the third portions  122  of the plate will require a force to be applied to properly position the plate  116  for connection. 
     Steps  502 - 506  comprise the steps necessary to connect the aperture plate to the frame  126 . Before final assembly of the printhead, it is also important (before, after or concurrently with the steps  502 - 506 ) to suitably position the glass substrate  150  on the frame  152 . In this regard, the tabs  154  are positioned on, or attached to, the frame  152  at locations within the printhead that will facilitate retention of the glass substrate on the frame  152  (step  508 ). Next, the cushion and seal member  156  is positioned on the frame  152  to be retained in position by the tabs (step  510 ). The substrate  150  is then pressed into position on the member  156  and between the tabs (step  512 ). 
     Once the steps  502 - 506  and steps  508 - 512  are completed, the resultant combinations of components are ready for final assembly into the printhead. In this regard, a sealing member  162  is positioned in the recess  166  of the frame  126  in a plane around the periphery of the printhead and/or frame  126  (step  514 ). In this configuration, on each side of the printhead, a spacer plate  170  is positioned between a second portion of the first plate  116  and portions of the glass substrate  150  lacking lenses (step  516 ). The plate  116  is then positioned over the glass substrate  150  and the spacer plate(s)  170  such that the first portion  118  of the first plate  116  is aligned with the lenses of the emitters on the glass substrate  150  and such that a focal gap f is established therebetween (step  518 ). The flange portion  158  of the frame  152  is then connected to the frame  126  at appropriate locations around the printhead such that the sealing member  162  is compressed between the flange  158  and the frame (step  520 ). In this configuration, the flange portion will act as a spring plate and provide compression to the components of the head. 
     It is to be appreciated, as noted, that these steps may be accomplished in any suitable order but, preferably, the steps entail compressing the components of the printhead together bending the third portion of the plate into position for attachment and spot welding the components at locations such as  128  and  160  in order to maintain a suitable level of compression. The compressive forces maintained in the printhead generate suitable forces on the aperture plate  116  and, consequently the spacer plate, to maintain the focal gap. 
     Replacement of epoxy by elastomer seals has numerous advantages. 1) The delamination failure mode is eliminated. 2) Cure time is eliminated. 3) Elastomer lifetime projections are easily made by measuring their stiffness over time at elevated temperatures. 4) Several elastomers are reliable and chemically inert even at the higher temperatures of 150° C. required for phase-change inks, including silicone, Viton and Kalrez. 5) Spring-loaded focal gap should be more stable than that of present epoxy bonded printheads. 6) The requirement to match thermal expansion of the aperture plate and printhead frame to the glass is relaxed, because there are no glue joints to shear off during assembly. Since alignment of apertures to lenses is needed only at the fixed operating temperature of the printhead, it may be possible to make both the aperture plate and the frames from stainless steel, thereby eliminating corrosion of alloy  42  in ink. 
     The above description merely provides a disclosure of particular embodiments of the invention and is not intended for the purposes of limiting the same thereto. As such, the invention is not limited to only the above-described embodiments. Rather, it is recognized that one skilled in the art could conceive alternative embodiments that fall within the scope of the invention.