Abstract:
An injection molded print head for an assembly of print heads for large scale printing of, e.g., billboards, banners, posters and the like, includes a nozzle plate that is bonded to a manifold plate. The manifold plate is formed with ink-receiving nozzle chambers that are coaxially registered with respective nozzles in the nozzle plate. The bonded manifold and nozzle plates may be removed from the balance of the print head for nozzle cleaning/replacement purposes. A transducer holder supports piezoelectric transducers that are coaxially registered with respective nozzle chambers. A pulse transmitting plate is disposed between the transducer holder and the manifold plate for transmitting energy from the transducers to the nozzle chambers to thereby controllably discharge ink through selected nozzles. The nozzles may be arranged in columns, with each column being canted at an oblique angle relative to the direction of print head movement over the substrate to be printed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to liquid dispensing apparatus and, in representatively illustrated embodiments thereof, more particularly provides piezoelectric print head apparatus and associated methods for use in conjunction with large scale print systems such as those utilized for billboards, banners, posters and the like.  
         [0002]     Large substrates for supporting images used in billboards, banners, posters and the like can be printed with printing machines that incorporate therein a number of individual print heads. Most printing machines of this type move their associated print heads across the substrate and deposit ink from the print heads onto the substrate. To enable the many individual print heads to precisely form the intended image on the substrate the print heads are typically controlled by a suitable printing computer electronically linked to corresponding electrical circuitry in the print heads.  
         [0003]     Conventionally constructed print heads, such as piezoelectric print heads, used in this type of large scale printing apparatus are subject to a variety of well known problems, limitations and disadvantages. For example, due to the very high degree of constructional precision and ink deposition accuracy required of the typical print head, which discharges ink through selectively variable ones of a very closely spaced array of tiny discharge nozzles or orifices, they have typically been fabricated using precision microfabrication technology in which various ink handling portions of a given print head are produced using multi-step precision clean room operations. The use of this very high cost clean room technology undesirably increases the final cost of the print heads, and thus the overall printing machine in which they are operatively incorporated.  
         [0004]     Not only does the fabricational cost of various portions of a typical print head tend to be quite high, but a great degree of precision is normally required to correctly assemble these high cost components into a finished print head having the high requisite degree of ink deposition accuracy. As a result, it is often difficult to maintain a desired level of repeatability in assemblage precision from print head to print head.  
         [0005]     Because of the conventional necessity of fabricating various intricate print head components such as shared wall piezoelectric ink chambers, it has been difficult to construct print heads which have a desirable degree of ruggedness. Due to a combination of their intricacy and requisite precision construction techniques they tend to be undesirably delicate and easily damaged if not handled quite carefully.  
         [0006]     As is well known in the printing arts, the leading cause of failure of conventional print heads is the clogging of their tiny ink jet discharge nozzles or orifices. Once this nozzle clogging occurs (typically due to particulate contaminants present in the ink or drying of the ink on the nozzle), the print head&#39;s operational life is effectively at an end since the nozzle portion of the print head, using conventional print head construction techniques, is permanently affixed to the balance of the print head. This substantially limits cleaning or replacement of the clogged ink discharge nozzle section of the print head except by specially trained technicians.  
         [0007]     The various ink discharge nozzles in a conventional print head are typically formed in a nozzle discharge plate structure which is fixedly secured to the balance of the print head. To provide the nozzle spacing and dimensional accuracy required, it is customary to form the nozzles with a laser prior to securement of the resulting apertured nozzle plate to the balance of the print head in a manner precisely aligning the laser-formed nozzles with associated ink holding chambers in the print head body portion to which the nozzle plate is fixedly secured. The need to do this stems from the necessity of causing the laser to pass through the nozzle plate in the same direction that ink will be forced outwardly through the resulting ink discharge nozzles. Because of this conventional construction technique it is often difficult to correctly align the series of ink discharge nozzles with their associated series of ink holding chambers.  
         [0008]     In one conventional form of an ink dispensing print head the portion thereof in which the ink holding chambers are disposed is formed from a piezoelectric material which rapidly deforms, and then returns to its original configuration, in response to a very short duration pulse of electrical current flowed therethrough and then terminated. To discharge ink from a given discharge nozzle, wall portions of its associated ink holding chamber are piezoelectrically deflected inwardly and then relaxed to trigger the ejection of a small quantity of ink outwardly through the nozzle onto an adjacent substrate. Because each ink holding chamber is not only an ink reservoir, but also an ink driving structure, no two immediately adjacent ink discharge nozzles whose ink chambers share a common deflectable driving wall may be simultaneously “fired” to discharge ink therefrom.  
         [0009]     As may be readily seen from the foregoing, a need exists for improved print head or other liquid dispensing apparatus and associated methods which eliminate or at least substantially reduce the above-mentioned problems, limitations and disadvantages typically associated with conventional print head apparatus and associated methods as generally described above. It is to this need that the present invention is primarily directed.  
       SUMMARY OF THE INVENTION  
       [0010]     In carrying out principles of the present invention, in accordance with representative embodiments thereof, this invention provides specially designed liquid dispensing apparatus and associated methods which are incorporated in an ink jet print head utilized in large scale printing operations such as printing on billboards, banners, posters and carried with other similar print heads for movement along a substrate to be printed upon.  
         [0011]     In a preferred structural arrangement thereof, the print head comprises a nozzle plate formed with plural ink nozzles which representatively face downwardly but could alternatively face upwardly if desired, and a manifold plate engaged with the nozzle plate and formed with plural ink nozzle chambers. A transducer holder mounted over the manifold plate supports plural piezoelectric transducers, each transducer being registered with a respective nozzle chamber which, in turn, is registered with one of the nozzles. A pulse transmitting plate is disposed between the transducer holder and the manifold plate and is used, in response to deflection of the transducers, to transmit energy, in the form of shock waves, from the transducers to the nozzle chambers to force ink outwardly therefrom via their associated nozzles.  
         [0012]     The chambers in the manifold plate serve merely to store the ink forced outwardly through their associated nozzles—their walls are not made of piezoelectric material which must be electrically deflected to force ink out of such nozzles and to laterally confine the ink-driving shock wave passing axially therethrough. This permits both the manifold plate and the transducer holder to be formed as inexpensive injection moldings to thereby provide the print head with a substantial degree of cost reduction and increased ruggedness compared to conventional piezoelectric print heads which depend on piezoelectric ink chamber wall deflection for creating operative ink discharge therefrom.  
         [0013]     The injection molded construction of the print head in its preferred form also substantially simplifies the construction and assembly thereof while maintaining the requisite degree of component-to-component alignment accuracy necessary to obtain the critical precision in the printing process. Further, this unique construction of the print head permits any two immediately adjacent nozzles to be “fired” (i.e., have ink discharged therefrom) simultaneously since their associated ink chamber walls do not have to be piezoelectrically defected to effect ink discharge therefrom.  
         [0014]     The pulse transmitting plate is disposed externally to the ink chambers. When it is desired to discharge ink from one of the nozzles, the pulsed piezoelectric transducer is electrically deflected to in turn exert a force against a portion of the plate overlying the ink chamber communicating with the nozzle to be fired. This plate-received force creates a shock wave which is transmitted through the selected chamber to discharge ink from its nozzle.  
         [0015]     According to another aspect of the invention, a spaced apart series of pulse-dissipating spacer structures are interposed between the manifold plate and the pulse transmitting plate and serve to create between such spacer structures pulse dissipation passages that helps to prevent energy from the created pulse from entering adjacent ink chambers, or at least substantially lessen the pulse energy entering adjacent chambers and undesirably discharging ink therefrom. Such pulse energy dissipation may also be achieved by the formation of a spaced series pulse dissipation cavities on the pulse transmitting plate side of the manifold plate. In an alternate embodiment of the pulse transmitting plate, the plate has lateral projections which are received within inlet end portions of the ink chambers. Accordingly, when a particular portion of the pulse transmitting plate is deflected by its associated piezoelectric member, the resulting pulse energy is transmitted via the deflected plate projection directly into the associated chamber, thereby in effect directing or focusing the pulse energy into the intended ink chamber.  
         [0016]     In accordance with another feature of the invention, the problem of clogging of the nozzles and the chambers in the manifold plate, which is normally the leading cause of print head failure, is uniquely addressed by attaching the nozzle assembly (i.e., the manifold plate and the nozzle plate secured thereto) to the balance of the print head in a manner permitting it to be easily manually removed to permit cleaning of the nozzles and associated ink chambers and replacement of the cleaned nozzle assembly. Alternatively, the removed nozzle assembly may be replaced with another nozzle assembly—either an identical or different nozzle assembly—very quickly, easily and accurately. Representatively, the nozzle assembly is removably and sealingly clamped to the balance of the print head.  
         [0017]     According to a further aspect of the invention, the nozzles in the nozzle plate are arranged thereon in plural columns each defining a nozzle line being canted at an oblique angle, representatively about three degrees, relative to the linear direction of operational movement of the print head. This provides the print head with a greater print resolution, in a direction transverse to such linear direction of operational movement, on the associate substrate to be printed.  
         [0018]     In yet another aspect of the invention the constructional accuracy of the print head is increased by securing the nozzle plate to a side of the manifold plate before the ink discharge nozzles are formed in the nozzle plate. Laser beams directed through the chambers in the manifold plate and onto the attached nozzle plate to form the ink discharge nozzles therein. In this manner the nozzles may be accurately aligned with their associated ink chambers without having to align previously formed nozzles with such chambers after the nozzles are formed in the nozzle plate.  
         [0019]     Representatively, other features are included in the print head including heating apparatus for selectively heating the manifold plate, filter apparatus for filtering liquid supplied to the nozzle chambers, and air removal apparatus for removing air from an interior portion of the print head communicating with the nozzle chambers.  
         [0020]     Principles of the present invention are not limited to print heads, but are also applicable to other types of liquid dispensing apparatus used to meter and/or deposit liquids other than ink. Principles of the invention are similarly not limited to large scale liquid dispensing operations, but are also applicable to smaller scale applications such as in smaller scale print heads, for example those used in personal computer printers.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  is a schematic perspective view of a large scale print head assembly embodying principles of the present invention and disposed over a substrate to be printed;  
         [0022]      FIG. 2  is an enlarged scale bottom (nozzle) side perspective view of an individual print head removed from the  FIG. 1  print head assembly;  
         [0023]      FIG. 3  is a partially exploded perspective view of the print head;  
         [0024]      FIG. 4  is an exploded top side perspective view of the print head;  
         [0025]      FIG. 4A  is an enlarged scale top side detail perspective view of a portion of a manifold plate section of the print head;  
         [0026]      FIG. 5  is a horizontally directed cross-sectional view through the fully assembled print head, with some of the piezoelectric transducer portions thereof having been removed for purposes of illustrative clarity; and  
         [0027]      FIG. 6  is a cross-sectional view through an alternate embodiment of the print head. 
     
    
     DETAILED DESCRIPTION  
       [0028]     Referring initially to  FIG. 1 , a system is shown, generally designated  10 , which includes a print machine  12  bearing plural print heads  14  according to the present invention. The machine  12  with print heads  14  can be moved in the directions indicated by the arrows  16  (along, e.g., a rail  17 ) to deposit ink by ink jet printing methods onto a substrate  18 , under the control of a processor  20 . The substrate  18  may be relatively large, e.g., several feet by several feet, for covering a billboard, banner, poster of the like. While only two print heads  14  are shown, it is to be understood that the print machine  12  may have any number of heads, e.g., four, sixteen, or any other appropriate number.  
         [0029]     Now referring to  FIGS. 2-5 , a first embodiment of the present print head can be seen. The print head includes a nozzle plate  22  that is formed with plural ink nozzles  24 , with each nozzle having a very small diameter, e.g., fifty microns. The nozzle plate  22  may be made of a polymer or metal material. in one embodiment the nozzle plate  22  is a flat parallelepiped-shaped plate having an entrance surface  26  ( FIG. 4 ) and an exit surface  28  ( FIG. 2 ), the nozzles  24  extending from surface to surface. Ink is deposited onto the substrate shown in  FIG. 1  through the nozzles  24 .  
         [0030]     In the embodiment shown in  FIGS. 2-5 , the nozzles  24  are arranged in co-parallel linear columns  30 . In non-limiting embodiments each column  30  may have sixteen nozzles  24 , and the nozzle plate  22  may be formed with thirty two columns  30 . The print head may move over the substrate along the illustrated operational movement line  32 , and each column  30  may be canted with respect to the line  32  of motion by an oblique angle  34 . In one embodiment the angle  34  is an acute angle of about three degrees or so. In this way, as the print head moves across the substrate a nozzle does not follow the exact path as the nozzle in front or behind, but rather a path that is offset by a small amount from the paths of the other nozzles. As understood herein, relatively powerful print control processors have sufficient processing power to account for the offset and use it advantageously.  
         [0031]     As shown, the entrance surface  26  of the nozzle plate  22  may be adhesively bonded to a surface of an injection molded, generally parallelepiped-shaped manifold plate  36 , the bonded-together nozzle plate and manifold plate forming the previously mentioned nozzle assembly. As shown in  FIG. 2 , the manifold plate  36  may be formed with an ink inlet conduit  38  and an ink outlet conduit  40 , between which ink can pass and flow into the cavities described further below.  
         [0032]     Specifically and referring to  FIGS. 4 and 4 A, the manifold plate  36  is formed with plural nozzle chambers  42  that extend all the way through the manifold plate  36 , with each nozzle  24  in the nozzle plate  22  being registered with a respective nozzle chamber  42 . The nozzle chambers  42  may be cylindrical as shown and preferably are coaxial with their respective nozzles  24 . Each nozzle chamber  42  may have a diameter of a millimeter or a bit larger. Ink from the inlet  38  can flow into the nozzle chambers  42 .  
         [0033]     In some implementations and as best shown in  FIGS. 4 and 4 A, spacers  44  may be formed integrally on the manifold plate  36  and may be juxtaposed with the nozzle chambers  42 . In less preferred implementations the spacers may be made separately from the manifold plate and adhered thereto. In the preferred implementation shown, substantially all nozzle chambers  42  are straddled by at least two opposed spacers  44 , it being understood that alternatively, the spacers may be formed on the pulse transmitting plate.  
         [0034]     As shown, the spacers  44  may be parallelepiped-shaped and may extend slightly above the surface  46  into which the nozzle chambers  42  are formed. A barrier structure, representatively a flat pulse transmitting plate  48 , one side of which may be copper, rests on the spacers  44  within a support flange  50  that is formed on the manifold plate  36  and that rises above and circumscribes the surface  46 . The spacers  44  thus slightly space the pulse transmitting plate  48  from the nozzle chambers  42  in the manifold plate  36 , as well as attenuate pulses intended to be directed into a nozzle chamber  42  from propagating to nearby nozzle chambers.  
         [0035]     Additionally, if desired for further pulse energy attenuation laterally outwardly of a nozzle chamber being fired, attenuation cavities  51  may be formed on the manifold plate  36  at what would be the intersection of adjacent spacers  44 , i.e., diagonally relative to the nozzle chambers  42 . Each attenuation cavity  51  may be about a millimeter or so in diameter and about a millimeter or so in depth, or have other suitable dimensions as needed to absorb shock wave energy before it is transmitted to an adjacent ink chamber.  
         [0036]     Returning to  FIG. 4  and as also shown in  FIG. 5 , an injection molded transducer holder  52  is disposed on the manifold plate  36  with the pulse transmitting plate  48  sandwiched therebetween. As shown best in  FIGS. 4 and 5 , the transducer holder  52  supports plural preferably piezoelectric transducers  54 , and each transducer  54  touches the pulse transmitting plate  48  and is registered with a respective nozzle chamber  42  of the manifold plate  36  and, hence, with a respective nozzle  24  in the nozzle plate  22 . Thus, a nozzle chamber  42  may be coaxial not only with its respective nozzle  24  but also with its respective transducer  54 . Like the nozzle chambers  42 , the transducers  54 , which may be made entirely of piezoelectric material or only partially of piezoelectric material, may be cylindrical, or have another suitable shape such as a rectangular shape.  
         [0037]     With respect to the illustrative non-limiting structure of the transducer holder  52  shown, each transducer  54  may be disposed in a respective transducer cavity  56  that is formed during injection molding in a holder section  58  of the transducer holder  52 .  FIG. 5  best shows that, recessed away from the surface of the holder section  58  that contacts the pulse transmitting plate  48  and circumscribing the holder section  58 , is a flange section  60 . The flange section  60  of the transducer holder  52  rests against the support flange  50  of the manifold plate  36 . A seal such as a resilient racetrack-shaped o-ring  62  ( FIGS. 3 and 5 ) is disposed in slight compression between the transducer holder  52  and manifold plate  36  just inboard of the support flange  50 /flange section  60  and, hence, surrounding the pulse transmitting plate  48 . To help engage the manifold plate  36  with the transducer holder  52  in proper registration, one or more locating pins  61  may be formed on the manifold plate  36  and may be closely received into respective pin channels  63  formed in the holder  52 .  
         [0038]     Still referring to  FIGS. 4 and 5 , a printed circuit board (PCB)  64  rests on top of the transducer holder  52  in electrical communication with each transducer  54 . The PCB  64  may be controlled by the processor  20  shown in  FIG. 1 . With the above structure in mind, signals from the PCB  64  may be generated to axially deform transducers  54  as selected by the processor  20 . When a transducer  54  deforms, a deflection is created on the pulse transmitting plate  48 , which relays the pulse, in the form of a shock wave, to the respective nozzle chamber  42  that is registered with the transducer  54 . The spacers  44  serve to confine the pulse to the intended nozzle chamber  42 . In turn, ink is caused to exit the nozzle  24  that is registered with the nozzle chamber  42  to thereby deposit ink onto the substrate  18 .  
         [0039]     Advantageously, the nozzle assembly that is established in the non-limiting embodiment shown by the nozzle plate  22  and manifold plate  36  can be easily manually disengaged from the remaining print head structure for cleaning. Stated differently, the manifold plate  36  may be removably engaged with the transducer holder  52  so that a person can easily disengage the manifold plate  36  (with nozzle plate  22 ) from the transducer holder  52  to clean the nozzles and nozzle chambers, and can then easily reengage the same nozzle assembly with the transducer holder  52  after cleaning. Or, a different nozzle assembly possibly having differently sized nozzles that are suitable for a different type of ink may be engaged with the transducer holder  52 .  
         [0040]     Excluded from the definition of “removably engaged” and “easily manually disengaged” (or “easily manually engaged”) is adhesive bonding, welding of any type, brazing, rf sealing, and riveting. Encompassed within the definition of “removably engaged” and “easily manually disengaged” are threaded fasteners. In a preferred embodiment, however, an engagement member such as one or more clamps  66  ( FIG. 5 ) can be used to clamp the manifold plate  36  (with nozzle plate  22 ) to the transducer holder  52 , such that a person can easily manipulate the clamp  66  without the need for tools to remove the manifold plate  36  from the remainder of the print head structure. The clamp  66  may be a simple metal U-shaped resilient clip that is sized for a snug interference fit around the manifold plate  36 /transducer holder  52 , or a spring loaded alligator-style clamp, or other convenient clamping mechanism that may be easily manually installed and removed.  
         [0041]     The above structure also affords further advantages. For instance, the manifold plate  36  may be formed as shown by injection molding, and the nozzle plate  22  may be a thin polymer or metal but without the nozzles  24  yet formed. Then, the nozzle plate  22  may be adhesively bonded to the manifold plate  36 , and a laser directed through the nozzle chambers  42  (typically sequentially) to form the nozzles  24  in the exposed area of the entrance surface  26  of the nozzle plate  22 . In this way, the nozzles  24  are automatically registered with their respective nozzle chambers  42 , and furthermore the laser beam exits the exit surface  28  of the nozzle plate  22 , leaving a structurally clean exit area where it is most needed, i.e., where ink subsequently exits the nozzle during operation. Further, any two immediately adjacent nozzles  24  can be simultaneously fired since it is not necessary to deflect any of the side walls of their associated chambers  42  to do so.  
         [0042]      FIG. 6  shows a print head  70  that is in all essential respects identical to the print head shown in  FIGS. 2-5 , except that a pulse transmitting plate  72  is formed with plural preferably cylindrical rods  74  extending into respective nozzle chambers  76  of a manifold plate  78 , to further focus shock wave pulses into the desired nozzle  80  of a nozzle plate  82 . The rods  74  may be stiff material, e.g., carbon fiber, and may be projections having non-cylindrical configurations, such as rectangular or other shapes if desired. As representatively illustrated, the bottom ends of the rods  75  are essentially flat. However, the lower rod ends could alternatively have other shapes such as, for example, concave or convex configurations if desired to better focus the shock waves through the ink chambers.  
         [0043]     As schematically depicted in phantom in  FIG. 4 , the print heads illustrated in  FIGS. 2-6  may have other desirable structures incorporated therein if desired. For example, a filter  84  may be installed on the print head, representatively on the ink inlet  38 , to filter out particulate matter in the incoming ink supply. Further, an air removal tube  86  may be coupled to a suitable source or negative pressure and extended into an interior portion of the print head, which communicates with the nozzle chambers, to remove unwanted air from such interior print head portion. Additionally, a heating structure, such as the illustrated electric heating structure  88  imbedded in the manifold plate  36 , may be used to heat the ink as needed to compensate for ink viscosity and/or variations in ambient print head operating temperatures.  
         [0044]     While principles of the present invention have been representatively illustrated as being embodied in a print head, the invention is not limited to print head applications, and may be advantageously utilized in a variety of other types of liquid dispensing apparatus used to meter and/or deposit liquids other than ink.  
         [0045]     The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.  
         [0046]     In such claims, reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more”. It is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. Absent express definitions herein, claim terms are to be given all ordinary and accustomed meanings that are not irreconcilable with the present specification and file history.