Patent Publication Number: US-2007120896-A1

Title: Drop generator

Description:
BACKGROUND  
      The subject disclosure is generally directed to drop emitting apparatus including, for example, drop jetting devices.  
      Drop on demand ink jet technology for producing printed media has been employed in commercial products such as printers, plotters, and facsimile machines. Generally, an ink jet image is formed by selective placement on a receiver surface of ink drops emitted by a plurality of drop generators implemented in a printhead or a printhead assembly. For example, the printhead assembly and the receiver surface are caused to move relative to each other, and drop generators are controlled to emit drops at appropriate times, for example by an appropriate controller. The receiver surface can be a transfer surface or a print medium such as paper. In the case of a transfer surface, the image printed thereon is subsequently transferred to an output print medium such as paper. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a schematic block diagram of an embodiment of a drop-on-demand drop emitting apparatus.  
       FIG. 2  is a schematic block diagram of an embodiment of a drop generator that can be employed in the drop emitting apparatus of  FIG. 1 .  
       FIG. 3  is a schematic elevational view of an embodiment of an ink jet printhead assembly.  
       FIG. 4  is a schematic cross-sectional view of an embodiment of a drop generator.  
       FIG. 5  is a schematic view of an embodiment of a drop generator.  
       FIG. 6  is a schematic view of another embodiment of a drop generator. 
    
    
     DETAILED DESCRIPTION  
       FIG. 1  is a schematic block diagram of an embodiment of a drop-on-demand printing apparatus that includes a controller  10  and a printhead assembly  20  that can include a plurality of drop emitting drop generators. The controller  10  selectively energizes the drop generators by providing a respective drive signal to each drop generator. Each of the drop generators can employ a piezoelectric transducer. As other examples, each of the drop generators can employ a shear-mode transducer, an annular constrictive transducer, an electrostrictive transducer, an electromagnetic transducer, or a magnetorestrictive transducer. The printhead assembly  20  can be formed of a stack of laminated sheets or plates, such as of stainless steel.  
       FIG. 2  is a schematic block diagram of an embodiment of a drop generator  30  that can be employed in the printhead assembly  20  of the printing apparatus shown in  FIG. 1 . The drop generator  30  includes an inlet channel  31  that receives ink  33  from a manifold, reservoir or other ink containing structure. The ink  33  flows into an ink pressure or pump chamber  35  that is bounded on one side, for example, by a flexible diaphragm  37 . An electromechanical transducer  39  is attached to the flexible diaphragm  37  and can overlie the pressure chamber  35 , for example. The electromechanical transducer  39  can be a piezoelectric transducer that includes a piezo element  41  disposed for example between electrodes  43  that receive drop firing and non-firing signals from the controller  10 . Actuation of the electromechanical transducer  39  causes ink to flow from the pressure chamber  35  through an outlet channel  45  to a drop forming nozzle or orifice  47 , from which an ink drop  49  is emitted toward a receiver medium  48  that can be a transfer surface, for example.  
      The ink  33  can be melted or phase changed solid ink, and the electromechanical transducer  39  can be a piezoelectric transducer that is operated in a bending mode, for example.  
       FIG. 3  is a schematic elevational view of an embodiment of an ink jet printhead assembly  20  that can implement a plurality of drop generators  30  ( FIG. 2 ) as an array of drop generators. The ink jet printhead assembly includes a fluid channel layer or substructure  131 , a diaphragm layer  137  attached to the fluid channel layer  131 , and transducer layer  139  attached to the diaphragm layer  137 . The fluid channel layer  131  implements the fluid channels and chambers of the drop generators  30 , while the diaphragm layer  137  implements the diaphragms  37  of the drop generators. The transducer layer  139  implements the piezoelectric transducers  39  of the drop generators  30 . The nozzles of the drop generators  30 . are disposed on an outside surface  131 A of the fluid channel layer  131  that is opposite the diaphragm layer  137 , for example.  
      By way of illustrative example, the diaphragm layer  137  comprises a metal plate or sheet such as stainless steel that is attached or bonded to the fluid channel layer  131 . Also by way of illustrative example, the fluid channel layer  131  can comprise a laminar stack of plates or sheets, such as stainless steel.  
       FIG. 4  schematically illustrates an embodiment of a drop generator that includes a pressure chamber  35  defined by chamber walls  235 , a diaphragm  37  disposed on the chamber walls  235  and overlying the pressure chamber  35 , and a piezoelectric transducer  39  having a bottom surface attached to the diaphragm  37 . The diaphragm  37  includes at least one recess, relief, groove, kerf or indentation  51  that is subjacent and underlies an associated edge or peripheral portion  239  of the piezoelectric transducer  39  such that the edge or peripheral portion  239  overhangs or overlies the recess which extends transversely from the transducer beyond the associated edge or peripheral portion. The recess can generally follow a contour of the associated peripheral portion. The recess can partially overlie a portion of the pressure chamber  35 .  
      More generally, the diaphragm includes at least one recess, relief, groove, kerf or indentation  51  that partially underlies a portion of the periphery or outer edge of the piezoelectric transducer such that such portion of the periphery of the piezoelectric transducer overhangs the recess and is not in contact with the diaphragm. The portion of the diaphragm that is in contact with the piezoelectric transducer can be considered an attachment region and comprises an area that is less than the area of the bottom surface of the piezoelectric transducer.  
      By way of illustrative example, the at least one recess, relief, groove, kerf or indentation  51  can be formed in a diaphragm, which is then attached to the chamber wall. The piezoelectric transducer is then attached to the diaphragm. Alternatively, the recess or recesses can be formed after a diaphragm is attached to the chamber wall. By way of illustrative examples, the recess or recesses can be formed by chemical etching, laser etching, laser ablation, machining, or other suitable process.  
      Each recess  51  can be filled with a fill material  151  such as a thermoplastic, thermoset, or other elastic or viscoelastic material having a modulus that is less than the modulus of the piezoelectric transducer or diaphragm material.  
      As illustrated in  FIG. 5 , an embodiment of the diaphragm  37  can include a single recess  51  that generally follows the entire periphery of the piezoelectric transducer  39  so as to form a closed loop. In such implementation, the piezoelectric transducer  39  is attached to a subjacent island portion  37 A of the diaphragm  37 . The island portion  37 A can completely underlap the piezoelectric transducer  39  such that the entire periphery of the piezoelectric transducer  39  can extend over the single closed loop recess. Also, the island portion  37 A of the diaphragm  37  to which the piezoelectric transducer  39  is attached can be completely within a projection of the inner surface of the chamber wall (i.e., within a projection of the outer boundary of the pressure chamber).  
      As illustrated in  FIG. 6 , another embodiment of the diaphragm  37  can include a first recess  51  and a second recess  51  that are generally opposite each other.  
      Each of the at least one recess  51  can overlie a portion of a chamber wall  235  and a portion of the pressure chamber, whereby the transverse extent of a recess  51  spans a portion of a projection of a subjacent outer boundary of the pressure chamber  35 , for example, as generally illustrated in  FIG. 4 .  
      By way of further illustrative example, the piezoelectric transducer  39  can extend transversely beyond a portion of a projection of the outer boundary of the associated pressure chamber  35 .  
      The disclosed structure can provide for reduced sensitivity to transducer alignment error, reduced cross-talk between drop generators and reduced firing energy requirements.  
      The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.