Abstract:
According to an embodiment of the present invention, a deflection electrode assembly is provided for use in a continuous ink jet printer of the type which projects a stream of ink drops toward a substrate and controls placement of the ink drops on the substrate by selectively charging the individual ink drops and passing the charged ink drops through a deflection field created by the deflection electrode assembly. The deflection electrode assembly includes a high voltage electrode, a low voltage electrode, and an insulating housing which positions the high and low voltage electrodes in a predetermined spaced relationship along the ink drop stream. The insulating housing also has an internal resistor in electrical connection to the high voltage electrode and an external circuit. The insulating housing also contains an insulating member which supports the high voltage electrode as well as minimizes the possibility for arcing between the two electrodes.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims priority of provisional application Ser. No. 60/581,045 filed on Jun. 17 2004. 
     
    
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     [Not Applicable] 
       MICROFICHE/COPYRIGHT REFERENCE  
       [0003]     [Not Applicable] 
       BACKGROUND OF THE INVENTION  
       [0004]     The present invention relates to ink jet printing, and in particular to an improved deflection electrode assembly for a continuous ink jet printer.  
         [0005]     Continuous ink jet printers are well known in the field of industrial coding and marking, and are widely used for printing information, such as expiry dates, on various types of substrate passing the printer on production lines. As shown in  FIG. 1 , a jet of ink is broken up into a regular stream of uniform ink drops by an oscillating piezoelectric element. The drops then pass a charging electrode where the individual drops are charged to selected voltages. The drops then pass through a transverse electric field (deflection field) provided across a pair of deflection electrodes. Each drop is deflected by an amount that depends on its respective charge. If a drop is uncharged, it will pass through the deflection electrodes without deflection. Uncharged and slightly charged drops are collected in a catcher and returned to the ink supply for reuse. A drop following a trajectory that misses the catcher will impinge on the substrate at a point determined by the charge on the drop. Often, each charged drop is interspersed by a guard drop with substantially no charge to decrease electrostatic and aerodynamic interaction between charged drops. As the substrate moves past the printer, the placement of the drop on the substrate in the direction of motion of the substrate will have a component determined by the time at which the drop is released. The direction of motion of the substrate will hereinafter be referred to as the horizontal direction, and the direction perpendicular to this, in the plane of the substrate will hereinafter be referred to as the vertical direction. These directions are unrelated to the orientation of the substrate and printer in space. If the drops are deflected vertically, the placement of a drop in the vertical and horizontal direction is determined both by the charge on the drop and the position of the substrate.  
         [0006]     As shown in  FIG. 1 , the print head of a continuous ink jet printer is often composed of a number of individual parts. For instance, the print head often contains a support frame, a low voltage electrode, a high voltage electrode, a resistor, an oscillating piezoelectric element, insulation, and a catcher. The high voltage electrode and low voltage electrode are generally separate and distinct pieces. The low voltage electrode is generally mounted to a support frame (not shown) for grounding. The high voltage electrode is typically connected in series with a resistor. Generally, the resistor limits discharge energy between the high voltage and low voltage electrodes under fault conditions.  
         [0007]     One lead of the resistor is typically electrically connected to the high voltage electrode, and the other lead of the resistor is typically electrically connected to an external power circuit. The resistor is typically located within the print head, as shown in  FIG. 1 . As such, the environment of the resistor is typically filled with corrosive inks and cleaning solutions which may attack and compromise the functionality of the resistor. In order to protect the resistor from its harsh environment, the resistor is typically wrapped in sealing materials, which extend several inches from the ends of the resistor. The wrapping results in a stiff cable which is difficult to route and place among various tubes and lines during assembly and maintenance of the print head. Further, over time, the corrosive liquids can penetrate the wrappings, causing the resistor to fail. Accordingly, it is desirable to locate and shield the resistor from corrosive elements without wrapping the resistor in sealing materials during installation.  
         [0008]     Also shown in  FIG. 1 , are the high voltage electrode and the low voltage electrode. The strength of the defection field, and thus proper operation of the ink jet, is a function of the spacing between the high voltage electrode and the low voltage electrode. If the gap between the electrodes is not optimized, the strength of the deflection field may be compromised, resulting in poor print quality and/or generating printer faults due to drops being deflected in undesirable locations.  
         [0009]     The high voltage electrode and low voltage electrode are typically mounted separately to support structure within the printhead. Such mounting configuration typically requires a manual configuration of the gap between the high voltage electrode and the low voltage electrode. Manual configuration of the gap between the electrodes is prone to human error, thus exposing the printer to sub-optimal performance. Accordingly, it is desirable to have an assembly in which the spacing between the electrodes is predetermined, automatic, and optimized.  
         [0010]      FIG. 1  also illustrates a dielectric insulator that may be used to prevent arching from the edges of a high voltage electrode to the ground electrode. Typically, the insulation is a loose piece, which is vulnerable to coming off during cleaning, or other operations. If the insulation does come off, the high voltage electrode may arc to the low voltage electrode, and the ink jet will operate improperly. Accordingly, it is desirable to have a special insulation which is robust during operation and maintenance.  
         [0011]     Therefore, a need exists for a system and method for facilitating easier installation and improving robustness of a continuous ink jet printer. Such a system and method may protect a resistor from a corrosive environment without being wrapped. Moreover, such a system and method may easily optimize the space between the high voltage electrode and low voltage electrode. Furthermore, such a system and method may incorporate insulation so it is not easily detached.  
       BRIEF SUMMARY OF THE INVENTION  
       [0012]     According to certain aspects of an embodiment of the present invention, a deflection electrode assembly is provided for use in a continuous ink jet printer of the type which projects a stream of ink drops toward a substrate and controls placement of the ink drops on the substrate by selectively charging the individual ink drops and passing the charged ink drops through an electric field created by the deflection electrode assembly. The deflection electrode assembly includes a high voltage electrode, a low voltage electrode, and an insulating housing for positioning the high and low voltage electrodes in a predetermined spaced relationship along the ink drop stream. The insulating housing has an opening for supporting the high voltage electrode at a predetermined distance from the low voltage electrode. Moreover, a portion of the insulating housing is partially between the high voltage electrode and the low voltage electrode. The portion of the insulating housing between the high voltage electrode and the low voltage electrode minimizes arcing by exposing the high voltage electrode along the path of the ink drop stream. The deflection electrode assembly further comprises a resistor which is hermetically sealed within the insulating housing. The resistor is connected in series between an external, high voltage power source and the high voltage electrode. Placing the resistor inside the insulating housing minimizes the resistor&#39;s exposure to corrosive elements and simplifies installation.  
     
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0013]      FIG. 1  shows the operation of a typical continuous ink jet printer and print head.  
         [0014]      FIG. 2  illustrates certain aspects of a deflection electrode assembly according to certain aspects of a specific embodiment of the present invention.  
         [0015]      FIG. 3  illustrates an exploded bottom view of an embodiment of the present invention.  
         [0016]      FIG. 4  illustrates a top, transparent view of an embodiment of the present invention.  
         [0017]      FIG. 5  illustrates a set screw from the deflection electrode assembly of  FIG. 2  and  FIG. 4 .  
         [0018]      FIG. 6  illustrates a threaded insert from the deflection electrode assembly of  FIG. 2  and  FIG. 4 .  
         [0019]      FIG. 7  is a front view of an embodiment of the present invention.  
         [0020]      FIG. 8  is a rear view of an embodiment of the present invention.  
         [0021]      FIG. 9  is a bottom view with the low voltage electrode mounted to the insulating housing.  
         [0022]      FIG. 10  is a top, opaque view of an embodiment of the present invention.  
         [0023]      FIG. 11  is a bottom view of the present invention with the high voltage electrode inserted into the insulating housing and the low voltage electrode removed.  
         [0024]      FIG. 12  is a side view of the present invention with the high voltage electrode inserted into the insulating housing and the low voltage electrode removed.  
         [0025]      FIG. 13  is a prospective view of the low voltage electrode. 
     
    
       [0026]     The foregoing summary, as well as the following detailed description of the preferred embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the preferred embodiments of the present invention, the drawings depict embodiments that are presently preferred. It should be understood, however, that the present invention is not limited to the arrangements and instrumentality shown in the attached drawings.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     Referring to the drawings, a deflection electrode assembly  200  according to certain aspects of an embodiment of the present invention includes a high voltage deflection electrode  210 , a low voltage (or ground) deflection electrode  220 , and an insulating housing  230 . As is explained in greater detail below, the insulating housing  230  functions to maintain the high and low voltage electrodes  210 ,  220  in a predetermined spacing relative to one another. The insulating housing  230  may be formed from any suitable dielectric material, but is preferably plastic. An external circuit (not shown) is connected to the deflection electrodes  210 ,  220  to create a deflection field between the electrodes so that the drops are vertically deflected in relation to their individual charges. For ease of reference herein, the deflection electrodes  210 ,  220  may be referred to as the high voltage deflection electrode  210  and the low voltage deflection electrode  220 , or simply as the high voltage electrode  210  and the low voltage electrode  220 .  
         [0028]     The low voltage deflection electrode  220  may be a generally planar deflection electrode positioned on one side of an ink drop stream (not shown). The ink drop stream is generally the path the ink drops take as the ink drops travel longitudinally between the high voltage electrode  210  and the low voltage electrode  220 . The low voltage deflection electrode  220  may also include a mounting portion  250 , for securing the low voltage deflection electrode  220  to a support frame (not shown) or other mounting structure in the print head. Specifically, the mounting portion  250  includes mounting apertures  255  that align with reciprocal apertures (not shown) in the support frame. Fasteners (not shown) extend through the apertures  255  in the mounting portion  250  and thread into the apertures in the support frame to secure the low voltage electrode  220  to the support frame in an electrically grounded relationship. This connection fixes the location of the low voltage electrode  220  on the support frame, and, hence, in relation to the other print head components, such as the drop generator and the charge electrode. An adjustment mechanism (not shown) is preferably provided for adjusting the position of the low voltage electrode  220  on the support frame to permit the low voltage electrode to be aligned with the ink drop stream.  
         [0029]     The high voltage deflection electrode  210  extends along the ink drop stream at a location opposite the low voltage deflection electrode  220 . The electrodes  210 ,  220  are spaced to define a gap  240  for the ink drop stream. The high voltage electrode  210  generally includes a front portion  212  and a rear portion  214  (see  FIG. 3 ). The rear portion  214  extends generally parallel to the low voltage deflection electrode  220 , whereas the front portion  212  angles away from the low voltage electrode  220  to generally conform to the path of the charged drops. The high voltage electrode  210  further includes a mounting bracket  225  for securing the high voltage electrode  210  to the insulating housing  230 . The mounting bracket  225  is in electrical connection with a screw  228 , which as will be shown below, is in electrical connection with an external power source through a resistor  310 .  
         [0030]     The insulating housing  230  functions to maintain the high and low voltage electrodes  210 ,  220  in a predetermined spaced relationship along the ink drop stream  240 . Specifically, the rear portion  214  of the high voltage electrode  210  slides into an opening  260  in the insulating housing  230 . The high voltage electrode is then secured to the insulating housing  230  by the mounting bracket  225  and the screw  228 . Since the low voltage electrode  220  is also fastened to the insulating housing  230 , the two electrodes are maintained in a predetermined spaced relationship (or gap)  240  relative to one another. As a result, mounting the electrodes  210 ,  220  in the print head is greatly simplified in comparison to prior designs in which the high and low voltage electrodes are separately mounted to the print head. In particular, the present design eliminates the need to field adjust the gap  240  between the high and low voltage electrodes because this relationship is precisely controlled by the precision manufactured insulating housing  230 .  
         [0031]      FIG. 3  shows an exploded bottom view of an embodiment of the present invention. The high voltage electrode  210 , the screw  228 , and the low voltage electrode  220  shown in  FIG. 2  are shown removed from the insulating housing  230  in  FIG. 3 . Also shown in  FIG. 3  are a resistor  310  and a metallic contact sleeve  320  as removed from a hole  370  in the insulating housing  230 . A lead  312  is also shown connected to the resistor  310 .  
         [0032]     The bottom portion of the high voltage electrode  210 , which in operation is facing the low voltage electrode  220 , is shown facing the viewer. The mounting bracket  225  of the high voltage electrode  210  is shown leaning away from the viewer. The view of the insulating housing  230  shows low voltage mounting brackets  330  through which the low voltage electrode  220  is mounted to the insulating housing  230 , e.g. by threaded fasteners (not shown).  
         [0033]     The insulating housing  230  includes an integral insulation member  340  that extends along the rear edge  314  and side edges  316 ,  318  of the high voltage electrode  210 . As shown in  FIG. 3 , the insulating member  340  extends inwardly beyond the edges  314 ,  317 , and  318  of the high voltage electrode  210 . Because the insulating member  340  overlaps the edges  314 ,  316 , and  318  of the rear portion  214  of the high voltage electrode  210 , the tendency for arcing to occur between the high voltage  210  and low voltage  220  electrodes is minimized.  
         [0034]     The insulating member  340  includes a longitudinal opening or void  344 , which exposes the high voltage electrode  210  along the ink drop stream. In the illustrated embodiment, the longitudinal opening  344  is in the form of a generally rectangular slot, but, as will be appreciated, the opening can assume other configurations without departing from the scope of the present invention. Removing the insulating material along the path of the ink drop stream  240  minimizes the deleterious effect that the accumulated micro-satellite drops have on the deflection field. For example, the longitudinal slot  344  may be on the order of 0.12 inches wide and it extends along substantially the entire length of the rear portion  214  of the high voltage electrode  210 . In this respect, the amount of overlap between the insulating member  340  and the rear edge  314  of the high voltage electrode  210  is minimal, so that the high voltage electrode  210  is exposed along the ink drop stream  240  for substantially the entire length of the high voltage electrode  210 . For example, the overlap along the rear edge  314  of the high voltage electrode  210  may be on the order of 0.010 inches.  
         [0035]     High voltage power is delivered to the electrode  210  through a resistor  310 . Specifically, the resistor  310  has a first end (or lead) connected to a power cable  312  and a second end (lead) connected to a metallic contact sleeve  320 . The metallic contact sleeve  320  in turn is in electrical contact with the high voltage electrode  210  through an assembly comprising a set screw  420 , a threaded inset  360  and mounting screw  228 .  
         [0036]     The resistor  310  and metallic contact sleeve  320  are inserted into a hole  370  in the insulating housing  230 . By inserting the resistor  310  into the insulating housing  230 , the resistor is protected from corrosive inks and cleaning solutions. Also, installation of the entire printer head is simplified, as the resistor  310  only has to be connected to an external circuit.  
         [0037]      FIG. 4  and  FIG. 10  show a top view of the embodiment of the present invention.  FIG. 10  illustrates an opaque top view illustrating the insulating housing  230 , the cable  312 , the high voltage electrode  210 , and the screw  228  as assembled.  FIG. 4  illustrates a transparent, close up view of  FIG. 10 .  
         [0038]     In  FIG. 4 , an epoxy  410  is shown around the metallic contact sleeve  320  and resistor  310  within the hole  370 . The epoxy  410  hermetically seals the resistor  310  and metallic contact sleeve  320  within the insulating housing  230 . The epoxy  410  also insulates the opposite leads of the resistor  310  from each other.  
         [0039]     Set screw  420  is in electrical contact with the metallic contact sleeve  320 . The use of the set screw  420  ensures a solid electrical contact with the metallic contact sleeve  320 . The set screw  420  is also in electrical contact with the screw  228  through a threaded insert  360 . The screw  228  is shown screwed into the threaded insert  360 , in contact with the set screw  420  and the high voltage electrode  210 . The screw  228  contacts the high voltage electrode  210  at the mounting portion  225  and supports the high voltage electrode  210  on the insulating housing  230 .  
         [0040]     The threaded insert  360  is in electrical contact with both the metallic contact sleeve  320  and the high voltage electrode  210 . The threaded insert  360  contains threads for receiving screw  228 . The threaded insert  360  and screw  228  serve to mount the high voltage electrode  210  to the insulating housing  230 .  
         [0041]      FIG. 5  further illustrates the set screw  420 . The set screw  420  may be screwed into the threaded insert  360  as a typical screw. The set screw  420  ensures a solid electrical contact with the metallic contact sleeve  320 . The set screw  420  also functions to hold the metallic contact sleeve  320  in place if one desires to remove the screw  228  from the insulating housing  230  for maintenance or repair.  
         [0042]      FIG. 6  further illustrates the threaded insert  360 . The threaded insert  360  is formed from an electrically conductive material, e.g., metal, and functions to provide a path for electrical connection between the metallic contact sleeve  320  and the high voltage electrode  210 . The threaded insert  360  also contributes to the mounting of the high voltage electrode  210  to the insulating housing  230 . Moreover, the location of the threaded insert  360  within the insulating housing  230  contributes to the predetermined spaced relationship of the high voltage and low voltage electrodes  210 ,  220 .  
         [0043]      FIG. 7  illustrates a front view of an embodiment of the present invention.  FIG. 7  illustrates the predetermined spaced relationship between the two electrodes  210 ,  220 . The high voltage electrode  210  is mounted to the insulating housing  230  by the screw  228 . The angle of the front of the high voltage electrode  212  can be seen. The longitudinal opening  344  in the insulating housing  230  can also be seen. As shown in  FIG. 7 , the insulating member  340  shields the edges of the high voltage electrode  210  from the low voltage electrode  220 .  
         [0044]      FIG. 8  illustrates a rear view of an embodiment of the present invention. The rear view illustrates the hole  370  in the insulating housing  230  in which the resistor  310  and metallic contact sleeve  320  are inserted. In operation, the ink drops enter this end of the deflection electrode assembly at the gap  240 . The ink drop stream moves along the gap  240  from back,  FIG. 8 , to front,  FIG. 7 , along the longitudinal opening  344 . The ink drops travel toward the viewer of  FIG. 7  through the gap  240 , i.e. the ink drops exit the deflection electrode assembly from the end displayed in  FIG. 7 .  
         [0045]      FIG. 9  illustrates the bottom view of an embodiment of the present invention. The low voltage electrode  220  is shown connected to the housing  230 . The low voltage electrode  210  includes mounting apertures  380  (see  FIG. 3 ) that are aligned with the low voltage mounting brackets  330 . Fastener  381  (see  FIG. 9 ) extends through the apertures  380  and thread into reciprocal apertures in the mounting brackets  330  to secure the low voltage electrode to the insulating housing  230 .  
         [0046]      FIG. 11  illustrates a bottom view of the present invention with the high voltage electrode  210  inserted into the insulating housing  230 , and the low voltage electrode  220  removed and not shown. In this view, the insulation member  340  that extends along the rear and side edges of the high voltage electrode  210  is visible. As shown in  FIG. 3 , the insulating member  340  extends inwardly beyond the edges of the high voltage electrode and overlaps a portion of the bottom of the high voltage electrode  210 . Because the insulating member  340  overlaps the edges of the rear portion of the high voltage electrode  210 , the tendency for arcing to occur between the high voltage  210  and low voltage  220  electrodes is minimized.  
         [0047]     Also seen in  FIG. 11  is the longitudinal opening or void  344 , which exposes the high voltage electrode  210  along the ink drop stream  240 . In the illustrated embodiment, the longitudinal opening  344  is in the form of a generally rectangular slot. But, as mentioned above and as will be appreciated, the opening can assume other configurations without departing from the scope of the present invention. Removing the insulating material along the path of the ink drop stream  240  minimizes the deleterious effect that the accumulated micro-satellite drops have on the deflection field.  
         [0048]      FIG. 12  illustrates a side view of the present invention with the high voltage electrode  210  inserted into the insulating housing  230  and the low voltage electrode  220  removed. In this view, the low voltage mounting brackets  330  through which the low voltage electrode  220  is mounted to the insulating housing  230  are shown. The size of the mounting brackets may contribute to the predetermined spaced relationship (or gap) between the two electrodes.  
         [0049]      FIG. 13  illustrates the low voltage electrode  220 . The low voltage electrode mounting members  380  are shown. The mounting members  380  are used to mount the low voltage electrode  220  to the insulating housing  230 . The mounting portion  250 , which is also shown, includes the mounting apertures  255 . Fasteners (not shown) extend through the apertures  250  in the mounting portion  250  and thread into the apertures in the support frame to secure the low voltage electrode to the support frame in an electrically grounded relationship.  
         [0050]     In operation of an embodiment, the low voltage electrode mount  250  may secure the deflection electrode assembly  200  as part of a print head on a grounded support frame (not shown). The extension of the low voltage electrode mount  250  contributes to the predetermined spaced relationship between the high and low voltage electrodes  210 ,  220 . The high voltage electrode  210  may be mounted to the insulating housing  230  via the threaded insert  360 , the screw  228 , the high voltage electrode mounting portion  225 , and the insulating member  340 . The insulating member  340  protects the high voltage and low voltage electrodes  210 ,  220  from arcing. The location the high voltage electrode is mounted also contributes to the predetermined spaced relationship between the high and low voltage electrodes  210 ,  220 . An external circuit may control the deflection field created between the high voltage electrode  210  and the low voltage electrode  220  through a resistor  310 , a metallic contact sleeve  320 , a set screw  420 , and a screw  228 . The resistor  210  and metallic contact sleeve  320  are hermetically sealed within the insulating housing  230 . An ink drop stream may be injected into the deflection electrode assembly  200  as part of a print head. Accordingly, ink may be vertically displaced on a substrate.  
         [0051]     Moreover, an embodiment of the invention may be constructed by sealing a resistor  310  within an insulated housing  230 . In the preferred embodiment, the resistor  310  is electrically connected to a metallic contact sleeve  320  which is also sealed within an insulating housing  230 . Next, a high voltage electrode  210  may be positioned on an insulating housing  230  having a predetermined spaced relationship with a low voltage electrode  220  along the ink drop stream.  
         [0052]     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.