Abstract:
A mailing machine print head and carriage that use one or more systems or elements to latch the print head in a controlled location and to guide it into and out of that location in a manner that prevents debris from being transferred to the electrical connector contacts is provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority under 35 U.S.C. section 119(e) from Provisional Patent Application Ser. No. 60/481,859, filed Jan. 5, 2004, entitled POSTAGE METER PRINT HEAD AND CARRIAGE, which is incorporated herein by reference in its entirety. 

   BACKGROUND 
   The illustrative embodiments described in the present application are useful in systems including those for providing funds accounting and evidencing and more particularly are useful in systems including those for providing for accounting of postage and evidence of postage by printing postage indicia on an envelope using an ink jet printer. 
   Mailing machines including postage meters often employ an ink-jet printing unit for printing evidence of postage payment in the form of postage indicia. Systems for printing information on a mailing medium are described in U.S. Pat. No. 6,550,994B2, issued Apr. 22, 2003 to Manduley. 
   The print head of an ink jet printing mechanism such as that in a mailing machine may become inoperable during the life of the printing mechanism. In such a situation, the print head would need to be replaced. If the print heads are removable, they are typically latched into a print head carriage. Many typical printing mechanism systems include latching mechanisms for latching a print head to a print carriage that use a large number of small parts. Using such a large number of small parts adds to the cost and complexity of the printing mechanism. 
   Additionally, such typical systems often do not adequately address that fact that the face of the print head and its surrounding edges may have accumulations of ink and paper dust on them. During the print head removal process, the debris can be transferred to the electrical connector contacts for the print head in the print carriage. Such debris could form an insulating barrier causing the new print head to malfunction. Furthermore, the typical latching mechanism is usually incorporated into the print carriage such that any malfunction or failure of the latching mechanism would require that a technician replace the entire print carriage. 
   Accordingly, the prior art does not provide a print head latching system that prevents or reduces debris accumulation. Furthermore, the prior art does not provide a print head latching system having a small number of parts that are incorporated into the print head. 
   SUMMARY 
   Accordingly, it is an object of the present application to describe illustrative print head latching systems that prevent or reduce debris accumulation. It is an additional object of the present application to describe illustrative print head latching systems having a small number of parts that are incorporated into the print head. 
   The illustrative embodiments of the present application describe a mailing machine print head and carriage that use one or more systems or elements to latch the print head in a controlled location and to guide it into and out of that location in a manner that prevents debris from being transferred to the electrical connector contacts. In at least one embodiment, the latching components are a part of the print head so that the operator can fix a broken latch problem by installing a new print head. 
   Therefore, it should now be apparent that the invention substantially achieves all the above aspects and advantages. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Various features and embodiments are further described in the following figures, description and claims. 

   
     DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention. As shown throughout the drawings, like reference numerals designate like or corresponding parts. 
       FIG. 1  is an isometric view of a postage meter in accordance with an illustrative embodiment of the application. 
       FIG. 2  is a partially exploded view showing some of the internal components of the postage meter of  FIG. 1 . 
       FIG. 3  is an isometric view of a print head carriage and a separate print head according to an illustrative embodiment of the present application. 
       FIG. 4  is an isometric view of a print head carriage having an installed print head according to an illustrative embodiment of the present application. 
       FIG. 5  is a partially exploded view showing the print head carriage and print head during print head installation according to an illustrative embodiment of the present application. 
       FIG. 6  is a partially exploded view showing the print head carriage and print head during print head installation according to an illustrative embodiment of the present application. 
       FIG. 7  is a partially cut away view along dotted dashed line A—A in  FIG. 6 . 
   

   DETAILED DESCRIPTION 
   In the illustrative mailing machine and postage meter described in the present application, a print head carriage and print head having a latching system is shown. 
   Referring now to the drawings, and particularly to  FIG. 1 , the reference numeral  10  generally indicates a postage meter provided in accordance with the invention. 
   The postage meter  10  includes a housing  12  formed of a lower case section  14  and an upper case section  16 . A slot  18  formed in the front  20  of the housing  12  allows a mail piece (not shown) to be transported through the postage meter  10 . The postage meter  10  also includes a transport unit  22  (partially visible through the slot  18 ) positioned at the slot  18  to transport the mail piece from an infeed side  24  of the slot  18  to an outfeed side  26  of the slot  18 . The postage meter  10  further includes a user interface  28  at the front  20  of the housing  12 , and a lever  30  positioned below the slot  18  to aid in clearing jams from the transport unit  22 . 
     FIG. 2  is a partially exploded view showing some of the internal components of the postage meter  10 . In addition to the above-mentioned transport unit  22  (which is more clearly visible in  FIG. 2 ), the postage meter  10  includes an ink jet print head  40 . In accordance with conventional practices, the transport unit  22  may operate to transport a mail piece (not shown) past the print head  40  so that the print head  40  may print a postage indicia on the mail piece. 
   The postage meter  10  also includes a waste ink purge unit  42 . At appropriate times, the purge unit  42  may come into engagement with the print head  40  to remove excess ink, dried or partially dried ink and/or air bubbles from the print head  40 . By a mechanism which is not shown, the print head  40  may be moveable in fore-and-aft directions between a print position adjacent the front of the meter  10  and a purge position that is aft of the print position. When in the print position, the print head  40  may operate to print postage indicia on mail pieces. When in the purge position, the print head  40  may be purged of waste ink by the purge unit  42 . Print head  40  includes a connector  41  having electrical contacts. 
   The postage meter  10  further includes a metal chassis  44 . The metal chassis  44  includes a vertical section  46  to which certain components (not shown in  FIG. 2 ) of the postage meter  10  may be mounted. The metal chassis  44  also includes a horizontal metal plate  48  which may be integrally formed with at least part of the vertical section  46  of the metal chassis. The metal plate  48  extends horizontally outwardly from the metal chassis  44  in a forward direction. 
   Also included in the postage meter  10  is a waste ink tray assembly  50 . When the postage meter  10  is in an assembled condition (not shown in  FIG. 2 ), the metal chassis  44  may rest on the bottom  52  of the lower case section  14  of the housing  12 , with the waste ink tray assembly  50  supported by and resting on the metal plate  48 . When the postage meter  10  is in its assembled condition, the waste ink tray assembly  50  is positioned below the purge unit  42  to receive from the purge unit  42  waste ink removed from the print head  40  by the purge unit  42 . 
   Referring to  FIGS. 3–7 , an illustrative printing mechanism according to an embodiment of the present application is shown. Many advantages of the present system exist, including, but not limited to reducing cost and avoiding operational problems of the system. Furthermore, such system allows a lower printer height. 
     FIG. 3  shows a print head  101  and print carriage  102  with the print head not installed. The print head carriage  102  includes a connector  103  that includes electrical contacts that are used to engage the electrical connector on the print head  101 . The print head electrical connector is shown in  FIG. 2  as connector  41 . The print head carriage  102  includes upper guide slots  104  and lower guide slots  105  for guiding the print head  101  into the installed position. 
   The print head  101  includes two sliding latches  106  that each has a latch  136  connected to a flexible spring loaded thumb ear  146 . The latches  136  engage the latch sockets  126  molded into the print head carriage  102 . The print head  101  includes a set of lower guide pins  120  and upper guide pins  122  that engage the respective guide slots  104 ,  105  of the print head carriage  102 . 
     FIG. 4  shows the print head  101  installed in the print carriage  102 . The upper guide pins  122  are installed into the upper guide slots  104  and the lower guide pins  120  are installed into the lower guide slots  105 . The print head  101  has compressed a loading spring when inserted into the print head carriage so that when thumb ears  146  are compressed, the latches  136  disengage the latch socket  126  and the spring will urge the print head upward into the guide slots. 
     FIG. 5  shows the print head  101  as it is being installed into the print head carriage  102 . The lower guide pins  120  on the print head are shown entering the slots lower guide slots  105  in the print head carriage  102 . The print head  101  is shown being inserted into the print carriage  102  in a partially installed position. As shown, the lower guide pins  120  keep the lower structure of the print head  101  away from the electrical connector contacts  103  on the print head carriage  102 . As the print head travels in the guide pins toward the end of the channel, the print head may then rotate to contact the inside wall of the print carriage. 
     FIG. 6  shows the print head  101  installed in the print carriage  102  and shows the upper guide pins  122  of the print head  101  in the upper guide slots  104  of the print head carriage  102 . The right side of the latching features is shown with latch  136  of the print head  101  engaged in latch socket  126  of print carriage  102 . 
   In  FIG. 7 , a partial cutaway of an illustrative printing mechanism along a section A—A of one latch is shown. The section is through the horizontal dashed-dotted line A—A line shown in  FIG. 6  and shows a cutaway of sliding latch  106  and the print carriage  102 . 
   Also included, but not shown in the figures is a ramped shape of the top of the latches that urge the print head downward to the vertical datum for the print head in the print carriage. Also included, but not shown in the figures is a single compression spring that is used to move the latches into their respective openings in the print carriage when they are released. Accordingly, in this illustrative embodiment, the system for control and latching of the print head requires only four parts including the two identical latches, a compression spring and a cover to trap them against the body of the print head. Additionally, in this illustrative embodiment, the four parts are a part of the print head assembly rather than a part of the print carriage assembly. In a situation in which the latches are broken, the print head may simply replaced by the operator rather than requiring that a technician replace the print carriage. In an alternative, the four parts are incorporated in the carriage. 
   The present application describes illustrative embodiments of a printing mechanism. The embodiments are illustrative and not intended to present an exhaustive list of possible configurations. Where alternative elements are described, they are understood to fully describe alternative embodiments without repeating common elements whether or not expressly stated to so relate. Similarly, alternatives described for elements used in more than one embodiment are understood to describe alternative embodiments for each of the described embodiments having that element. 
   The described embodiments are illustrative and the above description may indicate to those skilled in the art additional ways in which the principles of this invention may be used without departing from the spirit of the invention. Accordingly, the scope of each of the claims is not to be limited by the particular embodiments described.