Abstract:
A printer carriage has a chute for removably holding a print cartridge, and includes a set of datums on a forward portion of the chute for positioning the print cartridge. A spring-loaded clamp is movable by a handle between an open position which allows easy insertion and withdrawal of the print cartridge from the chute, and a closed position which applies a clamping force against a back wall of the print cartridge. The clamping force is preferably applied in both a forward and downward direction against a lower portion of the back wall to securely hold the print cartridge in the chute against the datums, and to provide conductive contact through a plurality of electrical interconnects between the carriage and the print cartridge. A method of installation and removal of a print cartridge employs access along a primarily vertical path through an open top of the chute. A printing system with the carriage and print cartridge preferably expels ink along an approximately horizontal path from an upstanding nozzle plate

Description:
RELATED APPLICATIONS 
     BACKGROUND OF THE INVENTION 
     This invention relates generally to removable inkjet print cartridges, and more specifically to the proper positioning of print cartridges on a carriage. 
     Numerous performance and reliability problems can result if a removable print cartridge is not properly positioned, mounted and held by a carriage in a printing system. These may include inconsistent electrical connections, premature flex circuit failures, misplaced ink droplets on print media, and other resulting deficiencies such as ink deprime problems in the print cartridge which prevent satisfactory ink ejection from the print cartridge. Such reliability is especially important in low cost monochrome type printers which are used to print point-of-sale receipts. 
     The rapid acceleration and deceleration of a scanning carriage can also cause a print cartridge to rock or change position in a carriage unless it is securely clamped into a proper printing location against positional datums in a carriage chute. 
     When a print cartridge reservoir is depleted, proper cartridge removal and replacement should be self explanatory without having to follow complicated instructions The cartridge should be easily accessible for removal. The position of a newly installed cartridge should be repeatable each time without any necessary calibration. Partial installation should be easily avoided, and any handle should therefore tend to remain in either an open or close position rather than somewhere in between. 
     BRIEF SUMMARY OF THE INVENTION 
     A unique printing system has been developed which incorporates one or more print cartridges individually mounted in their own separate carriages which scan back and forth across media in a print zone 
     The printer carriage has a cavity or chute for removable mounting of the print cartridge, and includes a set of support guides on a floor and a set of datums on a forward wall of the chute for positioning the print cartridge. A spring-loaded clamp is movable by a handle between a latched open position which allows easy insertion and withdrawal of the print cartridge from the chute, and a closed position which applies a clamping force against a back wall of the print cartridge. When the clamp is unlatched, a biasing spring pivots the clamp about an axis into the closed position such that a clamping force is applied in both a forward and downward direction against a lower portion of the back wall of the installed print cartridge to securely hold the print cartridge in the chute against the datums, and to facilitate conductive contact through a plurality of electrical interconnects between the carriage and the print cartridge. 
     A method of installation or removal of a print cartridge employs access along a vertical path through an open top of the chute when the clamp is in the open position. A printing system with the carriage and print cartridge expels ink along an approximately horizontal path from an upstanding nozzle plate while the clamp is in the closed position. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 shows a printer system incorporating an embodiment of the present invention with two carriage-mounted print cartridges. 
     FIG. 2 is a top perspective view of a carriage-mounted print cartridge with a handle upright and a clamp on closed position. 
     FIG. 3 is a top perspective view of the carriage without any print cartridge, with the handle upright and the clamp in closed position. 
     FIG. 4 is a side perspective view of the carriage of FIG.  3 ;, with a drive belt attached. 
     FIG. 5 is a side perspective view of the carriage of FIG. 3 without any print cartridge, with the handle down and the clamp in open position. 
     FIG. 6 is a top plan view of FIG.  5 . 
     FIG. 7 is a perspective end view of a front wall of the carriage with an exploded view of its flex circuit assembly showing the reverse side of the signal pads. 
     FIG. 8 is a front perspective view of the print cartridge of the previous figures. 
     FIG. 9 is a side view of the print cartridge of FIG.  8 . 
     FIGS. 10A,  10 B and  10 C are schematic drawings showing operation of the handle and clamp when the print cartridge is being installed/removed, and is in clamped printing position. 
     FIG. 11 is a top plan view showing a carriage with the handle, clamp, spring and flex circuit assembly removed 
     FIG. 12 is a end view of the handle. 
     FIG. 13 is a side view of the spring. 
     FIG. 14 is a side view of the clamp. 
     FIG. 15 is a end view of the clamp. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     An exemplary printing mechanism as shown in FIG. 1 includes a frame,  30 , carriage support bar  32 , media guide bar  34 , encoder strip  36 , and carriage drive motor  38 . A carriage member  40  may include a cylindrical bushing  42  which rides on the support bar  32  back and forth in a carriage scan direction  44  while media  45  is periodically advanced over a platen  46  in a media advance direction  47  through a print zone. The carriage drive motor  38  is typically mounted on a back of the frame  30  and rotates an axle  50  which carries a belt gear  52  which engages an inside toothed surface of a carriage drive belt  54 . The left end of the encoder strip is cut away so show details of the carriage drive mechanism. In order to facilitate proper positioning of the carriage over the print zone, a guide bracket (not shown) may be attached at the bottom front of the carriage  40  to slide along a guide bar  56 . Of course the unique carriage features described in more detail below can be utilized with any type of drive mechanism and support bar bearings as may be appropriate for the intended use of the printer, 
     In its simplest form, the invention can be implemented with a single print cartridge  60  mounted in carriage  40  and connected through a flex circuit  58  to an printer control unit such as a computer, sales register, etc. However for greater efficiency and throughput, the invention contemplates additional print cartridges such as  60 ′ with flex circuit  58 ′ and mounted in their own carriage  40 ′ which could be aligned with cartridge  40  for both passing over a same swath or alternatively be located in staggered relationship to print a double swath in a single pass. Although the features of the present invention are especially applicable for use with monochrome printheads, a person skilled in the art could implement the present invention with separate printheads each having a different color marking liquid, or even with tri-compartment print cartridges having three different types or different color liquids. 
     Also, although a preferred orientation of the printer carriage and print cartridge as shown in FIG. 1 currently provides a vertical platen with a nozzle plate ejecting marking liquid in an approximately horizontal direction onto the media, the unique carriage and cartridge system can also be used with print cartridges mounted over a horizontal platen having a nozzle plate ejecting marking liquid downwardly onto the media. 
     FIGS. 2-6 show additional features of the illustrated embodiment of the carriage  40 , including a U-shaped handle  70  mounted on hubs  72  for rotation forwardly shown by arrow  74  on handle axis  76  to an upright position (see FIGS. 2,  3  and  4 ), as well as rotation rearwardly shown by arrow  78  to a horizontal position (see FIGS.  5  and  6 ). Such rotation of the handle back and forth through a one-quarter turn (approximately 90 degrees) controls pivotal movement of clamp  80  which is mounted inside a lower rear portion  82  of the carriage. Accordingly clamp  80  moves back a forth between open and closed positions as described more fully below by pivoting forwardly shown by arrow  84  on clamp axis  86  well as rearwardly shown by arrow  88 . A biasing spring  90  applies a constant biasing force to the clamp in a generally forward direction  92  and is compressed in a rearward direction  94  when the clamp is retracted by the handle. 
     The carriage  40  includes a floor  100 , side walls  102  and front wall  104  which together form a cavity or chute with an open top for receiving the print cartridge  60 . The front wall carries the flex circuit assembly  105  which includes flex circuit  58  with fourteen electrical interconnects  106  in a two-row pattern which matches the corresponding fourteen signal pads  108  located on a lower front face of the print cartridge which activate ejection of ink or other marking liquid from nozzle plate  136  (See FIGS.  7 - 8 ). The flex circuit assembly  105  also includes two retainers  110  each having three pins for passing through slightly enlarged matching flex circuit openings  112  and through matching front wall openings  114  sized for a snug press-fit attachment to the front wall. 
     The front face of the print cartridge also includes two elongated recesses  126  which accommodate the previously mentioned retainers when the print cartridge is installed in the carriage chute. 
     Other flex circuit assembly parts include two cushion members  116  having raised pyramid shaped bumps or projections respectively matching each electrical interconnect, with the cushion members sized to fit into similarly shaped flat bottom grooves  117  on the inside of the front wall with some expansion space in each groove provided by an encircling raised perimeter ledge. This is an improvement over prior open-ended grooves that allowed the cushion to creep or “inch worm” its way out of the open end of the groove. Also, if adequate lateral expansion space is not provided in the groove, two undesirable consequences occur. First, the connector cushion is much stiffer, thus requiring more clamping force to ensure that the print cartridge is properly located in the carriage chute, secondly, the clamping force varies much more depending on the tolerances. The groove feature described herein avoids these problems by incorporating a completely enclosed groove with sufficient width for expansion under pressure. 
     Additional structural features of the carriage and their function are best understood by reference to FIG.  11 . The front wall  104  includes a set of positional datums which define horizontal, vertical and lateral position limits for the print cartridge generally and more importantly for the closely adjacent nozzle plate and electrical interconnects. This set of positional datums includes two holes  118  which are sized and located to receive datum bosses  120  on the lower front face of the print cartridge, and also includes two frictional surfaces  122  around the holes which engage matching areas  124  on the front face of the print cartridge. 
     The floor  100  of the carriage chute includes various support guides such as a pair of spaced apart ledges  140  in front corners with ramps  142 , and a pair of spaced apart raised legs  143  toward the back adjacent side walls  102 , and a central recess  144  which engages a bottom tab  145  on the print cartridge. These support guides facilitate the installation of the print cartridge in the carriage chute such that the aforementioned set of datums are properly aligned to assure proper predetermined forward, vertical, lateral and rotational positioning for the print cartridge in the carriage along with precise and secure alignment of the nozzle plate and electrical interconnects. 
     It is important to note that the aforesaid walls of the carriage chute are truncated and extend a distance  128  which is less than half the way up the front and rear heights  129 ,  130  of the print cartridge. This enables easy manual access to a print cartridge tab  132  and to the print cartridge walls  134  when installing or removing the print cartridge from the chute, and also exposes a nozzle plate  136  on the front face of the print cartridge for ejecting ink drops in an approximately horizontal path onto the print media Also the carriage is a unitary member molded from carbon fiber reinforced plastic. The carbon fiber makes the material conductive, thus providing an electric current path for electrostatic discharges (ESD). This prevents ESD from damaging the print cartridge. 
     Extending outwardly below the floor are two pair of L-shaped brackets  146  for receiving the carriage drive belt  54 . Optional apertures  148  are located in the floor and also in the bottom of the rear chute portion  82  in order to provide easy attachments to carriage components such as support guide bushings, encoder strip, etc. A slot  150  is provided through floor  100  at the base of front wall  101  to allow the flex circuit  58  to pass through the floor to inside the carriage chute. 
     FIGS. 12-15 show the individual parts which interact together inside the carriage to achieve the clamping and unclamping of the print cartridge. The handle  70  is made of a different color plastic from the carriage for easy user identification. Referring to FIG. 12 which shows a view of the front face of the handle  70 , the handle is molded as if it were a single layer shaped to form the previously identified solid hubs  72  rotatably mounted in holes  152 , spaced apart double layer arms  154  which join together at the top to form bridge  156  which carries upper grip  158  and forward tab  160 . A pair of semi-circular hollow cams  162  extend inwardly from the arms  54 , respectively with the outer convex cam surfaces facing rearwardly when the handle is in the upright position. 
     Referring to FIGS. 14-15, the clamp  80  includes a central body  164  having a circular groove  166  around a center post  168  for receiving an end of the biasing spring  90  (see FIG. 13) in order to hold the spring in compression against a pin  170  on a rear wall  172  of the carriage. Pivot posts  174  at the bottom of the clamp fit under wall extensions  176  to provide pivotal rotation around axis  86  as the clamp moves between an open latched position to a closed position. Latching occurs after rearwardly moving the handle to cause the cams  162  to rotatably slide down a cam follower  180  to be seated in a concave notch  178  on the clamp (see FIG.  10 A). 
     Movement of the clamp to the closed position is actuated by rotating the handle forwardly to disengage the cams from the notch, thereby allowing the biasing force of spring  90  to push the clamp (and the handle) toward the print cartridge in a smooth controlled movement as cams  162  ride up a smooth surface  179  of the cam follower  180 . When a flat protruding contact surface  182  on the central body  164  makes contact with a laterally extending ridge-like rib  184  located on a lower back portion of the print cartridge, the pivotal movement of the clamp as well as the partially downward facing contact surface creates a strong forward and partially downward clamping force against the print cartridge (see FIG.  10 B). 
     In this regard, by extending the rib  184  at least half and preferably almost the full width along the back of the cartridge and providing a downwardly angled shelf-like support  186  under the rib (see FIGS.  8 - 9 ), the clamping force caused by the biasing spring is not focused on one spot but instead is transmitted from the full length of the reinforced rib to pass through the walls of the print cartridge thereby minimizing excessive deflection of the plastic. In the presently preferred embodiment, a preferred force of about 4.5-5.0 pounds (with about 2.0 pounds of this force absorbed by the cushion members under the flex circuit interconnects) is aimed approximately 15 degrees below horizontal as shown by the line  188  in FIG.  10 C. Even though this magnitude of force was found to be optimum, increasing or decreasing variations of such angle and increasing or decreasing the amount of force dependent upon various parameters such as cartridge mass, carriage acceleration, reactive cushion force, # of electrical interconnects, etc., and the like may still achieve to a greater or lesser degree the benefits of the invention as set forth herein. 
     When the clamp is in such closed position, the handle is in an upright passive position and the handle has eliminated itself as receiving or absorbing any of the applied force from the spring. In this position the handle tab ( 160 ) is in a somewhat mating relationship with the tab handle ( 132 ) of the print cartridge. However when there is no print cartridge installed in the carriage, a stop ledge  189  on both side walls of the carriage chute prevents the handle and the clamp from moving past the “closed” upright position (see FIGS.  3 - 4 ). Furthermore, the stop ledge ( 189 ) acts as a guide along with tapered guides  190  on the front wall (see FIG. 5) to facilitate initial and satisfactory completion of the installation prior to moving the clamp into closed locked position. 
     It will be understood by those skilled in the art that while illustrated embodiments of the invention have been shown and described, changes and variations can be made without departing from the spirit and scope of the invention as set forth in the following claims: