Abstract:
A modular printer chassis, particularly for large scale printers, includes a lower media module which provides a rigid platen media support surface connected to an upper scanning carriage support module by a plurality of fasteners which are tightened at the time of assembly to thereafter permanently hold the modules, which are accurately positioned with the aid of a gauge at the time of assembly, in place so that the accurate inkjet printhead to media spacing in the print zone is maintained.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the art of computer driven inkjet printers/plotters, particularly large scale printers having printhead carriage scan widths of about 24 to 60 inches and above although the invention is also applicable to smaller printers as well. Precise spacing between the inkjet orifice plate or plates and the media on which printing is to take place is essential. For this reason, the media is generally supported on a rigid platen below a laterally scanning inkjet printhead or plural inkjet printheads all supported on a common scanning carriage. Those skilled in the art will appreciate that the greater the scan width, the harder it is to maintain precise and substantially constant spacing at all points along the scan width between the inkjet printhead or printheads and the platen supported media on which printing takes place. 
     It is accordingly the primary objective of the present invention to provide a rigid printer chassis structure which is easily assembled with precise spacing between the inkjet printhead orifices and the media but which also maintains the spacing throughout the design service life of the printer. 
     SUMMARY OF THE INVENTION 
     The present invention therefore provides a modular printer chassis comprising: a media module which includes a platen for supporting media on which printing is to take place; a carriage module including structure for supporting a laterally scanning printhead carriage having at least one inkjet printhead thereon in spaced relationship to said platen; and a plurality of fasteners connecting said media module to said carriage module, said fasteners being initially adjustable during connection of said modules to relatively position and thereafter permanently hold said modules in the selected position to accurately support a printhead a selected distance from said platen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a printer in which the invention is used. 
     FIG. 2 is a cross-sectional elevation view of one of the eight fastener connections, assembled but not tightened, which permit adjustment with three degrees of freedom of the connection of the carriage module to the media module during assembly. 
     FIG. 3 is a view like FIG. 2 showing the fastener connection tightened in place. 
     FIG. 4 is a schematic exploded isometric view of assembled modular elements of the printer showing a lower media module and an upper carriage module.. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A typical printer/plotter in which the modular printer chassis structure according to the present invention can be used is shown in FIG. 1 and, pursuant to the invention, includes a lower media module  20  which includes a rigid media support platen  22  and an upper carriage module  30  enclosed in an outer housing  12  which also encloses the scanning printhead carriage and support rods or guides  32 ,  34 , shown schematically in FIG. 2 in which the cover has been removed and shown in phantom for purposes of illustration. 
     The operative portions of the printer may be supported on a stand  12  and, in the example shown in FIG. 1 further include one or more offboard ink supplies  14  shown at the left side of the media and carriage modules and a printhead service station  16  shown at the right side of the modules. Large scale printers generally use large reservoirs or offboard ink supplies  14  which are connected by flexible ink tubes (not shown) to supply ink to the printhead or printheads mounted on the scanning carriage as is conventional. Smaller size printers such as desktop size printers, in which the modular configuration of the present invention is also applicable, typically use carriage mounted or “onboard” inkjet cartridges which contain a comparatively small supply of ink. 
     Turning now to FIG. 2 in which the elements of the invention have been shown in schematic block diagram form, it will be seen that the lower or media module  20  includes rigid laterally extending structure usually of sheet metal or extruded aluminum which provides a rigid platen structure  22  to afford a support surface for the media such as paper, transparency, vellum, etc., on which printing takes place. A media drive mechanism to accurately advance the media will also be provided as is conventional. The relatively rigid and expensive platen structure  22  is in turn connected to structural end members  24 ,  26  by any suitable means. The end members  24 ,  26  are preferably molded of rigid plastic for cost savings and ease of manufacture. The upper or carriage module  30  includes rigid, preferably steel, laterally extending beam structure  31 , broken away for clarity to show its cross-section, which defines an upper carriage guide  32 , the beam structure  31  also having a steel carriage support rod  34  affixed thereto. The beam structure  31  including the guide  32  and rod  34  may take any one of various configurations for suitably supporting a scanning inkjet printhead carriage. The carriage module  30  may also include a rigid ink tube guide  60  comprised of a pair of spaced channels suspended above the beam structure  31  if the printer employs offboard ink supplies. One form of ink tube guide suitable for use herein is disclosed in co-pending application Ser. No. 09/240,091 filed Jan. 29, 1999 owned by the assignee of the present invention, the teachings of which are incorporated herein by reference. Both the media module  20  and the carriage module  30  including the beam  31  and attached rod  34  are schematically depicted in boxes for ease of illustration. The ink tube guide  60  is shown partly broken away at its left end for clarity in illustration above the rigid beam structure  31  and support rod  34  however, the channels forming the guide  60  and the relative sizes and positions of the various rigid parts of the carriage module  30  are not critical to nor do they limit the invention. 
     The carriage module  30  is rigidly affixed to the media module  20  by a plurality of fasteners  40  each comprising a female member  42  received in an aperture  28  of complementary size formed in the end members  24 ,  26  of the media module and a male member or bolt  50  threadedly connected to the female member  42 . The upper ends of each of the fasteners  40  are received in suitably configured seats  33  molded in the end supports  36 ,  38  of the carriage module  30 , the seats  33  each providing engagement surfaces for a purpose to be described. The fasteners  40  define and maintain the spacing between the two modules  20 ,  30  both in vertical pure translation and tilt (rotation around any horizontal axis). 
     The individual fasteners are shown in FIGS. 3 and 4 to an enlarged scale. The fasteners  40  each include a female member  42  having a head  44  and a depending skirt  46  with a plurality of circumferentially spaced longitudinally extending slots (not shown) which allow the skirt to be radially expanded into firm engagement with the adjacent walls of the apertures  28  in the media module end members  24 ,  26 . The female members  42  are each preferably made of a relatively hard material such as aluminum or steel and are received in the apertures  28  in the relatively soft material of the plastic end members  24 ,  26  and then held in position therein by expansion of the skirt  46  on each fastener  40  into tight engagement with the walls of the apertures  28 . 
     The bolts  50  each having a head  52  and threaded shank are threadedly engaged with the skirt expanders  49  which, in the presently preferred embodiment shown, comprise separate parts having a tapered generally conical exterior surface slidably engageable with a tapered generally conical interior surface of the skirts  46 . Alternatively, the skirt expanders  49  need not be a part separate from the female member  42  but can instead be integrally formed with member  42  as an internally threaded lower end portion of the skirt  46  engageable with the threaded shanks of the bolts  50  as is well known in many different types of radially expandable fasteners which may be used to hold the modules  20 ,  30  in place. 
     The heads  52  of the bolts  50  are each configured to be engaged by a complementary shaped tool so that the bolts  50  can be rotated to secure the carriage module  30  in the intended position relative to the media module  20  during assembly at the factory. 
     The heads  44  of the female fastener members  42  preferably have an essentially flat upper clamping surface  48  and the lower ends of the heads  52  are also preferably flat and preferably receive washers  54  having a generally flat lower clamping surface  56 . The clamping  48  and  56  are drawn together during tightening of the female member  42  and bolt  50  and respectively engage the lower and upper sides of the seats  33  in the carriage module. 
     The modules  20 ,  30  are relatively positioned by first inserting the female members  42  partly into their respective apertures  28  and using a gauge to then precisely space the carriage module  30  from the media module  20  throughout the entire scanning length of the printhead carriage. The threaded bolts  50  are then inserted through apertures in the seats  33  into the skirt expanders  49  following which the bolts are tightened from the position shown in FIG. 3 to draw the skirt expanders  49  upwardly to radially expand the skirts  46  into tight engagement with the interior walls of the apertures  28  in the media module  20  and simultaneously clamp the oppositely facing engagement surfaces of the seats  33  of the carriage module  30  between the clamping surfaces  48 ,  56  of the fasteners  40 . Preferably, radially extending sharpened teeth or projections  47  are provided on the exterior surface of the fastener skirts  46  so that the projections can be forced into the relatively softer plastic material of the media module  20  to firmly hold the modules  20 ,  30  in the selected position following which the installation gauge or tools may be removed. 
     Although the fasteners  40  are shown in FIG. 2 with the female members  42  inserted into apertures  28  in the media module  20 , persons skilled in the art will readily appreciate that the female members  42  could instead be received in apertures in the end supports  36 ,  38  of the carriage module  30  and the bolts  50  could be affixed upwardly through the media module end members  24 ,  26  instead of as shown in FIG.  2 . 
     The presently preferred arrangement shown in FIG. 2 includes a total of eight fasteners  40  connecting the carriage module  30  to the media module  20 . The fasteners are arranged at four corners of the chassis assembly preferably in two planes, one, preferably a vertical plane, containing four fasteners at the front of the printer and the other plane, preferably also a vertical plane, containing four fasteners at the rear of the interconnected modules  20 ,  30 . Although, as shown, the planes in which the groups of fasteners are located are essentially parallel to each other, this too is not considered essential; however, the fasteners  40 , if all adjustable in parallel directions, e.g., vertical, can be positioned during assembly to linearly raise or lower the carriage module  30  a precise distance with respect to the media module  20 . Slight lateral and slight fore and aft adjustment of the carriage module  30  with respect to the media module  20  is also possible due to the provision of four fasteners  40  at each end by raising or lowering the front fasteners relative to the rear fasteners and/or by raising or lowering the left or right pairs of the fasteners in each end member relative to the other fasteners in each end member whereby adjustability with three degrees of freedom is attained. 
     Persons skilled in the art will also appreciate that various additional modifications can be made in the preferred embodiment shown and described above and that the scope of protection is limited only by the wording of the claims which follow.