Abstract:
An apparatus adapted to house page-wide arrays (PWAs) of print heads in a printing apparatus comprises a plurality of support structures each housing a PWA. Each PWA comprises a linear array of print nozzles in a lateral direction. The structures are stacked in a vertical array and are each attached to a wall structure at a closed lateral end of the structure. Opposite the closed end, each structure has an open end for lateral insertion and removal of the corresponding PWA. Between the open and closed ends, each structure has an opening in a front face through which the array of nozzles in the corresponding PWA may operate while housed in the structure. An adjustable protrusion extends within each structure from the closed end, whereby the lateral position of the corresponding PWA may be fixed relative to the closed end of the structure and the wall structure. A locking mechanism at the open end of the structure may be engaged to secure the PWA within each structure against the corresponding protrusion and prevented from moving in a lateral direction. When the locking mechanism is disengaged, the PWA may be removed or inserted through the open end of the structure. The lateral pressures applied by the locking mechanism and the protrusion in each structure fixes the lateral position of each PWA relative to each other and with respect to the wall structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is the first application filed for the present invention. 
     MICROFICHE APPENDIX 
     Not applicable. 
     TECHNICAL FIELD 
     The invention relates to modular page-wide array (PWA) print heads, and, in particular, to a method and apparatus for precision-mounting and removing page-wide array print heads by unskilled technicians. 
     BACKGROUND OF THE INVENTION 
     Recent developments in ink-jet printing technology have led to the realization of page-wide arrays (PWAs) of ink-jet print heads all oriented in the same direction in a linear array. Each print head is composed of a linear array of evenly-spaced ink-jet nozzles. The print heads in a PWA extend in the direction defined by the width of the print head (horizontally, for the purposes of discussion) across the entire width of the allowable printing area. Thus, the PWA does not need to move horizontally relative to the printing material, in order to provide print coverage across the width of the printing area. Rather the material to be printed is typically mounted on a web which passes vertically past the PWA. This permits printing at speeds heretofore impossible to achieve with ordinary ink-jet printers. 
     Additionally, multiple PWAs are organized in a vertical array, in which each PWA is offset by a fraction of the horizontal separation between adjacent nozzles within a print head. Thus, the cumulative effect of the vertical array of PWAs permit a print resolution in the horizontal direction which is a multiple of the print resolution of the print head in isolation. The print resolution in the vertical direction is defined by the speed at which the web passes relative to the vertical array of PWAs, together with the space between the nozzles of the PWA array and the web itself. 
     In addition to providing a greater horizontal print resolution, arrangements of multiple PWAs may be positioned in close proximity to produce a compact printing apparatus. The nature of the constituent PWAs define the function of the resulting apparatus, such as providing 4- or higher colour separation or ultra-high resolution monochrome printing. 
     While PWAs provide significant advantages in the printing art, the large number of print heads causes concomitant maintenance problems. Ink-jet cartridges, by their nature, require frequent, regular and relatively complex service. The large number and close proximity of the print heads within PWAs and the close proximity of PWAs within a printing apparatus, as well as the typically tight spacing between print head nozzles and the web exacerbates the problem. Typically, print heads are required to be removed in order to be serviced and or replaced. The nature of the PWA requires that the component print heads be precisely aligned within a PWA and with respect to other PWAs. While PWAs may be inserted and removed as a single replaceable unit, the installation and removal of PWAs has nevertheless typically required the use of highly skilled technicians and the process of removal and installation has been time-intensive, leading to considerable expense in the form of labour costs and down time of the printing apparatus. 
     What is therefore required is an apparatus for supporting multiple PWAs in a printing apparatus, so that the PWAs can be quickly removed and replaced by non-skilled technicians, while maintaining the precise alignment between PWAs in the printing apparatus. 
     SUMMARY OF THE INVENTION 
     Therefore an object of the invention is to provide a structure for maintaining a PWA in a precise orientation within a printing apparatus that permits rapid insertion and removal of the PWA by non-skilled personnel. 
     In accordance with the present invention, there is provided a bay for supporting a page-wide array (PWA) of print heads. The bay may be configured in a vertical array to permit multiple PWAs to be simultaneously supported in a printing apparatus. The bay includes a support structure having supporting surfaces for maintaining the proper vertical orientation of the PWA as it is inserted into, maintained within and removed from the bay. The spacing between the supporting surfaces of the bay is such that the PWA is sufficiently constrained from vertical movement, without unduly inhibiting the insertion and removal of the PWA. The supporting surfaces do not obstruct the nozzles of the PWA print head from projecting ink horizontally from a vertical face of the PWA. 
     The bay is fixed with reference to a wall structure and an adjustable protrusion permits horizontal precise positioning of the PWA within the bay with respect to the wall, which together provide for alignment of the PWA print head within the bay. The protrusion consists of a bolt having an exterior thread that engages an internal threaded bore in the wall to permit adjustment in the horizontal direction. The pitch of the exterior thread is sufficiently fine to permit precision alignment of the PWA relative to the wall. An internal bore in the bolt permits rotation of the bolt to the desired depth using an Allen key. The protrusion is locked into place relative to the wall by a nut that engages the exterior thread of the bolt within the bay. 
     The bay also provides a convenient locking mechanism disposed at an opening at an end distal from the wall. The PWA is inserted and removed through the opening when the locking mechanism is in an open position. The locking mechanism may be moved into a closed position where it applies a persistent force on a PWA situated in the bay, to urge the PWA print head into contact with the print head locater. Where the printing apparatus features a vertical array of bays, the locking mechanism of each bay is linked, so that the bays may be opened or closed by a single operation. 
     Also according to the objects of the invention, a printing apparatus with multiple page-wide array (PWA) print heads is provided. The printing apparatus includes a system for feeding a print medium at a predetermined rate across a printing area to a print output, a plurality of PWA print heads for imparting ink onto the print medium in accordance with a bit map received by a signal processing means of the printing apparatus, and a bay as described above for each of the PWAs. 
     A method for replacing a page-wide array (PWA) in a printing apparatus is also provided in accordance with an aspect of the invention. The method involves opening a locking mechanism that obstructs the opening to the bay that encloses the PWA; removing the PWA from the bay through the opening; inserting a replacement PWA print head into the bay through the opening; and closing the locking mechanism so that the locking mechanism urges the PWA print head into contact with a print head locater in a fixed position with reference to a wall to which the bay is attached, wherein the supporting structure of the bay constrains the vertical positioning of the PWA and the locking mechanism and the protrusion constrain the horizontal positioning of the PWA. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which: 
     FIG. 1 schematically illustrates a complement of four bays in accordance with an embodiment of the present invention; 
     FIG. 2 schematically illustrates an enlarged view of a back end of the four bays illustrated in FIG. 1; 
     FIG. 3 schematically illustrates an embodiment of a print head locater in accordance with the present invention; 
     FIG. 4 schematically illustrates an enlarged view of a front end of the four bays illustrated in FIG. 1; 
     FIG. 5 schematically illustrate s an embodiment of a locking mechanism in accordance with the present invention; 
     FIG. 6 schematically illustrates the four bays containing respective PWA print heads; and 
     FIG. 7 schematically illustrates an alternate view of FIG. 6 wherein both ends are in view. 
     It should be noted that throughout the appended drawings, like features are identified by like reference numerals. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention provides a method and apparatus for precisely aligning PWA print heads that may be removed and inserted by non-skilled personnel. 
     In a PWA printing apparatus, a print medium is typically transported between the PWAs an d a fixed print area at a predetermined rate. The print area is equidistant to all nozzles of the PWA. 
     Those having ordinary skill in this art will recognize that small differences in the angle (α) that the nozzles expel ink from an axis normal to the plane of the printing surface may be accommodated having regard to the small nominal distance (d) from the nozzle to the medium to be printed. The disparity in actual distance (d act ) is represented by the relation 
     
       
         d act =d sin (α) 
       
     
     Thus, if the nominal distance d is {fraction (1/32)} nd  of an inch and the permitted disparity d act  is ⅓ of the inter-nozzle separation (for example, {fraction (1/360)} th  of an inch), the permitted angular tolerance α will be about 1.7°. 
     FIG. 1 shows an exemplary printing apparatus  10  that includes four bays  12 , each adapted to hold a PWA in a vertical arrangement and having a common orientation. Each PWA contains a plurality of print heads in a horizontal array as a single replaceable unit. Those having ordinary skill in the art will recognize that printing configurations do not necessarily require or permit strictly vertical orientation of the printing area. The use of directional terminology in this description therefore, is merely exemplary and for convenience of explanation and should not be understood to limit the invention to embodiments having such an orientation. 
     The external portion of the PWA is composed of a rigid material that will maintain is precise shape despite the application of pressure from without. 
     As is well known in the art, four print heads are used in most color printers and presses, each of the four print heads supplying a respective one of the following colors of ink: cyan, magenta, yellow, and black. The alignment of PWA print heads in a color printing apparatus may depend upon color mixing and the amount of overlap between adjacent lines on the printing apparatus, as well as other factors, such as the print medium used, the operating temperature, the wetness of the ink when applied to the print medium, and the size and viscosity of ink droplets. In some cases, therefore, PWAs in a multi-colour printing apparatus must be aligned in a precision greater than that of the inter-nozzle distance of the PWA print head. 
     Those having ordinary skill in this art will readily recognize that a greater or lesser number of PWAs may be placed in vertical arrangement. For example, greater than 4-colour separation may be required. Further, the horizontal print resolution in either colour or monochrome print applications may require enhancement by using multiple PWAs each horizontally offset from the other. In order to ensure printing accuracy, each PWA must be offset by the same amount, namely the quotient obtained by dividing the inter-nozzle spacing in the print heads by the number of offset PWAs in the vertical array. The horizontal print resolution will thus be the product of the horizontal print resolution of the PWA and the number of offset PWAs in the array. 
     Each bay  12  is defined by a support structure that consists of vertical supports  13  and horizontal panels  14  that form the floor and ceiling of the bay  12 . The horizontal panels  14  are composed of a strong, smooth material that permits low friction insertion and removal fo the PWA, for example, stainless steel. Where multiple bays  12  are arranged in a vertical array, intermediate horizontal panels  14  may act as both the floor of an upper bay  12  and the ceiling of the immediately lower bay  12 . The horizontal panels  14  are approximately the shape of the PWAs to be housed within the bay  12  but slightly larger, so that the PWAs may be situated entirely or almost entirely within the bay  12 . The spacing between horizontal panels  14  is such that the PWA is sufficiently constrained vertically within the bay  12 . Taking the exemplary values for d and d act  set out above, in order to ensure that the permitted angular tolerance a remains less than 1.7°, experiments have shown that, depending upon the size of the PWA, a vertical disparity of up to an inch may be tolerated. 
     One of the sides of the bay  12  (the front face) corresponds to the side of the PWA from which the nozzles protrude. A printing area (not shown) extends roughly parallel to the respective front faces of the bays  12  in the vertical array. Along the front face, a floor lip  18  partially extends upwardly from the floor of the bay  12  and a ceiling lip  20  partially extends downwardly from the ceiling of the bay  12 , The profile of the floor lip  18  and the ceiling lip  20  is such that the flow of ink to the printing area from the nozzles in a PWA housed within the bay  12  will not be impeded, while preventing the PWA from falling out the front face of the bay  12 . 
     The side of the bay  12  opposite to the front face (the back face) may also feature a floor lip and a ceiling lip (not shown) to prevent the PWA from falling out the back face of the bay  12 . The profile of such floor and ceiling lips will be such as to permit access to the back of the PWA as is required for purposes of signal connection and the like as is common in the art. Frequently, once the PWA has been inserted into the bay  12 , as discussed below, a pressure plate (not shown) is also inserted, which forces the PWA forward toward the front face of the bay  12 . In such case, the pressure plate may have openings that correspond to connectors that may need to be attached to the back of the PWA, and the floor and ceiling lips need only have sufficient profile to guide the insertion of the pressure plate. 
     One side(the wall end) of the bay  12  adjacent to the front face is closed and is attached to a wall structure  40 . The wall structure  40  is fabricated of a resilient substance that is not deformed by stresses applied to it under normal operating conditions. Accordingly, the wall structure  40  may be considered to define a rigid plan from which the horizontal position of the PWAs mounted within the bays  12  may be defined. The wall structure  40  need not be strictly planar, so long as it provides a reliable reference point for the horizontal position of each PWA. 
     The wall end of the bay  12  may be independently fastened to the wall structure  40  by fasteners known in the art. Alternatively, the wall end of the bay  12  may be fastened to the wall structure  40  directly by a protrusion  42 . As is more closely shown in FIGS. 2 and 3, the protrusion  42  consists of a bolt  46  having an exterior thread and an correspondingly internally threaded nut  44 . The bolt  46  passes through an opening in the wall end of the bay  12  and engages a internally threaded bore (not shown) in the wall structure  40 . When the protrusion  42  is used to fasten the wall end of the bay  12  to the wall structure  40 , a second nut (not shown) or similar fastening means may be used on the other side of the wall structure  40 . 
     The pitch of the exterior thread on the bolt  46  is sufficiently fine to permit precise adjustment of the extent that the top  49  of the bolt  46  extends into the bay  12  from the wall end. In order to permit the bolt  46  to be threaded into the wall structure  40  without destroying the external thread pattern on the bolt, a polygonal internal bore extends axially through the bolt  46  from its top  49 , whereby an Allen key or other suitable device may be inserted so as to permit rotation of the bolt  46  and into the bore in the wall structure  40  to the desired depth. Once the bolt  46  has been positioned so that the top  49  extends into the bay  12  from the wall end to the desired extent, the position of the bolt  46  may be fixed by applying and tightening the nut  44  about the bolt and abutting the wall end of the bay  12 , so as to preclude any further movement of the bolt  46 . 
     While a plurality of protrusions  42  may be used within a bay, especially if the protrusions  42  are used to fasten the bay  12  to the wall structure  40 , preferably only one protrusion  42  per bay  12  is used for PWA alignment purposes, so as to considerably simplify the alignment process. If other protrusions  42  are used, these may be adjusted to protrude into the bay  12  a lesser distance than the protrusion  42  used for alignment. Preferably, the protrusion  42  used for alignment is aligned with the center of mass of the PWA so as not to apply any shearing force to the PWA when the bay  12  is locked, as discussed below. 
     The side of the bay  12  opposite the wall end (the insertion end)is shown in FIG.  4 . The opening in the insertion end is defined by a pair of the vertical supports  13  and a pair of the horizontal plates  14 . The vertical supports  13  in corresponding bays  12  form a rigid vertical pillar  50  that extends across the entire height of the vertical array of bays  12 . The horizontal plates  14  extend slightly beyond one of the pillars  50  (in FIG. 4, the pillar  50  proximate to the front face of the bay  12 ), and have a circular bore hole (not shown) therewithin, through which an axial rod  30  may be inserted, as may be better seen in FIG.  5 . 
     The axial rod  30  is seated within each bore hole by a seating ring  52  which snugly fits within the bore hole and through which the axial rod  30  may pass and be supported vertically, without being substantially impeded from about its axis. A footing  54  is attached to the axial rod  30  above each horizontal plate  52  and snugly engage the seating rings  52 . The axial rod  30  is not free to rotate with respect to the footings  54 . Each footing  54  is adapted to engage a bottom end of a spring  31  that surrounds the axial rod  30  above the footing  54 . The top end of the spring  31  is attached to a horizontal swing arm  28  that has a bore (not shown), through which the axial rod  30  may pass by way of an intermediate collar  56 . The collar  56  supports the swing arm  28 , which is free to rotate horizontally about the axial rod  30 . 
     The attachment of the top end of the spring  31  to the swing arm  28 , however, biases the swing arm  28  in a rotational direction away from the insertion end of the bay  12 (in the figures, in a counterclockwise direction when viewed from above). Thus, the axial rod  30 , the swing arms  28 , the springs  31 , the seating rings  52 , the footings  54  and the collars  56  all cooperate to provide a hinged locking mechanism  24  that is biased in the normally open position. 
     The far end of each swing arm  28  terminates in a contact pad  26  that is adapted to come into contact with an exposed end of the PWA when inserted into the bay  12 . The height of the springs  31  and the length of the swing arms  28  are such that the contact pad  26  will come into contact with the PWA at approximately its center of mass and approximately opposite to the corresponding protrusion  42  in the bay  12 . 
     A lever arm  32  is fixed to the top of the axial rod  30  and terminates in a knob  36  that is adapted to engage a clasp  34  attached to the uppermost bay  12  near its insertion end and proximate to the back face. The lever arm  32  is not free to rotate with respect to the axial rod  30 , so that when the knob  36  of the lever arm  32  engages the clasp  34 , the locking mechanism  24  may be engaged to close the insertion end of the bay  12  and apply lateral pressure on such PWAs as may be inserted into the bays  12  of the vertical array by the contact pads  26  on each swing arm  28 . 
     Because the pressure applied by the contact pad  26  on a PWA, when the locking mechanism  24  is engaged, is approximately opposite to the simultaneous and equal pressure applied by the protrusion  42  at the wall end, no shearing forces will be applied to the PWA. Additionally, the fine adjustment of the protrusion  42  and the rigid structure of the PWA ensures that the nozzles of the PWA, when inserted and locked, will be precisely aligned as required to provide a satisfactory printing result. 
     The process of inserting and removing a PWA from the bays  12  is easily accomplished by even unskilled technicians. To remove a PWA, the technician simply releases the knob  36  from the clasp  34 . The locking mechanism  24 , being biased in the open position, will spring open, exposing one end of the PWAs housed in the bays  12 . Additionally, the release of lateral pressure by the contact pads  26  on the PWAs, may cause the PWAs to extend slightly beyond the insertion end of the bay  12  and permit the PWA to be easily grasped. In any event, the PWA may be easily removed from the bay  12  through the insertion end, although, if a pressure plate has been inserted to urge the PWA forward toward the front face of the bay, such pressure plate will need to be removed first, again through the open insertion end of the bay  12 . 
     To insert the same or a replacement PWA, the technician need simply slide the PWA, properly oriented, into the appropriate bay  12  through the open insertion end. If a pressure plate is to be used, the pressure plate is slid into the bay  12  through the open insertion end, between the PWA and the back face of the bay  12 . When all PWAs (and pressure plates) have been inserted, the technician simply pushes the lever arm  32  toward the clasp  34  and engages the clasp  34  with the knob  36  to close the insertion end of each bay  12 . 
     FIGS. 6 and 7 illustrate the four bays containing respective PWA print heads, which are held in position by closure of the locking mechanism  24 . Many other embodiments of a locking mechanism are suitable for use in accordance with the present invention, the present locking mechanism being chosen because it is inexpensive, simple to operate, and reliable, and because it is well suited for insertion in many printing apparatuses. 
     The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.