Abstract:
A cleaning member is pivotally fixed to a support member to clean ink-jet print heads that are positioned on a print-head receptor module. The cleaning member pivots from a cleaning position to an idle position and the print-head receptor module is pivotally fixed to a support member to allow the module to pivot from a printing position to a cleaning position. The pivotal supports are positioned such that, when the module and the cleaning member are each in their respective cleaning positions, the cleaning member is positioned to clean ink jets inserted into the receptors.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to cleaning ink-jet printing apparatus, particularly apparatus used for commercial printing.  
         BACKGROUND  
         [0002]    Commercial printing may be done on multi-color continuous web printing presses. Paper rolls are unrolled along a paper path that includes separate stations for each color. An optional dryer may be placed after the final print station. The web is then slit into sheets and stacked.  
           [0003]    In inkjet printing, ink is ejected from a narrow orifice in the direction of a substrate. In one type of ink-jet printing, known as drop-on-demand printing, the ink is ejected in a series of droplets. The droplets may be produced and controlled using a piezoelectric inkjet head which has a large number of orifices, each of which is separately controllable to selectively eject ink at desired locations, or pixels, of the image. For example, an ink-jet head may have 256 orifices that have spacing for a printing resolution of at least 100 pixels (dots) per inch (dpi) and sometimes far more than that. This dense array of orifices allows complex, highly accurate images to be produced. In high performance print heads, the nozzle openings typically have a diameter of 50 microns or less, e.g., around 25 microns, are separated at a pitch of 25-300 nozzles/inch, have a resolution of 100 to 3000 dpi or more, and provide drop sizes of about 1 to 70 picoliters (pl) or less. Drop ejection frequency is typically 10 kHz or more. A drop-on-demand piezoelectric print head is described in U.S. Pat. No. 4,825,227, the entire contents of which is incorporated herein by reference.  
           [0004]    While such dense arrays of orifices produce complex, highly accurate images, image quality can deteriorate if one or more of the orifices become obstructed. For example, a partially obstructed orifice may alter the direction, size, or stability of the droplets. It is important to keep these apertures open and functional to avoid degradation of print quality. It is also important to clean the ink jets quickly without undue equipment down time. Moreover, since position of the ink jets relative to the paper is important, cleaning the heads should not unnecessarily dislocate the print-head module and should return it as close to its original position as possible.  
         SUMMARY  
         [0005]    In general, in a first aspect, the invention features an apparatus including a print bar for mounting a print head and a first pivot coupling to allow the print bar to pivot to or from a printing position.  
           [0006]    Embodiments of the apparatus may include one or more of the following features and/or features of other aspects.  
           [0007]    The apparatus may further include a cleaner in a cleaning position, wherein the pivot coupling allows the print bar to pivot (e.g., by about 90°) to a cleaning position in proximity to the cleaner. Additionally, the apparatus may include a second pivot coupling to allow the cleaner to pivot (e.g., by about 90°) between the cleaning position and an idle position. The print bar may be substantially non-parallel to the web when in the cleaning position (e.g., orthogonal to the web). The cleaner can use a vacuum to clean the print bar when the print bar and the cleaner are in their respective cleaning positions. The cleaner can use a cleaning fluid (e.g., a solvent) with or without a vacuum to clean the print bar when the print bar and the cleaner are in their respective cleaning positions. The cleaner can span the print bar.  
           [0008]    The apparatus may include a print support to register the print bar relative to a web when the print bar is in the printing position. The print bar and the support can include mating features that couple when the print bar is in the printing position. Alternatively, or additionally, the print bar and the cleaner can include mating features that couple when the print bar is in the cleaning position. The print bar may be substantially parallel to the web when in the printing position.  
           [0009]    In some embodiments, a print head mounted on the print bar jets ink substantially orthogonal to the web when the print bar is in the printing position.  
           [0010]    In a further aspect, the invention features a single-pass, web-based print station including the apparatus.  
           [0011]    In general, in another aspect, the invention features an apparatus for cleaning ink-jet heads mounted on a print bar. The apparatus includes a print bar pivotally fixed to a first support member to allow the print bar to pivot from a printing position to a cleaning position, and a cleaner adjustably coupled to a second support member to allow the cleaner to adjust from a cleaning position to an idle position, wherein the first support member is fixed relative to the second support member.  
           [0012]    Embodiments of the apparatus may include one or more of the following features and/or features of other aspects.  
           [0013]    The cleaner can be positioned to clean print heads mounted on the print bar when the print bar and the cleaner are each in their respective cleaning positions. The print bar and the cleaner can include mating features that couple when the print bar and the cleaning bar are each in their respective cleaning positions. The print bar and the first support member can include mating features that couple when the print bar is in the printing position.  
           [0014]    The apparatus can further include a drive to pivot the print bar and a drive to adjust the cleaning bar. In addition, the apparatus can include a controller to control the print bar pivot drive and the cleaning bar adjustment drive. The controller can include a processor to: (a) activate the print bar pivot drive to pivot the print bar to the printing position and the cleaning bar adjustment drive to adjust the clear bar to the idle position; and (b) activate the print bar pivot drive to pivot the print bar to the cleaning position and the cleaning bar adjustment drive to adjust the clear bar to the cleaning position. The apparatus can include a limit sensor to stop pivoting the print bar to the printing position and to stop adjusting the cleaning bar to the idle position, and to activate the print bar pivot drive to pivot the print bar to the cleaning position and the cleaning bar adjustment drive to adjust the cleaning bar to the cleaning position.  
           [0015]    The print bar can include mating features that engage mating features on the cleaner or first support.  
           [0016]    In general, in a further aspect, the invention features a method of cleaning print heads mounted on a print bar, where the print bar is pivotally fixed to a first support member to allow the print bar to pivot from a printing position to a cleaning position. The method includes: (a) providing a cleaning bar adjustably coupled to a second support member to allow the cleaning bar to adjust from a cleaning position to an idle position, the print bar being positioned such that, when the print bar and the cleaning bar are each in their respective cleaning positions, the cleaning bar is positioned to clean print heads mounted on the print bar; (b) pivoting the print bar from the printing position to the cleaning position; (c) adjusting the cleaning bar from the idle position to the cleaning position; and (d) cleaning print heads mounted on the print bar.  
           [0017]    The method may be implemented using the aforementioned apparatus.  
           [0018]    Embodiments may include one or more of the following advantages. Print head cleaning can be accomplished quickly and easily without disassembly of the printing system. The printing heads can be carried on a single moveable print bar which avoids realignment of the heads relative to one another after cleaning. The print bar motion is achieved by a pivoting coupling which permits highly accurate, reproducible realignment of the print bar with the substrate path after cleaning, and does not require movement of the paper path to access the face of the print heads. The cleaning apparatus can also be moved into a cleaning position by pivoting motion. Cleaning can be accomplished in a small physical space.  
           [0019]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0020]    [0020]FIG. 1 shows a generalized scheme for a commercial printing apparatus.  
         [0021]    [0021]FIGS. 2A and 2B are perspective views of a print bar.  
         [0022]    [0022]FIGS. 3A and 3B are side views of a print bar in a printing and cleaning position, respectively.  
         [0023]    [0023]FIGS. 4A and 4B are views of a print bar face and cleaning bar face, respectively.  
         [0024]    [0024]FIG. 5 is a greatly enlarged cross section of a portion of a cleaning bar and a print head in a cleaning position.  
         [0025]    [0025]FIG. 6 is a greatly enlarged cross section of a position of an alternate cleaning bar and a print head in a cleaning position.  
         [0026]    [0026]FIG. 7 is an exploded view of a pivoting coupling.  
         [0027]    [0027]FIG. 8A is an exploded view of a print head and FIG. 8B is a plan view of a printhead face.  
         [0028]    Like reference symbols indicate like elements. 
     
    
     DETAILED DESCRIPTION  
       [0029]    Referring to FIG. 1, a continuous web printing press layout  10  includes a series of stations or printing towers  12  for printing different colors onto a moving web  14 . The web  14  is driven from a supply roll  15  on stand  16  onto a paper path that leads sequentially to print stations  12 . An optional dryer  17  may be placed after the final print station. After printing, the web is slit into sheets that are stacked at station  19 . For printing wide-format webs, such as newsprint, the print stations accommodate a web width of about 30-33 inches or more. The web feed rate is in the range of about 3 meters/second or more. A general layout for offset lithographic printing that can be adapted for ink-jet printing is further described in U.S. Pat. No. 5,365,843, the entire contents of which is hereby incorporated by reference. Referring as well to FIGS. 2A and 2B, each print station includes a print bar  24 . The print bar  24  is a mounting structure for print heads  30  which are arranged in an array and from which ink is ejected to render a desired image on the web  14 . The printheads  30  are mounted in print bar receptacles  21  such that the faces of the printheads from which ink is ejected are exposed from the lower surface or face  23  of the print bar  24  (see also FIG. 4B). The print bar receptacles  21  also include mating features complementary to alignment features on the printheads to assure proper alignment of the printheads relative to one another. The print heads  30  can be arranged in an array to offset nozzle openings to increase printing resolution or printing speed.  
         [0030]    In a printing position, the print bar  24  is arranged above the web path to provide proper alignment and a uniform stand-off distance between the print heads  30  and the web  14 . In typical arrangement, the stand off distance between the web path and the print bar is between about 0.5 and one millimeter. The print heads  30  can be of various types, including drop on demand ink-jet print heads with arrays of small, finely spaced nozzle openings. Piezoelectric ink-jet print heads are described in Hoisington U.S. Pat. No. 5,265,315, Fishbeck et al. U.S. Pat. No. 4,825,227 and Hine U.S. Pat. No. 4,937,598, the entire contents each of which is hereby incorporated by reference. Other types of print heads can be used with the print bar, such as, for example, thermal ink jet print heads in which heating of ink is used to effect ejection. Continuous ink-jet heads, that rely on deflection of a continuous stream of ink drops can also be used.  
         [0031]    Referring as well to FIGS. 3A and 3B, the print bar  24  can be pivoted (arrows  50 ) between a printing position (FIG. 3A) and a cleaning position (FIG. 3B). The print bar  24  is attached to a pivot rod  25 . The pivot rod is rotatably coupled to a printing pivot base  26 . The printing pivot base  26  is attached to a frame  27  which provides a guide for the web  14 . The printing pivot base  26  is typically fixed relative to the web path. As illustrated in FIG. 3A, during printing, the print bar  24  is arranged in a generally parallel plane above the web path with face  23  of the print bar opposite the web  14 . In this condition, the print bar  24  engages print supports  28 , which are also attached to the frame  27  so that the print bar  24  is stabilized at a uniform stand-off distance from the web path. Referring as well to FIG. 4A, a view of the face  23  of the print bar, the print supports  28 , engage the print bar  24  at mating features  29 . The mating features  29 , e.g., apertures, are shaped to uniquely mate with the supports  28 , to assure alignment of the print bar  24  by minimizing skew in the plane of the print bar relative to the web path. More generally, the mating features can be any component(s) that assure print bar alignment. Examples include mechanical male and female interlocking features, magnetic components, vacuum seals, etc.  
         [0032]    Continuing to refer to FIGS. 3A and 3B, to access the cleaning position, the print bar  24  is pivoted about an axis of rotation defined by the pivot rod, (arrows  50 ) to an orientation out of the plane parallel to the print path to facilitate access to the face  23  of the print bar and face  22  print heads to permit cleaning using a head cleaner system  40 . The cleaning system  40  is connected to a vacuum source  41  to clean the faces of the print bar and print heads. The head cleaner system  46  includes a cleaning bar  44  fixed to a cleaner pivot rod  45 . The cleaner pivot rod  45  is rotatably coupled to a cleaner base  46 . The cleaner base  46  is attached to a frame (not shown) which is fixed relative to the printing bar base  26 . As illustrated in FIG. 3A, during printing, the cleaning bar  44  is positioned so that it does not interfere with the print bar  24 . For example, the cleaning bar  44  may be positioned above the printing bar  24  in a generally parallel plane. As illustrated in FIG. 3B, to effect cleaning the print bar  24  is pivoted (arrow  50 ) out of the plane parallel to the web path, e.g., into a plane perpendicular to the web path, and the cleaning bar is pivoted (arrow  52 ) into a plane parallel to and closely adjacent the face  23  of the print bar  24 . Referring as well to FIG. 4A, the face  43  of the cleaning bar  44  includes alignment features  48 , such as pins. In the cleaning condition, the alignment features  48  are shaped to engage the mating features  29 , on the print bar. The alignment features  48  also define a stand off distance between the cleaning bar face  43  and the print bar face  23  to avoid substantial contact with the print heads so that the print heads are not disturbed from their relative alignment on the print bar and the delicate nozzle openings are not damaged.  
         [0033]    Print bar base  26  includes a drive  91  (e.g., a stepper motor) that pivots print bar  24  between the printing position and the cleaning position. A controller  99  (e.g., including an electronic processor) controls the operation of print bar base drive  91 . Cleaner base  46  also includes a drive  92 , which adjusts cleaning bar  44  between its cleaning position and idle position. Controller  99  similarly controls the operation of cleaner base drive  92 . Controller  99  is also in communication with limit sensors  90  and  95  (e.g., optical sensors or electrical contact sensors), which are attached to print supports  28  and cleaner base  46 , respectively. Limit sensor  90  detects when print bar  24  is in the printing position and sends a signal to controller  99 , causing the controller to disengage the print bar base drive. Similarly, limit sensor  95  detects when the cleaner bar is in the cleaning position or idle position and causes the controller to disengage the cleaning bar drive. In the present embodiment, sensors  90  and  95  are attached to the print supports and cleaner base, respectively, however, in general, the limit sensors can be positioned at any location from which they can detect an appropriate print bar or cleaning bar position. Additional sensors can be included. For example, an additional sensor may be positioned to detect when print bar  24  is in the cleaning position.  
         [0034]    Referring to FIG. 4A and FIG. 4B, the face  43  of the cleaning bar  44  includes an array of vacuum apertures  47  which are in communication with the vacuum source. The vacuum apertures  47  are arranged in an array that complements the array of print heads  22  on print bar  24 , such that in the cleaning condition a vacuum aperture is associated with each print head. A sealing ring  49  ensures an air tight seal between the face  43  of cleaning bar  44  and the face  23  of print bar  24  when the cleaning bar and print bar are in their cleaning positions (see FIG. 3B). Optionally, cleaning bar  44  can include wipers for wiping the print heads during cleaning.  
         [0035]    Referring to FIG. 5, a greatly expanded cross-sectional view illustrating a single vacuum aperture  47  opposite the face  21  of a print head, the force of the vacuum removes (arrows  54 ) debris such as ink residue, dust, web fibers, and the like which could interfere with the performance of the print head nozzles  20 . The aperture  47  is in communication with a duct  48  which directs debris to collector, e.g., a filter (not shown).  
         [0036]    Referring to FIG. 6, in an alternate embodiment, a liquid solvent is supplied by conduit  60  to spray head  62 . During cleaning, the solvent is sprayed prior to or during the airflow generated by the vacuum source, to assist in removal of debris that could clog the print head. The stand off distance between the face of the cleaning bar and the face of the print bar may be small, e.g., about five millimeters or less.  
         [0037]    Referring to FIG. 7, an enlarged view of a pivoting coupling is provided. In FIG. 7, the pivot coupling is shown for print bar  24 . A similar coupling can be used for the cleaning bar. Print bar  24  includes mounting tabs  702  and  704 , each of which includes a hole,  712  and  714 , in which ball bearings  722  and  724  are fixed. Shoulder bolts  732  and  734  extend through mounting tabs  702  and  704 , respectively, and fasten to threaded holes in the side walls of print bar base  26 . Only threaded hole  716  in base side wall  726  is shown in FIG. 7. The shaft of each shoulder bolt is precision machined to mate exactly with the inner race of the respective ball bearings. The shoulder bolts secure the print bar to the print bar base, but allow the bar to pivot around the bearing axes. The bar, pivot coupling components, and base can be machined from materials that exhibit high environmental stability (e.g., are stable for operational temperature and humidity ranges), such as stainless steel or invar.  
         [0038]    Referring to FIGS. 8A and 8B, a suitable print head includes a print head  30 , module  70  which is positioned on a face plate  72  and to which is attached a flat print  74  delivery of drive signals that control ink ejection. The print head  30  includes ink path structure  76  for delivering ink to the module. The face  21  of the module includes an array of finely spaced nozzles  20  from which ink is ejected.  
         [0039]    In embodiments, other cleaning arrangements can be used. For example, the cleaning bar need not extend the full width of the print bar. Instead, the cleaning bar can be indexed across the print bar. The cleaning bar can be moved into a cleaning position using assemblies other from pivoting arrangements. For example, the cleaning bar may be slid in a plane parallel to its plane or translated traverse to its plane into proximity of the printing bar after the printing bar has been pivoted from the printing condition. The cleaning can be accomplished by apparatus other than cleaning bar. For example, a vacuum hose could be translated across the face of the print bar to sequentially vacuum portions of the print bar. A wiper could be used to wipe debris from the face of the print bar.  
         [0040]    In embodiments, other pivoting arrangements or orientations can be used. The axis of rotation of the pivot could be parallel to the web path. For example, the print bar could be coupled to a support at the edge of the web path or in the middle of the web path. The print bar and/or the cleaning bar may not be planar. For example, the print bar could have a curvature or receptacles that otherwise align printheads to follow a web path that has curvature. The cleaning bar can have a curvature complementary to the print bar curvature.  
         [0041]    While particularly beneficial for a large-scale, single-pass web based print stations as illustrated in FIG. 1, the cleaning arrangement can be used with other printing arrangements in which components such as a paper path or guide make cleaning operations difficult. For example, the cleaning system can be used with printing stations in which printing is conducted by single or multiple passes of a print head over a single print substrate or sheet.  
         [0042]    Still further embodiments are in the following claims.