Abstract:
A printer includes: a printhead assembly having a print zone and a belt assembly for feeding print media past the print zone in a media feed direction. The belt assembly includes: an endless belt tensioned between a first roller upstream of the print zone and a second roller downstream of the print zone; a drive mechanism for moving the endless belt in the media feed direction; and a fixed platen positioned in the print zone. The endless belt is guided around and below the fixed platen.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional application Ser. No. 62/204,211, filed Aug. 12, 2015, entitled “BELT ASSEMBLY FOR HIGH-SPEED INKJET PRINTING,” which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a belt assembly for a printer. It has been developed primarily to provide a media feed mechanism suitable for high-speed inkjet printing. 
       BACKGROUND OF THE INVENTION 
       [0003]    The Applicant has developed a range of Memjet® inkjet printers as described in, for example, WO2011/143700, WO2011/143699 and WO2009/089567, the contents of which are herein incorporated by reference. Memjet® printers employ a stationary printhead in combination with a feed mechanism which feeds print media past the printhead in a single pass. Memjet® printers therefore provide much higher printing speeds than conventional scanning inkjet printers. 
         [0004]    High-speed single-pass inkjet printing requires accurate media handling, especially in the print zone of the printhead, in order to provide acceptable print quality. For relatively narrow print zones (e.g. A4 size or narrower), a system of entry and exit rollers in combination with a fixed media platen generally provides sufficient stability in the print zone (see, for example, U.S. Pat. No. 8,523,316, the contents of which are herein incorporated by reference). However, for wider media widths and/or faster print speeds, more complex media feed mechanisms are required to provide acceptable print quality. For example, U.S. Pat. No. 8,540,361 describes a feed mechanism suitable for wideformat printing comprising a combination of a fixed vacuum platen, an upstream drive roller and a downstream vacuum belt mechanism. 
         [0005]    Vacuum belt mechanisms are an attractive means for moving print media at high speeds through a print zone. Various vacuum belt mechanisms for high-speed printing are described in, for example, US 2007/0247505, US 2007/0035605, US 2008/0218576, U.S. Pat. No. 6,328,439, U.S. Pat. No. 6,698,878 and WO02/78958. Referring to  FIGS. 1A and 1B , prior art vacuum belt mechanisms typically comprise an endless belt  1  tensioned between a first roller  3  positioned upstream of a print zone  5  and a second roller  7  positioned downstream of the print zone. A printhead assembly  9  is positioned over an upper surface of the belt  1  while a vacuum blower  11  is positioned below the belt for suctioning print media onto the upper surface. The printhead assembly  9  is liftable away from the belt to allow intervention from a maintenance station  13 , when required ( FIG. 2A ). Likewise, the entire vacuum belt mechanism  10  may be movable away from printhead assembly  9  to facilitate clearance of paper jams. 
         [0006]    A problem with prior art vacuum belt mechanisms, such as the mechanism described in connection with  FIG. 1A , is that the belt may become fouled with ink. Ink mist generated in the print zone during printing is drawn towards the belt by the vacuum blower, thereby fouling the belt and, consequently, fouling paper in contact with the belt. Furthermore, it is desirable for inkjet printheads to spit ink regularly so as to avoid nozzles becoming clogged with a plug of viscous ink. Typically, inkjet printheads perform a number of inter-page spits so as to reduce the frequency of maintenance interventions. However, endless belts are not amenable to inter-page spitting due to ink fouling. 
         [0007]    It would be desirable to provide a printer having a belt assembly suitable for high-speed inkjet printing. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a printer comprising:
       a printhead assembly having a print zone;   a belt assembly for feeding print media past the print zone in a media feed direction, the belt assembly comprising:
           an endless belt tensioned between a first roller upstream of the print zone and a second roller downstream of the print zone;   a drive mechanism for moving the endless belt in the media feed direction; and   a fixed platen positioned in the print zone,
 
wherein the endless belt is guided around and below the fixed platen.
   
               
 
         [0014]    The printer of the present invention enjoys the advantages of high-speed media feeding using an endless belt, whilst advantageously avoiding the usual problems of ink fouling the belt. 
         [0015]    Preferably, the fixed platen comprises a spittoon for receiving ink. The spittoon advantageously collects ink spitted from the printhead, such as inter-page spits which are used to maintain healthy nozzles during a print job. 
         [0016]    Preferably, the printhead assembly comprises one or more fixed inkjet printheads configured for singe-pass printing. 
         [0017]    Preferably, the printer further comprises a printhead lift mechanism for moving the printhead assembly between a printing position and a maintenance position. 
         [0018]    Preferably, the printer further comprises a maintenance station for capping and/or wiping the printhead in the maintenance position. 
         [0019]    Preferably, the printer further comprises a belt lift mechanism for moving the belt assembly towards and away from the printhead assembly. 
         [0020]    Preferably, the endless belt comprises an apertured belt and the belt assembly further comprises at least one vacuum blower for suctioning print media onto a surface of the apertured belt. 
         [0021]    Preferably, the belt assembly comprises one or more rollers for guiding the endless belt below the fixed platen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1A  is a schematic side view of a prior art vacuum belt assembly in a printing position; 
           [0024]      FIG. 1B  shows the prior art vacuum belt assembly of  FIG. 1A  in a maintenance position; 
           [0025]      FIG. 2A  is a schematic side view of a printer according to the present invention in a printing position; 
           [0026]      FIG. 2B  shows the printer of  FIG. 2A  in a maintenance position; 
           [0027]      FIG. 3  shows an alternative pathway of a belt around a fixed platen; and 
           [0028]      FIG. 4  is a schematic plan view of an apertured belt and fixed platen. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    Referring to  FIGS. 2A and 2B , there is shown a printer  100  comprising a belt assembly  21  and a printhead assembly  9 , in accordance with the present invention. The printhead assembly  9  has an associated print zone  5  which is defined by the printable area of the printhead assembly. The printhead assembly  9  may be comprised of one or more fixed inkjet printheads, each of which may be comprised of a plurality of individual printhead chips. By way of example, U.S. Pat. No. 8,540,361 (the contents of which are incorporated herein by reference) describes a printhead assembly comprising five staggered printheads, each printhead comprising eleven printhead chips butted in a row. Alternatively, the printhead assembly  9  may comprise a single printhead, as described in U.S. Pat. No. 8,523,316. Alternatively, the printhead assembly  9  may comprise a pair of overlapping printheads. 
         [0030]    The printhead assembly  9  is positioned over a fixed platen  20  positioned in the print zone  5  of the printhead assembly. An endless belt  1  feeds print media (e.g. paper  22 ) from an upstream side of the printhead assembly  9  to a downstream side. The endless belt  1  is tensioned between a first roller  3  positioned upstream of the printhead assembly  9  and a second roller  7  positioned downstream of the printhead assembly. The first roller  3  is an idler roller while the second roller  7  is a drive roller operatively connected to a drive mechanism indicated schematically by arrow  24 . In the embodiment shown in  FIG. 2A , additional rollers  26  guide the endless belt  1  around a loop. It will be appreciated that the number and position of additional rollers  26  is not particularly important to the present invention. 
         [0031]    An upstream vacuum blower  11 A and a downstream vacuum blower  11 B impart a suction force onto the belt  1  so as to draw the paper  22  onto an upper surface of the belt. As shown in  FIG. 4 , the belt  1  has a plurality of apertures  28  so that the paper  22  experiences a suction force through the belt. 
         [0032]    A plurality of guide rollers  30 A-D are positioned to guide the endless belt  1  in a path around and below the fixed platen  20 . Thus, the endless belt  1  does not move through the print zone  5  and the sheet of paper  22  is supported by the fixed platen  20  when moving through the print zone. The number and position of guide rollers  30  and the precise path of the endless belt  1  around the fixed platen  20  is not particularly important. For example, by way of an alternative arrangement, the endless belt  1  may follow a generally triangular path around the fixed platen  20  with one central guide roller  30 E positioned below the fixed platen ( FIG. 3 ). These and other guide roller arrangements will be readily apparent to the person skilled in the art. 
         [0033]    Turning to  FIG. 4 , the fixed platen  20  comprises a spittoon  32  in the form of an opening positioned opposite the print zone  5 . The spittoon  32  is positioned to collect ink spitted from the printhead assembly  9 , such as inter-page spits which are used to maintain nozzle health during print jobs. The spittoon  32  may comprise an absorbent material and/or a suitable arrangement for wicking ink away from the fixed platen  20 . Alternatively or additionally, the spittoon  32  may be connected to a vacuum source (not shown). For example, the fixed platen  20  may be in the form of a vacuum platen to further assist with paper control through the print zone  5 . 
         [0034]    Referring again to  FIG. 2A , the entire belt assembly  21 , including the fixed platen  20  and endless belt  1 , is operatively connected to a belt lift mechanism, which is schematically represented by arrow  34 . The belt lift mechanism  34  moves the belt assembly  21  towards and away from the printhead assembly  9  to facilitate clearance of paper jams. Suitable sensors (not shown) may be provided for detecting paper jams and actuating the belt lift mechanism  34  to lower the belt assembly  21  when a paper jam is detected. 
         [0035]    Similarly, the printhead assembly  9  is operatively connected to a printhead lift mechanism, which is schematically represented by arrow  36 . The printhead lift mechanism  36  moves the printhead assembly  9  towards and away from the fixed platen  20  and belt  1  to enable maintenance of the printhead assembly by the maintenance station  13 . The maintenance station  13  is operatively connected to a translation mechanism  38  for slidably moving the maintenance station towards and away from the printhead assembly  9 . U.S. Pat. No. 9,061,531, the contents of which are incorporated herein by reference, describes a printhead lift mechanism and sliding maintenance station suitable for maintaining a fixed inkjet printhead. Typically, the maintenance station  13  comprises a capping module and a wiping module, as described in U.S. Pat. No. 9,061,531. 
         [0036]      FIG. 2B  shows the printer  100  in a maintenance position whereby the printhead assembly  9  is lifted away from the fixed platen  20  and belt  1  by the printhead lift mechanism  36 , and the maintenance station  13  has slid beneath the printhead assembly  9  by operation of the translation mechanism  38 . The printhead(s) may be capped or wiped in this maintenance position. 
         [0037]      FIG. 2A  shows the printer  100  in a printing position. The endless belt  1  is driven at constant speed by the drive mechanism  24  to convey the paper  22  in the media feed direction. The paper  22  is initially fed onto an upper surface of an upstream portion  40  of the belt  1  by a suitable paper picker (not shown). The paper  22  is suctioned onto the belt  1  by the upstream vacuum blower  11 A and moved towards the print zone  5 . The paper  22  is then transferred from the belt  1  onto the fixed platen  20  to move through the print zone  5 . Finally, the paper  22  is transferred from the fixed platen  20  onto a downstream portion  42  of the belt  1  and moved away from the print zone  5 . The endless belt  1  and vacuum blowers  11 A and  11 B enable smooth transportation of the paper  22  at constant speed with excellent control of paper movement. Moreover, diverting the endless belt  1  around and below the fixed platen  20  in the print zone  5  avoids fouling of the belt by ink mist or spitted ink. The spittoon  32  in the fixed platen  20  collects any non-printing ink, which can be readily removed without contaminating the belt  1 . 
         [0038]    It will, of course, be appreciated that the present invention has been described by way of example only and that modifications of detail may be made within the scope of the invention, which is defined in the accompanying claims.