Abstract:
A printer includes a print zone, and a media output guide assembly downstream of the print zone to curve media between media side edges. The media output guide assembly includes: an inner guide; and a pair of outer guides, the media to pass between the inner guide and the outer guides with the inner guide above the media and the outer guides below the media. The media passing between the guides has, in a direction perpendicular to a media output direction, outer edges that droop around and below a top of the outer guides, elevated points at the tops of the outer guides and a central low point under the inner guide and between the outer edges.

Description:
BACKGROUND 
     Media may have a tendency to curl. This may complicate a proper output or stacking of printed media. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For the purpose of illustration, certain examples constructed in accordance with this disclosure will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates an example of a diagram of a printer; 
         FIG. 2  illustrates an example of a diagram of a transverse cross section of a media output guide assembly and curved media; 
         FIG. 3  illustrates a portion of an example printer with an example media output guide assembly in perspective view; 
         FIG. 4  illustrates a portion of the example printer with example media output guide assembly of  FIG. 3  in front view; 
         FIG. 5  illustrates a portion of the example printer with example media output guide assembly of  FIGS. 3 and 4 , in side view; 
         FIG. 6  illustrates the individual example media output guide assembly of  FIGS. 3-5  in perspective view; 
         FIG. 7  illustrates a flow chart of an example method of printing and ejecting media; and 
         FIG. 8  illustrates a flow chart of another example method of printing and ejecting media. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings. The examples in the description and drawings should be considered illustrative and are not intended as limiting to the specific example or element described. Multiple examples of printers or media output guide assemblies can be derived from the following description and drawings through modification, combination or variation of the different elements. 
       FIG. 1  illustrates an example of a printer  1 . The printer  1  includes a print zone  2 . The print zone  2  can be defined as the region where advancing media  3  is printed upon. In one example a print platen is provided in the print zone  2 . The printer  1  includes an imaging arrangement  4  to print onto the media  3  in the print zone  2 . For example, the print zone is defined by the imaging arrangement  4 . 
     The imaging arrangement  4  can be an electrophotographic or inkjet imaging arrangement. Examples of the imaging material are liquid or dry toner or ink. In one example the imaging arrangement  4  includes a receiving bay fixed to the printer  1  to receive an exchangeable cartridge that holds the imaging material. In other examples the imaging arrangement  4  includes a printhead assembly that is fixed to the printer  1 , wherein the printhead assembly can be a scanning or a page wide array printhead assembly. 
     In one example the printer  1  includes a media output tray  7 . The media output tray  7  includes a media support surface  8  to support the media  3  or media stack. 
     The printer  1  includes a media output guide assembly  5  to curve the media  3  downstream of the print zone  2 . A media output direction M runs from right to left in  FIG. 1 . The media output guide assembly  5  is to curve a middle portion  3 B of the media  3  by engaging the media  3  downstream of the print zone  2 . In one example the middle portion  3 C is curved so that it exhibits a U-shape. In one example the middle portion  3 C is curved towards the media support surface  8 . In the illustrated example the middle portion  3 C is curved downwards so that media side portions  3 C are above the middle portion  3 B. In other, not illustrated examples the media  3  may be stacked in an inclined or approximately vertical orientation or directly on a desk or table top. In these examples the “belly” of the U-shaped media would be directed towards the media support surface, that is, the media tray or desk or table top. 
     In a further example explanation, just after the print zone  2  the recently deposited imaging material may be wet, cooling down, drying, curing, fusing or undergoing some kind of temperature or state change. As a result thereof the media  3  may tend to curl. In again further examples certain media types, such as for example relatively thin paper or short grained paper, are extra sensitive to curl, especially in combination with the imaging material being wet, cooling down, drying, curing, fusing or undergoing some kind of temperature or state change. Intentionally curving the media  3  at output may help in these and other example situations. For example, curving the media  3  after the print zone  2  can inhibit curling of the media  3  over a direction perpendicular to the media output direction M. For example, the curving of the media  3  after the print zone  2  may stiffen the media  3  at output. 
       FIG. 2  illustrates an example diagram of a media output guide assembly  105  and a transverse cross section of media  103  advancing through the media output guide assembly  105 . The media  103  represents recently or currently printed media  103 . For example the media  103  is output or ejected towards the viewer. The media output direction could be horizontal, upwards or inclined with respect to a horizontal. Different printer types may have different ways of ejecting and stacking media. 
     In the example of  FIG. 2  the media output guide assembly  105  is provided with four example guides, of which two first guides  110  and two second guides  111 . As illustrated, the media output guide assembly  105  is to direct a middle portion  103 B towards a media support surface  108  and side portions  103 C away from the media support surface  108  so that the transverse cross section of the output media  103  includes a U-type shape. In one example the media support surface  108  is a support surface of a printer output tray that may be horizontal, inclined, or almost vertical. In another example the media support surface  108  is formed by a desk top surface on which a respective printer is placed, that is, the printer is to stack printed media onto the desktop on which it is placed. 
     In the example illustration, the first guide  110  contacts a first face of the printed media, while the second guide  111  contacts the opposite face of the printed media  103 . The second guide  111  presses into the media  103  to bow the middle portion  103 B towards the media support surface  108 , while the first guides  110  hold the side portions  103 C away from the media stack surface  108  so that the U-shaped cross section is formed. The point where the second guide  111  is to engage the media  3  is closer to the media support surface  108  than the point where the first guide  110  is to engage the media  3 . As illustrated, in operation, the U-shape in the media  103  may span between the first guides  110  and its width Uw may span more than half of a width W of a print zone and/or media output tray support surface. In a further example the distance GD between the inner second guides  111  is more than half of the width W of the print zone and/or media output tray support surface. For example the formed “belly” of the U-shaped media is relatively wide. 
     In other examples the media output guide assembly  105  may include other numbers of guides  110 ,  111 , such as for example only one second guide  111  to push the middle portion  103 C towards the media support surface  108 . 
       FIGS. 3-5  illustrate a portion of an example printer  201  including an example media output guide assembly  205  and  FIG. 6  shows the individual media output guide assembly  205  of  FIGS. 3-5 . In an example, the printer  201  includes output rollers  215 . The output rollers  215  are disposed near the print zone for example downstream of the print zone, for example at the edge of the print zone. The output rollers  215  are to aid in advancing the media during printing. For example, the output rollers  215  are to eject the media from the printer  201 . In an example bottom output rollers  215  are disposed over the width of the printer to engage a face of the printed media that is not currently being printed. For example, the output rollers  215  are to eject the media towards the media stack through a short acceleration, allowing the media to be advanced over a certain distance and then fall down onto a media support surface by gravity. The media output guide assembly  205  is arranged downstream of the print zone and downstream of the media output rollers  215  to curve the printed media that is advanced by the output rollers  215 . In certain examples the output rollers  215  are also arranged to return printed media for duplex printing. 
     The media output guide assembly  205  includes two top guides  211  to engage a top face of printed media. In an example the top face is the image face of the printed media. In case of duplex printing the image face is the face that is being printed, and/or the face with the most recently printed image. In one example the top guide  211  includes a low friction element to roll or slide over the image face during printing. For example the top guide  211  includes low friction wheel  216  such as a star wheel to roll over the image face during printing. 
     The media output guide assembly  205  includes two bottom guides  210  to engage a bottom face of printed media. The bottom guides  210  are arranged next to the top guides  211  on the outside of the top guides  211 . In an example the bottom face is the face of the media that is not being printed, or, in case of duplex printing, the face that was first printed. For example, in case of duplex printing the image on the bottom face may have already cooled down, cured, dried, fused, etc., so that there is less risk that the bottom guides  210  engage wetted imaging material. In one example the bottom guides  210  include a slide element such as a ski-like structure so that during media output the bottom face of the media slides over the bottom guide  210 . 
     The guides  210 ,  211  are arranged in pairs  212  wherein each pair  212  contains a bottom guide  210  and a top guide  211 . The distance between a bottom guide  210  and a top guide  211  within a pair  212  is smaller than the distance between the pairs  212 . The top guides  211  are disposed on the inside so that the distance between the top guides  211  is smaller than the distance between the bottom guides  212 . Consequently, in this example, the distance between the pairs  212  is determined by the distance between the top guides  211 . 
     A point of the top guides  211  that is to engage the media is lower than a point of the bottom guides  210  that is to engage the media. This is perhaps best viewable in  FIG. 5 . The top guides  211  are arranged on the inside of the bottom guides  210  and by having the engagement point lower than the engagement point of the bottom guides  210  the top guides  211  press the middle portion of the media down, that is, in operation. In turn, the bottom guides  210  are to press side portions of the media, on both sides of the middle portion, upwards so that a U-shape is formed in the output media, as diagrammatically illustrated in  FIG. 2 . 
     In one example that is perhaps best understood with reference to  FIGS. 5 and 6  at least one of the guides  210 ,  211  is retractable. For example at least the bottom guides  210  are retractable. In the illustrated example, both the top and bottom guides  211 ,  210  are retractable. In one example, the guides  210 ,  211  are to retract just before the output rollers  215  eject the printed media. 
     In an example the retractable top guide  211  includes a retractable arm  221 . In a further example, the arm  221  includes a rack  223  that is engaged by a pinion  225  or gear that in turn is drivable by a motor  227  ( FIG. 6 ). For example, further transmission elements  229  are to transmit motor axle rotation to the pinion  225  and, finally, to the guide wheel  216 . These further transmission elements  229  may include gears and axles. Both two top guides  211  may be drivable by the same motor  227  through said transmission elements  229 . 
     For example, the arm  221  is retractable and extendable over a straight line L over its own longitudinal axis. For example the top guide  211  includes a pivoting arm  231  to support and guide the retractable arm  221  during retraction and extension of the top guide  211 . One end of the pivoting arm  231  pivots with respect to the retractable arm  221  and another end is mounted to a printer part in a pivoting manner and has a fixed location. In an example, the pivoting arm  231  is telescopic. For example the arm  221  is to retract substantially upwards and extend substantially downwards. 
     In an example the retractable bottom guide  210  also includes a retractable arm  222 . In a further example, the bottom arm  222  includes a rack  224  that is engaged by a pinion  226  or gear that in turn is drivable by a motor  228 . For example, further transmission elements  230  are to transmit motor axle rotation to the pinion  226  and, finally, to the bottom guide arm  222 . The further transmission elements may include gears and axles. Both two bottom guides  222  may be drivable by the same motor  228  through said transmission elements  230 . 
     For example, the bottom arm  222  is retractable and extendable over a straight line Lb over its own longitudinal axis. For example the bottom arm  22  is extendable away from the print zone and retractable towards and partly under the print zone. 
     The printer  201  includes a drive circuit  240  to instruct the drive of the bottom and top guide  210 ,  211 . In the discussed example such guide drive includes motors  227 ,  228 . For example the guide drive includes open loop DC motors. For example, the drive circuit  240  is to instruct the guide drive to extend and retract the guides  210 ,  211 . For example the drive circuit  240  is to instruct the guide drive to extend and retract the guides  210 ,  211  before a trailing media edge passes and/or before the media is ejected. For example the drive circuit  240  is to instruct the media output rollers  215  to eject the media just after the guides  210 ,  211  are ejected. 
       FIG. 7  illustrates a flow chart of an example of a method of printing and ejecting media. For example the method includes advancing media over a print zone (block  300 ). For example the method includes printing on the advancing media (block  310 ). For example the method includes, during said printing, curving a middle portion of the media towards a media support surface so that a transverse cross section of the media includes a U shape (block  320 ). Such curving may occur downstream of the print zone. 
       FIG. 8  illustrates a flow chart of another example of a method of printing and ejecting media. For example the method includes advancing media over a print zone, wherein a general grain direction of grains in the media is perpendicular to the media advance direction (block  400 ). For example, the media is advanced in a landscape orientation or the media includes short grain paper. Here, the grain direction can be defined as a direction of the length of the grains. Here, short grained paper can be defined as paper wherein a length direction of the fibers in the paper is generally aligned with a short edge of the paper. For example the method includes printing on the advancing media (block  410 ), wherein the grain direction is perpendicular to the media advance direction. 
     In this example the media has a grain direction perpendicular to the media advance direction during printing. Therefore the fibers may offer relatively little resistance to curling and the short grained media may have a relatively strong tendency to curl at ejection, especially when the image has not fully dried, cured, fused or cooled down. In one example the method includes, while the image has not fully dried, cured, fused or cooled down, curving a middle portion of the media downwards so that a transverse cross section of the media includes a U shape (block  420 ). In one example this allows the short grain media to be stiffened and may prevent curling. The method includes a disengagement of the media by guides before a trailing edge has passed these guides (block  430 ). The method includes ejecting the media after the guides have disengaged the media (block  440 ). 
     While in this description directional indications including “bottom”, “top”, “downwards”, and “upwards” are used, these can be interpreted as relative. For example the examples mentioned with respect to  FIGS. 3-6  could also be implemented in a printer that has an approximately vertical or inclined media output tray. In such assembly, similar media output guide assemblies can be applied.