Abstract:
Systems and methods are provided for drying print media. The system comprises a dryer comprising an enclosure and a roller. The roller is proximate to an opening into the enclosure. A perimeter of the roller covers a portion of the opening, and an uncovered portion of the opening comprises a gap for a web of print media. The gap has a size defined on one side by the perimeter of the roller and on another side by a surface of the opening.

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of printing, and in particular, to dryers that dry marking material onto print media. 
     BACKGROUND 
     In continuous-forms printing systems, one or more marking engines are used to apply marking material (e.g., ink) onto a web of print media. The web is driven through the marking engines and into a dryer. As the web travels through the dryer, the dryer heats the web and dries the marking material onto the web. The web moves quickly across the printing system in order to enable fast printing speeds. For example, the web may travel at many linear feet per second through the printing system. This means that dryers must either occupy a large space within the print shop or use a great deal of heat to dry the web. For example, in many dryers, inked portions of the web transit the entire length of the dryer in a fraction of a second. 
     When dryers apply large amounts of heat to a web, there is a risk of a fire igniting along the web and escaping the dryer. To address this issue, dryers often use a tunnel that is bordered on all sides by solid walls. The web is heated as it travels through the tunnel, but the tunnel has narrow entrances which are so small that even if the paper is overheated, there is insufficient mass transfer of oxygen from the outside to enable the fire to leave the dryer via the tunnel. 
       FIG. 1  is a block diagram of a prior art dryer unit  110 . Dryer unit  110  includes an array of heating lamps  114  which heat web  120  as it travels through tunnel  112 . In  FIG. 1 , the radiant heat from radiant heating lamps  114  is indicated by element  116 . Rollers  130  and  140  position web  120  as it enters and exits dryer unit  110 , in order to tension web  120  during its transit through tunnel  112 . Tunnel  112  includes openings  118 , which are so narrow that any fires which start within dryer unit  110  do not have sufficient oxygen to escape along tunnel  112  and out of dryer unit  110 . Openings  118  are known in the art as fire enclosure openings because they prevent fires from spreading outside of dryer unit  110 . 
     Fire enclosure openings remain problematic in existing dryers. For example, even when tension is applied by rollers  130  and  140  to keep web  120  taut, web  120  may still experience upward and downward deflection along the scan direction as it travels through tunnel  112  (this is referred to as “flapping”). In addition, the web may exhibit wrinkling or puckering along the process direction due to excessive moisture from the applied marking material (this is referred to as “cockling”). This may cause further issues. 
       FIG. 2  is a block diagram illustrating limitations of a prior art drying unit. Here, only tunnel  112  of dryer unit  110  is illustrated. In  FIG. 2 , rollers  130  and  140  minimize deflection and deformation of web  120  at points  210  and  220 , respectively. However, as web  120  travels through tunnel  112 , it may deflect upward and/or downward by a small amount. Naturally, the amount of deflection depends on the distance to the nearest roller, physical properties of the web itself, travel speed of the web, and the amount of tension on the web. Because the narrow openings  118  are not very tall (e.g., only millimeters in height), web  120  may deflect into the ceiling of the fire enclosure openings formed by these openings  118  (e.g., at locations  230  and  240 ). This in turn smears marking material on web  120 , which reduces print quality and is undesirable. 
     Thus, manufacturers continue to search for systems that improve the capabilities of dryers for printing systems. 
     SUMMARY 
     Embodiments described herein use a roller to define a border of a fire enclosure opening for a dryer. Using a roller in this way prevents flapping of a web of print media as it travels through the fire enclosure opening. When the web travels within the fire enclosure opening, the web is held to the roller and therefore unlikely to experience any substantial deflection or wrinkling. Because deflection of the web of media at the roller itself is almost zero when it is in contact with the roller, the web is least likely to have an inked portion rub against the fire enclosure opening. 
     One embodiment is a dryer. The dryer comprises an enclosure that includes an opening for a web of print media to travel between an exterior of the enclosure and an interior of the enclosure. The dryer further comprises a heating element that is operable supply heat to the interior, and a roller proximate to the opening that aligns the web as the web travels within the interior. A perimeter of the roller covers a portion of the opening, and an uncovered portion of the opening comprises a gap for the web. The gap has a size defined on one side by the perimeter of the roller and on another side by a surface of the opening. 
     Another embodiment is another dryer. The dryer comprises an enclosure and a roller. The roller is proximate to an opening into the enclosure, wherein a perimeter of the roller covers a portion of the opening, and wherein an uncovered portion of the opening comprises a gap for a web of print media. The gap has a size defined on one side by the perimeter of the roller and on another side by a surface of the opening. 
     Another embodiment is a printing system. The system comprises a continuous-forms printer, and a printing system dryer operable to dry a web of print media that has been marked by the printer. The dryer includes an enclosure and a heating element located within an interior of the enclosure that is operable to generate heat within the enclosure. The dryer further includes a first roller located proximate to the enclosure that obscures a portion of an opening into the enclosure and positions the web of print media as the web enters the enclosure, where the unobscured portion of the opening is sufficiently small to prevent fires inside of the enclosure from leaving the enclosure via the entrance. The dryer further includes a second roller located proximate to the enclosure that obscures a portion of another opening into the enclosure and positions the web as the web exits the enclosure, where the unobscured portion of the other opening is sufficiently small to prevent fires inside of the enclosure from leaving the enclosure via the exit. 
     Other exemplary embodiments (e.g., methods and computer-readable media relating to the foregoing embodiments) may be described below. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG. 1  is a block diagram of a cut-away side view prior art drying unit. 
         FIG. 2  is a block diagram illustrating limitations of a prior art drying unit. 
         FIG. 3  is a block diagram illustrating a cut-away side view of a dryer unit in an exemplary embodiment. 
         FIG. 4  is a block diagram illustrating a front view of a dryer unit in an exemplary embodiment. 
         FIG. 5  is a block diagram illustrating a dryer unit implementing additional features in an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The figures and the following description illustrate specific exemplary embodiments of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within the scope of the invention. Furthermore, any examples described herein are intended to aid in understanding the principles of the invention, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the invention is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
       FIG. 3  is a block diagram illustrating a cut-away side view of a dryer unit  300  in an exemplary embodiment. Dryer unit  300  is used to dry incoming webs of print media that have been marked by a continuous-forms printer (e.g., an upstream printer, not shown). 
     According to  FIG. 3 , dryer unit  300  comprises an enclosure  310  that includes an interior  312 . Enclosure  310  also has an opening  318  for a web of print media to travel through. Enclosure  310  may comprise a solid material such as a metal or a plastic in combination with an insulating material, and will typically be chosen for its fire-resistant (or fireproof) properties, spectral or thermal reflectance, structural strength, etc. For example, the interior of enclosure  310  may comprise silver-plated aluminum. 
     An array of heating elements  314  are located within enclosure  310 . Heating elements  314  heat web of print media  320  as it transits interior  312  (e.g., along an open path within interior  312 ). Each heating element  314  may comprise a radiant heater (e.g., heat lamp), an inlet for hot gas to enter interior  312 , an electro-resistive heater, or various other components. Heat and/or mass flow from heating elements  314  is represented via element  316 . 
     Web  320  may comprise any suitable material capable of receiving marking material and being dried by dryer unit  300 . For example, web  320  may comprise a web of paper. In one embodiment, web  320  is oriented so that a wet, inked side of web  320  does not directly contact rollers  330  or  340  during the drying process. 
     Rollers  330  and  340  position web  320  as web  320  travels across interior  312 . For example, rollers  330  and  340  may comprise cylindrical devices that are freely rotatable or fixed. Rollers  330  and  340  may further apply tension to web  320 , and may further be driven by an outside force (e.g., a motor) to move web  320  through dryer unit  300 .  FIG. 4  further illustrates roller  330  as it positions web  320  for travel within enclosure  310 . 
     The size of each opening defined by enclosure  310  alone (e.g., opening  318 ) is fairly large. Specifically, these openings are large enough to allow a substantial amount of oxygen to enter interior  312 . This amount of mass transfer would allow a flame to escape interior  312  through one of the openings and enter the print shop. 
     To address this issue, rollers  330  and  340  each have perimeters that cover/block/obstruct/obscure a portion of an opening in enclosure  310 . For example, roller  330 , in combination with enclosure  310 , forms a gap (entrance  350 ) for web  320  to travel through. Entrance  350  has a size that is defined on one side by the perimeter of roller  330 , and that is defined on another side by a surface of enclosure  310  that forms a border of opening  318 . Entrance  350  is sufficiently small in size (d) that it prevents a fire from traveling outside of enclosure  310  via entrance  350 . Specifically, entrance  350  does not allow sufficient mass transfer of oxygen to enable anything more than minimal (i.e., substantially zero) fire escape. Roller  340 , in combination with enclosure  310 , forms a similarly-sized exit  360 .  FIG. 4  further illustrates the dimensions of entrance  350 . 
     Because entrance  350  and exit  360  have a small enough size (d), the linear flow of oxygen to the dryer is small enough to prevent the fire from escaping along any single opening. Thus, the gaps for entrance  350  and exit  360  form fire enclosure openings that enhance the safety of dryer unit  300 . At the same time, entrance  350  and exit  360  are located directly next to the rollers, where deflection of web  120  is minimal (because web  120  is more or less fixed to a roller at these locations). This means that web  120  resists deflection upward to contact dryer unit  300  and smear wet marking material. 
     Fire enclosure openings are dimensioned to prevent fire from escaping enclosure  310 . For this reason, even though multiple fire enclosure openings, in combination, may provide enough oxygen for a fire inside enclosure  310  to continue, the fire cannot substantially escape through any one of those openings. The fire escape is minimal and the ability of the fire to transfer to components outside of the enclosure is substantially zero. Fire enclosure openings are described in further detail, for example, in the Standard for Safety of Information Technology Equipment IEC/UL 60950-1 application guideline, issued by Underwriters Laboratories Inc.® and herein incorporated by reference. For example, such standards may restrict the height of the fire enclosure opening to less than 1 millimeter (mm), yet allow for any length. In one embodiment, the height of the fire enclosure opening depends on the thickness of web  320 , so that the fire enclosure opening is taller when thicker webs are used. For example, the fire enclosure opening may be 1.5 mm tall, where web  320  may have a thickness of up to 0.25 mm. Potentially, the fire enclosure opening could even be taller (e.g., even 12 mm tall). 
       FIG. 4  is a block diagram illustrating a front view of dryer unit  300  in an exemplary embodiment. Roller  330  positions web  320  as web  320  proceeds in its direction of travel and enters enclosure  310 . The size (d) of entrance  350  is very small (e.g., mere millimeters), which prevents fires inside of dryer unit  300  from escaping. 
     In a further embodiment, a dryer unit may utilize an exhaust port such as a vent that allows particulate, smoke, and dust to leave the interior of the dryer unit. The exhaust port may be passive, or may include a fan (or other device) in order to create a negative pressure that draws fire and smoke upward and out of the dryer unit via the exhaust port instead of an entrance or exit of the dryer unit. 
     In a further embodiment, rollers used for the dryer unit may be positioned to avoid direct heating from a heating element of the dryer unit, and/or may include heat reflective surfaces to prevent the rollers from overheating. 
     In a further embodiment, the rollers or enclosure may be adjustably positioned to alter the size of an entrance or exit. This may be desirable if some webs are thicker than others. For example, the rollers may be adjustably positioned such that if the rollers expand due to heating from the dryer (and thereby shrink the size of their corresponding entrance or exit), the rollers may be repositioned to account for this change. 
       FIG. 5  is a block diagram illustrating a dryer unit  500  implementing additional features in an exemplary embodiment. According to  FIG. 5 , enclosure  580  of dryer unit  500  includes an opening  518  which is partially covered by roller  530 . Because of the unique shape of opening  518 , web  520  enters a gap entrance  550  that is formed in the shape of an arc. The arc has a depth that extrudes into the page. This curving gap entrance  550  is defined by a curving surface of enclosure  580  on one side, and by a curved portion of the perimeter of roller  530  on the other side (the curved portion having an angle θ). Similarly, gap exit  560  is formed by enclosure  580  and roller  540 . These arcing gaps may have a thickness (e.g., 1 mm) that keeps them compliant with standards for fire enclosure openings. 
     In  FIG. 5 , the surface of dryer unit  500  includes reflective elements, which reflect heat from interior  512  back onto web  520  and away from rollers  530  and  540 . Rollers  530  and  540  have been positioned so that they are not directly heated by heating elements  514 . Furthermore, the reflective elements of interior  512  have been positioned so that reflected heat strikes web  520 , and not roller  530  or  540 . 
     In this embodiment, dryer unit  500  further includes an exhaust port  570 , which channels excess heat and exhaust out of dryer  500 . This serves to create a pressure gradient at the gaps that draws air from outside into the dryer, which reduces the chance of a fire leaving the interior via any gap. 
     Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.