Patent Publication Number: US-10308010-B2

Title: Infrared-heated air knives for dryers

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of printing, and in particular, to dryers for printing systems. 
     BACKGROUND 
     Dryers for printing systems may utilize infrared (IR) heating elements or actively blown air in order to directly heat a web of print media to a temperature at which ink ejected onto the web dries. Because the web proceeds quickly through the dryer, a careful balance must be achieved between underheating the web (resulting in applied ink not fully drying) and overheating the web (resulting in scorching of the ink and/or print media). These issues may be further complicated by the arrangement of various elements within the dryer. 
     Thus, designers of dryers for printing systems continue to seek out enhanced techniques for ensuring that inked webs of print media are fully dried, and without scorching. This ensures that print quality remains at a desired level. 
     SUMMARY 
     Embodiments described herein provide radiant dryers which include air knives that directly receive energy (e.g., IR energy) from internal heating elements that also radiate energy onto a web of print media. This results in the air knife increasing in temperature, causing air passing through the air knife to be heated by forced convective heat transfer with the air knife. The increase in air temperature increases the amount of moisture and ink vapor that may be drawn out of the web by the air. 
     One embodiment is an apparatus that includes a dryer for a continuous-forms printing system. The dryer includes heating elements located within an interior of the dryer that radiate infrared energy onto a web of printed media as the web travels through the interior, and an air knife that is interposed between the heating elements. The air knife includes a shell that directly absorbs infrared energy from the heating elements and also defines a passage for air to travel through the air knife onto the web. The shell directly absorbs infrared energy from each heating element that would otherwise overlap on the web with infrared energy from another heating element. 
     A further embodiment is an apparatus that includes multiple heating elements, and an air knife interposed between the heating elements. The air knife includes a shell having an exterior that directly absorbs infrared energy from the heating elements, a passage defined by the shell, and an inner surface of the shell heated by conductive heat transfer with the exterior the shell. Air exiting the air knife is heated by at least ten degrees Celsius via forced convective heat transfer with the shell. 
     A still further embodiment is a method that includes operating heating elements within an interior of a dryer to radiate infrared energy onto a web of printed media as the web travels through the interior, directly receiving infrared energy from the heating elements at a shell of an air knife, and heating air exiting a passage of the air knife by at least ten degrees Celsius via forced convective heat transfer with the shell. 
     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 diagram of a printing system in an exemplary embodiment. 
         FIGS. 2-6  are diagrams of a drying apparatus of a printing system in an exemplary embodiment. 
         FIG. 7  is a flowchart illustrating a method for operating a dryer of a printing system in an exemplary embodiment. 
         FIG. 8  is a diagram illustrating a further drying apparatus of a printing system in an exemplary embodiment. 
         FIG. 9  is a section cut diagram of the drying apparatus of  FIG. 8  in an exemplary embodiment. 
         FIG. 10  illustrates a vent plate for a return vent of the drying apparatus of  FIG. 8  in an exemplary embodiment. 
         FIG. 11  illustrates a processing system operable to execute a computer readable medium embodying programmed instructions to perform desired functions 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. 1  illustrates an exemplary continuous-forms printing system  100 . Printing system  100  includes production printer  110 , which is operable to apply ink onto a web  120  of continuous-forms print media. As used herein, the word “ink” is used to refer to any suitable marking fluid that can be applied by a printer onto web  120  (e.g., aqueous inks, oil-based paints, etc.). As used herein, the phrase “print media” (as in print media or printed media) refers to any substrate for receiving a marking fluid. Such substrates may include paper, coated paper, card stock, paper board, corrugated fiberboard, film, plastic, synthetics, textile, glass, tile, metal, leather, wood, composites, circuit boards or combinations thereof. Printer  110  may comprise an inkjet printer that applies colored inks, such as Cyan (C), Magenta (M), Yellow (Y), and Key (K) black inks. The ink applied by printer  110  to web  120  is wet, meaning that the ink may smear if it is not dried before further processing. One or more rollers  130  position web  120  as it travels through printing system  100 . 
     To dry the ink, printing system  100  also includes dryer  140  (e.g., a radiant dryer). Dryer  140  can be installed in printer  110 , or can be implemented as an independent device downstream from printer  110  (as shown in  FIG. 1 ). Web  120  travels through dryer  140  where an array of heating elements such as IR heat lamps radiate thermal energy to dry the ink onto web  120 . For example, web  120  may travel at a linear velocity of up to two hundred meters per minute through dryer  140 . Controller  142  manages the operations of dryer  140  and/or printer  110 . For example, controller  142  may manage various sensors, fans, heating elements, air logic, and other components at dryer  140 . Controller  142  may be implemented as custom circuitry, as a hardware processor executing programmed instructions, etc. 
     However, drying ink onto web  120  is not a simple process. Some colors of ink are vulnerable to scorching if they are exposed to too much heat. For example, “K black” ink and other dark colors are generally more absorbent of IR energy than lighter colors. Because the darker colors absorb more IR energy from the heating elements, they can reach a higher temperature than other colors of ink while drying. This means that dark inks may dry completely and overheat to the point that they risk scorching before lighter inks have fully dried. This issue is particularly prevalent in regions within dryer  140  where radiant energy from different heating elements overlaps onto web  120 . In order to address these concerns by reducing areas of radiative overlap while increasing the efficiency of an internal air knife, dryer  140  has been enhanced with a drying apparatus illustrated in  FIGS. 2-6 . 
       FIGS. 2-6  are diagrams of a drying apparatus  200  of dryer  140  in an exemplary embodiment. One or more of drying apparatus  200  may be utilized by dryer  140  to fully dry ink on web  120 .  FIG. 2  is a perspective view in which a left portion of dryer  140  has been subjected to a section cut.  FIG. 3  is a front view of drying apparatus  200  indicated by view arrows  3  of  FIG. 2 , and uses the same section cut as in  FIG. 2 .  FIG. 4  is a side view of drying apparatus  200  corresponding to view arrows  4  of  FIG. 3 . In  FIG. 4 , a section cut has been made to chamber  260  so as to illustrate internal features of chamber  260 . Meanwhile,  FIGS. 5-6  illustrate front section cut views of drying apparatus  200 . 
       FIG. 2  illustrates that drying apparatus  200  includes housing  210 , which surrounds various components of drying apparatus  200 . These components within interior  212  of drying apparatus  200  include heating elements  220 , which radiate IR energy onto web  120  as web  120  proceeds through dryer  140 . In this embodiment, heating elements  220  may include cylindrical heat lamps that have a circular cross section. Such heat lamps may comprise tungsten halogen bulbs having filaments that are heated to 3300 Kelvin or be comprised of carbon based filament heated to temperatures of about 2000 Kelvin. As such, in some embodiments heating elements  220  may emit light/energy at a broad range of frequencies, including the near IR band (e.g., having wavelengths ranging from 1.1-1.4 microns) and/or mid IR band (e.g., having wavelengths ranging from 2.2-2.8 microns). Reflectors (not shown) may also be utilized to reflect energy generated by heating elements  220  back towards web  120 , these reflective surfaces may also be integrated into the lamp housing. Heating elements  220  receive air from chambers  260 , and this fresh air passing over heating elements  220  ensures that integrated reflective coatings do not get damaged from overheating due to air stagnation. 
     Interior  212  also includes air knife  230 , which blows air onto web  120 . Air knife  230  may be operated, for example, to blow air out of an outlet at a rate of up to sixty meters per second, at a distance of less than two centimeters (e.g., a distance of ten millimeters) from the surface of web  120 . Incoming air for air knife  230  is thermally isolated from air for heating elements  220  by double wall  232 . Return vent  240  is also illustrated in  FIG. 2 . Return vent  240  draws in air blown by air knife  230 , in order to ensure that airflow remains restricted to interior  212  of drying apparatus  200 . This helps to ensure that ink vapors within the air that result from the drying process do not exit drying apparatus  200  proximate to web  120 . Return vents  240  include baffles  250  having slots  252  of varying sizes. 
     As shown in  FIG. 2 , the size of slots  252  is designed such that slot size decreases in locations with higher air velocity and increases in locations with lower air velocity. For example, slot size decreases as a baffle  250  proceeds away from an intake side (viewed in  FIG. 3 ). This feature ensures that incoming airflow is evenly distributed along the length of return vent  240 , as a majority of incoming airflow would otherwise be drawn to the exit portion of return vent  240  without having to substantially increase the size of the air plenum after the return vent  240 . This allows for the overall size of the drying apparatus  200  to remain much smaller. Furthermore, depending on airflow rate and the width of web  120 , the profiles of vent  240  and/or baffles  250  may change in order to account for one end of drying apparatus  200  drawing substantially more air than another end of drying apparatus  200 . This helps to reduce and/or eliminate a stagnation point which would otherwise proceed to the outlet end. 
       FIG. 3  illustrates an intake  310  on the intake side, which may be utilized to supply air to a chamber  260  within drying apparatus  200 . As shown in  FIG. 4 , airflow from a fan  420  may proceed from intake  310  into a chamber  260 , where plates  410  operate to evenly distribute flow along the length (L) of chamber  260  onto a heating element  220 . Although fan  420  is shown as integral with drying apparatus  200  in  FIG. 3 , in further embodiments fan  420  may be located separate from drying apparatus  200  via a duct (e.g., in order to avoid overheating the components of fan  420 ). In one embodiment, air provided to chamber  260  is sourced by a different air supply than the one which provisions air knife  230 . This allows for air of different temperature and pressure to be provided to air knife  230  and heating elements  220 . For example, hot air may be utilized by air knife  230 , while ambient temperature air may be utilized to cool heating elements  220  such that reflector temperature is minimized and fans are able to supply air to heating elements  220  without overheating. 
       FIGS. 5-6  illustrate additional features of air knife  230  and return vents  240 . Specifically,  FIG. 5  illustrates that air knife  230  includes an outlet  550  (e.g., an exit nozzle), which is defined by shell  510 . Shell  510  includes exterior  512 , along with an inner surface  514 . Inner surface  514  is heated by conductive heat transfer with exterior  512 . Shell  510  further defines passage  540 , through which air flows out of air knife  230 . The height (H) and width (W) of passage  540  are selected to ensure that a majority of air (or all air) flowing through passage  540  experiences forced convective heat transfer with inner surface  514 . For example, H may be chosen to extend to within one centimeter of web  120 , while W may be chosen based on a desired ratio of H to W (e.g., five to one) that ensures adequate heat transfer to air flowing through passage  540 . In one example, W is 1.5 millimeters. Furthermore, the thickness, thermal conductivity, and strength properties of shell  510  are chosen to ensure that radiant heat from heating elements  220  transfers readily from exterior  512  to inner surface  514 , as well as to ensure that shell  510  maintains structural integrity and uniformity of slot width even when heated to temperatures in excess of 250° C. For example, shell  510  may be made from a material having a thermal conductivity of at least twenty Watts per meter Kelvin, thermal expansion coefficient less than 40 microns per meter-Kelvin, and an ultimate tensile strength greater than 200 Megapascals (MPa). One example of such a material is stainless steel. In such an example, a distance between exterior  512  and inner surface  514  (i.e. a thickness of shell  510 ) may be chosen to be less than two millimeters in order to ensure rapid conduction of heat from exterior  512  to inner surface  514 . 
       FIG. 6  illustrates how the size of a region of overlap between heating elements  220  may be reduced or even eliminated by air knife  230 . Without air knife  230  being interposed between heating elements  220 , infrared energy from heating elements  220  would overlap onto web  120  within region  600 . However, with air knife  230  placed between heating elements  220 , the overlap may be reduced to region  650 , or may even be eliminated entirely. This reduces the chances of scorching at web  120 , while allowing for heating elements  220  to be positioned at a higher frequency in the paper feed direction (i.e., in series along the web direction), decreasing the overall drying web length or improving drying for a given area. 
     In further embodiments, heating elements  220  and multiple air knives  230  may be utilized in series, such that return air from the air knives  230  remains contained within one drying apparatus/assembly. This enhances the efficiency of the drying process in order to increase the overall drying power of a drying apparatus. 
     The particular arrangement, number, and configuration of components described herein is exemplary and non-limiting. Illustrative details of the operation of drying apparatus  200  and dryer  140  will be discussed with regard to  FIG. 7 . Assume, for this embodiment, that printer  110  has completed marking web  120  with ink, and that web  120  is being actively driven through dryer  140  in order to dry the ink onto web  120 . In one embodiment, the process includes measurement of output web temperature, and varying power output by heating elements  220  based on this output web temperature. This may further involve measuring outlet air temperature at air knife  230  to control power at heating element  220  and velocity of airflow. In one embodiment, power for heating elements  220  and airflow velocity from air knife  230  are both dynamically controlled based on web velocity. 
       FIG. 7  is a flowchart illustrating a method  700  for operating a dryer in an exemplary embodiment. The steps of method  700  are described with reference to printing system  100  of  FIG. 1 , but those skilled in the art will appreciate that method  700  may be performed in other systems. The steps of the flowcharts described herein are not all inclusive and may include other steps not shown. The steps described herein may also be performed in an alternative order. 
     According to method  700  drying apparatus  200  operates heating elements  220  within interior  212  of dryer  140  to radiate infrared energy onto web  120  as web  120  travels through interior  212  (step  702 ). This serves to heat web  120  and remove moisture from ink on web  120 . Exterior  512  of shell  510  of air knife  230  directly receives and absorbs infrared energy radiated by heating elements  220  (step  704 ). This energy is transferred via conduction to inner surface  514 . Thus, as air is forced through air knife  230 , a majority of air exiting passage  540  is heated by at least 10° Celsius via forced convective heat transfer with inner surface  514  of shell  510  (step  706 ). Furthermore, air within air knife  230  may be heated above ambient temperature (e.g., 20° Celsius) exclusively by this forced convective heat transfer with inner surface  514 . 
     This technique for heating air traveling out of air knife  230  provides multiple benefits. First, this ensures that air knife  230  provides heated air (e.g., air heated from ambient temperature to 50-150° Celsius) to web  120 . Hotter air has an increased capacity to carry moisture and ink vapors off of web  120 , and therefore increases the efficiency of the drying process. Second, method  700  eliminates the need for an independent heating apparatus for air within air knife  230 , which reduces the need for maintenance at drying apparatus  200 , as well as reducing the number of potential points of failure at drying apparatus  200 . Method  700  also uses more of the distribution of heat from IR lamps to improve the drying process, instead of allowing heat to be absorbed by nonfunctional drying components such as metal. This has the additional benefit of providing a user safety from stray light or hot surfaces. 
       FIGS. 8-10  illustrate an alternate embodiment of a drying apparatus  800  for dryer  140  of  FIG. 1 . Specifically,  FIG. 8  is a diagram illustrating a further drying apparatus of a printing system in an exemplary embodiment. As shown in  FIG. 8 , drying apparatus  800  includes housing  810 , which includes fans  820 , as well as ducts  830  and duct  840 .  FIG. 9  is a section cut diagram of drying apparatus  800 , and illustrates that fans  820  provide airflow over heating elements  950 , while duct  840  provides airflow for air knife  930 . Airflow travels through shell  920  before exiting air knife  930 . A return vent  940  is also illustrated, which is coupled with a corresponding return duct  830  in order to draw moist air out of drying apparatus  800 . In this embodiment, air provided by fans  820  comes from a separate supply (not shown). Thus, the air provided by fans  820  is cooler than air used for air knife  930 . This is to ensure that a reflector  952  may be adequately cooled. In order to ensure that air flowing through air knife  930  is properly heated, walls  932  for air knife  930  are double-walled to reduce heat loss with the cooled air, while shell  920  remains single walled, as the application of energy from heating elements  950  will ensure that shell  920  remains at a desired temperature. In further embodiments, it may be desirable to implement fans  820  as temperature-resistant fans capable of experiencing substantial amounts of heat without failing. 
       FIG. 10  illustrates a vent plate  1000  for a return vent  940  of the drying apparatus of  FIG. 8  in an exemplary embodiment. Vent plate  1000  serves a similar purpose to that of baffles  250  of  FIG. 2 . That is, vent plate  1000  is designed to ensure that airflow is received evenly along the length of return vent  940 . To this end, a variable pattern of holes  1010  has been applied to vent plate  1000 . The variable pattern is designed such that there are fewer holes in locations with higher air velocity and more holes in locations with lower air velocity. For example, distal portions of vent plate  1000  towards an intake side have a larger number of holes  1010  per unit area. In this embodiment, holes  1010  are equally sized. In this manner, the resistance to airflow at vent plate  1000  varies as a function of length, in order to account for imbalanced airflow that would otherwise result at an “open” return vent  940 . Furthermore, this embodiment illustrates that the smallest amount of holes per unit area is offset from the center of vent plate  1000  towards the right. This design feature may be utilized in order to account for stagnation points that may otherwise result from a sharp corner at drying apparatus  800 . The number of holes per unit area in vent plate  1000  may be defined based, for example, on a combination of quadratic and linear functions. 
     Embodiments disclosed herein include control devices that implement software, hardware, firmware, or various combinations thereof. In one particular embodiment, software is used to direct a processing system of dryer  140  to perform the various operations disclosed herein (e.g., related to operating various heating elements, fans, drive systems for a web, etc.).  FIG. 11  illustrates a processing system  1100  operable to execute a computer readable medium embodying programmed instructions to perform desired functions in an exemplary embodiment. Processing system  1100  is operable to perform the above operations by executing programmed instructions tangibly embodied on computer readable storage medium  1112 . In this regard, embodiments of the invention can take the form of a computer program accessible via computer-readable medium  1112  providing program code for use by a computer or any other instruction execution system. For the purposes of this description, computer readable storage medium  1112  can be anything that can contain or store the program for use by the computer. 
     Computer readable storage medium  1112  can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device. Examples of computer readable storage medium  1112  include a solid state memory, a magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disk, and an optical disk. Current examples of optical disks include compact disk-read only memory (CD-ROM), compact disk-read/write (CD-R/W), and DVD. 
     Processing system  1100 , being suitable for storing and/or executing the program code, includes at least one processor  1102  coupled to program and data memory  1104  through a system bus  1150 . Program and data memory  1104  can include local memory employed during actual execution of the program code, bulk storage, and cache memories that provide temporary storage of at least some program code and/or data in order to reduce the number of times the code and/or data are retrieved from bulk storage during execution. 
     Input/output or I/O devices  1106  (including but not limited to keyboards, displays, pointing devices, sensors, fans, motors, etc.) can be coupled either directly or through intervening I/O controllers. Network adapter interfaces  1108  may also be integrated with the system to enable processing system  1100  to become coupled to other data processing systems or storage devices through intervening private or public networks. Modems, cable modems, IBM Channel attachments, SCSI, Fibre Channel, and Ethernet cards are just a few of the currently available types of network or host interface adapters. Display device interface  1110  may be integrated with the system to interface to one or more display devices, such as printing systems and screens for presentation of data generated by processor  1102 . 
     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.