Patent Publication Number: US-9423177-B2

Title: Force-balancing gas flow in dryers for printing systems

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of dryers, and in particular, to dryers that actively generate airflow when drying printed media. 
     BACKGROUND 
     Businesses or other entities having a need for volume printing typically purchase a production printer. A production printer is a high-speed printer used for volume printing (e.g., one hundred pages per minute or more). Production printers are typically continuous-form printers that print on webs of print media that are stored on large rolls. 
     A production printer typically includes a localized print controller that controls the overall operation of the printing system, and a print engine (sometimes referred to as an “imaging engine” or as a “marking engine”). The print engine includes one or more printhead assemblies, with each assembly including a printhead controller and a printhead (or array of printheads). An individual printhead includes multiple tiny nozzles (e.g., 360 nozzles per printhead depending on resolution) that are operable to discharge ink as controlled by the printhead controller. A printhead array is formed from multiple printheads that are spaced in series across the width of the print media. 
     While the production printer is in operation, the web of print media is quickly passed underneath the printhead arrays while the nozzles of the printheads discharge ink at intervals to form pixels on the web. Some types of media used in inkjet printers are better suited to absorb the ink, while other types are not. Thus, a radiant dryer may be installed downstream from the printer. The radiant dryer assists in drying the ink on the web after the web leaves the printer. A typical radiant dryer includes an array of lamps that emit light and heat. The light and heat from the lamps helps to dry the ink as the web passes through the dryer. 
     In order to facilitate drying of the web, air may be actively forced through the dryer so that moisture-saturated air is driven out of the dryer, while dry air is brought into the dryer. However, active air flow can cause flutter at the web, which can result in warps and tears along the web, and may even break the web. Thus, it is undesirable to implement any active airflow that directly strikes the web. Furthermore, rollers are rarely used within the interior of a dryer to tension the web and prevent such flutter, because when tensioned rollers are heated to the operating temperature of the dryer, the rollers increase the risk of igniting the portion of the web that they are in contact with. Thus, web flutter in dryers that actively exchange air remains a problem. 
     SUMMARY 
     Embodiments described herein provide flow generators in a dryer that drive opposing jets of gas (e.g., air) onto opposite sides of a web of printed media as the web travels through a dryer. The jets balance out forces from each other that would otherwise warp or bend the web. The jets also move the air inside of the dryer along the direction of travel of the web and towards an exit. 
     One embodiment is dryer for a printing system. The dryer includes a heating element, a top flow generator, and a bottom flow generator. The heating element is within an interior of the dryer, and heats a web of printed media as the web travels across the interior. The top flow generator is within the interior, and directly projects a first jet of gas onto a top side of the web. The first jet of gas deflects air proximate to the web. The bottom flow generator is within the interior, and directly projects a second jet of gas onto an opposing side of the web. The second jet strikes the web at substantially the same location as the first jet, and compensates orthogonal force applied to the web by the first jet. Furthermore, the top and bottom flow generators are both oriented to project the jets partially in the direction of travel of the web. 
     Another embodiment is a method. The method includes driving a web of printed media through an interior of a dryer, and operating a heating element within the interior of the enclosure to heat a web of printed media as the web travels across the interior. The method also includes directly projecting a first jet of gas onto a top side of the web that deflects air proximate to the web within the interior. Further, the method includes directly projecting a second jet of gas onto an opposing side of the web that deflects air proximate to the web within the interior. The second jet strikes the web at substantially the same location as the first jet and compensates orthogonal force applied to the web by the first jet, and the first and second jets are projected partially in the direction of travel of the web. 
     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 drying system in an exemplary embodiment. 
         FIG. 2  is a flowchart illustrating a method for operating a drying system in an exemplary embodiment. 
         FIG. 3  is a diagram illustrating additional details of flow generators within a drying system in an exemplary embodiment. 
         FIG. 4  is a diagram illustrating a further drying system in an exemplary embodiment. 
         FIG. 5  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  is a diagram of a drying system  100  in an exemplary embodiment. Drying system  100  receives web of printed media  120  that has been marked by an upstream marking engine  102  and partially tensioned by roller  130 , which is located outside of drying system  100 . Drying system  100  dries web  120  with one or more heating elements  112 , such as radiant heat lamps. Radiant energy from heating elements  112  is reflected by thermal reflectors  114  in order to reduce waste heat and also to keep drying system  100  from overheating. 
     Drying system  100  has been enhanced to include flow generators  140 , which project impinging jets of gas directly onto web  120  as web  120  travels through drying system  100 . One flow generator  140  is located above web  120  and projects a jet downward onto web  120 , while another flow generator  140  is located below web  120  and projects a jet upward into substantially the same location on web  120 . 
     The jets increase the rate at which air is exchanged with within drying system  100 . This ensures that air within the dryer that is already saturated with moisture is quickly cycled out of drying system  100 . Additionally, the forces applied by the complementary jets can tension web  120  while web  120  is within drying system  120 , without placing a roller within the interior of drying system  100  and thereby increasing the risk of fire. 
     Gas source  150  provides a supply of gas to flow generators  140 , and may comprise a compressor or pressurized container. Flow controller  160  manages the rate at which gas is supplied to flow generators  140  from gas source  150 . For example, flow controller  160  may comprise a manual valve. In some embodiments, flow controller  160  comprises an electronically implemented controller (e.g., a circuit, or a processor implementing programmed instructions), that is capable of actively controlling the rate at which gas travels to flow generators  140 . Flow controller  160  may further provide a different rate of flow to top flow generator  140  than to bottom flow generator  140 . This may be done, for example, in response to detected variations in pressure from gas source  150 , to compensate for any other conditions that may change the flow characteristics between the top and bottom flow generators  140 , or for any other reason as desired. 
     Illustrative details of the operation of drying system  100  will be discussed with regard to  FIG. 2 . Assume, for this embodiment, that upstream marking engine  102  has marked web  120 , and that web  120  is being received at drying system  100  for processing. 
       FIG. 2  is a flowchart illustrating a method  200  for operating a drying system in an exemplary embodiment. The steps of method  200  are described with reference to drying system  100  of  FIG. 1 , but those skilled in the art will appreciate that method  200  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. 
     In step  202 , web  120  is driven through drying system  100 . For example, in one embodiment tensioned roller  130  drives web  120  through an interior of drying system  100 . In step  204 , heating elements  112  are operated to heat web  120  as web  120  travels across the interior of drying system  100 . 
     In step  206 , the airflow generator  140  (located above web  120 ) directly projects a top jet of gas onto web  120 . The jet of gas extends into the page in  FIG. 1  and along the width of web  120 . The jet deflects air proximate to web  120  while web  120  is within the interior of drying system  100 . The jet is projected at a sufficient speed and mass flow to substantially disrupt the laminar flow of a boundary layer of saturated, moist air at web  120 . By generating turbulent and/or chaotic flow at web  120 , flow generators  140  ensure that new, dry air is able to receive moisture from web  120  via convective mass transfer. 
     The top jet is oriented/angled so that it is partially projected in the direction of travel of web  120 , and is partially projected orthogonal to web  120 . This means that orthogonal force applied to web  120  by the top jet, if not compensated for, will deform web  120  downward. 
     In step  208 , the airflow generator  140  (located below web  120 ) projects a bottom jet of gas onto web  120  that also deflects air proximate to web  120  while web  120  is within the interior of drying system  100 . The bottom jet is applied at the same time as the top jet to substantially the same portion of web  120  as the top jet (but on a different side), and applies a compensating orthogonal force upward to balance the orthogonal force applied by the top jet. The bottom jet, like the top jet, is partially projected in the direction of travel of web  120 . 
     By utilizing method  200  described above, a dryer can achieve multiple benefits at once. First, drying system  100  can enhance the flow of air along the interior, and can specifically disrupt laminar boundary layer flow for air proximate to a web of printed media. This means that new air which is not saturated with moisture can engage in convective mass transfer with marked portions of web  120 . Second, because flow generators  140  apply complementary orthogonal forces to web  120 , web  120  is not deformed by the jets of gas. Third, complementary flow generators  140  are oriented to apply substantially balancing orthogonal forces to web  120 , which ensures that web  120  is properly positioned within drying system  100  without resorting to rollers, which may increase the risk of fire. Fourth, complementary flow generators  140  direct the flow of air along the direction of travel of web  120 , and therefore towards an exit of drying system  100 . This means that air is not driven towards marking engine  102 , which would reduce print quality. 
       FIG. 3  is a diagram  300  illustrating additional details of flow generators  140  within a drying system in an exemplary embodiment.  FIG. 3  shows that each flow generator  140  is oriented to project a jet of air at an angle of attack ( 8 ) toward web  120 . The jets projected at the angle of attack each include a vertical component and a horizontal component, resulting in vertical force applied to web  120  (F y ) and a horizontal force applied to web  120  (F x ). The vertical force applied by the top jet from the top flow generator  140  is compensated by the vertical force applied by the bottom jet from the bottom flow generator. As the vertical force is a function of the combination of linear speed, mass flow, and angle of attack, the top jet and the bottom jet may exhibit the same or different combinations of these variables, so long as the vertical forces are properly balanced. In one embodiment, the forces are balanced to account for the effect of gravity on the web, thereby improving the position of the paper in low tensioned systems. In such embodiments, the bottom jet may exert a larger force onto the web than the top jet, in order to compensate for the force of gravity. 
     Flow generators  140  may comprise air knives that have a nozzle width (W) into the page that substantially matches the width of web  120 . The nozzles of flow generators  140  may also have a length (L), and the nozzles may be located a distance (D) away from web  120 . In one embodiment, the ratio of L to D is about 1:7. Flow generators  140  may project any suitable gas such as air, carbon dioxide, nitrogen, argon, etc. 
     Examples 
     In the following examples, additional processes, systems, and methods are described in the context of a dryer that processes a printed web of media. 
       FIG. 4  is a diagram illustrating a drying system  400  in an exemplary embodiment. According to  FIG. 4 , web  420  comprises a web of paper that has been inked by print heads  402  of an upstream continuous-forms inkjet printer. The ink on web  420  is still wet as it enters drying system  400 . As web  420  travels through drying system  400  at a linear velocity of five feet per minute, web  420  is alternately heated by radiant heat lamps  412  and cooled by air knives  440 . Air knives  440  are driven by pressure generated at an air compressor, and air knives  440  are protected from radiant heating by reflectors  114 . Air knives  440  have a slot width of one millimeter, and project ambient temperature air at a rate of twenty feet per second onto the surface of web  420 , at a distance of one centimeter from the surface of web  420  at about a forty five degree angle of attack to web  420 . Air knives  440  are arranged in complementary pairs so that the vertical forces applied to web  420  substantially compensate each other and web  420  is not deflected. Furthermore, each pair of air knives  440  projects jets of air along the direction of travel of web  420 , and away from print heads  402 . This prevents disruptive air flow from interfering with the aerial dispersal of ink droplets onto web  420 . 
     In one particular embodiment, software is used to direct a processing system of flow controller  160  to dynamically regulate the amount of gas flow supplied to one or more flow generators (e.g., based on a determined speed of a web of print media).  FIG. 5  illustrates a processing system  500  operable to execute a computer readable medium embodying programmed instructions to perform desired functions in an exemplary embodiment. Processing system  500  is operable to perform the above operations by executing programmed instructions tangibly embodied on computer readable storage medium  512 . In this regard, embodiments of the invention can take the form of a computer program accessible via computer-readable medium  512  providing program code for use by a computer or any other instruction execution system. For the purposes of this description, computer readable storage medium  512  can be anything that can contain or store the program for use by the computer. 
     Computer readable storage medium  512  can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device. Examples of computer readable storage medium  512  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  500 , being suitable for storing and/or executing the program code, includes at least one processor  502  coupled to program and data memory  504  through a system bus  550 . Program and data memory  504  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  506  (including but not limited to keyboards, displays, pointing devices, etc.) can be coupled either directly or through intervening I/O controllers. Network adapter interfaces  508  may also be integrated with the system to enable processing system  500  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. Presentation device interface  510  may be integrated with the system to interface to one or more presentation devices, such as printing systems and displays for presentation of presentation data generated by processor  502 . 
     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.