Infrared-heated air knives for dryers

Systems and methods are provided for enhanced dryers for printing systems. 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.

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.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary continuous-forms printing system100. Printing system100includes production printer110, which is operable to apply ink onto a web120of 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 web120(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. Printer110may 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 printer110to web120is wet, meaning that the ink may smear if it is not dried before further processing. One or more rollers130position web120as it travels through printing system100.

To dry the ink, printing system100also includes dryer140(e.g., a radiant dryer). Dryer140can be installed in printer110, or can be implemented as an independent device downstream from printer110(as shown inFIG. 1). Web120travels through dryer140where an array of heating elements such as IR heat lamps radiate thermal energy to dry the ink onto web120. For example, web120may travel at a linear velocity of up to two hundred meters per minute through dryer140. Controller142manages the operations of dryer140and/or printer110. For example, controller142may manage various sensors, fans, heating elements, air logic, and other components at dryer140. Controller142may be implemented as custom circuitry, as a hardware processor executing programmed instructions, etc.

However, drying ink onto web120is 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 dryer140where radiant energy from different heating elements overlaps onto web120. In order to address these concerns by reducing areas of radiative overlap while increasing the efficiency of an internal air knife, dryer140has been enhanced with a drying apparatus illustrated inFIGS. 2-6.

FIGS. 2-6are diagrams of a drying apparatus200of dryer140in an exemplary embodiment. One or more of drying apparatus200may be utilized by dryer140to fully dry ink on web120.FIG. 2is a perspective view in which a left portion of dryer140has been subjected to a section cut.FIG. 3is a front view of drying apparatus200indicated by view arrows3ofFIG. 2, and uses the same section cut as inFIG. 2.FIG. 4is a side view of drying apparatus200corresponding to view arrows4ofFIG. 3. InFIG. 4, a section cut has been made to chamber260so as to illustrate internal features of chamber260. Meanwhile,FIGS. 5-6illustrate front section cut views of drying apparatus200.

FIG. 2illustrates that drying apparatus200includes housing210, which surrounds various components of drying apparatus200. These components within interior212of drying apparatus200include heating elements220, which radiate IR energy onto web120as web120proceeds through dryer140. In this embodiment, heating elements220may 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 elements220may 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 elements220back towards web120, these reflective surfaces may also be integrated into the lamp housing. Heating elements220receive air from chambers260, and this fresh air passing over heating elements220ensures that integrated reflective coatings do not get damaged from overheating due to air stagnation.

Interior212also includes air knife230, which blows air onto web120. Air knife230may 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 web120. Incoming air for air knife230is thermally isolated from air for heating elements220by double wall232. Return vent240is also illustrated inFIG. 2. Return vent240draws in air blown by air knife230, in order to ensure that airflow remains restricted to interior212of drying apparatus200. This helps to ensure that ink vapors within the air that result from the drying process do not exit drying apparatus200proximate to web120. Return vents240include baffles250having slots252of varying sizes.

As shown inFIG. 2, the size of slots252is 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 baffle250proceeds away from an intake side (viewed inFIG. 3). This feature ensures that incoming airflow is evenly distributed along the length of return vent240, as a majority of incoming airflow would otherwise be drawn to the exit portion of return vent240without having to substantially increase the size of the air plenum after the return vent240. This allows for the overall size of the drying apparatus200to remain much smaller. Furthermore, depending on airflow rate and the width of web120, the profiles of vent240and/or baffles250may change in order to account for one end of drying apparatus200drawing substantially more air than another end of drying apparatus200. This helps to reduce and/or eliminate a stagnation point which would otherwise proceed to the outlet end.

FIG. 3illustrates an intake310on the intake side, which may be utilized to supply air to a chamber260within drying apparatus200. As shown inFIG. 4, airflow from a fan420may proceed from intake310into a chamber260, where plates410operate to evenly distribute flow along the length (L) of chamber260onto a heating element220. Although fan420is shown as integral with drying apparatus200inFIG. 3, in further embodiments fan420may be located separate from drying apparatus200via a duct (e.g., in order to avoid overheating the components of fan420). In one embodiment, air provided to chamber260is sourced by a different air supply than the one which provisions air knife230. This allows for air of different temperature and pressure to be provided to air knife230and heating elements220. For example, hot air may be utilized by air knife230, while ambient temperature air may be utilized to cool heating elements220such that reflector temperature is minimized and fans are able to supply air to heating elements220without overheating.

FIGS. 5-6illustrate additional features of air knife230and return vents240. Specifically,FIG. 5illustrates that air knife230includes an outlet550(e.g., an exit nozzle), which is defined by shell510. Shell510includes exterior512, along with an inner surface514. Inner surface514is heated by conductive heat transfer with exterior512. Shell510further defines passage540, through which air flows out of air knife230. The height (H) and width (W) of passage540are selected to ensure that a majority of air (or all air) flowing through passage540experiences forced convective heat transfer with inner surface514. For example, H may be chosen to extend to within one centimeter of web120, 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 passage540. In one example, W is 1.5 millimeters. Furthermore, the thickness, thermal conductivity, and strength properties of shell510are chosen to ensure that radiant heat from heating elements220transfers readily from exterior512to inner surface514, as well as to ensure that shell510maintains structural integrity and uniformity of slot width even when heated to temperatures in excess of 250° C. For example, shell510may 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 exterior512and inner surface514(i.e. a thickness of shell510) may be chosen to be less than two millimeters in order to ensure rapid conduction of heat from exterior512to inner surface514.

FIG. 6illustrates how the size of a region of overlap between heating elements220may be reduced or even eliminated by air knife230. Without air knife230being interposed between heating elements220, infrared energy from heating elements220would overlap onto web120within region600. However, with air knife230placed between heating elements220, the overlap may be reduced to region650, or may even be eliminated entirely. This reduces the chances of scorching at web120, while allowing for heating elements220to 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 elements220and multiple air knives230may be utilized in series, such that return air from the air knives230remains 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 apparatus200and dryer140will be discussed with regard toFIG. 7. Assume, for this embodiment, that printer110has completed marking web120with ink, and that web120is being actively driven through dryer140in order to dry the ink onto web120. In one embodiment, the process includes measurement of output web temperature, and varying power output by heating elements220based on this output web temperature. This may further involve measuring outlet air temperature at air knife230to control power at heating element220and velocity of airflow. In one embodiment, power for heating elements220and airflow velocity from air knife230are both dynamically controlled based on web velocity.

FIG. 7is a flowchart illustrating a method700for operating a dryer in an exemplary embodiment. The steps of method700are described with reference to printing system100ofFIG. 1, but those skilled in the art will appreciate that method700may 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 method700drying apparatus200operates heating elements220within interior212of dryer140to radiate infrared energy onto web120as web120travels through interior212(step702). This serves to heat web120and remove moisture from ink on web120. Exterior512of shell510of air knife230directly receives and absorbs infrared energy radiated by heating elements220(step704). This energy is transferred via conduction to inner surface514. Thus, as air is forced through air knife230, a majority of air exiting passage540is heated by at least 10° Celsius via forced convective heat transfer with inner surface514of shell510(step706). Furthermore, air within air knife230may be heated above ambient temperature (e.g., 20° Celsius) exclusively by this forced convective heat transfer with inner surface514.

This technique for heating air traveling out of air knife230provides multiple benefits. First, this ensures that air knife230provides heated air (e.g., air heated from ambient temperature to 50-150° Celsius) to web120. Hotter air has an increased capacity to carry moisture and ink vapors off of web120, and therefore increases the efficiency of the drying process. Second, method700eliminates the need for an independent heating apparatus for air within air knife230, which reduces the need for maintenance at drying apparatus200, as well as reducing the number of potential points of failure at drying apparatus200. Method700also 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. 8-10illustrate an alternate embodiment of a drying apparatus800for dryer140ofFIG. 1. Specifically,FIG. 8is a diagram illustrating a further drying apparatus of a printing system in an exemplary embodiment. As shown inFIG. 8, drying apparatus800includes housing810, which includes fans820, as well as ducts830and duct840.FIG. 9is a section cut diagram of drying apparatus800, and illustrates that fans820provide airflow over heating elements950, while duct840provides airflow for air knife930. Airflow travels through shell920before exiting air knife930. A return vent940is also illustrated, which is coupled with a corresponding return duct830in order to draw moist air out of drying apparatus800. In this embodiment, air provided by fans820comes from a separate supply (not shown). Thus, the air provided by fans820is cooler than air used for air knife930. This is to ensure that a reflector952may be adequately cooled. In order to ensure that air flowing through air knife930is properly heated, walls932for air knife930are double-walled to reduce heat loss with the cooled air, while shell920remains single walled, as the application of energy from heating elements950will ensure that shell920remains at a desired temperature. In further embodiments, it may be desirable to implement fans820as temperature-resistant fans capable of experiencing substantial amounts of heat without failing.

FIG. 10illustrates a vent plate1000for a return vent940of the drying apparatus ofFIG. 8in an exemplary embodiment. Vent plate1000serves a similar purpose to that of baffles250ofFIG. 2. That is, vent plate1000is designed to ensure that airflow is received evenly along the length of return vent940. To this end, a variable pattern of holes1010has been applied to vent plate1000. 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 plate1000towards an intake side have a larger number of holes1010per unit area. In this embodiment, holes1010are equally sized. In this manner, the resistance to airflow at vent plate1000varies as a function of length, in order to account for imbalanced airflow that would otherwise result at an “open” return vent940. Furthermore, this embodiment illustrates that the smallest amount of holes per unit area is offset from the center of vent plate1000towards 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 apparatus800. The number of holes per unit area in vent plate1000may 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 dryer140to perform the various operations disclosed herein (e.g., related to operating various heating elements, fans, drive systems for a web, etc.).FIG. 11illustrates a processing system1100operable to execute a computer readable medium embodying programmed instructions to perform desired functions in an exemplary embodiment. Processing system1100is operable to perform the above operations by executing programmed instructions tangibly embodied on computer readable storage medium1112. In this regard, embodiments of the invention can take the form of a computer program accessible via computer-readable medium1112providing program code for use by a computer or any other instruction execution system. For the purposes of this description, computer readable storage medium1112can be anything that can contain or store the program for use by the computer.

Computer readable storage medium1112can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device. Examples of computer readable storage medium1112include 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 system1100, being suitable for storing and/or executing the program code, includes at least one processor1102coupled to program and data memory1104through a system bus1150. Program and data memory1104can 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 devices1106(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 interfaces1108may also be integrated with the system to enable processing system1100to 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 interface1110may 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 processor1102.