Chokes for microwave dryers that block microwave energy and enhance thermal radiation

Systems and methods are provided for chokes for microwave radiation. One embodiment is an apparatus that includes a choke assembly. The assembly includes a first choke plate, and a second choke plate. The assembly also includes a first layer disposed at a surface of the first choke plate. The first layer includes a material that attenuates microwave radiation via dielectric heating by converting the microwave radiation into heat, and a substance, disposed between the material of the first layer and the gap, that is transparent to the microwave radiation. The assembly further includes a second layer disposed at a surface of the second choke plate that faces the first layer. The second layer comprises the material that attenuates the microwave radiation via dielectric heating by converting the microwave radiation into heat, and the substance, disposed between the material of the second layer and the gap.

FIELD OF THE INVENTION

The invention relates to the field of dryers, and in particular, to continuous-process microwave dryers.

BACKGROUND

Production printing systems for high-volume printing typically utilize a production printer that marks a continuous-forms print medium (e.g., paper) with a wet colorant (e.g., an aqueous ink). After marking the continuous-forms print medium, a dryer downstream from the production printer is used to dry the colorant applied to the continuous-forms print medium. Microwave dryers may be employed as a dryer for a production printing system in some applications.

A microwave dryer utilizes microwave energy to heat the colorant to cause a liquid portion of the colorant to evaporate, thereby fixing the colorant to the continuous-forms print medium. A microwave source directs the microwave energy down a long axis of a waveguide, and a passageway through the waveguide is sized to enable the continuous-forms print medium to pass through the waveguide. As the continuous-forms print medium traverses the passageway, wet colorant applied to the continuous-forms print medium is exposed to the microwave energy and is heated.

To achieve a sufficient level of drying, microwave dryers generate a substantial amount of microwave radiation. This microwave radiation must be blocked before it exits the microwave dryer in order to ensure that the microwave radiation is contained within the desired dryer operating areas and that components external to the dryer are not heated by microwaves. At the same time, it remains important to reduce the path length occupied by drying systems in order to save space within a print shop.

SUMMARY

Embodiments described herein provide for chokes that attenuate microwave radiation emitted from microwave dryers that dry continuous-forms print media and/or other planar substrates. The chokes have been enhanced to convert microwave radiation into heat, thereby ensuring that drying continues as the continuous-forms media proceeds through the chokes. Furthermore, the chokes may utilize a substance that is transparent to microwave radiation in order to structurally support (e.g., encase) a material that performs the conversion of microwave radiation into heat.

One embodiment is an apparatus that includes a choke assembly. The assembly includes a first choke plate, and a second choke plate that is positioned a distance away from the first choke plate, resulting in a gap between the first choke plate and the second choke plate. The assembly also includes a first layer disposed at a surface of the first choke plate. The first layer includes a material that attenuates microwave radiation via dielectric heating by converting the microwave radiation into heat, and a substance, disposed between the material of the first layer and the gap, that is transparent to the microwave radiation. The assembly further includes a second layer disposed at a surface of the second choke plate that faces the first layer. The second layer comprises the material that attenuates the microwave radiation via dielectric heating by converting the microwave radiation into heat, and the substance, disposed between the material of the second layer and the gap, that is transparent to the microwave radiation.

A further embodiment is a system that includes a microwave dryer that applies microwave radiation to a planar substrate traveling through a waveguide of the microwave dryer in a process direction, and a choke assembly downstream of the microwave dryer. The choke assembly includes a first choke plate, and a second choke plate that is positioned a distance away from the first choke plate, resulting in a gap between the first choke plate and the second choke plate for receiving a planar substrate. The assembly also includes a first layer disposed at a surface of the upper choke plate. The first layer includes a material that attenuates microwave radiation via dielectric heating by converting the microwave radiation into heat; and a substance, disposed between the material of the first layer and the gap, that is transparent to the microwave radiation. The first layer also includes a second layer disposed at a surface of the second choke plate that faces the first layer. The second layer includes the material that attenuates the microwave radiation via dielectric heating by converting the microwave radiation into heat; and the substance, disposed between the material of the second layer and the gap, that is transparent to the microwave radiation.

A further embodiment is a method. The method includes drying a planar substrate via microwave radiation while a planar substrate travels in a process direction through a waveguide of a microwave dryer, transporting the planar substrate through a choke assembly disposed downstream of the microwave dryer, and receiving microwave radiation at the choke assembly from an opening of the microwave dryer via which the planar substrate exits the microwave dryer. The method also includes permitting the microwave radiation to transparently pass through a solid component of the choke assembly, and performing dielectric heating by converting received microwave radiation into heat, wherein the dielectric heating is performed by a material disposed along an interior of the choke assembly.

Other illustrative embodiments (e.g., methods and computer-readable media relating to the foregoing embodiments) may be described below.

DETAILED DESCRIPTION

The figures and the following description illustrate specific illustrative 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. 1is a block diagram of a printing system100in an exemplary embodiment. Printing system100comprises any system capable of marking print media (or other objects) and performing microwave drying as part of a continuous process. In this embodiment, printing system100includes printer110, microwave dryer120, and planar substrate130(e.g., a continuous-forms print medium, a continuous transport belt bearing cut-sheet print media, etc.). Planar substrate130travels along process direction150inFIG. 1to receive marking at printer110and drying at microwave dryer120.

Print controller112of printer110receives print data116which defines locations at which to mark underlying print media. Print data116may be defined according to a Page Description Language (PDL), such as Portable Document Format (PDF). Print data116is rasterized by print controller112into bitmap data. The bitmap data is used by marking engine114(e.g., a drop-on-demand print engine) of printer110to apply wet colorant as planar substrate130travels downstream towards microwave dryer120. In embodiments where planar substrate130is a continuous-forms print medium, planar substrate130is marked by marking engine114of printer110. In embodiments where planar substrate130comprises a continuous transport belt, items being carried by planar substrate130(e.g., cut-sheet print media) are marked by marking engine114of printer110. Some examples of print media include paper and textiles. Marking engine114may apply a wet or liquid colorant, such as one or more aqueous inks. Thus, printer110may comprise a continuous-forms inkjet printer, a cut-sheet inkjet printer, etc. Print controller112may be implemented as custom circuitry, as a hardware processor executing programmed instructions, etc.

Wet colorant applied by marking engine114is dried by microwave dryer120. Specifically, microwave dryer120applies microwave radiation126(e.g., microwave energy) from source124along waveguide122, which is disposed within housing125(e.g., a steel housing). Microwave radiation126heats wet colorant by electromagnetic heating (i.e., dielectric heating) to evaporate a liquid portion of the wet colorants. This fixes wet colorant to the medium that was marked.

In order to ensure that microwave radiation is attenuated prior to exiting microwave dryer120, choke assemblies140are disposed at one or more openings128of microwave dryer120. Choke assemblies140attenuate microwave radiation126such that microwave radiation exiting choke assemblies140is below a threshold level. For example, choke assemblies140may attenuate microwave radiation in accordance with, e.g., 29 Code of Federal Regulations § 1910.97 to ensure less than ten milliwatts per square centimeter of exposure. Choke assemblies140increase in temperature in response to attenuating the microwave radiation, which ensures that heated drying continues while planar substrate130travels through choke assemblies140.

FIG. 2is a side view of choke assembly140in an illustrative embodiment. In this embodiment, choke assembly140is located downstream of microwave dryer120, and proceeds to attenuate microwave radiation126. Choke assembly140comprises upper choke plates210, and lower choke plates220. Lower choke plates220are positioned a distance D1(e.g., one centimeter) below upper choke plates210. This forms gap250through which planar substrate130travels (i.e. passes through unimpeded). Vent holes260are also illustrated, which penetrate through upper choke plates210and lower choke plates220to enable convective heat transfer with the air.

Upper choke plates210include lower layer212, which directly receives microwave radiation126from microwave dryer120. That is, microwave radiation126directly strikes lower layer212, because lower layer212is disposed at lower surface214of upper choke plate210. Lower layer212comprises material230, which attenuates microwave radiation126by engaging in dielectric heating by converting microwave radiation126into heat (A). For example, material230may comprise particles of graphitized carbon black that have a particle size between 50 micrometers (μm) and 500 μm (e.g., 180 μm-250 μm), or may comprise another suitable susceptor material that performs dielectric heating in response to microwave radiation.

As distance (D2) from lower surface214increases, a concentration of material230within lower layer212(e.g., volume of material230per unit volume of lower layer212) may decrease. For example, material230may ramp down in concentration linearly within lower layer212as D2increases, from a first concentration (e.g., fifty percent) to a second concentration (e.g., ten percent).

Material230is structurally supported and protected by substance240. For example, a matrix of substance240may surround particles of material230. Hence, at least some amount of substance240is disposed between material230and gap250. Substance240is transparent to microwave radiation. As used herein, substances are transparent to microwave radiation if they exhibit a low index of refraction or low dielectric permittivity (e.g., between 2 and 4, such as 3) for microwave radiation between 2 and 3 GHz (e.g., 2.45 GHz). Substances may also be considered transparent to microwave radiation if they allow more than fifty percent (e.g., seventy five percent) transmission through microwave radiation between 2 and 3 GHz (e.g., 2.45 GHz). Substance240may comprise fused quartz, fused silica, another type of glass, etc. Substance240may also be chosen for exhibiting a melting point that is above a threshold amount, such as a melting point higher than one thousand degrees Celsius (° C.), such as >1600° C. Particles of material230may be “doped” into substance240, and may comprise a sub-layer of loose particles that are mechanically supported by substance240, etc.

As air travels through vent holes260(e.g., in the direction indicated by arrows262), the air is convectively heated by substance240, which is itself heated by material230. This ensures that the air is heated when it strikes planar substrate130, facilitating the drying process.

Lower choke plates220include upper layer222, which directly receives microwave radiation126from microwave dryer120. That is, microwave radiation126directly strikes upper layer222, because upper layer222is disposed at upper surface224of lower choke plate220. Upper layer222comprises material230as well as substance240in a similar manner to lower layer212. As distance (D2) from upper surface224increases, a concentration of material230within upper layer222may decrease. For example, material230may ramp down in concentration linearly within upper layer222as D2increases, from a first concentration (e.g., fifty percent) to a second concentration (e.g., ten percent).

FIG. 3further illustrates additional features of an illustrative choke assembly. Specifically,FIG. 3is a perspective view of vent holes310at choke assembly300. In this embodiment, vent holes310are placed into upper choke plates302, as well as lower choke plates304. Vent holes310proceed along the entire thickness (T) of the choke plates (e.g., including any layers in which material230and substance240ofFIG. 2may be disposed), resulting in passages320via which air may flow through the choke plates. This facilitates convective cooling of the choke plates during operation, which ensures that substance240and material230do not melt or otherwise overheat. At the same time, this heated air continues onward to strike planar substrate130, drying planar substrate130.

The particular arrangements, numbers, and configurations of components described herein are illustrative and non-limiting. Illustrative details of the operation of choke assemblies will be discussed with regard toFIG. 4. Assume, for this embodiment, that planar substrate130has traveled through printer110and that marking has been performed by marking engine114(either directly onto planar substrate130, or onto print media carried atop planar substrate130). Further, assume that planar substrate130is traveling downstream towards microwave dryer120.

FIG. 4is a flowchart illustrating a method400for utilizing a choke assembly for a microwave dryer in an illustrative embodiment. The steps of method400are described with reference to printing system100ofFIG. 1, but those skilled in the art will appreciate that method400may 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.

Planar substrate130enters microwave dryer120for drying. Thus, microwave dryer120dries planar substrate130while planar substrate130travels in process direction150through waveguide/cavity122(step402). Planar substrate130(e.g., printed media) is transported through gap250of choke assembly140, which is disposed at microwave dryer120(e.g., upstream of dryer120and abutting an entrance to dryer120, or downstream of dryer120and abutting an exit of dryer120) (step404). Planar substrate130may be driven, for example, by one or more drive rollers (not shown) that direct planar substrate130forward at a constant but adjustable rate of travel through microwave dryer120.

While planar substrate130travels through choke assembly140, material230, which is disposed along an interior of choke assembly140, receives microwave radiation126(step406). The microwave radiation is received from an opening of microwave dryer120via which planar substrate130travels (e.g., an entrance or exit of microwave dryer120). Substance240(which is a solid component of choke assembly140) permits the microwave radiation to transparently pass through it in order to reach material230(step408). In response to receiving microwave radiation126, material230performs dielectric heating that converts the received microwave radiation into heat (step410). Material230transfers heat to substance240(e.g., via conduction). In one embodiment, material230emits thermal radiation, and an amount of thermal radiation from material230may strike planar substrate130, ensuring that planar substrate130continues to be heated as it travels through choke assembly140. In addition, forced air passing through cylindrical vents310facilitates drying of planar substrate130by reducing the size of a boundary layer between a surface of substrate130and the impinging air. In further embodiments, apertures may be placed on sides of choke assembly to facilitate the extraction of the vaporized volatiles from choke assembly140.

Planar substrate130may then exit choke assembly140, while a new portion of planar substrate130enters microwave dryer120. In this manner, steps402-408may be performed concurrently with each other as part of a continuous printing and/or drying process. Thus, materials which normally would be incapable of supporting themselves (e.g. powdered materials) may be used in a manner that allows for both attenuation of microwave radiation and generation of heat.

FIG. 5is a perspective view of a frame500for a choke assembly in an illustrative embodiment. Frame500may be constructed, for example, from sheet metal or another structurally rigid material. In this embodiment, frame500includes a first set of horizontal frame elements510, which define upper compartments512in which upper choke plates210(e.g., including rods filled with material230) are disposed. A second set of horizontal frame elements510define lower compartments514in which lower choke plates220(e.g., including rods filled with material230) are disposed. Lips516are placed at lower edges of the compartments to ensure that choke plates do not fall through their respective compartments.

Vertical frame elements520unite the first set of horizontal frame elements510and the second set of horizontal frame elements510. The subset of frame elements510that are transverse to the direction of propagation of the planar substrate130cause a portion of the microwave energy that exits the microwave dryer120to be reflected back into the microwave dryer120. Meanwhile, mounting flange530, which is hollow, defines a female receptacle for covering an end of a microwave dryer. For a frame utilized at an entrance of a dryer, the process direction may be reversed. Vent holes540are also illustrated, via which evaporated volatiles within choke assembly500may be disposed.

In further embodiments, material230may be inserted via rods placed within a choke plate.FIGS. 6-7illustrate one such embodiment.FIG. 6illustrates choke plate600having bore holes630defining chambers632for receiving cylinders of material in an illustrative embodiment. The length of bore holes630may extend transversely across the path to further facilitate uniform drying. In this embodiment, choke plate600includes layer610, which is transparent to microwave radiation (e.g., a layer of fused quartz), as well as layer620, which is not transparent to microwave radiation (e.g., a layer of steel). This ensures that microwave radiation may travel freely to and/or from material230, without exiting choke plate600. Vent holes640, defining chamber642, are also illustrated. Vent holes640and chambers642collectively enable air to be forced downward through the vent holes640and chambers642. Note that vent holes640and passageways642do not intersect passageways632, and reside in between passageways632. Air that passes downward through passageways642provides the convective heating component from the surrounding heated substrate. This forced air is heated by choke plate600, and then directly impinges downward upon planar substrate130, further drying planar substrate130. If choke plate600is flipped vertically, then the air flow through the associated vent holes640and chambers642would impinge upon the planar substrate130in an upward direction. This downward/upward air flow also mitigates vertical fluttering of the planar substrate130as it propagates through a choke assembly. Choke plate600may be utilized as an upper choke plate at its current orientation, or may be flipped vertically to operate as a lower choke plate. While only one row of chambers632is illustrated in this embodiment, in further embodiments multiple rows of chambers632may be disposed within layer610.

FIG. 7illustrates cylinders for insertion into the bore holes ofFIG. 6in an illustrative embodiment. Cylinder710includes body712, which defines hole714and hollow chamber716, into which material230may be poured, packed, or otherwise distributed. Cylinder720includes body722, which defines hole724and hollow chamber726, into which material230may be poured, packed, or otherwise distributed. The diameters of holes in different cylinders may vary based on the amount of material230desired in each cylinder. These diameters may even vary between cylinders inserted into the same choke plate.

Examples

In the following examples, additional processes, systems, and methods are described in the context of a choke assembly for a microwave dryer.

In this example, microwave dryer120dries a planar substrate130comprising a continuous web of print media which has been marked by marking engine114of printer110. A choke assembly140is disposed at the entrance and exit of microwave dryer120. Choke assemblies140attenuate microwave radiation escaping from these openings in microwave dryer. In this example, choke assemblies140define a half-inch tall gap which is ten inches wide. Planar substrate130continues through choke assemblies140. Choke assemblies140are made from multiple choke plates, and each choke plate includes a layer of graphitized carbon black along a surface facing planar substrate130. Particles of the graphitized carbon black are encased by fused quartz. Microwave radiation transparently passes through the fused quartz and strikes the graphitized carbon black. The graphitized carbon black emits infrared blackbody radiation in response to absorbing microwave radiation from microwave dryer120. The blackbody radiation heats the fused quartz, and portions of the blackbody radiation may strike planar substrate130, heating planar substrate130. The fused quartz increases in temperature via thermal conduction with the encased particles of graphitized carbon black. Airflow travels through vent holes placed in the choke plates, heating in response to passing through choke assembly140(in particular, the fused quartz), and drying planar substrate130.

Control elements for various components described herein can take the form of software, hardware, firmware, or various combinations thereof. In one particular embodiment, software is used to direct a processing system of print controller112to perform the various printing operations disclosed herein, or to control a speed of a drive roller.FIG. 8illustrates a processing system800operable to execute a computer readable medium embodying programmed instructions to perform desired functions in an illustrative embodiment. Processing system800is operable to perform the above operations by executing programmed instructions tangibly embodied on computer readable storage medium812. In this regard, embodiments of the invention can take the form of a computer program accessible via computer-readable medium812providing program code for use by a computer or any other instruction execution system. For the purposes of this description, computer readable storage medium812can be anything that can contain or store the program for use by the computer.

Computer readable storage medium812can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor device. Examples of computer readable storage medium812include 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 system800, being suitable for storing and/or executing the program code, includes at least one processor802coupled to program and data memory804through a system bus850. Program and data memory804can 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 devices806(including but not limited to keyboards, displays, pointing devices, etc.) can be coupled either directly or through intervening I/O controllers. Network adapter interfaces808may also be integrated with the system to enable processing system800to 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 interface810may 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 processor802.