Abstract:
A modular magnetron for use in UV curing lamp assembly is disclosed. The modular magnetron includes a vacuum tube having a vacuum tube body, a top assembly, and a bottom assembly. The top assembly is configured to substantially overlay the vacuum tube. The bottom assembly is configured to substantially extend about the vacuum tube, the vacuum tube being positioned to partially protrude from the bottom assembly, the bottom assembly including a cooling assembly configured to employ a flexible clamp-type fitting about the vacuum tube body for substantially maintaining thermal and electrical conductivity. The top assembly is configured to be releasably fastened to the bottom assembly about the vacuum tube with removable fasteners.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to magnetrons, and more particularly, to a modularly assembled magnetron for use in ultraviolet radiation (UV) curing lamp assemblies. 
     BACKGROUND OF THE INVENTION 
     Radiant energy is used in a variety of manufacturing processes to treat surfaces, films, and coatings applied to a wide range of materials. Specific processes include but are not limited to curing (i.e., fixing, polymerization), oxidation, purification, and disinfection. Processes using radiant energy to polymerize or effect a desired chemical change is rapid and often less expensive in comparison to a thermal treatment. The radiation can also be localized to control surface processes and allow preferential curing only where the radiation is applied. Curing can also be localized within the coating or thin film to interfacial regions or in the bulk of the coating or thin film. Control of the curing process is achieved through selection of the radiation source type, physical properties (for example, spectral characteristics), spatial and temporal variation of the radiation, and curing chemistry (for example, coating composition). 
     A variety of radiation sources are used for curing, fixing, polymerization, oxidation, purification, or disinfections due to a variety of applications. Examples of such sources include but are not limited to photon, electron or ion beam sources. Typical photon sources include but are not limited to arc lamps, incandescent lamps, electrodeless lamps and a variety of electronic (i.e., lasers) and solid-state sources. 
     An apparatus for irradiating a surface with ultraviolet light includes a lamp (e.g., a modular lamp, such as a microwave-powered lamp having a microwave-powered bulb (e.g., tubular bulb) with no electrodes or glass-to-metal seals), the lamp having reflectors to direct light (photons) on to the surface. The source of microwave power is conventionally a magnetron, the same source of microwaves typically found in microwave ovens. The microwave-powered bulb typically receives microwaves generated by the magnetron through an intervening waveguide. 
       FIG. 1  depicts a conventional assembled magnetron  10  for use in a UV curing lamp assembly, while  FIG. 2  depicts an exploded view of the components of the magnetron  10  of  FIG. 1 . The magnetron  10  comprises a bottom yoke  12  having opposing rails  14  and a plurality of holes  15  formed therein, a bottom magnet  16  overlying the bottom yoke  12 , and a cooling assembly  18  overlying the bottom magnet  16  and configured to fit between the opposing rails  14  of the bottom yoke  12 . The bottom yoke  12 , the bottom magnet  16 , and the cooling assembly  18  each have a substantially circular bore hole  20 ,  22 ,  24  formed centrally therein and configured for receiving a vacuum tube  26 . 
     Referring now to  FIGS. 2 and 3 , the vacuum tube  26  has a substantially cylindrical shape and includes a top portion  28  enclosing a filament (not shown) that functions as a cathode, the top portion  28  having a pair of electrical connections  30  extending therefrom and electrically connected to the tube&#39;s internal filament (not shown). The top portion  28  overlies a vacuum tube body  32  which functions as an anode. The vacuum tube body  32  overlies an antenna dome  34  extending therefrom, the antenna dome  34  being configured to emit microwave radiation. 
     Referring again to  FIGS. 1 and 2 , the vacuum tube  26  is adapted to be inserted in the bore holes  20 ,  22 ,  24  such that the antenna dome  34  of the vacuum tube  26  extends a predetermined distance from the bottom yoke  12  and is configured to extend into a cavity of a waveguide (not shown). The bore holes  20 ,  22  each have substantially the same diameter as the antenna dome  34  of the vacuum tube  26 , while the bore hole  24  has substantially the same diameter as the vacuum tube body  32 . The small gap between the bore holes  20 ,  22  and antenna dome  34  contains a metal (stainless steel, brass, etc.) mesh gasket (not shown) to produce a reliable electrical connection with standard waveguide components, thereby reducing rf (radiofrequency) leakage and arcing between the two components. The cooling assembly  18  is typically sized and shaped to fit tightly about the vacuum tube body  32  for the purpose of dissipating heat generated in the vacuum tube  26 . In typical configurations, the cooling assembly  18  comprises a plurality of thin plates (“fins”) that are press-fit on to the vacuum tube body (anode)  32  with the assistance of lubricating oil. The top portion  28  of the vacuum tube  26  is configured to receive a top magnet  36  and a top yoke  38  overlying the top magnet  36 . The top magnet  36  and the top yoke  38  each have a substantially circular bore hole  40 ,  42  having substantially the same diameter as the top portion  28  of the vacuum tube  26 . A filter/connection box  43  overlies the top yoke  38  and is configured to receive the top portion  28  of the vacuum tube  26  (not shown) to make electrical connection with the filament leads  30 . The filter/connection box  43  contains the external connection leads  46 , which receive the magnetron input power. The top yoke  38  has a plurality of holes  44  which are adapted to be aligned with corresponding holes  15  in the opposing rails  14  of the bottom yoke  12 . The top yoke  38  is fastened to the bottom yoke  12  by means of screws or rivets (not shown) that are inserted into the aligned holes  15 ,  44  so as to encase the bottom magnet  16 , the cooling assembly  18 , the vacuum tube  26 , and the top magnet  36  therein and forming the assembled magnetron  10 . 
     Many sensitive applications require periodic replacement of magnetrons as a mechanism to ensure optimum process control. In addition, a magnetron may fail and have to be replaced in a UV lamp assembly. The most likely part to fail is the vacuum tube  26 , while other parts in the assembled magnetron  10  are much less likely to fail. Moreover, the portions of the assembled magnetron  10  overlying and underlying the vacuum tube  26  carry significant materials (copper, steel, ferrite) that are rarely recycled when a magnetron fails. 
     Accordingly, what would be desirable, but has not yet been provided, is a magnetron that facilitates replacement of the vacuum tube  26  without having to replace other parts in the magnetron. 
     SUMMARY OF THE INVENTION 
     The above-described problems are addressed and a technical solution achieved in the art by providing a modular magnetron. The modular magnetron comprises a bottom assembly, a top assembly, and a removable vacuum tube. The bottom assembly includes a bottom yoke, a bottom magnet, and cooling assembly. The top assembly includes a top magnet, a top yoke, and a filter/connection box. In a preferred embodiment, the bottom assembly and the top assembly are configured as non-disposable units. The vacuum tube is configured to be replaced during routine lamp maintenance or a vacuum tube failure. Also, this arrangement allows a ‘universal vacuum tube’ to be employed for both 2 kW and 3 kW applications, with the only vacuum tube product differentiators being the frequency range of operation (low, nominal, or high). 
     Once the vacuum tube is inserted into the cooling assembly and fastened, the top assembly is fastened to the bottom assembly by screws and nuts with alignment slots or stops in the top yoke and the bottom yoke, respectively. 
     According to an embodiment of the present invention, a modular magnetron for use in an ultraviolet radiation (UV) curing lamp assembly is disclosed, comprising: a vacuum tube having a vacuum tube body; a top assembly configured to substantially overlay the vacuum tube; and a bottom assembly configured to substantially extend about the vacuum tube, the vacuum tube being positioned to partially protrude from the bottom assembly, the bottom assembly including a cooling assembly configured to employ a flexible clamp-type fitting about the vacuum tube body for substantially maintaining thermal and electrical conductivity, wherein the top assembly is configured to be releasably fastened to the bottom assembly about the vacuum tube with removable fasteners. 
     According to an embodiment of the present invention, the cooling assembly may be liquid cooled. The cooling assembly may comprise a copper block heat sink. The copper block heat sink has a cylindrical interior aperture bored to match the outer diameter of the vacuum tube body, a facing side of the copper block heat sink being split and fastened with bolts to produce a tight clamp-on fit of the cooling assembly to the vacuum tube body of the vacuum tube to allow repeated vacuum tube removal upon loosening of the bolts. The copper block heat sink is threaded with holes for water connections. Alternatively, the cooling assembly may include a plurality of thin plates for use with forced air cooling. 
     According to an embodiment of the present invention, the top assembly further comprises at least one top magnet and the bottom assembly further comprises at least one bottom magnet, the at least one top magnet and the at least one bottom magnet each configured to substantially fit about the vacuum tube, the at least one bottom magnet being configured to underlay the cooling assembly. In some embodiments, one of the at least one top magnet and the at least one bottom magnet is made of one of a rare-earth material and Alnico. In other embodiments, at least one of the at least one top magnet and the at least one bottom magnet is an electromagnet. 
     According to an embodiment of the present invention, the top assembly further comprises a top yoke configured to overly the at least one top magnet and the vacuum tube and a connection box overlying the top yoke, and the bottom assembly further comprises a bottom yoke configured to underlay the at least one bottom magnet and to receive therethrough the vacuum tube. The top yoke is configured to be fastened to the bottom yoke with the removable fasteners. The top yoke and the bottom yoke may each have alignment slots or stops for receiving the removable fasteners. At least two parts comprising at least one of the top assembly and the bottom assembly are configured to be modular by being fastenable with removable fasteners. 
     According to an embodiment of the present invention, the vacuum top further comprises a top portion with electrical connections extending therefrom, the electrical connections each having one of a push-on type connector and a screw-terminal connection that is accessible through the connection box. The vacuum tube is configured to be keyed within the bottom assembly so that the electrical connections of the vacuum tube mate with the connection box. The connection box includes filter elements to reduce electromagnetic interference. The bottom assembly is configured to be fastened to a waveguide, the waveguide having an opening for receiving an antenna dome of the vacuum tube, the antenna dome being configured to emit microwave radiation. 
     According to an embodiment of the present invention, a method for manufacturing a modular magnetron for use in an ultraviolet radiation (UV) curing lamp assembly is disclosed, comprising the steps of: providing a vacuum tube having a vacuum tube body, a top assembly configured to substantially overlay the vacuum tube, and a bottom assembly configured to substantially extend about the vacuum tube, the vacuum tube being positioned to partially protrude from the bottom assembly, the bottom assembly including a cooling assembly comprising a flexible clamp-type fitting; fitting the flexible clamp-type fitting about the vacuum tube body; receiving the vacuum tube in the bottom assembly and the top assembly; and fastening the top assembly to the bottom assembly about the vacuum tube with releasably removable fasteners. The method may further comprise the step of liquid cooling the cooling assembly using a clamp-on a copper block heat sink. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention may be more readily understood from the detailed description of an exemplary embodiment presented below considered in conjunction with the attached drawings and in which like reference numerals refer to similar elements and in which: 
         FIG. 1  depicts a conventional assembled magnetron for use in a UV curing lamp assembly; 
         FIG. 2  depicts an exploded view of the components of the magnetron of  FIG. 1 ; 
         FIG. 3  depicts a vacuum tube for use in both the conventional magnetron of  FIG. 1  and in the present invention; 
         FIG. 4  shows a partial exploded perspective view of a modular magnetron mounted overlying a waveguide, according to an embodiment of the present invention; 
         FIG. 5  is an assembled perspective view of the modular magnetron and waveguide of  FIG. 4 , according to an embodiment of the present invention; and 
         FIG. 6  depicts a clamp-on liquid-cooled modular magnetron cooling assembly, according to an embodiment of the present invention. 
     
    
    
     It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention and may not be to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 4  shows a partial exploded perspective view and  FIG. 5  is an assembled perspective view of a modular magnetron  50  mounted overlying a waveguide  52 , according to an embodiment of the present invention. Referring now to  FIGS. 4 and 5 , the modular magnetron  50  includes a bottom assembly  54 , a vacuum tube  26 , and a top assembly  58 . The bottom assembly  54  includes a bottom yoke  60 , a bottom magnet  62 , and cooling assembly  64 . The top assembly  58  includes a top magnet  66 , a top yoke  68 , and a filter/connection box  70 . In a preferred embodiment, the bottom assembly  54  and the top assembly  58  are configured as non-disposable units. The vacuum tube  26  is configured to be replaced during routine maintenance or a vacuum tube failure. 
     The bottom assembly  54  is adapted to be mounted overlying the waveguide  52  in a way similar to the prior art (non-modular) magnetron of  FIGS. 1 and 2 , using screws and the original mounting holes (not shown) on the waveguide. According to a preferred embodiment of the present invention, the parts of the bottom assembly  54  may be “permanently” fastened together using a variety of techniques (rivets, screws, press fittings, etc.). According to other embodiments of the present invention, the bottom assembly  54  may be constructed to be modular, wherein removable fasteners such as stainless steel screws are employed, thereby allowing for the replacement of individual parts (e.g., the bottom magnet  62  may become de-magnetized if exposed to excessive heat). 
     According to another embodiment of the present invention, the top assembly  58  may be constructed to be modular, wherein removable fasteners such as stainless steel screws are employed to fasten the top yoke  68  to the a filter/connection box  70 , with the top magnet  66  unfastened, thereby allowing for the replacement of individual parts. 
     Referring now to  FIGS. 3-5 , the vacuum tube  26  is configured to be inserted through bottom assembly  54 , with the antenna dome  34  extending a predetermined distance into the waveguide  52 . The waveguide  52  possesses a mechanical lip (not shown), which fits into the metal (stainless steel, brass, etc.) mesh gasket (not shown) on the bottom assembly  54 . As with the magnetron assembly  10  of  FIGS. 1 and 2 , the vacuum tube  26  employed in the modular magnetron  50  of  FIGS. 4 and 5  requires intimate contact with the cooling assembly  64  to maximize the transfer of heat from the vacuum tube  26  for maintaining proper operation without damage. That is, the cooling assembly  64  requires a thermally conducting connection to the vacuum tube body (anode)  32 . Unlike the cooling assembly  18  of conventional magnetron assemblies  10  described in  FIGS. 1 and 2  above, in a modular design, the press-fit approach may not work reliably once the first vacuum tube  26  is removed, since the cooling assembly  64  may become deformed by minor imperfections of the first vacuum tube body  32  and/or by the process of removing the vacuum tube  26  from the modular magnetron assembly  50 . The cooling assembly  64  is configured to employ a flexible clamp-type design about the vacuum tube body  32  that also maintains thermal and electrical conductivity. The vacuum tube body  32  preferably receives a coating of thermal paste or oil before insertion in to the cooling assembly  64 . An example of flexible clamp-type design of the cooling assembly  64  is described below in connection with  FIG. 6 . 
     A ‘universal vacuum tube’ may be employed for both 2 kW and 3 kW applications, with the only vacuum tube product differentiators being the frequency range of operation (low, nominal, or high). 
     Once the vacuum tube  26  is inserted into the cooling assembly  64  and fastened, the top assembly  58  is connected to the bottom assembly  54 . According to an embodiment of the present invention, the two assemblies  54 ,  58  are fastened together by removable fasteners, such as screws  72  and nuts  74  with alignment slots or stops  76 ,  78  in the top yoke  68  and the bottom yoke  60 , respectively. Alternatively, according to another embodiment of the present invention, alignment slots may be located in the cooling assembly  64  instead of the bottom yoke  60 . According to certain embodiments of the present invention, the electrical connections  30  of the top portion  28  of the vacuum tube  26  may have a push-on type connector or may have a more robust screw-terminal connection that may be accessed through the connection box (top)  70 . (The connection box  70  may also contain various filter elements to reduce electromagnetic interference produced by the modular magnetron  50  or by the driving circuitry of the vacuum tube  26  (not shown)). The vacuum tube  26  may be keyed or aligned within the bottom assembly  54  so that the electrical connections  30  of the vacuum tube  26  may be reliably located and mate with the connection box  70  of the top assembly  58 . 
       FIG. 6  depicts a (machine-bore) clamp-on liquid-cooled modular magnetron cooling assembly  64 , according to an embodiment of the present invention. Also depicted in  FIG. 6  is the top assembly  58  fastened with removable fasteners (screws and nuts)  72 ,  74  to the bottom assembly  54 . The connection box  70  and the vacuum tube  26  of  FIGS. 4 and 5  are not shown. Still further depicted in  FIG. 6  are fastener bolts  80  in the bottom assembly  54  for fastening the bottom assembly  54  to the waveguide  52 . Referring now to  FIGS. 3 and 6 , the liquid cooled cooling assembly  64  design is constructed using a copper block heat sink  82 , with a cylindrical interior aperture (not shown) bored to closely match the outer diameter of the vacuum tube  26 . The facing side of the copper block heat sink  82  is split and fastened with bolts  84  to produce a reliably tight clamp-on fit of the cooling assembly  64  to the vacuum tube body  32 , and is configured to allow repeated vacuum tube removal upon loosening of the bolts  84 . White thermal (electronic) grease (paste)  86  may be employed to increase the heat transfer from the vacuum tube body  32  to the cooling assembly  64 . The copper block heat sink  82  has threaded holes  88  for water connections, although other fittings may be soldered or brazed to the copper block heat sink  82 . According to another embodiment, a similar clamp-on design may be used with air-cooled fins. 
     Conventional (microwave powered) UV curing lamps use either 2 kW or 3 kW magnetrons. The only difference between the 2 kW and 3 kW (output powers) designs is the strength of the magnetic field (i.e., the strengths of the magnets in the assembly). Using permanent magnets and a non-modular magnetron design, a truly universal magnetron cannot be produced, since the magnetic field (i.e., the magnets) cannot be changed. To make a truly universal magnetron, a replacement set of permanent magnets is needed using the modular magnetron design of the present invention to convert from 2 kW operation to 3 kW operation. With standard (inexpensive) ferrite magnets, a 3 kW magnetron may be configured to have three magnets replacing the top magnet  66  in the top assembly  58  compared to one magnet used in a 2 kW design. 
     According to another embodiment of the present invention, the top magnet  66  and the bottom magnet  62  may be a permanent magnet made of non-ferrite material. More expensive rare-earth and/or Alnico permanent magnets allow a 3 kW magnetron to use a single top magnet because much larger magnetic fields are generated because of better magnetic properties of these materials. 
     According to still another embodiment of the present invention, the permanent magnetic materials of one or both of the top magnet  66  and the bottom magnet  62  may be replaced with electromagnets. In this embodiment, a universal magnetron assembly can be produced, with the power levels (2-5 kW) determined by the magnetic field strength (i.e., with an electromagnet coil) and the level of the magnetron input signal delivered to the filament leads  30 . 
     The modular magnetron  50  has many advantages over prior art magnetron assemblies, such as the magnetron assembly  10  of  FIGS. 1 and 2 . Since a ‘universal vacuum tube’ is already used for both 2 kW and 3 kW applications, the only vacuum tube product (or stock) differentiator is the frequency range of operation (low, nominal, or high). Thus, the manufacturing, stocking, and tracking of many assembled magnetrons may be reduced to only a categorized frequency range. With a stackable assembly of magnets and cooling assembly (using a ‘clamp on’ cooling design as described above), magnetron replacement may be slightly more labor intensive but the flexible design greatly enhances manufacturability and reduces the number of required stock items. Since the lifetime of a UV curing lamp assembly is many years, and at constant operation, the magnetrons in the prior art are replaced (at least) yearly. In stark contrast, a modular magnetron provides significant savings in materials cost, manufacturability, and shipping (less than half the weight of the present magnetron is the vacuum tube), since “magnetron” replacement would entail only replacing the vacuum tube  26 . 
     With electromagnets (or a combination of permanent and electromagnets), the magnetic field of the magnetron becomes modifiable and thereby a truly ‘universal magnetron’ may be created that may be optimized for any output power level. 
     It is to be understood that the exemplary embodiments are merely illustrative of the invention and that many variations of the above-described embodiments may be devised by one skilled in the art without departing from the scope of the invention. It is therefore intended that all such variations be included within the scope of the following claims and their equivalents.