Compact microwave-powered lamp, inkjet printer using this lamp, and ultraviolet light curing using this lamp

[0002] The present invention is directed to a compact microwave-powered lamp, which is small and lightweight, and can provide focused light at a small distance from the lamp. The present invention is especially directed to an electrodeless compact microwave-powered lamp, for emitting ultraviolet light. Such a lamp can be used in small devices such as office products (e.g., inkjet printers for the office), and for larger devices, and not only for producing ultraviolet light for industrial applications.

[0003] The present invention is also directed to techniques using ultraviolet light or other type of light (e.g., visible light) for curing purposes (for example, for curing ultraviolet light curable inks, or coating materials, or various plastics). This aspect of the present invention is particularly directed to techniques for curing inkjet inks deposited, for example, by an inkjet printer, having utility in many applications including inkjet printers for the office.

[0004] Use of microwave-powered lamps for producing ultraviolet light for curing processes is known. It is known to use, e.g., electrodeless, microwave-powered lamps, to produce the ultraviolet light for such curing. However, existing electrodeless, microwave-powered lamps are too large, too heavy and use too much air for cooling, to be considered for some ultraviolet light curing processes. In addition, existing high-powered electrodeless lamps for ultraviolet light curing require an auxiliary ignitor bulb to start the main bulb emitting ultraviolet light, and it is desired to provide an electrodeless lamp that does not require such auxiliary ignitor bulb.

[0005] Moreover, existing arc lamps have a short lamp life, and the spectral output changes with use; this is especially true with iron additive lamps. In addition, peak energy focused by the arc lamp is inferior, because the bulb diameter is relatively large for a given power density, and the position of the arc is imprecisely located within the ellipse.

[0006] In both arc lamps and existing electrodeless lamps, portions of the elliptical reflector are removed, for air flow purposes, and this reduces the energy being focused by the reflector.

[0007] U.S. Pat. No. 5,998,934 to Mimasu et al. discloses a microwave-excited discharge lamp apparatus which emits light by discharge under a microwave electromagnetic field. The structure of this device includes a microwave generator for generating a microwave, a waveguide for propagating the microwave to a cavity resonator unit, and a microwave discharge lamp arranged in the cavity resonator unit, the microwave-excited discharge lamp apparatus including a rotary supporter for supporting the lamp rotatably, and a blow guide arranged around the lamp in the cavity resonator unit for conducting a cooling air to the lamp for cooling the lamp. According to U.S. Pat. No. 5,998,934, the microwave generator and the cavity are provided at opposite sides of the waveguide and at opposite ends thereof, and microwaves from the waveguide are introduced into the cavity through a curved reflector of the cavity-forming member.

[0008] In the structure of Mimasu et al., by having the microwave-introducing window (and structure for rotating the bulb) extending through the curved reflector forming the cavity in which the bulb is positioned, a substantial portion of the reflector is removed, whereby the curved portion of the reflector inefficiently reflects the light emitted from the bulb. Moreover, this structure of Mimasu et al., having the bulb rotator, microwave generator and RF cavity positioned so as to include structure on opposite sides of the waveguide structure, takes up a lot of room.

[0009] U.S. Pat. No. 5,866,990 to Ury et al. discloses a microwave-powered, electrodeless lamp, utilizing a single rotary motor to rotate the bulb and provide rotary motion to a blower or pump means for providing cooling fluid to the magnetron and/or to a forced gas cooling for providing cooler gas to the bulb. This patent discloses structure wherein the bulb is rotated to provide various advantages including temperature equalization around the bulb surface, improved spatial emission properties, discharge stabilization, elimination of visual “wobble”, increased efficiency and better cooling, and provides, for example, cooling of the magnetron used to provide the microwaves. The contents of U.S. Pat. No. 5,866,990 are incorporated herein by reference in their entirety.

[0010] U.S. Pat. No. 6,102,536 to Jennel discloses apparatus and a method for printing images on packaging material, including jetting ink through an inkjet print head onto a surface of a web. The printing site includes, inter alia, a printer and a curing device, the printer having at least one print head, for example, an inkjet print head. The curing device, where the inks are ultraviolet light-reactive inks, can, for example, be an ultraviolet light source. This is a typical illustrative example (and not to be limiting) of an environment for use of lamps (e.g., microwave-powered lamps) as in the present invention.

[0011] As can be seen from the foregoing, while various microwave-powered, e.g., electrodeless lamps, and also arc lamps, are known, it is still desired to provide microwave-powered lamps having a compact size, which are lightweight, and have stable light (e.g., stable ultraviolet light) spectral output. It is also desired to provide such a lamp which can operate on 120 or 230 volt power (residential or office power, rather than industrial levels), and has low air-cooling requirements. It is desired to provide such compact lamp, which has applicability to smaller devices such as office products. (e.g., inkjet printers). It is also desired to provide a lamp having a compact size and is lightweight, and yet wherein a tubular or cylindrical bulb of the lamp can be rotated.

[0012] It is also desired to provide techniques for printing, coating, marking or imaging including curing or drying the printed, coated, marked or imaged structure, using such lamp.

[0013] The foregoing objectives are achieved by the lamp structure and method of using such structure, according to the present invention, discussed in the following. Generally, the structure of the present invention includes a microwave generator, a waveguide, and an RF cavity. The RF cavity has positioned therein a bulb, of the microwave-powered lamp. The waveguide is provided for directing microwaves generated in the microwave generator to the cavity (which, as known in the art, is a cavity resonator, for accumulating microwave energy). The cavity is defined by end members and a member extending therebetween (this member extending therebetween being, e.g., curved, and having, for example, a cross-sectional shape of a partial ellipse with an opening at one end). This member extending between the two end members is, desirably, a primary reflecting member forming the boundary of the cavity. The cavity is positioned adjacent to the waveguide such that one of the end members is positioned so as to overlap a side of the waveguide. An RF slot extends from the waveguide through the side of the waveguide, and through this one of the end members positioned so as to overlap a side of the waveguide, into the RF cavity, for introduction of the microwaves from the waveguide into the RF cavity.

[0014] By providing the RF slot through the end member (e.g., end reflector) instead of, e.g., the reflecting structure between the end members (e.g., the member having the partial elliptical shape in cross-section), energy focus is improved. In addition, the compact nature of the structure can also be improved.

[0015] The cavity is positioned to overlap the side of the waveguide so that the RF slot can extend into the cavity. As can be appreciated, the cavity, extending along the side of the waveguide, can extend beyond the end of the waveguide.

[0016] Desirably, another end member defining the RF cavity, opposite the end member having the RF slot therethrough, has an opening therethrough for inserting the bulb into the RF cavity. Here also, by providing the bulb through this other end member, a break in the reflector surface between the end members (that is, the member extending between the end members) is avoided, improving effectiveness of emission of radiation (for example, ultraviolet light) from the lamp.

[0017] The structure according to the present invention can also include structure to rotate the bulb in the cavity, providing advantages of such rotation, as discussed previously, in a relatively compact structure.

[0018] In addition, the structure according to the present invention can also include structure (for example, but not to be limiting, a fan or blower, or a source of compressed cooling fluid (such as compressed air)) to pass cooling fluid (such as air) by the bulb for forced cooling of the bulb. This cooling fluid passing by the bulb passes through the RF slot in passing into the cavity or passing out of the cavity, providing a compact path for passing of the cooling fluid. Desirably, the, e.g., fan or blower is provided such that the cooling fluid passing by the bulb and through the RF slot also is forced to flow past the microwave generator (for example, magnetron), for also cooling the microwave generator.

[0019] Under some circumstances, rotation of the bulb, using the structure to rotate, provides sufficient bulb cooling without the need for additional cooling structure.

[0020] According to another aspect of the present invention, the RF slot between the waveguide and cavity is in one end member of the RF cavity, and the bulb of the microwave-powered lamp extends from an opposite end member of the cavity. The bulb is aligned with the RF slot when positioned in the RF cavity, so as to achieve most effective use of the microwave energy for emission of light (e.g., ultraviolet light) from the bulb. For example, this alignment is achieved by a central axis of the bulb (e.g., a cental axis of a tubular bulb), when extended beyond the bulb, intersecting the RF slot (desirably, a center line of the RF slot).

[0021] According to other aspects of the present invention, the microwave-powered lamp has a bulb which emits ultraviolet light and/or visible light, of relatively high intensity, and is used for ultraviolet or visible light curing of various materials, such as, but not limited to, paper, plastics, textiles and foils, and curing of inks and coatings of various materials, including inks and various plastics. In one embodiment of use of this compact microwave-powered lamp, the lamp is used as a curing device used in conjunction with a print head of an inkjet printer, for curing ultraviolet light-cured inks deposited by an inkjet printing head. The compact microwave-powered lamp according to the present invention can, for example, be used as a substitute for the described curing device in U.S. Pat. No. 6,102,536. Of course, the lamp according to the present invention is not limited to use in an inkjet printer, but rather has many various uses, including (but not limited to) any printing, marking, bonding or imaging process such as in medical uses, small-part curing and wire marking, packaging, and curing of component electronic structures.

[0022] The microwave generator utilized according to the present invention can be a conventional magnetron; for example, the microwave energy can be produced using a 1000 watt consumer oven magnetron. Various relatively small components can be used; for example, the bulb used can be a tubular bulb approximately 50 mm long, the outside diameter thereof chosen varying from 7 mm to 18 mm depending on the power level desired and the cooling scheme used. The waveguide can be small, e.g., very short (e.g., about 4.7 inches long by 2.8 inches wide by 1.7 inches high); and the height of the cavity, and minor and major diameters thereof, and the short waveguide, create compactness of the lamp.

[0023] Illustratively, the RF cavity can have a partial elliptical surface between the two end members, with the two end members being spaced 3.0 inches. The elliptical shape of the partial elliptical reflector can have a major diameter of 4.31 inches and a minor diameter of 3.54 inches. These dimensions are examples and are not to be limiting of the present invention.

[0024] In addition, according to the present invention, having cooling air at least for the bulb, and preferably for both the magnetron and bulb, passing through the RF slot, a further compact structure is provided, which is relatively quiet, especially for use in an office product (inkjet printer).

[0025] As compared to arc lamp alternatives, the microwave-powered lamp according to the present invention provides a stable ultraviolet light output during operation, a longer lamp life and higher peak energy at focus.

[0026] Moreover, as compared to alternative electrodeless lamp devices, the present invention provides a lamp of compact size, less weight and low air cooling requirements. Furthermore, the rotating tubular lamp provides for uniform stress along the bulb wall, with respect to both thermal and electric field stresses, as well as other benefits.

[0027] In addition, the microwave-powered lamp according to the present invention starts without an ignitor bulb. That is, with structure according to the present invention, sufficient microwave energy can be provided to the RF cavity to create an electric field in the RF cavity which ignites the lamp bulb without the need for an ignitor bulb.

[0028] Furthermore, by providing the RF slot on the end member, instead of through the, e.g., elliptical-shaped reflector, energy focus is improved and compactness is also improved. In addition, this structure permits the product focus to be closer to the lamp, for example, 0.38 inches versus 2.1 inches. By providing positioning of the slot relative to the bulb as in aspects of the present invention, effectiveness of use of the microwave energy is improved.

[0029] In addition, through use of cooling air flow through the RF slot, according to various aspects of the present invention, the same lamp configuration can be cooled with positive or negative pressure.

[0030] FIG. 1ais a perspective view of a first embodiment of the present invention.

[0031] FIG. 1bis a perspective of a second embodiment of the present invention.

[0032] FIG. 2 is a perspective, partially exploded view of a third embodiment of the present invention.

[0033] FIG. 3 shows the RF cavity of the present invention, showing bulb position therein.

[0034] FIG. 4 is a schematic view of a lamp according to the present invention, applied to ultraviolet curing.

[0035] FIGS. 5aand 5bare schematic views of use of the lamp according to the present invention in an inkjet system for wire marking, with FIG. 5ashowing a side view and FIG. 5bshowing a cross-section of FIG. 5athrough the lamp according to the present invention.

[0036] FIG. 6 is a schematic view of use of the lamp in an inkjet system for web printing.

[0037] FIG. 7 is a schematic view of use of the lamp according to the present invention in an inkjet system, according to another embodiment.

[0038] While the present invention will be described in connection with specific and preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. To the contrary, it is intended to cover all alterations, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

[0039] Throughout the present specification, where apparatus and methods are described as including or comprising specific components or structure, or specific processing steps, it is contemplated by the inventors that apparatus and methods of the present invention also consist essentially of, or consist of, the recited components or structure, or recited processing steps.

[0040] In the following descriptions of the drawing figures, like components in the different drawing figures are represented by the same reference characters.

[0041] The present invention contemplates, as one aspect thereof, structure of a microwave-powered lamp. The structure includes a microwave generator (for example, a magnetron, which can be a 1000 watt consumer oven magnetron) and an RF cavity, adapted to have positioned therein a bulb of the microwave-powered lamp. The bulb can be, for example, a bulb which includes a fill material such that, when the bulb is excited by microwaves, emits, for example, ultraviolet light or visible light. A waveguide for directing microwaves generated by the microwave generator to the RF cavity is connected between the microwave generator and the RF cavity. A slot is provided between an end member of the RF cavity and a side of the waveguide, for introduction of the microwaves from the waveguide into the RF cavity. Desirably, this slot is aligned with the bulb provided in the cavity. For example, a central line of the slot can intersect an extension of an axis of a tubular or cylindrical bulb in the RF cavity.

[0042] The present invention also contemplates that the bulb (e.g., a tubular bulb) is inserted into the RF cavity from an end member forming the cavity, which is opposite the end member (forming the cavity) that has the slot therein. Thus, according to an aspect of the present invention, the tubular bulb extends substantially perpendicular to the end member, forming the cavity, that has the slot therein for introduction of microwaves.

[0043] According to further aspects of the present invention, both the magnetron and the RF cavity are on the same side of the waveguide. Moreover, according to still further aspects of the present invention, the bulb can be rotated while emitting light, and cooling fluid, such as cooling air, can be caused to flow by the bulb, through the RF slot, for cooling the bulb. Desirably, such fluid flow also passes by the microwave generator (magnetron), to cool the microwave generator.

[0044] According to additional aspects of the present invention, the microwave-powered lamp, emitting ultraviolet light and/or visible light, can be utilized for ultraviolet light or visible light curing of various materials, such as, but not limited to, paper, plastics, textiles and foils, and also curing of, e.g., inks and coatings of various materials; and also can form part of an inkjet printing system for curing ultraviolet light curable inkjet printing ink.

[0045] FIG. 1ashows a microwave-powered lamp 1 according to the present invention. Shown is lamp 1, having magnetron 3 and RF cavity 7 on a same side of waveguide 5. The cavity 7 is defined by respective end members 9 and 11, and by member 17, which extends between end members 9 and 11 and provides a curved surface, which is preferably a reflecting surface. Desirably, member 17 has a shape of a partial ellipse, cut off to form the opening of cavity 7 which emits light. In the embodiment shown in FIG. 1a, the member 17 is made as a single member forming the cavity 7, but can be made of a plurality of parts connected together to form cavity 7.

[0046] Also shown in FIG. 1ais RF slot 15, for introducing microwaves from waveguide 5 into cavity 7. As can be appreciated from FIG. 1a, also shown is bulb 19, which is aligned with slot 15. For example, an extension of a central axis of bulb 19, which is tubular, intersects a central line extending in the lengthwise direction of slot 15.

[0047] FIG. 1aalso shows bulb rotation motor 21. This bulb rotation motor causes rotation of bulb 19 during operation of the lamp, providing advantages as discussed previously.

[0048] Also shown schematically in FIG. 1ais the air flow pattern through lamp 1. This represents flow of air past the bulb, for purposes of cooling the bulb. Although not shown in FIG. 1a, lamp 1 would, illustratively, be within a housing. Air flow 23awould pass by magnetron 3, to cool the magnetron, and then pass out of magnetron 3 as represented by arrow 23b. Air could then pass into waveguide 5 through holes 6 therein, as represented by arrow 23c. Air would then flow through RF slot 15, as represented by arrow 23d, to cool bulb 19 in cavity 7. Thus, the air flow could be used to cool both the bulb and magnetron.

[0049] While described as an air flow, as can be appreciated by one of ordinary skill in the art any cooling fluid can be utilized. Moreover, while air flow is shown in a direction from magnetron 3 to bulb 19, the air flow can be in the reverse direction.

[0050] FIG. 1bshows lamp 1′, which is similar to lamp 1 of FIG. 1abut differs therefrom in that light from lamp 1′ in FIG. 1bis directed in a different direction than that of light from lamp 1 in FIG. 1a. That is, in FIG. 1a, the opening in cavity 7 is such that light from lamp 1 is irradiated in a direction of the axis of waveguide 5 (the direction that microwaves pass through waveguide 5 from magnetron 3 to RF slot 15). In FIG. 1b, cavity 7′ has been rotated 90° such that light from lamp 1′ irradiates in a direction perpendicular to the axis of waveguide 5. As can be appreciated, other directions for light irradiation from the lamp can be achieved. Thus, the lamp according to the present invention provides excellent flexibility with respect to the direction that the light irradiates therefrom.

[0051] As can be appreciated from FIG. 1a, both magnetron 3 and cavity 7 are provided on a same side of waveguide 5. This provides a most compact structure, a desired feature according to the present invention.

[0052] However, according to the present invention, magnetron 3 and RF cavity 7 need not be on a same side of waveguide 5. FIG. 2 shows an embodiment where magnetron 3 and cavity 7 are both at the sides of waveguide 5 near respective ends thereof, similar to the embodiment shown in FIG. 1a, but are provided on opposite sides of waveguide 5, contrary to the embodiment in FIG. 1a.

[0053] Also shown in FIG. 2 is opening 25 for inserting bulb 19 into cavity 7. Further shown in FIG. 2 is RF screen 27 provided over the opening of the partial elliptical shaped cavity. As can be appreciated by one of ordinary skill in the art, this RF screen 27 is opaque to microwaves, yet is sufficiently transparent to emitted light such that an effective emission of light (e.g., ultraviolet light) from the lamp is achieved.

[0054] FIG. 3 shows a cross-section of the partial elliptical-shaped cavity 7 in FIG. 2. As can be appreciated from FIG. 3, bulb 19 is placed at primary focal point 31 within RF cavity 7. This focal point 31 is the focal point of a complete ellipse, which would be formed from the partial elliptical shape. By desirably forming a reflector surface 29 for the shaped member forming the RF cavity, light rays emitted from the bulb and represented by reference character 33 in FIG. 3, can be reflected through the opening in the cavity so as to most efficiently and effectively emit light of a focused nature from lamp 1.

[0055] FIG. 4 shows a complete lamp system for generating and emitting light. Shown by reference character 35 is a power supply. This power supply, for example, can be a 230 volt AC, 50 Hz, single phase, power supply. This power supply can be connected to the magnetron of lamp 1 by high-voltage cable 37, for example, a 6 meter high-voltage cable. Illustratively, the lamp (irradiator), seen in FIG. 4, can have dimensions of 165 mm×165 mm×200 mm (height), and can weigh, e.g., 2.9 kg. Use of this compact lamp structure enables outputted ultraviolet light to be focused as close as 7 mm from the irradiator (a distance represented by reference character 43 in FIG. 4).

[0056] Also shown schematically in FIG. 4 is air inlet 39 and exhaust air 41. This passage of air acts to cool both the magnetron and lamp bulb. Illustratively, and not to be limiting, the exhaust air can exit through a 2.5 inch ID hose, which is 4.5 meters long. The air can be forced into the air inlet by providing a negative air pressure of 40-50 mm H₂O at the air outlet.

[0057] In general, the microwave-powered lamp structure according to the present invention can be formed utilizing conventional materials as known in the art, and, as indicated previously, can use a conventional consumer oven magnetron. It is desired that lightweight materials (e.g., aluminum) be used, in order to provide the most lightweight lamp. The waveguide can have, for example, a rectangular cross-section, and be a box-shaped metal, of conventional metal materials. Holes 6 can be provided in waveguide 5, for purposes of facilitating flow of cooling fluid (e.g., air) between the magnetron and bulb through the RF slot, as discussed previously. The members forming boundaries of the RF cavity can be made of conventional materials; as indicated previously, it is desired that cavity 7 be provided with reflective material, known in the art, forming the boundaries thereof, for efficiently and effectively reflecting light emitted from bulb 19.

[0058] As discussed previously, while the compact lamp structure according to the present invention has many varied uses, one desirable use is as part of an inkjet system which uses, for example, ultraviolet light curable ink, with ultraviolet light from the compact microwave-powered lamp according to the present invention, having an ultraviolet light emitting bulb, being used to cure deposited ink.

[0059] Shown in FIGS. 5aand 5bis inkjet system 45 for depositing ink on a receiving member. The receiving member in system 45 in FIGS. 5aand 5bis wire 49, which is marked using inkjet head 47, and the deposited ink then cured using microwave-powered lamp 1. FIG. 5ashows schematically the inkjet head 47 and lamp 1 positioned with the lamp 1 just downstream from inkjet head 47, in a direction of wire 49 movement. FIG. 5bshows, for example, a cross-section through lamp 1, showing, schematically, reflector 29, bulb 19 and wire 49. As can be appreciated, light emitted from bulb 19 is reflected off reflector 29 and focused at wire 49, which is located at the second focal point of the complete ellipse which would be formed by completing the partial elliptical shape of reflector 29. Bulb 19 is provided at the other (primary) focal point of this complete ellipse.

[0060] Another embodiment of use of lamp 1 according to the present invention is seen in FIG. 6. This illustrates printing from an inkjet printer on a web as the ink-receiving material. Shown in FIG. 6 is inkjet head 48 and lamp 1, the lamp being downstream from inkjet head 48 in the direction of movement of web 51. After depositing of, for example, an ultraviolet light curable ink on web 51 from inkjet head 48, the ink is cured by irradiating ultraviolet light emitted from bulb 19 on web 51. FIG. 6 also shows reflector surface 29.

[0061] Shown in FIG. 7 is another embodiment of the present invention, using two compact microwave-powered lamps. These two lamps 53, 55 can each be a microwave-powered lamp according to-the present invention, each having reflector surface 29 and bulb 19. These two lamps sandwich inkjet head 50, and form a row therewith.

[0062] The inkjet head can deposit ink according to signals generated, for example, by a desktop computer, as known in the art. The printer can also deposit ink responsive to signals from other devices, including, for example, digital cameras, scanners, etc., as known in the art.

[0063] Accordingly, by the present invention, a compact microwave-powered lamp, capable of providing, e.g., stable ultraviolet light output during operation, having less weight and low air cooling requirements, and providing a rotating tubular lamp for uniform stress along the bulb wall from both thermal and electric field stresses, is achieved. Moreover, this, e.g., ultraviolet light-emitting lamp can start without an ignitor bulb, and can move the product focus closer to the lamp.

[0064] While several embodiments in accordance with the present invention have been shown and described, it is understood that the same is not limited thereto, but is susceptible of numerous changes and modifications as known to those skilled in the art. Therefore, we do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.