WO2004113795A1

WO2004113795A1 - Microwave oven lamp and attachment

Info

Publication number: WO2004113795A1
Application number: PCT/AU2004/000840
Authority: WO
Inventors: Robert William Cairns
Original assignee: Robert William Cairns
Priority date: 2003-06-26
Filing date: 2004-06-25
Publication date: 2004-12-29
Also published as: AU2003903234A0

Abstract

An illuminator for a microwave oven comprises a fluorescent tube having at least portion of an inside surface of an envelope coated with a fluorescing phosphor, non-metallic end caps and a plastics sheath forming a hermetically sealed assembly with a smooth crevice free external surface to provide a hygienic easily cleaned apparatus not conducive to harbouring bacteria.

Description

TITLE "MICROWAVE OVEN LAMP AND ATTACHMENT" FIELD OF THE INVENTION This invention is concerned with devices for illumination of the interior cavity of a microwave cooking oven during use.

The invention is concerned particularly although not exclusively with the illumination and sterilization of an interior cavity of a microwave cooking oven during use.

BACKGROUND TO THE INVENTION Most domestic and commercial kitchens now have a microwave oven. Many of these ovens are now of an age where the cooking chamber illumination lamp has exceeded its design life and the lamp does now not work. The replacement of this lamp is not within the ability of most microwave oven owners and a technician is required to carry out the work or the microwave oven is required to be removed to a service location.

As a result of this inconvenience and cost, many microwave oven owners with failed lamps do not replace the lamp and operate the oven with the disadvantage of not being able to observe the contents as they are heated nor is it possible to readily see the accumulation of splattered foodstuffs on the interior walls of the microwave oven. This inability to readily see the state of cleanliness is a particular problem in commercial kitchens due to a health risk arising from contaminated foodstuffs.

Commonly microwave ovens use a low power incandescent lamp for the illumination of the cooking chamber. Many of these incandescent lamps are required to be protected from the microwaves by a perforated metal screen otherwise the microwave energy makes the lamp inoperable. This perforated screen restricts the ability of the lamp to illuminate the interior of the oven and also restricts the ability of the operator to replace the lamp when the lamp ceases to operate. • It is known to employ fluorescent lamps to illuminate the interior cavity of a microwave oven.

Japanese Patent Application No 2000-048536 describes a planar board supporting a planar array of small fluorescent bulbs which may be located in different parts of the oven cavity to show the variation of intensity of microwave energy throughout the oven chamber during operation. Japanese Patent Application No 2001-193936 describes the substitution of a conventional incandescent light source in a microwave oven by a fluorescent lamp located in a recess in the oven wall and powered by a source of electricity coupled between opposing lamp terminals. The lamp is located behind a perforated screen and a glass partition in the oven wall. United States Patent No 5,166,528 describes a microwave actuated ultraviolet light sterilizer wherein a plurality of hollow quartz bulbs, containing a gas which emits UV light in response to microwaves, are supported in a non-conductive microwave transparent housing locatable within the cavity of the microwave oven. In use, an object to be sterilized such as a baby's bottle or the like is placed in the housing in the oven and the oven energized to cause UV radiation to be emitted by the gas in the bulbs.

German Patent No DE 4102822 describes the illumination of a microwave oven by partial exposure of a fluorescent tube, encased in a perforated metal tube and supported at opposite ends between silicone rubber bungs. The ends of the perforated metal tube are located in sheet metal sleeves locating the silicone rubber bungs, and one of the sleeves is telescopically slidable within the perforated metal tube against a helical coil spring to enable the assembly to be mounted between opposed walls of the oven interior.

While generally satisfactory for their respective intended purposes, none of the prior art devices is designed to both illuminate and sterilize the interior cavity of a microwave oven during operation or otherwise possesses characteristics unsuited to use in a microwave oven during the cooking of food.

Japanese Patent Application No 2000-048536 does not lend itself to use within a microwave oven during a food cooking process as it is unable to be mounted in a convenient position for illumination and avoid food accumulation on a surface having many crevices.

Japanese Patent Application No 2000-048536 while safely and hygienically located behind a metal screen/glass window is difficult to replace and thus suffers the disadvantages of incandescent lighting systems.

The sterilizer of United States Patent No 5,166,528 cannot be used in the presence of food due to its configuration and does not serve to illuminate the oven cavity.

The illuminator of German Patent NO DE 410 2822 suffers a number of disadvantages in that should the fluorescent tube fracture in use, fine glass particles can contaminate foodstuffs by escaping from the perforations in the outer tube. Moreover, should the tube fail, the abutment surface for the helical coil is lost such that the resilient mounting between opposite walls is lost. Probably the greatest disadvantage of this device is its complete unsuitability for use in either a domestic or commercial microwave oven due to the myriad of crevices which can entrap food particles and harbour life threatening bacteria. Moreover, the perforated metal sheath surrounding the fluorescent lamp is considered likely to generate a substantial amount of heat during use and even could cause arcing. With the sole exception of the device of United States Patent

No 5,166,528, none of the aforementioned devices is adapted for sterilization of a microwave oven whilst in use and with the sole exception of Japanese

Patent Application No 2001-193936, none of the aforementioned devices provides a smooth, crevice free, easily cleanable surface such as to avoid harbouring of bacteria therein or thereon.

Accordingly it is an aim of the present invention to overcome or ameliorate at least some of the problems associated with the prior art microwave oven illuminators/sterilizers.

SUMMARY OF THE INVENTION According to one aspect of the invention there is provided an illuminator for a microwave oven chamber, said illuminator comprising: a fluorescent lamp having a light pervious lamp envelope; non-metallic end caps mounted at opposite ends of said lamp envelope; and, an at least partially light pervious tubular plastics element secured over said lamp envelope whereby said fluorescent lamp is fully encapsulated by a non-metallic containment sheath.

Suitably, said tubular plastics element extends over an external surface of said end caps.

If required, said end caps are secured over an outer surface of said tubular plastics element adjacent opposite ends thereof. Preferably, said end caps include ferromagnetic mounting members.

The ferromagnetic mounting members may be radially spaced from an outer surface of said lamp envelope.

If required, said ferromagnetic mounting members are secured in respective recesses in said end caps by said tubular plastics element extending over an outer surface of said end caps.

Alternatively, said ferromagnetic mounting members are secured in respective recesses in said end caps by an adhesive compound.

Still further, said ferromagnetic mounting members may be secured in respective recesses in said end caps by mechanical engagement therewith.

The tubular plastics element may comprise a thermally shrinkable polymeric tubing.

Suitably, at least portion of an interior surface of said glass envelope is uncoated or at least partially coated with a visible light emitting phosphor whereby an increased level of ultra-violet irradiation emits, in use, from said at least portion of the interior surface of said glass envelope.

If required, said light pervious tubular plastics element may include visible light emitting phosphors. Preferably, said light pervious tubular plastics element includes a window region for directing UV light in a predetermined direction.

Suitably, at least one mounting member securable on an interior wall of said chamber, said illuminator, in use, being removably attachable to said at least one mounting member.

Preferably, said illuminator includes a smooth substantially crevice free outer surface. According to another aspect of the invention there is provided a method of illuminating a microwave oven chamber wherein an illuminator is located within said oven chamber whereby said illuminator is irradiated by at least portion of the microwave energy emitted in said chamber.

If required, said illuminator is positioned within such chamber so as to minimize direct exposure to microwave irradiation.

Preferably, said illuminator is positioned adjacent a junction between a top wall and a side wall of said chamber.

Most preferably, said illuminator is mounted adjacent an upper inner portion of a door to said chamber. The illuminator may be mounted in a receiving pocket in an inner surface of said door.

According to a still further aspect of the invention there is provided a microwave oven including an illuminator as hereinbefore described. Sterilization of wall surfaces and surfaces of articles located within a microwave oven during operation thereof may be effected by the location within an upper region of a chamber of said microwave oven of an illuminator as hereinbefore described.

BRIEF DESCRIPTION OF THE INVENTION In order that the various aspects of the invention may be more fully understood and put into practical effect, reference will now be made to preferred embodiments illustrated in the accompanying drawings in which:- FIG. 1 shows schematically one embodiment of an illuminator according to the invention; FIG. 2 shows schematically an alternative embodiment of the illuminator of FIG. 1 ;

FIG. 3 shows a preferred location of the illuminator/sterilizer lamp in a microwave oven;

FIG. 5 shows an alternative lamp mounting position;

FIG. 6 shows an enlarged partial view of a shrink wrapped illuminator;

FIG. 7 shows an alternative embodiment of the end cap of FIG. 6; and

FIG. 8 shows a partial cross-sectional view of a microwave oven door locating an illuminator/sterilizer according to the invention. DETAILED DESCRIPTION OF THE DRAWINGS In FIG. 1 , the illuminating device 1 comprises a clear plastics outer sheath 2 in which is slidably located a fluorescent tube 3 having a glass envelope with a phosphor material coating the inner surface of the envelope. Outer sheath 2 is sealed by heat resistant polymeric end caps 4 having secured in respective recesses therein, small ferromagnetic cylinders 5 of high magnetic strength/mass or volume ratio.

Suitably, end caps 4 are hermetically sealed to sheath 2 by an adhesive, thermal, solvent or friction welding.

Ferromagnetic cylinders 5 are a preferred method of magnetic attachment of the illuminator 1 to an interior wall of a microwave oven as their superior magnetic strength allows a relatively small magnet to be employed.

Apart from having a reduced mass or volume compared with conventional magnetic materials, ferromagnetic magnets are less susceptible to heating by microwave energy. As an alternative, a double sided adhesive pad 6 may be employed to secure the illuminator inside a microwave oven.

FIG. 2 shows schematically an alternative embodiment of the illuminator of FIG. 1.

In FIG. 2, a fluorescent lamp 8 may have a clear window 12 formed therein such that when exposed to microwave radiation, visible light emits from the phosphor coated portion 11 and sterilizing UV radiation emits from window 12. A clear UV resistant plastics sheath 10 is heat shrunk about the glass envelope of lamp 8 and polymeric end caps 10, each incorporating in a respective recess therein a ferromagnetic magnet 9. If required, the ends 13 of the heat shrunk sheath 10 are fused to polymeric end caps 10 by adhesive or by thermal welding to form a smooth seam free junction with the caps 10 and otherwise to have a smooth, cavity free surface all over.

FIG. 3 illustrates alternative embodiments of tubular plastics sheaths or cases for a fluorescent lamp 8.

FIG. 3A shows a rigid plastics outer tube 14 with an externally threaded end to which is secured a screw-threaded end cap 10 having a ferromagnetic magnet 9 located therein.

FIG. 3B shows a similar arrangement wherein end cap 10 engages with outer tube 14 by an internally threaded engagement.

In both the embodiments of FIG. 3A and FIG. 3B, end caps 10 may be hermetically sealed to a respective threaded tube portion 14 by an adhesive. Similarly, in both the embodiments of 3A and 3B, a heat shrunk outer sheath 15 may form a hermetic seal over end caps 10.

FIG. 4 shows a preferred mounting arrangement for the illuminator/sterilizers according to the invention. The generally cylindrical illuminator/sterilizer lamp assemblies

16 are preferably located adjacent the upper outer corners of the interior cavity 17a of a microwave oven 17 out of a direct radiation pathway from magnetron opening 18. In this position, an illuminator/sterilizer assembly 16 is mounted well above an item of food being cooked and generally is unlikely to come into contact with a user's hands when a food item is being removed from the oven interior 17a. Moreover, both a good distribution of visible and UV radiation is possible within the microwave oven and, after the cooking process illuminator/sterilizer device is easily removed, wiped clean and then replaced. FIG. 5 shows schematically a particularly preferred mounting of an illuminator/sterilizer according to the invention.

As shown, lamp assembly 19 is mounted in a recessed region 21 of door 20 with ferromagnetic mount 9 secured on an upper inner metal wall 20a of door 20 behind a masked region 21 of inner door glass 22. If required, an optical pathway 23 formed by optical fibres or the like is coupled to an illuminatable indicia 24 on the front of door 20 to indicate operation of illuminator/sterilizer assembly 19.

FIG. 6 shows an enlarged cross-sectional view of one end of an illuminator/sterilizer assembly.

As shown, fluorescent lamp glass envelope 25 has secured at one end a metallic cap 26 which may or may not have electrical terminals 26a protruding therefrom. A polymeric end cap 27 of HDPE, HMWPE polypropylene or similar polyolefin, halogenated or a copolymer thereof is suitably moulded with an eccentric outer wall with a thicker wall portion 28 to accommodate ferromagnet 29 in a recess therein and spaced from the glass envelope 25 or metal end cap 26 by a thermal insulating layer 30 to minimize the risk of thermal degradation of the magnetic strength of magnet 29. A heat shrunk sheath 31 of fluoropoly-ethylene, which is transparent to UV radiation and otherwise not degraded thereby, is shrunk over the outer surface of the assembly to form a smooth crevice free continuous skin and the end regions 31a are fused to form a continuous skin by thermal irradiation and pressure.

FIG. 7 shows an alternative embodiment to FIG. 8 in that end cap 27 includes a removable (or insertable) plug 33 to assist in the assembly of the apparatus. Plug 33 provides a means of sealing the edges 34 and, if required, plug 33 may be sealed in place with an adhesive to form a crevice free surface over the end of the assembly.

FIG. 8 shows a schematic cross-sectional view of portion of a microwave oven door 35 having a pocket or recess 36 into which an illuminator/sterilizer 37 according to the invention may be removably located by frictional engagement with resilient pocket walls 36a or the like. The illuminator/sterilizer 37 comprises a glass or quartz envelope 38, an inner phosphor coating 39, an uncoated window region 40 and a plastics outer sheath 41. If required, an optical pathway 42 may be coupled to an indicia on the outer face 43 of door 35 to indicate operation of illuminator/sterilizer 37. By selection of the width of window 40 and the geometry of the mouth 44 of recess 36, respective angles of radiation α, β of UV and visible radiation can be selected. It readily will be apparent to person skilled in the art that many modifications and variations may be made to the various aspects of the invention without departing from the spirit and scope thereof.

For example, the protective plastics outer sheath of the illuminator/sterilizer, apart from providing a secure means of retaining shattered glass particles and the contents of tube in the event of a tube implosion, can also be coloured to provide a range of colours to a user's choice. Alternatively, coloured plastics sleeves may be employed to alter the illumination hue within the microwave oven.

In a still further variation, the protective sheath or a removable plastics sleeve may include variable levels of pigmentation to provide differing levels of illumination within the oven. The sleeve may be formed from a co-extruded plastics tube having, say, a clear window extending over 25% of the circumference of the tube and three other regions over 25% of the circumference wherein those regions have differing levels of light permeation.

Claims

CLAIMS:

1. An illuminator for a microwave oven chamber, said illuminator comprising: a fluorescent lamp having a light pervious lamp envelope; non-metallic end caps mounted at opposite ends of said lamp envelope; and, an at least partially light pervious tubular plastics element secured over said lamp envelope whereby said fluorescent lamp is fully encapsulated by a non-metallic containment sheath.

2. An illuminator as claimed in claim 1 wherein said tubular plastics element extends over an external surface of said end caps.

3. An illuminator as claimed in claim 1 wherein said end caps are secured over an outer surface of said tubular plastics element adjacent opposite ends thereof.

4. An illuminator as claimed in any preceding claim wherein said end caps include ferromagnetic mounting members.

5. An illuminator as claimed in claim 4 wherein said ferromagnetic mounting members are radially spaced from an outer surface of said lamp envelope.

6. An illuminator as claimed in claim 5 wherein said ferromagnetic mounting members are secured in respective recesses in said end caps by said tubular plastics element extending over an outer surface of said end caps.

7. An illuminator as claimed in claim 5 wherein said ferromagnetic mounting members are secured in respective recesses in said end caps by an adhesive compound.

8. An illuminator as claimed in claim 5 wherein said ferromagnetic mounting members are secured in respective recesses in said end caps by mechanical engagement therewith.

9. An illuminator as claimed in any preceding claim wherein said tubular plastics element comprises a thermally shrinkable polymeric tubing.

10 An illuminator as claimed in any preceding claim wherein at least portion of an interior surface of said glass envelope is uncoated or at least partially coated with a visible light emitting phosphor whereby an increased level of ultra-violet irradiation emits, in use, from said at least portion of the interior surface of said glass envelope.

11. An illuminator as claimed in claim 1 wherein said light pervious tubular plastics element includes visible light emitting phosphors.

12. An illuminator as claimed in claim 1 wherein said light pervious tubular plastics element includes a window region for direction UV light in a predetermined direction.

13. An illuminator as claimed in any preceding claim including at least one mounting member securable on an interior wall of said chamber, said illuminator, in use, being removably attachable to said at least one mounting member.

14. An illuminator as claimed in any preceding claim including a smooth substantially crevice free outer surface.

15. A method of illuminating a microwave oven chamber wherein an illuminator according to any one of claims 1 to 14 is located within said oven chamber whereby said illuminator is irradiated by at least portion of the microwave energy emitted in said chamber.

16. A method as claimed in claim 15 wherein said illuminator is positioned within such chamber so as to minimize direct exposure to microwave irradiation.

17. A method as claimed in claim 16 wherein said illuminator is positioned adjacent a junction between a top wall and a side wall of said chamber.

18. A method as claimed in claim 15 or claim 16 wherein said illuminator is mounted adjacent an upper inner portion of a door to said chamber.

19. A method as claimed in claim 18 wherein said illuminator is mounted in a receiving pocket in an inner surface of said door.

20. A method for sterilization of wall surfaces and surfaces of articles located within a microwave oven during operation thereof, said method including the location within an upper region of a chamber of said microwave oven of an illuminator according to any one of claims 1 to 14.

21. A microwave oven including an illuminator according to any one of claims 1 to 14.