Field of the Invention

This invention concerns microwave-powered apparatus for heating foodstuffs, particularly pre-cooked foodstuffs-

Microwave is taken to mean all forms of electromagnetic energy in the microwave region, particularly those two frequencies most commonly used for heating ie, 2.45 GHz (2450 MHz) and in the range 800-1000 MHz.

Background to the Invention

With the increasing demand for fast food such as hot snacks at airports, railway stations and now on garage forecourts and motorway service areas and public places in general, there is a need to provide a facility by which the public can select and heat up ("regenerate") pre¬ cooked frozen foodstuffs quickly and easily. Microwave- powered heating chambers are well suited for this purpose, but standard microwave ovens are not necessarily ideal for the purpose. Particularly, the commonplace resonance cavity oven is inadequate for rapidly regenerating frozen food. Because of the size of the magnetron and power supply unit for such ovens, the actual bulk of the oven is greatly in excess of the heating chamber.

It is therefore an object of the present invention to

provide a smaller microwave-powered apparatus, primarily aimed at situations where the primary objective is to heat pre-cooked chilled or, particularly, deep-frozen foodstuffs, and possibly to provide a number of such microwave-powered chambers in a convenient location for use either by the public or by serving staff or the like.

Although reference has hitherto been made to fast food associated with travel, it is to be understood that the invention is in no way limited to such locations and the invention may be utilised in bars, sandwich bars, restaurants and snack bars, schools and colleges, student unions and works canteens and cinemas or theatres. Likewise, mobile locations eg outside catering units, trains, coaches, boats, ships and aircraft would be ideal fo this invention.

Summary of the Invention

In its broadest aspect the present invention provides microwave-powered apparatus for heating foodstuffs, particularly pre-cooked chilled or deep-frozen foodstuffs, comprising: a first unit, including a chamber into which a foodstuff can be located, and a movable closure-member for sealing the chamber after foodstuff has been located therein; and a remote power supply unit adapted to be connected to the electricity supply main and to be connected to the first unit by means of a flexible connector for conveying electrical power to a microwave energy source for introducing microwave energy to the chamber to heat foodstuff located therein.

The microwave energy source may form part of either the first unit or the power-supply unit.

In a first embodiment of the invention microwave-powered apparatus for heating foodstuffs, particularly pre-cooked foodstuffs, comprises: a first unit, including a chamber into which a foodstuff can be located; a movable closure member for sealing the chamber after foodstuff has been located therein; and a microwave energy source such as a magnetron associated with the chamber for introducing microwave energy to the chamber to heat foodstuff located therein; and a remote power supply unit adapted to be connected to the electricity supply main and to be connected to the first unit by means of a flexible connector for conveying electrical power to the microwave energy source of the first unit.

In a second embodiment of the invention microwave-powered apparatus for heating foodstuffs, particularly pre-cooked foodstuffs, comprises a first unit comprising a chamber into which a foodstuff can be located, and a movable closure member for sealing the chamber after the foodstuff has been located therein; and a power supply unit remote from the first unit and containing an electrical power supply and a microwave energy source such as magnetron, the power supply unit having provision for connection to the electricity supply main, and being connected to the first unit by means of a wave guide to enable microwave energy to be conveyed from the microwave energy source in the power supply unit to the chamber.

The first unit can be much smaller and lighter in weight than conventional domestic microwave ovens in which the power supply is integral with the heating chamber and microwave energy source, eg magnetron.

Clearly if the maximum reduction in size and weight is required, the second embodiment of the invention must be employed, but for many purposes a sufficient reduction in size and weight can be achieved using the first embodiment of the invention. An advantage of the second embodiment is the elimination of high tension electricity cables joining the magnetron units with their power source.

Apparatus constructed in accordance with the invention is not particularly suited to domestic installation and is not normally appropriate for domestic use. Conventional microwave ovens are better suited to domestic use, as these can be constructed so as to fit in with conventional kitchen surfaces, fittings and white goods so as to be capable of being fitted within a kitchen environment. The invention is aimed more at fixed installations in commercial situations where there is no problem about separation of the power supply unit, with or without the microwave energy source, and the heating chamber. Indeed in many situations there is much to be gained by separating the units, particularly from the safety view point.

In any situation where members of the general public have access to equipment of this nature, it is important that safeguards are built into the equipment to prevent either unauthorised use or dangerous operation. With all microwave energy sources, it is important that the source is not operated without a load in the chamber so as to absorb the radiated energy. To this end detector means together with a switching interlock is preferably provided so that operation of the microwave source is inhibited unless sufficient or appropriate foodstuff is located within the heating chamber to act as an electrical load,

thereby enable safe operation of the source.

In order to maximise the heating effect of the microwave energy and reduce' the heating-up time to the miminum, the microwave energy is preferably focused onto the foodstuff to be heated by using an appropriately shaped surface within the chamber; and by causing the microwave energy to enter the chamber in such a manner as to be incident on the reflecting surface and thereby to be focused or concentrated onto the foodstuff to be heated.

The shaped reflecting surface may. be at least in part mounted on or formed in the closure member.

Further safeguards may be built into the equipment where it is to be located in an ύnsupervised situation, such as a detector which is adapted to determine whether or not the product or its packaging which has been inserted into the chamber bears a particular identification such as a transponder or bar code or the like. In one embodiment, the identification is not something which is readily discernible and identifiable so that members of the general public are unaware of the nature of the identification on the foodstuff or the packaging.

Where this feature of the invention is incorporated, an interlock is conveniently provided to inhibit operation of the microwave energy source unless the identification detector has responded appropriately to the inserted foodstuff and detected the appropriate identification marked thereon. In this way the heating chamber will only be capable of operating if an appropriate foodstuff has been located therein and is prevented from operating in the event that any other substance has been introduced

into the heating chamber.

As a further refinement, the foodstuff (or packaging) may include supplementary coded data capable of being identified by either the first mentioned detector or a second detector so that provided the foodstuff indicates to the first detector that it is appropriate and may be heated by the heating chamber, the further information obtained from the supplementary data can be used to adjust the power and/or heating time and/or any other functions of the heating chamber such as whether or not a browning aid is to be incorporated in the heating-up, so that the user does not need to make any adjustments to the controls (indeed the need for controls is obviated) and the heating times and power are automatically set by the machine based on the information encoded by the product.

The first unit may be a free standing unit adapted to be mounted on a counter or worktop surface or may be adapted to be built into a surface so that only the closure member is visible. This reduces the height and bulk which would otherwise be above the work-level surface and is of particular advantage in situations such as bars and retail sales outlets where an operator stands on one side of a counter or worktop and members of the general public stand on the other side. In this situation it is clearly advantageous that the heating chamber is below the level of the worktop surface and only the closure member protrudes above the worktop surface.

The invention therefore also lies in a counter or worktop having integrally mounted therein or therebelow a heating chamber with an opening in the worktop or counter giving access to the heating chamber, and a closure member

movable relative to the counter or worktop for sealing the chamber during the heating process, together with a source of microwave energy such as a magnetron and associated power supply and control for introducing microwave energy into the chamber to heat foodstuffs inserted therein.

This counter or work-top could be part of a combined deep¬ freeze/area unit, providing for both the storage and rapid regeneration of frozen food in a single, portable unit.

Since the invention provides for the separation of the heating chamber from the electrical power supply and possibly even the microwave energy source, the chamber may be constructed in such a way that it can be sluiced through with water for cleaning purposes. Thus the lower end of the chamber may be provided with a drain hole and the microwave energy may be caused to enter the chamber through a window which is impervious to liquid but fully transparent to microwaves.

Where a drain outlet is provided at the bottom the the chamber, a flap valve is preferably provided to ensure that after water or other liquid has passed through the drain hole, the opening is closed off to prevent microwave energy from escaping into the drain.

Where the heating chamber is to be a free standing unit, and controls are to be provided, these may be located in a housing which itself protrudes from a main housing within which the chamber is located.

Since the main objective of heating apparatus as described is to bring frozen pre-cooked food to a serving temperature in the minimum possible time, it may be

advantageous to incorporate two or more microwave energy sources associated with the heating chamber to miminise standing waves which may otherwise set up in the chamber and allow a more uniform distribution of microwave energy in the chamber. This reduces the chance of local hot spots occuring within the chamber with resultant uneven heating through of the cooked foodstuff.

The invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a side view of a two-unit arrangement incorporating the invention; and

Figure 2 is a perspective view of the first unit, incorporating a heating chamber, of Figure 1 with the lid in an elevated position.

Detailed description of the Drawings

In Figure 1 a first unit of a microwave powered heating apparatus is formed from a base unit 10 and a cover 12 hinged at 14 to the base unit. The cover is domed and includes a handle 16 by which the cover can be lifted to give access to the chamber within the base unit 10 for inserting and removing foodstuffs.

Separate from the first unit is a power supply unit 18 having a cable and plug connection 20 for connection to the electricity supply main and a flexible connection 22 joining it to the base unit 10 for transmitting electrical energy from the power supply unit 18 to a magnetron (not shown) located within the base unit 10.

By separating the power supply unit 18 from the remainder of the heating chamber and the magnetron, so the size of the first unit can be reduced considerably and the power supply unit 18 (which will normally be heavy as well as bulky) can be located in a convenient position away from the heating chamber.

As shown in Figure 2, the upward hinging of the lid 12 gives access to the heating chamber 24 and the elevated position of the lid 12 in Figure 2 shows the internal concave surface 26 within the domed lid 12 formed from microwave reflecting material. When the lid 12 is in its closed position, this internal reflecting surface provides a means for focusing microwave energy onto the foodstuff located within the chamber 24.

A housing 28 extends forwardly from the generally cylindrical unit 10 and provides a mounting for controls such as 30 by which for example different heating times can be selected.

Although not shown an interlock may be provided with associated switching to prevent the electrical power being supplied to the magnetron unless the lid is in the closed position.

Also, a choke mechanism, preventing the escape of microwave energy during operation may be incorporated into the closure between the domed lid (12) and the chamber (24) .

A further refinement provides for a detector (not shown) located either within the base unit 10 or the lid 12 which determines whether or not an appropriate mass of material

capable of absorbing microwave energy is located within the chamber 24.

Again, although riot shown, the detector (or another detector) may be adapted to interrogate an identification tag or other coded device such as a bar code contained on the foodstuff (or at least on the packaging containing the foodstuff) , with means being provided either within the base unit 10 or within the power supply unit 18 to decode the interrogated information either and confirm that the foodstuff is appropriate and the heating cycle can be performed, or to determine and set the precise heating cycle to be followed.

If browning is required, a browning aid may be incorporated within the heating chamber in the form of an element of microwave absorbing material which will gain heat and generate infrared radiation when microwave energy impinges thereon. Means may be provided for shielding this element from microwave energy until an appropriate point in time during the heating cycle, or microwave energy may be focused onto the foodstuff during part of the cycle and at least in part onto the microwave energy absorbing browning aid during another part of the heating cycle as required.

This microwave-absorbing material may, for example, take the form of a shell within the dome. Preferably this shell is of low mass, thereby allowing rapid cooling afte the microwave source has been switched off.

The invention essentially allows a heating chamber to be located in the most convenient and unobtrusive manner, fo example in a bar counter or worktop surface. Because the

heavy and bulky power supply components have been relocated in a separate unit 18, the latter can be located either at floor level or even further remote from the worktop surface so that the latter does not have to carry the weight of the power supply unit as well as the heating chamber. It is to be understood that the magnetron need not be located within the unit 10 but may be located within the power supply unit 18 in which event the connection 22 between the power supply unit and the unit 10 must be in the form of wave guide as well as include electical conductors for conveying control signals and or the like between the two units.