GB2310990A

GB2310990A - Microwave food package heating apparatus

Info

Publication number: GB2310990A
Application number: GB9604649A
Authority: GB
Inventors: David Harvey Briggs
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-03-05
Filing date: 1996-03-05
Publication date: 1997-09-10
Also published as: GB9604649D0

Description

MICROWAVE FOOD PACKAGE HEATING APPARATUS This invention relates to microwave heating apparatus for heating packaged food. In the preferred embodiment, the invention provides a self-contained vending machine which, upon selection of one of a range of available products, will automatically deliver a package of the product to a microwave heating enclosure, heat the product, and deliver the heated package to an outlet.

The use of microwave ovens for heating food products is well known. It is known to provide microwave ovens in establishments such as petrol stations to enable a customer to heat a cold food product purchased from the petrol station. Cold food products intended to be heated in the microwave oven may be provided in close proximity to the microwave oven and instructions associated with the food product may be coordinated with the particular microwave oven provided in order to form an integrated hot food dispensing system. However, such system depends on the food product being selected, placed in the oven, and the oven correctly set to produce the required degree of heating. Also, if the food product is within a sealed container, the sealed container must be punctured before the food product is heated to avoid inadvertent bursting of the package. Additionally, in such installations there is the danger that the microwave oven may be used for heating products other than those for which it was intended with resultant possible damage to the microwave oven itself.

The above disadvantages mean that, in the prior art, use of microwave ovens for providing hot self-service food has been considerably less than satisfactory.

The preferred embodiment of the present invention provides an automatic system which, upon actuation of a selection button, automatically conveys a package of food to a microwave oven, heats the food within the package, and delivers the heated package to the customer.

If desired, the apparatus may be coin operated to form a self-contained vending machine suitable for use in a wide range of installations.

According to one aspect of the present invention there is provided apparatus for the microwave heating of a food package comprising: a microwave oven having a laterally facing aperture for receiving a food package to be heated; a source of food packages to be heated; and a carriage for receiving a food package to be heated from the source and conveying the food package through the aperture into the microwave oven, the carriage incorporating a closure member for closing the aperture when the food product is located within the oven and thereby preventing escape of microwave energy through the aperture whilst the food package is being heated.

According to another aspect of the present invention there is provided a microwave oven for heating a food package comprising a container in which the food is located and a closure membrane sealed to the periphery of the container about an upwardly open mouth of the container, the microwave oven comprising means for detecting the position of at least a portion of said membrane, and power control means for varying the power of the microwave oven in response to said detecting means whereby bursting of the package is preventing by reducing the power of the microwave oven in response to outward billowing of the membrane.

The invention will be better understood from the following description of a preferred embodiment thereof, given by way of example only, reference being had to the accompanying drawings wherein: Figure 1 is a schematic side view of a portion of an embodiment of the invention; Figure 2 is a view corresponding to Figure showing a food package contained in the microwave oven for heating; Figure 3 is a plan view of the carriage of the arrangement of Figures 1 and 2; Figure 4 is an end view of the carriage of Figure 3; Figures 5A-5D illustrate a sequence of movements of the carrier of the embodiment of Figures 1 and 2; and Figure 6 shows in detail and arrangement for detecting the position of a membrane closing a food package.

Referring firstly to Figure 1 of the drawings, the illustrated portion of an embodiment of the present invention comprises a track 1 along which a carriage 2 is moveable by suitable mechanical drive means (not shown).

At one end of the track 1 is located a microwave oven 3 having a heating chamber 4 defined by a box which is generally rectangular in plan view and which, on one side, is open to permit food products to be inserted into the chamber 3 by means of the carriage 2.

In the illustrated embodiment of the invention a microwave source is located beneath the chamber 4 and is connected to the chamber by wave guides 6 which direct microwave energy vertically upwardly into the chamber 4 and laterally into the chamber from opposite sides thereof.

With such an arrangement, food product located within the chamber is heated by direct radiation rather than by the establishment of standing waves within the chamber. In this respect, it is generally envisaged that any particular installation will, at any one time, only operate with packages of a particular size and shape. By appropriate modification of the wave guides the microwave oven may be "adjusted" to give optimum heating for the particular size and shape of food package with which it is required to operate at any one time.

Food packages are delivered, one at a time, to the microwave oven by the carriage 2. In Figure 1, a food package 7 is schematically illustrated.

Referring to Figures 3 and 4, the structure of the carriage is shown in more detail. The carriage comprises a platform 8 which is cantilevered out from a body portion 9 and is split into two parts 8A and 8B by a longitudinal slot 10. In use, food packages 7 are supported on the platform 8 for movement into and out of the microwave oven. In general, the food packages will be supplied from vertical stacks of food packages located above the line of the track 1. When a particular food package is selected the carriage will automatically move to beneath the stack and one food package will be released to fall onto the platform 8. Guides 11 will locate the food package centrally on the platform, and as the platform enters the chamber 4 it will strike a stop 12 which will ensure the correct longitudinal positioning of the food package within the chamber. Preferably, a detector 13, for example a probe attached to a microswitch, is provided for detecting the presence of a food package and preventing operation of the microwave oven if no food package is present.

The body 9 also carries a double closure member formed by two plates 14,15. When the carriage is in its fully advanced position as illustrated in Figure 2 the plates 14,15 seal the aperture 15 to prevent escape of microwave energy from the chamber 4. The plates 14,15 form a quarter-wave choke to ensure that, at most, insignificant quantities of microwave energy are able to escape past the plates 14,15.

Referring now to Figures 5A-5D the operating sequence of the device is illustrated.

After a food package 7 has been loaded onto the carriage the carriage advances to locate the food package within the microwave chamber. During this (forward) movement of the carriage a ratchet member, for example a spring 16, rides over the operating pin 17 of a discharge mechanism 18. The discharge mechanism comprises, in addition to the pin 17, an arm 19 which, with the pin 17, is mounted on a rod 20 for limited pivotal movement about a horizontal axis.

After an appropriate period of heating the carriage withdraws (Figure 5B) and the ratchet member 16 strikes the pin 17 thereby causing rotation of the arm 19 (Figure 5C). The arrangement is such that the free end of the arm 19 enters the slot 10 between the food package 7 and the plate 14. Continued rearward movement of the carriage (Figure 5D) causes the arm 19 to engage the food package and slide the food package off the platform 8 onto a suitable chute for delivery to a customer.

The invention is particularly suited to the heating for retail sale of packages of "ambient food". The term "ambient food" means food product which is cooked and sterilized and is located sealed within a plastic container. Because the food product is sterile the packages can be kept safely at ambient temperature.

Referring to Figure 6, food packages of this type commonly comprise a container 21 moulded from a suitable plastics material. The food product is loaded within the container 21 and the mouth 22 of the container is then sealed by means of a membrane 23 formed of a suitable material, for example a plastics film. The film 23 and the container 21 are both impervious to spoiling microorganisms, and the seal between the film 23 and the container 21 is also impervious to such micro-organisms.

Hence, after the food product has been sealed within the container the entire container may be sterilized and the resultant package may be kept at ambient temperature without risk of spoilage.

If such a container is heated in a microwave oven the expansion of the contents and the liberation of steam will tend to make the film 23 billow outwardly. If energy is applied at too high a rate a significant pressure will be built-up within the package and the package will eventually burst. In order to avoid this, it is conventional to pierce the film 23 before microwave heating of the package.

However, in the preferred embodiment of the invention means are provided for detecting the position of the film 23 and for controlling the power of the microwave oven in response to the position of the film so that bursting of the package is prevented.

In the illustrated embodiment of Figure 6 a vertically movable probe 24 is provided for detecting the position of the membrane 23. At the commencement of each heating cycle the probe 24 will be located at its lowest possible position with the bottom end of the probe slightly above the level of the mouth 22 of the container. When the food package is loaded into the chamber 4 the film 23 will be flat or slightly concave and accordingly the package will move as a clearance fit under the probe 24. Microwave energy at full power is then applied to the package with the result that, after a period of time, the film 23 will billow outwardly as illustrated in Figure 6. Such outward billowing will lift the probe 24. This movement of the probe is used to reduce the power level of the microwave oven whereby heating of the product continues but bursting of the container is avoided.

In the illustrated embodiment of the invention the probe 24 has secured to one side thereof a flag 25 which in use moves within a slot 26 to vary the extent to which light from a suitable source can fall onto a photoresistor 27. The output of the photo-resistor is, accordingly, indicative of the vertical position of the probe 24 and may be used by via suitable circuitry to control the power of the microwave oven. By this means, heating of the package may continue but bursting is avoided.

It will be noted that a particular advantage of the use of the means for detecting billowing of the closure membrane of the package is that the resultant apparatus, within a fixed heating period, applies a varying degree of total microwave energy to the package depending on the initial temperature of the package. If the package is initially cold (for example because the entire installation has been in an unheated warehouse over a cold weekend) a relatively long period of heating at full power will be necessary before the film 23 begins to billow.

Accordingly, if the microwave oven is set to heat the package for, say, a period of 60 seconds, in the case of a package which is initially relatively cold a significant proportion of that 60 second period will utilize full microwave power. In the alternative, if the package is initially relatively warm, for example, because the installation is located in a warm office building, then billowing of the film 23 will occur after a relatively short period and accordingly a relatively small proportion of the total 60 second heating time will utilize full power. It will be appreciated from the above that reasonably consistent final temperatures can be obtained even though the apparatus is set to heat all packages for the same length of time.

Claims

CLATMS:

1. Microwave heating apparatus comprising a microwave oven having an aperture for receiving food to be heated; a source of food to be heated; and a carriage for receiving food to be heated from the source and for conveying the food through the aperture into the microwave oven, the carriage incorporating a closure member for closing the aperture when the food is located within the oven and thereby preventing escape of microwave energy through the aperture whilst the food is being heated.

2. Microwave heating apparatus as claimed in Claim 1, wherein the aperture for receiving food is arranged so as to be laterally facing.

3. Microwave heating apparatus as claimed in Claim 1 or 2, wherein a microwave source is located beneath a chamber of the microwave oven adapted to receive the food to be heated.

4. Microwave heating apparatus as claimed in Claim 3, wherein the microwave source is connected to the chamber by means of wave guides.

5. Microwave heating apparatus as claimed in Claim 4, wherein the wave guides are adapted to direct microwave energy vertically upward into the chamber.

6. Microwave heating apparatus as claimed in Claim 4 or 5, wherein the wave guides are adapted to direct microwave energy laterally into the chamber.

7. Microwave heating apparatus as claimed in Claim 6, wherein the wave guides are adapted to direct microwave energy from opposite sides of the chamber.

8. Microwave heating apparatus as claimed in any of the preceding claims, wherein the microwave oven is provided with a stop member adapted to ensure correct longitudinal positioning of the food to be heated within the microwave oven.

9. Microwave heating apparatus as claimed in any of the preceding claims, wherein the microwave oven is provided with detecting means for detecting the presence of food within the microwave oven and inhibiting means responsive to the detecting means for preventing operation of the microwave oven.

10. Microwave heating apparatus as claimed in any of the preceding claims, wherein the source of food to be heated comprises a vertical stack of packaged food.

11. Microwave heating apparatus as claimed in any of the preceding claims, wherein a track is arranged between the aperture and the source of food to be heated, the track providing means for guiding the carriage.

12. Microwave heating apparatus as claimed in Claim 11, wherein driving means is provided for driveably moving the carriage along the track.

13. Microwave heating apparatus as claimed in any of the preceding claims, wherein food guide means is provided for locating received food in a desired position on the carriage.

14. Microwave heating apparatus as claimed in any of the preceding claims, wherein food discharging means is provided for dispensing food from the apparatus.

15. Microwave heating apparatus as claimed in Claim 14, wherein the food discharging means comprises an arm located between the aperture and the source of food to be heated, the arm being pivotally mounted and provided with an operating pin extending from the arm, the operating pin being adapted so as to engage the carriage and thereby rotate the arm into contact with the food to be dispensed and push the food from the carriage.

16. A microwave oven for heating a food package comprising a container in which the food is located and a closure membrane sealed to the periphery of the container about an open mouth of the container, the microwave oven comprising means for detecting the position of at least a portion of the membrane, and power control means for varying the power of the microwave oven in response to the membrane detecting means whereby bursting of the package is prevented by reducing the power of the microwave oven in response to outward blowing of the membrane.

17. A microwave oven as claimed in Claim 16, wherein the membrane detecting means comprises a probe member slidably mounted within the microwave oven and biased towards an extended position so as to abut the closure membrane when in use.

18. A microwave oven as claimed in Claim 17, wherein the membrane detecting means further comprises a light source, a photo-resistor and a flag; the flag being provided on the probe member and adapted to vary the light from the light source received by the photo-resistor with the extension of the probe member

19. A microwave oven according to Claim 18, wherein the power control means responds to the output of the photo-resistor.

20. Microwave heating apparatus as claimed in any of Claims 1 to 15, comprising a microwave oven as claimed in any of Claims 16 to 19.

21. Microwave heating apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.