GB2196218A - Rotating plate for microwave ovens - Google Patents

Abstract

A rotating plate (3) for a microwave oven (1) of the type including a temperature sensor (5) on a conductor (6) connected by a plug (7) to a socket in the oven (1) comprises drive means providing alternating movement having an alternating movement of approximately 360??? such that the conductor (6) is subjected only to a slight alternating torsion. A plurality of metal fins extend from the lower surface of the plate (3) to act as field agitators. <IMAGE>

Description

SPECIFICATION Rotating plate for microwave ovens OBJECT OF THE INVENTION The present invention, in accordance with the title of the specification, relates to a rotating plate for ovens, specifically for microwave ovens, which plate has been designed and structured in order that, in addition to afford ing an adequate movement to the product be ing cooked, it may also be used simultaneously with a cooking sensor to allow a certain automation in the timing of the cooking operation, or the actuation of an indicator of some other kind.

The invention likewise relates to the structure of the rotating plate, aimed at achieving a better distribution of the energy of the microwave oven and an improvement in the mean useful power obtained, the said structure likewise enabling the plate to be used in mixed ovens, i.e., ovens which, in addition to having a microwave system for heat generation, may also include conventional means therefor, such as a grill and/or turbo fan for establishing varying combinations of the two functions.

BACKGROUND OF THE INVENTION In ovens for food preparation, and specially in those wherein the heat is supplied by microwaves, a rotating plate or platform is usually provided on the base of the oven, in order that the position of the product to be cooked varies continuously with respect to the heat source, in order to achieve uniform cooking thereof, for in most cases uniformity of the heat supply is not as perfect as might be wished.

Apart from this, a cooking sensor is likewise usually provided, being generally known as a "food sensor" or "meatprobe", and cons isting of a spike which is embedded in the food to be cooked and is connected, through the corresponding electrical conductor, to a plug provided therefor on one of the inner walls of the oven, such that when the inside of the food reaches a certain tempera ture', the said sensor acts on the pertinent devices to bring about stopp ing of the oven, i. e., the end of the cooking operation, or the actuation of an indicator of some type.

As can be deduced from the above, it would be desirable for the two previously mentioned devices to be applied together in order to achieve both a perfect uniformity in the heat supply to the food, and thermal control therefor. This, however, is not feasible, for the electrical conductor does not allow the continuous rotation of the plate holding the food in which the sensor is embedded, for turning of the plate would result in successive twisting of the electrical conductor, until eventually the said conductor should break or prevent rotation of the plate.

There currently exist various solutions to this problem. One of the said solutions consists in installing a sensor element in the food to be cooked, which element emits a signal of some type, the said signal being sensed by a receiver installed within the actual oven and thus establishing a wireless connection between the two elements, i.e., there is no physical connection between the rotating plate and the body of the oven, and therefore no obstacle for rotation of the former. Obviously, this solution, though perfectly valid from an operative point of view, poses in turn an important problem based on the high cost thereof.

A further solution consists in providing sliding rotating contacts in the connector joining the conducting wire to the body of the oven, the stiffness of the actual conducting wire bringing about rotation of the said contacts, or by means of suitable transmissions, synchronised with the rotation of the food itself.

The problems derived from such a solution, apart from being likewise based on its high cost, extend to other aspects, such as, for example, functional guarantee of the rotating contacts, etc.

On the other hand, and as is likewise known, a magnetron is used in all microwave ovens, and consists of a microwave flow generator, the said microwaves having to be supplied to the oven in the most uniform manner possible as regards energy distribution.

In this respect, the applicant is the holder of utility model 253.689 which describes how microwave supply to the oven cavity is effected through two radiant apertures or windows, which allows an improvement in the distribution of the microwave energy, energy transmission from the magnetron to the radiant windows being effected through a wave guide having two symmetrical arms.

In view of the need to achieve an even more perfect uniformity in energy distribution than that achieved with two radiant windows, and particularly for very delicate dishes, the use of microwave ovens having a rotating metal plate or platform is likewise known, which, together with the two radiant windows, allows a very good distribution of the microwave energy.

However, and despite the provision of a mobile element within the oven cavity, namely the rotating plate, the arrangement of electromagnetic fields in the cavity is constant, which results in the appearance of hot points or areas and may also result in the operation of the magnetron under unfavourable conditions, subjected to certain loads.

DESCRIPTION OF THE INVENTION The rotating plate described by the invention has been designed to fully solve these problems, in their different aspects, simultane ously allowing movement of the food to be cooked in order to homogenize thermal supply thereto, and use of a conventional sensor, of the type consisting of a simple spike which is embedded in the food and is directly connected, through the corresponding electrical conductor, to a plug provided in one of the walls of the oven. The rotating plate of the invention further achieves an improvement in the microwave energy distribution and the mean useful power obtained.

In order to achieve the above, the invention is centred on the supp ly of alternating movement to the said rotating plate, with an approximate amplitude of 360 , such that during normal operation of the oven, the p late turns through app roximately 360" in one direction, then a further 360" in the opposite direction, and so on.

It can be easily inferred herefrom that the cooking uniformity achieved is similar to that obtained with conventional rotating plates turning continuously in the same direction, but that the problems of connection by means of an electrical conductor are fully solved, the said conductor being subjected only to a slight alternating torsion which, due to the flexibility thereof, is perfectly feasible, causing no damage to the wire nor constituting an obstacle for rotation.

If the heat source by itself achieves a diametrically symmetrical heat distribution, a turn of 1800 in either direction would be sufficient, or, if symmetries are different, the corresponding angle of rotation for each point of the food to pass, on rotation, all the points of the circumference or arc of -the circumference having a different heat intensity. Having pointed out this exception, we shall hereinafter refer to a rotation of 360" for greater clarity.

Various solutions have been foreseen to supply the aforementioned alternating movement to the plate.

One of these solutions, being the preferred embodiment by reason of its simplicity and low cost, consists in the use of a motor, of the synchronous, multipolar type having permanent magnets and being available on the market, the essential characteristic whereof is the ability to rotate in either direction, and with the particularity that when during rotation it comes up against a couple of resistance which it is unable to overcome and which resuits in stopping thereof, it immediately begins to turn in the opposite direction.With a motor of this type, it is sufficient to instail a fixed abutment on the base of the oven, and a cam or index on the axis of the rotating plate or platform, such that on normal rotation of the plate the cam will come up against the said abutment after each 360" turn, the motor thus stopping and immediately inverting its direction of rotation, i.e., achieving the desired alternating movement with an amplitude of approximately 360" Another solution consists in the use of a motor of the type which allows inversion of the direction of rotation by means of changing or inverting the polarity of the electrical source, in which case a two-way electrical commutator works together with the said motor, and the same cam or index as in the previous case is established on the axis of the plate or rotating platform, such that upon each complete turn of the plate, the cam will abut the electrical commutator, causing imme diate inversion of the direction of rotation of the motor, said inversion taking place after each complete turn of the plate, i.e., each time the cam abuts the commutator or, in other words, after each rotation through ap proximately 360".

It is also possible to use mechanical sys tems for obtaining this alternating movement, such as eccentrics, a crank-shaft assembly, racks, etc., which, being sufficiently known in the present art, will not be described herein, apart from the fact that they constitute less interesting solutions than those mentioned previously owing to their greater structural complexity.

As a complement hereto, and in accordance with the second objective of the invention, i.

e., achieving an additional improvement in the microwave energy distribution and the useful mean power obtained, a series of fins have been provided on the lower surface of the plate, which fins, due to the movement of the plate, create a permanent disturbance in the arrangement of electromagnetic fields within the cavity of the oven, in a manner similar to the well-known "stirrers" or electromagnetic field agitators.

This disturbance of the magnetic fields, achieved by means of the fins provided on the plate, is sufficient to prevent the appearance of hot points or areas on the walls of the oven cavity, thereby essentially avoiding the problem of hot areas on the glass part of the door.

This effect is particularly suitable in ovens foreseen for cooking at different heights on fixed grids, thereby eliminating the stationary situation which would otherwise result in such ovens.

On the other hand, and as previously mentioned, the useful mean microwave power af forded by the oven is increased with the inclu sion of the lower fins on the plate. In fact, rotation of the fins provided on the plate re sults in the variation of its relative position with respect to the electromagnetic fields, such that the impedance to the magnetron of the guide assembly and oven cavity is likewise variable. This, with a suitable design for the fins, allows the impedance, situated on the Rieke diagram, to move in the more favour able area thereof to obtain the maximum use ful power, whatever the load and arrangement thereof within the oven cavity.

More specifically, the rotating plate being described is comprised by a plate or platform consisting of a metal disc with an inlaid pro jection along its perimeter, and a slight inlaid projection in the centre thereof for coupling of the corresponding rotating axis, without same emerging on the operative area of the plate, to the lower surface of which disc are fitted, by welding or other means, six radial fins, placed equiangularly and complemented with three further fins which relate the free ends of the former alternately two by two.The height of these fins is limited by the distance be tween the base of the oven and the plate itself, which distance should be as small as possible in order to take up little useful vol ume from the cavity, the distance between the lower base of the fins and the bottom of the oven should in turn be as small as possible, taking into account mechanical tolerancies and the possibility of introducing arcs between the ends of the fins and the base of the oven.

This distance is critical for achieving optimum disturbance effects for the electromagnetic fields and variation of impedance of the cav ity.

However, it is important to emphasize that the number, arrangement and size of the fins is given merely by way of example, and correspond to an efficient solution which has been duly tested in the laboratory, but obviously there may exist other arrangements and configuration for the fins being being similarly valid and not affecting the essentiality of the invention, for the finding of such further possible solutions merely requires simple tests which lack all inventive merit once the fins themselves have been provided.

DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic front elevational view of an oven for preparing food having an alternating rotating plate made in accordance with the object of the present invention.

Figure 2 is a diagrammatic plan view of the plate and the base of the oven, showing the cam and complementary abutment for stopping the plate and thus also the motor, and inverting the direction of rotation of the latter.

Figure 3 is a side elevational view of the same assembly as in the preceding figure, the said motor being likewise shown.

Figure 4 is a similar view to that of Figure 2, but wherein the cam acts on an electrical two-way commutator.

Figure 5 is a lower plan view of the rotating plate, in accordance with a real representation thereof, showing the fins for achieving an improved energy distribution.

Figure 6 finally is a diametrical section of the plate shown in the preceding figure, along line A-B thereof.

PREFERRED EMBODIMENT OF THE INVENTION The invention, as foresaid, has been designed specifically for microwave ovens 1, and more concretely for ovens on the base 2 of which is provided a rotating plate 3, which supplies such rotating movement to the food 4 which is to be cooked, and further includes a cooking sensor comprised by a spike 5 which is embedded in the food 4 and which, through an electrical conductor 6 ending in a plug 7 which couples onto a plug-socket pro vided therefor on one of the side walls 8 of the oven, sends information to the.control cir cuit of the latter, to either stop the cooking operation on reaching a certain thermal level in the area wherein sensor 5 is embedded, to act on an indicator of some type, or to adt on any other elements provided for the function ing of the oven.

A sensor 5-6-7 as described obviously can not be used in a conventional rotating plate which is subjected to a continuous rotating movement in the same direction.

The invention is centred, as aforesaid, on affording an alternating movement with an amplitude of approximately 360O to rotating plate 3 with the basic elements shown in Figure 1 and mentioned above, such that the effect as regards the varying position between food 4 and the heat source of the oven is similar to what is conventionally achieved, whereas the electrical conductor 6 is subjected to a slight alternating twisting which causes no problem whatsoever.

In order to achieve the above, a radial cam or index 10 is fitted to the rotating axis 9 of plate 3, an abutment 11 established on base 2 of the oven as shown in Figure 2, or a twoway electrical commutator 12, as shown in Figure 4, assisting the said cam.

Specifically in the first case, where a simple abutment 11 is used, the axis 9 of the plate is coupled to that of a driving motor 13 aided by the corresponding reducer, which motor is of the synchronous, multipolar type having permanent magnets and being currently available on the market, its essential characteristic being that it may rotate in either direction and that, furthermore, on encountering a resistant couple which it is unable to overcome, in this case abutment 11 on which rests cam 10, it stops momentarily and immediately starts to turn in the opposite direction.

Thus, and in accordance with the above, motor 13 will start to turn in either direction when the oven begins to function, it will then stop momentarily when cam 10 related to the axis of the motor reaches abutment 11, and invert its direction of rotation, describing a further turn of approximately 360O until cam 10 once again reaches abutment 11, now on the opposite side, the motor once again inverting its direction of rotation, this operative cycle being repeated indefinitely.

This solution is obviously very attractive from a cost point of view, for a motor is needed in all cases for affording rotational movement to plate 3, wherefore this specific motor takes the place of the motor used conventionally, the only additional elements required being cam 10 and abutment 11, which elements are extremely simple, cost very little, and are quick, simple and easy to install.

Moreover, as shown in Figure 4, it is also possible to substitute said abutment 11 for a two-way electrical commutator 12, which feeds, specifically through connecting wires 14, a motor of the type which allows inversion of its direction of rotation by changing or inverting the polarity of its electrical supply, thereby achieving the same effect as in the preceding case, though with a slightly more complex structure.

In any case, both cam 10, and abutment 11 or electrical two-way commutator 12 would be situated under base 2 of the cooking chamber of the oven, in order that they are not affected by spilt grease or the like, and, furthermore, that they do not constitute an obstacle for cleaning the oven.

Finally, and as pointed out hereinbefore, mechanical systems may also be used for obtaining alternating movement, such as eccentrics, crank-shaft assemblies, racks, etc., although such solutions are of lesser interest by reason of their greater structural complexity.

As regards the specific structure of plate 3 itself, and as shown in Figure 5 and 6, the said plate is comprised by a metal, circular plate having a perimetral inlaid projection 15, obtained preferably by molding, which affords thereto a tray-like configuration, and a further central inlaid projection 16 through which said tray is coupled to the rotating axis 9 with the aid of a screw, the head whereof is housed in the said molding 16 and thus does not project with respect to the general operative plane of the plate or tray.

From this basic structure of plate 3 itself, and as a further characteristic of the invention, the said plate includes a plurality of radial fins 17, duly stiffened to the lower surface thereof, which fins are preferably six in number and are spaced equiangularly, these six fins being complemented by three additional fins 17' established transversally and alternately two by two between the free external ends of the fins 17, as shown specifically in Figure 5.

The said fins 17-17' may be comprised by separate, simple metal plates joined by welding along one of their longitudinal edges to the lower surface of plate 3 and being perpendicular tithe general plane thereof, or alternatively, each pair of radial fins 17, together with transversal fins 17' joining the two, may emerge from a flat common nucleus 18, being isosceles and trapezial in shape, through which the assembly is fitted, likewise by welding, to the lower surface of plate 3, as shown in Figure 6.

In any case, the fins achieve a disturbance in the arrangement of the electromagnetic fields within the oven cavity, thereby improving operation thereof, by preventing the formation of hot points or areas within the oven, and further defining more favourable working conditions for the magnetron, together with an improvement in the useful mean power obtained by varying the configuration of the electromagnetic field, further obtaining operation of the said magnetron within the more favourable area therefor, and thus extending its useful life.

Claims (7)

1. Rotating plate for microwave ovens, which, aiming at allowing, simultaneously to maintaining a continuous movement of the food with respect to the heat source of the oven to ensure perfect homogeneity in the cooking operation, the use of a cooking sensor of the simplest kind, being that in which the sensor is comprised by a spike which is embedded in the food to be cooked and which is related to the control circuit of the oven by means of a simple electrical conductor ending in a plug which is coupled to a socket operatively provided on one of the side walls of the oven, and to furthermore achieve a disturbance of the electromagnetic fields generated by the magnetron of the oven in order to eliminate the hot points or areas thereof, is essentially characterised in that it is aided by driving means which afford thereto an alternating movement having an amplitude of approximately 360 , such that the said electrical conductor is subjected only to a slight alternating torsion which is easily absorbed by the flexibility thereof, it having been further foreseen that a plurality of metal fins are fitted, preferably by welding, to the lower surface of the plate of the oven, and suitably distributed thereaiong.

2. Rotating plate, in accordance with claim 1, characterised in that the said means consist of a cam or index, duly fastened to the rotating axis of the plate, and being aided by a fixed abutment established on the base of the oven or on any other stationary part thereof, a motor of the synchronous, multipolar type having permanent magnets, capable of turning in either direction and which, on encountering a resistant couple which it is unable to overcome, stops momentarily and inverts its direction of rotation, being used a driving means.

3. Rotating plate, in accordance with the preceding claims, characterised in that the said abutment may optionally be substituted by a two-way electrical commutator, in which case the motor is in turn substituted by a motor of the type which inverts its direction of rotation upon inversion of its electrical supply.

4. Rotating plate, in accordance with claim 1, characterised in that the height of the metal fins provided on the tray constituting the said plate, on the lower face thereof, is limited by the distance between the base of the oven and the tray, it having been foreseen that the distance between the lower base of the said fins and the bottom of the oven is as small as possible, considering mechanical tolerancies, and thus ensuring that no arcs may appear between the said edges of the fins and the base of the oven.

5. Rotating plate, in accordance with claim 1 and 4, characterised in that the said fins are distributed along the lower surface of the oven at equal distances therebetween.

6. Rotating plate, in accordance with claims 1, 4 and 5, characterised in that the said fins comprise two groups, one in which the said fins adopt a radial arrangement and are preferably six in number and equiangularly distributed, and another in which the fins are arranged transversally and are preferably three in number, each of these latter fins relating the outer ends of the radial fins, alternately two by two.

7. A rotating plate for microwave ovens substantially as hereinbefore described with reference to and as shown in Figures 1 to 3, or in Figures 1 to 3 as modified by Figure 4 or in the aforesaid figures as modified by Figures 5 and 6 of the accompanying drawings.