This invention relates to microwave cooking apparatus .

Microwave cooking apparatus is well known. The microwave cooking apparatus comprises a housing, a working area inside the housing where cooking takes place, and a device for generating microwaves. The device for generating microwaves is usually a magnetron. The cooking action of the microwaves in the cooking area depends on the physical position of walls defining the cooking area and on the entry point of the microwaves . In the known microwave cooking apparatus, areas tend to be created where some waves within the cavity are stationary and this gives rise to high and low energy areas which can create hot and cold spots in the heated medium. This in turn gives rise to an uneven heating effect over the entire cooking area and thus uneven cooking.

In order to overcome the problem of stationary microwave areas, the known microwave cooking apparatus employs a turntable to move the product or products to be cooked in the housing, and/or a microwave stirring device for altering the plane and position of the stationary microwave areas. Sometimes the turntable and

the microwave stirring device are employed together and there are often instances where the microwave stirring device occupies too much space in the microwave cooking apparatus, or instances where the turntable is inappropriate.

It is an aim of the present invention to reduce the above mentioned problem.

Accordingly, in one non-limiting embodiment of the present invention there is provided microwave cooking apparatus comprising a housing, a cooking area inside the housing where cooking takes place, a device for generating microwaves, and feed means for controUably feeding the microwaves into the cooking area, the feed means being such that it comprises a waveguide for guiding the microwaves to at least two separate parts of the cooking area, obturator means for controUably blocking the waveguide in order to control the passage of the microwaves along the waveguide and thereby to control the way in which the microwaves enter the cooking area. and control means for operating the obturator means .

The use of the feed means in the microwave cooking apparatus of the present invention enables the microwave energy to be fed into the cooking area exactly where required and in the most efficient manner. The microwave cooking apparatus may advantageously be a

grill and combination oven including hot air circulation and steam, where even heating of food in the cooking area is required above and below or between metal shelves . The microwave cooking apparatus can be consumer cooking apparatus, multi-shelved catering equipment, or industrial microwave heating equipment.

The launching of the microwave energy into the cooking area from desired positions, for example those convenient to manufacturers, ensures that space within the microwave cooking apparatus is not wasted, and it also ensures that the efficiency of other components such for example as full-width grills and hot air circulating fans, is not compromised. The use of the feed means in the microwave cooking apparatus of the present invention enables for the microwave cooking apparatus to be designed and developed to a specific need, something that is extremely difficult to do at the present moment in time using conventional microwave engineering technology.

Usually, the microwave cooking apparatus will be one in which the obturator means comprises at least one plunger. Other types of obturator means may be employed including, for example, drums and flaps.

The microwave cooking apparatus may be one in which the waveguide has a plurality of sections leading to a plurality of parts of the cooking area, and in which the

obturator means comprises one of the plungers in at least one of the sections. There may be one of the plungers in each one of the sections.

The microwave cooking apparatus may be one in which there are two sections leading to two parts of the cooking area. Such an arrangement would usually be employed in microwave cooking apparatus manufactured for the domestic market. Alternatively, there may be four sections leading to four parts of the cooking area. Such an arrangement will usually be employed in the professional/industrial catering and industrial microwave equipment markets.

The microwave cooking apparatus may be one in which the plungers operate out of phase or in some phased relationship to each other, and thereby distributing the microwave energy with a minimum of stationary areas. The plungers preferably operate at quarter wavelength intervals out of phase with each other. The obturator means can be of a grounded or insulated floating design.

The control means may comprise a solenoid, a stepper motor, an electronic or electro-mechanical arrangement, or a rocking or reciprocating mechanism. Any suitable and appropriate type of control means may be employed. The control means may incorporate a fail safe device.

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

Figure 1 is a schematic view of known microwave cooking apparatus;

Figure 2 shows part of first microwave cooking apparatus of the present invention;

Figure 3 illustrates in more detail part of the microwave cooking apparatus shown in Figure 2;

Figure 4 shows part of second microwave cooking apparatus of the present invention;

Figure 5 shows part of third microwave cooking apparatus of the present invention; and

Figure 6 shows part of fourth microwave cooking apparatus of the present invention.

Referring to Figure 1, there is shown microwave cooking apparatus 2 comprising a housing 4 and a cooking area 6 inside the housing 4 where cooking takes place. Food to be cooked in the cooking area 6 is usually placed on a turntable 8. The microwave cooking apparatus 2 includes a device for generating microwaves in the form of a magnetron 10. The magnetron 10 generates the microwaves and they are directed to the cooking area 6 via feed means in the form of a waveguide 12.

The microwave cooking apparatus 2 shown in Figure 1 is such that the cooking area 6 often has stationary microwave areas giving rise to hot and cold spots within the cooking area 6. This in turn leads to an uneven heating effect in the cooking area 6 which can lead to uneven cooking of food. In order to overcome this problem, the microwave cooking apparatus 2 is provided with a microwave stirring device 14 operating in an enclosure 16 as shown. Still further, the turntable 8 is rotatable in order to rotate the food and thus expose the food to the microwaves coming from different angles and thus promote even cooking of the food. The microwave stirring device 14 and the enclosure 16 often occupy too much space within the housing 4 and this leads to design constraints in the designing of new microwave cooking apparatus.

Referring now to Figure 2, there is shown microwave cooking apparatus 2 in accordance with the present invention. Similar parts as in Figure 1 have been given the same reference numerals for ease of comparison and understanding. It will thus be seen that the microwave cooking apparatus 2 comprises the housing 4 and the cooking area 6.

The magnetron 10 in Figure 2 is shown in a position in which it is able to feed a waveguide 12 having a

first section 18 leading to a first outlet port 20 and a second section 22 leading to a second outlet port 24.

The microwave cooking apparatus 2 shown in Figure 1 has first obturator means 26 for blocking the first section 18, and second obturator means 28 for blocking the second section 22.

Figure 3 shows the first obturator means 26. The second obturator means 28 is similarly constructed. Thus the first obturator means 26 comprises a tube 30 fixed to the first section 18. The tube 30 has a reduced diameter open tubular section 32. An insulated shaft 34 slides backwards and forwards through the tubular section 32. The shaft 34 is connected to an obturator 36 which is provided with insulation 38.

As the obturator 34 is slid into the first section 18 of the waveguide 12, it first alters the phase of the launched wave and acts as a tuning device. When fully extended, the obturator 34 blocks the first section 18 and thus prevents the passage of the microwaves along the first section 18. The obturator 36 then acts as a short circuiting device to the microwaves. The microwaves are reflected by the obturator 36 and thus all the microwave energy generated by the magnetron 10 passes along the second section 22 of the waveguide 12 and enters the cooking area 6 through the second outlet port 24 in the waveguide 12.

During operation of the microwave apparatus 2, as the obturator 36 forming part of the first obturator means 26 is withdrawn from the first section 18, the obturator 36 forming part of the second obturator means 28 is caused by control means (not εhown) to enter the second section 22. The obturator 36 forming part of the second obturator means 28 thus blocks the microwaves passing along the second section 22 and it reflects these microwaves. Thus the microwave energy from the magnetron 10 then gets reflected through the first outlet port 20 in the waveguide 12. The first and the second obturator means 26, 28 operate one quarter of a wavelength out of phase with each other in order to ensure that the microwave energy entering the cooking area 6 from the first outlet port 20 and the second outlet port 24 does not have the same stationary areas.

The first and the second outlet ports 20, 22 can be situated at any suitable and appropriate physical position around the housing 4 so that they may be situated on the top, bottom, sides, corners or faces of the housing 4. Two sets of stationary microwave areas are generated. When both obturator means 26, 28 are withdrawn, microwave energy is able to enter both waveguides 20, 22 simultaneously, giving another set of stationary microwave areas in the cavity. As the obturator 36 of the firεt obturator means 26 is being

withdrawn and the obturator 36 of the second obturator means 28 is being inserted, further different types of microwave energy with different microwave stationary areas will be generated within the housing 4. It will thus be apparent that during operation of the microwave cooking apparatus 2, the microwave energy in the cooking area 6 is constantly changing and there are no permanent microwave stationary areas as in the known microwave cooking apparatus 2 shown in Figure 1.

The first and the second obturator means 26, 28 can be arranged to operate at any intermediate position that is acceptable to the magnetron 10 reverse power. By doing so the phase at the outlet ports 20, 24 will be changed giving a range of phase angles at the respective ports .

The microwave cooking apparatus 2 is not restricted to the design shown in Figures 2 and 3 and the waveguide 12 may have more than two sections 18, 22 with an obturator means in each section. More than one magnetron 10 may be employed if desired.

Figure 4 shows control means 40 for operating first obturator means 26 and second obturator means 28. A separate control means 40 is employed for each obturator means 26, 28. The illustrated control means 40 each comprises a cable 42 which passes over a pulley 44 and

is operated by drive means 46. The drive means 46 may include a solenoid or a stepper motor.

The length of the waveguide 12 and the particular arrangement of the waveguide 12 shown in Figure 4 will be specific to each particular microwave cooking apparatus 2 and especially the cooking area 6. The arranged position of the obturators 36 and the first and the second obturator means 26, 28 will be arranged to be a function of known microwave frequency and wavelength. The obturators 36 will be arranged such that they are never both in the closed position at the same time and fail-safe control means (not shown) may be employed to prevent this.

Figure 5 shows microwave control apparatus 2 in which the cooking area 6 contains shelves 48, two magnetrons 10 and two waveguides 12 which are employed to distribute the microwave cooking energy as shown.

Figure 6 shows a microwave cooking arrangement in which the microwave energy shown by arrows can be arranged to alternate from each εide of the housing 4 and between shelves 48.

There is currently an industry shift in both domestic and industrial catering microwave cooking apparatus towards combined microwave and steam/hot air and grill integrated systems. Most of the existing combined appliances have insufficient space around them

to incorporate the traditional microwave stirring device 14, enclosure 16 and turntable assembly. Many of the known appliances have thus not been fully progressed due to the tooling costs for making revisions to provide for the microwave energy. The microwave apparatus 2 shown in the present invention can be produced as a combined microwave and steam/hot air and grill integrated appliance without the problems previously facing the industry, this being due to the fact that it is no longer necessary to employ the microwave stirring device 14 and the enclosure 16, or turntable and similar microwave stirring arrangements. Still further, the use of the obturator means can avoid interfering with the efficient operation of other devices, such for example as grill elements and hot air circulation systems, as o ten occurs in known apparatus . The microwave cooking apparatus of the present invention is extremely flexible in design possibilities.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, the microwave cooking apparatus 2 shown in Figures 2 and 3 may be used with a turntable 8 if it iε desired to mount the food to be cooked on a turntable 8.

If the microwave cooking apparatus is such that space is not a problem then the microwave cooking apparatus may include i rotatable turntable and a microwave stirring device but then the presence of the feed means comprising the waveguide, the obturator means and the control means will promote a more even cooking than would otherwise be obtainable, which leads to enhanced cooking. Obturator means other than plungers may be employed so that, for example, the obturator means may be drums or flaps.

The microwave cooking apparatus of the present invention is not restricted to a conventional cooking area 6 and it can be applied to waveguides, high Q systems and slow wave structures etc. It can also be incorporated in cooking apparatus having two separate cavity means feeding energy into each individual cavity either separately or simultaneously, from the same microwave supply source.