CN115735413A

CN115735413A - Food preparation equipment

Info

Publication number: CN115735413A
Application number: CN202180046179.2A
Authority: CN
Inventors: S.格林瑟姆
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2020-06-30
Filing date: 2021-06-16
Publication date: 2023-03-03
Also published as: GB2596548A; GB202009987D0; GB2596548B; WO2022003322A1

Abstract

A food preparation device has a magnetic field generator. The magnetic field generator has a plurality of coils arranged in an annular array, and an excitation device configured to excite the plurality of coils. The plurality of coils has a first subset of coils configured to generate respective first magnetic fields for interacting with a susceptor of the food container, and the plurality of coils includes a second subset of coils configured to generate respective second magnetic fields for interacting with an agitator of the food container. The plurality of coils are arranged such that the coils of the second subset of coils are located in the middle of adjacent coils of the first subset of coils.

Description

Food preparation equipment

Technical Field

The present invention relates to a food preparation device.

Background

In the field of food preparation, traditional methods of cooking on a stove, for example, the stove is gas or electrically powered, can be energy inefficient. It is known that stoves for heating pots by magnetic induction, so-called induction cookers, offer a higher energy efficiency than gas or electrically driven stoves.

Disclosure of Invention

According to a first aspect of the present invention, there is provided a food preparation apparatus comprising a magnetic field generator comprising a plurality of coils arranged in an annular array, and excitation means configured to excite the plurality of coils, wherein the plurality of coils comprises a first subset of coils configured to generate respective first magnetic fields for interacting with a susceptor of a food container, and the plurality of coils comprises a second subset of coils configured to generate respective second magnetic fields for interacting with an agitator of the food container, the plurality of coils being arranged such that the coils of the second subset of coils are located in the middle of adjacent coils of the first subset of coils.

Since the coils of the second subset of coils are located in the middle of adjacent coils of the first subset of coils, the interaction of the food preparation device with the susceptor and the stirrer of the food container may be achieved at a common radial distance. Interaction of the food preparation apparatus with both the susceptor and the agitator of the food container may be achieved by the above-described device using a relatively compact arrangement and/or a device having fewer component parts, for example, one of the arrays being configured to interact with the susceptor and one of the arrays being configured to interact with the agitator, as compared to a device having nested annular arrays.

The plurality of coils may be arranged in an annular array such that the coils of the second subset of coils are located at substantially the same radial distance as the coils of the first subset of coils. The first subset of coils may be substantially aligned with the second subset of coils, e.g. substantially aligned in a circumferential direction.

The single coil of the second subset of coils may be located in between adjacent coils of the first subset of coils. This may be beneficial as it may reduce the distance between coils configured to generate respective first magnetic fields for interacting with the susceptor of the food container (i.e. coils configured to generate a thermal effect), for example compared to an arrangement in which a plurality of coils of the second subset of coils are located in between adjacent coils of the first subset of coils. This may provide better heat distribution within a food container received on the food preparation device in use.

The food preparation device may comprise a contact surface for receiving a food container, and the magnetic field generator may be arranged below the contact surface.

The excitation means may be configured to excite the first subset of coils at a different frequency, e.g. at a higher frequency, than the second subset of coils. Higher frequencies may more efficiently generate heat through interaction with the susceptor. The excitation means may excite the plurality of coils by applying a voltage across the coils.

The excitation means may be configured to sequentially excite the second subset of coils such that each of the second subset of coils has a first excitation state in which the coil generates its second magnetic field and a second excitation state in which the coil does not generate its second magnetic field. This may allow the second magnetic field to be generated only when required, and may enhance control of the stirrer movement, for example by interaction with the second magnetic field.

At least one of the second subset of coils may include a third energized state in which the coil is energized at a higher frequency than in the first energized state such that the coil interacts with the susceptor of the food container in the third energized state to heat the food container. This may be beneficial because it may enable one or more of the second subset of coils to interact with the susceptor of the food container, for example when it is not required that they interact with the agitator of the food container, for example to provide heat to the food container, for example to impart motion to the agitator of the food container.

The magnetic field generator may include a magnetic core assembly, each of the plurality of coils wound around a portion of the magnetic core assembly. This may be beneficial because the magnetic core assembly may provide a magnetic flux path, which may reduce magnetic losses compared to, for example, multiple coils without the magnetic core assembly.

The magnetic core assembly may include a first plurality of pole pairs corresponding to the first subset of coils and a second plurality of pole pairs corresponding to the second subset of coils, the first plurality of pole pairs defining a respective first flux path for the first magnetic field and the second plurality of pole pairs defining a respective second flux path for the second magnetic field. The pair of poles providing a flux path may better constrain the magnetic flux in use, for example to allow more flux to be associated with the susceptor and stirrer, thereby improving efficiency.

The magnetic core assembly may include a common toroidal core back, each of the plurality of coils being wound on the common toroidal core back. The common annular core backs may allow for easier alignment during the manufacturing process, which may reduce the cost and/or complexity of the manufacturing process.

The magnetic core assembly may include a plurality of arms extending from a common toroidal core back, each of the plurality of coils wound on the common toroidal core back between adjacent arms of the plurality of arms. Thus, the arms of the toroidal core back may act as a flux guide for the plurality of coils.

The magnetic core assembly may include a plurality of discrete cores arranged in an annular array, each discrete core including a core back and a plurality of arms, e.g., a pair of arms, extending from the core back. The plurality of discrete cores may confine the magnetic flux more than, for example, a common annular core, which may reduce magnetic losses. For example, a coil may be wound on each core back.

The magnetic core assembly may comprise a male magnetic core assembly. This may, for example, enable interaction with another male magnetic core assembly of the food container in use, thereby inhibiting movement of the food container relative to the food preparation device. This may be beneficial as it may effectively lock the food container to the food preparation device, e.g. such that rotation of the food container relative to the food preparation device is inhibited. This may be particularly beneficial in case, for example, the stirrer is hooked by an item inside the food container, which would otherwise cause the food container to rotate relative to the food preparation apparatus. This may allow the food container to be left unattended in use.

Providing corresponding male magnetic components in the food container and the food preparation device may also allow guiding the food container to a predetermined orientation relative to the food preparation device during placement of the food container on the food preparation device.

According to a second aspect of the invention, there is provided a food preparation device according to the first aspect of the invention, and a food container comprising a susceptor for interacting with a first magnetic field to heat a portion of the food container, and an agitator for interacting with a second magnetic field to move the agitator within the food container.

The stirrer and susceptor may comprise a common component, for example the stirrer is formed from susceptor material.

The food container may include another male magnetic assembly configured to interact with the male magnetic assembly of the food preparation device when the food container is placed on the food preparation device to inhibit movement of the food container relative to the food preparation device.

Where appropriate, preferred features of one aspect of the invention may be equally applied to other aspects of the invention.

Drawings

FIG. 1 is a schematic diagram of a food preparation system according to one example;

FIG. 2 is a schematic view of a first embodiment of a magnetic field generator for use in the food preparation system of FIG. 1;

fig. 3a is a schematic representation of a first excitation waveform of the excitation means of the magnetic field generator of fig. 2;

FIG. 3b is a schematic diagram of an electronic circuit for generating the excitation waveform of FIG. 3 a;

fig. 3c is a schematic diagram of a second excitation waveform of the excitation means of the magnetic field generator of fig. 2;

FIG. 3d is a schematic diagram of an electronic circuit for generating the stimulus waveform of FIG. 3 c;

FIG. 3e is a schematic diagram of the first embodiment of applied voltages relative to the supply voltage;

FIG. 3f is a schematic diagram of a first embodiment of applied voltages relative to a supply voltage;

FIG. 4a is a schematic perspective view of a magnetic core of the magnetic field generator of FIG. 2;

FIG. 4b is a schematic side view of the magnetic core of FIG. 4a placed under a food product container;

FIG. 5 is a schematic view of a first embodiment of a food container for use with the food preparation system of FIG. 1;

figure 6a is a schematic view of a first embodiment of a susceptor portion of the food product container of figure 5;

FIG. 6b is a schematic view of a first embodiment of a susceptor portion of the food product container of FIG. 5;

FIG. 7 is a schematic view of a blender of the food container of FIG. 5;

FIG. 8 is a schematic view of a second embodiment of a magnetic field generator for use in the food preparation system of FIG. 1;

FIG. 9 is a schematic view of a third embodiment of a magnetic field generator for use in the food preparation system of FIG. 1;

FIG. 10 is a schematic view of the magnetic field generator of FIG. 9 utilizing a first magnetic core arrangement;

FIG. 11 is a schematic view of the magnetic field generator of FIG. 9 utilizing a second magnetic core arrangement;

FIG. 12 is a schematic view of a fourth embodiment of a magnetic field generator for use in the food preparation system of FIG. 1;

FIG. 13 is a schematic view of a second embodiment of a food container for use with the food preparation system of FIG. 1;

FIG. 14 is a schematic view of a third embodiment of a food container for use with the food preparation system of FIG. 1;

FIG. 15 is a schematic view of a magnetic assembly of the food container of FIG. 14;

FIG. 16 is a schematic view of a fourth embodiment of a food container for use with the food preparation system of FIG. 1;

FIG. 17 is a schematic bottom view of a fifth embodiment of a food container for use with the food preparation system of FIG. 1;

FIG. 18 is a side schematic view of the food container of FIG. 17; and

fig. 19 is a schematic view of a fifth embodiment of a magnetic field generator for use in the food preparation system of fig. 1.

Detailed Description

A food preparation system according to the present invention is schematically illustrated in fig. 1 and generally designated 10. The food preparation system 10 includes a food preparation apparatus 100 and a food container 200 placed on the food preparation apparatus 100. The food preparation device 100 takes the form of an induction hob and may be used for heating food contained in the food container 200 in use, as will be described below.

The food preparation device 100 comprises a contact surface 102 on which the food container 100 can be placed and a magnetic field generator 104, which magnetic field generator 104 is arranged below the contact surface 102. It should be understood that the food preparation device 100 may comprise further features, such as user inputs, for example in the form of one or more user-actuatable buttons or the like, but these features are not shown here.

A first embodiment of the magnetic field generator 104 is schematically shown in the top view of fig. 2. The magnetic field generator 104 comprises six magnetic cores 106, each magnetic core 106 being wound with a respective coil 108, and an excitation means 110 for exciting the coils 108 (as shown in fig. 1). The excitation means 110 comprises an electronic circuit 112, which electronic circuit 112 is capable of converting the main power supply into a form suitable for exciting the coil 108. Examples of suitable excitation patterns and electronic circuits 112 of the excitation means 110 are described with reference to fig. 3 a-d.

As mentioned above, the food preparation apparatus 100 takes the form of an induction cooker. Induction cooktops operate by inducing eddy currents in an electrical conductor by varying the magnetic field applied in the electrical conductor. In the case of a fixed electrical conductor, as in the case of an induction cooker, the applied magnetic field must be varied to induce the desired eddy currents. Such variation may be achieved using Pulse Width Modulation (PWM), and adjusting the duty cycle and/or frequency of the PWM may provide variable heating control. It is also known to synthesize a low frequency voltage waveform from a DC voltage. If the frequency of the PWM is sufficiently high, the PWM frequency can be considered to be largely independent of the composition of the low frequency voltage. Thus, the present invention can provide variable induction heating while maintaining a low frequency voltage that can be used to drive the agitator of the food container 200.

In some embodiments, as will be described below, not all of the coils 108 need to be energized at the same time. This may result in different subsets of the coils 108 requiring an arrangement of discrete excitation patterns. For example, an excitation pattern in which the first subset of coils 108 is excited for a first time period 101 and the second subset of coils 108 is not excited during the first time period 101, and in which the second subset of coils 108 is excited for a second time period 103 and the first subset of coils 108 is not excited during the second time period 103. This excitation pattern is shown in fig. 3 a.

Fig. 3b shows an electronic circuit 112 for implementing the excitation pattern of fig. 3 a. The electronic circuit 112 is implemented as an AC-AC converter. The electronic circuit 112 includes an inductor L that collectively defines a low-pass filter _F And a capacitor C _F A first switching bridge SW1-4 for the first subset of coils 108 and a second switching bridge SW5-8 for the second subset of coils 108. The provision of two such switching bridges SW1-8 enables the first and second subsets of coils 108 to be independently excited. Thermal and speed fluctuations are acceptable to the food preparation system 10 of the present invention, and thus the electronic circuitry 112 may not require large energy storage components, such as DC link capacitors.

In other embodiments, each coil 108 may be energized simultaneously with each other coil 108. Thus, only one excitation pattern is required, as shown in fig. 3 c. As can be seen in fig. 3c, the voltage applied to the coil 108 alternates between positive and negative, where the voltage is applied with a positive voltage during the negative period of the AC power cycle and a negative voltage during the positive period of the AC power cycle.

Fig. 3d shows an electronic circuit 112 for implementing the excitation pattern of fig. 3 c. The electronic circuit 112 is implemented as an AC-AC converter. The electronic circuit 112 includes an inductor L that collectively defines a low pass filter _F And a capacitor C _F And a single bridge of switches SW1-4 for the plurality of coils 108.

The electronic circuit 112 of fig. 3d may be simpler than the electronic circuit 112 of fig. 3b, since fewer switches are required. In some examples, the switch may be a bidirectional gallium nitride (BiGaN) switch capable of operating at relatively high switching frequencies, e.g., greater than 100kHz. Reducing the number of required BiGaN switches can reduce cost.

It should be appreciated that in some embodiments, it may be beneficial to provide a separate transducer for each coil 108. In such an implementationIn one example, the PWM applied to each converter may be phase shifted, which is a common method used in parallel converter arrangements to increase the effective operating frequency seen by the input low pass filter, thereby allowing for L _F And C _F A more compact and cost-effective component selection is made.

The excitation patterns of fig. 3a and 3c depict an embodiment as shown in fig. 3e, wherein the applied voltage is applied unidirectionally only during each excitation period. In other embodiments, as shown in FIG. 3f, the applied voltage may be in two directions, positive and negative, during a single excitation period. This may provide the desired net positive voltage while maximizing the high frequency content, which is beneficial for inducing eddy currents in the susceptor material. However, in the embodiment of fig. 3f, a power input filter may be required to provide a general low-pass characteristic, in contrast to the embodiments of fig. 3a and 3 c.

Referring back to fig. 2, six magnetic cores 106 are arranged in a circular array. Each magnetic core 106 includes a core back 114, and first and

second arms

118, 120 extending from the core back 114 and having respective free ends 122. A coil 108 is wound on each core back 114. In fig. 2, the first and

second arms

118, 120 extend inwardly toward the center of the toroidal array of the magnetic core 106, but it should be understood that in alternative embodiments, the first and

second arms

118, 120 may extend outwardly from the core back 114. The first arm 118 and the second arm 120 are angled toward one another such that the distance (e.g., slot width) between the

arms

118, 120 decreases from the core back 114 to the free end 122.

The shape of the magnetic core 106 can be seen more clearly in fig. 4, where a single magnetic core 106 is shown separately. Each magnetic core 106 has a first pair of poles 126 on the core back 114 and a second pair of poles 130 on the first and

second limbs

118, 120 such that one pole 130 of the second pair of poles is located on each

limb

118, 120.

Each pole 126 of the first pair of poles has a substantially identical shape and has a substantially circular cross-sectional shape such that the poles 126 are substantially cylindrical. Of course, it will be appreciated that other cross-sectional shapes may also be suitably employed. A first pair of poles 126 extends upwardly from the core back 114 such that the poles 126 extend toward the contact surface 102. The first pair of poles 126 are spaced along the core back 114 such that the poles 126 are at opposite ends of the core back 114. The first pair of poles 126 together define a flux guide for guiding a magnetic flux generated when the coil 108 is energized in use, such that the poles 126 form part of a first magnetic circuit.

Each pole 130 of the second pair of poles has a substantially identical shape and a substantially circular cross-sectional shape such that the pole 130 is substantially cylindrical. The diameter of the second pair of magnetic poles 130 is smaller than the diameter of the first pair of magnetic poles 126 such that the second pair of magnetic poles 130 is smaller than the first pair of magnetic poles 126. A second pair of poles 130 extends upwardly from the free ends 122 of the first and

second arms

118, 120, respectively, such that the poles 130 extend toward the contact surface 102. As shown in fig. 4 and 4b, the length of the second pair of poles 130 is less than the length of the first pair of poles 126, although it is understood that the relative lengths may be adjusted depending on the desired application. The second pair of poles 130 together define a flux guide for guiding magnetic flux generated by the coil 108 when energized in use, such that the poles 130 form part of a second magnetic circuit.

As described above, the first arm 118 and the second arm 120 are angled toward one another, as best seen in fig. 2, such that the distance between the

arms

118, 120 decreases from the core back 114 to the free end 122. Since the first pair of poles 126 are located at opposite ends of the core back 114 and the second pair of poles 130 are located at the free ends 122 of the first and

second arms

118, 120, the distance between the first pair of poles 126, i.e., the air gap between the first pair of poles 126, is greater than the distance between the second pair of poles 130, i.e., the air gap between the second pair of poles 130.

As shown in fig. 4b, the first pair of poles 126 is longer than the second pair of poles 130. This means that the air gap between the first pair of magnetic poles 126 and the associated portion of the food container 200 is smaller than the corresponding air gap between the second pair of magnetic poles 130 and the associated portion of the food container 200. Thus, when the coil 108 is energized, first and second magnetic flux circuits, i.e., first and second magnetic fields, having different characteristics are generated at the first pair of magnetic poles 126 and associated portions of the food container 200 and the second pair of magnetic poles 130 and associated portions of the food container 200, which allows different portions of the food container 200 to have different functions, as will be described below. By varying the relative ratio of the air gap between the first pair of magnetic poles 126 and the associated portion of the food container 200 and the corresponding air gap between the second pair of magnetic poles 130 and the associated portion of the food container 200, the associated flux ratio between the first and second flux circuits can be adjusted.

The air gap between the first pair of magnetic poles 126 and the associated portion of the food container 200, and the air gap between the second pair of magnetic poles 130 and the associated portion of the food container 200, are selected to be less than the air gap between the pole pairs so that as much magnetic flux as possible is associated with the associated portion of the food container 200 in use. By increasing the air gap between the pole pair, flux leakage may be reduced, such that more flux is coupled to the relevant portion of the food container 200 in use.

It should also be appreciated that given the form of the plurality of magnetic cores 106, the plurality of magnetic poles are defined around an annular array, and the plurality of magnetic cores 106 define a first male magnetic component in the food preparation device 100.

A first embodiment of a food container 200 for a food preparation device 100 is schematically shown in cross-section in fig. 5.

The food container 200 includes an outer pan 202, an inner pan 204, a lid 206, a handle 208, and a stirrer 210. Here, the food container 200 is generally in the form of a saucepan.

The outer pot 202 includes a generally circular base 212 and a sidewall 214 extending upwardly from the periphery of the base 212 to define a hollow interior for receiving the inner pot 204. The outer pan 202 is formed of an insulating material, such as a suitable plastics material, so that the outer pan 202 is touch safe in use and also reduces heat loss, thereby improving thermal efficiency. A pick-up power coil 216 and a temperature sensor 218 are attached to the side wall 214 in the area where the handle 208 is connected to the side wall 214. In some embodiments, the temperature sensor 218 is held in contact with the inner pan 204 by a loading mechanism to ensure good thermal contact in use. The handle 208 is attached to the sidewall 214, is substantially hollow, and houses one or more electronic components 220, such as a transceiver or the like, configured to communicate the temperature within the food container 200 to a user. The pick-up power coil 216 is capable of interacting with the magnetic field generated by the magnetic field generator 104 in use for powering the temperature sensor 218 and/or other electronic components housed within the handle 208. Since the outer pan 202 is typically not in contact with food products during use, which may not require much cleaning, electrical components, such as the pick-up power coil 216, the temperature sensor 218, and the electrical components 220 within the handle 208 are attached to the outer pan 202.

The inner pan 204 includes a generally circular base 222 and a sidewall 224 extending upwardly from the base 222 to define a receiving space 226 for receiving food items. The diameter of the base 222 of the inner pan 204 is smaller than the diameter of the base 212 of the outer pan 202 so that the inner pan 204 can be received inside the outer pan 202. In fig. 5, the inner pan 204 is shown partially received within the outer pan, with the base 222 of the inner pan 204 being located on top of the base 212 of the outer pan 202 in the fully inserted state. In some embodiments, an interlock mechanism (not shown) is provided to lock the inner pan 204 to the outer pan 202 to inhibit relative movement between the inner pan 204 and the outer pan 202 in use and to allow the food product within the receiving space 226 to be poured out. A lid 206 may be attached to the upper perimeter of the inner pot 204 to seal the receiving space 226. In some embodiments, the lid 206 may be releasably locked to the inner pan 204, e.g., with a small gap between the lid 206 and the inner pan 204 to allow pressure equalization.

The base 222 of the inner pan 204 includes a susceptor portion 228 and a non-susceptor portion 230. The susceptor portion 228 includes an electrically conductive material, such as a ferrous material, for interacting with the magnetic field generated by the magnetic field generator 104 to cause eddy currents to flow within the susceptor portion 228, thereby causing heating of the receiving space 226. Thus, the food container 200 may be heated by so-called induction heating.

In some embodiments, the susceptor portion 228 includes an annular ring 232 with a plurality of protrusions 234 on the outer circumference of the annular ring 232, as schematically illustrated in fig. 6 a. Thus, the susceptor portion defines a second male magnetic component for interacting with the first male magnetic component in the food preparation apparatus 100.

In use, when the food container 200 is placed on the food preparation apparatus 100, the first convex magnetic assembly defined by the plurality of magnetic cores 106 interacts with the second convex magnetic assembly defined by the susceptor portion 228 such that movement (i.e., rotation) of the food container 200 relative to the food preparation apparatus 100 is inhibited. This may be beneficial as it may effectively lock the food container 200 to the food preparation device 100, e.g. such that rotation of the food container 200 relative to the food preparation device 100 is inhibited. This may be particularly beneficial in cases where, for example, the blender 210 is hooked by an item within the food container 200, which would otherwise cause the food container 200 to rotate relative to the food preparation device 210. This may allow the food container 200 to be left unattended in use.

Providing corresponding male magnetic components in the food container 200 and the food preparation device 100 may also allow for guiding the food container 200 to a predetermined orientation relative to the food preparation device 100 during placement of the food container 200 on the food preparation device 100.

In the embodiment of fig. 6a, the number of protrusions 234 corresponds to the number of poles of the second pair of poles 130 of the magnetic core 106 of the magnetic field generator 104. In an alternative embodiment, as shown in fig. 6b, the number of protrusions 234 is twice the number of second pairs of poles 130 of the magnetic core 106 of the magnetic field generator 104. This may reduce the extent to which the food container 200 is rotated relative to the food preparation apparatus 100 before being locked in place, for example during placement of the food container 200 on the contact surface 102, but may result in a reduction in the area of the associated magnetic pole face of the susceptor portion 228, which may reduce bulging. It should be appreciated that the number of poles of the susceptor portion 228 may be selected to reduce the allowable range of rotation during placement of the food container 200 while maintaining a good level of protrusion to lock the food container 200 in place and matching the number of projections 234 to the number of poles of the second pair of poles 130 of the magnetic core 106 may provide a suitable balance.

The non-susceptor portion 230 is formed of an electrically insulating material that allows the magnetic field generated by the magnetic field generator 104 to pass through. In the embodiment of fig. 5, the non-susceptor portion 230 is located substantially in the center of the base 222 and is generally circular. The susceptor portion 228 extends annularly around the non-susceptor portion 230 and substantially to the sidewall 224.

The agitator 210 is schematically illustrated in fig. 7, and includes a central body 236 and a plurality of arms 238 extending outwardly from the central body 236. In this embodiment, agitator 210 is an agitator, and each arm 238 has an agitator blade 240 that extends substantially perpendicular to one end of arm 238 to either side of arm 238. Each of the stirrer blades 240 is provided with a bar magnet 242 having north and south poles. The bar magnets 242 interact with the magnetic field generated by the magnetic field generator 104 as will be described below. Although a bar magnet 242 is shown here, it should be understood that in some embodiments, the agitator may simply comprise a ferrous structure. It will also be appreciated that in practice the structure of the stirrer 210 described above is enclosed within a housing which rotates with the structure in use.

The stirrer 210 has a diameter less than or equal to the diameter of the non-susceptor portion 230 and is placed within the receiving space 226 of the inner pan 204 such that the stirrer 210, and in particular the bar magnet 242, is located above the non-susceptor portion 230. This may facilitate the interaction of the bar magnet 242 with the magnetic field of the magnetic field generator 104. In some embodiments, the inner pan 204 and the stirrer 210 may include respective positioning features, such as corresponding protrusions and recesses, for positioning the stirrer 210 relative to the inner pan 204 while also allowing the stirrer 210 to rotate relative to the inner pan 204.

In use, the food container 200 is placed on the food preparation device 100, e.g., the first and second male magnetic assemblies interact to guide the food container 200 to a position on the contact surface 102 of the food preparation device 100. Food container 200 is positioned on contact surface 102 such that susceptor portion 228 of inner pan 204 covers poles 126 of the first pair of poles of each magnetic core 106 and non-susceptor portion 230 of inner pan 204 and stirrer 210 cover poles 130 of the second pair of poles of each magnetic core 106, as shown in fig. 4 b.

The coils 108 are energized by the energizing device 110 such that first and second magnetic flux circuits, i.e., first and second magnetic fields, are generated between the first pair of magnetic poles 126 and the susceptor portion 228 and between the second pair of magnetic poles 130 and the agitator 210 of each magnetic core 106. Given the difference in relative distances between the first pair of magnetic poles 126 and the susceptor portion 228 and between the second pair of magnetic poles 130 and the agitator 210, as shown in fig. 4b, the first and second magnetic circuits have different magnetic resistances. As described above, the magnetic fields generated at the first pair of magnetic poles 126 and the second pair of magnetic poles 130 have different characteristics due to the different magnetic resistances of the first and second magnetic flux circuits. In the present embodiment, the magnetic field generated at each first pair of magnetic poles 126 is a first varying magnetic field, i.e., an alternating magnetic field, which interacts with the susceptor portion 228 such that eddy currents are generated within the susceptor portion 228 and the receiving space 226 is heated. The magnetic field generated at each second pair of magnetic poles 130 is a second varying magnetic field, i.e., an alternating magnetic field, which interacts with the bar magnet 242 such that the stirrer 210 rotates within the receiving space 226. In this manner, the agitator 210 may be used to agitate food items received within the receiving space 226. The coil 108 is energized and the height and spacing of the

poles

126, 130 are selected so that less magnetic flux flows in the second magnetic field relative to the first magnetic field, thereby controlling the rotational speed of the stirrer 210 to a reasonable level of stirring.

In the manner described above, the food preparation system 10 may allow for heating and automatic stirring of the food container 200, with the male magnetic component leaving the food preparation system unattended in use. Temperature sensor 218 may monitor the temperature of the food in receiving space 226 and communicate the temperature to a user, such as a remote user, via a transceiver within handle 208. Additionally or alternatively, temperature sensor 218 may communicate a temperature to activation device 110, and in response, activation device 110 may control the activation of coil 108 to adjust the heating rate. Because the food container 200 includes the susceptor 228 and the agitator 210, e.g., the susceptor 228 and the agitator 210 as separate components, an improved heating pattern may be provided as compared to a situation where the agitator 210 also functions as the susceptor 228. For example, where the agitator 210 also acts as the susceptor 228, heating may only be provided in the immediate vicinity of the current location of the agitator 210. Conversely, the use of a separate susceptor 228 and agitator 210 may allow heating to be provided in areas away from the current location of the agitator 210. This may, for example, provide more uniform heating of the receiving space 226.

Although the blender 210 described above has blending blades 240, it should be understood that other forms of blenders that utilize rotational motion may be used with the food container 200. For example, a blender having a plurality of cutting blades may be used with the food container 200. Accordingly, the blender 210 of the food container 200 may be removed and replaced within the food container 200. For example, the agitator 210 may also be removable for cleaning. Assuming the use of a bar magnet 242, an appliance having a magnet or ferrous portion at one end may be used to engage the blender 210 and then remove the blender from the food container 200. In this way, the agitator 210 may be safely removed during use, as the user does not directly contact the agitator 210.

Although described above as having a plurality of discrete magnetic cores 106, as schematically illustrated in fig. 8, other embodiments of the magnetic field generator 400 may include a single annular core back 402 with a plurality of arms 404 extending inwardly from the single annular core back 402. In a manner similar to the embodiment of the magnetic field generator 104 of fig. 2, a first pair of poles 408 is located on the toroidal core back 402 and a second pair of poles 412 is located at the free ends 414 of the arms 404. A coil 416 is wound on the single annular core back 402 between the first pair of poles 406. Such a magnetic field generator 400 may operate in a manner similar to the magnetic field generator 104 of fig. 2. For example, using a single ring back may increase ease of alignment during manufacturing, but may result in increased magnetic losses due to flux leakage along the ring back 402.

In some embodiments, all of the second pair of magnetic poles 130 of the magnetic field generator 104 may not be needed to effect rotation of the agitator 210. For example, it may be that only every other second pair of magnetic poles 130 is required to effect rotation of the agitator 210. In this case, the coils 108 corresponding to the second pair of magnetic poles 130 that do not need to achieve rotation may be energized differently, e.g., at a higher frequency, than the coils 108 corresponding to the second pair of magnetic poles 130 that need to achieve rotation, such that the second pair of magnetic poles 130 that do not need to achieve rotation of the stirrer 210 instead define a magnetic flux circuit and generate a varying magnetic field for interacting with a susceptor of the food container 200 to heat the receiving space 226. It should be understood that in such embodiments, the shape of the susceptor portion 228 may vary accordingly, or even the agitator 210 may include a susceptor, such as an additional susceptor. In such an embodiment, the coils 108 in a single annular array may be considered to be used to provide both heating and rotation, with the coils used for rotation in between the coils used for heating.

Fig. 9 schematically shows another embodiment of a magnetic field generator 500. In this embodiment, the magnetic field generator comprises a plurality of coils 502 arranged in an annular array, the coils 502 in the annular array being at a substantially common radial distance from a center point of the annular array. The coil 502 includes a first subset of coils 506 and a second subset of coils 508. Each coil 502 of the second subset of coils 508 is located in the middle of an adjacent coil of the first subset of coils 506 in the circular array.

The first subset of coils 506 is configured to generate a respective first magnetic field in use. In particular, the excitation means of the magnetic field generator 500 is configured to deliver a varying voltage over the first subset of coils 506, thereby generating a corresponding first magnetic field. The excitation frequency is selected such that the corresponding first magnetic field is capable of interacting with the susceptor of the food container to heat the food container.

The second subset of coils 508 is configured to generate a corresponding second magnetic field in use. In particular, the excitation means of the magnetic field generator 500 are configured to deliver a varying voltage over the second subset of coils 508, thereby generating a corresponding second magnetic field. The excitation frequency is selected such that the respective second magnetic field is different from the first magnetic field and such that the respective second magnetic field is capable of interacting with the stirrer of the food container.

Since the coils 502 of the second subset of coils 508 are located in the middle of adjacent coils 502 of the first subset of coils 506, the interaction of the food preparation device with the susceptor and the stirrer of the food container may be achieved at a common radial distance. Furthermore, such a device may be a relatively compact arrangement and/or a device having fewer component parts, for example, in which one array is configured to interact with the susceptor and one array is configured to interact with the stirrer, as compared to a device having nested annular arrays.

The food product container 200 of fig. 5 may be adapted for use with the magnetic field generator 500 of fig. 9 when the food product container 200 comprises a susceptor portion 228 having a shape as shown in fig. 6 a. In particular, the food container 200 may be placed on the contact surface 102 of the food preparation device 100 such that the protrusions 234 of the susceptor portion 228 are aligned with the coils 502 of the first subset of coils 506, such that the first magnetic field generated by the first subset of coils 506 may interact with the susceptor portion 228 to cause heating of the receiving space 226 of the food container 200. The plurality of coils 502 define a first convex magnetic assembly for interacting with a second convex magnetic assembly defined by the susceptor portion 228, as previously described.

It will be appreciated that some of the modifications of the stirrer 210 described above may be employed to facilitate use with the magnetic field generator 500 of fig. 9. In particular, the length of the plurality of arms 238 may extend such that the bar magnet 242 is located at substantially the same radial distance as the protrusion 234, or the number of magnetic poles present in the agitator 210 may vary such that the magnetic poles of the agitator 210 are always predictable to allow rotation. In this case, when placed on the contact surface 102 of the food preparation apparatus 100, the coils 502 of the second subset of coils 508 may be located in the middle of the adjacent protrusion 234 of the susceptor portion 228 of the food container 200, e.g. such that the non-susceptor portion covers the coils 502 of the second subset of coils 508. This may facilitate interaction between the second magnetic field generated by the second subset of coils 508 and the agitator 210 to rotate the agitator 210 within the receiving space 226 of the food container 200.

In some embodiments, it may not be necessary for all coils 502 of the second subset of coils 508 to cause rotation of the agitator 210 at the same time. In this way, the coils 502 of the second subset of coils 508 may be sequentially energized to drive the agitator 210 in rotation. In such an embodiment, the coils 502 of the second subset of coils 508 may be considered to have a first excitation state in which the coils 502 generate their respective second magnetic fields and a second excitation state in which the coils 502 do not generate their respective second magnetic fields. In some embodiments, the coils 502 of the second subset of coils 508 may have a third energized state in which they interact with a susceptor portion of the food product container to heat the food product container. In such embodiments, it may be necessary to modify the susceptor portion and/or the stirrer as compared to the previous embodiments, for example by providing a stirrer which also comprises susceptor material.

Although a plurality of coils 502 are shown only schematically in fig. 9, in practice a plurality of coils 502 may be wound on the core for guiding the magnetic flux generated in use. Fig. 10 and 11 illustrate an example embodiment utilizing a magnetic core having a plurality of coils 502. In the embodiment of fig. 10, each of the plurality of coils is wound on a core back 510 of a separate magnetic core, each magnetic core including a pair of upwardly extending poles 512. In the embodiment of fig. 11, each of the plurality of coils 502 is wound on a common annular core back 514, and a plurality of pairs of poles 516 extend upwardly from the common annular core back 514. It will be appreciated that the number of coils 502 has been reduced in the embodiment of fig. 10 and 11 for ease of illustration, and that the number of coils and poles may be selected based on, for example, the susceptor portion of the food container.

Fig. 12 illustrates another embodiment of a suitable magnetic field generator 600. The magnetic field generator 600 of fig. 12 utilizes the same plurality of magnetic cores 106 as the magnetic field generator 104 of fig. 2 (not described here for the sake of brevity), but differs in that each magnetic core 106 is wound with a first coil 602 and a second coil 604, respectively. A first coil 602 is wound around the pole 126 of the first pole pair, here the left hand pole 126, and a second coil 604 is wound around the second arm 120.

In use, the first coil 602 is energized to produce a first magnetic flux circuit, i.e. a first magnetic field, at the pole 126 of the first pole pair, and the second coil 604 is energized to produce a second magnetic flux circuit, i.e. a second magnetic field, at the pole 130 of the second pole pair. Since separate coils are used to generate the first and second magnetic fields, the energization of the first coil 602 and the second coil 604 may be selected such that the first and second magnetic fields provide different functions when interacting with the food container 200 in use, such as providing heating and rotation as described above. This arrangement provides two independent magnetic circuits while using a common core back. In some embodiments, the first coil 602 is excited at a higher frequency than the second coil 604.

An alternative embodiment of a food container 700 for use with the magnetic field generator 104 of fig. 2 is schematically illustrated in cross-section in fig. 13.

Food container 700 of fig. 13 is substantially identical to the food container of fig. 5, except for the form of food-holding basket 702 and stirrer 704.

Food-holding basket 702 includes a base 706, a sidewall 708 extending upwardly from susceptor 706 to define a housing 710, and a plurality of legs 712 extending downwardly from base 706. The length of the legs 712 is such that the base 706, and thus the housing 710, is positioned within the receiving space 226 above the agitator 704. This divides the receiving space 226 into a liquid storage portion 714 located below the base 706 and a food receiving portion defined by the housing 710 located above the base 706. The base 706 thereby acts as a food holding surface. The base 706 and side wall 708 have a plurality of apertures that allow liquid to flow from the liquid storage portion 714 to the housing 710 and vice versa.

The agitator 704 has a form sufficient to transfer droplets from the liquid storage portion 714 to the housing as the agitator 704 rotates within the liquid storage portion 714, for example using appropriately shaped blades or the like.

In use, a food item is placed in the housing 710, a liquid (e.g., water) is placed in the liquid storage portion 714 of the food container 700, and the food container 700 is placed on the food preparation apparatus 100 of fig. 2, e.g., the first and second male magnetic assemblies interact to guide the food container 700 to a position on the contact surface 102 of the food preparation apparatus 100. The food container 700 is positioned on the contact surface 102 such that the susceptor portion 228 of the inner pan 204 covers the poles 126 of the first pair of poles of each magnetic core 106 and the non-susceptor portion 230 of the inner pan 204 and the agitator 704 cover the poles 130 of the second pair of poles of each magnetic core 106.

The coil 108 is energized by the energizing device 110 such that first and second magnetic flux loops, i.e., first and second magnetic fields, are generated at the poles of the first pair of poles 126 and the poles of the second pair of poles 130 of each magnetic core 106. As described above, the magnetic fields generated at the first pair of magnetic poles 126 and the second pair of magnetic poles 130 may have different characteristics due to the different magnetic resistances of the first and second magnetic flux circuits and the excitation frequency of the coil 108. In the present embodiment, the magnetic field generated at the first pair of magnetic poles 126 is a first varying magnetic field, i.e., an alternating magnetic field, that interacts with the susceptor portion 228 such that eddy currents are generated within the susceptor portion 228 and the liquid within the liquid reservoir 714 is heated.

The magnetic field generated at the second pair of magnetic poles 130 is a second varying magnetic field, i.e., an alternating magnetic field, that interacts with agitator 704, e.g., with the magnets of agitator 704, such that agitator 704 rotates within liquid storage portion 714. Rotation of agitator 704 within liquid storage portion 714 transfers droplets of heated liquid from liquid storage portion 714 to housing 710 where the droplets of heated liquid contact food items held within housing 710 and are used to cook the food items. The droplets of heated liquid may then be returned to liquid storage portion 710 through apertures formed in base 706 and sidewall 708 of food-holding basket 702. It should be understood that in some embodiments, the base 706 may not include an aperture and the sidewall 708 includes an aperture, or vice versa.

Thus, the food container 700 may be used in a splatter cooking method wherein food is cooked via interaction with heated droplets, such as heated water droplets. Such splatter cooking may have relatively high energy efficiency, as no phase change is required, but may generally require a longer cooking time. Because the food container 700 provides automation of the heating and movement of the agitator, the food container 700 may be left unattended in use, which may facilitate cooking methods such as splash cooking.

Furthermore, the interaction of the food container 700 and the male magnetic component of the food preparation device 100 may effectively lock the food container 700 to the food preparation device 100, e.g., such that rotation of the food container 700 relative to the food preparation device 100 is inhibited. This may be particularly beneficial in the event, for example, that the blender is caught by an item falling into the liquid storage portion 714, which would otherwise cause the food container 700 to rotate relative to the food preparation device 100. This may allow the food container 700 to be left unattended in use, which is particularly advantageous for splatter cooking methods, which typically require relatively long periods of time.

When the heated droplets are returned to the liquid storage portion 714 in use, a relatively small amount of liquid may be required, thereby improving liquid efficiency.

Food-holding basket 702 and stirrer 704 may be removed from food container 700, and in particular, inner pan 204. This may allow the food container to provide the blending function of the embodiment of fig. 2 and the splatter cooking function of fig. 13 while minimizing the required components, for example by allowing the outer pan 202 and the inner pan 204 to be used for both functions. In other embodiments, for example, the food-holding basket may be integrally formed with the inner pan 204, and the inner pan 204 may be replaceable to provide a different function.

Another alternative embodiment of a food container 800 for use with the magnetic field generator 104 of fig. 2 is schematically illustrated in cross-section in fig. 14.

The food container 800 shares the outer pan 202, lid 206, handle 208, and related features of the food container embodiment of fig. 5, but differs in the form of the inner pan 802 and stirrer 804. In some embodiments, the inner pan 802 of the food container of fig. 14 may have a different diameter than the inner pan 204 of the food container 200 of fig. 5. This may allow for a nested arrangement of the inner pan within the outer pan 202 for storage. In use, the food preparation device 100 may sense which inner pan is received within the outer pan 202, or may be provided with such information, for example, via user input.

The inner pan 802 includes a generally circular base portion 806 and a sidewall 808 extending upwardly from the base portion 806 to define a receiving space 810. The susceptor portion 806 is hollow and houses a magnetic assembly 812 of the stirrer 804.

The agitator 804 includes a magnetic assembly 812 and a plurality of chopping blades 814 fixedly attached to the magnetic assembly 812. The beater 804 as shown in fig. 14 has a magnetic assembly 812 received in the base portion 806 of the inner pan 802 and a plurality of chopping blades 814 received in the receiving space 810, the plurality of chopping blades 814 being connected to the magnetic assembly by a connector portion 816. However, it should be understood that in other embodiments, the magnetic assembly 812 may include a housing that enables the magnetic assembly 812 and the plurality of shredder blades 814 to be located within the receiving space 810.

As shown schematically in fig. 15, the magnetic assembly 812 includes an annular array of bar magnets 818. The connecting portion 816 is a rigid connection and may include a shaft retained within a bearing assembly.

In use, the food container 800 is placed on the food preparation device 100 of fig. 2 such that the bar magnet 818 of the stirrer 804 overlies the first pair of poles 126 of each magnetic core 106.

The coils 108 are energized by the energizing device 110 such that a magnetic flux circuit, i.e., a magnetic field, is generated at the pole 126 of the first pair of poles of each core 106. In this embodiment, the magnetic field generated at the first pair of magnetic poles 126 is a varying, i.e., alternating magnetic field that interacts with the bar magnet 818 of the agitator 804 to drive the agitator 804, and thus the plurality of shredding blades 814, within the receiving space 810 to rotate. This allows food, such as vegetables, etc., to be shredded when placed in the receiving space 810 of the food container 800.

Here, the first pair of magnetic poles 126 of the magnetic field generator 104 is used to provide a rotational function, in contrast to the use of the second pair of magnetic poles 130 of the magnetic field generator to provide a rotational function for the food container of fig. 5. The poles of the first pair of poles 126 are located at a larger radius than the poles of the second pair of poles 130 and therefore may provide a greater torque, which is beneficial when using the shredding blade 814.

As schematically shown in fig. 15, the food container 800 may also be provided with a convex magnetic assembly 820, which may also be a susceptor material, which interlocks with the convex magnetic assembly defined by the magnetic core 106 of the magnetic field generator 104, e.g., with the magnetic poles 130 of the second pair of magnetic poles 130, to prevent rotation of the food container 800 relative to the food preparation device 100 in a manner similar to that previously described with respect to the food container 200 of fig. 5.

Another alternative embodiment of a food container 900 for use with the magnetic field generator 104 of fig. 2 is schematically illustrated in cross-section in fig. 16. Here, the food container 900 takes the form of a blender jug.

The food container 900 includes a cylindrical base portion 902, a sidewall 904 extending upwardly from the base portion 902 to define a receiving space 906, a handle 908, a lip 910, a stirrer 912, and a male magnetic component 914. The lip 910 enables the contents of the food container 900 to be poured out of the receiving space 906, while the handle 908 is shaped so that it can be grasped by a user. Here, the base portion 902, side wall 904, handle 908, and lip 910 may be formed of a thermally insulating material, such as plastic, as part of a single or multi-step molding process.

The stirrer 912 of the food container 900 of fig. 16 has substantially the same form as the stirrer 804 of the food container 800 of fig. 14, in particular comprises an annular array of bar magnets, as schematically shown in the embodiment of fig. 15. The base portion 902 is hollow in nature and houses a magnetic assembly 916 of the agitator 912, including a bar magnet, with the chopping blades 918 of the agitator 912 located in the receiving space 906. The male magnetic component 914 has substantially the same structure as the male magnetic component 820 shown in fig. 15 and is embedded in the lower wall of the base portion 902.

In use, the food container 900 is placed on the food preparation apparatus 100 of fig. 2 such that the bar magnet of the agitator 912 overlies the poles 126 of the first pair of poles of each magnetic core 106 and the male magnetic component 914 overlies the poles 130 of the second pair of poles of each magnetic core 106.

The coils 108 are energized by the energizing device 110 such that a magnetic flux circuit, i.e., a magnetic field, is generated at the pole 126 of the first pair of poles of each core 106. In this embodiment, the magnetic field generated at the first pair of magnetic poles 126 is a varying, i.e., alternating magnetic field that interacts with the bar magnets of the agitator 912 to drive rotation of the agitator 912, and thus the rotation of the shredding blade 918 within the receiving space 906. This allows food, such as vegetables or fruits, to be shredded when placed in the receiving space 906 of the food container 900. The convex magnetic assembly 914 interacts with the magnetic flux circuit (i.e., magnetic field) generated at the pole 130 of the second pair of poles of each magnetic core 106 to lock the food container 900 to the contact surface 102 of the food preparation device 100, e.g., such that rotation of the food container 900 relative to the contact surface 902 is inhibited.

In some embodiments, the food container 900 may be provided with a gear arrangement connecting the magnets of the agitator 912 to the plurality of chopping blades 918. This may provide further torque increase while reducing speed.

Fig. 17 and 18 schematically illustrate another alternative embodiment of a food container 1000 for use with the magnetic field generator 104 of fig. 2.

The food container 1000 includes a generally circular base 1002 and a sidewall 1004 extending upwardly from the base 1002 to define a receiving space for containing food items. A plurality of filaments 1006 made of a ferrous material, such as an elongated strip of ferrous material, are applied to the base 1002 and the side wall 1004. In particular, each filament 1006 is a continuous filament that extends along the base 1002 and up the sidewall 1004. The plurality of filaments 1006 define a plurality of poles P1-P12 of a convex magnetic assembly on the susceptor and base 1002.

For example, when considering the filaments defining pole P1 and pole P9, the continuous nature of filament 1006 can be seen. Specifically, filament 1006 extends from an upper region of sidewall 1004 to base 1002 at pole P1, extends through base 1002 from pole P1 to pole P9, and extends from pole P9 along sidewall 1004 to an upper region of sidewall 1004. As shown, the plurality of filaments 1006 extend substantially the entire height of the sidewall 1004. The plurality of filaments 1006 are positioned along the base 1002 such that the circular region 1008 is located at the center of the base 1002. The circular region 1008 is formed of a non-susceptor material, such as a non-ferrous material that allows the passage of the magnetic field generated by the magnetic field generator 104. In use, a stirrer, such as stirrer 210 of the embodiment of fig. 5, may be placed in the receiving space above circular area 1008.

In use, the food container 1000 is placed on the food preparation device 100 of fig. 2, e.g., the corresponding male magnetic components interact to guide the food container 1000 into position on the contact surface 102 of the food preparation device 100. The food container 1000 is positioned on the contact surface 102 such that the susceptor defined by the plurality of filaments 1006 overlies the poles 126 of the first pair of poles of each magnetic core 106 and the circular region 1008 and stirrer 210 of the food container 1000 overlies the poles 130 of the second pair of poles of each magnetic core 106.

The coils 108 are energized by the energizing device 110 such that first and second magnetic flux loops, i.e., first and second magnetic fields, are generated at the poles of the first pair of poles 126 and the poles of the second pair of poles 130 of each magnetic core 106. As described above, the magnetic fields generated at the first pair of magnetic poles 126 and the second pair of magnetic poles 130 may have different characteristics due to the different magnetic resistances of the first and second magnetic flux circuits and the excitation frequency of the coil 108. In the present embodiment, the magnetic field generated at the first pair of magnetic poles 126 is a first varying magnetic field, i.e., an alternating magnetic field, which interacts with the plurality of filaments 1006 such that eddy currents are generated within the plurality of filaments 1006 and the receiving space is heated. The magnetic field generated at the second pair of magnetic poles 130 is a second varying magnetic field, i.e., an alternating magnetic field, which interacts with the bar magnet 242 of the agitator (if present) such that the agitator rotates within the receiving space 226. In this way, the beater can be used to stir the foodstuff received in the receiving space.

Since the plurality of filaments 1006 extend up along the base 1002 and along the side walls 1004, a better heat distribution within the receiving space may be achieved compared to, for example, arrangements in which the susceptor does not extend up along the side walls 1004. For example, in view of the presence of the plurality of filaments 1006, heat may be conducted upward along the sidewall 1004. Because the plurality of filaments 1006 are relatively thin, the thickness of the base 1002 can be reduced, which can facilitate interaction with the magnetic field generated by the magnetic field generator 104, for example, by bringing the agitator 210 closer to the magnetic field generator.

Although not shown here, it is understood that a layer of insulating material may be provided on the base 1002 and/or the side walls 1004 to improve thermal efficiency and/or to increase user safety.

In each of the embodiments of the magnetic field generator described previously, a single toroidal arrangement of coils and cores has been described, for example corresponding to a single ring of an induction hob. Induction cooktops typically include more than a single ring, and it will be appreciated that the foregoing embodiments of the magnetic field generator can be extended to provide a food preparation apparatus 100 having a multi-ring structure.

An example of such a multiple ring structure 1100 is schematically illustrated in fig. 19.

Here, four magnetic field generators 104 according to the embodiment of fig. 2 are positioned as outer rings 1102. The inner ring 1104 includes an array of C-shaped magnetic cores 1106 that also share the first pair of poles 126, the coil 108, and the core back 114 of each outer ring 1102. Each C-shaped magnetic core 1106 includes a core back and a plurality of poles 1108 extending upwardly from the core back, e.g., in a direction toward the contact surface 102 of the food preparation device 100 (out of the page in fig. 19). Each core back of C-shaped magnetic core 1106 is wound with a respective coil 1110. In use, the coil 1110 of the C-shaped core 1106 and the coil 108 of the shared core 106 of the outer ring 1102 may be energized in accordance with a food container received on the contact surface of the food preparation device 100 to provide any of the heating, rotating or locking functions previously described.

The phase shift of the PWM can also be applied to the operation of the multiple loop structure 1100 of fig. 19 when multiple loops are operating simultaneously. Each of these loops may operate at the same or different PWM duty cycles depending on heating requirements (burst mode control is also applicable). The interaction of the four loops can be properly controlled to avoid periodic random combinations of coil currents that produce short-term high power supply input current values.

While several embodiments of the food container are described herein as having an outer pan, it will be appreciated that the outer pan is an optional feature that may provide increased safety or thermal efficiency, but the inner pan may be used alone if desired.

Claims

1. A food preparation apparatus comprising a magnetic field generator comprising a plurality of coils arranged in an annular array, and an excitation device configured to excite the plurality of coils, wherein the plurality of coils comprises a first subset of coils configured to generate respective first magnetic fields for interacting with susceptors of a food container, and the plurality of coils comprises a second subset of coils configured to generate respective second magnetic fields for interacting with an agitator of the food container, the plurality of coils being arranged such that the coils of the second subset of coils are located in the middle of adjacent coils of the first subset of coils.

2. A food preparation apparatus according to claim 1, wherein said excitation means is configured to excite said second subset of coils in a sequence such that each of said second subset of coils has a first excitation state in which the coil generates its second magnetic field and a second excitation state in which the coil does not generate its second magnetic field.

3. A food preparation apparatus according to claim 2, wherein at least one of the second subset of coils has a third energized state in which it is energized at a higher frequency than in the first energized state, such that it interacts with the susceptor of the food container to heat the food container in the third energized state.

4. A food preparation device according to any of the preceding claims, wherein the magnetic field generator comprises a magnetic core assembly, each of the plurality of coils being wound around a portion of the magnetic core assembly.

5. The food preparation apparatus of claim 4, wherein the magnetic core assembly includes a first plurality of pole pairs corresponding to the first subset of coils and a second plurality of pole pairs corresponding to the second subset of coils, the first plurality of pole pairs defining respective first flux paths for a first magnetic field and the second plurality of pole pairs defining respective second flux paths for a second magnetic field.

6. A food preparation device according to claim 4 or 5, wherein said magnetic core assembly comprises a plurality of discrete magnetic core portions arranged in an annular array, each discrete magnetic core portion comprising a core back and a plurality of arms extending from said core back.

7. A food preparation device according to claim 4 or 5, wherein said magnetic core assembly comprises a common annular back, each of said plurality of coils being wound on said common annular back.

8. The food preparation device of claim 7, wherein said magnetic core assembly comprises a plurality of arms extending from said common ring back, each of said plurality of coils wound on said common ring back between adjacent arms of said plurality of arms.

9. A food preparation device according to any of claims 4 to 8, wherein said magnetic core assembly comprises a convex magnetic core assembly.

10. A food preparation system comprising a food preparation apparatus according to any of the preceding claims, and a food container comprising a susceptor for interacting with the first magnetic field to heat a portion of the food container, and an agitator for interacting with the second magnetic field to move the agitator within the food container.