GB2520922A - Battery powered food or beverage induction heater - Google Patents

Abstract

A battery powered induction heater apparatus, comprising an LC tank circuit, an LC tank driver circuit, a timing circuit and a current sense circuit whereby in use the LC tank circuit is configured to produce a resonant frequency which is reached when the vessel containing the food or beverage product is place above it, the current sense circuit is configured to detect a current increase through the inductor of the primary windings, the timing circuit is configured to receive a signal from the logic circuit and to send control signals to the driver circuit, the driver circuit being configured to provide a pulsed wave signal to the LC tank circuit, the form of the pulsed wave signal being dependent upon the signals received from the timing circuit.

Description

BATTERY POWERED FOOD or BEVERAGE INDUCTION HEATER

DESCRIPTION

The present invention relates generally to a battery powered induction heater apparatus for keeping food and beverages warm.

Induction heating is a widely recognised method of heating / cooking food and has found use in keeping food and beverages warm generally when the induction heating elements are powered by mains electricity.

In many applications it is desirable to keep food or beverages that have been prepared at a warm temperature until the person eating/drinking them is ready to consume them.

A typical example of this would be in a hospital setting where a patient may have a meal prepared for them but not be ready to consume the meal and thus it is desirable to maintain the meal at a temperature suitable for consumption.

There are many other examples where is it desirable to keep food or beverages at an above ambient temperature until they are consumed.

In many such applications is would be desirable to maintain the temperature of the food or beverage without the need for mains powered electrical devices.

It would therefore be desirable to have an improved apparatus for providing a means of maintaining the temperature of a food or beverage by means of a battery powered induction heating process.

In a first aspect, the invention provides a battery powered induction heating apparatus, for use in maintaining the temperature of a food or beverage in a vessel placed above the apparatus, the apparatus comprising an [C tank circuit, an [C tank driver circuit, a timing circuit and a current sense circuit whereby in use; the LC tank circuit is configured to produce a resonant frequency which is reached when the vessel containing the food or beverage product is placed above it, the current sense circuit is configured to detect a current increase through the inductor of the primary windings, the timing circuit is configured to receive a signal from the current sense circuit and to send control signals to the driver circuit, the driver circuit being configured to provide a pulsed wave signal to the LC tank circuit, dependent upon the signals received from the timing circuit.

The LC tank circuit comprises a coiled inductor wound in a circular fashion.

In a preferred embodiment the coiled inductor comprises a number of ferrite magnetic cores positioned underneath the coiled inductor and configured to direct

and concentrate the magnetic field above the core.

In an especially preferred embodiment there are six magnetic ferrite cores positioned approximately uniformly around the diameter of the coiled inductor.

In a preferred embodiment the coiled inductor is positioned between 7mm and 10mm below the surface on which the vessel is positioned.

In an especially preferred embodiment the coiled inductor is positioned between 8.2mm and 8.8mm below the surface on which the vessel is positioned.

In a preferred embodiment the system resonance of the LC tank circuit is configured to be between 24Khz and 28Khz.

In an especially preferred embodiment the system resonance of the LC tank circuit is configured to be between 25.8Khz and 26.2Khz.

In a preferred embodiment the inductance of the LC tank circuit is between 70 and pH.

In a preferred embodiment the battery cell voltage is 3V and there are at least 6 cells providing a total battery voltage of 18V.

In a preferred embodiment the LC tank driver circuitry comprises a half bridge coil driver circuit.

In an especially preferred embodiment the half bridge coil driver circuitry provides power by means of an insulated gat bipolar transistor.

In a preferred embodiment the timing circuit comprises a microcontroller configured to produce an output through a pulse width modulated signal interface at approximately the system resonance of the [C circuit.

In a preferred embodiment the duty cycle of the pulse width modulated signal output of the microcontroller is dynamically adjusted in response to the current signal as detected by the current sense circuit.

In this manner, the apparatus is able to maintain the temperature of food or a beverage contained in a vessel placed above the induction coil for a period determined by the power stored by the batteries.

This has the advantage that is it easier to make the induction heater in a portable format for use in mobile catering applications.

This further has the advantage that it is possible to configure the apparatus to maintain the food or beverage at an approximately constant temperature, without further heating or cooking the food or beverage. This is especially advantageous in situations where the food or beverage is being consumed by vulnerable persons such as patients in hospital, elderly people in a nursing home or children in a school etc. The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.

Figure 1 shows a high level block schematic drawing of the electronic components and configuration of one embodiment of the apparatus.

Figure 2 shows an electronic schematic drawing of the half bridge coil driver circuit of driver circuit one embodiment of the apparatus.

Figure 3 shows an electronic schematic drawing of frequency generation of the timing circuit of embodiment of the apparatus.

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn to scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally or spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components or groups thereof. Thus, the scope of the expression "a device comprising a means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B. Similarly, it is to be noticed that the term "connected", used in the description, should not be interpreted as being restricted to direct connections only. Thus, the scope of the expression "a device A connected to a device B" should not be limited to devices or systems wherein an output of device A is directly connected to an input of device B. It means that there exists a path between an output A and an input B which may be a path including other devices or means. "Connected" may mean that two or more elements are either in direct physical or electrical contact, or that two or more elements are not in direct contact with each other but yet still co-operate or interact with each other.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention.

Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may refer to different embodiments. Furthermore, the particular features, structures or characteristics of any embodiment or aspect of the invention may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment.

Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form yet further embodiments, as will be understood by those skilled in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practised without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this

description.

In the discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of the values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.

The invention will now be described by a detailed description of several embodiments of the invention. It is clear that other embodiments of the invention can be configured according to the knowledge of persons skilled in the art without departing from the true spirit or technical teaching of the invention, the invention being limited only by the terms of the appended claims.

Figure 1 shows a high level block schematic drawing of the electronic components and configuration of one embodiment of the apparatus.

is the LC tank circuit.

The LC tank circuit comprises a coiled inductor of diameter 150mm for a larger version (for maintaining temperature of food in a vessel). A smaller version is of diameter 80mm for maintaining the temperature of a beverage in a mug.

The inductance otthe coil is 100 pH and the insulation is chosen to withstand a peak voltage of 300V. The coil can withstand 5.8 A of current.

The coil contains 6 ferrite magnetic cores, positioned below the coil to direct and

concentrate the magnetic field above the coil.

The vessel containing the food or beverage is positioned between 8.2mm and 8.8mm above the coil.

The LC tank circuit is driven by means of a driver circuit 20. The driver circuit comprises a IGBT 60 (insulated gate bipolar transistor) configured to provide power to the LC tank circuit. Further detail of the driver circuit is provided in Figure 2 described below.

The current sensing circuit 30 is used to detect vessels on the induction cooktop.

When the vessel is kept on top of the induction cooktop, the current sense circuit detects the current increase in the primary windings through the inductor and signals to the timing circuit 40 to take the appropriate action. When there is no vessel on top of the induction cooktop the current sense disables the output of the timing circuit.

Power to drive the driver circuitry and general electronic system power is provided by the batteries 50. Six NCR1865OA batteries are provided to provide a total of 18V for the driver circuitry. The 1 8V is stepped down and regulated for the power of the electronic components not in the driver circuitry. The batteries have been selected to maintain the food or beverage for 20 mins at a temperature of 60 deg C. The timing circuitry 40 is used to generate the desired frequency of 27kHz for driving the [C tank circuit 10 through the driver circuit 20. The timing circuit 40 will wake up every 500msec and check the signal from the current sense circuit 30. If the timing a circuit detects the signal from the current sensing circuit then it will drive the LC tank circuit at maximum power. If the current sensing circuitry signal is absent then the timing circuit 40 will go to sleep again until it is woken up after 500 msec.

A detailed configuration of the timing circuitry 40 using a P1C16F1933 microcontroller is shown in Figure 2.

Figure 2 shows an electronic schematic drawing of the half bridge coil driver circuit of driver circuit one embodiment of the apparatus.

Figure 3 shows an electronic schematic drawing of frequency generation of the timing circuit of embodiment of the apparatus.