Patent Description:
In particular, the present invention relates to the sector of kitchen worktops and induction cooking.

Induction hobs are used to cook food at high temperatures, being normally inserted inside a recess in the kitchen worktop which is made of wood, stone, agglomerate stone, glass ceramic, etc..

A material which is particularly popular because of its aesthetic and structural features is sintered stone such as Lapitec®, an article manufactured in the form of plates consisting of ceramic mineral aggregates with dimensions of less than a few millimetres which are compacted by means of vacuum vibrocompression and sintered, after drying, at temperatures normally above <NUM>.

The induction hobs comprise an actual cooking surface on top of which the metal containers containing the food to be heated are placed, whereby said containers may be pots, pans or the like.

An inductor is positioned underneath the hob, for each heating area, while the induced article consists of said container to be heated, in particular the metal bottom which is sufficiently thick and necessarily made of ferromagnetic material so as to allow heating of the bottom and therefore the food.

As is well known, when the inductor is energized, an electromagnetic field is generated in the induced article, i.e. in the bottom of the container making contact with the overlying surface, as a result of magnetic induction.

The electromagnetic field generates induced currents which, as a result of the Joule effect, heat the bottom of the container. When the bottom of the container is heated, the food contained inside it is heated by means of conduction.

The food therefore is not heated directly (as occurs in the case of microwave ovens), but indirectly.

One of the main advantages of induction hobs is that of allowing energy savings compared to conventional systems such as gas or electric systems.

Moreover, in induction hobs, the cooking surface, since it is not made of electromagnetic material, is not heated directly by the inductor, but is heated by means of thermal induction from the bottom of the pot heated by the inductor.

In this description "pot" will be used to refer to a generic container for cooking food, this term referring not only to pots, but also to pans, etc..

The cooking times for heating the pots are significantly reduced and the response times following a variation in the heat intensity are practically instantaneous.

The induction surfaces (which are normally made of glass ceramic) are aesthetically attractive and, precisely because they are flat, are fairly easy to clean, even though it is well-known that dirt which is difficult to remove may become lodged in the space between the hob and the countertop inside which it is set.

In order to manufacture these hobs, non-ferromagnetic and therefore non-magnetic materials which have an optimum resistance to high temperatures and low thermal expansion coefficient are used.

It is clear that heating of the hob surface, if excessive, may in any case damage the material, resulting even in breakage thereof.

In particular, with regard to the resistance of the hob surface and its thermal expansion coefficient, the following two factors must be considered:.

It is clear that, the greater the final temperature reached by the surface and the greater the slope of the heating ramp, the greater will be the thermal shocks affecting the hob surface.

These shocks generate thermal expansion which could result in breakage of the material.

Usually glass ceramic induction hobs have a thickness of about <NUM>, which thickness is sufficient for providing the hob with a suitable mechanical strength even at the high temperatures mentioned above.

The induction hobs present on the market are equipped with a control and safety system which prevents operation of the hob when a temperature of the hob surface of <NUM> detected by a temperature probe - for example an NTC (negative temperature coefficient) thermistor located in the centre of the inductor and in contact with the bottom surface of the hob - is reached.

As mentioned above, heating of the hob surface is due to the phenomenon of thermal conduction between the bottom of the pot, which is subject to heating due to the induced currents, and the hob surface itself.

Since the bottom of the pot may reach temperatures higher than <NUM> in particular cooking conditions, the hob surface may also reach these temperatures at the points which make contact with the pot.

Another problem is due to the fact that, once cooking has finished and the pot removed from the hob surface, even though not heated directly, the hob remains in any case hot even for a fairly long period of time.

Therefore, there is the risk, in the event of accidental contact, of a person being scalded since it is not at all obvious that the hob is still hot.

Different solutions have been developed in order to overcome these problems and prevent the material from breaking.

For example, it is known to use removable protection elements (mats) made of insulating material to be positioned between the hob surface and the pot. These mats prevent the bottom of the pot from heating the hob surface, while allowing the bottom of the pot to be heated in any case by means of the inductor.

It is also known to provide continuous countertops in which a zone which may be heated by means of inductors is provided. The main advantage of these countertops is that there are no joints between which stubborn particles of dirt may become lodged.

However, these applications are limited to the heating of pre-cooked food so that normally they operate at fairly low temperatures, normally of less than <NUM>.

In fact the use of this solution for the proper cooking of food is not recommended, since the cooking zone is not entirely easy to identify and, moreover, the system could function, even with better operating conditions, without the use of the removable protection element.

A countertop for a kitchen furniture according to the preamble of appended claim <NUM> is known from <CIT>.

The object is to overcome the drawbacks of the prior art.

A first task of the present invention is to be able to provide a continuous countertop with an induction hob, preferably made of Lapitec®, without the risk of the hob breaking or being damaged owing to the high temperatures involved, and where use thereof does not pose any danger for the user.

Another object is to prevent the induction hob from becoming excessively hot during cooking so that, once the container has been removed, the danger of possible scalding following accidental contact is reduced.

The object and the tasks are achieved with a countertop for kitchen units having a hob according to claim <NUM>, and a kitchen furniture according to claim <NUM>.

The advantages and the characteristic features of the present invention will emerge clearly from the detailed description which follows of a number of examples of embodiment, provided by way of a non-limiting example, with reference to the attached drawings in which:.

Even though <FIG> show the induction hob <NUM> separately, it is to be understood that it is intended to be mounted on a countertop <NUM> of the type shown in <FIG> and <FIG>.

The hob <NUM> comprises a plurality of magnetic inductors <NUM> designed to be used for cooking food and located underneath a plurality of cooking areas <NUM> of said hob <NUM>, and a plurality of removable protection elements <NUM> designed to be positioned on top of said cooking areas <NUM>.

In accordance with a possible embodiment of the present invention, the magnetic inductor <NUM> may comprise means for detecting the pot resting on the hob surface, which are designed to transmit this information to a control unit for selectively controlling switching-on of the inductors depending on the form of the surface on which the pot rests.

The hob further comprises at least one safety device <NUM> designed to ensure the correct positioning of the removable protection elements <NUM>.

The purpose of the safety device <NUM> is to prevent the use of the induction heating at high temperatures without the use of the removable protection element and therefore avoid the risk of accidental damage to the hob surface and injury of the persons using the hob. Advantageously, the safety device <NUM> may have a dual function, allowing the electrical power to be supplied only if:.

Therefore, should the removable protection element <NUM> not be located over the cooking area <NUM> or should it not be correctly positioned, the electrical energization of the corresponding magnetic inductor <NUM> would not be allowed.

In fact, if the removable protection element <NUM> should not be positioned on the cooking area <NUM> or should it be positioned incorrectly, the hob <NUM> would not be suitably insulated and would therefore be heated excessively by the bottom of the pot <NUM> (shown in <FIG>) with the risk of breaking or creating danger for the user.

In accordance with the present invention, the safety device <NUM> uses radiofrequency identification, which below will be indicated by the abbreviation RFID (Radio Frequency IDentification). As is known, this technology is based on the identification and/or automatic storage of information relating to objects, based on the capacity for storage of data by particular electronic labels called transponders or tags and on the capacity of the latter to respond to remote interrogation by special fixed or portable apparatus called receivers or readers. This identification is performed by means of radiofrequency, via a receiver is able to read the information contained in the electronic tag interrogated.

As is known, an RFID system consists of three basic elements:.

The main element which characterizes an RFID system is the electronic tag which comprises:.

In accordance with alternative embodiments it may also comprise a battery if it has an active function rather than a passive function.

In accordance with the present invention the removable protection element comprises two electronic tags <NUM>, and the hob <NUM> comprises receivers <NUM>. The receivers are positioned underneath the hob.

For each electronic tag <NUM> inserted in the removable protection element <NUM> there is a corresponding receiver <NUM> positioned underneath the hob <NUM> and able to read the respective electronic tag.

<FIG> shows a possible embodiment of the hob according to the present invention, provided with four inductors <NUM>, and therefore four cooking areas <NUM>; each cooking area <NUM> is provided with a removable protection element <NUM> which has two electronic tags <NUM>. As can be seen from the figure, the electronic tags <NUM> are combined with two receivers <NUM> positioned underneath the hob (for this reason they are shown in broken lines).

Two electronic tags <NUM> are sufficient for positioning the removable protection element because there are only two possible positions of the element on the hob, these being diametrically opposite each other.

In accordance with alternative embodiments of the present invention, the electronic tags <NUM> for each removable protection element <NUM> may be three in number, and therefore the hob <NUM> may be provided with three corresponding receivers <NUM>.

Only when the removable protection element has been placed on top of the hob <NUM> with its two electronic tags <NUM> located in the vicinity of the respective receiver <NUM> located below the hob, is activation of the hob enabled by a control unit (not shown), and the associated magnetic inductor will be energized.

The connections between the receivers and the control unit and the inductors will not be further described since they may be easily realized by the person skilled in the art. Advantageously, the use of several electronic tags and several receivers also allows control of the correct alignment of the removable protection element, and therefore the pot, with the inductor.

In accordance with the present invention, in the case of cooking areas <NUM> of the same size, the two receivers are located in the same relative position, while, in the case of cooking areas <NUM> of different size, the two receivers are arranged in a different position so as to be able to use the appropriate flat element, eliminating the risk of using an element which is no suitable for a given cooking area.

Therefore the safety device <NUM> not only has the function of ensuring that the removable protection element <NUM> has been placed on the induction surface and that it is positioned correctly, but also that the element used is that suitable for a given cooking area <NUM>.

The removable protection elements may have different dimensions depending on whether a single cooking area or a set of cooking areas is/are to be protected and enabled.

In the hob shown in <FIG> which is not according to the invention, the hob <NUM> is provided with only one removable protection element <NUM>, on top of the four cooking areas <NUM>.

The removable protection element is therefore provided with two electronic tags <NUM> and the hob is provided with two corresponding receivers <NUM>.

In accordance with a possible embodiment of the present invention, the hob <NUM> may be provided with a safety system (not shown in the attached figures) which prevents operation of the hob when a maximum temperature of the hob is reached. Advantageously, the hob may comprise an NTC sensor located in the centre of the inductor and in contact with the bottom surface of the hob. The safety system may for example interrupt the electric power supply to the inductors as soon as the temperature detected exceeds a critical maximum temperature which may be for example set at <NUM>.

Alternatively, a temperature-sensitive element could be incorporated in the electronic tag so that, if the measured temperature exceeds a limit value, the electric power supply to the cooking area concerned is immediately interrupted.

With reference to the removable protection element <NUM>, this is made of non-magnetic material so as to allow the electromagnetic radiation to pass through it and thus heat the container. The material must moreover have a good resistance to high temperatures, since it makes contact with the hot container. Finally, the material must be able to withstand all those substances and liquids, also in a heated state, which could come out of the pots and damage the material. The material must be such as to allow easy washing of the element, preferably in a dishwasher.

As regards the heat insulation, it should be noted that it depends on:.

The degree of insulation obtained with be all the greater the lower the heat conductivity of the material and the greater the thickness (obviously the thickness must be as small as possible so as not limit the effectiveness of the magnetic induction).

In accordance with a possible embodiment of the present invention, materials with a low coefficient of conductivity are used so as to reduce as far as possible the thickness of the removable protection element.

Advantageously, the removable protection element may be made of food-grade silicone.

It is known in fact that food-grade silicone has the following properties:.

Advantageously, the silicone used for manufacture of the removable protection element is characterized by a heat conductivity of about <NUM> Wm-<NUM>-<NUM>.

In accordance with a possible embodiment of the present invention, the thickness of the removable protection element may range between <NUM> and <NUM>, and is preferably in the region of <NUM>.

Moreover, the food-grade silicone used for manufacture of the removable protection element may be washed also in a dishwasher, is foldable and is resistant to temperatures ranging from -<NUM> to +<NUM>.

According to a possible embodiment of the invention, the removable protection element may be made with holes, or shaped or have incisions formed therein.

In the embodiments shown in <FIG> and the alternative hob not part of the present invention shown in <FIG>, the protection element comprises incisions <NUM> which extend radially and are angularly equidistant.

In accordance with a possible embodiment shown in <FIG>, the removable protection element <NUM> may be formed as a meshwork, i.e. with holes <NUM> which cover most of its surface. Owing to the incisions, shaped parts or holes, the removable protection element is not deformed and remains flat.

Moreover, air is an optimum insulating material and in particular has a degree of insulation <NUM> times greater than that of silicone, so that the insulating characteristics of a removable protection element provided with holes are even greater, resulting in the advantage of the hob being heated less.

With a system of this type, it is therefore advantageous to use Lapitec® as the material for manufacture of the continuous countertop <NUM> with induction hob. Lapitec® is a material which is very popular on the market, with optimum characteristics not only in terms of appearance, but also in terms of resistance to impacts, wear, cutting and acid or corrosive substances, being easy to clean.

Thus, the countertop <NUM> and the bob <NUM> may be made as a single sheet of sintered stone, i.e. sheet of Lapitec®.

Advantageously, the sheet of Lapitec® used may have a thickness less than or equal to <NUM>, preferably of between <NUM> and <NUM>, and even more preferably in the region of <NUM>.

Advantageously, it is possible to provide a kitchen furniture, not shown in the figures, comprising a countertop <NUM> and a hob <NUM> of the type described above, characterized by the fact that there is continuity of material between the at least one cooking area <NUM> and the countertop <NUM>.

Moreover, as has been seen, with the hob according to the present invention the risk of scalding in the event of accidental contact with the hob following use is also reduced.

It is also possible to use the conventional pots and pans used for induction ovens.

Finally, another advantage consists in the use of food-grade silicone which, having been tested for applications in the food sector, may also come into contact with the food without contaminating it. In particular, it may be washed in a dishwasher both because it is resistant to high temperatures and because it does not pose a health hazard, avoiding the release of harmful substances.

Another advantage arises from its good chemical resistance, including its resistance to acids, so that, in the event of spillage of liquids or substances during cooking, it is not altered in any way. Furthermore, owing to the high incision and tear resistance, it may be used in the kitchen without the risk of being damaged. Since it also has an excellent ageing resistance it has a relatively long working life. Finally, since it is flexible, it may be handled and folded without any damage.

In accordance with a possible embodiment of the present invention, the removable protection element may have a variable thickness. For example, it could have a greater thickness in the zones where the temperature reached is higher.

In the case of a removable protection element positioned in a single cooking area, it could be incorporated in the bottom of the pot <NUM> in order to ensure thermal separation between the bottom of the pot and the hob surface as for example shown in <FIG>.

Advantageously, the removable protection element could be glued and may then be replaced when worn.

Claim 1:
Countertop (<NUM>) for kitchen furniture comprising a hob (<NUM>) with a plurality of magnetic inductors (<NUM>) designed to be used for cooking food and located underneath a plurality of cooking areas (<NUM>) of said hob (<NUM>), said hob (<NUM>) further comprising a plurality of removable protection elements (<NUM>) designed to be positioned on top of said plurality of cooking areas (<NUM>);
wherein said hob (<NUM>) is provided with at least one safety device (<NUM>) designed to ensure correct positioning of the removable protection elements (<NUM>); and
wherein there is continuity of material between the cooking areas (<NUM>) of said hob (<NUM>) and the countertop (<NUM>);
characterized in that the safety device (<NUM>) uses RFID technology and comprises two electronic tags (<NUM>) provided on the removable protection elements (<NUM>), and two corresponding receivers (<NUM>) positioned underneath the hob (<NUM>) and in that each cooking area (<NUM>) is provided with a removable protection element (<NUM>) and in that cooking areas (<NUM>) of the same size have receivers (<NUM>) arranged in the same relative position and cooking areas (<NUM>) with different dimensions have receivers (<NUM>) arranged in different positions so as to be able to use the appropriate removable protection element (<NUM>).