Device for determining the presence and/or the temperature of a food preparation container positioned on a glass ceramic heater

Abstract: A device for determining the presence and/or the temperature of a food preparation container (5) positioned on a glass ceramic cooking hob (1), this latter comprising an upper surface (3) facing the container (5) and heater elements (8) preferably of radiation type, such as halogen lamps or the like, said device comprising a plurality of spacer means (25) interposed between the container (5) and the upper surface (3) of the cooking hob (1), said spacer means (25) supporting said container (5) and being associated with said hob (1), said means (25) enclosing sensor means (31) able to determine the presence and/or the temperature of said container (5), said sensor means (31) being connected to means (20) for controlling the operation of the heater elements (8) which on the basis of the determination made by said sensors (31) act on said heater elements (8).

Description: This invention relates to a device for determining the presence and/or the temperature of a food preparation container positioned on a glass ceramic cooking hob, this latter comprising an upper surface facing the container and heater elements, preferably of radiation type such as halogen lamps or the like, provided below the container-supporting hob plate in correspondence with a respective cooking zone. Various devices are known for determining the presence of a container (or saucepan) on the cooking hob or for determining the temperature of said saucepan, and controlling the heater element operation on the basis thereof. These devices are however not always able to perform both operations (of determining presence and temperature). Some of these known devices are however able to perform both functions via sensor elements for example of capacitive or inductive type. These known devices are of high constructional and operational costs which often limit their use to glass ceramic cooking hobs intended for a large number of users. In addition, these known devices often have the serious drawback of altering or at least disturbing the transfer of energy from the heater element or elements to the saucepan. In this respect, the fact that the sensors are in contact with and/or in the vicinity of the saucepan means that this latter is at least partly screened from the radiant energy originating from the heater element or elements provided below the surface on which the saucepan rests. US-A-3 209 106 discloses a device for determining the temperature of a food preparation container positioned on a hob of a surface heater which may be of metal coated with porcelain or other heat resistant material. The heat transfer member is slightly raised from the plane of the hob surface and its expansion and contraction actuates a switch to control the heating mechanism and therefore the temperature. FR-A-2 669 404 discloses a heating plate or a utensil for cooking provided with bosses to reduce the surface area of contact between the hob surface and the utensil inorder to reduce the amount of conductive heating produced therebetween. US-A-2 552 480 relates to an electrical heating system for controlling the heating units of cooking stoves and also for sensing the presence or absence of a cooking utensil. A resistance unit is located under the cooking utensil, pushed upwards against the utensil by a spring mechanism. An object of the present invention is to provide a device of the stated type by which both the presence of a saucepan on the glass ceramic hob in correspondence with the cooking zone and the temperature of said container during food preparation can be determined. A further object is to provide a device of the stated type which enables the operation of each heater element to be controlled on the basis of the measured temperature of the container positioned in the cooking zone corresponding to said element. A further object is to provide a device of the stated type which does not disturb the heating of the container during the preparation of the food contained in it. A further object is to provide a device of the stated type which allows easy cleaning of each cooking zone on the glass ceramic hob, is of high sensing reliability, is of low cost and is easily arranged within the cooking hob. These and further objects which will be apparent to the expert of the art are attained by a device in accordance with the introduction to the main claim, characterised as defined in the characterising part of that claim. The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which: Figure 1 is a perspective view of the top of a cooking hob according to the invention; and Figure 2 is a schematic section on the line 2-2 of Figure 1. With reference to said figures, a glass ceramic cooking hob is indicated overall by 1 and comprises a hob plate 2 with an upper surface 3 on which there are provided cooking zones 4 for receiving containers 5 (only one of which is shown in the figures) for food preparation. Usual heater elements 8, preferably of radiation type such as halogen lamps or the like, are provided below the hob plate 2 in correspondence with the cooking zones 4. Each heater element or halogen lamp 8 is connected to a power line 10 via electrical branches 11 and 12 connected to its ends 8A and 8B. A power regulator 15 of known type (such as a potentiometer) is connected into one of these branches to enable the feed power to the lamp 8 to be regulated by a corresponding knob 16 positioned on the surface 3 of the hob plate 2. Advantageously, this regulation of the power absorbed by the lamp (and consequently of the power emitted by this latter in the form of radiation) is achieved via a control unit 20 preferably of microprocessor type, to which all the knobs 16 of the cooking hob 1 are connected. The unit 20 is connected to the power regulator 15. Within each cooking zone 4 there is provided a plurality of spacer means in the form of hemispherical elements 25 arranged to support the containers 5 positioned on the cooking zones 4 and to maintain these containers raised from the surface 3. Specifically, each zone 4 comprises three hemispherical elements 25 arranged at the vertices of an equilateral triangle and comprising a hollow body 26 with an upper cap 27 of glass ceramic or similar material, said cap being connected in any known manner to a lower metal portion 29. This latter and said cap together define a cavity 30 housing a sensor 31 (of capacitive or inductive type) able to determine the presence of the container 5 on its associated hemispherical element 25 and the container temperature during the preparation of its contained food. Each hemispherical element 25 can contain one sensor 31, or alternatively a single sensor is provided for each plurality of hemispherical elements 25 associated with a corresponding cooking zone 4. The portion 29 acts as a shield for the sensor 31 by shielding it from the heat generated by the lamp 8. This sensor is connected to an electrical branch 33 which by passing through a hole 34 in the plate 2 connects the sensor to the unit 20. The hole 34 is formed through the plate 2 at a depression 36 provided in this plate and into which the portion 29 of the hemispherical element 25 is fixed (by any known means). Alternatively, the portion 29 can be connected to the plate 2 by one or more annular magnets 39 provided on the lower surface 40 of the plate 2 and fixed thereto in known manner. The magnet or magnets act on the portion 29 of the hemispherical element 25 to retain it associated with the plate 2. In this case, the connection between the unit 20 and the sensor 21 is made via an electric branch silk-screen printed on the plate 2, which is therefore not provided with a hole 34. Consequently, in this modification, the hemispherical element 25 is completely removable from the plate 2, this resulting in greater simplicity of construction and cleaning thereof. Removability of the hemispherical element 25 can however be achieved in known manner even if this element is of the type shown in the figures. It will now be assumed that the described glass ceramic hob of the embodiment shown in the figures is to be used. If there is no container 5 present on a considered cooking zone 4, the sensor or sensors present in this zone feed no electrical signal to the unit 20. As this signal is absent, a movable contactor 43 arranged to cooperate with fixed contacts 44 provided in the power line 10 is kept open by the unit 20. The lamp 8 is therefore unable to heat the zone 4. On the basis of a known comparison algorithm, the unit 20 does not close the contactor 43 until a signal arrives from the sensor or sensors 31, even if the knob 16 corresponding to this lamp 8 is rotated (in known manner) to operate it, hence this heater element is not activated. When a container 5 is placed on the zone 4, each sensor 31 generates a signal U which reaches the unit 20 via the electrical branch 33. This unit therefore closes the contactor 43 across the contacts 44 to allow the lamp 8 to be powered. The heater element can then be operated in the required manner by rotating the knob 16. When the temperature of the container 5 reaches a predetermined value defined by the angular position of the knob 16 on the plate 2, said value being ascertained in known manner by the unit 20 on the basis of the determination by the sensor 31, said unit 20 acts on the regulator 15 to reduce the heating power of the lamp 8. This does not depend on said angular position of the knob 16. If the temperature falls below said value, the unit 20 senses this via the sensor 31 and acts on the regulator 15 to set the heating power of the element or lamp 8 to the value defined by the angular position of the knob 16. The invention therefore enables the presence of the saucepan or container 5 on a cooking zone to be ascertained and the temperature of said saucepan (and hence by known comparison algorithms the temperature of its contained food) to be controlled. One embodiment of the invention has been described in detail. Modifications are however possible and are to be considered as falling within the scope of the present document as defined in the claims.

Claims: A device for determining the presence and/or the temperature of a food preparation container (5) positioned on a glass ceramic cooking hob, this latter comprising an upper surface (3) facing the container (5) and heater elements (8) preferably of radiation type, such as halogen lamps provided below the container-supporting hob plate (2) in correspondence with a corresponding cooking zone (4), characterised by comprising a plurality of spacer means (25) interposed between the container (5) and the upper surface (3) of the cooking hob (1), said spacer means (25) supporting said container (5) and being associated with said hob (1), with said means (25) there being associated sensor means (31) able to determine the presence and/or the temperature of said container (5), said sensor means (31) being connected to means (20) for controlling the operation of the heater elements (8) which on the basis of the determination made by said sensors (31) act on said heater elements (8) to regulate their operation. A device as claimed in claim 1, characterised in that the spacer means are elements (25) having a body (26) with which the sensor means (31) are associated, said body (26) comprising a portion (29), facing the upper surface (3) of the cooking hob, which is arranged to screen said means (31) from the heat generated by the heater elements (8). A device as claimed in claim 2, characterised in that the body (26) of the spacer means has a hollow part (30) and contains the sensor means (31) in this hollow part (30). A device as claimed in claim 3, characterised in that the body (26) of the spacer means (25) is of hemispherical shape and comprises a spherical part or cap (27) located at the top and arranged to cooperate with the food container (5), said part (27) being connected in known manner to the screening portion (29) facing the surface (3) of the cooking hob (1). A device as claimed in claim 1, characterised in that the spacer means (25) are removably associated with the cooking hob (1). A device as claimed in claim 5, characterised by comprising a magnetic connection between the spacer means (25) and the cooking hob. A device as claimed in claim 5, characterised by comprising silk-screen printed electrical connections provided on the hob plate (2) of the cooking hob to cooperate with the sensor means (31) in order to connect these latter to the control means (20). A device as claimed in claim 1 or 7, characterised in that the control means are a control unit (20), preferably of microprocessor type. A device as claimed in claim 8, characterised in that the control unit (20) controls the opening and closure of a movable contactor (43) connecting together fixed contacts (44) provided in the power line (10) to the heater elements. A device as claimed in claim 8, characterised in that the control unit (20) operates on a usual power regulator (15) for the heater elements (8). A device as claimed in claim 8, characterised in that the control unit (20) is connected to one or more knobs for operating the heater elements (8). A device as claimed in claim 1, characterised in that the sensor means (31) are a capacitive sensor. A device as claimed in claim 1, characterised in that the sensor means (31) are an inductive sensor. A device as claimed in claim 1, characterised in that the sensor means (31) are associated with a plurality of spacer means (25). A device as claimed in claim 1, characterised in that the sensor means (31) are associated with only one of the plurality of spacer means provided for each cooking zone (4). A device as claimed in claim 1, characterised in that the spacer means are arranged at the vertices of an equilateral triangle in correspondence with a respective cooking zone.

Inventors: ASJES RONALD JAN, FRANZETTI GIOVANNI, KOKKELER FRANCISCUS, MARITAN MARCO C O WHIRLPOOL IT, ASJES, RONALD JAN, FRANZETTI, GIOVANNI, KOKKELER, FRANCISCUS, MARITAN, MARCO, Asjes, Ronald Jan, c/o Whirlpool Italia s.r.l., Franzetti, Giovanni, c/o Whirlpool Italia s.r.l., KOKKELER, FRANCISCUS, C/O WHIRLPOOL ITALIA S.R.L., Maritan, Marco, c/o Whirlpool Italia s.r.l.
Applicants: WHIRLPOOL EUROP, WHIRLPOOL EUROPE B.V.
Application year: 1993
Main classification: H05B3
IPC codes: H05B3