EP2194754A1

EP2194754A1 - Sensor arrangement for cookware detection

Info

Publication number: EP2194754A1
Application number: EP08021142A
Authority: EP
Inventors: Andrei Uhov; Roberto Giordano; Filippo Tisselli
Original assignee: Electrolux Home Products Corp NV
Current assignee: Electrolux Home Products Corp NV
Priority date: 2008-12-05
Filing date: 2008-12-05
Publication date: 2010-06-09

Abstract

Sensor arrangement (1) for determining the presence/absence and/or position of a metal containing cookware (9) with a heating element (8) of a cooking appliance (7), comprising metal sensitive first (2) and second sensors (3) designed for respectively generating first and second sensor signals and being positioned offset relative to each other, and a circuitry (6) designed for obtaining a differential signal value of the first and second sensor signals.

Description

The present invention in particular relates to a sensor arrangement for cookware detection.
Metal sensitive cookware detection systems are used for semi-automatically operating cooking hobs of household cooking apparatus. Such cookware detection systems are used for activating or deactivating a cooking hob dependent on the absence and presence, respectively, of the cookware on the cooking hob. If, for example, a cookware is removed from the cooking hob the cooking hob can be deactivated for security reasons and/or for saving energy. Likewise, it is possible to activate or deactivate heating circuits of a single cooking hob dependent on the position or coverage of the cookware compared to the cooking hob.
Such systems using capacitive or optical measurement principles are known from EP 0 374 868 A1 , EP 0 883 327 B1 , GB 2 335 551 A and US 6 259 069 B1 , for example. Optical measurement systems are suitable for non-metallic cookware, as well. In this case, there is the problem that the hob may be activated upon any object positioned thereon. This problem can be at least partially reduced to metal containing cookware if detection systems using capacitive measurement principles are used. Such systems can use metal induced changes of capacitors. Another possibility to selectively detect metal containing cookware consists in using inductive measurement principles. Here impacts of metal containing cookware on inductances are used for cookware detection. Such systems are known from DE 100 42 775 A1 , DE 600 28 485 and DE 601 19 016 , for example.
Starting from this, it is an object to provide a sensor arrangement for determining the presence/absence and/or position of a metal containing cookware, being easy to implement, reliable, effective in cookware detection and universally applicable. Further, a cooking appliance and a method of determining the presence/absence and/or position of a metal containing cookware shall be presented.
This object is achieved by claims 1, 8 and 11. Advantageous embodiments result from respective dependent claims.
In a first aspect of the invention, a sensor arrangement for determining the presence/absence and/or position of a metal containing cookware with a heating element of a cooking appliance is provided. The sensor arrangement comprises metal sensitive first and second sensors, preferably of inductive type. The first and second sensors are designed for respectively generating first and second sensor signals. As the first and second sensors are metal sensitive, the first and second sensor signals are indicative of metal containing cookware positioned - at least partially - on the heating element.
Further, a circuitry is provided, designed for obtaining a differential signal value of the first and second signals'. The differential signal value, being a compensation value of the first and second signal or representing their difference for example, can be used to determine the presence or absence of the metal containing cookware with the heating element. Alternatively, or in addition, it is possible to use the differential signal value for determining the position of the metal containing cookware relative to the heating element. In the latter case it is possible to use the differential signal value for selectively powering sub-heating elements of the heating element. Based on the finding that a cookware is present or absent, the heating element can be activated and deactivated, respectively. As can be seen, the sensor arrangement is for semi-automatically operating the cooking appliance, particularly for reasons of secure and energy effective operation of the cooking appliance.
In general, metal containing cookware can be recognized by signal changes with the first and/or second sensor signals. Such signal changes usually are relatively small compared to absolute signal values of the first and second sensors, complicating effective cookware detection and/or localization.
According to the invention, the differential signal value is used for cookware detection and/or localization. Hence, small signal changes can be observed nearly irrespective of the absolute signal values of the first and second sensors. Therefore, even small signal changes can be determined with high accuracy using common amplification techniques, for example. As a result, it is possible to reliably and accurately determine the presence/absence and/or position of the cookware. The sensor arrangement according to the invention can be easily implemented and be used with nearly any cooking appliance.
The first and second sensor can be of inductive type. In this case each sensor may comprise a receiver coil and a transmitter coil. The transmitter coils are designed for respectively generating electromagnetic fields for respectively inducing the first and second sensor signals in corresponding receiver coils. A metal containing cookware on or put on the heating element gives rise to changes in the first and/or second signal, depending inter alia on the distance between the respective first and second sensor and the cookware. As the first and second sensors are displaced from each other respective changes will in general be different, and hence the differential signal value, as for example the difference between the first and second signal, will also be changed.
The transmitter and receiver coils can, in general, be of any type and shape. In particular, they can be of rectangular coil type. Windings of corresponding transmitter and receiver coils can be arranged in a common plane. Each transmitter coil preferably surrounds the respective receiver coil. Such coils types and shapes allow for flat shaped and space saving sensor arrangements.
The first and second sensors and the circuitry can be designed such that absent any metal containing cookware the differential signal value is close to zero. This is of particular advantage if surroundings of the first and second sensors in their final mounting position are different with regard to non-cookware metal objects.
The sensor arrangement can be implemented with almost any heating element in particular with cooking hobs, and more specifically with hobs powered by electricity or gas. In this case, the first and second sensors can be positioned offset parallel to a plane spanned by the cooking bob. One of the first and second sensors can be positioned within an effective cooking hob area. The other one of the first and second sensors can be positioned at a border area or outside the effective cooking bob area. An effective cooking hob area shall be understood to be an area of the cooking hob, which area has a given size and can be selectively heated. A single cooking hob may comprise one or more effective cooking hob areas. A sensor arrangement may be provided for the cooking hob as a whole or for each effective cooking hob area.
The circuitry can make up a compensating circuit combination of the first and second sensor signals. In such a compensating circuit combination the first and second signal will greatly cancel out each other if no cookware is present, provided that values of first and second signals are widely similar. Cookware induced changes in the first and second signal will lead to a noticeable change in the differential signal value. If the first and second sensor signals are alternating current signals that are phase shifted by 180 degrees, for example, a bucking circuitry leads to a compensation of the first and second signals in absence of a cookware. Instead or in addition to bucking or compensating circuitries, electronic components for determining the differential signal from the first and second signals can be used.
In a second aspect of the invention a cooking appliance which can be a household cooking appliance is provided. The cooking appliance comprises at least one electricity or gas powered heating element and at least one sensor arrangement according to the first aspect of the invention. The at least one sensor arrangement is assigned to at least one of the at least one heating element. Here it is possible that one or more sensor arrangements are assigned to a single heating element. Further combinations are conceivable. As to advantages of the cooking appliance, reference is made to the advantages of the first aspect of the invention.
In a third aspect of the invention a method of determining the presence/absence and/or position of a metal containing cookware with a heating element of a cooking appliance according to the second aspect of the invention is provided. The method comprises the steps of:

generating the first and second sensor signals;
obtaining or determining a differential signal value of the first and second sensor signals; and
determining, as the case may be, the presence/absence and/or position of the cookware relative to the cooking element, using the differential signal value.

As already mentioned, using the differential signal value for determining the presence/absence and/or position of the cookware has some advantages as compared to using absolute signal values. Inter alia presence/absence and/or position can be determined more accurately. As to further advantages, reference is made to details given in connections with the first aspect of the invention.
If inductive first and second sensors comprising transmitter and receiver coils are used, the fist and second sensor signals can be generated by powering respective transmitter coils by alternating currents to generate respective electromagnetic fields. The electromagnetic fields in turn effect alternating induction currents, i. e. first and second sensor signals, in respective receiver coils.
If bucking or compensation circuits are used for obtaining the differential signal value, it is of particular advantage if the first and second sensor signals are phase shifted by 180 degrees. In this case it is possible that a simple summation of the first and second signals cancel out each other in absence of a cookware. Therefore the differential signal can be obtained in a simple way. Other possibilities for obtaining the differential signal are conceivable. For example it is possible to use electronic components designed for subtracting in-phase first and second sensor signals, for example.
The presence of a cookware can be determined by comparing the differential signal value with a preset threshold. If, for example, the differential signal value exceeds or is below the threshold, presence or absence of a cookware can be assumed. For determining the position of the cookware relative to the heating element it is possible to use information about a mounting position of at least one of the first and second sensors in combination with a signal value of the differential signal. For reasons of accuracy, it is of advantage if at least the mounting position of the sensor positioned within the cooking area is used.
Further aspects of the invention will be described with reference to the drawings, in which

FIG 1: illustrates a schematic representation of a sensor arrangement according to the first aspect of the invention;
FIG 2: diagrams signal behaviour over time for three selected signals of the sensor arrangement;
FIG 3: schematically illustrates a cooking appliance comprising a sensor arrangement according to FIG 1.

FIG 1 illustrates a schematic representation of a sensor arrangement 1 according to the first aspect of the invention. The sensor arrangement 1 comprises a metal sensitive first sensor 2 and a metal sensitive second sensor 3 positioned offset from the first sensor 2.
The first 2 and second sensors 3 are of inductive type. Hence each of the first 2 and second sensors 3 comprises a receiver coil 4 and a transmitter coil 5.
The transmitter coils 5 are connected in series. The receiver coils 4 are connected by circuitry 6 to make up a compensating or bucking circuit combination.
In the present case, both the transmitter coils 5 and receiver coils 4 are of rectangular coil type. Windings of the receiver coils 4 are arranged within windings of the corresponding transmitter coils 5. The windings of each sensor 2, 3 preferably lie in a common plane.
Upon powering the transmitter coils 5 with alternating current, corresponding electromagnetic fields will be generated at the windings of receiver coils 4. The electromagnetic fields induce alternating currents in the receiver coils 4, i. e. first and second sensor signals.
FIG 2 shows the signal behaviour over time of first and second receiver coil sensor signals induced by the electromagnetic fields of the transmitter coils 5. Abscissa and ordinate are given in arbitrary units (a.u.).
FIG 2a and 2b diagram in solid lines the first and second sensor signals of the first 2 and second sensors 3 in absence of any metal containing cookware. The first and second sensor signals show sinusoidal behaviour. Due to the bucking circuit combination of the receiver coils 4 the first and second signals are phase shifted by 180 degrees.
If no metal object, such as a metal containing cookware, is present, the first and second sensor signals compensate each other. Therefore a differential signal value of the first and second sensor signal is close to zero.
Let us now assume, a metal object is in proximity to the first sensor 2 not influencing the second sensor 3. The metal object will influence the inductance of the first sensor 2. This will result in a shift of the first sensor signal, as depicted by a dashed line in FIG 2a.
Due to the shift in the first sensor signal and still the same second sensor signal, the differential signal value will be no longer close to zero. Hence the differential signal value is representative of a metal object, such as a metal cookware, being present or absent, or more generally speaking in close proximity of the first sensor. The differential signal value can be amplified for more accurate detection of the presence of absence of a metal object.
The time course of amplified differential signal value is depicted in FIG 2c. In order to determine whether a metal object is present or absent, a preset threshold T can be used, as indicated in FIG 2c. If the absolute value of the differential signal value exceeds the threshold T the presence of a metal object is assumed. If the absolute value of the differential value is below the threshold T it is assumed that no metal object is present.
FIG 3 schematically illustrates a top view of a cooking appliance 7. The cooking appliance 7 is a household cooking appliance comprising two cooking hobs 8 which may be gas-powered hobs or of any other type.
A sensor arrangement 1 is assigned to each cooking hob 8. The sensor arrangements 1 make it possible to determine the presence or absence of a metal containing cookware 9 with the respective cooking hob 8. In this way cooking processes can be semi-automated. Further the operation of the cooking hobs 8 can be controlled for reasons of energy consumption and security reasons. The latter is of special advantage for gas-powered cooking hobs, as the gas-feed can be interrupted if the cookware is removed from the cooking hob 8.
As can be seen from FIG 3, the first 2 and second sensors 3 of each of the sensor arrangements 1 are positioned offset from each other in a plane below and parallel to a plane spanned by the respective cooking hob 8. In the present example the first sensors 2 are positioned within an effective cooking area of the respective cooking hob 8. The second sensors 3 are positioned outside the respective cooking area.
Positioning the metal containing cookware 9, like a pot for example, on the cooking hob 8 on the left-hand side in FIG 3 will influence the first sensor 2 and therefore change the first sensor signal as described on connection with FIG 2a. This change can be detected by means of the differential signal as described in connection with FIG 2. As the differential signal value exceeds the threshold T, the presence of a cookware can be assumed, and the cooking hob 8 can be activated. The sensor arrangement of cooking hob 8 on the right-hand side in FIG 3 is not significantly influenced by cookware 9. Therefore the respective differential signal value rests below the threshold T and the right-hand cooking hob 8 is kept inactivated.
The influence the cookware exerts on the first sensor 2 is inter alia dependent on the distance between cookware, i. e. metal object, and first sensor 2. The nearer the metal part of the cookware, the bigger the signal change and hence the bigger the absolute value of the differential signal value. These facts together with a known position of the first sensor 2 can be used to determine the approximate position of the cookware 9 relative to the cooking hob 8. It should be mentioned that the term "position" shall be interpreted broadly and not be read as "exact position". It will be understood that using more than one sensor arrangement 1 with a single cooking hob 8 the position of the cookware 9 can be determined more accurately. If the position of the cookware is known, the cooking hob 8 can be selectively activated which is of particular advantage if the cooking hob 8 has several heating zones that can be separately activated.
Although the invention has been described in connection with a household cooking appliance having two cooking hobs, the invention is not restricted to that kind of household cooking appliance.
From the discussion above, it becomes clear that the object of the invention is achieved by the invention as set out in the claims.

List of reference signs

1: sensor arrangement
2: first sensor
3: second sensor
4: receiver coil
5: transmitter coil
6: circuitry
7: cooking appliance
8: cooking hob
9: cookware

T: threshold

Claims

Sensor arrangement (1) for determining the presence/absence and/or position of a metal containing cookware (9) with a heating element (8) of a cooking appliance (7), comprising
- metal sensitive first (2) and second sensors (3) designed for respectively generating first and second sensor signals and being positioned offset relative to each other, and

- a circuitry (6) designed for obtaining a differential signal value of the first and second sensor signals.
Sensor arrangement (1) according to claim 1, each sensor (2, 3) comprising a receiver coil (4) and a transmitter coil (5) for respectively generating electromagnetic fields for respectively inducing the first and second sensor signals in the respective receiver coil (4).
Sensor arrangement (1) according to claim 2, the transmitter (5) and receiver coils (4) respectively being rectangular coils, windings of corresponding transmitter (5) and receiver coils (4) preferably lying in a common plane, each transmitter coil (5) preferably surrounding the respective receiver coil (4).
Sensor arrangement (1) according to at least one of claims 1 to 3, the heating element being a cooking hob (8), preferably a gas-powered cooking hob.
Sensor arrangement (1) according to at least one of claims 1 to 4, the first (2) and second sensors (3) and the circuitry (6) being designed such that absent any metal containing cookware (9) the differential signal value is close to zero.
Sensor arrangement (1) according to at least one of claims 1 to 5, the circuitry (6) making up a compensating circuit combination of the first and second sensor signals.
Sensor arrangement (1) according to at least one of claims 1 to 6, the circuitry (6) comprising an electronic component for determining the differential signal from the first and second sensor signals.
Cooking appliance (7), preferably household cooking appliance, comprising at least one electricity or gas powered heating element (8), at least one sensor arrangement (1) according to one of claims 1 to 7, the at least one sensor arrangement (1) being assigned to at least one of the at least one heating element (8).
Cooking appliance (7) according to claim 8, the first (2) and second sensors (3) being positioned offset in a plane parallel to a plane spanned by the heating element (8), preferably a cooking hob (8).
Cooking appliance (7) according to at least one of claims 8 and 9, one of the first (2) and second sensors (3) being positioned within an effective cooking hob area, the other one being positioned at a border area or outside the effective cooking hob area.
Method of determining the presence/absence and/or position of a metal containing cookware (9) with a heating element (8) of a cooking appliance (7) according to at least one of claims 8 to 10, the method comprising the steps of
- generating first and second sensor signals;

- obtaining or determining a differential signal value of the first and second sensor signals and

- determining, as the case may be, the presence/absence and/or position of the cookware (9) relative to the heating element (8), using the differential signal value.
Method according to claim 11, the fist and second sensor signals being generated by powering respective transmitter coils (5) of first (2) and second sensors (3) by alternating currents to generate respective electromagnetic fields effecting alternating induction currents in respective receiver coils 4.
Method according to at least one of claims 11 and 12, the first and second sensor signals are phase shifted by 180 degrees.
Method according to at least one of claims 11 to 13, wherein the presence/absence of a cookware (9) is determined by comparing the differential signal value with a preset threshold (T), and presence of a cookware (9) is assumed if the absolute value of the differential signal value exceeds the threshold (T).
Method according to at least one of claims 11 to 14, wherein in determining the position of the cookware (9) relative to the heating element (8) a mounting position of at least one of the first (2) and second sensors (3), preferably at least the mounting position of the one sensor (2) positioned within the effective cooking hob area, is used in combination with a signal value of the differential signal.