Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2002-06-10
2004-05-04
Jeffery, John A. (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S521000, C099S385000, C099S331000
Reexamination Certificate
active
06730888
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns a method for controlling the grilling, or toasting, of a food product in a toaster, and more particularly the use of one or several photosensitive sensors for carrying out this control.
It is known, in bread toasting appliances, to provide a time delay that is adjustable by the user, in order to fix the cooking time for the bread. This simple method does not always give satisfactory results, notably because of lack of initial knowledge of the time necessary to obtain a given toasting or color for the bread.
Other systems propose a determination of the color of the bread during the course of toasting with the aid of a specific sensor measuring the reflectivity, produced by the bread, of a light signal.
The document WO89/01279 describes such a sensor using an electronic control circuit for an electric device for cooking food products having a maximalizing circuit intended to determine, by a first signal V
1
, the maximum level of light reflected by the food product, then to measure the light reflected by the food product leading to a second signal V
2
, the maximalizing circuit having an amplifier supplying a signal V
3
proportional to the difference between the V
2
and V
1
, a comparator permitting a comparison of V
3
with a preset signal V
B
, which is proportional to a desired cooking level. The comparator emits a signal at the end of cooking to deactivate the cooking when the preset signal and the third signal are substantially equal. The signal V
2
is constructed around a resistance whose value depends on the quantity of incident light. Such resistances are commonly called LDR.
Such a devices is rather complex and costly with regard to elements since it comprises several electrical signals to compare, amplifiers, comparators and necessitates the establishment of a comparison voltage value V
B
.
Moreover, from the standpoint of security, a conventional time delay requires a safety device detecting the start of burning of the bread and any presence of flames in the toaster.
In addition, when the power of the heating elements is substantial, it is necessary that the device have a significant response, a response that conventional time delays cannot provide.
BRIEF SUMMARY OF THE INVENTION
The present invention seeks to overcome these drawbacks by providing a simplified process for controlling the degree of browning of a food product disposed in a grilling appliance, by the evolution of the light coming from the food product being grilled.
The present invention is achieved with the aid of a method for controlling the grilling, or toasting, of a food product placed in a grilling appliance of the toaster or oven type, said appliance comprising, in particular, heating elements, a heating chamber, a grilling selector for adjusting the level of browning of the food product, means for stopping the supply of electricity to the heating elements when the level of toasting is achieved, said device having a light-receiving system composed of at least one photo-resistive element of the LDR type, the light reflected by the food product being grilled or toasted being brought up to the surface of said element(s), characterized in that it consists in measuring the evolution in time of a signal G representative of the light reflectivity of the food product, and converting at least one characteristic of that evolution into at least one of the grilling or toasting states of the food product.
According to the invention, one of the grilling or toasting states is manifested by a slope of the signal G stabilizing at a determined value, or by a zero slope, or by an inversion of the slope, or by a point of inflexion in the slope of the curve, or by a difference in the curve or in the slope of the curve by a certain amount with respect to said value for shorter times.
The grilling states being correlated with a particular evolution of the signal, this curve becomes universal and a simple calibration in the factory permits establishment of the desired relationships.
Advantageously, this method consists equally in determining the ambient temperature within the appliance, and in blocking a new cooking cycle when the value of the ambient temperature exceeds a predetermined value.
This particularity is notably important for high heating power levels being able to lead to, when numerous cycles are effectuated, a temperature elevation that could be dangerous for the user.
Advantageously, the method also consists in determining the signal representative of the light reflectivity at two instants that are close together and following the application of electricity to the heating elements in order to determine, according to the evolution of this signal, the presence or not of a food product in the heating chamber.
It can be, in effect, desirable, for example in the case of a toaster, to block the operation of the appliance when no slice is placed to be toasted in the heating chamber. A rapid decrease in the light reflectivity signal permits the absence of bread to be identified.
Advantageously, the method for controlling grilling consists equally in halting the supply of electricity to the heating elements when, following the start of delivery of electricity to said heating elements, the light reflectivity signal is below a predetermined value.
This system permits avoiding, on the one hand, regrilling a food product that has already been grilled, and, on the other hand, blocking the toasting of special breads, of which the presence of grains or other ingredient gives it a dark color. It is known that this bread is difficult to toast, the automatic toasting procedure such as described previously is thus not desirable.
Advantageously, the method for controlling grilling is associated with a method for controlling grilling with a time delay where different grilling states, determined by the grilling selector, correspond to cooking times calibrated in the factory.
Thus, the device for controlling by a photo-resistive element only determines certain grilling states or is used, for safety purposes, as a fuse.
Another object of the present invention, is to provide a low cost system permitting toasting of any type of bread, stale or frozen, by controlling the toasting color assumed by the bread, and this regardless of the parameters of use or characterization of the toaster: duration of stoppage between cycles, partial or complete loading of the bread carriage, variation of the power supply voltage, power and type of heating bars.
The present invention also has for its object a device for controlling the grilling of a food product placed in a grilling appliance of the toaster or oven type, said appliance comprising notably heating elements, a grilling selector permitting adjustment of the level of browning of the food product, means for stopping the supply of electricity to the heating elements when the grilling level is attained, a microcontroller, said device having a light receiving system composed of at least one photo-resistive element of LDR type, the light reflected by the food product being grilled being brought up to the surface of said element(s), inserted in an electronic circuit permitting measurement of a voltage, characterized in that this voltage is transformed into a signal G which can be the value of the resistance of the photo-resistive element or of one of the photo-resistive elements, or a magnitude proportional to said resistance, said signal being stored at successive instants in the microcontroller, in order to determine the evolution of said signal and to stop the heating elements according to at least one predetermined evolution criterion.
This device permits freedom from numerous variables determining the grilling of the food products and notably of bread and which can vary in an undesirable manner with the level of voltage of the supply mains, or according to the heating powers used or the aging of the heating elements, for example.
According to the invention, the predetermined evolution criteria represent different grilling states o
Browdy and Neimark , P.L.L.C.
Jeffery John A.
SEB S.A.
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