HEATING APPLIANCE

Abstract: A cooking appliance (1) has a sensor (9) for detecting vapor gen­ erated from heated food (3) and a control circuit (10) which executes arithmetic operation on the heated state of food (3) according to signal outputs from the sensor (9) and controls the heating source (7) on the basis of the arithmetic operation result. The control circuit (10) is operated so as not to read signal outputs from the sensor (9) for a specified period of time after the food (3) is reversed and/or its position is changed before the sensor (9) detects the heated state detection point.

Description: Background of the Invention The present invention relates to a cooking appliance as a microwave oven and an electric oven for heating objects including food. Conventionally, the microwave oven with moisture sensor determines that the food is completely heated by detecting vapor amount generated from the heated food. The output from the moisture sensor increases as vapor is generated from the heated food. When the output reaches a specified value (detection point), additional heating time required for completing the food is calculated on the basis of the constant stored in the LSI. The oven then continues heat­ ing the food for the calculated period of time and stops heating so that the most optimally heated food can be ob­ tained. The constant is different between foods. For a certain kind of food, the user may be required to open the oven door in the middle of the heating process and to re­ verse and/or change the position of the food for more uni­ form heating. Usually, this intermediate food handling operation is carried out when the sensor output reaches the detection point level. For some foods, however, the intermediate food handling operation may be necessary at a particular time. Frozen Hamburger Patties which are among the list of foods to be cooked by a sensor-equipped oven is an example. They needs to be reversed and/or moved in the middle of cooking so as to be uniformly heated. The sensor output increase for this food is, however, very slow. If the food is heated until the output reaches the detection point, therefore, it may be overheated locally, depending upon the quantity. If the food is reversed and/or moved at this stage, optimally heated food cannot be expected. That is, depending upon the quantity, the food may be required to be reversed and/or moved earlier than the detection point. One to three frozen hamburger patties can be optimally cooked if they are reversed and/or moved at the detection point. Four to six hamburger patties could be overheated locally if they were not moved until the detection point; they must be moved earlier than the detection point. Fig. 2 shows the relationship between sensor output and heating time for four or more hamburger patties. They are supposed to be heated each in a case. Here, the detection point level of sensor output is considered to be 10 bits. The oven is designed to carry out additional heating after the sensor output reaches 10 bits. When the oven door is opened to take out the ham­ burger patties and reverse and/or change the positions in the middle of heating, part of vapor generated from the food and accumulated within the heating chamber flows out of the oven, so that the output of the detector sensor drops. It begins rising when the food is returned and heated again in the oven. Therefore, if this intermediate food handling operation is conducted before the sensor output reaches the detection point, the time required for the output to reach the detection point is a little longer than that for the case where the oven door is not opened until the detection point is reached. The arithmetic operation for calculating the additional heating time required after the detection point is reached takes account of this time lag. If this intermediate food handling operation is carried out before the detection point is reached, not outside the oven but in the oven, vapor and heat accumulated within the case are released all at once into the heating chamber when the case covers are opened. The vapor thus released partly flows into the exhaust duct leading to the detector sensor which is installed immediately above the heating chamber. Moreover, the magnetron cooling fan which generates air stream in the heating chamber stops, when the door is opened, causing the vapor to stay in a part of the exhaust duct. If the door is closed and the heater is actuated with this state, the magnetron is energized and the magnetron cool­ ing fan starts operating. This generates air current which sends the vapor staying in the exhaust duct to the detector sensor. When the sensor output at the intermediate food handling operation time (TA) is closed to the detection point as shown in Fig. 2, the sensor output will reach the detection point immediately after the heating is resumed. As a result, the oven will be turned off before the food is sufficiently heated. Summary of the Invention To overcome the above conventional problem, an object of the present invention is to provide a cooking appliance capable of heating food optimally even if the oven door is opened to reverse and/or change the position of the food in the heating chamber at a specified time in the middle of the heating process before the sensor output reached the detec­ tion point. Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. A cooking appliance of the present invention comprises a detector element for sensing physical amount generated by heating the food and a control circuit for controlling heating means according to the output from the detector ele­ ment, is characterized in the following point. That is, when the user reverses and/or changes the position of the food at a specified time (W1 of Fig. 2), according to the signal output from the detector element, before the signal output reaches a predetermined detection point level, the control circuit does not read signal output from the detector ele­ ment for a specified period of time (W2 of Fig. 2), say, about 30 to 60 seconds after the heating is resumed, so that vapor accumulated in the exhaust duct in the area near the detector element is released outside the oven during the above specified period of time, thereby enabling the detec­ tor element to detect the vapor amount in the heating cham­ ber accurately. According to the present invention, if the oven door is opened to reverse the food before the detection point is reached, the control circuit will not read signal output from the detector element for a specified period of time after the door is closed and heating is resumed. During this specified period, the vapor accumulated in large amount in the exhaust gas near the detector element can be released, stabilizing the vapor amount in the exhaust duct, which fa­ cilitates accurate detection of the vapor amount. Therefore, in cooking a large quantity of food in the cooking heater, if the oven door is opened to carry out the intermediate food handling operation in the heating chamber at a pre­ determined timing before the output reaches the detection point, the detector element can detect the vapor amount ac­ curately, so that additional heating is conducted for ade­ quate period of time to yield optimally cooked food. Accord­ ing to the present invention, the user can reverse and/or change the position of the food at a timing most suitable to obtain uniformly heated food, irrespective of the quantity of the food. Brief Description of the Drawings The present invention will become more fully understood from the detailed description given hereinbelow and the ac­ companying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: Fig. 1 is a schematical drawing of the microwave oven of the present invention viewed from the front; Fig. 2 is a graph showing the relationship between the out­ put of the detector element and the heating time for four hamburgers; and Fig. 3 is a flowchart of the procedures for controlling the microwave oven in heating food. Detailed Description of the Invention Fig. 1 is a schematical drawing showing a microwave oven 1 of an embodiment of the present invention viewed from the front. The housing 2 of the microwave oven 1 contains a cooking chamber 4 in which to heat food 3. The food 3 is placed on a turntable 5. The housing 2 has a door 6 for airtightly closing the cooking chamber 4. Electromagnetic wave from heater means 7 realized by magnetron or the like material is supplied through a wave guide 8 to the cooking chamber 4, to heat the food 3. An exhaust duct (not shown) is provided in the upper part of the housing 2 so that vapor generated from the food 3 heated in the cooking chamber 4 is led to the oven exterior. A detector element 9 is pro­ vided in the exhaust duct to detect the vapor amount. Signal output from the detector element 9 is sent to a con­ trol circuit 10 which is connected with a setter 20 retain­ ing constants for various foods. When the signal output from the detector element 9 reaches a predetermined first discrimination level ℓ1 (See Fig. 2), the control circuit 10 reads the constant of the food being heated, stored in the setter 20. Using this constant, the control circuit 10 calculates the appropriate additional heating time for the food and controls the heater means 7 to heat the food addi­ tionally for the calculated period of time. The control circuit 10 is connected to an alarm generating buzzer 11 which informs the user of the intermediate food handling timing -- the time for opening the oven door 6 to reverse and/or change the position of the food 3. Fig. 2 shows the relationship between the output of the detector element 9 and the heating time for four Frozen Hamburger Patties (hereinafter called hamburgers). Fig. 3 is a flowchart of the procedures for cooking food in the microwave oven 1 of the present invention. When operation starts in the step n1, the heater means 7 heats the food 3 in the step n2. In the step n3, it is judged whether or not the predetermined time W1 has elapsed. The time W1 is usually shorter than the time required for the output of the detector element 9 to reach the detection point level ℓ1. For four or more hamburgers, for example, the time W1 is about three minutes. When the time W1 has elapsed, operation process moves to the step n4 where the buzzer 11 sounds an alarm, informing the user of the inter­ mediate food handling timing. Then the user opens the door 6, reverse and/or change the position of the food and close the door 6. At the same time as the heating operation is resumed, the operation process moves to the step n5 where it is judged whether or not the predetermined period W2 has elapsed since the heating is resumed after the intermediate food handling operation. For the four or more hamburgers, the time W2 is about 30 seconds. In the step n7, it is judged whether or not the signal output from the detector element 9 has reached the detection point level ℓ1. In this embodiment of the invention, the output of 10 bits is selected for the detection point level ℓ1. If the detection point level ℓ1 has not been reached in the step n7, the heater means 7 continues heating the food 3 until the detector output reaches the level ℓ1. When the level ℓ1 is reached, the control circuit 10 reads the constant for the food from the setter 20 and calculates the appropriate additional heating time "t". In the step n8, the food 3 is further heated by the heater means 7 for the time "t". Then the heater means 7 is stopped in the step n9 and the heating process ends in the step n10. As understood from the above description, the data is not read for the specified period of time after the inter­ mediate food handling operation. Therefore, if the detector output reaches 10 bits or the detection point level within 30 seconds after the intermediate food handling operation which was conducted before the output reaches the detection point level, or specifically after the four hamburgers have been heated for three minutes, the control circuit ignores the signal output, thus preventing the heater means from being turned off before the food is heated sufficiently. In the above embodiment, the invention is described for the case where frozen hamburger patties are heated in the cooking heater. The present invention may be used for heat­ ing any other object if it can be heated. According to the present invention, when heating is resumed after the intermediate food handling operation con­ ducted before the detector output reaches a specified value fixed for each food (in other words, after the food is heated for a predetermined period of time), the control circuit does not read detector signal output for a specified period of time. According to the present invention, since the control circuit does not read detector signal output for the speci­ fied period of time after the heating operation is resumed following the intermediate food handling operation, vapor accumulated in the exhaust duct leading to the detector ele­ ment is allowed to be released outside the oven, resulting in stabilized vapor amount in the exhaust duct. This enables the detector element to sense accurate amount of vapor gen­ erated in the heating chamber and facilitates the user to carry out the intermediate food handling operation at the most optimal timing for the food, irrespective of the de­ tection point level, whereby the food can be heated uniformly and optimally. According to the present invention, even if the oven door is opened before the detector output reaches the de­ tection point level, the detector element senses the vapor amount accurately so that additional heating can be carried out for the period most suitable to yield the optimally cooked food, and that food of any quantity can be heated uniformly because intermediate food handling operation tim­ ing can be selected appropriately according to the quantity of the food. While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as claimed.

Claims: 1. A cooking appliance including a sensor for detecting vapor generated from heated food and a control circuit which executes arithmetic operation on the heated state of the food according to signal outputs from the sensor and con­ trols the heating source on the basis of the arithmetic operation result, said control circuit being operated so as not to read signal output from the sensor for a spec­ ified period of time after the food is reversed and/or its position is changed before the sensor detects the heated state detection point. 2. A cooking appliance having a sensor (9) for detecting an environmental condition which varies in accordance with the cooking state of food being heated by the appliance, and a cooking control means (10) for controlling the heating of the food in accordance with the sensor output, said cooking control means being arranged to respond to the sensor output reaching a given point, characterised in that said cooking control means is adapted so that if heating is interrupted before said output reaches said given point and subsequently resumed after rearrangement of the food, the sensor output is ignored during a predetermined period following the resumption of heating. 3. A cooking appliance according to claim 2 wherein said cooking control means (10) is adapted to respond to the sensor output reaching the given point to determine the length of an additional cooking period. 4. A cooking appliance according to claim 2 or claim 3 wherein said sensor is a vapour sensor located in the region of a gas exhaust from a heating chamber (4) of the appliance. 5. An electrical oven having a heating control means which uses a sensor output for detecting a predetermined cooking stage, the sensor (9) being adapted to sense an environmental condition created by the cooking of the food (3), wherein said control means ignores the sensor output for a given period following resumption of cooking if cooking was interrupted prior to said cooking stage being reached.

Inventors: MASAKO, HIROSHIMA
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1987
Main classification: H05B6
IPC codes: H05B6