GB2173919A

GB2173919A - Control of cooking appliances

Info

Publication number: GB2173919A
Application number: GB08509780A
Authority: GB
Inventors: Takeshi Tanabe; Kuniyoshi Fujikawa; Takatoshi Yasuda; Nobuo Takeoka
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1985-04-16
Filing date: 1985-04-17
Publication date: 1986-10-22
Also published as: GB2173919B; GB8509780D0

Abstract

In a cooking appliance (e.g. a microwave oven) in which food stored in a heating chamber is cooked by heating means, a first sensor (12) for detecting a cooking completion condition and a second sensor (18) for measuring the weight of food to be cooked stored in the heating chamber provide inputs to a control system. The variation of the output of the first sensor over a predetermined time is computed and if this is less than a critical value the output of the second (weight) sensor is examined. If this output is too low it is assumed that there is no food load in the chamber and the heating means is switched off. <IMAGE>

Description

SPECIFICATION Cooking appliance BACKGROUND OF THE INVENTION The present invention relates to a cooking appliance such as a microwave oven.

In the conventional microwave oven, a completion of cooking is detected in a such manner that gas or moisture produced by cooked food in a heating chamber when heating is detected by detecting means, or in a such manner that a surface temperature of the food to be cooked is detected by an infrared light detector, or in a such manner that a temperature of exhaust air from the heating chamber is detected by a thermister. When a cooking condition becomes a predetermined cooking completion of food to be cooked, the induction heating device is stopped.

In the conventional techniques, if power is applied to a magnetron for producing a high frequency when food to be cooked is not stored in the heating chamber, referred to as no-load condition, the gas or the moisture is not produced in the heating chamber. Accordingly, in the microwave oven in which the cooking completion of the food is judged by detecting the gas or the moisture from cooked food, the heating operation is continuously carried out. Further, a temperature of the heating chamber is locally and highly increased, so that the cooking appliance becomes danger ous.

In the microwave oven including an infrared light detecting means or the thermister, when the food to be cooked is not stored in the heating chamber, the heating operation is continuously carried out for a long time until the temperature in the heating chamber is increased to a predetermined high temperature.

As the heating chamber are made of a metal material for refiecting microwave, an increase of the temperature in the heating chamber is small as compared with the increase of temperature of food which easily can absorb a high frequency signal and has a high dielectric constant. Accordingly, the heating period even in the no-load condition results in continuing for a long time.

Accordingly, it is desired that an improved cooking apparatus such as a microwave oven can detect whether food to be cooked is present or abscent in the heating chamber and enables a heating operation for a short time even when the food to be cooked is not stored or a little amount of the food to be cooked is stored in the heating chamber.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved cooking appliance which can detect whether food to be cooked is present or abscent in a heating chamber and enables a heating operation for a short time even when the food to be cooked is not stored or a little amount of the food to be cooked is stored in the heating chamber.

It is another object of the present invention to provide an improved cooking appliance which can eliminate excess heating even when food to be cooked is absent or a little amount of the food is present in a heating chamber.

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 of 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.

To achieve the above object, according to a preferred embodiment of the present invention, a cooking appliance in which food stored in a heating chamber is cooked by heating means comprises first detecting means for detecting a cooking completion condition of food to be cooked, measuring means for measuring weight of food to be cooked stored in the heating chamber, second detecting means for detecting a variation of the output of the first detecting means, means for comparing the output of the second detecting means with the output of the measuring means, and means for controlling the operation of the heating means depending on the output of the comparision means.

The operation of the heating means is stopped when the variation of the output of the cooking completion detecting means is less than a predetermined value and at the same time the weight of food measured by the weight measuring means is less than a predetermined weight.

BRIEF DESCRIPTION OF THE DRA WINGS The present invention will be better understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: Figure 1 shows a front view of a microwave oven of a preferred embodiment of the present invention; Figure 2 shows a sectional view of the microwave oven of Fig. 1; Figure 3 shows a circuit diagram of the microwave oven of Figs. 1 and 2; Figure 4 shows a graph for explaining a time chart of outout level of a completion condition detecting means 12; and Figure 5 shows a flowchart for explaining an heating operation of the microwave oven of the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows a front view of a microwave oven according to a preferred embodiment of the present invention. Fig. 2 shows a sectional view of the microwave oven of Fig. 1.

A heating chamber 4 is stored into a housing 1 of the microwave oven. An operation panel 2 having a heating key 3 is provided on a front wall of the housing 1 of a microwave oven. When the heating key 3 is depressed, a high frequency produced from a magnetron 5 is introduced into a heating chamber 4, and then, food to be cooked on a tray 6 is heated. A door 7 is pivotably provided on the front of the housing 1 to open or close the heating chamber 4. In the embodiment of the present invention, an "auto" heating key 8 is provided on the operating panel 2. When the "auto" heating key 8 is depressed, the magnetron 5 is driven to produce the high frequecy.

When the heating key 3 is depressed after cooking information relating to a heating time or weight of food to be cooked or the like are mannually inputted by input keys on the operating panel 2, the microwave heating starts.

When only the "auto" heating key 8 is depressed, the cooking information relating to the heating time or the weight of food etc. is readout from a memory, and then the microwave heating is carried out depending on the cooking information.

When the microwave heating is carried out, air is introduced into the heating chamber 4 from an air inlet 10 by driving a fan 9, and gases in the heating chamber 4 are exhausted from an exhaust outlet 11 to the outside.

A cooking completion detecting means 12 such as a sensor which detects a gas or a moisture produced by heating the food, or a sensor which detectes an infranged light depending on a surface temperature of cooked food, or a sensor which detectes a temperatuer of an exhaust air from the exhaust outlet 11 is provided adjacent the exhaust outlet 11.

A rotating axis 13 is provided at the substantial center portion of the bottom wall of the heating chamber 4, and is disposed in a vertical direction. One upper end of the rotating axis 13 is detachably connected to a substantial center portion of a tray 6. The rotating axis 13 is rotatably supported by a bearing 14, and is inserted into a hole formed in a gea 15 so that the gear 15 is fixed to the rotating axis 13. A gear 16 is driven by a motor 17 is engaged with the gear 15. When the food is heated, the tray 6 is rotated around the rotating axis 13, so that the rotat ing of the tray 6 prevents the temperature of cooked food from unevenlly changing. The tray 6 may be moved up/down in the vertical direction with the rotating axis 13 in cooperation with the rotation of the tray 6.

Condenser means 18 comprises a pivotable electrode plate 19 and a fixed electrode plate 20. One end of the pivotable electrode plate 19 is pivotably connected by a horizonatal hinge pin 22, and the other end of the pivotable electrode plate 19 is connected to a spring 21 to pull the pivotable electrode plate 19 in the upper direction as shown in Fig. 2.

The lower end of the rotating axis 13 is in contact with a substantial center portion of the pivotable electrode plate 19. The pivotable electrode plate 19 is moved in the vertical direction around the horizoantal hinge pin 22 depending on the weight of food to be cooked on the tray 6 againgst the power of the spring 21. Accordingly, an angle between the pivotable electrode plate 19 and the fixed electrode plate 20 is changed depending the weight of food, so that the capacitance of the condenser means 18 is varied.

Fig. 3 shows a circuit diagram of the microwave oven of Figs. 1 and 2. When the heating key 3 or the "auto" heating key 8 provided at the operating panel 2 is depressed, such keyed signals are fed to an interface 23. An output from the cooking completion detecting means 12 is applied to the interface 23 through an anolog/digital convertor 24. The condenser means 18 which varies the capacitance dependeing on the weight of food to be cooked on the tray 6, is connected to an oscillating circuit 25. When the capacitance of the condenser means 18 is changed based on the weight of food on the tray 6, an oscillating frequency of the oscillating circuit 25 is changed. The output of the oscillating circuit 25 is fed to the interface 23.

The interface 23 is connected to a processing circuit 26 such as a microprocessor. The processing circuit 26 includes a centarl processing unit 27 (CPU), a read only memory (ROM) 28 containing programs or the like, and a random access memory (RAM) 29 for an arithmetic operation, or the like. The output of the interface 30 is applied to the switching transistor 30 connected to the relay coil 32 in series. When the switching transistor 30 is electrically connected, the relay coil 32 is excited, thereby electrically connecting the relay switch 33. In this reason, the alternative power from a plug 34 is applied to a high power generating transformer 35 to thereby excite the magnetron 5. The output pulses of the oscillating circuit 25 is counted up by the processing circuit 26 each a constant period.

Accordingly, the oscillating frequency of the oscillating circuit 25 is detected depending on the counting numbers.

Referring to Fig. 4, the heating key 3 or the "auto" heating key 8 is depressed at a time tl. According to the depression of the heating key, the motor 17 is driven, and the switching transistor 30 and the relay switch 33 are electrically connected to excite the magnetron 5.

When the magnetron 5 is excited, the food disposed on the tray 6 in the heating chamber 4 is started to heat.

According to the heating, the output of the cooking completion detecting means 12 is increased as indicated by a line L1. When the output of the completion detecting means 12 is arrived at the predetermined value VL at a time t2, the processing circuit 26 is operated in a such manner that the switching transistor 30 and the relay switch 33 are cut off to stop the exciting of the magnetron 5 and the driving of the motor 17.

When the food to be cooked is not stored in the heating chamber 4, and the heating key 3 or the "auto" heating key 8 is depressed, the motor 17 is driven and the magnetron 5 is excited, and then the heating is carried out.

However, no gases or no moisture is produced from the heating chamber 4, or the temperature in the heating chamber is not increased or is not substantially increased. Accordingly, the output of the completion detecting means 12 is less than the predetermined value VL for a long time, and is constant as indicated by a line L2.

Conventionally, because the output level of the comletion detecting means 12 is less than the predetermined value, the magnetron 5 is continuously excited. To resolve this problem, the present invention is investigated. The operation of the microwave oven of the present invention will be described with reference to Fig. 5.

Step nl: The heating key 3 or the "auto" heating key 8 is depressed to drive the motor 17 and to excite the magnetron 5.

Step n2: The weight G of food to be cooked disposed on the tray 6 in the heating chamber 4 is measured in a such manner that the oscillating frequency of the oscillating circuit 25 corresponding to the capacitance of the condenser means 18 is detected by the operation of the processing circuti 26. The weight G is stored into a storing area of the random access memory 29.

Step n3: The switching transistor 30 and the relay switch 33 are electrically connected to excite the magnetron 5, so that the high frequency waveform is applied to the heating chamber 4.

The motor 17 is driven and then the tray 6 is rotated by the motor 17.

Step n4: An output voltage V, of a cooking completion detecting means 12 when the heating is started is stored into a storing area of the random acess memory 29. It may be evident that any other types of information from the cooking completion detecting means 12 can be selected.

Step n5: When the heating is carried out by a predetermined period W2 after starting the heating, the output voltage V2 of the cooking completion detecting means 12 is stored in a storing area of the random acess memory 29.

Step n6: It is judged whether the difference between the first and second voltages V1 and V2 is more than a predetermined value AV.

V2-V, > AV (1) When the difference of the first and the second voltages V, and V2 is equal to or less than the predetermined value AV, step n7 is carried out.

Step n7: It is judged whether the weight G of the food previously measured is more than a predetermined weight value, for example, about 100 g. If the weight G is equal to or less than the predetermined weight value, step n8 is carried out. The predetermined weight value can be changed according to the cooking applicance.

Step n8: It is judged that no food to be cooked is stored on the tray 6 in the heating chamber 4.

Step n9: The switching transistor 30 and the relay switch 33 are cut off to stop the exciting of the magnetron 5. Therefore, after the generation of the high frequency is stopped, step n10 is carried out, so that the heating operation is stopped.

As described above, when no food to be cooked is stored in the heating chamber 4, or a little amount of the food to be cooked is stored, the high frequency from the magnetron 5 becomes unnecessary generated for a long time.

In step n6, when the formula(1) is satisfacted, step n1 1 is carried out.

Step n11: The output of the cooking completeion detecting means 12 is successively detected, always.

Step n12: It is judged whether the voltage outputted from the cooking completion detecting means 12 is arrived at the predetermined voltage value VL. If the output voltage of the completeion detecting means 12 is arrived at the predetermined voltage value VL, step n9 is carried out to stop the operation of the magentron 5. When the operation of the magnetron 5 is stopped, in step n10, the cooking of food is completed.

When the difference between the first and the second output voltages V1 and V2 is equal to or less than the prederemined V, there is possibility that much amount of food lapped by a lap for preventing the generation of gases and moisture from cooked food may be stored in the heating chamber 4, or that refrigerated food may be stored in the heating chamber. In this case, step n7 is executed to judge whether the food to be cooked is more than the predetermined weight value. If the weight of food is more than the predetermined weight value, even when the variation of the cooking completion detecting signal from the cooking completion detecting means 12 is slow, the heating is continuously performed. In step null, the voltage level is successively detected, and then the operation is forwarded to step n12.

As described above, when no food to be cooked is stored in the heating chamber or a little amount of the food is stored in a heating chamber, unnecessary heating is not continued. Therefore, the microwave oven can be safely used.

Although the present invention is applied to the microwave oven, the present invention may be applied to various type of cooking applicances for heating.

As described above, according to the present invention, even when no food to be cooked is stored in the heating chamber or a little amount of the food is stored in the heating chamber, the cooking appliciance enable a suitable heating operation without unnecessary heating. Therefore, no accident of the cooking appliance can be generated and the cooking appliance is safely used.

When no food to be cooked is stored in the heating chamber or a little amount of food is stored in the heating chamber, the heating time of the heating operation can be reduced, for example, within about twenty minitues by detecting the cooking completion signal in cooperation with the measuring of the weight of food to be cooked.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.

Claims

1. A cooking appliance in which food stored in a heating chamber is cooked by heating means comprising: first detecting means for detecting a cooking completion of food to be cooked; measuring means for measuring weight of food to be cooked stored in the heating chamber; second detecting means for detecting a variation of the output of the first detecting means; means for comparing the output of the second detecting means with the measuring means; and means for controlling the operation of the heating means depending on the output of the comparision means.

2. The cooking appliance of claim 1, wherein the operati.on of the heating means is stopped when the variation of the output of the cooking completion detecting means is less than a predetermined value and at the same time the wieght of food measured by the weight measuring means is less than a predetermined weight.

3. A cooking appliance substantially as herein described with reference to the accompanying drawings.