JPS63170883A - Microwave oven - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises an oven cavity in which an object to be heated is placed, a microwave generator for emitting microwave energy into the cavity to heat said object, and an air flow within the cavity. The present invention relates to a microwave oven comprising a fan device for generating energy, a humidity detector for detecting a change in the humidity of the air in the cavity, and a control means for controlling the supply of energy to an object according to the detected humidity. .

Especially in the thawing process, as the process progresses rapidly,
If the process is not stopped in an appropriate amount of time, the temperature of some parts of the object will rise to an unacceptable level. It is now common to use low power levels to prevent overheating. This results in, on the one hand, a very slow processing speed that is easy to visually inspect, and on the other hand, a slow processing speed that results in a long time for temperature equalization, where the heat of superheated parts is transferred to cooler parts. It becomes necessary.

Since it is difficult to detect the defrosting state instantly, it is extremely difficult to automatically control the defrosting process. The known method is based on the principle of detecting changes in the dielectric properties that occur during the ice-water phase transition by means of microwaves, using microwaves at a frequency different from that of the supplied energy if desired. However, the accuracy of this detection method decreases due to changes in the geometric form of the food, and furthermore, ion conduction due to salts contained in the food causes disturbances. Alternatively, methods are known that are based on the principle of determining the weight of an object as a function of the supplied energy. This detection method also has drawbacks. That is, the energy required for thawing cannot be calculated accurately enough. However, the energy corresponding to this weight depends on the type of object to be thawed,
This is because it depends on the substantial degree of moisture content, temperature at the time of thawing, etc. Furthermore, this known method also requires consideration of the weight of the plates or trays on which the objects are placed in the oven chamber. As a result, objects often become overheated. It is known that when the thawing mode is controlled by weight detection, the subsequent cooking mode is controlled by humidity detection. In this way, humidity detection can also be performed during the defrost mode if an error occurs under abnormal conditions, such as when the object is defrosted abnormally.

Therefore, it is an object of the present invention to be able to automatically thaw an object, to control the thawing state of the object with higher precision than known methods, and in particular to control the moment when energy supply is stopped with higher precision. It provides a microwave oven.

The microwave oven according to the invention is characterized in that, in a microwave oven of the type mentioned at the beginning of the specification, the defrosting mode is controlled only by the detected humidity change. The present invention is characterized in that the humidity of the air surrounding frozen food initially decreases significantly due to the condensation of moisture on the food, and then after continuous thawing, the humidity gradually increases, and the rate of this increase is natural logarithmic with the humidity. It is based on the fact that increasing saturated vapor pressure depends on the increase. Therefore, by blowing air onto the food to be thawed and measuring the humidity of the air that has passed through the food, a humidity indicating signal can be obtained, and this humidity indicating signal is highly accurate and indicates the thawing state of the food. This signal can be used to control the decompression process.

A preferred embodiment of the present invention provides that the control means is configured to detect a minimum humidity value, and after reaching this minimum humidity value, when the difference between the minimum humidity value and the detected humidity value reaches a predetermined value, the defrosting It is characterized by being configured to stop the mode.

A microwave oven according to another embodiment of the invention is characterized in that the humidity change corresponds to a humidity gradient, and the defrosting mode is stopped when the control means detects a predetermined positive humidity gradient. do.

Another embodiment of the present invention is a microwave oven, wherein the oven cavity has an inlet opening communicating with the outside air and an outlet opening communicating with the inlet of the channel, the outlet of the channel opening towards the outside, and The fan device is located inside the channel and generates a flow of air flowing from the outside into the oven cavity through the chable to the outside.
The humidity detector is located downstream of the oven cavity inside the channel.

Yet another embodiment of the microwave oven is characterized in that the control means is capable of performing the defrosting process in a plurality of cycles, each cycle having at least two time periods, and in a first time period the microgenerator and the fan device are activated. operate together, and the second
The present invention is characterized in that both the microwave generator and the fan device are inoperative during this period. By performing defrosting in a plurality of cycles, a clear humidity difference can be detected at the start of each ON period of one cycle, and energy supply can be controlled with high precision.

During periods when the microwave generator is off, the cooler parts of the food are overheated by conduction from the hotter parts.

In another embodiment of the invention, the control means may be operable to lengthen the first period of the next cycle after a predetermined number of cycles depending on the detected humidity value relative to the predetermined difference value. With this configuration, it is possible to shorten the total thawing time.

Furthermore, in another embodiment, the control means is operative to initiate defrosting in a first cycle, and
The time period has a predetermined duration that depends on the minimum amount of matter in the critical state.

Furthermore, another embodiment of the microwave oven according to the invention is characterized in that a channel is provided outside the oven cavity, both ends of which open into the oven cavity;
The fan device is located inside the channel to circulate the airflow in a closed loop, and the humidity sensor is located downstream of the oven cavity in the airflow inside the channel. In this type of microwave oven, humidity is detected in a so-called "closed system".

It is known in microwave ovens to provide humidity sensing to control the process when the oven is in cooking mode. In this case, it is necessary that the microwave oven be in an "open system". In a microwave oven, when both defrosting mode and cooking mode are controlled by humidity detection, the system changes from "closed system" to "open system".
It is possible to achieve a configuration that switches to This embodiment therefore provides a branching channel opening into said channel at one end and the outside at the other end, a pulp at the junction of these channels, and a valve which allows air to flow between the two locations. It is characterized by being configured to switch between a position where air circulates in a closed loop and a position where air flows out to the outside.

Hereinafter, the present invention will be described in detail based on the drawings.

In FIG. 1, reference numeral 1 designates the housing of a microwave oven, which housing 1 has an oven cavity 2 in which an article (object) 3 to be heated is placed.

The oven cavity 2 has an artificial opening 4 connected to the outside air and an outlet opening 5 connected to the inlet of the channel 10.

A fan 6 is placed in the channel 10 generating an air flow to cool the magnetron 7, ie the microwave source.

Air passes at least partially through the oven cavity 2. Before being discharged to the outside, the air flow or a part of this air flow passes through a humidity sensor 8 of known type, which is arranged downstream of the oven cavity 2 with respect to the direction of the air flow. The article 3 is placed in an open container 9 in order to distribute microwave energy within the oven cavity in a known manner, not shown. This open container 9 is rotated by known drive means or is stationary. When stationary, an appropriately shaped and slotted disk placed above the galley on the front side of the magnetron 7 is rotated by an air flow flowing in an appropriate direction.

A humidity sensor 8 detects the absolute humidity inside the oven cavity. The detected signal is supplied to a control means including a microprocessor, which controls the supply of energy to the oven cavity in response to the humidity change detected by the microprocessor.

The above process is shown in FIGS. 2 and 3. FIG. 2 shows the output signal corresponding to humidity from the humidity sensor as a function of time, and FIG. 3 shows the energy delivered to the oven cavity as a function of time.

Sequential cycles I, n, I[I, IV, V,
The decompression is performed at Vl, ----, and each cycle consists of at least two periods 1 and 2. Microwave energy is supplied to oven cavity 2 and fan 6 is activated during the first period of each cycle. During the second period of each cycle, no energy is supplied and the fan 6 is also turned off. A third period can also be used if desired, in which only the fan 6 is activated and no energy is supplied to the cavity. Alternatively, only the fan may be turned on and off by continuously supplying energy.

During the first period of the first cycle I, the humidity inside the cavity becomes approximately equal to the humidity of the outside air due to air circulation.

When the fan 6 is switched off in the second period of cycle (2), the temperature and humidity of the cavity will be affected by the frozen food. If the item 3 is frozen, moisture will condense on the item 3 and the humidity of the air within the cavity will decrease. When air circulation is started in period 1 of the next cycle H, this air is blown onto the humidity sensor 8. This humidity sensor 8 emits a signal, which is the first of the cycle
It shows a sharp decline in the first part of the period. This sudden drop indicates a drop in air humidity, which occurred during the second period of cycle (1).

The same phenomenon is repeated in the first period of cycle ■, but
The sudden drop in the output signal from the humidity sensor becomes slightly smaller. In cycle (2), even if the fan is turned on in period 1, no noticeable change in humidity occurs in the signal from the humidity sensor 8.

In the next cycle V, a signal is obtained from the humidity sensor indicating that the humidity within the cavity has increased, and in the next cycle 2, a signal is obtained indicating that the air humidity has further increased. The thawing process is performed at the instant t4 when the difference between the minimum humidity value corresponding to the decrease in period 1 of cycle ■ and the humidity value detected in cycle ■ after reaching the minimum value in this cycle ■ reaches a predetermined value ΔH. can be stopped. Period l of cycle I is a period of time when the amount of food such as bread (e.g. 50g
rolls) corresponds to the period of thawing a small amount of a critical state product with a small specific heat.

2. If the humidity change detected after 3 cycles is still small, the thawing process can also be lengthened by lengthening the first p, u interval of the next cycle, and the predetermined value Δ
You can also repeat it 5 or 6 times until you reach H (4th
(see figure).

In another embodiment, the airflow is circulated in a closed loop as shown in FIG. Portions corresponding to the microwave open in FIG. 1 are designated by the same reference numerals with the letter A added thereto. Both ends of channel IOA are opened toward oven cavity 2A. This system can be used only for decompression processing. The food is frozen and does not generate enough moisture to cause agglomeration on the walls of the cavity.

FIG. 6 shows two typical temperature and humidity regimes used in the "closed system" thawing process.

Curve T1 shows the temperature of the air as a function of time;
2 shows the humidity of the air as a function of time.

For clarity of the drawing, the dew point of the air on the drawing has been chosen to indicate humidity. This size has a clear relationship with absolute humidity.

Initially, the temperature and humidity inside the oven cavity are the same as the outside air. When the frozen food is placed in the oven cavity 2A and the magnetron is started, the humidity begins to decrease in a short time due to agglomeration on the cold surface and the temperature also begins to decrease (time period t, a tb). Momentarily, too, the humidity reaches its minimum value. The surface of the food product is then heated to such an extent that agglomeration is terminated. At the same time, the temperature of the air inside the cavity decreases until a predetermined moment is reached at which the temperature decrease is stopped by heat supplied from the walls or the like. On the other hand, temperature changes are substantially more gradual than humidity changes.

While thawing continues, the humidity begins to rise at an increasing rate corresponding to the saturated vapor pressure in the air increasing approximately natural logarithmically with temperature. According to the invention, the thawing process is automatically stopped at an instant determined by the measured humidity change ΔH. The only condition in which the oven is switched off may be the condition in which the dew point during rising reaches, for example, instant tc in FIG. 6. Dew point temperature or humidity is the 6th
Follow the dashed line in the diagram. If switching off does not occur,
The dew point temperature will follow the dot curve.

Alternatively, the time derivative of the humidity curve can be used as a control parameter to turn off the oven. The humidity gradient is first negative, then reaches zero, the lowest value of humidity, and then becomes positive. When a predetermined positive slope is reached, the magnetron is turned off. Furthermore, the second high humidity gradient value can be used as a cant-off safety feature independent of the extensions of the invention described below.

In more developed systems, the switching-off instant is based on an experimentally determined function and is dependent on the measurement of the time from the start to the predetermined dew point temperature reached. By measuring the time from this start until the dew point temperature is reached, a valid correlation to the amount of food is obtained and this correlation can be used to control the selected off by using the humidity indication signal as the control signal. The activation time can be extended beyond the instant at which the "limit value" based on the switching criterion is reached.

Another embodiment is to appropriately control the microwave power in response to changes in dew point temperature, stopping the power supply at a predetermined limit and then lowering the dew point temperature (based on temperature changes due to conduction in the food). When the voltage drops below another predetermined value, power supply is restarted. In this system, the number of cycles can be fixed or can be made dependent on the time period until the first stop based on an algorithm in which the number of cycles increases with the time length of the period.

The present invention can also use ambient humidity as a correction parameter. In this system, the initial values of FIG. 6 are stored in the processing unit, and if the initial values are relatively high, the limits are adjusted according to the process described above to compensate for external influences.

In another embodiment, the limit value can be adjusted externally within a predetermined period of time. In this case, the user can choose between weak defrosting (for example, when thawing fish pieces to the extent that they can be separated into individual pieces) or strong defrosting (for example, when cooking vegetables for another purpose). This adjustability can be used to compensate for manufacturing tolerances in the overall system, so that the best conditions can be selected at the user's direction.

If the thawing process is performed in a "closed system" and the subsequent cooking process is also controlled by humidity detection, this control must be performed in the oven in an "open system" state.

A microwave oven having both "open system" and "closed system" modes is shown in FIG.

Members that are the same as those described above are designated by the same reference numerals with the letter B added. One end of the channel IOB is open to the cavity 2B, and the other end is opened to the outside. branch channel IOB,
It connects near the exit opening between the cavity and channel 8B. A valve 12B is provided at the connection part of these channels,
This valve 12B allows switching between two positions: one in which air circulates in a closed loop (defrost mode) and one in which air is blown out (cooking mode).

[Brief explanation of the drawing]

1 is a diagram showing the configuration of a microwave oven with an "open system"; FIG. 2 is a graph showing a humidity hourly curve for a multi-cycle defrosting process for the oven shown in FIG. 1; Figure 3 is a diagram showing the energy-hour curve corresponding to Figure 2, Figure 4 is a diagram showing the energy-hour curve similar to Figure 3 using a different cycle, and Figure 5 is a diagram showing the "closed system". FIG. 6 is a diagram showing the temperature (humidity) hourly curve for FIG. 5; FIG. 7 is a "closed system" and an "open system". 1 is a diagram showing the configuration of a microwave oven including 1...Housing 2...Oven cavity 3...Item 4...Inlet opening 5...
・Outlet opening 6...Fan 7...Mazunetron 8...Humidity sensor 9...Container
10...Channel 12...Valve Patent Applicant: NV Philips Fluirampenfabriken

Claims (1)

[Claims] 1. An oven cavity in which an object to be heated is placed, a microwave generator that radiates microwave energy into the cavity to heat the object, and a fan that generates an air flow within the cavity. Detecting a defrosting mode in a microwave oven comprising: a device; a humidity detector for detecting a change in the humidity of air in the cavity; and a control means for controlling the supply of energy to an object in accordance with the detected humidity. A microwave oven characterized in that it is configured to be controlled only by changes in humidity. 2. The control means is set to detect a minimum humidity value, and after reaching this minimum humidity value, the defrosting mode is stopped when the difference between the minimum humidity value and the detected humidity value reaches a predetermined value. A microwave oven according to claim 1, characterized in that the microwave oven comprises: 3. The first aspect of the present invention is characterized in that the humidity change corresponds to a humidity gradient, and the defrosting mode is stopped when the control means detects a predetermined positive humidity gradient.
Microwave oven as described in section. 4. The oven cavity has an inlet opening that communicates with the outside air and an outlet opening that communicates with the inlet of the channel, the outlet of the channel opens toward the outside, and the fan device is located inside the channel and has an outlet opening that communicates with the inlet of the channel. 2. The humidity sensor is located downstream of the oven cavity inside the channel, and the humidity sensor is located downstream of the oven cavity inside the channel. microwave oven. 5. The control means is capable of carrying out the defrosting process in a plurality of cycles, each cycle having at least two periods, in the first period the micro-generator and the fan device operate together, and in the second period 5. The microwave oven according to claim 4, wherein both the microwave generator and the fan device are inoperative. 6. The control means is operable to lengthen the first period of the next cycle after a predetermined number of cycles depending on the detected humidity value relative to the predetermined difference value. A microwave oven according to range 5. 7. Patent characterized in that the control means are operative to initiate defrosting in a first cycle, the first period of this first cycle having a predetermined period depending on the minimum amount of matter in the critical state. A microwave oven according to claim 6. 8. A channel is provided outside the oven cavity, both ends of the channel open into the oven cavity, the fan device is located inside the channel to circulate the air flow in a closed loop, and the humidity detector is configured to 4. Microwave oven according to claim 2, characterized in that it is located downstream of the oven cavity in the air flow inside the channel. 9. A branching channel is provided with one end opening into the channel and the other end with the outside, and a valve is provided at the junction of these channels, by means of which air circulates between the two locations, i.e. in a closed loop. 9. The microwave oven according to claim 8, wherein the microwave oven is configured to be switched between a position and a position where air flows out.