JPS593647B2 - High frequency heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency heating device having a control function to automatically properly heat an object to be heated.

By supplying high-frequency power into the heating chamber that houses the object to be heated,
In equipment that heats objects to be heated using high-frequency waves, high-frequency heating detects the temperature of the air flowing out of the heating chamber or the temperature of the air inside the heating chamber, indirectly detects the temperature of the object to be heated, and automatically controls the heating time. A device has been invented.

This type of high-frequency heating device has the advantage that it does not damage the heated object, compared to contact type devices that use a probe-shaped temperature sensing element to directly detect the temperature of the heated object. This is extremely useful.

The general structure of the above-mentioned high frequency heating device of this type of invention will be explained with reference to FIG.
3 is a heating chamber of a high-frequency heating device that houses the heating chamber 1, and 3 is a door of the heating chamber 1 for supplying and discharging objects to be heated.

As is well known, this door 3 is designed to prevent the high-frequency power supplied to the heating chamber 1 from leaking to the outside through the opening, and allows the inside of the heating chamber 1 to be observed if necessary. The finder is formed using a perforated metal plate, a transparent glass plate, etc.

4 is a plate on which the object to be heated 2 is placed.

Reference numeral 5 denotes an opening which shields the inside and outside of the heating chamber 1 using high-frequency waves to allow air to flow through the opening.

Reference numeral 6 denotes an opening which shields the interior and exterior of the heating chamber 1 using high-frequency waves, as described above, to allow air to flow therethrough, and in this device, air flows out from here.

Reference numeral 7 denotes a blower device that forcibly causes the above-mentioned air flow, and exhausts the exhaust gas to the outside of the high-frequency heating device through an exhaust path 8.

A magnetron 9 generates high-frequency power, and is installed on the ceiling wall of the heating chamber 1 with an antenna protruding.

Although not shown in FIG. 1, the magnetron 9 is cooled by a cooling device.

10 and 11 are openings 5 provided in the heating chamber 1, respectively.
This is an opening connected to the opening 6 and formed at the outermost side of the high-frequency heating device, and is provided in consideration of harmonizing with other external appearance.

Reference numeral 12 denotes a partition plate that isolates the above-mentioned magnetron antenna from the atmosphere inside the heating chamber, and is made of a material with low high frequency power loss.

13 and 14 are openings 5 provided in the heating chamber 1, respectively.
and a temperature sensing element, such as a thermistor, installed outside the opening 6 in a portion not exposed to high frequency power.

These temperature sensing elements 13 and 14 are connected to an automatic control device 15.
When the high-frequency heating device is activated, the automatic control device 15 receives a temperature signal of the air flowing into the heating chamber 1 from the temperature sensing element 13 and a signal of the air flowing out from the heating chamber 1 from the temperature sensing element 14. The temperature signals of the temperature sensing elements 13 and 1 are received and compared, and the temperature signals of the temperature sensing elements 13 and 1 are set to a predetermined state.
When the difference between the signal values of No. 4 and No. 4 reaches a predetermined value, the power supply device 16 is controlled, thereby stopping the operation of the magnetron 9 and the blower 7, and ending the high-frequency heating.

Reference numeral 17 denotes a guide plate that guides the air flowing into and out of the heating chamber 1 so that it comes into contact with the object to be heated 2 as much as possible and also incorporates the steam generated from the object to be heated 2.

In this way, a high-frequency heating device that detects the temperature rise of the air flowing out of the heating chamber 1 during high-frequency heating, indirectly detects the temperature of the object to be heated 2, and automatically controls the heating time, does not require a cumbersome timer. Although no setting operations are required, and therefore the usability of the high-frequency power heating device is significantly improved, it also has some undesirable drawbacks.

In other words, when trying to perform highly accurate automatic control, heating chamber 1
Since the amount of air flowing through the heating chamber 1 must be reduced, the water vapor generated from the heated object 2 cannot be properly discharged to the outside of the heating chamber 1, and condensation often occurs on the heating chamber walls and the inside of the finder of the door 3. This may cause water to accumulate in the heating chamber 1 or impede the see-through function of the finder.

This phenomenon also occurs in the exhaust path 8.

This is due to the temperature of the air flowing into the heating chamber 1 during high-frequency heating, the heat transfer from the object to be heated 2, and the temperature of the air flowing into the heating chamber 1.
The temperature rises due to the water vapor generated from the heating chamber 1.
This is because it is convenient for highly accurate automatic control to have as large a temperature difference as possible between the temperature of the air flowing out of the heating chamber 1 and the temperature of the air flowing out from the heating chamber 1. It arises from the fact that

Incidentally, since the heating chamber wall and the finder of the door 3 are not heated by high frequency power during high frequency heating, their temperature is usually lower than the atmospheric temperature in the heating chamber.

Therefore, even if the amount of water vapor in the atmosphere has not reached the saturation point, the parts that come into contact with the heating chamber walls and the finder are always in a state of being easily saturated, and when the temperature of the air flowing into the heating chamber 1 is low. Condensation often occurs in heated objects that generate large amounts of water vapor.

In addition, when the temperature difference between the air flowing into the heating chamber 1 and the air flowing out reaches a predetermined value and the operation of the magnetron 9 and blower 7 is stopped, the atmosphere in the heating chamber is already saturated. The one that is easy to heat is placed in heating chamber 1.
As the water stagnates inside, and its temperature continues to drop, it becomes even more likely to form condensation.

If such a phenomenon becomes serious, water may overflow from the heating chamber and enter the power supply, creating an extremely dangerous situation.

This is a matter of concern as a product and must be removed.

However, from the standpoint of improving the accuracy of automatic control, condensation and improving accuracy are in a mutually contradictory relationship, and therefore it is extremely difficult to satisfy both.

That is, the relationship between the amount of air that flows into the heating chamber 1, circulates, and flows out during high-frequency heating, and the temperature difference between the temperature of the air that flows in and the temperature of the air that is heated by the object to be heated 2 and then flows out. The trend is as shown in Figure 2.

That is, if an attempt is made to prevent condensation of water vapor by increasing the air volume, a large temperature difference cannot be achieved, resulting in a decrease in detection accuracy.

On the other hand, if an attempt is made to increase the temperature difference and improve the detection accuracy by reducing the air flow rate, dew condensation will occur on the walls of the heating chamber 1 and the like.

In addition, among the cases where heating time is automatically controlled using temperature detection as described above, in the field of reheating, which only requires heating pre-cooked food to an edible temperature, the amount of steam generated from the heated food is Even if a large amount of When it is desired to maintain heated food at a certain temperature for a certain period of time, condensation becomes a serious problem.

So, let's explain such a case using an actual example.

In other words, most vegetables maintain a temperature of about 60 to 70 degrees Celsius for a while as the temperature rises, and then raise it to about 100 degrees Celsius and maintain that temperature for a while. It is known that the most effective cooking method is to complete the alpha conversion of beta starch.

Therefore, we started high-frequency heating by setting the temperature detection mechanism of the high-frequency heating device so that the temperature of the potato, which is the object to be heated, was kept constant at a certain value of 60 to 70 degrees Celsius. At the same time, when the magnetron's oscillation operation is turned ON and OFF repeatedly, if the amount of water vapor generated from the potatoes exceeds the saturation point of the atmosphere in the heating chamber, or even if the amount is not so large, it will cause damage to the walls of the heating chamber. If the finder surface is quite cold, the water vapor in the atmosphere will quickly condense on the wall surface, leading to the aforementioned problem.

The present invention was made in view of this situation, and is designed to prevent condensation from occurring even when high-frequency heating is performed by maintaining a certain temperature of a heated object for a certain period of time (hereinafter referred to as temperature holding). It is something.

To this end, the present invention periodically increases or decreases the amount of air flowing through the heating chamber 1 while maintaining the temperature, and periodically releases the atmosphere of the heating chamber, which is prone to condensation, to the outside, even though it is convenient for temperature detection. This prevents condensation inside the heating chamber.

Specifically, as shown in Figure 3, the amount of circulating air is alternately changed Q.
1. Q2 to prevent dew condensation within the heating chamber 1.

That is, when high-frequency heating is started with the amount of circulating air Q1, and the temperature T1 of the potato, which is the object to be heated, rises as shown in Fig. 4 and reaches the upper limit T3 of the temperature to be maintained, the air is circulated in the heating chamber. Since the air is also warmed and the difference between the temperature of the incoming air and the temperature of the outgoing air is a value corresponding to the temperature of the object to be heated, the automatic control device 15 operates to cause the magnetron 9 to oscillate. At the same time as stopping the blower 7, the number of revolutions of the blower 7 is increased to increase the amount of air flowing inside the heating chamber Q2.

The time t1 during which this air amount is increased Q2 is the heating chamber 1.
Although it depends on the volume of the heating chamber, it is sufficient if the heating chamber continues for 2 to 3 seconds, for example, if the volume is 2 (if the circulating air volume is 2 m'/mm in the heating chamber, G at most).

However, this value of 2 to 3 seconds is based on 2M of air in the heating chamber.
It is the time required to thoroughly exhaust the air, and it goes without saying that the structure of the heating chamber 1 is designed to take time to ventilate, or the air inflow opening 5 and air outflow opening 6 are
Depending on the position, etc., it may be necessary to make the above duration a little longer.

When the above-mentioned air amount is increased Q2 and the atmosphere in the heating chamber is exhausted, the automatic control device 15
enters the temperature detection mode, and the temperature rise value of the air flowing out from heating chamber 1 decreases, reaching the lower limit T of the temperature of the potato, which is the object to be heated.
When the value corresponding to 2 is reached, the automatic control device 16 operates again to cause the magnetron 9 to oscillate.

Note that time t2 means that after the amount of air flowing in the heating chamber 1 returns to Ql, which is convenient for temperature detection, it becomes a steady flow state, and the temperature increase value of the air flowing out from the heating chamber 1 becomes This is enough time to adjust to the temperature of the object.

The magnetron 9 oscillates and the temperature of the object to be heated starts to rise again, but in the present invention, as shown in FIG.
At this point, the automatic control device 16 stops the oscillation of the magnetron 16 and releases the temperature detection mode.

Then, the air volume increases Q2L, and after t1 + t2 hours have passed, the temperature detection mode is entered again, and the lower limit of the maintenance temperature T2
When this happens, the magnetron 9 is made to oscillate.

Since then, high-frequency heating has continued in this connection,
Predetermined heating is completed while maintaining the temperature of the object to be heated within a constant temperature range.

In this way, the present invention detects the temperature rise value (temperature difference) between the temperature of the air flowing out from the heating chamber and the temperature of the incoming air, indirectly detects the temperature of the object to be heated, and automatically controls the heating. In a heating device, even when the temperature of the heated object is maintained at a predetermined value for a certain period of time while detecting the temperature, there is no condensation on the heating chamber walls or viewfinder, and all kinds of problems are almost completely eliminated. can do.

In addition, in the above-described embodiment, the amount of air flowing through the heating chamber can be increased or decreased by controlling the rotation speed of the blower.
This may be achieved by other means.

For example, the air flowing out from the heating chamber may be sucked into a blower for cooling the magnetron, and the opening degree of a resistor, ie, a damper, etc. in the flow path may be adjusted.

In this case, there is an advantage that only one blower is required.

Furthermore, when the oscillation operation of the magnetron is stopped to increase the amount of air circulating in the heating chamber, part or all of the warm air after cooling the heating element such as the magnetron may be mixed and used.

This is effective in lowering the water vapor saturation point of the atmosphere in the heating chamber, and even if condensation occurs, it can be removed.

In this case, the hot air can be used effectively by appropriately switching the air path.

Alternatively, as a means for obtaining hot air, instead of using hot air after cooling a heating element such as a magnetron as described above, the air flowing into the heating chamber may be directly heated.

However, when using hot air in this way, the heating chamber wall,
It is important to keep the finder, temperature sensing element, etc. from heating up, and for this purpose, determine the hot air mixing rate, hot air temperature, hot air supply time, etc. appropriately to avoid adverse effects on the subsequent temperature detection. must be avoided.

In addition, in the explanation of the embodiment, a case was shown in which the magnetron's oscillation operation was stopped when the temperature of the heated object reached the upper limit of the set temperature, and high-frequency heating was completely stopped. Heating may be continued by lowering the high frequency power to such an extent that the temperature does not rise or a sudden temperature drop does not occur.

In this case, since the number of times of heating using high-output radio-frequency power is reduced, the condition may be improved depending on the type of the object to be heated.

Further, in the description of the embodiment, a case has been shown in which the cycle of increasing/decreasing the amount of circulating air is set to a constant value, but there is no particular need for it to be fixed in this way.

That is, it may be changed as appropriate according to the temperature increase characteristics (temperature increase slope), water vapor generation characteristics, etc. of the object to be heated.

Specifically, the automatic control device is made to determine and recognize whether the slope of the temperature rise curve of the object to be heated is steep or gentle. If a large amount of water vapor is expected to be generated, control may be performed to shorten the cycle of increasing and decreasing the amount of air.

Conversely, if the slope is steep, the control device may similarly extend the cycle.

Further, the length of this cycle may be determined depending on the humidity level by operating a humidity detection mechanism.

In addition, in the example shown in the embodiment, even if the atmosphere in the heating chamber reaches the saturation point during one cycle of increasing/decreasing the air amount, the air amount will not be increased until a predetermined period of time has elapsed. It is quite conceivable that the above-mentioned abnormal situation may occur during the cycle.

For such a case, a humidity detection mechanism may be activated to prevent dew condensation by increasing the amount of air as needed during the cycle.

Again, sufficient time must be allowed for the circulating air to reach a steady state before the temperature sensing mechanism is placed in the sensing position.

In the above embodiments of the present invention, the heating is controlled by detecting the temperature of the air inside the heating chamber or the temperature of the air flowing out from the heating chamber. Heating can also be controlled by detecting the humidity of the air flowing out of the room.

Note that when detecting temperature or humidity in the heating chamber, it is necessary to prevent the detection element from being exposed to high frequency power.

If the sensing element is to be used by exposing it to high-frequency power, it is of course necessary to ensure that it does not adversely affect users or control equipment outside the heating chamber.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a general temperature-sensing high-frequency heating device including the present invention, Fig. 2 is a relationship between the amount of air circulating in the heating chamber and the temperature difference between inflow and outflow air during high-frequency heating, and Fig. 3 This is a diagram conceptually showing a cycle of increasing and decreasing the amount of circulating air that is repeated after the first operation of the automatic control device, and FIG. FIG. 3 is a diagram illustrating how a predetermined value is maintained. 1...Heating chamber, 2...Object to be heated, 3.
...Door, 5゜6...Opening, 7...
・Blower, 8... Exhaust path, 9... Magnetron, 13, 14... Temperature detection element, 15
... Automatic control device, 16 ... Power supply device.

Claims (1)

[Claims] 1. While the object to be heated in the heating chamber is being high-frequency heated by the oscillation of the magnetron, the temperature of the air in the heating chamber or the temperature of the air flowing out from the heating chamber to the outside is detected,
In devices that automatically control heating, when the temperature of the heated object is maintained at a certain predetermined temperature for a certain period of time, the amount of air flowing through the heating chamber is increased or decreased, and at an appropriate point in the air increase/decrease cycle. A high-frequency heating device characterized in that a magnetron is controlled by a temperature detection mechanism.