JPH0438115B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an induction heating cooker equipped with a heat retention cooking function.

[Technical background of the invention and its problems]

In general, an induction heating cooker generates a high-frequency magnetic field from a heating coil and applies it to the object to be heated, that is, a pot, on a top plate, thereby creating an eddy current in the pot.The pot self-heats due to eddy current loss. Cooking is done by heating.

By the way, in such an induction heating cooker, a temperature sensor is attached to the back of the top plate, and the heating output is controlled according to the difference between the temperature detected by this temperature sensor and a preset temperature. There are some devices that enable thermal cooking in which the temperature of the food in the pot is maintained at the above-mentioned set temperature.

However, such induction heating cookers have the disadvantage that the temperature of the food cannot be accurately detected at the start of keeping warm cooking because there is a bottom plate and a top plate between the food in the pot and the temperature sensor. . In other words, for example, if you place a pot that has been heated in another cooker on the top plate and start cooking while keeping it warm, the temperature detected by the temperature detector will not change even if the food temperature is higher than the set temperature, as shown in Figure 1. is below the set temperature, the heating output is at its maximum,
Rather than keeping the food warm, the food temperature greatly exceeds the set temperature (overshoot).

To deal with this, some devices maintain the heating output at a constant low level until the temperature detected by the temperature sensor reaches the set temperature. In this case, even if you place a pot heated by another cooker on the top plate and start keep-warm cooking, the heating output remains constant at a low level, so the food temperature will not rise any further.
Overshoots as described above can be prevented. However, if the food temperature is initially below the set temperature, there is a drawback that it takes a long time for the food temperature to reach the set temperature, as shown in FIG.

[Purpose of the invention]

This invention was made in view of the above-mentioned circumstances, and its purpose is to prevent the food temperature from greatly exceeding the set temperature and to quickly bring the food temperature to the set temperature. I can,
To provide an excellent induction heating cooker that enables optimum heat-retaining cooking.

[Summary of the invention]

This invention provides a first thermal cooking means that controls the heating output according to the difference between the temperature detected by the temperature sensor and the set temperature, and reduces the heating output until the temperature detected by the temperature sensor reaches the set temperature. A second heat-retaining cooking means for maintaining a constant level is provided, and this first
Alternatively, the second heat-retaining cooking can be selectively performed.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In FIGS. 3 and 4, reference numeral 1 denotes a main body of the induction heating cooker, and a top plate 3 is provided on the upper surface of the main body 1 on which a pot 2, which is an object to be heated, is placed. Furthermore, on the front of the main unit 1, there is a cooking mode selection knob 4 and an output/temperature setting knob 5.
is provided. A coil support plate 6 is disposed in the main body 1 corresponding to the top plate 3 at a distance from the back surface of the top plate 3, and a heating coil 7 is provided on the coil support plate 6. A temperature sensor, such as a thermistor 8, for detecting the temperature of food is mounted approximately at the center of the back surface of the top plate 3, and this thermistor 8 is connected to a circuit board 9 on the bottom plate of the main body. Furthermore, the circuit board 9
includes an inverter circuit 1 that drives the heating coil 7.
0, a fan 11 for cooling the heating coil, and a cooking mode selection switch 12 connected to the knob 4.
is connected.

As shown in FIG. 5, the cooking mode selection knob 4 can arbitrarily select a heating cooking mode, a heating keeping cooking (first keeping warming cooking) mode, a keeping warming cooking (second keeping warming cooking) mode, and a frying cooking mode. It's becoming like that. Here, the heating cooking mode is set using knob 5.
is used for setting the heating output, and the heating output is controlled only according to the set output of the knob 5, regardless of the temperature detected by the thermistor 8. In the heat retention cooking mode, the knob 5 is used for temperature setting, and the heating output is controlled according to the difference between the temperature detected by the thermistor 8 and the set temperature of the knob 5. In the heat retention cooking mode, the knob 5 is used for temperature setting, and the heating output is maintained at a constant low level until the temperature detected by the thermistor 8 reaches the set temperature of the knob 5.
In the fried food cooking mode, the knob 5 is set to a high temperature corresponding to tempura or fry cooking, and the heating output is controlled according to the difference between the temperature detected by the thermistor 8 and the set temperature of the knob 5.

FIG. 6 shows the main part of the control circuit.

First, the knob 5 is connected to a sliding terminal of a sliding resistor 5a, and a DC voltage Vcc is applied to both ends of the sliding resistor 5a via resistors 21 and 22 in series.

Further, the cooking mode selection switch 12 includes selection switches 12 ₁ and 12 ₂ . In the selection switch 12 ₁ , contact a closes in situations where heating output control based on temperature is required, such as heat retention cooking mode, heat retention cooking mode, deep frying cooking mode, etc., and heating output independent of temperature as in heat cooking mode. Contact b is designed to close in situations where control is required. In the selection switch 12 ₂ , contact a closes in situations where high-level heating output control is required, such as heating cooking mode, heating keeping cooking mode, and frying cooking mode, and high-level heating output control like keeping warm cooking mode is performed. Contact b is designed to close in situations where no contact is required. Then, a series circuit of resistors 23 and 24 and a resistor 25,
A DC voltage Vcc is applied to each of the 26 series circuits, and the voltage generated at the interconnection point of the resistors 23 and 24 is supplied to the signal processing circuit 30 via the contact a of the selection switch ₁₂₁ , and The voltage generated at the interconnection point is supplied to the signal processing circuit 30 via contact b of the selection switch 12 ₁ .

Therefore, the thermistor 8 is included in the signal processing circuit 30.
is connected. The signal processing circuit 30 mainly includes a differential amplifier 21, and corrects the voltage across the thermistor 8 using the output voltage of the selection switch ₁₂₁ , and outputs the amplified signal. In this case, the correction based on the output voltage of the selection switch 12 ₁ deals with the fact that the sliding terminal voltage of the sliding resistor 5a based on the sliding position of the knob 5 is common regardless of the cooking mode. That is, the selection switch 12
If the contact _a of the selection switch 12 is closed, the voltage across the thermistor 8 is corrected to correspond to the detected temperature, and if the contact b of the selection switch ₁₂ is closed, the voltage across the thermistor 8 is ignored and detected. This makes temperature invalid.

The output voltage of the signal processing circuit 30 is determined by the difference detection circuit 40.
supplied to This difference detection circuit 40 mainly includes a differential amplifier 41, and outputs a voltage corresponding to the difference between the output voltage of the signal processing circuit 30 and the sliding terminal voltage of the sliding resistor 5a. Thus, the output voltage V ₀ of the difference detection circuit 40 is applied to the Zener diode 52 via the resistor 51 and to the Zener diode 54 via the resistor 53. And the voltage across the Zener diode 52
V ₁ is the contact a on the heat retention cooking side of the selection switch 12 ₂
is also extracted through the Zener diode 54
The voltage V ₂ across is extracted via the thermal cooking side contact b of the selection switch 12 ₂ and becomes the heating output control voltage Vout.

Further, the output voltage V ₀ of the difference detection circuit 40 is supplied to the minimum heating output setting circuit 60 . This minimum heating output setting circuit 60 determines the output voltage of the difference detection circuit 40.
V ₀ is applied between the base and emitter of the NPN transistor 63 through the resistors 61 and 62 in series, and the collector voltage of the transistor 63 is
A voltage is applied between the base and emitter of an NPN transistor 64, and the collector of the transistor 64 is connected to the movable terminal of the selection switch ₁₂₂ .
Further, it has a comparison circuit 67 that compares the reference voltage Vref generated at the interconnection point of the resistors 65 and 66 with the voltage generated at the interconnection point of the resistors 61 and 62. connected to the base. That is, the minimum heating output setting circuit 60 turns on the transistor 64 when the output voltage V ₀ of the difference detection circuit 40 becomes below a certain value, and forcibly sets the heating output control voltage V _put to zero level.

Next, the operation in the above configuration will be explained.

Assume that the pot 2 is placed on the top plate 3, the heating and keeping-warm cooking mode or the keeping-warm cooking mode is selected with the knob 4, and the keep-warm temperature is set with the knob 5. When the cooking start operation is performed, as shown in FIG. 7, if the temperature detected by the thermistor 8 is much lower than the set temperature and the temperature difference is large, the output voltage V ₀ of the difference detection circuit 40 becomes a high level. , as the temperature difference becomes smaller, the output voltage V ₀ becomes lower level. on the other hand,
The voltage V ₁ across the Zener diode 52 maintains the Zener voltage level if the output voltage V ₀ is equal to or higher than the Zener voltage level (high level).
When the output voltage V ₀ becomes less than the Zener voltage level, it matches the output voltage V ₀ . Furthermore, the voltage V ₂ across the Zener diode 54 maintains the Zener voltage level if the output voltage V ₀ is equal to or higher than the Zener voltage level (low level);
When V ₀ goes below the Zener voltage level, it matches its output voltage V ₀ .

However, when cooking a pot (including food) that has cooled down after a while after being heated, turn knob 4.
Select the heating and keeping warm cooking mode. Then, the voltage V ₁ across the Zener diode 52 is extracted as the heating output control voltage Vout, and the heating output is controlled according to the heating output control voltage Vout. That is, as shown in FIG. 8, the heating output is initially set at the maximum level, and decreases as the temperature detected by the thermistor 8 approaches the set temperature. Furthermore, when the temperature detected by the thermistor 8 reaches just before the set temperature, the heating output becomes the minimum level. Then, when the detected temperature reaches the set temperature, the transistor 64 of the minimum heating output setting circuit 60 is turned on, and the heating output control voltage Vout is forcibly brought to the zero level, whereby the heating output is brought to the zero level. Thereafter, the heating output is controlled according to the difference between the detected temperature and the set temperature.

In this way, when heating and keeping warm cooking is performed, the heating output is set according to the difference between the detected temperature and the set temperature, so even if the initial temperature of the pot is low, the temperature of the food in the pot can be quickly adjusted. It is possible to reach the set temperature.

If you want to immediately heat a pot that has been heated in another cooker, use knob 4 to select the heat retention cooking mode. Then, the voltage V ₂ across the Zener diode 54 is extracted as the heating output control voltage Vout, and the heating output is controlled according to the heating output control voltage Vout. That is, as shown in FIG. 9, the heating output is maintained at a constant minimum level until just before the temperature detected by the thermistor 8 reaches the set temperature. Then, when the temperature detected by the thermistor 8 reaches the set temperature, the transistor 64 of the minimum heating output setting circuit 60 is turned on, and the heating output control voltage Vout is forcibly brought to the zero level, whereby the heating output becomes the zero level. Thereafter, the heating output is controlled according to the difference between the detected temperature and the set temperature.

In this way, if you use thermal cooking, the heating output will be maintained at a constant minimum level until the detected temperature reaches the set temperature, so even if the food in the pot is hot, the temperature of the food will not exceed the set temperature. It won't happen.

In this way, by selectively using heat-retaining cooking and heat-retaining cooking depending on the situation, optimal heat-retaining cooking can be performed.

Incidentally, in the above embodiment, the heating output during thermal cooking is maintained at a constant minimum level, but it is not necessarily required to be at the minimum level as long as it is kept at a constant low level. In addition, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without changing the gist.

〔Effect of the invention〕

As described above, according to the present invention, the food temperature does not greatly exceed the set temperature, and the food temperature can quickly reach the set temperature, making it possible to achieve optimal thermal cooking. We can provide induction heating cookers.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams for explaining heat retention cooking using a conventional induction heating cooker, respectively. FIG. 3 is an external perspective view of an embodiment of the present invention, and FIG. 4 is an internal mechanism of the same embodiment. FIG. 5 is a specific configuration diagram of the cooking mode selection knob and its surrounding parts in the same embodiment, FIG. 6 is a configuration diagram of the main part of the control circuit in the same embodiment, and FIGS. 7 and 8 9 and 9 are diagrams for explaining the operation of the same embodiment, respectively. 1...Main body, 2...Pot, 3...Top plate, 4...Cooking mode selection knob, 5...Output/
Temperature setting knob, 7... Heating coil, 8... Thermistor (temperature detector), 12... Cooking mode selection switch, 30... Signal processing circuit, 40... Difference detection circuit, 60... Minimum output setting circuit.

Claims (1)

[Claims] 1. In an induction heating cooker comprising a temperature sensor for detecting food temperature attached to the back side of a top plate on which an object to be heated is placed, the heating output is adjusted according to the difference between the temperature detected by the temperature sensor and the set temperature. a first heat-retaining cooking means for controlling the heat-retaining cooking means; a second heat-retaining cooking means for maintaining the heating output at a constant low level until the temperature detected by the temperature sensor reaches the set temperature; and the first or second heat-retaining cooking means. An induction heating cooker characterized by comprising a selection means for selecting.