JPH067513B2 - Induction heating cooker - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an induction heating cooker having a temperature control function.

(B) Conventional technology In the past, temperature control using an induction heating cooker provided a temperature detection means such as a thermistor on the back of the top plate, which is the surface on which cooking utensils such as pans are placed, to detect the heat received from the cooking pan The temperature is detected by the means, the detected temperature is compared with the temperature set by the temperature setting means, and the oscillation of the switching element is controlled so that the detected temperature becomes equal to the set temperature. The cooker having such a configuration is excellent in that the cooker is inexpensive and easy to use.

However, in such induction heating cookers, as described above, the temperature detecting means is provided on the back surface of the top plate, so when using a pan with a high center of bottom surface and a high thermal conductivity, a pan with a high thermal conductivity is used. The heat is delayed from being transmitted to the temperature detecting element, and the temperature Tth detected by the temperature detecting means at the beginning of cooking is detected.
As the temperature of the pan becomes higher and the temperature T _{B of the} food increases accordingly, the temperature of the food in the pan greatly exceeds the set temperature Tref as shown in FIG. There was a risk of such problems. Also, the bottom of the pot is flat,
When a material having poor heat conduction is used as the material of the pan, if the temperature T _B of the food in the pan becomes lower than the detected temperature Tth detected by the temperature detecting means at the beginning of the cooking, as shown in FIG. There was an inconvenience to say.

Therefore, after the temperature control operation is started in the induction heating cooker and the detected temperature detected by the temperature detecting means reaches the set temperature for the first time, after a predetermined time delay of about 3 to 4 minutes, the food in the cooking utensil is delayed. Japanese Patent Application Laid-Open No. 59-91690 discloses a technique for performing light emission display assuming that the temperature is stable.

(C) Problems to be solved by the invention However, in the case of a pan having high heat conduction and the bottom closely adhering to the top plate, the temperature Tth detected by the temperature detecting means and the pan as shown in FIG. The temperature T of the food inside
B is almost the same, 3 ~ after the detected temperature reaches the set temperature
After the delay of 4 minutes, displaying the stability of the temperature of the cooked product results in a waste of unnecessary power and heating time.

(D) Means for solving the problem Temperature detecting means for detecting the temperature of the cooking utensil through the top plate,
A temperature setting means for setting a temperature, a comparing means for comparing the temperature detected by the temperature detecting means with a set temperature of the temperature setting means, and a switching element for making the detected temperature equal to the set temperature by the output from the comparing means. There is provided an operation control means for controlling the operation of the above and a shift means for observing a change state of the detected temperature before the detected temperature reaches the set temperature after the heating is started and for shifting the set temperature according to the detected state.

E) Since the temperature is controlled so that the detected temperature becomes the set temperature shifted by the shift means at the start of heating operation, the cooking temperature can be brought close to the set temperature in a stable state.

F) Example FIG. 1 is a block diagram showing an example of the induction heating cooker of the present invention, in which (1) is an induction heating coil (2), a resonance capacitor (3), a switching transistor (4), Shows an inverter circuit consisting of a damper diode (5), etc., and by turning on and off the switching transistor (4),
A high-frequency current is supplied to the induction heating coil (2) to induction-heat a cooking pot (7) arranged in proximity to the heating coil (2) via a top plate (6). (8) is an input power detection circuit that detects the input power to the inverter (1), (9) is an input power setting circuit that sets the input power to the inverter (1), (10)
Is a temperature detection circuit consisting of a series connection of a thermistor (11) and a resistor (12) that detects the temperature of the pan (7) from the back of the top plate (6), (1
3) is a temperature setting circuit for setting the temperature of the pot (7), (14) is the input power detection circuit (8), input power setting circuit (9), temperature detection circuit (10) and temperature setting circuit ( An analog multiplexer for time-divisionally selecting the signal from 13), and the signal from this multiplexer (14) is A / D converted by an A / D conversion circuit (15). (16) is input power control means for controlling the input power by comparing the detected power and the set power supplied from the A / D conversion circuit (15), and temperature control for controlling the temperature by comparing the detected temperature and the set temperature. A microcomputer provided with a means and a timer means for measuring time, and when heating is selected by the operation mode selection means (17), the input power control means operates to turn on the switching element (4). When the ON period data Pcon according to the period is adjusted and the heat retention mode is selected, the set input power is set to 400 W so that the heating output becomes low, and the heating state is maintained. Further, when the operation mode (17) becomes tempura, the set input power is set to the maximum level of 1300 W, and the temperature control means also works to set temperature Tref. When Tref> Tth, the oscillation start signal for starting the heating operation by the inverter is started. And an oscillation stop signal for stopping the heating operation by the inverter at TrefTth. Further, the microcomputer (16) has a calculating means for calculating a predetermined temperature T ₁ (for example, T ₁ = Tref / 2) lower than the set temperature Tref, and stops the oscillation when the detected temperature Tth reaches T _1. The means for observing the change ΔTm of Tth, the means for shifting the set temperature Tref to T′ref according to the change ΔTm, and the set temperature after the detected temperature Tth reaches T′ref after re-oscillation And means for returning to Tref. Reference numeral (18) is a notification device such as a display device or a buzzer, which is operated by a notification signal from the microcomputer (16). (19) is the microcomputer
The ON period length corresponding to the ON period data Pcon from (16) is applied to the switching transistor via the drive circuit (20).
An operation control circuit for turning on / off (4) is shown. The start / stop of oscillation of the inverter circuit (1) is controlled by an oscillation start / stop signal from the microcomputer (16).

In such induction heating cooker, when the heating state is selected by the operation mode selection means (17), the input control means in the microcomputer (16) operates, and the detected input power and the set input power are compared, The ON period data Pcon is adjusted so that the detected input power becomes equal to the set input power, and the operation control circuit (19) switches the switching transistor accordingly.
Controls the operation of (4). Also, operation mode selection means (17)
When the heat retention mode is selected by, the input power setting means
Regardless of the setting in (9), the set input power is set to a low level, for example, 400 W in the microcomputer (16), and the same operation as described above is performed.

On the other hand, when the operation mode selection means (17) sets the ceiling plastic mode, the set input power level in the microcomputer (16) is the highest level regardless of the set value in the input power setting means (9). For example, it is set to 1300 W, and the power control unit controls the heating of 1300 W in response to this. At the same time, the temperature control means in the microcomputer (16) operates to compare the detected temperature Tth given through the A / D conversion circuit (15) with the set temperature Tref to obtain Tref.
When Tth is reached, an oscillation stop signal is sent to the operation control circuit (19), and when Tth <Tref is reached, an oscillation start signal is sent to the operation control circuit (19). In this way, the temperature of the pan (7) is controlled by intermittently oscillating the inverter circuit (1).

Further, at the time of this temperature control operation, a temperature lower than this, for example, T ₁ = Tref / 2 is calculated from the set temperature Tref. This T ₁ and the detected temperature Tth are constantly compared,
When the detected temperature Tth reaches T ₁ , the oscillation is temporarily stopped and the state is maintained for a predetermined time t ₀ . The change ΔTm in the detected temperature Tref during this period is detected, and whether ΔTm is zero or not is compared. When this ΔTm is zero, it is judged that the temperature Tth detected in the pan (7) and the temperature of the cooking product such as the top-grade oil in the pan (7) are substantially equal as shown in FIG. Tr
The ef is not changed and the oscillation is restarted. When the detected temperature Tth reaches the set temperature Tref, the oscillation of the inverter is stopped and a notification signal is sent to the notification means (18) to notify the user of light emission, sound, etc., and thereafter, the detected temperature Tth.
Temperature control is performed so that th is maintained at the set temperature Tref.

On the other hand, when ΔTm is not zero, it is determined that the temperature Tth of the pan (7) is different from the temperature of the cooking product as shown in FIG. 3 or 4, and the set temperature Tref is set to T′ref.
(T'ref = Tref-kΔTm: k is a constant) and the detected temperature Tth is compared with T'ref to obtain this Tt.
When h reaches T'ref, the inverter oscillation is stopped and a notification signal is sent to the notification means (18) to notify of light emission, sounding and the like. That is, here, in the case where the temperature of the cooked food is lower than the detected temperature Tth as shown in FIG. 3, ΔTm becomes negative, T′ref = Terf−kΔTm is set higher than Tref, and In the case where the temperature of the cooked food is high as shown in FIG. 4, ΔTm becomes positive, and T′ref = T
ref-kΔTm is set lower than Tref, and Tth
K is adjusted to an appropriate positive number so that the temperature of the cooked product becomes Tref when becomes T'ref. Then, each time the detected temperature Tth reaches T'ref and the oscillation is stopped, T'ref is gradually brought closer to Tref, and finally returns to the original set temperature Tref. A flowchart showing such an operation is shown in FIG.

In the present embodiment, the heating is temporarily stopped and the heating state is observed, but the ΔTm corresponding to the integrated power from the start of heating may be observed to determine the shift state of the set temperature.

G) Effect of the invention As described above, the induction heating cooker of the present invention shifts the set temperature by observing the temperature change state before the detected temperature reaches the set temperature, and the temperature of the cooked food becomes stable at the set temperature. Since they are close to each other, power loss due to overheating at the beginning of heating operation and abnormal high temperature of cooking can be prevented, and it takes time to bring the temperature of cooking to the set temperature due to insufficient heating It also eliminates the inconvenience of becoming longer.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an induction heating cooker according to the present invention, and FIG.
FIGS. 4 to 4 are characteristic diagrams showing changes in the temperature detected by the cooking device of the present invention and the temperature of the food, FIG. 5 is a flow chart showing the operation of the cooking device of the present invention, and FIGS. 6 to 8 are conventional cooking processes. It is a characteristic view which shows the detected temperature in a container and the change of the temperature of a cooking object. (1) ... Inverter circuit, (7) ... Pot, (10) ... Temperature detection circuit,
(13)… Temperature setting circuit, (16)… Microcomputer, (1
7) ... Operation mode selection means, (18) ... Notification means, (19) ... Operation control circuit.

Claims (1)

[Claims] Claim: What is claimed is: 1. An induction heating cooker for induction heating a cooking utensil disposed in proximity to a heating plate by generating a high-frequency alternating magnetic field in the induction heating coil, wherein cooking is performed via the top plate. Temperature detecting means for detecting the temperature of the tool, temperature setting means for setting the temperature, comparing means for comparing the temperature detected by the temperature detecting means and the set temperature of the temperature setting means, and the output from the comparing means The operation control means for controlling the heating operation so that the detected temperature becomes equal to the set temperature, and the change state of the detected temperature after the start of heating and before the detected temperature reaches the set temperature are observed, and the set temperature is set according to the changed state. An induction heating cooker provided with shift means for shifting.