JPH05315068A - Small article load detecting method for induction heating cooking device - Google Patents

Abstract

PURPOSE:To perform stable detection for small articles against a fluctuation of power supply voltage and a change of pot loads. CONSTITUTION:Input power given to a load is adjusted (step 103, 104) to a fixed level by the predetermined timing, to detect (step 105) input voltage at this time. In accordance with this input voltage, the fixed input power level is corrected to readjust the input power to his correction level (step 106), thereafter to detect (step 107) the input power from an input current and input voltage, and this input voltage is compared with a preset fixed small article detection level (step 108) to perform small article load detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small load detecting method for an induction heating cooker.

[0002]

2. Description of the Related Art Conventionally, in an induction heating cooker, a small load is detected in order to prevent the small load from being heated when a small load such as a spoon that is different from a normal load such as a pan is placed. It is designed to stop heating. That is, by utilizing the fact that the input power to the small load is smaller than the input power to the normal load, the input power given to the load is detected, and when the input power is smaller than the predetermined small load detection level, the small load is detected. It is detecting.

[0003]

However, if the power supply voltage fluctuates, the input voltage applied to the load also fluctuates. Therefore, if the small object load detection level is constant, erroneous detection may occur. Therefore, the small object detection level may be lowered in anticipation of the fluctuation of the power supply voltage, but if the small object detection level is too low, there is a risk that it may be determined to be normal for a different pan load. It is also proposed to change the small object load detection level according to the fluctuation of the power supply voltage, but this has a problem that the operation is unstable and the circuit configuration becomes complicated. The present invention has been made in view of the above problems, and an object of the present invention is to provide a small load detection method for an induction heating cooker that can perform stable small product detection with respect to fluctuations in power supply voltage and changes in pan load. It is what

[0004]

In order to achieve the above-mentioned object, a method for detecting small items of an induction heating cooker according to the present invention comprises:
The input power applied to the load is adjusted to a constant level at a predetermined timing, the input voltage at this time is detected, the constant input power level is corrected according to this input voltage, and the input voltage is readjusted to the correction level. After that, the input electric power is detected from the input current and the input voltage, and the small object load is detected by comparing the input voltage with a preset constant small object detection level.

[0005]

When the input power applied to the load is adjusted to a constant level at a predetermined timing, the actual input power should be at the constant level unless the power supply voltage fluctuates, but if the power supply voltage fluctuates, It does not reach that level.
Therefore, if the input voltage when the input power is adjusted to a constant level is detected, and the input power level is corrected and readjusted according to the input voltage, the actual input power becomes the initial constant level. Therefore, the small object load can be detected by detecting the input power at this time and comparing it with a preset constant small object detection level. That is, when the detected input power is lower than the small object detection level, the small load is determined, and when the detected input power is high, the normal load is determined.

[0006]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 2 shows an electric circuit of an induction heating cooker for carrying out the small load detection method according to the present invention. A full-wave rectifier circuit 3 and a smoothing circuit 6 including a choke coil 4 and smoothing capacitors 5a and 5b are connected to the AC power source 1 via a filter 2, and a DC power source can be obtained by these. This DC power supply has a heating coil 7 and a transistor 8
Are connected in series, a resonance capacitor 9 is connected in parallel to the heating coil 7, and a diode 10 is connected in parallel to the transistor 8.

An input current detecting circuit 11 is provided after the filter 2, and an input voltage detecting resistor 12 and a voltage dividing resistor 13 are connected to the rectified and smoothed DC power source. A transistor drive circuit 14 is provided at the base of the transistor 8, and a collector-emitter voltage detection resistor 15 and a voltage dividing resistor 16 are connected to the collector side. The transistor drive pulse generation circuit 17 includes a trigger generation circuit 18a, a self-excited oscillator 18, a comparator 19, and an AND circuit 20. The trigger generation circuit 18a includes the collector-emitter voltage detection resistor 15 and the voltage dividing resistor 1
6 is detected, and a trigger signal is emitted at the timing when the voltage becomes minimum. Self-excited oscillator 1
Reference numeral 8 applies a sawtooth wave or a triangular wave to the comparator 19 based on the trigger signal from the trigger generation circuit 18a. The comparator 19 is a sawtooth wave signal from the self-excited oscillator 18 and a D / A from a microcomputer 21 described later.
The rectangular pulse signal is output based on the signal output. The AND circuit 20 receives the rectangular pulse signal from the comparator 19 and the energization permission signal or the energization non-permission signal from the microcomputer 21 as an input signal and outputs a drive pulse to the transistor drive circuit 14.

The microcomputer 21 receives an input current detection signal (Pi) from the input current detection circuit 11 and an input voltage detection signal (Pi) from the input voltage detection resistor 12.
v) is used as an input signal and a predetermined program stored in the ROM is executed to output the D / A signal to the comparator 19 via the D / A converter 22 and
The transistor drive circuit 14 is controlled by outputting an energization permission signal or a non-permission signal to the ND circuit 20. The heating coil 7, the resonance capacitor 9,
The transistor 8, the diode 10, the transistor drive pulse generation circuit 17, the microcomputer 2
1, the DA converter 22 and the like form an inverter circuit.

The control operation by the microcomputer 21 of the induction heating cooker having the above configuration will be described below with reference to the flowchart of FIG. When the AC power supply 1 is turned on, the self-excited oscillator 18 oscillates and the microcomputer 21
Is the transistor drive pulse generation circuit 1 in step 101.
An H (high) energization permission signal is output to the AND circuit 20 of No. 7. Next, at step 102, the set power P set by the operator by the output setting means (not shown) in advance.
The corresponding D / A signal is output to the comparator 19 of the transistor drive pulse generation circuit 17 via the D / A converter 22. As a result, the comparator 19 becomes the microcomputer 2
The comparator 19 compares the sawtooth wave signal from the self-excited oscillator 18 with the D / A signal from 1 as a threshold value, and outputs the H signal only when the sawtooth wave signal is larger than the threshold value. Outputs a rectangular pulse signal corresponding to the set power P. Further, the AND circuit 20 is the microcomputer 2
Since the energization permission signal of H is input from 1, the rectangular pulse signal from the comparator 19 is passed as it is and output to the transistor drive circuit 14. As a result, the LC resonance circuit oscillates to heat the load such as a pan placed on the heating coil 7.

Next, the microcomputer 21 waits for a predetermined time in step 103, and then in step 104 outputs a D / A signal corresponding to the constant input power P ₀ . The step 103 is to wait for a predetermined time every time the predetermined time elapses, that is, at a predetermined timing with a constant input power P _0.
This is for outputting a considerable D / A signal. After this,
In step 105, the input voltage Pv is detected, and in step 10
In step 6, a correction power P ₀ ′ corresponding to the input voltage Pv is selected from a table stored in the POM in advance, and a D / A signal corresponding to this correction power P ₀ ′ is output. Table 1 is an example of the correction table when the constant input power P ₀ is 600 W. Here, the corrected power P ₀ ′ is a converted value when the input voltage is 100V.

[Table 1] Input voltage Pv (V) Corrected electric power P ₀ ′ (W) 90 or less 740 (constant) 91 724 92 709 93 694 ... 99 612 100 600 101 101 588 102 577 103 565 ... 109 504 110 or more 496 ( (Constant)

Subsequently, the microcomputer detects the input power W on the basis of the input current Pi and the input voltage Pv in step 107, and determines whether the detected input power W is larger than a predetermined small object detection level K ₀ in step 108. If W> K ₀ , the procedure returns to step 101 and the above steps are repeated. If W> K _0, step 10
In step 9, it is determined that there is an abnormality, that is, an accessory, and an L (low) energization non-permission signal is output.

FIG. 3 shows an example of changes in the D / A signal output and the input voltage of the microcomputer 21 when the pan load is normal. According to this, while the D / A signal corresponding to the set power P is being output, the constant power P is set at a predetermined timing.
A D / A signal corresponding to ₀ is output. The set power P ₀
Input power equal to the set power P is obtained in response to a considerable D / A signal output, but the input power changes according to the power supply voltage that fluctuates from time T. Further, in response to the D / A output corresponding to P ₀ output at a predetermined timing, the input power drops to P ₀ at the same timing,
When the power supply voltage fluctuates from the time point T, the input power at the time of outputting the D / A signal corresponding to P ₀ changes according to the fluctuation of the power supply voltage as shown by P ₀₁ , ..., P ₀₅ in the figure.

[0013] Thus, by comparing the input power W and the small detection level K ₀ in this state, K ₀ at time P ₀₂ and P ₀₃
The following is a possibility that a small item is erroneously detected. However, the microcomputer 21 outputs the D / A signal corresponding to P ₀ according to the input voltage Pv shown in Table 1.
'Selects the, in the figure P _01' compensation power P ₀ according to the table shown in, ..., P ₀₅ 'as shown in, the correction power P _0'
Since the D / A signal corresponding to is output, the input power becomes a constant level P ₀ in response to this. Therefore, if the input power W at the time of outputting the D / A signal corresponding to the corrected power P ₀ ′ is detected and the input power W is compared with the predetermined small object detection level K ₀ , the small object load or the pan The load is accurately detected.

FIG. 4 shows an example of changes in D / A signal output and input power of the microcomputer 21 when a small load is applied. In this example, the microcomputer 21 outputs the D / A signal corresponding to the set power P, but the input power is not the set power level P but is considerably low because the load is small. Further, the input power is lower than P ₀ for the D / A signal corresponding to P ₀ output at a predetermined timing. If the power supply voltage fluctuates from time T, the input power also fluctuates accordingly. However, as in the case of the pan load, P ₀ corresponds to D /
The correction power P ₀ ′ is selected according to the input voltage Pv at the time of outputting the A signal, and the D / A signal output corresponding to the correction power P ₀ ′ is output as shown by P ₀₁ ′, ..., P ₀₄ ′ in the figure. As a result, a constant input power can be obtained. Therefore, if the input power at this time is detected and compared with the small object detection level K ₀ , it can be accurately detected that it is a small object load.

As described above, since the D / A signal output from the microcomputer 21 at a predetermined timing is a signal corresponding to the constant power P ₀ , the set power P is variously changed or the pan load is changed. Even then, the input power at the timing of small object detection is always constant, and stable small object detection can be performed.

[0016]

As is apparent from the above description, according to the present invention, the input power is adjusted to a constant level according to the fluctuation of the power supply voltage, and the input power detected at this time and the constant small object detection level are adjusted. Therefore, stable small object load detection can be performed regardless of fluctuations in the power supply voltage. Moreover, since the small object load detection level of the input power is constant, the circuit configuration is simple. Further, since the input power is adjusted to a constant level at a predetermined timing, there is an effect that stable small object load detection can be performed even when the set power or the pan load changes.

[Brief description of drawings]

FIG. 1 is a flowchart of a method for detecting a small load of an induction heating cooker according to the present invention.

FIG. 2 is an electric circuit diagram of an induction heating cooker in which the small load detection method according to the present invention is implemented.

FIG. 3 D / A of microcomputer under normal load
It is a figure which shows the time change of a signal output and input electric power.

FIG. 4 D / A of a microcomputer when a small object is loaded
It is a figure which shows the time change of a signal output and input electric power.

[Explanation of symbols]

 11 ... Input current detection circuit, 12 ... Input voltage detection resistor, 21 ... Microcomputer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshinori Sasaki 1-20-5 Tenma, Kita-ku, Osaka-shi, Osaka Inside Zojirushi Mahobin Co., Ltd.

Claims (1)

[Claims] 1. An input power applied to a load is adjusted to a constant level at a predetermined timing to detect an input voltage at this time, and the constant input power level is corrected according to the input voltage to obtain a correction level. After readjusting the input power, the input power is detected from the input current and the input voltage, and the small load detection is performed by comparing the input voltage with a preset constant small object detection level. A small load detection method for induction heating cookers.