JPH0718553B2 - Heater - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heating device using a plurality of heaters (heating sources) such as an electric oven, a toaster range, and a microwave oven.

Conventional technology In the temperature control of an oven, etc., in order to keep the temperature inside the heating chamber constant, conventionally, a thermistor for measuring the temperature inside the heating chamber was used, and when a predetermined temperature was reached, the output of the heat source such as a heater was turned off. Reduce or block. In addition, generally well-known temperature control is performed such that the heater is energized again when the temperature of the thermistor falls below a predetermined value.

Problems to be Solved by the Invention However, in the temperature control by such a conventional method, there is an effect that the temperature in the heating chamber can be made substantially constant, but a temperature-sensing device such as a thermistor for measuring the temperature can be used. Elements are needed. Therefore, there is a big drawback that the cost becomes high.

When the heat-sensitive element is used, there is a problem that the cost becomes high and the temperature of the heat-sensitive element needs to be adjusted, which requires time and effort for manufacturing.

Although the temperature of the heat sensitive element can be controlled, the ambient temperature of the food placed in the heating chamber causes a delay time due to the heat capacity of the heater and the heating chamber and the heat capacity of the food, so some correction is required. I have a problem.

Means for Solving the Problems A heater serving as a heat source for heating, a heating chamber heated by the heater, a driving means for controlling the energy supplied to the heater, and the energy supplied to the heater are integrated according to a predetermined arithmetic expression. And an energy calculation means for subtracting, and an output determination means for comparing the amount of energy obtained by the energy calculation means with a predetermined target value to determine the output of the heating heat source. The energy calculation means increases the amount of energy according to a predetermined calculation formula, and when the value reaches a predetermined value, the output determination means decreases the average power to the heater.

Further, when the average power to the heater is cut off, the energy calculation means reduces the energy calculation amount according to a predetermined calculation formula. When the heating command is again issued by the user of the appliance, the energy control means for energizing the heater again and performing the above control is started with the energy calculation value amount at that time as a starting point. .

Since the increase / decrease in the energy calculation amount corresponding to the working temperature is always estimated, it is possible to perform the control almost equivalent to the temperature control using the temperature sensor.

The temperature of the heating chamber is constantly estimated and controlled on the basis of the amount of heat applied by applying electricity in the past. Therefore, the temperature of the heating chamber is controlled not by the feedback loop using a temperature sensitive element such as a thermistor but by the open loop control.

Therefore, it has a great effect that the configuration is simplified.

Example Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 3 is a cross-sectional view of a main part of an embodiment of a household microwave oven using the present invention. In the figure, 1 is a heating chamber. 2 is an upper heater provided in the upper part of the heating chamber,
It consists of a heating wire covered with quartz glass. Reference numeral 3 is a planar heater which is attached in close contact with the lower surface of the heating chamber and is called a lower heater. A magnetron 4 can radiate radio waves into the heating chamber 1 to heat the food 9. Reference numeral 5 is a food placing table, which can be engaged with a shaft 7 of a turntable motor 6 penetrating the lower surface of the heating chamber 1 and the central portion of the lower heater 3 to rotate. Reference numeral 8 is a cooling fan, and the magnetron 4 cools a high voltage transformer, a control circuit, and the like, which are not shown.

With these configurations, the food 9 placed in the heating chamber 1 is
Oven heating can be performed by heating with an electric wave or by raising the temperature in the heating chamber using an upper heater and a lower heater.

FIG. 4 shows an embodiment of the electronic circuit and control circuit of the household microwave oven of the embodiment of the present invention shown in FIG. In the figure, 10 is an outlet to a commercial power source, 11 is a door switch that opens and closes in conjunction with the door of the heating chamber,
One of them 12 is input to the microcomputer 13. 2 and 3 are the above-mentioned upper heater and lower heater, respectively. 8 is a cooling fan, 14 is a high-voltage power supply,
Supply power to the magnetron 4. Ry1 to Ry5 are relays, and their contacts are opened and closed by the control circuit. Reference numeral 15 is a low voltage source that supplies a control circuit and operating power supplies for Ry1 to Ry5. The microcomputer 13 stores a program for executing an example of a control sequence according to the present invention, which will be described later. Further, a clock signal 16 for generating a timing signal synchronized with the commercial power source 10 is input as an input. Also, the type of heating sequence, such as "toaster", "pizza",
Enter "microwave oven heating" and enter "heating time"
Also, the setting means 17 including an operation switch for instructing start and stop of heating is connected. Reference numeral 18 denotes a display unit that displays the type of heating sequence that has been set, the heating time, or the remaining heating time. Reference numeral 19 is a driving IC for driving the relays Ry1 to Ry5. In addition to these, a buzzer (not shown) that sounds according to the operation of the setting means is included.

FIG. 1 shows an embodiment of a block diagram of a control unit in an embodiment of the present invention. This is constituted by a program in the microcomputer 13 shown in FIG.

First, the setting unit 20 gives the heating sequence and the heating time set by the setting means to the operation command unit 21, and the operation command unit 21 starts and interrupts the heating operation by the door signal, the setting contents and the heating start input. , Instruct to finish.

The time measuring means 22 uses the clock signal 16 shown in FIG. 4 as a reference pulse generating section 23 and inputs a clock pulse, and measures a fixed time, for example, a time such as 1 second or 1 minute, and assigns it to each block. Give a time signal. The energy calculating means 24 is means for constantly calculating and storing the amount of energy supplied to the heater according to a procedure which will be described later in detail, and is constituted by a memory and a program in the microcomputer. Furthermore, the end-time energy storage means 25 stores the amount of energy calculated by the energy calculation means 24 at the end of heating such as the end of heating time, a cancel operation by the user, or the door being opened by the user during heating. It is a memory for storing.

The output determination means 26 combines the signals of the heating sequence, the current energy amount by the energy calculation means 24, the end point energy storage means 25, the time measurement means 22 and the like, by means of the means according to the present invention described in detail later, It is a means for determining the output of the heat source (heater) 27. This output drives a heat source such as a heater through the driving means 28, for example, the driving IC 19 shown in FIG.

The first feature of the configuration of the present invention is that there is no temperature measuring means such as the thermistor. Therefore, the control system does not include any heat source or any feedback from the heating chamber.

The second feature is that the calculation means for constantly calculating the amount of energy is provided even when the heating is finished, a predetermined value is set for the calculated value, and the output of the heat source is finally determined. That is, it has the output determining means of.

Now, in order to describe the operation of each block described above in detail, one embodiment of the heating sequence according to the present invention will be described with reference to FIG.

FIG. 2A is a diagram showing an embodiment of the calculation of the amount of energy according to the present invention as well as the relationship between the temperature and the time of a predetermined portion of the heating chamber by heating the heater.

When heating the heater (heat source output) at a constant maximum output, for example, 1 KW, until the time t ₁ , the curve a from the initial value Y _O
As described above, the temperature rises exponentially with a delay element and continues to rise as shown by the dotted line b after t ₁ to reach the equilibrium temperature. It can be easily confirmed by experiments that this curve is a rising curve that is almost determined by the heat capacity in the heating chamber, the amount of food, and the temperature. Then, in the actual temperature control, it is necessary to keep the temperature constant at a preset temperature. Therefore, in the present invention, the heat source output is reduced from P ₁ to P ₂ . This allows the temperature to be balanced and constant at Y _M , as in c.

It is possible to experimentally determine how much these outputs should be selected. Then, at the time t ₂ , if heating is completed,
The temperature decreases exponentially like d.

By simulating such a physical phenomenon as it is by using a theoretical analysis formula, it is possible to perform necessary temperature control without constructing a feedback loop using a temperature sensor. It is a basic idea.

That is, the curve of a rising of the start of heating, for simplicity, assuming as _{y = (Y M -Y O)} · t / t 1 + Y O trendline straight e made ..., the set temperature yn
In this case, the time tx for switching the heat source from the maximum output P ₁ to the next low output P ₂ is calculated from tx = (yn−Y _O ) ・ t ₁ / (Y _M −Y _O ) using the above approximation formula. be able to.

As described above, according to the present invention, the time for switching the output of the heat source can be immediately determined by the arithmetic expression shown in the above embodiment. This eliminates the need for an element such as a thermistor.

There are two problems here.

The first problem is that when the residual heat remains in the heating chamber, such as the first time and the second time, it is necessary to change the heating time of the heat source depending on the rest time.

Therefore, one embodiment of the present invention is characterized in that even when the heat source is not operating, the decrease in the temperature is calculated and stored.

FIG. 2B shows an example of such a case. This is an example in which heating is performed by the heat source P ₁ until time t _3, heating is stopped for a period from time t ₃ to t ₄ , and heating is performed again from t _{4 to} t ₅ . Next Once temperature was reached rising Y ₃ by curve f respectively decreased by a curve g, Yuku rises by a curve h at the time when decreased to Y _4. By fitting an approximate curve determined by experiments to each curve, it is possible to reliably control the temperature to a predetermined temperature.

The second problem is that if the type and amount of food change, the above approximation formula must be changed.

Therefore, in the embodiment of the present invention, such a problem is solved by dividing the heating sequence into groups so that such a difference does not occur so much when the heating sequence is selected. For example, if you classify them as toasters and pizzas, it is almost unnecessary to consider the difference in the amount of food.

In the above description, the description has been made by focusing on the temperature change, but not only the temperature, so in the following description, the term energy will be used.

FIG. 5 shows still another embodiment. In FIG. 5, the word “temperature” used in the above description is replaced with the word “energy”, and what is indicated by various curves is approximated by a straight line.

First, heating is performed at the maximum output of the heat source output P1 until time t1. At this time, the energy calculation means uses the calculation expression Y = A · t + U _O ≡f ₁ (t) as the current energy calculation amount Y (t is time, A is a predetermined constant, and U _O is an initial value). Value) is calculated, and the heat source output is reduced to P ₂ at time t ₁ when this Y reaches a predetermined maximum value Y _M.

Then, at t ₂ , the time set for heating has ended, so heating ends. When the energy calculation amount Y reaches Y _M , the heating output is reduced, so the calculation amount Y is also kept at Y _M. Then until a predetermined time T ₁ after the heating is finished, the energy calculation amount Y has been left Y _M, until subsequent T _2, the first subtractive g ₁ using (T), T ₂ thereafter The energy calculation amount is calculated by the second subtraction formula g ₂ (T).

With these approximation formulas, the temperature change described with reference to FIG. 2 can be approximated.

FIG. 6 shows another embodiment in which the energy calculation amount Y is further advanced.
It shows that the cooking is finished before reaching Ym, and the cooking is restarted after a pause for a certain time).

FIG. 6 shows a case where the first heating is started in the same manner as in the above-mentioned FIG. 5 and ended at time t ₃ (0 <t ₃ <t ₁ ).

At this time, it is assumed that the energy calculation amount y = f ₁ (t) is calculated and the value is Y ₁ , for example.

After that, since it was left to stand until time t ₄ , as shown in FIG. 5, after heating was completed, until a certain time T ₁ ,
The energy calculation amount Y has been left Y _1, energy calculation amount by the use of a first subtractive g ₁ (T) until later T _2, T ₂ after the second subtractive g ₂ (T) It is assumed that the energy calculation amount Y has been reduced to Y ₂ . When a heating command is given at this point, heating is performed at the heating output P ₁ as in the beginning. Then, the energy calculation amount y increases similarly calculated by the function of y = f ₁ (t),
After this value becomes equal to the energy calculation amount Y ₁ at the end point, the energy calculation amount is calculated using the _second increasing function y = f ₂ (t), and the calculated value is a predetermined value. Y _M
It is characterized in that it is operated with the same heating output until reaching.

The reason for introducing the second increasing function f ₂ is, as explained in the principle of FIG. 2, that the actual physical phenomenon is an exponential change having a delay element, whereas in the present embodiment, Since an approximate expression is used, an error occurs. A second increasing function is introduced to correct the error.

For example, assuming that f ₁ = V _O + t as the first increasing function and f ₂ = V _O + 3t (V _O is a constant) as the second increasing function, the time T _{X at} which the heating output P ₁ should be continued is Tx ( It can be uniquely determined as Y ₁ −Y ₂ ) / 1 + (Y _M −Y ₁ ) / 3.

Further, the means for reducing the heat source output to P ₂ can be substantially reduced by setting a certain predetermined cycle, for example, 40 seconds, and changing the ratio of the time when the heater is energized and the time when it is not energized. . For example, by repeating 20 seconds of energization and 20 seconds of non-energization, the output can be substantially half that of continuous energization.

EFFECTS OF THE INVENTION With the above configuration, the present invention has the following effects.

(1) Since a thermosensitive element such as a thermistor is not used, the structure is simple and the cost can be reduced.

(2) Since the amount of energy stored by past heating is estimated, accurate control can be performed.

(3) It can be performed only with time measurement and a simple arithmetic expression.

(4) When a plurality of heaters such as an upper heater and a lower heater are provided, the heat distribution can be made uniform by individually controlling the output of each heater.

[Brief description of drawings]

FIG. 1 is a control block diagram of a heater in one embodiment of the present invention, FIGS. 2A and 2B are explanatory views showing the temperature change and the heat source output change, and FIG. The figure is the same control circuit diagram, and FIG. 5 and FIG. 6 are explanatory views showing the calculation amount calculated by the energy calculating means. P ₁ , P ₂ …… Heat source (heater) output, 2 …… Upper heater,
3 ... Lower heater, 13 ... Microcomputer, 16 ...
... Reference pulse generator.

Continuation of the front page (56) References JP-A-49-62273 (JP, A) JP-A-55-33522 (JP, A) JP-A-50-43542 (JP, A) Actual development Sho-62-69702 (JP , U)

Claims (2)

[Claims] 1. A heating chamber and a heat source for heating the heating chamber,
A setting section for setting the heating operation of the heating chamber, a time measuring means for generating a reference time base, an operation command section for instructing start and end of the heating operation by a signal from the setting section, and a heating operation and a heating stop. Energy calculation means for calculating an energy calculation value at regular time intervals according to a predetermined calculation formula, and an output determination for decreasing the heating output of the heat source when the energy calculation value reaches a predetermined value. A heater having means. 2. The energy calculation means has at least two predetermined calculation expressions, and during the heating operation, the first calculation formula is used.
The calculation value of the
When the value reaches a predetermined value, the increase of the value is stopped, the value is kept at the predetermined value, and while the heating operation is stopped, the calculated value is changed in accordance with a second predetermined arithmetic expression. The heater according to claim 1, characterized in that the heater comprises energy calculating means for decreasing the energy.