KR100214598B1 - Microwave oven with temperature sensor - Google Patents

Abstract

The present invention relates to a microwave oven using a thermopile type temperature sensor and an automatic thawing method thereof. In the related art, in order to measure the weight of a thermopile type infrared sensor and a food for measuring the surface temperature of the food when the frozen food is thawed. Since the weight sensor must be used, it may cause a cost increase, and in case of a large load due to the magnetron output after the initial heating time (T1), it takes a long time to end the thawing, and in the case of a small load The output of magnetron is strong compared to the size of the load, which can cause the meat food to become partially ripe or thaw, causing the internal components of the meat to come out. There is a problem that occurs.

Therefore, the present invention can read the data of the thermopile type temperature sensor and control the output of the magnetron according to the data, and from the data to determine the optimum thawing end by grasping when the food surface becomes ice from water Improve the condition and finish the thawing in a short time.

Description

Microwave oven and thermo thawing method using thermopile type temperature sensor

1 is a block diagram of a conventional microwave oven.

2 is a waveform diagram showing the output value of the magnetron in FIG.

3 is a flow chart illustrating a conventional method for automatically thawing a microwave oven.

4 is a graph of L values over time in FIG.

5 is a block diagram of a microwave oven using the present invention thermopile type temperature sensor.

6 is a view of the relationship between the size of the food and the sensor located in the cavity side in FIG.

Figure 6a shows a large diet.

6b is a case of small food.

7 is a relation between the size of the frozen food and the sensor field of view when the sensor is located at the top of the cavity.

8 is a graph showing the change and the rate of change of the food surface temperature when the frozen food is heated.

9 is a change in the surface temperature measured by the thermopile type temperature sensor according to the size of the frozen food,

FIG. 9a is a diagram showing when food is placed in the center of the turntable,

Fig. 9B is a diagram showing the change when food is eccentric from the center of the turntable.

10 is an exemplary diagram for calculating the ON time ratio of the mark netron.

FIG. 11 is a magnetron on / off waveform diagram when, in FIG. 5, t _s is constant and t _{on is} changed.

FIG. 12 is a magnetron on / off waveform diagram when, in FIG. 5, t _on is constant and t _s changes.

13 is a block diagram of a microwave oven showing a process of thawing frozen food using a thermopile type temperature sensor.

FIG. 14 is a curve diagram of the maximum, average and minimum temperature in FIG.

15 is a graph showing an example of determining additional thawing time in the present invention.

16 is a flowchart illustrating an automatic thawing method of a microwave oven using the present invention thermopile type temperature sensor.

FIG. 17 is an overall timing diagram of automatic thawing in FIG.

FIG. 18 is an illustration of the case where auto thawing is performed by turning on / off the magnetron according to time in FIG.

19 is an exemplary view showing the form of temperature change rate.

FIG. 20 is a flowchart illustrating a method of determining an inflection point according to whether ΔTmaxf is increased in FIG. 11.

* Explanation of symbols for main parts of the drawings

1: Thermopile type temperature sensor 2: Condenser

3: amplification unit 4: analog / digital conversion unit

5: microcomputer 6: magnetron on / off switch

7: magnetron 8: turntable driving motor

9: turntable 10: food

11: cavity 51: voltage signal sampling unit

52: voltage signal processor 53: temperature data sampling unit

54: magnetron on / off time calculation and abnormal phenomenon determination unit

55: magnetron on / off switch control unit

The present invention relates to an automatic defrosting method in a microwave oven using a thermopile type temperature sensor. In particular, the surface temperature of food is detected using a thermopile type temperature sensor, and the surface temperature of the food is determined according to the size or weight of the food. Microwave oven using thermopile type temperature sensor to improve the thawing condition and reduce the thawing time by optimally adjusting the output of the magnetron and setting the end time to terminate the thawing in the optimum thawing state. It relates to an automatic thawing method.

In the conventional microwave oven, as shown in FIG. 1, the turntable 30 is placed at the center of the heating type, puts a load 31, and rotates to enable crack heating: heating the load 31. And a magnetron 27 which is a heating source for supplying electromagnetic waves to the heating chamber 11 through a waveguide; and a turntable motor 29 for rotating the turntable 30. Thermopile type infrared sensor 21 and: the interior lamp (32) that illuminates the heating chamber when cooking food, and: cooling fan (28) for cooling the heated magnetron (27): whether the operation of each part according to the switch selection And a microcomputer 22 for determining cooking or thawing time, etc .: the interior lamp 32, the magnetron 27, the cooling fan 28, and the turntable motor 29 according to the control output of the microcomputer 22. Control switch (2) 3-26) and: It is composed of a weight sensor not shown in the figure connected to the turntable motor shaft to sense the weight of food.

Looking at the conventional technology configured as described above are as follows.

When the consumer puts food to be thawed on the turntable 30 in the heating chamber, closes the microwave oven door and presses the thawing switch, the microcomputer 22 recognizes thawing, and the first cooling fan control switch ( 25, the turntable motor control switch 26 and the high light control switch 23 are turned on to drive the cooling fan 28, the turntable motor 29 and the high light 32.

The turntable 30 on which the sea animal is placed by the turntable motor 29 starts to rotate.

As the turntable 30 rotates, the microcomputer 22 starts to measure the weight of the sea animal using a weight sensor connected to the turntable motor shaft and calculates the turntable rotation time Q. The time Q is Using the one cycle time (TO) of the commercial power source and the coefficient (P) of the turntable motor is calculated as follows.

Q = (1 / TO) / P

Here, assume that P = 5 and TO = 20 msec, and Q = 10 seconds.

As described above, when the calculation of one rotation time Q of the turntable is finished and a predetermined time (about 250 msec) has elapsed, the microcomputer 22 performs the magnetron 27 during the one rotation time Q of the turntable calculated above. ) Is turned off and the duntable 30 is rotated again to complete the weight (W) measurement of the food to be thawed.

The thawing time T1 set in proportion to the measured weight W is calculated as follows.

T1 = 0.06 * W

The microcomputer 22 controls the magnetron 27 to turn on the magnetron 27 so as to produce a high output of 600 watts for the T1 time set above, and then rotates the magnetron 27 during one rotation time Q of the turntable to produce a constant output of 300 watts. During the turn time Q of the turntable 30 again, the operation of turning off the magnetron 27 is alternately repeated as shown in FIG.

When the on / open operation of the magnetron 27 is repeated in this way, the microcomputer 22 measures the value detected by the thermopile infrared sensor 21 to remove the influence of electromagnetic noise, and the voltage data 11 Here's how to get it. The voltage data V is obtained using the voltage V1 obtained by amplifying the output of the thermopile infrared sensor 21, the voltage V2 of the thermistor, and the reference voltage V3 of the infrared sensor 21.

V = R * (V1-V3) + S * V2 + T

Here, R, S, and T are all constants.

Thereafter, even if the thermopile type infrared sensor 21 does not detect the end of thawing, the point at which the thawing ends unconditionally (TLmax, abbreviated to the maximum thawing end point below) and the thermopile type infrared sensor 21 detect the end of thawing. Even if the uninterrupted heating time (TLmin, abbreviated as the minimum thawing end time) is obtained as follows.

TLmax = 2 * W

TLmin = 1 * W

As a result, the time during which the thermopile-type infrared sensor 21 detects the end of thawing is the time between the maximum thawing end time point TLmax and the minimum thawing end time point TLmin.

If the minimum thaw end time and the maximum thaw end time have not passed after the one rotation time of the turntable after the second time has passed, the evaluation of how much vibration of the voltage data measured during one rotation time of the turntable has occurred The value (L) and the value (M) for determining whether the temperature of the food rises sharply are obtained as L = min / ave and M = dv / dt.

Where min is the minimum voltage value at one rotation of the turntable, ave is the average value, and dv / dt is the derivative of the voltage over time.

If the evaluation value (L) for determining the vibration degree of the voltage data after the minimum thawing end time and the maximum thawing end time has not passed as shown in (a) of FIG. 4 is compared with the reference value of 0.994. , The value M for determining whether the temperature of the food rises sharply is also compared with the reference value of 10 to determine the end of thawing.

In the case of a large load that is difficult to increase the center temperature as shown in (b) of FIG. 4, when the evaluation value (L) is continuously larger than the reference value of 0.994, the maximum thawing end point (TLmax) is reached. End thawing.

In addition, as shown in (c) of FIG. 4, when the food temperature is extremely high and low, the thawing is terminated at the minimum thawing end point (TLmin).

Referring again to the above-described process based on the defrosting method flow chart shown in FIG. 3, once the defrost key is selected, the microcomputer 22 recognizes it and firstly the interior lamp 32, the cooling fan 28, and the turntable. The motor 29 is controlled to brighten the inside of the heating chamber through the interior lamp 32, and the weight sensor connected to the turntable motor shaft measures the weight of the sea animal to be thawed by the turntable 30 rotating by the turntable motor 29. In addition, the cooling fan 28 allows external cold air to be introduced into the heating chamber.

When the turntable 30 rotates in this way, the microcomputer 22 calculates one rotation time Q of the turntable and starts to control the magnetron 27 in time after about 250 msec. During the T1 time after the time Q, a high output of 600 watts is output, and then the magnetron outputs of 300 watts and 0 watts are alternately operated at intervals of one rotation time Q of the turntable.

First, the magnetron 27 is turned off during one rotation time Q of the turntable obtained above so as not to operate.

In this way, when the magnetron 27 is in the off state, the microcomputer 22 detects the output of the thermopile infrared sensor 21 to output voltage data (V = R * (V1-V3) + S * V2 + T). The reason for obtaining voltage data in the off state is to remove the influence of electromagnetic noise.

When the rotation time (Q) of the turntable has elapsed, the measurement of the weight (W) using the weight sensor is completed, and the thawing time (T1) is determined based on the measured weight (W) and the output value (600 watt) of the magnetron 27. The minimum and maximum thawing end points (TLmin, TLmax) are calculated again.

In general, the end point of thawing is a time between the minimum and maximum end points (TLmin, TLmax) obtained above.

When one rotation time of the turntable after the second time has elapsed, it is checked whether the minimum thawing end point (TLmin) has elapsed, and when the minimum thawing end point has elapsed, it is again checked whether the maximum thawing end point (TLmax) has elapsed.

As a result of the check, if the maximum thawing end point (TLmax) has not elapsed, an evaluation value (L = min / ave) of how much the vibration of the voltage data measured during the turntable rotation time and whether or not the temperature of the food increases rapidly The value M to be judged (M = dv / dt) is determined. If the evaluation value L is not greater than the reference value of 0.994, the thawing ends. If the value M is greater than the reference value of 10, the thawing ends.

However, when thawing frozen foods using the prior art as described above, a thermopile-type infrared sensor for measuring the surface temperature of the food and a weight sensor for measuring the weight of the food must be used, causing a cost increase. In the case of a large load due to the magnetron output after the time T1 for the initial high output thawing, it takes a long time until the thawing is completed, and in the case of a small burr, the magnetron output is stronger than the load size. There is a problem that the meat part is partially ripened or over thawed, the internal components of the meat can come out.

In addition, when frozen food is eccentric at the center of the turntable, there is a problem that an error occurs at the end of thawing.

Accordingly, an object of the present invention for solving the problems as described above is the increase of the cost added by using a conventional weight sensor, and incomplete defrosting caused by controlling the output of the magnetron at a constant rate regardless of the size of the load, The present invention provides a microwave oven using a thermopile type temperature sensor and an automatic thawing method thereof to solve a problem such as misjudgment of the end time of thawing caused by eccentricity at the turntable of food using a thermopile type temperature sensor.

Another object of the present invention is to read the data of the thermopile type temperature sensor and control the output of the magnetron according to the data, by determining the optimum thawing end point by grasping the point of time when the surface of the food is from ice to water from the data The present invention provides a microwave oven using a thermopile type temperature sensor which improves the state of thawing and completes thawing in a short time, and an automatic thawing method thereof.

The automatic thawing method of the microwave oven using the thermopile type temperature sensor of the present invention for achieving the above object, as shown in Figure 16, the first step of initializing the parameters for the defrosting performance upon thawing key input: A second step of starting the thawing by turning off the magnetron and sensing the initial temperature for a predetermined time (tp) and starting the thawing: in the second step, the voltage obtained by analog / digital conversion to the food surface temperature at the start of thawing ( A third step of converting V) into a temperature T; and a fourth step of calculating temperature data Tf from which noise is removed by filtering the temperature T converted in the fourth step by using a digital filter. And fifth step of obtaining maximum, minimum, and average values of the temperature data calculated in the fourth step during the magnetron on / off period (tm), and: when the magnetron on / off period has elapsed in the fifth step. A sixth step of determining the magnetron on / off time, additional thawing time, and whether there is an abnormality: if the abnormality is not detected in the sixth step, outputting a control signal to the magnetron on / off switch and repeating the above operation If it is determined that the abnormal phenomenon is a seventh step of terminating the thaw magnetron off.

In the third step, a time for detecting an initial temperature at the thawing progress time t at the moment when the sampling time ts of the voltage signal which has performed analog / digital conversion has elapsed while counting the time t after thawing has progressed ( The first step of calculating the time tr subtracted tp): the time tr obtained in the first step, a time point tc at which the surface temperature change rate of the food starts to increase, and addition from this time point tc. The second process of comparing the thaw time (ta) plus the value (tc + ta) and: In the second process, if the time tr is greater than the value (tc-ta), the magnetron is turned off to terminate the thaw, or the analog / Comprising a third process of converting the voltage (V) subjected to the digital conversion into a temperature (T), the magnetron on / off time calculation in the sixth step is the first process of filtering for the maximum value (Tmax) that can vibrate fine And calculating the change value ΔTmaxf of the highest value filtered in the first step. A second step of determining whether the calculated change value is increased; if the change value is determined to be increased in the second step, an additional thawing time is calculated, and if it is not increased, the on-time ratio of the magnetron is calculated, The third step is to calculate the off time.

The configuration of the microwave oven using a thermopile type temperature sensor for performing the method consisting of each step, as shown in Figure 5, is located in the center of the heating chamber 11 to put the load 10 One turntable 9 and: a thermopile type temperature sensor 1 which detects the infrared radiation emitted from the load for the turntable 9 and converts it into a voltage and is positioned obliquely so that the turntable 9 can be seen from the upper side of the heating chamber. And: a light condenser 2 for condensing infrared rays emitted from the load to the thermopile type temperature sensor 1 and narrowing the viewing angle of the temperature sensor as necessary; and from the thermopile type temperature sensor 1 An amplifier 3 for amplifying the sensed signal to a predetermined level; and an analog / digital conversion for converting the analog sense signal amplified by the amplifier 3 into digital data. And (4): a microcomputer (5) for processing digital data transmitted through the analog / digital converter (4) and performing a corresponding algorithm; and: magnetron on / off controlled by the microcomputer (5). The food heating means controlled by the switch 6 and the magnetron on / off switch 6 constitutes the magnetron 7.

When described in detail with respect to the operation and effect of the present invention configured as described above.

When the frozen food 10 to be thawed is placed on the turntable 9 located in the center of the heating chamber 11, and the defrosting key is not shown and pressed, the microcomputer 5 recognizes the magnetron for thawing. A control signal is output to the on / off switch 6 to control the magnetron 7 on / off.

At this time, the turntable driving motor 8 rotates the turntable 9 at regular time intervals so that food is uniformly heated.

As the food is heated, when infrared radiation is emitted from the food, it is condensed by the condensing lens or concave reflector 2 and sent to the thermopile type temperature sensor 1, and it is also able to detect infrared light best from the food. By adjusting so that the thermopile type temperature sensor 1 can exist at the position, the viewing angle is narrowed as necessary to increase the output voltage of the sensor.

In the above, the thermopile type temperature sensor 1 is positioned obliquely so that the turntable 9 can be seen from the upper side of the cavity as shown in FIG. 5 or appropriately laterally at the center of the cavity as shown in FIG. The distance between the center and the side portion of the tentable (9) can measure the temperature instead of measuring only the temperature of the central portion of the turntable (9).

In this way, the sensing signal from the thermopile type temperature sensor 1 located is received by the amplifier 3 and amplified to be processed by the analog / digital converter 4 located at the rear end. If (4) operates with 8 bits and uses 5 volts of power, the resolution of the analog / digital converter 4 becomes 5/256 = 0.0195 volts.

Therefore, if the temperature of the food in 1 ℃ unit to measure the amplification rate so that the output of the amplifier 3 is greater than 0.0195V / ℃.

When the amplification rate is amplified and transmitted to the analog / digital converter 4, the analog / digital converter 4 converts the detected signal into digital data and provides the same to the microcomputer 5.

The microcomputer 5 processes the input temperature data of the food and performs an algorithm for controlling the output of the magnetron therefrom to control the output of the magnetron, which will be described in detail later.

At this time, when the frozen food is heated by the magnetron 7 as a heat source, the change of the food surface temperature exhibits the same characteristics as in FIG.

That is, as shown in (a) of FIG. 8, two inflection points appear at the surface temperature change, and the surface temperature of the food is still rising in the ice state until the first inflection point appears, and from the first inflection point to the second inflection point. The ice of 0 degreeC turns into water of 0 degreeC.

At this time, the energy supplied by the magnetron 7 is consumed by the phase change in which 0 ° C of ice turns into 0 ° C of water, so that there is no change in food surface temperature.

From the second inflection point, the surface temperature of the food, which is changed to water, is continuously heated by the heat source.

After further heating, the water phase turns into water vapor, and the surface temperature of the food stays at 100 ° C.

In FIG. 8B, since the temperature change rate decreases until the phase transition appears, the temperature change rate becomes zero since there is no temperature change when the phase transition appears, and then the temperature change rate increases.

Therefore, when thawing frozen food, the completion time of thawing can be determined based on the end of the phase transition from ice to water, when the temperature change rate is greater than zero. It can be seen that.

However, when measuring the surface temperature of food using a thermopile type temperature sensor in an actual microwave oven, a temperature change as shown in FIG. 9 appears rather than a temperature change as shown in FIG.

In other words, when there is a phase change from ice to water, there should be no change in temperature ideally. In FIG. 9, it can be seen that the measured temperature increases in the phase transition section, which is caused by the viewing angle of the thermopile type temperature sensor and the size of food. 6 to 7 can be described.

6 shows the relation between the viewing range when the thermopile type temperature sensor 1 is located at the upper side of the cavity and the size of the food. (A) shows that the food is large enough to emit only infrared light emitted from the surface of the food. The incident change of the surface temperature of the food at this time by being incident on the thermopile type temperature sensor 1 exhibits the same characteristics as in FIG.

On the other hand, in (b) of FIG. 6, since the size of food is small, not only the infrared rays emitted from the food but also the infrared rays emitted from the turntable 9 enter the thermopile type temperature sensor 1 together.

Therefore, the surface temperature change of the food in the case as in FIG. 6 (b) has the same characteristics as in FIG.

(B) and (c) of FIG. 7 show the relationship between the viewing range and the size of the food when the thermopile type temperature sensor 1 is located in the upper cavity. Although it has the same characteristics as in Fig. 8, when measuring the surface temperature of frozen food with a thermopile type temperature sensor in a microwave oven, in many cases, it shows the same pattern as in Fig. 9.

This is because, even if the food is large, when the shape is irregular or eccentric in the center of the turntable 9, infrared rays emitted from the turntable other than the food are incident on the thermopile type temperature sensor.

This relationship between the field of view of the sensor and the size of the food can be indirectly grasped the size of the food from the measured surface temperature of the food, and also in part by appropriately adjusting the output power of the magnetron according to the size of the food. This means less problems with overthawing or less thawing.

For example, as shown in FIG. 9, it can be seen that the small temperature of the phase change from ice to water is higher than that of the large food.

And when the surface temperature of big load and small load is the same, the big load should take longer heating time of the magnetron than the small load.If the measured temperature on the thermopile type temperature sensor is used, the optimum magnetron output power depends on the size of the load. Can be determined.

That is, when the magnetron is controlled in two stages of on / off, if the magnetron on time ratio is P and the food surface temperature is T, the magnetron on time ratio P can be determined by the following general formula.

At this time, if the magnetron on time is ton and the off time is toff, P = (ton + toff), and the on / off period of the magnetron (hereinafter, denoted by tm) becomes constant.

P = f (T) ........ (1)

Here, f () represents a function, which can be a linear expression for T or nonlinear.

Since the on / off period of the magnetron is constant, T for the calculation of Equation (1) is measured or calculated at regular time intervals (tm), and thus the on-time ratio (P) of the magnetrons is determined at regular time intervals (tm). It is recalculated and changed.

For example, in Figure 9, when heating a small load near -5 ° C and a large load, if the ratio of magnetron on time is 80% (e.g. 2 seconds off if 8 seconds on) for a large load, The load should be heated at a smaller magnetron on-time ratio (eg 60%) to avoid partial overthawing, which can be determined by determining the magnetron on-time ratio in inverse proportion to the measured food surface temperature.

That is, the magnetron on time ratio P can be determined by a simple linear proportional equation as follows.

P = K1 * (Tr-T) ....... (2)

Where K1 is a proportionality constant and Tr refers to the X-intercept.

An example of the above formula (2) is shown in FIG. 10. Since the magnetron on time ratio P cannot be greater than 1, if T is less than -5 ° C, P = 1.

The calculation of the magnetron on time ratio (P) by Equation (2) uses only the food surface temperature itself measured by the thermopile type temperature sensor, which makes the sensor vulnerable to a single component error or various environmental factors.

In order to compensate for this, the magnetron on time ratio P can be calculated by adding a temperature change rate as follows.

P = K1 * (Tr-T) + K2 * ΔT ....... (3)

Here, ΔT is a change value of the food surface temperature with respect to the unit time. For example, when the on / off period tm of the magnetron is constant at 10 seconds, the change in the food surface temperature changed in 10 seconds.

In addition, in order to supplement the above formula (2) and to consider the initial temperature of the food can be used the following linear equation.

P = K1 * {Tr-[K2 * T + K3 * (T-TO)]} ........ (4-1)

= K1 * [Tr-(T + K3 * TO)] ....... (4-2)

Here, TO is the initial temperature of the food measured by the thermopile type temperature sensor, (T-TO) is the difference between the present temperature and the initial temperature, K2 and K3 are the weights less than 1, K2 + K3 = If the values are set to satisfy 1, K2 can be erased as in Equation (4-2).

11 shows an example of the magnetron on / off when the on / off period tm of the magnetron is constant as in Equations (1) to (4-2).

Although the ratio of the time when the on / off period tm of the magnetron was made constant was calculated as in the formulas (1) to (4-2), the magnetron on time (ton) or the magnetron off time (toff) was calculated. It is also possible to control the on / off of the magnetron by keeping a constant, and by calculating a new on / off period (tm) of the magnetron in accordance with the measured food surface temperature.

At this time, the on / off period (tm) of the magnetron can be calculated as follows using the on-time ratio (P) of the magnetron calculated from the formula (1) to formula (4-2).

tm = P * ton ....... (5)

Here, equation (5) is a case where the on time (ton) of the magnetron is kept constant, and equation (6) is a case where the off time (toff) of the magnetron is kept constant.

As shown in FIG. 12, an example of maintaining the magnetron on time (ton) and controlling the on / off of the magnetron by the newly calculated on / off period (tm) of the magnetron is shown in FIG.

From the above description, it can be seen that the thermopile type temperature sensor can be used to thaw frozen food in a microwave oven to determine not only the optimum end point of thawing but also the optimum magnetron on / off ratio according to the load.

That is, since the surface temperature of the food can be grasped directly, it is possible to perform optimal heating to prevent over thawing or less thawing and to terminate thawing at an optimum time point.

In particular, the optimum magnetron on / off time control not only affects the thawing quality but also the thawing time. For example, if the ratio of the magnetron is too small, the thawing time becomes longer, and in the case of meat, The internal components are taken out to reduce the quality of meat. On the contrary, too much on-time ratio of magnetron results in partial overthawing, which results in a severe deterioration in thawing quality, especially when frozen foods are ash type.

13 is a block diagram illustrating the process of thawing frozen food using a thermopile type temperature sensor in a microwave oven based on what has been described above.

When the consumer wants to thaw the frozen food, open the microwave oven door, place it on the turntable, and press the thawing key (not shown). To occur.

When the electromagnetic wave generated in this way passes through the frozen food and the infrared rays emitted accordingly are condensed by the condenser 2 of the sensor module, and the thermopile type temperature sensor 1 receiving the condensed infrared rays is converted into a voltage value and outputted, The frozen food surface temperature (Ts) obtained by amplifying the voltage value to have a constant gain in the amplifier 3 is measured, and the temperature Te other than the food is read together according to the size of the food. That is, the food surface temperature Ts and the non-food temperature Te such as the turntable read the temperature T + W1 * Ts + W2 * Te added with the weight of W1 and W2, respectively.

The weight of the W1, W2 is changed according to the size of the food and the internal temperature of the microwave heating chamber (11).

When the voltage V corresponding to the temperature (T = W1 * Ts + W2 * Te) is output from the thermopile type temperature sensor 1 to the analog / digital converter 4, the voltage V The analog / digital converter 4 converts the digital voltage signal and outputs the digital voltage signal to the microcomputer 5.

The voltage signal sampling unit 51 inside the microcomputer 5 provided from the analog / digital converter 4 samples at a predetermined time interval ts.

The sampled voltage signal is converted into a temperature T by the voltage signal processing unit 52, and the converted temperature data is processed so that the thawing algorithm of the present invention can be performed.

The voltage signal processor 52 includes a digital filter algorithm, an average value calculation algorithm, a maximum value calculation algorithm, a minimum value calculation algorithm, and the like.

Here, the digital filter algorithm is a part for removing electromagnetic noise that may be included in the sampled voltage signal and is expressed in a linear form as follows.

Tf (t) = θ1 * Tf (t-ts) + θ2 * Tf (t-2 * TS) + ... + θn * Tf (t-n * ts) +

ω0 * T (t) + ω1 * T (t-ts) + ... ωm * T (t-ts) ....... (7)

Where Tf (t) is the filtered temperature at time t, Tf (t-ts) is the filtered temperature at time t-ts, and θ1 to θn are the weights of the filtered past temperature values. T (t) is the noise-mixed temperature value converted by the voltage signal sampled at time t, and ω 0 to ωm are weights for past values of the noise-mixed temperature.

For the convenience of calculation in the microcomputer 5, θ1 to θn are all 0, and ω0 to ωm are all 1 / m, so that a simple average value of the past and present measurement temperatures can be taken.

In addition, the average value calculation algorithm, the maximum value calculation algorithm, and the minimum value calculation algorithm of the voltage signal processor 52 are parts for obtaining the average value, the maximum value, and the minimum value for a specific time tm for the temperature values Tf filtered by the digital filter. .

The temperature data sampling unit 53 calculates the magnetron on / off time and the abnormality determination unit 54 calculates the temperature data calculated by the voltage signal processor 52 with respect to the average value Tmean and the maximum value Tmax obtained therefrom. In order to be able to read at intervals of time (tm), the sample is sampled and output to the on / off time calculation and abnormality determination unit 54 of the magnetron.

Accordingly, the on / off time calculation and abnormality determination unit 54 of the magnetron using the sampled average value (Tmean) and the maximum value (Tmax) by the formula (1)-equation (6), etc. To calculate the on / off time, to determine the additional thaw time (ta) to terminate the thaw at the optimum time, and to determine whether the algorithm or food abnormal state.

The calculation of the optimum magnetron on / off time using the equations (1) to (6) may use all of the filtered temperature values (Tf), average values (Tmean), maximum values (Tmax), and minimum values (Tmin), but the minimum value. Use Tmin because (Tmin) is the closest to the average of the actual surface temperature of the food.

That is, the on time ratio P (or on / off time) of the magnetron is calculated by using the minimum value Tmin instead of the food surface temperature T to which the temperature other than the food is added in equations (1) to (6). .

The thaw is determined using the maximum value Tmax. FIG. 14 shows that the maximum value Tmax is most preferable for the determination of the end point of thawing. That is, as shown in (b) of FIG. 8, the end point of thawing (or additional thawing time) can be determined at the time when the temperature change rate increases (the second inflection point in the temperature change curve). Tmax) shows the clearest inflection point in the curve.

In the calculation of the additional thawing time, as in FIG. 15, the time at the time of the second inflection point tc may be used, the temperature of the food Tc at that time may be used, and the food at that time may be used. You can also specify a certain amount of time in any batch.

The additional thawing time ta using the time point tc at which the second inflection point occurs and the food temperature Tc at that time may be calculated by the following linear equation.

ta = C1 * tc + C2 ....... (8)

ta = C3 * Tc + C4 ...... (9)

Where C1, C2, C3, and C4 are all constant values.

Determination of food abnormality is based on Tmean. If the Tmean is greater than a certain temperature (for example, 20 ℃), the microwave user presses the thawing key while the product is currently thawed or no-load. As it can be judged by the situation, immediately turn off the magnetron and stop thawing.

The use of a mean value (Tmean) to determine whether there is an abnormal state of food is because the mean value (Tmean) more accurately represents the overall state of food than the maximum value (Tmax) or the minimum value (Tmin).

If the maximum value (Tmax) is used, the peak value (Tmax) during the magnetron on / off cycle (tm) time will exceed 20 ° C when the small load is located eccentrically in the center of the turntable during the summer and therefore less thawed. There is a problem in stopping thawing.

Likewise, if the minimum value Tmin is used, it is not good because the temperature change is small in the latter part of the thawing as shown in FIG.

The calculation of the mean (Tmean) can take a simple arithmetic mean, but for convenience of calculation it is also possible to use a value of (Tmax + Tmin) / 2.

The magnetron on / off time calculation and abnormality determination unit 54 determines whether the algorithm is in abnormal operation from the current magnetron on time ratio and the elapsed time up to the present time, and defrosts when the algorithm is in a normal state and the entire cooking time elapses. Quit.

For example, if the magnetron on time ratio P is calculated as P = 0.5 * (15-T) as in the example of FIG. 10, and the calculated value is less than 0.2, the thawing algorithm has failed to find the inflection point in the temperature change curve. In this case, the inflection point at which the rate of change of temperature starts to increase is shown in the measurement temperature below 10 ° C and the magnetron on time ratio (P) at 10 ° C = 0.5 * (15-10). The current value is 0.2 because it is 0.25, because the current minimum temperature is 11 ° C and the point of inflection point has already passed.

If the current magnetron on time ratio P is small and a long time after the thawing algorithm has been performed, the thawing algorithm also determines that the inflection point has not been found in the temperature change curve and terminates thawing.

For example, in FIG. 10, when the current magnetron on time ratio P is 0.3 and 5 minutes have passed since the thawing algorithm is performed, thawing is terminated.

When the on / off control signal is calculated according to the magnetron on / off time calculated by the magnetron on / off time calculated by the abnormal phenomenon determination unit 54 and whether or not the thawing end is determined, the magnetron on The magnetron 7 is controlled by turning on or off the magnetron on / off switch 6 received from the on / off switch controller 55.

Based on the operation described so far, based on the time chart of the thawing algorithm embedded in the microcomputer 5 shown in FIG. 17, the overall time chart shown in FIG. 18, and the flowchart of the automatic thawing method shown in FIG. Let's look at it.

First, when the user inputs a key for thawing, the variables for executing the algorithm are initialized, and zero is substituted for ti.

When thawing is started after initializing the variables, the magtetron 7 is turned off by the time (tp), which is the sum of one turn time of the turntable and the response time until the turntable motor 8 rotates normally. Measure the initial temperature.

If one rotation time of the turntable is 10 seconds and it takes 3 seconds for the turntable 9 to stably rotate, tp = 13 (10 + 3) seconds.

Next, the process proceeds to the step of obtaining tr (= t-tp) at the instant when ts, which is the sampling time of the sensor voltage signal through analog / digital conversion, continues counting the time t after the thawing operation has elapsed. Here, INT (t / ts) means take only the integer part of the value of t divided by ts.

Next, calculate tr = t-tp, compare the two values of tr and tc + ta, and if tr is large, turn off the magnetron (7) and stop thawing. Where tc denotes a time point at which the surface temperature change rate of the food starts to increase as shown in FIG. 9 and ta denotes an additional thawing time from the tc time point. tc is initialized to a large value (e.g., 10000 seconds), ta = 0, and if tr is less than tctta, the voltage signal V output from the analog / digital converter 4 is read and the voltage is In this case, the converted temperature data T is filtered using a digital filter such as Equation (7) to calculate the temperature data Tf from which noise is removed.

Thereafter, the maximum value Tmax, the minimum value Tmin, and the average value Tmean during the magnetron on / off period tm are obtained for the filtered temperature data Tf. Then, if tr and ti + tm are compared, if the turnover tm has not elapsed, that is, if tr and ti + tm are different, the control signal is output to the magnetron on / off switch 6, and the process so far repeated, and the magnetron on When the / off period (tm) time has elapsed (that is, tr and tittm are the same), the magnetron on / off time, additional thawing time and abnormality are determined.

Here, if the magnetron on / off period (tm) is constant and only the on / off time (ton / toff) is adjusted when calculating the on / off time of the magnetron, the magnetron on / off period (tm) has elapsed. It can be determined by checking whether tr / tm and INT (tr / tm) are equal.

When the time of the magnetron on / off period (tm) has elapsed, the filter is filtered for a maximum value (Tmax) that may vibrate finely. The filtering at this time takes the average of Tmax (t-tm) and Tmax (t) as follows. do.

Tmax (t) is the maximum value Tmax calculated at time t.

Therefore, the change value? Tmaxf of the filtered temperature data Tmaxf is calculated as follows.

ΔTmaxf (t) = Tmaxf (t)-Tmaxf (t-tm) ... (11)

[Delta] Tmaxf (t) is a value of [Delta] Tmaxf calculated at time t.

When the change value ΔTmaxf (t) of the filtered temperature data is calculated as described above, it is determined whether the calculated change value ΔTmaxf of the temperature data is increased, as shown in FIG. 19. Depending on the conditions, the point of increase of ΔTmaxf is different. In particular, in the case of (b) of FIG. 19, it is impossible to determine whether the inflection point is due to the simple increase of ΔTmaxf.

In other words, (b) in (b) of FIG. 19 represents an actual inflection point, and the case of recognizing (a) as an inflection point causes less thawing.

In the case of a small load, since the inflection point appears in a short time as shown in FIG. 19 (c) (d), the number of ΔTmaxf data for determining the inflection point is limited.

FIG. 20 shows an inflection point determination method for solving a problem such as limiting the number of ΔTmaxf data. In the case of tr3 * tm, two ΔTmaxf ( t) When only data is used and tr3 * tm, it is determined whether ΔTmaxf is increased by using three ΔTmaxf (t) data.

If it is determined that ΔTmaxf (t) is increased, the additional thawing time is calculated as in Eq. (8) or (9) and the present time t is substituted for the variable tc.

The next step is to determine the magnetron on / off time using equations (1) to (7).

The next step is to determine whether the algorithm is performing abnormally or whether the food is in an abnormal state.The average value is determined by using the average value, the ratio of the magnetron on time, and the elapsed time so far. The thawing is terminated and the control signal is output to the magnetron on / off switch 6 in the case of abnormality.

That is, if the average value (Tmean) during the magnetron on / open cycle (tm) is higher than or equal to a certain temperature, it is determined that there is no load or an over-thawing state due to an abnormal operation of the thawing algorithm, and the magnetron on time ratio (P) is lower than or equal to the predetermined value If Tmean is greater than a certain temperature and greater than a certain time after the start of thawing, it is determined that the thawing algorithm is abnormal and the magnetron 7 is turned off to end the thawing.

Then, for the new magnetron on / off cycle time (tm), initializing the variable values necessary to calculate the variable values and replacing tr with ti.

Repeat the same process as above.

So far, the output of the magnetron is controlled in two stages of on or off, but if the magnetron can be controlled in multiple stages (for example, analog control), the magnetron on / open time calculation section can be changed to the magnetron output calculation section. .

That is, the magnetron on-time ratio P calculated by Formula (1)-Formula (5) can be made into the magnetron output quantity Pm. For example, if the maximum possible power (Wmax) of the magnetron is 1000 watts, and the magnetron on time ratio (P) calculated in equations (1) to (5) is P = 0.05, the magnetron output is 0.5 * 100 watts = 500 This is determined by the wattage. This is calculated as Pm + P * Wmax.

As described in detail above, the present invention can control the output of the magnetron to continuously change using the measurement data of one thermopile type temperature sensor, so that it can be appropriately heated to the size of the food regardless of the size of the food and thus thawed. This will save you as much time as possible.

And the end point of thawing is determined by grasping the inflection point of the food surface temperature change curve, so the optimum time is determined regardless of the magnitude of the load, continuous operation of the microwave, shape of the food, fluctuations in the power supply voltage, and position on the food turntable. Defrosting can be completed, and even if the user of the microwave oven performs a defrosting operation by mistake, there is an effect that the magnetron stops immediately by detecting an abnormal phenomenon.

Claims (10)

The thermopile type temperature sensor 1, the condenser 2, and the output of the sensor are amplified and converted into digital data through an amplifier 3 and an analog / digital converter 4, and then an algorithm is performed. In the microwave oven composed of a magnetron on / off switch 6 controlled by a microcomputer 5 and a magnetron 7 which is a food heating means controlled by the magnetron on / off switch 6, the micron The computer 5 has a voltage signal sampling section 51 for reading and sampling the voltage signal output from the analog / digital conversion section 4 at predetermined time intervals; The noise contained in the temperature is removed using a filtering filter, and the maximum value Tmax, minimum value Tmin, and average value of the removed temperature Tf are respectively calculated during the magnetron on / off cycle. Voltage signal 52 and; A temperature data sampling unit 53 for sampling the maximum, minimum, and average values of the temperature Tf calculated by the voltage signal processing unit 52 for each magnetron on / off cycle time; and in the voltage signal processing unit 52: Using the calculated values, the optimum magnetron on / off time is calculated for each magnetron on / off cycle time, and the thawing end point is determined so that the thawing can be terminated at the optimum time. When there is a phenomenon, the on / off time calculation of the magnetron to terminate the thawing and the abnormal phenomenon determination unit 54 and: output a control signal to the magnetron control switch 6 in accordance with the determination result of the determination unit 54 of the magnetron Microwave oven using a thermopile type temperature sensor, characterized in that it comprises a magnetron switch control unit 55 for controlling the operation. The digital filter algorithm of claim 1, wherein the voltage signal processor 52 removes noise that may be included in temperature data using a digital filter to obtain a pure temperature value Tf (t). The electronic device using a thermopile type temperature sensor comprising a mean calculation algorithm, a peak calculation algorithm, a minimum calculation algorithm for finding average, maximum, and minimum values for a predetermined time with respect to the filtered temperature values Tf (t). range. The microwave oven according to claim 2, wherein the temperature value Tf (t) filtered by the digital filter is calculated by the following linear equation. Tf (t) = θ1 * Tf (t-ts) + θ2 * Tf (t -2 * ts) + ... θn * Tf (t-n * ts) + ω0 * T (t) + ω1 * T ( t-ts) + ... ωm * T (T-ts) Where Tf (t-ts) is the filtered temperature value at time t-ts, θ1 to θn are the weights of the filtered past temperature values, and T (t) is converted by the voltage signal sampled at time t. The noisy temperature values, ω 0 to ω m, are weighted values of past values of the noisy temperature. The first step of initializing the variables for the thawing operation when the thawing key is selected by the user: When the thawing starts, the magnetron is turned off for a certain time (tp), the initial temperature is sensed, and the magnetron is turned on again to perform the thawing operation. Second step to perform: In the second step, the magnetron is turned off when the thawing time has elapsed, and when the thawing time has not elapsed, the voltage (V) obtained by analogue / digital conversion with respect to the surface temperature of food is converted into temperature (T). The third step of converting: The fourth step of calculating the filtered temperature data (Tf) by using a digital filter for the temperature (T) converted in the third step: The filtered temperature calculated in the fourth step A fifth step of obtaining maximum, minimum, and average values of the magnetron on / off period tm for the data; and determining whether the magnetron on / off period has elapsed in the fifth step. If not, output the control signal to the magnetron on / off switch to repeat the above operation, and if it has elapsed, the sixth step of determining the magnetron on / off time, additional thawing time, and whether there is an abnormality: the abnormality in the sixth step If it is not a phenomenon, the control signal is output to the magnetron on / off switch, and the above operation is repeated, and if it is determined to be abnormal, the thermopile type temperature is characterized in that it comprises a seventh step of terminating the thawing by turning off the magnetron. Automatic thawing method of microwave oven using sensor. 5. The thermopile type temperature sensor of claim 4, wherein the time tp for detecting the initial temperature in the second step is a time obtained by adding one rotation time of the turntable to the response time until the turntable motor rotates normally. Automatic thawing method of microwave oven. The method of claim 4, wherein the third step detects an initial temperature at the thawing progress time (t) at the moment when the sampling time (ts) of the voltage signal which has performed analog / digital conversion has elapsed while counting the time (t) at which the thawing proceeds. A first step of obtaining a time tr subtracted from the time tp; and a time tr obtained in the first step, a time point tc at which the surface temperature change rate of food starts to increase, and a time point tc A second process comparing the value of the additional thawing time (ta) plus (tc + ta) from the second process; if the time tr is greater than the value (tc + ta) in the second process, the magnetron is turned off to terminate the thawing. Or a third process of converting the voltage (V), which has undergone analog / digital conversion, into a temperature (T). The method of claim 4, wherein the magnetron on / off period calculation in the sixth step comprises the first step of filtering for the maximum value (Tmax) that can vibrate finely: and the change value (△ Tmaxf) of the maximum value filtered in the first step And a second process for determining whether the calculated change value is increased or not: if it is determined that the change value is increased in the second process, an additional thawing time is calculated; if it is not increased, the on time ratio of the magnetron is calculated and the magnetron is turned on. Automatic defrosting method of a microwave oven using a thermopile type temperature sensor, characterized in that the third step of calculating the time and the off time. 8. The method of claim 7, wherein the change of the filtered maximum value (ΔTmaxf) is increased using only two change values (ΔTmaxf) for small loads and only three change values (ΔTmaxf) for large loads. Automatic thawing method of a microwave oven using a thermopile type temperature sensor characterized in that it determines whether the increase. The method of claim 7 or 8, wherein the determination of whether the change value? Tmaxf is increased is determined by subtracting the time tp for detecting the initial temperature from the thawing progress time t by the time tr of the magnetron on / off. When smaller than (3 * tm), ΔTmaxf, which is the current change value, and ΔTmaxf (tr-tm), which is the value of ΔTmaxf before tm hours, are compared. A first process of determining that the increase is small and not increasing ΔTmaxf: when the time tr is greater than the three periods of magnetron on / off (3 * tm), the current ΔTmaxf value ΔTmaxf (t) ΔTmaxf (tr-tm) and ΔTmaxf (tr-2 * tm) before tm time and before 2 * tm time, ΔTmaxf (tr) is greater than ΔTmaxf (tr-tm), and 0 Using a thermopile type temperature sensor, characterized in that a second process for determining that ΔTmaxf increases if ΔTmaxf (tr-2 * tm) + δ is greater than the smaller positive δ Automatic defrosting of a microwave oven. The method according to claim 4, wherein in the seventh step, whether the abnormal state is determined is an overload state due to no load or an abnormal operation of the thawing algorithm when the average value is above a certain temperature, and the magnetron on time ratio is below a certain value or the average value is greater than the constant temperature. Automatic thawing method of microwave oven using thermopile type temperature sensor, characterized in that it is judged as abnormal operation of thawing algorithm if it is bigger than a certain time after starting thawing.