JP2623904B2 - Heating device and control method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating apparatus having a detection system that detects high-temperature steam generated by an object to be heated as it is heated, and controls a heating source based on a detection signal of the high-temperature steam. It relates to a control method.

2. Description of the Related Art Heating apparatuses equipped with a system for automatically detecting the finish of heating of an object to be heated have been put to practical use in various forms. The most common sensing element used in such an automatic heating device sensing system is a humidity sensor that detects a change in humidity. However, the humidity sensor detects changes in the electrical resistance of the element due to water molecules adsorbed on the element surface. A complicated configuration and operation were required, such as regularly baking the surface with a heater.

On the other hand, we take out a high-temperature vaporized substance such as water vapor generated by the object to be heated through heating through a vent provided on the wall of the heating chamber, and apply this gas to a pyroelectric element provided outside the heating chamber to make this pyrotechnic. A system for detecting the finish of heating based on the voltage generated by an electric element is under study as proposed in Japanese Patent Application No. 63-274836. In the case of this method, the detection mechanism is based on the physical phenomenon of heat transfer between the pyroelectric element and the vapor, so that the sensitivity changes drastically due to dirt on the element surface like a conventional humidity sensor. There is an advantage in that a very simple detection system can be configured in principle.

Problems to be Solved by the Invention However, in this method, since the temperature change of the pyroelectric element due to the heat of the steam is used, even if it is not steam generated from the object to be heated, high-temperature air, that is, hot air is suddenly hit. The pyroelectric element reacts and generates a voltage even in the case where it occurs.
Therefore, when the heating device is a microwave oven having an electric heater or a gas heater as a second heat source in addition to the microwave, a large amount of residual hot air of these heater heat sources remains in the heating chamber immediately after the heater is heated. I have. Therefore, when microwave heating is performed in this state, the pyroelectric element generates a voltage in response to the residual hot air irrespective of the heating state of the food to be heated, and is distinguished from the voltage due to the steam generated by heating the food. There was a problem that erroneous detection was not possible.

The above-described problem occurs not only after heating a microwave oven with a heater but also after heating for a long time even when heating only with a microwave, and a similar phenomenon naturally occurs due to a rise in the temperature of a heating chamber or the like. Therefore, it has been difficult to accurately detect the heating state of the food (finished heating) without error.

Further, when the temperature of the pyroelectric element itself increases, the temperature difference between the pyroelectric element and the steam generated from the food decreases, and the detection sensitivity itself decreases. As described above, since the detection sensitivity changes variously depending on various use conditions, there is also a problem that it is difficult to secure a stable detection accuracy.

The present invention solves such a conventional problem, and does not erroneously detect the residual hot air in the heating chamber even when repeatedly used continuously in a state where the apparatus main body is twisted to a certain extent such as immediately after heating of the heater, and furthermore, the sensitivity is improved. An object is to realize a system using a pyroelectric element that can accurately detect a change.

Means for Solving the Problems In order to solve the above problems, the heating device of the present invention is processed by a voltage sensor signal processing means generated by a pyroelectric element, and then processed by a control unit for receiving and detecting and controlling. It has a configuration like the following. That is, the voltage output of the pyroelectric element immediately after the start of heating is measured for a first predetermined time, and the measured signal level is used as a noise level, which is a detection level from a relational expression predetermined based on the noise level. The control unit has a method and a function of determining a finish by detecting a voltage output equal to or higher than a threshold value output by the pyroelectric element due to steam generated from the food. is there.

Function The present invention is also applicable to the case where a voltage is generated in the pyroelectric element due to a large amount of residual hot air remaining in the heating chamber immediately after heating of the heater, and this voltage cannot be directly distinguished from a signal voltage due to steam which should be originally detected. Since the threshold value for detection is set according to the voltage level generated by the residual hot air, the residual hot air is erroneously detected and is quickly cut off, or conversely, the threshold is uniformly set in order to avoid such erroneous detection. The detection delay and the detection error that occur when the distance is set to a high value can be prevented.

Embodiment Hereinafter, a microwave oven with a heater, which is a heating device according to an embodiment of the present invention, will be described with reference to the drawings.

As shown in FIG. 2, the microwave oven 30 has an operation unit 13 on the front side for inputting an instruction for operation control of the device, and a body 31 on the outside.
A door 32 is provided at the opening of the heating chamber 1 so as to be openable and closable.

As shown in FIG. 1, a magnetron 3 for supplying a microwave to the wall of the heating chamber 1 for heating the object 2 and an upper heater 35 and a lower heater 34 as second heat sources for heating the object 2.
And a lamp 14 for illuminating the inside of the heating chamber 1.
During heating of the object 2 on which the object to be heated 2 provided in the heating chamber 1 is placed, the object 2 is rotated to achieve uniform heating. The fan motor 16 sends the wind for cooling the magnetron 3, the lamp 14, the high-pressure transformer 15 for supplying a high voltage to the magnetron 3, the steam gas generated from the object 2 to be heated, and the like into the heating chamber 1 to discharge the gas to the outside of the heating chamber. Generates wind and fan motor
The direction and amount of the wind generated by the orifice 17 provided beside the 16 are regulated.

These high-voltage transformer 15, fan motor 16, and turntable motor 18 are controlled by the driving unit 11,
The operation of the driving unit 11 is controlled by a control signal from the control unit 4.

There are two exhaust passages through which the air sent from the fan motor 16 enters the heating chamber 1 and then exits the heated object 2 outside the machine body containing the steam gas. A first exhaust passage which passes from the first exhaust port 19 through the first exhaust port 26 via the first exhaust guide 21 and a second exhaust guide 22 and a ventilation pipe from the second exhaust port 20 23 Further exhaust guide A24 and exhaust guide B25
This is a second exhaust passage that passes through the second exhaust port 27 through the second exhaust passage. The heat-sensitive surface of the pyroelectric element 5 having pyroelectricity is exposed on the inner wall surface of the second exhaust passage.

FIG. 3 is a detailed explanatory view of the pyroelectric element 5, showing a flat ceramic plate 36 having a pyroelectric effect and electrodes formed on both surfaces thereof.
37, an electrode 38 and a metal plate 39 such as stainless steel adhered to one surface of the electrode 38. The metal plate 39 functions as a heat-sensitive surface of the pyroelectric element 5. When a high-temperature gas such as steam hits the metal plate 39, heat is transferred to the ceramic plate 36 through the metal plate 39, and the ceramic plate 36 is heated. Generate voltage due to the pyroelectric effect. In the case of the pyroelectric element 5 shown in FIG. 3, the electrode 38 on the side bonded to the metal plate 39 is a ceramic plate.
The wire is partially extended to the opposite surface through a part of the peripheral end of 36, and the extraction of the lead wire 40 from the electrodes 37, 38 is performed by the metal plate 3
The structure is possible only with the surface that is not bonded to 9.

For example, PZT (lead zirconate titanate) or the like is conceivable for the ceramic plate 36. The pyroelectric element 5 is polarized such that the electrode 37 side has a positive polarization polarity and the electrode 38 side has a negative polarization polarity. Under this polarization condition, a positive voltage (plus ) Occurs.

Heated object 2 placed in heating chamber 1 as shown in FIG.
(Food) is dielectrically heated by the microwave (high frequency) of 2450 MHz generated by the magnetron 3. When the temperature of the object 2 to be heated rises with heating and reaches a temperature close to the boiling point of water, a large amount of high-temperature steam is generated, and this steam passes through a second exhaust port 20 provided on the ceiling of the heating chamber 1. Cylindrical ventilation pipe
The light is guided to 23 and strikes the pyroelectric element 5. The vapor that has hit the pyroelectric element 5 gives the pyroelectric element 5 a large amount of heat energy,
Naturally, this heat energy includes a large amount of latent heat generated by the condensation of steam on the surface of the pyroelectric element 5.

The rapid temperature rise of the pyroelectric element 5 thus generated disturbs the polarization parallel state inside the pyroelectric element 5, and generates a pulse signal of a rapid voltage change at the electrode on the element surface. This pulse signal also appears when the temperature drops abruptly, such as when cold air hits a warmed element, but the pulse signal is generated with a characteristic opposite to that when the temperature rises.

Since the steam generated from the object to be heated 2 (food) fluctuates and moves in the air at a lower temperature than the steam, the amount of steam hitting the pyroelectric element 5 fluctuates temporally and spatially.
Therefore, even if the temperature of the object to be heated 2 (food item) becomes equal to or higher than a certain temperature and steam is generated constantly, the pyroelectric element 5 rises in temperature at a certain moment with a large amount of steam, but at the next moment. The temperature changes (temperature fluctuations), that is, thermal transfer is repeated, such that the amount of steam hitting becomes small and the temperature drops, and the next moment the temperature rises again due to the receipt of a large amount of steam.

As a result, while the object to be heated 2 (food) continues to generate high-temperature steam, the pyroelectric element 5 has an irregular positive and negative pulse-like shape in response to the above-described thermal transfer (fluctuation in temperature). Continue to generate signal voltage (AC voltage).

When the temperature of the object to be heated 2 approaches the boiling point of water by performing microwave heating in this way, steam is rapidly generated from the object to be heated 2, and this steam corresponds to fluctuation between the electrodes of the pyroelectric element 5. Positive and negative pulsed voltage with large amplitude (AC voltage)
v (several mv). Thus, the pyroelectric element 5
Control unit 4 via voltage sensor signal processing means 12 generated in
Conveyed to.

For example, if the article to be heated 2 is a reheating menu (reheating of food), the temperature becomes sufficiently high for heating when a large amount of steam starts to be generated.
The outline of the basic detection system is to determine that the magnetron 3 and the cooling fan 16 are stopped when the voltage generated thereby reaches a predetermined detection level (threshold).

The control unit 4 outputs a display output signal to the operation unit 13 or outputs a signal for driving the driving unit 11 based on an input signal input from the input keyboard of the operation unit 13 and activates the magnetron 3 to operate the object to be heated. In addition to the function of heating the rotating base 2 and the function of rotating the turntable 33, a judgment for controlling each part is made based on a signal voltage transmitted from the pyroelectric element 5 via the sensor signal processing means 12.

Next, a method of detection and control by the control unit which plays a central role of the present application will be described with reference to FIGS.

First, the procedure and method for controlling heating and automatic detection in this embodiment will be described with reference to the flowchart shown in FIG. First, when the object 2 to be heated is put into the heating chamber 1 and the heating start key is pressed, a control signal from the control section 4 is transmitted to the control means 11, and the control means 11 controls the magnetron 3 (high-voltage transformer).
15), driving of the fan motor 16, the turntable motor 18 and the like is started (a). The counting of the elapsed heating time T is started in the control section 4 (b). Wait until the heating elapsed time T is the start time T ₁ of the predetermined time (c). The voltage value D of the signal voltage is read by the measuring means 6 (d). The maximum value D _m to the voltage value D read on the recording unit 7 records, the subsequent new read voltage value D is the value to the maximum value D _m is larger than the maximum value D _m recorded (e) . Time T _{2 at which} predetermined time ends
(E) is repeated until (f). Determining a threshold value corresponding to a maximum value D _m recorded in the recording unit 7 at the threshold setting unit 8 (g). T ₂ later, 1 added to the count N if Kose signal voltage threshold predetermined time or more in Comparative measuring means 9 (N = N + 1) to (h). Step (h) is repeated until the count N reaches a predetermined numerical value (for example, 5) (i). N
If T = 5, T = t ₄ is recorded as the detection time, and control of each unit including the magnetron is performed correspondingly (T).

The outline of the method of determination and control has been described above according to the flowchart. Next, the relationship between the output signal and the determination will be mainly described with reference to FIG.

The measuring means 6 provided in the control unit 4 to the maximum value D _m is the recording means 7 of the voltage value D which is repeatedly measured (between the time T ₂ from T ₁₎ for a predetermined time after the start of heating Be recorded. Then, the threshold selecting means 8 of the control unit 4
Determining a threshold value as a detection level for the recorded value D _m in.

T ₂ Hereinafter country comparison measuring means 9 identifies whether this threshold the detection signal has reached, the count N of the counter provided in the comparative measurement means 9 Once beyond the threshold constant number setting continuously 1 is added (N = N + 1). The count N of this counter is a preset number of times, for example, 5
Once you reach in time, detection time t ₄ as time doneness of heated state of the object to be heated 2 reaches a reasonable state is recorded.
However, as for the number of pulse signals exceeding the threshold value, a method is employed in which when the time exceeding the threshold value is longer than a predetermined time, for example, 100 ms.

The first table is an example of a classification table used to select a threshold.

That is, in the first table are three types of constant 0.5,0.4,3.0 as constants for threshold settings are provided by three ranges of values of D _m, the threshold is determined according to this table.

Next, the relationship between the signal level and detection time t ₄ in the case of using the first table in accordance with Figure 4 will be described. FIG. 6 (a)
Fig. 4 (b) is an example in which heating is started from a state where the microwave oven is cold (a state where the microwave oven has been left for a certain period of time or more since the previous use), and Fig. 4 (b) shows a large amount of residual hot air in the heating chamber 1 immediately after heating the heater. This is an example where heating was started in a state where there was a problem. In the case of FIG. 4 (a), the signal level is almost zero and is detected within the first predetermined time (from T ₁ to T ₂ ) from the start of heating to the generation of steam from the article to be heated 2. The maximum value _Dm is 0.2v, and the threshold value is set to 0.5v. So that the finished detection time t ₄ is determined by the result comparison measuring means 9. On the other hand, in the case of FIG. 4 (b), a signal level of a considerable amplitude is observed immediately after the start of heating due to the influence of a large amount of residual hot air in the heating chamber 1, the maximum value _Dm is 0.7v, and the threshold value is It is set to 1.1 V, which is higher than the signal level (D _m ) generated due to the residual hot air, and of course, higher than that in the case of FIG.

Since more than the threshold value for determining the Tori finish detection time t _d description is set corresponding to the signal voltage due to the residual hot air or the like to be detected even before the heating steam is generated from the heated object 2, immediately after heater Even in the case of such a hot condition, erroneous detection (early disconnection) due to signal voltage due to residual hot air does not occur.

In addition, when the maximum value D _m is equal to or more than a certain value, in the example of Table 1,
When 2.5 <D _m, the threshold is fixed at 3.0 regardless of the value of D _m
The reason for this is to prevent a situation where the threshold value is too large to be detected (a signal due to steam generated from the object to be heated does not reach the threshold value).

Although the pyroelectric element 5 of the present embodiment is formed of a ceramic element having pyroelectricity, this element may also have piezoelectricity, for example, a piezoelectric element such as a piezoelectric buzzer or an ultrasonic microphone. It goes without saying that the content of the present invention can be satisfied as long as it has pyroelectricity even if it uses characteristics.

Effects of the Invention As described above, according to the heating device of the present invention, the following effects can be obtained.

In the determination of the detection by the control unit, the maximum value of the signal voltage is captured for a certain period (first predetermined time) after the start of heating, and a threshold value which is a detection level is set for this maximum value according to a certain rule. , by detecting the effective voltage signal level in such a way that the time of voltage pulses over a certain time width exceeds this threshold is counted more than a certain number of times (e.g. 5 times) and detection time t _4, the heater Even when the noise signal level due to the residual steam in the heating chamber is high, such as immediately after heating, the problem that the noise signal is erroneously detected and the noise signal is quickly cut off can be solved.

In particular, the measuring means prompts the maximum value of the signal voltage for a certain period and determines a threshold value for this value, while the comparison measuring means counts signal pulses exceeding the threshold value for a certain time width or more. By changing the method of determining the signal voltage, the noise signal and the steam signal can be more reliably separated.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of a heating device according to one embodiment of the present invention, FIG. 2 is an external perspective view of the device, FIG. 3 (a) is a plan view of a pyroelectric element of the device, and FIG. 4 (b) is a cross-sectional view of the device, FIGS. 4 (a) and 4 (b) are diagrams showing a signal change of a detection signal of the pyroelectric element over time in the device, and FIG. 5 is an embodiment of the present invention. It is a flowchart. 1 ... heating room, 2 ... object to be heated, 3 ... magnetron,
4 ... Control unit, 5 ... Pyroelectric element.

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Shinichi Sakai 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Masaaki Sano 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (3)

(57) [Claims] A heating chamber for accommodating the object to be heated, a heating means for heating the object to be heated, a ventilation path for guiding a part of the gas in the heating chamber to the outside of the heating chamber, and a focus disposed in the ventilation path. An electric element, a sensor signal processing unit for extracting an output signal of the pyroelectric element, and a control unit for controlling the heating unit based on an output of the sensor signal processing unit. During, the first storage means for storing the maximum value of the output voltage from the sensor signal processing means, and a predetermined relational expression set in advance based on the maximum value stored in the first storage means A threshold value is calculated, and the threshold value setting means for storing the value is compared with a threshold value to determine whether an output voltage from the sensor signal processing means has reached the threshold value after the predetermined time, and the determination result is output. Determining means for performing the determination, Heating apparatus comprising a control means for controlling the heating means by an output from the stage. 2. A heating chamber for accommodating an object to be heated, a heating means for heating the object to be heated, a ventilation path for guiding a part of the gas in the heating chamber to the outside of the heating chamber, and a focus disposed in the ventilation path. An electric element, a sensor signal processing unit for extracting an output signal of the pyroelectric element, and a control unit for controlling the heating unit based on an output of the sensor signal processing unit. A first value for detecting a maximum value of the output voltage from the signal processing means and storing a first value which is the maximum value;
A second step of calculating a threshold value according to a preset relational expression according to the first value, and storing the value; and an output voltage from the sensor signal processing means. Measuring at least one of a frequency that is continuous for a predetermined time or more over a second value or an accumulated time that is at least the second value,
A method of controlling a heating device including a pyroelectric element sensor, comprising a third step of controlling operation of a heating unit by detecting that a predetermined value has been reached. 3. The relational expression set in advance in the second step is such that when the first value is equal to or more than a predetermined value, the second value is set to a predetermined constant value regardless of the magnitude of the first value. Item 3. A method for controlling a heating device according to Item 2.