JP2584057B2 - Heat cooker with weight detection function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heating device that measures the weight of an object to be heated during heating and performs optimal heating according to the weight.

<Prior Art> There have already been many ideas on a heating device that automatically controls heating by detecting the weight of an object to be heated. For example, by using a capacitance-type pressure sensor in which a detection electrode is formed at a predetermined interval, a detection electrode is formed at a central portion, and a pair of alumina sintered bodies having a reference capacitance is formed at an outer peripheral portion thereof, and the influence of temperature characteristics is obtained. The realization of a high-precision weight detection device that does not receive the signal is already a well-known technique.

Hereinafter, a conventional example will be described with reference to FIG. Substrate 35
And the diaphragm 19 are formed of a thin plate of an insulating material such as alumina, and the periphery thereof is sealed with a sealing material 20 while maintaining a certain distance d.
Sealed in.

On the opposing surfaces of the substrate 35 and the diaphragm 19, a detecting electrode 21 as a weight detecting means is formed at the center and a reference electrode 22 as a temperature correcting means is formed around the center by printing.

When a load P due to a heated object is applied to the diaphragm 19,
The diaphragm 19 bends as shown by the broken line, and the capacitance Cw formed by the detection electrode changes. However, the reference electrode 22 arranged around the detection electrode is a fulcrum seal material 20.
, And the change in the capacitance Cr due to the load P is slight. As described above, since the capacitance Cr and the detection capacitance Cw are formed of the same material and in close proximity, the temperature characteristics become substantially equal. Here, the temperature characteristics can be successfully eliminated by measuring Cw and Cr and taking the ratio of both.

Now, assuming that no load P is applied to the sensor at all, the area of the detection electrode is Sw, the area of the reference electrode is Sr, the gap between the electrodes determined by the thickness of the sealing material is d, and the dielectric constant of air ε. Then Becomes

When calculating Cw / Cr here, the ratio in the no-load state, that is,
The initial ratio R ₀ is Thus, the term of the gap between the electrodes is completely eliminated, and is expressed by the ratio of the respective electrode areas.

<Problem to be Solved by the Invention> However, in this configuration, the relative positional relationship between the paired electrodes is shifted due to the variation in the printing position of each electrode and the variation in the bonding of the diaphragm 19 and the substrate 35. As a result, the electrode area in the equation (1) changes equivalently, and the initial ratio R _0, that is, the zero point as the balance varies. When this capacitance type pressure sensor is used as a weight detecting device, in addition to the sensitivity adjusting means for adjusting the variation of the sensitivity of the sensor, a zero point adjusting means for adjusting the variation of 0 points is used. There is a problem that it is necessary to secure weighing performance for performing adjustment according to each sensor.

Further, in a use environment in which impact loads frequently occur, such as a heating device in which both the substrate 18 and the diaphragm 19 are made of a material having a very fragile property of alumina, the problem of destruction is inevitable. Various mechanical or structural measures have been devised for the protection. (Japanese Unexamined Patent Publication No. 62-17
No. 4094).

In addition, in the conventional configuration, it is necessary to draw the reference capacitance and the detection capacitance from a pair of terminals to an external detection circuit with four lead wires, which is very troublesome in terms of man-hours. Since the stray capacitance also differs depending on the forming of the lead wire, the large number of lead wires leads to an increase in the variation in the initial ratio _R0 of the sensor capacitance ratio.

Accordingly, the present invention provides a heating device provided with a weight detection device that has a small output variation at zero load, does not require zero-point adjustment, and is not easily broken by an impact load.

A second object is to simplify the system, reduce man-hours, and suppress the influence of stray capacitance by reducing the number of lead wires to the external capacitance detection circuit.

<Means for Solving the Problems> In order to achieve the first object, the present invention provides a heating chamber for accommodating an object to be heated, heating means coupled to the heating chamber, and a weight of the object to be heated. Load detection means for detecting
A control unit that changes power supply to the heating means according to the detected weight, wherein the weight detection means includes a common electrode substrate made of a metal material, a diaphragm made of a thin plate of alumina sintered body, and a common electrode substrate and the diaphragm. A seal portion that is coupled to each other at the outer peripheral portions thereof, a detection electrode formed at the center of the diaphragm, and a reference electrode formed at a substantially unflexible portion around the detection electrode; An electrostatic capacitance type weight sensor is used which measures the ratio between the detection capacitance between the substrate and the detection electrode and the reference capacitance between the common electrode substrate and the reference capacitance to detect the weight.

Further, in order to achieve the second object, the present invention brings the common electrode substrate into contact with a conductive portion having the same potential as the metal chassis of the heating device main body, and similarly sets the ground potential in the capacitance detection circuit to the metal chassis of the heating device main body. The configuration is such that the reference potential is measured between the ground potential and the reference electrode, and the detection capacitance is measured between the ground potential and the detection electrode.

<Operation> The heating device of the present invention is configured such that the substrate facing the diaphragm is configured as a common electrode substrate made of a metal material, so that the common electrode substrate viewed from both electrodes (reference electrode and detection electrode) with a small gap therebetween is formed. It can be regarded as an electrode that extends substantially infinitely. Therefore, even if the relative positional relationship between the two electrodes and the common electrode substrate is deviated due to the deviation of the printing position of the detection electrode and the reference electrode, the deviation of the bonding between the diaphragm and the common electrode substrate, and the like, which occur during the manufacturing, the detection capacitance and the reference are not changed. The capacity will not be affected at all. Therefore, in the method of detecting weight based on the ratio of the two capacities, the output value when no load is applied to the sensor shows a completely constant value. There is no need to provide them. As a result, the entire system can be simplified, the adjustment work can be omitted, and the man-hour can be greatly reduced. Since the substrate supporting the load is made of a metal material, the problem of the substrate being damaged by an impact load does not occur.

Also, since the common electrode substrate is in contact with the metal chassis of the main body of the heating device, and the ground potential of the external capacitance detection circuit is also the same as the potential of the metal chassis, the lead wire from the sensor to the external circuit is pulled out to the diaphragm side. Only two electrodes from the reference electrode and the detection electrode are required, and the system can be simplified. Further, variation in the initial capacitance ratio _R0 due to the stray capacitance of the lead wire can be reduced.

<Example> Hereinafter, a heating device in the present invention will be described with reference to the drawings.

FIG. 3 is a perspective view of the main body of the heating device according to the present invention.

A door 2 and an operation panel 3 are provided on the front of the main body 1 so as to be openable and closable.
Is provided. A keyboard 4 for instructing various kinds of heating and a display unit 5 are arranged on the operation panel 3.

FIG. 4 is a block diagram showing one embodiment of the system configuration of the acceleration device according to the present invention.

Various heating commands input from the keyboard 4 on the operation panel 3 are decoded by the control unit 6 and a predetermined display is performed on the display unit 5.

An object to be heated 9 is placed on a mounting table 8 in a heating chamber 7 and heated by a magnetron as a heating means 10. The power supply of the magnetron 10 is controlled by the control unit 6 via the driver 11.

The mounting table 8 is rotated by a motor 12 at the time of heating in order to improve uneven heating of the object 9 to be heated. And, the support rotation axis of the motor 12 which freely moves in the thrust direction.
An electrostatic capacitance type weight sensor 13 is mechanically engaged with the tip of 17 to transmit the weight of the object 9 to be heated and the mounting table 8.

FIG. 1 shows an embodiment of the structure of the capacitance type weight sensor 13 according to the present invention. (A) is a sectional view, and (b) is a developed view of a sensor.

The common electrode substrate 18 is a flat plate made of a metal material, and the diaphragm 19 is a flat plate made of a ceramic material such as alumina porcelain. Both are sealed with a sealing material 20 around the gap d. As a material of the sealing material 20, an epoxy resin adhesive, a glass frit, or the like is used. A detection electrode 21 is provided substantially at the center of the surface of the diaphragm 19 facing the common electrode substrate 18, and a reference electrode serving as a temperature detection means is provided at a portion of the outer periphery of the detection electrode 21 close to the sealing material 20.
22 is formed by printing or the like.

Assume that the capacitance between the common electrode substrate 18 and the detection electrode 21 is a detection capacitance 15 (hereinafter Cw), and the capacitance between the common electrode substrate 18 and the reference electrode 22 is a reference capacitance 15 (hereinafter Cr). When a load P is applied, the diaphragm 19 bends as shown by a broken line,
The detection capacity Cw changes, and the reference capacity Cr arranged near the sealing material 20 hardly changes.

Here, since the reference capacitance Cr is made of the same material as the detection capacitance Cw, and is arranged very close to each other, it is considered that both have substantially the same temperature characteristics.

As a method for eliminating this temperature characteristic, there is a method of taking the ratio of each capacitance such as Cw / Cr.

When this Cw / cr is defined as R and the temperature characteristic of R is calculated, ## EQU1 ## and the difference is the form of the temperature characteristic of each capacitor, and both are well erased.

In this embodiment having such a configuration, the detection electrode 21
Alternatively, the electrode facing the reference electrode 22 is formed of a single flat common electrode substrate 18, and the gap d between the electrodes is as small as about 100 microns in order to have a sufficiently large value with respect to the stray capacitance. ing.

The solid angle when viewing the common electrode substrate 18 from the reference electrode 22 and the detection electrode 21 across this minute gap is 360 °, which can be regarded as a flat plate extending to infinity. This means that the reference capacitance 14 and the detection capacitance 15 do not vary even if there is a variation in manufacturing work such as a deviation in the printing position of the reference electrode 22 and the detection electrode 21 or a deviation in the bonding between the diaphragm 19 and the common electrode substrate 18. Indicates a constant capacitance value.

As another parameter for determining the capacitance value, there is a gap d between the electrodes. In this state, when no load is applied, the diaphragm 19 and the common electrode substrate 18 have a parallel positional relationship, and the respective capacitances are divided. For example, it can be completely erased as shown by the equation (1).

Returning to FIG. 4, the detection capacitance 15 and the reference capacitance 14 are detected by the capacitance detection circuit 16, and are subjected to division processing by the control unit 6 composed of a microcomputer to calculate the capacitance ratio R.

FIG. 5 is a load characteristic diagram of the capacitance type weight sensor according to one embodiment of the present invention. The vertical axis R is Cw / Cr, and the horizontal axis W is the load applied to the sensor. Thus, the load applied to the sensor is 0 g
Since there is almost no variation in R at the point (1), adjustment as a balance at the point 0 is unnecessary. After that, it is only necessary to adjust the sensitivity variation which is determined by the thickness of the diaphragm, so that the system can be simplified and the man-hours for adjustment work relating to weighing accuracy can be greatly reduced.

Next, an embodiment of the method of adjusting the sensitivity and how the weight w is calculated from the volume ratio R by the method will be described.

W-R characteristics of the sensor of the control unit 6 in a standard characteristic (tentatively called curve of (a) in FIG. ^{5.) W = aR 2 + bR} + c (a, b, c; constant) (2) Is stored as a quadratic expression. Of course, this curve may be represented by a higher-order equation.

The sensitivity adjustment is performed under the load condition of the mounting table 8, which is the zero point of the heating device. As an example, the sensitivity adjustment of the sensor shown in FIG. First, the control unit 6 measures the capacitance ratio Rb (2)
The mounting table weight Wp 'is calculated from the equation. This is heavier than the actual mounting table weight Wp, and the sensitivity can be corrected by multiplying by the correction coefficient of Wp / Wp '. In other words, the calculation result under the load condition of the mounting table
What is necessary is just to determine the sensitivity correction coefficient which becomes Wp. It goes without saying that the sensitivity correction coefficient Wp / wp 'can be stored using a storage medium such as a semi-fixed volume or a non-volatile RAM.

Thereafter, the weight W can be calculated by a sequence of multiplying the value calculated from the measured capacity ratio R by the relationship of the formula (2) by the sensitivity correction coefficient read from the storage medium.

Next, an example of a mounting structure of the capacitance type weight sensor will be described with reference to FIG. The motor mounting bracket 25 is mounted on the bottom of the heating chamber 7 by spot welding, and the motor 12 and the sensor mounting bracket 26 are mounted thereon by screwing. The capacitance type weight sensor 13 is mounted on a sensor fixing bracket 26, and is fixed by a metallic sensor cover 29 that covers the entire sensor and electromagnetically shields the sensor. The sensor cover 29 has claws 29-a and 29-b, is inserted into a hole formed in the sensor fixing bracket 26, and is fixed by bending the tip. A load transmitting member 28 having a planar contact surface with the diaphragm 19 is mounted on a substantially central portion of the diaphragm 19 so as to receive a load and press the diaphragm 19 with a constant pressing area. The load transmitting member 28 is disposed just below the lower end of a support rotating shaft 27 that is driven to rotate by the motor 12 and is movable in the thrust direction. In addition, the load transmitting member 28 has a shell-shaped upper portion and the upper portion protrudes from a hole drilled in the sensor cover 29, and has a proper clearance between the hole diameter and the diameter of the protruding portion, thereby performing horizontal position regulation. , And movable vertically.

With such a configuration, the object to be heated 9 and the mounting table 8
Is transmitted to the capacitance type weight sensor 13 through the support rotating shaft 17 and the load transmitting member 28.

As described above, in this embodiment, since the common electrode substrate 18 is formed of a metal material having excellent impact strength, the common electrode substrate 18 is commonly used for various impact loads in use, such as a drop of an object to be heated on a mounting table. The problem that the electrode substrate 18 is broken does not occur at all, and the structure becomes mechanically robust.

Next, an example of a specific circuit configuration will be described with reference to FIG. The control unit 6 is formed by a microcomputer, and includes a keyboard 4
Form a key matrix is connected to the input terminal I ₀ ~I _3. The fluorescent display tube as the display means 5 receives the digit control signal S _0.
Are dynamic lighting control by to S ₄ and the display data signal O ₀ ~ O _7.

The driver 11 is composed of a relay 29 and a high voltage booster 30,
Controls power supply to magnetron 10 by Y signal.

The capacitance detection circuit 16 includes a single oscillation circuit 35 composed of an astable multivibrator using an operational amplifier, and switching means 32. The switching means 32 has a detection capacity.
Cw and the reference capacitance Cr are alternately switched and input to the input terminal Tc of the built-in counter of the microcomputer 6. To control the switching is switching gate signal E _0.

The switching means 32 is constituted by an analog switch, but this can be realized by other semiconductor switching means or a relay.

Reference numeral 33 denotes a level shift circuit that performs voltage conversion and waveform shaping, and may be added as needed.

For example, an analog switch can be realized by upc-4066, an operational amplifier can be realized by TL082, and a microcomputer can be realized by MB-88515, but it goes without saying that any device having a function corresponding thereto can be used. The oscillation cycle T of the oscillation circuit 35 used here is considered from the time when the rectangular wave signal output from the terminal of the operational amplifier is inverted, and the capacitance C (Cw
Cr is selected by the switching means 32. ) And the voltage of the terminal is changed by the time constant of the resistor R _3, the resistor R ₁
And minute when the output again terminal when it becomes equal to the voltage of the determined terminal by pressure is calculated believe inverted _{T = 2CR 3 · 1n (1} + 2R 1 / R 2) of R ₂ ...... (3) switching means 32 If the frequency when the detection capacitor 14 side is selected is Fw and the frequency when the reference capacitor 15 side is selected is Fr, both frequencies are respectively Becomes Since the oscillation circuit is the same, when the calculation of Fr / Fw is performed from the frequency measured inside the microcomputer 6, the common term is completely eliminated and Fr / Fw = Cw / Cr, and the target capacitance ratio can be measured. it can.

In the present embodiment, the capacitance type weight sensor 13 is placed on the sensor fixing bracket 26 and brought into contact with the common electrode substrate 18 so as to make the potential of the heating device main body equal to that of the metal chassis. Since this potential is generally the ground potential on the circuit, the capacitance detection circuit 16 measures the capacitance between the ground potential and the reference electrode as a reference capacitance Cr, and measures the capacitance between the ground potential and the detection electrode as a detection capacitance Cw. Therefore, the number of lead wires drawn from the capacitance type weight sensor 13 is two, and the number of assembling steps can be reduced. Further, by reducing the number of lead wires, the influence of the stray capacitance on the sensor capacitance is also reduced, which contributes to the reduction of the variation of the capacitance ratio in the no-load state (the variation of the zero load point).
Further, since the metal chassis of the heating device body surrounding the sensor is all at the potential of the common electrode substrate 18, the electromagnetic shielding effect is also improved.

<Effects of the Invention> As described above, the following effects can be obtained in the heating device of the first aspect.

(1) Since the substrate facing the diaphragm is a conductive common electrode substrate made of a metal material, the common electrode substrate viewed from both electrodes (reference electrode and detection electrode) with a small gap therebetween is substantially infinite. The detection capacity between the common electrode substrate and the detection electrode and the reference capacitance between the common electrode substrate and the reference electrode depend on the variation in electrode printing position during manufacturing and the variation in bonding between the diaphragm and the common electrode substrate. And show a substantially constant value. Therefore, in the method of detecting weight based on the ratio of both capacitances, the output value when no load is applied to the sensor becomes a constant value, and it is not necessary to provide a zero-point adjusting means for adjusting the zero-point variation. And the system can be simplified.

(2) Since the common electrode substrate can be made of a metal material having excellent toughness and less likely to cause stress breakdown, impact resistance is improved.

(1) Since the common electrode substrate is in contact with the metal chassis of the main body of the heating device, and the ground potential of the external capacitance detection circuit is also the same as the potential of the metal chassis. Only two wires need to be drawn from the sensor to the capacitance detection circuit from the reference electrode and the detection electrode on the diaphragm side, and the system can be simplified.

(2) Since the metal chassis surrounding the sensor is all at the same potential as the common electrode substrate, the electromagnetic shielding effect is improved.

[Brief description of the drawings]

FIG. 1 (a) is a cross-sectional view of a capacitive weight sensor relating to a heat cooker with a weight detection function according to one embodiment of the present invention, and (b).
Is an exploded view of the same configuration, FIG. 2 is a circuit diagram of the cooking device, and FIG.
Fig. 4 is a perspective view of the main body of the cooking device, Fig. 4 is a block diagram showing a configuration of the cooking device, Fig. 5 is a characteristic diagram of a capacitance type weight sensor related to the cooking device, and Fig. 6 is a characteristic diagram of the cooking device. FIG. 7A is a sectional view of a capacitance type weight sensor relating to a conventional heating device, and FIG. 7B is an exploded view of the same structure. 1 ... heating device main body, 6 ... control unit, 7 ... heating chamber, 8
...... Mounting table, 9 ... Heated object, 10 ... Heating means, 13 ...
Capacitance type weight sensor, 14 ... Reference capacitance, 15 ... Detection capacitance, 16 ... Capacitance detection circuit, 18 ... Common electrode substrate, 19 ...
Diaphragm, 20 …… Seal material, 21 …… Detection electrode, 22…
... reference electrode.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenzo Koji 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2-68884 (JP, A)

Claims (2)

(57) [Claims] 1. A heating chamber for placing an object to be heated, a heating means coupled to the heating chamber, a weight detecting means for detecting a weight, and a weight of the object to be heated based on output data of the weight detecting means. A control unit for measuring and changing power supply to the heating means in accordance with the weight thereof, wherein the weight detection means comprises a common electrode substrate made of a metal material and a thin plate of an alumina sintered body, and is spaced apart by a predetermined distance. A diaphragm opposing the common electrode substrate, a seal portion connecting the common electrode substrate and the diaphragm to each other at an outer peripheral portion thereof, and a cover formed at a central portion of a surface of the diaphragm opposing the common electrode substrate. A detection electrode for sensing the weight of the heated object, and a reference electrode formed in a portion where the diaphragm does not bend substantially around the detection electrode, between the common electrode substrate and the detection electrode Weight detection function with cooking device has a configuration for measuring the weight ratio of the reference capacitance is a capacitance is measured between the detected capacitance is the capacitance the common electrode substrate and the reference electrode. 2. A metal chassis forming a heating chamber main body,
A capacitance-type weight sensor responsive to the weight of the object to be heated, capacitance detection means for detecting the capacitance of the capacitance-type weight sensor having the same ground potential as the metal chassis, and the capacitance detection means A controller for measuring the weight of the object to be heated from the output data of the capacitor, wherein the capacitance-type weight sensor is made of a metal material and is in contact with the metal chassis, and is made of a thin plate of a sintered body of alumina. A diaphragm facing the common electrode substrate at a predetermined interval,
A seal portion that couples the common electrode substrate and the diaphragm to each other at an outer peripheral portion thereof, and a detection electrode formed at a central portion of a surface of the diaphragm facing the common electrode substrate and sensing the weight of the object to be heated, And a reference electrode formed substantially in a portion where the diaphragm does not bend around the detection electrode, wherein the capacitance detecting means includes a ground potential, a detection capacitance of the detection electrode, the ground potential, and the reference electrode. And a control unit for calculating a ratio between the reference capacity and the detection capacity to obtain a weight, thereby obtaining a weight detection function-added heat cooker.