JPH0330721Y2 - - Google Patents

Description

[Detailed description of the invention] <Technical field> The present invention relates to a weight detection device for a microwave oven.
More specifically, the present invention relates to a device in which the weight of an object to be heated placed on a turntable is detected by detecting a voltage generated in a piezoelectric transducer.

<Prior Art> Microwave ovens equipped with weight sensors that measure the weight of an object to be heated and control heating based on the measured weight have been rapidly becoming popular in recent years, and are expected to become even more popular in the future. However, the conventional microwave oven with a weight sensor has a disadvantage that the manufacturing cost is high because there are many parts that make up the weight sensor and precision in assembling the parts is required.

Therefore, in view of the above drawbacks, a support roller that supports the turntable and rotates on the bottom of the heating chamber is disposed inside the heating chamber, and piezoelectric conversion is applied to the roller rotation locus on the bottom of the heating chamber that generates stress due to the rotation of the support roller. By arranging an element to detect the voltage generated in the piezoelectric transducer when the support roller rotates, and detect the weight of the object to be heated placed on the turntable, A weight detection device for a microwave oven that has fewer components and is inexpensive has been proposed.

Hereinafter, the weight detection device for the microwave oven will be explained based on the drawings.

Figure 3 is a side sectional view of the main parts of the microwave oven, Figure 4 is a top view of the bottom of the heating chamber with the turntable shown in Figure 3 removed, and Figure 5 is an enlarged detailed sectional view of the turntable. .

In the figure, 1 is a heating chamber, 2 is a turntable on which the object to be heated is placed, and 3 is a support roller that supports the turntable 2 and rotates on the bottom surface of the heating chamber 1. As shown in FIG. 4, it is a Y-shaped support roller. an arm 3a, a roller 3b rotatably pivoted to the tip of the arm 3a,
3b, 3b, and is rotated by the rotation of a turntable motor 5 attached to the lower surface of the bottom wall 1a of the heating chamber 1 with a motor attachment angle 4.

That is, a coupling portion 3c of the arm 3a that is detachably fitted to the coupling ring 6 that is pivotally attached to the rotating shaft of the turntable motor 5.
The rotational force of the motor 5 is transmitted to the support roller 3, and the bottom surface of the heating chamber 1 and the rollers 3b, 3b,
3b draws a rotation locus 7 as indicated by a dashed line in FIG.

Reference numeral 8 denotes a piezoelectric element disposed on the back side of the rotation locus 7 of the bottom wall 1a of the heating chamber 1, the details of which will be described later with reference to FIG. 9 is a magnetron that generates high frequency radio waves, 10 is a waveguide that guides the high frequency radio waves into the heating chamber 1, 11 is a cabinet forming the outer shell of the microwave oven, and 12 is a door.

The piezoelectric element 8 is constructed by laminating a base electrode plate 8a, a piezoelectric ceramic 8b, and a vapor-deposited electrode 8c as shown in FIG. A voltage as shown in Figure 7 is induced and output. The peak value V ₁ of this output voltage is detected an appropriate number of times by a detection circuit (not shown) through a filter circuit formed by a resistor R and a capacitor C shown in Fig. 8, and the average value is taken. is proportional to the weight of the object to be heated, as shown in FIG.

FIG. 10 is a circuit diagram for controlling the magnetron 9 in response to the detected weight of the object to be heated.
This circuit detects the output voltage peak value a predetermined number of times, calculates the weight based on the average value, controls the relay 14, controls the magnetron 9, and controls the heating of the heated object. In addition, 15 is a heating start switch, 16 is a fuse, and 17 is a high voltage transformer.

The above-described weight detection device for a microwave oven has a simple structure of the detection section, has a small number of component parts, and is easy to assemble. Furthermore, even though the table on which the object to be heated is placed is a turntable, the output voltage peak value of the piezoelectric element 8 is detected an appropriate number of times and the weight is detected based on the average value, so that uneven loads and center loads can be detected. The difference is small and the weight detection accuracy is high.

However, the piezoelectric ceramic 8b of the piezoelectric element 8 easily absorbs moisture, and the output voltage of the piezoelectric element 8 varies even though the weight is the same due to changes in the humidity of the atmosphere, resulting in poor weight detection accuracy. .

<Purpose> The present invention was developed in view of the above-mentioned drawbacks, and its purpose is to enable highly accurate weight detection that is unaffected by changes in atmospheric humidity by applying a resin coating to the piezoelectric element. shall be.

<Embodiment> An embodiment of the weight detection device for a microwave oven according to the present invention will be described below with reference to the drawings.

The present invention is characterized in that, as shown in FIG. 1, a resin-based coating 8d (fluororesin in the embodiment) is applied to the upper part of the vapor deposition electrode 8c to improve moisture resistance.

As a result, the piezoelectric ceramic 8b is protected from moisture by the resin-based coating 8d, making it less susceptible to changes in humidity as shown by the solid line in FIG. 2, allowing stable and highly accurate weight detection.
In addition, the solid line in the figure indicates "with coating", and the dashed line indicates "without coating".

<Effects> In the present invention, a support roller that supports a turntable and rotates on the bottom surface of the heating chamber is disposed in the heating chamber, and a piezoelectric transducer is disposed corresponding to the rotation locus of the roller, so that the support roller rotates on the bottom surface of the heating chamber. In a weight detection device configured to detect the weight of an object to be heated placed on the turntable by detecting the voltage generated in the piezoelectric transducer when it rotates, the piezoelectric transducer is coated with a resin. This method has high practical value because it allows highly accurate weight detection that is unaffected by changes in atmospheric humidity.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the main part of the piezoelectric element of the present invention, and FIG. 2 is a relationship diagram between the output voltage of the piezoelectric element and humidity for the same weight, where the solid line shows the case with coating and the dashed line shows the case without coating. Figure 3 is a side sectional view of the main parts of the microwave oven, Figure 4 is a top view of the bottom of the heating chamber with the turntable in Figure 3 removed, and Figure 5 is a side sectional view of the main part of the microwave oven.
The figure is an enlarged detailed sectional view of a conventional turntable section, FIG. 6 is a sectional view of a main part of a piezoelectric element section, FIG. 7 is an output voltage waveform diagram of the piezoelectric element shown in FIG.
The figure is an RC filter circuit diagram of the piezoelectric element output voltage, FIG. 9 is a relationship diagram between the output peak voltage average value and weight, and FIG. 10 is a magnetron control circuit diagram. Code, 1... heating chamber, 2... turntable,
3...Support roller, 3b...Roller, 7...Rotation locus of roller, 8...Piezoelectric element, 8b...Piezoelectric ceramic, 8d...Coating.

Claims (1)

[Claims for Utility Model Registration] A support roller that supports a turntable and rotates the bottom wall of the heating chamber is disposed in the heating chamber, a piezoelectric transducer is disposed corresponding to the rotation locus of the roller, and In a weight detection device for a microwave oven that detects the voltage generated in the piezoelectric transducer when the roller rotates to detect the weight of the heated object placed on the turntable, the piezoelectric transducer , a weight detection device for a microwave oven characterized by being coated with a resin.