JPH0325147Y2 - - 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 weight detection device for a microwave oven. Regarding something that detects weight.

<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-mentioned drawbacks, a support roller that supports the turntable and rotates on the bottom of the heating chamber is disposed inside the heating chamber, and a piezoelectric transducer 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 4 is a side sectional view of the main parts of the microwave oven, Figure 5 is a top view of the bottom of the heating chamber with the turntable shown in Figure 4 removed, and Figure 6 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. 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.

8 is a Unimolk type piezoelectric element arranged on the back side of the rotation locus 7 of the bottom wall 1a of the heating chamber 1, details of which are shown in Section 7.
This will be described later based on the figures. 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 8 is induced and output. The peak position _V1 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. 9, and the average value is taken. is proportional to the weight of the object to be heated, as shown in FIG.

FIG. 11 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, since the piezoelectric element 8 is attached to the back surface of the bottom wall 1a with adhesive, it has the following drawbacks.

Since the piezoelectric element is bonded to the back surface of the bottom wall 1a of the heating chamber, the output of the piezoelectric element is small.

Variations in the material of the bottom wall 1a of the heating chamber cause variations in the output of the piezoelectric element 8.

When coating the bottom wall 1a of the heating chamber, variations in the thickness of the coating film cause variations in the output of the piezoelectric element 8.

The durability of the adhesive cannot be trusted.

There is a possibility that the characteristics of the piezoelectric element 8 may change due to heat.

<Purpose> The present invention was developed in view of the above-mentioned drawbacks, and by making the piezoelectric element into a disk shape and supporting the peripheral edge in an annular shape, more stable and highly accurate weight detection can be performed. The purpose is to

<Embodiment> Hereinafter, one embodiment of the weight detection device for a microwave oven of the present invention will be described based on the drawings.

FIG. 1 is an enlarged detailed sectional view of the turntable section according to the present invention, and the same or equivalent parts as in the conventional example are given the same reference numerals and the explanation thereof will be omitted.

In the figure, reference numeral 18 denotes a resin attachment member for attaching the disc-shaped piezoelectric element 8, and a hole is provided in the center to release the stress strain of the piezoelectric element 8. 19
is a mounting bracket for mounting the annular mounting member 18, and a hole having an inner diameter slightly larger than the outer diameter of the piezoelectric element 8 is provided in the center of the shallow dish-shaped downward bulge, and the bulge is A prepared hole for a screw is provided at the periphery of the part, and is spot welded to the back surface of the bottom wall 1a. 20 is a resin having a cross section such that the upper end of the upper protrusion faces a hole 21 bored on the roller rotation locus of the bottom wall 1a of the heating chamber, and the end face of the lower protrusion comes into contact with the upper surface of the piezoelectric element 8. The height of the knob 20 is such that the upper end of the upper protrusion protrudes approximately 0.2 to 0.3 mm from the upper surface of the bottom wall 1a of the heating chamber when the knob 20 is installed, and the height of the knob 20 is such that the upper end of the upper protrusion protrudes from the top surface of the bottom wall 1a of the heating chamber by approximately 0.2 to 0.3 mm, and The diameter is set smaller than the size of the round hole 18a of the mounting member 18. This is to apply a force to the center of the piezoelectric element 8 in a spot to obtain a large output with high precision.

The piezoelectric element 8 is mounted through the round hole 18 of the mounting member 18.
a and the piezoelectric element 8 concentrically, fix the peripheral edge of the piezoelectric element 8 to the mounting member 18 with adhesive, and then attach the knob 20.
are fixed concentrically to the piezoelectric element 8 with adhesive, and then attach the mounting member 18 to the mounting bracket 19 with screws 22, 22 so that the upper end of the upper protrusion of the knob 20 faces the hole 21 in the bottom wall 1a of the heating chamber. This is done by fixing it in place.

FIGS. 2a and 2b are main part sectional views showing other embodiments of the piezoelectric element 8 mounting structure according to the present invention, and FIG. Figure 2b shows the bottom wall 1 of the heating chamber.
A hole for fitting the piezoelectric element 8 is bored in the hole a, the base electrode plate 8a of the piezoelectric element 8 is fitted into the hole, and the piezoelectric element 8 is attached with a mounting member 18''.

Note that the peripheral edge of the base electrode plate 8a is attached to the mounting member 18,
The radial dimension of the annularly supported portion of 18' and 18'' is set to 0.5 to 3 mm.
The larger the outer diameter and the thinner the thickness, the higher the cost, but the larger the outer diameter, the higher the cost, and if the thickness is too thin, there is a risk of damage due to large distortion, so it is important to consider cost, reliability, performance, etc. comprehensively. Judging from this, the base electrode plate 8a of the unimorph type piezoelectric element 8 has an outer diameter of φ15 mm to φ28 mm and a thickness of 0.15 mm to 0.25 mm, and the piezoelectric ceramic 8b has an outer diameter of φ13 mm to φ25 mm and a thickness of 0.15 mm.
It is better to set it to mm~0.25mm.

FIG. 3 is a diagram showing the relationship between the output voltage and the weight when the piezoelectric element 8 is fully supported by the mounting member (A in the figure) and when it is supported in an annular shape (B in the figure).
Compared to case A when fully supported, case B when circular support is used.
The output voltage is several times higher.

Therefore, highly accurate weight detection can be performed, and the S/N ratio (signal-to-noise ratio) is improved, so that weight detection can be performed with less variation.

<Effects> In the present invention, a support roller that supports the turntable and rotates on the bottom of the heating chamber is disposed in the heating chamber, and when the support roller rotates, the voltage generated in the piezoelectric transducer element is detected, and the turntable is rotated. In a weight detection device designed to detect the weight of an object to be heated placed on top, a large output can be obtained by forming the piezoelectric transducer into a disk shape and supporting the peripheral edge in an annular shape. This device has high practical value as a weight detection device for a microwave oven because it can detect weight more stably and with high precision than the conventional method.

[Brief explanation of the drawing]

FIG. 1 is an enlarged detailed cross-sectional view of the turntable part of the microwave oven according to the present invention, FIG. 2 is a cross-sectional view of main parts showing another embodiment of the piezoelectric element mounting structure according to the present invention, and FIG. It is a relationship diagram between output voltage and weight,
Figure 4 is a side sectional view of the main parts of the microwave oven, Figure 5 is a top view of the bottom of the heating chamber with the turntable shown in Figure 4 removed, and Figure 6 is an enlarged detailed sectional view of the conventional turntable. 7 is a cross-sectional view of the main part of the piezoelectric element section, FIG. 8 is an output voltage waveform diagram of the piezoelectric element shown in FIG. 7, FIG. 9 is an R-C filter circuit diagram of the piezoelectric element output voltage, and FIG. The figure is a relationship diagram between the output peak voltage average value and the weight, and FIG. 11 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, 20: knob (power transmission body).

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, and a voltage generated in a piezoelectric transducer when the support roller rotates is detected, The weight detection device for a microwave oven configured to detect the weight of an object to be heated placed on the turntable, characterized in that the piezoelectric transducer is formed into a disk shape, and the periphery is supported in an annular shape. Microwave oven weight detection device.