KR940010286B1 - Weight-measuring device for a range - Google Patents

Abstract

The apparatus compensates the food weight sensing signal from a piezoelectric device varying to the outdoor temperature so that it can make the definite measurement possible. The apparatus comprises a microprocessor (2) controlling the overall processes of the microwave oven; a rotary motor (8) rotating a table (7) according to a drive device (3); a support roller (11) rotating the bottom face of a heating chamber by supporting the rotary table (7); a rotary ring (6) supporting the roller (11); the piezoelectric device (13) sensing the food weight laid on the table (7); a signal processor (14) compensating the temperature variation as well as processing the signal from the piezoelectric device (13).

Description

Weight sensing device for temperature compensation of microwave oven

1 is a main configuration diagram of a conventional microwave oven.

2 is a bottom view of the heating chamber in the state in which the turntable is removed.

An enlarged cross sectional view of a portion according to claim 1 for making the turntable rotatable.

4 is a sectional view of principal parts of the piezoelectric element according to FIG.

5 is a waveform diagram of an output voltage of the piezoelectric element according to FIG. 4;

6 is a filter circuit diagram of R-C of the piezoelectric element output voltage according to FIG.

7 is a weight compensation circuit diagram for temperature compensation of the present invention microwave oven.

8 is an enlarged cross sectional view of a portion enabling the turntable rotation according to the present invention;

9 is a structure and side cross-sectional view of a sensor according to the present invention.

10 is a state diagram of a heating chamber bottom with the turntable removed according to the present invention.

11 is a sectional view of principal parts of a piezoelectric sensing sensor according to the present invention;

12 is a change in capacitance when the support roller according to the present invention passes.

13 is a relationship between the capacitance change of the present invention and the weight.

14 is a detection circuit diagram by a piezoelectric element.

15 is an output waveform diagram according to FIG.

16 and 17 are detailed circuit diagrams of the sensor signal processing means according to FIG.

18 is a characteristic diagram of a capacitance-temperature relationship of a piezoelectric element.

19 is a waveform diagram of a hold voltage of a peak hold portion in the signal processing means of the present invention.

20 is a relationship between output voltage and weight of the offset adjustment unit in the signal processing means of the present invention.

21 is an output voltage waveform diagram of an amplifier section according to temperature in the signal processing means of the present invention.

* Explanation of symbols for main parts of the drawings

1: control panel 2: microprocessor

3: driving means 4: magnetron

5: high pressure transformer 6: heating chamber

7: rotating table 8: rotating motor

9: lamp 10: fan motor

11: support roller 12: rotary ring

13 piezoelectric element 14 signal processing means

18: rubber

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weight sensing apparatus of a microwave oven, and more particularly, to a weight compensation apparatus for a temperature compensation of a microwave oven, in which a weight can be accurately measured by compensating that a weight sensing signal by a piezoelectric element changes with temperature.

The main components of the conventional microwave oven, as shown in FIG. 1, is a rotary motor 5 for driving the rotary table 2 for placing the food to be thawed and heated in the heating chamber 1, and the rotary table ( 2) a support roller 3 for supporting and rotating the bottom of the heating chamber 1, a piezoelectric element 8 installed on the rear surface of the heating chamber bottom wall 1a for sensing the weight of food, and generating high frequency radio waves. It consists of a magnetron (9), a waveguide (10) for guiding high frequency radio waves generated in the magnetron (9) into the heating chamber (1), a cabinet (11), and a door (12).

In the conventional microwave oven configured as described above, when the user puts food on the rotary table 2 in the heating chamber 1 and presses the start cooking button, the magnetron 9 is driven and the magnetron 9 is driven. Radio waves are generated to heat food in the heating chamber 1 via the waveguide 10.

At this time, the heating time detects the voltage generated in the piezoelectric element 8 attached to the rear surface of the heating chamber bottom wall 1a, measures the weight of the food, and heats it for a predetermined time according to the measured weight.

Here, in order to detect the weight of the food placed on the rotary table 2, as shown in FIGS. 2 and 3, the Y-shaped arm 3a and the tip of the arm 3a can be freely rotated. It consists of rollers 3b, 3b, and 3b installed so as to be rotated by the rotation of the rotary motor 5 attached to the motor mounting angle 4 on the lower surface side of the bottom wall 1a of the heating chamber 1.

That is, the coupling 6 provided on the rotating shaft of the rotary motor 5 and the coupling part 3c of the arm 3a which is easy to attach or detach from this coupling 6 are inserted, and the rotational force of the motor 5 is The bottom surface of the heating chamber 1 and the rollers 3b, 3b, and 3b are transferred to the support rollers 3 to draw the rotational track 7 as indicated by the dashed-dotted line in FIG.

In the piezoelectric element 8, as shown in FIG. 4, the base electrode plate 8a, the piezoelectric ceramic 8b, and the deposition electrode 8c are laminated, and these are attached to the lower surface of the bottom wall 1a by an adhesive and roll roller 3b. Passes through the upper surface of the bottom wall 1a, and maintains the voltage as shown in FIG.

The peak value (V ₁ ) of this output voltage is properly detected several times as a detection circuit (not shown) through a filter circuit provided with a resistor (R) and a capacitor (C) shown in FIG. In short, the average is proportional to the weight of the food.

As described above, the weight of the food can be sensed using the piezoelectric element, but the output voltage changes according to the amount of impact of the piezoelectric element changes with temperature, so that the magnitude of the signal changes when the environmental temperature changes.

This has a problem of being a dimensional cause of weight sensing depending on the environmental temperature.

Therefore, in order to solve the conventional problem and to sense the correct weight, the present invention connects two identical piezoelectric elements to the same branch circuit and inputs the outputs of the piezoelectric elements to the inverting and non-inverting inputs of the amplifier. Invented a weight compensation device for temperature compensation of a microwave oven to compensate for changes in temperature by offsetting the change, described in detail below with reference to the accompanying drawings.

7 is a temperature compensation weight sensing circuit diagram of the microwave oven of the present invention, as shown therein, a microprocessor (2) for performing commands by key input of the operation unit (1) and controlling the overall operation of the microwave oven; A driving means (3) for operating the system by supplying operating power under the control of the microprocessor (2), and a rotary table on which food in the heating chamber (6) is placed in accordance with the driving output of the driving means (3); 7) a rotary motor 8 for driving the lamp, a lamp 9 for displaying the cooking progress state of the food, a fan motor 10 for supplying air to the heating chamber 6, and the rotary table 7 A support roller 11 for supporting and rotating the bottom of the heating chamber 6, a rotation ring 12 for supporting the support roller 11, and a support roller 11 attached to the support table 11 on the rotary table 7 Piezoelectric element 13 for sensing the weight of the food is placed, and the piezoelectric element 13 The signal processing according to the received detection signal was composed of signal processing means (14) for output to said microprocessor (2).

Referring to the operation and effect of the present invention configured as described above in detail.

When the user puts food to cook on the rotary table 7 of the heating chamber 6 and presses the cooking start button on the operation unit 1, the key signal of the cooking start button is inputted from the microprocessor 2 and the pan first. The air temperature of the heating chamber 6 is made parallel while driving the motor 10 to introduce air into the heating chamber 6.

In this manner, after a predetermined time elapses after the initial operation, the microprocessor 2 performs the heating operation.

The magnetron 4 is driven under the control of the driving means 3 as the heating operation is performed, and as the magnetron 4 is driven, high frequency electric waves are generated to heat food contained in the heating chamber 6, and also rotate. The rotary table 7 is rotated by the motor 8.

At this time, the lamp 9 lights up as the food is cooked.

As in the above operation, when the rotary table 7 rotates, the support roller 11 exerts pressure on the piezoelectric element 13 according to the weight of the food placed on the rotary table 7.

The state diagram of the bottom portion of the heating chamber with the rotary table 7 removed is as shown in FIG.

Here, when the rotary table 7 rotates by the driving of the rotary motor 12, as shown in FIGS. 8 and 11, the support roller 11 presses and passes the rubber 18 protruding from the bottom wall of the heating chamber. The piezoelectric element 13 has a piezoelectric material between the two pole plates 13-a and 13-b, as shown in FIG. 9B, and a rubber on the piezoelectric element 13 (18), as shown in FIG. 9A.

As such, the piezoelectric element 13 receives a pressure proportional to the weight of the food through the rubber 18, and the capacitance value changes according to the degree of force, which is shown in FIG. 13. When the capacitance change is shown in FIG. 12, the change in capacitance with respect to the pressing force in proportion to the weight is shown.

If this is expressed as relation, it is as follows.

here Flux density, : Field strength, Polarization : Susceptance, ε ₀ : permittivity in air ε _R : relative dielectric constant When pressure is applied to the piezoelectric element 13, polarization Is changing and this information As the change in, the relative dielectric constant (ε _R ) changes, resulting in a change in the correction capacitance (C).

C =

S: Piezoelectric element cross section

d: spacing of piezoelectric elements

The change in capacitance C is processed through the detection circuit of FIG. 14, which is solved as follows.

Where V _o : Charging start point : Discharge start point voltage, R _p: R is a parallel combined resistance of ₁ + R _2.

As shown in Equations (1) and (2), when the value of the capacitance C becomes large, the output voltage v decreases, and conversely, when the value of capacitance C decreases, the output voltage also increases. As shown.

Piezoelectric device (Piezo Device) in the sensor signal processing means 14 for receiving and processing the sensor signal sensed by the piezoelectric element 13, as shown in Figure 16 and 17, the piezoelectric element 13 Amplifying a signal detected and filtered by a sensor signal received from the sensor detectors 141 and 141 'through sensor detectors 141 and 141', detectors 142 and 142 'and filters 143 and 143', respectively. An amplification unit 144, an offset adjusting unit 45 for adjusting an offset (off-set) with respect to the signal amplified by the amplifying unit 144, and an offset is adjusted through the offset adjusting unit 145. A peak hold unit 146 that holds a peak value from the signal and outputs the result to the microprocessor 147, and resets the peak value to the peak hold unit 146 under the control of the microprocessor 147. The reset part 148 is comprised.

When a sensor signal is detected from the piezoelectric element 13 in the sensor detectors 141 and 141 ', the detected signal is detected and filtered through the detectors 142 and 142' and the filters 143 and 143 '. Amplified by the amplifier 144, the amplified output voltage (V ₃ ) is

V ₃ = (V ₂ -V ₁ ).

The voltage V ₃ amplified by the amplifier 144 may be constantly adjusted by appropriately adjusting the variable resistor R _x .

And finally V ₃ voltage in accordance with the 'capacitor (CS _2), the value turns detector (142) and a filter (143') via V ₂ voltage is constant the sensor detecting unit 141, by the pressure of the roller (11) Will also change.

Then, after adjusting the output voltage of the amplifier 144 to the offset adjusting unit 145 and sending it to the peak holding unit 146, the amplifier 144 as the diode D ₂₁ and the capacitor C ₂ . The peak value of the voltage V ₃ is held and the charge charged through the transistor Q ₁ is discharged after the value is read by the microprocessor 147.

Through this operation, an output value proportional to the weight can be obtained as in the 20th degree.

However, as shown in FIG. 18, the piezoelectric element has a characteristic of changing capacitance due to temperature. When the ambient temperature changes during the operation of the microwave oven, the capacitance C _s is changed and the initial voltage V _os is changed. When reading from the microprocessor, an error occurs. As shown in FIG. 21, when the temperature T is T ₃ <T ₂ <T ₁ , the output waveform of the voltage V ₃ amplified through the amplifier 144 is amplified. green to temperature T _3, T _2, and a voltage corresponding to T ₁ corresponds to the v _{OS3, OS2} v, v _OS1, respectively, the same weight when the weight.

To compensate for this change in temperature, connect the capacitance (C _S ) in parallel and input its output to the inverting input of the differential amplifier to offset the change in temperature (V ₁ ) and (V ₂ ) of the temperature. You can.

That is, instead of canceling the change of V ₁ and V ₂ with respect to the temperature, only the change in the capacitance C _S22 at the time of the peak hold changed by pressing the roller can be output.

Therefore, it is possible to eliminate the error on the temperature of the piezoelectric element by installing to detect the ambient temperature, such as C _S11 and C _S22 .

As described above, the present invention connects two identical piezoelectric devices to the same sensing circuit and compensates the signals detected by the piezoelectric elements with the temperature, and the two piezoelectric device outputs are inverted and non-inverting input of the operational amplifier. By inputting, the effect of making accurate weight can be measured by offsetting the change in capacitance due to temperature.

Claims (3)

To the microprocessor 2 which executes a command by key input of the operation unit 1 and controls the overall operation of the electronic rail, and the drive means 3 which supplies the operating power under the control of the microprocessor 2. A rotary motor 8 for rotating the rotary table 7 of the heating chamber 6, a support roller 11 for supporting the rotary table 7 to rotate the bottom surface of the heating chamber 6, and A rotary ring 12 supporting the support roller 11, a piezoelectric element 13 attached to the support roller 11 to sense the weight of food placed on the rotary table 7, and the piezoelectric element 13. A temperature sensing weight sensing device for a microwave oven comprising signal processing means for receiving a sense signal received from the signal processing and performing the temperature compensation. The microwave oven according to claim 1, wherein the piezoelectric element (13) measures the weight of food as the pressure when the rubber (18) protruding from the bottom wall of the heating chamber is pressed when the support roller (11) rotates. Weight compensation device for temperature compensation. 2. The signal processing unit (14) according to claim 1, wherein the signal processing means (14) includes sensor detectors (141, 141 '), detectors (142, 142'), and filter (143) for detecting a signal input from the piezoelectric element (13). Amplifying unit 144 and offset adjusting unit 145 for receiving and amplifying the signals received and filtered from the signals received from the sensor detection units 141 and 141 'through the inverting and non-inverting terminals. Peak hold unit 146 for holding a peak value with respect to the output signal of the amplification unit 144 whose offset is adjusted through the &lt; RTI ID = 0.0 &gt; A temperature compensation weight sensing device for a microwave oven comprising a reset unit (148) which is reset in accordance with the above and outputs to the peak hold unit (146).