JPH0267931A - Weight detecting apparatus - Google Patents

Abstract

PURPOSE:To make is possible to detect a weight highly accurately even during the rotation of a rotary table by synchronizing the rotating speed of a synchronous motor with the weight measuring speed of a weight sensor based on the output signal of a power-source-frequency detecting means. CONSTITUTION:During cooking, a mounting table 5 is rotated by a synchronous motor 6, and irregular heating is prevented. The weight of a food is detected with a weight sensor 1. The operation of a magnetron 7 and the motor 6 are controlled with a control part 3. The frequency of a commercial power source 4 is detected with a power-source-frequency detecting means 2. The output signal from the means 2 and the sensor 1 are inputted into the control part 3. Overall cooking control is performed with the control part 3. In this way, the weight can be detected highly accurately even during the rotation of the mounting table 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a weight detection device in which a table for placing an object to be measured rotates, and is particularly widely used in automatic cooking in a microwave oven.

BACKGROUND OF THE INVENTION In recent years, the mainstream of microwave ovens has been to rotate the food table to prevent uneven heating. Also.

The number of models that make cooking easier through automated cooking control is increasing year by year, and the technology of various sensors is improving accordingly. There are two main ways in which weight detection devices can be used in microwave ovens. One is to measure the weight of food at the start of cooking and set the cooking time, and the other is to detect a decrease in the weight of food during cooking to detect the completion of cooking. In particular, the latter requires a highly accurate weight detection device to detect a weight loss of several grams.

However, the problem that the invention seeks to solve is the cooking process due to weight reduction.''-Although there have been many inventions regarding the cooking process by weight reduction.
-8305Q Publication, JP-A-58-153023, JP-A-60-+50314, Utility Model 60-11
No. 1404 and Japanese Unexamined Patent Publication No. 62-68025), neither of these methods is applicable to microwave ovens of the rotating food table type that have become mainstream in recent years. This is because the weight detecting section detects the weight of the food via the mounting table, so if the mounting table rotates during cooking, a large detection error will occur. FIG. 6 shows an example of detection errors caused by rotation of the mounting table (Japanese Patent Publication No. 62-3893). The vertical axis represents the detected weight value, and the horizontal axis represents time, and the vertical axis has an amplitude of about 10 grams for a 200 gram object to be measured. The amplitude of the weight value seen in this example is a problem that will occur no matter what kind of weight detection device is installed as long as the microwave oven rotates the mounting table. This was a drawback that made it impossible to utilize detection technology.

The present invention solves these conventional problems,
We have realized a weight detection device that can stably detect heavy loads even while the mounting table is rotating, and can detect even the slightest loss of food when a microwave oven is installed.

Means for Solving the Problems The weight detection device of the present invention includes a mounting table on which an object to be measured is placed;
The synchronous motor is equipped with a synchronous motor that rotates the mounting table, a weight sensor that measures the weight of the object on the mounting table, and a power frequency detection means that detects the power frequency. This configuration synchronizes the rotation speed of the weight sensor with the snow scene measurement speed of the weight sensor.

The weight detection device of the present invention detects the rotation speed of the synchronous motor, whose rotation speed is determined by the power frequency, using the power frequency detection means, and reads the weight using the weight sensor in synchronization with the rotation speed, thereby detecting the rotation of the mounting table. This makes it possible to significantly reduce the error associated with weight loss and to detect weight with high precision.

Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is an external perspective view of a microwave oven equipped with a weight detection device as an embodiment of the present invention. There is a door 9 on the front of the main body 8 that can be opened and closed freely, and when the door 9 is opened, a heating chamber 10 can be seen. The food is placed on a placing table 6 at the bottom of the heating chamber 10. The user also operates the operation panel 11 to instruct cooking.

FIG. 1 is a block diagram thereof. During cooking, the mounting table 6 is rotated by the synchronous motor e to prevent uneven heating.

Food weight is detected by a weight sensor 1. The operation of the magnetron 7 and the synchronous motor 6 is controlled by the control section 3. The frequency of the commercial power supply 4 is detected by the power supply frequency detection means 2. The output signals of the power supply frequency detection means 2 and the weight sensor 1 are input to the control section 3, and the control section 3 performs overall cooking control.

As shown by the solid line in FIG. 3a, the heavy electric current detection value draws a waveform that is as reproducible as the position error. One period of the waveform is measured by the mounting table 6.
In this case, it is equal to the rotation period of 10 seconds. When the control unit 3 processes this detected weight value as a weight, if all the data is processed uniformly, the amplitude of the waveform will become an error as it is. In this case, the error is about 8 grams.

Therefore, A, B, C, D, on Figure 3 a! As shown in each point represented by , only one piece of data is valid in a - period. The data acquisition interval is 10 seconds of the waveform period. This apparently eliminates the detection error caused by the rotation of the mounting table 6, and the broken line connecting each point horizontally becomes the transition of the detected weight value.

The synchronous motor 6 is an AC motor whose rotation speed is proportional to the power frequency of the commercial power supply 4. Characteristics include small rotational irregularities and constant rotational speed regardless of the size of the load. The rotation speed of Rogue is generally expressed by the following formula.

(Rotor rotation speed) = 12oXf/P f is the power frequency p is the number of poles.

Further, the rotation speed of the motor output shaft can be determined by multiplying the rotor rotation speed by the reduction ratio provided by the gear. Therefore, if you want to know the rotational speed of the output shaft of the synchronous motor 6 with high accuracy, it is sufficient to detect the current power frequency.

Commercial power frequency in Japan is 1460 Hz and eoll
z, but its true value is by no means stable. Normally, the accuracy is ±0.1%, but when electricity demand increases such as during the summer, it is ±0.6%, and if various factors such as substation capacity are taken into account, fluctuations of ±1% or more are expected. be done. In other words, the rotational speed of the synchronous motor 6 also varies accordingly.

The above figure 3 & is 6 rpm when the power frequency is 60 Hz.
A synchronous motor with an output shaft rotation speed of is taken as an example.

This means that it takes 10 seconds for one rotation of the mounting table.

For convenience of explanation, the power supply frequency is (80X10/11)H
Suppose it becomes 2.

One rotation of the mounting table takes 11 seconds. At this time, the critical value fluctuates at a cycle of 11 seconds, as shown in FIG. On the other hand, if you unilaterally continue to take weight data every 10 seconds,
The waveform cycle cannot be synchronized, and errors appear dispersed over a long period of time, as shown by the broken line connecting F, G, I(, r, and J).If the measurement is continued further, the error will appear for 110 seconds as shown in Figure 3C. It can be seen that the error forms one waveform in the period.If superposition detection is always performed every 10 seconds in this way, the period of the waveform of this error is the 4th waveform.
Draw a hyperbola related to the rotation period of the mounting table as shown in the figure.

In other words, if the cycle of weight detection and the cycle of rotation of the mounting table are not synchronized, a phenomenon will occur where it appears as if the superposition is increasing or decreasing over many minutes, even if the weight is not actually changing. .

The role of the power supply frequency detection means is to determine the period of superimposition detection and the rotation period of the mounting table. The power supply frequency detection means counts the number of rectangular waves of the commercial power supply, as shown in FIG. 6, and detects that the motor output shaft has rotated once. In the motor of this example, one revolution is 10 when 601-)z
Since the time is seconds, it is sufficient to count the rectangular wave of the commercial power supply eoo times. Even if the power supply frequency fluctuates, if a measurement command signal is sent to the superimposition sensor every 600 counts, weight data can be detected in synchronization with the rotation of the mounting table.

Returning to the explanation of FIG. 3 again, if the rotation of the mounting table and weight measurement are synchronized by the power supply frequency detection means, even if the mounting table rotates every 11 seconds, F.

As shown by the broken line connecting G', H', I', and J', errors due to rotation were completely canceled.

Effects of the Invention As described above, the superimposition checking device of the present invention synchronizes the rotational speed of the mounting table and the speed of superimposition detection by detecting fluctuations in the power frequency. This is extremely effective in practice since it eliminates the accompanying fluctuation error in the detected value, allows highly accurate weight detection even while the mounting table is rotating, and does not affect the accuracy at all even when the power supply frequency fluctuates.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is an external perspective view thereof, Fig. 3 is an output waveform diagram of the detected weight value, Fig. 4 is a characteristic diagram of the power supply frequency and detection error, FIG. 5 is a principle diagram of the power supply frequency detection means, and FIG. 6 is a conventional weight detection value output waveform diagram. 1... Weight sensor, 2... Power frequency detection means, 3... Control unit, 4... Commercial power supply, 6... Loading Placement, 6... Name of agent for synchronous motor Patent attorney Shigetaka Awano and 1 other person (Mz) Fig. 11 (Fig. b) B% “Nmon Kudoriichi) 8 cases i5 (“Bottle - snoring (change)

Claims (1)

[Claims] It is equipped with a mounting table on which the object to be measured is placed, a synchronous motor for rotationally driving the mounting table, a weight sensor for measuring the weight of the object to be measured on the mounting table, and a power frequency detection means for detecting the power frequency. . A weight detection device configured to synchronize the rotational speed of the synchronous motor and the weight measurement speed of the weight sensor using an output signal of the power supply frequency detection means.