JPH0711444B2 - Weight detector - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weight detection device in which an object mounting base rotates, and in particular, it is widely used for automatic cooking in a microwave oven.

2. Description of the Related Art In recent years, as a microwave oven, a model in which a food placing table is rotated to prevent uneven heating has become mainstream. In addition, the number of models that can easily cook by automating cooking control is increasing year by year, and the technology of various sensors is improving accordingly. There are roughly two ways to use the weight detection device in such a microwave oven. One is to measure the weight of food at the start of cooking and set the cooking time, and the other is to detect the decrease in the weight of food during cooking and detect the finish of cooking. In particular, the latter requires a highly accurate weight detection device to detect a weight loss of several grams.

The problem to be solved by the invention However, there are many devised methods for detecting the cooking finish due to the reduction in weight (Actually, Kai 51-83).
050, JP 58-153023, JP 60-50314
No. 60-111404, JP-A No. 62-66025), none of them are applicable to the food table rotating type microwave oven, which is the mainstream in recent years. Because
This is because the weight detection unit detects the weight of food through the mounting table, and thus a large detection error occurs if the mounting table rotates during cooking. FIG. 6 shows an example of detection error caused by rotation of the mounting table (Japanese Patent Publication No. 62-3893). The vertical axis is the weight detection value, and the horizontal axis is the time. The vertical axis has an amplitude of about 10 grams with respect to the measured object of 200 grams. The amplitude of the weight value as seen in this example is a problem that occurs even if any weight detection device is installed as long as it is a microwave oven that rotates the mounting table. It was a drawback that the detection technology could not be used.

The present invention is to solve such conventional problems,
A weight detection device capable of performing stable weight detection even during rotation of the mounting table is realized, and even when a microwave oven is mounted, a minute weight loss of food can be detected.

Means for Solving the Problems A weight detection device of the present invention is a mounting table for mounting an object to be measured,
A synchronous motor for rotating the mounting table, a weight sensor for measuring the weight of the object to be measured on the mounting table, and a power supply frequency detecting means for detecting the power supply frequency are provided, and the synchronous motor is provided by the output signal of the power supply frequency detecting means. It is configured such that the rotation speed of the and the weight measurement speed of the weight sensor are synchronized.

Effect The weight detection device of the present invention detects the rotation speed of the synchronous motor whose rotation speed is determined by the power supply frequency by the power supply frequency detection means, and reads the weight with the weight sensor in synchronization with the rotation speed to rotate the mounting table. It is possible to detect the weight with high accuracy by significantly reducing the error caused by.

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

FIG. 2 is an external perspective view of a weight detecting device mounted on a microwave oven as an embodiment of the present invention. A door 9 that can be freely opened and closed is provided on the front surface of the body 8 so that the heating chamber 10 can be seen when the door 9 is opened. The food is placed on the placing table 5 on the bottom of the heating chamber 10. Further, the user operates the operation panel 11 to instruct cooking.

FIG. 1 is a block diagram thereof. The table 5 is rotated by the synchronous motor 6 during cooking to prevent uneven heating.
The weight of food is detected by the weight sensor 1. The control unit 3 controls the operation of the magnetron 7 and the synchronous motor 6. The frequency of the commercial power source 4 is detected by the power source frequency detecting means 2. The output signals of the power supply frequency detecting means 2 and the weight sensor 1 are input to the control unit 3, and the control unit 3 performs the overall cooking control.

As shown by the solid line in FIG. 3a, the weight detection value draws a reproducible waveform like a position error. Mounting table 5 for one cycle of waveform
It is equal to the rotation cycle of 10 seconds in this case. When the control unit 3 processes the detected weight value as the weight, if all the data are processed uniformly, the amplitude of the waveform becomes an error as it is. In this case, the error is about 8 grams. Therefore, like the points indicated by A, B, C, D, and E in FIG. The data acquisition interval is 10 seconds of the waveform period.
In this way, apparently, the detection error due to the rotation of the mounting table 5 is eliminated, and the broken line connecting the points horizontally indicates the transition of the weight detection value.

The synchronous motor 6 is an AC motor whose rotation speed is proportional to the power supply frequency of the commercial power supply 4. The features are that the rotation unevenness is small and the rotation speed is constant regardless of the magnitude of the load. The rotation speed of the rotor is generally expressed by the following equation.

(Rotor speed) = 120 × f / P f is the power supply frequency P is the number of poles.

Further, the rotation speed of the motor output shaft may be obtained by multiplying the rotation speed of the rotor by the reduction ratio of the gear. Therefore, if it is desired to know the rotational speed of the output shaft of the synchronous motor 6 with high accuracy, the power supply frequency at that time may be detected. The commercial power frequency in Japan is set to 50Hz and 60Hz, but the true value is never stable. Usually, the accuracy is ± 0.1%, ± 0.5% when the power demand increases in the summer, etc., and possibly ± 1% or more fluctuation is expected considering various factors such as substation capacity. That is, the number of revolutions of the synchronous motor 6 also varies accordingly.

The above-mentioned FIG. 3a shows an example of a synchronous motor having an output shaft rotation speed of 6 rpm when the power supply frequency is 60 Hz. this is,
One rotation of the mounting table requires 10 seconds. For convenience of explanation, considering the case where the power supply frequency is (60 × 10/11) Hz, one rotation of the mounting table is 11 seconds. At this time, the weight value fluctuates in a cycle of 11 seconds as shown in FIG. 3b. On the other hand, if we continue to collect weight data unilaterally every 10 seconds, it will not be synchronized with the waveform cycle and will be dispersed for a long time like the broken line connecting F, G, H, I, and J, and the error will be appear. When the measurement is further continued, it can be seen that an error forms one waveform at a period of 110 seconds as shown in FIG. Thus weight detection is always 10
When performed every second, the cycle of this error waveform draws a hyperbola relating to the rotation cycle of the mounting table as shown in FIG. In other words, if the cycle of weight detection and the cycle of rotation of the mounting table are not synchronized, even if the weight does not actually change, a phenomenon occurs in which the weight increases or decreases over many minutes. .

It is the role of the power supply frequency detecting means to synchronize the cycle of weight detection and the rotation cycle of the mounting table. As shown in FIG. 5, the power supply frequency detecting means counts the number of rectangular waves of the commercial power supply and detects that the motor output shaft has rotated once.
In the motor of this embodiment, one revolution is 10 seconds at 60 Hz, so it is sufficient to count the rectangular wave of the commercial power source 600 times. Even if the power supply frequency fluctuates, if the measurement command signal is issued to the weight sensor every 600 counts, the weight data can be detected in synchronization with the rotation of the mounting table.

Returning to the explanation of FIG. 3b again, if the rotation of the mounting table and the weight measurement are synchronized by the power supply frequency detecting means, the mounting table will be
Even if it was rotated in the cycle of 11 seconds, the error due to rotation was completely canceled as indicated by the broken line connecting F, G ', H', I ', and J'.

EFFECTS OF THE INVENTION As described above, the weight detection apparatus of the present invention synchronizes the rotation speed of the mounting table and the speed of the weight detection by detecting the fluctuation of the power supply frequency, and therefore, is accompanied by the rotation of the mounting table. It is highly effective in practical use, because it eliminates the error in fluctuation of the weight detection value, enables highly accurate weight detection during rotation of the mounting table, and has no influence on the accuracy even when the power supply frequency fluctuates.

[Brief description of drawings]

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 same weight detection value, and 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 detecting means, and FIG. 6 is a conventional weight detection value output waveform diagram. 1 ... weight sensor, 2 ... power supply frequency detecting means, 3 ...
… Control unit, 4 …… Commercial power supply, 5 …… Standing table, 6 …… Synchronous motor.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenzo Ochi 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP 54-153666 (JP, A) JP 57- 79600 (JP, A)

Claims (1)

[Claims] 1. A mounting table for mounting an object to be measured, 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 supply for detecting a power supply frequency. A weight detection device comprising frequency detection means, wherein the rotation speed of the synchronous motor and the weight measurement speed of the weight sensor are synchronized by an output signal of the power supply frequency detection means.