JPH0823417B2 - 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 proposals regarding the detection of the cooking finish due to the reduction in weight (Actually, Kai 51-8).
3050, JP58-153023, JP60-50314
No. 60-111404, Japanese Utility Model Laid-Open No. 62-66025) are not applicable to the food table rotating type microwave oven, which is the mainstream in recent years. Because the weight detection unit detects the weight of food through the mounting table,
This is because a large detection error occurs if the mounting table rotates during cooking. FIG. 7 is an example of detection error generation due to rotation of the mounting table. (Japanese Examined Patent Publication No. 62-3893) The vertical axis is the weight detection value and the horizontal axis is time, and it has an amplitude of about 10 grams above and below a 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 a conventional problem, and realizes a weight detection device capable of performing stable weight detection even during rotation of the mounting table, and can detect a minute weight loss of food when mounted in a microwave oven. It is a thing.

Means for Solving the Problems A weight detection device of the present invention includes a mounting table for mounting an object to be measured, a synchronous motor for rotationally driving the mounting table, and a weight sensor for measuring the weight of the object to be measured on the mounting table. And a power supply cycle detecting means for detecting a power supply cycle, wherein the rotation cycle of the mounting table and the weight measurement cycle of the weight sensor are synchronized by an output signal of the power supply cycle detecting means, and the rotation cycle of the mounting table is an integer of the power supply cycle. If the weight is not doubled, the weight is measured by the control means that synchronizes with each rotation of the mounting table.

Function In the weight detecting device of the present invention, the mounting table is rotationally driven by the synchronous motor whose rotational speed is determined by the power supply frequency. Therefore, in order to detect the rotation cycle of the mounting table, the number of cycles of the power supply cycle may be counted. By detecting this by the power supply cycle detecting means and measuring the weight with the weight sensor in synchronization with the rotation cycle of the mounting table, the weight detection error caused by the rotation of the mounting table can be significantly reduced, and the weight can be detected with high accuracy. Is something that can be done.

Also, if the rotation cycle of the mounting table is not an integral multiple of the power cycle due to the reduction ratio of the synchronous motor, etc.,
Since it is not possible to synchronize each rotation of the mounting table, a plurality of types of weight measurement cycles are combined to synchronize each plural rotations of the mounting table for time correction.

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

FIG. 2 is an external perspective view of the weight detection device of the embodiment mounted on a microwave oven. 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 cycle of the commercial power source 4 is detected by the power cycle detecting means 2. The output signals of the power supply cycle detection means 2 and the weight sensor 1 are input to the control unit 3, and the control unit 3 performs overall cooking control.

 Further, FIG. 8 shows an example of the power supply cycle detecting means 2.

First, the commercial power supply AC 100V is stepped down by a transformer, and further converted into half-wave DC. This is processed into a 5V rectangular wave and input to the input port of the microcomputer. The microcomputer judges the rise from 0V to 5V and counts one cycle. By repeating this count, the power supply cycle is detected.

As shown by the solid line in FIG. 3A, the weight detection value draws a reproducible waveform due to the position error. One cycle of the waveform is equal to the rotation cycle of the mounting table 5, and here an example of one cycle of 10 seconds is given. 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, A, B, C, on Fig. 3 (a)
Like each point represented by D and E, it was made to validate only one data in one cycle. 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 number of revolutions of the synchronous motor 6 depends on the commercial power source 4
It is an AC motor that is proportional to the power supply frequency. 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. 3 (a) 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 means that 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. 3 (b). On the other hand, if the weight data is unilaterally collected every 10 seconds, the waveform is not synchronized with the period of the waveform and is dispersed over a long time like a broken line connecting F, G, H, and I, and an error appears. 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, if the weight detection is always performed every 10 seconds, the cycle of the waveform of this error 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. .

The role of the power supply cycle detecting means is to synchronize the cycle of weight detection with the rotation cycle of the mounting table. The power supply cycle detection means counts the number of rectangular waves of the commercial power supply as shown in FIG. 5 to detect 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. FIG. 9A shows a flowchart in which the microcomputer used as a part of the control unit and the power supply cycle detection means detects the weight every 600 counts. 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. 3 (b) again, if the rotation of the mounting table and the weight measurement are synchronized by the power supply cycle detecting means, even if the mounting table rotates in the cycle of 11 seconds, F, G ', H'. The error due to rotation is completely cancelled, as indicated by the broken line connecting I and I '.

Here, the example of counting the rectangular wave of the commercial power supply 600 times was given as the first example. Naturally exists. As an example, let us consider the case where a commercial power supply rectangular wave is required 563.75 times for one rotation of the mounting table. At this time, the number of times after the decimal point cannot be easily counted. Therefore, if counting the square wave 564 times was regarded as one rotation of the mounting table, the synchronization deviation was added and the weight detection error occurred.

Therefore, in order to solve this problem, the method shown in the time chart of FIG. 6 and the flowchart of FIG. 9 (b) was adopted. The first rotation of the mounting table considers the square wave 563 count as one rotation. From the second rotation to the fourth rotation, each square wave 564 count is regarded as one rotation. By repeating these two steps, the weight detection error during one rotation is small, and the weight detection without the weight detection error due to the addition of the synchronization deviation can be performed.

EFFECTS OF THE INVENTION As described above, the weight detection device of the present invention detects the fluctuation of the power supply frequency to synchronize the rotation cycle of the mounting table with the cycle of the weight detection. It eliminates the fluctuation error of the weight detection value, can detect the weight with high accuracy during the rotation of the mounting table, and does not affect the accuracy at all even when the power supply frequency fluctuates. Even with this mounting table, the same effect can be obtained by combining a plurality of weight detection cycles.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a perspective view of the same, FIG. 3 is an output waveform diagram of the same weight detection value, and FIG.
FIG. 5 is a characteristic diagram of the power source frequency and detection error, FIG. 5 is a principle diagram of the power source frequency detecting means, FIG. 6 is a time chart of the same operation, FIG. 7 is a conventional weight detection value output waveform diagram, and FIG. FIG. 9 is a block diagram of a power supply cycle detecting means in an embodiment of the present invention, and FIG. 9 is a flowchart thereof. 1 ... weight sensor, 2 ... power supply cycle detecting means, 6 ...
Synchronous motor.

Claims (1)

[Claims] 1. A mounting table on which an object to be measured is mounted, 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 cycle are detected. A power supply cycle detecting means, wherein the power supply cycle detecting means counts the number of cycles of the power supply cycle to a predetermined integer number of times to interlock with the rotation of the synchronous motor, and the rotation cycle of the mounting table and the weight of the weight sensor. The configuration is such that the measurement cycle is synchronized, and when the rotation cycle of the mounting table is not an integral multiple of the power supply cycle, the weight is measured by the control means that synchronizes with each rotation of the mounting table. Detection device.