JPS5839921A - Method for testing internal pressure of sealed containers - Google Patents

Abstract

PURPOSE:To decide whether a quality of various cans is good or not, by detecting the maximum peak level in a detecting signal in case of stamping a can, multiplying it by a ratio set in advance, and setting it as a reference level. CONSTITUTION:A detecting signal for can cover vibration in case of stamping a can is detected by a vibration detector TS, and this detected signal is inputted to plural specific frequency band-pass filters F1-Fn. Subsequently, the maximum peak level in an output signal of said filter is detected by level amplifiers A1- An, and a ratio multiplier (r) set in advance by a reference level setting device PS is multiplied by the maximum peak level, which is set as a reference level. Subsequently, when the lowest frequency is selected out of a peak signal exceeding the reference level, fundamental frequency can be detected exactly as to not only a can whose cover surface is flat but also a special can, and whether a quality of a can is good or not is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects vibrations of the lid of a sealed container having a metal lid, such as a can, by applying a magnetic impact force to the lid of the can. The vibration of the lid is input as an electrical signal to a band-pass filter arrayed in large numbers, and from among the frequency components distributed in the electrical signal, a spectrum analysis is performed to extract the fundamental frequency component. The present invention relates to a method for inspecting the internal pressure of a sealed container that reliably determines whether it is defective.

In general, various automatic inspection methods have been implemented in place of the manual inspection method for the internal pressure of canned goods, but with these methods,
The types and sizes of cans that can be detected are limited. For example, it is relatively easy to detect with a line checker that inspects individual canned goods, but once the canned goods are stored in a case,
The vibration detection waveform of the can lid changes and cannot be easily detected.

Also, cans that are relatively large in size, especially cans that are sealed with a lid material that has an expansion ring with concentric irregularities on the can lid surface, are more expensive than cans that have a flat lid surface. , the characteristic damped vibration waveform during can sealing is often complex.

Therefore, when detecting the fundamental frequency that is approximately proportional to the internal pressure from the vibration waveform of the can lid as described above, there are two methods: to obtain the fundamental frequency from the pitch of the waveform by converting the vibration waveform into a simple waveform, or to use a complex filter. There is a way to measure a single fundamental frequency. However, these methods
Detection of the fundamental frequency is uncertain and detection errors are likely to occur.

Next, regarding the above-mentioned examples of difficult-to-detect cans, FIGS. 1 to 8 show waveform diagrams obtained by spectrum analysis and measurement of vibration waveforms at the time of striking.

In each of these figures, the horizontal axis represents the frequency and the vertical axis represents the signal level. Figure 1 is an example of a normal internal pressure canister, (a) is when the can is at rest, (b) ) is when the can is stored in a case and is moving, Figure 2 is an example of a can with low negative pressure without deformation, (a) is when the can is in a stationary state, and (b) is when the can is in a stationary state. When a can is stored in a case and is being moved, Figure 8 shows an example of a defective can in which the can is deformed by an external impact and at the same time a low negative pressure is created, and (a) is an example in which the can is in a stationary state. In some cases, (b) shows a case where the can is stored in a case and is being moved.

As shown in each of the above figures (a), when the can is in a stationary state, the maximum peak level becomes the fundamental frequency and has a correlation with the negative pressure inside the can, so it is impossible to judge whether it is good or bad using conventional methods. It's relatively easy.

However, as shown in each figure (b), the waveform detected when the can is sealed while it is stored in a case and during transportation is different from the waveform in each figure (a) even if the can is the same. Compared to , many peaks appear even in the high frequency range. Among the above-mentioned peaks, there are those at a level higher than the peak level of the low-range fundamental frequency, and FIGS. 2(b) and 3(b) show typical examples thereof. There is.

Therefore, as in the conventional method, the vibration frequency is measured from the waveform signal obtained by inputting the signal of the vibration of the can lid at the time of striking into a single or two filters, and the vibration frequency is within the set frequency range. In the method of making a pass/fail judgment by checking whether or not the vibration frequency exists, the vibration frequency is detected as a value obtained by averaging a large number of peak frequencies. However, it may not be possible to detect the can as a defective can.

Also, as another method of detecting the fundamental frequency 11.

There is a method of detecting the fundamental frequency f+ by comparing the maximum peak level or the second peak level and selecting the frequency of the lowest force, but in the case of a special waveform as mentioned above, an additional It becomes necessary to compare and select the peak levels including up to the third peak level. As the cross-sectional shape of the can lid changes from a flat shape to a complicated shape, many high-order harmonic peak signals are generated.
Moreover, it may exhibit a peak level higher than the fundamental frequency level. Therefore, as the cross-sectional shapes of can lids become more diverse, the number of peak levels to be compared is determined by -
Since it is difficult to generalize, one possible solution to this problem is to set a specific level adapted to the vibration waveform unique to the can as described above, and to compare all peaks that exceed this specific level. It will be done.

However, even for cans of the same type, the seal detection signal level for can lids is not constant; in particular, the seal detection signal level for cans stored in a case varies considerably depending on the shape of the case and the position of the can. When detecting by setting a certain specific level as described above, for example, if the overall signal level is small, the fundamental frequency may be missed, and conversely, if the signal level is too large, the peak level may be lost due to unnecessary noise components. This may lead to errors in frequency selection and is not necessarily a good idea.

This invention was made with the above points in mind,
The maximum peak level of the can lid tracking motion detection signal at the time of striking is detected, a specific ratio multiplier adapted to the vibration waveform unique to the can is set in advance, and the detected maximum peak level is multiplied by the multiplier to determine the threshold value. By determining the level and using it as a reference level, and selecting the lowest frequency from among the peak signals that exceed the reference level, we can measure not only cans with flat can lids but also special cans with can lids with expansion rings. Inspection performance can be improved by reliably detecting the fundamental frequency of cans, determining whether or not the fundamental frequency is within a preset range of good can frequencies, and determining the quality of cans. Improvement 7: Certain O Next, FIG. 4, which shows one embodiment of the present invention, will be described.

In the same figure, a vibration detector T8 detects the inherent damped vibration that occurs when the lid surface of a can C is vibrated by an electromagnetic shock when it reaches a predetermined position by a position detector K (not shown). Outputs an electrical signal and sends the output signal to a preamplifier PA
K, and inputs the signal to a plurality of specific frequency band-pass filters F1 to Fn arranged in large numbers within a frequency band effective for detection and selection, in which adjacent frequencies are at least connected to each other, and the signal is input to a vibration detector T8. After subdividing the can lid vibration detection signal from the sub-band F wave, the maximum peak level detector MR detects the signal with the maximum peak level PIj'rI from each output signal from the level amplifier A+-An, and The ratio multiplier γ set by the level setter PS, for example 0.75, is converted to the maximum peak level PLm by the multiplier J.
K multiplication, the multiplied calculation value γ・PLm is set as a reference level, and one or more peak level signals exceeding the reference level γ・PLm are selected from among the output signals from each level amplifier A1 to An. , is detected by a peak level detector PR, and among the peak level signals, the peak frequency of the peak signal obtained from the lowest frequency band P wave detector is selected as the fundamental frequency f1 by the fundamental frequency selector FR.

Next, depending on the type of canned food to be detected, the reference frequency range fsxfs', which has been experimentally determined in advance, is set using the frequency setter F8.
1 frequency comparator FC, the fundamental frequency f
+ is within the reference frequency range fs-fs', and the fundamental frequency f1 is within the reference frequency range fs-,=
If it is outside fs', the defective determination device NGK determines that it is defective due to insufficient internal pressure or an abnormality due to deformation, expansion, etc.
Outputs defective signal S.

In addition, the present invention provides a method for detecting an expansion can with a positive pressure in which the frequency of the fundamental frequency signal is within a normal range among expansion cans. It is also effective as a detecting power method for the fundamental frequency signal when determining whether the signal is defective by comparing the level of the fundamental frequency with the level of the fundamental frequency.

As described above, according to the internal pressure inspection method for sealed containers of the present invention, it is possible to judge whether various types of cans are good or bad, and it is also possible to reliably judge the good or bad of cans that are stored in a case and are being moved. It is possible to make judgments and improve inspection performance.

[Brief explanation of the drawing]

Figures 1 to 8 are waveform diagrams obtained by spectrum analysis of the vibration detection signal of the lid part during canning. Figure 1 is an example of a normal can, and Figure 2 is an example of an undeformed low negative pressure can. Figure 3 shows an example of a modified low-negative pressure can, where (a) shows the can in a stationary state, (b) shows the can in a case when it is moving, and Figure 4 shows a case in which the can is in a moving state. 1 is a block diagram of an embodiment of a method for inspecting internal pressure of a sealed container according to the present invention; FIG. C... Canister to be inspected, T8... Vibration detector, PA...
・Preamplifier, F+A-Fn・-bandpass filter, A
+-An... Level amplifier %P8... Reference level setter, MR... Maximum peak level detector, J... Multiplier, PR... Peak level detector, FR... Fundamental frequency Selector, FS...Frequency setter, 10゛C...
Frequency comparator, NG...failure judge. Agent Patent Attorney Sotabe Fujita Figure 1 1 1 l 1 1' + l + l
+ lFigure 2 111111111.1.1 Figure 3 Figure 4 6-

Claims (1)

[Claims] A vibration detector detects the vibration of the end face of the metal sealed container by applying an impact force to the end face, and the output electric signal from the detector is transmitted to a plurality of concatenated electrical signals whose adjacent frequencies in each band are at least small. A specific frequency is input to a band-pass filter, the maximum peak level of the output signal of each band-pass filter is detected, the maximum peak level is multiplied by a preset ratio to obtain a reference level, and each of the above-mentioned signals exceeding the reference level is determined by multiplying the maximum peak level by a preset ratio. Among the output signals of the band-pass filter, the lowest frequency peak frequency is detected to obtain the fundamental frequency, and it is determined whether the fundamental frequency is within a preset frequency range, and if it is outside the frequency range. A method for inspecting the internal pressure of a sealed container, characterized in that the sealed container is determined to be defective and a defect signal is output.