JP2008185345A - Vibration measuring method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a property of a measuring object nondestructively by three-point supporting. <P>SOLUTION: This vibration measuring method includes the first process for applying a sound wave vibration to the measuring object by an excitation signal generation device, the second process for monitoring the sound wave vibration applied by the excitation signal generation device, the third process for receiving vibration of the measuring object by a vibration sensor, and the fourth process for acquiring the signal received by the monitor and the vibration sensor and analyzing a characteristic of the measuring object. This device has characteristics wherein the excitation signal generation device and the vibration sensor are installed on the same circumference so that an angle becomes perpendicular which is formed by a straight line passing the center point O of the measuring object and a contact point A between the excitation signal generation device and the measuring object and a straight line passing the center point O and a contact point B between the vibration sensor and the measuring object, and a support point C is installed on the same circumference so that each angle formed by the straight line AO and a straight line CO and by the straight line BO and the straight line CO becomes equal, and the measuring object can be measured by the three-point supporting. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and apparatus for nondestructively measuring vibration and hardness of an object using sound wave vibration.

Conventionally, a laser Doppler device or the like has been used to measure the vibration characteristics of an object. It is a large device using an exciter and a laser vibrometer. Although a small and portable vibration measuring device has been developed, there is no object that has a function of monitoring the excitation vibration, and it has been impossible to measure the detailed vibration characteristics of the object to be measured. In addition, there is a technique for measuring a measurement object by supporting three points, but the three points are not arranged at positions where detailed vibration characteristics of the measurement object can be measured. In the apparatus of the present invention, since it is supported at three points arranged at a specific angle on the same circumference, the hardness of the measurement object is measured only by the resonance frequency regardless of the mass or size of the measurement object. can do.
Depending on the object to be measured, there is an object in which it is difficult to specify the resonance frequency even if fast Fourier analysis is performed, but in the apparatus of the present invention, phase data can be acquired from the signal of the vibration monitor and the signal of the vibration sensor, Since the vibration mode can be measured from the phase data, the resonance frequency can be accurately specified.
JP-A-9-274022 JP-A-10-318991 JP 10-318992 A JP2002-296254 JP 2005-134114 A

According to the apparatus of Patent Document 1 (Japanese Patent Laid-Open No. 9-274022), a microphone is applied to a melon, and vibration is imparted to the face of the melon by striking. In striking, measurement errors are likely to occur due to differences in striking points and striking strength. Moreover, the apparatus of patent document 1 must measure the diameter of a melon with an ultrasonic wave, correct | amend a diameter, and must judge the maturity of a melon.
According to the devices of Patent Document 2 (Japanese Patent Laid-Open No. 10-3189921) and Patent Document 3 (Japanese Patent Laid-Open No. 10-3189922), a measurement object is placed on a weighing scale, a sound collecting microphone is installed thereon, and Vibration analysis is performed by hitting the side with a hammer. After placing the measurement object on the weighing scale, it is necessary to bring the sound collecting microphone into contact with the measurement object. Since the hammer is struck with a hammer, the hammer strength and signal are not monitored. The result of frequency analysis differs depending on Moreover, the correction | amendment of the magnitude | size by mass is also required.
According to the apparatus of Patent Document 4 (Japanese Patent Laid-Open No. 2002-296254), melon is measured with an excitation signal generator and an acceleration sensor, a transfer function is obtained from the excitation vibration energy and the detected vibration energy, and the fruit diameter and hardness are measured. is doing. For measuring hardness, the resonance frequency by vibration analysis is higher than the transfer function. According to Patent Document 4, the correlation between the transfer function, the fruit diameter, and the hardness is about 0.8, and the correlation between the hardness and the resonance frequency is 0.9 or more, but the accuracy is inferior.
According to the apparatus of Patent Document 5 (Japanese Patent Laid-Open No. 2005-134114), a method for supporting a measurement object with three-point support is specified, but the three-point support structure is located at the apex of an equilateral triangle in plan view. It is provided in the part. If the angle between the excitation point and the center point of the measurement object and the reception point is not a right angle or 180 degrees, the vibration of the second resonance frequency representing the hardness of the measurement object cannot be detected. Since it is 120 degrees in the apparatus 5, detailed vibration characteristics cannot be measured.

  Therefore, the present invention vibrates the measurement object with the vibration signal generator, and subtracts the vibration signal of the measurement object received by the vibration sensor and the vibration signal of the monitor installed in the vibration signal generator. By acquiring the signal of only the object and supporting it at three points arranged at a specific angle, vibration analysis and hardness comparison of the measurement object can be easily performed without the need for correction of the diameter and mass of the measurement object. It is a thing made for the purpose of proposing the technology which can do.

In the first aspect of the vibration measuring method according to the present invention, the first step of applying the sonic vibration to the measurement object by the vibration signal generator and the sonic vibration applied by the vibration signal generator are monitored. A second step, a third step of receiving vibrations of the measurement object by a vibration sensor, and a fourth step of acquiring signals received by the monitor and the vibration sensor and analyzing characteristics of the measurement object It is characterized by including.
In the second invention, the vibration signal generation device and the vibration sensor include a center point O of the measurement object, a straight line passing through a contact point A of the vibration signal generation device and the measurement object, the center point O, and the It is installed on the same circumference so that the angle formed by the straight line passing through the contact point B of the vibration sensor and the measurement object is a right angle, and the support point C is placed on the same circumference with the straight line AO and the straight line BO. It is characterized in that it is installed so that the angle formed by CO is equiangular, and the measurement object can be measured by supporting three points.
The third aspect of the invention is characterized in that the excitation signal generator vibrates in accordance with an input voltage and can simultaneously monitor the excitation vibration.
In the fourth invention, the measurement object is obtained by subtracting the data obtained by fast Fourier analysis of the signal of the vibration sensor that has received the vibration of the measurement object vibrated by the vibration signal generator and the data obtained by performing the fast Fourier analysis of the monitor signal. It is configured to obtain a vibration spectrum distribution of an object, and is characterized in that it is configured to obtain phase data by comparing a signal of a vibration sensor and a signal of a monitor.
The fifth invention is characterized in that the hardness of the measurement object can be compared only by the value of the resonance frequency of the measurement object by fixing three support points.

According to the method and apparatus for measuring the vibration of fruits and vegetables by the three-point support structure according to the present invention, a signal of a vibration sensor that applies a sound wave vibration to a measurement object, monitors the vibration of vibration, and receives a vibration of the measurement object. By acquiring, the characteristics of the measurement object can be analyzed. Moreover, it is possible to compare the hardness of the cross-sections cut at the three support points of the measurement object only by the resonance frequency, regardless of the size and mass, by simply fixing the measurement object with the three-point support.

Hereinafter, a detailed description will be given with reference to the drawings showing the best mode of a vibration measuring apparatus used in a vibration measuring method according to the present invention.
FIG. 1 shows a configuration diagram of a vibration measuring apparatus according to the present invention. In this figure, 1 to 20 kHz of 1 to 20 kHz is obtained from 6 excitation signal generators that place 1 measurement object on the 3 points of support of 2 excitation signal generators, 4 vibration sensors, and 5 support rods. Outputs sound wave signals using audible frequency bands such as sweep sine wave, white noise, pink noise. 7 generates a sound wave vibration from the vibration signal generator 2 via the DA converter circuit 7. The vibration signal generator 2 incorporates three monitors for acquiring the vibration signal. The vibration signal generator 2 acquires the vibration applied to the measurement object 1 and inputs the vibration to the AD converter circuit 8. The vibration of the measuring object 1 vibrated by the sound wave vibration is acquired by four vibration sensors and input to the AD conversion circuit 10. The signal acquired by the monitor 3 and the vibration sensor 4 is subjected to fast Fourier transform and frequency response calculation by the arithmetic unit 9 to display the vibration spectrum and phase data.

The excitation signal generator 2 uses a self-excitation type piezoelectric element, and the vibration sensor uses a separate excitation type piezoelectric element. The vibration monitor and vibration sensor use vibration energy as an electrical signal. Anything can be used as long as it can convert the electric signal into vibration energy.

The self-excited piezoelectric element is divided into a part that converts an electric signal into vibration energy and a part that converts vibration energy generated by the electric signal into an electric signal. It has a function to do.

For excitation, a speaker or a vibrator transducer that can convert an electrical signal into vibration energy may be used. An acceleration pickup or the like that can convert vibration energy into electric energy may be used for the vibration monitor and vibration sensor.

  The excitation signal generator 2, the vibration sensor 4 and the support point 5 are installed as shown in FIG. The same circle in which the angle AOB formed by connecting the contact point A between the vibration signal generator 2 and the measurement object 1, the center O of the measurement object 1, and the contact point B between the vibration sensor 4 and the measurement object 1 is a right angle. The vibration signal generator 2 and the vibration sensor 4 are installed on the circumference. Furthermore, the same circumference where the vibration signal generator 2 and the vibration sensor 4 are installed so that the contact point C between the support bar 5 and the measurement object 1 is at a position where the angle AOC and the angle BOC are the same angle. The support bar 5 is installed on the top.

  If the angle AOB is an angle other than 45 degrees and 135 degrees, the second resonance frequency can be measured. However, since the vibration level of the measurement object is stronger at the right angle, the second resonance frequency can be measured with high accuracy.

  Conventionally, for vibration measurement, vibration has been received by a vibration sensor disposed 180 degrees opposite to the excitation point of the object to be measured. However, the contact point A, the center point O, and the contact point C shown in FIG. Measurement is possible even when the angle formed by the angle AOB is a right angle.

  The arithmetic unit 9 has a function of taking the received signal through the AD conversion circuit 8 and analyzing the frequency spectrum distribution of the vibration of the measurement object. In analyzing the frequency spectrum distribution, for example, a technique such as fast Fourier transform processing can be used. Further, it has a function of calculating the frequency response of the signals of the vibration monitor 3 and the vibration sensor 4 and calculating the phase angle. Thereby, the vibration mode of the measurement object can be specified.

Next, a measurement flowchart of the vibration measuring apparatus is shown in FIG. In step S1, at the start of measurement, it is checked whether or not the state of the vibration signal generator, vibration sensor, etc. is normal, and each part and each variable are initialized.
Next, in step S2, the state of the measurement start switch is checked. If pressed, the process proceeds to step S3, where an excitation signal is output in the frequency band, and the excitation signal generator is vibrated.
In step S4, the input of vibration signals from the vibration monitor and vibration sensor installed in the vibration signal generator is monitored, and the detection of vibration signals from the vibration monitor and vibration sensor is awaited. If a vibration signal is input, it will progress to step S5.
In step 5, fast Fourier transform and phase angle calculation are performed while converting the input vibration signal into a digital signal to obtain the frequency characteristic of the measurement object.
In step S6, the second resonance frequency, the third resonance frequency, and the fourth resonance frequency are calculated from the frequency characteristic and phase angle data.
In step S7, an internal defect is determined from the ratio of the second resonance frequency, the third resonance frequency, and the fourth resonance frequency, and the value of the second resonance frequency is used for the hardness.
In step S8, the determination result of step S7 is displayed on the display.

  In Example 1, a rubber ball, which is an elastic body, was measured as a measurement object using the vibration measuring device at a position perpendicular to the 180 degrees. As a result, data measured at 180 degrees are shown in FIG. 4, and data measured at 90 degrees are shown in FIG. In both FIG. 4 and FIG. 5, the second resonance peak including the hardness information of the measurement object was obtained. Peaks appear at the 90 ° and −90 ° positions of the phase, but when the excitation and reception angles are measured at right angles, the frequency interval of the phase change is doubled when it is 180 degrees due to the vibration mode. As a result, although odd-numbered peaks are less likely to appear, there is no problem because the second resonance frequency value is used for the hardness of the measurement object.

  In Example 1, although the diameter on the circumference where the excitation signal generator, the vibration sensor, and the support rod are installed is 2 cm, it is not limited to this. The diameter on the circumference is set in advance so that all measurement objects can support three points.

  In Example 2, the vibration analysis was performed by measuring the vibration of only the measurement object that was vibrated by vibrating the measurement object without monitoring the excitation signal. A vibration ball was vibrated as an object to be measured by the vibration generator, and the vibration characteristics were examined by performing fast Fourier transform only on the signal detected by the vibration sensor without monitoring the vibration. The results are shown in FIG. Although the second resonance peak can be confirmed, the phase data of the measurement object cannot be calculated because the vibration vibration is not monitored. Therefore, detailed vibration characteristics of the measurement object cannot be measured, and it cannot be determined whether the second peak is the second resonance peak.

In Example 3, a rubber ball, which is an elastic body as a measurement object, was measured using the vibration measuring device. The difference in the second resonance frequency was measured when the rubber ball was warmed and softened and when the rubber ball was cooled and hardened. As shown in FIG. 7, the second resonance frequency of the rubber ball warmed and softened is lower than the second resonance frequency of the rubber ball cooled and hardened. That is, the hardness of the measurement object can be compared only by measuring the second resonance frequency.
Since these second resonance frequencies are highly correlated with the hardness as shown in FIG. 8, the hardness of the fruits and vegetables can be inspected nondestructively by using the vibration device.

In Example 4, as a measurement object, a watermelon having a normal inside and a watermelon having an abnormality inside were measured by the vibration measuring device. The vibration spectrum obtained by the measurement is shown in FIG. In the normal watermelon vibration spectrum, a plurality of sharp peaks appear, and the second resonance frequency and the third resonance frequency can be clearly confirmed. On the other hand, in a watermelon having an abnormality inside, a peak after the third resonance frequency cannot be clearly confirmed. Moreover, it can be confirmed that the abnormal watermelon has a lower second resonance frequency than that of the normal watermelon, and the flesh is soft. Furthermore, the frequency ratio between the second resonance peak and the third resonance peak is also smaller than that of a normal watermelon, and an internal abnormality can be determined by looking at this ratio.

In addition, as a database of correlations for evaluating quality, an evaluation standard according to the type and variety of the fruits and vegetables to be measured is obtained in advance through experiments, etc., and registered in the computer of the analyzer, etc. The evaluation may be performed with reference to the evaluation criteria.
The evaluation can also be performed by using the signal intensity of the second resonance frequency and the signal intensity and frequency ratio of the fourth resonance frequency.

The present invention can be used not only for fruits and vegetables but also for a technique for inspecting the hardness and the internal state of an object such as a sphere or a cone without contact.

It is a block diagram of embodiment of the apparatus used for the measuring method concerning this invention. It is a figure which shows the three-point support structure used for the said method. It is a flowchart figure which shows the flow of a measurement. 4 is a graph showing measurement results of vibration of a measurement object at 180 degrees measurement in Example 1. 6 is a graph showing the vibration measurement result of the measurement object at the time of right angle measurement in Example 1. It is a graph which shows the vibration analysis result only of the vibration sensor in Example 2. FIG. It is the figure which showed the difference in the vibration spectrum by the difference in the hardness of the measuring object in Example 3. FIG. It is a graph which shows the correlation between a resonant frequency and the hardness of a fruit. It is the graph which compared the vibration spectrum of the normal watermelon in Example 4, and the watermelon with abnormality.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement object 2 Excitation signal generator 3 Excitation monitor 4 Vibration sensor 5 Support bar 6 Excitation signal generator 8 AD conversion circuit 9 Arithmetic unit

Claims (5)

A first step of applying a sonic vibration to the measurement object by the vibration signal generator, a second step of monitoring the sonic vibration applied by the vibration signal generator, and a vibration sensor for the vibration of the measurement object A vibration measurement method comprising: a third step of receiving in step 4; and a fourth step of acquiring signals received by the monitor and the vibration sensor and analyzing characteristics of the measurement object. The vibration signal generator and the vibration sensor include a center point O of the measurement object, a straight line passing through a contact point A of the vibration signal generator and the measurement object, the center point O, the vibration sensor, and the measurement object. Are installed on the same circumference so that the angle formed by the straight line passing through the contact point B is at a right angle, and the angles formed by the straight line AO and the straight line BO and the straight line CO are all equiangular on the same circumference. Thus, the vibration measuring apparatus is characterized in that the supporting point C is installed and the measurement object can be measured by supporting three points. The vibration measuring apparatus according to claim 2, wherein the vibration signal generator vibrates according to an input voltage and can simultaneously monitor the vibration vibration. The analysis means subtracts the data obtained by fast Fourier analysis of the signal of the vibration sensor that has received the vibration of the measurement object vibrated by the vibration signal generator and the data obtained by fast Fourier analysis of the signal of the monitor. The vibration measurement device according to claim 2, wherein the vibration measurement device is configured to obtain phase data by comparing a vibration sensor signal and a monitor signal. 5. The vibration measuring device according to claim 2, wherein the three-point support is capable of comparing the hardness of the measurement object only by the value of the resonance frequency of the measurement object by fixing the three support points.

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