JPH03120459A - Detection of defect - Google Patents

Abstract

PURPOSE:To easily detect a defect by applying an oscillation to an object to be measured having the circular or elliptic cross section and exciting at least two places with a space of different angle deviated from a specified angle each other at the positions along the cross section. CONSTITUTION:Two positions with the space of different angle deviated from 90 deg.Xn (=90 deg., 180 deg., 270 deg.) on the object to be measured, e.g. the 1st exciting position P1 and 2nd position P2 distant from the P1 by 22.5 deg., are excited. For this procedure, a stage for measurement is made capable of turning within the horizontal face and the cylindrical object to be measured is placed thereon by making it to align so as the center line position coincides with a turning center position of the stage. Then, the position P1 on the side peripheral face of object is excited at first, and after that, the stage is turned by 22.5 deg. to excite the position 2 on the side peripheral face of the object. Consequently, even if a fundamental natural oscillation is too large or the oscillation due to the defect is too large at one of the excited positions P1, such oscillation states do not occur at another excited position P2. Thus, by superposing both oscilla tion analyses results, existence of defect can be easily discriminated.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for detecting defects such as cracks, dents, and cavities in an object to be measured.

[Conventional technology]

For example, if cylinder parts or piston parts used in the piston mechanism of an automobile engine have defects such as cracks, cavities, or dents, the piston mechanism will fail. Therefore, it is preferable that parts having these cracks, cavities, and dents can be detected on the parts manufacturing line before engine assembly. By the way, conventional methods for detecting this type of defect include a method using reflection of ultrasonic waves, a method using acoustic emission (AE) to detect sound when a crack occurs, an observation method using a CCD camera, an X-ray photography method, and a color check method. method, eddy current method, etc.

[Problem to be solved by the invention]

However, each of the above conventional methods has the following handling problems. In other words, for example, ultrasonic flaw detection is a method of detecting defects by bringing it into contact with a Δ-1 fixed object, but due to the straightness of the ultrasonic waves, only the area where the sensor is applied can be measured, and defects may be caused by misalignment on the sensor connection surface. It is difficult to distinguish between waves because of reflections or because the visible waveforms differ depending on slight angle differences. Further, in the case of the AE method, it is a contact method like the ultrasonic flaw detection method, and 11-1 cannot be determined unless the crack is progressive. On the other hand, if the crack is progressive, the crack will be measured as it expands. Furthermore, the observation method using a CCD camera has the disadvantage that even if there are blemishes or patterns other than defects such as cracks or dents, the judgment is disturbed, and cavities called "su" in cast objects cannot be judged. In addition, X-ray photography is effective because it allows direct visual observation, but
Adjustment of the amount of Xl19I is troublesome and it may not be possible to observe it, and it is not possible to inspect all the objects to be measured, so it is not suitable for inspection on a production line. Furthermore, in the eddy current method, it is necessary to rotate the object to be measured at high speed. Furthermore, in order to increase the sensitivity, it is necessary to bring the sensor closer to the object to be measured and move it in a negative direction; however, if the object to be measured has unevenness, measurement is extremely difficult. Therefore, in view of the above points, the inventor of the present invention has devised a new detection method that can detect defects in a workpiece without contact and is easy to handle. This novel defect detection method is a method in which vibration is applied to an object to be measured and defects are detected from the natural vibration of the object. That is, this new defect detection method is as follows. First, the detection principle of this new defect detection method and apparatus will be considered. This method was created by the inventor as a result of research, as explained below. For example, consider a hollow cylindrical cylinder part made of a cast material as the object to be measured. Now, vibration is applied to this cylinder part by applying a shock, etc., and this vibration is picked up by a vibration detection sensor with a displacement type or a sharp direction. Then, in the case of a hollow cylinder without defects such as cracks, cavities, dents, etc., when the spectrum of its natural vibration is analyzed, as shown in Figure 2A, the first, second, etc.
..., a spectrum having one peak for each order is obtained. The frequency at which the peak appears in this spectrum is determined by the shape and size of the object to be measured. On the other hand, when there is a crack penetrating the cylindrical wall of the object to be measured (hereinafter referred to as a crack), when paying attention to the odd-order spectrum such as the 1st and 3rd order, the peak of the spectrum is divided into two. can be observed. This is the third
As shown in the figure, due to the presence of the crack 1, the vibration waves propagating on the cylindrical side surface of the cylinder 2 cannot pass through the crack 1, and the vibration propagation path is detoured as shown by the dotted line 3 in the figure. This is because the vibration spectrum due to cracks is generated on the lower frequency side than the basic natural spectrum of the cylinder component. In other words, when only cracks exist in the cylinder part, the peak 12 of the vibration spectrum due to the crack is separated below the peak 11 of the first spectrum of the basic natural vibration spectrum, as shown in Figure 2B. appear. The sum of the energies of both spectra is equal to the energy of the primary spectrum in the case of no crack in FIG. 2A. The secondary spectrum remains with one peak. In this case, the size (length) of the crack is proportional to the frequency difference fK between peaks 11 and 12 of the spectrum. Here, the size of a crack refers to the volume of the cracked part, but if the object 7]P1 is a cylinder, the thickness is constant and the width of the crack is so small that it can be ignored, so
This will show the length of the crack. In the case of the cylinder part of this example, a frequency difference tK-5Hz was found to indicate the presence of a crack of length 41II. Note that when the crack is minute, the Q value (=(f+f2)/fo, see FIG. 4) of these odd-order spectra becomes large and the width becomes wide. This is considered to be because the fundamental natural vibration spectrum and the spectrum of vibration due to cracks are observed as a combination without being separated. Therefore, by detecting the magnitude of the Q value of the odd-order, for example, first-order spectrum, it is possible to determine the presence or absence of cracks. Next, if the cylinder part of the object to be measured has a non-penetrating defect such as a blowhole or a dent that does not penetrate the wall of the cylinder,
If there are no other cracks that are penetrating defects, Fig. 2C
As shown in the figure, an odd-order spectrum such as a first-order or third-order spectrum is not divided into two, and blowholes etc. cannot be detected just by focusing on the odd-order spectrum. This is because the vibration that appears as a primary spectrum is a vibration along the circumference, and if it does not penetrate the cylindrical wall, such as in a dent, there is no need for a detour and the vibration does not separate into two peaks. be. However, if we pay attention to even-order, for example, second-order spectra,
When looking at a portion such as a depression in the thickness direction, it is possible to consider a detour route, so it is possible to observe that the spectrum is divided into two. In other words, Fig. 2C shows a case where only non-penetrating defects such as cavities and dents exist, and the secondary spectrum is divided into two peaks: peak 13 of the basic natural vibration spectrum and peak 14 of the vibration spectrum due to the non-penetrating defect. The peaks are separated. In this case as well, the energy of both (
The sum of amplitudes) is equal to that without a non-penetrating defect,
The spectrum of vibrations due to non-penetrating defects appears lower in frequency than the second-order fundamental natural vibration spectrum for the same reason as described above. In this case as well, the frequency difference f 11 between the peaks 13 and 14 of both spectra is proportional to the size of the non-penetrating defect. In addition, when there are through-hole defects and non-through-hole defects at the same time (a crack is often followed by a dent as in C),
As shown in the second diagram, when we look at the primary spectrum and secondary spectrum of the fundamental natural vibration, both spectra have two peaks. For the primary spectrum, peak 1
5 is a spectrum of fundamental natural vibration, and a peak 16 below it is a spectrum of vibration due to a penetrating defect such as a crack. Regarding the secondary spectrum (1), peak 17 is the spectrum of the fundamental natural vibration, and peak 18 below it is the spectrum of vibration due to non-penetrating defects such as dents.However, in this case, the non-penetrating The size of the defect is influenced by the presence of cracks, which are penetrating defects, in the spectrum due to non-penetrating defects, so from the frequency difference f H between the two peak positions in the secondary spectrum,
It is obtained by subtracting the frequency difference fK between the two peak positions for the primary spectrum. When a non-penetrating defect such as a cavity or a dent is minute, the spectrum of the non-penetrating defect is hidden in the second-order fundamental eigenspectrum, as in the case of cracks, but its Q value becomes large. By determining the magnitude of the Q value, micro cavities and dents can be detected. By the way, the novel defect detection method described above requires the object to be measured to be vibrated, but if the object to be measured is vibrated at only one location, the following r! There is rIlfi. In other words, as mentioned above, when the vibration is applied, the sum of the energy of the basic natural vibration and the energy of the vibration of the defective part is:
Although it is constant regardless of the excitation position, since the magnitude of both vibrations differs depending on the excitation position, the ratio of the energy (peak value) of the spectrum of both vibrations differs depending on the excitation position. For example, when the object to be measured is a cylinder, as shown in FIG. 5, the excitation position is set on the circumference 5 along the outer circumference of the cylinder, and the object 11
When the peak value of the primary spectrum of the natural vibration of the FJ constant is plotted as the magnitude from the center 0 point of the circumference 5, the peak value of the spectrum of the basic natural vibration becomes as shown in waveform 6, The spectrum of vibration due to the defect is as shown in waveform 7. The reason why waveform 6 or 7 repeats almost the same waveform every 90 degrees is that when a cylindrical object is vibrated at one point, if there is no defect, the primary vibration will be as shown in Figure 6, as shown by the - dotted chain line. The vibration repeats the state shown by 8 and the state shown by the two-dot chain line 9, and the position B, which is 180 degrees different from the excitation position A, vibrates in exactly the same way, and the position C, which is 90 degrees different from the excitation position A, vibrates in exactly the same way.
, D vibrate in opposite phases. Therefore, even if the vibration is applied at any of the positions A, B, C, and D that are different from each other by 90 degrees, the result shown in FIG. 5 can be obtained. As is clear from FIG. 5, at the excitation position where the peak of the spectrum of fundamental natural vibration is large, the peak of the spectrum of vibration due to defects becomes small, and vice versa. In order to quickly determine the presence of two spectral peaks when a defect exists in the object to be measured, it is sufficient to be able to vibrate at a position where both peaks have the same amplitude. However, since the position of the defect in the object to be measured is originally unknown, it is impossible to determine the position of the vibration excitation relative to the position of the defect. For this reason, in the case of excitation at only one location, the vibration of the defective part may be too large or the fundamental natural vibration may be too large depending on the position of excitation. In such a case, it becomes difficult to distinguish between a spectral change due to a difference in the material of the object to be measured and a spectral change due to the presence of a defect, and there is a problem in that it takes a long time to make the distinction. In view of the above points, it is an object of the present invention to provide a vibration excitation method that facilitates defect detection in the above-described novel defect detection method. A method of applying vibration, picking up the vibration, and detecting defects from the natural vibration of the object to be measured, the method comprising: applying vibration, picking up the vibration, and detecting defects from the natural vibration of the object to be measured;
This is a defect detection method in which at least two locations that differ by an angular interval deviated from (n-1+2+3) are vibrated.

[Effect]

90@Xn (■90@180@270") Since the excitation is performed at 4 different angular intervals, for example 2rf, the basic natural vibration is too large at one excitation position, or the vibration due to defects is too large. However, such a problem does not occur at the other excitation position. Therefore, by overlapping the vibration analysis results of both, it becomes possible to easily determine the presence or absence of a defect.

[Means to solve the problem]

This invention applies to objects with a circular or elliptical cross section.

【Example】

Hereinafter, an embodiment of the defect detection method according to the present invention will be described with reference to the drawings. FIG. 7 shows an embodiment of a defect detection device to which the method of the present invention is applied. This example automatically inspects all cylindrical cylinder parts flowing on a production line, and This is an example of a device that separates defective products from defective products. A cylinder component as the object to be measured 21 is transported on a line by a transport device 23 controlled by a control device 22 including, for example, a microcomputer, and is carried onto a measurement stage 24 and placed thereon. The measurement stage 24 is made of, for example, hard rubber. The object to be measured 21 is placed on this measurement stage 24.
When it is detected, for example, by a sensor provided on the measurement stage 24 that the measurement stage 24 has been placed, the control device 22
The vibration device 25 is driven to vibrate the object 21 to be measured. In this example, the vibration device 25 applies, for example, an impulse shock to the object to be measured 21 with an impact object such as a weight. The weight drive mechanism is configured with a cam mechanism or the like so that the weight immediately separates from the object to be measured after the impact. In this case, the vibration device 25 is configured to impact the cylindrical object 21 at a plurality of locations on its outer peripheral surface simultaneously or sequentially. These multiple impact points are 90°
, 180°, and 270° apart. FIG. 1 is a diagram for explaining the vibrating part of the vibrating device 25, and FIG. 1A is a cross-sectional view of a cylindrical cylinder, and FIG. 1B is a longitudinal cross-sectional view. In this example, the object 71?1 constant object 21 is vibrated at a 2tl position, and as shown in FIG.
, and a second position P2 that is 22.5@ away from the excitation position P1. Therefore, in this example, the measurement stage 24 is rotatable in a horizontal plane, and the cylindrical object 21 is positioned and mounted so that its center line matches the rotational center position of the measurement stage 24. be placed. First, the position P1 of the side peripheral surface of the object to be measured 21 is excited by the vibration device 25, and then the measurement stage 24
is rotated by 22.5 degrees, and the position P2 of the side circumferential surface of the object to be measured 21 is
Excite. In addition, in this example, as shown in FIG. 1B, the vibrating part in the axial direction of the object to be measured 21 is located at a position shifted from the center of gravity position (theoretical center of gravity position determined from the shape) P3, for example, The upper end position of the measurement object 21 is set to P4. In this way, when vibration is applied at a position shifted from the center of gravity, the mass (weight) is different between the upper half and the lower half of the theoretical center of gravity determined by the shape (generally, this is the case with all materials). ), another peak appears in the spectrum of the first-order and second-order natural vibrations in addition to the above-mentioned peaks. The frequency position of this peak is
It depends on the mass of the upper and lower half of , and the heavier one (
For example, the lower half of the spectrum appears at a higher frequency position, and the lighter side (for example, the upper half) appears at a lower frequency position. When the defect is in the upper half, the vibration spectrum due to the defect appears as a pair in the fundamental natural vibration spectrum at the lower frequency position, and when the defect is in the lower half, the fundamental natural vibration spectrum at the higher frequency position appears as a pair. A pair of vibration spectra due to the defect appears in the spectrum. Therefore, it can be determined whether the defect is in the upper half or the lower half of the object to be measured, depending on which fundamental natural vibration spectrum the spectrum of the paired defect appears. If the defect appears on both sides, it can be seen that the defect exists in the center of the object to be measured. As described above, the vibration of the excited i1?1 constant object 21 is detected without contact by the sensor 27 of the output vibration receiving device 26, converted into an electrical signal, and then sent to the signal conditioner 28 as a predetermined signal. Processing is done. The sensor 27 is
Any device that can detect vibrations can be used, and a displacement meter or the like can also be used. However, in order to avoid picking up noise vibrations from the surroundings as much as possible, it is preferable to use one that has sharp directivity in the direction of the object to be measured. In the signal conditioner 28, the electrical signal is amplified, and unnecessary high and low acid components are removed (trend removal). In the case of the cast iron cylinder part in this example, the primary spectrum of the fundamental natural vibration appears at, for example, 1.5kHz, and the secondary spectrum appears at about 2.5kHz.
This is because it appears at approximately 4kHz which is 8 times higher. The electrical signal from the output vibration receiving device 26 is supplied to the arithmetic processing/determination device 30 via the transmission line 29 . The arithmetic processing/judgment device 30 has, for example, a microcomputer, and performs arithmetic processing and judgment operations, which will be described later, using software, and this processing is shown in functional blocks as shown in the figure. That is, the manually input electric signal is supplied to the gate means 31. Then, the natural vibration component of the shape of the object to be measured 21 is extracted from the vibration of the object to be measured 21 after being vibrated or impacted by the window signal WI from the window Wl forming means 32. That is, the vibration in question here is the natural vibration of the shape of the object to be measured. However, when the object to be measured is forced to vibrate, the forced vibration initially generates longitudinal waves similar to seismic waves, which are mixed with natural vibrations. If the defect is a fairly large rack or dent, the above method may be able to detect the defect even if vibrations other than these natural vibrations are present. However, it is usually difficult to detect defects unless vibrations other than these natural vibrations are removed as much as possible. So, in this example, we solve this problem as follows. That is, when exciting the object 21 to be measured, there are the sine wave method and the impulse impact method. In the case of the sine wave method, the object 21 to be measured is vibrated under certain conditions, and at a certain moment, Stop this. Then, vibration measurement is started after a short period of time has elapsed since the stop. In the case of the impulse impact method, measurement is started immediately after a short period of time has elapsed after the vibration is applied, such as by applying an impact. In this case, the time from when the vibration stops or when the impact starts until the measurement starts can be determined as follows. That is, the velocity C of the sound wave traveling through the object to be measured 21 varies depending on the Young's modulus E (modulus of elasticity) and the density of the object, and is determined from the following relationship. For example, in the case of the impulse impact method in this example, if the object 21 is a cylindrical cast iron cylinder, the velocity of the longitudinal wave is 4560 m/s, and the velocity of the transverse wave is 1/1.8, which is approximately 2
780 m/s, and the time-series waveform of vibrations picked up immediately after the impact is shown in Figure 8A. In this waveform, the transverse wave is detected after the early longitudinal wave only portion continues for about 26 μSaC. Then, after the peak value of the vibration of the transverse wave is passed, the vibration decays exponentially and gradually stops. As can be seen from the waveform in Figure 8A, the vibration after excitation is the same as that of an earthquake wave, so as mentioned above, fast longitudinal waves and slow waves are mixed, and the vibration Forced vibration remains, and a natural vibration waveform specific to the shape of the object to be measured 21 is not formed. It is thought that the natural oscillation wave peculiar to this shape is one that is observed 11FJ just before it stops, like the "sawing motion" of a top, for example. Therefore, in this case, vibrations after the point where the transverse wave passes its peak value and begins to attenuate are extracted. For this reason, a rectangular wave window WI as shown in FIG. 8B is set, and the vibration wave is extracted in this example using this window W. In this example, the window WI is activated 20cm5f3e after the impact, and the window width is set to 200m5ec. Therefore, the window Wl forming means 32 forms the window WI based on the vibration start information from the control device 22. As described above, the natural vibration component of the shape of the object to be measured 1 is extracted using the window W1. Then, the natural vibration part is converted into digital data by the A/D conversion means 33 and written into the memory means 34. Then, this digital data is read from the memory means 34, and in the waveform emphasizing means 35, an emphasizing window W2 from the window W2 forming means 36 is applied to this digital data. This window W2 is as follows. In other words, even if the natural vibration waveform part specific to the shape of the object to be measured 21 is extracted using the window wI, minute racks and cavities are likely to be hidden in the spectrum of the basic natural vibration. The only way to detect it is by using the Q value of the spectrum. Therefore, as much as possible, the spectral waveform of the fundamental natural vibration should be
It is conceivable to make the width of the base smaller to make it easier to identify cracks and cavities. In order to do this, the spectrum waveform shown in Figure 4 must be corrected to suddenly attenuate from 50% of the peak (the Q value remains unchanged), as indicated by the dotted line 19 in the figure. good. In this way, the "base" of the spectral waveform becomes narrower, and even if it is a small rack or dent, the minute defect is treated not as the Q value of the spectrum, but as the basic natural vibration spectrum and the spectrum of vibration due to the defect. This increases the number of things that can be separated and detected. In order to emphasize the spectrum as described above, it is sufficient to further add a waveform enhancement window W2 formed by the following equation to the picked up vibration waveform. y-macos' (xωt) +bcos 2 (xωt+r)+ -+kcos' (xωt +n r) +Nico, where τ indicates a time delay, for example, λ/4 (λ is wavelength). Further, in this example, it is set to a-b-...-. This emphasis window w2 has a waveform as shown in FIG. 8C. FIG. 9A shows the spectrum of the entire vibration before applying the above-mentioned natural vibration extraction window w1 and emphasis window w2 to the vibration of the picked up object 21 to be measured. In addition, FIG. 9B shows the natural vibration extraction window w1.
20 m immediately after the impact of the vibration of the object to be measured 21
The vibration spectrum extracted after 5oc is shown, and the separation between the fundamental natural vibration spectrum and the vibration spectrum due to the defect can be observed. Furthermore, FIG. 9C shows the spectrum waveform after applying the above-mentioned emphasis window w2, and it can be seen that the fundamental natural vibration spectrum and the vibration spectrum of defects such as cracks or dents are more clearly separated. . The data thus emphasized is supplied to spectrum analysis means 37 and subjected to spectrum analysis. Similarly to the window W1, the window W2 is also formed based on the vibration start information from the control device 22. FIG. 10A shows the first-order spectrum at the excitation position P1. In the figure, 41 is the spectrum of the basic natural vibration of the upper half of the object to be measured 21, 42 is the spectrum of the defect paired therewith, and 43 is the basic natural spectrum of the lower half of the object to be measured 21. In this case, the peak of the spectrum of the defect is small, and it is difficult to distinguish the presence or absence of the defect from variations in the material of the object to be measured 21, and it takes a long time. but,
In this example, position P2 is 22.5@ farther than position P1.
is being excited. As shown in FIG. 10B, in the first-order spectrum at the excitation position P2, the vibration spectrum 42 due to the defect has a larger amplitude than the basic natural vibration spectrum 43. When the two spectra are superimposed, it becomes as shown in Figure 10C, and the n1 constant 21
It can be clearly seen that there is a crack in the upper half. Similarly, FIG. 11A shows the second-order spectrum at the excitation position P1. Here, 51 is the spectrum of the fundamental natural vibration for the upper half, and 53 is the spectrum of the fundamental natural vibration for the lower half. In this case, defects such as dents are hidden in the spectrum of the fundamental natural vibration. FIG. 11B shows the secondary spectrum at the excitation position P2, which is 22.5' away from the excitation position pi, in which the spectrum 52 of vibration due to the defect appears as a large peak. Therefore, when the spectra at both excitation positions P1 and P2 are superimposed, the result is as shown in FIG. 11C, and the spectrum of vibration due to the defect can be clearly recognized. In this case, it can be clearly determined that a non-penetrating defect such as a dent exists in the upper half of the object 21 to be measured. The determining means 38 uses the superimposed spectra at the two vibration positions as described above to determine the presence of a vibration spectrum due to a defect, for example, in the following manner. That is, in the determination means 38, as shown in FIG.
From the spectrum liquid form, a predetermined frequency range of the primary spectrum and a frequency range of the secondary spectrum dl,
Within d2, for example, up to five peak values are determined in descending order of amplitude, and the frequencies and peak values are stored. Next, regarding the first-order and second-order spectra, the frequency range d is considered to be a pair between the spectrum of the fundamental natural vibration and the spectrum of the vibration of the defect. da (ds, d4<d+, dz) is determined in advance, and a search is made to see if there is a pair of frequency values of the five peak values within this frequency range d, d4. Then, when the pair is detected for the primary spectrum, the higher frequency of the lower frequency pair is recognized as the primary fundamental natural vibration spectrum position,
its frequency position), the frequency width d is narrower,
It is determined whether or not there is a peak other than the basic natural vibration spectrum (of course, a pair of peaks is also acceptable) within a predetermined frequency width d5, and if there is a peak, the object to be measured 21
It is determined that there is a crack. Similarly, for the secondary spectrum, if the pair is detected, the higher frequency of the lower frequency pair is
It is recognized as the next basic natural vibration spectrum position, and based on that frequency position, it is determined whether there is a peak other than the basic natural vibration spectrum within a predetermined frequency width d6 narrower than the frequency width d4. , if there is a peak, the 8-
3. The fixed object 21 is determined to have a cavity or a dent. FIG. 13 shows a flowchart of the operation of the arithmetic processing/judgment device 30 described above. Parts determined to be defective in the manner described above are excluded from the line as defective products by the selection device 40. Furthermore, parts determined to be free of defects are transported to the next process. Hereinafter, the above defect determination is sequentially performed for all parts. By vibrating the object to be measured at a plurality of locations as described above, the presence or absence of defects can be detected reliably and quickly from the primary and secondary spectra. Further, as in the example shown in the figure, by exciting a position shifted from the center of gravity, it becomes easy to determine whether the defect exists in the upper half or the lower half in the axial direction. In the above example, vibration was applied at two locations shifted by 22.5 degrees.
Any position other than 90"180@270' may be used. For example, two points shifted by 45 degrees may be vibrated. Incidentally, FIGS. 14A-C and 1
Figures 5A to 5C show the first-order and second-order spectra when the upper half of the object to be measured is vibrated at two positions shifted by 45@. In the primary spectrum at the first excitation position in FIG. 14A, the fundamental natural vibration spectrum is hidden because the defect spectrum is large. For this reason, they cannot be recognized as a pair and cannot be distinguished from variations in material. However, since the basic natural vibration spectrum appears in the primary spectrum at the second excitation position in Figure B, the fundamental natural vibration spectrum and the vibration due to the defect are obtained by superimposing the spectra at the two vibration positions as shown in Figure C. can be clearly recognized as a pair with the spectrum of Similarly, defects can be clearly recognized in the secondary spectrum of FIG. 15 by superimposing the spectra of the two excitation positions. From this spectrum, it can also be recognized that there is a small depression or cavity in the lower half of the object to be measured 21. In addition, in the apparatus shown in FIG. 7, the primary and secondary spectra are analyzed in the arithmetic processing/determination device, and the determination is made based on the fact that if there is a defect, the spectrum is separated into two. As mentioned above, the first-order spectrum or the second-order spectrum
As a result of the analysis of the next spectrum, even if the spectrum is not separated, the magnitude of its Q value is further measured, and if this Q value is larger than the value without defects such as cracks, it is determined that there is a defect. However, the accuracy can be further improved. Moreover, instead of spectrum analysis, cracks can be detected by time-series converting the vibration waveform data stored in the memory, detecting the envelope, and counting the number of peaks. Although the case where the object to be measured is a cylindrical cylinder has been described above, the object to be measured 21 may have a cross-sectional external shape of a circle or an ellipse. Moreover, the material does not matter. In addition, in the above example, the measurement stage is rotated to sequentially excite the first vibration position P1 and the second vibration position P2, but the measurement stage is not rotated and multiple vibrations are excited. The two vibrating positions P1 and P2 may be vibrated simultaneously using a weight or the like. Further, the number of vibration positions is not limited to two, but may be three or more. Furthermore, it goes without saying that the vibration method is not limited to the impulse impact method, and that various vibration methods can be employed.

【Effect of the invention】

As explained above, the defect detection method according to the present invention is
This method excites the object to be measured and uses a sensor to detect the inherent vibrations of the object itself in a non-contact manner, so there is no diffused reflection due to misalignment when the sensor contacts the sensor, and the waveform is is simple and easy to distinguish. That is,
When measuring the presence or absence of defects occurring inside the object to be measured, there are few factors that disturb the measurement, and stable measurement is possible, and the judgment operation and judgment contents are simple, so the judgment can be made in a short time. I can do it. Furthermore, according to the method of this invention, even if the object to be measured has wrinkles or irregularities, as long as they can be distinguished from natural vibrations, defects such as cavities such as cracks and cavities, and dents can be detected. There is. Furthermore, according to the method of the present invention, vibration is applied to at least 2tI locations, excluding positions that differ by 90' Although it takes a long time to detect defects, the spectra of defects can be clearly identified in a short time.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an example of the vibration excitation method in the defect detection method of the present invention, FIG. 2 is a spectrum diagram for explaining the defect detection method according to the present invention, and FIG. 3 is a diagram for explaining an example of the vibration method in the defect detection method of the present invention. 4 is a diagram for explaining the Q value, and FIG. 5 is a diagram showing the change in the peak value of the spectrum when the excitation position is changed in the circumferential direction. Figure m6 is an explanatory diagram of the primary vibration of a cylindrical object to be measured, Figure 7 is a diagram showing an embodiment of a device to which the defect detection method according to the present invention is applied, and Figures 8 and 9 are illustrations of this example. Figures 10 and 11 for explaining natural vibration extraction and emphasis according to the invention
The figure is a diagram for explaining spectra at two excitation positions, Figure 12 is a diagram for explaining the operation of the device in the example in Figure 7, and Figure 13 is a diagram for explaining the operation in the example in Figure 7. An example flowchart, FIGS. 14 and 15, are diagrams for explaining spectra at other example excitation positions. 11.15. Spectrum of first-order fundamental natural vibration 12.1
6; Spectrum of vibration of crack (penetrating defect) 13.17; Spectrum of second-order fundamental natural vibration 14.1
8. Spectrum of vibration of non-penetrating defects such as blowholes and dents 21; Object to be measured 25; Vibration device Pl; First vibration position P2; Second vibration position

Claims (1)

[Claims] A method for detecting defects from the natural vibrations of the object by applying vibration to an object to be measured having a circular or elliptical cross section and picking up the vibrations, the method comprising: detecting a defect at a position along the cross section; , and 90°×n(n
= 0, 1, 2, 3) A defect detection method in which vibration is applied at at least two locations that differ by an angular interval deviated from 0, 1, 2, 3).