JP4407817B2 - Inspection object discrimination method and apparatus - Google Patents

Description

  The present invention relates to a method and apparatus for discriminating an inspection object suitable for inspection of surface defects of a forged product such as a connecting rod (connecting rod) used in an engine, a member made of a cast product or a sintered body, and the like. is there.

  Conventionally, as a surface defect inspection method for this type of member or the like, the surface of an inspection object is imaged with a CCD camera or the like, image processing is performed on the obtained image signal, and the processing result image is displayed and observed. There was a method (for example, refer patent document 1).

JP-A-3-209113

In the above-described prior art, since fine powder is sprayed on the surface of the inspection object before imaging, there is an advantage that surface defects such as cracks are easily discriminated compared to a method of simply imaging the surface of the inspection object, but visually Since it was a reliable inspection, the detection power was low and there was a risk of overlooking surface defects.
Therefore, the vibration (sound) generated by hitting the inspection object is subjected to frequency analysis to acquire a fundamental wave unique to the inspection object or a waveform adjacent thereto, and a waveform including the peak value is acquired in advance. A method has been proposed in which the presence or absence of a surface defect on an inspection object is determined based on the frequency difference from the reference waveform.
According to this, the detection power can be improved in that the inspection is not based on visual inspection, but the above-mentioned frequency difference is small, and it becomes difficult to set a threshold value (frequency) used for determining the presence or absence of surface defects such as cracks. It was. For this reason, there are cases where the discrimination accuracy cannot be increased, and there has been a demand for improvement in this regard. Further, in this method, internal defects (internal structure defects such as internal oxidation) of the inspection object cannot be determined, and if it is desired to detect internal defects, it must be performed separately by a different method. There was also a demand for improvements in this regard.

An object of the present invention has been made in view of the circumstances described above, the power to detect surface defects compared to test relying on visual is high and Ki internal defects out be detected by a common component, Furthermore, when a change in temperature occurs in the test object with the temporary stop of the line in the mass production process of the test object is also to provide a test object discrimination method and apparatus can determine the surface defects and internal defects It is in.

In order to achieve the above object, the inspection object discrimination method according to claim 1 of the claims includes the inspection that occurs at each position while continuously hitting a plurality of positions along a desired direction of the inspection object. Receive vibrations of the object, perform frequency analysis on each received vibration, obtain waveform data including peak values in the same order wave in the frequency distribution specific to the inspection object, and Using any one data as a reference, the frequency change rate between the reference data values is obtained, and the presence or absence of a surface defect or an internal defect of the inspection object is determined based on the obtained change in the frequency change rate. It is characterized by that.

The inspection object discriminating apparatus according to claim 2 of the claim includes an excitation means for striking the inspection object, a vibration receiving means for receiving vibration of the inspection object caused by the striking, and the inspection The moving means for moving the hit position of the object and the vibration of the test object generated by hitting the test object are continuously received at a plurality of positions along the desired direction of the test object. Frequency analysis for each of the vibrations obtained, each obtaining waveform data including a peak value in the same order wave in the frequency distribution specific to the inspection object, based on any one of those data, Analyzing and discriminating means for determining a frequency change rate between each of the reference data values and determining the presence or absence of a surface defect or an internal defect of the inspection object based on the obtained change in each frequency change rate And wherein the Rukoto.

According to the first aspect of the present invention, the presence or absence of a defect is determined for each of a plurality of inspection objects manufactured at the same design value in an environment where temperature changes can occur between them. A method for discriminating an object to be inspected, which receives vibrations (sounds) caused by striking continuously applied to a plurality of positions of the object to be inspected , performs frequency analysis on each of the obtained vibrations, and has a frequency unique to the object to be inspected. Acquires waveform data including peak values in the same order wave in the distribution, and determines the presence or absence of surface defects or internal defects on the inspection object by changing each frequency change rate between the multiple waveform data It is. That is, the presence / absence of a surface defect or an internal defect is determined using waveform data obtained by itself (within the same inspection object).
When there is a change in the environment such as a mass production line and a temperature change occurs between manufactured parts, products, etc. (inspection object), the frequency distribution inherent to the inspection object fluctuates, and the above-mentioned inherent frequency is changed. The discriminating method used cannot be discriminated. However, even if a temperature change occurs in an environment such as a mass production line, its own temperature does not change during a continuous blow (short time). Therefore, even when a temperature difference occurs between products that are inspection objects due to temporary suspension of a mass production line or the like, surface defects and internal defects of a specific inspection object can be determined.
Further, the presence / absence of a surface defect or an internal defect of the inspection object is determined based on a change in each frequency change “rate” between the plurality of waveform data acquired as described above. Therefore, each of a plurality of products, that is, inspection objects, manufactured at the same design value in an environment where temperature changes can occur between each other, especially manufactured on a mass production line where a temperature difference can occur between products due to temporary stoppage, etc. As for, surface defects and internal defects can be discriminated.
Furthermore , according to the present invention, the approximate position where the surface defect or internal defect is generated can be found by the fact that the frequency change rate is reduced at the defect position such as cracking or internal oxidation .
According to the invention described in claim 1 of the scope of claims, the detection capability can be improved because the inspection of the surface defect is not a visual inspection.
Moreover, internal defects can also be detected by a common method (configuration). That is, if the frequency of the vibration of the inspection object generated by applying the impact is analyzed, a frequency distribution and a natural frequency specific to the inspection object are obtained as a result. The frequency distribution obtained as a result of the frequency analysis shows a unique pattern reflecting the presence or absence of defects on the surface of the inspection object or inside. Therefore, waveform data (frequency distribution data) for a plurality of positions of the inspection object is acquired, and the frequency change rate between each value is obtained based on any one of the data, and each frequency change rate is calculated. According to the change, the presence or absence of a surface defect or an internal defect of the inspection object can be determined. At this time, it can be determined by repeating a common method for itself, that is, one inspection object.

The invention according to claim 2 of the appended claims is a device to which the test object determination method according to claim 1, the test object determination method according to claim 1 on the basis of the action described above Has the same effect.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol shows the same or an equivalent part between each figure.
First, an inspection object discrimination method according to the present invention (first invention) will be described.
If an object such as a member or product is hit and free vibration is applied, the object vibrates at a natural frequency (natural frequency) f given by the following equation (1).
f = [(α ² / L ² ) × (EI / ρS) ^1/2 ] / 2π (1)
Where α is a constant, L is the length of the object to be inspected, E is the elastic modulus (Young's modulus: σ / ε), I is the moment of inertia, ρ is the density, S is the cross-sectional area, and π is the circumference.
Then, with this natural frequency as a fundamental wave, a higher-order wave is generated on the higher frequency side.

FIG. 1 is a diagram showing a frequency distribution waveform obtained by frequency analysis of the vibration of such an object, with the horizontal axis representing the frequency (0 Hz to 40 kHz) and the vertical axis representing the energy (signal intensity). Yes. As can be seen from this figure, the frequency distribution waveform includes the fundamental wave P1 and a number of higher-order waves P2 on the higher frequency side.
In FIG. 1, two frequency distribution waveforms P11 and P12 are shown. However, if the materials of the two objects are different, the frequency distribution waveforms are also different. That is, the frequency distribution waveform is unique to the object. From this, it can be seen that the difference in material appears as a difference in frequency distribution waveform.

Further, even when the object has surface defects such as cracks or internal defects (defects of internal structure such as internal oxidation), if frequency analysis is performed, each of them shows a unique, that is, different frequency distribution waveform.
FIG. 2 shows a large number of inspection objects (members and products having the same design value) having various attributes as described above in the frequency region higher than the fundamental wave P1 (see FIG. 1), here, a sintered connecting rod. The frequency distribution waveform of is shown.
As shown in FIG. 2, the frequency at which the peak value of the frequency distribution waveform differs depending on the size of surface defects (here, cracks), and when internal defects (in this case, internal oxidation) occur, a roughly defined frequency region is obtained. The peak value of the frequency distribution waveform appears inside. In addition, there is a frequency difference between these peak values. For an object having no defect (non-defective product), peak values are generally concentrated on a higher frequency side than a defective product (defective product).
From this, and from comparison with FIG. 1, in the frequency distribution waveform obtained by frequency analysis, if the waveform including the peak value of the higher order wave separated from the fundamental wave to the higher frequency side is compared, It can be seen that the difference from the defective product can be determined with higher accuracy, and the difference in material (whether it is a different material or not) can also be determined with high accuracy.

The determination will be further described with reference to FIGS.
3 can easily determine whether or not there is a crack, FIG. 4 can determine whether or not quenching has been completed, and FIG. 5 can determine whether or not one material is the same as the other material for inspection objects having the same design value. Represents.
That is, in FIGS. 3 to 5, the frequency difference (width) fw between the waveforms including the peak value detected between the reference object and the inspection object is compared between the fundamental wave or the adjacent waves. It is the figure which contrasted and contrasted the case (each (a) figure) and the case (each (b) figure) where it compared between the waveforms containing the peak value of the higher order wave far from the fundamental wave to the high frequency side. . Note that the waveforms in each figure are obtained by superimposing the waveforms obtained by analyzing the same reference object and inspection object multiple times and analyzing them.
Here, the reference material is a non-defective product in FIG. 3, a hardened product (hardened product) in FIG. 4, one material: S48C (carbon steel) in FIG. 5, and an inspection object is also a defective product, It refers to an unquenched product or the other material: SCr20 (chromium steel). The reference object and the inspection object are manufactured and processed with the same design value. In each waveform in FIGS. 3 to 5, solid lines 31, 41, 51 indicate the waveform of the reference object, and broken lines 32, 42, 52 indicate the waveform of the inspection object. 3 to 5 are compared with each other in the cases shown in FIGS. 3 to 5B, that is, between waveforms including the peak value of the higher order wave separated from the fundamental wave to the higher frequency side. In each case, it can be seen that the frequency difference fw is larger than the case shown in each figure (a). Therefore, it can be seen that it is easy to set a threshold value (frequency) as a boundary value in determining whether the product is a non-breaking good product, a hardened product, or the same material.
It goes without saying that this threshold value is set within the range of the illustrated frequency difference fw, but the signal level range shown on the vertical axis may also be set as the threshold value (upper and lower limit values). According to this, the accuracy of discrimination can be increased. The threshold value related to the frequency is also set within the range of the frequency difference fw, and is also set on the opposite side (right side in the figure) across the peak value frequency, that is, set as the upper and lower limit values. Good.
Regarding the determination of internal oxidation, a frequency difference is generated between waveforms including the peak value in the frequency distribution waveform obtained by frequency analysis according to the presence or absence and the degree thereof, so that it can be determined as described later.
In FIG. 1, f11 indicates a frequency region (about 0 Hz to 40 kHz) that is a target of frequency analysis in the method of the present invention, and f12 is a frequency region (0 Hz) that is a target of frequency analysis in the conventional inspection object discrimination method. About 10 kHz). It can be seen that the frequency region f11 in the method of the present invention covers a wide range from the audible range to the ultrasonic range.

FIG. 6 is a diagram showing a frequency distribution waveform obtained by performing frequency analysis on each of a large number of samples in order to determine the presence or absence of internal oxidation in a region away from the fundamental wave P1 (see FIG. 1) on the higher frequency side. It is. Since the fundamental wave P1 is lower than the minimum frequency 9800 Hz shown on the horizontal axis, it is not shown in FIG.
In FIG. 6, among the frequency regions A to C, a sample group showing a peak value waveform (a waveform including a peak value) in the highest frequency region A is a good product group having no internal oxidation. The sample group showing the peak value waveform in the next highest frequency region B is a sample group that has a slight internal oxidation but can be discriminated as a non-defective product. The sample group showing the peak value waveform in the frequency region C is a sample group that has internal oxidation and is identified as a defective product.
If there is internal oxidation, fine pores are scattered in the body tissue and the strength is lowered. Fine pores appear as the degree of internal oxidation increases, and the degree of strength reduction increases.

  According to FIG. 6, it is possible to determine the presence or absence of internal oxidation depending on whether the peak value waveform in the region away from the fundamental wave P1 to the higher frequency side is in the frequency regions A and B or C. I understand that. That is, it can be seen that whether or not the internal oxidation is a non-defective product can be determined by a threshold value that is easily set within a large frequency difference (width).

Therefore, the vibration (sound) of the inspection object generated by hitting the inspection object is received in a wide band, for example, 0 Hz to 40 kHz, and the received vibration is subjected to frequency analysis, and is inherent to the inspection object. Waveform data including a peak value in a predetermined higher-order wave on the frequency side higher than the fundamental wave of the inspection object in the frequency distribution (frequency spectrum) is acquired. Between this waveform data and the reference waveform data obtained by frequency analysis in advance under the same conditions as the inspection of the inspection object (basically both waveform data) It is possible to determine whether the product is a non-defective product, whether the inspection object is quenched, and whether it is a specific material.
In addition, the waveform data including the peak value in a predetermined higher frequency wave higher than the fundamental wave of the inspection object, that is, the higher-order wave selected in advance by experiment or calculation, and the reference object related to the inspection object In the case of the frequency difference from the reference waveform data obtained by frequency analysis in advance under the same conditions as inspecting the inspection object, it becomes easy to select a threshold value used for discrimination of the inspection object. This is because the frequency difference between the two waveform data is larger than the frequency difference in the case of comparison between the fundamental wave P1 or the waves adjacent thereto.
The method of the present invention has been made based on the above findings.

FIG. 7 is a block diagram showing an embodiment of an inspection object discriminating apparatus (second invention) to which the method of the present invention (first invention) described above is applied.
As shown in the figure, the inspection object discriminating apparatus includes an excitation unit 71, a vibration receiving unit 72, an analysis discriminating unit 73, and a monitor 74.
In this case, the vibration means 71 is a means for striking the inspection object (here, the sintered connecting rod) 75, and is composed of, for example, a hammer driven by air pressure. Here, the inspection object 75 is placed on a support stand 76 such as a rubber plate so that it can freely vibrate when hit.
The vibration receiving means 72 is means for receiving the vibration (sound) of the inspection object 75 generated by hitting by the vibration means 71 in a wide band. Here, the vibration receiving means 72 is composed of a microphone having a bandwidth of 0 Hz to 40 kHz, and is an inspection object. It is arranged close to the object 75.

The analysis discriminating means 73 performs frequency analysis on the vibration received by the vibration receiving means 72 and has a predetermined higher order on the frequency side higher than the fundamental wave of the inspection object 75 in the frequency distribution unique to the inspection object 75. Acquire waveform data including peak values in the wave. Between the waveform data and the reference waveform data obtained by performing frequency analysis on the reference object related to the inspection object 75 in advance under the same conditions as the inspection of the inspection object 75, both waveforms here. This is means for discriminating the inspection object 75 based on the frequency difference between peak values of data. Specifically, it is means for discriminating whether or not the inspection object is a non-defective product, whether or not the inspection object 75 is quenched, and further whether or not it is a specific material.
As the analysis discriminating unit 73, for example, a computer that executes the analysis discriminating process as described above by executing a program in which necessary items are described is used, and the discrimination result by the analysis discriminating unit 73 is displayed on the monitor 74. For example, in the case of surface crack inspection, the product number and serial number of the inspection object 75 and whether there is a crack or not are displayed on the monitor 74.

Next, a method for discriminating an inspection object using such an apparatus will be described.
In FIG. 7, first, the inspection object 75 is placed on the support base 76 and the position of the support base 76 is adjusted to align the inspection object 75 with the vibration means 71, and then the vibration means 71. Is driven and hits the inspection object 75.
Due to this impact, free vibration is generated in the inspection object 75, and this vibration is received by the vibration receiving means 72. The reception band is a wide band from 0 Hz to 40 kHz. The vibration receiving means 72 converts the received vibration into an electrical signal and gives it to the analysis discriminating means 73.
The analysis discriminating unit 73 performs frequency analysis by performing Fourier transform on the received signal (vibration data) from the vibration receiving unit 72. An example of the frequency distribution waveform obtained by frequency analysis in this way is the waveform shown in FIG.

The frequency distribution waveform illustrated in FIG. 1 includes the shape, size, density, and material of the inspection object 75, the presence or absence of defects on the surface and inside, or the property of whether or not the inspection object has been quenched (attributes). The unique pattern is reflected. In other words, although it is a member or product manufactured and processed with the same design value (hereinafter collectively referred to as a product), if there is a slight difference in form, internal structure, etc. between individual products, that is a frequency distribution waveform ( Frequency distribution data).
Therefore, for products having the above-mentioned attributes (reference products such as non-defective products and hardened products), a frequency analysis is performed in advance under the same conditions as the inspection of the inspection object 75 to obtain a large number of frequency distribution waveforms, and as reference waveform data By storing it, it can be used for discrimination of the inspection object 75, that is, whether it is a non-defective product, whether it is a quenched product, or the like.
That is, for a certain inspection object 75, whether the frequency distribution waveform obtained by vibration measurement and frequency analysis is the same as one of the frequency distribution waveforms (reference waveform data) of the reference object stored in advance is compared. Then, it can be determined whether the inspection object 75 is a non-defective product or a quenched product.

  Here, as described above, if waveform data including a peak value in a predetermined higher-order wave on the frequency side higher than the fundamental wave is used as the frequency distribution data, the reference waveform data of the reference object and the waveform data of the inspection object 75 are used. The frequency difference between the threshold value and the threshold value becomes large, and it becomes easy to set a threshold value or the like that becomes a boundary value when the inspection object 75 is determined, thereby improving the determination accuracy. In addition, by preparing the reference waveform data in advance, various determinations can be made in the same manner using a common procedure.

  As described above, according to the inspection object discriminating method and apparatus according to the first and second inventions, inspection of defects on the surface and inside, whether the inspection object is quenched, or whether it is a specific material. Can be determined with high efficiency and low cost. Further, since the inspection object is discriminated without visual observation, the inspection and discrimination can be performed with high accuracy.

It will now be described a third according to the invention (according to claim 1) inspection object determination method.
First, as shown in FIG. 8, the test object (sintered connecting rod) 75 is continuously struck at a plurality of positions along a desired direction, in the illustrated example, at five positions a to e. The vibration (sound) generated in is received in a wide band, here in a band from 0 Hz to 40 kHz. Then, frequency analysis is performed on each received vibration, and waveform data including peak values in the same order wave in the frequency distribution (frequency spectrum) unique to the inspection object, for example, the fundamental wave and the same order higher order wave, is obtained. Get each. Then, using any one of these data, for example, data at the first hitting position (a) (basically peak value data) as a reference, a frequency change rate between the reference data value is obtained and obtained. The presence or absence of a surface defect or an internal defect of the inspection object 75 is determined based on the change in each frequency change rate.

FIG. 9 is a graph showing in an easy-to-understand manner how surface defects and internal defects of the inspection object 75, specifically, the presence or absence of cracks and internal oxidation can be determined by the change in the frequency change rate. The striking position is shown with the frequency change rate on the vertical axis.
FIG. 9 shows the change curves of the frequency change rates respectively obtained at the positions i to e in three modes. In this case, the change curve 91 is an example of a test object having no cracks and a little internal oxidation, the change curve 92 is a test object having an internal oxidation, and the change curve 93 is a curve of a test object having a crack. ing. It should be noted that the rate of change in each of the positions A to E is “1” when the inspection object 75 has neither cracks nor internal oxidation.
In this way, by looking at the forms of the change curves 91 to 93, that is, by obtaining the respective frequency change rates, it is possible to determine the presence or absence of surface defects and internal defects of the inspection object 75. As can be seen from the curves 91 and 92, since the frequency change rate is reduced at the defect position such as a crack or internal oxidation, the approximate position where the defect occurs can also be known. In the example shown in the drawing, it can be seen that defects are generated at the positions B and C.
Application of the inspection object discrimination method according to the above-described third invention to the apparatus (fourth invention : invention according to claim 2 ) is achieved, for example, by moving the support base 76 in FIG. The vibrating means 71 strikes the inspection object 75 in accordance with the movement of the support base 76, and the vibration receiving means 72 receives the vibration of the inspection object 75 at the timing of striking at each stop position. This can be realized by configuring.

According to the inspection object discriminating method and apparatus according to the third and fourth inventions described above (the inventions according to claims 1 and 2), there are changes in the environment such as the mass production line, Even if a temperature change occurs between a product or the like (inspection object), its own temperature does not change during a continuous blow (short time).
Therefore, even when a temperature difference occurs between products that are inspection objects due to temporary suspension of a mass production line or the like, surface defects and internal defects of a specific inspection object can be determined.
Further, the presence / absence of a surface defect or an internal defect of the inspection object is determined based on a change in each frequency change “rate” between the plurality of waveform data acquired as described above. Therefore, each of a plurality of products, that is, inspection objects, manufactured at the same design value in an environment where temperature changes can occur between each other, especially manufactured on a mass production line where a temperature difference can occur between products due to temporary stoppage, etc. As for, surface defects and internal defects can be discriminated.
Furthermore, according to the present invention, since the frequency change rate is reduced at the defect positions such as cracks and internal oxidation, there is an advantage that the approximate position where the surface defect or the internal defect is generated can be recognized.
According to the third and fourth aspects of the invention, the detection of surface defects can be improved because it is not a visual inspection.
Moreover, internal defects can also be detected by a common method (configuration). That is, if the frequency of the vibration of the inspection object generated by applying the impact is analyzed, a frequency distribution and a natural frequency specific to the inspection object are obtained as a result. The frequency distribution obtained as a result of the frequency analysis shows a unique pattern reflecting the presence or absence of defects on the surface of the inspection object or inside. Therefore, waveform data (frequency distribution data) for a plurality of positions of the inspection object is acquired, and the frequency change rate between each value is obtained based on any one of the data, and each frequency change rate is calculated. According to the change, the presence or absence of a surface defect or an internal defect of the inspection object can be determined. At this time, it can be determined by repeating a common method for itself, that is, one inspection object.
In the apparatus shown in FIG. 7, a microphone, that is, a non-contact type vibration receiving unit is used as the vibration receiving unit. However, the present invention is not limited to this, and a contact type vibration receiving unit may be used.

It is a figure which shows the frequency distribution waveform obtained by frequency-analyzing the vibration of an object. It is a figure which shows the frequency distribution waveform about many test objects. It is a figure for demonstrating that the presence or absence of the crack of a test target object can be discriminate | determined by this invention. It is a figure for demonstrating that it can be discriminate | determined whether the test target object has been hardened similarly. It is a figure for demonstrating that it can discriminate | determine whether one material is the same as the other material similarly about a test object. It is a figure which shows the frequency distribution waveform obtained by performing frequency analysis about many samples. It is a block diagram showing one embodiment of the inspection subject discriminating device by the present invention. FIG. 8 is a procedure explanatory diagram of an inspection object discrimination method according to an invention different from FIG. 7. It is a graph which shows a mode that a test target object can be discriminate | determined in invention same as the above.

Explanation of symbols

71: vibration means, 72: vibration receiving means, 73: analysis discrimination means, 74: monitor, 75: inspection object.

Claims (2)

An inspection object discriminating method for discriminating the presence or absence of a defect for each of a plurality of inspection objects manufactured with the same design value in an environment where temperature changes can occur between each other,
Wherein while adding continuously striking the plurality of positions along the desired direction of the inspection object receiving the vibration of the object to be examined occurring in each position, a frequency analysis for each of the vibration which is the received, specific to the inspection object Waveform data including peak values in the same-order wave in the frequency distribution of the respective frequency data are obtained, and the frequency change rate between the reference data values is obtained with any one of the data as a reference. A method for discriminating an inspection object, comprising: discriminating the presence or absence of a surface defect or an internal defect of the inspection object based on a change in each frequency change rate. An inspection object discriminating apparatus that discriminates the presence or absence of defects for each of a plurality of inspection objects manufactured with the same design value in an environment where temperature changes can occur between each other,
And vibration means for applying a continuously blow to the test object,
Vibration receiving means for receiving vibration of the inspection object generated by the hitting;
Moving means for moving the hit position of the inspection object;
The vibration of the inspection object generated by hitting the inspection object is continuously received at a plurality of positions along the desired direction of the inspection object, the frequency analysis is performed for each received vibration, and the inspection object Waveform data including peak values in the same-order wave in the frequency distribution unique to the object is acquired, and the frequency change rate between the reference data values is obtained based on any one of the data. An inspection object discriminating apparatus comprising: an analysis discriminating unit that determines the presence or absence of a surface defect or an internal defect of the inspection object according to the obtained change in each frequency change rate.

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