JP3593544B2 - Metal surface defect detection method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a defect detection method for a metal surface, and more particularly to a defect detection method for detecting a defect on a metal surface having a chamfered portion typified by an end face of a bearing.
[0002]
[Prior art]
2. Description of the Related Art In recent component production lines, there has been an increase in the number of inspections performed on a surface of a workpiece by an image processing technique at the end of a processing step. Specifically, the image processing apparatus includes at least an image processing device, illumination, and a TV camera, captures illumination light reflected on the surface of the workpiece by the TV camera, and converts the captured image into various images in the image processing device. The processing technology is applied to determine the presence or absence of a defect. As an image processing technique in this case, a template matching method or a method of extracting an image feature amount such as an area has been generally used.
[0003]
With respect to the inner and outer races (the inner race and the outer race) of the bearing, a defect inspection of the raceway surface (the surface in contact with the rolling elements such as balls and rollers) and the end surface is performed. Here, considering the inner and outer ring end surfaces of the bearing, as shown in FIG. 3, the respective boundary portions between the outer peripheral surface and the inner peripheral surface of the end surface are chamfered. This chamfering is performed in a chamfering process in a bearing production line. However, in general, chamfering does not greatly affect machining accuracy, and thus chamfering is often performed relatively rough. Therefore, the size of each of the end face portion and the chamfered portion may vary considerably depending on the workpiece.
[0004]
[Problems to be solved by the invention]
Here, a problem when the template matching method most frequently used as an image processing technique is applied to the defect inspection of the inner and outer ring end faces of the bearing will be described. First, as described above, the end faces of the inner and outer rings of the bearing are chamfered, and since the tolerance of the chamfer amount is large, the size of each of the end face portion to be inspected and the chamfered portion is limited. The results vary considerably depending on the workpiece, and as a result, a good inspection cannot be performed by the template matching method on the assumption that the size of the inspection portion is constant. Second, in the template matching method, it is difficult to detect a small defect such as a minute flaw because the acquired image data of the workpiece and the image data of the template are compared with each other. Third, the surface roughness of the processed end surface may vary depending on the workpiece depending on the type of the grinding wheel that has processed the end surface, the degree of wear, and the like. In this case, depending on the setting of the threshold value for defect determination, In some cases, those having poor surface roughness may be erroneously recognized as defects.
[0005]
Further, when there is a mark on the end face, the following problem occurs in addition to the above problem. First, since the inspection for missing a mark or the inspection for a defect other than the mark is performed, the phase of the mark must be firstly adjusted. In this case, the phase matching with the master pattern is performed. Thereafter, template matching is performed. In particular, if the image size is increased to increase the detection accuracy, the inspection time becomes extremely long. Second, since the size and length of the stamp in the acquired image change depending on the depth of the stamp, this may be erroneously recognized as a defect. Third, in the defect inspection in the template matching method, it is necessary to mask a certain range including the stamp as a dead zone, so that a defect near the stamp cannot be detected.
[0006]
The present invention has been made to solve the above-mentioned problems, and its purpose is to(1)Good inspection can be performed regardless of the amount of chamfer,(2)Small defects such as small scratches can be detected reliably,(3)Good inspection can be performed regardless of surface roughness, (Four)Shortening the inspection time including the phase alignment of the stamp,(Five)Good inspection can be performed regardless of the depth of the stamp,(6)Defects near the stamp can also be detectedIt is.
[0007]
[Means for Solving the Problems]
Said(1)Or(3)In order to achieve the object of the invention, in the invention according to claim 1, an object to be inspected is photographed by a TV camera, and image processing is performed on the photographed image to detect a defect on the surface of the object to be inspected. In the method for detecting a defect on a metal surface, an inspection area on the surface of an inspection object is divided into a plurality of minute areas, and a standard deviation relating to luminance is measured in each of the minute areas. Calculate the degree of correlation with the standard deviation of the master work without defects, and compare the degree of correlation with a preset threshold value for defect detection to detect the presence or absence of defects on the surface of the inspection object. Asare doing.
[0008]
By adopting such a procedure,Since the standard deviation of the luminance in the corresponding area between the master work and the inspection object is compared, the sizes of the comparison target areas do not necessarily have to be the same as in the template matching method. If the size of the divided area is reduced by using the standard deviation, detection of a small defect such as a minute flaw can be easily dealt with. Further, the use of the standard deviation makes it possible to detect a defect in consideration of the surface roughness, so that there is no erroneous determination that a defect exists only due to poor surface roughness.
[0009]
further,Said(Four)Or(6)In order to achieve the purpose ofIn the invention according to claim 1,If there is a standard deviation equal to or greater than a preset marking recognition level among the standard deviations for each minute area on the surface of the inspection object, the defect of the marking is also inspected. The specific processing procedure is as follows. First, the amount of positional deviation is calculated from the degree of correlation between the standard deviation of each minute area on the surface of the inspected object and the standard deviation of each minute area on the master work. After the alignment of the data of the inspection object and the master work, the positions of the inspection object and the master work having the standard deviation equal to or higher than the engraving recognition level are recognized as the engraved block, and the inspection object and the master work are recognized. The difference between the degree of correlation and the width of the engraved block is determined for each corresponding engraved block, and the degree of correlation is smaller than a preset threshold value, or the difference in the engraved block width is a preset tolerance. If either of them is larger than the above, it is determined that a defect exists in the engraved portion.
[0010]
here,Due to this procedureThe operation will be described. Since the standard deviation regarding the luminance is greatly different between the place where the marking is present and the place where the marking is not present, first, in the defect inspection of the marking, data alignment between the surface of the inspection object and the master work is performed. Next, a portion having a standard deviation equal to or higher than the stamp recognition level for each of the inspection object and the master work is recognized as a stamp block. Then, the correlation between the standard deviation of each minute region on the surface of the inspection object and the standard deviation of each minute region of the master work is obtained for each of the corresponding engraved blocks of the inspection object and the master work. If it is smaller than the threshold value, it is determined that a defect exists in the engraved portion. Further, a difference in the width of the engraved block is obtained for each of the corresponding engraved blocks of the inspection object and the master work. Even when the difference is larger than a preset allowable value, a defect in the engraved portion is determined. Is determined.
[0011]
Claim 1According to the invention, since the alignment of the data between the surface of the inspection object and the master work is performed based on the correlation between the standard deviations of the two luminances, it is necessary to set a large image size in order to increase the inspection accuracy. Therefore, the time required for positioning the stamp is shorter than that of the template matching method.Also,A part having a standard deviation equal to or higher than the marking recognition level for each of the inspection object and the master work is recognized as a marking block, and the standard deviation of each minute area on the surface of the inspection object for each corresponding marking block of the inspection object and the master work. The defect of the marking is detected based on the correlation between the standard deviation and the standard deviation of each minute area in the master work, and the difference of the width of the marking block. Therefore, depending on the depth of the marking as in the template matching method And good inspection can be performed.further,As for the defect inspection of the inspection area other than the engraved area, the data obtained by canceling (deleting) the data of the standard deviation of the part recognized as the engraved block from the data of the standard deviation of the entire inspection area may be used. It is not necessary to mask a certain range including the inspection area near the marking, and therefore, the defect can be detected also in the inspection area near the marking.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows an example of a system configuration including an image processing apparatus to which the defect inspection method of the present invention is applied. The bearing 22 as the inspection object is placed on the inspection table 21 with the end surface as the inspection surface facing upward. A TV camera 24 such as a CCD camera is provided above the bearing 22, and its optical axis is perpendicular to the end surface of the bearing 22 as an inspection surface. A ring illumination 23 as an illuminating device is provided between the inspection table 21 and the TV camera 24, and the optical axis of the TV camera 24 passes through substantially the center of an annular portion of the ring illumination 23. The reason for this configuration is to irradiate illumination uniformly on the annular inspection surface and efficiently receive the reflected light.
[0013]
The image processing device 25 obtains a captured image captured by the TV camera 24 and performs image processing described later. The image processing device 25 has a storage device for storing image data such as a captured image and a master image. The panel keys 26 are used by an operator to input data, command codes, and the like to the image processing device 25. The monitor TV 27 displays various images such as a photographed image and an image-processed image, and is also used for displaying various setting parameters and inspection results. In addition, if necessary, a loader for automatically carrying in / out the bearing 22 as the inspection object onto the inspection table 21 may be provided.
[0014]
Here, processing performed in the image processing device 25 will be briefly described with reference to FIG. 12 showing a control circuit in the image processing device 25. When an operation command is input from the outside, the CPU 37 as a control processor sends signals to an address generation circuit 34 for generating an address in the VRAM 33 and controlling the same and a synchronization control circuit 32 for controlling a synchronization signal of the TV camera 24. . The TV camera 24 receives a signal from the synchronization control circuit 32, captures an image of the inspection object, and transmits the captured image to the A / D converter 31. The A / D converter 31 converts the input video signal into 8-bit data of 256 gradations, and stores this in a VRAM 33 as an image memory.
[0015]
Next, the CPU 37 sets the specified area in the address generation circuit 34 and sets the calculation contents in the image calculation circuit 35, so that the data in the specified area is automatically transferred from the VRAM 33 to the image calculation circuit 35. When the designated operation is executed in the image operation circuit 35 and the operation is completed, the address generation circuit 34 transmits an end signal to the CPU 37, and in response thereto, the CPU 37 receives the operation result from the image operation circuit 35. The D / A converter 36 converts the above-mentioned 8-bit data of 256 gradations into analog data for image display, the RAM 38 is used as a memory for storing registered data such as non-defective data and the like, and a ROM 39 is used as a control memory. It is a memory for storing programs, and the I / O 40 is an interface with an external device.
[0016]
Hereinafter, the procedure of the defect inspection of the bearing 22 in the present embodiment will be described with reference to the flowchart shown in FIG. 1 and FIGS.
[0017]
Step 1: Input an image.
In this step, an image is input from the TV camera 24. The image captured by the TV camera 24 is analog data, which is converted into digital data of 256 gradations by A / D (analog / digital) conversion processing and stored. The defect inspection is performed for the inner ring of the bearing 22 in the same procedure as for the outer ring, but only the outer ring will be described here.
[0018]
Step 2: detect an edge position.
In this step, the boundary (edge) between the end face and the outer peripheral chamfer and the boundary (edge) between the end face and the inner peripheral chamfer are set for the outer ring of the bearing 22. In the outer ring of the bearing 22, each boundary between the outer peripheral surface and the inner peripheral surface at the end surface is chamfered, and these are referred to as an outer peripheral chamfer and an inner peripheral chamfer, respectively. In the present embodiment, the inspection is performed in each area of the end face, the outer peripheral chamfering, and the inner peripheral chamfering. Accordingly, a process of dividing the captured image captured by the TV camera 24 into respective areas of the end face, the outer peripheral chamfer, and the inner peripheral chamfer is performed first. The specific procedure of this processing is as follows. First, as shown in FIG. 3B, the boundary (edge) between the end face and the outer peripheral chamfer and the boundary between the end face and the inner peripheral chamfer for the outer ring of the non-defective bearing 22. (Edge) is set in advance, and then, this data is compared with the image data captured by the TV camera 24, the most similar part is set as an edge detection point, and this detection point is set as the boundary ( Edge position). The data of the non-defective bearing 22 is measured in advance for a master work having no defect, and the data is registered in the RAM 38.
[0019]
Step 3: Set an inspection area.
In this step, as shown in FIG. 4, based on the edge position obtained in Step 2 and the sizes of the outer diameter and the inner diameter of the outer ring of the bearing 22, three areas, that is, chamfered areas (outer peripheral chamfered portions) A and the inner peripheral chamfered portion C) and the other area (end face B).
[0020]
Step 4: Check the width of the end face B.
In this step, the width of the end face B is calculated based on the end face B set in step 3, and if the width is out of the allowable range, it is determined that the chamfering is defective. Move to This is because when the chamfer amount is large, the width of the end face portion B becomes small, while when the chamfer amount is small, the width of the end face portion B becomes large. The width of the end face portion B can be easily obtained based on the edge position at the boundary between the end face and the outer peripheral chamfer obtained in step 2 and the edge position at the boundary between the end face and the inner peripheral chamfer.
[0021]
Step 5: Measure the standard deviation of the entire circumference.
In this step, if it is not determined in step 4 that the chamfering is defective, each of the inspection areas (the outer chamfer A, the end face B, and the inner chamfer C) is divided into minute areas. The standard deviation in each minute area is measured for the entire circumference of the end face of. Specifically, a minute area is set for each of the three divided areas as shown by a hatched area in FIG. 4, and the minute area is rotated and moved once by one along the ring-shaped inspection area. The variation (standard deviation) in the reflection intensity of the light is measured.
[0022]
FIG. 5 shows an example of measurement data in each inspection area. (A), (b), and (c) are measurement data of the outer peripheral chamfered portion A, the end surface portion B, and the inner peripheral chamfered portion C, respectively. Is the standard deviation. 6 to 8 and 10 to 11 described later, the horizontal axis represents the rotational angle position, and the vertical axis represents the standard deviation. (B) In the figure, the standard deviation of the location where the inscription (the character of “NACHI”) exists is high. In the present embodiment, the measurement data of the end face portion B is used for the defect inspection of the stamp and the defect inspection other than the stamp, while the measurement data of the outer peripheral chamfered portion A and the inner peripheral chamfered portion C are used for undulations and scratches. Used for inspection. FIGS. 6A and 6B show examples of measurement data when the swell is present in the inspection area and FIG. 6B is when there is a flaw in the inspection area.
[0023]
Step 6: It is determined whether or not the end face B is engraved.
In this step, as shown in FIG. 7B, if the standard deviation in the minute area of the end face B measured in step 5 is equal to or larger than the preset marking recognition level, the end face B is used. It is determined that there is an engraved mark, and the process proceeds to Step 7 and subsequent steps for inspecting for a defect of the engraved mark. On the other hand, if there is no standard deviation equal to or greater than the marking recognition level at the end face B, it is determined that there is no marking at the end face B, and the processing of steps 7 to 11 is skipped, and the process proceeds to step 12. In addition, as for the outer peripheral chamfered portion A and the inner peripheral chamfered portion C, of course, there is no engraved mark in this inspection area. Therefore, similarly, the processing of steps 7 to 11 is skipped, and the process proceeds to step 12.
[0024]
Step 7: Align the marking.
In this step, if it is determined in step 6 that the end face B is engraved, the non-defective data (FIG. 7A) and the measurement data (FIG. b)) and alignment. This is because, in order to inspect a mark defect, it is necessary to first match the position (phase) of the mark portion of the non-defective product data with the measurement data. As for the details of the alignment, the correlation between the two data is obtained by the normalized correlation while shifting the measurement data by one degree with respect to the non-defective data around the center position of the outer ring (center position of the ring). The amount of phase shift between the two is calculated based on the position where the degree of correlation is the largest, and the position of the measurement data is corrected by the amount of phase shift to perform positioning.
[0025]
Step 8: Check the engraved part.
In this step, each of the portions that are equal to or higher than the above-described stamp recognition level set in advance as shown in FIG. 7B is referred to as a stamp block, and a master work having no defect is measured in advance for each stamp block. The engraved block width is obtained from the registered degree of correlation between the non-defective data and the measured data, and the start point and end point of each engraved block, and the difference between the non-defective data and the measured data is obtained. Then, by comparing the difference between the correlation degree and the width with a preset allowable value, the defect determination of the engraved portion is performed.
[0026]
Step 9: Whether the difference is within the allowable range.
In this step, either the degree of correlation between the non-defective data and the measurement data in step 8 is smaller than a preset threshold value, or the difference between the engraved block widths is larger than a preset allowable value. In the case of (1), it is determined that a defect exists in the engraved portion, and the masking process of the next step 10 is not performed on the engraved block determined to have the defect. On the other hand, if the degree of correlation between the non-defective data and the measured data is larger than the preset threshold value and the difference between the engraved block widths is smaller than the preset allowable value, a defect exists in the engraved part. It is determined not to be performed, and the process proceeds to step 10.
[0027]
Step 10: Mask the engraved part.
In this step, when it is determined in step 9 that there is no defect in the engraved part, masking is performed on the part recognized as the engraved part. FIG. 9 shows an example of masking. This is because it is necessary to mask the data of the engraved part in the inspection other than the engraved part thereafter. FIG. 8C shows the masking of the engraved portion by canceling the engraved portion from the measured data of FIG. 8B. FIG. 8E shows an example in which it is determined that the engraved portion has a defect.FIG. 8 (f)Shown in
[0028]
Step 11: Remeasure the standard deviation.
In this step, the standard deviation for each minute area is measured again for the inspection area after the masking of the engraved portion in step 10.
[0029]
Steps 12 to 14: Calculate the degree of correlation and determine the presence or absence of a defect.
In these steps, the standard deviation data of each minute area measured in step 5 or step 11 and the standard deviation data of the outer peripheral chamfered portion A and the inner peripheral chamfered portion C jumped from step 6 are defective. Is determined. More specifically, based on the correlation level calculation reference level, which is a level preset based on the allowable surface roughness, as shown in FIG. 10, the non-defective data and the measurement data are set for each set comparison range. Is calculated for the entire comparison range (step 13), and the lowest correlation degree in the entire comparison range is set as the overall correlation degree, which is set in advance. The threshold value is compared with a threshold value for defect detection (step 14). If the overall degree of correlation falls below the threshold value, it is determined that a defect exists in the inspection area, and the process proceeds to the determination NG process of step 16. If, on the other hand, the overall degree of correlation does not fall below the threshold value, it is determined that no defect exists in the inspection area, and the flow proceeds to the determination OK processing in step 15. It is also possible to determine that a defect exists in a comparison range having a degree of correlation lower than the defect detection threshold. As described above, since the standard deviation regarding the luminance in the corresponding area between the master work and the inspection object is compared, the sizes of the comparison target areas are not necessarily equal to each other as in the template matching method. Good.
[0030]
By the way, FIG. 10 shows a case where the entire circumference of the end face is divided into 12 as a comparison range, but a small defect can be detected by setting a large number of divisions. This is because the comparison range is narrowed by setting a large number of divisions, so that defects in the comparison range are relatively emphasized. As a result, even if a small defect is not overlooked, the correlation of the comparison range can be reduced. This is due to the fact that the degree is reduced. In the case of a surface having a rough surface, the standard deviation of the luminance measured as shown in FIG. 11B is smaller than that of the registered image in FIG. Since the overall size is large, it can be determined that the surface roughness is defective.
[0031]
Steps 15 and 16: judgment OK and judgment NG.
In these steps, judgment OK or judgment NG is output based on the result of the above-described comparison processing. These outputs are displayed on the monitor TV 27 or sent to an external device via the I / O 40 in the image processing device 25.
[0032]
As described above, in the present embodiment, it is possible to arbitrarily set the stamp recognition level, the correlation calculation reference level, and the threshold value for defect detection, which are set in advance, for each area of the chamfered part and the end face part. In addition, since the range in which the correlation calculation is performed can be arbitrarily set, the defect inspection can be performed with high accuracy. The time required for the above-mentioned series of processing depends on the number of divisions of the entire circumference of the bearing end face, but it takes only about 0.5 seconds for both the inner and outer rings. Defect inspection can be performed.
[0033]
【The invention's effect】
The present inventionAccording to the method for detecting a defect on a metal surface, an object to be inspected is photographed by a TV camera, and the photographed image is subjected to image processing to detect a defect on the surface of the object to be inspected. The inspection area is divided into a plurality of minute areas, and a standard deviation relating to luminance is measured in each of the minute areas, and a correlation between the standard deviation and the standard deviation of a master work having no defect previously measured and registered. The degree of correlation is calculated, and the degree of correlation is compared with a preset threshold value for defect detection to detect the presence or absence of a defect on the surface of the inspection object. Thus, since the standard deviation regarding the luminance in the corresponding region between the master work and the inspection object is compared, the sizes of the comparison target regions may not necessarily be the same as in the template matching method. As a result, even if the inspected object has been chamfered, a good inspection can be performed without depending on the magnitude of the chamfer amount. Also, by using the standard deviation, if the size of the region to be divided is reduced, a small defect such as a small flaw can be reliably detected. Furthermore, by using the standard deviation, it is possible to detect a defect in consideration of the surface roughness, so that it is not erroneously determined that a defect exists due only to poor surface roughness. And a good inspection can be performed.
[0034]
Furthermore, according to the present invention,Based on the degree of correlation between the standard deviation of each minute area on the surface of the inspection object and the standard deviation of each minute area in the master work, both positions are aligned, and a point having a standard deviation equal to or higher than the mark recognition level for each of both is marked. The difference between the correlation degree and the width of the engraved block is obtained for each of the corresponding engraved blocks, and a defect of the engraved portion is detected based on the difference. Therefore, the inspection time including the phase alignment of the mark can be shortened, good inspection can be performed regardless of the depth of the mark, and a defect near the mark can be detected.
[Brief description of the drawings]
FIG. 1 is a flowchart illustrating a procedure of a defect inspection performed in an image processing apparatus 25 according to an embodiment of the present invention.
FIG. 2 is a diagram showing an example of a system configuration including an image processing device 25 to which the defect inspection method of the present invention is applied.
FIG. 3 is a diagram showing an end face of a bearing as an inspection object 22, showing an edge detection point when specifying an inspection area.
FIG. 4 is a diagram showing an inspection area of a bearing outer ring as an inspection object in one embodiment of the present invention.
FIG. 5 is a diagram illustrating an example of measurement data in each inspection area according to the embodiment of the present invention.
FIG. 6 is a diagram illustrating an example of measurement data when an swell or a flaw exists in an inspection area according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating an example of measurement data, non-defective data, and determination data when a mark is present in an inspection area according to an embodiment of the present invention.
FIG. 8 is a diagram showing an example different from FIG. 7 among the measurement data, the non-defective data, and the determination data when an inscription is present in the inspection area according to the embodiment of the present invention.
FIG. 9 is a diagram illustrating an example of masking of an engraved portion according to an embodiment of the present invention.
FIG. 10 is a diagram showing an inspection method in an inspection area where no stamp is present, according to an embodiment of the present invention.
FIG. 11 is a diagram showing a difference in measurement data due to a difference in surface roughness in one embodiment of the present invention.
FIG. 12 is a block diagram showing an internal configuration of an image processing device 25 according to an embodiment of the present invention.
[Explanation of symbols]
21 Inspection table
22 Bearing outer ring (inspection object)
23 Ring lighting (lighting equipment)
24 TV camera
25 Image processing device
26 Panel key
27 Monitor TV
31 A / D converter
32 Synchronous control circuit
33 VRAM
34 Address Generation Circuit
35 Image operation circuit
36 D / A converter
37 CPU
38 RAM
39 ROM
40 I / O

Claims (1)

A defect detection method for detecting a defect on a surface of a test object by photographing the test object with a TV camera and performing image processing on the photographed image, the method comprising :
Divide the inspection area on the surface of the inspection object into a plurality of minute areas,
Measuring a standard deviation relating to luminance in each of the minute regions,
Calculate the degree of correlation between the standard deviation and the standard deviation in the master work having no defect that has been measured and registered in advance,
By comparing the degree of correlation with a predetermined threshold value for defect detection, a defect detection method for a metal surface that detects the presence or absence of a defect on the surface of an inspection object ,
If there is a standard deviation equal to or greater than the preset marking recognition level among the standard deviations for each minute area on the surface of the inspection object, the defect of the marking is also inspected. The processing procedure is
Alignment is performed by calculating the amount of misalignment from the degree of correlation between the standard deviation of each minute region on the surface of the inspection object and the standard deviation of each minute region in the master work,
After the alignment, a point having a standard deviation equal to or more than the above-described marking recognition level is recognized as a marking block for each of the inspection object and the master work. Determine the difference in the width of the engraved block, if the correlation degree is smaller than a preset threshold, or if the difference in the engraved block width is larger than a preset allowable value, A method for detecting a defect on a metal surface, characterized in that it is determined that a defect is present in the engraved portion.

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