JP2002310940A - Product inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a product inspection method in which the quality of a quartz plate 2 can be determined accurately. SOLUTION: A first histogram is created on the basis of the image of the quartz plate 2 photographed by a CCD camera 4. Then, a processor 6 changes the parameter of a contrast and that of a brightness regarding a luminance in such a way that the luminance in a range from a minimum luminance S up to a maximum luminance L before and after a most frequent value Max in the first histogram becomes a gradation of 0 to 255. After that, the quartz plate 2 is photographed again by the CCD camera 4, and the processor 6 creates a second histogram on the basis of image data by the CCD camera 4. On the basis of the second histogram, a threshold value is set. On the basis of the image data, the quality of the quartz plate 2 is determined by the threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an article inspection method, and more particularly, to an article inspection method suitable for use in, for example, surface inspection of a quartz plate.

[0002]

2. Description of the Related Art Conventionally, in a method of inspecting the surface of a plate-like article, the quality of the article is inspected as follows. That is, first, light is irradiated to an article to be inspected, and reflected light reflected from the article is photographed by photographing means. Next, the reflected light photographed by the photographing means is captured by the image capturing means, and a histogram expressed by the relationship between the luminance and the number of pixels is created for the image of the reflected light captured by the image capturing means. Thereafter, the luminance at the position where the rate of change of the number of pixels in the histogram is switched is set as a threshold, and when the number of pixels on the defective side exceeding the threshold is larger than a predetermined number of pixels, the inspection target An article has been determined to be defective.

[0003]

By the way, in the above-mentioned conventional inspection method, the image of the article photographed by the photographing means is taken as A
When converting an analog signal into a digital signal by an / D converter (analog / digital converter), the parameters of contrast and brightness relating to luminance are set to predetermined fixed values. In addition, the smoothness of the surface of each article varies, and when the article is located at the inspection position, the inclination angle may vary depending on the support state of each article. Therefore, the image of the article is represented by A /
Even if a histogram is created based on the image data converted by the D-converter, there is a drawback that it is difficult to grasp in detail the change in the number of pixels in the luminance range around the mode, which is the inspection area of the article. Was. Therefore, conventionally, it has been difficult to set an accurate value as the threshold value when determining a threshold value as a criterion for determining the quality of an article in the histogram. Further, even if an attempt is made to determine the presence or absence of a scratch or a stain on an article based on image data obtained by converting the image of the article with an A / D converter, it is difficult to determine the difference because the difference in luminance between the articles is small. There was also. Therefore, in the conventional article inspection method, it has been pointed out that it is difficult to accurately judge the quality of the article.

[0004]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention provides a method for photographing an article to be inspected by photographing means, from a minimum luminance to a maximum luminance based on an image of the article photographed by the photographing means. A first histogram represented by the number of pixels according to the difference in luminance at a predetermined number of gradations is created, and the first histogram is created.
The minimum brightness and the maximum brightness before and after the brightness that is the mode value or the average value of the article area in the histogram are obtained, and the difference between the brightness in the range from the minimum brightness to the maximum brightness as a predetermined number of gradations is determined. A second histogram represented by the corresponding number of pixels is created, and a threshold value is determined based on a change in the number of pixels according to the difference in luminance in the second histogram, and the quality of the article is determined based on the threshold value. An article inspection method is provided. According to such a configuration, the second histogram is created for the range from the minimum luminance to the maximum luminance in the first histogram. Therefore, in the second histogram, the change in the number of pixels according to the difference in luminance can be grasped in detail and accurately. Therefore, the threshold value can be accurately set in the second histogram. Therefore, the quality of the article can be accurately determined as compared with the related art.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the illustrated embodiment. In FIG. An article to be subjected to quality inspection by the article inspection apparatus 1 is a substantially square thin plate-like quartz plate 2 (see FIG. 2). The quartz plate 2 is a thin plate having a length of less than 10 mm and a thickness of less than 1 mm each, and the inner side of the circle shown by the imaginary line is an effective area (inspection area) 2 ′.
And Then, the inspection apparatus of this embodiment inspects the effective area 2 ′ of the quartz plate 2 to determine whether there is a flaw and whether or not the surface has a stain. Note that the shape of the quartz plate 2 to be inspected may be substantially rectangular, and the dimensions of the quartz plate 2 are illustrative, but are not limited to the quartz plate 2 having the above dimensions. Further, the shape of the effective area 2 'of the quartz plate 2 may be elliptical or rectangular.
As shown in FIG. 1, the crystal plate 2 is supplied to a supply position of an index table. The gripper 3 of the index table grips the supplied crystal plate 2 and rotates by a predetermined angle to perform a predetermined process for each position. The crystal plate 2 supplied to the supply position is gripped by the gripper 3 and subjected to predetermined processing such as position correction at a predetermined position, and then is sequentially supplied to the inspection position A and horizontally supported. . At the inspection position A, the gripper 3 first supports the crystal plate 2 horizontally so that the surface thereof is positioned upward, and in this state, the article inspection device 1 inspects the surface of the crystal plate 2. Then, after the gripper 3 moves to the next position to invert the quartz plate 2, the article inspecting apparatus 1 is further held in a state in which the quartz plate 2 is horizontally supported so that the back surface faces upward at the inspection position B.
The inspection of the back surface of the quartz plate 2 is performed by the inspection.
At the inspection positions A and B, when the quality inspection on the front and back surfaces of the quartz plate 2 by the article inspection device 1 is completed,
The gripper 3 moves the quartz plate 2 after the inspection from the inspection position B to the next position, performs a predetermined process, and releases it at the discharge position. The crystal plate 2 separated from the gripper 3 is transported to the next step by a separate robot hand. In the meantime, a new quartz plate 2 is sequentially supplied to the inspection positions A and B by the gripper 3.

The article inspection apparatus 1 according to the present embodiment has an inspection position A
Is provided with a CCD camera 4 as a photographing means. The CCD camera 4 has a light source 5 through an optical fiber.
Are connected to the optical fiber and the CC
Light is emitted by the coaxial epi-illumination toward the crystal plate 2 supplied to the inspection position A via the D camera 4. When light is applied to the quartz plate 2 at the inspection position A, the reflected light reflected by the quartz plate 2 is photographed by the CCD camera 4. The article inspection device 1 includes a processing device 6 as a determination unit. As the processing device 6, an FA personal computer, a personal computer, or the like can be used. In this embodiment, a personal computer is used. An image captured by the CCD camera 4 is converted from an analog signal to a digital signal by an A / D converter 6A of the processing device 6, and is captured by a capturing unit 6B. The image captured by the capturing unit 6B is transmitted to the image processing unit 6
Read into C. The image processing unit 6C sets the vertical axis to the number of pixels and sets the horizontal axis to 0 to 25 based on the read image data.
A first histogram expressed as luminance (brightness) of 256 gradations of 5 is created (see FIG. 3). At this time, in the present embodiment, when capturing an image captured by the CCD camera 4, the contrast and brightness parameters relating to brightness are set at 0.5: 0.5.

Here, as described above, the article to be inspected is the translucent quartz plate 2. Therefore, the front and back surfaces of the quartz plate 2 are substantially uniform flat surfaces. Therefore, as shown in FIG. 3, a peak of the number of pixels is firstly observed around a luminance of 38 in the background portion surrounding the crystal plate 2, and a mode of the crystal plate 2 is observed at a luminance of 112. . Processing device 6 as determination means
Has a threshold value setting unit 6D. As will be described in detail later, the threshold value setting unit 6D sets, for example, the luminance of a required portion in the histogram shown in FIG. 5 as threshold values M1 and M2. I am trying to do it. The threshold value M1 at which the luminance is smaller than the mode value (left side) is a threshold value based on which it is determined whether or not the surface of the quartz plate 2 has a flaw. On the other hand, the side where the luminance is larger than the mode (right side)
The threshold value M2 is a threshold value used as a basis for determining whether or not the surface of the quartz plate 2 has a stain. When the first histogram shown in FIG. 3 is obtained, the threshold value setting unit 6D determines that the block of the number of pixels at which the mode value Max is obtained is the area of the crystal plate 2 to be inspected. By making a determination, the above-described threshold value is set.

[0008] Then, as exemplified in FIG.
In the case of a non-defective product having no scratches or stains, as shown on the leftmost side of FIG. 4, the distribution of the luminance (the luminance on the large side and the luminance on the small side) on the left and right sides of the mode X is reduced. It has become. On the other hand, in the case of a defective product in which the quartz plate 2 is damaged, a large luminance distribution appears on the left side (small side) adjacent to the mode Y as shown on the right side of FIG. It has become. Further, in the case of a defective product having a stain on the quartz plate 2, a large luminance distribution on the right side (larger side) adjacent to the mode Z as shown in the center of FIG. ing. By the way, in the histogram shown in FIG. 4, it is difficult to understand the change in the number of pixels due to the difference in luminance. Therefore, in the present embodiment, as will be described later, after the first histogram is created, the crystal plate 2 is again photographed by the CCD camera 4 using the CCD camera 4, and the capturing unit 6B
After the second histogram shown in FIG. 5 is created from the captured image, the required luminances before and after the mode in the second histogram are set as the thresholds M1 and M2. Further, the processing device 6 includes a determination unit 6E, and as described later, the quartz plate 2 is
Based on the image captured and captured by the CD camera, the determination unit 6E determines the quality of the quartz plate 2 as follows. That is, the determination unit 6E first obtains the total number of pixels (corresponding to the total area) in the inspection target area (the effective area 2 ′ in FIG. 2) whose luminance is smaller than the threshold value M1. At the same time, the number of pixels in a lump having a luminance smaller than the threshold value M1 is also obtained. If the number of pixels obtained in this way is larger than one of the predetermined number of pixels, the surface of the quartz plate 2 to be inspected is damaged and defective. The decision is made. On the other hand, if the obtained number of pixels is smaller than the predetermined number of pixels, the determination unit 6E determines that the crystal plate 2 to be inspected has no damage and is a non-defective product. Like that.

[0009] The determination unit 6E determines the inspection target area (FIG. 2).
, The total number of pixels having a luminance higher than the other threshold value M2 is obtained. At the same time, the number of pixels in a lump having a luminance higher than the threshold value M2 is also obtained. If the number of pixels thus obtained is larger than one of the predetermined number of pixels, the surface of the quartz plate 2 to be inspected is determined to be defective due to a stain on the surface. Like that. On the other hand, when the obtained number of pixels in the inspection target area is smaller than both the predetermined number of pixels set in advance, the judgment unit 6E determines that the inspection target quartz plate 2 has no stain Is determined. Further, the processing device 6 includes a display unit 6F, and the result of the determination by the determination unit 6E is displayed on the display unit 6F.

In this embodiment, the image processing unit 6
After the first histogram is created by C, the setting of the contrast and brightness parameters relating to the brightness is changed, and then the crystal plate 2 is photographed by the CCD camera 4 again. That is, after creating the first histogram shown in FIG. 3, the image processing unit 6C sets the luminance of the minimum luminance S in the first histogram to 0 and the luminance of the maximum luminance L of the first histogram to 255. Next, the setting of the contrast and brightness parameters relating to the luminance is changed. For example,
Initially, the contrast and brightness parameters relating to luminance were set to 0.5: 0.5, but 0.9:
Change to 0.7. Then, after the image processing unit 6C changes the setting of the contrast and brightness parameters relating to the brightness, the CCD processing unit 6C re-enters the CCD
The crystal plate 2 is photographed by the camera 4. An image photographed by the CCD camera 4 is transmitted to an A / D converter 6 of a processing device 6.
The signal is converted from an analog signal to a digital signal by A and is taken into the taking section 6B. And the capturing unit 6
The image captured in B is read by the image processing unit 6C, and the image processing unit 6C expresses a second gradation expressed as 256 tones from 0 to 255 based on the read image data.
A histogram is created (see FIG. 5).

As described above, before the CCD camera 4 again photographs the crystal plate 2, the image processing section 6C has changed the settings of the contrast and brightness parameters relating to luminance. Therefore, in the second histogram shown in FIG. 5, the change in the number of pixels in the range from the minimum luminance S to the maximum luminance L before and after the mode Max in the first histogram of FIG. 3 is displayed in more detail. be able to. That is, according to the second histogram shown in FIG. 5, a change in the number of pixels from the minimum luminance S to the maximum luminance L before and after the mode Max can be displayed in more detail.
FIG. 6 and FIG. 7 show comparison between the first histogram and the image corresponding to the second histogram. That is, the case where the quality of the crystal plate 2 is determined based on the image image of FIG. 6 corresponding to the first histogram, and the case where the quality of the crystal plate 2 is determined based on the image image of FIG. 7 corresponding to the second histogram. It is clear that the determination of pass / fail based on FIG. 7 can be performed more accurately.
In the present embodiment, the image processing unit 6
When C creates the second histogram, the threshold value setting unit 6D uses the threshold value M1,
Set M2. Thereafter, the determination unit 6E applies threshold values M1, M to the image captured by the image capturing unit 6B.
2, the number of pixels is calculated to determine whether or not the quartz plate 2 is damaged, and whether or not the quartz plate 2 is stained. The result of the determination by the determination unit 6E is displayed on 6F.

As described above, in this embodiment, the quartz plate 2
After the image is captured by the CCD camera 4, the setting of the contrast and brightness parameters relating to the luminance is changed. Thereafter, the crystal plate 2 is again captured by the CCD camera 4 to capture the image, and the second image in the captured image is captured. A histogram is created, a threshold is set, and the quality of the quartz plate 3 is determined based on the captured image. As can be understood by comparing the first histogram of FIG. 3 with the second histogram of FIG. 5, according to the second histogram, the minimum luminance S before and after the mode Max is obtained.
, The variation in the number of pixels ranging from to the maximum luminance L can be expressed in more detail. Therefore, the threshold values M1, M2
Can be set to an accurate luminance. Further, as is apparent from a comparison between the image image of FIG. 6 corresponding to the first histogram shown in FIG. 3 and the image image of FIG. 7 corresponding to the second histogram of FIG. The counting of the number of pixels by the determination unit 6E can be performed more accurately. Therefore, it is possible to accurately determine the quality of the quartz plate 2 as compared with the related art.

In the above embodiment, the above-described processing is performed on the assumption that when the quartz plate 2 is photographed by the CCD camera 4, not only the quartz plate 2 but also the surrounding background portion is photographed. The following processing may be performed. That is, since the area of the quartz plate 2 is determined in advance, CC
When photographing the crystal plate 2 by the D camera 4, only the crystal plate 2 may be photographed and the background portion may not be photographed. In this manner, if the first histogram corresponding to FIG. 3 is created based on the image data of the crystal plate 2 captured by the CCD camera 4, the portion corresponding to the background portion in FIG. And a first histogram in which only the change in the number of pixels of the blocks before and after the block is displayed. After obtaining such a first histogram, a second histogram may be created in the same manner as in the above-described embodiment, and the same processing as in the above-described embodiment may be performed.
Even in such an embodiment, the same operation and effect as those of the above embodiment can be obtained.

Further, the following processing may be performed.
That is, when photographing the quartz plate 2 with the CCD camera 4,
A square circumscribing the effective area 2 'of the crystal plate 2 may be assumed based on the image data of the crystal plate 2, and a histogram of only the inside area of the assumed square may be created. In this way, it is possible to obtain the first histogram in which only the mode Max and the change in the number of pixels of the blocks before and after it are displayed without displaying the portion corresponding to the background portion in FIG. After obtaining such a first histogram, a second histogram may be created in the same manner as in the above-described first embodiment, and the same processing as in the above-described embodiment may be performed. Even in such an embodiment, the same operation and effect as those of the above embodiment can be obtained. Further, in the above embodiment, a block of a certain number of pixels having the mode Max in the first histogram of FIG. 3 is defined as an area of the crystal plate 2 and the second histogram is calculated based on the mode Max. Creating. However, the above-described processing may be performed by using the average value of the luminance that is the area of the crystal plate 2 instead of the mode Max. After the second histogram is created and the threshold values M1 and M2 are set on the second histogram, the brightness of the defective area exceeding the threshold values M1 and M2 is set on the second histogram. The quality of the crystal plate 2 may be determined by counting the number of pixels. That is, the setting of the threshold values M1 and M2, the counting of the number of pixels, and the determination of pass / fail may be performed based on the second histogram.

--- (Second Embodiment) In the first embodiment, the setting of the contrast and brightness parameters relating to the luminance is changed again by the image processing section 6C, and then the CCD camera 4 operates again. The crystal plate 2 is photographed. On the other hand, if a memory is provided in front of the A / D converter 6A in the processing device 6 for storing an image of the crystal plate 2 captured by the CCD camera 4 almost as it is, the crystal plate 2 Need only be taken once. That is, in this case, first CC
The image data of the crystal plate 2 captured by the D camera 4 is stored in a memory, converted into a digital signal by an A / D converter 6A, captured by a capture unit 6B, and a digital signal relating to the crystal plate 2 is stored. Next, based on the image data read from the capturing unit 6B, the image processing unit 6C
The first histogram shown in FIG. 3 is created. next,
The image processing unit 6C determines that the luminance of the minimum luminance S becomes 0 in the first histogram shown in FIG.
The setting of the contrast and brightness parameters relating to the luminance is changed so that the luminance of 255 becomes 255. After that, the image data stored in the memory is again transferred to the A / D converter 6.
An analog signal is converted into a digital signal by A, and the digital signal is captured by the capturing unit 6B. The image processing unit 6C reads the image data captured by the capturing unit 6B, and the image processing unit 6C creates the second histogram shown in FIG. I do.

Thereafter, as in the first embodiment, the threshold setting unit 6 in the second histogram of FIG.
D sets threshold values M1 and M2, and then sets the threshold value M based on the image data captured by the capture unit 6B.
At 1, M2, the determination unit 6E determines whether the crystal plate 2 is damaged or not and whether it is stained. The result of the determination by the determination unit 6E is displayed on the display unit 6F. In the second embodiment, since a memory for storing image data is provided before the A / D converter 6A, C
The photographing of the crystal plate 2 by the CD camera 4 need only be performed once. In the second embodiment, as in the first embodiment, the quality of the quartz plate 2 can be accurately determined. In the second embodiment, the photographing of the quartz plate 2 needs to be performed only once, so that the time required to determine the quality of the quartz plate 2 can be reduced as compared with the first embodiment. In each of the above embodiments, the gradation number of the luminance in the first histogram and the gradation number of the luminance in the second histogram are the same, but the gradation number of the luminance in the second histogram is changed to the luminance number in the first histogram. May be different from the number of gradations. In short, it is only necessary that the change in the number of pixels according to the difference in luminance can be grasped more accurately when the second histogram is created, that is, the second histogram is compared with the first histogram.
The luminance per gradation in the histogram may be reduced. Further, according to each of the above-described embodiments, it is also possible to inspect the surface of the quartz plate 2 for cracks, chips, coat deviations, and the like. Further, in each of the above-described embodiments, the case where the present invention is applied to the surface inspection apparatus for the quartz plate 2 is described. However, the presence or absence of a scratch or a cavity inside the quartz plate 2 is inspected using transmitted light in addition to reflected light. It may be used for inspection. Further, the present invention can be used not only as a quartz plate but also as a surface inspection device for glass, metal, mirror, and the like.

[0017]

As described above, according to the present invention, there is obtained an effect that the quality of an article can be more accurately determined as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

FIG. 2 is a plan view showing a quartz plate.

FIG. 3 is a view showing a first histogram created by an image processing unit 6C shown in FIG. 1;

FIG. 4 is a diagram showing a distinction between good and defective products displayed on a histogram.

FIG. 5 is a diagram showing a second histogram.

FIG. 6 is an image image of the quartz plate 2 corresponding to the first histogram.

FIG. 7 is an image image of the quartz plate 2 corresponding to a second histogram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Article inspection apparatus 2 ... Quartz plate (article) 4 ... CCD camera (photographing means) 5 ... Light source 6 ... Processing apparatus 6D ... Threshold value setting part

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G051 AA90 AB02 CA04 CB01 DA08 EA11 EA16 EB01 EC02 EC03 5B057 AA01 BA02 DA03 DB02 DB09 DC23 DC36 5C082 AA01 AA11 AA27 BA16 BA35 CB05 MM01 MM10

Claims (4)

[Claims] An object to be inspected is photographed by photographing means, and the number of pixels corresponding to a difference in luminance at a predetermined number of gradations from a minimum luminance to a maximum luminance based on an image of the article photographed by the photographing means. The first histogram represented by the following formula is created, and the minimum luminance and the maximum luminance before and after the luminance that is the mode or the average value of the article area in the first histogram are obtained, and the range from the minimum luminance to the maximum luminance is obtained. Creates a second histogram represented by the number of pixels according to the difference in luminance with the luminance of the predetermined number of gradations, and sets a threshold based on the change in the number of pixels according to the difference in luminance in the second histogram. And determining whether the article is good or bad based on the threshold value. 2. After obtaining the minimum luminance and the maximum luminance in the first histogram, the luminance in a range from the minimum luminance to the maximum luminance can be recognized as a difference in luminance of the predetermined gradation. 2. The method according to claim 1, further comprising: photographing the article again by the photographing means; and generating the second histogram represented by the number of pixels corresponding to a difference in luminance based on the image of the article photographed by the photographing means. 2. The article inspection method according to 1. 3. A method according to claim 2, wherein a specific luminance is set as a threshold based on a change in the number of pixels according to a difference in luminance in the second histogram, and the number of pixels according to the luminance of the defective area exceeding the threshold 3. The article inspection method according to claim 1, wherein the quality of the article is determined based on the number of pixels. 4. The article inspection method according to claim 1, wherein the article to be inspected is a quartz plate or a glass product.