JPH11344449A - Appearance inspecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and rapidly inspect the appearance of an inspection object. SOLUTION: A method for inspecting only a specific area to which predetermined processing is applied of an object to be inspected has step S1 taking the image of the object to be inspected before processing to store the same, step 2 taking the image of the object to be inspected after processing, step 3 forming a difference image by subtracting one of the taken image after processing and the stored image before processing from the other one of them, and step S5 judging whether processing is proper on the basis of the image of the specific area in the difference image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an appearance inspection method for inspecting an object to be inspected, in particular, a printed circuit board.

[0002]

2. Description of the Related Art Conventionally, in order to inspect the appearance of an inspection object such as a printed circuit board, the inspection object is imaged by a camera, the obtained image is binarized, and the area of a high-luminance area is calculated. Thus, the judgment was made based on the size of the area. In addition, when it is desired to inspect only a portion where the cream solder is printed on the printed circuit board, an area having a luminance value specific to the cream solder is extracted by, for example, ternarization, and its area is calculated. It is judged by.

[0003]

However, in the above-described conventional visual inspection method, all regions satisfying a certain range of luminance conditions are extracted as inspection target regions and their areas are calculated. However, there is an inconvenience that the determination is performed even in an area that is not the inspection target area. For example, even when it is desired to inspect only the cream solder area, the luminance of the silk-printed part, the copper foil part, the pattern part of the board, and the like, which may be similar to the luminance of the cream solder, may be the inspection target area. It is quite possible that it is extracted as

[0004] In such a case, not only erroneous pass / fail judgment is performed, but also unnecessary calculation and judgment processing are performed, so that the time required for judgment becomes longer. On the other hand, it is conceivable that a worker manually removes these areas that are not actually the inspection target areas while looking at the monitor, and inspects only the true inspection target areas. Obviously it takes time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and accurately and quickly extracts only a place where a test object such as a printed circuit board is to be inspected, thereby achieving a highly accurate appearance inspection. It is an object of the present invention to provide a visual inspection method capable of performing the following.

[0006]

In order to achieve the above object, the present invention provides a method for inspecting only a specific area in which a predetermined process has been performed on an object to be inspected. Imaging the object and storing the image; capturing the processed inspection object; subtracting one of the captured processed image and the stored unprocessed image from the other to obtain a difference. There is proposed an appearance inspection method including a step of generating an image and a step of determining whether or not processing is appropriate based on an image of a specific region appearing in the difference image.

In the above-described visual inspection method, the step of determining whether or not the processing is appropriate includes the step of setting a pixel value having an absolute value equal to or less than a predetermined value to a zero value in the generated difference image. It is effective.

[0008]

According to the appearance inspection method of the present invention, the difference image is generated by subtracting the images before and after the processing, so that only the different part before and after the processing, that is, only the processed area is reliably extracted. Is done. As a result, even if there is a non-processed area having a luminance close to the luminance of the processed specific area, such an area is deleted from the difference image and excluded from the inspection target.

Further, by setting the value of a pixel having an absolute value equal to or less than a predetermined value in the difference image to a zero value, an error included in both images due to a change in imaging conditions such as a change in illumination can be eliminated. It is possible to more reliably exclude only the processed specific area and to determine whether the processing is appropriate.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the appearance inspection method according to the present invention will be described below with reference to FIG.
The appearance inspection method according to the present embodiment is a method of extracting and inspecting only a copper foil portion on which a cream solder is printed, as an inspection region, from among the copper foil portions of the printed circuit board, and as shown in FIG. It includes a first imaging step S1, a second imaging step S2, a difference image generation step S3, an unnecessary pixel removal step S4, and a determination step S5.

The first imaging step S1 includes a step S11 of imaging a printed circuit board (bare board) before printing the cream solder, and a storing step of storing the captured image of the bare board in a memory (not shown). S12
Is provided. The second imaging step S2 captures an image of the printed circuit board after printing the cream solder.

The difference image generating step S3 includes the step of
The difference image between the two images is generated by subtracting the image of the bare board stored in the storing step S12 from the image of the printed circuit board after printing the cream solder obtained in the imaging step S2. For example, under ideal conditions such as the same lighting conditions, it is estimated that in the images before and after the cream solder printing process is performed, the region where the pixel value is different is only the specific region where the cream solder is printed. be able to. Therefore, only the specific region is extracted from the difference image obtained by subtracting the corresponding pixels between the two images.

The unnecessary pixel removing step S4 is performed for the purpose of removing any error from the image to be determined when the difference image obtained in the difference image generating step S3 contains any error. It is.
For example, if the first and second imaging steps S1 and S2 are not performed under the ideal conditions described above, that is, the luminance of the pixel that should be originally obtained as the same luminance differs due to a change in the illumination condition or the like. In the case where the image is captured as a pixel having, the difference image shows the luminance corresponding to the variation of the illumination. This luminance value is, for example, the first
If the illumination in the imaging step S1 is brighter, the value is a negative value, and if the illumination is opposite, the value is a positive value.
Its absolute value is small. Therefore, by setting a certain threshold value and setting pixels having a value equal to or less than the threshold value to zero, these unnecessary pixels can be removed from the inspection target.

In the determination step S5, for example, the difference image is obtained in the difference image generation step S4.
The error has been removed in the unnecessary pixel removal step S4,
The area of the image corresponding to the specific area is calculated. Thereafter, the calculated area is compared with, for example, a set value set in advance, and if they are equal, it is determined that the cream solder printing process is appropriate, and the area is too large or too small with respect to the set value. If so, it is determined that the processing is inappropriate.

In this case, according to the appearance inspection method according to the present embodiment, a difference image is generated from images before and after a process such as cream solder printing, and only a specific region subjected to the process is reliably extracted. By doing so, the inspection is performed, so that the inconvenience of processing an area other than the specific area as an inspection target is avoided, and an effect that an accurate and quick inspection can be performed is achieved.

In this embodiment, a printed circuit board is assumed as an inspection object, and cream solder printing processing is assumed as a processing. Alternatively, any other inspection object and processing, such as a component, may be used. The inspection may be performed by a missing item inspection device that detects and inspects the presence of a defect, a defect inspection device that inspects a defect, and an inspection device that aims to find contamination.

In the difference image generating step S3, the difference image is generated by subtracting the image before the processing from the image after the cream solder printing processing. Conversely, the difference image is generated from the image before the processing. A difference image may be generated by subtracting a subsequent image.

[0018]

As described above in detail, according to the appearance inspection method of the present invention, the difference image is generated by subtracting the image before and after the processing, so that only the processed area can be reliably detected. Can be extracted. As a result, even if there is a non-processed area having a luminance close to the luminance of the specific area where the processing has been performed, the appearance inspection is performed in a state where such an area is excluded from the inspection target, so that accurate and quick inspection is performed. Is achieved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing one embodiment of a visual inspection method according to the present invention.

[Explanation of symbols]

 S1, S2 imaging step S3 difference image generation step S4 unnecessary pixel removal step S5 determination step

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshiaki Sato 1-1-1 Fukuura, Kanazawa-ku, Yokohama, Kanagawa

Claims (2)

[Claims] 1. A method for inspecting only a specific area in which a predetermined process has been performed on an inspection object, the method comprising: capturing an inspection object before processing and storing an image thereof; Imaging a test object; subtracting one of the captured image after processing and the stored image before processing from the other to generate a difference image; and an image of a specific region appearing in the difference image Determining the suitability of the processing based on the visual inspection method. 2. The step of judging whether the processing is appropriate or not,
2. The visual inspection method according to claim 1, further comprising: setting a value of a pixel having an absolute value equal to or smaller than a predetermined value to a zero value in the generated difference image.