JPH08247960A - Visual inspection device - Google Patents

Abstract

PURPOSE: To enable highly accurate inspection by performing a judgment of whether pixel signals at image pickup points of a subject are within a proper range or not based on a reference value and an adjusting value determined for each of pixel signals of an acceptable product. CONSTITUTION: A plurality of acceptable products identical to work of a subject are photographed previously. Upper and lower limit master images corresponding to reference values determined for each of pixel signals at image pickup points are calculated to set 3 and 4. Likewise, upper and lower adjusting values are set 5 and 6. Then, the pixel signals of an image signal obtained by photographing the work are inputted into a comparator 2 to judge whether the pixel signals are within a proper range between the image 3 + the adjusting value 5 and the image 4 - the adjusting value 6 per pixel for each of color surfaces of three colors, red, green and black. Based on the results of the judgment, when the pixel signals are outside the range in any or all of the three colors surfaces or in any surface in the combination of the two colors, a density mode judging device 7 determines a product to be a rejected. An area mode judging device 8 performs a judgment of area for the rejected product and when the area is determined to be smaller, the product is accepted. Thus, rejection is decided finally thereby enabling highly accurate inspection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a visual inspection apparatus.

[0002]

2. Description of the Related Art In printed circuit boards and the like, scratches on gold-plated parts, discoloration, swelling of solder, copper appearance on solder surface,
There may be problems such as solder squeezing out, chipping of solder pad, defective resist, defective silk printing, foreign matter adhesion, short circuit of printed wiring, wiring break, chipped printed wiring board, mixing of different printed boards. In the past, these inspections were mainly conducted by visual sensory tests. However, visual inspection has variations due to inspectors,
Since there is a problem with inspection accuracy, various mechanical inspections using image signals have been attempted.

[0003]

However, in the case of mechanically inspecting based on an image signal, when a printed circuit board is a measurement object, a so-called erroneous report is generated, which is determined to be a defective product although it is a good product. There was a problem that there was a problem that sufficient inspection accuracy could not be obtained. This false alarm is caused by a difference in color of each printed circuit board, a positional shift of the circuit pattern, a variation in the width of the circuit pattern, and the like. There was a problem that it was simply judged as a defective product. The present invention aims to solve the above-mentioned problems of the prior art.

[0004]

In order to achieve the above object, the appearance inspection apparatus of the present invention takes an image of an object to be inspected and outputs a plurality of pixel signals at a plurality of imaging points covering the object to be inspected. A means for outputting an image signal having, and a reference value determined for each of the image pickup points based on a plurality of pixel signals at the same image pickup point obtained by picking up an image of a plurality of standard products that are the same as the object to be inspected. Based on the similarly determined tolerance and
Means for determining a proper range of the pixel signal at each of the imaging points, and means for determining whether or not each pixel of the image signal from the means for outputting the image signal is within the determined proper range, It is characterized by having. As the means for outputting the image signal, an image pickup device using a CCD or the like can be used, and it is desirable to use one capable of color imaging. The obtained image signal is judged by the means for judging whether each image signal is within the proper range. This proper range is determined by means for determining the proper range. The means for determining the appropriate range determines the appropriate range based on the reference value and the allowable value. The reference value and the permissible value are determined by using the same plurality of standard products as the object to be inspected. For this standard product, for example, a good product may be used. An average value of pixel signals of a plurality of standard image signals at the same imaging point (the same point) can be used as a reference value.
This average value means not only a simple average but also an average value obtained by removing the maximum value and the minimum value. It is also possible to adopt median, mode, etc. instead of the average value. As the allowable value, it is desirable to use the degree of dispersion such as dispersion of a plurality of pixel signals at the same point. A standard deviation or the like may be used in addition to the variance. By using such a dispersion degree as the allowable value, it is possible to compensate for the color difference depending on the inspection object. Further, as the allowable value, the upper limit value and the lower limit value in the vicinity of 8 of the pixel can be used. By using the upper limit value and the lower limit value in the vicinity of 8, it is possible to compensate for the positional deviation of the circuit and the difference in the pattern width in the circuit pattern inspection or the like. Further, the dispersion value and the upper limit value in the vicinity of 8 and the dispersion value and the lower limit value are appropriately scaled and then compared, and for example, a larger value is selected based on the comparison result, and the average value is set as the allowable value. It is desirable to set the range by adjusting it from the above. When the image signal includes a color signal, the reference value and the allowable value are determined for each color by the means for determining the proper range, and are determined for each color by the determination means. It is also possible to further include means for judging whether the object to be inspected is acceptable or not based on the judgment made by the judging means for each pixel. For example, the image signal includes a color signal, and in the means for determining the proper range, the reference value and the allowable value are determined for each color, and further the determination means makes a determination for each pixel for each color. In this case, it is possible to judge the pass / fail of the inspected object based on the judgment for each color. It is desirable that the result of the judgment made by the judging means be displayed by the display means for each arbitrary range. The inspection apparatus of the present invention can be used for inspection of various objects, but is most effective when used for appearance inspection of a printed circuit board.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a visual inspection apparatus for a printed circuit board will be described below with reference to the drawings. FIG. 1 is an external view of the appearance inspection apparatus, in which a work W, which is a printed circuit board placed on an imaging table 20, is attached to a CCD camera 1.
The inspection is carried out by taking a picture of the image and analyzing the image signal. The work W is conveyed by the conveyer 21, placed on the imaging table 20, and again conveyed by the conveyer 22 when the photographing is completed. In the imaging table 20, the work W is positioned exactly, and is positioned at the same position as a non-defective product which is previously imaged in order to set the reference value and the allowable value.

The image signal of the work W taken by the CCD camera 1 is sent to the comparator 2 as shown in FIG. In the comparator 2, each pixel signal of the image signal is individually compared with each pixel signal of the upper limit master image and the lower limit master image, and it is determined for each pixel whether or not it is within the range of the upper limit master image and the lower limit master image. It is like this. That is, in the comparator 2,

[Equation 1] Is being made. Here, baseU (x, y): upper limit master image baseL (x, y): lower limit master image target (x, y): work W image permitU (x, y): upper limit adjustment value permitL (x, y): Lower limit adjustment value x, y: Pixel position coordinate

The upper limit master image setting device 3 and the lower limit master image setting device 4 are constructed so that the upper limit master image and the lower limit master image are determined as follows. Now, the same good printed circuit board as the work W is k1,
k2 and --kn, and these printed circuit boards are CC
Image is taken by the D camera 1, an image signal is obtained, baseU and baseL are calculated according to the following formulas, and the upper limit master image and the lower limit master image are set in the upper limit master image setting device 3 and the lower limit master image setting device 4. I am supposed to keep it.

[Equation 2]

(Equation 3) Here, the left term on the right side is the average value of the pixels at the same point (the same image pickup point) in each non-defective product, and this is the reference value. The average value may be a simple average, but it is desirable to use an average value from which the maximum value and the minimum value are removed. Alternatively, the median or mode may be used. In addition, it can be used as a non-defective product by replacing the non-defective printed circuit board with a defective printed circuit board by a drawing function.

MAX (A, B) and MAX (A, C)
Is an allowable value added to the above reference value, A is a standard deviation, B is an upper limit value in the vicinity of 8 and C is a lower limit value in the vicinity of 8. A is defined as follows.

[Equation 4] Here, σ is a standard deviation, and a is an integer. In this embodiment, arbitrary values of a = 1, 2, 3, --- are appropriately used. Due to this A, it is possible to compensate for the color difference at the same position due to the work W, and it is possible to prevent erroneous notification due to the color difference for each printed circuit board.

Next, B and C are defined as follows.

(Equation 5) Here, as in the case of a, any value of b = 1, 2, 3, --- is appropriately used for b. P is the value of each pixel signal as shown in FIG. 3, and the maximum value of the values in the 8 neighborhoods centering on P 5 is replaced with the value of P 5, and this is made the upper limit of the 8 neighborhoods. Similarly, the minimum value among the values in the eight neighborhoods is replaced with the value of P5, and this is set as the lower limit value in the eight neighborhoods. This process is executed for all pixels. By adding the upper limit value and the lower limit value in the vicinity of 8 as described above, it becomes possible to compensate for the deviation of the edge portion of the circuit pattern on the printed circuit board, the difference in the pattern width, and the like. As shown in FIG. 4, assuming that the pixel signal of the circuit pattern portion is represented by ff (hexadecimal), if the minimum value and the maximum value near 8 are replaced with the original value of (A), ( As shown in B) and (C).
Here, paying attention to the columns of and, when replaced with the minimum value, the ff portion becomes small and the circuit pattern becomes thin. On the other hand, when the value is replaced with the maximum value, the ff portion increases and the circuit pattern becomes thick. By adding the correction term based on 8 neighborhoods in this way, it becomes possible to absorb the deviation of the edge portion of the circuit pattern of the substrate and the difference of the pattern width.

Next, permitU (x, y) and permitL (x, y) in the equation 1 are permissible values that can be arbitrarily designated by the user, and by this setting, the pass / fail criteria can be tightened or loosened. It has become. In addition, it is possible to absorb this when a specific point has specificity. In the embodiment of FIG. 2, the upper limit adjusting device 5 and the lower limit adjusting device 6 are configured so that the user can adjust them.

In the above formula 2, A and B are compared and the larger A or B is defined as MAX (A, B), and this is added to the average value. In the above formula 3, A and C are compared and the larger A or C is MA.
X (A, C) is set, and this is subtracted from the average value. When calculating the above A, B, and C, the values of a = 1, 2, 3, ---, b = 1, 2, 3, --- are appropriately adjusted as described above.

The judgment according to the above-mentioned formula 1 is carried out for each color plane of RGB in the comparator 2, and the judgment result is sent to the density mode judgment device 7. In the density mode determination device 7, for example, the pass / fail of the printed circuit board to be inspected is determined based on the following determination criteria. 3OR: If any of the R, G, and B surfaces has a rejected pixel of Formula 1, it is determined as a defective product. 3AND: If all the R, G, and B planes have rejected pixels of Formula 1, it is determined as a defective product. 2AND: Combination of R and G, G and B, B and R,
If there is a rejected pixel of Formula 1 on any surface, it is determined as a defective product.

The area mode determination device 8 further performs area determination on the printed circuit board which has been determined to be defective according to the above-mentioned criteria, thereby finally determining the defective product. That is, even if the density mode determination device 7 determines that the defect is present, it can be passed if the area of the defect is small. When determining the area, a method of dividing the image into a grid and determining the area within the grid can be adopted.

The result of the judgment made by the area mode judging device 8 that the product is defective or non-defective is displayed on the display device 9. In this embodiment, as shown in FIG. 5, it is possible to display in which part of the arbitrarily delimited area the pixel that does not satisfy the expression 1 is displayed.

In the embodiment described above, the printed circuit board is photographed by the CCD camera 1 and it is determined whether or not all the pixels belong to the proper range determined based on the non-defective product, so that the accuracy is extremely high. High-quality inspection can be performed.
Moreover, the appropriate range is determined based on the value statistically processed with the non-defective product as a reference, and the allowable value is added by the 8-neighbor processing, so that the color difference due to the substrate, the positional deviation of the circuit pattern, the width difference, etc. Can be absorbed. Further, since this is based on a non-defective product by a sensory test, it will simulate the judgment standard of a skilled inspector, and an extremely highly accurate inspection with few false alarms can be realized.

[0016]

As described above, according to the appearance inspection apparatus of the present invention, there is an effect that the inspection can be performed with high accuracy and less false alarm.

[Brief description of drawings]

FIG. 1 is an external elevation view showing an embodiment of the present invention.

FIG. 2 is a functional block diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram of the vicinity of 8 in one embodiment of the present invention.

FIG. 4 is an explanatory diagram of 8-neighborhood processing according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram of a display example according to an embodiment of the present invention.

[Explanation of symbols]

1: CCD camera, 2: comparator, 3: upper limit master image setting device, 4: lower limit master image setting device, 5: upper limit adjusting device, 6: lower limit adjusting device, 7: density mode determination device,
8: Area mode determination device, 9: Display device, 20: Imaging table, 21: Conveyor, 22: Conveyor.

Claims (10)

[Claims] 1. A means for picking up an image of an object to be inspected and outputting an image signal having a plurality of pixel signals at a plurality of imaging points covering the object to be inspected, and a plurality of standard products identical to the object to be inspected. Based on a reference value determined for each of the imaging points based on a plurality of pixel signals at the same imaging point obtained by imaging, and a similarly determined allowable value, the pixel signal of each of the imaging points A unit for determining an appropriate range, and a unit for determining whether or not each pixel of the image signal from the unit for outputting the image signal is within the determined appropriate range. Appearance inspection device. 2. The appearance inspection apparatus according to claim 1, wherein the reference value is an average value of a plurality of pixel signals at the same imaging point. 3. The appearance inspection apparatus according to claim 1, wherein the allowable value is a value determined based on a scatter degree of a plurality of pixel signals at the same imaging point. 4. The appearance inspection apparatus according to claim 1, wherein the allowable value is an upper limit value and a lower limit value in the vicinity of 8 of individual pixel signals at the same imaging point. 5. The allowable value is compared with a value determined on the basis of the degree of dispersion of a plurality of pixel signals at the same imaging point and an upper limit value in the vicinity of 8 of individual pixel signals at the same imaging point. , One of the dispersion values or upper limit values selected by the comparison result and a value determined based on the dispersion value and the lower limit value are compared, and the dispersion value or the lower limit value selected by the comparison result is compared. The visual inspection apparatus according to claim 1, wherein one of the values is set as the allowable value. 6. The image signal includes a color signal, the reference value and the allowable value are determined for each color in the means for determining the proper range, and are determined for each color in the determination means. Item 1. The visual inspection device according to 1 or 2 or 3 or 4 or 5. 7. The appearance inspection apparatus according to claim 1, further comprising means for determining whether the object to be inspected is acceptable or not based on the determination of each pixel by the determination means. 8. The image signal includes a color signal, and in the means for determining the proper range, the reference value and the allowable value are determined for each color, and the determination means makes a determination for each pixel for each color. The appearance inspection apparatus according to claim 1, further comprising means for determining whether the object to be inspected is acceptable based on the determination for each color. 9. The object to be inspected is a printed circuit board, 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8.
Appearance inspection device described in. 10. The judgment result by the judgment means is
The visual inspection apparatus according to claim 1, further comprising display means for displaying each arbitrary range.