JPH0587782B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention [Industrial Application Field] The present invention relates to an apparatus for inspecting defects such as surface morphology of an object.

[Prior Art] Conventionally, the presence or absence of irregularities on the surface of an object has been inspected by an inspector based on visual or tactile sense. This visual or tactile inspection by the inspector is likely to be influenced by the inspector's subjectivity or level of skill, and there are problems with the uniformity of the inspection, as well as the fact that the inspection requires a lot of effort and time, resulting in a decrease in efficiency. It was hot. To solve these problems, for example, the ``Method for Inspecting Surface Defects of Objects'' disclosed in JP-A No. 52-90988 and JP-A No. 52-90988,
Inventions and proposals have been made, such as the "Surface Inspection Apparatus" shown in No. 71289 and the "Surface Texture Measuring Method and Apparatus" shown in Japanese Patent Application Laid-open No. 58-97608.
These inventions and proposals project striped bright and dark patterns, etc. on the surface of the object being inspected, and if there are defects such as unevenness on the object surface, the projected stripes, etc. may become distorted or distorted.
The disturbance is used to inspect the surface of an object for defects.

[Problems to be Solved by the Invention] The above-mentioned inventions and proposals can determine the presence or absence of defects on the surface of an object by the distortion and disturbance of the striped pattern projected on the surface of the object to be inspected, and improve the uniformity of the inspection. Although it has the excellent effect of improving work efficiency and improving work efficiency, it still has the following problems.

(a) In other words, in the above-mentioned inventions and proposals, the presence or absence of defects on the surface of an object is determined by the inspector determining the degree of distortion and disturbance such as striped patterns.
There was still a problem with the lack of uniformity in test results.

(b) Also, as in the invention disclosed in JP-A No. 58-97608, the rectangular wave pattern reflected from the surface to be measured is projected and imaged onto the imaging plane by an imaging optical system, and the image is formed. Some proposals have been made to quantify and detect the surface texture of the surface to be measured by Fourier transforming the spatial light intensity distribution on the surface, but this requires complicated operations and is difficult to detect defects on the surface of the object. Problems that could be considered were that the presence or absence could not be detected automatically, or that the device would be quite complex.

Due to the above-mentioned problems, labor-saving inspection for defects on the surface of objects and unmanned inspection using robots and the like are hindered.

The surface defect inspection device of the present invention was made to solve the above problems, and its purpose is to objectively, quantitatively, and automatically inspect the presence or absence of defects on the surface of an object.

Configuration of the Invention [Means for Solving the Problems] The surface defect inspection apparatus of the present invention is configured as follows. That is, as the basic configuration is illustrated in FIG. 1, the surface defect inspection apparatus of the present invention includes: a bright and dark pattern projection means M1 that projects a predetermined bright and dark striped pattern on the surface to be inspected; an imaging means M2 that scans an image of the bright and dark striped pattern projected on the surface to be inspected in a direction intersecting the striped pattern and images it as a light intensity level signal; and the level signal imaged by the imaging means M2. a change detection means M3 for differentiating the change signal to obtain a level change signal; and a defect detecting means M3 for extracting irregular portions of the change signal as defects on the surface to be inspected by comparing the change signal with a predetermined reference value. It is configured to include: a portion extracting means M4;

The change degree detection means M3 may be any means that differentiates the intensity level signal of the light imaged by the image pickup means M2 and generates a level change signal, and may be a so-called CR differentiation circuit using a capacitor and a resistor. It can be configured as a discrete circuit, or it can be configured to first convert the intensity level signal of the imaged light into a digital image signal, and then differentiate the converted digital image signal using a logical operation circuit using a microcomputer or the like. It is possible to do so.

[Function] The surface defect inspection apparatus of the present invention having the above configuration functions as follows.

The surface defect inspection apparatus of the present invention scans an image of a light and dark striped pattern projected on the surface to be inspected by the light and dark pattern projection means M1 in a direction intersecting the striped pattern using the imaging means M2, and captures the image as a light intensity level signal. Then, the intensity level signal of the imaged light is differentiated by the change degree detection means M3 to obtain a level change degree signal, and then the said change degree signal is compared with a predetermined reference value using the defect extraction means M4. This serves to extract irregular portions of the change rate signal as defects on the surface to be inspected.

Generally, when an image of a bright and dark striped pattern projected on the surface to be inspected is detected as a light intensity level signal by the imaging means M2, the signal is a signal that repeats a high level in bright areas and a low level in dark areas at regular intervals. By differentiating the light intensity level signal from this imaging means using the change degree detection means M3, it is possible to detect areas where the degree of change in the level signal is large, in other words, the boundary between the high level in bright areas and the low level in dark areas. It can be detected separately from the level part of . on the other hand,
If there is a defect such as unevenness on the surface to be inspected, the level of the defect that is distorted or disturbed by this defect is a so-called intermediate level signal that does not belong to either the high level of the bright area or the low level of the dark area. A variation signal obtained by differentiating this portion is detected as a signal that does not have a boundary between the high level of the bright portion and the low level of the dark portion. Defect extraction means are
By comparing the degree of change signal with a predetermined reference value, a portion that does not have this boundary, that is, an irregular portion of the degree of change signal, is extracted as a defective portion. Note that even if the intensity level of light in a defective part is not detected as an intermediate level, a part that does not have a boundary between a high level in a bright part and a low level in a dark part can be detected as a defective part. The present invention aims to provide an apparatus that detects surface defects by applying this phenomenon.

[Example] Next, a preferred example will be described with reference to the drawings in order to further clarify the structure of the surface defect inspection apparatus of the present invention.

FIG. 2 is a block diagram showing the configuration of a surface defect inspection apparatus according to an embodiment of the present invention.

The surface defect inspection device of this embodiment mainly includes a striped pattern projection device 1 as a bright and dark pattern projection means for projecting a bright and dark striped pattern onto the surface of the object to be inspected OB to be inspected for the presence or absence of defects such as irregularities. , an imaging device 2 serving as an imaging means for photographing a virtual image of a striped pattern projected on the surface of the object to be inspected OB and outputting a light intensity level signal;
, a change degree detection circuit 3 as change degree detection means for differentiating the intensity level signal of light outputted by the imaging device 2 to obtain a level change degree signal, and a change degree detection circuit 3
A defect extracting circuit 4 as a defect extracting means for extracting a defect on the surface of the object to be inspected OB by comparing a level change signal outputted by a predetermined reference value with a predetermined reference value.
It is composed of and.

The striped pattern projection device 1 is composed of a flat plate 10 having a large number of equally spaced slits and a light source 11 that emits scattered light. The distance between both bright and dark areas is 1.5mm). In this embodiment, the object to be inspected OB is a shiny iron plate, and the striped pattern is projected as a virtual image.

The imaging device 2 includes an imaging tube (hereinafter simply referred to as a TV camera) 20 that photographs a striped pattern appearing on the surface of the object to be inspected OB.

The degree of change detection circuit 3 includes a distributor 30 and a differentiation circuit 3.
1, an absolute value circuit 32, and the like.

The defect extraction circuit 4 is a low pass filter circuit 4
0, comparator 41, mixer 42, image contraction circuit 43
, a defective part determination circuit 44, and the like.

In addition, CRT display DP1 has TV camera 20.
It displays the striped pattern photographed by
The CRT display DP2 displays the image signal (video signal) output from the mixer 42. CRT display DP3 has image contraction circuit 43
This is to display the video signal output from. In addition, the image shrinkage circuit 43 of the defect extraction circuit 4
As shown in FIG.
2, etc., and an external input circuit 53 and an external output circuit 54 are interconnected by a bus 55 to form an integral structure as a logic operation circuit.

Next, the operation of the surface defect inspection apparatus of this embodiment will be explained using the timing chart shown in FIG. 4 as appropriate.

A virtual image of the striped pattern projected onto the object to be inspected OB by the striped pattern projection device 1 is converted into a video signal VD1 (video signal VD1 in the timing chart in FIG. 4) by the TV camera 20 and sent to the distributor of the change degree detection circuit 3. 30. Also, this video signal
VD1 is also output to CRT display DP1,
Images taken by the TV camera 20 are reproduced on the screen of the CRT display DP1. When the surface of the object to be inspected OB is smooth, the video signal VD1 outputted from the TV camera 20 is a sinusoidal signal that has regular high levels in bright areas and low levels in dark areas, which are inherent in the striped pattern. However, when there are defects such as unevenness, the striped pattern is distorted and disturbed by the defect, resulting in a so-called intermediate level signal that does not belong to either the high level of the bright area or the low level of the dark area. (Figure 4 timing chart video signal
VD1 section bad). The intermediate level portion bad, which is distorted and disturbed by this defective portion, can also be observed on the screen of the CRT display DP1, as illustrated pictorially in FIG. Note that the video signal VD1 from the TV camera 20 is a video signal obtained by scanning orthogonal to the striped pattern on the object to be inspected OB. Therefore, the timing chart shown in FIG. 4 uses time t as a parameter.

Here, the video signal VD1 input to the distributor 30 of the change degree detection circuit 3 is the video signal of the image.
VD2 and synchronization signal SS (Fig. 4 Timing chart) Video signal VD2, synchronization signal SS
SS). Since the video signal VD2 of the video signal VD1 has a positive level and the synchronization signal SS has a negative level,
The distributor 30 can be easily configured using a rectifier or the like.

The video signal VD2 output from the distributor 30 is
It is input to the differentiation circuit 31.

The differentiating circuit 31, which is composed of a capacitor, a resistor, etc., detects the boundary between the high level in the bright part of the sinusoidal video signal VD2 and the low level in the dark part, or the boundary part between the low level in the dark part and the high level in the bright part. is detected as a sudden fall or rise of the signal (Figure 4 timing chart change degree signal DD1). That is, the differential circuit 3
1 is a video signal as a light intensity level signal
It detects parts where the degree of change in the VD2 level is large. Here, in the intermediate level portion bad that is distorted and disturbed by the defective portion, no portion with a large level change is detected. Therefore, the intermediate level part bad indicating the defective part is output as a zero level, similar to the bright and dark parts of the striped pattern (the fourth
Fig. Timing chart Change degree signal DD1 section
bad).

The change degree signal DD1 output from the differentiating circuit 31 is
It is input to the absolute value circuit 32. Negative level signals such as dark portions of the change degree signal DD1 inputted to the absolute value circuit 32 are converted into positive level signals (change degree signal DD2 in the timing chart of FIG. 4).
In other words, the change degree signal DD1 input to the absolute value circuit 32 is a change degree signal that has been full-wave rectified here.
It becomes DD2.

Change degree signal output from absolute value circuit 32
DD2 is input as is to the positive side of the comparator 41 of the defect extraction circuit 4, and is also input to the negative side of the comparator 41 via the low-pass filter circuit 40 of the defect extraction circuit 4. .

The low-pass filter circuit 40 is configured as a so-called integrating circuit, and receives the input change degree signal DD2.
A floating threshold signal SL is created based on (Figure 4 timing chart floating threshold signal SL). As shown in the timing chart of FIG. 4, this floating threshold signal SL is a signal that is smaller than the rising signal of the change degree signal DD2 and larger than the zero level.

The comparator 41, which uses the floating threshold signal SL as a reference value for comparison, sets the border between the bright and dark parts of the striped pattern to a high level, and sets the other parts to a low level.
The video signal VD3 of the value signal is output to the mixer 42 (Fig. 4 timing chart video signal
VD3).

The video signal VD3 is input to the mixer 42,
The mixer 42 also receives the synchronizing signal SS separated by the above-mentioned distributor 30 in order to output the video to the CRT display DP2, and receives the video signal SS.
VD3 is the video signal VD4 including the synchronization signal SS (Figure 4 timing chart video signal
VD4). The video signal VD4 containing the synchronization signal SS is
Image contraction circuit 43 configured as a logic operation circuit
is output to. Note that the video signal VD4 is also output to the CRT display DP2, and the high level signal of the video signal VD4 is displayed as a bright portion on the screen of the CRT display DP2. That is, the boundary between the bright and dark areas displayed on the above-mentioned CRT display DP1 is displayed as a bright area on the screen, and an intermediate level area indicating the bright area, dark area, and defective area is displayed on the screen.
"bad" is displayed as a dark part.

Video signal input to image contraction circuit 43
As is well known, VD4 is a signal that follows the scanning line shown in FIG. In other words, in the scanning line rn where the intermediate level part bad appears, the video signal VD4
The number of pixels in the dark area forming the striped pattern is small, and the number of pixels in the intermediate level area bad is large. As a result, when the number of pixels forming a dark area is less than a predetermined number, the image shrinking circuit 43 performs a so-called image shrinking operation in which the pixels forming a dark area become pixels of a bright area. This image shrinking operation is performed until the dark part of the striped pattern disappears (fourth
Figure Timing Chart Video Signal VD5). Here, the screen size of CRT displays DP1, DP2, and DP3 is 100 mm x 100 mm, and the horizontal and
The number of pixels in each vertical line is 512.
Therefore, the area of one pixel is approximately 0.2×0.2 mm ² .
Further, the image shrinking work is performed as follows. That is, in one scanning line, only when a predetermined number or more of pixels continue as a dark part, it is considered a dark part, and this operation is performed until the vertical stripes at predetermined intervals disappear.

The video signal VD5 from which the dark parts of the striped pattern have been removed is
The signal is output to the defective part determination circuit 44. Note that this video signal VD5 is also output to the CRT display DP3, and the intermediate level portion bad is displayed on the screen. At this time, the intermediate level portion bad is an image that has been slightly contracted by the image contraction circuit 43.

The defective portion determination circuit 44 determines the area size of the intermediate level portion bad. In this embodiment, when the size of the intermediate level part BAD is equal to or larger than the size equivalent to a circle with a diameter of about 1 mm, that is, when the number of pixels of the intermediate level part BAD is 25 or more, the intermediate level part BAD is regarded as a defective part. , outputs an NG signal.

The flowchart shown in FIG. 6 is a flowchart showing the processing of the image shrinkage circuit 43 and the defective part determination circuit 44, which are configured as logic operation circuits. Image shrinkage circuit 43 and defect determination circuit 4
Step 4 extracts the intermediate level part bad according to this "defect part extraction/judgment process" (step 100), determines the size of the area of the intermediate level part bad, and when the area is larger than a predetermined area, a defective part is present and an NG signal is sent. Output (steps 110 to 120).

According to the surface defect inspection device of this embodiment, defective parts such as irregularities on the object to be inspected OB can be accurately and automatically detected as parts that do not include the boundary between the bright and dark parts of the bright and dark striped pattern using a simple configuration. can be detected. Therefore, even if the surface coating color etc. of the inspected object OB differs each time it is inspected, since there is no boundary between the bright and dark areas of the striped pattern in the defective area, the light of the surface coating color will be different. It has the excellent effect of being able to detect defective parts regardless of strength levels.

As a result, surface inspection of objects can be performed unmanned using industrial equipment such as robots, which has the excellent effect of significantly increasing work efficiency. In addition, the intermediate level part on the object to be inspected OB
The size of bad can be quantified and compared with a quantitative value (in this example, 25 pixels or more) to determine that it is a defective area, so the inspection results are objective and extremely reliable. It also has the effect of being able to automatically obtain the information. Furthermore, defects such as irregularities can be detected as intermediate level areas (bad) where there is no boundary between bright and dark areas, so when the surface of the object to be inspected OB is curved, etc., the interval between bright and dark striped patterns can be detected. Even if the area becomes narrower, the area of the stripes that are distorted and disturbed by the defect remains constant and has the excellent effect of allowing accurate inspection results to be obtained. In addition, in this example, the interval between the bright and dark areas of the bright and dark pattern was set to 1.5 mm, but the accuracy of defect detection can be improved by making the stripe interval narrower than the size of the defect you want to detect. It also has the effect of being able to Furthermore, in this example,
Since the status of each stage of the inspection process can be viewed using three CRT displays, erroneous detection can be prevented by using this together with the output results of the defective part determination circuit 44, and the position of the defective part can be confirmed. It also has the effect of being able to.

In addition, even if the defective part on the object to be inspected OB is not detected as an intermediate level part, but is detected as the same level as the high level of the bright part or the low level of the dark part, the defective part does not have the above boundary part, so the defective part cannot be detected as an intermediate level part. It also has the effect of being able to detect.
Furthermore, since the intensity level signal of the light is differentiated and converted into an absolute value to obtain the degree of change signal DD2, there is little possibility that noise in the "bad" area will appear as a peak in the video signal VD3. Therefore, it has the effect of high S/N.

In addition, by converting into absolute values, it is possible to increase the number of data to be compared with the floating threshold signal SL as a predetermined reference value, which has the effect of increasing the accuracy of extracting defective parts. .

Although one embodiment of the surface defect inspection device of the present invention has been described above in detail, the surface defect inspection device of the present invention is not limited to the above embodiment in any way, and may be modified in various ways without departing from the gist of the present invention. It can be implemented in the following manner. For example, the change degree detection circuit 3 and defect extraction circuit 4 of this embodiment may be implemented as a logic operation circuit using a microcomputer or the like.
It is also conceivable to configure them in one piece as shown below. That is, as shown in the block diagram of FIG. 7 and the flowchart of FIG.
0 to a digital video signal (step 210), and then imported into the memory 151 (step 220). After that, the differential calculation circuit 152 detects the boundary between the bright area and the dark area (step 230),
The image shrinkage circuit 153 extracts the intermediate level part having no boundary part (step 240), and the defect determination circuit 154 determines the size of its area (step 250). At this time, if the area is larger than a predetermined area, an NG signal is output from the I/O port 155 (step 260).

Effects of the Invention According to the surface defect inspection device of the present invention, it has a simple configuration and has an excellent effect of being able to automatically detect defects such as irregularities on an object to be inspected. As a result, surface inspection of objects can be performed unmanned using industrial equipment such as robots, which has the excellent effect of significantly increasing work efficiency. In addition, in order to extract areas on the surface to be inspected where there is no boundary between the bright and dark areas of the striped pattern as defective areas, it is possible to detect not only uneven areas but also areas where the intensity of light is different, such as It has the excellent effect of being able to extract areas where the material has partially changed or where the coating has deteriorated as defective areas. In addition, the size of the area on the object to be inspected where there is no boundary between the bright and dark areas of the striped pattern can be quantified and compared with the quantitative value and determined to be a defective area, so the inspection results will Another effect is that objective and highly reliable test results can be automatically obtained. Furthermore,
Defects such as irregularities can be detected as areas where there is no boundary between the bright and dark parts of the striped pattern, so when the surface of the object to be inspected is curved, the interval between the bright and dark striped patterns becomes narrower. However, defects may cause distortion and
This has the excellent effect that the area of the disturbed stripes is constant and accurate inspection results can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating the basic configuration of a surface defect inspection apparatus according to the present invention, FIG. 2 is a block diagram illustrating the configuration of a surface defect inspection apparatus according to an embodiment of the present invention, and FIG. Defective part determination circuit 4
4 is a timing chart showing the output signals of each part, FIG. 5 is an explanatory diagram showing the scanning lines of the CRT display DP2, and FIG. 6 is an image shrinking circuit 43 as a logic operation circuit and a defective part. FIG. 7 is a flowchart showing the "defect part extraction/judgment process" carried out by the judgment circuit 44. FIG.
The figure is a flowchart showing the processing performed by the logical operation circuit. 1... Striped pattern projection device, 2... Imaging device, 3...
...change detection circuit, 4...defect part extraction circuit, bad
...Intermediate level section, DP1, DP2, DP3...
CRT display, OB...Object to be inspected.

Claims (1)

[Scope of Claims] 1. A light and dark pattern projection means for projecting a predetermined light and dark striped pattern on the surface to be inspected; and an image of the light and dark striped pattern projected on the surface to be inspected by the light and dark pattern projecting means; an imaging means for scanning in a direction intersecting the direction of the light and capturing an image as a light intensity level signal; a change detection means for differentiating the level signal imaged by the imaging means to obtain a level change signal; and a change degree signal. A surface defect inspection apparatus comprising: defect extracting means for extracting an irregular portion of a change degree signal as a defect on a surface to be inspected by comparing the change rate signal with a predetermined reference value.