JPS63171345A - Apparatus for inspecting surface flaw - Google Patents

Abstract

PURPOSE:To automatically detect the flaw part on an article to be inspected, by differentiating the level signal obtained by picking up the image of a surface to be inspected by an image pickup means to form a level change degree signal and comparing said change degree signal with a predetermined reference value. CONSTITUTION:The image of the light and shade stripe pattern projected on a surface to be inspected by a light and shade pattern projecting means M1 is picked up as a light intensity level signal by an image pickup mean M2 and the light intensity level signal of the picked-up image is differentiated by a change degree detection means M3 to form a level change degree signal. When a flaw part such as unevenness is present on the surface to be inspected, the level of the flaw part is detected as an intermediate level signal not belonging to both of the high level of a light part and the low level of a shade part by said flaw part and the change degree signal obtained by differentiating the flaw part is detected as a signal not having the boundary part of the high level of the light part and the low level of the shade part. Then, by comparing the change degree signal with a predetermined reference value using a flaw part extraction means 4, the irregular part of the change degree signal can be extracted as the flaw part of the surface to be inspected.

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 1] Conventionally, the presence or absence of irregularities on the surface of an object has been inspected by an inspector based on the sense of sight or touch.

This visual or tactile inspection by the inspector is likely to be influenced by the inspector's subjectivity or skill level, and there are problems with the uniformity of the inspection, and the inspection requires a lot of effort and time, which reduces efficiency. there were. As a solution to these problems, for example, Japanese Patent Application Laid-Open No. 52-90988
``Method for inspecting surface defects of objects'' shown in
Inventions and proposals have been made, such as the "Surface Inspection Apparatus" disclosed in Japanese Patent Application No. 71289, and the "Surface Texture Measuring Method and Apparatus" disclosed in Japanese Patent Application Laid-Open No. 58-97608. These inventions and proposals project striped bright and dark patterns on the surface of the object being inspected, and if there are defects such as unevenness on the surface of the object,
This method uses the distortion and disturbance of the projected striped pattern to inspect the surface of an object for defects.

[Problems to be Solved by the Invention] The above inventions and proposals can determine the presence or absence of defects on the surface of an object based on distortions and disturbances such as striped patterns projected on the surface of the object to be inspected. improve your sexuality,
Although this method has the excellent effect of increasing 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, so the inspection results still lack uniformity. Such problems were considered.

(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 an 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 include that the presence or absence cannot 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-mentioned problems, and its purpose is to objectively, regularly, and automatically inspect the presence or absence of defects on the surface of an object.

SUMMARY 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 (Ml) that projects a predetermined bright and dark striped pattern on the surface to be inspected; and the bright and dark pattern projection means. an imaging means (M2) for imaging an image of the bright and dark striped pattern projected on the surface to be inspected by (Ml) as a light intensity level signal, and the imaging means (M2)
a change detecting means (M3) for differentiating the level signal imaged by the above to obtain a level change signal; A defect extracting means (M4) for extracting a defect on the inspection surface.

The change degree detection means (M3) may be any means that differentiates the intensity level signal of the light imaged by the imaging means (M2) and generates a level change degree signal, and may be a so-called CR using a capacitor and a resistor. It can be configured as a discrete circuit such as a differential circuit, or it can be configured by converting the intensity level signal of the imaged light into a digital image signal and then converting the converted digital image signal into a logical operation circuit using a microcomputer or the like. It is conceivable to adopt a configuration that performs differentiation.

[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 images a bright and dark striped pattern image projected on the surface to be inspected by a bright and dark pattern projection means (Ml) as a light intensity level signal by an 11i image means (M2), and The intensity level signal of the light is differentiated by the change degree detection means (M3) to obtain a level change degree signal, and then the defect extraction means (M4)
By comparing the change degree signal with a predetermined reference value using , irregular portions of the change degree signal are extracted as defects on the surface to be inspected.

In general, an image of light and dark stripes projected on the surface to be inspected is
When detected as a light intensity level signal by the ff1 imager (M2), it becomes a signal that repeats a high level in bright areas and a low level in dark areas at regular intervals.

If the intensity level signal of the light produced by the VA image means is differentiated using the degree of change detection means (M3), it is possible to find the area where the degree of change in the level signal is large, in other words, the boundary between the high level in the bright area and the low level in the dark area. can be detected separately from other level parts.

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 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. 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.

[Embodiment] Next, a preferred embodiment will be described with reference to the drawings in order to further simplify 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 apparatus of this embodiment mainly includes a striped pattern projection device 1 as a bright and dark pattern projection means for projecting a striped bright and dark 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; and an imaging device 2 serving as an imaging means for capturing a virtual image of a striped pattern projected on the surface of the object to be inspected OB, and differentiating the light intensity level signal outputted by the imaging device 2 to determine the level. Defects on the surface of the object to be inspected 08 are detected by comparing the level change signal output from the change degree detection circuit 3 with a predetermined reference value. and a defective part extraction circuit 4 as a defective part extracting means for extracting a defective part.

The striped pattern projection device M1 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 1.5 mm). 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 R image device 2 is comprised of a video tube (hereinafter simply referred to as a TV camera 20) that captures the striped pattern on the surface of the object to be inspected OB.

The degree of change detection circuit 3 includes a distributor 30. It is composed of a differentiation circuit 31, an absolute value circuit 32, and the like.

The defect extraction circuit 4 includes a low-pass filter circuit 40, a comparator 41 . It is composed of a mixer 422, an image shrinkage circuit 43, a defect determination circuit 44, and the like.

Note that the CRT display DP1 displays the striped pattern photographed by the TV camera 20, and the CRT display DP2 displays the image signal (
video signals). The CRT display DP3 displays the video signal output from the image contraction circuit 43. Further, as shown in FIG. 3, the image contraction circuit 43 and the defect determination circuit 44 of the defect extraction circuit 4 are operated by a well-known CPU 50. ROM51 and RAM5
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 a striped pattern projected onto the object to be inspected OB by the striped pattern projection device @1 is transmitted by a video signal VD1 (
FIG. 4 is a timing chart in which the video signal is converted into a video signal (MDI) and output to the distributor 30 of the change degree detection circuit 3. Further, this video signal VD1 is transmitted to the CRT display DP.
The image taken by the TV camera 20 is also output to the CRT display DP1 and reproduced on the screen of the CRT display DP1. T
When the surface of the object to be inspected OB is smooth, the video signal VD1 outputted from the V camera 20 is a sinusoidal signal that regularly has high levels in bright areas and low levels in dark areas, which are inherent to the striped pattern. However, when there is a defect such as unevenness, i, t, the striped pattern is distorted and disturbed by the defect, resulting in a so-called intermediate level 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 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 MDI 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.

Video signal input to the distributor 30 of the change degree detection circuit 3 @
Here, the VDI is separated into a video signal @VD2 of the image and a synchronization signal SS (timing chart in FIG. 4: video signal VD2. synchronization signal SS). Since the video signal VD2 included in 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.

Video signal VD2 output from distributor 30 is input to differentiation circuit 31.

Differential circuit 31 composed of capacitors, resistors, etc.
represents 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 from the low level in the dark part to the high level in the bright part as a sudden fall or rise of the signal. (Figure 4 timing chart change degree signal DD1). In other words,
The differentiating circuit 31 detects a portion where the level of the video signal V D 2 as a light intensity level signal has a large change. 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 outputted as a zero level like the bright part and the dark part of the striped pattern (timing chart in FIG. 4, change degree signal DD1 section bad).

The degree of change signal DD1 output from the differentiating circuit 31 is input to the absolute value circuit 32. A negative level signal such as a dark part of the change degree signal DD1 inputted to the absolute value circuit 32 is converted into a positive level signal here (see timing chart in Fig. 4).
change degree signal DD2). In other words, the degree of change signal DD1 input to the absolute value circuit 32 becomes the degree of change signal DD2 which is full-wave rectified here.

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

The low-pass filter circuit 40 is configured as a so-called integrator circuit, and generates a floating threshold signal SL based on the input variation signal @002 (see timing chart in Fig. 4).
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.

A comparator 41 that uses the floating threshold signal SL as a reference value for comparison.
is a binary video signal V in which the border between the bright and dark parts of the striped pattern is at a high level, and the other parts are at a low level.
D3 is output to the mixer 42 (timing chart in FIG. 4, video signal VD3).

The video signal VD3 is input to the mixer 42, and the sync signal @SS separated by the above-mentioned distributor 30 is also input to the mixer 42 in order to output the video to the CRT display DP2. VD3 is a video signal vD4 including a synchronization signal @SS (timing chart in FIG. 4, video signal VD4). The video signal VD4 containing the synchronization signal SS is output to an image contraction circuit 43 configured as a logic operation circuit. Incidentally, the video signal VD4 is
Although it is also output to the CRT display DP2, 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 area and the dark area displayed on the above-mentioned CRT display DP1 is displayed as a bright area on the screen, and the bright area, the dark area, and the intermediate level area bad indicating the defective area are displayed as the dark area. .

As is well known, the video signal VD4 input to the image contraction circuit 43 is a signal that follows the scanning lines shown in FIG.

That is, in the scanning line rn where the intermediate level portion baci appears, the number of pixels in the dark portion forming the striped pattern of the video signal VD4 is small, and the number of pixels in the intermediate level portion 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 continued until the dark part of the striped pattern disappears (timing chart in FIG. 4, video signal VD5).

Here, CRT display DPI, DP2. The screen size of the DP3 is 10100 mm x 100, and the number of pixels in each horizontal and vertical scanning line is 512.

Therefore, the area of one pixel is approximately 0°2×0.2 mm2. Further, the image shrinking work is performed as follows.

That is, in one scanning line, only when the number of pixels constituting a dark area continues for a predetermined area or more is a dark area, and this operation is performed until the vertical stripes at a predetermined interval disappear.

The video signal VD5 from which the dark part of the striped pattern has been removed is output to the defective part determination circuit 44. In addition, this video message @VD5
is also output to the CRT display DP3, and the intermediate level part 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 size of the area of the intermediate level portion bad. In this embodiment, the intermediate level part ba
When the size of d 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 in the intermediate level portion bad is 25 or more, the intermediate level portion bad is determined to be a defective portion and an NG signal is output.

Note that the flowchart shown in FIG.
4 is a flowchart showing the process of step 4. Image contraction circuit 4
3 and the defective part determination circuit 44 extracts the intermediate level part bad according to this "defect part extraction and determination process" (step 100), and determines the size of the area of the intermediate level part bad, and if the area is larger than a predetermined area, there is a defective part. and outputs an NG signal (steps 110 to "+20>").

According to the surface defect inspection device of this embodiment, defective parts such as irregularities on the object to be inspected 08 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 intensity of light of the surface coating color will vary. It has an excellent effect of being able to detect defective parts without depending on the level.

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 size of the intermediate level part bad on the object to be inspected OB can be quantified and compared with a constant value (in this example, 25 pixels or more) and determined to be a defective part. Another effect is that objective and highly reliable test results can be automatically obtained. Furthermore, defective areas such as unevenness are defined as intermediate level areas where there is no boundary between bright and dark areas (bad).
Therefore, even if the interval between bright and dark stripes becomes narrow when the surface of the inspection object OB is curved, the area of the stripes distorted or disturbed by the defect remains constant and accurate inspection results can be obtained. It has the excellent effect of being able to obtain

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 that it can be improved. Furthermore, in this embodiment, three CRT displays are used to allow the status of each stage of the inspection process to be viewed.
By using it in conjunction with the output result of the defective part determination circuit 44, it is possible to prevent erroneous detection and also has the effect that the position of the defective part can be confirmed.

Furthermore, even if the defective part on the object to be inspected 08 is not detected as an intermediate level part and 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 boundary part, so the defective part It also has the effect of being able to detect.

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, it is also conceivable that the degree of change detection circuit 3 and the defect extraction circuit 4 of this embodiment are configured as a logical operation circuit using a microcomputer or the like, as described below.

That is, as shown in the block diagram of FIG. 7 and the flowchart of FIG. After converting the signal to a video signal (step 210),
151 (step 220). After this, the differential calculation circuit 152 detects the boundary between the bright and dark areas (step 230), and the image contraction circuit 153 extracts an intermediate level area that does not have the boundary (step 240), and the defect determination circuit 154 The size of the area is determined (step 250). At this time, if the size of the area is greater than or equal to a predetermined area, an NG signal is output from the I10 port 155 (step 260).

According to the surface defect inspection apparatus of the present invention, it has a simple configuration and has the excellent effect of automatically detecting defects such as irregularities on an object to be inspected. This results in
The surface inspection of objects can be performed unmanned using industrial equipment such as robots, and has the excellent effect of significantly increasing work efficiency. 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 benefit is that objective and extremely 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 can be detected. Even if the width is narrowed, the area of the stripes distorted and disturbed by the defect remains constant, which has the excellent effect of allowing accurate inspection results to be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating the basic configuration of a surface defect inspection device according to the present invention, FIG. 2 is a block diagram illustrating the configuration of a surface defect inspection device according to an embodiment of the present invention, and FIG. 3 is a block diagram illustrating the configuration of a surface defect inspection device according to an embodiment of the present invention.
3 and a block diagram showing the defect determination circuit 44, FIG. 4 is a timing chart showing output signals of each part, FIG. 5 is an explanatory diagram showing scanning lines of the CRT display DP2, and FIG.
The figure is a hob flowchart showing the "defect part extraction/judgment processing" performed by the image shrinkage circuit 43 and the defect part determination circuit 44 as logic operation circuits, and FIG. FIG. 8 is a block diagram showing how the logic operation circuit is integrated. FIG. 8 is a flow chart showing the processing performed by the logical operation circuit. 1... Striped pattern projection device 2... Positive image device 3... Change degree detection circuit 4... Defect part extraction circuit bad... Intermediate level part, DPI, DP
2. DP3...CRT display OB...Object to be inspected

Claims (1)

[Scope of Claims] Light and dark pattern projecting means for projecting a predetermined light and dark striped pattern onto the surface to be inspected; and a light intensity level signal representing the 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 capturing an image as a 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 by comparing the change signal with a predetermined reference value. A surface defect inspection apparatus comprising: defect extracting means for extracting the irregular portion of the surface as a defect on the surface to be inspected.