JPH0752159B2 - Surface defect inspection device - Google Patents

Description

The present invention relates to an apparatus for inspecting defects such as surface morphology of an object.

[Prior Art] Conventionally, the inspection of the presence or absence of irregularities on the surface of an object has been performed by an inspector based on the visual sense or the sense of touch.
This visual or tactile inspection of the inspector is apt to involve the inspector's subjectivity or proficiency, and there is a problem regarding the uniformity of the inspection, and there is a problem that the labor and time required for the inspection increase and the efficiency deteriorates. there were. In order to solve these problems, for example, invention proposals such as "a surface defect inspection method for an object" disclosed in JP-A-52-90988 have been made. These inventions, proposals, etc. project a striped light-dark pattern on the surface of the object to be inspected, and if there are defects such as irregularities on the surface of the object, use the fact that the projected striped pattern is distorted / disturbed. The surface is inspected for defects.

[Problems to be Solved by the Invention] In the above inventions and proposals, since it is possible to determine the presence or absence of defects on the object surface by the distortion / disturbance such as the stripe pattern projected on the object surface to be inspected, it is possible to perform uniform inspection. To improve
Although it has an excellent effect that the work efficiency can be improved, the presence of defects on the object surface is judged by the inspector still judging the degree of distortion / disturbance such as striped pattern. However, there is still a problem that the inspection result is not uniform. For this reason, attempts have been made to quantify the distortion / disturbance such as the striped pattern and to determine the presence or absence of defects on the object surface as a quantitative value.
It has not been resolved yet. As a result,
Labor saving in defect inspection of an object surface and unmanned operation using a robot are hindered.

The present invention has been made to solve the above problems, and an object thereof is to provide a surface defect inspection apparatus capable of objectively, quantitatively and automatically inspecting the presence or absence of defects on the surface of an object. I am trying.

Configuration of the Invention [Means for Solving the Problems] The surface defect inspection apparatus of the present invention is configured as follows. That is, the surface defect inspection apparatus of the present invention comprises a light and dark pattern projecting means for projecting a predetermined light and dark pattern onto the surface to be inspected, a bright portion of the light and dark pattern projected onto the surface to be inspected by the light and dark pattern projecting means, and An intermediate density portion detecting means for detecting an intermediate density portion which does not belong to any of the dark areas, and an intermediate density portion having an area of a predetermined area or more is extracted from the intermediate density portion detected by the intermediate density portion detecting means. And a defective portion detecting unit which is a defective portion on the surface to be inspected.

Here, the light-dark pattern projecting means is means for projecting a predetermined light-dark pattern on the surface to be inspected, and a predetermined pattern, for example, a striped light-dark pattern is projected on the surface to be inspected using a projector or the like. Various configurations such as the above configuration can be considered. The bright and dark pattern projected on the surface to be inspected may be a virtual image generated by reflection on the surface to be inspected, or may be simply a projected image.

The intermediate density portion detecting means for detecting the intermediate density portion is a means for detecting a so-called intermediate density portion which does not belong to either the light portion or the dark portion of the light-dark pattern projected on the surface to be inspected by the light-dark pattern projecting means. Therefore, various configurations can be provided, such as a configuration in which the intermediate density portion is detected by comparing the brightness of the bright and dark pattern imaged by the one-dimensional or two-dimensional image pickup means with a predetermined reference value. As such a predetermined reference value, a constant value may be used in a place where the brightness of the light-dark pattern can be adjusted to a constant value, or a value based on an average value of the brightness of the light-dark pattern may be used. Incidentally, the intermediate density portion is generated as the light and dark pattern projected on the surface of the object to be inspected is distorted and disturbed by defects such as irregularities on the object surface, so it is set as a level that does not belong to either the light portion or the dark portion of the light and dark pattern. It is used for detection and detection of surface defects.

The defective portion detecting means is a means for extracting an intermediate density portion having an area equal to or larger than a predetermined area among the intermediate density portions detected by the intermediate density portion detecting means, and making the defective surface portion to be inspected, It can be considered to be configured as a discreet circuit or as a logical operation circuit using a microcomputer or the like.

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

The surface defect inspection apparatus of the present invention detects the intermediate density portion of the light-dark pattern projected on the surface to be inspected by the light-dark pattern projecting means by the intermediate density portion detecting means, and the intermediate density portion detected by the intermediate density portion detecting means. Among them, the defective portion detecting means extracts the intermediate density portion having an area equal to or larger than a predetermined area as a defective portion on the surface to be inspected.

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

FIG. 1 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 the present embodiment is roughly composed of a striped pattern projection device 1 for projecting a striped light-dark pattern on the surface of an object OB to be inspected for the presence or absence of defects such as irregularities, and an object OB to be inspected. An intermediate density portion detection device 3 that captures a striped virtual image projected on the surface and detects an intermediate density portion that does not belong to either a bright portion or a dark portion of the bright and dark pattern, and is detected by the intermediate density portion detection device 3. The determination device 5 is configured to extract an intermediate density portion having an area of a predetermined area or more from the intermediate density portions and output a surface inspection result of the inspection object OB.

The striped pattern projection apparatus 1 is composed of a flat plate 10 having a large number of slits at equal intervals and a light source 11 for emitting scattered light, and a striped pattern of a predetermined pitch (in the present embodiment, on the surface of the inspection object OB). The distance between the bright and dark areas is 1.5 mm). In this embodiment, the object OB to be inspected is an iron plate having gloss, and the striped pattern is projected as a virtual image. When the object OB to be inspected is an object having no gloss, the light source 11 is configured to emit parallel light, and a striped pattern can be projected on the surface of the object OB to be inspected.

The intermediate density portion detection device 3 is an image pickup tube (hereinafter, simply referred to as a TV camera) 30 that captures a striped pattern on the surface of the inspection object OB.
And a distributor 31, a high-pass filter circuit 32, and an absolute value circuit for detecting the intermediate density portion of the striped pattern photographed by the TV camera 30.
33, a low-pass filter circuit 34, a comparator 35, and a mixer 36. CRT display DP1 is TV camera 30
It displays the striped pattern projected by
The display DP2 displays the intermediate density portion output from the mixer 36.

The determination device 5 is composed of an image contraction circuit 51 and a defective portion extraction circuit 52. The determination device 5 is configured as a logical operation circuit using a so-called microcomputer. The CRT display DP3 displays an image (video signal) output from the image contraction circuit 51.

Next, the operation of the surface defect inspection apparatus according to the present embodiment will be described by appropriately using the timing chart shown in FIG. The timing chart shown in FIG. 2 represents the output signals of the respective portions of the intermediate density portion detection device 3 and the determination device 5.

The virtual image of the striped pattern projected on the inspection object OB by the striped pattern projection device 1 is converted into a video signal VD1 (timing chart video signal VD1 in FIG. 2) from the TV camera 30 and the distributor 3
Output to 1. The video signal VD1 is also output to the CRT display DP1, and the image captured by the TV camera 30 is reproduced on the screen of the CRT display DP1. TV
The video signal VD1 output from the camera 30 is the object OB to be inspected.
When the surface of is in a smooth state, it becomes a sinusoidal signal having a high level of a bright part and a low level of a dark part which are originally in a striped pattern in a regular state, but when there is a defective part such as unevenness, The defective portion distorts and disturbs the striped pattern, and has a so-called intermediate density signal which does not belong to either the high level of the bright portion or the low level of the dark portion (timing chart video signal VD1 in FIG. 2).
The intermediate density portion bad which is distorted / disturbed by this subsequent depression can be observed on the screen of the CRT display DP1 as shown pictorially in FIG. The video signal VD1 from the TV camera 30 is a video signal obtained by scan scanning orthogonal to the striped pattern on the inspection object OB. Therefore, the timing chart shown in FIG. 2 uses the time t as a parameter.

The video signal VD1 input to the distributor 31 is separated into an image video signal VD2 and a sync signal SS (FIG. 2, timing signal video signal VD2, sync 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 31 can be simply configured by using a rectifier or the like.

The video signal VD2 output from the distributor 31 is input to the high pass filter circuit 32. The video signal VD2 input to the high pass filter circuit 32 is converted into a video signal VD3 in which the offset voltage component is removed and the bright portion of the striped pattern has a positive level and the dark portion has a negative level. As a result, the intermediate density portion bad or the boundary portion between the light portion and the dark portion of the striped pattern is set to a signal of almost zero level (timing chart video signal VD3 in FIG. 2). The offset voltage is a light / dark level signal of the object OB itself.

The video signal VD3 from which the offset voltage has been removed by the high pass filter circuit 32 is input to the absolute value circuit 33. A negative level signal such as a dark portion of the video signal VD3 input to the absolute value circuit 33 is converted into a positive level signal here (timing chart video signal VD4 in FIG. 2). That is, the video signal VD3 input to the absolute value circuit 33 becomes the full-wave rectified video signal VD4 here.

The video signal VD4 output from the absolute value circuit 33 is input to the plus side of the comparator 35 as it is, and is also input to the minus side of the comparator 35 via the low pass filter circuit 34.

The low-pass filter circuit 34 is configured as a so-called integrating circuit and produces a floating threshold signal SL based on the input video signal VD4 (timing chart of FIG. 2, floating threshold signal SL). As shown in the timing chart of FIG. 2, the floating threshold signal SL is a signal smaller than the high level signal in the bright portion of the video signal VD4 and larger than the intermediate density portion bad.

The comparator 35 using the floating threshold signal SL as a reference value for comparison is
A binary video signal VD5 having a bright portion at a high level and a dark portion at a low level is output to the mixer 36 (FIG. 2 timing chart video signal VD5).

The video signal VD5 is input to the mixer 36, and this mixer 3
To the CRT display DP2, the sync signal SS separated by the distributor 31 described above is also input to the CRT display DP2, and the video signal VD5 is a video signal VD6 including the sync signal SS.
(Fig. 2 Timing chart Video signal VD
6). The video signal VD6 including the synchronization signal SS is determined by the determination device 5
Is output from the image contraction circuit 51. The video signal VD6
Is also output to the CRT display DP2, but the low level signal of the video signal VD6 is displayed as a dark part on the screen of the CRT display DP2. That is, the boundary line between the bright portion and the dark portion and the intermediate density portion bad displayed on the CRT display DP1 described above are displayed as the dark portion on the screen.

Video signal VD input to the image contraction circuit 51 of the determination device 5
As is well known, 6 is a signal according to the scanning line shown in FIG. That is, in the scanning line rn in which the intermediate density portion bad appears, the number of pixels in the dark portion forming the striped pattern of the video signal VD6 is small, and the number of pixels in the intermediate density portion bad is large. As a result, the image contraction circuit 51 performs a so-called image contraction operation in which the dark area pixels are bright area pixels when the number of dark area pixels is greater than or equal to a predetermined number. This image contraction work is performed until the dark portion of the striped pattern disappears (timing chart video signal VD7 in FIG. 2). Where CRT display DP1,
The screen size of DP2 and DP3 is 100 mm × 100 mm, and the number of pixels in each horizontal and vertical scanning line is 512. Therefore, the area of one pixel is about 0.2 × 0.2 mm ² . The image contraction work is performed as follows. That is, in one scanning line, a dark portion of one pixel is made only when the number of pixels forming a dark portion continues for a predetermined number (2 to 3 pixels in this embodiment), and this work eliminates vertical stripes at predetermined intervals. Up to.

The video signal VD7 from which the striped dark portion is erased is output to the defective portion extraction circuit 52. The video signal VD7 is a CRT.
It is also output to the display DP3, and the intermediate density portion bad is displayed on the screen. The intermediate density portion bad at this time is an image that has been subjected to interference contraction by the image contraction circuit 51.

In the defect extraction circuit 52. The size of the area of the intermediate density portion bad is determined. In this embodiment, when the size of the intermediate density portion bad is equal to or larger than the size corresponding to a circle having a diameter of about 1 mm, that is,
When the number of pixels in the intermediate density bad is 25 pixels or more, the intermediate density part bad
Is a defective portion and an NG signal is output.

The flow chart shown in FIG. 4 is a flow chart showing the operations performed by the intermediate density portion detecting device 3 and the determining device 3 of the present embodiment described in detail above. Therefore, when the video signal VD1 from the TV camera 30 is once converted into a digital image signal and the intermediate density portion detection device 3 and the determination device 5 are configured as a logical operation circuit,
The above-described processing may be implemented according to the flowchart shown in the figure.

According to the surface defect inspection apparatus of the present embodiment, the defective portion such as unevenness on the inspection object OB is accurately and automatically used by using the intermediate density portion included in the image of the inspection object OB surface captured by the TV camera 30. Can be detected. Also, an intermediate density portion generated at the boundary between the bright and dark portions of the light and dark pattern due to the image contraction work,
The defective portion can be detected by clearly distinguishing from the intermediate density portion bad due to the defect.

As a result, there is an excellent effect that the surface inspection of the object can be unmanned by using the industrial equipment such as the robot and the working efficiency can be remarkably improved. Further, the size of the intermediate density portion bad on the object OB to be inspected can be digitized, and is compared with a quantitative value (25 pixels or more in this embodiment) to be a defective portion, so that the inspection result is uniform. There is also the effect that it is possible to obtain highly reliable inspection results. Further, since a defective portion such as unevenness can be detected as an intermediate density portion bad, when the surface of the object OB to be inspected is a curved surface or the like, even if the interval of the bright and dark striped patterns becomes narrow, the defect portion causes distortion. The area of the disturbed fringes becomes constant, which has an excellent effect that an accurate inspection result can be obtained. Further, in the present embodiment, the interval between the bright and dark parts of the light and dark pattern is 1.5 mm, but if the stripe interval is narrower than the size of the defect to be detected, the accuracy of defect detection will be improved. It also has the effect of being able to. Furthermore, in this embodiment, the state of each stage of the inspection process can be viewed by using three CRT displays.
By using it together with the output result of the determination device 5, it is possible to prevent erroneous detection and to confirm the position of the defective portion.

As described above, one embodiment of the surface defect inspection apparatus of the present invention has been described in detail, but the surface defect inspection apparatus of the present invention is not limited to the above embodiment, and various implementations are possible within the scope not departing from the present invention. Of course, you can do

EFFECTS OF THE INVENTION The surface defect inspection apparatus of the present invention has an excellent effect that it is possible to automatically detect a defective portion such as unevenness on an object to be inspected. As a result, there is an excellent effect that the surface inspection of the object can be unmanned by using the industrial equipment such as the robot and the working efficiency can be remarkably improved. In addition, the size of the intermediate density portion on the inspected object can be quantified, and compared with the quantitative value, it is judged as a defective portion, so the inspection result has uniformity and is extremely reliable. It also has the effect of being able to obtain. Further, since a defective portion such as unevenness can be detected as an intermediate density portion, when the surface of the object to be inspected is a curved surface or the like, even if the interval between the bright and dark striped patterns becomes narrow, the defective portion distorts or is disturbed. Has an excellent effect that the area is constant and an accurate inspection result can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a surface defect inspection apparatus according to an embodiment of the present invention, FIG. 2 is a timing chart showing output signals of respective parts, and FIG. 3 is an explanatory view showing scanning lines of the CRT display DP2. , FIG. 4 shows the intermediate density portion detection device 3
And a flowchart showing the operation performed by the determination device 5,
Is. 1 ... Stripe pattern projection device 3 ... Intermediate density part detection device 5 ... Judgment device DP1, DP2, DP3 ... CRT display OB ... Inspected object bad ... Intermediate density part rn ... Scan line

Claims (1)

[Claims] 1. A light-dark pattern projection means for projecting a predetermined light-dark pattern onto a surface to be inspected, and both light and dark portions of the light-dark pattern projected onto the surface to be inspected by the light-dark pattern projecting means. The intermediate density portion detecting means for detecting the intermediate density portion, and the intermediate density portion having an area of a predetermined area or more among the intermediate density portions detected by the intermediate density portion detecting means are extracted to extract the intermediate density portion. A surface defect inspection apparatus comprising: a defective part detecting unit which is a defective part.