JPH0511573B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an inspection method for inspecting a plate-like object such as a transparent or translucent film or sheet to detect defects such as contamination of foreign matter and hard eyes. .

[Conventional technology and its problems]

When manufacturing transparent or semi-transparent films, sheets, etc., there is a risk that some parts of the raw material may not be completely dissolved, or that once melted material may re-solidify in the piping line and mix into the solution. As a result, defective parts called "fissure eyes", which are made of the same material as the good quality part but have a different density, may occur, or bulges and dents may be formed on the surface, resulting in defective parts. Since such defective parts are transparent or semitransparent like the good quality parts of the plate-shaped body, it is difficult to visually observe and distinguish them. Furthermore, conventionally, methods have been used that utilize the degree of light transmittance to detect foreign substances mixed into a transparent or semi-transparent plate; There was a problem that transparent defective parts could not be detected or detection was not reliable.

For this reason, a flying spot method is used in which the laser beam is scanned with a polygon mirror, but this method has the problems of complicating the optical system and making the device expensive.

Therefore, it is an object of the present invention to accurately detect not only defects caused by opaque foreign matter but also transparent or translucent spots as well as good quality parts, and to be able to detect them at low cost without using complicated equipment. An object of the present invention is to provide a method for inspecting defects on a transparent or semi-transparent plate-like body, which can be carried out in a number of ways.

[Means for solving problems]

In order to solve the above-mentioned problems, the defect inspection method of the present invention detects that the refractive index of light is different from that of the good quality part in the defect part which is made of the same material as the good quality part but has a different density, and also the defect inspection method This method takes advantage of the fact that light is refracted differently in defective areas due to lens action than in good-quality areas, and is a line consisting of multiple lines arranged at equal intervals narrower than the size of the defective area to be detected. Column 1 is transferred to the CCD via a transparent or semi-transparent plate 2 to be inspected.
An image is taken by an imaging device 3 such as a camera, a defective part of the plate-shaped body 2 is detected as a disturbance in the line array 1, and a signal including an irregular part corresponding to the disturbance in the line array is obtained. is passed through a bandpass filter to cut out the irregular portions, and then converted into a voltage proportional to the envelope by an envelope circuit, and further, a portion higher than the threshold is extracted as a rectangular wave by a comparator circuit. This is inverted by an inverting circuit to obtain a detection signal.

[Effect]

When the line arrays 1 arranged at equal intervals narrower than the size of the defect to be detected are observed through the transparent or translucent plate-like body 2 to be detected, the third
As shown in the figure, if there is a defective part 2a in the plate-shaped body 2 that is made of the same material as the good quality part but has a different density, or a defective part 2a in which a part of the surface is raised or depressed, the light will not be absorbed in that part. Since the way of refraction is different from that of other parts, the line array 1 is disordered, that is, the interval between the line arrays, the thickness and shade of the lines are observed to be different from those of the good quality part, which makes it possible to distinguish between the good quality part and the defective part 2a. A distinguishable defective portion 2a is detected. Further, if there is a defective part in the plate-shaped body 2 due to the contamination of opaque foreign matter, the line array 1 is not observed in that part. Then, such a disordered arrangement is
The image is captured by an imaging device such as a CCD camera, and a signal containing irregular parts corresponding to the disturbance of the line array is obtained.
This signal is passed through a band pulse filter, an envelope circuit,
A detection signal is obtained by sequential processing by a comparator circuit and an inversion circuit.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows a defect inspection device for carrying out the method of the present invention, in which a line array 1 consisting of a plurality of straight lines arranged at equal intervals narrower than the size of the defect to be detected is the base of a rectangular parallelepiped. A two-dimensional imaging device 3 is depicted on the top surface of a base 4 and is attached to the base 4 via a support rod 5 so as to be movable up and down. Imaging device 3
As a CCD using a CCD image sensor
A camera is used. This imaging device 3 is adjusted so that the line array 1 is located within its imaging field of view. The base 4 includes a control circuit for adjusting the field of view of the imaging device 3 and moving the imaging device 3 up and down, a signal processing circuit for determining a defective portion from a signal from the imaging device 3, and a signal processing circuit for determining a defective portion from a signal from the imaging device 3. It has a built-in memory circuit that stores the position, size, etc., and a display that displays the position, size, etc. of the defective part.

FIG. 5 is a block diagram showing the configuration of the signal processing circuit. 10 is a bandpass filter that passes only a certain frequency portion of the signal, and 11 is an envelope circuit that uses a half-wave or full-wave rectifier circuit and a low-pass filter to extract a voltage proportional to the envelope of the signal. 12 is a comparator circuit that compares whether the voltage is higher or lower than a certain threshold value, and 13 is an inverting circuit that inverts the output.

Next, the operation of this device will be explained. The imaging device 3 horizontally scans the line array 1 in a direction orthogonal thereto through the transparent or semi-transparent plate-like body 2 to be inspected (see FIG. 6). Since the line arrays 1 are arranged at equal intervals, a regular pulse signal with a constant period can be obtained (see FIG. 7). However, in the plate-like body 2,
If there is a defective part 2a made of the same material as the good quality part but with a different density or a defective part 2a where a part of the surface is raised or depressed, the way light is refracted in that part is different from that in other parts. , an image is taken of the line array 1 whose interval, line thickness, and density have changed, and a signal whose period, pulse width, etc. differ from the regular pulse signal described above appears (see () to () in Fig. 7). . In the signal processing circuit, the pulse signal is first passed through a band pass filter 10, and the signal portion other than the signal portion having the same frequency as the regular signal is cut out, resulting in a waveform as shown in FIG. Next, this signal is converted into a voltage proportional to the envelope by the envelope circuit 11 (Fig. 7), and further compared by the comparator circuit 12 to see whether it is higher or lower than the threshold value T _H , as shown in Fig. 7. The waveform will be as follows. Then, it is inverted by the inverting circuit 13 and used as a detection signal (see FIG. 7).

When one horizontal scan is completed, a similar horizontal scan is performed with a predetermined distance shifted in the direction perpendicular to the horizontal scan. This is repeated sequentially as shown in I to 6 of FIG. 6, and the required range is two-dimensionally scanned, and the presence or absence of the defective portion 2a and its size are inspected.

Further, if there is an opaque defective part in the plate-like body 2, the line array 1 will not be imaged in that part,
Since the signal corresponding to this line array 1 does not appear, the regularity of the signal is disturbed and a detection signal is obtained in the same way as above.

As the imaging device 3, in addition to a CCD camera, a camera using a solid-state imaging device such as a MOS image sensor or an imaging tube is used.

In addition, instead of using the two-dimensional imaging device 3 as in the above embodiment, a one-dimensional imaging device 6 using a line sensor such as a CCD or a MOS image sensor is used as shown in FIG. By scanning the line array 1 in a direction perpendicular to it through a transparent or translucent plate-like body 2, and moving the plate-like body 2 in the direction along the line array 1 using the conveying device 7. Accordingly, the required range of the plate-shaped body 2 may be scanned two-dimensionally. In FIG. 8, 6a is a light source that supplies illuminance necessary for using the imaging device 6, 7a is a driving motor for the conveying device 7, and 7b is a conveying belt. Reference numeral 9 denotes a processing device for obtaining a defect detection signal from the output signal of the imaging device 6.

According to the detection method of the present invention, the detection resolution of the defective part 2a is determined by the interval between the line arrays 1, so by changing the interval between the line arrays 1, the size of the detectable defective part 2a can be easily adjusted. You can choose.

The defect inspection method of the present invention also includes a case where the line array 1 is visually observed through the plate-shaped object 2 to be inspected without using an imaging device.

〔Effect of the invention〕

As detailed above, the defect inspection method of the present invention utilizes differences in light refraction rather than the magnitude of light transmittance, so it detects not only defects caused by opaque foreign matter but also defects that are the same as good quality parts. It is also possible to reliably detect transparent or translucent defects such as defects with different densities depending on the material and defects where a portion of the surface is raised or depressed. Moreover, by simply observing the line array through the transparent or semi-transparent plate-like object to be inspected, defective parts of the plate-like object can be easily and inexpensively inspected using a simple device. Furthermore, in the present invention, by imaging a standard line array at regular intervals through a transparent or semi-transparent plate-like body to be inspected, defects in the plate-like body are detected as disturbances in the line array, and the image is obtained by imaging. Since the detection circuit extracts only the irregular portions corresponding to the disturbances in the line array from the received signal, as long as the line arrays are arranged at exactly equal intervals, the relative relationship between the imaging device and the line array is Even if the target positional relationship changes after setting, the defective part can be detected accurately.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the defect inspection method of the present invention;
FIG. 2 is a front view showing the method, FIG. 3 is a plan view showing the principle of the method of the present invention, FIG. 4 is a perspective view showing an example of an apparatus for carrying out the method of the present invention, and FIG.
The figure is a block diagram showing the configuration of the signal processing circuit of the same device, FIG. 6 is a plan view showing scanning of a plate-like object by the imaging device, and FIG. FIG. 5 is an operating characteristic diagram showing signals of each part corresponding to FIG. 5, and FIG. 8 is a perspective view showing another example of an apparatus for carrying out the method of the present invention. Explanation of symbols, 1... Line array, 2... Transparent or translucent plate-like body, 2a... Defect part, 3, 6... Imaging device, 10... Band pass filter, 11... Envelope circuit, 12... Comparator circuit, 13...
Inverting circuit.

Claims (1)

[Claims] 1 In an inspection method that detects defects by inspecting a transparent or translucent plate-like object, a line array consisting of a plurality of lines arranged at equal intervals narrower than the size of the defect to be detected is inspected. By capturing an image with an imaging device such as a CCD camera through a transparent or semi-transparent plate-like body, disturbances in the line array caused by defects in the plate-like body are imaged, and countermeasures are taken to deal with the disorder in the line array. A signal containing an irregular part is sent from the imaging device to a bandpass filter to cut out the irregular part, converted into a voltage proportional to the envelope by an envelope circuit, and further converted to a voltage proportional to the envelope by a comparator circuit. A defect inspection method for a transparent or semi-transparent plate-shaped body, characterized in that the defect is detected by extracting a portion higher than the value as a rectangular wave and inverting it by an inverting circuit to obtain a detection signal.