JP3247646B2 - Calibration method for surface inspection equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In the production line and the inspection line of a plate-shaped member such as a steel plate, a non-ferrous metal plate, paper or a non-woven fabric, an optical inspection is performed on the surface of the member.
A determination is made as to whether there is a quality problem. The present invention relates to a method of calibrating an optical system of a surface inspection apparatus used for such an inspection, and particularly to an easy calibration method without stopping a transport line.

[0002]

2. Description of the Related Art As shown in FIG. 1, as a surface inspection apparatus for a plate-like inspection object, a point light source (laser light) 1 is directed in a direction perpendicular to the conveying direction of the inspection object 2 (hereinafter, width direction). A method is known in which the surface of the object to be inspected is scanned while being scanned, and the reflected light is received by a photoelectric element such as the photomultiplier tube 3. As another method, as shown in FIG. 2, there is known a mechanism in which a belt-like light source 4 is irradiated in the width direction of the surface of the test object 2 and reflected light is received by an image pickup device 5 such as a CCD array sensor. It is widely used for surface inspection of metal plate, printing paper, pulp, non-woven fabric, etc.

The inspection performance of the surface inspection apparatus is deteriorated due to minute displacement of the light source and the light receiver, contamination of the light emitting window of the light source and the light receiving window of the light receiver, decrease in the amount of light due to aging of the light source, and failure. Inevitably, the calibration of the optical system is usually performed on a regular basis.

[0004] As a document relating to the calibration of a surface inspection apparatus, for example, Japanese Patent Application Laid-Open No. Hei 8-136473 has first and second lines on or near the path of an object to be inspected sequentially sent out. A reference plate for defect detection having at least two parallel lines having different widths between them is arranged, and the surface of the reference plate is irradiated with illumination light from a light source. A method of adjusting a defect detection device that converts an image into an electric signal and observes the electric signal as a visible image is disclosed.

[0005]

However, the above conventional method has the following disadvantages. 1) Since the manufacturing process or the inspection process needs to be stopped at the time of calibration, particularly in a continuous operation line such as a steel plate manufacturing process, the production efficiency of a product is reduced. 2) A lot of trouble and time are required to move the light source and the light receiver off-line for calibration and to set a calibration reference plate. 3) Since the actual object to be inspected and the reference plate have different light reflectivities and transport speeds at the time of the inspection, the results of the off-line calibration do not necessarily reflect the on-line inspection performance. 4) The calibration reference plate becomes dirty, rusted or deformed during long-term use, and cannot be calibrated based on a certain standard.

To cope with such a conventional problem, Japanese Patent Application Laid-Open No. 8-136471 discloses a technique in which a calibration reference plate is moved to an intermediate position between a light source in a line and an object to be inspected. A method has been proposed in which a fixed mirror for guiding the reflected light from the light receiving device to the light receiver is provided, so that the inspection device can be calibrated without being retracted out of the transport line.

In this method, however, the mechanism for calibration is very complicated, and the problems 3) and 4) have not yet been solved. An object of the present invention is to propose a new calibration method that can solve the conventional problems as described above.

[0008]

According to the present invention, a surface of a plate-like inspection object is irradiated with light, reflected light from the surface is detected by a light receiver, and the inspection is performed based on the intensity of the received light signal. To calibrate the optical system of a surface inspection device for inspecting the surface of a body, an inspection object is provided with an opening that penetrates the inspection object, the reflected light intensity at this opening is measured, and the reflected light intensity is used for calibration. A calibration method for a surface inspection apparatus characterized in that it is determined that calibration of an optical system of a surface inspection apparatus is necessary when a threshold value is exceeded, and calibration of the optical system is performed. Upon irradiation, the object to be inspected is supported by a support member having a different reflectance from the object to be inspected.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a calibration method according to the present invention will be described with reference to an example of a surface inspection apparatus installed in a continuous steel sheet manufacturing line. In the steel sheet production line, the front and rear ends of each lot (coil) are welded at the entry side of the line, respectively.
Rolling, pickling, plating, annealing, etc. are performed while transporting this at high speed, and the process of winding in a coil shape for each lot by cutting the welded part at the exit side of the line, The surface inspection is usually performed on the exit side of the line in order to inspect an abnormality occurring in the line.

[0010] In such a production line, the area near the welded portion of the steel sheet is usually cut off by a cutting machine to produce scrap. An opening K as shown in FIGS. 3A and 3B is provided.

The dimension of the opening K provided in the coil in the longitudinal direction and the width direction is constant in any lot as shown in FIG. 3B as D _L and D _c . The dimension D _{L in the} longitudinal direction should not be too large in order to prevent the product yield from deteriorating. In particular the dimensions need only transport the coil stably for dimensions of D _c is not limited.

When the surface inspection device inspects the opening K of the coil at the line exit side, the reflected light intensity at the position of the opening is higher than that of other regions when the optical system of the device is sufficiently adjusted. Become smaller. In particular, when irradiating the test object with light, it is preferable to support the test object with a support member having a different reflectance from the test object. FIG. 4 shows an example in which a rubber roll 6 is used as a supporting member for supporting the object to be inspected. In this case, the intensity of the reflected light at the opening K is significantly smaller than at other portions. Such a roll may be a flat support.

FIG. 5 shows the position in the width direction and the intensity of the received light signal when the surface of the coil is inspected by providing an opening in the vicinity of the joint of the coil. When the adjustment of the optical system is insufficient in such measurement, as shown in comparison with FIG.
The difference in the reflected light intensity from the opening and the portion without the opening is smaller than in FIG. Therefore, in the calibration method according to the present invention, a "calibration threshold value" is provided in advance as shown by a broken line in FIGS. 5 and 6, and the optical system in the surface inspection apparatus is determined by measuring whether or not the threshold value is exceeded. Determine if calibration is necessary.

FIG. 7 shows a flowchart of the calibration procedure according to the present invention. In FIG. 4 described above, a case where a rubber roll is used as a member for supporting the coil is shown as an example. However, depending on the type of the object to be inspected, it may be better to increase the light reflectance of the support member. In the present invention, the supporting member is not limited to rubber, and a supporting member having a clearly different light reflection intensity may be selected.

In the above-described calibration method, it is preferable to open the reference opening at a fixed position in order to prevent a defect generated in the inspection object from being mistaken for a reference opening. Therefore, the width (see FIG. 5) corresponding to the diameter of the aperture in the light receiving signal waveform can be measured, and this value can be used to prevent erroneous recognition as a defect.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An opening having a diameter of 10 mm (D _L : 25) was formed in the vicinity of a welded portion of a coil on the entrance side of a steel sheet surface treatment line.
mm, D _c: 214mm) and provided, was calibrated in the surface inspecting apparatus in the left side of the line. As an inspection device, a belt-shaped white light source and a CCD array sensor as shown in FIG. 2 were used, and the inspection was performed in a state of being wound around a rubber roll as shown in FIG.

After the optical system was sufficiently adjusted and used continuously for three months, the intensity of reflected light at the position of the aperture was examined. The results shown in Table 1 were obtained.

[0018]

[Table 1]

The reflected light intensity is a dimensionless quantity expressed in 8 bits and 256 gradations, and the reflected light intensity of the sound portion of the coil is always 128 (median of 256 gradations) by the automatic gain control circuit.
This is the value after being controlled to become. In this example, the operation was performed such that "calibration was required" when the reflected light intensity from the reference aperture became 20 or more. The value of 32 in Table 1 is a value that requires adjustment of the optical system. When the line was actually stopped and the optical system was examined, it was found that the receiver was displaced by 1.8 mm. Was readjusted, and the calibration was performed again. As a result, the reflected light intensity from the reference aperture was 14, and it was confirmed that the optical system could be calibrated according to the present invention.

[0020]

According to the present invention, there is no need to stop the line at the time of calibrating the surface inspection apparatus, and there is no need for a reference plate for calibration, so that simple and quick calibration can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a surface inspection apparatus using a point light source.

FIG. 2 is a diagram showing a configuration of a surface inspection apparatus using a CCD array sensor.

3A is a diagram showing a region near a welded coil, and FIG. 3B is a plan view of FIG. 3A.

FIG. 4 is a diagram showing an example in which a rubber roll is used as a support member for supporting a test object.

FIG. 5 is a diagram showing the relationship between the intensity of a received light signal and the position in the width direction of the test object when the optical system is correctly adjusted.

FIG. 6 is a diagram showing the relationship between the intensity of a received light signal and the position in the width direction of the test object when the optical system is not properly adjusted.

FIG. 7 is a diagram showing a flowchart of a calibration procedure according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Point light source 2 Inspection object 3 Photomultiplier tube 4 Strip light source 5 Image sensor 6 Rubber roll K Opening

Claims (2)

(57) [Claims] 1. A surface inspection for irradiating light to a surface of a plate-like inspection object, detecting reflected light from the surface with a light receiver, and inspecting the surface of the inspection object based on the intensity of the received light signal. In calibrating the optical system of the apparatus, an opening is formed in the test object through the test object, the reflected light intensity at this opening is measured, and when the reflected light intensity exceeds the calibration threshold, the surface is measured. A calibration method for a surface inspection device, comprising determining that calibration of an optical system of an inspection device is necessary, and performing calibration of the optical system. 2. The calibration method according to claim 1, wherein when irradiating the test object with light, the test object is supported by a support member having a different reflectance from the test object.