JPH0612343B2 - Surface inspection device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a surface inspection apparatus for optically detecting a surface defect of a running object.

[Technical background of the invention and its problems]

For example, as shown in FIG. 1 (A), surface defects of the test object 1 such as a steel plate or an aluminum plate formed by a rolling mill include linear marks 2 and 3 such as welding marks and breaks, and stains. There is an area-based flaw 4, and regarding the linear flaws 2 and 3, there are a flaw 3 generated in a direction orthogonal to the running direction of the subject and a flaw 2 other than that.

The optical surface inspection device optically scans the width direction of the subject to detect the reflected light reflected from the width direction surface,
The flaw detection signal is extracted by differentiating the detection signal.

In this method, as shown in FIGS. 1 (C) and (D), it is possible to identify and detect an area flaw 4 such as dirt or a linear flaw 2 that is not orthogonal to the traveling direction of the subject 1. ，
It is orthogonal to the traveling direction of the subject 1 shown in FIG. 1 (B). That is, it was difficult to detect the linear flaw 2 that coincides with the optical scanning direction.

That is, since the linear flaw 3 that coincides with the optical scanning direction appears as a change in the scanning signal level for each scanning, it is difficult to detect even if the signal for one scanning is differentiated.

[Object of the Invention]

The present invention provides a surface inspection apparatus capable of accurately detecting a linear flaw that matches the optical scanning direction.

[Outline of Invention]

According to the present invention, a scanning signal for each scanning is stored, the signal is compared with the signal one cycle before, the determination is made, and the distribution of the determination signal in the flow direction of the object is determined. This is a surface inspection device capable of separating and detecting many flaws from many flaws.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS.

Reference numeral 10 denotes, for example, a laser light source, and a laser beam 11 from the laser light source 10 is applied to the surface in the width direction of a subject 13 traveling by a polygon mirror rotating mirror 12.
That is, the width direction of the subject 13 is scanned by the laser beam 11. The laser beam 11 is detected by the detection head 14 after the light amount changes due to the reflection and absorption on the surface of the subject.

The signal detected by the detection head 14 is supplied to the filter circuit 16 via the amplifier 15. The filter circuit 16 removes a noise component (denoted by symbol V _N in FIG. 1D) from the detection signal and smoothes it. The smoothed detection signal is A / D conversion circuit 1 that proportionally integrates the signal, holds the integrated value, and then performs A / D conversion.
7 is being supplied. The output of the A / D conversion circuit 17 is supplied to the register group 20 in the subsequent stage.

The register group 20 has the same number of registers 21 as the mirror surface of the rotary mirror 12, and the registers 21 and the A / D conversion circuit 17 are switched in synchronization with the rotation of the rotary mirror 12.

That is, each register 21 stores a signal corresponding to each mirror surface of the rotary mirror 12. A register 22 is further connected to each of these registers 21. These registers 22 are for storing and retaining the N-1 cycle signals stored prior to the N cycle signals supplied to the register 21. The output of the register 22 and the output of the register 21 are supplied to the subsequent arithmetic circuit group 23.

The arithmetic circuit group 23 has the same number of arithmetic circuits 24 as the number of the registers 21 or 22, respectively. Each of these arithmetic circuits 24 calculates the difference between signals for two consecutive cycles for each mirror surface of the rotating mirror 12.

The reason why the signals of the respective mirror surfaces are compared in this way is to eliminate an error due to a difference in reflectance between the mirror surfaces of the rotating mirror 12. Of course, if it is possible to make the reflectances of the respective mirror surfaces exactly the same, it is not necessary to make such a comparison for each mirror surface.

However, as shown in FIGS. 3 (A) and 3 (B), the reflectances on the respective mirror surfaces are generally different, and even if they are manufactured identically, they change over time. FIG. 3 (B) is a waveform diagram showing the reflectances corresponding to the respective mirror surfaces a, b, ... Shown in FIG. 3 (A).

The output of each of these arithmetic circuits 24 is the A / D converter 17
And the register 21 are connected in the same manner as the rotating mirror 1 described above.
It is taken out in synchronization with 2. Then, these arithmetic circuits 24
The output of is compared with the set value from the setting circuit 26 in synchronization with the subject 13 in the comparison and determination circuit 25. The result of this comparison judgment is the tracking circuit 2 as shown in FIG.
7 is tracked in the moving direction and stored. Fourth
The figure (A) shows that the subject 13 is not scanned for each scan but
Are shown separately for each predetermined movement unit of
(B) shows the storage state of the tracking circuit 27 for each section, and the shaded portion in the storage content indicates a defect. The output of the tracking circuit 27 is supplied to the determination circuit 28 in the subsequent stage, and the defect type is determined from the distribution state of the comparison determination result stored in the tracking circuit 27 in the moving direction of the subject 13.

That is, when the stored determination result is, for example, three or more consecutive defects, it is determined to be a surface defect 4, and when the stored determination result is two or less, the direction coincides with the scanning direction of the laser beam 11. It is determined as defects 3 and 3'occurring in

〔The invention's effect〕

Since the present invention is configured as described above, it is possible to separate and detect a linear flaw generated in a direction coinciding with the optical scanning direction from other flaws.

[Brief description of drawings]

FIG. 1 is a diagram showing the state of the surface of a subject and the waveform of a detection signal corresponding to each flaw type, FIGS. 2 to 4 are diagrams for explaining one embodiment of the present invention, and FIG. 2 is a circuit configuration. FIG. 3 and FIG. 3 are diagrams for explaining the reflectance of each mirror surface of the rotating mirror that scans the laser beam, and FIG. 4 is a diagram for explaining the distribution of the determination result corresponding to the flaw type. 10 ... laser light source 11 ... laser beam 12 ... polygon mirror 13 ... object 14 ... detection head 20 ... register group 23 ... arithmetic circuit group 25 ... comparison judgment circuit 26 ... setting circuit 27 ... tracking Circuit 28: Discrimination circuit

Claims (1)

[Claims] 1. A surface inspection apparatus for inspecting a surface of an object to be inspected by scanning the surface of the object to be inspected in the width direction and detecting a reflected light from the surface of the object to be inspected by a detection head. A comparison determination for comparing the scanning means having one scanning cycle, the storage means for storing the scanning signals for two consecutive cycles of the scanning means, and the scanning signal for two consecutive cycles stored in the storage means A surface inspection apparatus comprising: a means; and a detection means for detecting a flaw type from the distribution in the moving direction of the determination result determined by the comparison determination means.