JPH0450528B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an apparatus for optically detecting flaws containing dirt on the surface of an object to be inspected such as a strip steel plate, and particularly to a surface inspection device having a function of determining the type of flaw. Regarding equipment.

[Technical background of the invention and its problems]

Conventionally, surface inspection devices that optically detect surface flaws on a test object take advantage of the fact that the amount of reflected light changes depending on the condition of the surface. For example, a laser beam is scanned in the width direction of the surface of the test object. It is known to detect surface flaws by integrating reflected light signals in each width direction over a certain length of the object.

In such an apparatus, the type of a surface flaw is determined mainly based on the shape of the detected surface flaw.

However, even if the flaws have the same shape, they are often completely different types of flaws. For example, in steel plates, scratches and defects called slivers, where mixed foreign matter is stretched and appear on the surface, are:
Both are detected as linear flaws, and both scratches and scale are detected as a collection of fine dot-like flaws.

Therefore, there is a need for a surface inspection apparatus having a function of identifying types of surface flaws that are detected as having the same shape.

[Purpose of the invention]

The present invention provides a surface inspection device having a function of identifying types of surface flaws detected as having the same shape.

[Summary of the invention]

The present invention focuses on the fact that even flaws with the same shape have different reflection/absorption characteristics, and calculates the shape of the detected flaw, that is, the ratio of the area of the reflective or absorbing portion to the total area of the flaw. This is a surface inspection device that has the function of identifying types of surface flaws.

[Embodiments of the invention]

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

Reference numeral 10 indicates an object to be inspected, such as a strip-shaped steel plate, which is conveyed in the direction of arrow A. A laser light source 12 is arranged above the surface of the subject 10 to irradiate the surface of the subject 10 with laser light via a rotating mirror 11. The laser light from this laser light source 12 is
The rotating mirror 11 irradiates the surface of the subject 10 so as to scan it in its width direction, as shown by arrow B. A detection head 13 is arranged in the direction in which this laser light is reflected. This detection head 13
receives reflected light from the surface of the subject 10 and converts it into an electrical signal. That is, the detection head 13 sequentially detects flaw signals in each width direction of the object 10 by scanning the object 10 with the laser beam in the width direction and by moving the object 10 . Further, this detection head 13 is connected to a pulse height discrimination circuit group 15 via an amplifier 14.

This wave height discrimination circuit group 15 is connected to the detection head 1.
The first,
It is composed of second wave height discrimination circuits 16 and 17. This first wave height discrimination circuit 16 is for extracting a reflective flaw signal from the reflected light signal from the detection head 13, and receives an appropriate positive level discrimination signal in addition to the output of the detection head 13. has been done.

Further, the second pulse height discrimination circuit 17 is for extracting an absorbing flaw signal in contrast to the first pulse height discrimination circuit 16, and is inputted with an appropriate negative level discrimination signal.

The two wave height discrimination circuits 16 and 17 are connected to the OR circuit 1
8, the first pulse height discrimination circuit 16 is also directly connected to a histogram generation circuit group 20.

This histogram creation circuit group 20 creates a histogram by integrating the flaw signals in each width direction output from the respective wave height discrimination circuits 16 and 17 for each predetermined length of the object 10. It is composed of histogram creation circuits 21 and 22. This first histogram creation circuit 21 is connected to the first pulse height discrimination circuit 16, and the second histogram creation circuit 22 is connected to both pulse height discrimination circuits 16 and 17 via an OR circuit 18. ing.

In addition, this second histogram creation circuit 22
is connected to the flaw cutting circuit 23. The flaw extraction circuit 23 extracts, for example, a portion of the created histogram showing a peak value as a representative flaw.

Further, both the histogram creation circuits 21 and 22
is connected to the counter group 24. This counter group 24 has first and second counters each receiving a signal from the flaw cutting circuit 23 as a gate signal.
It consists of counters 25 and 26. The first histogram creation circuit 21 is connected to the first counter 25, and the second histogram creation circuit 21 is connected to the second counter 26.
Histogram creation circuits 22 are connected to each.

Further, this counter group 24 is connected to a division circuit 27. This division circuit 27 divides the output of the first counter 25 by the output of the second counter 26, and divides the reflective flaw signal discriminated by the first wave height discrimination circuit 16 with respect to the total area of the representative flaw. This is to calculate the area ratio corresponding to the representative flaw.

Further, this division circuit 27 is connected to a comparison judgment circuit 28.
It is connected to the. The comparison/determination circuit 28 compares the output of the division circuit 27 with the set value S from the setting circuit 30 to determine whether the flaw is reflective or absorbent, and compares the result with the flaw shape from the flaw shape determination circuit 31. This is to identify the type of typical flaw from the signal.

That is, a scratch and a sliver, or a scratch and a scale, which are recognized as having the same shape by the flaw shape determination circuit 31, are identified based on the reflectivity of the flaw obtained from the comparison and determination circuit 28. In addition, this comparison/determination circuit 28 determines that the representative flaw is
In order to know at which position of 0, a synchronous pulse generator 32 is connected which outputs a signal of the traveling position of the subject 10. Note that 33 is a roll connected to this synchronous pulse generator 22.

Next, the operation of one embodiment configured as described above will be explained with reference also to FIGS. 2 to 5.

Laser light from the laser light source 12 is scanned in the width direction of the subject 10 via the rotating mirror 11. This laser light is reflected by the surface of the subject 10 and supplied to the detection head 13. This head 1
3, an electrical signal corresponding to the surface condition of the subject 10 is obtained. At this time, the polarity of the signal may be either positive or negative depending on the optical characteristics, that is, the reflection and absorption characteristics of the flaw on the surface. The signal from this detection head 13 is passed through an amplifier 14 to a pulse height discrimination circuit group 1.
5 and is binarized. Here, among the signals, a signal of positive polarity, that is, a reflective signal, is sent to the first pulse height discrimination circuit 16, and a signal of negative polarity, that is, an absorbing signal, is passed to the second pulse height discrimination circuit 17, respectively.
Valued. Furthermore, this pulse height discrimination circuit group 15 uses the synchronization pulse from the synchronization pulse generator 32 to perform quantization into pixels of an appropriate size.

This state is shown in FIG. Figure 2 shows the subject 10.
This shows an example of an image of the flaw itself on the surface of , 40, 50, and 60 indicate the flaw shape,
50a is a reflective flaw, 40b, 50b, 60b
indicate absorbable flaws. The reflective scratches 40a, 50a serve as positive electrodes in FIG. 3, and the absorbent scratches 40b, 50b, 60b serve as negative poles.

Next, the signals thus binarized into positive and negative signals are supplied via the OR circuit 18, and the positive polarity signal is directly supplied to the subsequent histogram generation circuit group 20. The positive and negative signals supplied through the OR circuit 18 are used by a second histogram creation circuit 22 to total the number of flaws within a certain length range in the longitudinal direction of the object to be inspected, thereby obtaining a histogram as shown in FIG.

On the other hand, the first histogram creation circuit 21 to which the positive signal from the first pulse height discrimination circuit 16 is supplied obtains a histogram as shown in FIG. 5 in the same manner as the second histogram creation circuit 22.

That is, this first histogram creation circuit 2
1, the second histogram creation circuit 22 creates a histogram of the entire flaw, which is a combination of the reflective flaw and the absorptive flaw.

Further, the output of the second histogram creation circuit 22 is supplied to a flaw extraction circuit 23, and a representative flaw area 50' is extracted. This selection is performed, for example, by using a portion within one third of the height from the highest value of the histogram as a representative flaw site (referred to as the profile method).

The signal of the selected representative flaw 50' is supplied to each counter 25, 26 of the counter group 24 as a gate signal. Therefore, the number of pixels of the representative flaw site 50 in the reflective histogram supplied to the first counter 25 is counted. That is, the number of positive electrode (reflective) pixels in the representative flaw site 50 is counted. On the other hand, the second counter 26 counts the number of pixels of both positive and negative polarities of the representative flaw area, that is, the number of pixels of the entire representative flaw area.

The number of pixels of the entire representative flaw site and the number of positive pixels are then supplied to a division circuit 27, where the latter is divided by the former to determine the ratio of the reflective flaw site to the entire flaw. The output of the division circuit 27 is compared with the setting signal S from the setting circuit 30 by the comparison/judgment circuit 28 to obtain the degree of reflection/absorption of the representative flaw site 50. The reflection/absorption characteristics of flaws are different even for the same shape, and the setting signal S can be determined by knowing the characteristics in advance.

Further, the comparison and determination circuit 28 is supplied with a shape signal of a representative flaw portion from a flaw shape determination circuit 31 and a flaw position signal from a synchronization pulse generator 32, respectively.

Therefore, by this comparison judgment circuit 28,
It becomes clear at what position, what shape, and what kind of reflection/absorption characteristics the flaw exists on the subject 10. That is, unlike the conventional method, it is possible to determine a finer type of flaw than by determining the type of flaw based on shape.

〔Effect of the invention〕

Since the present invention is configured in this way, even if the flaw has the same shape, the reflection and absorption characteristics of the flaw are utilized,
By detecting the degree of reflection and absorption, it becomes possible to discriminate the type of flaw more precisely.

[Brief explanation of the drawing]

The figures are for explaining one embodiment of the present invention, and FIG. 1 is a circuit configuration diagram, FIG. 2 is a diagram showing the state of a flaw on the surface of an object to be inspected, and FIG. 3 is a state in which the flaw is quantized. The figures shown in FIG. 4 and FIG. 5 are diagrams showing histograms, respectively. 10... Subject, 12... Laser light source, 13
... Detection head, 15 ... Wave height discrimination circuit group, 16
...First wave height discrimination circuit group, 17... Second wave height discrimination circuit group, 18... OR circuit, 20... Histogram creation circuit, 21... First histogram creation circuit, 22... Second histogram creation circuit,
23...Flaw cutting circuit, 24...Counter group,
25... first counter, 26... second counter, 27... division circuit, 28... comparison judgment circuit,
30...setting circuit, 31...flaw shape determination circuit.

Claims (1)

[Claims] 1. In a surface inspection device that optically scans the surface of a moving object in the width direction and detects flaws on the surface of the object by receiving reflected light from the surface, a detection head that receives reflected light from the object. and a first pulse height discriminator circuit that discriminates the detection signal from the detection head in each width direction of the surface of the object to be inspected at a predetermined positive level and outputs it as a binary flaw signal; A second pulse height discriminator circuit discriminates at a predetermined negative level and outputs a binary flaw signal, and a flaw signal for each width direction from either the first or second pulse height discriminator circuit is output to the test object. a first histogram creation circuit that creates a histogram by adding each predetermined length of the first and second histograms;
a second histogram creation circuit that adds both flaw signals in each width direction from the wave height discrimination circuit for each predetermined length of the object to create a histogram; and a flaw section that selects a representative flaw signal from the output of this circuit. an extraction circuit; a first counter that counts the area of a representative flaw in the output of the first histogram creation circuit using the output of the circuit as a gate signal; and creation of the second histogram using the output of the flaw extraction circuit as a gate signal. a second counter that counts the area of the representative flaw as a circuit output; and the first or second pulse height discriminator circuit that divides the first counter output by the output of this counter to calculate the total area of the representative flaw. A division circuit that calculates the area ratio of a flaw corresponding to a representative flaw, and a comparison judgment circuit that compares the output from this division circuit with a predetermined value and determines the type of flaw of the representative flaw. Features of surface inspection equipment.