JP2510430B2 - Strip surface defect inspection method in continuous annealing furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspection method for strips in a continuous annealing furnace, and more particularly to a surface defect inspection method capable of detecting the occurrence of heat buckle in its initial stage.

[0002]

2. Description of the Related Art In a continuous annealing line for heat-treating a steel strip in a predetermined heat cycle, the annealing is caused by uneven tension distribution and temperature distribution in the strip width direction, strip meandering, etc. When compressive stress in the width direction is generated in the strip running in the furnace, and when this compressive stress exceeds the buckling strength of the strip, it is lengthened to the widthwise center of the strip or the contact portion with the shoulder drop portion of the hearth roll. It is known that wrinkles along the direction cause a so-called heat buckle. This heat buckle not only becomes a surface defect and reduces the product value, but there is also a risk that the strip will contact the equipment inside the furnace because the center of the strip shifts.
In some cases, it may be impossible to continue the operation or the hearth roll may be damaged. Therefore, if this heat buckle occurs, measures must be taken to immediately suppress it.

As a means for detecting the occurrence of the heat buckle, the reflected light of the laser light applied to the strip surface at an angle is imaged by a CCD camera or the like, and the signal is processed to detect the unevenness of the strip surface. A method of comparing this unevenness amount with a predetermined reference value is proposed in, for example, Japanese Patent Laid-Open No. 63-274806.

[0004]

However, in practice, since the signal due to the laser beam scanning contains various noise components which are harmful for discriminating the heat buckle, the signal of the judgment of the heat buckle is used. The setting was complicated, and it was difficult to detect the heat buckle especially at the early stage of occurrence. Therefore, it is inevitable that the heat buckle will grow to some extent at the time when the occurrence of the heat buckle can be detected, and it is possible to sufficiently satisfy the demand to reduce the occurrence of defective parts as much as possible. There wasn't.

The present invention has been devised in order to eliminate such disadvantages of the prior art, and its main purpose is to provide a continuous annealing furnace capable of detecting the occurrence of heat buckle in its initial stage. An object of the present invention is to provide a surface defect inspection method for strips.

[0006]

A signal obtained by scanning a strip surface running in a continuous annealing furnace in the width direction with a laser beam and receiving the reflected light with a photoelectric conversion element a method of inspecting a surface defect of the strip by treating the width direction scanning by the laser beam, substantially rows that have the same time at a plurality of locations adjacent to each other in the running direction of the strip, said plurality of laser
The strip of abnormal sites detected on each scan line of light
If the continuity is calculated by calculating the continuity in the traveling direction of
Judge the detected abnormality as the pre-symptom of the heat buckle,
If there is no continuity, the detected anomaly could be a noise or another source.
It is achieved by determining that it is due to the cause .

[0007]

[Function] As a pre-stage symptom of occurrence of heat buckle, it is known that relatively small wrinkles are intermittently formed in the strip of the hearth roll on the shoulder drop portion obliquely from the outer end to the center. According to the above configuration, if the positions of the defect detection signals obtained from a plurality of locations adjacent to each other in the traveling direction of the strip are regularly displaced in the width direction, it is possible to determine that the wrinkles are diagonal, and thus, It is possible to detect the pre-stage symptoms of the heat buckle.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to specific embodiments shown in the accompanying drawings.

FIG. 1 shows an example of the structure of the heat buckle detecting device. The detection device comprises a projector 1 composed of a He-Ne laser and a photoreceiver 2 composed of a CCD camera, which irradiates a laser beam toward a position adjacent to a portion wound around a hearth roll 3 and reflects the reflected light. An image signal obtained by picking up the light from the light receiver 2 is processed by the processing device 4, and the pre-heatbuckle symptom 6 generated on the surface of the strip 5 is detected from this data.

As shown in FIG. 2 together, a plurality of (for example, three) laser oscillators 1a and an optical system are provided inside the projector 1. Each of them has a laser light blocker 1b and a polarized light quantity. An adjuster 1c and an optical power meter 1d are provided so that the light quantity of the laser oscillator 1a can be adjusted to be constant. In addition, a beam expander 1e and a polygon scan mirror 1f are provided inside the projector 1, and a laser spot of 1 mmφ is irradiated on the surface of the strip 5 about 2000 mm apart to remove the shoulder drop portion of the hearth roll 3. Scanning is performed in a width direction at a plurality of positions (three places) parallel to the traveling direction of the strip 5 so as to include (line L in FIGS. 1 and 2). By changing the irradiation direction of the laser light emitted from the laser oscillator 1a with the pair of reflecting mirrors 1g, the total length of the projector 1 is shortened.

As shown in FIG. 3 as well, a plurality of light receivers 2 are installed in parallel in the width direction so as to face the surface of the strip 5 in the range including the shoulder drop portion of the hearth roll 3. Each CCD camera 2a consists of CCD cameras 2a
The fields of view V1 to V5 of the V.sub.1 and V.sub.5 are designed to overlap each other somewhat. By doing so, the CCD camera 2a
The resolution can be increased by reducing the imaging range per unit, and the resolution per CCD pixel is 0.5
mm can be obtained. In addition, on the front surface of the lens of the CCD camera 2a, for example, the interference filter 2 of 632.8 nm is used.
b is provided so that only laser light of a specific wavelength can be transmitted.

The shape of the surface defect is discriminated from the image obtained by the light receiver 2. The outline of the image signal processing according to the present invention is shown in FIG.
This will be described below with reference to the flowchart of FIG. First, an image input is obtained from the general surface on which the heat buckle 6 is not generated (step 1). On the other hand, the number of pixels sensitive within a predetermined sampling time is integrated for each level of the luminance signal,
Histogram calculation is performed (step 2). If the surface of the strip 5 is normal, this histogram is for the brightness where the number of pixels is sharply decreased, as shown in FIG. A binarization threshold value is set with a margin ratio (for example, brightness of about 20% higher) (step 3). Then, the image input signal is binarized based on this threshold value (step 4). Note that this binarization threshold value can also be set based on the total sum of pixels from the highest luminance side (for example, 1,500 to 1,800 pixels).

Next, each processing of thinning, elimination of isolated points, complementation of missing points, and filtering is performed (steps 5 to 5).
8) Convert to a displacement data array in the plate width direction. This is regressed by a predetermined functional expression to extract only the heat buckle component as shown in FIG. 6 (step 9), and the wave height value h and wave width value w of this heat buckle data array in the plate width direction are extracted.
Is calculated (step 10).

Image data obtained by performing the above-described series of processes for each CCD camera 2a is combined (step 1).
1) If the data for the entire board width direction is obtained, the feature amount is calculated from the data (step 12).

In this way, the three laser oscillators 1a are
As shown in FIG. 6, when the heat buckle data array obtained by scanning at 5 is regularly deviated in the width direction, it is projected obliquely at an angle α with respect to the running center of the strip 5. It can be judged that the strip is running, that is, the heat buckle is occurring. If the deviation in the width direction is not regular or the three images are discontinuous, it can be understood that it is due to noise or another cause.

The feature amount of the heat buckle thus obtained is compared with a predetermined allowable value (step 1
3) If it is equal to or more than the allowable value, an alarm is issued (step 14) or the rotation speed and the rotation torque of the hearth roll 3 are controlled by a separate control device,
The operating condition is appropriately changed so that the heat buckle is eliminated. When it is determined that a heat buckle has occurred, the image data is recorded in the external storage device 7 and saved as verification data.

[0017]

As described above, according to the present invention, since the strip surface is inspected on the basis of a plurality of signals at positions parallel to each other, the possibility of erroneous judgment due to the intervention of noise or the like is reduced. Since it can be made extremely small, the pre-stage symptoms of the heat buckle can be diagnosed from a relatively small amount of deformation. Therefore, it is possible to take an early action, and it is possible to exert a great effect in reducing the occurrence of defective portions.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a heat buckle detection device according to the present invention.

FIG. 2 is an internal configuration diagram of the projector 1.

FIG. 3 is an internal configuration diagram of a light receiver 1.

FIG. 4 is a flowchart relating to image signal processing according to the present invention.

FIG. 5 is an example of a histogram.

FIG. 6 is an example of a heat buckle waveform.

[Explanation of symbols]

 1 Emitter 2 Light receiver 3 Hearth roll 4 Processor 5 Strip 6 Heat buckle Pre-stage symptom 7 External storage device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 63-153679 (JP, A) JP-A 63-274806 (JP, A) JP-A 1-136055 (JP, A)

Claims (1)

(57) [Claims] 1. A surface defect of a strip is processed by scanning a surface of a strip running in a continuous annealing furnace with a laser beam in a width direction and processing a signal obtained by receiving the reflected light by a photoelectric conversion element. a method of inspecting the width direction scanning by the laser beam, substantially rows that have the same time at a plurality of locations adjacent to each other in the running direction of the strip, is detected in each scan line of said plurality of laser beam
Continuity of the abnormal area in the running direction of the strip
Of the detected anomaly, if there is continuity,
Judgment is the anterior symptom of the knuckle and is detected if there is no continuity
Surface defect inspection method of the strip in a continuous annealing furnace which was characterized and this <br/> for determining abnormality to be due to noise or other causes.