JPH10122842A - Method for measuring flatness of steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for accurately measuring flatness of a hot rolled steel plate with a simple apparatus constitution. SOLUTION: The method for measuring flatness of a steel plate comprises the steps of emitting a laser beam 4 to a half mirror 2 mounted at 45 degrees obliquely at an end of a rotary shaft of a motor, emitting its reflected beams 21, 22 obliquely onto a feeding steel plate 5 to form loci 5 of the two laser spots, then detecting the spots of two points on the sheet 5 by a two-dimensional CCD camera 8 disposed above perpendicularly to the feeding direction of the plate 5, and measuring change of the spot loci from a straight line of the perpendicular direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring flatness of a steel sheet, and more particularly to a method for accurately measuring the flatness of a traveling hot-rolled steel sheet with a simple apparatus configuration.

[0002]

2. Description of the Related Art It is important to accurately measure the shape, particularly the flatness, of a traveling hot-rolled steel sheet in order to improve the shape and quality of a steel sheet material. Conventionally, as a method of measuring the shape of a steel sheet, for example, a method of determining the position of an irradiated spot laser beam by a triangulation method using two cameras arranged at different positions (Japanese Patent Laid-Open No. 7-77414), A method (Japanese Patent Laid-Open No. 7-243820) for reducing a measurement error due to a scanning speed non-uniformity in one scanning cycle in a light beam scanning unit, and a method in which almost entire reflected light from an object to be inspected is incident on a condenser lens. There has been proposed a method of accurately detecting a defect of an object to be inspected by detecting the amount of light with a photodiode or the like (JP-A-7-270336). However, these are good for measurement of cold-rolled steel materials, but are not suitable for hot-rolled steel materials, and have problems such as a large-scale apparatus and poor accuracy.

[0003] As a method for measuring the shape of a hot-rolled steel sheet,
Optical cutting method using laser-based triangulation (Matsui et al., "Sumitomo Metals" vol. 41, p. 69 (1989)), and laser moire method using grating and laser, "Matsuo et al.," Materials and Processes "vol.
1, pp. 1581 (1983)) and a method of irradiating a laser beam to a steel sheet surface with a rotating mirror and a parabolic mirror, converting reflected light into an electric signal by a light receiving device, and calculating the intensity of the reflected light (Japanese Patent Laid-Open No. 60-6095
No. 03 gazette) has been proposed. However, the optical cutting method and the laser moiré method cannot measure the amount of change of the shape in absolute value, and have a problem in maintaining accuracy due to a relative measurement method in which a correction method is determined in advance and an actual measurement value is corrected, and the apparatus is complicated. Further, the method of combining the rotating mirror and the parabolic mirror has a problem that the device becomes complicated.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for accurately measuring the flatness of a running steel sheet, particularly a hot-rolled steel sheet, with a simple apparatus configuration.

[0005]

Under such circumstances, the present inventors have made intensive studies and completed the present invention. That is, according to the present invention, a laser beam is made incident on a half mirror mounted at a 45-degree angle to the tip of the rotating shaft of a motor, and the reflected light is emitted obliquely onto a traveling steel plate to form a locus of two laser spots. Then, two laser spots on the steel plate are detected with a two-dimensional CCD camera positioned perpendicularly and upward to the running direction of the steel plate, and the displacement of the spot trajectory from a vertical straight line is measured. And a method for measuring the flatness of a steel sheet.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 1 is a diagram showing a method of forming a double beam, which is a main part of the measuring method of the present invention. Figure 2 shows the trajectory of a laser spot on a running steel plate and a two-dimensional CCD.
FIG. 3 is a diagram illustrating a positional relationship between cameras. FIG. 3 is a diagram showing a positional relationship between a double beam scanner and a traveling steel plate.
FIG. 4 is a plan view of an optical scanner that forms a double beam. FIG. 5 is a diagram showing an example of a beam spot trajectory observation screen using a two-dimensional CCD camera. FIG. 6 is a diagram showing a mutual positional relationship between laser spots on a steel plate.
FIG. 7 shows a signal processing flow in the image processing apparatus.

As shown in FIG. 1, a laser beam 4 is made incident on a half mirror 2 attached to a rotating shaft tip 10 of a motor 1 at an angle of 45 degrees from a front surface. The half mirror 2 has been subjected to a surface treatment so as to reflect twice on the front surface and the back surface. The thickness of the half mirror is not particularly limited, but is preferably about 1.0 cm. In FIG. 1, a laser generator (laser light source) 3 is provided in front of the motor shaft. If the laser beam is incident from the front by using mirrors 11 and 12 as shown in FIG. The positional relationship of the device 3 is not limited. When the half mirror 2 rotates by the rotation of the motor 1, the two reflected beams 21 and 2 reflected by the half mirror 3
2 rotates on a plane perpendicular to the incidence of the laser beam while maintaining the distance d ₀ .

As shown in FIG. 2 and FIG. 3, the reflected beams 21 and 22 generated from the optical scanner 7 including a motor, a half mirror, and a laser generator are positioned above the traveling steel plate 5 and are reflected by the traveling steel plate 5. When projected upward, a locus 6 of two laser spots is formed on the steel plate. The reflected beams 21 and 22 are projected obliquely to the traveling steel plate 5. The preferable projection angle (incident angle θ) is 3
It is 0 ° to 60 °, and it is particularly preferable to set it to 45 ° from the viewpoint of increasing the measurement accuracy.

In the present invention, the two-dimensional CCD camera 8 is located at a right angle and obliquely to the running direction of the steel plate. The shooting angle (δ) formed from the direction of the camera 8 and the trajectory line of the laser spot on the steel plate is not particularly limited.
Degrees to 50 degrees is preferred. The reason for setting the photographing angle in this way is that, for example, if the width of the steel plate is 1 m and the displacement in the vertical direction is 1 cm, the change range of the laser spot also changes to almost the same extent. Therefore, the measurement visual field is 1 m × 1 cm, which is an extremely elongated visual field. When this is measured with a camera, the change in the laser spot trajectory is small, so that the resolution is not significantly deteriorated, so that the change in the trajectory of the fine laser spot compressed in the longitudinal direction can be obtained on an enlarged screen. be able to. In addition, as shown in FIG. 1, the interval between the two laser spots is always d ₀ , and the swell (displacement) of the steel sheet may be obtained based on this.

In the method of the present invention, a screen obtained by measuring the trajectory of the laser spot on the steel plate with the two-dimensional CCD camera is as shown in FIG. If the steel plate is flat, the laser spot moves on two straight lines (FIG. 5A). When the steel plate moves up and down, the trajectory moves left and right while keeping a straight line (FIG. 5).
(B)). On the other hand, for a non-flat steel plate, the trajectory of the laser spot deviates from a straight line and shows a curve corresponding to the undulation of the steel plate (FIG. 5C). Thus, the undulation of the steel sheet can be measured as a deviation of the laser spot from the straight line.

Next, the measurement principle of the method of the present invention will be described. As shown in FIG. 6, when the steel plate shifts up and down by d from the reference position, the laser spot moves right and left by u from the reference position, and the movement distance is expressed by the following equation (1). u = d × tan θ (1) (where, θ represents the irradiation angle of the reflected beam.) The beam interval u ₀ is expressed by the following equation (2). u ₀ = d ₀ / cos θ (2) Here, when the ratio between u and u _{0 is obtained} , the vertical movement distance (flatness) d of the steel sheet is expressed by the following equation (3). d = (u / u ₀ ) × (d ₀ / sin θ) (3) From the expression (3), d is always accurate without being affected by the parallax of the camera.
It can be seen that can be measured. Further, as is clear from the equations (1) and (2), the closer the irradiation angle is to the horizontal, the larger the moving distances u and u ₀ are, and the higher the measurement accuracy is.

In the method of the present invention, it is preferable to make the rotation cycle of the half mirror coincide with the scanning cycle of the two-dimensional CCD camera, since the laser spot is always stably displayed on the screen.

Further, in the method of the present invention, if the wavelength of the laser is in the ultraviolet region and the camera is equipped with a filter that transmits only the light in the ultraviolet region of the laser wavelength range, the steel plate is glowed to 1000 ° C. or more. In addition, a clear laser spot can be detected by the camera by removing the heat radiation of the steel plate. The wavelength in the ultraviolet region is preferably 0.3 μm or less.

In the present invention, the output of the two-dimensional CCD camera is input to an image processing device. As shown in FIG. 7, the image processing apparatus first detects only a laser spot by a binarization process. Next, the center of gravity of the spot image is calculated, and this position is set as a laser spot position. The locus of the laser spot is detected as the locus of the center of gravity. A reference line is set in the vertical direction on the screen, and a deviation from the reference line is determined. The average value of the deviation is ignored as the vertical movement of the steel sheet, and the deviation from the average value is regarded as a displacement indicating flatness. The amount of displacement on the screen may be obtained by taking the ratio between the two laser spots in order to correct the parallax from the distance between the two laser spots, and calculating the effective amount of displacement d from equation (3).

In the present invention, the steel sheet is not particularly limited, and may be, for example, a cold-rolled steel sheet, a flat plate of paper, plastic, fiber material, or the like, in addition to a hot-rolled steel sheet.

The steel sheet may be in a stationary state or a running state. The required measurement density can be obtained by selecting the synchronization time between the scanning cycle of the camera and the rotation speed of the half mirror. For example, when a traveling steel plate of 2 m / sec is synchronized in 1/60 sec, the measurement density of 2/60 m is obtained. Becomes

[0017]

The present invention will be described in more detail with reference to the following examples, which are merely illustrative and do not limit the present invention.

(Measurement of Flatness of Dummy Steel Plate) A dummy steel plate having a width of 500 mm and a thickness changed in 10 steps every 5 mm was measured. Fig. 3 shows the configuration of the laser beam scanner.
And as shown in FIG. An air-cooled argon laser having an output of 50 mW and a wavelength of 488 nm was used as a laser light source. A half mirror was attached to the tip of the motor shaft so as to be rotatable at a 45 degree angle. The irradiation angle was 45 degrees, the scanning cycle of the camera was 1/60 sec, and the rotation speed of the half mirror was 60 r.ps.

A two-dimensional CCD camera equipped with an interference filter that transmits only the wavelength of the argon laser was set at a photographing angle of 45 degrees so that a field of view could be taken at right angles beside the steel plate. In addition, the direction of the scanning line of the camera and the traveling direction of the steel plate were matched. Therefore, the displacement direction of u coincides with the scanning direction of the camera. The output of the two-dimensional CCD camera was taken into an image processing apparatus and performed in the same manner as in the above-mentioned image processing method, and the effective displacement d (flatness) was obtained. The results are shown in Table 1. Note that d ₀ = 10 mm, l is the distance from the camera to the measurement point, u is the displacement, and u ₀ is the reference spot interval.

[0020]

[Table 1]

As apparent from Table 1, according to the method of the present invention, the accuracy of the flatness of the dummy steel plate was measured within ± 2 mm.

(Measurement of flatness of hot-rolled steel sheet) The flatness of the dummy steel sheet was changed except that the steel sheet surface temperature was 1100 ° C., the moving speed of the steel sheet was 1.5 m / sec, and the distance from the camera to the center line of the steel sheet was 2.5 m. The measurement was carried out in the same manner as the degree measurement method. The obtained results were compared with the results obtained by measuring the center line of a steel sheet with a contact displacement meter. The results are shown in FIG. The measurement accuracy showed a high accuracy within ± 3 mm.

[0023]

According to the method of the present invention, the flatness of a running steel plate can be accurately measured with a simple apparatus configuration. Also,
In this method, a two-dimensional CCD camera is arranged obliquely from above and corrected by the reference length, so that dimensions on the screen can be converted to dimensions on the steel sheet without being affected by the distance (steel width). In addition, in the present method, even if the width of the steel plate changes, the end portion is automatically detected, and the measurement position in the width direction can be determined. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method of forming a double beam, which is a main part of a measurement method of the present invention.

FIG. 2 is a diagram showing a locus of a beam spot on a running steel plate according to the present invention and a positional relationship of a two-dimensional CCD camera.

FIG. 3 is a diagram showing a positional relationship between the double scanner of the present invention and a running steel plate.

FIG. 4 is a plan view showing an optical scanner for forming a double beam according to the present invention.

FIG. 5 is a diagram showing a mutual positional relationship between laser spots on a steel plate according to the present invention.

FIG. 6 is a diagram illustrating an example of a locus observation screen of a laser spot by the two-dimensional CCD camera of the present invention.

FIG. 7 is a diagram showing a signal processing flow in an image processing apparatus using a two-dimensional CCD camera of the present invention.

FIG. 8 is a correlation diagram between the measurement method of the present invention and a measurement method using a contact displacement meter.

[Explanation of symbols]

 Reference Signs List 1 motor 2 half mirror 3 laser light source 5 steel plate 8 two-dimensional CCD camera

Claims (3)

[Claims] 1. A laser beam is made incident on a half mirror mounted at a 45-degree angle to the tip of a rotating shaft of a motor, and the reflected light is radiated obliquely on a traveling steel plate to form a trajectory of two laser spots. Then, two laser spots on the steel plate are detected with a two-dimensional CCD camera positioned perpendicularly and upward to the running direction of the steel plate, and the displacement of the spot trajectory from a vertical straight line is measured. The method for measuring flatness of a steel sheet. 2. The method for measuring flatness of a steel sheet according to claim 1, wherein the rotation cycle of the half mirror and the scanning cycle of the two-dimensional CCD camera are made coincident to detect the two laser spots. 3. The wavelength of the laser beam and the two-dimensional CCD.
3. The method for measuring flatness of a steel sheet according to claim 1, wherein a detection wavelength of the camera is in an ultraviolet region, and a laser spot is detected by removing thermal radiation light of the steel sheet that glows red.