JPH09229874A - Apparatus for monitoring surface of metal band - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily monitor defects such as stains or the like of surface-treated stainless steel plates and steel plates, etc. SOLUTION: One-dimensional image sensors 3-5 are arranged in the bread direction of the surface of a transferred metal band 1. Outputs if the image sensors are stored overflowing in a first memory. When a detect is detected, the storing operation by the first memory is continued after a time point when the defect is detected until a part of the detected defect occupies, e.g. half a storing area of the capacity of the first memory. Then the stored content in the first memory is transmitted to a second memory, and a still image displayed. A inspector 9 can detect sort and size of the defect from the still image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal band surface monitoring device for monitoring defects such as stains on the surface of a metal band such as a steel plate and a stainless steel plate which are passed and conveyed at high speed.

[0002]

2. Description of the Related Art A typical prior art for monitoring the surface of a metal strip such as a surface-treated stainless steel sheet and a steel sheet to be conveyed is a defect in which the surface of the metal strip is imaged by using a two-dimensional camera. Monitor for dirt.

In this prior art, since the field of view of the camera is a two-dimensional plane, a light source that radiates uniform light within the range of the field of view of the camera is required, and it is difficult to manufacture such a light source.
Therefore, there is a problem in that the image of the two-dimensional camera is liable to be bright and dark due to the difference in the amount of light emitted from the light source, and therefore only a rough, low-precision monitoring can be performed.

In another prior art, a linear light source such as a fluorescent lamp irradiates the metal strip in the width direction, and the illuminance distribution of the light rays reflected on the surface of the metal strip is detected using a one-dimensional image sensor. The illuminance distribution is calculated by a calculation circuit and analyzed, and a complicated logical calculation is performed to determine the quality of the surface of the metal strip.

In this prior art, since it is premised that inspection is performed with high precision with respect to quality needs without the intervention of an operator, the hardware and software of the arithmetic circuit are very large in scale. However, the structure is complicated and therefore expensive. Further, since the same inspection result as the inspection by the human eye is required, it is necessary to set a wide variety of conditions such as the degree of stain, which is a defect, the color, and the size. This condition setting is troublesome because it needs to be reviewed even during operation. Therefore, there is a big problem that performing such automated monitoring according to the prior art is extremely troublesome.

Further, conventionally, an operator visually inspects the surface of a metal strip to be conveyed, for example, to inspect for defects. In this prior art, when the operator is very tired and the reflectance of the surface of the metal strip is high, accurate monitoring can be continued for about 10 minutes at most, and defects may be overlooked.

[0007]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a surface of a metal strip capable of monitoring the surface of, for example, a surface-treated steel plate or a stainless steel plate with high accuracy and with a simple structure. It is to provide a monitoring device.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a one-dimensional image sensor extending in the width direction of a metal strip to be conveyed and detecting the surface of the metal strip, and position detecting means for detecting the position of the metal strip in the conveying direction. In response to the output of the one-dimensional image sensor and the position detecting means, the output of the one-dimensional image sensor is sequentially shifted over a predetermined distance in the carrying direction, and the old stored contents are overflowed and erased. When the output of the first memory, the second memory, and the one-dimensional image sensor is level-discriminated to detect a defect on the surface of the metal strip, and the defect is detected in response to the output of the level-discriminating device. The output of the one-dimensional image sensor is the first
Means for sequentially storing in the memory in the shift direction of the first memory until a predetermined store area is reached, and when the predetermined store area is reached, the stored contents of the first memory are transferred to the second memory. And a display means for displaying the contents stored in the second memory, the surface monitoring device for the metal strip. The present invention also includes a first alarm sound generating means that is provided in the vicinity of the one-dimensional image sensor and that generates a first alarm sound when a defect is detected in response to the output of the level discriminating means.
It is provided in the inspection area on the downstream side of the one-dimensional image sensor in the conveying direction of the metal strip, and responds to the output of the level discrimination means,
Second alarm sound generating means for generating a second alarm sound different from the first alarm sound when the detected defect portion of the metal band reaches the inspection area when the defect is detected. Is characterized by. The present invention is also responsive to the output of the position detecting means and the level discriminating means, when a defect is detected, a means for outputting a defect position signal indicating the position of the detected defect portion of the metal strip, and the metal strip. For storing the defective position and the identification code in the second memory together with the contents transferred from the first memory, in response to the output of the identification code for identifying the defective position signal output means and the output of the defective position signal output means and the identification code generating means. And means for doing so. Further, according to the present invention, a one-dimensional image sensor that extends in the width direction of a conveyed metal strip and detects the surface of the metal strip, a position detection unit that detects a position of the metal strip in the conveyance direction, and an output of the one-dimensional image sensor. Is provided in the vicinity of the level discriminating means for detecting a defect on the surface of the metal strip by discriminating the level, and in response to the output of the level discriminating means, when a defect is detected, a first alarm sound is generated. The first alarm sound generating means and the one-dimensional image sensor are provided in the inspection area on the downstream side of the metal strip in the conveying direction, and when the defect is detected in response to the output of the level discriminating means, the metal strip is detected. Responsive to the outputs of the second alarm sound generating means for generating a second alarm sound different from the first alarm sound when the defective portion reaches the inspection area, and the outputs of the position detecting means and the level discriminating means. ,
When a defect is detected, a means for outputting a defect position signal indicating the position of the detected defect portion of the metal strip, a means for generating an identification code for identifying the metal strip, a one-dimensional image sensor and a position detecting means. A first memory and a second memory which store the output of the one-dimensional image sensor while sequentially shifting it over a predetermined distance in the carrying direction in response to the output of And when a defect is detected in response to the output of the level discrimination means, the output of the one-dimensional image sensor is stored in the first memory,
Sequential storage is performed in the shift direction of the second memory until a predetermined store area is reached, and when stored in the predetermined store area, the stored contents of the image in the first memory are transferred to the second memory. Means, a defect position signal output means, and a means for storing the defect position and the identification code in the second memory together with the contents transferred from the first memory in response to the outputs of the means and the second memory. A surface monitoring apparatus for a metal strip, comprising: a display unit for displaying an image transferred from the first memory stored in, a defect position, and an identification code. Further, according to the present invention, the level discriminating means attenuates the output of the one-dimensional image sensor and sets the output of the one-dimensional image sensor by the discriminating level setting means, which outputs with a predetermined time constant. And a circuit for performing level discrimination at the discriminated discrimination level.

According to the invention, the intensity of the reflected light on the surface of the metal strip is detected by the one-dimensional image sensor extending in the width direction of the metal strip which is continuously passed and conveyed, and the output of the image sensor is Store the data in the first memory while sequentially shifting it, and store the old contents stored earlier.
When the level discriminating means detects a stain, which is a defect on the surface of the metal band, overflows and disappears, and until the detected defect reaches a predetermined store area in the shift direction of the first memory, for example, The position of the store capacity of 1/2 in the shift direction of all the store areas of one memory is reached, or the detected defect portion is the first
The output of the one-dimensional image sensor is sequentially shifted and stored in the first memory until just before the memory overflows. When the defective portion reaches the predetermined store area in this way, the stored contents of the first memory are transferred to the second memory, and the image transferred to the second memory is visually confirmed by the display means, for example, by a cathode ray tube and liquid crystal. It is displayed or printed using a printer or the like, printed on recording paper, and output. The operator can immediately determine what kind of defect is by looking at the image displayed by such display means, and there is only one defect in the metal band transport direction. It is possible to make a judgment by inferring whether or not they are scattered in a plurality of places, and further whether they are continuous in the transport direction. According to the present invention, when a defect on the surface of the metal strip is detected, the first alarm sound generating means provided in the vicinity of the one-dimensional image sensor generates the first alarm sound.
The warning sound of may be, for example, a human voice such as “Dirt was detected.” Or a buzzer sound. An inspection area is provided on the downstream side of the one-dimensional image sensor in the transport direction of the metal strip, and the operator is
The surface of the metal strip is monitored. When the output of the one-dimensional image sensor is applied to the level discriminating means and a defect on the surface of the metal strip is detected, the first alarm sound is generated as described above, and the detected defect portion indicates the inspection area. When the second alarm sound is reached, a second alarm sound different from the first alarm sound, for example, a music box sound, classical music, or a buzzer sound is generated by the second alarm sound generating means. The operator listens to this second alarm sound and looks at the defect on the surface of the metal strip. Therefore, it is possible to prevent the operator from overlooking the defect. Further, the second alarm sound is not mistaken for the first alarm sound. Further according to the invention, not only the image of the surface of the metal strip transferred from the first memory stored in the second memory by the display means is displayed, but also by the display means, for example, in the same screen, The position of the detected defect portion of the metal strip, for example, the length from the leading edge of the transport direction of the metal strip is displayed, and an identification code for identifying the metal strip,
For example, the coil number is displayed. An image of such a defect on the surface of the metal strip, the defect position, and the identification code are visually displayed by the display means and printed on the recording paper, so that the use of the metal strip can be accurately grasped. become able to. Further, according to the present invention, in order to set the discrimination level of the level discriminating means, the output of the one-dimensional image sensor is attenuated by, for example, a voltage dividing circuit, and further, it is blunted by a predetermined time constant using an integrating capacitor or the like. By delaying and discriminating the output of the one-dimensional image sensor at the discrimination level thus obtained, accurate level discrimination can be continued irrespective of the reflectance of the surface of various metal bands.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a simplified perspective view showing the structure of an embodiment of the present invention. A metal strip 1 such as a steel plate or a stainless steel plate is surface-treated and then conveyed in a conveyance direction 2. The one-dimensional image sensors 3 to 5 are arranged adjacent to each other at a fixed position in the middle of the transportation path of the metal strip 1 to detect the surface of the metal strip 1. The one-dimensional image sensors 3 to 5 are CCDs extending in the width direction of the metal strip 1.
Light-receiving elements composed of (charge-coupled elements) are arranged, and an image of the surface of the metal strip 1 is formed on the light-receiving elements by a condenser lens. Each light-receiving element has a level corresponding to the amount of light received. Output an electric signal. One-dimensional image sensors 3, 4, 5 are provided adjacent to each other in the width direction (3 in this embodiment) according to the size of the width of the metal strip 1.

Position detecting means 6 is provided for detecting the position of the metal strip 1 in the transport direction 2. This position detecting means 6
Includes, for example, a roller that rotates in contact with the surface of the metal strip 1, a pulse generator that generates a pulse at each predetermined rotation angle of the roller, and a counter that counts the pulses from the pulse generator. It is possible to detect the length from the most downstream end of the metal strip 1 to the position detected by the one-dimensional image sensors 3 to 5.

A first alarm sound generating means 7 is provided at a position where the one-dimensional image sensors 3 to 5 are provided. In the inspection area 8 downstream of the one-dimensional image sensors 3 to 5 in the transport direction 2 of the metal strip 1, a worker 9 visually monitors the surface of the metal strip 1. This inspection area 8 has a second
An alarm sound generating means 10 is provided. The one-dimensional image sensors 3 to 5 and the inspection area 8 may be separated from each other by about 300 m in the transport direction 2 of the metal strip 1. The width of the metal strip 1 may be, for example, 600 to 1500 mm.

FIG. 2 is a sectional view showing a configuration related to the one-dimensional image sensor 3. The metal strip 1 runs horizontally in the one-dimensional image sensors 3 to 5, and the one-dimensional image sensors 3 to 5 are arranged immediately above it. The elongated light sources 11 and 12 realized by a fluorescent lamp or the like extend along the width direction of the metal strip 1 at intervals in the transport direction 2 and illuminate the surface of the metal strip 1. The reflected light on the surface of the metal strip 1 is guided to the one-dimensional image sensors 3 to 5 as indicated by reference numeral 13. The light sources 11 and 12 are covers 1 made of a light-shielding material.
The reflected light 13 of the metal band 1 is guided to the one-dimensional image sensors 3 to 5 through the elongated openings 16 formed in the covers 14 and 15 and covered with the covers 4 and 15.

FIG. 3 is a block diagram showing an electrical configuration of the embodiment of the present invention shown in FIGS. 1 and 2.
The images of the one-dimensional image sensors 3 to 5 are input to the processing circuit 17 realized by a microcomputer or the like. For example, the metal strip 1 has a speed of 180 m / min, and the 1-dimensional image is obtained every 1 mm in the transport direction 2. The outputs of the sensors 3-5 are derived and stored in the memory M1. Memory M1
Indicates the output of each light receiving element of the one-dimensional image sensors 3 to 5 by a predetermined distance L1 in the transport direction 2, for example, 1 mm.
Each time it is stored, the data is sequentially shifted and stored, and the old stored contents that have been stored earlier overflow and disappear sequentially. The output of the position detecting means 6 is also given to the memory control circuit 18, whereby the second
The store operation of the memory M2 is controlled.

Signal generating means 19 implemented by a host computer or the like for controlling the surface treatment of the metal strip 1
From, the identification code, which is the coil number of the metal strip 1, is derived via the line 20. The stored contents of the memory M2 are visually displayed by a visual display means 21 realized by a cathode ray tube or liquid crystal, and printed on recording paper by a printer 22.

FIG. 4 is a simplified plan view showing a state in which the surface of the metal strip 1 is imaged by the one-dimensional image sensors 3-5. Fields of view 3a, 4 of the one-dimensional image sensors 3-5
a and 5a are provided adjacent to each other. The memory M1 is sequentially stored in the transport direction 2 of the metal strip 1 by the length L1 as described above. When there is a defect, which is a stain indicated by reference numeral 24, on the surface of the metal strip 1, the stain 24
Are detected by the one-dimensional image sensor 3 during the transportation of the metal strip 1.

FIG. 5 shows a signal waveform obtained from the one-dimensional image sensor 3. An output 25 from the light receiving element corresponding to the intensity of the reflected light on the surface of the metal strip 1 is obtained over the width W1 of the visual field 3a of the one-dimensional image sensor 3, and a waveform 27 whose level is reduced corresponding to the dirt 24 is obtained. To be
The output of this one-dimensional image sensor 3 is used as a discrimination level 28
The dirt 24 can be detected by performing level discrimination according to. In this embodiment, it is detected that the waveform 27 corresponding to the dirt 24 has become equal to or lower than the discrimination level 28, and the dirt is detected. As described above, when the output 26 of the one-dimensional image sensor 3 is discriminated by the discriminating level 28, the output 26 is attenuated by, for example, a resistance voltage dividing circuit, and a circuit having a predetermined time constant including an integrating capacitor is used. The output 26 can be applied to blunt and delay and thus a discrimination level 28 can be obtained. The output 26 and the discrimination level 28 are compared by the comparison circuit, and the waveform 27 corresponding to the dirt 24 is detected by the discrimination level 28.
The dirt can be detected when the following occurs.

FIG. 6A is a diagram for explaining the contents stored in the memory M1. After the processing circuit 17 detects the dirt 24 by the output of the one-dimensional image sensor 3, the leading end 31 of the image 30 in the conveyance direction 2 is stored in the memory M1 shown in FIG.
(1) The output of the one-dimensional image sensor 3 is sequentially shifted and stored until it reaches a predetermined store area in the shift direction from the bottom to the top. Image 3 of dirt 24
In the embodiment of the present invention, when the leading end portion 31 of 0 reaches the store area at the center position of the memory M1 in the shift direction, the stored content of the first memory M1 is stored in the second memory M1.
2 and stored as shown in FIG. 6 (2). FIG.
In (1), the shift direction from the bottom to the top of the first memory M1 is shown corresponding to the length L1 of the metal strip 1 in the transport direction 2, and the tip end portion 31 is from the bottom to the top in FIG. 6 (1). To L1 /
When it is shifted by 2 and reaches the central store area in the shift direction, the transfer operation to the second memory M2 is performed and a still image is obtained.

FIG. 7 is a front view showing the screen of the visual display means 21. The image stored in the second memory M2 is displayed as a still image, as indicated by the reference numeral 32, the image 33 corresponding to the stain 24 is visually displayed, and the leading edge portion 34 thereof is shown. In the screen where the image 32 of the display means 21 is displayed, in the display area 35, the coil number “123” of the metal strip 1 and the position “456” of the metal strip 1 where the tip portion 34 of the dirt 24 is present are displayed. Is displayed. This display "456" represents the length (unit: m) from the tip of the metal strip 1 to the tip 34 of the stain 24. The display contents of the visual display means 21 thus obtained can also be directly printed on the recording paper by the printer 22.

FIG. 8 is a flow chart for explaining the operation of the processing circuit 17. Moving from step a1 to a2, the length from the most downstream end of the metal strip 1 in the transport direction 2 to the portion immediately below the one-dimensional image sensors 3 to 5, and thus the position of the metal strip in the transport direction is detected. . In step a3, when it is determined that the metal strip 1 has traveled the predetermined length L1, the outputs of the one-dimensional image sensors 3 to 5 are sequentially read into the memory M1 in step a4. At step a5, the outputs of the respective one-dimensional image sensors 3 to 5 are level-discriminated as described with reference to FIG. When it is determined in step a6 that the metal strip 1 is contaminated, the position of the metal strip 1 obtained from the position detection means 6 is stored in the memory 37 provided in the processing circuit 17 in step a7.
At step a8, the first alarm sound generating means 7
The first alarm sound is generated at the position where the three-dimensional image sensors 3 to 5 are provided. The first alarm sound may be a voice of a person such as "dirt has been detected."

In step a9, after the dirt 24 (see FIG. 4 described above) is detected, the tip portion 31 of the image 30 is the length in the carrying direction 2 of the metal strip 1 which can be stored in the first memory M1. When the fact that it reaches 1/2 of L1 is detected by the reading operation of the memory M1 or by the output of the position detecting means 6, in the next step a10,
The contents stored in the memory M1 are transferred to the second memory M2. Accordingly, in step a11, the second memory M2
The stored contents are displayed on the screen by the visual display means 21 and printed on the recording paper by the printer 22.

When it is determined by the output of the position detecting means 6 that the tip of the dirt 24 has reached the inspection area 8 in step a12, the second step is performed in step a13.
The second alarm sound is generated by the alarm sound generating means 10.
The second alarm sound is an alarm sound different from the first alarm sound, and may be, for example, a music box sound, classical music, a buzzer sound, or a human voice.

In another embodiment of the present invention, the one-dimensional image sensors 3 to 5 may be provided individually or in a number of 4 or more. The present invention can be implemented extensively in connection with stainless steel and other metals.

FIG. 9 is a simplified system diagram showing the step of performing the surface treatment of the metal strip. The metal strip 1 is, for example, a stainless steel plate, the surface of which is coated with a chromic acid solution by spraying from a nozzle in the application region 38, and then the rubber strip 39 having elasticity is squeezed to uniformly coat the surface. Form a thin treated layer to improve corrosion resistance. A surface monitoring device according to the invention is provided downstream of the roll 39 at the position indicated by reference numeral 40. The state of the treatment layer formed by the roll 39 can be monitored by the surface monitoring device of the present invention.

[0025]

According to the present invention, by using the one-dimensional image sensor, it is possible to prevent erroneous detection due to unevenness of the illuminance of the light source and perform highly accurate surface monitoring.

Further, according to the present invention, the structure is simple,
It is inexpensive and easy to implement.

Further, according to the present invention, when a defect such as a stain is detected on the surface of the metal strip, the detected defect portion is set to 1 until the predetermined store area in the shift direction in the first memory is reached. The output of the three-dimensional image sensor is stored in the first memory, the stored contents of the image stored in the first memory are transferred to the second memory, the still image is stored, and displayed by the display means. Can easily inspect the surface defect by looking at the displayed image including the defect. As described above, in the present invention, in combination with the work step in which the operator looks at the image on the display means to determine the type of defect, the degree of defect, etc., highly accurate surface monitoring is achieved as a whole.

Further, according to the present invention, at the position where the one-dimensional image sensor is provided, when the defect is detected, the first alarm sound is generated, and in the inspection area on the downstream side thereof,
When the defect reaches the inspection area, a second alarm sound different from the first alarm sound is generated to alert the operator. Therefore, the operator can monitor the defect in the inspection area by observing the surface of the metal strip when listening to the second alarm sound without being confused with the first alarm sound. Therefore, there is also an effect that the burden on the operator for inspection can be reduced. As a result, the worker can continue to monitor the defects on the surface of the metal strip in the inspection area for a long time, and there is no risk of overlooking the defects, which reduces the burden on the worker.

Further, by using the level discriminating means of the present invention, an appropriate discrimination level can be set irrespective of the fluctuation of the reflectance of the surface of the metal strip, and the surface of the metal strip can be monitored reliably.

[Brief description of drawings]

FIG. 1 is a perspective view showing a simplified configuration of an embodiment of the present invention.

FIG. 2 is a sectional view showing a configuration related to a one-dimensional image sensor 3.

FIG. 3 is a block diagram showing an electrical configuration of the embodiment of the present invention shown in FIGS. 1 and 2;

FIG. 4 is a one-dimensional image sensor 3-5 for the surface of the metal strip 1.
It is the simplified top view which shows the state imaged by.

FIG. 5 is a diagram showing a signal waveform obtained from the one-dimensional image sensor 3.

FIG. 6 is a diagram for explaining stored contents of a memory M1.

7 is a front view showing the screen of the visual display means 21. FIG.

FIG. 8 is a flowchart for explaining the operation of the processing circuit 17.

FIG. 9 is a simplified system diagram showing a step of performing a surface treatment of a metal strip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal band 2 Transport direction 3-5 1-dimensional image sensor 3a, 4a, 5a Field of view 6 Position detection means 7 1st alarm sound generation means 8 Inspection area 9 Worker 10 2nd alarm generation means 11, 12 Light source 13 Reflected light 14 , 15 cover 16 opening 17 processing circuit 18 memory control circuit 19 signal generating means 20 line 21 visual display means 22 printer 24 dirt 27 waveform 28 discrimination level 30, 32, 33 image 31, 34 tip 35 display area 37 memory 38 coating area 39 rubber rolls M1, M2 memory

Claims (5)

[Claims] 1. A one-dimensional image sensor that extends in the width direction of a conveyed metal strip and detects the surface of the metal strip, a position detection unit that detects the position of the metal strip in the conveyance direction, and a one-dimensional image sensor and position. In response to the output from the detecting means, the output of the one-dimensional image sensor is sequentially shifted over a predetermined distance in the carrying direction, and the old stored contents are overflowed and erased, and a first memory and a second memory. And a level discriminating means for level discriminating the output of the one-dimensional image sensor to detect a defect on the surface of the metal strip, and, in response to the output of the level discriminating means, when the defect is detected, the output of the one-dimensional image sensor is detected. The first memory is sequentially stored in the shift direction of the first memory until a predetermined store area is reached, and when the predetermined store area is reached, the first store is executed. Means for transferring the stored content of the memory in the second memory, the surface monitor of the metal strip, characterized in that it comprises a display means for displaying the stored contents of the second memory. 2. A first alarm sound generating means, which is provided near the one-dimensional image sensor, generates a first alarm sound when a defect is detected in response to the output of the level discriminating means, and a one-dimensional image. It is provided in the inspection area downstream of the sensor in the direction of conveyance of the metal band, and responds to the output of the level discrimination means,
Second alarm sound generating means for generating a second alarm sound different from the first alarm sound when the detected defect portion of the metal band reaches the inspection area when the defect is detected. The surface monitoring device for a metal strip according to claim 1, wherein 3. A means for outputting a defect position signal representing the position of the detected defect portion of the metal strip when a defect is detected in response to the outputs of the position detection means and the level discrimination means, and the metal strip. Storing the defective position and the identification code in the second memory together with the contents transferred from the first memory, in response to the outputs of the identification code for identifying the defect position signal output means and the identification code generating means. The surface monitoring device for a metal strip according to claim 1 or 2, further comprising: 4. A one-dimensional image sensor that extends in the width direction of a conveyed metal strip and detects the surface of the metal strip, a position detection unit that detects the position of the metal strip in the conveyance direction, and an output of the one-dimensional image sensor. And a level discriminating means for discriminating the surface of the metal strip to detect a defect, and a first alarm sound when a defect is detected in response to the output of the level discriminating means provided in the vicinity of the one-dimensional image sensor. The first alarm sound generating means and the inspection area provided downstream of the one-dimensional image sensor in the transport direction of the metal strip, and responsive to the output of the level discriminating means,
Second alarm sound generating means for generating a second alarm sound different from the first alarm sound when the detected defect portion of the metal band reaches the inspection area when the defect is detected, and position detection Means for outputting a defect position signal indicating the position of the detected defect portion of the metal strip in response to the output of the means and the level discrimination means, and an identification code for identifying the metal strip. In response to the outputs of the one-dimensional image sensor and the position detecting means, the one-dimensional image sensor output is stored while being sequentially shifted over a predetermined distance in the transport direction, and the old stored contents overflow. The first to erase
When a defect is detected in response to the outputs of the memory, the second memory, and the level discrimination means, the output of the one-dimensional image sensor reaches the first memory and reaches a predetermined store area in the shift direction of the second memory. When sequentially stored up to the predetermined store area, means for transferring the stored contents of the image of the first memory to the second memory, defect position signal output means, and identification code generation means Means for storing the defect position and the identification code in the second memory together with the contents transferred from the first memory, and an image transferred from the first memory stored in the second memory, A surface monitoring device for a metal band, comprising: a display unit for displaying a defect position and an identification code. 5. The level discriminating means sets a discriminating level setting means for attenuating the output of the one-dimensional image sensor and outputting with a predetermined time constant, and an output of the one-dimensional image sensor for discriminating level setting means. 5. The surface monitoring device for a metal strip according to claim 4, further comprising a circuit for performing level discrimination at the determined discrimination level.