JPH0643097A - Method for measuring alloying degree of galvanized sheet iron - Google Patents

Abstract

PURPOSE:To prevent that an error occurs and a measurement cannot be made by the vibration of a steel plate and the fluctuation of a pass line, and to remove the error occurring due to the radiation of a furnace wall. CONSTITUTION:A longitudinal scan mirror 6 and a lateral scan mirror 7 are provided, and a laser beam is scanned in the shape of a plane on a steel plate. The maximum value of a light-reception level detected during the plane scanning is utilized. A period of a laser beam being off is set, a background light level is detected, and a regular reflection light level is found from the maximum value-background light level. An angle divergence of the steel plate is detected from the scan position at the time when the maximum value is detected, and the angle correction is conducted. The moving average value of a plurality of plane scan times is computed, and it is prevented that the alloying unevenness, etc., exert an adverse effect on the measured result. A current corresponding to the background light level is allowed to flow to the input of an amplifier 31, and the saturation of the input level is prevented.

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 the degree of alloying of a galvanized steel sheet, which is used, for example, to measure the degree of alloying of a galvanized steel sheet in which the alloying of the surface layer is in progress in an alloying furnace. You can.

[0002]

2. Description of the Related Art Galvanized steel sheets are characterized by high corrosion resistance and low rust resistance. Among them, alloyed galvanized steel sheets are excellent in coatability and have few troubles during press working. Widely used in applications such as automobiles and home appliances.

In the case of producing an alloyed galvanized steel sheet, generally, the steel sheet is first passed through a hot dip zinc bath at a predetermined temperature (for example, 460 ° C.) to form a galvanized layer on the surface, and then it is alloyed. Put in a chemical furnace and heat to about 500 to 600 ° C. This heat treatment causes diffusion to form an alloy of iron and zinc in the plated layer.

An important factor in producing an alloyed galvanized steel sheet is to maintain a proper degree of alloying of the plated layer. That is, in the case of insufficient alloying (referred to as "burning"), the paintability is deteriorated, and if alloying proceeds excessively, powdering may occur during press working or defective spot welding may easily occur. Generally, a proper alloyed plated layer of an alloyed galvanized steel sheet is considered to have an iron content of about 10%.

The degree of alloying of the surface layer portion of the galvannealed steel sheet can be changed by adjusting the temperature of the alloying furnace and the passage speed of the steel sheet (that is, the residence time in the alloying furnace). However, even if those conditions are controlled to be constant, the alloying degree changes due to another factor. That is, the degree of progress of alloying changes depending on the trace element concentration in the zinc bath and the trace chemical components contained in the steel sheet material.Therefore, the temperature of the alloying furnace and the steel sheet passing speed should be kept constant. However, the alloying degree of the surface layer of the steel sheet changes for each coil. Therefore, in order to properly control the alloying degree of the surface layer portion of the galvannealed steel sheet, it is necessary to measure the alloying degree.

As a technique for measuring the degree of alloying of the surface layer portion of an alloyed galvanized steel sheet, there has been conventionally used a technique disclosed in JP-A-58-16.
No. 061 and Japanese Patent Laid-Open No. 58-210550 are known. In the former technology, the surface of the steel sheet is irradiated with visible light and the intensity of diffusely reflected light from the steel sheet is measured to detect the degree of alloying.In the latter technology, the steel sheet is irradiated with light and the direction of specular reflection is detected. The intensity distribution of the reflected light is measured by the photodetector arranged, and the degree of alloying is detected from the size of the half width of the light intensity distribution.

[0007]

With respect to a steel sheet having a galvanized layer formed on the surface through the molten zinc bath, the surface cannot be touched until the alloying treatment is completed. The steel plate has a long distance (eg 1
00m) is transported in the vertical direction without any support, and passes through an alloying furnace in the meantime. For this reason, it is inevitable that the steel sheet undergoing alloying undergoes vibrations or path line fluctuations in the carrying direction, width direction, thickness direction, and the like.

When the alloying degree is measured by the conventional technique with respect to a steel sheet having vibrations or fluctuations in the pass line, an accurate measurement result cannot be obtained. That is, when detecting irregularly reflected light, if the incident angle and the reflection angle of the light on the steel plate change due to vibration or path line variation, the intensity of the irregularly reflected light incident on the fixed photodetector changes, resulting in a detection error. Occurs. When detecting the distribution of specular reflection light, if the incident angle and reflection angle of light on the steel plate change due to vibration or path line fluctuation, the direction of specular reflection light deviates from the detector position. The intensity distribution cannot be detected, and the focus shift of the light-receiving lens occurs due to the distance variation between the steel plate and the detector, resulting in a measurement error.

Further, in the alloying furnace, since light is emitted from the furnace wall, in addition to the reflected light from the steel plate, the light emitted from the furnace wall also enters the photodetector, which causes a detection error.

Therefore, the first object of the present invention is to accurately measure the alloying degree even when vibrations of the steel sheet and fluctuations of the pass line occur, and eliminate the measurement error caused by the light emission from the furnace wall. This is the second issue.

[0011]

In order to solve the above-mentioned first problem, in the first invention, in the method for measuring the alloying degree of a galvanized steel sheet being conveyed on a line, galvanization is performed. While irradiating the surface of the steel plate with light,
The position of the irradiation light is repeatedly scanned in a plane shape in the conveying direction and the width direction of the galvanized steel sheet, and in the regular reflection direction of the irradiation light,
The intensity of the reflected light is detected substantially continuously by a photodetector placed at a position that is sufficiently large distance from the surface of the galvanized steel plate compared to the variation of the pass line, and at least during one surface scan. The alloying degree is obtained based on the maximum value of the detected reflected light intensity distribution.

Further, in order to solve the second problem, in the second invention, the light irradiating the surface of the galvanized steel sheet is temporarily blocked, and at that time, the received light intensity detected by the photodetector is changed. As the background light level, the alloying degree is obtained based on the difference between the maximum value of the reflected light intensity distribution detected during at least one surface scan and the background light level.

According to the third aspect of the invention, the light irradiating the surface of the galvanized steel sheet is temporarily blocked, and the received light intensity detected by the photodetector at that time is set as the background light level, and at least one surface scanning is performed. In accordance with the position where the maximum value in the reflected light intensity distribution detected in appears, the maximum value is corrected for the scanning angle, and the difference between the corrected maximum value and the background light level is calculated. The degree of alloying is calculated based on

Further, in the fourth aspect of the invention, the light irradiating the surface of the galvanized steel sheet is temporarily cut off, and the received light intensity detected by the photodetector at that time is set as the background light level, and one surface scanning is performed. The difference between the maximum value of the reflected light intensity distribution detected therein and the background light level is averaged over a plurality of surface scans, and the alloying degree is obtained based on the result.

In the fifth aspect of the invention, the light irradiating the surface of the galvanized steel sheet is temporarily blocked, and the signal level corresponding to the received light intensity detected by the photodetector at that time is set as the background light level. A constant current proportional to the background light level is injected into the signal processing circuit of the photoreceiver and the current is held for at least one surface scan time.

[0016]

In the present invention, the surface of the galvanized steel sheet is irradiated with light, and the degree of alloying is determined based on the intensity of the specularly reflected light from the steel sheet. As described above, the galvanized steel sheet conveyed on the line causes vibrations and path line fluctuations. Therefore, even if the position of the light source that irradiates the steel sheet with light is constant, the direction of the specular reflection light, and The optical path length from the light source to the light receiver varies. However, in the present invention, since the position of the irradiation light is repeatedly scanned in a plane shape in the conveying direction and the width direction of the galvanized steel sheet, even if the direction of the specular reflection light changes, the light reception is always performed during one surface scanning. Since the specularly reflected light is incident on the vessel, the maximum value of the received light level can be reliably detected as the intensity of the specularly reflected light, and the accurate degree of alloying can be obtained based on this. Moreover, since the position where the reflected light is detected is a position that is sufficiently larger than the path line variation from the surface of the galvanized steel sheet, the variation of the optical path length from the light source to the light receiver due to the variation of the path line. Does not cause a large detection error.

Further, in the second aspect of the invention, it is possible to eliminate the measurement error caused by the light emission from the furnace wall. That is,
By temporarily shutting off the light that illuminates the surface of the galvanized steel sheet, it is possible to detect only the intensity of external light (background light level) due to light emission from the furnace wall (background light level),
By taking the difference between the maximum value of the reflected light intensity distribution and the background light level, it is possible to accurately obtain the level of only regular reflection light excluding the extraneous light component.

Further, in the third aspect of the invention, the error caused by the vibration (angle) of the steel sheet can be further reduced. Depending on the angle of the steel plate surface to which the light is irradiated, the incident angle on the detector surface when the specularly reflected light enters the light receiver, and the incident angle and the reflection angle on the steel plate surface change. The magnitude of the maximum value detected by the light receiver during one scanning also changes due to the influence of the angle of the steel plate surface. When the angle of the steel plate surface changes, 1
Since the position (timing) at which the maximum light receiving level appears during one scanning changes, the present invention detects the angle of the steel sheet according to the position where the maximum light receiving level is detected, and the maximum light receiving level that can occur according to the detected angle. The error of is corrected.

Further, according to the fourth aspect of the present invention, it is possible to prevent the abnormal degree of alloying from being detected even when there is uneven alloying on the surface of the galvanized steel sheet. That is, the galvanized steel sheet surface may locally have uneven alloying or a portion where particulate zinc is adhered. Therefore, only one surface scanning including the reflected light level from the portion may occur. When the maximum value of the reflected light intensity distribution of is used, an abnormal alloying degree is temporarily detected. However, in the present invention, the detected values obtained by a plurality of surface scans are averaged, and the alloying degree is obtained based on the result, so unless the alloying degree of the steel sheet is actually abnormal, the abnormal alloying degree is It will never be detected.

In the fifth aspect of the invention, it is possible to prevent the level of the signal processing circuit from being saturated due to the change of the background light level. Reflected light from the steel plate and background light due to light emission from the furnace wall are incident on the light receiver, but the level of the background light greatly changes according to the change in the furnace temperature and the like. When the background light level changes, the output level of the photodetector fluctuates, so that the circuit that processes the signal of the photodetector causes saturation of the input level and the like, and the maximum value may not be accurately detected. However, in the present invention, the signal level corresponding to the received light intensity detected by the photodetector when the light irradiating the surface of the galvanized steel sheet is blocked,
The background light level is set, and a constant current proportional to the background light level is injected into the signal processing circuit of the photodetector, and the current is held for at least one surface scanning time. The input level of the signal processing circuit when canceling and not receiving the reflected light can be made substantially zero, thereby preventing saturation of the signal level.

[0021]

FIG. 3 shows a part of a production line for carrying out the present invention.
Shown in. Referring to FIG. 3, the steel sheet that enters this process is first immersed in a molten zinc bath at 460 ° C. in a zinc pot, and zinc plating adheres to its surface. The steel sheet on which the galvanized layer is formed is conveyed vertically from the zinc pot and heads for the heat retention furnace. An alloy of zinc and iron is formed on the surface of the steel sheet by diffusion when passing through the inside of the heat-retaining furnace controlled at a temperature of 500 to 600 ° C. The higher the temperature and the longer the residence time of the steel sheet in the furnace, the more alloying proceeds.

In order to measure the alloying degree of the steel sheet, three alloying sensors are installed at different positions on the wall surface of the heat insulation furnace. The electric signals output from the three alloying sensors are input to the arithmetic board. Each alloyed sensor is housed in a stainless steel cylindrical container, and the entire circumference thereof is water-cooled. The cylindrical shape of the container is designed so that the water pressure is evenly applied to the surroundings. The detection surface of the alloying sensor faces the opening of the wall surface with the quartz glass in between. If zinc fume scattered from the inside of the furnace adheres to the quartz glass, it adversely affects the measurement. Therefore, nitrogen gas is sprayed from the periphery of the quartz glass into the furnace (nitrogen purge). Water for water cooling and gas for nitrogen purging are supplied through a valve stand located near each alloying sensor.

A cross-section of the furnace and one alloyed sensor is shown enlarged in FIG. This will be described with reference to FIG. An opening 1a is formed in the wall 1 of the heat retention furnace for measurement. An alloying sensor is installed so as to face the opening 1a. The alloying sensor casing 2 is attached to the wall 1 by a hinge 4. The casing 2 has a cylindrical shape as described above, and the quartz glass 3 is attached to the opening of the detection surface.

Inside the casing 2, a laser light source 5,
A vertical scanning mirror 6, a horizontal scanning mirror 7, a light receiving unit 8 and a processing unit 10 are installed. Although not shown, each of the vertical scanning mirror 6 and the horizontal scanning mirror 7 has a scanning mechanism. In the former, the reflection direction is changed in the vertical direction (the length direction of the steel plate) about the center of the mirror. The latter oscillates so that the reflection direction changes left and right (the width direction of the steel plate) about the center of the mirror. The vertical scanning mirror-6 has a swing frequency of 350 Hz and a swing angle of ± 7.5.
The horizontal scanning mirror 7 has a swing frequency of 20 Hz and a swing angle of ± 10 degrees.

The laser light source 5 is a semiconductor laser oscillator and has a built-in automatic adjusting mechanism for maintaining a constant output level. The laser light emitted from the laser light source 5 first goes to the vertical scanning mirror 6 and then the vertical scanning mirror 6 and the horizontal scanning mirror 7.
Is reflected on each surface of the steel sheet and irradiated on the surface of the steel sheet. Since the vertical scanning mirror 6 and the horizontal scanning mirror 7 are constantly oscillating, the position of the laser light irradiated on the surface of the steel sheet is repeated on the surface of the steel sheet in a predetermined range in the vertical and horizontal directions. Scanned and surface scanned. The specular reflection light of the laser light incident on the steel plate surface is
It appears in the direction of the reflection angle that coincides with the incident angle to the steel plate surface, and its intensity is determined by the light reflectance of the steel plate surface. Since the light reflectance of the steel plate surface changes depending on the alloying degree as described later, the alloying degree can be measured based on the intensity of specularly reflected light.

The light receiving unit 8 is arranged at a position where the regular reflection light reaches. A convex lens is attached to the light receiving surface of the light receiving unit to converge the incident light and guide it to the surface of the photodiode 9 which is a planar light receiving element. Since the steel plate is not supported near the furnace at all, vibration and fluctuation of the pass line occur in various directions. When the angle of the steel plate surface changes due to vibration, the incident angle and the reflection angle of the laser light change, and the position where the specular reflection light reaches changes, but in this embodiment, the laser light is changed to the vibration frequency ( Number H
Since surface scanning is performed at a frequency higher than that of z), specular reflection light surely enters the light receiving unit 8 for a short time during one surface scanning. Further, the variation of the pass line, that is, the positional deviation that can occur in the steel sheet is about ± 50 mm, but the distance between the mirror 7 and the steel sheet and the distance between the steel sheet and the light receiving unit 8 are sufficiently large (800 m).
m), the change in the optical path length from the light source to the light receiver due to the change in the pass line is small, and the accompanying change in the intensity of the incident light in the light receiving unit 8 is small.

A shutter plate 11 capable of closing the opening 1a is arranged between the alloying sensor and the wall surface of the furnace.
A calibration plate 12 having a constant light reflectance is mounted on the surface of the shutter plate 11 on the alloyed sensor side. At the time of measurement, the shutter plate 11 is opened as shown in FIG. 1. By moving the shutter plate 11 to close the opening 1a, the laser light emitted from the mirror 7 is moved to a predetermined level on the surface of the calibration plate 12. Since the light is reflected at the reflectance and enters the light receiving unit 8, the characteristics of the alloying sensor can be calibrated based on the light receiving level at this time.

The electrical circuit configuration of one alloyed sensor is shown in FIG. Referring to FIG. 2, angle sensors 21 and 22 and a photodiode 23, which are not shown in FIG. 1, are provided. The angle sensors 21 and 22 detect the angles (swing position) of the vertical scanning mirror 6 and the horizontal scanning mirror 7, respectively. The photodiode 23 is used to monitor the output of the laser light emitted from the laser light source 5.

The photodiode 9 outputs a current signal proportional to the intensity of the received light. This signal is amplified by the preamplifier 31, and its output level is converted into a digital amount by the A / D converter 32. The control unit 35
It includes a mirror driver for energizing a mirror swing mechanism (not shown) and a circuit for generating various timing signals based on the scanning angle signal. The laser driver 37 is responsive to the on / off signal output from the control unit 35 to generate a laser beam.
The energization / de-energization of the oscillator 5 is controlled.

The information on the received light level output from the A / D converter 32 is the peak value detection circuit 33 and the background value detection circuit 3.
The peak value input to 6 and output from the peak value detection circuit 33 is input to the angle correction calculation circuit 34. Then, from the output level of the angle correction calculation circuit 34, the background value detection circuit 36
The value obtained by subtracting the output level of is input to the moving average calculation circuit 40. The value output by the moving average calculation circuit 40 is D
Is converted into an analog voltage signal by the / A converter 41,
Further, it is converted into a current signal by the V / I converter 42 and output as a measurement result.

FIG. 4 shows changes in the light-receiving level detected by the light-receiving unit 8 for two surface scans for each of the three types. The top part is when the steel plate is in the standard state (angle), and the center part is that the steel plate angle is shifted in the vertical direction compared to the standard state due to the vertical vibration of the steel plate. What is shown below is when the angle of the steel sheet is laterally displaced from the standard state due to the lateral vibration of the steel sheet.

Referring to FIG. 4, the received light level changes oscillatingly in accordance with the vertical scanning and the horizontal scanning, but when the maximum value appears in one surface scanning, the specularly reflected light is emitted. It is considered that it is when the light enters the light receiving unit 8. The magnitude of the maximum value for each surface scan is detected by the peak value detection circuit 33 in FIG. 2 and output to the angle correction calculation circuit.

However, the maximum value detected by the peak value detection circuit 33 includes, in addition to the specular reflection light, the component of the external light generated by the light emission of the furnace wall. Therefore, in this embodiment, the background light detection circuit 36 detects the external light level. That is, a laser pause period of about 1 msec is provided between each surface scan, the laser oscillator 5 is deactivated at that time, and the A / D converter 32 outputs in synchronization with this. The background value detection circuit 36 is controlled to hold the received light level, that is, the external light level. By subtracting this external light level from the detected maximum value, the received light level excluding the influence of the external light, that is, the signal level according to the light reflectance of the steel plate can be obtained.

Actually, when the angle of the steel plate changes due to the vibration of the steel plate, the received light level changes as shown in FIG.
As the deviation from the steel plate angle in the standard state increases,
The received light level decreases. In order to exclude the influence of such an angle, the angle correction calculation circuit 34 of FIG. 2 performs a correction process. As can be seen from FIG. 5, the relationship between the angle shift amount and the light reception level reduction amount is substantially constant. Therefore, in this embodiment, a memory table in which constants corresponding to the respective angular deviations are arranged is provided in the angle correction arithmetic circuit 34. Then, the memory table is searched from the detected amount of angular deviation, a necessary constant is input, and the maximum value is multiplied to obtain the corrected maximum value.

As can be seen from FIG. 4, the amount of angular deviation can be obtained from the scanning position where the maximum value is detected. That is, the amount of angular deviation in the vertical direction can be detected as a change in the position (phase) at which the maximum value in the vertical scanning cycle is detected, and the amount of angular deviation in the horizontal direction can be detected as the maximum value in the horizontal scanning cycle. It can be detected as a change in position (phase). That is, these are detected as changes in the elapsed time from the scanning reference timing to the time when the maximum value is detected.

In the apparatus of FIG. 2, in synchronization with the signal output when the peak value detection circuit 33 detects the maximum value,
Since the scanning angle holding circuit 39 holds the information of the vertical scanning angle and the horizontal scanning angle output from the control unit 35,
The angle correction calculation circuit 34 inputs the information of the vertical scanning angle and the horizontal scanning angle held by the scanning angle holding circuit 39, and performs the correction calculation based on the information.

By the way, since uneven alloying or the like may occur on the surface of the steel sheet, the maximum value of the received light level detected may become abnormally large or small. As a result of one surface scanning. If only the above is used, a measurement error is likely to occur. Therefore, in this embodiment, the moving average calculation circuit 4
At 0, the moving average value is obtained from the values obtained in the past 40 surface scans, and the calculation result is output.

As described above, each alloying sensor outputs an electric signal corresponding to the light reflectance of the steel plate surface. FIG. 6 shows changes in the light reflectance with the progress of alloying of the steel sheet. A range of about 0.2 to 0.3 of reflectance is a proper alloying range, but as the alloying progresses, the light reflectance decreases,
When alloying progresses to some extent, it enters the proper alloying range. In this embodiment, the three alloying sensors are arranged at different positions as shown in FIG.
By referring to the output values of the individual alloying sensors, it is possible to check at which position the steel sheet is within the proper alloying range. By utilizing the result, the energy consumption is minimized and the alloying degree of the steel sheet is appropriately maintained by adjusting the temperature of the heat retaining furnace or adjusting the residence time of the steel sheet in the heat retaining furnace. It will be possible.

Referring again to FIG. 2, the signal output from the preamplifier 31 is also input to the sample hold circuit 38. A laser energizing signal output from the control unit 35 is applied to the control input terminal of the sample hold circuit 38. Therefore, the sample hold circuit 38
Is to sample the level of the signal output from the preamplifier 31 when the laser oscillator 5 is deactivated, hold the level, and inject a current corresponding to the level into the input terminal of the preamplifier 31, The current is held for at least one surface scanning time. The current value at this time is adjusted in advance so as to match the current output by the photodiode 9. When the laser oscillator 5 is energized, the level held by the sample hold circuit 38 does not change, and the current value it injects into the preamplifier 31 does not change, either. Therefore, when the laser oscillator 5 is deenergized, that is, when there is no reflected light, the compensation current of the same level is injected in the opposite direction so as to cancel the current output by the photodiode 9. Therefore, even when the intensity of the external light due to the light emitted from the furnace wall is increased, the input level of the preamplifier 31 is not likely to be saturated, and the correct reception level of the specular reflection light is detected.

[0040]

As described above, according to the present invention, the position of the irradiation light is repeatedly scanned in the plane direction in the conveying direction and the width direction of the galvanized steel sheet, so that even if the direction of the specular reflection light is changed, During surface scanning, specularly reflected light always enters the light receiver, and the maximum value of the received light level can be reliably detected as the intensity of specularly reflected light. You can ask. Moreover, since the position where the reflected light is detected is a position that is sufficiently larger than the path line variation from the surface of the galvanized steel sheet, the variation of the optical path length from the light source to the light receiver due to the variation of the path line. Does not cause a large detection error.

In the second aspect of the invention, it is possible to eliminate the measurement error caused by the light emission from the furnace wall. That is,
By temporarily shutting off the light that illuminates the surface of the galvanized steel sheet, it is possible to detect only the intensity of external light (background light level) due to light emission from the furnace wall (background light level),
By taking the difference between the maximum value of the reflected light intensity distribution and the background light level, it is possible to accurately obtain the level of only regular reflection light excluding the extraneous light component.

Further, in the third aspect of the invention, the error caused by the vibration (angle) of the steel plate can be further reduced. That is, depending on the angle of the steel plate surface irradiated with light, when the specularly reflected light is incident on the light receiver, the incident angle at the photodetector detection surface, and the incident angle and the reflection angle at the steel plate surface change, The magnitude of the maximum value detected by the light receiver during one scanning also changes due to the influence of the angle of the steel plate surface, so the angle of the steel plate was detected from the position where the maximum light receiving level was detected, and was detected. It is possible to correct the error of the maximum light receiving level that may occur depending on the angle.

Further, in the fourth aspect of the present invention, it is possible to prevent the abnormal degree of alloying from being detected even when there is uneven alloying or the like on the surface of the galvanized steel sheet. That is, the galvanized steel sheet surface may locally have uneven alloying or a portion where particulate zinc is adhered. Therefore, only one surface scanning including the reflected light level from the portion may occur. When the maximum value of the reflected light intensity distribution of is used, an abnormal alloying degree may be detected temporarily, but the detected values obtained by multiple surface scans are averaged, and based on the result, By determining the degree of alloying, the averaged or correct degree of alloying is detected.

In the fifth invention, it is possible to prevent the level of the signal processing circuit from being saturated due to the change of the background light level. Reflected light from the steel plate and background light due to light emission from the furnace wall are incident on the light receiver, but the level of the background light greatly changes according to the change in the furnace temperature and the like. When the background light level changes, the output level of the light receiver fluctuates, so that the input signal may be saturated in the circuit (preamplifier 31 in FIG. 2) that processes the signal of the light receiver, and the maximum value may not be accurately detected. Occurs. However, in the present invention, the signal level corresponding to the received light intensity detected by the light receiver when the light irradiating the surface of the galvanized steel sheet is blocked is held as the background light level, and a constant current proportional to the background light level is maintained. , Since it is injected into the circuit that processes the signal of the photodetector, the background light level is canceled by the injected current, and the input level of the signal processing circuit when the reflected light is not received can be made to approach substantially zero. Even when the emission intensity of the signal becomes strong, the signal level is prevented from being saturated, and the correct light reception level of the specular reflection light is detected.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing one alloyed sensor of FIG.

FIG. 2 is a block diagram showing a signal processing circuit of the alloying sensor.

FIG. 3 is a perspective view showing a part of a production line for carrying out the present invention.

FIG. 4 is a waveform diagram showing three examples of changes in light reception level.

FIG. 5 is a graph showing a change in light receiving sensitivity according to a steel plate angle.

FIG. 6 is a graph showing the relationship between the temporal change in light reflectance and the appropriate degree of alloying.

[Explanation of symbols]

1: Furnace wall 1a: Opening 2: Casing 3: Quartz glass 5: Laser light source 6: Vertical scanning mirror 7: Horizontal scanning mirror 8: Light receiving unit 9: Photodiode 10: Processing unit 21 , 22: angle sensor 23: photo diode 31: preamplifier 32: A / D converter 33: peak value detection circuit 34: angle correction calculation circuit 35: control unit 36: background value detection circuit 37: laser Driver 38: Sample Ho
Field circuit 39: scanning angle holding circuit 40: moving average calculation circuit 41: D / A converter 42: V / I converter

Claims (5)

[Claims] 1. A method for measuring the degree of alloying of a galvanized steel sheet conveyed on a line, wherein the surface of the galvanized steel sheet is irradiated with light, and the position of the irradiation light is set in the conveying direction of the galvanized steel sheet. Repeatedly scanning the surface in the width direction, in the direction of specular reflection of the irradiation light, by a light receiver arranged at a position sufficiently large distance from the surface of the galvanized steel sheet compared to the path line fluctuation, Alloying of galvanized steel sheet, characterized in that the intensity is detected substantially continuously and the degree of alloying is determined based on the maximum value of the reflected light intensity distribution detected in at least one surface scan. Degree measuring method. 2. The light irradiated onto the surface of the galvanized steel sheet is temporarily blocked, and the received light intensity detected by the photodetector at that time is taken as the background light level, and the light is detected during at least one surface scan. The method for measuring the degree of alloying of a galvanized steel sheet according to claim 1, wherein the degree of alloying is obtained based on the difference between the maximum value of the reflected light intensity distribution and the background light level. 3. The light irradiated to the surface of the galvanized steel sheet is temporarily blocked, and the received light intensity detected by the photodetector at that time is used as the background light level, and the light is detected during at least one surface scan. Depending on the position where the maximum value appears in the reflected light intensity distribution, the scanning angle is corrected to the maximum value, and the alloying degree is determined based on the difference between the corrected maximum value and the background light level. The method for measuring the degree of alloying of a galvanized steel sheet according to claim 1, which is obtained. 4. The reflection that is detected during one surface scan by temporarily blocking the light irradiating the surface of the galvanized steel sheet and setting the received light intensity detected by the photodetector at that time as the background light level. The alloying degree measurement of the galvanized steel sheet according to claim 1, wherein the difference between the maximum value of the light intensity distribution and the background light level is averaged over a plurality of surface scans, and the alloying degree is obtained based on the result. Method. 5. The light irradiating the surface of the galvanized steel sheet is temporarily blocked, and the signal level corresponding to the received light intensity detected by the photodetector at that time is set as the background light level, and is proportional to the background light level. The method for measuring the degree of alloying of a galvanized steel sheet according to claim 1, wherein a constant current is injected into a circuit for processing a signal of the light receiver, and the current is held for at least one surface scanning time.