A multi-interference optical path matched steel coating film thickness on-line measuring device and method

Abstract

The application discloses a kind of steel coating film thickness on-line measuring device and method of multiple interference optical path matching, comprising: probe, with multiple, different angles are arranged and the coating film layer of steel coating plate is detected;Host, with multiple, with the probe corresponding connection, for the probe provides infrared light source and measures out spectrum;Signal processing computer is connected with the host, according to the interference degree of each wavelength in the spectrum, calculates the film thickness intensity curve.The present application utilizes interference factor is microcosmic factor, there is difference under different angles, and steel coating film thickness is macroscopic factor, thickness is same under different angles, by multiple optical path mutual matching, eliminate interference factor in interference spectrum, realize steel coating film thickness accurate measurement.

Description

Technical Field

[0001] This invention relates to the technology for measuring the thickness of steel coatings, and more specifically, to an online measurement device and method for the thickness of steel coatings using multi-interference optical path matching. Background Technology

[0002] In recent decades, the technology of coated steel sheets has developed rapidly, with significant improvements in the variety, quality, and performance of coated steel sheets, and a substantial expansion in the application areas of coated steel sheets. As applications deepen, users have increasingly higher performance requirements for coated steel sheets. To further improve the quality of coated steel sheets, manufacturers have conducted extensive research on steel coating films. The weather resistance, durability, and especially cost-effectiveness of steel coating products are closely related to film thickness; therefore, the precise online measurement and control of film thickness is a key research area in current steel coating technology.

[0003] The main physical properties and surface quality of coated steel sheets are closely related to the thickness of the coating film. Because the coating film is very thin but almost opaque, with a relatively rough surface, and the steel substrate is also relatively rough, achieving accurate online film thickness measurement and further predictive control is extremely difficult. During continuous high-speed production of coated steel sheets, the coating film thickness is related to many factors, including the characteristics of the coating itself, the coating machine, and the production process. These factors include: coating viscosity, solid content, solvent content, coating roller pressure, roller speed, roller gap, coating roller characteristics, temperature, and the surface characteristics of the strip (including the coating / passivation layer). Changes in these factors will cause changes in film thickness. Therefore, accurate online measurement of the steel coating film thickness, and thus accurate online control, is essential. Currently, the industry uses the method of measuring the dry film thickness of the finished product. Some production lines use online sampling, offline measurement, and then online adjustment of process parameters to adjust the film thickness. This method has a long response time, and the process parameters and coating machine status change frequently, which is detrimental to the stability of the coating film thickness quality of the steel sheets.

[0004] Traditional methods for measuring the thickness of steel coatings are mostly used for offline laboratory sampling. These methods can be divided into two main categories: dry film and wet film. Generally, the measurement of dry film thickness includes several methods such as magnetic thickness gauges, micrometers, metallographic microscopy, and other non-magnetic thickness gauges.

[0005] There are roughly four main techniques for online measurement of steel coating thickness: X-ray method, infrared absorption method, thermal wave method, and interferometry. The first three methods are greatly affected by the environment, and their effectiveness is inconsistent for various steel coating types during large-scale production. Interferometry, a non-contact optical measurement technique, is more suitable for online film thickness measurement. It utilizes the interference between reflected light from the surface, intermediate, and substrate layers of the film system to detect the film thickness. This method offers high accuracy and can resolve the thickness of multiple layers. However, for cold-rolled steel coatings, the scattering of pigment particles, the roughness of the coating surface, and the roughness of the substrate coating cause the interference light to be scattered, resulting in severe interference. Conventional interferometry methods struggle to obtain reliable thickness information from a small amount of unstable interference light. If the interference between reflected light fails, leading to erroneous calculations, it will severely impact production. Summary of the Invention

[0006] To address the aforementioned deficiencies in existing technologies, the present invention aims to provide an online measurement device and method for steel coating film thickness using multi-interference optical path matching. This method utilizes the fact that interference factors are microscopic and vary at different angles, while the steel coating film thickness is a macroscopic factor and remains the same at different angles. By matching multiple optical paths, interference factors in the interference spectrum are eliminated, thereby achieving accurate measurement of the steel coating film thickness.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] On the one hand, a multi-interference optical path matching online measurement device for steel coating thickness includes:

[0009] The probe has multiple probes arranged at different angles to detect the coating layer of steel coated plates;

[0010] The host unit, comprising multiple units, is connected to the corresponding probes to provide infrared light sources for the probes and measure their spectra.

[0011] A signal processing computer, connected to the host computer, calculates the film thickness intensity curve based on the degree of interference of each wavelength in the spectrum.

[0012] Preferably, the probe has two sets of optical fibers, one set being an outgoing optical fiber and the other set being a reflecting and receiving optical fiber.

[0013] Preferably, the host computer includes a light source and a spectrometer;

[0014] The infrared light emitted by the light source is transmitted to the probe through the output optical fiber and then irradiates the coating layer;

[0015] The reflected light from the coating layer is transmitted to the probe through the reflective receiving optical fiber, where it forms interference light that is then transmitted to the spectrometer.

[0016] Preferably, the reflected light includes reflected light from the upper surface of the coating layer and reflected light from the lower surface between the coating layer and the substrate.

[0017] On the other hand, a multi-interference optical path matching method for online measurement of steel coating thickness uses the aforementioned multi-interference optical path matching steel coating thickness online measurement device to measure the coating thickness of the steel coating plate.

[0018] Multiple probes are arranged above the steel coated plate. Infrared light emitted from the light source is transmitted to the probe through the outgoing optical fiber and then irradiates the same working point of the coating layer. The reflected light at the working point is transmitted to the probe through the reflecting receiving optical fiber, forming interference light on the probe and then transmitted to the spectrometer. The spectrometer measures the spectrum of the interference light, and the signal processing computer calculates the film thickness intensity curve based on the degree of interference of each wavelength in the spectrum.

[0019] Preferably, all the reflected light is transmitted to the same probe; and / or

[0020] The reflected light is transmitted in a crisscross pattern to different probes.

[0021] Preferably, the wavelength of the infrared light emitted by the light source is less than 3 μm.

[0022] This invention provides a multi-interference optical path matching online measurement device and method for steel coating film thickness. When the steel coating film is transparent to the near-infrared band (wavelength less than 3 μm), near-infrared interferometry is used to achieve preliminary interference detection of the steel coating film. Then, using the multi-path interferometry technology of this patent application, invalid peaks caused by interference are eliminated, and the effective interference intensity peaks generated by the film thickness are detected, thereby calculating the steel coating film thickness. The actual effect is excellent when the steel coating film can transmit near-infrared light, significantly superior to traditional single-path interferometry detection methods. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the basic optical principle of thickness measurement in a traditional fiber optic spectrometer;

[0024] Figure 2 This is a schematic diagram of the film thickness interference intensity curve measured by a traditional fiber optic spectrometer.

[0025] Figure 3 This is a schematic diagram of the film thickness-strength curve in traditional steel coating thin film interferometry.

[0026] Figure 4 This is a schematic diagram of the measurement process in Embodiment 1 of the online steel coating thickness measurement device of the present invention;

[0027] Figure 5 This is a schematic diagram of the film thickness interference intensity curves of probes B and C in Embodiment 1 of the online steel coating film thickness measurement device of the present invention;

[0028] Figure 6 This is a schematic diagram of embodiment 2 of the online steel coating thickness measuring device of the present invention. Detailed Implementation

[0029] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] Combination Figure 1 The basic optical path of the traditional film thickness fiber interferometry technique shown includes a host 1 (containing a light source 2 and a fiber optic spectrometer 3), a probe 4 and a signal processing computer 5. Each probe 4 typically contains two sets of optical fibers: an outgoing fiber and a reflecting and receiving fiber.

[0031] Infrared light from the light source 2 inside the host 1 is transmitted to the probe 4 through the output optical fiber and exits as OA1 from the end of the output optical fiber, illuminating the steel coating film 100 of the steel coated plate being tested. The reflected light from the upper surface of the steel coating film 100 is OAR1, and the reflected light from the lower surface between the steel coating film 100 and the substrate 101 is OAR2. The reflected light OAR1 and OAR2 interfere at the entrance of the reflective receiving optical fiber of the probe 4. The interfered light enters the probe 4 and then enters the fiber optic spectrometer 3 along the reflective receiving optical fiber. The fiber optic spectrometer 3 measures the spectrum of the interfered light, and the signal processing computer 5 calculates the film thickness intensity curve based on the degree of interference of each wavelength in the spectrum. Figure 2 As shown. Figure 2 The peak value 'a' corresponds to the actual film thickness of the steel coating film 100 being tested. In an ideal thin film without interference, the film thickness can be detected simply by identifying the peak value 'a' and the corresponding film thickness position.

[0032] A single-layer ideal film has only one interference peak, but due to the numerous interfering factors in steel-coated films, these factors can generate additional peaks, such as... Figure 3 As shown, the main peak amplitude decreases because the pigment in the steel coating absorbs a large amount of light. Besides the interference peak 'a' generated by the interference of the basic film thickness, there are other interference peaks such as 'b', 'c', and 'd' caused by other interfering factors. Some peaks are relatively low, while others are relatively high, even higher than the basic interference peak 'a'. This can mislead the film thickness detection, making it easy to accept peaks caused by higher interfering factors as the detection result.

[0033] The present invention provides an online measurement device for steel coating thickness using multi-interference optical path matching, which, in order to eliminate errors caused by interference factors in steel coating films, includes:

[0034] The probe 6 has multiple probes arranged at different angles to detect the coating layer 100 of the steel coated plate.

[0035] The main unit 7, which has multiple components, is connected to the probe 6 to provide an infrared light source for the probe 6 and measure the spectrum of the interference light.

[0036] The signal processing computer 8 is connected to the host computer 7 and calculates the film thickness intensity curve based on the degree of interference of each wavelength in the spectrum.

[0037] The working process of the signal processing computer 8 is as follows:

[0038] 1) The light beam generated by the broadband light source is transmitted to the probe through optical fiber and output from the probe to illuminate the steel film under test;

[0039] 2) The reflected light from the upper and lower surfaces of the thin film enters the probe and then enters the fiber optic spectrometer along the optical fiber;

[0040] 3) The spectrometer obtains the received light spectrum of the steel thin film containing interference information through detection by the internal grating and CCD;

[0041] 4) The computer reads the spectral data of the reflected light containing interference information through the communication loop. The spectral data of the emitted light exhibits interference ripples similar to a cosine curve;

[0042] 5) The computer calculates the interference ripple information of the spectral data, and the corresponding film thickness can be initially calculated according to the Fresnel formula;

[0043] 6) If the probe is not vertical but tilted, trigonometric function correction is required to obtain the direct film thickness value;

[0044] 7) Due to interference factors, the interference spectrum is not a completely ideal spectrum. The film thickness value calculated from it is a curve with multiple peaks. The peak indicates that the film thickness at that location is more likely to be high.

[0045] 8) The computer analyzes the film thickness curves obtained from multiple optical paths and identifies the positions of overlapping peaks, which correspond to the actual film thickness.

[0046] 9) The computer sends the result to the user;

[0047] 10) The computer then begins the next acquisition and calculation of spectral data.

[0048] Example 1

[0049] Combination Figure 4As shown, the online steel coating thickness measurement device in this embodiment includes two main units 7 (including light source 8 and fiber optic spectrometer 9, light source 10 and fiber optic spectrometer 11), three probes 12, 13, 14 and signal processing computer 15. Each probe 12, 13, 14 has two sets of optical fibers: an outgoing optical fiber and a reflecting and receiving optical fiber.

[0050] The working mechanism of probe 12 is the same as that of traditional fiber optic interferometry for film thickness measurement. Probes 13 and 14 have no other influence on probe 12 except for contributing some incoherent scattered light sources to each other. The outgoing light from light source 10 enters probe 13 through the outgoing fiber and exits through the port of the outgoing fiber. The outgoing light OB1 illuminates the same working point as probe 12. The reflected light OBR1 from the upper surface of the steel coating film and the reflected light OBR2 from the lower surface interfere at probe 14 and enter probe 14, and then enter the fiber optic spectrometer 11 along the reflection receiving fiber.

[0051] Fiber optic spectrometer 11 measures the spectrum of the interference light between reflected light OBR1 and reflected light OBR2. Then, signal processing computer 15 calculates the film thickness intensity curve based on the degree of interference at each wavelength in the spectrum. Figure 5 As shown, the increase in film thickness and optical path caused by the incident light angle OB1 is a constant and can be eliminated. Figure 5 The midpoint peak value 'a' corresponds to the actual film thickness of the steel coating being measured. Besides the interference peak value 'a' generated by the interference of the basic film thickness, there are other interference peak values ​​such as 'b1', 'c1', and 'd1' caused by other interfering factors. Since these interferences are microscopic factors, they change significantly when the incident angle of OB1 changes. This leads to a difference between the interference peak values ​​b1, c1, and d1 and the interference peak values ​​b, c, and d detected by probe 12 (e.g., ...). Figure 3 The results show significant differences, with substantial variations in the position, amplitude, and shape of the interference peaks. However, the principal interference peak 'a' corresponding to the film thickness remains the same regardless of whether it is probe 12, probe 13, or probe 14, exhibiting relatively little variation.

[0052] By comparing the peak values ​​of the interference intensity curves of the two optical paths, the peak 'a' with similar position, amplitude, and shape is the peak caused by the film thickness interference effect, and the position corresponding to this peak is the film thickness being measured. Interference peaks caused by interference factors, such as b / b1, c / c1, and d / d1, have significantly different positions, amplitudes, and shapes, and can be excluded.

[0053] Different optical paths contain microscopic interference factors with different angles and other characteristics, which cancel each other out. This allows for the stable detection of film thickness data through the peak value α.

[0054] Example 2

[0055] To better eliminate the influence of interference factors on interferometric measurements, this embodiment can add one or more optical paths. To reduce the complexity of equipment installation, probes 13 and 14 can be used. Previously, probe 13 only used the outgoing optical fiber; now it can utilize the receiving optical fiber. Similarly, probe 14 previously only used the receiving optical fiber; now it can utilize the outgoing optical fiber. An additional host unit 7 (light source 16 and spectrometer 17) is also added, as detailed below. Figure 6 As shown.

[0056] The added optical paths OC1, OCR1, and OCR2, although similar to optical paths OB1, OBR1, and OBR2 except for their reverse direction, exhibit different characteristics at the microscopic level due to the very small size of the interfering factors. This results in a new interference intensity curve that differs from the original one. While the film thickness corresponds to a relatively constant position and amplitude of the main interference peak, the interference peaks formed by each interfering factor vary significantly.

[0057] By comparing multiple interference intensity curves in this way, interference peaks caused by interfering factors can be eliminated more reliably, and the correct interference peaks caused by film thickness factors can be obtained, thus obtaining accurate film thickness values.

[0058] In addition to probes 13 and 14, more probes can be added to perform detection at the same working point, forming a comparison optical path, which will result in more stable detection. However, this is more complex and costly in engineering, and therefore less valuable.

[0059] In a production environment, if there are large interference factors, such as large foreign objects in the coating, the amplitude, position, and shape of the main interference peaks of the film thickness of different optical paths OA1, OAR1, OAR2 and OB1, OBR1, OBR2 will also have large differences. In this case, the two interference intensity curves will not have a common peak a.

[0060] At this time, the signal processing computer 15 can issue a warning message to notify the control system or operator that there may be a quality problem with the current steel coating thickness, which is of guiding significance for production.

[0061] In summary, this invention utilizes a multi-optical-path method to eliminate the influence of steel coating thickness interference factors on the interference spectrum, thereby enhancing the interference effect of the basic film thickness. At the same film thickness detection location on the same steel coating plate, two or more fiber optic spectrometers are used to construct different detection optical paths with incident light from different directions. The characteristics of various microscopic interference factors in different detection optical paths, such as surface ripples, pigment particles, and substrate surface texture, are different, while the film thickness being measured is the same. Therefore, the interference spectral peaks of the interference factors are inconsistent, while the interference spectral peaks of the film thickness can reinforce each other. By eliminating false peaks and retaining true values, the true film thickness data can be determined.

[0062] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A multi-interference optical path matched steel coating film thickness on-line measuring device, characterized in that, The application relates to a steel coating film thickness on-line measuring device. The probe has multiple probes arranged at different angles and used for detecting the coating film of a steel coating plate. The probe has two groups of optical fibers, one group of which is an outgoing optical fiber and the other group of which is a reflection receiving optical fiber. The host computer is connected with the probe and used for calculating a film thickness intensity curve according to the interference degree of each wavelength in the spectrum. The steel coating film thickness on-line measuring device performs the following operations: 1) a light beam generated by a broadband light source is transmitted to the probe through an optical fiber and is output from the probe to irradiate a steel film to be measured; 2) reflected light from the upper surface and the lower surface of the film enters the probe and enters the optical fiber spectrometer along the optical fiber; 3) the optical fiber spectrometer detects the received steel film reflected light spectrum containing interference information through an internal grating and a CCD; 4) a computer reads the spectrum data of the reflected light containing interference information through a communication loop; the spectrum data of the reflected light presents interference ripples similar to a cosine curve; 5) the computer calculates the interference ripple information of the spectrum data, and according to the Fresnel formula, a corresponding film thickness value can be preliminarily calculated; 6) if the probe is not vertical but is inclined to irradiate, a trigonometric function correction is performed to obtain a direct film thickness value; 7) due to interference factors, the interference spectrum is not a complete ideal spectrum, and the film thickness value calculated according to the interference spectrum is a curve with multiple peak values, and the peak values represent that the positions are more likely to be used for calculating the film thickness; 8) the computer analyzes the film thickness curves calculated by multiple light paths incident on the same working point of the coating film at different angles, and the positions with overlapping peak values correspond to the actual film thickness; 9) the computer sends the result to a user; 10) the computer then starts the collection and calculation of the next spectrum data. The steel coating film thickness on-line measuring device is used for measuring the film thickness of the coating film of a steel coating plate. ​ ​ ​ ​ 2. A multi-interference optical path matched steel coating film thickness on-line measurement method, characterized in that: ​ A plurality of probes at different angles are arranged above the steel coated plate, the infrared light emitted by the light source is transmitted to the probes through the outgoing optical fiber, and then irradiated to the same working point of the coating layer, the reflected light at the working point is transmitted to the probes through the reflected receiving optical fiber, the interference light is formed on the probes and then transmitted to the spectrometer, the spectrum of the interference light is measured by the spectrometer, and the film thickness intensity curve is calculated by the signal processing computer according to the interference degree of each wavelength in the spectrum; the computer analyzes the film thickness curves calculated by the plurality of light paths incident to the same working point of the coating layer at different angles, and the position with overlapping peak values corresponds to the actual film thickness.

3. The multi-interference optical path matched steel coating film thickness on-line measurement method according to claim 2, characterized in that: The reflected light is transmitted to the same probe; and / or The reflected light is transmitted to different probes in a cross manner.

4. The multi-interference optical path matched steel coating film thickness on-line measurement method according to claim 2, characterized in that: The wavelength of the infrared light emitted by the light source is less than 3 μm.

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