System and method for measuring thickness of oil film on surface of plate strip based on infrared multi-point differential absorption

Abstract

The invention discloses a plate strip surface oil film thickness measuring system and method based on infrared light multipoint differential absorption, which are used for measuring the thickness of a to-be-measured oil film coated on a to-be-stamped plate strip, and comprise an infrared light source, a measuring light path diaphragm, a focusing lens, a motor, a filtering wheel disc and a detector, infrared light sources are arranged on the two sides of the upper portion of a to-be-stamped plate strip correspondingly, and light source window pieces are arranged on the infrared light sources correspondingly. A measuring light path diaphragm, a focusing lens and a detector are sequentially arranged on the measuring light path right above the to-be-stamped plate strip from bottom to top; a motor is arranged on one side of the measuring light path, an output shaft of the motor is connected with the center of the light filtering wheel disc to drive the light filtering wheel disc to rotate, six circular reference signal windows are evenly distributed on the light filtering wheel disc, and oil liquid samples to be measured with the thicknesses sequentially increased are sealed in the six circular reference signal windows through two transparent window pieces respectively. And the six circular reference signal windows can sequentially pass through a measuring light path between the focusing lens and the detector.

Description

Technical Field

[0001] The invention relates to the field of non-contact film thickness high-precision measurement based on the principle of infrared light absorption by materials, and in particular to a system and method for high-precision measurement of surface oil film thickness during stamping processing of automobile bodies. Background Art

[0002] Stamping is a commonly used parts processing method in modern industry, with higher processing accuracy and production efficiency than traditional methods. Stamping dies are usually complex in shape, and a very thin lubricating oil film needs to be applied to the surface of the stamped parts during the stamping process, which has an important influence and effect on the consumption of deformation force during the stamping process, the surface quality, internal quality, service life, processing accuracy and mold loss of metal workpieces.

[0003] The thickness of the oil film on the surface of stamping parts is the main factor affecting product quality and processing accuracy. If the oil film is too thin, it will cause surface scratches, causing the metal to crack during the stretching process, and will also affect the corrosion resistance of the product, seriously affecting the appearance and quality of the product. If the oil film is too thick, it will cause local wrinkling and other situations. Too much oil will accumulate on the surface during the stamping process, forming oil bags. Secondly, it will increase the vacuum effect during the stamping process, affect the air discharge of the mold, and cause the part to hold the mold more severely. Taking the stamping of automobile bodies as an example, according to incomplete statistics, the number of plate scratches caused by the oil film thickness not meeting the requirements is more than 1,300 times a day. The online high-precision measurement of the oil film thickness on the surface of stamping parts is a pain point that needs to be solved urgently. Under the premise of high-precision measurement of the oil film thickness on the surface of stamping parts, timely adjustment of the production process and process of stamping parts that do not meet the requirements can greatly reduce the cost and the probability of defective product overflow.

[0004] At present, the thickness of the oil film on the surface of stamping parts in actual production is at the μm level, which requires very high measurement accuracy, and the production workshop environment is complex and has large interference. How to achieve fast online high-precision measurement of the ultra-thin oil film thickness on the surface of stamping parts in a strong interference environment is a key issue and technical problem that needs to be solved urgently.

[0005] There are many methods to measure oil film thickness, but their respective limitations hinder their field applications. Contact measurement will destroy the oil film, and oil film thickness is mainly measured by non-contact methods. Among the non-contact measurement methods, electrical methods based on resistance, capacitance or eddy current principles are easily affected by noise from oil characteristics and electromagnetic interference. At the same time, the measurement principle of electrical methods also limits the application of long-distance measurement in assembly line industry sites.

[0006] In recent decades, non-destructive measurement based on ultrasound has been well developed and widely used in oil film thickness measurement. However, the measurement accuracy will be significantly affected by the acoustic characteristics and thermal effects of the sensor, and it is more susceptible to interference from ultrasonic waves generated by mechanical vibration on industrial production lines. In comparison, the optical method is not limited by the measurement distance and electromagnetic interference, and has great advantages in measuring the oil film thickness on the surface of metal plates and strips at industrial production sites. At present, the commonly used optical detection methods mainly include optical interference, laser induced fluorescence, infrared absorption, etc., all of which have high measurement accuracy and resolution. Among them, the measurement principles and data processing processes of optical interference and laser induced fluorescence are relatively complex. Infrared absorption detection methods mainly include spectrophotometry and dual-wavelength detection. The dual-wavelength detection method requires narrow-band filters with different central wavelengths as measurement channels and reference channels. Narrow-band filters that meet the requirements in the mid-infrared band are not easy to obtain and are costly. Among them, the optical path structure and data processing process of the spectrophotometry method are relatively simple, but the general method requires measuring the light intensity of dark noise and the blank state of the object being measured as a reference. The measurement process is complicated and easy to introduce unnecessary errors. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art in the application of oil film thickness measurement on the surface of plates and strips in industrial sites, and to provide a system and method for measuring the oil film thickness on the surface of plates and strips based on multi-point differential absorption of infrared light. The measurement system and method are based on the characteristics of the selective absorption of infrared light by the oil film to be measured and the Lambert-Beer law, and a measurement optical path structure of dual-light source common optical path reflection absorption is designed. The common absorption of infrared light by the oil film to be measured and the oil film of specified thickness is used as the measurement signal, and the measurement signal is collected to perform differential operations to solve the values ​​of some unknown parameters. The values ​​of the remaining unknown parameters are obtained by calibration, and the thickness value of the oil film to be measured is solved to obtain the thickness value of the oil film to be measured, thereby realizing online measurement of the ultra-thin oil film thickness on the surface of the plate and strip to be stamped under a complex industrial environment.

[0008] The objective of the present invention is achieved through the following technical solutions:

[0009] A plate strip surface oil film thickness measurement system based on infrared light multi-point differential absorption, used to measure the thickness of the oil film to be measured coated on the plate strip to be punched, including an infrared light source, a measuring light path window, a focusing lens, a motor, a filter wheel, and a detector;

[0010] Infrared light sources are respectively provided on both sides above the plate strip to be punched, and light source windows are provided on the infrared light sources; a measuring light path directly above the plate strip to be punched is provided with a measuring light path window, a focusing lens and a detector from bottom to top; a motor is provided on one side of the measuring light path, and the motor output shaft is connected to the center of the filter wheel to drive the filter wheel to rotate, and six circular reference signal windows are evenly distributed on the filter wheel, and the six circular reference signal windows are respectively sealed with oil samples to be tested with increasing thicknesses through two transparent window pieces, and when the filter wheel rotates, the six circular reference signal windows can pass through the measuring light path between the focusing lens and the detector in sequence.

[0011] Furthermore, the focusing lens includes a first focusing lens and a second focusing lens which are sequentially arranged from bottom to top on the measuring light path, and the second focusing lens is located on a conjugate image plane of the first focusing lens.

[0012] The present invention also provides a method for measuring the oil film thickness on the plate strip surface based on infrared light multi-point differential absorption, comprising:

[0013] S1. Use Fourier infrared spectrometer to measure the infrared absorption spectrum of the oil sample to be tested, determine the maximum absorption band range of the oil sample to be tested and the minimum theoretical value d of the oil thickness required for the light within the maximum absorption band to be completely absorbed min ;

[0014] S2. Based on the theoretical value of minimum oil film thickness d min , determine the thickness d1-d6 of the oil sample to be tested sealed in the six circular reference signal windows <d min , and the thickness of d1-d6 increases successively;

[0015] S3. Make the surface of the plate to be punched blank, that is, the thickness of the oil film to be measured is zero, and irradiate the light emitted by the infrared light source to the plate to be punched through the light source window. The light reflected by the plate to be punched passes through the measuring light path window, focusing lens, and filter wheel on the measuring light path in turn and enters the detector; the filter wheel is driven by a motor to rotate, and the detector receives 6 groups of reference light intensity signals of the oil samples to be tested with different thicknesses d1-d6;

[0016] S4. Based on the reference light intensity signal after being absorbed by the oil samples of different thicknesses, the constant parameters of the measurement system are obtained by using the differential algorithm and the linear least squares method for fitting and calibration;

[0017] S5. According to the calibrated constant parameters of the measurement system, the thickness of the oil film to be measured is measured online in real time, and the thickness value of the oil film to be measured is obtained by calculation.

[0018] Furthermore, in step S3, the Beer-Lambert law is used to calculate the absorption of infrared light by the oil film to be tested, and the formula is:

[0019]

[0020] In the formula, I ab is the light intensity transmitted after being absorbed by the oil film to be tested, I d is the intensity of light incident on the surface of the oil film to be tested after diffuse reflection, ε is the absorption coefficient of the oil sample to be tested in the infrared light band, C is the concentration of the oil sample to be tested, and n oil is the refractive index of the oil sample to be tested, d x is the oil film thickness to be measured, θ is the angle between the light source and the horizontal direction of the measuring system; for a certain measuring system and oil sample to be measured, εCn oil and θ are constants, and Q is also a constant.

[0021] Furthermore, according to the Lambert-Beer law, the light intensity received by the detector through the six circular reference signal windows is expressed as

[0022]

[0023] In the formula, I mean is the light intensity received by the detector through n circular reference signal windows, d n The thickness of the oil sample to be tested is encapsulated inside the circular reference signal window;

[0024] The loss of light entering the measurement optical path before reaching the detector photosensitive surface includes the normal absorption of the oil film, the absorption and scattering of the measurement system, optical devices and air, and the light intensity I absorbed by the oil sample to be measured encapsulated in the circular reference signal window. oil The light intensity I after reflection and absorption of the measured oil film ab The relationship between

[0025] I oil =I ab β(1-ρ0)(1-ρ1)(1-ρ2)(1-ρ3)(1-ρ4)

[0026] Where, β is the ratio coefficient of infrared light entering the measuring optical path after being reflected and absorbed by the oil film to be measured; ρ0 is the loss rate caused by the structure of the measuring system, including the absorption, reflection and scattering of the measuring system components; ρ1 is the loss rate caused by the optical elements themselves in the measuring system, including the absorption and reflection of the optical path windows and focusing lenses; ρ2 is the loss rate caused by the absorption and scattering of dust and oil on the surface of the optical device; ρ3 is the loss rate caused by the environment of the measuring system, including the absorption and scattering of air and suspended particles in the air; ρ4 is the loss rate caused by absorption and reflection of the plate strip to be punched;

[0027] The light intensity of the circular reference signal window received by the above detector is expressed as

[0028]

[0029] Where k = β(1-ρ0)(1-ρ1)(1-ρ2)(1-ρ3)(1-ρ4), which represents the overall transmittance of the measurement system;

[0030] According to Fresnel's reflection law, the reflection of light on the surface of different media is only related to the refractive index. Under non-ideal conditions, the light intensity received by the detector is expressed as

[0031]

[0032] Where Δd is the thickness of the absorbing oil equivalent to the reflection and refraction losses;

[0033] For all channels, there is the same reflection, which is equivalent to the measurement system error. The above formula is equivalent to

[0034]

[0035] For a fixed measurement system, k and I are obtained d are constants, I k1 It is also a constant.

[0036] Furthermore, the specific steps of step S4 are as follows:

[0037] The surface of the sheet to be stamped is blank, and the thickness of the oil film to be measured is d x = 0, the light intensity I of the six circular reference signal windows received by the detector mea1 -I mea6 It is expressed as:

[0038]

[0039] Where d1-d6 are the thickness of the oil sample sealed in the six circular reference signal windows, Q and I k1 is the constant parameter of the measurement system; the value of the constant Q and I are obtained from the above formula k1 Irrelevant, avoid I k1 The value of affects Q, and Q is solved directly; combining the above equations, we get:

[0040]

[0041] Q i Represents several calculation results, where m and n have Combinations can be calculated The final Q value is obtained by taking the average value as shown below:

[0042]

[0043] On the basis of obtaining the Q value, As a variable combination, linear least squares fitting is used to obtain I k1 The value of .

[0044] Furthermore, the specific steps of step S5 are as follows:

[0045] During the measurement process, an oil film is applied on the surface of the plate to be stamped. Using the constant parameters of the measurement system obtained by calibration, the six oil film thicknesses d to be measured are calculated according to the light intensity value received by the detector through the circular reference signal window. xi The calculation formula is as follows:

[0046]

[0047] In the measurement system, the detector converts the received infrared light into voltage output. The final value is the voltage value rather than the light intensity value. The light intensity is expressed as the optical power per unit area, and the unit is W / m 2 , the conversion relationship between voltage and light intensity is expressed as:

[0048] V=R·P o =R.I.S

[0049] Where R is the light responsivity of the detector, I is the light intensity received by the detector, and S is the photosensitive area of ​​the detector; then d xi It is expressed as:

[0050]

[0051] Where V mean is the voltage value corresponding to the circular reference signal window light intensity signal output by the detector, V k1 is the constant parameter I k1 Corresponding voltage value; d n is the thickness of the oil sample to be tested sealed in the nth circular reference signal window; n = 1.2…6;

[0052] The six thickness values ​​calculated by the above formula are averaged to obtain the final oil film thickness d to be measured. x As shown below, it has higher accuracy and reliability than a single calculated value;

[0053]

[0054] Furthermore, the thickness of the oil samples to be tested sealed in the six circular reference signal windows ranges from 50 to 100 μm.

[0055] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0056] 1. High measurement accuracy and strong anti-interference ability: The present invention is based on an optical measurement method of the infrared light absorption characteristics of the oil film to be measured in a specific band, combined with the Lambert-Beer law, and reduces the electromagnetic interference problem of the electrical measurement method and the mechanical vibration influence of the ultrasonic measurement method through a multi-point differential absorption algorithm, thereby significantly improving the measurement accuracy and environmental adaptability.

[0057] 2. Multi-point differential algorithm simplifies the calibration process: By encapsulating multiple reference oil film samples of known thickness in the filter wheel, the measurement system can complete calibration and measurement at the same time, avoiding the need to establish an additional calibration standard source. The multi-point differential algorithm directly calculates some parameters to be solved, converts nonlinear fitting into linear fitting, reduces the number of calibration parameters, simplifies the calibration process and improves fitting accuracy.

[0058] 3. Dual-light source common optical path design unifies system errors: The measurement system adopts a dual-light source common optical path reflection and absorption structure, and integrates a multi-point measurement structure inside the measurement system, so that all errors caused by measurement system errors, devices and environmental interference are unified into common errors. The measurement system parameters can be obtained through a single calibration, avoiding the separate measurement of the reference signal, thereby simplifying the measurement process and reducing the error caused by the reference signal measurement.

[0059] 4. Signal modulation based on correlation filtering improves signal-to-noise ratio: The filter wheel modulates the optical signal to a fixed frequency to facilitate subsequent filtering and signal acquisition. Combined with the correlation filtering design, it effectively reduces the impact of industrial site environmental noise on signal acquisition and significantly improves the signal-to-noise ratio of the measurement system.

[0060] 5. Real-time online measurement, adaptable to various environments: The system achieves real-time online measurement of the oil film thickness to be measured by calibrating the key constant parameters obtained, and can operate stably in the industrial assembly line environment to meet the needs of high-precision and fast measurement. The system is also suitable for other film thickness measurement scenarios.

[0061] 6. The measurement results are stable and accurate: The present invention calculates multiple thickness values ​​through a differential algorithm and takes the average value as the final result, eliminating the random error in a single measurement. The verification process is simple and easy to implement, with high measurement accuracy, further improving the stability and reliability of the measurement results.

[0062] 7. Wide application prospects: The measurement method designed by the present invention is not only suitable for high-precision measurement of the oil film thickness on the surface of the plate strip during the stamping process of the automobile body, but can also be extended to non-contact measurement of the thickness of other industrial films, providing reliable technical support for different fields. It can meet the needs of measuring the oil film thickness on the surface of any large-area stamping parts, and has good application prospects in the measurement of other film thicknesses besides oil film. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 Schematic diagram of the optical path structure of the measurement system in this embodiment is shown.

[0064] Figure 2 Shown is a schematic diagram of the detector output signal after modulation and processing.

[0065] Figure 3 Shown is a schematic flow chart of the oil film thickness measurement method of this embodiment.

[0066] Figure numerals: 101-infrared light source, 102-light source window, 103-plate strip to be punched, 104-oil film to be measured, 105-measuring light path window, 106-focusing lens, 107-focusing lens, 108-motor, 109-filter wheel, 110-circular reference signal window, 111-circular reference signal window, 112-circular reference signal window, 113-circular reference signal window, 114-circular reference signal window, 115-circular reference signal window, 116-detector. DETAILED DESCRIPTION

[0067] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0068] Example 1

[0069] See Figure 1 , this embodiment provides a plate strip surface oil film thickness measurement system based on infrared light multi-point differential absorption, which is used to measure the thickness of the oil film 104 to be measured coated on the plate strip 103 to be punched, including an infrared light source 101, a measuring light path window 105, a focusing lens 106, a focusing lens 107, a motor 108, a filter wheel 109, and a detector 116;

[0070] Infrared light sources 101 are respectively provided on both sides above the plate strip 103 to be punched, and light source windows 102 are provided on the infrared light sources 101; the measuring light path directly above the plate strip 103 to be punched is provided with a measuring light path window 105, a focusing lens 106, a focusing lens 107 and a detector 116 from bottom to top, wherein the focusing lens 107 is located on the conjugate image plane of the focusing lens 106; a motor 108 is provided on one side of the measuring light path, and the output shaft of the motor 108 is connected to the center of the filter wheel 109 to drive the filter wheel 109 to rotate, and six circular reference signal windows 110-115 are evenly distributed on the filter wheel 109, and the six circular reference signal windows are respectively sealed with oil samples to be tested with increasing thickness through two transparent windows, and when the filter wheel 109 rotates, the six circular reference signal windows can pass through the measuring light path between the focusing lens 107 and the detector 116 in sequence.

[0071] Example 2

[0072] In order to measure the oil film thickness on the strip surface, we first need to understand what parameters need to be obtained for the measurement results. The following first uses formulas and existing technical principles to derive the parameters required for the measurement process:

[0073] First, the infrared absorption spectrum of the oil sample to be tested is measured by Fourier infrared spectrometer to determine the maximum absorption band range of the oil sample to be tested and the minimum theoretical value of the oil thickness d required for the light in the maximum absorption band to be completely absorbed. min .

[0074] Then select a continuous infrared light source whose emission wavelength can cover the maximum absorption band range of the sample.

[0075] The infrared light source 101 generates a wide spectrum of infrared light, which passes through the light source window 102 and reaches the oil film to be tested on the surface of the stamping part. The light intensity emitted by the infrared light source 101 is expressed as

[0076]

[0077] Where I0 is the total light intensity emitted by the infrared light source, I(λ) is the light intensity distribution function, λ1 is the lower limit of the wavelength of the continuous light source emission spectrum, and λ2 is the upper limit of the wavelength of the continuous light source emission spectrum.

[0078] The light reaches the oil film 104 to be tested coated on the surface of the plate strip 103 to be stamped, and enters the measuring optical path after being reflected and absorbed by the oil film to be tested. When the light passes through the surface of the plate strip 103 to be stamped and the oil film to be tested, it follows the Lambertian diffuse reflection. The light intensity after diffuse reflection is I d Expressed as

[0079] I d =2δK d I0 max(0,cosθ) (2)

[0080] In the formula, I d is the light intensity after diffuse reflection, δ is the transmittance of the light source window 102, K d is the diffuse reflection coefficient, I0 is the total light intensity emitted by the infrared light source, that is, the incident light intensity, and θ is the angle between the incident light and the surface normal of the sheet to be stamped.

[0081] The infrared light reaching the oil film to be tested on the surface of the plate to be stamped includes diffuse reflection and absorption. The absorption of infrared light by the oil film 104 to be tested satisfies the Lambert-Beer law, which can be expressed as

[0082] I ab =I d e -εCL (3)

[0083] In the formula, I abis the intensity of light transmitted after being absorbed by the oil film to be tested, ε is the absorption coefficient of the oil sample to be tested in the infrared light band, C is the concentration of the oil sample to be tested, and L is the optical path length.

[0084] like Figure 1 As shown, from the definition of optical path and the path of reflection and absorption, we can get

[0085]

[0086] Where n oil is the refractive index of the oil sample to be tested, d x is the oil film thickness to be measured, and θ is the angle between the incident light and the surface normal of the sheet to be stamped.

[0087] According to the above formula, the absorption of infrared light by the oil film to be measured satisfies the Lambert-Beer law and can be described as

[0088]

[0089] For a certain measurement system and oil film to be measured, εCn oil and θ are constants, then Q is a constant.

[0090] The light reflected and absorbed by the oil film 104 to be measured passes through the measuring optical path window 105 , is imaged by the focusing lens 106 , and is imaged again by the focusing lens 107 .

[0091] The measurement optical path is approximately an ideal optical system, and the imaging of focusing lens 106 and focusing lens 107 satisfies the Gaussian formula, which is expressed as

[0092]

[0093] Where l is the object distance, l' is the image distance, f is the object focal length, and f' is the image focal length.

[0094] The light beam enters the filter wheel 109, and the motor 108 drives the filter wheel 109 provided with n circular reference signal windows to rotate, and sequentially scans the light beam focused by the lens group.

[0095] According to the Lambert-Beer law, the light intensity received by the detector 116 through the n circular reference signal windows is expressed as

[0096]

[0097] In the formula, I mean is the light intensity received by the detector through n circular reference signal windows, d n It is the thickness of the oil sample to be tested encapsulated inside the circular reference signal window.

[0098] The loss of light entering the measurement optical path before reaching the detector photosensitive surface includes the normal absorption of the oil sample to be tested encapsulated inside the reference signal window, as well as the absorption and scattering of the measurement system, optical devices and air. The light intensity I oil The light intensity I after reflection and absorption of the measured oil film ab The relationship between

[0099] I oil =I ab β(1-ρ0)(1-ρ1)(1-ρ2)(1-ρ3)(1-ρ4) (8)

[0100] In the formula, β is the proportional coefficient of infrared light entering the measuring optical path after being reflected and absorbed by the oil film to be measured; ρ0 is the loss rate caused by the system structure, including absorption, reflection, and scattering of system components; ρ1 is the loss rate caused by the optical components themselves in the system, mainly the absorption and reflection of optical windows and lenses; ρ2 is the loss rate caused by the absorption and scattering of dust and oil on the surface of optical devices; ρ3 is the loss rate caused by the system environment, mainly including the absorption and scattering of air and suspended particles in the air; ρ4 is the loss rate caused by absorption and reflection of the sheet to be stamped.

[0101] like Figure 1 As shown, the measurement system is a common optical path structure. The light intensity loss of all circular reference signal windows due to the system, optical devices and environment is equal. The light intensity of the circular reference signal window received by the detector is expressed as

[0102]

[0103] Wherein, k = β(1-ρ0)(1-ρ1)(1-ρ2)(1-ρ3)(1-ρ4), which represents the overall transmittance of the measurement system.

[0104] The above formula only considers the light intensity received by the detector under the condition of circular reference signal window encapsulation oil film absorption. In fact, when the light beam passes through a certain thickness of oil film, in addition to absorption consumption, there are also certain reflection, refraction and other losses. According to Fresnel's reflection law, it can be known that the reflection of light on the surface of different media is only related to the refractive index. Therefore, the light intensity received by the detector under non-ideal conditions is expressed as

[0105]

[0106] Where Δd is the thickness of the absorbing oil equivalent to the loss of reflection, refraction, etc.

[0107] As shown in the above formula, the same reflection exists for all channels, which can be equivalent to the system error. Therefore, the above formula can be equivalent to

[0108]

[0109] Where, for a fixed system k and I ab are all constants, so I k1 is a constant.

[0110] At this point, as shown in the above formula, it is known that if the unknown constant parameter I of the measurement system can be obtained k1 and Q, the oil film thickness d to be measured can be calculated using the signal output by the detector x The value of .

[0111] like Figure 1 As shown, six light-transmitting circular reference signal windows are arranged on the filter wheel, and the thicknesses of the oil samples to be tested encapsulated between each pair of transparent window pieces in the circular reference signal window 110 to the circular reference signal window 115 are d1, d2, d3, d4, d5, and d6, respectively. What the detector receives is the light intensity absorbed by the oil film to be tested and the oil sample to be tested encapsulated with known thickness.

[0112] Since the common oil film thickness range in automobile body stamping is 5-20μm, based on this, the thickness range of d1-d6 is 50-100μm (100μm <d min ), and the thickness of d1-d6 increases successively.

[0113] See Figure 3 , when the surface of the sheet to be stamped is blank, that is, the thickness of the oil film to be measured is d x Parameter calibration is performed when =0, and the light intensity of the reference signal window received by the detector is expressed as.

[0114]

[0115] From the above formula, we can get that the value of constant Q is related to I k1 Irrelevant, avoid I k1 The value of affects Q, and Q is solved directly. Combining the above equations, we can get:

[0116]

[0117] As shown above, Q i Indicates multiple calculation results, where m and n have Combination forms can be calculated The final Q value can be obtained by taking the average value as shown below

[0118]

[0119] On the basis of obtaining the Q value, As a variable combination, I can be obtained by linear least squares fitting. k1The value of .

[0120] During the measurement, an oil film is applied to the surface of the stamping plate, and the Q and I are obtained using the above calibration. k1 According to the light intensity of the circular reference signal window received by the detector, the 6 oil film thicknesses d to be measured can be calculated as shown in formula (11): xi As shown below

[0121]

[0122] In the measurement system, the detector converts the received infrared light into voltage output. The final value is the voltage value instead of the light intensity value. The light intensity is expressed as the optical power per unit area, and the commonly used unit is (W / m 2 ), the conversion relationship between voltage and light intensity is expressed as

[0123] V=R·P o =R·I·S (16)

[0124] In the formula, R is the light responsivity of the detector, I is the light intensity received by the detector, and S is the photosensitive area of ​​the detector. Then, in practical engineering applications, formula (15) is expressed as

[0125]

[0126] Where V mean is the voltage value corresponding to the light intensity signal of the measurement window output by the detector, V k1 is parameter I k1 The corresponding voltage value.

[0127] The six thickness values ​​calculated by the above formula are averaged, and the final value of the oil film thickness to be measured is as follows, which has higher accuracy and reliability than a single calculated value.

[0128]

[0129] In summary, the infrared light multi-point differential absorption method proposed in this embodiment can well realize the measurement of the oil film thickness on the surface of the plate strip to be stamped. The optical path structure of dual-light source common optical path reflection and absorption makes the system errors of all reference signal windows uniform, and the required parameter values ​​can be obtained through a single calibration. In addition, the multi-point measurement structure is integrated into the measurement system to realize the integration of calibration and measurement, avoid the establishment of an additional calibration standard source, and simplify the calibration process. The method of the present invention can realize multiple measurements of the measured value at one time, and greatly improves the stability and accuracy of the measurement results through averaging.

[0130] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solution of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, a person of ordinary skill in the art can also make many forms of specific changes under the guidance of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A plate strip surface oil film thickness measurement system based on infrared light multi-point differential absorption, used to measure the thickness of the oil film to be measured on the plate strip to be stamped, characterized in that: It includes infrared light source, measuring optical path window, focusing lens, motor, filter wheel and detector; Infrared light sources are respectively provided on both sides above the plate strip to be punched, and light source windows are provided on the infrared light sources; a measuring light path directly above the plate strip to be punched is provided with a measuring light path window, a focusing lens and a detector from bottom to top; a motor is provided on one side of the measuring light path, and the motor output shaft is connected to the center of the filter wheel to drive the filter wheel to rotate, and six circular reference signal windows are evenly distributed on the filter wheel, and the six circular reference signal windows are respectively sealed with oil samples to be tested with increasing thicknesses through two transparent window pieces, and when the filter wheel rotates, the six circular reference signal windows can pass through the measuring light path between the focusing lens and the detector in sequence.

2. According to claim 1, a plate and strip surface oil film thickness measurement system based on infrared light multi-point differential absorption is characterized in that: The focusing lens comprises a first focusing lens and a second focusing lens which are arranged in sequence from bottom to top on the measuring light path, and the second focusing lens is located on the conjugate image plane of the first focusing lens.

3. A method for measuring the oil film thickness on the surface of a plate strip based on infrared multi-point differential absorption, based on the plate strip surface oil film thickness measurement system according to any one of claims 1-2, characterized in that: include: S1. Use Fourier infrared spectrometer to measure the infrared absorption spectrum of the oil sample to be tested, determine the maximum absorption band range of the oil sample to be tested and the minimum theoretical value d of the oil thickness required for the light within the maximum absorption band to be completely absorbed min ; S2. Based on the theoretical value of minimum oil film thickness d min , determine the thickness d1-d6 of the oil sample to be tested sealed in the six circular reference signal windows <d min , and the thickness of d1-d6 increases successively; S3. Make the surface of the plate to be punched blank, that is, the thickness of the oil film to be measured is zero, and irradiate the light emitted by the infrared light source to the plate to be punched through the light source window. The light reflected by the plate to be punched passes through the measuring light path window, focusing lens, and filter wheel on the measuring light path in turn and enters the detector; the filter wheel is driven by a motor to rotate, and the detector receives 6 groups of reference light intensity signals of the oil samples to be tested with different thicknesses d1-d6; S4. Based on the reference light intensity signal after being absorbed by the oil samples of different thicknesses, the constant parameters of the measurement system are obtained by using the differential algorithm and the linear least squares method for fitting and calibration; S5. According to the calibrated constant parameters of the measurement system, the thickness of the oil film to be measured is measured online in real time, and the thickness value of the oil film to be measured is obtained by calculation.

4. The method for measuring the oil film thickness on the strip surface based on infrared multi-point differential absorption according to claim 3 is characterized in that: In step S3, the Beer-Lambert law is used to calculate the absorption of infrared light by the oil film to be tested, and the formula is: In the formula, I ab is the light intensity transmitted after being absorbed by the oil film to be tested, I d is the intensity of light incident on the surface of the oil film to be tested after diffuse reflection, ε is the absorption coefficient of the oil sample to be tested in the infrared light band, C is the concentration of the oil sample to be tested, n oil is the refractive index of the oil sample to be tested, d x is the oil film thickness to be measured, θ is the angle between the light source and the horizontal direction of the measuring system; for a certain measuring system and oil sample to be measured, εCn oil and θ are constants, and Q is also a constant.

5. The method for measuring the oil film thickness on the strip surface based on infrared multi-point differential absorption according to claim 4 is characterized in that: According to the Lambert-Beer law, the light intensity received by the detector through the six circular reference signal windows is expressed as In the formula, I mean is the light intensity received by the detector through n circular reference signal windows, d n The thickness of the oil sample to be tested is encapsulated inside the circular reference signal window; The loss of light entering the measurement optical path before reaching the detector photosensitive surface includes the normal absorption of the oil film, the absorption and scattering of the measurement system, optical devices and air, and the light intensity I absorbed by the oil sample to be measured encapsulated in the circular reference signal window. oil The light intensity I after reflection and absorption of the measured oil film ab The relationship between I oil =I ab β(1-ρ0)(1-ρ1)(1-ρ2)(1-ρ3)(1-ρ4) Where, β is the ratio coefficient of infrared light entering the measuring optical path after being reflected and absorbed by the oil film to be measured; ρ0 is the loss rate caused by the structure of the measuring system, including the absorption, reflection and scattering of the measuring system components; ρ1 is the loss rate caused by the optical components themselves in the measuring system, including the absorption and reflection of the optical path window and the focusing lens; ρ2 is the loss rate caused by the absorption and scattering of dust and oil on the surface of the optical device; ρ3 is the loss rate caused by the environment of the measuring system, including the absorption and scattering of air and suspended particles in the air; ρ4 is the loss rate caused by absorption and reflection of the plate strip to be punched; The light intensity of the circular reference signal window received by the above detector is expressed as Where k = β(1-ρ0)(1-ρ1)(1-ρ2)(1-ρ3)(1-ρ4), which represents the overall transmittance of the measurement system; According to Fresnel's reflection law, the reflection of light on the surface of different media is only related to the refractive index. Under non-ideal conditions, the light intensity received by the detector is expressed as Where Δd is the thickness of the absorbing oil equivalent to the reflection and refraction losses; For all channels, there is the same reflection, which is equivalent to the measurement system error. The above formula is equivalent to For a fixed measurement system, k and I are obtained d are constants, I k1 Also a constant.

6. The method for measuring the oil film thickness on the strip surface based on infrared multi-point differential absorption according to claim 3 is characterized in that: The specific steps of step S4 are as follows: The surface of the sheet to be stamped is blank, and the thickness of the oil film to be measured is d x = 0, the light intensity I of the six circular reference signal windows received by the detector mea1 -I mea6 It is expressed as: Where d1-d6 are the thickness of the oil sample sealed in the six circular reference signal windows, Q and I k1 is the constant parameter of the measurement system; From the above formula, we can get the value of constant Q and I k1 Irrelevant, avoid I k1 The value of affects Q, and Q is solved directly; combining the above equations, we get: Q i Represents several calculation results, where m and n have Combinations can be calculated The final Q value is obtained by taking the average value as shown below: On the basis of obtaining the Q value, As a variable combination, linear least squares fitting is used to obtain I k1 The value of .

7. The method for measuring the oil film thickness on the strip surface based on infrared multi-point differential absorption according to claim 3 is characterized in that: The specific steps of step S5 are as follows: During the measurement process, an oil film is applied on the surface of the plate to be stamped. Using the constant parameters of the measurement system obtained by calibration, the six oil film thicknesses d to be measured are calculated according to the light intensity value received by the detector through the circular reference signal window. xi The calculation formula is as follows: In the measurement system, the detector converts the received infrared light into voltage output. The final value is the voltage value instead of the light intensity value. The light intensity is expressed as the light power per unit area, in W / m2. The conversion relationship between voltage and light intensity is expressed as: V=R·P o =R·I·S Where R is the light responsivity of the detector, I is the light intensity received by the detector, and S is the photosensitive area of ​​the detector; then d xi It is expressed as: Where V mean is the voltage value corresponding to the circular reference signal window light intensity signal output by the detector, V k1 is the constant parameter I k1 The corresponding voltage value; d n is the thickness of the oil sample to be tested sealed in the nth circular reference signal window; n = 1.2…6; The six thickness values ​​calculated by the above formula are averaged to obtain the final oil film thickness d to be measured. x As shown below, it has higher accuracy and reliability than a single calculated value; 8. The method for measuring the oil film thickness on the strip surface based on infrared multi-point differential absorption according to claim 3 is characterized in that: The thickness of the oil samples to be tested sealed in the six circular reference signal windows ranges from 50 to 100 μm.

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