Stamping part surface oil film thickness measuring device and method based on correlation filtering

Abstract

The invention relates to a device and a method for measuring the thickness of an oil film on the surface of a stamping part based on correlation filtering. The measuring device comprises an infrared light source, a focusing lens group, a light filtering wheel disc and a detector, a normal absorption window and a saturated absorption window are arranged on the light filtering wheel disc, and the normal absorption window and the saturated absorption window can rotate to a light path which can be detected by the detector through rotation of the light filtering wheel disc; the normal absorption window and the saturated absorption window are sealed by two transparent window sheets, and the space between the two transparent window sheets for packaging the normal absorption window is not filled; and a tested oil film sample with a certain thickness is packaged between two transparent window sheets of the saturated absorption window.

Description

Technical Field

[0001] The invention relates to the field of high-precision non-contact film thickness measurement based on optical principles, and in particular to the field of 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. During the stamping process, a very thin lubricating oil film needs to be applied to the surface of the stamped parts, 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. At the same time, the oil film can increase the lubrication between the mold and the surface of the stamped parts, which can reduce wear, reduce surface roughness, reduce friction coefficient, and improve fatigue life.

[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 actual production of stamping parts requires 3 to 5 g / m2 of oil coating on the surface. 2 The oil film thickness is at the μm level, which requires very high measurement accuracy. In addition, the production workshop environment is complex and has large interference. How to achieve fast online high-precision measurement of 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] At present, the commonly used methods for measuring oil film thickness include resistance method, capacitance method, eddy current method, optical detection method, ultrasonic detection method, quality control method, X-ray method, etc.

[0006] The principle of the resistance method is simple, but the resistance of the oil film is large and difficult to calibrate, and it is not easy to get the absolute value of the oil film thickness. The capacitance method is determined by the distance between the two surfaces. It is easily interfered when the distance is large, and it is easy to break down when the oil film is too thin. The eddy current method uses the eddy current effect of metal conductors and is easily interfered by surrounding metal objects on the production line. The X-ray method uses the transmittance of X-rays. Most of the stamping parts are metal parts that are not easy to penetrate. X-rays also have strong radiation and are not very safe. The attenuation and reflection characteristics of ultrasonic waves vary greatly when passing through thin layers, which makes signal processing complicated and difficult to accurately judge the true thickness of the oil film.

[0007] The optical measurement method can take into account both measurement distance and accuracy, is not susceptible to electromagnetic interference, and is more suitable for industrial field environments than the above methods. Summary of the invention

[0008] The purpose of the present invention is to address the deficiencies of the prior art and propose a method for measuring the oil film thickness on the surface of stamping parts based on correlation filtering. This measurement method is based on the existence of a maximum absorption peak of the measured oil film in the infrared band and the Lambert-Beer law. It designs a reflection and absorption optical path structure to detect the light intensity signal of the measured oil film under normal absorption and saturation absorption of infrared light. Through the correlation filtering technology, the thickness of ultra-thin oil films on the surface of stamping parts in complex industrial environments can be measured. At the same time, the measurement error caused by the loss of light intensity due to light reflection, refraction, etc. under saturation absorption is corrected. The technical solution is as follows:

[0009] A device for measuring the oil film thickness on the surface of a stamping part based on correlation filtering comprises an infrared light source, a focusing lens group, a filter wheel and a detector. A normal absorption window and a saturated absorption window are arranged on the filter wheel. The rotation of the filter wheel can make the normal absorption window and the saturated absorption window rotate to the optical path that can be detected by the detector. The normal absorption window and the saturated absorption window are both sealed by two transparent window pieces, and no filling is done between the two transparent window pieces that encapsulate the normal absorption window. A measured oil film sample with a certain thickness is encapsulated between the two transparent window pieces of the saturated absorption window.

[0010] Furthermore, a bandpass filter whose central wavelength and half-width are equivalent to the maximum absorption wavelength and half-width of the measured oil film sample is detachably installed at the front end of the detector.

[0011] Furthermore, the focusing lens group includes a first focusing lens and a second focusing lens, and the second focusing lens is located on a conjugate image plane of the first focusing lens.

[0012] Furthermore, when the thickness of the oil film to be measured is detected, the distance between the two transparent window pieces used to encapsulate the normal absorption window is equal to the thickness of the oil film encapsulated in the saturated absorption window.

[0013] The present invention also provides a method for measuring the oil film thickness on the surface of a stamping part using the above-mentioned measuring device, which is characterized by comprising the following steps:

[0014] The infrared absorption spectrum of the oil film sample to be tested is measured by Fourier infrared spectrometer to determine the maximum absorption band range of the sample and the absorption coefficient k of the sample;

[0015] Select a continuous infrared light source whose emission wavelength can cover the maximum absorption band of the oil film sample to be tested;

[0016] The infrared light source generates wide-spectrum infrared light, which is reflected and absorbed by the oil film to be measured, and then forms an image after passing through the focusing lens group;

[0017] The filter wheel rotates so that the normal absorption window and the saturation absorption window sequentially scan the light beam focused by the lens group that can be detected by the detector;

[0018] Select a bandpass filter with a central wavelength and half-width equivalent to the maximum absorption wavelength and half-width of the sample, and install it in the front end of the detector to ensure that the detector receives light intensity that is only the band that can be absorbed by the measured oil film sample. When the thickness of the oil film packaged in the saturated absorption window is 0, record the signal amplitude output by the detector, which is recorded as V oil0 ;

[0019] Remove the bandpass filter installed at the front end of the detector, and record the signal amplitude output by the detector when the thickness of the oil film encapsulated in the saturated absorption window is 0, which is recorded as V0;

[0020] According to the Lambert-Beer law, the theoretical value d of the minimum thickness of the encapsulated oil film required for the saturation absorption window is calculated. min ; Calibrate the absorption coefficient K of the saturated absorption window;

[0021] Determine the saturation absorption window for measuring the thickness of the oil film being measured;

[0022] Rotate the filter wheel so that the detector receives the light intensity passing through the normal absorption window and the saturation absorption window alternately;

[0023] The detector converts the optical signal into an electrical signal, and after conditioning, amplification, and collection, it outputs a modulated signal, which is the detector output voltage;

[0024] Determine the model for calculating the measured oil film thickness, and the expression is as follows:

[0025]

[0026] d oil is the measured oil film thickness, V mea is the voltage value corresponding to the normal absorption window output by the detector, V refis the voltage value corresponding to the saturated absorption window output by the detector, ρ4 is the transmittance of the saturated absorption window, and β is the unknown quantity to be calibrated;

[0027] The measurement system is calibrated using n stamping parts with different specified oil film thicknesses sprayed on their surfaces as input. The output voltage of the measurement system is recorded respectively, and the functional relationship between the oil film thickness and the output voltage value of the measurement system detector is obtained by fitting.

[0028] Furthermore, the absorption coefficient K of the saturated absorption window is calibrated. Specifically, a group of saturated absorption windows are made, and oil films of different specified thicknesses are encapsulated between two transparent windows that encapsulate each saturated absorption window. The signal amplitudes output by the detector are recorded respectively, which are recorded as V oilt ; Among them, the thickness of each oil film of the package should be less than the theoretical value d min ; The absorption coefficient K is obtained by performing least square fitting based on the data of the measured oil film with different thicknesses and the signal amplitude output by the detector.

[0029] Furthermore, the method for determining the saturation absorption window for measuring the oil film thickness is as follows:

[0030] The oil film is encapsulated inside the saturated absorption window, and the thickness is the theoretical calculated value d min , record the detector output signal amplitude V out ; If V out ≤V0-V oil0 , it indicates that the package oil film thickness meets the use requirements; if V out >V0-V oil0 , then increase the oil film thickness, increase the thickness d a for

[0031]

[0032] Adjust the thickness of the oil film inside the saturated absorption window to d min +d a , record the detector output signal amplitude, if it is not satisfied, increase the thickness of the oil film inside the saturated absorption window by d a , repeat the test until V out ≤V0-V oil0 ; Obtain the saturation absorption window for measuring the oil film thickness.

[0033] Furthermore, the distance between the two transparent windows used to encapsulate the normal absorption window is adjusted to ensure that it is equal to the thickness of the oil film encapsulated by the saturated absorption window used to measure the thickness of the oil film to be measured.

[0034] Furthermore, when measuring the thickness of the oil film to be measured, after the output voltage value of the detector is collected, the measured value of the thickness of the oil film to be measured is obtained according to the fitted functional relationship.

[0035] The method for measuring the oil film thickness on the surface of stamping parts based on correlation filtering proposed by the present invention has the following beneficial effects:

[0036] (1) The method for measuring the oil film thickness on the surface of stamping parts based on correlation filtering adopted by the present invention is an optical measurement method based on the absorption characteristics of the measured oil film to infrared light in a specific band. Compared with the electrical measurement method, it has high measurement accuracy and strong anti-interference ability.

[0037] (2) The optical path structure designed in the present invention realizes the complementarity of light sources and guarantees the light intensity reaching the measured oil film to the greatest extent. At the same time, the measurement optical path and the reference optical path are integrated inside the system, so that the errors caused by system errors, devices and environmental interference become common mode errors. In addition, it avoids measuring the reference signal separately, simplifying the measurement process. At the same time, the reference signal can be measured in real time, reducing the error caused by the reference signal measurement and improving the measurement accuracy and environmental adaptability of the system.

[0038] (3) The modulation optical path based on correlation filtering designed in the present invention modulates the output effective signal into a fixed frequency through the filter wheel, which facilitates subsequent filtering and signal collection and greatly improves the signal-to-noise ratio of the system.

[0039] (4) The correlation filtering technology proposed in the present invention eliminates the errors caused by system, device and environmental interference in principle, while also avoiding the influence of environmental changes on the measurement results, improving the stability and measurement accuracy of the measurement system, and is more suitable for industrial sites with complex environments.

[0040] (5) The measurement method proposed in the present invention has a simple verification process, is easy to implement, and has high measurement accuracy. It can meet the needs of measuring the oil film thickness on the surface of any stamping part with a large area, and also has good application prospects in the measurement of other film thicknesses besides oil film. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Shown is a schematic diagram of the optical path structure.

[0042] Figure 2 Shown is a schematic diagram of the detector output signal after modulation and processing.

[0043] Figure 3 Shown is a flow chart of the oil film thickness measurement method of the present invention.

[0044] Explanation of the numbers in the figure: infrared light source 101, light source window 102, measured oil film 103, measuring light path window 104, focusing lens (L1) 105, focusing lens (L2) 106, motor 107, normal absorption window 108, saturation absorption window 109, filter wheel 110, detector 111. DETAILED DESCRIPTION

[0045] Based on the Lambert-Beer law, the present invention proposes a method for measuring the oil film thickness on the surface of stamping parts based on correlation filtering, which belongs to the category of optical measurement. Figure 1 As shown, it mainly includes: an infrared light source 101, a light source window 102, a measured oil film 103, a measuring light path window 104, a focusing lens (L1) 105, a focusing lens (L2) 106, a motor 107, a normal absorption (measurement signal) window 108, a saturated absorption (reference signal) window 109, a filter wheel 110, and a detector 111.

[0046] Firstly, the infrared absorption spectrum of the sample is measured by Fourier transform infrared spectrometer to determine the maximum absorption band range of the sample and the absorption coefficient k of the sample.

[0047] Select a continuous infrared light source with an emission wavelength that covers the maximum absorption band of the sample.

[0048] The infrared light source 101 generates a wide-spectrum infrared light, which passes through the light source window 102 and reaches the oil film to be measured on the surface of the stamping part. The light intensity emitted by the light source is expressed as

[0049]

[0050] In the formula, I0 is the total light intensity emitted by the light source, is the light intensity corresponding to the maximum absorption band of the sample being tested, It is the light intensity corresponding to the band that the sample does not absorb.

[0051] The light reaches the surface of the oil film 103 to be measured, and enters the measuring optical path after being reflected and absorbed by the oil film. When the light passes through the stamping surface and the oil film to be measured, it follows the Lambertian diffuse reflection. The light intensity after reflection is expressed as

[0052] I d =K d I0max(0,cosθ)

[0053] In the formula, I d is the reflected light intensity, K d is the diffuse reflection coefficient, I0 is the incident light intensity, and θ is the angle between the incident light and the surface normal.

[0054] The light reflected and absorbed by the measured oil film 103 passes through the optical window 104 of the measuring optical path part, is imaged by the focusing lens (L1) 105, and is imaged again by the focusing lens (L2) 106, wherein the focusing lens (L2) 106 is located on the conjugate image plane of the focusing lens (L1) 105.

[0055] The measurement optical path is approximately an ideal optical system, and the imaging of focusing lenses L1 and L2 satisfies the Gaussian formula, which can be expressed as

[0056]

[0057] The light beam enters the modulated optical path, and the motor 107 drives the filter wheel with two circular light-transmitting windows to rotate, and sequentially scans the light beam focused by the lens group. The inside of the light-transmitting window is sealed by two transparent window sheets that allow the light beam to pass normally. Figure 1 As shown, the transparent window pieces of the normal absorption window 108 are not filled, and the detector receives the light intensity that is only absorbed by the oil film to be measured on the surface of the stamping part; a certain thickness of the oil film sample to be measured is encapsulated between the transparent window pieces of the saturated absorption window 109 to ensure that the light in the infrared light corresponding to the maximum absorption band of the oil film to be measured is completely absorbed, and the light received by the detector only contains the band that is not absorbed by the oil film to be measured.

[0058] Select a bandpass filter with a central wavelength and half-width that are exactly the same as the maximum absorption wavelength and half-width of the sample, and install it in front of the detector 111 to ensure that the light intensity received by the detector is only the band that can be absorbed by the measured oil film sample. When the thickness of the oil film encapsulated in the saturated absorption window 109 is 0, record the signal amplitude output by the detector, which is recorded as V oil0 .

[0059] Remove the filter installed at the front end of the detector 111, and record the signal amplitude output by the detector when the thickness of the oil film packaged in the saturated absorption window 109 is 0, which is recorded as V0.

[0060] The absorption of infrared light by the oil film inside the saturated absorption window 109 follows the Lambert-Beer law, which is expressed as

[0061]

[0062] In the formula, I oil0 It represents the light intensity signal received by the detector when the thickness of the oil film encapsulating the saturated absorption window 109 is 0, I oilt It represents the light intensity signal (transmission absorption) received by the detector when the thickness of the oil film encapsulated by the saturated absorption window 109 is not 0, G represents the photoelectric conversion coefficient of the detector, k represents the absorption coefficient of the measured oil film, c represents that the concentration of the measured oil film sample is a constant, l represents the optical path difference, and d represents the oil film thickness.

[0063] According to the above formula, the theoretical value d of the minimum thickness of the encapsulated oil film required for the saturated absorption window 109 is calculated: min .

[0064] The absorption coefficient K of the saturation absorption window 109 is calibrated. Specifically, 5 groups of oil films of specified thickness are encapsulated between the transparent window pieces of the saturation absorption window 109, and the thickness increases by 0.5 mm. The signal amplitudes output by the detector are recorded respectively, which are recorded as V oilt Among them, the encapsulated oil film thickness is less than the theoretical value d min .

[0065] The absorption coefficient K was obtained by performing least square fitting based on the data of 5 groups of oil films of specified thickness and the detector output signal.

[0066] An oil film is encapsulated inside the saturated absorption window 109, and the thickness is the theoretical calculated value d min , record the detector output signal amplitude V out If V out ≤V0-V oil0 , it indicates that the package oil film thickness meets the use requirements;

[0067] If V out >V0-V oil0 , then it is necessary to increase the oil film thickness, increase the thickness d a for

[0068]

[0069] The thickness of the oil film inside the saturated absorption window 109 is adjusted to d min +d a , record the detector output signal amplitude until it meets V out ≤V0-V oil0 .

[0070] The distance between the transparent window pieces inside the normal absorption window 108 is adjusted to ensure that the thickness of the oil film packaged inside the saturated absorption window 109 is equal.

[0071] The detector 111 receives the light intensity through the two windows 108 and 109 alternately, which are expressed as

[0072]

[0073] In the formula, is the light intensity received by the detector after I0 is absorbed by the measured oil film, I ref is the light intensity received by the detector after saturation absorption, which does not include the light in the maximum absorption band of the oil film, that is,

[0074] The detector 111 converts the optical signal into an electrical signal, and outputs a modulated signal after conditioning, amplification, and collection. The modulated signal output includes two effective signals, both of which include common mode errors such as system error, error caused by ambient light interference, and light intensity loss caused by device contamination and reflection. The frequency of the modulated signal is determined by the motor speed.

[0075] By using the correlation filtering technology on the acquired modulated signal, the value of the measured oil film thickness can be calculated, as shown below.

[0076] Among them, in the saturated absorption state, the light intensity received by the detector that does not contain the maximum absorption band is expressed as

[0077]

[0078] Under normal absorption conditions, the light intensity received by the detector that does not include the maximum absorption band is expressed as

[0079]

[0080] Under normal absorption conditions, the light intensity of the maximum absorption band received by the detector is expressed as

[0081]

[0082] Among them, ρ0, It is the transmittance of the system, including scattered infrared light, absorption and reflection of system components such as lenses and optical windows.

[0083] ρ1, It is the transmittance of dust, oil, etc. on the surface of optical components in the system.

[0084] ρ2, It is the permeability of air and suspended particles in the air.

[0085] ρ3, It is the transmittance of the stamping surface to be tested.

[0086] ρ4 is the transmittance of the saturation absorption window 109 .

[0087] is the transmittance of the oil film to be tested.

[0088] Divide the collected normal absorption and saturation absorption signals to eliminate the common mode error, which is expressed as

[0089]

[0090] Simplified,

[0091]

[0092] in,

[0093]

[0094] Since complete absorption and normal absorption are in the same working environment and within the same system, the light intensity loss caused by factors such as the system, optical devices, stray light interference, stamping reflection, and light intensity that does not enter the measurement light path is equal, that is,

[0095]

[0096] Combining the above formula, we can get the oil film permeability to be measured: It can be expressed as

[0097]

[0098] The selective absorption of infrared light by the measured oil film satisfies the Lambert-Beer law, which can be expressed as

[0099] I=I0·e -kcl

[0100] Where I0 is the incident light intensity and I is the reflected light intensity.

[0101] The transmittance of infrared light after being absorbed by the measured oil film is expressed as

[0102]

[0103] When light passes through a medium, there are three possibilities: transmission, absorption, and reflection, and T+A+R=1. A is the absorptivity, T is the transmittance, and R is the reflectivity.

[0104] Based on the above formula, in the measurement method proposed by the present invention, Lambert-Beer law can be specifically expressed as

[0105]

[0106] In the formula, k is the absorption coefficient of the oil film to infrared light, c is the concentration of the oil film sample to be measured, and l is the optical path of infrared light in the oil film to be measured.

[0107] Pick It is a constant and will not change with the change of the emitted light power. Therefore, the absorption rate can be accurately measured even if the emitted light power is not absolutely stable.

[0108] The transmittance ρ4 of the saturated absorption window 109 can be calibrated. In the absence of an oil film to be measured, a pure oil block is placed in the optical path to ensure that the light in the maximum absorption band is completely absorbed. The light intensity received by the detector is the transmitted light intensity, which is recorded as I oil The light intensity received by the detector corresponding to the optical path without the pure oil block is the incident light intensity, denoted as I noil,but

[0109]

[0110] Measured oil film thickness d oil is a function of the absorptivity and is expressed as

[0111] d oil =f(I ref ,I mea ).

[0112] Light intensity is a physical quantity that describes the radiation energy or flux of light passing through a unit area in unit time. The commonly used unit is watt / square meter (W / m 2 ), then the light intensity is expressed as the optical power per unit area. In the measurement system, the detector receives infrared light and then converts it into voltage output. The conversion relationship is expressed as

[0113] V=R·P o =R.I.S

[0114] Where R is the light responsivity of the detector, I is the light intensity received by the detector, and S is the photosensitivity area of ​​the detector.

[0115] Combining the detector photoelectric conversion relationship and the Lambert-Beer law specified above, the relationship between the system output voltage and the optical path length of infrared light in the measured oil film can be obtained, which is expressed as

[0116]

[0117] Where V mea V is the voltage value corresponding to the normal absorption window of the detector output collected by the system. ref The voltage value corresponding to the saturation absorption window of the detector output collected by the system.

[0118] Taking the logarithm of both sides, we get

[0119]

[0120] The above formula can be expressed as

[0121]

[0122] In the formula, is the proportionality factor

[0123] The measurement method proposed in the present invention is based on the reflection and absorption of infrared light by the measured oil film, and the optical path is related to the actual oil film thickness d oil The relationship is expressed as

[0124]

[0125] Where θ2 is the refraction angle of the light on one side of the oil film being measured, which can be calculated by the law of refraction, n oil is the refractive index of the measured oil film.

[0126] The expression of the measured oil film thickness is as follows:

[0127]

[0128] Where, d oil is the thickness of the oil film being measured, θ2 is the refraction angle of the light on one side of the oil film being measured, which can be calculated by the law of refraction, n oil is the refractive index of the oil film being measured, V mea V is the voltage value corresponding to the normal absorption window 108 of the detector output collected by the system, ref is the voltage value corresponding to the saturated absorption window 109 output by the detector collected by the system, ρ4 is the transmittance of the saturated absorption window 109, and β is the unknown quantity to be calibrated.

[0129] The measurement system is calibrated using n stamping parts with oil films of different specified thicknesses sprayed on their surfaces as input. The measurement results of the system output are recorded respectively, and the accurate functional relationship between the oil film thickness and the system output voltage value is obtained by fitting.

[0130] After the system calibration is completed, the unknown thickness of the oil film on the stamping surface is measured, and the measurement data is processed and displayed in the host computer to obtain the final measurement result of the oil film thickness on the stamping surface.

[0131] From the derivation process and final result of the oil film thickness measurement expression, it can be seen that the system error, the error caused by the device and the environment are filtered out and will not affect the final measurement result. The measurement process does not need to calibrate the system dark noise and the incident light intensity, and the measurement error caused by factors such as temperature change and contamination of the optical device over time will not affect the final oil film thickness measurement result. It is explained that the method for measuring the oil film thickness on the surface of stamping parts based on correlation filtering proposed by the present invention can avoid the influence of complex working environment on the measurement result, and can well realize the measurement of ultra-thin oil film thickness on the surface of stamping parts under complex industrial environment.

Claims

1. A device for measuring the oil film thickness on the surface of stamping parts based on correlation filtering, comprising an infrared light source, a focusing lens group, a filter wheel and a detector, wherein a normal absorption window and a saturated absorption window are arranged on the filter wheel, and the rotation of the filter wheel can make the normal absorption window and the saturated absorption window rotate to the optical path that can be detected by the detector; the normal absorption window and the saturated absorption window are both sealed by two transparent window pieces, and no filling is done between the two transparent window pieces encapsulating the normal absorption window; and a measured oil film sample of a certain thickness is encapsulated between the two transparent window pieces of the saturated absorption window.

2. The device for measuring the oil film thickness on the surface of stamping parts according to claim 1, characterized in that: A bandpass filter whose central wavelength and half-width are equivalent to the maximum absorption wavelength and half-width of the measured oil film sample is detachably installed at the front end of the detector.

3. The device for measuring the oil film thickness on the surface of stamping parts according to claim 1, characterized in that: The focusing lens group includes a first focusing lens and a second focusing lens, and the second focusing lens is located on a conjugate image plane of the first focusing lens.

4. The device for measuring the oil film thickness on the surface of stamping parts according to claim 1, characterized in that: When testing the thickness of the oil film being measured, the distance between the two transparent windows used to encapsulate the normal absorption window is equal to the thickness of the oil film encapsulated in the saturated absorption window.

5. The method for measuring the oil film thickness on the surface of a stamping part implemented by the device according to any one of claims 1 to 4 is characterized in that: The following steps are involved: The infrared absorption spectrum of the oil film sample to be tested is measured by Fourier infrared spectrometer to determine the maximum absorption band range of the sample and the absorption coefficient k of the sample; Select a continuous infrared light source whose emission wavelength can cover the maximum absorption band of the oil film sample to be tested; The infrared light source generates wide-spectrum infrared light, which is reflected and absorbed by the oil film to be measured, and then forms an image after passing through the focusing lens group; The filter wheel rotates so that the normal absorption window and the saturation absorption window sequentially scan the light beam focused by the lens group that can be detected by the detector; Select a bandpass filter with a central wavelength and half-width equivalent to the maximum absorption wavelength and half-width of the sample, and install it in the front end of the detector to ensure that the detector receives light intensity that is only the band that can be absorbed by the measured oil film sample. When the thickness of the oil film packaged in the saturated absorption window is 0, record the signal amplitude output by the detector, which is recorded as V oil0 ; Remove the bandpass filter installed at the front end of the detector, and record the signal amplitude output by the detector when the thickness of the oil film encapsulated in the saturated absorption window is 0, which is recorded as V0; According to the Lambert-Beer law, the theoretical value d of the minimum thickness of the encapsulated oil film required for the saturation absorption window is calculated. min ; Calibrate the absorption coefficient K of the saturated absorption window; Determine the saturation absorption window for measuring the thickness of the oil film being measured; Rotate the filter wheel so that the detector receives the light intensity passing through the normal absorption window and the saturation absorption window alternately; The detector converts the optical signal into an electrical signal, and after conditioning, amplification, and collection, it outputs a modulated signal, which is the detector output voltage; Determine the model for calculating the measured oil film thickness, and the expression is as follows: d oil is the measured oil film thickness, V mea is the voltage value corresponding to the normal absorption window output by the detector, V ref is the voltage value corresponding to the saturated absorption window output by the detector, ρ4 is the transmittance of the saturated absorption window, and β is the unknown quantity to be calibrated; The measurement system is calibrated using n stamping parts with different specified oil film thicknesses sprayed on their surfaces as input. The output voltage of the measurement system is recorded respectively, and the functional relationship between the oil film thickness and the output voltage value of the measurement system detector is obtained by fitting.

6. The method for measuring the oil film thickness on the surface of stamping parts according to claim 5, characterized in that: The absorption coefficient K of the saturated absorption window is calibrated. Specifically, a group of saturated absorption windows are made, and oil films of different specified thicknesses are encapsulated between two transparent windows that encapsulate each saturated absorption window. The signal amplitudes output by the detector are recorded respectively, which are recorded as V oilt ; Among them, the thickness of each oil film of the package should be less than the theoretical value d min ; The absorption coefficient K is obtained by performing least square fitting based on the data of the measured oil film with different thicknesses and the signal amplitude output by the detector.

7. The method for measuring the oil film thickness on the surface of stamping parts according to claim 5, characterized in that: The method for determining the saturation absorption window for measuring the oil film thickness is as follows: The oil film is encapsulated inside the saturated absorption window, and the thickness is the theoretical calculated value d min , record the detector output signal amplitude V out ; If V out ≤V0-V oil0 , it indicates that the package oil film thickness meets the use requirements; if V out >V0-V oil0 , then increase the oil film thickness, increase the thickness d a for Adjust the thickness of the oil film inside the saturated absorption window to d min +d a , record the detector output signal amplitude, if it is not satisfied, increase the thickness of the oil film inside the saturated absorption window by d a , repeat the test until V out ≤V0-V oil0 ; Obtain the saturation absorption window for measuring the oil film thickness.

8. The method for measuring the oil film thickness on the surface of stamping parts according to claim 7, characterized in that: Adjust the distance between the two transparent windows used to encapsulate the normal absorption window to ensure that it is equal to the thickness of the oil film encapsulated by the saturated absorption window used to measure the thickness of the oil film to be measured.

9. The method for measuring the oil film thickness on the surface of a stamping part according to claim 5, characterized in that: When measuring the thickness of the oil film to be measured, after collecting the output voltage value of the detector, the measured value of the thickness of the oil film to be measured is obtained according to the fitted function relationship.

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