CN116593008A - A method of measuring truck brake temperature based on infrared thermal imaging technology - Google Patents

Abstract

The invention discloses a freight car brake temperature measurement method based on an infrared thermal imaging technology, and relates to the technical field of infrared thermal imaging. According to the invention, a series of parameter values of a thermal imager are constrained and measured according to an experimental environment, and an infrared thermal image of a wagon wheel part during braking is obtained by using the thermal imager; since the thermal imager receives radiation not only from the wheels themselves, but also from the surroundings, reflected by the surface of the object, both of which are to some extent attenuated by the atmosphere in the measuring path, the atmosphere itself constitutes a third source of radiation in the process; calculating the radiation power of the three radiation sources respectively through the constrained thermal imager parameter values, and calculating the total radiation power through the associated coefficients; finally, through the measured infrared thermal image pixel values, pixel division intervals and temperature measurement general formulas, the maximum temperature, average temperature and the like of the wagon wheel positions can be accurately calculated after the wagon wheel positions are accurately divided.

Description

A method of measuring truck brake temperature based on infrared thermal imaging technology

technical field

The invention belongs to the technical field of infrared thermal imaging, in particular to a method for measuring the brake temperature of a truck based on the infrared thermal imaging technology, which belongs to a more superior and more accurate technology based on the existing infrared thermal imaging technology.

Background technique

The existing infrared thermal imaging temperature measurement technology uses the radiant energy, radiance, color, etc. from the object to measure the temperature. The temperature sensitive element is not in contact with the measured object, so the temperature measured by this technology is not the real temperature of the object. , but the radiation temperature. For example, CN202110764064.9 is a device and method for measuring model surface emissivity in a high-temperature flow field environment, and the disclosed technical scheme; although the radiation temperature has been corrected by the atmospheric transfer factor, there is still a gap between it and the real temperature of the object surface. There are certain differences; when using this technology to measure temperature, it is easily affected by its own characteristics and external factors, and at present there is mainly the problem of emissivity (emissivity) ε, that is, the numerical accuracy of the emissivity indicated by the measured target object will be affected. Seriously affect the accuracy of precise temperature measurement.

On the basis of infrared thermal imaging technology, the method of measuring the brake temperature of trucks by establishing a corresponding relationship after accurately determining the parameters has a wide range of applications in the fields of microelectronics, paper industry, automobile industry, plastic injection molding and home appliance design. . The existing infrared thermal imaging temperature measurement technology has certain limitations in the measurement of emissivity and the temperature measurement when the environment changes, and cannot meet the needs of actual measurement. Therefore, there is a need for a more effective and accurate emissivity ε, and a temperature measurement method that can be adapted to various environments.

Contents of the invention

The invention provides a method for measuring the brake temperature of a truck based on infrared thermal imaging technology. The method only checks the brake temperature of a truck from a real-time single-frame image stream, which includes a set of thermal imaging images and corresponding visible light images; the general idea Yes: After determining the short-wave n value used by the thermal imager, accurately measure the emissivity ε and other parameters of the truck wheel (the target object to be measured), perform temperature measurement calculations, finally obtain the wheel position image, and calculate the wheel position Maximum temperature and average temperature; Compared with the existing infrared thermal imaging temperature measurement technology, parameters such as emissivity ε can be accurately measured, and can be fused with visible light images to further improve the accuracy of temperature measurement at the braking position of the truck and solve the problem Problems in the background technology.

In order to solve the problems of the technologies described above, the present invention is achieved through the following technical solutions:

A method for measuring the brake temperature of a truck based on infrared thermal imaging technology of the present invention is a method for accurately measuring the emissivity ε or emissivity parameter of the target object at the brake part of the truck. By substituting the temperature formula, the brake part of the truck can be obtained as The temperature value of the target object, the main steps of the method are as follows:

After crumpling a large sheet of aluminum foil, unroll the foil and attach it to a piece of cardboard of the same size.

Place this piece of cardboard in front of the object to be measured, making sure the side with the aluminum foil is facing the thermal imager. The emissivity is set to 1.0 by default, and the apparent temperature of the aluminum foil is measured and recorded.

Select the location to place the sample (truck wheel material), and determine and set the reflected apparent temperature according to the previous process.

Place a piece of insulating tape with a known high emissivity (emission value) on the sample (truck wheel material), and then heat the sample to at least 20°C higher than room temperature to keep the heating even.

Focus and automatically adjust the thermal imager, freeze the image in the thermal imager, and then adjust the level and temperature width to obtain the best image brightness and contrast; set the radiation value of the insulating tape, which is the emission value, usually 0.97.

Measure the temperature of the tape using one of the following thermal imager measurement functions: ① Isotherm (used to determine the temperature and uniformity of sample heating); ② Spot (simple and straightforward); ③ Box averaging, i.e. suitable for different surface emission values various surfaces; note the temperature.

Finally, move the measurement function to the sample (truck wheel material), change the emissivity setting until it reads the same value as the previously measured temperature, and record the emissivity at this time, which is the emissivity ε of the truck wheel material.

In order to seek further precise settings, after obtaining the emissivity, you can continue to set parameter values such as relative humidity, distance from the thermal imager to the truck wheel, etc. Also, relative humidity can usually be left at the default value of 50% for short distances and normal humidity.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention can make the calculation result of the general temperature formula more accurate through the unique method of accurately measuring the emissivity at the brake wheel of the truck, and setting the experimental parameter values such as relative humidity and distance under different environments;

(2) Compared with the existing thermal imaging principle temperature measurement technology, the present invention provides a truck brake temperature measurement method based on infrared thermal imaging technology, which can obtain higher accuracy on average, and can accurately and effectively obtain temperature value;

(3) The present invention can divide the wheel area after being fused with the visible light image, further improving the accuracy of temperature measurement;

(4) The present invention also does not require user interaction.

Of course, any product implementing the present invention does not necessarily need to achieve all the above-mentioned advantages at the same time.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that are required for the description of the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. Those of ordinary skill in the art can also obtain other drawings based on these drawings without any creative effort.

Fig. 1 is the overall flowchart of a kind of method for measuring the brake temperature of a truck based on infrared thermal imaging technology in the present invention;

Fig. 2 is the schematic diagram of the model for accurately simulating and measuring emissivity ε in a specific embodiment of the present invention;

Fig. 3 is the model schematic diagram of calculating total radiation power W in the specific embodiment of the present invention;

In the accompanying drawings, the list of parts represented by each label is as follows:

1-surrounding environment, 2-object, 3-atmosphere, 4-thermal imager.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The present invention aims to propose an improved infrared thermal imaging technology to more effectively and accurately measure the emissivity ε, which is used to solve the problem of determining the brake temperature of trucks. In the present invention, the process of accurately measuring the emissivity ε can be adapted to various environments. Subsequently, in the process of calculating the temperature value, the thermal image of the brake wheel of the truck can be obtained separately in real time (the display mode of the thermal image is set to grayscale thermal image display in advance), so as to obtain the maximum temperature, average temperature and other values at the wheel , to avoid the problem that other areas of the truck (such as the body) have an error effect on the temperature at the wheel. Finally, the present invention can be combined with the corresponding visible light image to further accurately measure the temperature value of the brake wheel position of the truck, and can also realize the temperature control and early warning function, effectively reducing the occurrence of traffic accidents.

Below in conjunction with accompanying drawing, scheme of the present invention will be further described:

As shown in Figure 1, the present invention provides a method for measuring the brake temperature of a truck based on infrared thermal imaging technology. The main steps of the method are as follows:

S1. The overall idea of the constructed method for accurately measuring the emissivity ε is: the emissivity ε of the sample (truck brake vehicle) is measured in equivalent simulation with an insulating tape of known emissivity.

1) Prepare a large sheet of aluminum foil, and after crumpling, unfold the aluminum foil and stick it on a piece of cardboard of the same size.

2) As shown in Figure 2, place the cardboard in front of the object to be measured, making sure that the side with the aluminum foil is facing the thermal imager (reference number 4). The emissivity is set to 1.0 by default, and the apparent temperature of the aluminum foil is measured and recorded.

3) Select a location to place the sample (sample material of the same material as the truck wheel), and determine and set the reflected apparent temperature according to the previous process.

4) Place a piece of insulating tape with a known high emissivity (emission value) on the sample, and then heat the sample to at least 20°C higher than room temperature to keep the heating even. .

5) Focus and automatically adjust the thermal imager (reference number 4), freeze the image in the thermal imager (reference number 4), and then adjust the level and temperature width to obtain the best image brightness and contrast. Set the radiation value (emission value) of the insulating tape, usually 0.97.

6) Measure the temperature of the tape using one of the measurement functions of the following thermal imager (reference number 4): ① isotherm (used to determine the temperature and uniformity of sample heating); ② point (simple and direct); ③ box average (for various surfaces with different surface emissivity values). Note the temperature.

7) Finally, move the measurement function to the sample (truck wheel material), change the emissivity setting until it reads the same value as the previously measured temperature, and record the emissivity at this time, which is the emissivity of the truck wheel material.

S2. Calculate the total radiation power W from the precisely measured radiation rate ε with the associated coefficient, and the solution steps are as follows:

As shown in Figure 3, the thermal imager (reference number 4) receives not only the radiation from the object (reference number 2) itself. It also collects radiation from the surroundings that is reflected by the surface of the object (reference number 2). Both radiations are attenuated to some extent by the atmosphere along the measurement route. In the process, the atmosphere itself becomes a third source of radiation.

Assuming that the received radiation power W comes from a short-distance blackbody temperature source T _source , the thermal imager output signal U _source generated by it is part of the power input (power linear thermal imager). We can write the following formula (1):

U _source ＝CW(T _source ) (1)

There is also a simpler annotation:

U _source = CW _source (2)

Here C is a constant; if the radiation source is a radiation gray body ε, the received radiation rate should be εW _source .

Similarly, three received radiation power conditions can be written:

1) Radiation from the object (reference number 2) = ετW _obj , where ε is the emissivity of the object (reference number 2) and τ is the transmission rate of the atmosphere. The temperature of the object (reference number 2) is T _obj .

2) Reflected radiance of the surrounding radiation source = (1-ε)τW _obj , where (1-ε) is the reflectance of the object (reference number 2). The ambient radiation source has a temperature T _refl . It is assumed here that the temperature T _refl is the same for all radiating surfaces within the hemisphere of any point on the surface of the object (reference number 2 ). Of course this is a simplified form of the real situation. The simplification process is necessary to derive an effective formula, T _refl and can (at least in theory) be assigned to represent the effective temperature of the complex environment.

Note that the emissivity=1 of the surrounding environment (reference number 1 ) is also assumed. This is true according to Kirchhoff's laws. All radiation that falls on surrounding surfaces ends up being absorbed by the same surfaces. Thus emissivity = 1 (although recent discussions call for considering the entire sphere around the object (figure number 2)).

Atmospheric radiation = (1-τ)τW _atm , where (1-τ) is the emissivity of the atmosphere. The temperature of the atmosphere is T _atm . The total received radiated power can now be expressed in equation (3):

W _total -ετW _obj +(1-ε)τW _refl +(1-τ)W _atm (3)

Multiplying each condition by the constant C of Equation 1 and substituting the product CW for the corresponding U according to the same equation yields Equation (4):

U _total -ετU _obj +(1-ε)U _refl +(1-τ)U _atm (4)

Solve formula (4) to obtain the general measurement formula of U _obj :

S3. According to the Stephen-Boltzmann formula:

W=σT ⁿ [Watt/m ² ] (6)

Wherein, σ is Boltzmann's constant=5.670373(21)×10 ^-8 W/(m ² ·K ^-4 ), and error values are in brackets.

When using thermal imagers with different wavelength bands (spectral ranges), the value of n is different, such as: HgCdTe (8-13 μm) short-wave thermal imager, n=4.09; HgCdTe (6-9 μm) short-wave thermal imager, n=5.33; for InSb (2-5μm) short-wave thermal imager, n=8.68.

Substituting formula (6) into formula (7), the calculation formula of the real surface temperature can be obtained through the total emissivity of different positions:

Where T _total represents the radiation temperature indicated by the thermal imager (reference number 4).

When measuring temperature at close range, τ=1, formula (7) can be written as:

When the measured surface temperature is high, T _refl /T _obj is very small, then formula (7) can be written as:

S4. After constructing the ROI area for each frame of the truck thermal image and the visible light image, perform subordinate operations on each frame of the image in the ROI area of the thermal image:

① Morphological operation. The image in the ROI area of the thermal image is first opened (corroded first, then expanded), and the small noise points are removed, and the noise reduction operation is performed; then the closed operation (first expanded, then corroded), is performed.

②Contour detection. Specific technologies and methods are used to accurately extract and display the target contour in the ROI area.

③ Obtain the outline of the wheel. Using specific techniques and methods, find out the wheel profile among all the profiles. If the required wheel profile is not detected, skip this frame and check the next frame; if the required wheel profile is detected, then detect the wheel profile.

④ Obtain the image of the wheel. After the vehicle outline is detected, a specific method is used to extract the wheel image in the ROI area, so that the influence of the area around the truck wheel on the wheel temperature detection can be removed.

After the above operations, a certain frame of thermal imaging image containing the wheels of the truck can be accurately obtained.

Use S1 to obtain the emissivity ε and the general temperature formula obtained by S3, and combine the image of the truck wheel area obtained in the previous step with the pixel value of each pixel on the thermal image, combined with the temperature displayed on the thermal image The value and temperature measurement interval are fused with the visible light image to accurately calculate the temperature value of each pixel at the truck wheel.

Compared with the set temperature warning threshold (warning temperature: 70°C; alarm temperature: 80°C), the brake temperature of the truck can be judged.

The invention evaluates the advantages of combining infrared thermal imaging technology and actual environmental factors, and verifies the stability detection problem between real-time frames and frames, making the temperature measurement range of key frames accurate to ±2°C or ±2% of reading within. In addition, the present invention can be effectively fused with the visible light image of the truck to meet the requirements of accurate identification and positioning, and can also realize the feature of accurately measuring the temperature of the brake position of the truck under different environments.

The preferred embodiments of the invention disclosed above are only to help illustrate the invention. The preferred embodiments are not exhaustive in all detail, nor are the inventions limited to specific embodiments described. Obviously, many modifications and variations can be made based on the contents of this specification. This description selects and specifically describes these embodiments in order to better explain the principle and practical application of the present invention, so that those skilled in the art can well understand and utilize the present invention. The invention is to be limited only by the claims, along with their full scope and equivalents.

Claims (5)

1. A method for measuring the temperature of truck brakes based on infrared thermal imaging technology, is characterized in that, comprises the steps: S1. Constraint setting and accurate measurement of a series of parameter values of the thermal imager, and image analysis of the brake wheel parts of the truck; S2, respectively calculate the radiation power of three kinds of radiation sources by the constrained thermal imager parameter values, calculate the total radiation power w with the associated coefficient; three kinds of radiation sources are target object, surrounding environment (reference number 1) ,atmosphere; S3. According to the total radiant power w obtained in the step S2, the Stephen-Boltzmann law is substituted into the Boltzmann constant σ, and the measured value of the brake temperature of the truck is obtained through equation deformation; S4. Through the fusion of the temperature map of the thermal imager and the visible light image, the image of the wheel position is accurately divided, the maximum temperature and the average temperature of the wheel position are calculated, and the warning temperature threshold is compared. 2. a kind of method for measuring the temperature of truck brakes based on infrared thermal imaging technology according to claim 1, is characterized in that, described S1 step comprises following sub-steps: S11. Plug in the thermal imager device and connect it to the computer through a network cable, open the device web client, accurately measure the emissivity ε of the truck wheel according to the actual scene, and set the relative humidity, distance from the truck wheel, effective temperature around the truck wheel and the atmosphere A series of parameter value parameters for temperature; S12. After the parameter setting is completed, adjust the angle of the thermal imager and the picture presentation; start video recording of the target object before the truck is about to pass by; stop video recording of the truck wheels after the truck leaves; S13. Step S12 is repeated to save and analyze the thermal imager images and visible light images at the braked wheels of different trucks. 3. a kind of method for measuring the temperature of truck brakes based on infrared thermal imaging technology according to claim 1, is characterized in that, in the described S2 step, calculating the total radiation power w comprises the following sub-steps: S21. There is a linear relationship between the black body temperature edge T _source from the short distance and the part of the power input in the generated thermal imager output signal U _source , and the linear relationship is: U _source ＝CW(T _source ) Formula I Expressed with a simple annotation, namely U _source = CW _source Formula II Among them, C is a constant; if the radiation source is a radiation that raises ε, the received radiation rate is εW _source ; S22. Radiation rate from the truck wheel, that is, the target object = ετW _obj , where τ is the transmission rate of the atmosphere; set the temperature of the target object as T _obj ; S23, the reflected radiation rate from the surrounding radiation source=(1-ε)τW _refl , where (1-ε) is the reflective wall of the object; the temperature of the surrounding radiation source is set as T _refl ; S24, radiation from the atmosphere=(1-τ)τW _atm , where (1-τ) is the radiation rate of the atmosphere; the temperature of the atmosphere is set as T _atm ; S25. The total radiation power received is expressed as W _total -ετW _obj +(1-ε)τW _refl +(1-τ)W _atm Formula III S26. Multiply each condition of the above equation by the constant C, and replace the result CW with the corresponding U according to the same equation, and solve U _obj : Among them, U _obj is the output voltage T _obj of the thermal imager calculated by the temperature black body, which is directly converted into the voltage of the actual required object temperature; U _total is the output voltage of the thermal imager measured in the actual situation; U _refl is the output voltage obtained according to the calibration The thermal imager output voltage T _refl of the temperature blackbody; U _atm is the thermal imager output voltage T _atm of the temperature blackbody obtained according to the calibration. 4. a kind of method for measuring the temperature of truck brakes based on infrared thermal imaging technology according to claim 1, is characterized in that, described S3 step comprises following sub-steps: S31. According to the Stephen-Boltzmann formula: W=σT ⁿ [Watt/m ² ] Formula V where σ is the Boltzmann constant, which is a constant value Error values are in brackets; When using thermal imagers with different wavelength bands or spectral ranges, the value of n is different, such as: Short-wave thermal imager for HgCdTe (8-13 μm), n=4.09; short-wave thermal imager for HgCdTe (6-9 μm), n=5.33; short-wave thermal imager for InSb (2-5 μm), n=8.68; S32. Substituting formula V into formula IV, through the total emissivity of different positions, the calculation formula of the real surface temperature is obtained: Among them, T _total represents the radiation temperature indicated by the thermal imager; S33. When the temperature is measured at a short distance, τ=1, and the formula VI is written as: When the measured surface temperature is high, T _refl /T _obj is very small, then formula VI is written as: 5. a kind of method for measuring the temperature of truck brakes based on infrared thermal imaging technology according to claim 1, is characterized in that, the calculation steps of maximum temperature and average temperature in the described S4 step are as follows: S41. After constructing the ROI area on the thermal imaging image and the visible light image of the truck, perform morphological operations, contour detection, outlier elimination, and wheel detection operations, and finally determine the wheel area image of the truck; S42. Perform linear conversion to calculate the maximum temperature and average temperature of the truck wheel area through the temperature range of the thermal imager and the pixel value ratio of the wheel area, and at the same time match the warning threshold temperature specified by the national standard (warning temperature: 70°C; alarm temperature: 80°C ) to complete the warning function.