Compensation calibration system and method of large-aperture closed structure thermal imager

Abstract

The invention discloses a compensation calibration system and method for a large-aperture closed structure thermal imager. The system comprises a distributed temperature sensor group, a calibration mechanism, a focusing motor, a control and data acquisition module and a data processing module. The distributed temperature sensor group detects the temperature of each temperature area of the thermal imager; the calibration mechanism sets a working environment temperature and provides a calibration target; the focusing motor adjusts the focusing amount; the control and data acquisition module obtains multiple parameters and controls related parts; the data processing module constructs and stores a mathematical model of the relationship between the temperature and focusing amount data based on the temperature and focusing amount data of clear imaging under different working conditions. The influence of temperature change on imaging of the thermal imager is effectively compensated, and the imaging stability and definition of the thermal imager in a wide temperature range environment are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of thermal imaging technology, specifically to a compensation calibration system and method for a large-aperture, enclosed structure thermal imager. Background Technology

[0002] Infrared imaging technology is a high-tech field that many countries are vigorously developing, with wide applications in both civilian and military sectors. High-performance infrared thermal imagers often employ a closed structure to ensure reliability, equipped with large-aperture lenses, and capable of operating across a wide range of high and low temperatures. When a thermal imager is installed as a payload in a closed system or is itself a closed structure, natural heat dissipation is limited, and the self-heating of the imager components causes uneven temperature distribution in the lens. Furthermore, changes in the ambient temperature of the natural environment and the upstream system will also lead to uneven temperature distribution in the lens. Compared to visible light optical systems, the optical material parameters used in thermal imager lenses vary significantly with temperature. As ambient temperature changes, the refractive index of infrared optical materials, the curvature and thickness of optical elements, and the spacing of optical components all change. This is especially true when using large-aperture lenses, which are more sensitive to temperature changes, leading to a decrease in image quality and causing blurry images. Summary of the Invention

[0003] The purpose of this invention is to provide a compensation calibration system and method for a large-aperture enclosed structure thermal imager to solve the problem of image blurring caused by temperature changes in thermal imagers.

[0004] To solve the above-mentioned technical problems, the present invention provides a compensation calibration system for a large-aperture enclosed structure thermal imager, comprising: A distributed temperature sensor array, comprising temperature sensors deployed in different temperature zones within the thermal imager, is used to detect the temperature of each temperature zone within the thermal imager. The calibration mechanism is used to set the operating temperature of the thermal imager and to provide the calibration observation target for the thermal imager. The focusing motor, located in the thermal imager, is used to control the position of the focusing lens inside the thermal imager in order to set the focusing amount of the thermal imager. The control and data acquisition module is used to acquire the temperature of each temperature zone of the thermal imager, control the calibration mechanism to change the working environment temperature of the thermal imager, control the focusing motor to change the focusing amount of the thermal imager, control the focal length of the thermal imager, acquire the focusing amount, and acquire the image clarity of the thermal imager. The data processing module is used to construct a mathematical model representing the relationship between the temperature and the focus of each temperature region when the thermal imager is clear under different working ambient temperatures and focal lengths, and to store the constructed mathematical model in the thermal imager's storage unit.

[0005] According to the above scheme, the calibration mechanism includes a high and low temperature chamber, a collimator, a target, and a blackbody arranged in sequence. The high and low temperature chamber is equipped with an infrared window. During calibration, a thermal imager is placed inside the high and low temperature chamber and acquires an image of the target in front of the blackbody through the infrared window and the collimator. The working environment temperature and the heating and cooling rate are adjusted by remote control.

[0006] According to the above scheme, the division of temperature zones is determined based on the internal components of the thermal imager, circuit layout, working environment, and upper-level system environment, and at least one temperature sensor is set in each temperature zone.

[0007] According to the above scheme, the mathematical model is a multiple linear regression mathematical model, and the linear relationship between the temperature and the focusing amount in each temperature region is expressed as follows:

[0008] In the above formula, U is the focusing amount. This indicates the temperature in different temperature zones. This represents the control coefficient for a certain temperature range. This is the focusing compensation amount.

[0009] According to the above scheme, the multiple linear regression mathematical model includes two different sets of linear relationships, which correspond to the heating and cooling processes of the working environment temperature, respectively.

[0010] According to the above scheme, the multiple linear regression mathematical model includes multiple sets of different linear relationships, each corresponding to a different temperature range of the working environment.

[0011] This invention also provides a compensation calibration method for a large-aperture enclosed structure thermal imager, comprising: S1. Align the thermal imager with the target to be observed, set the ambient temperature to one extreme value of the operating temperature range and keep it warm. S2. To change the ambient temperature at a certain rate of temperature change to the extreme value at the other end of the operating temperature range; S3. Set the thermal imager to the specified focal length, and at that focal length, control the focusing motor to traverse the entire stroke of the focusing amount and acquire the image of the thermal imager and the temperature of each temperature region. S4. Store the position of the focusing motor and the temperature of each temperature zone when the image is clearest at this focal length. S5. Repeat S3~S4 to iterate through all focal lengths of the thermal imager; S6. Perform non-uniformity correction on the thermal imager image; S7. Repeat steps S5 to S6 at the set time intervals; S8. When the heat preservation time exceeds the set duration, continue with the subsequent steps; S9. Repeat steps S2 to S8 to iterate through all preset temperature change rates; S10. Based on the temperature of each temperature region and the focusing amount when the thermal imager image is clear under different working ambient temperatures and different focal lengths, construct a mathematical model characterizing the relationship between the temperature of each temperature region and the focusing amount, and store the constructed mathematical model in the storage unit of the thermal imager.

[0012] According to the above scheme, step S901 is executed before step S10. Step S901 includes: placing the thermal imager in the set simulated working environment and pointing the thermal imager at a target at approximately infinity. Steps S3 to S7 are repeated to obtain the temperature of each temperature area and the focusing amount when the thermal imager image is clear under different working environment temperatures and different focal lengths.

[0013] The present invention also provides a large-aperture enclosed structure thermal imager, which is calibrated using the compensation calibration method described above.

[0014] This invention also provides a compensation method for a large-aperture enclosed structure thermal imager. The method involves acquiring the temperature of each temperature zone of the thermal imager through temperature sensors deployed in different temperature zones within the imager, obtaining the target focusing amount based on the temperature of each temperature zone and the current focal length of the thermal imager, and then controlling the focusing motor to perform focusing based on the target focusing amount. The mathematical model is obtained through the compensation calibration method described above.

[0015] Beneficial effects This invention, by deploying a distributed temperature sensor array in different temperature zones within the thermal imager, can accurately detect the actual temperature of each zone, solving the problem that single temperature detection cannot comprehensively reflect the differences in internal temperature distribution within the thermal imager. This provides accurate temperature data support for subsequent focus compensation. The calibration mechanism can flexibly set the operating environment temperature of the thermal imager and provide a stable calibration observation target, ensuring the controllability and consistency of the calibration process under different temperature conditions, making the acquired temperature and focus-related data more representative. The focus motor can precisely adjust the position of the focusing lens to change the focus amount. Combined with the control and data acquisition module, it comprehensively controls and acquires temperature, ambient temperature, focus amount, focal length, and image sharpness, achieving comprehensive acquisition of clear imaging-related data under multiple parameters, avoiding errors and data omissions caused by manual operation. The data processing module constructs and stores mathematical models of the relationship between temperature and focusing amount in each temperature region based on clear imaging data under different working temperatures and focal lengths. This enables the thermal imager to quickly determine the appropriate focusing amount based on the real-time detected temperature of each region during actual operation. This effectively compensates for the imaging effects caused by changes in the refractive index of infrared optical materials, curvature of optical elements, thickness, and spacing due to temperature variations. It significantly improves the imaging blurring problem caused by temperature fluctuations in large-aperture enclosed structure thermal imagers and greatly enhances their imaging quality stability in a wide range of high and low temperature environments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a compensation calibration system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a thermal imager and calibration mechanism according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the optical system, circuit layout, and temperature zone division of a thermal imager according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the scatter linear relationship between the predicted values ​​and the actual sampled values ​​of a mathematical model according to an embodiment of the present invention. Figure 5 This is a schematic diagram of the imaging effect of a thermal imager after continuous operation according to an embodiment of the present invention.

[0017] In the diagram: 1. Thermal imager; 2. High and low temperature chamber; 3. Infrared window; 4. Collimator; 5. Target; 6. Blackbody; 101. First temperature region; 102. Second temperature region; 103. Third temperature region; 104. Fourth temperature region; 105. Fifth temperature region; 106. Sixth temperature region. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0019] See Figure 1 This embodiment discloses a compensation calibration system for a large-aperture enclosed structure thermal imager 1, comprising: A distributed temperature sensor group includes temperature sensors deployed in different temperature zones within the thermal imager 1, used to detect the temperature of each temperature zone of the thermal imager 1. The calibration mechanism is used to set the operating ambient temperature of the thermal imager 1 and to provide the calibration observation target for the thermal imager 1. A focusing motor, located in the thermal imager 1, is used to control the position of the focusing lens inside the thermal imager 1 in order to set the focusing amount of the thermal imager 1. The control and data acquisition module is used to acquire the temperature of each temperature zone of the thermal imager 1, control the calibration mechanism to change the working environment temperature of the thermal imager 1, control the focusing motor to change the focusing amount of the thermal imager 1, control the focal length of the thermal imager 1, acquire the focusing amount, and acquire the image clarity of the thermal imager 1. The data processing module is used to construct a mathematical model representing the relationship between the temperature of each temperature region and the focusing amount when the thermal imager 1 is clear under different working ambient temperatures and different focal lengths, and to store the constructed mathematical model in the storage unit (non-volatile memory) of the thermal imager 1.

[0020] Specifically, the control and data acquisition module includes a calibration mechanism control interface, a thermal imager 1 control interface, a temperature reading interface, a thermal imager 1 image acquisition interface, an image gradient calculation submodule, and a data storage submodule. The thermal imager 1 control interface and the thermal imager 1 image acquisition interface are both connected to the thermal imager 1, and the temperature reading interface is connected to each temperature sensor.

[0021] Further, see Figure 2 The calibration mechanism includes a high and low temperature chamber 2, a collimator 3, a target 5, and a blackbody 6 arranged in sequence. The high and low temperature chamber 2 is equipped with an infrared window 3. During calibration, the thermal imager 1 is placed inside the high and low temperature chamber 2 and acquires the image of the target 5 in front of the blackbody 6 through the infrared window 3 and the collimator 3. The working environment temperature and heating and cooling rate are adjusted by remote control.

[0022] Specifically, the calibration mechanism control interface is connected to the high and low temperature chamber 2.

[0023] Furthermore, the division of temperature zones is determined based on the internal component composition, circuit layout, working environment, and upper-level system environment of the thermal imager 1 (determined through thermal analysis, thermal simulation, or regional temperature measurement analysis). At least one temperature sensor is set in each temperature zone (in this embodiment, one temperature sensor is set in one temperature zone).

[0024] Specifically, the distributed temperature sensor group also includes a temperature reading circuit.

[0025] See Figure 3 In this embodiment, the thermal imager 1 consists of 13 optical lenses. According to thermal analysis, the oblique incidence of external sunlight, the heating of the first and second circuit board groups behind the optical lenses, and the heating of the upper-level system circuit group at the top of the thermal imager 1 have a significant impact on the temperature of the optical lenses. In this embodiment, the outermost lens of the thermal imager 1 is divided into a temperature zone every 120° (i.e., the first temperature zone 101, the second temperature zone 102, and the third temperature zone 103), the middle of the optical system is divided into a temperature zone (i.e., the fourth temperature zone 104), and the rear of the optical system is divided into two temperature zones (i.e., the fifth temperature zone 105 and the sixth temperature zone 106), for a total of 6 temperature zones.

[0026] Furthermore, the mathematical model is a multiple linear regression model (parameters are estimated using the least squares method), and the linear relationship between temperature and focusing amount in each temperature region is expressed as follows:

[0027] In the above formula, U is the focusing amount. This indicates the temperature in different temperature zones. This represents the control coefficient for a certain temperature range. This is the focusing compensation amount.

[0028] Specifically, after obtaining the mathematical model of multiple linear regression, the accuracy of the model is determined by analyzing indicators such as model fit, root mean square error, mean absolute error, normality, and heteroscedasticity.

[0029] Furthermore, the multiple linear regression mathematical model includes two different sets of linear relationships, corresponding to the heating and cooling processes of the working environment temperature, respectively.

[0030] Furthermore, the multiple linear regression mathematical model includes multiple sets of different linear relationships, each corresponding to a different temperature range of the working environment.

[0031] Specifically, when there is a large difference in the fitting of the linear relationship between the heating and cooling processes during the calibration process, the relationship data can be divided into two processes: heating and cooling. The two processes can also be divided into multiple temperature ranges for fitting to obtain the optimal multiple linear regression mathematical model.

[0032] This embodiment also provides a compensation calibration method for a large-aperture enclosed structure thermal imager 1, including: S1. Align the thermal imager 1 with the calibrated observation target, set the working environment temperature to one extreme value (high temperature extreme value or low temperature extreme value) of the working temperature range, and keep it warm; S2. To change the ambient temperature at a certain rate of temperature change to the extreme value at the other end of the operating temperature range; S3. Set the thermal imager 1 to the specified focal length, and at that focal length, control the focusing motor to traverse the entire stroke of the focusing amount and acquire the image of the thermal imager 1 and the temperature of each temperature region. S4. Store the position of the focusing motor and the temperature of each temperature zone when the image is clearest at this focal length. S5. Repeat S3~S4 to iterate through all focal lengths of thermal imager 1; S6. Perform non-uniformity correction on the image of thermal imager 1; S7. Repeat steps S5 to S6 at the set time intervals; S8. When the heat preservation time exceeds the set duration, continue with the subsequent steps; S9. Repeat steps S2 to S8 to iterate through all preset temperature change rates; S10. Based on the temperature of each temperature region and the focusing amount when the thermal imager 1 is clear under different working ambient temperatures and different focal lengths, construct a mathematical model characterizing the relationship between the temperature of each temperature region and the focusing amount, and store the constructed mathematical model in the storage unit of the thermal imager 1.

[0033] Specifically, in the above method, the control and data acquisition module acquires images of the thermal imager 1 through the image acquisition interface of the thermal imager 1 and transmits them to the image gradient calculation submodule; the image gradient calculation submodule adjusts the thermal imager 1 to the specified focal length through the control interface of the thermal imager 1.

[0034] In this embodiment, the focal length of the thermal imager 1 is divided into 13 different levels, the time interval set in step S7 is 10 minutes, the duration of the heat preservation time set in step S8 is 1 hour, and all the preset temperature change rates in step S9 include 1℃ / s, 2℃ / s, 3℃ / s, and 5℃ / s.

[0035] Further, before executing step S10, step S901 is executed. Step S901 includes: placing the thermal imager 1 in the set simulated working environment and pointing the thermal imager 1 at a target at approximately infinity, repeating steps S3 to S7, and obtaining the temperature of each temperature area and the focusing amount when the thermal imager 1 image is clear under different working environment temperatures and different focal lengths.

[0036] Specifically, during the calibration process in a simulated working environment, thermal imager 1 is made to work continuously for 24 hours.

[0037] The relationship between temperature and focusing amount in each temperature region when the image is clear at a certain focal length, obtained by the method in this embodiment (total of m groups):

[0038] In the table, temperatures 1 to n represent temperature values ​​in different temperature zones.

[0039] Specifically, the partial data on the relationship between the temperature of the six temperature zones obtained in this embodiment and the focusing amount (encoder code value) when the image is clear is shown in the following table:

[0040] The parameters of the calculated multiple linear regression mathematical model are shown in the table below:

[0041]

[0042] After verification, the mathematical model's goodness of fit, root mean square error, mean absolute error, normality, and heteroscedasticity meet the requirements for use with thermal imager 1. The scatter plot linear relationship between the mathematical model's predicted values ​​and the actual sampled values ​​is shown in [reference needed]. Figure 4 .

[0043] This embodiment also provides a large-aperture closed-structure thermal imager 1, which is calibrated using the compensation calibration method described above.

[0044] This embodiment also provides a compensation method for a large-aperture enclosed structure thermal imager 1. The temperature of each temperature region of the thermal imager 1 is obtained by temperature sensors arranged in different temperature regions inside the thermal imager 1. Based on the temperature of each temperature region and the current focal length of the thermal imager 1, a target focusing amount is obtained by combining the constructed mathematical model. The focusing motor is controlled to focus according to the target focusing amount. The mathematical model is obtained by the compensation calibration method described above.

[0045] Specifically, the thermal imager 1 is equipped with a storage unit and a focusing mechanism; the focusing mechanism includes a temperature reading module, a calculation module, and a drive module. When the thermal imager 1 is working, the temperature reading module acquires the temperature values ​​of each temperature sensor in real time and transmits them to the calculation module. The calculation module reads the mathematical model from the storage unit and calculates the target focusing amount by combining it with the temperature values ​​of each temperature region. The drive module drives the focusing motor to perform focusing according to the target focusing amount, thereby achieving focusing compensation for temperature changes.

[0046] In this embodiment, the images obtained by thermal imager 1 working continuously for two hours according to the above compensation method are shown below. Figure 5 As can be seen, thermal imager 1 can still achieve clear imaging after continuous operation.

[0047] The present invention has at least the following beneficial effects: The advantages of the invention compared to the prior art include: 1. This invention solves the problem that the refractive index of infrared optical materials, the curvature and thickness of optical elements, and the spacing of optical components in a large-aperture / closed-structure thermal imager 1 change with the ambient temperature, which leads to a decrease in the imaging quality of the lens of the thermal imager 1 and causes the thermal imager 1 to blur. 2. By adopting a temperature zone division method, the problem that a single temperature sensor cannot characterize the temperature distribution of the thermal imager 1 lens is solved. It also addresses the issues of a large number of temperature sensors, installation difficulties, and high costs associated with measuring the temperature of all optical materials and support structures of the thermal imager 1 lens. 3. The control and data acquisition module automatically controls and acquires the parameters of the high and low temperature chamber 2 and the thermal imager 1, providing data support for the establishment of mathematical models, reducing the difficulty of operation and labor costs, and facilitating the mass production of the thermal imager 1.

[0048] 4. The control and data acquisition module can also be used to collect data from the thermal imager 1 during actual operation, accumulate and improve relevant data, and optimize the mathematical model through the data processing module to improve the focusing compensation effect.

[0049] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0050] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A compensation calibration system for a large-aperture enclosed structure thermal imager, characterized in that, include: A distributed temperature sensor array, comprising temperature sensors deployed in different temperature zones within the thermal imager, is used to detect the temperature of each temperature zone within the thermal imager. The calibration mechanism is used to set the operating temperature of the thermal imager and to provide the calibration observation target for the thermal imager. The focusing motor, located in the thermal imager, is used to control the position of the focusing lens inside the thermal imager in order to set the focusing amount of the thermal imager. The control and data acquisition module is used to acquire the temperature of each temperature zone of the thermal imager, control the calibration mechanism to change the working environment temperature of the thermal imager, control the focusing motor to change the focusing amount of the thermal imager, control the focal length of the thermal imager, acquire the focusing amount, and acquire the image clarity of the thermal imager. The data processing module is used to construct a mathematical model representing the relationship between the temperature and the focus of each temperature region when the thermal imager is clear under different working ambient temperatures and focal lengths, and to store the constructed mathematical model in the thermal imager's storage unit.

2. The compensation calibration system for a large-aperture enclosed structure thermal imager according to claim 1, characterized in that, The calibration mechanism includes a high-low temperature chamber, a collimator, a target, and a blackbody arranged in sequence. The high-low temperature chamber is equipped with an infrared window. During calibration, a thermal imager is placed inside the high-low temperature chamber and acquires images of the target in front of the blackbody through the infrared window and the collimator. The ambient temperature and heating / cooling rate are adjusted remotely.

3. The compensation calibration system for a large-aperture enclosed structure thermal imager according to claim 1, characterized in that, The division of temperature zones is determined based on the internal components of the thermal imager, circuit layout, working environment, and upper-level system environment. At least one temperature sensor is installed in each temperature zone.

4. The compensation calibration system for a large-aperture enclosed structure thermal imager according to claim 1, characterized in that, The mathematical model is a multiple linear regression model, and the linear relationship between temperature and focusing amount in each temperature region is expressed as follows: In the above formula, U is the focusing amount. This indicates the temperature in different temperature zones. This represents the control coefficient for a certain temperature range. This is the focusing compensation amount.

5. The compensation calibration system for a large-aperture enclosed structure thermal imager according to claim 4, characterized in that, The multiple linear regression mathematical model includes two different sets of linear relationships, corresponding to the heating and cooling processes of the working environment temperature.

6. The compensation calibration system for a large-aperture enclosed structure thermal imager according to claim 4, characterized in that, The multiple linear regression mathematical model includes multiple sets of different linear relationships, each corresponding to a different temperature range of the working environment.

7. A compensation calibration method for a large-aperture enclosed structure thermal imager, characterized in that, include: S1. Align the thermal imager with the target to be observed, set the ambient temperature to one extreme value of the operating temperature range and keep it warm. S2. To change the ambient temperature at a certain rate of temperature change to the extreme value at the other end of the operating temperature range; S3. Set the thermal imager to the specified focal length, and at that focal length, control the focusing motor to traverse the entire stroke of the focusing amount and acquire the image of the thermal imager and the temperature of each temperature region. S4. Store the position of the focusing motor and the temperature of each temperature zone when the image is clearest at this focal length. S5. Repeat S3~S4 to iterate through all focal lengths of the thermal imager; S6. Perform non-uniformity correction on the thermal imager image; S7. Repeat steps S5 to S6 at the set time intervals; S8. When the heat preservation time exceeds the set duration, continue with the subsequent steps; S9. Repeat steps S2 to S8 to iterate through all preset temperature change rates; S10. Based on the temperature of each temperature region and the focusing amount when the thermal imager image is clear under different working ambient temperatures and different focal lengths, construct a mathematical model characterizing the relationship between the temperature of each temperature region and the focusing amount, and store the constructed mathematical model in the storage unit of the thermal imager.

8. The compensation calibration method for a large-aperture enclosed structure thermal imager according to claim 1, characterized in that, Before executing step S10, step S901 is executed. Step S901 includes: placing the thermal imager in the set simulated working environment and pointing the thermal imager at a target at approximately infinity. Steps S3 to S7 are repeated to obtain the temperature of each temperature area and the amount of focus when the thermal imager image is clear under different working environment temperatures and different focal lengths.

9. A large-aperture enclosed structure thermal imager, characterized in that, Calibration is performed using the compensation calibration method described in claim 7.

10. A compensation method for a large-aperture enclosed structure thermal imager, characterized in that, Temperatures in different temperature zones of the thermal imager are obtained by temperature sensors deployed within the thermal imager. Based on the temperatures of each temperature zone and the current focal length of the thermal imager, a target focusing amount is obtained by combining the constructed mathematical model. The focusing motor is then controlled to focus according to the target focusing amount. The mathematical model is obtained by the compensation calibration method described in claim 7.

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