Servo-mechanism-free defocusing amount automatic compensation control system for aerial camera

Abstract

The invention relates to a servo-mechanism-free defocusing amount automatic compensation control system for an aerial camera, and belongs to the technical field of photoelectric instruments. According to different influences of the height, temperature and air pressure of a camera on an imaging focal plane, a temperature balance point is controlled through data calibration and temperature adjustment, the temperature balance point is slightly higher than a temperature point changing along with the height, and therefore automatic compensation of the comprehensive defocusing amount caused by the height, temperature and air pressure factors is completed. The system does not need any servo mechanism, only needs software to control the working temperature and keep the temperature balance point, can realize automatic focusing of the imaging focal plane along with the application environment, can adapt to different environmental conditions and different flight heights, and is good in thermodynamic property.

Description

Technical Field

[0001] The invention belongs to the field of technology, and in particular relates to a servo-free mechanism defocus automatic compensation control system for an aerial camera. Background Art

[0002] Aerial cameras are optical imaging devices carried on aircraft to photograph ground targets. They have the advantages of large field of view and high resolution, and are an important means of military reconnaissance, resource exploration, and terrain mapping. When aerial cameras are taking photos in the air, the actual aviation environment in flight is relatively complex. The optical system may cause the imaging sensor to deviate from the image plane due to the photographing distance, ambient temperature, and atmospheric pressure, resulting in defocus, which seriously affects the image quality. In order to achieve high-resolution imaging, aerial cameras must compensate for the defocus of the camera to ensure the clarity and resolution of the image.

[0003] Adjusting the focal plane is to ensure that the image is always formed on the photosensitive surface of the receiving medium. At present, the methods commonly used to adjust the focal plane of aerial cameras are mainly divided into the following methods: program control method, photoelectric autocollimation method, method combining image processing and autocollimation, ground calibration method and focusing method based on image processing. The program control method is relatively easy to implement, but the accuracy of its focal plane detection is not high, and the usage scenario is single, and it has only been applied in some early aerial cameras; the focusing-related mechanism of the photoelectric autocollimation method is very complex, and it takes a long time to complete the focus, and the real-time performance is poor; the focusing speed of the method combining image processing and autocollimation has been improved to a certain extent, but it still requires a complex focusing mechanism and most of it is currently in the experimental stage; the ground calibration method is relatively easy to operate, but because it needs to be simulated in the laboratory in advance, the environmental factors in the actual flight process will affect its accuracy, and the focusing error is large; in recent years, the focusing method based on image processing has gradually become one of the mainstream focusing methods due to its strong real-time performance, high flexibility and no need for additional focusing mechanism. However, most of the current focus detection methods based on image processing require taking multiple repeated photos of the same target and then combining them with corresponding evaluation functions to achieve focus plane detection. Aerial cameras take photos of ground scenes during flight, and the images are in a state of continuous change, which increases the difficulty of focus detection. Therefore, it is impossible to use traditional clarity detection methods to complete the focus plane detection of aerial cameras. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] The technical problem to be solved by the present invention is to provide a servo-free defocus automatic compensation control system for an aerial camera to solve the problem that the servo system focusing system of the existing short focal length aerial camera is complex and has limited usability.

[0006] (II) Technical solution

[0007] In order to solve the above technical problems, the present invention provides a servo-free mechanism defocus automatic compensation control system for an aerial camera. The automatic compensation control system performs temperature adjustment and controls the temperature balance point through data calibration according to the different effects of the camera's altitude, temperature and air pressure on the imaging focal plane, so that the temperature balance point is slightly higher than the temperature point that changes with altitude, thereby completing the automatic compensation of the comprehensive defocus amount caused by altitude, temperature and air pressure factors.

[0008] Wherein, the automatic compensation control system includes: a temperature sensor, a fan, a heater, a main control controller, and an altitude measurement component;

[0009] The altitude measurement component obtains the working altitude of the aerial camera, the corresponding atmospheric pressure and the ambient temperature, finds the defocus amount caused by the working altitude, the ambient temperature and the atmospheric pressure according to the calibration data, and calculates the temperature of the balance point that needs to be controlled;

[0010] If it is higher than the ambient temperature, the main control system starts the heater and heats it to the equilibrium point temperature;

[0011] If it is lower than the ambient temperature, the main control system starts the fan to cool down to the equilibrium point temperature, thereby completing the automatic compensation of the defocus amount of the objective lens assembly.

[0012] Wherein, the heater and the fan are respectively arranged on the front and rear sides of the lens in the objective lens assembly.

[0013] (III) Beneficial effects

[0014] Compared with the prior art, the present invention has the following beneficial effects: the system does not require any servo mechanism, only needs software to control the working temperature and maintain the temperature balance point, so that the imaging focal plane can be automatically focused according to the application environment, can adapt to different environmental conditions and different flight altitudes, and has good thermodynamic performance. The optical system of this system eliminates the complicated camera focusing mechanism, greatly simplifies the camera structure, and greatly improves the reliability of the camera. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a system structure diagram of the present invention;

[0016] Figure 2 This is a flow chart of the thermal control of the system of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, content, and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings and examples.

[0018] The present embodiment provides a servo-free mechanism for an aerial camera to automatically compensate for defocus. The automatic compensation control system performs temperature adjustment and controls the temperature balance point through data calibration according to the different effects of the camera's altitude, temperature and air pressure on the imaging focal plane, so that the temperature balance point is slightly higher than the temperature point that changes with altitude, thereby completing automatic compensation for the comprehensive defocus caused by altitude, temperature and air pressure factors.

[0019] Wherein, the automatic compensation control system includes: a temperature sensor, a fan, a heater, a main control controller, and an altitude measurement component;

[0020] The altitude measurement component obtains the working altitude of the aerial camera, the corresponding atmospheric pressure and the ambient temperature, finds the defocus amount caused by the working altitude, the ambient temperature and the atmospheric pressure according to the calibration data, and calculates the temperature of the balance point that needs to be controlled;

[0021] If it is higher than the ambient temperature, the main control system starts the heater and heats it to the equilibrium point temperature;

[0022] If it is lower than the ambient temperature, the main control system starts the fan to cool down to the equilibrium point temperature, thereby completing the automatic compensation of the defocus amount of the objective lens assembly.

[0023] Wherein, the heater and the fan are respectively arranged on the front and rear sides of the lens in the objective lens assembly.

[0024] The optical system uses two detectors for splicing imaging. The number of detector pixels is 30K×5K, the pixel size is 4.6μm, the design focal length is 126mm, the pixel resolution is ≤0.19m (flight altitude 5000m), and the field of view is ≥35°; the lens adopts a coaxial transmission system, the low-temperature slope of the imaging lens structure is about 2μm / °, the focal length is designed to be 126mm, the relative aperture is 6, and the semi-focal depth of the optical system is 0.035mm. This optical system, according to the different effects of altitude, temperature and air pressure on the imaging focal plane, through data calibration, temperature adjustment, and the use of heaters and fans to control the temperature balance point, so that the balance point is slightly higher than the temperature point that changes with altitude, thereby realizing automatic compensation of the comprehensive defocus amount caused by altitude, temperature and air pressure factors.

[0025] According to the ideal imaging model of the optical system of the aerial camera, for a point on the object plane, after passing through the optical system, a clear image is presented on the image plane, and this ideal optical system should conform to the Gaussian imaging formula. If the position of the imaging detector is at the same position as the ideal image plane, the image received by the detector is a point; on the contrary, if the detector is not at the same position as the ideal image plane, a diffuse spot is presented on the detector. The size of this diffuse spot depends on the distance between the detector and the ideal image plane. When the distance between the detector and the image plane is closer, the size of the diffuse spot is smaller and the image is clearer; the farther the distance between the detector and the focal plane, the larger the size of the diffuse spot, the more blurred the image is, and it is a defocused state, and the defocus amount needs to be compensated. The defocus degree of the optical system can be characterized by the distance between the current position of the detector and the standard focal plane position. When the detector and the focal plane are at the same position, the optical system is in a focused state. When the defocus compensation work of the aerial camera is completed, if the distance between the image detector and the image plane position is less than the semi-focal depth of the optical imaging system at this time, a clear image can be obtained.

[0026] When a camera is taking aerial photos at high altitude, the defocus of the optoelectronic system is mainly caused by altitude, temperature and air pressure. The relationship between the focal plane and air pressure is: as the aircraft's flight altitude increases, the atmospheric pressure becomes lower and lower. For every 9 meters increase in altitude, the atmospheric pressure will drop by 100Pa. The decrease in atmospheric pressure will cause the refractive index of the air to change, which in turn affects the focal plane position of the camera. The lower the atmospheric pressure, the smaller the refractive index of the air, causing the focal plane of the aerial camera to be biased toward the objective lens. After calculating the atmospheric refractive index for the atmospheric pressure corresponding to different flight altitudes, the optical lens material parameters and design parameters are substituted using optical software to obtain the defocus amount of the optical lens caused by the change in atmospheric pressure, as shown in Table 1.

[0027] It can be known from Gauss's imaging theorem that when the focal length of the optical system remains unchanged, the change of the imaging distance is negatively correlated with the change of the image distance of the optical system. Therefore, the defocus amount of the aerial camera caused by the change of the imaging distance must be compensated accordingly, otherwise the optical system cannot complete clear imaging. Through the analysis and calculation of the optical lens system of the present invention, the optical lens distance defocus data is obtained, as shown in Table 2.

[0028] The relationship between the focal plane and temperature is: the higher the altitude, the lower the temperature. When the altitude is below 15km, the temperature decreases by 0.6℃ for every 100m increase in altitude. Therefore, the temperature of the aerial camera during actual operation is much lower than the temperature on the ground. The relationship between the imaging temperature and the clear focal plane is that when the temperature decreases, the focal plane moves backward; when the temperature increases, the focal plane moves forward. Taking the working temperature of the optical lens processing and adjustment as the 20℃ reference temperature, according to the thermal design analysis, the temperature level of the lens is 20°±4°. The thermal analysis and optical calculation of the optical lens and the barrel material of the optical lens are carried out to obtain the optical lens temperature defocus data (Table 3). When the working temperature of the camera optical lens deviates from the reference temperature by ±4°, the optical lens temperature defocus is not greater than 0.005mm, which meets the condition of being less than the half-focus depth of focus (0.027m), and the imaging quality can be guaranteed. Therefore, thermal control measures must be taken for the optical lens to ensure the temperature level of 20℃±4℃.

[0029] When aerial cameras take photos at high altitudes, the comprehensive defocus of the optical lens is affected by air pressure, temperature and altitude. The thermal control system can be used to adjust the thermal control balance point of the optical lens to compensate for the defocus, so that the defocus is controlled within half of the focal depth, without affecting the image quality. The defocus and compensation temperature of the optical lens for high-altitude photography are shown in Table 4. The low-temperature slope of the imaging lens structure is about 2μm / °. The design method of temperature and air pressure balance is adopted. The balance point is slightly higher than the temperature point that changes with altitude, and the balance can be achieved by heating. For example, at an altitude of 5km, the ambient temperature is about -10°, and the atmospheric pressure is about 540.5mB. At this time, the defocus caused by the lens structure temperature is 0.060mm, the defocus caused by the air pressure is -0.023mm, and the defocus caused by the altitude is -0.0032mm, with a difference of 0.0338mm. According to the low-temperature slope of the imaging chip structure (2μm / °), the temperature needs to be increased to 16.9°, and the temperature balance point is set to 6.9±4 degrees to compensate for the defocus of the camera's optical lens. The thermal control system collects ambient temperature and aerial photography altitude information, calculates the optical system defocus and equilibrium temperature value through a curve fitting algorithm, and completes automatic temperature control by controlling the heater and fan, compensating for the defocus caused by the aerial camera's high-altitude photography, so that the optical lens defocus is less than the half-focal depth, thereby obtaining a clear image. The thermal control flow chart is as follows: Figure 2 shown.

[0030] Table 1 shows the defocus data of the optical lens caused by the change of atmospheric pressure;

[0031] Table 2 shows the defocus data of the optical lens due to distance changes;

[0032] Table 3 shows the defocus data of the optical lens caused by temperature changes;

[0033] Table 4 shows the equilibrium temperature data of the optical lens defocus compensation control.

[0034] Table 1

[0035] Altitude (km) Atmospheric pressure (mB) Atmospheric refractive index Defocus(mm) 0 1013.0 1.000276 0 1 898.8 1.000251 -0.005 2 795.0 1.000227 -0.01 3 701.2 1.000205 -0.015 4 616.6 1.000185 -0.019 5 540.5 1.000166 -0.023 6 472.2 1.000149 -0.027 7 411.1 1.000133 -0.03 8 356.5 1.000119 -0.033 9 308.0 1.000105 -0.036 10 265.0 1.000093 -0.038 ∞ 0 1 0

[0036] Table 2

[0037] (km) Rear working distance change (mm) Defocus(mm) 1 69.7971 0.0070 2 69.7892 0.0064 3 69.7866 0.0053 4 69.7853 0.0040 5 69.7845 0.0032 6 69.7839 0.0026 7 69.7836 0.0023 8 69.7833 0.0020 9 69.7831 0.0018 10 69.7829 0.0016 ∞ 69.7813 0

[0038] Table 3

[0039]

[0040]

[0041] Table 4

[0042]

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A servo-free defocus automatic compensation control system for an aerial camera, characterized in that: The automatic compensation control system performs temperature adjustment and controls the temperature balance point through data calibration according to the different effects of the camera's altitude, temperature and air pressure on the imaging focal plane, so that the temperature balance point is slightly higher than the temperature point that changes with altitude, thereby completing automatic compensation for the comprehensive defocus amount caused by altitude, temperature and air pressure factors.

2. The servo-less defocus automatic compensation control system for an aerial camera according to claim 1, characterized in that: The automatic compensation control system includes: a temperature sensor, a fan, a heater, a main control controller, and an altitude measurement component; The altitude measurement component obtains the working altitude of the aerial camera, the corresponding atmospheric pressure and the ambient temperature, finds the defocus amount caused by the working altitude, the ambient temperature and the atmospheric pressure according to the calibration data, and calculates the temperature of the balance point that needs to be controlled; If it is higher than the ambient temperature, the main control system starts the heater and heats it to the equilibrium point temperature; If it is lower than the ambient temperature, the main control system starts the fan to cool down to the equilibrium point temperature, thereby completing the automatic compensation of the defocus amount of the objective lens assembly.

3. The servo-less defocus amount automatic compensation control system for an aerial camera according to claim 1, characterized in that: The heater and the fan are respectively arranged on the front and rear sides of the lens in the objective lens assembly.

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