RU2623417C2 - Optical system of thermal imaging device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: optical system includes a lens, a radiation receiver with a cooled diaphragm, an information processing unit, a temperature sensor, a positioning unit and an information processing unit. The lens includes two components. The first component has a positive optical force and consists of a convex-concave positive lens and a negative convex-concave lens. The second component has a negative optical power and consists of a movable, under the control of the positioning unit, a negative convex-concave lens and a positive convex-concave lens. The distances between the first and second components _d1 and between the lenses of the second component d₂ satisfies the following conditions: 0.2f'<d₁<0.4f'; 0.1f'<d₂<0.2f', where f' is the focal length of the system.

EFFECT: increasing the angular resolution of the device, providing compensation for the thermal defocusing of the image, and correcting the inhomogeneity of the parameters of the photosensitive elements of the radiation receiver.

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Description

The invention relates to infrared optical systems and can be used to create thermal imaging devices with cooled matrix radiation detectors.

A known optical system for thermal imaging devices (see patent RU 2449328 A1, IPC ⁷ G02B 13/14, 23/12, publ. 04/27/2012), containing the input and projection lenses between which an intermediate image is formed, and a radiation matrix receiver with a cooled diaphragm. The system has the following characteristics: a spectral range of 3 ... 5 microns, a focal length of 60 mm, a length from the first lens to the image plane of 150 mm. The system contains a defocusing element mounted with the possibility of input-output it into the optical path. With the help of this element, the correction of the heterogeneity of the parameters of the photosensitive elements of the radiation receiver (calibration) is necessary for the operation of infrared systems.

The disadvantages are the small focal length and the large length of the optical system.

An optical imaging device with IR calibration is also known (see patent FR 2928462 A1, IPC ⁷ G02B 13/14, 15/16, H04N 5/235 publ. September 11, 2009), comprising an input lens, a projection lens, a receiver radiation with a cooled diaphragm, information processing unit, positioning unit and calibration unit. The focal length of the system is variable, with the maximum focal length f ' _max = 135 mm, the minimum - f' _min = 25 mm. The device operates in the spectral range of 3 ... 5 μm, the matrix format of the radiation receiver 384 × 288 elements in increments of 15 μm. The length of the optical system of the device from the first lens to the image plane is at least 170 mm. The described device provides calibration, which is carried out by moving two lenses that are installed in a position that provides complete defocusing of the image from an infinitely distant object.

The disadvantages of the described device are the large length of the optical system, a small linear field of view, and the calibration as a result of the movement of two optical elements.

Closest to the technical nature of the claimed system, selected as a prototype, is an optical system for an infrared camera (see patent US 5909307 A, IPC ⁷ G02B 13/14, publ. 06/01/1999), containing a lens and a radiation receiver with cooled diaphragm. The lens operates in the spectral range of 3 ... 5 μm and consists of two components, with the first component made in the form of a negative convex-concave lens, the second component is generally positive and contains the first positive convex-concave, the second negative convex-concave and the third biconvex lens ; near the first lens of the second component is the aperture diaphragm. The focal length of the lens f '= 22.1 mm, the length L from the first surface of the first component to the image plane is 80 mm. For the optical power of the lens ϕ, the optical forces of the first ϕ ₁ and second ϕ ₂ components, the distance between them d and the length of the second component d ₂ the following relations are fulfilled:

1) 0.5ϕ <-ϕ ₁ <0.7ϕ;

2) 0.55ϕ <ϕ ₂ <0.87ϕ;

3) 1.55 / ϕ <d <1.98 / ϕ;

4) d ₂ <2.1 / ϕ.

The disadvantages of the described system include the following. When working with a standard radiation detector having a matrix format of 640 × 512 with an element pitch of 15 μm, the elementary field of view of this optical system is γ = 15 / f '= 0.68 mrad, which does not provide sufficient angular resolution of the thermal imaging device. In the described system, the compensation of thermal defocusing of the image is carried out, presumably, by moving the entire lens, since it has small overall dimensions, and when the lens diameters and length increase (in the case of increasing the focal length of the system) it becomes unacceptable. In addition, in this system there is no possibility of correcting the heterogeneity of the parameters of the photosensitive elements of the radiation receiver.

The problem to which the invention is directed is to increase the angular resolution of a thermal imaging device while providing compensation for thermal defocusing of the image and correcting the heterogeneity of the parameters of the photosensitive elements of the radiation receiver by moving one of the elements of the system.

The problem is solved due to the fact that in the optical system of a thermal imaging device consisting of a lens containing a first component successively arranged along the optical axis, the first lens of which is made convex-concave, and the second component, made in the form of two convex-concave lenses, and a receiver radiation with a cooled diaphragm, the output of which is connected to the input of the information processing unit, a temperature sensor and a positioning unit are introduced, connected to the input and output of the information processing unit, respectively Actually, in the first component of the lens, the first lens is positive and an additional negative convex-concave lens is introduced, while the optical power of the first component is generally positive, in the second component, the first lens is negative and mounted to move along the optical axis under the control of the positioning unit, the second positive lens is formed, the optical power of the second component generally negative, and the distance between the first and second components ₁ and d between the lenses a second component d ₂ satisfy the following conditions:

0.2f '<d ₁ <0.4f'; 0,1f '<d ₂ <0,2f', where f 'is the focal length of the system.

In FIG. 1 shows an optical diagram of a thermal imaging device.

In FIG. Figure 2 shows the ray path in the system with the arrangement of elements corresponding to the operating mode (a) and calibration mode (b).

In FIG. Figure 3 presents graphs of the function of energy concentration (FFE) of the system for temperatures of 20, 60, and minus 50 ° С.

The optical system of a thermal imaging device consists of a lens containing the first component I successively arranged along the optical axis, including the first positive 1 and second negative 2 convex-concave lenses, and the second component II, including the movable first negative 3 and the second positive 4 convex-concave lenses, the distances between the first and second components d ₁ and between the lenses of the second component d ₂ satisfy the following conditions: 0.2f '<d ₁ <0.4f'; 0,1f '<d ₂ <0,2f' (f 'is the focal length of the system), radiation receiver 5 with a cooled diaphragm 6, the output of which is connected to the input of the information processing unit 7, the temperature sensor 8 connected to the input of the information processing unit 7 , and a positioning unit 9, which controls the first lens 3 of the second component II and is connected to the output of the information processing unit 7. Additionally, an information display device (monitor) 10 is shown.

The information processing unit 7 can be made on the basis of microprocessors such as a digital signal processor TMS320 DM642 or the like and memory chips that provide communications with the positioning unit 9 and the temperature sensor 8, electronically processes the signal and displays it on the monitor screen 10. The positioning unit 9 can be made in the form of a stepper motor moving the lens 3 along the optical axis.

Table 1 shows the technical specifications of the system.

The design parameters of a specific example of the lens performance are shown in table 2.

Table 3 shows the values of the movements of the lens 3 depending on the ambient temperature.

As follows from table 1, the elementary field of view of this optical system is γ = 15 / f '= 0.13 mrad, which is 5 times less than in the prototype, while its length is slightly increased. The design, in which the lens 3 is mounted with the ability to move along the optical axis, allows compensation for the defocusing of the image when the temperature changes (see Fig. 3) and partial defocusing of the image to perform correction of the heterogeneity of the sensitive elements of the radiation receiver (see Fig. 2b).

The optical system of a thermal imaging device operates as follows. Infrared radiation from an infinitely distant object enters the lens, where it passes through the lenses 1-4 of the first I and second II components and is focused in the plane of the sensitive elements of the radiation receiver 5, the output signals from which are sent to the information processing unit 7, and the exit pupil of the system is combined with cooled diaphragm 6.

In the operating mode, the temperature sensor reads into the information processing unit 7, the signal from which enters the positioning unit 9. In accordance with this signal, the lens 3 is moved along the optical axis to a predetermined position (see table 2) and the image is defocused when the temperature changes .

In calibration mode, the signal from the information processing unit 7 enters the positioning unit 9, and the lens 3 moves along the optical axis to the position at which the system is partially defocused. Then, the output signals from the radiation receiver 5 enter the information processing unit 7, where corrective corrections are calculated for each element of the radiation receiver 5, which are taken into account when forming the image in the operating mode, after which the corrected image is displayed on the monitor screen 10.

Thus, the implementation of the optical system of the thermal imaging device in accordance with the proposed technical solution allows to increase its angular resolution while providing compensation for thermal defocusing of the image and correcting the inhomogeneity of the parameters of the photosensitive elements of the radiation receiver by moving one of the elements of the system, which improves the operational characteristics of the device as a whole.

Claims (2)

The optical system of a thermal imaging device, consisting of a lens containing a first component sequentially arranged along the optical axis, the first lens of which is convex-concave, and the second component, made in the form of two convex-concave lenses, and a radiation receiver with a cooled diaphragm, the output of which is connected to input of the information processing unit, characterized in that a temperature sensor and a positioning unit are introduced, connected to the input and output of the information processing unit, respectively, in the first component From the lens, the first lens is positive and a negative convex-concave lens is introduced, while the optical power of the first component is generally positive, in the second component the first lens is negative and mounted to move along the optical axis under the control of the positioning unit, the second lens is made positive, wherein the optical power of the second component generally negative, and the distance between the first and second components d between the lenses ₁ and d ₂ of the second component udo satisfies the following conditions: 0.2f '<d ₁ <0.4f'; 0,1f '<d ₂ <0,2f', where f 'is the focal length of the system.

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