Double-Fresnel-lens circular scanning device of manned and airborne dual-band water depth measurement laser radar

Abstract

The invention discloses a double-Fresnel-lens circular scanning device of a manned and airborne dual-band water depth measurement laser radar, according to the principle that laser can deflect in different directions after penetrating through lenses with different thicknesses, double Fresnel lenses are mounted inside and outside a hollow motor, and relative movement of the Fresnel lenses is realized through rotation of the motor, so that the laser can deflect in different directions after passing through the lenses with different thicknesses. A laser beam is deflected into a perfect circle trajectory, the laser beam deflection device is applied to a manned airborne dual-band water depth measurement laser radar, the size and weight of the manned airborne dual-band water depth measurement laser radar are greatly reduced, and the calibration difficulty of the laser radar is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of laser detection, and in particular to a dual-band water depth measurement laser radar scanning method. Background Art

[0002] At present, water depth measurement laser radars mostly use double wedges or refractive wedges to achieve laser scanning. However, double wedges are suitable for small laser radars, such as land laser radars, but cannot be used for large manned aircraft laser radars due to their large size and heavy weight. Refractive wedges are prone to wedge angle errors during installation, causing the scanning trajectory to become oval, which brings great difficulties to laser radar calibration and error correction.

[0003] For example, in 2016, Zhu Jingguo et al. published a paper titled "Design and Implementation of Airborne Laser Radar Dual Wedge Scanning System" in the journal Infrared and Laser Engineering. They designed a pair of wedges with a wedge angle of 16° and a diameter of 320 mm. Each time the wedge mirror rotates 3.6°, the scanning pointing error is less than 50μrad, and the scanning field of view is 32.03°. Although the pair of wedges can be used, they are large in size and heavy in weight.

[0004] Another example is a variable laser radar scanning angle device (patent number ZL201922200749.1), which adds optical wedges with different wedge angles to the scanning device, so that the radar has a variety of scanning ranges and can better adapt to the different altitudes and terrains of the aircraft. This variable angle double optical wedge is larger in size and heavier in weight.

[0005] In 2021, Zhou Guoqing published a paper titled "Design of an Airborne Single-Frequency Water Depth Measurement LiDAR Optomechanical System" in the journal Infrared and Laser Engineering, using a refractive optical wedge to achieve circular scanning. The refractive optical wedge can theoretically emit a circular laser beam, but the tolerance in the actual installation process will cause the wedge angle to change, resulting in an oval scanning trajectory.

[0006] In view of the problems of large size, heavy weight and track deformation in the scanning method adopted by the above-mentioned dual-frequency water depth measurement laser radar system, the present invention discloses a double Fresnel mirror circular scanning device for manned aircraft-borne dual-band water depth measurement laser radar. When the laser beam irradiates the center of the Fresnel mirror, the two Fresnel mirrors move relative to each other, the concave angle of the mirror changes continuously, and the laser beam deflected in the center is scanned in a positive circle, and the device has a small size and light weight. Summary of the invention

[0007] The invention discloses a double-Fresnel mirror circular scanning device of a manned aircraft-borne dual-band water depth measurement laser radar.

[0008] The present invention is implemented by the following technical solutions:

[0009] The dual-Fresnel mirror circular scanning device of the manned dual-band water depth measurement laser radar consists of a hollow motor and two Fresnel mirrors. A Fresnel mirror is installed outside the hollow motor and a Fresnel mirror is installed inside. When the motor rotates, the Fresnel mirror will also rotate, forming a continuously changing angle, ensuring that the angle between the laser emitted from the middle and the vertical line is 10°, and the trajectory on the water surface is a perfect circle. The angles of the Fresnel grooves are different, but they all focus the light to form a central focus, which is the focus of the lens. Each groove can be regarded as an independent small lens, adjusting the light into parallel light or focusing.

[0010] S1: Establish the circular scanning principle. Establish a plane rectangular coordinate system xOy on the imaging plane at a distance of z0 from the rotating double Fresnel axis. The projection point of the rotating Fresnel mirror axis on the plane is O(x0, y0). Assume that any point on the scanning trajectory is P(x p ,y p ). Set the initial positions of the two prisms and control their rotation direction and rotation speed to be the same (i.e. no relative rotation, ω1=ω2=ω). Then the scanning trajectory of the rotating dual prism system on the plane xOy is a circle with O as the center and r as the radius. When the laser radar and the target object have axial relative motion, the radius r will change accordingly. P(x p ,y p ) The moving trajectory of point will also change accordingly, and the scanning area on plane xOy will be in the shape of a ring.

[0011] S2: Construct constraint conditions. When the top angle of the Fresnel mirror is small, the azimuth angle and the elevation angle of the outgoing light beam have the following relationship, see formula (1).

[0012] (1)

[0013] Where θ is the azimuth angle of the outgoing beam, φ is the pitch angle of the outgoing beam, α is the top angle of the Fresnel mirror, n is the refraction of the prism, and θ1 and θ2 are the rotation angles of the two Fresnel mirrors at time t. For θ1 and θ2, the above settings follow formula (2).

[0014] (2)

[0015] In the formula, the azimuth angle θ changes uniformly with time t, and the pitch angle φ is a constant, so the scanning trajectory is a uniform circular scan.

[0016] The device consists of a hollow motor, two Fresnel mirrors, screws, etc.

[0017] The hollow diameter of the hollow motor is 200mm, the repeatability accuracy is ±5 arc seconds, the matching motor is a 2.5KW servo motor, the rated speed is 3000rpm, the load is approximately 1500Kg, the parallelism is ≤1 thread, the interior is coated with a black light-absorbing coating, there are 6 threaded holes with a diameter of 5mm, and the absolute rotation angle is fed back in real time through the encoder.

[0018] Two Fresnel mirrors, with a diameter of 200mm and a focal length of 140mm, are made of K9 glass and are resistant to high temperatures. They are fixed to the inside and outside of the hollow motor with glass glue.

[0019] Screw, head thickness 3.2mm, head diameter 8.5mm, thread diameter 5mm, screw length 6mm, surface coated with black light-absorbing coating.

[0020] Compared with the prior art, the present invention has the following advantages: (1) The use of double Fresnel mirrors greatly reduces the volume and weight of the scanning device; (2) It consists of a hollow motor and two Fresnel mirrors, one Fresnel mirror is installed outside the hollow motor, and the other Fresnel mirror is installed inside. When the motor rotates, the Fresnel mirror will also rotate to form a continuously changing angle, ensuring that the angle between the laser emitted from the middle and the vertical line is 10°, the field of view angle is 20°, and the trajectory on the water surface is a perfect circle; (3) The device consists of a hollow motor, two Fresnel mirrors, screws, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The circular scanning principle of the Fresnel mirror of the present invention

[0022] Figure 2 The front side of the Fresnel mirror circular scanning device of the present invention is

[0023] Figure 3 The reverse side of the Fresnel mirror circular scanning device of the present invention DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, preferred embodiments are given below and the specific implementation of the present invention is further described in detail in conjunction with the accompanying drawings.

[0025] Example:

[0026] Combination Figure 1, which describes a dual-Fresnel mirror circular scanning device of a manned dual-band water depth measurement laser radar. The scanning device consists of a hollow motor and two Fresnel mirrors, one of which is installed outside the hollow motor and the other inside. When the motor rotates, the Fresnel mirror will also rotate, forming a continuously changing angle, ensuring that the angle between the laser emitted from the middle and the vertical line is 10°, the field of view angle is 20°, and the trajectory on the water surface is a perfect circle. The angles of the Fresnel grooves are different, but they all focus the light to form a central focus, which is the focus of the lens. Each groove can be regarded as an independent small lens to adjust the light into parallel light or concentrated light. After receiving the signal from the integrated control system, the scanning system controls the hollow motor to rotate at the system set speed, and sends the system status and rotation angle data to the integrated control system in real time. Specific steps S1-S2.

[0027] Combination Figure 2 and Figure 3 , indicating that the device consists of a hollow motor, two Fresnel mirrors, screws, etc.

[0028] The hollow diameter of the hollow motor is 200mm, the repeatability accuracy is ±5 arc seconds, the matching motor is a 2.5KW servo motor, the rated speed is 3000rpm, the load is approximately 1500Kg, the parallelism is ≤1 thread, the interior is coated with a black light-absorbing coating, there are 6 threaded holes with a diameter of 5mm, and the absolute rotation angle is fed back in real time through the encoder.

[0029] Two Fresnel mirrors, with a diameter of 200mm and a focal length of 140mm, are made of K9 glass and are resistant to high temperatures. They are fixed to the inside and outside of the hollow motor with glass glue.

[0030] The screw has a head thickness of 3.2 mm, a head diameter of 8.5 mm, a thread diameter of 5 mm, a screw length of 6 mm, and a black light-absorbing coating on the surface. The above embodiments are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and deformations without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

[0031] The technical contents not described in detail in the present invention are all known technologies.

Claims

1. Manned airborne dual-frequency phase multi-feature water measurement laser radar, characterized in that: The scanning device consists of a hollow motor and two Fresnel mirrors. A Fresnel mirror is installed outside the hollow motor and a Fresnel mirror is installed inside. When the motor rotates, the Fresnel mirror will also rotate to form a variable angle, ensuring that the angle between the laser emitted from the middle and the vertical line is 10°, the field of view angle is 20°, and the trajectory on the water surface is a perfect circle. The groove angles of the Fresnel mirror are different, but they all focus the light to form a central focus, which is the focus of the lens. Each groove can be regarded as an independent small lens to adjust the light into parallel light or focusing. Specific implementation: S1: Establishing the Circular Scanning Principle A rectangular coordinate system xOy is established on the imaging plane at a distance z0 from the rotating double Fresnel axis. The projection point of the rotating Fresnel mirror axis on the plane is O(x0, y0). Assume that any point on the scanning trajectory is P(x p ,y p ); set the initial positions of the two prisms, control their rotation direction and rotation speed to be the same (i.e. no relative rotation, ω1=ω2=ω), then the scanning trajectory of the rotating dual prism system on the plane xOy is a circle with point O as the center and r as the radius; when the laser radar and the target object have axial relative motion, the radius r will change accordingly, P(x p ,y p ) The moving trajectory of point will also change accordingly, and the scanning area on plane xOy will be in the shape of a ring; S2: Constructing constraints When the Fresnel mirror vertex angle is small, the azimuth angle and the pitch angle of the outgoing light beam have the following relationship, see formula (1); (1) Where θ is the azimuth angle of the outgoing beam, φ is the pitch angle of the outgoing beam, α is the top angle of the Fresnel mirror, n is the refraction of the prism, θ1 and θ2 are the rotation angles of the two Fresnel mirrors at time t respectively; for θ1 and θ2, according to the above settings, follow formula (2) (2) In the formula, the azimuth angle θ changes uniformly with time t, and the pitch angle φ is a constant, so the scanning trajectory is a uniform circular scan.

2. The manned airborne dual-frequency phase multi-feature water-measuring laser radar according to claim 1 is further characterized by: The device consists of a hollow motor, two Fresnel mirrors, screws, etc. The hollow diameter of the hollow motor is 200mm, the repeatability is ±5 arc seconds, the motor is a 2.5KW servo motor, the rated speed is 3000rpm, the load is about 1500Kg, the parallelism is ≤1 thread, the interior is coated with a black light-absorbing coating, there are 6 threaded holes, the diameter is 5mm, and the absolute rotation angle is fed back in real time through the encoder; Two Fresnel mirrors, with a diameter of 200mm and a focal length of 140mm, made of K9 glass, resistant to high temperatures; fixed to the inside and outside of the hollow motor with glass glue respectively; Screw, head thickness 3.2mm, head diameter 8.5mm, thread diameter 5mm, screw length 6mm, surface coated with black light-absorbing coating.

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