A four-quadrant positioning tracking method based on cone scanning

Abstract

The present invention discloses a four-quadrant positioning and tracking method based on conical scanning, comprising the following steps: using a laser spot with a divergence angle to actively illuminate a small moving target to be detected; using a receiving telescope and a conical scanning mirror to receive and image the target reflected light, so that the position of the target image on the four-quadrant detector is deflected; the conical scanning mirror is rotated at a uniform speed to make the target on the image plane perform uniform circular motion around the centroid of the non-deflected target image; according to the residence time length of the target spot in the four quadrants and the centroid calculation formula, the centroid coordinates of the non-deflected image target are solved. By using the present invention, the nonlinear positioning error and the requirements for the target size of the traditional four-quadrant detector can be avoided, and the large offset detection of low-speed small-scale targets or light spots can be realized, and it can be used for optical tracking under simple backgrounds such as the sky and the ocean, optical guidance or precise tracking and aiming of light spots in optical communications, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric tracking, and in particular relates to a four-quadrant positioning tracking method based on cone scanning. Background Art

[0002] The four-quadrant detector has the characteristics of small size, high sensitivity and wide dynamic range, and is widely used in precision optoelectronic systems such as target tracking, laser guidance, space laser communication, laser alignment, etc. For example, the Chinese patent document with publication number CN115473578A discloses a communication, ranging and positioning integrated device based on the four-quadrant detector, including a first optical terminal and a second optical terminal, the first optical terminal and the second optical terminal are placed in the atmospheric channel, and the link is kept unobstructed; the first optical terminal and the second optical terminal have the same structure, and both include a modulator, a laser, an optical power amplifier, a four-quadrant detector, a signal light modulation and demodulation measurement and control board and an optical system; the first optical terminal and the second optical terminal receive the optical signal sent by the other party and the signal light reflected by the other party when they are emitted by themselves, and after receiving the optical signal, the first optical terminal and the second optical terminal perform calculation on the received signal light through their respective signal light modulation and demodulation measurement and control boards to obtain the calculation result, and the calculation result is the received communication information and position and orientation.

[0003] At present, there are many methods for detecting the real displacement and solving the target spot in four quadrants. For example, the Chinese patent document with the publication number CN115046475A discloses a high-precision laser spot position detection method based on a four-quadrant detector. According to the infinite integral fitting algorithm, the relationship between the actual value of the spot position and the solved value is obtained; the error compensation factor function is introduced to process the relationship between the actual value of the spot position and the solved value, and the residual error between the estimated value and the actual value of the spot position is obtained; according to the principle of least squares method, the optimal equivalent spot radius is obtained; based on the Tanh function fitting algorithm, the parameters of the control waveform shape are introduced to obtain the actual value of the spot position; a mathematical model of the residual error of the spot position is constructed to minimize its square sum and obtain the optimal control waveform shape parameters; according to the optimal equivalent radius, the optimal control waveform shape parameters and the establishment of a new mathematical model of residual error, the spot position is obtained.

[0004] A Chinese patent document with publication number CN114964085A discloses a method for solving the laser spot position based on a four-quadrant detector. First, the laser spot energy adopts a Gaussian distribution model to derive the corresponding relationship between the detector output voltage and the laser spot energy, and obtain the relationship equation of the spot position coordinates; through Taylor expansion, retain the cubic terms to obtain the algebraic equation of the spot position coordinates; solve the algebraic equation to obtain the coordinates of the center position of the laser spot.

[0005] However, there is a nonlinear error between the actual displacement of the target spot detected by the traditional four-quadrant detection and the calculated coordinate results. In addition, when the target image spot is small (the spot diameter is much smaller than the radius of the four-quadrant detector), it is impossible to achieve positioning and tracking with a large offset.

[0006] Therefore, it is urgent to design a new four-quadrant positioning tracking method to avoid the shortcomings of the traditional four-quadrant detection system. Summary of the invention

[0007] The invention provides a four-quadrant positioning and tracking method based on cone scanning, which can avoid the nonlinear positioning error of a traditional four-quadrant detector and the requirement on the target size.

[0008] A four-quadrant positioning tracking method based on cone scanning comprises the following steps:

[0009] (1) Use a laser spot with a divergence angle to actively illuminate the small moving target to be detected;

[0010] (2) Using a receiving telescope and a conical scanning mirror to receive and image the reflected light from the target, the position of the target image on the four-quadrant detector is deflected;

[0011] (3) The conical scanning mirror is rotated at a uniform speed to make the target on the image plane perform uniform circular motion around the centroid of the undeflected target image;

[0012] (4) Based on the residence time of the target light spot in the four quadrants and the centroid calculation formula, the centroid coordinates of the undeflected image target are solved.

[0013] In step (1), after the laser emits the laser, it passes through the beam expansion and divergence mirror group and the emission mirror group in sequence to generate a laser spot with an emission angle.

[0014] The laser emits continuous laser or high repetition rate pulse laser;

[0015] For continuous lasers, the length of time the target spot stays in the four quadrants is the continuous time-intensity signal; for high-repetition-rate pulsed lasers, the length of time the target spot stays in the four quadrants is expressed as the number of pulses.

[0016] In step (2), the receiving telescope is a transmission receiving telescope, and the conical scanning mirror is an optical wedge that rotates at a constant speed around the central axis.

[0017] Alternatively, the receiving telescope is a recursive or reflecting telescope, and the conical scanning mirror is an off-axis rotating reflecting mirror.

[0018] Furthermore, the reflecting telescope may be a Cassegrain telescope. In this case, the receiving telescope uses a primary mirror of the Cassegrain telescope, and the conical scanning mirror uses a secondary mirror of the Cassegrain telescope that rotates off-axis.

[0019] In step (4), the centroid coordinates of the target in the undeflected image are solved according to the target's residence time in the four quadrants and the centroid calculation formula. The specific formula is:

[0020] ;

[0021] ;

[0022] ;

[0023] In the formula, It represents the radius of the target in uniform circular motion on the image plane of the four-quadrant detector. , , , Respectively represent the length of time the target stays in the four quadrants, Indicates the centroid coordinates of the target image in the undistorted case with positive and negative signs.

[0024] The diameter of the image of a small moving target on the four-quadrant detector target surface is much smaller than the radius of the four-quadrant detector target surface; the deflection radius produced by the conical scanning mirror on the four-quadrant detector target surface is adjusted according to actual conditions, but should be smaller than the radius of the four-quadrant detector target surface.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Compared with the traditional four-quadrant positioning and tracking method, the present invention has the characteristics of more accurate and linear position estimation and the ability to detect large offsets of low-speed, small-scale target light spots. It can be used for optical tracking of small targets in simple backgrounds such as the sky and the ocean, precise tracking and aiming of light spots in optical guidance or optical communications, etc.

[0027] 2. The positioning and tracking method according to the present invention can avoid the shortcomings of the traditional four-quadrant detection system, such as nonlinear positioning solution and inability to locate small-scale targets, and achieve high-precision, small target image spot, and larger offset positioning and tracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0029] Figure 1 The present invention is a flowchart of a four-quadrant positioning and tracking method based on cone scanning according to an embodiment of the present invention.

[0030] Figure 2 Schematic diagram of the optical path system used in an embodiment of the present invention.

[0031] Figure 3 Schematic diagram of the structure of the first conical scanning mirror in an embodiment of the present invention.

[0032] Figure 4 Schematic diagram of the structure of the second conical scanning mirror in an embodiment of the present invention.

[0033] Figure 5 It is a schematic diagram of the principle of solving the centroid coordinates of the undeflected image target in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] It should be noted that, in the absence of conflict, the features in the following embodiments and implementations may be combined with each other.

[0036] like Figure 1 As shown, a four-quadrant positioning tracking method based on cone scanning includes the following steps:

[0037] S1, uses a laser spot with a certain divergence angle to actively illuminate a small moving target.

[0038] The optical path system used in the present invention is as follows Figure 2 As shown, it includes a laser 1, a beam expansion and divergence mirror group 2, a transmitting mirror group 3, a small moving target to be detected 4, a receiving telescope 5, a conical scanning mirror 6, and a four-quadrant detector 7.

[0039] In step S1, after the laser 1 emits the laser, it passes through the beam expansion and divergence mirror group 2 and the emission mirror group 3 in sequence, and generates a laser spot with a certain emission angle to illuminate the small moving target 4 to be detected.

[0040] In this embodiment, the laser 1 can emit continuous laser or high repetition rate pulsed laser. For continuous laser, the length of time the target spot stays in the four quadrants is a continuous time-intensity signal; for high repetition rate pulsed laser, the length of time the target spot stays in the four quadrants is expressed as the number of pulses.

[0041] S2, using a conical scanning mirror and a receiving telescope to receive and image the target reflected light, so that the target image position on the four-quadrant detector is deflected.

[0042] In the embodiment of the present invention, the conical scanning mirror can be implemented in two ways. The first conical scanning mirror structure is as follows: Figure 3 As shown, the receiving telescope adopts a transmission receiving telescope 11, and the conical scanning mirror adopts an optical wedge 12 that rotates at a constant speed around the central axis.

[0043] The target reflected light is received by the transmission receiving telescope 11, and the position of the target spot image on the target surface of the four-quadrant detector is deflected by the optical wedge 12. The entire system becomes a non-coaxial receiving optical path structure by rotating the optical wedge 12. The uniform rotation of the optical wedge 12 generates a circular track scan of the target image spot on the image plane of the four-quadrant detector 13.

[0044] The second conical scanning mirror structure can use a reflective or catadioptric telescope. Figure 4 As shown, the receiving telescope adopts the primary mirror 21 of the Cassegrain telescope, and the conical scanning mirror adopts the off-axis rotating secondary mirror 22 in the Cassegrain telescope.

[0045] The target reflected light is received by the primary mirror 21 of the Cassegrain telescope, and the position of the target spot image on the target surface of the four-quadrant detector is deflected by the secondary mirror 22 that rotates off-axis. The entire system becomes a non-coaxial receiving light path structure by the secondary mirror 22 that rotates off-axis. The secondary mirror 22 rotates at a uniform speed to generate a circular track scan of the target image spot on the image plane of the four-quadrant detector 23.

[0046] S3, by uniformly rotating the conical scanning mirror, the target light spot on the image plane makes uniform circular motion around the centroid of the undeflected target image.

[0047] S4, solving the centroid coordinates of the undeflected target image according to the residence time length of the target light spot in the four quadrants and the derived centroid solution method.

[0048] like Figure 5 As shown in the figure, (a) shows the target image spot of the four-quadrant detector around the centroid Make uniform circular motion; (b) represents the length of time the target light spot stays in the four quadrants.

[0049] The specific formula of the centroid solution method is as follows:

[0050] ;

[0051] ;

[0052] ;

[0053] In the formula, It represents the radius of the target in uniform circular motion on the image plane of the four-quadrant detector. , , , Respectively represent the length of time the target stays in the four quadrants, The centroid coordinates of the target image without deflection including positive and negative signs. The Cartesian coordinate system used takes the intersection of the four quadrants as the origin and the boundary line between the two quadrants of the four-quadrant detector as the coordinate axis.

[0054] Compared with the traditional four-quadrant positioning and tracking method, the present invention has the characteristics of more accurate and linear position estimation algorithm and the ability to detect large offsets of low-speed, small-scale target light spots. It can be used for optical tracking of small targets in simple backgrounds such as the sky and ocean, precise tracking and aiming of light spots in optical guidance or optical communications, etc.

[0055] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A four-quadrant positioning tracking method based on cone scanning, characterized in that: The following steps are involved: (1) Use a laser spot with a divergence angle to actively illuminate the small moving target to be detected; (2) Using a receiving telescope and a conical scanning mirror to receive and image the reflected light from the target, the position of the target image on the four-quadrant detector is deflected; The deflection radius of the conical scanning mirror on the four-quadrant detector target surface should be smaller than the radius of the four-quadrant detector target surface; (3) The conical scanning mirror is rotated at a uniform speed to make the target on the image plane perform uniform circular motion around the centroid of the undeflected target image; (4) Based on the residence time of the target light spot in the four quadrants and the centroid calculation formula, the centroid coordinates of the undeflected image target are solved.

2. The four-quadrant positioning tracking method based on cone scanning according to claim 1 is characterized in that: In step (1), after the laser emits the laser, it passes through the beam expansion and divergence mirror group and the emission mirror group in sequence to generate a laser spot with an emission angle.

3. The four-quadrant positioning tracking method based on cone scanning according to claim 2 is characterized in that: The laser emits continuous laser or high repetition rate pulse laser; For continuous lasers, the length of time the target spot stays in the four quadrants is the continuous time-intensity signal; for high-repetition-rate pulsed lasers, the length of time the target spot stays in the four quadrants is expressed as the number of pulses.

4. The four-quadrant positioning tracking method based on cone scanning according to claim 1, characterized in that: In step (2), the receiving telescope is a transmission receiving telescope, and the conical scanning mirror is an optical wedge that rotates at a uniform speed around the central axis.

5. The four-quadrant positioning tracking method based on cone scanning according to claim 1, characterized in that: In step (2), the receiving telescope is a recursive or reflecting telescope, and the conical scanning mirror is an off-axis rotating reflecting mirror.

6. The four-quadrant positioning tracking method based on cone scanning according to claim 5, characterized in that: The receiving telescope adopts the primary mirror of the Cassegrain telescope, and the conical scanning mirror adopts the secondary mirror of the Cassegrain telescope that rotates off-axis.

7. The four-quadrant positioning and tracking method based on cone scanning according to claim 1, characterized in that: In step (4), the centroid coordinates of the target in the undeflected image are solved according to the target's residence time in the four quadrants and the centroid calculation formula. The specific formula is: ； ； ； In the formula, It represents the radius of the target in uniform circular motion on the image plane of the four-quadrant detector. , , , Respectively represent the length of time the target stays in the four quadrants, Indicates the centroid coordinates of the target image in the undistorted case with positive and negative signs.

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