Laser optical axis and detector automatic alignment method and system

Abstract

The invention discloses a laser optical axis and detector automatic alignment method and system. The method comprises the following steps: controlling a three-axis displacement table to scan echo signal coordinates to automatically adjust laser emission power; an echo signal space range is determined through scanning, and initial particles are arranged on an axial plane with small light spots and strong light intensity; after setting particle swarm parameters, iteratively updating an inertia weight and a particle number by using a dynamic PSO particle swarm optimization algorithm, calculating particle positions, obtaining a light intensity value, and determining a close-range optimal relative position; meanwhile, the image distance difference between far and near targets is calculated, and the Z axis of the three-axis displacement table is controlled to complete axial compensation; the echo deviation angle and the radial displacement are calculated according to the motor rotating speed, the target distance and the light velocity, the X axis is controlled to complete radial compensation in combination with the radius of the target surface of the detector, and accurate alignment is achieved. The alignment efficiency and precision are greatly improved, and the defects that a traditional method is slow in positioning and low in precision are overcome.

Description

Technical Field

[0001] The present invention belongs to the field of laser radar detection technology, and more specifically, relates to a method and system for automatically aligning a laser optical axis with a detector. Background Art

[0002] In the field of LiDAR detection technology, as an active three-dimensional spatial information acquisition technology, LiDAR has been widely used in surveying and mapping, remote sensing, autonomous driving, and other fields. To improve its detection range, it is necessary to utilize the physical optical focal characteristics of the optical system receiving the echo to accurately position the detector at the point of maximum echo signal intensity, achieving overlap with the optical focal point, thereby optimizing the system's detection performance.

[0003] At present, the position adjustment of the laser optical axis and the detector mainly relies on manual experience. The existing method usually uses a tool to fix the optical structure, manually adjusts the detector position, and uses an oscilloscope to find the point with the strongest echo amplitude before fixing it. This method has significant defects: first, the adjustment process is highly dependent on the operator's experience, and it is difficult to ensure the adjustment accuracy, which cannot meet the needs of high-precision detection; second, the optical axis adjustment process is complicated and requires multiple links such as indoor coarse adjustment, outdoor fine adjustment, dynamic off-target compensation, etc., resulting in a long assembly cycle and low efficiency; third, due to the lack of a unified adjustment strategy, the existing method is difficult to adapt to different optical structures and has poor universality, which limits its application in diversified products.

[0004] Furthermore, existing technologies lack control over laser power. They are unable to automatically adjust the transmission power based on factors such as target distance and laser model, making it prone to echo signal saturation or being drowned out by noise, which affects the determination of the focal position. In terms of spatial search, the lack of efficient algorithms makes it difficult to quickly locate the optimal position of the detector. Furthermore, existing methods are unable to achieve dynamic and precise compensation for off-target errors during long-distance ranging during motor rotation, limiting the long-range detection performance of lidar under high-speed scanning.

[0005] Therefore, there is an urgent need for a method and device for automatic alignment of the laser optical axis and the detector that can overcome the above-mentioned defects, so as to achieve fast and stable automatic alignment, reduce manual intervention, improve assembly efficiency, and have good versatility and adaptability to meet the needs of the development of lidar technology. Summary of the Invention

[0006] The present invention proposes a method and device for automatically aligning the laser optical axis and detector, which can quickly and stably realize automatic alignment between the optical axis of the lidar optical system and the detector in a single scenario, with low manual intervention and effectively improving the system assembly efficiency.

[0007] In view of the above defects or improvement needs of the prior art, as a first aspect of the present invention, a method for automatically aligning a laser optical axis and a detector is provided, comprising: S1. Scan the three-axis translation stage to obtain the coordinates of the echo signal, automatically adjust the laser ranging module's transmission power based on the feedback, and confirm the final transmission power; S2. Scan and determine the spatial range of the echo signal by controlling the three-axis translation stage; Initial particles are randomly arranged on the axial plane where the smaller the spot area is, the greater the received light intensity is; After completing the particle swarm parameter setting, the inertia weight and particle number are iteratively updated through the dynamic PSO particle swarm optimization method; Calculate and update the particle position and obtain the received light intensity value, converge to determine the optimal relative position between the laser optical axis and the detector at close range; S3. Calculate the difference between the image distance of the near-range target and the image distance of the infinitely distant target to determine the distance the detector needs to move along the optical axis. Axial compensation is achieved by controlling the Z-axis of the three-axis translation stage to move the corresponding distance. Based on the motor speed, target distance and speed of light, the target echo offset angle caused by the time difference during the laser scanning process is calculated, and then the maximum radial displacement of the echo spot center is obtained. Combined with the radius constraint of the circular detector target surface, the distance the detector needs to move radially along the optical axis is determined, and the X-axis of the three-axis translation stage is controlled to move this distance to complete radial compensation.

[0008] Furthermore, the specific method for automatically adjusting the transmission power of the laser ranging module according to the feedback in S1 is: The initial laser emission power is set to an empirical constant, and the three-axis translation stage is controlled to perform a rapid and rough scan in space. If the detector does not receive valid echo information, the emission power energy is too low. The system automatically increases the energy and rescans until the detector receives a valid echo signal. If the detector receives a saturated signal, the transmitted power energy is too high, and the received light intensity near the signal saturation area is higher than that in other areas. The position information of the saturated signal area is retained, the laser power is lowered and the range is scanned again until there is no intensity saturation point in the area and the detector can receive valid echo information.

[0009] Furthermore, the calculation method of the light intensity received in S2 is: Consider the laser as a Gaussian beam, the target as a Lambertian plane, and ignore the influence of aberrations. According to the Gaussian imaging formula, the light intensity distribution on the image plane under ideal conditions is: , in, is the light intensity coefficient, 、 Represents the radial spatial position, The light intensity at the target position is reduced to the central light intensity The beam radius at is the distance between the laser emitted by the lidar and the target, is the focal length; Considering diffraction and defocus, the spatial intensity distribution of parallel light emitted by an infinitely distant point light source after passing through the special-shaped aperture stop and optical system is: , in, is the defocus amount, is the incident plane wave amplitude, is the wave number, is the complex amplitude transmittance of the special-shaped aperture; Among them, for a point target at close range, it is equivalent to an infinitely far target passing through a concave lens and then being focused by the optical system; at this time, the focal plane of the equivalent optical system composed of the virtual concave lens and the optical system is the image plane of the point target at close range, that is, the equivalent focus is the image distance; The three-dimensional spatial energy distribution of the light intensity of the point light source is regarded as a point spread function, and the final light intensity distribution of the echo spot at the detector target surface is: , According to the formula at close range The equivalent focal position of the optical system under the condition of φ is the position where the light spot intensity is maximum.

[0010] Furthermore, the particle swarm parameters in S2 include: Initial search particle number , minimum threshold of particle number, inertia weight The maximum value and minimum value , individual learning factor, group learning factor, maximum number of iterations and a search boundary in three-dimensional space; wherein the initial number of particles is not less than 30.

[0011] Furthermore, the inertia weight iterative update method in S2 is: In each iteration, the inertia weight is updated using a quadratic function, and the weight calculation formula is: , in, is the number of current iterations. By dynamically adjusting the inertia weight, the inertia weight decreases slowly in the early stage and the proportion of global search is larger. In the later stage, the inertia weight decreases faster and the search precision in the local space is enhanced, which conforms to the actual search rule of global search first and local search later.

[0012] Furthermore, the iterative updating method of the number of particles in S2 is: Dynamically adjust the number of particles and reduce the number of particles based on the number of iterations. The calculation formula is: , in, is the number of current iterations, The minimum threshold for the number of particles to be set; By dynamically adjusting the number of particles during the iteration process, the particles with the largest difference from the target are removed. Particles are used to improve the overall computing efficiency, reduce redundancy, and achieve fast and stable convergence of the system.

[0013] Furthermore, the specific method for calculating the axial compensation in S3 is: For echoes at different distances, long-distance echoes can be approximated as parallel light, with the light spot focused at the focal point of the optical system; short-distance echoes focus at a position behind the focal point, which can be calculated using the Gaussian imaging formula: , in, is the image distance, The distance between the indoor close-range target and the ranging module; In order to meet the needs of long-distance distance measurement, the detector position is compensated along the axial direction and the distance is moved for: , Where, Indicates focal length.

[0014] Furthermore, the specific method for calculating the radial compensation in S3 is: When the motor rotates at high speed, there is a time difference between laser emission and echo reception. During this time difference, the scanning mechanism has rotated a certain angle, resulting in an offset between the laser foot point and the instantaneous field of view center when the target echo is received by the lidar. In other words, the focus position of the echo after the receiving optical system is offset from the center of the detector target surface. The offset angle is: , in, is the laser scanning line speed, is the distance between the target and the lidar, is the speed of light; When the offset angle exceeds the field of view, the ranging module will not be able to receive the echo signal, which seriously affects the long-distance ranging capability of the laser radar under high-speed scanning. Through radial offset, the system can still receive echo signals of different distances when the motor is rotating. Taking into account the radius of the circular detector target surface, Constraints and effective detection capabilities for targets at different distances at different speeds, radial compensation The following conditions must be met: , , in, It indicates the maximum displacement of the echo spot center under the limitation of the system's maximum rotation speed and maximum distance measurement index.

[0015] As a second aspect of the present invention, a system for automatically aligning a laser optical axis and a detector is provided, comprising: The transmission power adjustment unit is used to obtain the coordinates of the echo signal by controlling the three-axis translation stage to scan, automatically adjust the transmission power of the laser ranging module according to the feedback, and confirm the final transmission power; A spatial search unit, used for determining the spatial range of the echo signal by controlling the three-axis translation stage to scan; Initial particles are randomly arranged on the axial plane where the smaller the spot area is, the greater the received light intensity is; After completing the particle swarm parameter setting, the inertia weight and particle number are iteratively updated through the dynamic PSO particle swarm optimization method; Calculate and update the particle position and obtain the received light intensity value, converge to determine the optimal relative position between the laser optical axis and the detector at close range; The dynamic compensation off-target unit is used to calculate the difference between the image distance of the close-range target and the image distance of the infinitely far target, and obtain the distance that the detector needs to move along the optical axis. The axial compensation is completed by controlling the Z axis of the three-axis translation stage to move the corresponding distance. Based on the motor speed, target distance and speed of light, the target echo offset angle caused by the time difference during the laser scanning process is calculated, and then the maximum radial displacement of the echo spot center is obtained. Combined with the radius constraint of the circular detector target surface, the distance the detector needs to move radially along the optical axis is determined, and the X-axis of the three-axis translation stage is controlled to move this distance to complete radial compensation.

[0016] As a third aspect of the present invention, a computer-readable storage medium is further provided, on which a computer program is stored, and the computer program is used by a processor to execute any step of the method for automatically aligning the laser optical axis and the detector.

[0017] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art: 1. The method for automatically aligning the laser optical axis and the detector of the present invention realizes adaptive adjustment of the laser emission power by establishing an emission power control algorithm. During the detection process, for different long and short targets and laser models, the system sets the initial laser emission power as an empirical constant and controls the three-axis translation stage to scan the echo signal. If no valid echo is received, the power is automatically increased; if a saturated signal appears, the position is recorded and the power is reduced and rescanned until a valid and non-saturated echo signal is obtained. This algorithm effectively avoids the problem of signal saturation due to excessive emission power, or the echo being drowned in noise due to too low power, ensures that the laser emission power is always in the appropriate range, provides a stable signal basis for accurately judging the focus position, and significantly improves the reliability and stability of the alignment process.

[0018] 2. The automatic alignment method of the laser optical axis and the detector of the present invention realizes the rapid and accurate positioning of the equivalent focal position of the close-range target by constructing a spatial search algorithm and combining it with the dynamic PSO particle swarm optimization algorithm. In three-dimensional space, the precision displacement stage is first controlled to perform a millimeter-level traversal coarse search to determine the echo signal area, and then the initial search particles are reasonably arranged on the key plane according to the spot size and intensity distribution characteristics. During the operation of the algorithm, the inertia weight is updated by a quadratic function to balance the global and local search capabilities; the number of particles is dynamically adjusted based on the number of iterations to reduce redundant calculations. After multiple iterations, the particle position is updated and the received light intensity is recorded, and finally the position of the maximum received light intensity is obtained by convergence, realizing micron-level precision search, greatly improving the alignment efficiency and accuracy, and overcoming the defects of slow positioning and low accuracy of traditional methods.

[0019] 3. The automatic alignment method of the laser optical axis and the detector of the present invention solves the off-target problem in medium and long-distance ranging and motor rotation scenarios by establishing a dynamic compensation off-target algorithm. The axial offset is calculated according to the Gaussian imaging formula, and the precision three-axis translation stage is controlled to move along the Z axis to compensate for the defocus caused by the change in target distance; the echo offset angle and the maximum radial displacement are calculated based on the motor speed, target distance and speed of light, and the radial compensation amount is determined according to the detector target surface constraint, and the X-axis movement is controlled to complete the radial compensation. The algorithm effectively eliminates the influence of distance and motor rotation factors on echo reception, ensuring that the detector can accurately receive the echo signal under different working conditions, significantly improving the detection performance and adaptability of the laser radar in dynamic environments, and enabling the system to maintain a good working condition in complex application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a method for automatically aligning a laser optical axis and a detector according to an embodiment of the present invention; Figure 2 A diagram showing the arrangement of devices according to an embodiment of the present invention; Figure 3is an algorithm flow chart of an embodiment of the present invention; Figure 4 2 is a diagram of system units according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0022] Example 1 Please refer to Figure 1 This embodiment 1 provides a method for automatically aligning a laser optical axis and a detector, comprising: S1. Scan the three-axis translation stage to obtain the coordinates of the echo signal, automatically adjust the laser ranging module's transmission power based on the feedback, and confirm the final transmission power; S2. Determine the spatial range of the echo signal by controlling the three-axis translation stage to scan; randomly place initial particles on the axial plane where the smaller the spot area, the greater the received light intensity; after completing the particle swarm parameter setting, iteratively update the inertia weight and particle number using the dynamic PSO particle swarm optimization method; calculate and update the particle position and obtain the received light intensity value, converging to determine the optimal relative position between the laser optical axis and the detector at close range; S3. Calculate the difference between the image distance of the close-range target and the image distance of the infinitely distant target to determine the distance the detector needs to move axially along the optical axis. Axial compensation is achieved by controlling the Z-axis of the three-axis translation stage to move the corresponding distance. Calculate the target echo offset angle caused by the time difference during the laser scanning process based on the motor speed, target distance, and speed of light, and then determine the maximum radial displacement of the echo spot center. Combined with the radius constraint of the circular detector target surface, determine the distance the detector needs to move radially along the optical axis. Control the X-axis of the three-axis translation stage to move this distance to achieve radial compensation.

[0023] This embodiment 1 further explains the above content: Please refer to Figure 2This embodiment 1 proposes a method and device for automatically aligning the laser optical axis and detector. The laser radar transmitting laser and the receiving echo optical system, PD board, and high-speed ADC acquisition chip in the ranging module are fixed. A photodetector is mounted on a precision three-axis translation stage, where the Z-axis direction of the translation stage is the axial direction of the optical axis, and the X and Y directions are the radial directions of the optical axis. In an indoor environment, a control device is used to transmit laser light toward a fixed target. By controlling the movement of the precision three-axis translation stage within space, the maximum position of the light intensity received by the detector is found, completing the focus position search within a close range. A dynamic miss-compensation algorithm is then established to compensate for scan misses during long-range ranging.

[0024] Please refer to Figure 3 In this embodiment 1, the relative position between the detector and the optical system is controlled by controlling the laser emission power and the movement of the precision three-axis translation stage.

[0025] (1) Establishing a transmit power control algorithm For targets of varying distances and laser types, the corresponding laser power emission levels vary. If the emission power is too strong, numerous saturation points will appear within the scanning area; if the emission power is too low, the echo signal will be drowned out by ambient noise. Both situations will affect the determination of the focal position. Therefore, a emission power control algorithm is established based on the strength of the received signal: the initial laser emission power is set to an empirical constant, and the three-axis translation stage is controlled to perform a rapid and rough scan within the space. If the detector does not receive valid echo information, the emission power energy is too low, and the system automatically increases the energy and rescans until the detector receives a valid echo signal. If the detector receives a saturated signal, the emission power energy is too high, and the received light intensity near the signal saturation area is higher than in other areas. The location information of the saturated signal area is retained, and the laser power is lowered and scanned again within this range until no intensity saturation points appear within the area and the detector can receive valid echo information. Ensure that the laser emission power is controlled within the appropriate range during subsequent scanning.

[0026] (2) Establishing a spatial search algorithm Due to the influence of various factors such as laser beam energy distribution, target surface characteristics, anisotropic aperture, defocus, diffraction, and aberration, the echo is focused on the detector target surface as a light spot with a certain spatial energy distribution. For ease of analysis, the laser is considered a Gaussian beam, the target is considered a Lambertian plane, and the influence of aberrations is ignored. According to the Gaussian imaging formula, under ideal conditions, the light intensity distribution on the image plane is: , in, is the light intensity coefficient, 、 Represents the radial spatial position, The light intensity at the target position is reduced to the central light intensity The beam radius at is the distance between the laser emitted by the lidar and the target, is the focal length.

[0027] Considering diffraction and defocus, the spatial intensity distribution of parallel light emitted by an infinitely distant point light source after passing through the special-shaped aperture stop and optical system is: , in, is the defocus amount, is the incident plane wave amplitude, is the wave number, is the complex amplitude transmittance of the special-shaped aperture.

[0028] For a point target at close range, it can be equivalent to an infinitely distant target passing through a concave lens and then being focused by the optical system. In this case, the focal plane of the equivalent optical system composed of the virtual concave lens and the optical system is the image plane of the point target at close range, that is, the equivalent focus is the image distance.

[0029] The three-dimensional spatial energy distribution of the light intensity of the point light source is regarded as a point spread function, and the final light intensity distribution of the echo spot at the detector target surface is: , According to the above formula, close distance The equivalent focal position of the optical system under the condition of is the position of the maximum intensity of the spot. A precision translation stage is moved in three-dimensional space to perform a millimeter-level traversal coarse search to find the area where the detector receives the echo signal. The PSO particle swarm optimization algorithm is used to find the position of the maximum intensity point in space. The specific steps are as follows: According to the above formula, the received light intensity distribution in space has the following characteristics: the closer to the focal position, the greater the intensity value and the smaller the spot radius; the farther away from the focal position, the smaller the intensity value and the larger the spot radius. When selecting the initial search particles, the spot size and maximum intensity value on each XY plane are comprehensively considered. More initial search particles are set on planes with smaller spots and larger intensity values. A total of no fewer than 30 initial search particles are set, and their initial velocity is set to 0.

[0030] Set the initial number of search particles , inertia weight The maximum value and minimum value , individual and group learning factors, maximum number of iterations And the search boundary in three-dimensional space. In order to find the location of the maximum light intensity point in space as accurately and quickly as possible, the dynamic PSO particle swarm algorithm is used.

[0031] In each iteration, the inertia weight is updated using a quadratic function, and the weight calculation formula is: , in, The number of current iterations. By dynamically adjusting the inertia weight, the inertia weight decreases slowly in the early stages, giving a greater weight to the global search. Later, the inertia weight decreases more rapidly, enhancing the search precision within the local space. This conforms to the actual principle of searching globally first and then locally.

[0032] Dynamically adjust the number of particles and reduce the number of particles based on the number of iterations. The calculation formula is: , in, is the number of current iterations, The minimum threshold for the number of particles is set. By dynamically adjusting the number of particles during the iteration process, the particles with the largest difference from the target are removed. Particles can improve the overall computing efficiency, reduce redundancy, and achieve fast and stable convergence of the system.

[0033] Based on the PSO particle swarm optimization algorithm, through multiple iterations, the speed and position of each particle are updated, the detector is moved to the corresponding position, and the received light intensity at the corresponding position is recorded, so as to find the local and global optimal positions, and finally converge to the position of the maximum received light intensity, realizing micron-level precision search of the equivalent focus position at close distances indoors.

[0034] (3) Establish a dynamic compensation off-target algorithm It can achieve good echo reception effect even when the motor is rotating at long or short distances.

[0035] For echoes at different distances, long-distance echoes can be approximated as parallel light, with the light spot focused at the focal point of the optical system; short-distance echoes focus at a position behind the focal point, which can be calculated using the Gaussian imaging formula: , in, is the image distance, The distance between the indoor close-range target and the ranging module. In order to meet the needs of long-distance ranging, the detector position is compensated along the axial direction and the distance is moved. for: , When the motor rotates at high speed, there is a time difference between laser emission and echo reception. During this time difference, the scanning mechanism has rotated a certain angle, resulting in an offset between the laser foot point and the instantaneous field of view center when the target echo is received by the lidar. In other words, the focus position of the echo after the receiving optical system is offset from the center of the detector target surface. The offset angle is: , in, is the laser scanning line speed, is the distance between the target and the lidar, When the offset angle exceeds the field of view, the ranging module will not be able to receive the echo signal, which seriously affects the long-distance ranging capability of the laser radar under high-speed scanning. Through radial offset, the system can still receive echo signals at different distances while the motor is rotating. The radial compensation size Satisfied with: , , in, It indicates the maximum displacement of the echo spot center under the limitation of the system's maximum speed and maximum distance index. Taking into account the existence of a circular detector target with a radius of Constraints and effective detection capabilities for targets at different distances at different speeds, radial compensation The above formula needs to be satisfied.

[0036] By controlling the precision three-axis translation stage, after completing the radial and axial compensation of the detector, the relative position between the detector and the optical system is fixed using welding, gluing and other fixing methods to complete the automatic alignment of the position between the laser optical axis and the detector.

[0037] In some specific scenarios, the above method is specifically applied in a preferred embodiment. The preferred embodiment involves the following parts: a laser for emitting pulsed laser, a laser wavelength , laser divergence angle The optical system of the ranging module is used to collimate the emitted pulse laser and focus the target echo, and the aperture of the receiving optical system ,focal length ; Detector, used for photoelectric conversion of reference light and target echo, using APD detector, detector target radius ; Shaping and amplification circuit, used to shape and amplify the weak signal after the detector's photoelectric conversion; ADC acquisition circuit, using a high-speed ADC chip to digitize the echo analog signal; control and signal processing module, used to process the digitized echo signal, in addition to controlling components such as lasers and peripheral sensors; detector clamping and moving device, used to adjust the relative position relationship between the detector or the circuit board where the detector is located and the optical system, clamping the detector on a precision three-axis translation stage controlled by a stepper motor, the movable range of the precision three-axis translation stage is ±1cm, controlling the relative position relationship between the detector and the optical system, and the control accuracy can reach sub-micron level; control method for automatic alignment of the laser optical axis and the detector, controlling the movement of the precision three-axis translation stage and the real-time reception of the echo signal intensity.

[0038] The detector clamping and moving device can be an internal module of the laser radar, or it can be an auxiliary device during the installation and adjustment process, and it will be removed after the detector position is adjusted and fixed.

[0039] The method of the preferred embodiment adjusts the relative position relationship between the detector and the optical system. Therefore, the detector does not move, and the method of adjusting the position of the optical system is also included in the content of the preferred embodiment.

[0040] The following are the specific implementation steps of the preferred embodiment.

[0041] Step 1: Determine the transmit power of the laser ranging module. Set up a standard reflectivity plate with a reflectivity of 80% as a target at a distance of 10.5 meters from the ranging module in an indoor environment. Return the precision three-axis translation stage to its center position. If the initial transmission power is manually set to 100, the three-axis translation stage is controlled to move in an S-shaped manner within the measuring range to roughly scan the echo signal intensity and its corresponding coordinate position. At this time, due to the low power and no valid echo signal, the system automatically controls the laser to adjust the transmission power to 110. At this time, a valid echo signal appears within the range and there is no saturated echo signal, and the transmission power adjustment is completed. If the initial transmission power is manually set to 150, the three-axis translation stage is controlled to move in an S-shaped manner within the measuring range to roughly scan the echo signal intensity and its corresponding coordinate position. At this time, due to the high power, multiple saturated echo signals are received. The system records the spatial position of the saturated echo signal, reduces the transmission power, and performs an S-shaped movement scan on the saturated echo signal area until no saturated echo signal appears in the area and a valid echo can be received. The system automatically controls the laser to adjust the transmission power to 115, and the transmission power adjustment is completed.

[0042] Step 2: Establish a spatial search algorithm to automatically locate the laser optical axis and the detector in a close-range environment. By controlling the three-axis translation stage to move in an S-shaped manner within the range, the spatial range in the spatial domain where the echo signal can be received is found. The spot area on axial planes with different radial values ​​was calculated. Taking into account the spot area size and the maximum received light intensity, more initial particles were randomly placed on axial planes with smaller spot areas and greater received light intensities, ensuring that the number of initial particles was no less than 30. The experiment found that there were five controller axial planes that received valid echoes. Based on the spot area size and the maximum received light intensity on these planes, 10, 8, 6, 4, and 2 initial particles were randomly placed, respectively.

[0043] Set the initial number of search particles , minimum threshold of particle number 5, inertia weight The maximum value is 0.9 and the minimum value is 0.4, the individual learning factor is 2, the group learning factor is 2, the maximum number of iterations is 10, and the search boundary in the three-dimensional space Using the dynamic PSO particle swarm algorithm, the inertia weight and the number of search particles are dynamically adjusted in each iteration, the particle position is calculated and updated, and the received light intensity value at the corresponding position is obtained. After multiple iterations, the global optimal position is converged, and the optimal relative position of the laser optical axis and the detector in a close-range environment is found.

[0044] Step 3: Establish a dynamic compensation miss-target algorithm to complete the position compensation in a dynamic environment at medium and long distances. The calculation formula for infinite distance and 10.5 The axial offset between the distances is approximately 97.82 , control the Z direction of the precision three-axis translation stage to compensate for the axial offset; in the measurement range of , maximum motor speed Revolutions per second, depending on radial compensation The maximum off-target amount of the target at this time is calculated by the relevant formula , so to ensure All echo spots can be detected by the detector, and the radial deviation is set to , control the precision three-axis translation stage to compensate for radial offset in the X direction and complete dynamic compensation for off-target.

[0045] Step 4: After automatically aligning the laser optical axis and the detector, secure the detector and the optical system using a fixture. This fixture can be a mechanical structure such as a set screw or locking mechanism, or it can be made of materials such as optical adhesive, UV adhesive, or solder.

[0046] Example 2 Please refer to Figure 4 This embodiment 2 provides a system for automatically aligning a laser optical axis and a detector, comprising: The transmission power adjustment unit is used to obtain the coordinates of the echo signal by controlling the three-axis translation stage to scan, automatically adjust the transmission power of the laser ranging module according to the feedback, and confirm the final transmission power; The spatial search unit is used to determine the spatial range of the echo signal by controlling the three-axis translation stage to scan; randomly arrange initial particles on the axial plane where the smaller the spot area, the greater the received light intensity; after completing the particle swarm parameter setting, the inertia weight and particle number are iteratively updated through the dynamic PSO particle swarm optimization method; calculate and update the particle position and obtain the received light intensity value, and converge to determine the optimal relative position between the laser optical axis and the detector at close range; The dynamic compensation off-target unit is used to calculate the difference between the image distance of the close-range target and the image distance of the infinitely distant target, and to obtain the distance that the detector needs to move axially along the optical axis. The axial compensation is completed by controlling the Z-axis of the three-axis translation stage to move the corresponding distance. According to the motor speed, target distance and speed of light, the target echo offset angle caused by the time difference during the laser scanning process is calculated, and the maximum radial displacement of the center of the echo spot is obtained. Combined with the radius constraint of the circular detector target surface, the distance that the detector needs to move radially along the optical axis is determined, and the X-axis of the three-axis translation stage is controlled to move this distance to complete the radial compensation.

[0047] Example 3 This embodiment 3 also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, it can implement any step of a method for automatically aligning a laser optical axis and a detector.

[0048] The computer-readable storage medium may include: a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, etc., which can store program codes.

[0049] For an introduction to the computer-readable storage medium provided in this application, please refer to the above method embodiment, and this application will not go into details here.

[0050] It will be easily understood by those skilled in the art that the above description is only 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 in the scope of protection of the present invention.

Claims

1. A method for automatically aligning a laser optical axis and a detector, characterized in that: include: S1. Scan the three-axis translation stage to obtain the coordinates of the echo signal, automatically adjust the laser ranging module's transmission power based on the feedback, and confirm the final transmission power; S2. Determine the spatial range of the echo signal by controlling the three-axis translation stage to scan; randomly place initial particles on the axial plane where the smaller the spot area, the greater the received light intensity; after completing the particle swarm parameter setting, iteratively update the inertia weight and particle number using the dynamic PSO particle swarm optimization method; calculate and update the particle position and obtain the received light intensity value, converging to determine the optimal relative position between the laser optical axis and the detector at close range; S3. Calculate the difference between the image distance of the close-range target and the image distance of the infinitely distant target to determine the distance the detector needs to move axially along the optical axis. Axial compensation is achieved by controlling the Z-axis of the three-axis translation stage to move the corresponding distance. Calculate the target echo offset angle caused by the time difference during the laser scanning process based on the motor speed, target distance, and speed of light, and then determine the maximum radial displacement of the echo spot center. Combined with the radius constraint of the circular detector target surface, determine the distance the detector needs to move radially along the optical axis. Control the X-axis of the three-axis translation stage to move this distance to achieve radial compensation.

2. The method for automatically aligning a laser optical axis and a detector according to claim 1, characterized in that: The specific method for automatically adjusting the transmission power of the laser ranging module according to the feedback in S1 is: The initial laser emission power is set to an empirical constant, and the three-axis translation stage is controlled to perform a rapid and rough scan in space. If the detector does not receive valid echo information, the emission power energy is too low. The system automatically increases the energy and rescans until the detector receives a valid echo signal. If the detector receives a saturated signal, the transmitted power energy is too high, and the received light intensity near the signal saturation area is higher than that in other areas. The position information of the saturated signal area is retained, the laser power is lowered and the range is scanned again until there is no intensity saturation point in the area and the detector can receive valid echo information.

3. The method for automatically aligning a laser optical axis and a detector according to claim 1, wherein: The calculation method of the light intensity received in S2 is: Consider the laser as a Gaussian beam, the target as a Lambertian plane, and ignore the influence of aberrations. According to the Gaussian imaging formula, the light intensity distribution on the image plane under ideal conditions is: ， in, is the light intensity coefficient, 、 Represents the radial spatial position, The light intensity at the target position is reduced to the central light intensity The beam radius at is the distance between the laser emitted by the lidar and the target, is the focal length; Considering diffraction and defocus, the spatial intensity distribution of parallel light emitted by an infinitely distant point light source after passing through the special-shaped aperture stop and optical system is: ， in, is the defocus amount, is the incident plane wave amplitude, is the wave number, is the complex amplitude transmittance of the special-shaped aperture; Among them, for a point target at close range, it is equivalent to an infinitely far target passing through a concave lens and then being focused by the optical system; at this time, the focal plane of the equivalent optical system composed of the virtual concave lens and the optical system is the image plane of the point target at close range, that is, the equivalent focus is the image distance; The three-dimensional spatial energy distribution of the light intensity of the point light source is regarded as a point spread function, and the final light intensity distribution of the echo spot at the detector target surface is: ， According to the formula at close range The equivalent focal position of the optical system under the condition of φ is the position where the light spot intensity is maximum.

4. The method for automatically aligning a laser optical axis and a detector according to claim 1, wherein: The particle swarm parameters in S2 include: Initial search particle number , minimum threshold of particle number, inertia weight The maximum value and minimum value , individual learning factor, group learning factor, maximum number of iterations and a search boundary in three-dimensional space; wherein the initial number of particles is not less than 30.

5. The method for automatically aligning a laser optical axis and a detector according to claim 1, wherein: The inertia weight iterative update method in S2 is: In each iteration, the inertia weight is updated using a quadratic function, and the weight calculation formula is: ， in, is the number of current iterations. By dynamically adjusting the inertia weight, the inertia weight decreases slowly in the early stage and the proportion of global search is larger. In the later stage, the inertia weight decreases faster and the search precision in the local space is enhanced, which conforms to the actual search rule of global search first and local search later.

6. The method for automatically aligning a laser optical axis and a detector according to claim 1, characterized in that: The iterative updating method of the number of particles in S2 is: Dynamically adjust the number of particles and reduce the number of particles based on the number of iterations. The calculation formula is: ， in, is the number of current iterations, The minimum threshold for the number of particles to be set; By dynamically adjusting the number of particles during the iteration process, the particles with the largest difference from the target are removed. Particles are used to improve the overall computing efficiency, reduce redundancy, and achieve fast and stable convergence of the system.

7. The method for automatically aligning a laser optical axis and a detector according to claim 2, characterized in that: The specific method for calculating the axial compensation in S3 is: For echoes at different distances, long-distance echoes can be approximated as parallel light, with the light spot focused at the focal point of the optical system; short-distance echoes focus at a position behind the focal point, which can be calculated using the Gaussian imaging formula: ， in, is the image distance, The distance between the indoor close-range target and the ranging module; In order to meet the needs of long-distance distance measurement, the detector position is compensated along the axial direction and the distance is moved for: ， Where, Indicates focal length.

8. The method for automatically aligning a laser optical axis and a detector according to claim 2, wherein: The specific method for calculating the radial compensation in S3 is: When the motor rotates at high speed, there is a time difference between laser emission and echo reception. During this time difference, the scanning mechanism has rotated a certain angle, resulting in an offset between the laser foot point and the instantaneous field of view center when the target echo is received by the lidar. In other words, the focus position of the echo after the receiving optical system is offset from the center of the detector target surface. The offset angle is: ， in, is the laser scanning line speed, is the distance between the target and the lidar, is the speed of light; When the offset angle exceeds the field of view, the ranging module will not be able to receive the echo signal, which seriously affects the long-distance ranging capability of the laser radar under high-speed scanning. Through radial offset, the system can still receive echo signals of different distances when the motor is rotating. Taking into account the radius of the circular detector target surface, Constraints and effective detection capabilities for targets at different distances at different speeds, radial compensation The following conditions must be met: ， ， in, It indicates the maximum displacement of the echo spot center under the limitation of the system's maximum rotation speed and maximum distance measurement index.

9. A laser optical axis and detector automatic alignment system, characterized in that: include: The transmission power adjustment unit is used to obtain the coordinates of the echo signal by controlling the three-axis translation stage to scan, automatically adjust the transmission power of the laser ranging module according to the feedback, and confirm the final transmission power; The spatial search unit is used to determine the spatial range of the echo signal by controlling the three-axis translation stage to scan; randomly arrange initial particles on the axial plane where the smaller the spot area, the greater the received light intensity; after completing the particle swarm parameter setting, the inertia weight and particle number are iteratively updated through the dynamic PSO particle swarm optimization method; calculate and update the particle position and obtain the received light intensity value, and converge to determine the optimal relative position between the laser optical axis and the detector at close range; The dynamic compensation off-target unit is used to calculate the difference between the image distance of the close-range target and the image distance of the infinitely distant target, and to obtain the distance that the detector needs to move axially along the optical axis. The axial compensation is completed by controlling the Z-axis of the three-axis translation stage to move the corresponding distance. According to the motor speed, target distance and speed of light, the target echo offset angle caused by the time difference during the laser scanning process is calculated, and the maximum radial displacement of the center of the echo spot is obtained. Combined with the radius constraint of the circular detector target surface, the distance that the detector needs to move radially along the optical axis is determined, and the X-axis of the three-axis translation stage is controlled to move this distance to complete the radial compensation.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: The computer program is executed by a processor to implement the method for automatically aligning a laser optical axis and a detector as described in any one of claims 1 to 8.

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