Wide-angle laser ranging automatic calibration method

Abstract

A wide-angle laser ranging automatic calibration method relates to the technical field of laser ranging, and comprises the following steps: step S1, device performance grading: in a fixed scene, a test cloth with standard reflectivity is used, the optical axis of the wide-angle laser ranging module is vertically aligned with the test cloth, the distance between the wide-angle laser ranging module and the test cloth is changed, the TOF value and the PEAK value corresponding to different distances are collected, the distance-data change rate is analyzed, and the product performance is graded to ensure the consistency of qualified devices; step S2, switching reflectivity and collecting TOF value and PEAK value under different distances: step S3, according to the TOF value and PEAK value data distribution collected in step S2, a three-dimensional coordinate system is constructed, the data points are nonlinearly curved surface fitted, and a calibration equation is generated. The scheme automatically switches the reflectivity of the measured object by using the wide-angle laser ranging automatic calibration method, automatically collects data in the working range, and automatically completes the calibration work.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser ranging technology, in particular to a wide-angle laser ranging automatic calibration method. BACKGROUND

[0002] Large unmanned aerial vehicles (such as 4-axis / 6-axis models) need to perform flight obstacle avoidance during take-off, landing and cruising to ensure flight safety. Due to the unfolded size of the fuselage generally exceeding 1.5m x 1.5m, and the influence of crosswind, a safety space of 1.5 times the size of the fuselage (2.25m x 2.25m) must be reserved to avoid collision. This rigid requirement exposes the limitations of traditional obstacle avoidance technology:

[0003] Ultrasonic obstacle avoidance: 1. The measurement distance is limited by the frequency of the sound wave, and the lower the frequency, the farther the measurement. Although ultrasonic obstacle avoidance can achieve medium-distance detection, the low-frequency probe is bulky, forcing the unmanned aerial vehicle to sacrifice the effective payload space; 2. If ultrasonic waves need to be tested at a long distance, the sound field angle cannot be made too large. According to the 2.25m x 2.25m protective surface, multiple ultrasonic waves are needed to protect the surface. The limited characteristics of the sound field angle require multiple sensor arrays to cover the protective surface; 3. In order to maintain the high sensitivity of the ultrasonic wave, the sensor generally adopts an open design, and the open sensitive element design is easily eroded by the environment, significantly shortening the service life; 4. The propagation of sound waves is affected by temperature and humidity, and an additional environmental sensor is needed to compensate for the error.

[0004] Single-point laser obstacle avoidance: laser emitting circuit plus collimating lens for laser ranging. The field of view angle of the collimating lens is generally about 1.2°, and its purpose is to better converge the laser beam into a small spot with collimated laser. Such a spot on a diffuse reflective measured object has better light energy and can measure farther and more accurately. However, with a collimating lens with a field of view angle of only 1.2°, although high-precision ranging can be achieved, the single-point detection range is too small. To cover the 2.25m x 2.25m protective space area, multiple sensors need to be densely deployed, significantly increasing the system complexity and cost.

[0005] Visual obstacle avoidance: relies on environmental lighting conditions, and the reliability drops sharply in strong light reflection, night or fog scenes, requiring the fusion of multiple sensor redundancy design.

[0006] To break through the above limitations, a 20° field of view lens is used to replace the traditional collimating lens, and the single-point detection range is expanded by more than 16 times. However, the wide-angle design introduces new physical defects: the light energy per unit area of the collimated laser lens is smaller at different distances, and the light energy per unit area of the collimated laser lens is also smaller for different reflectivity detection objects at the same distance, which will result in ranging errors when ranging. Specifically:

[0007] 1, spot energy decay: the laser beam diverges at a 20° cone angle, and the spot area expands in a square level as the distance increases, and the unit area light energy decays sharply.

[0008] 2, reflectivity interference superposition: at the same distance, the light energy of a low reflectivity object (such as a dark wall) may be less than 10% of that of a high reflectivity object (such as a reflective sign), further amplifying the ranging deviation.

[0009] Error nature: TOF (Time of Flight) ranging value depends on light energy intensity, and actual light energy is subject to the inverse square law of distance and the linear relationship of reflectivity, resulting in systematic deviation between wide-angle laser TOF calculation result and actual distance.

[0010] The existing calibration method tries to solve the above errors, but falls into a new dilemma:

[0011] Fixed scene calibration: calibrate the ranging according to the fixed application scene of the product, and when the application scene of the product changes, the ranging needs to be calibrated by re-collecting data, which is not convenient for actual application.

[0012] Manual data collection: data collection is performed manually, which cannot ensure the integrity of data collection for different application scenes. Moreover, the data collection by manual method takes a long time and is not suitable for mass production.

[0013] Device batch difference uncontrollable: due to the inconsistency of laser emitting tube and laser receiving tube at device level, and the requirement of laser receiving tube signal processing part for electrical noise, the performance of different wide-angle laser ranging modules in the same batch has certain difference. SUMMARY

[0014] In view of the shortcomings of the prior art, the purpose of the present application is to provide a wide-angle laser ranging automatic calibration method.

[0015] In order to achieve the above purpose, the present application adopts the following technical solutions.

[0016] A wide-angle laser ranging automatic calibration method, the device adopted by the method comprises a wide-angle laser ranging module, a linear guide rail bearing the wide-angle laser ranging module, and a test cloth with different emissivity; the method comprises the following steps:

[0017] Step S1, device performance grading: under a fixed scene, a test cloth with standard reflectivity is used, and the optical axis of the wide-angle laser ranging module is vertically aligned with the test cloth, the distance between the wide-angle laser ranging module and the test cloth is changed, and the TOF value and the PEAK value corresponding to different distances are collected, the distance-data change rate is analyzed, and the product performance is graded to ensure the consistency of qualified devices;

[0018] Step S2, switch reflectivity and collect TOF values and PEAK values at different distances:

[0019] Step S3, according to the data distribution of TOF values and PEAK values collected in step S2, construct a three-dimensional coordinate system, and perform nonlinear surface fitting on the data points to generate a calibration equation.

[0020] Further, step S1 includes:

[0021] Step S101, reference data collection:

[0022] Reflectivity setting: the reflectivity of the test cloth with standard reflectivity is 40%;

[0023] Distance scanning: the wide-angle laser ranging module moves uniformly along the linear guide rail, and the distance between the wide-angle laser ranging module and the test cloth is from 1m to 10m;

[0024] Signal acquisition: collect a set of TOF values and PEAK values at equal intervals;

[0025] Step S102, performance grading analysis:

[0026] Curve drawing: generate a distance-TOF / PEAK curve, with distance as the horizontal axis and TOF value / PEAK value as the vertical axis;

[0027] Slope calculation: calculate the TOF value slope and PEAK value slope of the wide-angle laser ranging module and the test cloth at a distance from 7m to 8m;

[0028] Step S103, product performance grading and processing:

[0029] Grading standard:

[0030] A level: if the TOF value slope and the PEAK value slope are ≥0.9, the wide-angle laser ranging module corresponding to the slope is defined as A level, triggering the subsequent process;

[0031] B level: if 0.8≤TOF value slope and PEAK value slope<0.9, the wide-angle laser ranging module corresponding to the slope is defined as B level, triggering the subsequent process;

[0032] C / D level: if the TOF value slope or the PEAK value slope is <0.8, the wide-angle laser ranging module corresponding to the slope is defined as C / D level, and an alarm is prompted for repair.

[0033] Further, in step S2, test cloths with different reflectivities are switched from the lowest reflectivity of 5% to the highest reflectivity of 90% to ensure the completeness of the collected data covering different reflectivities in the application scenario of wide-angle laser ranging calibration;

[0034] Collecting TOF value and PEAK value of each reflectivity in the application range of wide-angle laser ranging to ensure the data integrity of different reflectivity in the application environment of the product;

[0035] The test cloth is replaced in turn according to 5%, 10%, 20%, 40%, 50%, 60%, 80% or 90% reflectivity, and then the TOF value and PEAK value at the interval of 4m, 5m, 6m, 7m, 8m and 9m are collected respectively for each test cloth.

[0036] Further, in step S3, when constructing the three-dimensional coordinate system, the X axis is the TOF value, the Y axis is the PEAK value, and the Z axis is the interval;

[0037] The fitting generates a calibration equation:

[0038] Z=-785.9+4.126*X+0.2364*Y-0.002398*X*X-0.0007536*X*Y+0.00001505*Y*Y; wherein Z is the calibrated interval value, X is the TOF value, and Y is the PEAK value;

[0039] When the wide-angle laser ranging module measures the distance in different environments, as long as the reflectivity of the measured object is between 5% and 90%, it can be brought into the calibration equation to calculate the calibrated interval value.

[0040] A wide-angle laser ranging automatic calibration method further comprises step S4: full-scene data re-collection and verification of the calibration result:

[0041] The diffuse reflection cloth with reflectivity of 5%, 10%, 20%, 40%, 50%, 60%, 80% or 90% is switched in turn, and then for each diffuse reflection cloth, the wide-angle laser ranging module moves uniformly along the linear guide rail, the interval between the wide-angle laser ranging module and the diffuse reflection cloth is from 50cm to 1000cm; TOF value and PEAK value are collected at 10cm intervals; the TOF value and PEAK value are brought into the calibration equation to obtain the calibrated interval value; then error determination is performed, the error between the calibrated interval value and the actual distance value is calculated, the wide-angle laser ranging module with error within ±10cm within the interval of 5m or within ±50cm outside the interval of 5m is calibrated as qualified; otherwise, it is calibrated as unqualified.

[0042] Further, the wide-angle laser ranging module comprises a wide-angle laser ranging drive board, a laser emitting lamp bead, a wide-angle emitting lens, a receiving lens and a laser receiving APD;

[0043] The wide-angle laser ranging drive board controls the laser pulse frequency and the bias voltage of the laser receiving APD;

[0044] The laser emitting lamp bead emits infrared laser pulses;

[0045] Wide-angle transmitting lens, 20° field of view, conical diffusion of light spot;

[0046] Receiving lens, collecting diffuse reflected laser, focusing to laser receiving APD photosurface;

[0047] Laser receiving APD: avalanche photodiode, converting optical signal to electrical signal;

[0048] Wide-angle laser ranging module, its working principle includes the following two stages:

[0049] Pulse emission stage: wide-angle laser ranging drive board controls laser emitting beads to produce infrared pulse, which is optically diffused by wide-angle transmitting lens; due to the 20° field of view of the lens, the laser beam is diffused outward in the form of a cone with an apex angle of 20°, resulting in the area of the light spot expanding with the square of the transmission distance;

[0050] Optical focusing stage: diffuse reflected light is focused by the receiving lens to the photosurface of the laser receiving APD.

[0051] Further, the linear guide rail is provided with a sliding rod; the sliding rod is provided with a clamp for fixing the wide-angle laser ranging module; the test cloth is arranged opposite to the wide-angle laser ranging module and is arranged perpendicular to the linear guide rail.

[0052] The present scheme adopts a wide-angle laser ranging automatic calibration method to automatically switch the reflectivity of the measured object, automatically collect data within the working range, and automatically complete the calibration work, which has the following advantages:

[0053] Dynamic reflectivity full-scene coverage mechanism: the 8-grade reflectivity test plate (5% / 10% / 20% / 40% / 50% / 60% / 80% / 90%) is automatically switched by the roller module driven by the stepping motor, which completely simulates the physical scene from asphalt pavement (5%) to reflective sign (90%). This design breaks through the limitation of traditional manual calibration which can only cover 3-4 kinds of reflectivity, ensures data collection under 48 groups of reflectivity-distance combinations (6 distances x 8 reflectivities), and eliminates the distortion of the calibration model caused by the lack of reflectivity dimension. The roller switching time is <0.5 seconds, which is 60 times more efficient than manual operation, and the reflectivity calibration error is controlled within ±2%, which fundamentally solves the calibration failure problem of extreme scenes (such as 5% low reflectivity long distance).

[0054] Device grading-calibration coupling screening system: based on TOF / PEAK rate of change quantitative analysis to establish device grading standard: under the fixed 40% reflectivity, through 1m-10m module moving scanning, calculate the 7m-8m key interval slope k. Set threshold grading: k≥0.9 is A level (high sensitivity APD), 0.8≤k<0.9 is B level, k<0.8 is C / D level (eliminate repair). The mechanism will intercept 15% low sensitivity module in front of the calibration process.

[0055] Three-dimensional nonlinear error compensation model: the quadratic surface equation of TOF-PEAK-distance is created. The model represents the nonlinear coupling effect of energy attenuation and reflectivity through cross term (-0.0007536XY) and quadratic term (-0.002398X 2 ). In the physical layer: X 2 term suppresses long distance overshoot error, Y 2 term compensates for low reflectivity signal delay, realizes dynamic error correction in 5%-90% reflectivity, 4m-9m distance range, and breaks through the bottleneck of linear calibration model failure in boundary scene.

[0056] Full automatic closed-loop calibration architecture: build four-stage non-intervention process of grading, acquisition, fitting and verification. Among them, the grading screening automatically identifies A / B level module; the data acquisition guide rail and the roller cooperate to generate a full parameter matrix; the surface fitting outputs the calibration equation in real time through the least square method; the closed-loop verification determines the error by secondary scanning. Establish the verification process and open the industrial production path. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 It is a structure diagram of a wide-angle laser ranging automatic calibration device;

[0058] Figure 2 It is a working principle diagram of a wide-angle laser ranging module;

[0059] Figure 3 It is a flowchart of the present application;

[0060] Figure 4 It is a grading principle diagram of wide-angle laser ranging;

[0061] Figure 5 It is a distance-TOF / PEAK curve diagram;

[0062] Figure 6 It is a three-dimensional distribution scatter diagram of TOF value and PEAK value under 5%-90% reflectivity interval and 4m-9m test distance;

[0063] Figure 7 It is a three-dimensional visualization diagram after fitting the plane. DETAILED DESCRIPTION

[0064] The application will be described in further detail below with reference to the drawings.

[0065] Term explanation:

[0066] TOF value, time of flight, unit ns, refers to the time difference from the emission of laser pulse to the detection by the receiver.

[0067] PEAK value, echo peak value, unit mV, refers to the voltage peak value of the laser echo signal converted by the APD.

[0068] Figure 1 It is a structural schematic diagram of a wide-angle laser ranging automatic calibration device; Figure 2 It is a working principle diagram of a wide-angle laser ranging module; as Figure 1 and Figure 2 As shown in the drawings, a wide-angle laser ranging automatic calibration device comprises a wide-angle laser ranging module, a linear guide rail bearing the wide-angle laser ranging module, a test cloth with different emissivity, and a roller shutter module for switching the test cloth.

[0069] The wide-angle laser ranging module comprises a wide-angle laser ranging drive board, a laser emitting lamp bead, a wide-angle emitting lens, a receiving lens, and a laser receiving APD.

[0070] The wide-angle laser ranging drive board controls the laser pulse frequency (1-10 kHz) and the bias voltage of the laser receiving APD.

[0071] The laser emitting lamp bead emits 905 nm infrared laser pulses.

[0072] The wide-angle emitting lens has a 20° field of view, causing the light spot to spread in a conical shape.

[0073] The receiving lens collects the diffused laser and focuses it to the light-sensing surface of the laser receiving APD.

[0074] The laser receiving APD is an avalanche photodiode that converts optical signals into electrical signals.

[0075] The working principle of the wide-angle laser ranging module comprises the following two stages:

[0076] Pulse emission stage: the wide-angle laser ranging drive board controls the laser emitting lamp bead to generate infrared pulses, which are optically diffused by the wide-angle emitting lens; due to the 20° field of view characteristic of the lens, the laser beam spreads outward in a conical shape with an apex angle of 20°, resulting in the area of the light spot expanding with the square of the transmission distance.

[0077] Optical focusing stage: the diffused light is focused by the receiving lens to the light-sensing surface of the laser receiving APD. The optical design of the receiving lens ensures the effective collection of scattered light within a 20° field of view while suppressing the interference of environmental stray light.

[0078] The linear guide rail is provided with a sliding rod, and the sliding rod is provided with a clamp for fixing the wide-angle laser ranging module.

[0079] The test cloth is arranged opposite to the wide-angle laser ranging module and is arranged perpendicularly to the linear guide rail.

[0080] The roller shutter module is provided with a roller shutter stepping motor, and the output shaft of the roller shutter stepping motor is wound with the test cloth.

[0081] In the scheme, the test cloths with different reflectivities are connected in sequence to form a roller shutter, and the roller shutter stepping motor switches the test cloth with a corresponding reflectivity (5%, 10%, 20%, 40%, 50%, 60%, 80% or 90%) to the working position (the facing position of the wide-angle laser ranging module) by rotating the output shaft. Of course, other methods for switching the test cloth can also be used; the patent application is not limited to the roller shutter module, and also includes other equivalent devices capable of switching the test cloth with a corresponding reflectivity.

[0082] The device moves the wide-angle laser ranging module through the linear guide rail, so as to change the distance between the wide-angle laser ranging module and the test cloth. Of course, the distance can also be changed by moving the test cloth through the linear guide rail.

[0083] Figure 3 The flowchart is the process of the application; as shown in the figure, a wide-angle laser ranging automatic calibration method comprises the following steps: Figure 3

[0084] Step S1, device performance grading: under a fixed scene, a test cloth with a standard reflectivity is used, the optical axis of the wide-angle laser ranging module is aligned perpendicularly to the test cloth, the distance between the wide-angle laser ranging module and the test cloth is changed, TOF values and PEAK values corresponding to different distances are collected, the distance-data change rate is analyzed, and the product performance is graded to ensure the consistency of qualified devices.

[0085] Step S101, reference data collection:

[0086] Reflectivity setting: the roller shutter module is switched to the 40% reflectivity test cloth (standard reflectivity reference).

[0087] Distance scanning: the wide-angle laser ranging module moves at a constant speed along the linear guide rail, the moving speed is 0.5 m / s, and the distance between the wide-angle laser ranging module and the test cloth is from 1 m to 10 m.

[0088] Signal collection: a group of TOF values and PEAK values are collected every 10 cm.

[0089] Step S102, performance grading analysis:

[0090] ​Curve drawing: generate distance-TOF / PEAK curve, horizontal axis is distance, vertical axis is TOF value / PEAK value;

[0091] Slope calculation: calculate the slope of TOF value and the slope of PEAK value of the wide-angle laser ranging module and the distance from 7m to 8m interval of the test cloth.

[0092] Step S103, grading and processing product performance.

[0093] Grading standard:

[0094] A level: if the slope of TOF value and the slope of PEAK value≥0.9, the wide-angle laser ranging module corresponding to the slope is defined as A level, triggering the subsequent process;

[0095] B level: if 0.8≤TOF value slope and PEAK value slope<0.9, the wide-angle laser ranging module corresponding to the slope is defined as B level, triggering the subsequent process;

[0096] C or D level: if the slope of TOF value or the slope of PEAK value<0.8, the wide-angle laser ranging module corresponding to the slope is defined as C or D level, and the alarm prompts repair.

[0097] Taking the wide-angle laser obstacle avoidance module of the unmanned aerial vehicle as an example, first, fix the wide-angle laser ranging module on the module fixing support of the aluminum alloy slide rod, then click to start the photoelectric switch, the system will control the guide rail collection module to collect TOF value and PEAK value at different distances under the 40% reflectivity test cloth, then the system analyzes the TOF value and PEAK value and grades the module, if it is A or B level product, the system controls the linear guide rail and roller motor module to automatically collect TOF value and PEAK value of different reflectivity plates at different distances, and according to the data distribution, the module is calibrated, after calibration, the system controls the linear guide rail and roller stepper motor to sample TOF value and PEAK value of different reflectivity plates at different distances again, and then judges whether the calibration result of the module is qualified according to the sampled data. If the result of the previous grading is C or D level product, the system will prompt that the module performance is not up to standard and needs to be returned to the production line for repair.

[0098] Figure 4 is the wide-angle laser ranging grading principle diagram. As Figure 4As shown, the automatic exposure is closed, the emission drive is adjusted to a fixed power, infrared laser is emitted, the light is diffused through the emission lens according to a 20° pointing angle, and as the test cloth with a reflectivity of 40% moves along the Z-axis direction, the emission spot becomes larger and larger, the energy per unit area of the spot on the test cloth becomes smaller and smaller, and then the energy returned to the laser receiving APD (avalanche photodiode) also becomes smaller and smaller. At this time, if the sensitivity of the laser receiving APD is low, as the test cloth moves along the Z-axis direction, the change rate of the TOF value and the PEAK value measured by the module will be very small. If the sensitivity of the laser receiving APD is high, as the test cloth moves along the Z-axis direction, the change rate of the TOF value and the PEAK value measured by the module will be greater than that of the low-sensitivity laser receiving APD.

[0099] In the wide-angle laser ranging module, the sensitivity of the laser receiving APD (avalanche photodiode) has a significant batch difference: high-sensitivity APD: can detect weak return light (such as long-distance low-reflectivity scene). Low-sensitivity APD: cannot trigger an effective signal when the return light energy is below the threshold. If not graded, low-sensitivity APD will fail in long-distance / low-reflectivity scenes.

[0100] Figure 5 is a distance-TOF / PEAK curve; Figure 5 In the method, the performance of the wide-angle laser ranging module can be graded according to the change rate of the TOF value and the change rate of the PEAK value. For example, data with a slope greater than or equal to 0.9 is classified as A, data with a slope of 0.8-0.9 is classified as B, data with a slope of 0.7-0.8 is classified as C, and data with a slope less than 0.7 is classified as D. In this way, the performance of the wide-angle laser ranging module can be graded. Modules with performance levels A and B are selected, and then subsequent calibration operations are performed. Modules with performance levels C and D are returned to the production line for repair.

[0101] Step S2: Switch the reflectivity and collect the TOF value and the PEAK value at different distances:

[0102] Switch the test cloth with different reflectivities from the lowest reflectivity of 5% to the highest reflectivity of 90% to ensure the completeness of the data collected for the wide-angle laser ranging calibration in different reflectivity coverage in the application scenario;

[0103] Collect the TOF value and the PEAK value of each reflectivity within the application range of the wide-angle laser ranging to ensure the data integrity of different reflectivities in the application environment of the product.

[0104] The test cloth is replaced in turn according to the reflectivities of 5%, 10%, 20%, 40%, 50%, 60%, 80%, or 90%, and then the TOF value and the PEAK value at distances of 4m, 5m, 6m, 7m, 8m, and 9m are collected for each test cloth.

[0105] Table 1 is a summary table of TOF values at different reflectivity 4m to 9m.

[0106]

[0107] Table 2 is a summary of PEAK values at different reflectivity 4m to 9m.

[0108]

[0109] As can be seen from Table 1 and Table 2, the TOF value becomes larger and the PEAK value becomes smaller as the measured distance becomes farther. At the same distance, the TOF value becomes smaller and the PEAK value becomes larger as the reflectivity increases.

[0110] Step S3, according to the TOF value and PEAK value data distribution of full reflectivity (5%-90%) and full distance (4m-9m) collected in step S2, a three-dimensional coordinate system is constructed, and a least square method is used to perform nonlinear surface fitting on the data points to generate a calibration equation.

[0111] When constructing the three-dimensional coordinate system, the X axis is the TOF value, the Y axis is the PEAK value, and the Z axis is the distance (unit: cm).

[0112] Figure 6 is a three-dimensional distribution scatter plot of TOF value and PEAK value under 5%-90% reflectivity interval and 4m-9m test distance. As can be seen from Figure 6 , the point set at each fixed distance shows a straight line distribution, then a least square method is used to perform three-dimensional smooth fitting on the collected data, and the fitting parameters are generated after the fitting is completed.

[0113] Figure 7 is a three-dimensional visualization diagram after fitting the plane; from Figure 7 , the fitted plane can be seen.

[0114] After fitting, the generated calibration equation is obtained:

[0115] Z=-785.9+4.126*X+0.2364*Y-0.002398*X*X-0.0007536*X*Y+0.00001505*Y*Y; where Z is the calibrated distance value; X is the TOF value; Y is the PEAK value.

[0116] In this way, when the wide-angle laser ranging module measures the distance in different environments, as long as the reflectivity of the measured object is between 5% and 90%, it can be brought into the equation to calculate the calibrated distance value.

[0117] Step S4, full scene data reacquisition and verification of calibration results:

[0118] The control roller stepping motor module switches the diffuse reflection cloth with reflectivity of 5%, 10%, 20%, 40%, 50%, 60%, 80% or 90% in turn, then for each diffuse reflection cloth, the wide-angle laser ranging module moves at a constant speed along the linear guide rail, the distance between the wide-angle laser ranging module and the diffuse reflection cloth is from 50 cm to 1000 cm; the TOF value and the PEAK value are collected at 10 cm intervals; the TOF value and the PEAK value are brought into the calibration equation to obtain the calibrated distance value; then error determination is performed, the error between the calibrated distance value and the actual distance value is calculated, the wide-angle laser ranging module with the error within ±10 cm within a distance of 5 m or within ±50 cm outside a distance of 5 m is calibrated as qualified; otherwise, it is calibrated as unqualified.

[0119] It can be understood that, for those skilled in the art, equivalent replacements or changes can be made according to the technical solutions and the inventive concept of the present application, and all these changes or replacements shall belong to the protection scope of the claims appended to the present application.

Claims

1. An automatic calibration method for wide-angle laser ranging, characterized in that, The device used includes a wide-angle laser ranging module, a linear guide rail supporting the wide-angle laser ranging module, and test cloths with different emissivity; it includes the following steps: Step S1, Device Performance Grading: In a fixed scenario, a test cloth with standard reflectivity is used, and the optical axis of the wide-angle laser ranging module is vertically aligned with the test cloth. The distance between the wide-angle laser ranging module and the test cloth is changed, and the TOF value and PEAK value corresponding to different distances are collected. The distance-data change rate is analyzed, and the product performance is graded to ensure the consistency of qualified devices. Step S2: Switch reflectivity and collect TOF and PEAK values ​​at different spacings: Step S3: Based on the distribution of TOF and PEAK values ​​collected in step S2, construct a three-dimensional coordinate system, perform nonlinear surface fitting on the data points, and generate calibration equations. It also includes: Step S4, re-acquiring data from the entire scene and verifying the calibration results: The diffuse reflective fabrics with different reflectivities are switched sequentially. Then, for each diffuse reflective fabric, the wide-angle laser ranging module moves at a constant speed along a linear guide rail. The TOF and PEAK values ​​are collected. The TOF and PEAK values ​​are substituted into the calibration equation to obtain the calibrated distance value. Then, the error is judged, and the error between the calibrated distance value and the actual distance value is calculated. The wide-angle laser ranging module is calibrated as qualified if the error is controlled within ±10cm within 5m or within ±50cm beyond 5m; otherwise, it is calibrated as unqualified.

2. The automatic calibration method for wide-angle laser ranging according to claim 1, characterized in that, Step S1 includes: Step S101, Baseline Data Acquisition: Reflectance setting: The standard reflectance of the test cloth is 40%; Distance scanning: The wide-angle laser ranging module moves at a constant speed along the linear guide rail, and the distance between the wide-angle laser ranging module and the test cloth ranges from 1m to 10m; Signal acquisition: A set of TOF and PEAK values ​​were acquired at equal intervals; Step S102, Performance grading analysis: Curve plotting: Generates a distance-TOF / PEAK curve, with the horizontal axis representing distance and the vertical axis representing the TOF / PEAK value; Slope calculation: Calculate the TOF and PEAK slopes for the distance between the wide-angle laser ranging module and the test cloth in the range of 7m-8m. Step S103: Classify and process product performance: Grading standards: Grade A: If the slope of the TOF value and the slope of the PEAK value are ≥0.9, the wide-angle laser ranging module corresponding to this slope is classified as Grade A, triggering the subsequent process; Class B: If the slope of the TOF value is less than 0.8 and the slope of the PEAK value is less than 0.9, the wide-angle laser ranging module corresponding to this slope is classified as Class B, triggering the subsequent process; C / D grade: If the slope of the TOF value or the slope of the PEAK value is <0.8, the wide-angle laser ranging module corresponding to this slope is classified as C / D grade, and an alarm is triggered to indicate that it should be returned for repair.

3. The automatic calibration method for wide-angle laser ranging according to claim 2, characterized in that, In step S2, test cloths with different reflectivities are switched, from the lowest reflectivity of 5% to the highest reflectivity of 90%, to ensure the integrity of the collected data covering different reflectivities in the application scenario for wide-angle laser ranging calibration. Collect the TOF and PEAK values ​​for each reflectivity within the application range of wide-angle laser ranging to ensure the data integrity for different reflectivities in the product's application environment; The test cloths were changed sequentially according to reflectance of 5%, 10%, 20%, 40%, 50%, 60%, 80%, or 90%. Then, the TOF and PEAK values ​​were collected for each test cloth at spacings of 4m, 5m, 6m, 7m, 8m, and 9m.

4. The automatic calibration method for wide-angle laser ranging according to claim 3, characterized in that, In step S3, when constructing the three-dimensional coordinate system, the X-axis represents the TOF value, the Y-axis represents the PEAK value, and the Z-axis represents the spacing. The calibration equation is obtained after fitting: Z = -785.9 + 4.126*X + 0.2364*Y – 0.002398*X*X – 0.0007536*X*Y + 0.00001505*Y*Y; where Z is the calibrated spacing value; X is the TOF value; and Y is the PEAK value. When measuring distances in different environments, as long as the reflectivity of the object being measured is between 5% and 90%, the wide-angle laser ranging module can be used in the calibration equation to calculate the calibrated distance value.

5. The automatic calibration method for wide-angle laser ranging according to any one of claims 1 to 4, characterized in that, The wide-angle laser ranging module includes a wide-angle laser ranging driver board, a laser emitting LED, a wide-angle emitting lens, a receiving lens, and a laser receiving APD; Wide-angle laser ranging driver board, which controls the laser pulse frequency and the bias voltage of the laser receiving APD; Laser-emitting LED beads emit infrared laser pulses; Wide-angle emission lens with a 20° field of view, causing the light spot to spread in a cone shape; A receiving lens collects diffusely reflected laser light and focuses it onto the photosensitive surface of the laser receiving APD. Laser receiving APD: This is an avalanche photodiode that converts optical signals into electrical signals; The working principle of a wide-angle laser ranging module includes the following two stages: Pulse emission stage: The wide-angle laser ranging driver board controls the laser emission lamp to generate an infrared pulse, which is optically diffused through the wide-angle emission lens; due to the 20° field of view characteristic of the lens, the laser beam diffuses outward in a cone shape with a 20° apex angle, causing the spot area to increase quadratically with the transmission distance; Optical focusing stage: Diffuse reflected light is focused by the receiving lens onto the photosensitive surface of the laser receiving APD.

6. The automatic calibration method for wide-angle laser ranging according to claim 5, characterized in that, The linear guide rail is slidably equipped with a slide rod; the slide rod is equipped with a clamp for fixing the wide-angle laser ranging module; the test cloth is arranged opposite to the wide-angle laser ranging module and perpendicular to the linear guide rail.

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