Solid-state laser radar production line pulse width and temperature combined automatic calibration method

Abstract

Aiming at the defects in the prior art, the invention provides a solid-state laser radar production line pulse width and temperature combined automatic calibration method so as to overcome the problems of long calibration time, repeated operation and poor compensation consistency of different batches. According to the method, the principle of'priority pulse width compensation and temperature compensation following 'is adopted, in the pulse width compensation process, a dynamic compensation method is adopted, temperature compensation data are collected after single-time pulse width compensation is finished, and temperature compensation calculation is started under the condition that pulse width compensation is finished after single-round temperature cycle; temperature compensation adopts a linear fitting method, and by calculating the centroid of an imaging point, centroid offset relative to normal temperature at different temperatures is compensated, and a temperature compensation parameter file is generated to be applied to a subsequent algorithm, so that pulse width and temperature joint automatic calibration of the solid-state laser radar is realized.

Description

Technical Field

[0001] This invention relates to lidar calibration technology, and more particularly to an automatic calibration method for pulse width and temperature in a solid-state lidar production line. Background Technology

[0002] Solid-state lidar has entered the mass production stage for automotive applications. Pure solid-state lidar based on dToF (direct time of flight) typically uses a VCSEL array as the transmitter and a SPAD (single-photon avalanche diode) array as the receiver.

[0003] Furthermore, the pulse width of VCSELs drifts with temperature, current, and batch variations. This drift is converted into a trigger timing offset after passing through the leading edge discrimination circuit, causing the ranging value of the same target to shift back and forth depending on the temperature or channel, forming a non-negligible fixed deviation. Targets with different reflectivities will amplify this deviation, causing white walls and black pillars to be measured as having different depths at the same distance. Due to inconsistent pulse widths, multi-channel chips exhibit layered misalignment in the point cloud, affecting subsequent fusion and localization.

[0004] Temperature is the primary external factor contributing to the aforementioned drift. The vehicle environment requires the radar to operate at full performance between -40°C and 85°C. Experiments show that temperature alone can cause a change of approximately 0.3 ns in the equivalent pulse width of the VCSEL, corresponding to a near 5 cm "moving wall" illusion. Simultaneously, the SPAD breakdown voltage decreases with increasing temperature, relatively raising the discrimination threshold and further amplifying inter-channel dispersion. The two temperature coefficients, with opposite directions and different amplitudes, result in a non-zero slope in the single-module full-temperature ranging curve after superposition, with inconsistent slopes across channels, causing overall point cloud shift and internal misalignment.

[0005] Existing methods for pulse width and temperature compensation of solid-state lidar mostly rely on manual operation and separate compensation stations, which suffer from drawbacks such as inconsistent compensation, repetitive work, and low degree of automation.

[0006] Therefore, this invention proposes an automatic calibration method for pulse width and temperature in solid-state lidar production lines, which compresses the ranging error of solid-state lidar to a range acceptable for autonomous driving. Summary of the Invention

[0007] In view of the deficiencies of the above-mentioned existing technologies, the present invention provides a method for jointly and automatically calibrating the pulse width and temperature of a solid-state lidar production line to overcome the problems of long calibration time, repetitive operations, and poor compensation consistency for different batches. In the present invention, the principle of "prior pulse width compensation and temperature compensation following" is adopted. During the pulse width compensation process, a dynamic compensation method is used. After a single pulse width compensation is completed, data for temperature compensation is collected. After a single temperature cycle, when the pulse width compensation has been completed, temperature compensation calculation is started. The temperature compensation uses the linear fitting method. By calculating the centroid of the imaging points, the centroid offset relative to room temperature at different temperatures is compensated, and a temperature compensation parameter file is generated for use in subsequent algorithms, realizing the joint and automatic calibration of the pulse width and temperature of the solid-state lidar.

[0008] To achieve the above object, the specific implementation steps of the present invention are as follows:

[0009] S1: Set the calibration temperature range and change step size;

[0010] S2: Collect and calculate the full width at half maximum (FWHM) of the laser output at room temperature;

[0011] S3: Set the temperature of the incubator;

[0012] S4: Pulse width compensation;

[0013] S5: Collect temperature compensation data;

[0014] S6: Temperature compensation calculation.

[0015] In the above S1, set the lowest temperature Tmin and the highest temperature Tmax of the calibration temperature, and set the temperature change step size of the incubator as ΔT. Then the number of temperature points collected in a single temperature cycle is K = (Tmax - Tmin) / ΔT.

[0016] In the above S2, at room temperature, deploy a data collection environment in the incubator, collect one frame of raw data, and calculate the FWHM F.

[0017] In the above S3, set the temperature of the incubator as Tmin. After the module stabilizes, collect one frame of raw data, calculate the FWHM Fi, and calculate |F - Fi|.

[0018] In the above S4, when |F - Fi| > 200 ps, pulse width compensation is performed.

[0019] S401: When F < Fi, perform negative compensation on the lidar. After compensation, re-collect raw data, and loop to execute S401 until |F - Fi| <= 200 ps. Then the pulse width compensation at this temperature ends, and enter S5.

[0020] S402: When F>F_i, perform positive compensation on the lidar, and then re-acquire raw data. Execute S401 repeatedly until |F-F_i|<=200ps, at which point pulse width compensation ends and proceeds to S5.

[0021] S403: When |F-F_i|<=200ps, pulse width compensation ends at this temperature, and proceeds to S5.

[0022] In step S5, a frame of raw data is acquired as temperature compensation data at that temperature. After acquisition, the process returns to step S3, increments the temperature step once, and continues with steps S3 and S4. When Tmin reaches Tmax, the process proceeds to step S6.

[0023] In step S6, after the temperature polling process from Tmin to Tmax ends, temperature compensation calculation is performed.

[0024] S601: Calculate the centroid of the histogram of the entire pixel based on the raw data collected at different temperatures in S5 above.

[0025] S602: Using 10x10 pixels as a pixel block, take the average value and list the centroid scatter plots at different temperatures.

[0026] S603: Perform linear fitting on the scatter plot in S602, and output the temperature compensation file based on the fitted curve to complete the temperature compensation of the lidar. Attached Figure Description

[0027] Figure 1 This is the overall flowchart of the present invention;

[0028] Figure 2 A comparison chart of pulse width compensation results;

[0029] Figure 3 The graph shows the results of the linear fitting for temperature compensation. Detailed Implementation

[0030] The invention will now be further described with reference to the accompanying drawings.

[0031] The present invention provides a method for jointly and automatically calibrating the pulse width and temperature of a solid-state lidar production line to overcome the problems of long calibration time, repetitive operations, and poor compensation consistency for different batches. In the present invention, the principle of "prior pulse width compensation and temperature compensation following" is adopted. During the pulse width compensation process, a dynamic compensation method is used. After the single pulse width compensation is completed, data for temperature compensation is collected. After a single round of temperature cycling, when the pulse width compensation has been completed, temperature compensation calculation is started. The temperature compensation uses the linear fitting method. By calculating the centroid of the imaging points, the centroid offset relative to room temperature at different temperatures is compensated, and a temperature compensation parameter file is generated for use in subsequent algorithms, realizing the joint and automatic calibration of the pulse width and temperature of the solid-state lidar.

[0032] To achieve the above object, referring to the attached Figure 1 , the specific implementation steps of the present invention are as follows:

[0033] S1: Set the calibration temperature range and the change step size;

[0034] S2: Collect and calculate the full width at half maximum (FWHM) of the laser output at room temperature;

[0035] S3: Set the temperature of the temperature chamber;

[0036] S4: Pulse width compensation;

[0037] S5: Acquisition of temperature compensation data;

[0038] S6: Temperature compensation calculation.

[0039] In the step S1, set the lowest temperature Tmin and the highest temperature Tmax of the calibration temperature, and set the temperature change step size of the temperature chamber as ΔT. Then the number of temperature points collected in a single round of temperature cycling is K = (Tmax - Tmin) / ΔT.

[0040] In the step S2, at room temperature, deploy a data acquisition environment in the temperature chamber, and collect one frame of raw data to calculate the full width at half maximum F.

[0041] In the step S3, set the temperature of the temperature chamber as Tmin. After the module is stable, collect one frame of raw data, calculate the full width at half maximum Fi, and calculate |F - Fi|.

[0042] Referring to the attached Figure 2 , in the step S4, when |F - Fi| > 200 ps, the pulse width is compensated.

[0043] S401: When F < Fi, perform negative compensation on the lidar. After compensation, re-collect raw data, and loop to execute S401 until |F - Fi| <= 200 ps. After the pulse width compensation at this temperature is completed, enter S5.

[0044] S402: When F>F_i, perform positive compensation on the lidar, and then re-acquire raw data. Execute S401 repeatedly until |F-F_i|<=200ps, at which point pulse width compensation ends and proceeds to S5.

[0045] S403: When |F-F_i|<=200ps, pulse width compensation ends at this temperature, and proceeds to S5.

[0046] In step S5, a frame of raw data is acquired as temperature compensation data at that temperature. After acquisition, the process returns to step S3, increments the temperature step once, and continues with steps S3 and S4. When Tmin reaches Tmax, the process proceeds to step S6.

[0047] See attached document Figure 3 In step S6, after the temperature polling from Tmin to Tmax ends, temperature compensation calculation is performed.

[0048] S601: Calculate the centroid of the histogram of the entire pixel based on the raw data collected at different temperatures in S5 above.

[0049] S602: Using 10x10 pixels as a pixel block, take the average value and list the centroid scatter plots at different temperatures.

[0050] S603: Perform linear fitting on the scatter plot in S602, and output the temperature compensation file based on the fitted curve to complete the temperature compensation of the lidar.

[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for automatic calibration of pulse width and temperature in a solid-state lidar production line, characterized in that, Adopting the principle of "priority pulse width compensation and temperature compensation following", in the process of pulse width compensation, a dynamic compensation method is used. After the single - pulse width compensation is completed, the data for temperature compensation is collected. After a single - round temperature cycle, when the pulse width compensation has been completed, the temperature compensation calculation is started. The temperature compensation uses the linear fitting method. By calculating the centroid of the imaging points, the centroid offset relative to the normal temperature at different temperatures is compensated, and a temperature compensation parameter file is generated for use in subsequent algorithms to achieve the joint automatic calibration of the pulse width and temperature of the solid - state lidar. The specific implementation steps of the present invention are as follows: S1: Set the calibration temperature range and change step size; S2: Collect and calculate the full - width at half - maximum (FWHM) of the laser output at normal temperature; S3: Set the temperature of the temperature chamber; S4: Pulse width compensation; S5: Temperature compensation data collection; S6: Temperature compensation calculation.

2. The method for automatic calibration of pulse width and temperature in a solid-state lidar production line as described in claim 1, characterized in that, In S2, at normal temperature, deploy a data collection environment in the temperature chamber, collect one frame of raw data, and calculate the FWHM F. In S3, set the temperature of the temperature chamber to Tmin. After the module stabilizes, collect one frame of raw data, calculate the FWHM Fi, and calculate |F - Fi|. In S4, when |F - Fi|>200 ps, when F < Fi, perform negative compensation on the lidar. After compensation, re - collect raw data, and loop through S401 until |F - Fi|<=200 ps. Then the pulse width compensation at this temperature ends, and enter S5. When F>Fi, perform positive compensation on the lidar. After compensation, re - collect raw data, and loop through S401 until |F - Fi|<=200 ps. Then the pulse width compensation at this temperature ends, and enter S5. When |F - Fi|<=200 ps, the pulse width compensation at this temperature ends, and enter S5. In S5, collect one frame of raw data as the temperature compensation data at this temperature. After the collection ends, return to S3, step the temperature once, and continue to execute S3 and S4. When Tmin steps to Tmax, enter S6. In S6, after the temperature polling from Tmin to Tmax ends, perform temperature compensation calculation; according to the raw data at different temperatures collected in S5 above, calculate the histogram centroid of all pixels; Take every 10x10 pixels as a pixel block, take the mean value, list the centroid scatter plot at different temperatures; perform linear fitting according to the above scatter plot, and output a temperature compensation file according to the fitting curve to complete the temperature compensation of the lidar.

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