Laser ranging calibration method and lidar ranging system

Abstract

This application provides a laser ranging calibration method and a lidar ranging system. The laser ranging calibration method includes: initializing multiple TDC ranging circuits; wherein each TDC ranging circuit includes a comparator and a TDC connected in sequence; acquiring calibration measurement values ​​obtained by the multiple TDC ranging circuits based on the same echo signal; using one TDC ranging circuit as a reference TDC ranging circuit, calculating the deviation value corresponding to each TDC ranging circuit based on the deviation between the calibration measurement values ​​of other TDC ranging circuits and the calibration measurement value of the reference TDC ranging circuit; during laser ranging, acquiring the measurement values ​​obtained by each TDC ranging circuit from the target echo signal, correcting the measurement values ​​according to the deviation values ​​corresponding to each TDC ranging circuit, and obtaining the measurement distance value based on the corrected measurement correction value.

Description

Technical Field

[0001] This application relates to the field of laser ranging technology, and in particular to a laser ranging calibration method and a lidar ranging system. Background Technology

[0002] In recent years, with the popularization and application of unmanned equipment, LiDAR has attracted increasing attention. LiDAR uses its high-speed emitted laser beam for distance detection and point cloud imaging, featuring high precision, strong penetration, long operating range, and real-time performance. Currently, it has high development prospects in multiple fields such as autonomous driving, robot navigation, road monitoring, and terrain mapping, and market demand is increasing daily.

[0003] Time-to-digital converters (TDCs) are currently a commonly used method for measuring time intervals. Due to their high-precision measurement advantages, they are widely used and have become an indispensable key technology in fields such as laser ranging, atomic physics, and aerospace.

[0004] Currently known lidar ranging solutions mainly include single-channel TDC ranging circuits and dual-channel TDC ranging circuits. For single-channel TDC ranging circuits, echo drift caused by echo power conversion can easily lead to significant measurement errors. For dual-channel TDC ranging circuits, in practical applications, uncontrollable factors such as hardware trace delays, controller internal delays, and individual component differences can cause inconsistent ranging results for the same echo signal, making it difficult to obtain reliable ranging results. Current methods for handling measurement errors in dual-channel TDC ranging circuits primarily focus on processing the signal data acquired during the ranging process to eliminate errors. Examples include designing complex noise processing circuits to process the signal data, processing parameters affected by external factors such as temperature and voltage, and fitting data obtained from multiple TDC ranging circuits.

[0005] However, the above-mentioned approach of processing the signal data collected during the ranging process to eliminate measurement errors has several drawbacks. First, the uncontrollable factors affecting the inconsistency of ranging results from multiple TDC ranging circuits in practical applications are complex and highly variable, making it difficult to accurately measure all of these uncontrollable factors. This often leads to complex processing solutions. Second, for different TDC ranging hardware circuit compositions, such as increasing or decreasing the number of TDC ranging circuits, it is necessary to specifically analyze and process the problems existing in practical applications before designing or adjusting the processing method. This results in poor ability of the processing solution to cope with changes in actual application scenarios, increasing the complexity of the processing solution. Summary of the Invention

[0006] To address the aforementioned problems, this application provides a simpler laser ranging calibration method and a lidar ranging system that improves measurement accuracy and anti-interference capabilities, and is highly portable.

[0007] A first aspect of this application provides a laser ranging calibration method, comprising:

[0008] The multi-channel TDC ranging circuit is initialized; wherein each TDC ranging circuit includes a comparator and a TDC connected in sequence;

[0009] Acquire calibration measurement values ​​obtained by multiple TDC ranging circuits based on the same echo signal;

[0010] Using one of the TDC ranging circuits as a reference TDC ranging circuit, the deviation value corresponding to each TDC ranging circuit is calculated based on the deviation between the calibration measurement value of other TDC ranging circuits and the calibration measurement value of the reference TDC ranging circuit.

[0011] During laser ranging, the measured values ​​of the target echo signal obtained by each of the TDC ranging circuits are acquired, and the measured values ​​are corrected according to the deviation values ​​corresponding to each of the TDC ranging circuits. The measured distance value is obtained based on the corrected measurement value.

[0012] In another aspect, this application provides a lidar ranging system, including a memory, a controller, and a multi-channel TDC ranging circuit connected to the controller;

[0013] Each TDC ranging circuit includes a comparator and a TDC connected in sequence;

[0014] The memory stores a computer program, and the controller is used to execute the computer program to implement the laser ranging calibration method described in any embodiment of this application.

[0015] The laser ranging calibration method provided in the above embodiments initializes multiple TDC ranging circuits by performing calibration before laser ranging, obtains calibration measurement values ​​obtained by the multiple TDC ranging circuits based on the same echo signal, uses one of the TDC ranging circuits as a reference TDC ranging circuit, calculates the deviation value corresponding to each TDC ranging circuit based on the deviation between the calibration measurement values ​​of the other TDC ranging circuits and the calibration measurement value of the reference TDC ranging circuit, and corrects the measurement value in the subsequent laser ranging process using the deviation value obtained through calibration. Specifically, the deviation value obtained by calibration before ranging is used to eliminate measurement errors generated in the subsequent ranging process. The deviation value obtained during the calibration process is equivalent to the error calibration value obtained under the influence of all uncontrollable factors that affect the inconsistency of ranging results of multi-channel TDC ranging circuits in actual applications. This avoids the need to analyze each influencing factor in actual applications and design specific processing methods. It not only simplifies the implementation scheme, but also improves measurement accuracy and anti-interference ability. In addition, regardless of changes in actual application scenarios or hardware circuits, the updated deviation value that can eliminate measurement errors can be obtained by performing calibration before laser ranging. It has strong applicability to changes in application scenarios and hardware circuits, thus making the solution highly portable.

[0016] In the above embodiments, the lidar ranging system and the corresponding lidar ranging calibration method embodiments are based on the same concept, and thus the corresponding lidar ranging calibration method embodiments have the same technical effect, which will not be repeated here. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of an optional application scenario of the laser ranging calibration method in one embodiment;

[0018] Figure 2 This is a flowchart of a laser ranging calibration method in one embodiment;

[0019] Figure 3 This is a schematic diagram of the structure of a lidar ranging system in one embodiment;

[0020] Figure 4 This is a flowchart of a laser ranging calibration method as an optional specific example. Detailed Implementation

[0021] The technical solution of this application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings. The described embodiments should not be regarded as limitations on this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In the following description, the phrase "some embodiments" refers to a subset of all possible embodiments. It should be noted that "some embodiments" can be the same subset or different subsets of all possible embodiments, and can be combined with each other without conflict.

[0024] In the following description, the terms "first," "second," and "third" are used merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first," "second," and "third" can be interchanged in a specific order or sequence where permissible, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein. It is also understood that the step numbers involved in the various method embodiments do not represent a unique execution order of the steps. Steps that do not involve a necessary sequential relationship for data flow can be executed simultaneously or interchanged in order, so that the embodiments of this application described herein can be implemented in an order other than that illustrated or described herein.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit the implementation of this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The terms "connected" and "linked" should be interpreted broadly, for example, they can refer to a direct connection or an indirect connection through an intermediate medium, or a connection within two elements. Those skilled in the art will understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0026] Please see Figure 1As an optional application scenario of the laser ranging calibration method in this application embodiment, the lidar ranging system includes a memory 11, a controller 12, and a multi-channel TDC ranging circuit 13 connected to the controller 12. The multiple TDC ranging circuits 13 are connected in parallel. Each TDC ranging circuit 13 includes a comparator 131 and a TDC 132 connected in series. In each TDC ranging circuit 13, the negative input of the comparator 131 is used to set the threshold of the comparator 131, and the positive input of the comparator 131 is used to receive the echo signal. One input (start) of the TDC 132 is connected to the output of the corresponding comparator 131, and one input (stop) is connected to the input time signal. The comparator 131 outputs the recognition result of the echo signal to the TDC 132 by comparing the received echo signal with the corresponding threshold. The TDC 132 quantizes the echo time based on the output result of the corresponding comparator 131 and the corresponding input time signal. The memory 11 may store a computer program for implementing the laser ranging calibration method. The controller 12 executes the computer program for the laser ranging calibration method, calculates the deviation value corresponding to each TDC ranging circuit 13 based on the quantization result of TDC 132 through calibration, and corrects the real-time measured value by using the deviation value obtained through calibration in the ranging process, so as to realize the laser ranging calibration method described in the embodiments of this application.

[0027] Please see Figure 2 The laser ranging calibration method provided in one embodiment of this application can be applied to... Figure 1 The laser ranging system shown includes a laser ranging calibration method comprising:

[0028] S101, Initialize the multi-channel TDC ranging circuit; wherein, each of the TDC ranging circuits includes a comparator and a TDC connected in sequence.

[0029] Multiple TDC ranging circuits are connected in parallel. In each TDC ranging circuit, the negative input of the comparator is used to set the comparator threshold, and the positive input is used to receive the echo signal. One input (start) of the TDC is connected to the output of the corresponding comparator, and one input (stop) is connected to the input time signal. Initializing the multiple TDC ranging circuits means setting the operating parameters of all circuit components in each TDC ranging circuit, except for the TDC itself, to the same initial values. When calibrating the laser ranging, the multiple TDC ranging circuits are first initialized. By performing calibration measurements while keeping each TDC ranging circuit initialized, differences caused by various uncontrollable factors such as differences in hardware wiring, individual component differences, and differences in internal controller delays can be measured in practical applications. Calibration can be triggered by the user manually pressing a button or by checking whether preset calibration conditions are met. For example, when the laser radar ranging system is powered on each time, calibration is automatically performed.

[0030] S103, acquire the calibration measurement values ​​obtained by the multiple TDC ranging circuits based on the same echo signal.

[0031] The multi-channel TDC ranging circuit performs measurements based on the same echo signal, and records the output results of the specified electronic components in each TDC ranging circuit as calibration measurement values.

[0032] S105, taking one of the TDC ranging circuits as a reference TDC ranging circuit, calculate the deviation value corresponding to each of the TDC ranging circuits based on the deviation between the calibration measurement value of the other TDC ranging circuits and the calibration measurement value of the reference TDC ranging circuit.

[0033] The reference TDC ranging circuit can be any one of multiple TDC ranging circuits. It can be a pre-designated TDC ranging circuit, or a TDC ranging circuit can be randomly selected during calibration. By calculating the deviation between the calibration measurements of other TDC ranging circuits and the calibration measurements of the reference TDC ranging circuit, the deviation value corresponding to each TDC ranging circuit is calculated. This reveals the differences between the various TDC ranging circuits caused by uncontrollable factors such as differences in hardware routing, individual component variations, and differences in controller internal delays.

[0034] S107, during the laser ranging process, the measured values ​​of the target echo signals obtained by each of the TDC ranging circuits are acquired, and the measured values ​​are corrected according to the deviation values ​​corresponding to each of the TDC ranging circuits. The measured distance value is obtained based on the corrected measurement value.

[0035] After obtaining the deviation values ​​of other TDC ranging circuits relative to the reference TDC ranging circuit through calibration, in the actual laser ranging process, when each TDC ranging circuit obtains the measurement value of the target echo signal according to the actual measurement process, the reference TDC ranging circuit is still used as a reference. The measurement value of each TDC ranging circuit is corrected according to the deviation value corresponding to each TDC ranging circuit. The corrected measurement value is obtained on the basis that the hardware routing, device performance, internal delay of the controller and other influencing factors of the reference TDC ranging circuit are consistent. Thus, the corrected measurement value can also be regarded as the measurement value obtained after eliminating the differences caused by various uncontrollable factors such as differences in hardware routing, individual differences in devices and differences in internal delay of the controller between different TDC ranging circuits.

[0036] The laser ranging calibration method provided in the above embodiments utilizes the deviation value obtained by calibration before ranging to eliminate measurement errors generated during subsequent ranging. The deviation value obtained during calibration is equivalent to the error calibration value obtained under the influence of all uncontrollable factors affecting the inconsistency of ranging results of multi-channel TDC ranging circuits in actual applications. This avoids the need to analyze each influencing factor in actual applications and design specific processing methods, which not only simplifies the implementation scheme but also improves measurement accuracy and anti-interference capability. In addition, regardless of changes in actual application scenarios or hardware circuits, an updated deviation value that can eliminate measurement errors can be obtained by performing calibration before laser ranging. This method has strong applicability to changes in application scenarios and hardware circuits, thus making the solution highly portable.

[0037] In some embodiments, step S101 initializes the multi-channel TDC ranging circuit, including:

[0038] Set the same initial threshold for the comparators in the multi-channel TDC ranging circuit.

[0039] When calibrating laser ranging, the multi-channel TDC ranging circuit is first initialized. By setting the comparators in the multi-channel TDC ranging circuit to the same initial threshold, it is easy to compare the differences in the measurement results of each TDC ranging circuit for the same echo signal, thus revealing the differences in the measurement consistency of each TDC ranging circuit relative to the same reference TDC ranging circuit.

[0040] In some embodiments, in step S105, taking one of the TDC ranging circuits as a reference TDC ranging circuit, the deviation value corresponding to each of the TDC ranging circuits is calculated based on the deviation between the calibration measurement value of the other TDC ranging circuits and the calibration measurement value of the reference TDC ranging circuit, including:

[0041] The calibration measurement values ​​include the output of the comparator obtained by each of the TDC ranging circuits measuring the same echo signal and the digital value of the TDC. Based on the output of the comparator and the digital value of the TDC, the quantization parameters of the TDC in each of the TDC ranging circuits are calculated.

[0042] The first TDC ranging circuit is used as the reference TDC ranging circuit;

[0043] Based on the quantization parameters of the TDC in other TDC ranging circuits and the quantization parameters of the TDC in the reference TDC ranging circuit, calculate the measurement consistency quantization error of the other TDC ranging circuits relative to the reference TDC ranging circuit;

[0044] When the calibration termination condition is met, the deviation value of each TDC ranging circuit is obtained based on the measurement consistency quantization error.

[0045] In this embodiment, when calibrating laser ranging, multiple TDC ranging circuits measure based on the same echo signal, and record the output results of the comparators and TDCs in each TDC ranging circuit as calibration measurement values. Specifically, the comparator compares the received echo signal with a threshold, outputting a high or low level depending on whether the echo signal intensity exceeds the corresponding threshold. The TDC uses the comparator's output as a test signal at one input (stop), and represents the time difference between this signal and the test signal at another input (start) using a digital signal. In each TDC ranging circuit, based on the output result of the corresponding comparator at the corresponding threshold using the same echo signal, the TDC quantizes the time difference between the received echo signal and the test signal at the same input (start) and represents it as a digital signal to obtain the TDC's quantization parameters. In each measurement and calculation, the test signal at the input terminal (start) of the TDC is the start signal of the current laser emission time, and the test signal at the input terminal (stop) is the laser signal emitted back by the object in the target's field of view, which is identified by the comparator based on the intensity of the received echo signal after the current laser emission. By accurately obtaining the laser reflection time through the laser emission time, and using the time difference and laser propagation speed, the distance to the object can be accurately determined. In a multi-channel TDC ranging circuit, the first TDC ranging circuit is selected as the reference TDC ranging circuit. The measurement consistency quantization error among the multiple TDC ranging circuits is determined by calculating the differences in quantization parameters between the other TDC ranging circuits and the reference TDC ranging circuit. This measurement consistency quantization error is understood to be due to differences in hardware routing, device performance, and controller internal delays between the other TDC ranging circuits and the reference TDC ranging circuit. Assuming the influence of various uncontrollable external factors on the measurement accuracy of the reference ranging circuit is A, the deviation of each TDC ranging circuit refers to the deviation caused by the part of the various uncontrollable external factors affecting its measurement accuracy that differs from the reference ranging circuit, using A as the standard. During calibration, the measurement consistency quantization error corresponding to each measurement can be calculated through a certain number of measurements. When the calibration termination condition is met, the deviation of the other TDC ranging circuits relative to the reference TDC ranging circuit is determined by comprehensively considering the multiple measurement results during the calibration process.

[0046] In the above embodiments, by calibration and calculating the deviation of the multi-channel TDC ranging circuits relative to the reference TDC ranging circuit, the measurement difference produced by each TDC ranging circuit in the influence of various uncontrollable external factors on the measurement accuracy is different from that of the reference ranging circuit.

[0047] Optionally, the laser ranging calibration method further includes:

[0048] The calibration cycle is set according to the power-on duration of the lidar ranging system. When a calibration reaches the specified calibration cycle, the calibration termination condition is considered met; and / or,

[0049] Determine whether the number of times the measurement consistency quantification error is measured and calculated within a single calibration has reached the upper limit. If the upper limit is reached, the calibration termination condition is considered met; and / or,

[0050] Determine whether the current measurement consistency quantization error is less than the threshold value. If so, it is considered to meet the calibration termination condition.

[0051] During calibration, the measurement consistency quantification error corresponding to each measurement can be calculated through a certain number of measurements. In a single calibration process, the calibration termination condition may include one or more of the following: Performing a calibration each time the lidar ranging system is powered on; setting the calibration cycle based on the power-on time required for the lidar ranging system to power on; determining whether the calibration termination condition is met based on whether the calibration execution time reaches the calibration cycle; setting an upper limit on the number of measurements performed in a single calibration; determining whether the calibration termination condition is met based on whether the number of measurements and calculations of the measurement consistency quantification error within a single calibration reaches the upper limit; setting a threshold value for the measurement consistency quantification error between each TDC ranging circuit; determining whether the calibration termination condition is met based on whether the measurements and calculations of the measurement consistency quantification error within a single calibration are all within the threshold value. When multiple calibration termination conditions are included, it can be considered that the calibration is complete when any one of the multiple calibration termination conditions is met, and the subsequent lidar ranging process begins.

[0052] In the above embodiments, the setting of one or more calibration termination conditions can control the time required for a single calibration, avoid program errors entering a deadlock waiting state, and ensure the normal use and working efficiency of the lidar ranging system.

[0053] In some embodiments, in step S107, during laser ranging, the measured values ​​of the target echo signals obtained by each of the TDC ranging circuits are acquired, and the measured values ​​are corrected according to the deviation values ​​corresponding to each of the TDC ranging circuits. The measured distance value is obtained based on the corrected measurement values, including:

[0054] During laser ranging, the measurement threshold of the comparator in each TDC ranging circuit is dynamically determined based on the echo characteristics and pre-stored threshold parameters.

[0055] Acquire the measured values ​​of the target echo signal obtained by each of the TDC ranging circuits;

[0056] The measured value is corrected according to the deviation value corresponding to each TDC ranging circuit. The distance is calculated based on the corrected measurement value obtained from each TDC ranging circuit to obtain the measured distance value.

[0057] The lidar ranging system can pre-store the threshold parameters of the comparators in each TDC ranging circuit in its system memory. Upon power-on, each TDC ranging circuit is first calibrated by initializing the threshold values ​​of the comparators in each TDC ranging circuit. After calibration, the deviation values ​​of each TDC ranging circuit relative to the reference TDC ranging circuit are obtained, and then the system enters the laser ranging working state. At this time, the pre-stored threshold parameters of the comparators in each TDC ranging circuit are read from the system memory to dynamically determine the measurement threshold of the comparators in each TDC ranging circuit and execute the following laser ranging process: obtain the measurement values ​​of the target echo signals obtained by each TDC ranging circuit; correct the measurement values ​​according to the deviation values ​​of each TDC ranging circuit; and perform ranging calculation based on the corrected measurement values ​​obtained by each TDC ranging circuit to obtain the measured distance value. The pre-stored threshold parameters of the comparators in each TDC ranging circuit can be a set of fixed parameter values ​​pre-set according to the main application scenarios of the lidar ranging system; or a pre-set threshold parameter determination strategy, such as starting with b and decreasing or increasing the threshold of the comparator of each TDC ranging circuit with c as the gradient; or multiple sets of parameter values ​​set for different application scenario types. When the lidar ranging system is turned on, a matching set of parameter values ​​is read according to the application scenario type selected by the user or the default application scenario type.

[0058] In the above embodiments, multiple threshold parameters of the comparators in each TDC ranging circuit are pre-stored in memory. After calibration, when entering the actual laser ranging working state, the measurement threshold of the comparators in each TDC ranging circuit is dynamically determined according to the pre-stored threshold parameters. Multiple TDC ranging circuits with different measurement thresholds are used to measure the same echo signal. The deviation values ​​of each TDC ranging circuit obtained during the calibration process are used to correct and eliminate errors. Based on the corrected measurement correction value, the most accurate distance of the current echo signal is calculated according to the ranging algorithm. By using the measurement of multiple TDC ranging circuits with different measurement thresholds, the problem of large errors that are easy to exist in single TDC ranging circuits is reduced. Furthermore, the consistency of the output of multiple TDC ranging circuits is maintained through calibration. The multi-channel measurement results are used to avoid noise interference, compensate for echo drift errors, and improve the accuracy of the ranging results.

[0059] In some embodiments, step S107 further includes the following during the laser ranging process:

[0060] After each calibration, during the laser ranging process based on the obtained deviation value, the duration of the current laser ranging is calculated. When the duration reaches a preset threshold, the process returns to the step of initializing the multi-channel TDC ranging circuit.

[0061] The system allows setting calibration trigger conditions. During extended operation of the lidar ranging system, it continuously checks whether these conditions are met to determine if a recalibration is necessary to ensure the accuracy of the current ranging result. For example, when the lidar ranging system is powered on, it first performs a calibration. After calibration, it enters the actual laser ranging state and calculates the duration of the current laser ranging. When the duration reaches a preset threshold, it returns to the initialization step of the multi-channel TDC ranging circuit and performs a recalibration. After calibration, it re-enters the actual laser ranging state. This process can be repeated.

[0062] In the above embodiments, by setting a periodic calibration mechanism, the lidar ranging system automatically performs a calibration once a preset period is reached during long-term operation, thereby addressing the problem of the accuracy of ranging results being affected by changes in the surrounding environment during long-term operation.

[0063] In some embodiments, step S107 further includes the following during the laser ranging process:

[0064] After each calibration, during the laser ranging process based on the obtained deviation value, the temperature of the TDC in each TDC ranging circuit is obtained. If the temperature change of the TDC exceeds the preset temperature, the process returns to the step of initializing the multi-channel TDC ranging circuit.

[0065] The system allows setting calibration trigger conditions. During prolonged operation of the lidar ranging system, it continuously checks whether these conditions are met to determine if a recalibration is necessary to ensure the accuracy of the current ranging results. For example, when the lidar ranging system is powered on, it first performs a calibration. After calibration, it enters the actual laser ranging state and monitors the temperature of the TDC (Transient Control Center). If the TDC temperature exceeds a preset temperature, or if the TDC temperature exceeds a preset temperature within a set time period, it returns to the initialization step of the multi-channel TDC ranging circuit and performs a recalibration. After calibration, it re-enters the actual laser ranging state. This process can be repeated.

[0066] In the above embodiments, by setting up a system based on monitoring the temperature change of the TDC and performing calibration when the temperature change of the TDC exceeds a certain threshold, the system can address the issue of the accuracy of ranging results being affected by changes in the surrounding environment during long-term operation of the lidar ranging system. If the temperature change of the TDC is too large or too fast, it means that the quantization offset of the TDC is large. By automatically performing calibration based on the monitoring results of the TDC temperature, the system can address the issue of the accuracy of ranging results being affected by changes in the surrounding environment during long-term operation.

[0067] In some embodiments, the step of correcting the measured value based on the deviation value corresponding to each of the TDC ranging circuits, and performing distance calculation based on the corrected measured value obtained from each of the TDC ranging circuits to obtain the measured distance value includes:

[0068] The measured value is corrected according to the deviation value corresponding to each TDC ranging circuit. The corrected measurement value obtained after correction by each TDC ranging circuit is used to complete the echo time identification. The time value determined by the echo time identification is substituted into the ranging algorithm to obtain the measured distance value.

[0069] The deviation of each TDC ranging circuit relative to the reference TDC ranging circuit can be positive or negative. Echo time identification refers to using the output results of comparators of each TDC measuring the same echo signal under different measurement thresholds as input. By quantizing the time interval between the start time of the emitted laser and the time of the received echo signal, the reception time of the echo signal is measured. Based on the current measurement results of each TDC's quantized output, the current measurement results of each TDC are corrected according to the deviation values ​​corresponding to each TDC ranging circuit obtained through calibration. Echo time identification is then completed based on the corrected measurement value. In this way, the output of multiple TDC ranging circuits is kept consistent through calibration, noise interference is avoided by using multiple measurement results, echo drift error is compensated, and the accuracy of the ranging results is improved.

[0070] In another aspect of the embodiments of this application, please refer to Figure 3 Furthermore, a lidar ranging system is provided, including a memory, a controller, and a multi-channel TDC ranging circuit connected to the controller; wherein each of the TDC ranging circuits includes a comparator and a TDC connected in sequence; the memory stores a computer program, and the controller is used to execute the computer program to implement the lidar ranging calibration method described in any embodiment of this application.

[0071] Optionally, the controller is an FPGA chip; the memory includes an internal memory, which pre-stores threshold parameters of the comparators in each of the TDC ranging circuits. The pre-stored threshold parameters of the comparators in each TDC ranging circuit are used by the multi-channel TDC ranging circuits to perform measurements at different measurement thresholds during actual laser ranging, reducing the large errors that are common in single-channel TDC ranging circuits. Furthermore, calibration maintains consistency in the outputs of the multi-channel TDC ranging circuits, utilizes multi-channel measurement results to avoid noise interference, compensates for echo drift errors, and improves the accuracy of the ranging results.

[0072] Please refer to the following: Figure 4 In order to gain a more comprehensive understanding of the laser ranging calibration method provided in the embodiments of this application, the laser ranging calibration method is applied to... Figure 3 The laser ranging system shown is used as an example to illustrate an optional method, in which the laser ranging calibration method includes:

[0073] S11, Initialization of the lidar ranging system. The lidar ranging system can reach a stable state, i.e., enter lidar ranging mode, 1 second after power-on. The 1-second power-on period can be used as a calibration cycle to complete the hardware circuit configuration and TDC carry chain calibration within that 1-second period.

[0074] S12, the comparators in the multi-channel TDC ranging circuit are set to the same initial threshold a; in the calibration state, the multi-channel comparators are first set to the same initial threshold a to facilitate the comparison of the measurement results of each TDC and expose the measurement consistency error of each TDC relative to the first TDC.

[0075] S13, Calibration Measurement: The multi-channel TDC ranging circuit measures the outputs of different comparators for the same echo, and calculates the deviation value of each TDC through multiple measurements. In calibration mode, the computer program executing the calibration algorithm collects the measurement consistency error of each TDC relative to the first TDC within a specified number of measurements, and finally calculates the measurement deviation value of each TDC.

[0076] S14, After calibration, the system enters laser ranging mode and reads the corresponding thresholds from system memory to dynamically set the thresholds of the comparators in each TDC ranging circuit. The thresholds read from system memory can be a fixed set of threshold parameters or a set of threshold parameters matched to the echo characteristics. In laser ranging mode, setting different thresholds for each comparator allows the TDC to adapt to measuring echoes under different comparator thresholds, improving measurement accuracy.

[0077] S15, Actual Measurement: Based on the measurement deviations of multiple TDCs, different measurement results of the same echo are corrected and applied to the ranging algorithm to calculate the distance. In actual laser ranging work, the measurement values ​​of each TDC are corrected according to their deviations to ensure consistency in the output of each TDC. Then, the corrected values ​​of each TDC are input into the ranging algorithm to complete time identification, avoid noise interference, compensate for echo drift errors, etc., to obtain a more accurate measured distance value.

[0078] In the above embodiments, the consistency of each TDC output can be automatically corrected through calibration before actual measurement, without the need for extensive prior calibration work. By using a multi-channel TDC ranging circuit, the timing of laser echoes can be determined more flexibly, making it suitable for scenarios with large variations in echo intensity. Furthermore, noise interference can be avoided, further improving measurement accuracy and anti-interference capabilities. The calibration scheme does not depend on any specific TDC hardware circuit, making it highly portable and unaffected by changes in hardware circuits after implementation.

[0079] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A laser ranging calibration method, characterized in that, include: The multi-channel TDC ranging circuit is initialized; wherein each TDC ranging circuit includes a comparator and a TDC connected in sequence; Acquire calibration measurement values ​​obtained by multiple TDC ranging circuits based on laser echo signals reflected from the same target; Using one of the TDC ranging circuits as a reference TDC ranging circuit, the deviation value of each TDC ranging circuit relative to the reference TDC ranging circuit is calculated based on the deviation between the calibration measurement value of the other TDC ranging circuits and the calibration measurement value of the reference TDC ranging circuit. During laser ranging, the measured values ​​of the target echo signal obtained by each TDC ranging circuit are acquired, and the measured values ​​are corrected according to the deviation values ​​corresponding to each TDC ranging circuit. The measured distance value is obtained based on the corrected measurement value. After each calibration, during the laser ranging process based on the obtained deviation value, if at least one of the current laser ranging duration and the temperature change of the TDC in each of the TDC ranging circuits meets the calibration trigger condition, the process returns to the step of initializing the multi-channel TDC ranging circuit; The step of using one of the TDC ranging circuits as a reference TDC ranging circuit, and calculating the deviation value of each TDC ranging circuit relative to the reference TDC ranging circuit based on the deviation between the calibration measurement values ​​of other TDC ranging circuits and the calibration measurement value of the reference TDC ranging circuit, includes: The calibration measurement values ​​include the output of the comparator obtained by each of the TDC ranging circuits measuring the same echo signal and the digital value of the TDC. Based on the output of the comparator and the digital value of the TDC, the quantization parameters of the TDC in each of the TDC ranging circuits are calculated. The first TDC ranging circuit is used as the reference TDC ranging circuit; Based on the quantization parameters of the TDC in other TDC ranging circuits and the quantization parameters of the TDC in the reference TDC ranging circuit, calculate the measurement consistency quantization error of the other TDC ranging circuits relative to the reference TDC ranging circuit; When the calibration termination condition is met, the deviation value of each TDC ranging circuit is obtained based on the measurement consistency quantization error.

2. The laser ranging calibration method as described in claim 1, characterized in that, The initialization of the multi-channel TDC ranging circuit includes: Set the same initial threshold for the comparators in the multi-channel TDC ranging circuit.

3. The laser ranging calibration method as described in claim 1, characterized in that, Also includes: The calibration cycle is set according to the power-on time of the lidar ranging system. When a calibration reaches the calibration cycle, it is considered that the calibration termination condition has been met. And / or, Determine whether the number of times the measurement consistency quantification error is measured and calculated within a single calibration has reached the upper limit. If the upper limit is reached, the calibration termination condition is considered to be met. And / or, Determine whether the current measurement consistency quantization error is less than the threshold value. If so, it is considered to meet the calibration termination condition.

4. The laser ranging calibration method as described in claim 1, characterized in that, In the laser ranging process, the measured values ​​of the target echo signals obtained by each of the TDC ranging circuits are acquired, and the measured values ​​are corrected according to the deviation values ​​corresponding to each TDC ranging circuit. The measured distance value is obtained based on the corrected measurement value, including: During laser ranging, the measurement threshold of the comparator in each TDC ranging circuit is dynamically determined based on the echo characteristics and pre-stored threshold parameters. Acquire the measured values ​​of the target echo signal obtained by each of the TDC ranging circuits; The measured value is corrected according to the deviation value corresponding to each TDC ranging circuit. The distance is calculated based on the corrected measurement value obtained from each TDC ranging circuit to obtain the measured distance value.

5. The laser ranging calibration method as described in claim 4, characterized in that, Determine whether the duration of the current laser ranging meets the conditions for calibration triggering, including: The duration of the current laser ranging is calculated, and when the duration reaches a preset threshold, the conditions for calibration triggering are determined to be met.

6. The laser ranging calibration method as described in claim 4, characterized in that, Determining whether the temperature change of the TDC in each of the TDC ranging circuits meets the calibration triggering conditions includes: The temperature of the TDC in each of the TDC ranging circuits is obtained. If the temperature change of the TDC exceeds the preset temperature, it is determined that the calibration trigger condition is met.

7. The laser ranging calibration method as described in claim 4, characterized in that, The step of correcting the measured value based on the deviation value corresponding to each of the TDC ranging circuits, and calculating the distance based on the corrected measured value obtained from each of the TDC ranging circuits to obtain the measured distance value includes: The measured value is corrected according to the deviation value corresponding to each TDC ranging circuit. The corrected measurement value obtained after correction by each TDC ranging circuit is used to complete the echo time identification. The time value determined by the echo time identification is substituted into the ranging algorithm to obtain the measured distance value.

8. A lidar ranging system, characterized in that, Includes a memory, a controller, and a multi-channel TDC ranging circuit connected to the controller; Each TDC ranging circuit includes a comparator and a TDC connected in sequence; The memory stores a computer program, and the controller is used to execute the computer program to implement the laser ranging calibration method as described in any one of claims 1 to 7.

9. The lidar ranging system as described in claim 8, characterized in that, The controller is an FPGA chip; the memory includes an internal memory, which pre-stores threshold parameters of the comparators in each of the TDC ranging circuits.

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