Laser radar ranging system based on direct flight time

Abstract

The invention discloses a laser radar ranging system based on direct flight time, and the system comprises a laser transmitting module which is used for transmitting a laser pulse signal; the laser receiving module is used for receiving echoes reflected by the target; the data processing module is connected with the output end of the laser receiving module and is used for processing the laser pulse signal and calculating a time difference according to the laser pulse signal; the time sequence control module is connected with the laser emission module and is used for recording a first timestamp of laser pulse signal emission; the recording module is connected with the laser receiving module and is used for starting the laser receiving module and recording a second timestamp for receiving echoes when the first timestamp is recorded; the time calibration module is connected with the data processing module and is used for providing a time calibration signal for the data processing module; and the distance measuring module is used for measuring and calculating the distance according to the time difference. According to the invention, the laser radar ranging of the target can be realized by using the direct time-of-flight method.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar ranging, and particularly relates to a lidar ranging system based on direct time of flight. Background Art

[0002] Lidar ranging, short for laser detection and ranging system, is a system integrating three technologies: laser, global positioning system (GPS), and inertial measurement device. It calculates the distance between the target and the transmitter by emitting a laser signal to the target and receiving the reflected signal, and using parameters such as time difference, phase difference, or frequency change.

[0003] Chinese Patent (CN118283972A) discloses a lidar ranging system, belonging to the technical field of lidar. It includes a lidar body and a tripod for mounting the lidar body. An installation shell is provided at the upper end of the tripod. One end of the protective shell is connected by a hinge with an end cover that covers the transmitting end and the receiving end. A driving component for first driving the end cover to flip open and then driving the protective shell to move and adjust is provided inside the installation shell. Through the mutual cooperation of the elastic rope, the first fixing sleeve, the second fixing sleeve, the connecting block, the moving plate, and the smooth section and the threaded section of the rotating shaft, it is used to switch the connection between the connecting block and the moving plate and the smooth section and the threaded section of the rotating shaft for cooperation. On the one hand, it can realize the opening and closing of the end cover, and on the other hand, it can realize the moving adjustment of the lidar, which is convenient for performing two distance measurements and comparing the difference between the two distance measurement values with the moving adjustment value of the lidar, further improving the reliability of the measurement result. However, although the above lidar ranging system can also complete the measurement of the distance, it does not have a timing control module inside, so it cannot standardize and calibrate the timestamp. During subsequent measurements, the timestamp is prone to confusion and other situations, affecting the final test accuracy. At the same time, it cannot record the timestamps of each point, which is also inconvenient for subsequent record query, and the actual application effect is not good. Summary of the Invention

[0004] Aiming at the deficiencies of the above-mentioned prior art, the technical problem to be solved by the present invention is: to provide a lidar ranging system based on direct time of flight, which can realize lidar ranging of the target by using the direct time of flight method.

[0005] To solve the above technical problem, the first technical solution adopted by the present invention is a lidar ranging system based on direct time of flight, and the system includes:

[0006] A laser emission module for emitting laser pulse signals;

[0007] A laser reception module for receiving the echo reflected from the target;

[0008] A data processing module, connected to the output end of the laser receiving module, for processing laser pulse signals and calculating the time difference according to the laser pulse signals;

[0009] A timing control module, connected to the laser transmitting module, for recording the first timestamp of the emission of the laser pulse signal; connected to the laser receiving module, for turning on the laser receiving module when the first timestamp is recorded and recording the second timestamp of the received echo; connected to the data processing module, for providing a time calibration signal for the data processing module;

[0010] A ranging module, connected to the timing control module, for calculating the distance according to the time difference.

[0011] Furthermore, the system further includes a multi-level encryption module, connected to the output end of the ranging module, for protecting the integrity of the measurement result and preventing the measurement result from being tampered with or stolen.

[0012] Furthermore, the multi-level encryption module includes:

[0013] A data packaging sub-module, for encapsulating ranging data into a standard data packet in a preset format;

[0014] A data packet grouping sub-module, connected to the output end of the data packaging sub-module, for splitting the standard data packet into fixed-size groups according to the requirements of adaptation for transmission and encryption processing;

[0015] An MD5 encryption sub-module, connected to the output end of the data packet grouping sub-module, for encrypting the groups using the MD5 algorithm to generate ciphertext;

[0016] An RAS encryption sub-module, connected to the output end of the MD5 encryption sub-module, for encrypting the ciphertext using the RAS algorithm.

[0017] Furthermore, the laser transmitting module includes:

[0018] A pulse generation sub-module, connected to the timing control module, for generating a laser pulse signal through a laser diode and sending a generation completion signal to the timing control module;

[0019] A pulse modulation sub-module, connected to the output end of the pulse generation sub-module, for adjusting the pulse characteristics of the laser pulse signal according to the ranging requirements;

[0020] A pulse amplification sub-module, connected to the output end of the pulse modulation sub-module, for using an amplifier to enhance the energy of the laser pulse signal, thereby extending the ranging distance.

[0021] Furthermore, the laser receiving module includes:

[0022] A lens sub-module for focusing laser pulse signals;

[0023] A laser filtering sub-module, connected to the output end of the lens sub-module, for filtering ambient light;

[0024] The lens sub-module, the filter sub-module, and the sensor sub-module are all connected to the timing control module. When the timing control module records the first timestamp, it sends start signals to the lens sub-module, the filter sub-module, and the sensor sub-module.

[0025] Further, the laser receiving module further includes:

[0026] A reception adjustment sub-module for dynamically adjusting reception parameters according to requirements;

[0027] A sensor sub-module, connected to the output end of the reception adjustment sub-module, for converting laser pulse signals into electrical signals;

[0028] A positioning sub-module, connected to the output end of the sensor sub-module, for positioning the echo direction and position.

[0029] Further, the sensor sub-module is an avalanche photodiode or a single-photon avalanche photodetector diode.

[0030] Further, the data processing module includes:

[0031] An electrical signal amplification sub-module for amplifying the amplitude of the echo of the laser pulse signal;

[0032] A frame-by-frame reading sub-module for performing segmentation processing on the laser pulse signal according to the period of the laser pulse signal;

[0033] An electrical signal filtering sub-module, connected to the output end of the electrical signal amplification sub-module, for filtering noise and interference in the laser pulse signal;

[0034] An electrical signal digitization sub-module, connected to the output end of the electrical signal filtering sub-module, for converting the laser pulse signal into a digital signal;

[0035] A data calculation sub-module, connected to the output end of the electrical signal digital processing sub-module, for calculating the time difference according to the digital signal and the time calibration signal;

[0036] A data control sub-module for data stream management, data storage management, and data synchronization management inside the data processing module.

[0037] Further, the timing control module includes:

[0038] A clock circuit sub-module for generating clock signals;

[0039] A timing control circuit sub-module for generating control timings of the laser emission module, laser reception module, data processing module, and ranging module;

[0040] A clock circuit monitoring sub-module for monitoring the clock circuit sub-module in real time and calibrating the clock circuit sub-module when the timing of the clock circuit sub-module is inaccurate;

[0041] A timing control circuit monitoring sub-module connected to the output end of the clock circuit monitoring sub-module for monitoring the timing control circuit sub-module in real time when the clock circuit monitoring sub-module monitors that the timing of the clock circuit sub-module is accurate;

[0042] A time reference generation sub-module connected to the output end of the timing control circuit monitoring sub-module for generating a time calibration signal when the timing control circuit monitoring sub-module monitors that there is no abnormality in the clock circuit monitoring sub-module.

[0043] To solve the above technical problems, the second technical solution adopted by the present invention is: to provide a direct time-of-flight lidar ranging method for the lidar ranging system described in any one of the above, the method comprising the following steps:

[0044] S1: Transmit a laser pulse signal through the laser emission module, record the first timestamp when the laser pulse signal occurs by using the timing control module, and turn on the laser reception module;

[0045] S2: Receive the echo reflected from the target through the laser reception module, record the second timestamp by using the timing control module, and generate a time calibration signal;

[0046] S3: Process the laser pulse signal through the data processing module and calculate the time difference according to the time calibration signal;

[0047] S4: Calculate the distance by using the time difference through the ranging module.

[0048] A lidar ranging system based on direct time-of-flight of the present invention has at least the following beneficial effects: 1. Through a multi-level encryption module, multi-level encryption processing is performed on the ranging result, so as to be able to protect the integrity of the measurement result and prevent the measurement result from being tampered with or stolen; 2. Through the timing control module, accurate generation of the time reference signal is ensured, so as to ensure that the emission, reception, data processing, and distance measurement of the laser pulse signal are carried out under strict synchronous timings, thereby avoiding ranging errors caused by time deviation. Description of the Drawings

[0049] The accompanying drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0050] Figure 1 It is a system block diagram of an embodiment of the time-of-flight-based lidar ranging system of the present invention.

[0051] Figure 2 It is a module block diagram of an embodiment of the laser emission module of the present invention.

[0052] Figure 3 It is a module block diagram of an embodiment of the laser receiving module of the present invention.

[0053] Figure 4 It is a module block diagram of an embodiment of the data processing module of the present invention.

[0054] Figure 5 It is a module block diagram of an embodiment of the timing control module of the present invention.

[0055] Figure 6 It is a module block diagram of an embodiment of the multi-level encryption module of the present invention.

[0056] Figure 7 It is a flowchart of an embodiment of the ranging accuracy compensation method of the present invention. Detailed implementation manners

[0057] The present invention will be further described below with reference to the accompanying drawings.

[0058] Please refer to Figure 1 , which is a system block diagram of an embodiment of the time-of-flight-based lidar ranging system of the present invention. This lidar ranging system may specifically include the following modules:

[0059] The laser emission module 100 is used to emit laser pulse signals. The main principle of ordinary laser ranging is to record the time difference between the laser from the transmitter to the target and then back to the receiver after being reflected by the target, and then use the ranging formula to calculate the distance between the transmitter and the target. Therefore, the laser emission module 100 is essential in laser ranging, and this module can generate laser pulse signals.

[0060] Please refer to Figure 2 , this laser emission module 100 may include the following sub-modules:

[0061] The pulse generation sub-module, connected to the timing control module 400, is used to generate a laser pulse signal through a laser diode and send a generation completion signal to the timing control module 400. This solution uses direct time-of-flight laser ranging. Based on the principle of the above-mentioned ordinary laser ranging, timing control is also introduced, which can improve the ranging accuracy. The above-mentioned pulse generation sub-module can generate a laser pulse through a laser diode. At the same time, the pulse generation sub-module can be connected to the timing control module 400, so as to generate the repetition frequency of the pulsed laser based on the system clock. In addition, the pulse generation sub-module can also adjust the parameters of the generated laser pulse, such as wavelength, pulse width, and power, etc.

[0062] The pulse modulation sub-module, connected to the output end of the pulse generation sub-module, is used to adjust the pulse characteristics of the laser pulse signal according to the ranging requirements. After the laser pulse signal is generated by the above-mentioned pulse generation sub-module, the laser pulse signal needs to be modulated by the pulse modulation sub-module. Specifically, the modulation process can include pulse width modulation (dynamically adjusting the width of the laser pulse signal) and amplitude modulation (controlling the peak power of the laser pulse signal to control the power consumption).

[0063] The pulse amplification sub-module, connected to the output end of the pulse modulation sub-module, is used to increase the energy of the laser pulse signal by using an amplifier, so as to extend the ranging distance. Furthermore, in order to increase the energy of the laser pulse signal to improve the ranging distance, the laser pulse signal needs to be amplified in pulse energy by the pulse amplification sub-module. Its specific implementation can be through a semiconductor amplifier, an optical fiber amplifier, or pulse compression.

[0064] The laser receiving module 200 is used to receive the echo reflected from the target. Another essential module in the direct time-of-flight lidar ranging system is the laser receiving module 200. The laser receiving module 200 is used to capture the echo of the laser pulse signal reflected by the target and convert the echo of the laser pulse signal. In addition, the laser receiving module 200 can also be connected to the output end of the laser generating module 100 and perform feedback adjustment on the laser generating module 100 according to the echo signal.

[0065] Please refer to Figure 3 , this laser receiving module 200 may include the following sub-modules:

[0066] The lens sub-module is used to focus the laser pulse signal; this lens sub-module is an optical lens assembly, which can collect and focus the laser pulse signal through the lens.

[0067] The laser filtering sub-module, connected to the output end of the lens sub-module, is used to filter the ambient light; specifically, the laser filtering sub-module can accurately match the wavelength of the laser pulse signal through a filter, so as to filter out other non-laser pulse signal lights.

[0068] The lens sub-module, the filter sub-module, and the sensor sub-module are all connected to the timing control module 400. When the timing control module 400 records the first timestamp, it sends a start signal to the lens sub-module, the filter sub-module, and the sensor sub-module. The timing control module 400 in this solution can not only play the role of timing control, but also be connected to the lens sub-module, the filter sub-module, and the sensor sub-module, and when recording the first timestamp generated by the laser emission module 100 (this first timestamp is the time point when the laser pulse signal occurs), control the lens sub-module, the filter sub-module, and the sensor sub-module to start the detection window, thereby reducing the synchronization error.

[0069] In some embodiments, based on the above lens sub-module, filter sub-module, and sensor sub-module, the laser receiving module 200 may further include the following sub-modules:

[0070] A reception adjustment sub-module for dynamically adjusting reception parameters according to requirements; specifically, it may include adaptive control, dynamic focus adjustment, temperature compensation, and interference suppression. Among them, adaptive control can monitor the echo signal intensity and dynamically adjust the laser diode bias voltage of the laser emission module 100 according to the intensity of the echo signal; dynamic focus adjustment can drive a microelectromechanical (MEMS) actuator to finely adjust the lens focal length based on target distance estimation (such as through previous ranging results) to ensure that the echo is accurately focused on the sensitive area of the sensor; temperature compensation can adjust the breakdown voltage of the laser diode by monitoring the ambient temperature to suppress the gain fluctuation caused by temperature drift; and interference suppression can select whether to enable polarization enhancement according to the change of the environment to suppress noise.

[0071] A sensor sub-module, connected to the output end of the reception adjustment sub-module, for converting the laser pulse signal into an electrical signal; this sensor sub-module is an optoelectronic sensor that can convert the laser pulse signal echo into an electrical signal, facilitating subsequent data extraction and processing.

[0072] A positioning sub-module, connected to the output end of the sensor sub-module, for positioning the echo direction and position. The main function of this positioning sub-module is to accurately analyze the direction and position of the laser pulse signal echo, thereby improving the spatial resolution and multi-target recognition ability. Its specific implementation can be through spot position detection, field of view angle calibration, and multi-target separation. Among them, spot position detection can use a position detector and determine the spot center coordinates according to the photocurrent distribution, and then deduce the angle of the laser pulse echo; field of view angle calibration can map the laser pulse signal echo into the global coordinate system through the angle feedback of the laser galvanometer; and the multi-target recognition ability can use clustering analysis of multi-point echoes of the same laser pulse signal to distinguish the distances and azimuths of different targets.

[0073] In some embodiments, the sensor sub-module is an avalanche photodiode or a single-photon avalanche photodetector.

[0074] The data processing module 300 is connected to the output end of the laser receiving module 200, and is configured to process the laser pulse signal and calculate the time difference according to the laser pulse signal.

[0075] Please refer to Figure 4 , this data processing module 300 may include the following sub-modules:

[0076] The electrical signal amplification sub-module is configured to amplify the amplitude of the echo of the laser pulse signal; through the electrical signal amplification sub-module, the amplitude of the weak electrical signal can be increased, so as to facilitate subsequent signal digitization and time difference calculation. The specific implementation of signal amplification can be achieved by a transimpedance amplifier to amplify the echo electrical signal, and by an operational amplifier to suppress noise, thereby improving the subsequent ranging accuracy.

[0077] The frame-by-frame reading sub-module is configured to perform segmentation processing on the laser pulse signal according to the period of the laser pulse signal; this frame-by-frame reading sub-module determines the period of the laser pulse signal through the time calibration signal provided by the timing control module. For example, N periods can be divided into a data frame (that is, the laser emission module emits N laser pulse signals within a single frame), which is convenient for the construction of the laser pulse signal histogram and the calculation of the ranging distance in the later stage.

[0078] The electrical signal filtering sub-module is connected to the output end of the electrical signal amplification sub-module and is configured to filter the noise and interference in the laser pulse signal; this electrical signal filtering sub-module can use an analog filter to perform frequency screening and filtering on the read laser pulse signal, so as to achieve the effect of filtering the noise and interference in the laser pulse signal.

[0079] The electrical signal digitization sub-module is connected to the output end of the electrical signal filtering sub-module and is configured to convert the laser pulse signal into a digital signal; this electrical signal digitization sub-module converts the analog signal of the laser pulse into a digital signal through an ADC analog-to-digital converter.

[0080] The data calculation sub-module is connected to the output end of the electrical signal digital processing sub-module and is configured to calculate the time difference according to the digital signal and the time calibration signal; furthermore, through this data calculation sub-module, the laser pulse signal that has been filtered and converted into a digital signal can be analyzed and processed. The specific processing method can be to perform a time-of-flight histogram statistics on the N laser pulse signals within the single frame recorded above, and then the time-of-flight of the laser pulse signal can be obtained according to this time-of-flight histogram.

[0081] A data control sub-module for managing the data flow, data storage, and data synchronization within the data processing module. This data control sub-module mainly realizes the management of the data flow, the management of cached data, error detection and correction, and the synchronization and coordination of data.

[0082] A timing control module 400 is connected to the laser emission module 100 and is used to record the first timestamp of the laser pulse signal emission; it is connected to the laser reception module 200 and is used to turn on the laser reception module 200 when the first timestamp is recorded and record the second timestamp of the received echo; it is connected to the data processing module 300 and is used to provide a time calibration signal for the data processing module 300.

[0083] In some embodiments, refer to Figure 5 , this timing control module 400 may include the following sub-modules:

[0084] A clock circuit sub-module for generating a clock signal;

[0085] A timing control circuit sub-module for generating the control timings of the laser emission module 100, the laser reception module 200, the data processing module 300, and the ranging module 500;

[0086] A clock circuit monitoring sub-module for monitoring the clock circuit sub-module in real time and calibrating the clock circuit sub-module when the timing of the clock circuit sub-module is inaccurate;

[0087] A timing control circuit monitoring sub-module is connected to the output end of the clock circuit monitoring sub-module and is used to monitor the timing control circuit sub-module in real time when the clock circuit monitoring sub-module monitors that the timing of the clock circuit sub-module is accurate;

[0088] A time reference generation sub-module is connected to the output end of the timing control circuit monitoring sub-module and is used to generate a time calibration signal when the timing control circuit monitoring sub-module monitors that there is no abnormality in the clock circuit monitoring sub-module.

[0089] Specifically, the timing control module 400, which is an essential module for the direct time-of-flight method, can perform the following specific workflow: continuously monitor the clock circuit to check whether the timing is accurate. If the timing is accurate, proceed to the next step; if not, zero-adjust and debug the clock circuit, then monitor the timing control circuit to check whether each control instruction can operate normally. If it can operate normally, proceed to the next step; if not, correct the timing control circuit, automatically generate a time reference signal. This generated reference signal represents the time origin of timing, record the laser pulse emission time, record the laser pulse reception time, and calculate the difference between the two.

[0090] To protect the integrity of the measurement results and prevent the measurement results from being tampered with or stolen, in this embodiment, the system may further include the following module: a multi-level encryption module 600, connected to the output end of the ranging module 500.

[0091] In some embodiments, please refer to Figure 6 , this multi-level encryption module 600 may include:

[0092] A data packaging sub-module, configured to encapsulate ranging data into a standard data packet in a preset format;

[0093] A data packet grouping sub-module, connected to the output end of the data packaging sub-module, and configured to split the standard data packet into fixed-size groups according to the requirements of adaptation for transmission and encryption processing;

[0094] The MD5 encryption sub-module is connected to the output end of the data packet grouping sub-module and is used to encrypt the said grouping by using the MD5 algorithm to generate ciphertext. The encryption process of the MD5 algorithm is as follows: First, information padding is performed. MD5 uses 512-bit grouping when processing plaintext. Each grouping consists of 16 32-bit sub-groupings. After information encryption, four 32-bit groupings are output. The combination of the 32 groupings is the MD5 value, which is a 128-bit hash value. Since the MD5 output value is a fixed-length value, the remainder of the byte length divided by 512 is equal to 448. Therefore, the information length of the plaintext is extended to n*512 + 448 bits. To complete information padding, several 0-bit positions need to be padded after the information until the above condition is met and then stop. Then, a 64-bit information length suffix is added. At this time, the information byte length is n*512 + 448 + 64 = (n + 1)*512 bits, which is exactly an integer multiple of 512 bits. The MD5 algorithm performs four rounds of cyclic operations and needs to set four 32-bit integer parameters, defined as link variables, which are a = 0x01234567; b = 0x89abcdef; c = 0xfedcba98; d = 0x76543210. Each round of the loop is very similar. A non-linear function transformation is performed on three of a, b, c, and d, and the resulting result is added to the fourth variable to complete the encryption.

[0095] The RAS encryption sub-module is connected to the output end of the MD5 encryption sub-module and is used to encrypt the said ciphertext by using the RAS algorithm. Specifically, the above MD5 encryption is actually a process of converting the ranging result into a fixed hash value. That is to say, the above ciphertext is actually the conversion of the MD5 hash value of the ranging result. Since there is still a vulnerability of collision attack in the simple MD5 conversion, in order to further improve the protection of the ranging result, the ciphertext can be further encrypted. For example, in this solution, the RAS encryption sub-module is adopted, and the above ciphertext can be further encrypted through the RAS encryption algorithm. The specific process of the RAS encryption algorithm is as follows: 1. Generate keys. First, select two large prime numbers p and q, let n = p×q, calculate the Euler's totient function φ(n) = (p - 1)×(q - 1), select an integer e that satisfies 1 < e < φ(n) and e is relatively prime to φ(n), and then find an integer d such that d×e ≡ 1 mod φ(n), indicating that d is the modular multiplicative inverse of e. Then, take (n, e) as the public key and (n, d) as the private key; after obtaining the public key and the private key, use the public key to encrypt the above ciphertext to obtain the second ciphertext c ≡ m e mod n, where m represents the positive integer converted from the above ciphertext and m < n; then the above second ciphertext c can be decrypted according to the private key to obtain m ≡ c d mod n.

[0096] The ranging module is connected to the timing control module and is used to calculate the distance based on the time difference. After obtaining the time difference, this ranging module can calculate the target distance according to the ranging formula.

[0097] Please refer to Figure 7 , which is a flowchart of an implementation manner of the direct time-of-flight lidar ranging method of the present invention. The direct time-of-flight lidar ranging method of this implementation manner is used to implement the direct time-of-flight lidar ranging system described in the above implementation manner. Specifically, the direct time-of-flight lidar ranging method of this implementation manner includes the following steps:

[0098] S1: The laser emission module 100 emits a laser pulse signal, and the timing control module 400 records the first timestamp when the laser pulse signal occurs and turns on the laser receiving module 200;

[0099] S2: The laser receiving module 200 receives the echo reflected from the target, the timing control module 400 records the second timestamp, and generates a time calibration signal;

[0100] S3: The data processing module 300 processes the laser pulse signal and calculates the time difference according to the time calibration signal;

[0101] S4: The ranging module 500 calculates the distance using the time difference.

[0102] The present invention performs multi-level encryption processing on the ranging result through a multi-level encryption module, so as to protect the integrity of the measurement result and prevent the measurement result from being tampered with or stolen; at the same time, it can also ensure the precise generation of the time reference signal through the timing control module, so as to ensure that the emission, reception, data processing, and distance measurement of the laser pulse signal are carried out under a strict synchronous timing, thereby avoiding ranging errors caused by time deviation.

[0103] The above content only expresses the preferred implementation manners of the present invention, and its description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A lidar ranging system based on direct time-of-flight, characterized in that, Comprising: A laser emission module for emitting laser pulse signals; A laser reception module for receiving echoes reflected from a target; A data processing module connected to the output end of the laser reception module, for processing laser pulse signals and calculating a time difference based on the laser pulse signals; A timing control module connected to the laser emission module, for recording a first timestamp of the emission of the laser pulse signal; connected to the laser reception module, for turning on the laser reception module when the first timestamp is recorded and recording a second timestamp of receiving the echo; connected to the data processing module, for providing a time calibration signal to the data processing module; A ranging module connected to the timing control module, for calculating a distance based on the time difference.

2. The time-of-flight based lidar ranging system according to claim 1, wherein This system further includes a multi-level encryption module connected to the output end of the ranging module, for protecting the integrity of the measurement result and preventing the measurement result from being tampered with or stolen.

3. The time-of-flight based lidar ranging system according to claim 2, wherein The multi-level encryption module includes: A data packaging sub-module for encapsulating ranging data into a standard data packet in a preset format; A data packet grouping sub-module connected to the output end of the data packaging sub-module, for splitting the standard data packet into groups of a fixed size according to the requirements of adaptation for transmission and encryption processing; An MD5 encryption sub-module connected to the output end of the data packet grouping sub-module, for encrypting the groups using the MD5 algorithm to generate ciphertext; An RAS encryption sub-module connected to the output end of the MD5 encryption sub-module, for encrypting the ciphertext using the RAS algorithm.

4. The time-of-flight based lidar ranging system according to claim 1, wherein The laser emission module includes: A pulse generation sub-module connected to the timing control module, for generating a laser pulse signal through a laser diode and sending a generation completion signal to the timing control module; A pulse modulation sub-module connected to the output end of the pulse generation sub-module, for adjusting the pulse characteristics of the laser pulse signal according to ranging requirements; A pulse amplification sub-module connected to the output end of the pulse modulation sub-module, for enhancing the energy of the laser pulse signal using an amplifier so as to extend the ranging distance.

5. The time-of-flight based lidar ranging system according to claim 1, wherein The laser reception module includes: A lens sub-module for focusing the laser pulse signal; A laser filtering sub-module connected to the output end of the lens sub-module, for filtering ambient light; The lens sub-module, the filter sub-module, and the sensor sub-module are all connected to the timing control module. When the timing control module records the first timestamp, a start signal is sent to the lens sub-module, the filter sub-module, and the sensor sub-module.

6. The time-of-flight based lidar ranging system according to claim 5, characterized in that, The laser reception module further includes: A reception adjustment sub-module for dynamically adjusting reception parameters according to requirements; A sensor sub-module connected to the output end of the reception adjustment sub-module, for converting the laser pulse signal into an electrical signal; A positioning sub-module connected to the output end of the sensor sub-module, for positioning the direction and position of the echo.

7. The time-of-flight based lidar ranging system according to claim 6, wherein The sensor sub-module is an avalanche photodiode or a single-photon avalanche photodetector.

8. The time-of-flight-based lidar ranging system according to claim 1, characterized in that, The data processing module includes: An electrical signal amplification sub-module for amplifying the amplitude of the echo of the laser pulse signal; A frame-by-frame reading sub-module for segmenting a laser pulse signal according to the period of the laser pulse signal; An electrical signal filtering sub-module connected to the output end of the electrical signal amplification sub-module for filtering noise and interference in the laser pulse signal; An electrical signal digitization sub-module connected to the output end of the electrical signal filtering sub-module for converting the laser pulse signal into a digital signal; A data calculation sub-module connected to the output end of the electrical signal digital processing sub-module for calculating a time difference according to the digital signal and a time calibration signal; A data control sub-module for data stream management, data storage management and data synchronization management inside the data processing module.

9. The time-of-flight based lidar ranging system according to claim 1, wherein The timing control module includes: A clock circuit sub-module for generating a clock signal; A timing control circuit sub-module for generating control timings of the laser emission module, the laser reception module, the data processing module and the ranging module; A clock circuit monitoring sub-module for monitoring the clock circuit sub-module in real time and calibrating the clock circuit sub-module when the clock circuit sub-module has inaccurate timing; A timing control circuit monitoring sub-module connected to the output end of the clock circuit monitoring sub-module for monitoring the timing control circuit sub-module in real time when the clock circuit monitoring sub-module monitors that the clock circuit sub-module has accurate timing; A time reference generation sub-module connected to the output end of the timing control circuit monitoring sub-module for generating a time calibration signal when the timing control circuit monitoring sub-module monitors that the clock circuit monitoring sub-module has no abnormality.

10. A lidar ranging method based on direct time-of-flight, for the lidar ranging system according to any one of claims 1-9, characterized in that, The method includes the following steps: S1: Transmit a laser pulse signal through the laser emission module, record the first timestamp when the laser pulse signal occurs by using the timing control module, and turn on the laser reception module; S2: Receive the echo reflected from the target through the laser reception module, record the second timestamp by using the timing control module, and generate a time calibration signal; S3: Process the laser pulse signal through the data processing module and calculate the time difference according to the time calibration signal; S4: Calculate the distance by using the time difference through the ranging module.

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