A lidar echo processing system and method

Abstract

The present invention relates to a lidar echo processing system and method. The lidar echo signal processing system includes: a transmitting module for emitting pulsed laser, including a laser driving circuit, a laser, and a beam shaping module; a receiving module for receiving reflected light, including a receiving optical lens and a photodetector; a sampling module for sampling and analyzing, including a voltage threshold setting circuit and a voltage comparison circuit; and a main control and signal processing module, which is used to provide a trigger signal for the laser transmitting module, collect the echo time width signal, distinguish dark count noise and real echo signals, and perform time-of-flight measurement. Thus, by adding a screening mechanism during the echo signal processing, the present invention filters out noise, and can reduce the false alarm rate without increasing the system power consumption and the lens aperture.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar, and particularly to a lidar echo processing system and method. Background Art

[0002] Lidar is an active detection means for spatial information. Its basic working principle is similar to that of traditional radar: lidar emits laser towards the target to be detected, and then the receiver collects the optical signal reflected by the target. By measuring the round-trip time of the transmitted signal, the distance to the target is determined. Due to the advantages of high coherence, directionality, monochromaticity, etc. of laser, lidar systems can achieve long-distance and high-precision ranging functions and have been applied in many fields such as autonomous driving, three-dimensional building modeling, topographic mapping, rendezvous and docking, etc.

[0003] Lidar often uses the pulsed time-of-flight method to extract distance signals. Its basic principle is to emit a laser pulse beam with short duration and high peak power towards the target. The light reflected by the target is collected by the receiving lens of the lidar, and its arrival time information is recorded. By subtracting it from the time of sending the pulse, the round-trip time of the laser pulse to the target point is obtained, and then the target distance information is calculated from the speed of light.

[0004] When other factors such as the peak power of the emitted laser and the receiving lens remain unchanged, the intensity of the reflected light received by the lidar will rapidly decrease as the target distance increases, resulting in a decrease in the signal-to-noise ratio, which in turn affects the ranging accuracy and increases the false alarm rate and missed alarm rate. To compensate for this performance degradation, generally, increasing the peak power of the emitted laser and the aperture of the receiving lens are used to make up for it. However, increasing the peak power of the laser will cause the power consumption to increase exponentially accordingly, increasing the system burden, and the excessive peak power of the laser is likely to cause harm to the human eye, limiting the application of lidar; while increasing the aperture of the receiving lens not only increases the weight of the device, but also enhances the background light entering the receiving field of view, reducing the signal-to-noise ratio.

[0005] Therefore, it is necessary to improve the existing technology to overcome the above technical defects. Summary of the Invention

[0006] The purpose of the present invention is to provide a lidar echo processing system and method that can solve the problem of dark count noise interference of the detector itself in the echo signal and effectively reduce the false alarm rate.

[0007] To achieve the foregoing purpose, the present invention provides a lidar echo signal processing system, and the lidar echo signal processing system includes:

[0008] A transmitting module for emitting pulsed laser, including a laser driving circuit, a laser, and a beam shaping module;

[0009] A receiving module for receiving reflected light, including a receiving optical lens and a photodetector;

[0010] A sampling module for performing sampling analysis, including a voltage threshold setting circuit and a voltage comparison circuit; and

[0011] A main control and signal processing module, which is used to provide a trigger signal for the laser emission module, collect the echo time width signal, distinguish the dark count noise and the real echo signal, and perform time-of-flight measurement.

[0012] As a further improvement of the present invention, the working process of the lidar echo signal processing system includes:

[0013] At the beginning of a measurement, the main control and signal processing module generates a trigger signal to the emission module, driving the emission module to emit laser light. The laser light is shaped by the beam shaping module into a pulsed laser with directivity and is emitted to the surface of the target point. The reflected light after being reflected by the target is transmitted by the optical lens of the receiving module to the photodetector, converted into an electrical signal, and then input into the voltage comparison circuit together with several preset voltage thresholds. The voltage comparison circuit will output a positive flip signal and a negative flip signal respectively at the moment when the voltage amplitude of the signal is greater than or less than a certain voltage threshold. According to the time difference between the positive and negative flip signals, it is judged whether the signal is a dark count noise signal or a real echo signal. If it is a real echo signal, the difference between the positive flip moment and the laser emission trigger signal generation moment is obtained to get the pulse flight time, and then it is converted into the target distance. If it is a dark count noise signal, it will not be processed, so as to achieve the purpose of eliminating false counts and reducing the false alarm rate.

[0014] As a further improvement of the present invention, the laser driving circuit drives the pulsed laser to emit laser light, which is shaped by the beam shaping module into a beam with a small divergence angle and then irradiated to the surface of the target point.

[0015] As a further improvement of the present invention, the method for distinguishing dark count noise includes the method of discrimination according to the proportional relationship of the flip duration corresponding to multiple voltage thresholds.

[0016] As a further improvement of the present invention, the method for distinguishing dark count noise includes the method of extracting shape parameters after fitting the flip moment to perform discrimination according to the inherent time domain information of the dark count pulse.

[0017] As a further improvement of the present invention, the main control and signal processing module is a separate main control module and signal processing module, or an integrated module.

[0018] The present invention also adopts the following technical solution:

[0019] A lidar echo signal processing method, including:

[0020] Step 1: The lidar emits a laser pulse signal to the target to be detected;

[0021] Step 2: The receiving lens receives the optical pulse signal reflected by the target to be detected and transmits it to the photodetector;

[0022] Step 3: The photodetector converts the optical pulse signal into an electrical pulse signal;

[0023] Step 4: The backend processing circuit sets several voltage thresholds and acquires the time width information of the electrical pulse signal in the echo detection channel exceeding the corresponding voltage thresholds;

[0024] Step 5: According to the time width information, distinguish whether the signal is a noise signal generated by the detector dark count or a real echo signal;

[0025] Step 6: If it is a noise signal, no subsequent processing is performed. If it is a real echo signal, the difference between its arrival time and the emission time is taken as the pulse flight time, and then the target distance is solved according to the speed of light.

[0026] As a further improvement of the present invention, Step 1 includes that the laser driving circuit drives the pulsed laser to emit laser, and after being shaped into a beam with a small divergence angle by the beam shaping module, it irradiates the surface of the target point.

[0027] As a further improvement of the present invention, the method for distinguishing the dark count noise signal and the real signal includes the method of discrimination according to the duration and proportional relationship of the corresponding flip signals of multiple voltage thresholds.

[0028] As a further improvement of the present invention, the method for distinguishing the dark count noise signal and the real signal includes the method of extracting the shape parameters after fitting the flip moment to perform discrimination according to the inherent time domain information of the dark count pulse.

[0029] Advantages of the present invention: The present invention filters out noise by adding a screening mechanism in the echo signal processing process. With such a setting, the false alarm rate can be reduced without increasing the system power consumption and the lens aperture. Brief Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the system implementation framework of the present invention;

[0031] Figure 2 It is a schematic diagram of the principle of the system of the present invention for filtering out dark counts. Detailed Embodiments

[0032] The present invention will be described in detail below in conjunction with the specific embodiments shown in the drawings.

[0033] It should be noted that: Unless otherwise specifically stated, the relative arrangements, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present invention.

[0034] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way a limitation on the present invention or its application or use.

[0035] Technologies and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies and devices should be regarded as part of the specification.

[0036] In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Accordingly, other examples of the exemplary embodiments may have different values.

[0037] It should be noted that: Similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it is not necessary to discuss it further in subsequent figures.

[0038] The lidar echo signal processing system of the present invention, the lidar echo signal processing system includes:

[0039] A transmitting module for emitting pulsed laser, including a laser driving circuit 11, a laser 12, and a beam shaping module 13;

[0040] A receiving module for receiving reflected light, including a receiving optical lens 21 and a photodetector 22;

[0041] A sampling module for performing sampling analysis, including a voltage threshold setting circuit 31 and a voltage comparison circuit 32; and

[0042] A main control and signal processing module 4, the main control and signal processing module 4 is used to provide a trigger signal for the laser transmitting module, collect the echo time width signal, discriminate the dark count noise and the real echo signal, and perform time-of-flight measurement.

[0043] The working process of the lidar echo signal processing system includes:

[0044] At the start of a measurement, the main control and signal processing module 4 generates a trigger signal to the transmitting module, driving the transmitting module to emit a laser. The laser passes through the beam shaping module 13 and becomes a pulsed laser with good directivity, which is emitted onto the surface of the target point. The reflected light after being reflected by the target is transmitted by the optical lens 21 of the receiving module to the photodetector 22. After being converted into an electrical signal, it is input together with several preset voltage thresholds into the voltage comparison circuit 32. When the voltage amplitude of the signal is greater than or less than a certain voltage threshold, the voltage comparison circuit 32 will respectively output a positive flip and a negative flip signal. According to the time difference between the positive and negative flip signals, it is determined whether the signal is a dark count noise signal or a real echo signal. If it is a real echo signal, the difference between the positive flip moment and the laser emission trigger signal generation moment is obtained to get the pulse flight time, and then the target distance is calculated. If it is a dark count noise signal, no processing is performed, so as to achieve the purpose of eliminating false counts and reducing the false alarm rate.

[0045] Among them, the laser driving circuit 11 drives the pulsed laser 12 to emit a laser. After being shaped by the beam shaping module 13 into a beam with a small divergence angle, it is irradiated onto the surface of the target point.

[0046] The present invention also provides a method for processing lidar echo signals, including:

[0047] Step 1: The lidar emits a laser pulse signal to the target 5 to be detected;

[0048] Step 2: The receiving lens receives the optical signal reflected by the target 5 to be detected and transmits it to the photodetector 22;

[0049] Step 3: The photodetector 22 converts the optical signal into an electrical signal;

[0050] Step 4: The backend processing circuit sets several voltage thresholds and acquires the time width information of the signal in the echo detection channel exceeding the corresponding voltage threshold;

[0051] Step 5: According to the time width information, it is distinguished whether the signal is a noise signal generated by the detector dark count or a real echo signal;

[0052] Step 6: If it is a noise signal, no subsequent processing is performed. If it is a real echo signal, the difference between its arrival time and the emission time is taken as the pulse flight time, and then the target distance is solved according to the speed of light.

[0053] Since the time-domain characteristics of the electrical pulse signal generated by the internal dark count of the photodetector 22 are known, it can be used to distinguish whether the detected pulse signal is an interference signal generated by the detector dark count or a real reflected light pulse signal received by the lidar, thereby improving the signal-to-noise ratio and reducing the false alarm rate.

[0054] The method for distinguishing dark count noise in the present invention can be based on the proportional relationship between the flip durations corresponding to multiple voltage thresholds, or can be any method for discrimination based on the inherent time-domain information of dark count pulses, such as extracting shape parameters after fitting the flip moments.

[0055] Compared with the prior art, the present invention has the following advantages:

[0056] On the one hand, it has the advantage of small system overhead: By using digital signal processing methods to distinguish dark count noise and real echo signals, only existing hardware circuits such as voltage comparators and time measurements in the ranging scheme for pulse flight time measurement are required to achieve the effect of reducing the false alarm rate, without additional weight and power consumption overhead.

[0057] On the other hand, it has the advantage of good real-time performance: In this method, the lidar echo detection channel is in a continuous working mode, and any echo trigger can be discriminated and processed in real time, with good real-time performance, and is suitable for lidar systems with high scanning rates.

[0058] It should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments understandable by those skilled in the art.

[0059] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the spirit of the present invention's technology should be included in the protection scope of the present invention.

Claims

1. A lidar echo signal processing system, characterized in that: The lidar echo signal processing system includes: A transmitting module for emitting pulsed laser light, including a laser driving circuit, a laser, and a beam shaping module; A receiving module for receiving reflected light, including a receiving optical lens and a photodetector; A sampling module for performing sampling analysis, including a voltage threshold setting circuit and a voltage comparison circuit; and a main control and signal processing module, which is used to provide a trigger signal for the laser transmitting module, collect the echo time width signal, distinguish dark count noise and real echo signals, and perform time-of-flight measurement; the working process of the lidar echo signal processing system includes: At the start of a measurement, the main control and signal processing module generates a trigger signal to the transmitting module, driving the transmitting module to emit laser light. After being shaped by the beam shaping module, the laser light becomes a pulsed laser with directivity and is emitted onto the surface of the target point. The reflected light after reflection by the target is transmitted by the optical lens of the receiving module to the photodetector, converted into an electrical signal, and then input into the voltage comparison circuit together with several preset voltage thresholds. The voltage comparison circuit will output positive and negative flip signals respectively at the moment when the voltage amplitude of the signal is greater than or less than a certain voltage threshold among the several voltage thresholds. According to the time difference between the positive and negative flip signals, it is judged whether the signal is a dark count noise signal or a real echo signal. If it is a real echo signal, the difference between the positive flip moment and the laser emission trigger signal generation moment is obtained to get the pulse flight time, and then the target distance is calculated. If it is a dark count noise signal, no processing is performed to achieve the purpose of eliminating false counts and reducing the false alarm rate.

2. The lidar echo signal processing system according to claim 1, characterized in that: Among them, the laser driving circuit drives the pulsed laser to emit laser light, which is shaped by the beam shaping module into a beam with a small divergence angle and then irradiated onto the surface of the target point.

3. The lidar echo signal processing system according to claim 1, characterized in that: The method for distinguishing dark count noise includes the method of discrimination according to the proportional relationship of the flip duration corresponding to multiple voltage thresholds.

4. The lidar echo signal processing system according to claim 1, characterized in that: The method for distinguishing dark count noise includes the method of discrimination by fitting the flip moment and extracting shape parameters to identify according to the inherent time-domain information of the dark count pulse.

5. The lidar echo signal processing system according to claim 1, characterized in that: The main control and signal processing module is a separate main control module and signal processing module, or an integrated module.

6. A lidar echo signal processing method, comprising: Step 1: The lidar emits a laser pulse signal to the target to be detected; Step 2: The receiving lens receives the light pulse signal reflected by the target to be detected and transmits it to the photodetector; Step 3: The photodetector converts the light pulse signal into an electrical pulse signal; Step 4: The backend processing circuit sets several voltage thresholds and collects the time width information of the electrical pulse signal in the echo detection channel exceeding the corresponding voltage thresholds; Step 5: According to the time width information, distinguish whether the signal is a noise signal generated by detector dark count or a real echo signal; Step 6: If it is a noise signal, no subsequent processing is performed. If it is a real echo signal, the difference between the arrival time and the emission time is obtained as the pulse flight time, and then the target distance is calculated according to the speed of light.

7. The lidar echo signal processing method according to claim 6, characterized in that: Among them, Step 1 includes the laser driving circuit driving the pulsed laser to emit laser light, which is shaped by the beam shaping module into a beam with a small divergence angle and then irradiated onto the surface of the target point.

8. The lidar echo signal processing method according to claim 6, characterized in that: The method for distinguishing the dark count noise signal and the real signal includes the method of discrimination according to the duration and proportional relationship of the flip signals corresponding to multiple voltage thresholds.

9. The lidar echo signal processing method according to claim 6, characterized in that: The method for distinguishing the dark count noise signal and the real signal includes the method of discrimination according to the inherent time domain information of the dark count pulse by extracting the shape parameters after fitting the flip moment.

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