CN109597052B - Laser radar echo data extraction method and extraction device - Google Patents
Laser radar echo data extraction method and extraction device Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
The invention provides a laser radar echo data extraction method and device, wherein the device comprises a storage module, an echo ranging processing module, a time measuring module, a control module, a multi-channel triggering module, a laser transmitting module and an echo data extraction module, wherein the storage module is electrically connected with the echo ranging processing module, the echo ranging processing module is connected with the time measuring module, the time measuring module is connected with the multi-channel triggering module, the multi-channel triggering module is connected with the echo data extraction module, and the control device is independently connected with the laser transmitting module. Compared with the prior art, the method has the beneficial technical effects of being easy to realize, having smaller power consumption on the premise of ensuring the measurement precision, and being suitable for a high-performance miniaturized laser radar system.
Description
Technical Field
The invention relates to the technical field of laser radar ranging, in particular to a laser radar echo data extraction method and device.
Background
The basic working principle of the active detection method based on the laser radar in the prior art is that laser is emitted to a target to be detected through the laser radar, the laser irradiates the target to be detected and then is reflected on the surface of the target to be detected, then a receiver receives a laser signal reflected by the target to be detected, and the distance between the laser radar and the target to be detected is obtained after the round trip time of the laser signal is measured. Due to the characteristics of high coherence, directivity, monochromaticity and the like of laser, the laser radar can realize the functions of long-distance and high-precision ranging in an active detection mode, and is widely applied to various aspects such as automatic driving, building three-dimensional modeling, topographic mapping and the like.
In the prior art, a time-of-flight ranging method generally adopted by a laser radar is to continuously transmit light pulses to a target object, then receive a light beam returned from the target object by using a sensor, and obtain the distance from a light source to the target object by detecting the flight round trip time of the light pulses. When the return time of a certain light pulse is obtained, the return time is compared with the sending time of the light pulse to obtain the time when the laser does not strike the target object, and the obtained flight time is multiplied by the light speed to obtain the distance data of the target object from the light source.
In the existing time-of-flight ranging method, the sensor can obtain the distance data of the target object from the light source, and also can obtain the amplitude data of the light pulse from the returned data, and further obtain the reflectivity of the target object through the amplitude data of the light pulse, wherein the reflectivity data can be used as an effective basis for applying analysis to the beard light pulse data.
In the prior art, the amplitude information method is usually adopted to measure the amplitude data of the optical pulse by combining a peak value holding circuit with an analog-to-digital converter, and obviously, the method needs to provide additional circuit resources such as the peak value holding circuit, and in the other prior art, the amplitude data and the time data of the laser radar echo pulse are simultaneously extracted through a high-speed analog-to-digital converter, however, the power consumption of the high-speed analog-to-digital converter with the conversion rate reaching 10G, which is required by practical use, can be greatly reduced, the manufacturing cost is high, the cost for using the high-speed analog-to-digital converter is high, and in addition, the volume of the high-speed analog-to-digital converter is also large, so that the method is not applicable to the miniaturized laser radar.
Because the light intensity of the reflected light pulse received by the laser radar decreases with the increase of the distance between the target object and the transmitting light source under the premise that the peak power of the transmitted laser and other equipment factors such as a receiving lens for receiving the light pulse reflected by the target object remain constant, the amplitude of the received echo electric signal decreases proportionally, and then, when the distance between the target object and the transmitting light source is far, the accuracy of ranging by the time-of-flight ranging method decreases to a large extent due to the decrease of the light intensity and the decrease of the amplitude of the echo electric signal. In long-term practice, two methods of increasing the peak power of the emitted laser and increasing the aperture of the receiving lens have been proposed to solve the above technical problems in the prior art, however, the two methods also have respective disadvantages:
1) In one possible approach, a method of increasing the peak power of the emitted laser may be used to increase the ranging accuracy and extend the detectable distance of the laser radar, however, correspondingly, increasing the peak power of the emitted light source will increase the electrical power consumption of the laser radar correspondingly, which will increase the system load of the whole device of the laser radar apparatus, and in addition, the continuous laser pulse emitted by the excessively high peak power will also cause a certain damage to the vision of the operator, which is not beneficial to continuous measurement or long-term measurement, and obviously, such a method can solve the problem of insufficient accuracy of the laser radar for long-distance ranging, but also limits the applicability of such a method.
2) In another possible approach, increasing the aperture of the receiving lens may be employed to improve the accuracy of ranging. However, increasing the aperture of the receiving lens tends to increase the overall quality of the device, and more importantly, increasing the receiving lens also tends to enhance the background light entering the receiving field of view, which in turn reduces the signal-to-noise ratio of the system.
Aiming at the technical problems, in order to compensate for the performance deterioration in the prior art, a constant ratio discriminator is provided, and a special pulse edge extraction circuit is adopted, but the constant ratio discriminator needs to have extremely strict setting requirements on parameters so as to ensure normal operation, so that the requirements of operators using the equipment measuring team are further improved, and the difficulty of measurement is improved due to the complicated setting process. In view of this, a new measuring method and measuring device should be provided to solve the above technical problems existing in the prior art.
Disclosure of Invention
The invention is made to solve the technical problems, and aims to provide a laser radar echo data extraction method and device which are easy to realize, have smaller power consumption on the premise of ensuring measurement accuracy, and are suitable for a high-performance miniaturized laser radar system.
In order to achieve the above object, the present invention provides a method for extracting laser radar echo data, comprising the steps of: s1, acquiring echo pulse sets under different distances and different reflectivities, normalizing the echo pulse sets, and then acquiring average response echo pulse Plus under different distances and different reflectivities mean The method comprises the steps of carrying out a first treatment on the surface of the S2, according to the average response echo pulse Plus mean Generating simulated echo pulses Plus of different amplitudes sim Setting a threshold value and simulating echo pulse Plus sim Each data in the pulse amplitude-threshold time width table is respectively compared with the threshold value, and a pulse amplitude-threshold time width table is constructed; s3, triggering the real echo in parallel, measuring crossing time data of crossing the threshold value by the real echo, obtaining a trusted time stamp group of triggering time, and subtracting the time of crossing the threshold value by the real echo to obtain a threshold time width group of the current pulse of the real echo; s4, obtaining an amplitude estimation value Amp of the current pulse according to the pulse amplitude-threshold time width table and the threshold time width group est The method comprises the steps of carrying out a first treatment on the surface of the S5, according to the amplitude estimation value Amp est Average response echo pulse Plus mean Set of trusted time stamps for trigger time for current pulse Plus recon Reconstructing to obtain current pulse Plus recon Finally, the current pulse Plus is obtained recon Is used for the time of arrival data of the (c).
Preferably, in said step S1, a high speed comparator or a high is passedThe high-speed comparator or the high-speed analog-digital converter obtains echo pulse sets under different distances and different reflectivities, the sampling rate of the high-speed comparator or the high-speed analog-digital converter is not lower than 10G, and then the average value of echo pulse signals obtained by normalizing the echo pulse sets can be calculated after alignment, so as to obtain the average response echo pulse Plus mean 。
Preferably, in the step S2, the threshold may be multiple paths, and the simulated echo pulse Plus sim By averaging the response echo pulses Plus mean Multiplying the plurality of amplitude coefficients.
Preferably, in the step S4, a least square weighted fitting may be performed on the current threshold time width set and the time width set corresponding to different amplitude values in the pulse amplitude-threshold time width table, and then the amplitude value with the smallest fitting error is used as the amplitude estimation value Amp of the current pulse est 。
Preferably, in said step S5, the current pulse Plus recon In the case of reconstitution, plus can be used recon The time position with the middle amplitude of 0 is taken as the arrival time value of the current echo pulse.
Preferably, in said step S5, said current pulse Plus recon Can satisfy the following conditions: plus (Plus) recon (x)＝Amp est ·Plus mean (x-t), where t is the time offset and x is the arrival time.
Correspondingly, the invention also provides a laser radar echo data extraction device based on the above content, which comprises the following modules:
the device comprises a storage module, an echo ranging processing module, a time measuring module, a control module, a multi-channel triggering module, a laser emitting module and an echo data extracting module, wherein the storage module is electrically connected with the echo ranging processing module, the echo ranging processing module is connected with the time measuring module, the time measuring module is connected with the multi-channel triggering module, the multi-channel triggering module is connected with the echo data extracting module, and a control device is independently connected with the laser emitting module.
Further, the device comprises the following modules:
the laser emission module is used for completing laser emission and comprises an electric control galvanometer and a laser; the control module is used for realizing control logic and controlling the emission of the laser and generating a synchronous signal; an echo receiving module comprising receiving optics and a photoelectric sensor; the multi-channel triggering module comprises a multi-channel voltage threshold setting circuit and a multi-channel voltage comparison circuit; a storage module for pre-storing average response pulse data and the pulse amplitude-threshold time width table; the time measuring module comprises a clock counting circuit and a delay chain high-resolution time interpolation circuit; the echo data extraction module is used for matching and reconstructing the received time stamp group signals and completing extraction of echo time data and amplitude data, wherein when the laser radar echo data extraction device works, laser signals are transmitted to the echo receiving module after being reflected by a target object at the beginning of one measurement, the echo receiving module converts the received laser signals into electric signals and then enters the multi-channel triggering module, the multi-channel voltage threshold setting circuit and the multi-channel voltage comparison circuit in the multi-channel triggering module input the triggering signals of the laser signals into the time measurement module to obtain a trusted time stamp group of triggering time, the trusted time stamp group of the triggering time is calculated and then extracted to obtain a threshold time width group of current pulse, the amplitude of the current pulse is matched with the average response pulse data prestored in the storage module and the pulse amplitude-threshold time width table, and finally the current pulse arrival time stamp information is obtained by utilizing the amplitude, the average response pulse data and the trusted time group of the triggering time.
According to the description and practice, in the method and the device for extracting the laser radar echo data, echo pulse sets under different distances and different reflectivities are obtained in advance through the multipath high-speed comparator and the high-speed analog-to-digital converter, the echo pulse sets are stored in the memory, echo pulse signals obtained after normalization of the echo pulse sets are aligned and then averaged, the average response echo pulse is obtained, simulated echo pulses with different amplitudes are generated according to the average response echo pulse, the simulated echo pulses are compared with the threshold value, a pulse amplitude-threshold time width table is constructed, the pulse amplitude-threshold time width table is also stored in the memory, the real echo is triggered in parallel, the moment that the current real echo passes through the threshold value is measured, a stamp group of the trigger time is obtained, the threshold time width group of the current pulse of the real echo is then estimated, and finally the amplitude estimated value of the current pulse is reconstructed through the amplitude estimated value, so that the arrival time data of the current pulse is obtained. The method and the device for extracting the laser radar echo data have the advantages of improving the applicability of the method and the device for extracting the laser radar echo data, reducing the measuring cost and guaranteeing the safety of measuring staff.
Drawings
FIG. 1 is a flow chart illustrating steps of a lidar echo data extraction method according to an embodiment of the present invention;
FIG. 2 is a schematic diagram showing a frame structure of a laser radar echo data extraction device according to an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating multi-channel triggering of echoes in the lidar echo data extraction method shown in FIG. 1;
FIG. 4 is a schematic diagram showing the echo reception time extracted in the laser radar echo data extraction method shown in FIG. 1;
FIG. 5 is a schematic diagram showing the reconstruction of echoes in the lidar echo data extraction method shown in FIG. 1;
FIG. 6 is a schematic diagram showing calculation of a pulse amplitude estimation percentage error distribution after reconstruction of echoes in the laser radar echo data extraction method shown in FIG. 1;
fig. 7 is a schematic diagram showing a pulse time estimation percentage error distribution derived from the pulse amplitude estimation percentage error distribution shown in fig. 6.
Detailed Description
Embodiments of a method and apparatus for extracting lidar echo data according to the present invention will be described below with reference to the accompanying drawings. Those skilled in the art will recognize that the described embodiments may be modified in various different ways without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive in scope. Furthermore, in the present specification, the drawings are not drawn to scale, and like reference numerals denote like parts.
Fig. 1 is a flowchart showing steps of a lidar echo data extraction method according to an embodiment of the present invention. As shown in fig. 1, the laser radar echo data extraction method described in this embodiment of the invention includes the steps of: s1, acquiring echo pulse sets under different distances and different reflectivities, normalizing the echo pulse sets, and then acquiring average response echo pulse Plus under different distances and different reflectivities mean The method comprises the steps of carrying out a first treatment on the surface of the S2, according to the average response echo pulse Plus mean Generating simulated echo pulses Plus of different amplitudes sim Setting a threshold value and simulating echo pulse Plus sim Each data in the pulse amplitude-threshold time width table is respectively compared with the threshold value, and a pulse amplitude-threshold time width table is constructed; s3, triggering real echoes in parallel, and measuring crossing of the real echoes by crossing the threshold valueThe time data are obtained, a trusted time stamp group of the trigger time is obtained, and then the time of the real echo crossing the threshold value is subtracted to obtain a threshold value time width group of the current pulse of the real echo; s4, obtaining an amplitude estimation value Amp of the current pulse according to the pulse amplitude-threshold time width table and the threshold time width group est The method comprises the steps of carrying out a first treatment on the surface of the S5, according to the amplitude estimation value Amp est Average response echo pulse Plus mean Set of trusted time stamps for trigger time for current pulse Plus recon Reconstructing to obtain current pulse Plus recon Finally, the current pulse Plus is obtained recon Is used for the time of arrival data of the (c).
Specifically, in step S1, echo pulse sets at different distances and at different reflectivities are obtained by a high-speed comparator or a high-speed analog-to-digital converter, the sampling rate of the high-speed comparator or the high-speed analog-to-digital converter is kept at not lower than 10G, and then the echo pulse signals obtained by normalizing the echo pulse sets are aligned and then an average value is calculated to obtain an average response echo pulse Plus mean 。
In step S2 in this embodiment of the invention, a multiple threshold value may be set, emulating an echo pulse Plus sim By averaging the response echo pulses Plus mean Multiplying by a plurality of different amplitude coefficients. To meet production requirements, the number of amplitude coefficients needs to meet the range of echo amplitudes that may be acceptable and the corresponding amplitude resolution.
In step S3, the real echo is triggered by the multi-path high-speed comparator, and the time when the echo pulse crosses the threshold value is measured with high precision to obtain a set of trusted time stamps for the trigger time, which in this embodiment of the invention is labeled as [ TS ] pos (1)，TS neg (1)，…，TS POS (n)，TS POS (n)]. The difference in the same threshold up-down crossing times is then calculated to obtain the threshold time width set of the current pulse, which in this embodiment of the invention is labeled [ TW (1), …, TW (n)]. In addition, in step S3, the multi-way high-speed comparator is pulsedThe threshold value used in the amplitude-threshold time width table is set, and the high-precision measurement can be realized by carrying chain interpolation in a special time measuring chip or a programmable logic device.
In step S4, the least square weighted fitting is performed on the current threshold time width group and the time width group corresponding to different amplitude values in the pulse amplitude-threshold time width table, and then the amplitude value with the smallest fitting error is used as the amplitude estimation value Amp of the current pulse est 。
In step S5, the current echo pulse Plus recon In the case of reconstitution, plus is added recon The time position with the middle amplitude of 0 is taken as the arrival time value of the current echo pulse. And, in step S5, the current pulse Plus recon The following formula is satisfied:
Plus recon (x)＝Amp est ·Plus mean (x-t), where t is the time offset and x is the arrival time.
Correspondingly, the invention also provides a laser radar echo data extraction device based on the method, and fig. 2 is a schematic diagram showing a frame structure of the laser radar echo data extraction device according to one embodiment of the invention. As shown in fig. 2, the laser radar echo data extraction device according to an embodiment of the present invention includes a laser transmitting module 1, a control module 2, an echo receiving module 3, a multi-channel triggering module 4, a storage module 5, a time measuring module 6, and an echo data extraction module 7.
The storage module is electrically connected with the echo ranging processing module, the echo ranging processing module is connected with the time measuring module, the time measuring module is connected with the multi-channel triggering module, the multi-channel triggering module is connected with the echo data extraction module, and the control device is connected with the laser transmitting module independently.
Specifically, the laser emission module 1 is used for completing laser emission and comprises an electric control galvanometer and a laser; the control module 2 realizes control logic and controls the emission of the laser and generates a synchronous signal; the echo receiving module 3 comprises a receiving optical sensor and a photoelectric sensor; the multi-channel triggering module 4 comprises a multi-channel voltage threshold setting circuit and a multi-channel voltage comparison circuit; the storage module 5 is used for pre-storing average response pulse data and a pulse amplitude-threshold time width table; the time measurement module 6 comprises a clock counting circuit and a delay chain high-resolution time interpolation circuit; the echo data extraction module 7 is used for matching and reconstructing the received time stamp group signals and completing extraction of echo time data and amplitude data, wherein when the laser radar echo data extraction device works, when one measurement starts, laser signals are transmitted to the echo receiving module 3 after being reflected by a target object, the received laser signals are converted into electric signals by the echo receiving module 3 and then enter the multi-channel triggering module 4, a multi-channel voltage threshold setting circuit and a multi-channel voltage comparison circuit in the multi-channel triggering module 4 are used for inputting the triggering signals of the laser signals into the time measurement module 6 to obtain a trusted time stamp group of the triggering time, the trusted time stamp group of the triggering time is calculated and extracted to obtain a threshold time width group of the current pulse, the amplitude of the current pulse is estimated by utilizing the average response pulse data and the pulse amplitude-threshold time width table in the storage module 5, the current pulse is reconstructed by utilizing the amplitude, the average response pulse data and the trusted time stamp group of the triggering time of the current pulse, and finally the arrival time information of the current pulse is obtained.
Fig. 3 is a schematic diagram showing multi-channel triggering of echoes in the method for extracting laser radar echo data shown in fig. 1. Fig. 4 is a schematic diagram showing an echo receiving time extracted in the laser radar echo data extraction method shown in fig. 1. Fig. 5 is a schematic diagram showing reconstruction of echoes in the lidar echo data extraction method shown in fig. 1. As shown in fig. 3 to 5, in one application of the method for extracting laser radar echo data according to the embodiment of the present invention, a laser radar is used for ranging, a silicon photomultiplier is used as a photodetector, and the size of a photosensitive element is 6mm x 6mm. The laser uses 905nm and peak power 1W. The echo signal amplitude at about 50cm was measured by the peak hold circuit to be 1v. Echo pulses at 8820 different reflectivities were then acquired using a high sampling rate oscilloscope, the sampling rate was kept at 25GSPS, and the average response pulse was calculated with reference to fig. 3.
And then 8 paths of threshold values are adopted for pulse triggering, and the triggering threshold values of each path are respectively set to be [0.02,0.04,0.1,0.2,0.3,0.4,0.5 and 0.6] V. The simulated triggering is shown in fig. 4 using simulated pulses with average response pulses in the range of 50mv to 1v, resulting in a pulse amplitude-threshold time width table.
Setting eight paths of high-speed comparators to trigger real echoes, setting 8 paths of thresholds according to the above, and obtaining a trigger threshold group after receiving echo signals. And recording the triggering time of the echo while receiving the echo to obtain a triggering time stamp group, and calculating by using the triggering time stamp group to obtain a threshold time width group.
As shown in fig. 5, the amplitude value of the current pulse is estimated by matching the data of the threshold time width group in the pulse amplitude-threshold time width table, and then the amplitude estimated value, the average response pulse and the trigger time stamp group are calculated to reconstruct the current pulse. As shown in fig. 6, 8000 pulses are obtained through the post-processing of the above process, the amplitude data and the time data of the pulses are extracted, and compared with the real pulses, the pulse amplitude estimation percentage error distribution is calculated, as shown in fig. 7, the average amplitude estimation percentage error is 2.9% through the pulse amplitude estimation percentage error distribution shown in fig. 6, and then the average time extraction error is calculated to be 101ps.
According to the description and practice, in the method and the device for extracting laser radar echo data, echo pulse sets under different distances and different reflectivities are obtained in advance through the multipath high-speed comparator and the high-speed analog-to-digital converter, the echo pulse sets are stored in the memory, echo pulse signals obtained after normalization of the echo pulse sets are aligned and then the mean value is calculated, average response echo pulses are obtained, simulated echo pulses with different amplitudes are generated according to the average response echo pulses, then the simulated echo pulses are compared with the threshold value, a pulse amplitude-threshold time width table is constructed, the pulse amplitude-threshold time width table is also stored in the memory, then the real echo is triggered in parallel, the moment that the current real echo passes through the threshold value is measured, a stamp group of the trigger time is obtained, then the threshold time width group of the current pulse of the real echo is obtained, and then the amplitude estimation value of the current pulse is estimated, and finally the current pulse is reconstructed through the amplitude estimation value, so that the arrival time data of the current pulse is obtained. The measuring cost is reduced, and the safety of measuring personnel is also ensured.
The method and apparatus for extracting lidar echo data according to the present invention are described above by way of example with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that various modifications may be made to the lidar echo data extraction method and apparatus of the present invention as set forth above without departing from the scope of the present invention. Accordingly, the scope of the invention should be determined from the following claims.
Claims (3)
1. A method for extracting laser radar echo data, which is characterized by comprising the following steps:
s1, acquiring echo pulse sets under different distances and different reflectivities, normalizing the echo pulse sets, and then acquiring average response echo pulse Plus under different distances and different reflectivities mean ；
S2, according to the average response echo pulse Plus mean Generating simulated echo pulses Plus of different amplitudes sim Setting a threshold value and simulating echo pulse Plus sim Each data in the data storage unit is respectively carried out with the threshold valueComparing and constructing a pulse amplitude-threshold time width table, wherein in the step S2, the threshold is multiple paths, and the simulation echo pulse Plus sim By averaging the response echo pulses Plus mean Multiplying a plurality of amplitude coefficients to obtain;
s3, triggering the real echo in parallel, measuring crossing time data of crossing the threshold value by the real echo, obtaining a trusted time stamp group of triggering time, and subtracting the time of crossing the threshold value by the real echo to obtain a threshold time width group of the current pulse of the real echo;
s4, obtaining an amplitude estimation value Amp of the current pulse according to the pulse amplitude-threshold time width table and the threshold time width group est ；
S5, according to the amplitude estimation value Amp est Average response echo pulse Plus mean Set of trusted time stamps for trigger time for current pulse Plus recon Reconstructing to obtain current pulse Plus recon Finally, the current pulse Plus is obtained recon In said step S5, the current pulse Plus recon In the case of reconstitution, plus is added recon The time position with the medium amplitude of 0 is taken as the arrival time value of the current echo pulse, and the current pulse Plus recon The method meets the following conditions:
Plus recon (x)＝Amp est ·Plus mean (x-t), where t is the time offset and x is the arrival time.
2. The method for extracting echo data from laser radar according to claim 1, wherein in the step S1, echo pulse sets at different distances and different reflectivities are obtained by a high-speed comparator or a high-speed analog-to-digital converter, the sampling rate of the high-speed comparator or the high-speed analog-to-digital converter is not lower than 10G, and then the echo pulse signals obtained by normalizing the echo pulse sets are aligned and then the average value is calculated to obtain the average response echo pulse Plus mean 。
3. As in claim 1In the step S4, a least square weighted fitting is performed on a current threshold time width set and a time width set corresponding to different amplitude values in a pulse amplitude-threshold time width table, and then the amplitude value with the smallest fitting error is used as an amplitude estimation value Amp of the current pulse est 。
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| CN110187356B (en) * | 2019-06-14 | 2021-07-09 | 中国科学技术大学 | Remote super-resolution single photon imaging reconstruction method |
| CN110488241A (en) * | 2019-08-26 | 2019-11-22 | 苏州迈斯泰克达光电科技有限公司 | A kind of laser radar multiple echo information extraction element and method |
| CN111025260B (en) * | 2019-10-18 | 2023-07-07 | 西安天谛伟创探测技术有限公司 | Target distance judging method |
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