CN118938174B - ToF and FMCW laser radar panoramic scanning composite detection method and device - Google Patents
ToF and FMCW laser radar panoramic scanning composite detection method and device Download PDFInfo
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- CN118938174B CN118938174B CN202411429200.9A CN202411429200A CN118938174B CN 118938174 B CN118938174 B CN 118938174B CN 202411429200 A CN202411429200 A CN 202411429200A CN 118938174 B CN118938174 B CN 118938174B
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
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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
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/50—Systems of measurement based on relative movement of target
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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
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/50—Systems of measurement based on relative movement of target
- G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
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Abstract
The invention discloses a method and a device for comprehensively detecting TOF and FMCW laser radars, which comprise a TOF laser radar module, an FMCW laser radar module, a spectroscope module, a peripherally scanning module and a signal processing module, wherein the spectroscope module is respectively connected with the TOF laser radar module and the FMCW laser radar module and is used for emitting photosynthetic beams and receiving optical beam splitting, the peripherally scanning module is connected with the spectroscope module and is used for emitting and receiving laser and realizing non-image peripherally scanning, the signal processing module is connected with the TOF laser radar module and the FMCW laser radar module and is used for processing the acquired target receiving light beams and realizing parallel synchronous measurement of distance and vector speed between the laser radar device and a target. The invention realizes the horizontal 360-degree periscope composite detection of the ToF and FMCW laser radar, can acquire high-resolution point cloud data in a two-dimensional direction, and realizes accurate synchronous ranging and speed measurement.
Description
Technical Field
The invention relates to the technical field of laser radars, in particular to a method and a device for detecting a laser radar, and particularly relates to a method and a device for comprehensively scanning and compositely detecting a ToF and FMCW laser radar.
Background
The ToF laser radar refers to a direct Time of Flight (ToF) laser radar, and obtains the distance information of a target object by directly measuring the round trip Time difference of emitted laser pulses and calculating based on the propagation speed of light in the air. The FMCW laser radar refers to a frequency modulation continuous wave (Frequency Modulated Continuous Wave, FMCW) laser radar, adopts a coherent detection technology, carries out linear modulation on the light frequency of emitted laser, generates beat frequency signals through interference between received light signals and local oscillator light, thereby indirectly obtaining flight time and calculating the distance of a target object, and simultaneously can measure the instantaneous radial vector speed of the target object according to Doppler frequency shift information.
The scanning type three-dimensional imaging laser radar is formed by a laser incoherent or coherent ranging system and a light beam scanning device, and is a relatively mature three-dimensional imaging laser radar technology developed at present. The scanning type three-dimensional imaging laser radar is required to realize the rapid measurement of each point, the scanning device controls the laser radar optical axis to point to different directions, the distances of each point on a target object are sequentially measured, and meanwhile, the azimuth angle-pitch angle of the light beam pointing direction is recorded, so that the distance-azimuth angle-pitch angle image of the target object can be obtained. On one hand, in order to realize non-blind area detection on the periphery of a laser radar platform and ensure that a remote target can be effectively resolved, the laser radar requires a horizontal view angle and a vertical view angle which are as large as possible, and a region of interest must have a sufficiently high horizontal angle resolution and a sufficiently high vertical angle resolution, and on the other hand, the laser radar platform needs to realize synchronous ranging and speed measurement in a region of interest (ROI) and has complete anti-interference capability.
Chip-level packaging, image-level point cloud resolution, instantaneous speed of directly acquired point clouds, and complete immunity to interference are considered typical features of future vehicle-mounted lidars. But neither ToF nor FMCW is fully available at present. The advantages of ToF and FMCW are highlighted, the composite detection of ToF and FMCW is realized, and the method is a laser radar technology route with high cost performance.
In practical applications, some lidars require a 360 ° horizontal angle of view and an angular vertical angle of view. The horizontal mechanical rotation and vertical linear array receiving and transmitting mode is a typical representation of the 360-degree periscope scanning mode, wherein the motor drives the optical machine structure of the upper bin to integrally rotate for 360 degrees in the horizontal direction to obtain a 360-degree horizontal view field, the linear arrays of the laser emitting module and the detection module are arranged in a matching mode in the vertical direction to form multi-line scanning in the vertical direction, and a specific included angle exists between each scanning wire harness, so that uniform or non-uniform angle coverage to a certain extent in the vertical direction is realized, and the angle resolution in the vertical direction is realized. The scanning mode realizes solid scanning in one dimension, can reduce the movement quantity of one dimension, can realize two-dimensional scanning of a target object only by mechanical scanning along the other dimension, greatly improves the scanning efficiency of a system, is the most widely applied and mature laser radar panoramic scanning scheme at present, and is typically represented by Panda128, OT128 and fast-focusing Ruby Plus of He's science and technology. However, the scheme needs to precisely align the transmitting optical module and the receiving optical module of each channel, the crosstalk between different ranging channels ensures that the assembly and installation precision requirement is quite high, the moment of inertia of the upper bin is large, the wireless power supply and wireless communication between the upper bin and the lower bin are also solved, the structure is complex, the size is large, the power consumption is high, the cost is high, and the requirements on heat dissipation, the process and the like are also quite high. Therefore, a 45 ° turning mirror scanning method capable of reducing the moment of inertia has been developed. The Chinese patent with publication number CN107643525A discloses a 45-degree rotating mirror-based linear array laser radar circumferential non-image rotation imaging system, and the patent application proposes to compensate the rotation of a 45-degree rotating mirror by utilizing the synchronous rotation of the other Han's prism mirror rotation effect, and realizes 360-degree circumferential non-image rotation imaging of the linear array laser radar through linear array light beam scanning. The linear array distance measuring module has the advantages that only the 45-degree mirror and the image-eliminating rotary prism rotate in the scanning process, the linear array distance measuring module is fixed, the system rotation inertia is small, and the caliber of the compensating prism limits the scanning range and the vertical direction view angle of the linear array distance measuring module. The Chinese patent publication No. CN109471126A discloses a vibration-rotation combined circumferential scanning device of a linear array laser radar, and the patent application proposes that a two-axis vibrating mirror realizes local two-dimensional scanning, and then a 45-degree reflecting mirror rotating around an axis is used for realizing 360-degree circumferential scanning of linear array laser ranging.
At present, a laser radar device capable of realizing ToF and FMCW composite detection and 360-degree periscope scanning has not been reported yet.
Disclosure of Invention
The invention aims to provide a method and a device for comprehensively detecting the head-up scanning of ToF and FMCW laser radars. The invention realizes the horizontal 360-degree periscope composite detection of the ToF and FMCW laser radars, can acquire high-resolution point cloud data in a two-dimensional direction, and realizes accurate synchronous ranging and speed measurement.
The technical scheme of the invention is that the method for comprehensively scanning and compositely detecting the ToF and FMCW laser radars comprises a ToF laser radar module and an FMCW laser radar module, wherein the ToF laser radar module and the FMCW laser radar module are respectively connected with a spectroscope module and a signal processing module, and the spectroscope module is connected with a peripherally scanning module;
The ToF laser radar module is provided with M groups of emission channels and M groups of receiving channels which are distributed in one-dimensional space, M laser pulses are emitted through the M groups of emission channels, M laser pulses are emitted through the spectroscope module and the periscope scanning module, M emission light beams are formed in one-dimensional vertical direction and rotated in the horizontal direction by 360 degrees through the periscope scanning module, and two-dimensional periscope scanning is achieved;
The FMCW laser radar module is used for generating N groups of emission channels and N groups of receiving channels with time dimension through the bidirectional optical switch array, continuously emitting N FMCW light beams, emitting N FMCW light beams through the spectroscope module and the periscope scanning module, forming N emission light beams in a one-dimensional vertical direction, rotating 360 degrees in a horizontal direction through the periscope scanning module to realize two-dimensional periscope scanning, and after the N emission light beams are emitted to a target object, carrying out coherent reception on N receiving light beams returned by the target object through the periscope scanning module and the spectroscope module and a local oscillation light beam of the FMCW laser radar module to obtain a coherent detection signal of the target object;
the detection signals of the ToF laser radar module and the FMCW laser radar module are processed by digital signals in the signal processing module, so that the parallel synchronous measurement of the distance and the vector speed between the laser radar device and the target is realized.
According to the method for comprehensively scanning and compositely detecting the ToF and FMCW laser radars, M emission light beams formed by the ToF laser radar module in the one-dimensional vertical direction respectively correspond to unique vertical direction space angles, the direct detection signals obtained by the ToF laser radar module are used for measuring round trip time differences of the M emission light beams and the M receiving light beams through the signal processing module, and ToF distance point cloud data of an object with M points are calculated based on the propagation speed of light in the air and the horizontal scanning angle of the weekly scanning module.
According to the method for comprehensively scanning and compositely detecting the ToF and FMCW laser radar, the FMCW laser light source module of the FMCW laser radar module generates continuous laser which is linearly modulated by symmetric triangular waves, the continuous laser is amplified and split and then is divided into outgoing beams and local oscillation beams, the outgoing beams pass through the optical circulator and then sequentially pass through the bidirectional optical switch array, the collimation directional transmitter, the spectroscope module and the peripherally scanning module to be outgoing to a target, wherein output ports of the bidirectional optical switch array are distributed along one-dimensional direction and are all arranged on a focal plane of the collimation directional transmitter transmitting optical assembly, optical signals output by different ports are outgoing towards different angles after passing through the transmitting optical assembly, N transmitting beams are formed in one-dimensional vertical directions, each transmitting beam corresponds to a unique vertical direction space angle, the N transmitting beams rotate 360 DEG in horizontal directions by the peripherally scanning module, N receiving beams returned by the target are combined and interfered by the beams to generate beat signals, the beat signals are mixed by the optical mixer to output in-phase signals and quadrature signals with the same-phase signals, the same-phase signals and the quadrature signals are respectively received by the balance detector, and then the analog-digital converter is used for completing analog-digital conversion, and the calculation of the FPGA data of the target point cloud point, and the target point cloud point can be obtained.
According to the method for comprehensively scanning and compositely detecting the ToF and FMCW laser radar, the signal processing module is used for synchronously measuring and fusing the ToF distance point cloud data and the FMCW distance point cloud data according to the detection signals of the ToF laser radar module and the FMCW laser radar module, and acquiring the high-resolution point cloud information in a two-dimensional direction, so that accurate synchronous distance measurement and speed measurement are realized.
The device for realizing the aforementioned TOF and FMCW laser radar panoramic scanning composite detection method comprises:
The ToF laser radar module is used for directly detecting a target object;
The FMCW laser radar module is used for coherent detection of a target object;
The spectroscope module is connected with the ToF laser radar module and the FMCW laser radar module and is used for combining the emitted light and the received light of the ToF laser radar module and the FMCW laser radar module into beams so as to realize the wavelength multiplexing of the two types of laser radars;
The system comprises a beam splitter module, a panoramic scanning module, a frequency conversion module and a frequency conversion module, wherein the panoramic scanning module is connected with the beam splitter module and is used for emitting and receiving lasers of the ToF laser radar module and the FMCW laser radar module and realizing two-dimensional panoramic scanning of the ToF laser beam and the FMCW laser beam;
the signal processing module is connected with the ToF laser radar module and the FMCW laser radar module and is used for processing detection signals acquired by the ToF laser radar module and the FMCW laser radar module so as to realize parallel synchronous measurement of the distance and the vector speed between the laser radar device and the target object.
The ToF laser radar module comprises a ToF laser light source module, a ToF laser transmitting module and a ToF laser receiving module, wherein the ToF laser light source module is connected with the spectroscope module through the ToF laser transmitting module, and the ToF laser receiving module is connected with the spectroscope module and the signal processing module.
The FMCW laser radar module comprises an FMCW laser light source module, an FMCW laser transmitting module and an FMCW coherent receiving module, wherein the FMCW laser light source module is connected with the spectroscope module through the FMCW laser transmitting module, and the FMCW coherent receiving module is connected with the spectroscope module and the signal processing module.
The FMCW laser light source module is a linear frequency modulation continuous wave laser light source, the FMCW laser emission module comprises a laser amplifier connected with the FMCW laser light source module, the laser amplifier is sequentially connected with an optical beam splitter, an optical circulator, a bidirectional optical switch array and a collimation directional emitter along the laser transmission direction, output ports of the bidirectional optical switch array are distributed along a one-dimensional direction and are all arranged on a focal plane of the collimation directional emitter emission optical assembly, optical signals output by different ports are emitted towards different angles after passing through the emission optical assembly, the FMCW coherent receiving module comprises an optical mixer, an output end of the optical mixer is connected with a photoelectric balance detector, and the optical beam splitter and the optical circulator are connected with the optical mixer together.
The device comprises a beam splitter module, a peripheral scanning module and a power supply module, wherein the beam splitter module is a dichroic beam splitter, the peripheral scanning module comprises a de-image rotating prism and a peripheral rotating mirror which are arranged along the laser transmission direction of the dichroic beam splitter, the de-image rotating prism and the peripheral rotating mirror are respectively connected with a servo motor, and under the control of the servo motor, the de-image rotating prism and the peripheral rotating mirror rotate in the same direction according to a 1:2 rotation ratio to realize non-image rotation 360-degree peripheral scanning.
In the device, the signal processing module comprises an analog-to-digital converter connected with the ToF laser radar module and the FMCW laser radar module, and the analog-to-digital converter is connected with a field programmable gate array module.
Compared with the prior art, the invention realizes horizontal 360-degree periscope composite detection of the TOF and FMCW laser radars on the premise of limited volume increase, efficiently combines respective advantages of the TOF and FMCW laser radars, not only can acquire high-resolution point cloud data in a two-dimensional direction, but also can realize synchronous ranging and speed measurement in a region of interest (ROI). In addition, the invention gets rid of the complex upper and lower bin structures of the traditional multi-line panoramic scanning laser radar, has no fast axis scanning, small moment of inertia, simple structure, high reliability, integration and miniaturization, low system cost and good development prospect in the laser radar fields of vehicles, ships and the like.
Drawings
Fig. 1 is a schematic view of the structure of the device of the present invention.
Fig. 2 is a schematic structural diagram of a ToF laser light emitting module.
Fig. 3 is a schematic structural diagram of the ToF laser receiving module.
Fig. 4 is a schematic structural diagram of an FMCW lidar module.
Fig. 5 is a schematic diagram of a ToF laser transmitter module.
Fig. 6 is a schematic diagram of a ToF laser receiving module.
Fig. 7 is a schematic diagram of a timing waveform relationship of a transmit-receive signal of the ToF lidar module.
Fig. 8 is a schematic diagram of waveform relationship and frequency difference of a symmetric triangle wave chirped continuous wave reception-local oscillation beam of an FMCW lidar module.
FIG. 9 is a schematic view of a scan-field coordinate system of a lidar device including the range R, azimuth of a targetAnd pitch angle。
Fig. 10 shows a schematic diagram of connection relation between a1×n bidirectional optical switch array and an N-channel collimation directional emitter, wherein output ports of the 1×n bidirectional optical switch array are arranged along a one-dimensional direction and are all arranged on a focal plane of an N-channel collimation directional emitter emission optical component, and optical signals output by different ports are emitted towards different angles after passing through the emission optical component.
Fig. 11 shows a schematic diagram of an embodiment of the composite detection of 905nmToF lidar and 1550nmFMCW lidar.
Fig. 12 shows a composite probe point cloud distribution diagram of the ToF lidar and the FMCW lidar.
Reference numerals:
1. The system comprises a ToF laser radar module, a2, FMCW laser radar module, a 3, a spectroscope module, a 4, a periscope scanning module, a 5, a signal processing module, a 6, a ToF laser light source module, a 7, a ToF laser transmitting module, an 8, a ToF laser receiving module, a 9, an FMCW laser light source module, a 10, an FMCW laser transmitting module, an 11, an FMCW coherent receiving module, a 12, a laser amplifier, a 13, a 1 x 2 optical beam splitter, a 14, an optical circulator, a 15, a 1 x N bidirectional optical switch array, a 16, N channel collimation directional transmitter, a 17, a2 x 4 90o optical mixer, a 18, a photoelectric balance detector, a 19, a resolution prism, a 20, a periscope rotating mirror, a 21, a servo motor, a 22, an analog-to-digital converter, a 23 and a field programmable gate array module.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not intended to be limiting.
Example 1 ToF and FMCW composite detection periodogram laser radar device, as shown in FIG. 1, comprises:
the ToF laser radar module 1 is used for directly detecting a target object;
The FMCW laser radar module 2 is used for coherent detection of a target object;
The beam splitter module 3 is connected with the ToF laser radar module 1 and the FMCW laser radar module 2, the beam splitter module 3 is used for combining and splitting laser beams of the ToF laser radar module 1 and the FMCW laser radar module 2 to realize wavelength multiplexing of the two types of laser radars, wherein if the wavelengths of the ToF laser radar module 1 and the FMCW laser radar module 2 are different, the beam splitter module 3 is a dichroic beam splitter, the dichroic beam splitter selectively reflects or enhances incident light with different wavelengths, so as to realize beam combination of the emitted light and beam splitting of the received light of the short-wave ToF laser radar and the long-wave FMCW laser radar, and if the wavelengths of the two types of laser are not different, the beam splitter module can be a polarization beam splitter, the polarization beam splitter selectively transmits or reflects the incident light with orthogonal polarization, so as to realize beam combination of the emitted light of the orthogonal polarization ToF laser radar and the FMCW laser radar and beam splitting of the received light. In the embodiment of the present invention, for the sake of simplifying the description, only the first case is considered, that is, the wavelengths of both the ToF lidar module 1 and the FMCW lidar module 2 differ.
The system comprises a beam splitter module 3, a periscope scanning module 4, a periscope rotating mirror 20, a resolution rotating mirror 19 and a frequency mirror 20, wherein the periscope scanning module 4 is connected with the beam splitter module 3, and is used for emitting and receiving laser of the ToF laser radar module 1 and the FMCW laser radar module 2 and realizing 360-degree resolution-free periscope scanning;
The signal processing module 5 is connected with the ToF laser radar module 1 and the FMCW laser radar module 2, and the signal processing module 5 processes target receiving light beams acquired by the ToF laser radar module 1 and the FMCW laser radar module 2 to realize parallel synchronous measurement of the distance and the vector speed between the laser radar device and the target.
In this embodiment, the ToF laser radar module 1 includes a ToF laser light source module 6, a ToF laser transmitting module 7, and a ToF laser receiving module 8, where the ToF laser light source module 6 is connected to the beam splitter module 3 through the ToF laser transmitting module 7, and the ToF laser receiving module 8 is connected to the beam splitter module 3 and the signal processing module 5. The ToF laser light source module 6 is configured to emit laser pulses, as shown in fig. 2, where the ToF laser light emitting module 7 has M groups of emission channels with a spatial dimension, and the M groups of emission channels pass through an emission lens, then exit through a dichroic spectroscope, a racemization prism, and a periscope rotating mirror, and form M emission beams in a one-dimensional vertical direction and rotate 360 ° in a horizontal direction, where each emission beam corresponds to a unique spatial angle, and as shown in fig. 3, the ToF laser receiving module 8 has M groups of receiving channels with a spatial dimension, and the M groups of receiving channels receive the M receiving beams returned by the target through the emission lens, so as to realize direct detection of the target.
In this embodiment, as shown in fig. 4, the FMCW laser radar module includes an FMCW laser light source module 9, an FMCW laser emission module 10, and an FMCW coherent receiving module 11, where the FMCW laser light source module 9 is connected to the spectroscope module 3 through the FMCW laser emission module 10, and the FMCW coherent receiving module 11 is connected to the spectroscope module 3 and the signal processing module 5. The FMCW laser light source module 9 is a linear frequency modulation continuous wave laser light source, the FMCW laser light emitting module 10 comprises a laser amplifier 12 connected with the linear frequency modulation continuous wave laser light source, the laser amplifier 12 is sequentially connected with a 1×2 optical beam splitter 13, an optical circulator 14, a 1×N bidirectional optical switch array 15 and an N-channel collimation directional emitter 16 along a laser transmission direction, output ports of the 1×N bidirectional optical switch array 15 are distributed along a one-dimensional direction and are all arranged on a focal plane of an N-channel collimation directional emitter 16 for emitting optical components, optical signals output by different ports are emitted towards different angles after passing through the emission optical components, the FMCW coherent receiving module 11 comprises a 2×4 90o optical mixer 17, an output end of the 2×4 90o optical mixer 17 is connected with a photoelectric balance detector 18, and the 1×2 optical beam splitter 13 and the optical circulator 14 are connected with the 2×4 90o optical mixer together.
In this embodiment, the signal processing module 5 includes an analog-to-digital converter 22 connected to the ToF lidar module 1 and the FMCW lidar module 2, that is, the analog-to-digital converter 22 is connected to the ToF laser receiving module 8 of the ToF lidar module 1 and the photoelectric balance detector 18 of the FMCW lidar module 2, the analog-to-digital converter 22 is used for converting analog-to-digital signals, and the analog-to-digital converter 22 is connected to a field programmable gate array module 23 (abbreviated as FPGA module), where the field programmable gate array module 23 is used for processing digital signals.
In the method, based on the ToF and FMCW composite detection panoramic scanning laser radar device in embodiment 1, the ToF laser radar module has M groups of emission channels and M groups of receiving channels which are one-dimensionally and spatially distributed, the ToF laser radar module emits M laser pulses (which may also be referred to as M short wavelength lasers) through the M groups of emission channels (i.e., the ToF laser emission module has M groups of ToF emission units, fig. 5 shows a stacked schematic diagram of the M groups of emission units), the laser pulses are emitted through the spectroscope module and the panoramic scanning module, M emission beams are formed in a one-dimensional vertical direction, each emission beam corresponds to a unique vertical spatial angle, the M emission beams rotate 360 ° in a horizontal direction through the panoramic scanning module, after the M emission beams are emitted to a target, M receiving beams returned by the target are received by the M groups of receiving channels (i.e., the ToF receiving module has M groups of ToF receiving units, fig. 6 shows a stacked schematic diagram of the M groups of ToF receiving units), so that the target point is directly received, and the target point is directly or directly matched with the target is directly received.
The FMCW laser radar module generates N groups of transmitting channels and N groups of receiving channels with time dimension (namely sequential gating) through controllable gating of the 1 XN bidirectional optical switch array, the FMCW laser radar module continuously transmits N frequency modulation continuous waves, the N frequency modulation continuous waves are emitted through the spectroscope module and the periscope scanning module, N transmitting light beams are formed in a one-dimensional vertical direction, each transmitting light beam corresponds to a unique vertical direction space angle, the N transmitting light beams rotate 360 degrees in a horizontal direction through the periscope scanning module, after the N transmitting light beams are transmitted to a target object, N receiving light beams returned by the target object are coherently received with local oscillation light beams of the FMCW laser radar module after passing through the periscope scanning module and the spectroscope module, so that coherent detection of the target object is realized, and complete matching of transmitting or receiving fields is realized.
The detection signals of the ToF laser radar module and the FMCW laser radar module are subjected to ADC sampling and digital signal processing in the signal processing module, so that the parallel synchronous measurement of the distance and the vector speed between the laser radar platform and the target object is realized.
Specifically, for the ToF laser radar module, the power of the emitted light beam output by the ToF laser light source module is a time function with a gaussian model, which may be expressed as:
;
In the formula, Is the initial energy of the emitted beam; Is the pulse width of the emitted light beam, Representing time;
according to the lidar equation, the power of the received beam may be expressed as:
;
Wherein, Is the initial energy of the emitted beam; Is the pulse width of the emitted beam; Is the atmospheric transmittance; Is the efficiency of the ToF laser transmitter module; Is the efficiency of the ToF laser receiving module; is the target reflectivity; Is the optical lens diameter; is the period of the microwave frequency modulation signal; is the target receive delay.
The TOF laser radar module obtains target receiving delay by measuring the time difference between the emitted light beam and the received light beamFurther obtain the distance of the targetCan be expressed as:
;
Wherein, Is the speed of light; is the target receive delay.
Fig. 7 is a schematic diagram showing a time-series waveform relationship between a transmitted beam and a received beam of the ToF lidar module.
For the FMCW laser radar module, the FMCW laser light source module generates continuous laser with frequency linearly modulated, symmetric triangular wave linear modulation is adopted, the frequency of the modulated signal changes into symmetric triangle with time, and in one period, the first half part is called forward frequency modulation #) The latter half is called negative frequency modulation). Fig. 8 shows a waveform relationship and a frequency difference (beat frequency) of a symmetric triangle wave chirped continuous wave reception-local oscillation beam.
The continuous laser of the symmetric triangular wave linear frequency modulation generated by the linear frequency modulation continuous wave laser source is amplified by a laser amplifier and then is divided into a local oscillation beam and an emergent beam by a 1X 2 optical beam splitter;
Most of the energy (99%) is taken as an emergent beam, passes through the optical circulator, and then is emergent through the 1 XN bidirectional optical switch array, the N-channel collimation directional emitter, the dichroic spectroscope, the racemization prism and the periscope rotating mirror, N emission beams are formed in the one-dimensional vertical direction, each emission beam corresponds to a unique vertical direction space angle, the N emission beams rotate 360 degrees in the horizontal direction, and the N emission beams are emitted to a target, as shown in fig. 10.
Wherein, the 1 XN bidirectional optical switch array is sequentially conducted, and at a certain momentThe channel is on and the light field of the emitted beam can be expressed as:
;
In the formula, ;Time is; Amplitude; is a frequency modulation period; The frequency modulation initial frequency is adopted; for the frequency modulation rate, The frequency modulation bandwidth is adopted; Is the first Initial phase of the rising section of each channel; Is the first Initial phase of each channel descending section; Is an exponential function with a natural constant as a base;
The received beam of the target being a time delay The optical field can be expressed as:
;
In the formula, Is the amplitude of the received light beam,Is the noise phase of the received beam.
A small part of energy (99%) is used as a local oscillation beam, and the local oscillation beam is time delayThe optical field can be expressed as:
;
Wherein: Is the amplitude of the local oscillator beam, Is the noise phase of the local oscillator beam.
After the received light beam and the local oscillator light beam of the target are combined, the interference light field is expressed as:
;
Time delay of received light beam Time delay with local oscillator beamExpressed as:
;
Wherein: is the target distance; is the radial velocity of the relative motion of the radar device and the target; Is the doppler shift caused by the radial velocity of the relative motion of the radar device and the target.
The four paths of output in-phase signals and quadrature signals with quadrature characteristics after being mixed by the 2×4 90o optical mixer are as follows:
;
;
Wherein: Is the first Channel mixing noise phase; is the direct current associated with the received beam; Is the direct current related to the local oscillator beam;
The in-phase signal and the quadrature signal are respectively received by the photoelectric balance detector, and the output of the in-phase signal and the quadrature signal through the photoelectric balance detector is respectively as follows:
;
;
Wherein: The response rate of the photoelectric detector which is an in-phase signal; the response rate of the photoelectric detector is the response rate of the orthogonal signal; And Noise phases of the in-phase signal and the quadrature signal, respectively;
for simplicity, the amplitudes of the in-phase signal and the quadrature signal are replaced by the following formula;
;
the in-phase signal and the quadrature signal are respectively reduced to:
;
;
The in-phase signal and the quadrature signal with quadrature characteristic are subjected to analog-digital conversion by an analog-digital converter, and then are collected by a field programmable gate array module to carry out spectrum processing:
First, an in-phase signal and a quadrature signal are respectively subjected to Fast Fourier Transform (FFT), and the in-phase signal fourier transform is expressed as:
;
The fourier transform of the quadrature signal is expressed as:
;
The two signals are subjected to cross spectrum processing:
;
Wherein: representing conjugate operation;
finally, only the imaginary part is taken to obtain:
;
therefore, the position and the positive and negative of the spectrum peak value are extracted by a gravity center method, and the positive frequency modulation and the negative frequency modulation in the process of positive frequency modulation and negative frequency modulation can be respectively obtained :
;
The above formula can be obtained:
;
since the Doppler frequency is proportional to the speed of relative motion of the radar platform and the target, the Doppler frequency shift is positive and negative and is related to the direction of the radial speed of the relative motion, the positive frequency shift represents the relative motion of the radar platform and the target, and the negative frequency shift represents the relative motion of the radar platform and the target. The magnitude and direction of the radial velocity of the relative motion of the radar platform and the target can be obtained by Doppler frequency shift, and can be expressed as follows:
;
Wherein: Representing wavelength;
the distance of the target point can also be obtained from the above equation:
。
In this embodiment, N emission beams of the FMCW lidar module are all coaxially emitted or received in parallel, and complete matching of the emission or reception fields of view is achieved. And performing real-time parallel fast Fourier transform on each acquired sampling data by using a field programmable gate array module, so as to realize the sequential measurement of the distance and the speed of N point targets.
Further, in order to increase the emission point frequency of the ToF laser radar module, J ToF laser radar modules are adopted to be combined, J ToF laser radar modules correspond to J ToF laser emission modules, output ports are distributed along one-dimensional directions, JM emission beams are formed in one-dimensional vertical directions, each emission beam corresponds to a unique vertical direction space angle, JM emission beams rotate 360 degrees in the horizontal direction to achieve two-dimensional circular scanning, JM receiving beams returned by the target are received by a photoelectric detector of a JM receiving channel after being emitted to the target, detection signals of the ToF laser radar modules are subjected to analog-to-digital conversion through an analog-to-digital converter, round trip time differences of JM emission beams and JM receiving beams are respectively and directly measured through a field programmable gate array module (FPGA module), and the distance point cloud information of the target of the points is calculated based on the propagation speed of light in the air and the horizontal scanning angle of the JM scanning module. Therefore, the total point frequency and the one-dimensional vertical direction point cloud number of the ToF laser radar module are both improved by J times.
Similarly, in order to increase the emission point frequency of the FMCW laser radar module, K FMCW laser radar modules may be used to combine, the K FMCW laser radar modules correspond to the K1×n bidirectional optical switch arrays and the KN channel collimation directional emitter, where output ports of the K1×n bidirectional optical switch arrays are arranged along a one-dimensional direction and are all disposed on a focal plane of the KN channel collimation directional emitter emission optical assembly, optical signals output by different ports are emitted towards different angles after passing through the emission optical assembly, KN emission beams are formed in a one-dimensional vertical direction, each emission beam corresponds to a unique vertical direction space angle, the KN emission beams rotate 360 ° in a horizontal direction, and after the KN emission beams are emitted to a target, K receiving beams returned by the target are respectively coherently mixed with K beams of the FMCW laser radar module after passing through the perioral scanning module and the spectroscope module, so as to realize coherent detection of the target. Therefore, the total point frequency of the FMCW laser radar module and the number of the point clouds in the one-dimensional vertical direction are increased by K times.
Further, in this embodiment, the ToF lidar module and the FMCW lidar module collect angle information between the radar device and the target according to the field programmable gate array module, respectivelyThe three-dimensional space coordinates of the target point P are obtained by conversion, and are expressed as follows in fig. 9:
;
In the ToF lidar module, the emission frequency of each of the ToF laser light source modules is The transmission repetition frequency of the M groups of stacked transmitting units is alsoEach emission unit corresponds to one scanning line in the vertical direction, namely M scanning lines in the vertical direction, and the coverage view field isThe frame rate isThe horizontal angle resolution and the vertical angle resolution are respectively:
。
In the FMCW laser radar module, the emission frequency of the FMCW laser light source module is Each channel of the 1 XN bidirectional optical switch array corresponds to one scanning line in the vertical direction, namely N scanning lines in the vertical direction, and the coverage view field isThe frame rate isThe horizontal angle resolution and the vertical angle resolution are respectively:
。
Therefore, by combining the ToF laser radar module and the FMCW laser radar module, the present invention can realize the composite detection point cloud distribution of the two, as shown in FIG. 12. Because the ToF laser light source module of the ToF laser radar module can be integrated through a semiconductor process, the high-resolution point cloud distribution with a large field angle can be realized. Whereas FMCW range point cloud data of the FMCW lidar module may be concentrated in a region of interest (also referred to as an ROI) that is complementary to the ToF range point cloud data of the ToF lidar module. On one hand, the laser radar platform can provide a large horizontal view angle and a large vertical view angle, has high enough horizontal angle resolution and vertical angle resolution, realizes non-blind area detection on the periphery of the laser radar platform and ensures that a remote target can be effectively resolved, and on the other hand, the laser radar platform can simultaneously realize distance measurement and speed measurement in an ROI region and has complete anti-interference capability.
Example 3 based on examples 1 and 2, as shown in fig. 11, a 905nm TOF laser radar module and a 1550nm FMCW laser radar module were used for composite detection. And a coated dichroic spectroscope is adopted to realize high transmission of short wave 905nm laser and high reflection of long wave 1550nm laser. The image-rotation eliminating prism adopts an achromatic dove prism, so that the image-rotation compensation can be realized in the wave bands of 905nm and 1550 nm. The periscope rotating mirror adopts a 45-degree total reflection mirror, and adopts a coating film to realize high reflection of laser of short wave 905nm and long wave 1550 nm.
The method is characterized in that the dove prism and the 45-degree total reflection mirror are respectively connected with servo motors, under the control of the two servo motors, the dove prism and the 45-degree total reflection mirror rotate in the same direction according to a rotation speed ratio of 1:2 to realize non-image rotation periscope scanning, the rotation speed of the dove prism is 1800 DEG/s, the corresponding frequency is 5Hz, the rotation speed of the 45-degree total reflection mirror is 3600 DEG/s, and the corresponding frequency is 10Hz, and in order to ensure complete image racemization, the initial phase difference and complete phase locking between the two servo motors are required to be ensured.
The transmitting end of the TOF laser radar module is integrated with 256 independent VCSELs, the transmitting point frequency of each laser is 37.5kHz, and the receiving end is integrated with 32 silicon-based photomultiplier (SiPM) single photon detector modules. The transmitting end and the receiving end adopt coaxial light paths, and complete matching of transmitting or receiving fields of view is realized. The rotation range of the periscope is 360 degrees horizontally, the vertical upper and lower ranges of the laser beams are 25.6 degrees, namely the total view field is 360 degrees multiplied by 25.6 degrees, the horizontal resolution is 0.096 degrees, the vertical resolution is 0.1 degrees, each frame of point cloud can form 3750 lattices in the horizontal direction, 256 lattices are formed in the vertical direction, the frame frequency is 10Hz, and the total point frequency of ToF distance point cloud data is 9.6MHz.
In order to increase the point frequency, the FMCW laser radar module integrates 8 independent FMCW transmitting and receiving units, the transmitting point frequency of each FMCW unit is 300kHz, the symmetric triangular wave is linearly modulated, the frequency sweep bandwidth is 2GHz, the distance measurement resolution is 7.5cm, and the speed measurement resolution is 0.465m/s. The 8 coherent receiving ends all adopt a 2X 4 90-degree optical mixer and a photoelectric balance detector. Each FMCW transmitting and receiving unit is connected with a1 x 8 silicon-based bidirectional high-speed electro-optic switch, and 8 silicon-based bidirectional high-speed electro-optic switches of 1 x 8 form an electro-optic switch array of 64 units. The 64-unit electro-optical switch array is connected with the 64-channel collimation emitter, the output ports of the 64-unit bidirectional optical switch array are distributed along a one-dimensional direction and are arranged on the focal plane of the 64-channel collimation directional emitter emission optical assembly, and optical signals output by different ports are emitted towards different angles after passing through the emission optical assembly.
The FMCW laser radar module continuously emits 64 frequency modulation continuous waves, the 64 frequency modulation continuous waves are emitted through the spectroscope module and the periscope scanning module, 64 emission light beams are formed in the one-dimensional vertical direction, each emission light beam corresponds to a unique vertical direction space angle, and the 64 emission light beams rotate by 360 degrees in the horizontal direction. After 64 emission light beams are emitted to a target object, 64 receiving light beams returned by the target object are subjected to coherent mixing with local oscillation light beams after passing through a periscope scanning module and a spectroscope module, so that coherent detection of the target object is realized. The 64 transmitting light beams of the FMCW laser radar module are all coaxially and parallelly transmitted or received, and complete matching of the transmitting or receiving field of view is realized. The rotation range of the periscope rotating mirror is 360 degrees horizontally, the vertical upper and lower ranges of the laser beams are 6.4 degrees, namely the total view field is 360 degrees multiplied by 6.4 degrees, the horizontal resolution is 0.096 degrees, the vertical resolution is 0.1 degrees, each frame of point cloud can form 3750 dot matrixes in the horizontal direction, 64 dot matrixes are formed in the vertical direction, the frame frequency is 10Hz, and the total point frequency of FMCW distance point cloud data is 2.4MHz.
The ROI area is set as a field of view area of the center 360 ° x 6.4 °. In the ROI area, the ToF distance point cloud data array of each frame is 3750 multiplied by 64, the FMCW distance point cloud data array of each frame is 3750 multiplied by 64, and the ToF distance point cloud data and the FMCW distance point cloud data are distributed at equal intervals in the vertical direction, so that the resolution of the composite view field in the vertical direction is 0.05 degrees, the resolution of the composite view field in the horizontal direction is 0.096 degrees, the high-resolution point cloud information is obtained in the two-dimensional direction, the ranging resolution of the ROI area is 7.5cm, the speed measuring resolution is 0.465m/s, and accurate synchronous ranging and speed measuring are realized.
In summary, the invention realizes the horizontal 360-degree periscope composite detection of the ToF and FMCW laser radars on the premise of limited volume increase, efficiently combines the TOF and FMCW laser radar technologies, highlights the respective advantages, not only can acquire high-resolution point cloud data in a two-dimensional direction, but also realizes synchronous ranging and speed measurement in a region of interest (ROI). In addition, the invention gets rid of the complex upper and lower bin structures of the traditional multi-line periscope laser radar, has no fast axis scanning, small moment of inertia, simple structure, high reliability, integration and miniaturization, low system cost and good development prospect in the laser radar fields of vehicles, ships and the like.
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