ToF and FMCW laser radar panoramic scanning composite detection method and device

Abstract

The present invention discloses a composite detection method and device of ToF and FMCW laser radar circumferential scanning, including a ToF laser radar module, an FMCW laser radar module, a spectroscope module, a circumferential scanning module and a signal processing module; the spectroscope module is respectively connected to the ToF laser radar module and the FMCW laser radar module, and is used to emit a photosynthetic beam and receive a split light beam; the circumferential scanning module is connected to the spectroscope module, and is used to emit and receive lasers, and realize image-free circumferential scanning; the signal processing module is connected to the ToF laser radar module and the FMCW laser radar module; the signal processing module processes the acquired target receiving beam, and realizes the parallel synchronous measurement of the distance and vector velocity between the laser radar device and the target object. The present invention realizes the horizontal 360º circumferential composite detection of ToF and FMCW laser radars, can obtain high-resolution point cloud data in two-dimensional directions, and realizes accurate synchronous distance measurement and velocity measurement.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and more particularly to a detection method and device for laser radar, and more particularly to a ToF and FMCW laser radar panoramic scanning composite detection method and device. Background Art

[0002] ToF laser radar refers to direct time-of-flight (ToF) laser radar, which directly measures the round-trip time difference of the emitted laser pulse and calculates the distance information of the target object based on the propagation speed of light in the air. Its advantages are simple system, fast response speed, high detection accuracy, and easy multi-channel transmission / reception to generate high-resolution point clouds. It is currently the most mature mainstream automotive laser radar technology solution. Its disadvantages are that it cannot achieve synchronous distance and speed measurement, and its anti-interference ability is poor. FMCW LiDAR refers to Frequency Modulated Continuous Wave (FMCW) LiDAR, which uses coherent detection technology to linearly modulate the optical frequency of the emitted laser, and generates a beat frequency signal by interfering the received optical signal with the local oscillator light, thereby indirectly obtaining the flight time and calculating the distance of the target object. At the same time, it can measure the instantaneous radial vector velocity of the target object according to the Doppler frequency shift information. Its advantages are the ability to simultaneously measure distance and speed, high measurement dynamic range, high ranging and speed measurement accuracy, strong adaptability to harsh environments, and complete anti-interference ability (including ambient light and other LiDARs). Its disadvantage is that the system is complex. If multi-channel transmission / reception is used, it will take up much larger structural space and system resources than ToF, and it is difficult to obtain high-resolution point clouds.

[0003] Scanning 3D imaging LiDAR is composed of a laser incoherent or coherent ranging system with a beam scanning device. It is a relatively mature 3D imaging LiDAR technology. Scanning 3D imaging LiDAR requires rapid measurement of each point. The scanning device controls the LiDAR optical axis to point in different directions, measures the distance of each point on the target in turn, and records the azimuth-elevation angle of the beam pointing at the same time, so that the distance-azimuth-elevation angle image of the target can be obtained. On the one hand, in order to achieve blind-free detection around the LiDAR platform and ensure that long-distance targets can be effectively distinguished, the LiDAR requires as large a horizontal and vertical field of view as possible, and must have sufficiently high horizontal and vertical angular resolutions in the area of ​​interest; on the other hand, the LiDAR platform needs to achieve simultaneous ranging and speed measurement in the ROI area, and have complete anti-interference capabilities.

[0004] Chip-level packaging, image-level point cloud resolution, instantaneous speed of directly acquiring point clouds, and complete anti-interference are considered typical features of future automotive LiDARs. However, neither ToF nor FMCW have them at present. Highlighting the respective advantages of ToF and FMCW and realizing ToF and FMCW composite detection is a cost-effective LiDAR technology route.

[0005] In practical applications, some laser radars require a 360° horizontal field of view and a certain vertical field of view. "Horizontal mechanical rotation + vertical linear array transceiver" is a typical representative of this 360° panoramic scanning method: in the horizontal direction, the motor drives the optical-mechanical structure of the upper warehouse to rotate 360° as a whole to obtain a 360° horizontal field of view; in the vertical direction, the laser emission module and the linear array of the detection module are matched and arranged to form a multi-line scan in the vertical direction. There is a specific angle between each scanning beam, so as to achieve a certain degree of uniform or non-uniform angle coverage in the vertical direction and achieve angular resolution in the vertical direction. This scanning method realizes solid-state scanning in one dimension, which can reduce the amount of motion in one dimension. Only mechanical scanning along another dimension is required to achieve two-dimensional scanning of the target object, which greatly improves the scanning efficiency of the system. It is currently the most widely used and most mature laser radar panoramic scanning solution. Typical representatives are Panda128 and OT128 of Hesai Technology and Ruby Plus of RoboSense. However, this solution requires precise alignment of the transmitting and receiving optical modules of each channel. The crosstalk between different ranging channels requires a very high assembly and installation precision. The upper warehouse has a large moment of inertia, and wireless power supply and wireless communication between the upper and lower warehouses must be solved. The structure is complex, the size is large, the power consumption is high, the cost is high, and the requirements for heat dissipation and process are also high. Therefore, the 45° rotating mirror scanning method that can reduce the moment of inertia came into being. The Chinese invention patent with publication number CN107643525A discloses a circumferential non-image rotation imaging system of a linear array laser radar based on a 45° rotating mirror. The patent application proposes to use the image rotation effect of the synchronously rotating Behan prism to compensate for the image rotation problem of the 45° rotating mirror rotation, and realize 360° circumferential non-image rotation imaging of the linear array laser radar through linear array beam scanning. The advantage is that only the 45° mirror and the de-image rotation prism rotate during the scanning process, while the linear array ranging module is fixed and the system moment of inertia is small; the disadvantage is that the compensation prism aperture limits the scanning range and vertical field of view of the linear array ranging module. The Chinese invention patent with publication number CN109471126A discloses a vibration-rotation combined circumferential scanning device for a linear array laser radar. The patent application proposes a two-axis galvanometer to achieve local two-dimensional scanning, and then a 45° rotating mirror is used to achieve 360° circumferential scanning of the linear array laser ranging. The advantage is that only the 45° mirror rotates during the scanning process, while the linear array ranging module is fixed, the system has a small rotational inertia, and the two-dimensional galvanometer galvanometer compensation overcomes the inconsistent vertical field of view in different orientations caused by image rotation; the disadvantage is that the control of the two-dimensional galvanometer galvanometer and the 45° rotating mirror is relatively complicated, and the aperture of the two-dimensional galvanometer galvanometer is limited.

[0006] At present, there is no report on a laser radar device that can realize ToF and FMCW composite detection and 360° panoramic scanning. Summary of the invention

[0007] The purpose of the present invention is to provide a ToF and FMCW laser radar panoramic scanning composite detection method and device. The present invention realizes the horizontal 360° panoramic composite detection of two types of ToF and FMCW laser radars, can obtain high-resolution point cloud data in two-dimensional directions, and realize accurate synchronous distance measurement and speed measurement.

[0008] The technical solution of the present invention is: a composite detection method of ToF and FMCW laser radar circumferential scanning, comprising 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 to a spectroscope module and a signal processing module, and the spectroscope module is connected to a circumferential scanning module;

[0009] The ToF laser radar module has M groups of transmitting channels and M groups of receiving channels distributed in one-dimensional space, and M laser pulses are emitted through the M groups of transmitting channels. The M laser pulses are emitted through the spectroscope module and the panoramic scanning module to form M transmitting light beams in the one-dimensional vertical direction, and are rotated 360° in the horizontal direction through the panoramic scanning module to achieve two-dimensional panoramic scanning; after the M transmitting light beams are emitted to the target object, the M receiving light beams returned by the target object are received by the M groups of receiving channels of the ToF laser radar module after passing through the panoramic scanning module and the spectroscope module, so as to obtain a direct detection signal of the target object;

[0010] The FMCW laser radar module generates N groups of transmission channels and N groups of receiving channels with a time dimension through a bidirectional optical switch array; the FMCW laser radar module continuously transmits N FMCW light beams, which are then emitted through a spectroscope module and a panoramic scanning module to form N transmission light beams in a one-dimensional vertical direction, and are rotated 360° in the horizontal direction through the panoramic scanning module to achieve two-dimensional panoramic scanning; after the N transmission light beams are emitted to the target object, the N receiving light beams returned by the target object are coherently received with the local oscillator light beam of the FMCW laser radar module after passing through the panoramic scanning module and the spectroscope module to obtain a coherent detection signal of the target object;

[0011] The detection signals of the ToF laser radar module and the FMCW laser radar module are respectively subjected to digital signal processing in the signal processing module to realize parallel synchronous measurement of the distance and vector velocity between the laser radar device and the target.

[0012] In the above-mentioned ToF and FMCW laser radar panoramic scanning composite detection method, the M emission light beams formed by the ToF laser radar module in the one-dimensional vertical direction respectively correspond to unique vertical spatial angles; the direct detection signal obtained by the ToF laser radar module measures the round-trip time difference between the M emission light beams and the M receiving light beams through the signal processing module, and based on the propagation speed of light in the air and the horizontal scanning angle of the panoramic scanning module, calculates the ToF distance point cloud data of the target object at M points.

[0013] The aforementioned ToF and FMCW laser radar panoramic scanning composite detection method, the FMCW laser light source module of the FMCW laser radar module generates a continuous laser with symmetrical triangular wave linear modulation, which is divided into an outgoing beam and a local oscillator beam after amplification and beam splitting, and the outgoing beam passes through an optical circulator, and then passes through a bidirectional optical switch array, a collimated directional transmitter, a spectroscope module and a panoramic scanning module in sequence to emit to the target, wherein the output ports of the bidirectional optical switch array are arranged along a one-dimensional direction and are all arranged on the focal plane of the collimated directional transmitter's emitting optical component, and the optical signals output from different ports are emitted in different angles after passing through the emitting optical component. The N transmitting light beams are emitted in the one-dimensional vertical direction, each of which corresponds to a unique vertical spatial angle. The N transmitting light beams are rotated 360° in the horizontal direction by the panoramic scanning module. The N receiving light beams returned by the target are combined with the local oscillator light beam for interference to generate a beat signal. The beat signal is mixed by an optical mixer to output an in-phase signal and an orthogonal signal with orthogonal characteristics. The in-phase signal and the orthogonal signal are received by a photoelectric balanced detector respectively, and then the analog-to-digital conversion is completed by the analog-to-digital converter. The data are collected and spectrally processed by the field programmable gate array module to calculate the FMCW distance point cloud data of the target object at N points.

[0014] The aforementioned ToF and FMCW laser radar panoramic scanning composite detection method, the signal processing module performs synchronous measurement and fusion of ToF distance point cloud data and FMCW distance point cloud data according to the respective detection signals of the ToF laser radar module and the FMCW laser radar module, obtains high-resolution point cloud information in the two-dimensional direction, and realizes accurate synchronous distance measurement and speed measurement.

[0015] The device for implementing the aforementioned ToF and FMCW laser radar panoramic scanning composite detection method comprises:

[0016] ToF LiDAR module for direct detection of targets;

[0017] FMCW LiDAR module for coherent detection of targets;

[0018] A spectroscope module is connected to the ToF laser radar module and the FMCW laser radar module; the spectroscope module is used to combine the emission light beams and split the receiving light beams of the ToF laser radar module and the FMCW laser radar module to achieve wavelength multiplexing of the two types of laser radars;

[0019] A panoramic scanning module connected to the spectroscope module; the panoramic scanning module is used to emit and receive lasers from the ToF laser radar module and the FMCW laser radar module, and to achieve two-dimensional panoramic scanning of the ToF laser beam and the FMCW laser beam;

[0020] A signal processing module is connected to the ToF laser radar module and the FMCW laser radar module; the signal processing module processes the detection signals obtained by the ToF laser radar module and the FMCW laser radar module to realize parallel synchronous measurement of the distance and vector velocity between the laser radar device and the target object.

[0021] In the aforementioned device, the ToF laser radar module includes a ToF laser light source module, a ToF laser transmitting module and a ToF laser receiving module; the ToF laser light source module is connected to the spectroscope module via the ToF laser transmitting module; the ToF laser receiving module is connected to the spectroscope module and the signal processing module.

[0022] In the aforementioned device, the FMCW laser radar module includes an FMCW laser light source module, an FMCW laser emission module and an FMCW coherent receiving module; the FMCW laser light source module is connected to the spectroscope module via the FMCW laser emission module; the FMCW coherent receiving module is connected to the spectroscope module and the signal processing module.

[0023] In the aforementioned device, the FMCW laser light source module is a linear frequency modulated continuous wave laser light source; the FMCW laser transmitting module includes a laser amplifier connected to the FMCW laser light source module, and the laser amplifier is sequentially connected to an optical beam splitter, an optical circulator, a bidirectional optical switch array and a collimated directional transmitter along the laser transmission direction, wherein the output ports of the bidirectional optical switch array are arranged along a one-dimensional direction and are all arranged on the focal plane of the emitting optical component of the collimated directional transmitter, and the optical signals output from different ports are emitted at different angles after passing through the emitting optical component; the FMCW coherent receiving module includes an optical mixer, and the output end of the optical mixer is connected to a photoelectric balanced detector; the optical beam splitter and the optical circulator are connected to the optical mixer together.

[0024] In the aforementioned device, the beam splitter module is a dichroic beam splitter; the panoramic scanning module includes a de-image rotation prism and a panoramic rotating mirror arranged along the laser transmission direction of the dichroic beam splitter; the de-image rotation prism and the panoramic rotating mirror are respectively connected to servo motors, and under the control of the servo motor, the de-image rotation prism and the panoramic rotating mirror rotate in the same direction at a speed ratio of 1:2 to achieve image-free 360° panoramic scanning.

[0025] In the aforementioned device, the signal processing module includes an analog-to-digital converter connected to the ToF laser radar module and the FMCW laser radar module, and the analog-to-digital converter is connected to a field programmable gate array module.

[0026] Compared with the prior art, the present invention realizes the horizontal 360º panoramic composite detection of ToF and FMCW laser radars under the premise of limited increase in volume, and efficiently combines the respective advantages of TOF and FMCW laser radars, which can not only obtain high-resolution point cloud data in the two-dimensional direction, but also realize synchronous ranging and speed measurement in the region of interest (ROI). In addition, the present invention gets rid of the complex upper and lower warehouse structure of the traditional multi-line panoramic scanning laser radar, has no fast axis scanning, has a small moment of inertia, a simple structure, high reliability, can be integrated and miniaturized, and has a low system cost. It has good development prospects in the field of vehicle-mounted and ship-mounted laser radars. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the device of the present invention.

[0028] Figure 2 It is a structural diagram of the ToF laser emission module.

[0029] Figure 3 It is a structural diagram of the ToF laser receiving module.

[0030] Figure 4 It is a structural diagram of the FMCW lidar module.

[0031] Figure 5 This is a schematic diagram of the principle of the ToF laser emission module.

[0032] Figure 6 This is a schematic diagram of the principle of the ToF laser receiving module.

[0033] Figure 7 It is a schematic diagram of the timing waveform relationship of the transmit-receive signal of the ToF lidar module.

[0034] Figure 8 It is a schematic diagram of the waveform relationship and frequency difference of the symmetrical triangle wave linear frequency modulation continuous wave receiving-local oscillator beam of the FMCW laser radar module.

[0035] Fig. 9 It is a schematic diagram of the scanning field coordinate system of the laser radar device, including the distance R and azimuth of the target object. and pitch angle .

[0036] Fig.10 A schematic diagram of the connection relationship between a 1×N bidirectional optical switch array and an N-channel collimated directional transmitter is given; the output ports of the 1×N bidirectional optical switch array are arranged along a one-dimensional direction and are all set on the focal plane of the transmitting optical component of the N-channel collimated directional transmitter. The optical signals output from different ports are emitted at different angles after passing through the transmitting optical component.

[0037] Fig.11A schematic diagram of an embodiment of composite detection of 905nmToF laser radar and 1550nmFMCW laser radar is given.

[0038] Fig.12 A schematic diagram of the composite detection point cloud distribution of ToF lidar and FMCW lidar is given.

[0039] Reference numerals:

[0040] 1. ToF laser radar module; 2. FMCW laser radar module; 3. Spectroscope module; 4. Panoramic scanning module; 5. Signal processing module; 6. ToF laser light source module; 7. ToF laser emission module; 8. ToF laser receiving module; 9. FMCW laser light source module; 10. FMCW laser emission module; 11. FMCW coherent receiving module; 12. Laser amplifier; 13. 1×2 optical beam splitter; 14. Optical circulator; 15. 1×N bidirectional optical switch array; 16. N-channel collimated directional transmitter; 17. 2×4 90º optical mixer; 18. Photoelectric balanced detector; 19. De-image rotation prism; 20. Panoramic rotating mirror; 21. Servo motor; 22. Analog-to-digital converter; 23. Field programmable gate array module. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0042] Embodiment 1: A ToF and FMCW composite detection periscopic scanning laser radar device, such as Figure 1 As shown, including:

[0043] ToF laser radar module 1, used for direct detection of targets;

[0044] FMCW LiDAR module 2, used for coherent detection of targets;

[0045] The spectroscope module 3 is connected to the ToF laser radar module 1 and the FMCW laser radar module 2. The spectroscope module 3 is used to combine and split the laser beams of the ToF laser radar module 1 and the FMCW laser radar module 2 to achieve wavelength multiplexing of the two types of laser radars. If the wavelengths of the ToF laser radar module 1 and the FMCW laser radar module 2 are different, the spectroscope module 3 is a dichroic spectroscope, which selectively increases the transmittance or reflection of incident light of different wavelengths to achieve the combination of the emission light of the short-wave ToF laser radar and the long-wave FMCW laser radar and the splitting of the received light. If the wavelengths of the two types of lasers are the same, the spectroscope module can be a polarization spectroscope, which selectively transmits or reflects the orthogonally polarized incident light to achieve the combination of the emission light of the orthogonally polarized ToF laser radar and the FMCW laser radar and the splitting of the received light. In the embodiment of the present invention, in order to simplify the description, only the first case is considered, that is, the wavelengths of the ToF laser radar module 1 and the FMCW laser radar module 2 are different.

[0046] A circumferential scanning module 4 is connected to the spectroscope module 3, and is used to emit and receive lasers of the ToF laser radar module 1 and the FMCW laser radar module 2, and realize 360° non-image rotation circumferential scanning; the circumferential scanning module 4 includes an image derotation prism 19 and a circumferential rotation mirror 20 arranged along the laser transmission direction of the dichroic spectroscope; the image derotation prism 19 and the circumferential rotation mirror 20 are respectively connected to servo motors 21, and under the control of the two servo motors, the image derotation prism 19 and the circumferential rotation mirror 20 rotate in the same direction at a speed ratio of 1:2 to realize non-image rotation circumferential scanning. In order to ensure complete image derotation, it is necessary to ensure the initial phase difference and complete phase lock between the two servo motors;

[0047] The signal processing module 5 is connected to the ToF laser radar module 1 and the FMCW laser radar module 2; the signal processing module 5 processes the target receiving light beams obtained by the ToF laser radar module 1 and the FMCW laser radar module 2 to realize parallel synchronous measurement of the distance and vector velocity between the laser radar device and the target object.

[0048] In this embodiment, the ToF laser radar module 1 includes a ToF laser light source module 6, a ToF laser emitting module 7 and a ToF laser receiving module 8; the ToF laser light source module 6 is connected to the spectroscope module 3 via the ToF laser emitting module 7; the ToF laser receiving module 8 is connected to the spectroscope module 3 and the signal processing module 5. Among them, the ToF laser light source module 6 is used to emit laser pulses, such as Figure 2As shown, the ToF laser emission module 7 has M groups of emission channels in the spatial dimension. The M groups of emission channels pass through the emission lens, and then pass through the dichroic beam splitter, the de-image rotation prism and the periscopic rotating mirror to form M emission light beams in the one-dimensional vertical direction and rotate 360° in the horizontal direction. Each emission light beam corresponds to a unique spatial angle; Figure 3 As shown, the ToF laser receiving module 8 has M groups of receiving channels in a spatial dimension. The M groups of receiving channels receive M receiving light beams returned by the target through the transmitting lens to achieve direct detection of the target.

[0049] In this embodiment, Figure 4 As shown, 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; the FMCW laser light source module 9 is connected to the spectroscope module 3 via the FMCW laser emission module 10; 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 modulated continuous wave laser light source; the FMCW laser transmitting module 10 includes a laser amplifier 12 connected to the linear frequency modulated continuous wave laser light source, and the laser amplifier 12 is sequentially connected to a 1×2 optical beam splitter 13, an optical circulator 14, a 1×N bidirectional optical switch array 15 and an N-channel collimated directional transmitter 16 along the laser transmission direction, wherein the output ports of the 1×N bidirectional optical switch array 15 are arranged along a one-dimensional direction and are all arranged on the focal plane of the transmitting optical component of the N-channel collimated directional transmitter 16, and the optical signals output from different ports are emitted at different angles after passing through the transmitting optical component; the FMCW coherent receiving module 11 includes a 2×4 90° optical mixer 17, and the output end of the 2×4 90° optical mixer 17 is connected to a photoelectric balanced detector 18; the 1×2 optical beam splitter 13 and the optical circulator 14 are connected to the 2×4 90° optical mixer together.

[0050] In this embodiment, the signal processing module 5 includes an analog-to-digital converter 22 connected to the ToF laser radar module 1 and the FMCW laser radar module 2, that is, the analog-to-digital converter 22 is respectively connected to the ToF laser receiving module 8 of the ToF laser radar module 1 and the photoelectric balanced detector 18 of the FMCW laser radar module 2, and the analog-to-digital converter 22 is used to realize the conversion of analog-to-digital signals; the analog-to-digital converter 22 is connected to a field programmable gate array module 23 (referred to as FPGA module), and the field programmable gate array module 23 is used to realize the processing of digital signals.

[0051] Embodiment 2: A composite detection method of ToF and FMCW laser radar for panoramic scanning is based on the ToF and FMCW composite detection and panoramic scanning laser radar device in Embodiment 1. In this method, the ToF laser radar module has M groups of transmitting channels and M groups of receiving channels distributed in one-dimensional space. The ToF laser radar module transmits through M groups of transmitting channels (i.e., the ToF laser transmitting module has M groups of ToF transmitting units, Figure 5 A schematic diagram of stacking M groups of transmitting units is given) to emit M laser pulses (also called M short-wavelength lasers), which are then emitted through the spectroscope module and the panoramic scanning module to form M transmitting beams in the one-dimensional vertical direction. Each transmitting beam corresponds to a unique vertical spatial angle. The M transmitting beams are rotated 360° in the horizontal direction by the panoramic scanning module. After the M transmitting beams are emitted to the target, the M receiving beams returned by the target are received by M groups of receiving channels (i.e., the ToF laser receiving module has M groups of ToF receiving units, Figure 6 A stacking diagram of M groups of ToF receiving units is given to achieve direct detection of M point targets, obtain direct detection signals of the targets, and achieve complete matching of the transmitting or receiving fields of view.

[0052] The FMCW laser radar module generates N groups of transmitting channels and N groups of receiving channels with a time dimension (i.e., sequentially selected) through controllable gating of a 1×N bidirectional optical switch array. The FMCW laser radar module continuously emits N frequency-modulated continuous waves, which are then emitted through a spectroscope module and a panoramic scanning module to form N transmitting light beams in a one-dimensional vertical direction. Each transmitting light beam corresponds to a unique vertical spatial angle. The N transmitting light beams are rotated 360° in the horizontal direction through the panoramic scanning module. After the N transmitting light beams are emitted to the target object, the N receiving light beams returned by the target object are coherently received with the local oscillator light beam of the FMCW laser radar module after passing through the panoramic scanning module and the spectroscope module, thereby realizing coherent detection of the target object and achieving complete matching of the transmitting or receiving field of view.

[0053] The detection signals of the ToF laser radar module and the FMCW laser radar module are respectively subjected to ADC sampling and digital signal processing in the signal processing module, so as to realize parallel synchronous measurement of the distance and vector velocity between the laser radar platform and the target object.

[0054] Specifically, for the ToF laser radar module, the power of the emission light beam output by the ToF laser light source module is a time function with a Gaussian model, which can be expressed as:

[0055] ;

[0056] In the formula, is the initial energy of the emitted beam; is the pulse width of the transmitted beam, Indicates time;

[0057] According to the lidar equation, the power of the received beam can be expressed as:

[0058] ;

[0059] in, 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 emission 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 reception delay.

[0060] The ToF laser radar module obtains the target reception delay by measuring the time difference between the transmitted light beam and the received light beam. , and then get the distance of the target , which can be expressed as:

[0061] ;

[0062] in, It is the speed of light; is the target reception delay.

[0063] Figure 7 A schematic diagram of the timing waveform relationship between the emitted light beam and the received light beam of the ToF lidar module is given.

[0064] For the FMCW laser radar module, the FMCW laser light source module generates a continuous laser with linear frequency modulation, using symmetrical triangular wave linear modulation. The frequency of the modulation signal changes in a symmetrical triangle over time. In one cycle, the first half is called forward frequency modulation ( ), the second half is called negative frequency modulation ( ). Figure 8 A schematic diagram of the waveform relationship and frequency difference (beat frequency) of the symmetrical triangle wave linear frequency modulated continuous wave receiving-local oscillator beam is given.

[0065] The linear frequency modulated continuous wave laser light source generates a symmetrical triangle wave linear frequency modulated continuous laser, which is amplified by a laser amplifier and then divided into a local oscillator beam and an output beam by a 1×2 optical beam splitter;

[0066] Most of the energy (99%) is used as the outgoing beam, passes through the optical circulator, and then exits through the 1×N bidirectional optical switch array, N-channel collimated directional transmitter, dichroic beam splitter, de-image rotation prism and periscopic rotating mirror, forming N emission beams in the one-dimensional vertical direction. Each emission beam corresponds to a unique vertical spatial angle. The N emission beams rotate 360° in the horizontal direction and are emitted to the target, such as Fig.10 shown.

[0067] Among them, the 1×N bidirectional optical switch array is turned on in sequence. When the channel is turned on, the light field of the emitted light beam can be expressed as:

[0068] ;

[0069] In the formula, ; For time; is the amplitude; is the frequency modulation period; is the initial frequency of FM; is the frequency modulation rate, is the FM bandwidth; For the The initial phase of the rising segment of each channel; For the The initial phase of the descending segment of each channel; It is an exponential function with a natural constant as base;

[0070] The received beam at the target is time delayed The linear frequency modulation signal, the light field can be expressed as:

[0071] ;

[0072] In the formula, is the amplitude of the received beam, is the noise phase of the received beam.

[0073] A small part of the energy (99%) is used as the local oscillator beam, which is time-delayed The linear frequency modulation signal, the light field can be expressed as:

[0074] ;

[0075] Where: is the amplitude of the local oscillator beam, is the noise phase of the local oscillator beam.

[0076] After the target's receiving beam is combined with the local oscillator beam, the interference light field is expressed as:

[0077] ;

[0078] Time delay of the received beam Time delay with the local oscillator beam It is expressed as:

[0079] ;

[0080] Where: is the target distance; is the radial velocity of the relative motion between the radar device and the target; It is the Doppler frequency shift caused by the radial velocity of the relative motion between the radar device and the target.

[0081] After being mixed by the 2×4 90° optical mixer, the four outputs of in-phase and quadrature signals with orthogonal characteristics are:

[0082] ;

[0083] ;

[0084] Where: It is Channel mixing noise phase; is the DC quantity associated with the received beam; is the DC quantity associated with the local oscillator beam;

[0085] The in-phase signal and the orthogonal signal are received by the photoelectric balanced detector respectively, and the in-phase signal and the orthogonal signal are output by the photoelectric balanced detector respectively:

[0086] ;

[0087] ;

[0088] Where: is the photodetector responsivity for in-phase signals; is the photodetector responsivity for the orthogonal signal; and are the noise phases of the in-phase and quadrature signals, respectively;

[0089] For simplicity, the following formula is used to replace the amplitude of the in-phase signal and the orthogonal signal;

[0090] ;

[0091] Then the in-phase signal and the quadrature signal are simplified to:

[0092] ;

[0093] ;

[0094] The in-phase signal and the orthogonal signal with orthogonal characteristics are converted from analog to digital by the analog-to-digital converter, and then collected by the field programmable gate array module for spectrum processing:

[0095] First, the in-phase signal and the orthogonal signal are subjected to fast Fourier transform (FFT) respectively. The Fourier transform of the in-phase signal is expressed as:

[0096] ;

[0097] The Fourier transform of the orthogonal signal is expressed as:

[0098] ;

[0099] The two signals are processed by cross spectrum:

[0100] ;

[0101] Where: represents the conjugate operation;

[0102] Finally, we only take the imaginary part and get:

[0103] ;

[0104] Therefore, by extracting the peak position and positive and negative of the spectrum by the centroid method, we can get the positive and negative frequency modulation processes respectively. :

[0105] ;

[0106] From the above formula we can get:

[0107] ;

[0108] Since the Doppler frequency is proportional to the speed of relative motion between the radar platform and the target, the positive and negative Doppler frequency shift is related to the direction of the relative motion radial velocity. A positive frequency shift represents that the radar platform and the target are moving towards each other, and a negative frequency shift represents that the radar platform and the target are moving away from each other. Therefore, the magnitude and direction of the relative motion radial velocity between the radar platform and the target can be obtained from the Doppler frequency shift, which can be expressed as:

[0109] ;

[0110] Where: Indicates wavelength;

[0111] The distance to the target point can also be obtained from the above formula:

[0112] .

[0113] In this embodiment, the N emission beams of the FMCW laser radar module are all coaxially transmitted or received in parallel, and the transmission or reception field of view is completely matched. A field programmable gate array module is used to perform real-time parallel fast Fourier transform on each sampled data obtained, thereby realizing the sequential measurement of the distance and speed of N point targets.

[0114] Furthermore, in order to increase the emission point frequency of the ToF laser radar module, a combination of J ToF laser radar modules is used. J ToF laser radar modules correspond to J ToF laser emission modules. The output ports are arranged in a one-dimensional direction, forming JM emission beams in the one-dimensional vertical direction. Each emission beam corresponds to a unique vertical spatial angle. The JM emission beams rotate 360° in the horizontal direction to achieve two-dimensional panoramic scanning. After the JM ToF emission beams are emitted to the target, the JM receiving beams returned by the target pass through the panoramic scanning module and the spectroscope module, and are received by the photoelectric detectors of the JM receiving channels. The detection signal of the ToF laser radar module is converted by the analog-to-digital converter. The round-trip time difference of the JM emission beams and the JM receiving beams is directly measured by the field programmable gate array module (FPGA module), and the target distance point cloud information of JM points is calculated based on the propagation speed of light in the air and the horizontal scanning angle of the panoramic scanning module. In this way, the total point frequency of the ToF laser radar module and the one-dimensional vertical point cloud number are increased by J times.

[0115] Similarly, in order to increase the emission point frequency of the FMCW laser radar module, a combination of K FMCW laser radar modules can be used. The K FMCW laser radar modules correspond to K 1×N bidirectional optical switch arrays and KN channel collimated directional transmitters, wherein the output ports of the K 1×N bidirectional optical switch arrays are arranged in a one-dimensional direction and are all set on the focal plane of the emission optical component of the KN channel collimated directional transmitter. The optical signals output from different ports are emitted at different angles after passing through the emission optical component, forming KN emission beams in the one-dimensional vertical direction. Each emission beam corresponds to a unique vertical spatial angle. The KN emission beams rotate 360° in the horizontal direction. After the KN emission beams are emitted to the target, the KN receiving beams returned by the target are coherently mixed with the K local oscillator beams of the FMCW laser radar module after passing through the panoramic scanning module and the spectroscope module, so as to realize the coherent detection of the target. In this way, the total point frequency of the FMCW laser radar module and the number of one-dimensional vertical point clouds are increased by K times.

[0116] Furthermore, in this embodiment, the ToF laser radar module and the FMCW laser radar module respectively collect the angle information between the radar device and the target according to the field programmable gate array module. The three-dimensional space coordinates of the target point P are obtained by conversion, such as Fig. 9 As shown, it is expressed as:

[0117] ;

[0118] In the ToF laser radar module, the emission frequency of each ToF laser light source module is , the transmission repetition frequency of the stacked M groups of transmitting units is also , each transmitting unit corresponds to a scan line in the vertical direction, that is, M scan lines in the vertical direction, covering a field of view of , the frame rate is , the horizontal angle resolution and vertical angle resolution are:

[0119] .

[0120] In the FMCW laser radar module, the emission frequency of the FMCW laser light source module is Each channel of the 1×N bidirectional optical switch array corresponds to a scan line in the vertical direction, that is, N scan lines in the vertical direction, covering a field of view of , the frame rate is , the horizontal angle resolution and vertical angle resolution are:

[0121] .

[0122] Therefore, by integrating 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, such as Fig.12 As shown. Since the ToF laser light source module of the ToF lidar module can be integrated through semiconductor technology, a point cloud distribution with a large field of view and high resolution can be achieved. The FMCW distance point cloud data of the FMCW lidar module can be concentrated in the region of interest (also known as ROI), which complements the ToF distance point cloud data of the ToF lidar module. On the one hand, it can provide a large horizontal field of view and a vertical field of view, and have a sufficiently high horizontal angular resolution and vertical angular resolution to achieve blind spot detection around the lidar platform and ensure that long-distance targets can be effectively distinguished; on the other hand, it can simultaneously achieve distance measurement and speed measurement in the ROI area, and has complete anti-interference capabilities.

[0123] Example 3: Based on Example 1 and Example 2, Fig.11As shown, a 905nm TOF laser radar module and a 1550nm FMCW laser radar module are used for composite detection. A coated dichroic beam splitter is used to achieve high transmittance of short-wave 905nm laser and high reflection of long-wave 1550nm laser. The image rotation prism uses a chromatic aberration-designed Dove prism to ensure that image rotation compensation can be achieved in both the 905nm and 1550nm bands. The panoramic rotating mirror uses a 45° full-reflection mirror and uses coating to achieve high reflection of short-wave 905nm and long-wave 1550nm lasers.

[0124] The dove prism and the 45° total reflection mirror are respectively connected to servo motors. Under the control of the two servo motors, the dove prism and the 45° total reflection mirror rotate in the same direction at a speed ratio of 1:2 to achieve image rotation-free circumferential scanning. The speed of the dove prism is 1800° / s, corresponding to a frequency of 5Hz, and the speed of the 45° total reflection mirror is 3600° / s, corresponding to a frequency of 10Hz. In order to ensure complete elimination of image rotation, it is necessary to ensure the initial phase difference and complete phase locking between the two servo motors.

[0125] The transmitter of the TOF LiDAR module integrates 256 independent VCSEL lasers, each with a transmission frequency of 37.5kHz, and the receiver integrates 32 silicon-based photomultiplier tubes (SiPM) single-photon detector modules. The transmitter and receiver use coaxial optical paths and achieve complete matching of the transmitting or receiving field of view. The rotation range of the panorama mirror is 360° horizontally, and the vertical range of the laser beam is 25.6°, that is, the total field of view is 360°×25.6°, the horizontal resolution is 0.096°, and the vertical resolution is 0.1°. Each frame of the point cloud can form 3750 dots in the horizontal direction and 256 dots in the vertical direction. The frame rate is 10Hz, and the total dot frequency of the ToF distance point cloud data is 9.6MHz.

[0126] In order to increase the frequency, the FMCW laser radar module integrates 8 independent FMCW transmitting and receiving units. The transmitting frequency of each FMCW unit is 300kHz, symmetrical triangle wave linear modulation, sweep bandwidth 2GHz, ranging resolution 7.5cm, and speed resolution 0.465m / s. The 8 coherent receiving ends all use 2×4 90° optical mixers and photoelectric balanced detectors. Each FMCW transmitting and receiving unit is connected to a 1×8 silicon-based bidirectional high-speed electro-optical switch, and 8 1×8 silicon-based bidirectional high-speed electro-optical switches form a 64-unit electro-optical switch array. The 64-unit electro-optical switch array is connected to a 64-channel collimated transmitter. The output ports of the 64-unit bidirectional optical switch array are arranged in a one-dimensional direction and are all set on the focal plane of the 64-channel collimated directional transmitter transmitting optical components. The optical signals output from different ports are emitted at different angles after passing through the transmitting optical components.

[0127] The FMCW LiDAR module continuously emits 64 frequency modulated continuous waves, which are then emitted through the spectroscope module and the panoramic scanning module to form 64 emission beams in the one-dimensional vertical direction. Each emission beam corresponds to a unique vertical spatial angle, and the 64 emission beams rotate 360° in the horizontal direction. After the 64 emission beams are emitted to the target, the 64 receiving beams returned by the target are coherently mixed with the local oscillator beam after passing through the panoramic scanning module and the spectroscope module to achieve coherent detection of the target. The 64 emission beams of the FMCW LiDAR module are all coaxially transmitted or received in parallel, and the transmission or reception field of view is fully matched. The rotation range of the panoramic rotating mirror is 360° horizontally, and the vertical range of the laser beam is 6.4°, that is, the total field of view is 360°×6.4°, the horizontal resolution is 0.096°, and the vertical resolution is 0.1°. Each frame of point cloud can form 3750 dots in the horizontal direction and 64 dots in the vertical direction. The frame rate is 10Hz, and the total point frequency of FMCW distance point cloud data is 2.4MHz.

[0128] The ROI area is set as a field of view of 360°×6.4° in the center. In the ROI area, the array of each frame of ToF distance point cloud data is 3750 × 64, and the array of each frame of FMCW distance point cloud data is 3750 × 64. The ToF distance point cloud data and the FMCW distance point cloud data are equally spaced in the vertical direction, so the vertical resolution of the composite field of view is 0.05° and the horizontal resolution is 0.096°. Thus, high-resolution point cloud information is obtained in the two-dimensional direction, and the ranging resolution of the ROI area is 7.5cm, and the speed resolution is 0.465m / s, achieving accurate synchronous ranging and speed measurement.

[0129] In summary, the present invention realizes the horizontal 360° panoramic composite detection of ToF and FMCW laser radars under the premise of limited increase in volume, efficiently combines TOF and FMCW laser radar technologies, highlights their respective advantages, and can not only obtain high-resolution point cloud data in two-dimensional directions, but also realize synchronous ranging and speed measurement in the region of interest (ROI). In addition, the present invention gets rid of the complex upper and lower warehouse structure of traditional multi-line panoramic laser radars, has no fast axis scanning, has a small moment of inertia, a simple structure, high reliability, can be integrated and miniaturized, and has a low system cost. It has good development prospects in the field of vehicle-mounted and ship-mounted laser radars.

Claims

1. ToF and FMCW laser radar panoramic scanning composite detection method, characterized by: It includes 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 to a spectroscope module and a signal processing module, and the spectroscope module is connected to a panoramic scanning module; The ToF laser radar module has M groups of transmitting channels and M groups of receiving channels distributed in one-dimensional space, and M laser pulses are emitted through the M groups of transmitting channels. The M laser pulses are emitted through the spectroscope module and the panoramic scanning module to form M transmitting light beams in the one-dimensional vertical direction, and are rotated 360° in the horizontal direction through the panoramic scanning module to achieve two-dimensional panoramic scanning; after the M transmitting light beams are emitted to the target object, the M receiving light beams returned by the target object are received by the M groups of receiving channels of the ToF laser radar module after passing through the panoramic scanning module and the spectroscope module, so as to obtain a direct detection signal of the target object; The FMCW laser radar module generates N groups of transmitting channels and N groups of receiving channels with a time dimension through a bidirectional optical switch array; The FMCW laser radar module continuously emits N FMCW light beams, which are then emitted through the spectroscope module and the panoramic scanning module to form N emission light beams in a one-dimensional vertical direction, and are rotated 360° in the horizontal direction through the panoramic scanning module to achieve two-dimensional panoramic scanning; after the N emission light beams are emitted to the target object, the N receiving light beams returned by the target object are coherently received with the local oscillator light beam of the FMCW laser radar module after passing through the panoramic scanning module and the spectroscope 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 respectively subjected to digital signal processing in the signal processing module to achieve parallel synchronous measurement of the distance and vector velocity between the laser radar device and the target; The FMCW laser light source module of the FMCW laser radar module generates a continuous laser with symmetrical triangular wave linear modulation, which is divided into an outgoing beam and a local oscillator beam after amplification and beam splitting. The outgoing beam passes through an optical circulator, and then passes through a bidirectional optical switch array, a collimated directional transmitter, a spectroscope module and a panoramic scanning module in sequence to be emitted to the target, wherein the output ports of the bidirectional optical switch array are arranged in a one-dimensional direction and are all arranged on the focal plane of the emitting optical component of the collimated directional transmitter. The optical signals output from different ports are emitted at different angles after passing through the emitting optical component, forming N in a one-dimensional vertical direction. The N transmitting beams are rotated 360° in the horizontal direction by the panoramic scanning module. The N receiving beams returned by the target are combined with the local oscillator beam for interference to generate a beat signal. The beat signal is mixed by the optical mixer to output an in-phase signal and a quadrature signal with orthogonal characteristics. The in-phase signal and the quadrature signal are received by the photoelectric balanced detector respectively, and then the analog-to-digital converter is used to complete the analog-to-digital conversion. The data are collected and spectrally processed by the field programmable gate array module to calculate the FMCW distance point cloud data of the target object at N points.

2. The ToF and FMCW laser radar panoramic scanning composite detection method according to claim 1 is characterized in that: The M emission light beams formed by the ToF laser radar module in the one-dimensional vertical direction respectively correspond to unique vertical spatial angles; the direct detection signal obtained by the ToF laser radar module measures the round-trip time difference between the M emission light beams and the M receiving light beams through the signal processing module, and based on the propagation speed of light in the air and the horizontal scanning angle of the panoramic scanning module, calculates the ToF distance point cloud data of the target object at M points.

3. The ToF and FMCW laser radar panoramic scanning composite detection method according to claim 1 is characterized in that: The signal processing module performs synchronous measurement and fusion of ToF distance point cloud data and FMCW distance point cloud data according to the respective detection signals of the ToF laser radar module and the FMCW laser radar module, obtains high-resolution point cloud information in a two-dimensional direction, and realizes accurate synchronous distance measurement and speed measurement.

4. A device for implementing the ToF and FMCW laser radar panoramic scanning composite detection method according to any one of claims 1 to 3, characterized in that: include: ToF laser radar module (1), used for direct detection of targets; FMCW laser radar module (2) for coherent detection of targets; A spectroscope module (3) is connected to the ToF laser radar module (1) and the FMCW laser radar module (2); the spectroscope module (3) is used to combine the emission light beams of the ToF laser radar module (1) and the FMCW laser radar module (2) and split the received light beams, thereby realizing wavelength multiplexing of the two types of laser radars; A panoramic scanning module (4) is connected to the spectroscope module (3); the panoramic scanning module (4) is used to emit and receive lasers from the ToF laser radar module (1) and the FMCW laser radar module (2), and to achieve two-dimensional panoramic scanning of the ToF laser beam and the FMCW laser beam; A signal processing module (5) is connected to the ToF laser radar module (1) and the FMCW laser radar module (2); the signal processing module (5) processes the detection signals acquired by the ToF laser radar module (1) and the FMCW laser radar module (2) to achieve parallel synchronous measurement of the distance and vector velocity between the laser radar device and the target object.

5. The device according to claim 4, characterized in that: The ToF laser radar module (1) comprises a ToF laser light source module (6), a ToF laser emission module (7) and a ToF laser receiving module (8); the ToF laser light source module (6) is connected to the spectroscope module (3) via the ToF laser emission module (7); and the ToF laser receiving module (8) is connected to the spectroscope module (3) and the signal processing module (5).

6. The device according to claim 4, characterized in that: The FMCW laser radar module (2) comprises an FMCW laser light source module (9), an FMCW laser emission module (10) and an FMCW coherent receiving module (11); the FMCW laser light source module (9) is connected to the spectroscope module (3) via 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).

7. The device according to claim 6, characterized in that: The FMCW laser light source module (9) is a linear frequency modulated continuous wave laser light source; the FMCW laser transmitting module (10) comprises a laser amplifier (12) connected to the FMCW laser light source module (9); the laser amplifier (12) is sequentially connected to an optical beam splitter (13), an optical circulator (14), a bidirectional optical switch array (15) and a collimated directional transmitter (16) along a laser transmission direction, wherein the output ports of the bidirectional optical switch array (15) are arranged along a one-dimensional direction and are all arranged on the focal plane of a transmitting optical component of the collimated directional transmitter (16); optical signals output from different ports are emitted at different angles after passing through the transmitting optical component; the FMCW coherent receiving module (11) comprises an optical mixer (17); an output end of the optical mixer (17) is connected to a photoelectric balanced detector (18); the optical beam splitter (13) and the optical circulator (14) are connected to the optical mixer together.

8. The device according to claim 4, characterized in that: The beam splitter module (3) is a dichroic beam splitter; the panoramic scanning module (4) comprises a de-image rotation prism (19) and a panoramic rotating mirror (20) arranged along the laser transmission direction of the dichroic beam splitter; the de-image rotation prism (19) and the panoramic rotating mirror (20) are respectively connected to a servo motor (21); under the control of the servo motor (21), the de-image rotation prism (19) and the panoramic rotating mirror (20) rotate in the same direction at a speed ratio of 1:2 to achieve 360° panoramic scanning without image rotation.

9. The device according to claim 4, characterized in that: The signal processing module (5) comprises an analog-to-digital converter (22) connected to the ToF laser radar module (1) and the FMCW laser radar module (2), and the analog-to-digital converter (22) is connected to a field programmable gate array module (23).

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