Ranging method and system for laser radar

Abstract

The invention provides a distance measuring method for a laser radar. The method comprises the following steps: generating a frequency sweeping light beam; the swept-frequency light beam is split into a signal light beam and a local oscillation light beam, each of the signal light beam and the local oscillation light beam comprises a first frequency raising stage, a second frequency raising stage, a first frequency lowering stage and a second frequency lowering stage, the slope of the first frequency raising stage is different from that of the second frequency raising stage, and the slope of the first frequency lowering stage is different from that of the second frequency lowering stage; transmitting a signal light beam; receiving a reflected light beam; detecting the beat frequency of a first frequency raising stage, the beat frequency of a second frequency raising stage, the beat frequency of a first frequency lowering stage and the beat frequency of a second frequency lowering stage between the local oscillator light beam and the reflected light beam; and measuring the speed of the target object and / or the distance between the target object and the laser radar by using two of the beat frequency of the first frequency raising stage, the beat frequency of the second frequency raising stage, the beat frequency of the first frequency lowering stage and the beat frequency of the second frequency lowering stage.

Description

Technical Field

[0001] The present application relates to the field of laser radar technology, and in particular, to a ranging method and system for laser radar. Background Art

[0002] LiDAR can accurately measure the position (distance and angle), motion state (speed, vibration and posture) and shape of the target object, detect, identify, distinguish and track the target object. LiDAR can be divided into pulsed LiDAR and frequency modulated continuous wave LiDAR according to the working mode. A typical frequency modulated continuous wave LiDAR emits a laser beam and uses a detector to receive the reflected beam of the target object from the nearby environment, thereby calculating information such as the distance and speed of the target object. However, the reflected beam used to calculate the distance and speed includes the optical Doppler frequency shift introduced by the movement of the target object. When the speed of the target object is fast, the frequency shift caused by the Doppler effect is greater than the frequency offset caused by the flight time of the reflected beam, which will lead to errors in the calculation of close-range information, resulting in measurement blind spots. Summary of the invention

[0003] In response to the related problems of laser radar, the present application provides a ranging method and system for laser radar to solve the problem that the reflected light beam used to calculate the distance and speed includes an optical Doppler frequency shift introduced due to the movement of the target object. When the speed of the target object is fast, the frequency shift caused by the Doppler effect is greater than the frequency offset caused by the flight time of the reflected light beam, which will cause errors in the calculation of close-range information, thereby causing the problem of measurement blind spots.

[0004] In a first aspect, the ranging method for a laser radar includes: generating a swept frequency beam; splitting the swept frequency beam into a signal beam and a local oscillator beam, wherein each of the signal beam and the local oscillator beam includes a first frequency up-conversion stage, a second frequency up-conversion stage, a first frequency down-conversion stage, and a second frequency down-conversion stage, the slope of the first frequency up-conversion stage is different from the slope of the second frequency up-conversion stage, and the slope of the first frequency down-conversion stage is different from the slope of the second frequency down-conversion stage; transmitting the signal beam; receiving a reflected beam generated by the reflection of the signal beam after encountering a target object; detecting the beat frequency of the first frequency up-conversion stage, the beat frequency of the second frequency up-conversion stage, the beat frequency of the first frequency down-conversion stage, and the beat frequency of the second frequency down-conversion stage between the local oscillator beam and the reflected beam; and using two of the beat frequencies of the first frequency up-conversion stage, the beat frequency of the second frequency up-conversion stage, the beat frequency of the first frequency down-conversion stage, and the beat frequency of the second frequency down-conversion stage to determine the speed of the target object and / or the distance between the target object and the laser radar.

[0005] Optionally, using two of the beat frequencies of the first up-frequency stage, the beat frequency of the second up-frequency stage, the beat frequency of the first down-frequency stage and the beat frequency of the second down-frequency stage to determine the speed of the target object and / or the distance between the target object and the laser radar includes: using the beat frequency of the first up-frequency stage and the beat frequency of the second up-frequency stage to determine the speed of the target object and / or the distance between the target object and the laser radar; or using the beat frequency of the first down-frequency stage and the beat frequency of the second down-frequency stage to determine the speed of the target object and / or the distance between the target object and the laser radar.

[0006] Optionally, using the beat frequency of the first up-conversion stage and the beat frequency of the second up-conversion stage to determine the distance between the target object and the laser radar includes: using the following formula to obtain the distance D between the target object and the laser radar:

[0007] D=k 0 ×(f bu2 -f bu1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

[0008] Optionally, Among them, f B1 is the sweep bandwidth of the linear frequency modulation of the first triangle wave, f B2 is the sweep bandwidth of the linear frequency modulation of the second triangle wave, T is the period of the up-sweep and down-sweep, and c is the vacuum beam.

[0009] Optionally, using the beat frequency of the first frequency reduction stage and the beat frequency of the second frequency reduction stage to determine the distance between the target object and the laser radar includes: using the following formula to obtain the distance D between the target object and the laser radar:

[0010] D=k 0 ×(f bd2 -f bd1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, f bd1 is the beat frequency of the first frequency reduction stage, f bd2is the beat frequency of the second frequency reduction stage.

[0011] Optionally, using the beat frequency of the first frequency-upgrading stage and the beat frequency of the second frequency-upgrading stage to determine the speed of the target object includes: obtaining the speed V of the target object using the following formula:

[0012] V=k 1 ×(k f ×f bu1 -f bu2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

[0013] Optionally, using the beat frequency of the first frequency reduction stage and the beat frequency of the second frequency reduction stage to determine the speed of the target object includes:

[0014] Use the following formula to obtain the velocity V of the target object:

[0015] V=k 1 ×(k f ×f bd1 -f bd2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, f bd1 is the beat frequency of the first frequency reduction stage, f bd2 is the beat frequency of the second frequency reduction stage.

[0016] Optionally, k 1 =λ / 2, f B1 is the sweep bandwidth of the linear frequency modulation of the first triangle wave, f B2 is the sweep bandwidth of the linear frequency modulation of the second triangle wave, and λ is the wavelength of the local oscillator beam.

[0017] In a second aspect, the present application provides a ranging system for a laser radar. The ranging system includes: a laser source, configured to generate a swept frequency beam; a beam splitter, configured to split the swept frequency beam into a signal beam and a local oscillator beam, wherein each of the signal beam and the local oscillator beam includes a first up-conversion stage, a second up-conversion stage, a first down-conversion stage, and a second down-conversion stage, the slope of the first up-conversion stage is different from the slope of the second up-conversion stage, and the slope of the first down-conversion stage is different from the slope of the second down-conversion stage; an optical transceiver, configured to transmit the signal beam and receive a reflected beam generated by the reflection of the signal beam after encountering a target object; a mixer, configured to perform optical mixing between the local oscillator beam and the reflected beam; a balanced detector, configured to obtain the local oscillator beam and A beat frequency electrical signal between the reflected light beams; a detector, configured to obtain the beat frequency electrical signal from the balanced detector, and detect the beat frequency of the first up-conversion stage, the beat frequency of the second up-conversion stage, the beat frequency of the first down-conversion stage, and the beat frequency of the second down-conversion stage between the local oscillator light beam and the reflected light beam according to the beat frequency electrical signal; and a measurer, using the beat frequency of the first up-conversion stage and the beat frequency of the second up-conversion stage to determine the speed of the target object and / or the distance between the target object and the laser radar; or using the beat frequency of the first down-conversion stage and the beat frequency of the second down-conversion stage to determine the speed of the target object and / or the distance between the target object and the laser radar.

[0018] Optionally, the measuring device is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k 0 ×(f bu2 -f bu1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

[0019] Optionally, the measuring device is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k 0 ×(f bd2 -f bd1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, fbd1 is the beat frequency of the first frequency reduction stage, f bd2 is the beat frequency of the second frequency reduction stage.

[0020] Optionally, the measuring device is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0021] (k f ×f bu1 -f bu2 ) / (k f -10, where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

[0022] Optionally, the measuring device is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0023] (k f ×f bd1 -f bd2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, f bd1 is the beat frequency of the first frequency reduction stage, f bd2 is the beat frequency of the second frequency reduction stage.

[0024] In a third aspect, the present application provides a ranging system for a laser radar. The measurement system includes: a signal source transmitting module, a beat frequency signal acquisition module and a measurement module. The signal source transmitting module is used to transmit a periodic frequency modulated continuous wave to the target object, wherein the time-frequency waveform of the frequency modulated continuous wave of a frequency sweep cycle includes a first frequency increase stage, a second frequency increase stage, a first frequency reduction stage and a second frequency reduction stage, the slope of the first frequency increase stage is different from the slope of the second frequency increase stage, and the slope of the first frequency reduction stage is different from the slope of the second frequency reduction stage. The beat frequency signal acquisition module is used to obtain the beat frequency f of the first frequency reduction stage based on the reflected signal returned by the target object, respectively. bd1 , the beat frequency f of the second frequency reduction stage bd2 , the beat frequency f of the first frequency-upgrading stage bu1 and the beat frequency f of the second up-conversion stage bu2The measurement module is configured to use the beat frequency f of the first up-conversion stage bu1 and the beat frequency f of the second up-conversion stage bu2 , determine the speed v of the target object and / or the distance D between the target object and the laser radar; or use the beat frequency f of the first frequency reduction stage bd1 and the beat frequency f of the second frequency reduction stage bd2 , determine the speed v of the target object and / or the distance D between the target object and the laser radar.

[0025] Optionally, the measurement module is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k 0 ×(f bu2 -f bu1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage.

[0026] Optionally, the measurement module is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k 0 ×(f bd2 -f bd1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage.

[0027] Optionally, the measurement module is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0028] (k f ×f bu1 -f bu2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage.

[0029] Optionally, the measurement module is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0030] (k f ×f bd1 -fbd2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency increase stage.

[0031] In a fourth aspect, the present application provides an autonomous vehicle, comprising a laser radar according to the second aspect or the third aspect.

[0032] Compared with the related art, the above solution of the embodiment of the present application has at least the following beneficial effects:

[0033] By adopting the two triangular wave waveforms with different sweep frequency bandwidths and different slopes provided in the present application, it can be ensured that in any case, at least two beat frequencies can be used to calculate the distance and speed of the target object, thereby avoiding the ranging blind spot of the laser radar. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the continuous wave laser radar of the present application;

[0035] Figure 2A The schematic diagram of measuring a stationary target object using a related triangle wave linear frequency modulation continuous wave laser radar is shown;

[0036] Figure 2B A schematic diagram of measuring a target object moving toward a laser radar using a related triangular wave linear frequency modulation continuous wave laser radar is shown;

[0037] Figure 2C A schematic diagram showing the principle of using a related triangular wave linear frequency modulation continuous wave laser radar to measure a target object moving away from the laser radar;

[0038] Figure 3 A schematic diagram showing a measurement blind area caused by the Doppler effect when using a related laser radar measurement;

[0039] Figures 4A-4D Schematic diagram of different waveforms of triangular waves provided in some embodiments of the present application;

[0040] Figure 5 A schematic diagram showing a method for measuring a target object moving toward a laser radar using a ranging method provided by the present application is shown;

[0041] Figure 6 A schematic diagram showing the principle of using the laser radar ranging method provided by the present application to measure a target object moving away from the laser radar;

[0042] Figure 7A flowchart of the laser radar ranging method provided by the present application is shown;

[0043] Figure 8 A schematic diagram showing the structure of a laser radar ranging system provided by the present application is shown;

[0044] Fig. 9 Another schematic diagram showing the structure of the laser radar ranging system provided by the present application; and

[0045] Fig. 10A and Fig. 10B An example autonomous vehicle according to an embodiment of the present application is illustrated. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0047] refer to Figure 1 , Figure 1 It is a schematic diagram of the structure of the continuous wave laser radar of the present application. The continuous wave laser radar 1 of the present application adopts the working principle of coherent reception. By comparing the instantaneous frequency relationship between the reflected light beam reflected from the target object 2 and the local oscillator light beam of the laser radar 1, the distance between the target object 2 and the laser radar 1 and the speed of the target object can be given at the same time.

[0048] The existing frequency-modulated continuous wave laser radar FMCW (Frequency-Modulated Continuous Wave) emits a continuous laser beam, and the frequency of the laser beam is modulated to change periodically. Figure 2A As shown, the time domain waveform of the frequency change is a periodic symmetrical triangular wave. The frequency change process of the transmitted light beam corresponding to the rising edge of the triangular wave is called "up-sweep" or the frequency increase stage, and the frequency change process of the transmitted light beam corresponding to the falling edge of the triangular wave is called "down-sweep" or the frequency decrease stage. The triangular wave FMCW laser radar mixes the received reflected light beam (called "echo beam") reflected and / or scattered on the target object with the local reference beam (called "local oscillator beam") to obtain the beat frequency signal of the local oscillator beam and the echo beam (called the intermediate frequency signal f IF), and then use the spectrum analysis algorithm (based on discrete Fourier transform FFT and its deformation, expansion and other algorithms) to analyze the frequencies of the beat frequency signals (also called "upward sweep frequency band intermediate frequency signal" and "downward sweep frequency band intermediate frequency signal") corresponding to the rising edge and falling edge of the triangle wave, and obtain the distance between the target object and the laser radar and the radial velocity of the target object relative to the laser radar.

[0049] refer to Figure 2A , Figure 2A The schematic diagram of the measurement of a stationary target object using a related triangle wave FMCW laser radar is shown. Figure 2A In the figure, the solid triangle wave is the instantaneous time-frequency relationship of the radar signal beam or local oscillator beam, and the dotted triangle wave is the reflected beam of the stationary target object, where τ is the delay of the reflected beam of the stationary target object, which is caused by the laser beam flying back and forth between the target object and the laser radar. bu 、f bd are the beat frequencies of the reflected light beam from the stationary target object in the upper and lower sweep parts, T is the period of the upper and lower sweeps, and f B is the sweep bandwidth of the linear frequency modulation. Figure 2A The beat frequency f of the upconversion phase of the reflected beam is bu and the beat frequency f in the frequency reduction stage bd They are:

[0050]

[0051] Assuming that the distance between the target object and the laser radar is D, then D = τ*c / 2, where c is the speed of light and λ is the wavelength of the laser. Figure 2A In the time-frequency relationship diagram, the beat frequency f of the reflected beam in the frequency-up phase is bu and the beat frequency f in the frequency reduction stage bd The relationship between the distance D to the target object is as follows:

[0052]

[0053] Figure 2B The schematic diagram of the measurement of a target object moving toward the laser radar using a related triangular wave linear frequency modulation continuous wave laser radar is shown. Figure 2B In the figure, the solid triangle wave is the instantaneous time-frequency relationship of the radar signal beam or local oscillator beam, and the dashed triangle wave is the reflected beam of the target object moving toward the lidar, where τ is the delay of the reflected beam of the target object, and f bu 、f bd are the beat frequencies of the reflected light beam of the target object in the upper sweep part and the lower sweep part, T is the period of the upper sweep and the lower sweep, and f B is the sweep bandwidth of the linear frequency modulation, f v=(f bd -f bu ) / 2, fv is the Doppler frequency shift of the echo signal caused by the radial motion of the target object relative to the laser radar, where when the radial relative motion speed of the target object is toward the laser radar, f v The value of is positive, that is, greater than 0.

[0054] Figure 2B In the above example, the beat frequencies of the reflected light beam in the up-conversion stage and the down-conversion stage are:

[0055]

[0056] The distance D and speed ν of the target object are as follows:

[0057]

[0058] Figure 2C The schematic diagram of the use of a triangular wave linear frequency modulation continuous wave laser radar to measure a target object moving away from the laser radar is shown. Figure 2C In the figure, the solid triangle wave is the instantaneous time-frequency relationship of the radar signal beam or local oscillator beam, and the dotted triangle wave is the reflected beam of the target object moving away from the lidar, where τ is the delay of the reflected beam of the target object, and f bu 、f bd are the beat frequencies of the reflected light beam of the target object in the upper sweep part and the lower sweep part, T is the period of the upper sweep and the lower sweep, and f B is the sweep bandwidth of the linear frequency modulation, f v =(f bd -f bu ) / 2, fv is the Doppler frequency shift of the echo signal caused by the radial motion of the target object relative to the laser radar, where the radial relative motion speed of the target object is away from the laser radar, and f v The value of is negative (i.e. less than 0).

[0059] Figure 2C In the above example, the beat frequencies of the reflected light beam in the up-conversion stage and the down-conversion stage are:

[0060]

[0061] The distance D and speed ν of the target object are as follows:

[0062]

[0063] The above formulas 3 to 6 all assume that f bu and f bd is greater than 0, the calculated distance D between the target object and the laser radar and the speed ν of the target object need to use the above fbu and f bd However, when the actual speed v of the target object is fast, the frequency shift caused by the Doppler effect may be greater than the frequency shift caused by the flight time of the reflected beam, resulting in the beat frequency f in the upconversion phase between the received local oscillator beam and the reflected beam. bu The actual value of is negative, such as Figure 3 As shown. Although the beat frequency f between the received local oscillator beam and the reflected beam is bu It is actually a negative value (less than 0), but the laser radar converts the frequency f bu It is judged to be a positive value (greater than 0), so when the above formula is used to calculate the distance and speed of the target object, errors will occur in the calculation of the distance and speed, resulting in a measurement blind spot. In addition, when the laser radar's rotating mirror device rotates at high speed, a large Doppler frequency shift will also be generated. The Doppler frequency shift introduced by the rotation of the rotating mirror and the Doppler frequency shift of the target object will be superimposed on each other, which will also cause the frequency shift caused by the Doppler effect to exceed the frequency offset caused by the flight time of the reflected light beam, resulting in calculation errors of the distance and speed of the target object, causing a measurement blind spot. In addition, when f bu and / or f bd If the value is small enough, practical circuit design and computational limitations will cause the LiDAR ranging system to be unable to detect the f. bu or bd , and thus the distance D and speed v of the target object cannot be accurately calculated.

[0064] In view of the above problems, the present application provides a laser ranging method of an FMCW laser radar, which uses two triangular waveforms of different shapes in the same frequency sweep cycle. Figures 4A-4D As shown, unlike the traditional triangular wave FMCW laser radar, in one sweep period T, the frequency modulated continuous wave includes two triangular waves. The shapes of the two triangular waves are different. The slope of the frequency increase phase of the first triangular wave is different from the slope of the frequency increase phase of the second triangular wave, and the slope of the frequency decrease phase of the first triangular wave is different from the slope of the frequency decrease phase of the second triangular wave. For example, in some embodiments, reference Figures 4A-4D, the absolute value of the slope of the first triangular wave in the frequency increase phase is equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase; the absolute value of the slope of the first triangular wave in the frequency increase phase is equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase. In other embodiments, the absolute value of the slope of the first triangular wave in the frequency increase phase is not equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase; the absolute value of the slope of the first triangular wave in the frequency increase phase is not equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase. In still other embodiments, the absolute value of the slope of the first triangular wave in the frequency increase phase is equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase; the absolute value of the slope of the first triangular wave in the frequency increase phase is not equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase. In other embodiments, the absolute value of the slope of the first triangular wave in the frequency increase phase is not equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase; the absolute value of the slope of the first triangular wave in the frequency increase phase is equal to the absolute value of the slope of the second triangular wave in the frequency decrease phase. In one frequency sweep cycle, the two triangle waves have different shapes, but their working principles are similar. Figure 4D The example in which the slope of the frequency increasing stage of the first triangular wave is smaller than the slope of the frequency increasing stage of the second triangular wave is used for explanation.

[0065] like Figure 5 As shown in Figure 1, when the target object moves toward the laser radar, due to the Doppler effect, the frequency of the reflected beam increases compared to the frequency of the local oscillator beam. bu1 and f bu2 The reduced value may be smaller than the minimum value that can be detected by actual circuit design or calculation method, or even f bu1 and f bu2 It may be negative. In this case, f bd1 and f bd2 may still be a large positive value. You can use f bd1 and f bd2 To calculate the distance and speed of the target object. Figure 5 In the figure, the solid triangle wave is the instantaneous time-frequency relationship of the radar signal beam or local oscillator beam, and the dotted triangle wave is the instantaneous video relationship of the reflected beam of the target object, where τ is the delay of the reflected beam of the stationary target object, which is caused by the laser beam flying back and forth between the target object and the laser radar. T is the period of the up-sweep and down-sweep frequency, and f bu1 、f bd1 are the beat frequencies of the reflected light beam of the first triangular wave in the upper sweep part and the lower sweep part, respectively, and f B1 is the sweep bandwidth of the linear frequency modulation of the first triangle wave. bu2 、f bd2 are the beat frequencies of the reflected light beam of the second triangular wave in the upper sweep part and the lower sweep part, respectively, and f B2is the sweep bandwidth of the linear frequency modulation of the second triangle wave.

[0066] Using the triangular wave signal of the present application, the beat frequency of the first triangular wave waveform in the frequency reduction stage is

[0067]

[0068] The beat frequency of the second triangle waveform during the frequency reduction phase is

[0069]

[0070] Then the distance D and speed v of the target object are as follows:

[0071]

[0072] like Figure 6 As shown in Figure 1, when the target object moves away from the laser radar, due to the Doppler effect, the frequency of the reflected beam decreases compared to the frequency of the local oscillator beam. bd1 and f bd2 The reduced value may be smaller than the minimum value that can be detected by actual circuit design or calculation method, or even f bd1 and f bd2 It may be negative. In this case, f bu1 and f bu2 may still be a large positive value. You can use f bu1 and f bu2 To calculate the distance and speed of the target object. Using the triangular wave signal of the present application, the beat frequency of the first triangular wave waveform in the frequency-up phase is

[0073]

[0074] The beat frequency of the second triangle waveform during the upconversion phase is

[0075]

[0076] Then the distance D and speed v of the target object are as follows:

[0077]

[0078] By adopting the two triangular wave waveforms with different sweep frequency bandwidths and different slopes provided in the present application, it can be ensured that in any case, at least two beat frequencies can be used to calculate the distance and speed of the target object, thereby avoiding the ranging blind spot of the laser radar.

[0079] In some embodiments, when the beat frequency of the up-conversion phase and the beat frequency of the down-conversion phase are calculated using the above formulas 3 to 6, when the target object moves toward the laser radar, f vis a positive value. When the target object moves away from the laser radar, f v is a negative value. According to the above formula 3 and formula 4,

[0080]

[0081] When the target object moves toward the lidar, f bd >f bu ; When the target object moves away from the laser radar, f bu >f bd According to f bu and f bd The size of the value can determine the direction of movement of the target object. Based on the FMCW laser radar including two triangular waveforms of different shapes in the same sweep cycle of the present application, the present application provides a method for determining the speed and distance of the target object by using the beat frequency values ​​in two stages of the first frequency increase stage, the first frequency decrease stage, the second frequency increase stage, and the second frequency decrease stage. The method includes the following steps 1-3:

[0082] Step 1: Determine (f bu1 +f bu2 ) is greater than (f bd1 +f bd2 ). If (f bu 1+f bu 2) Greater than (f bd1 +f bd2 ), then it can be determined that the target object is moving away from the laser radar. bu1 +f bu2 ) is less than (f bd1 +f bd2 ), then it can be determined that the target object is moving towards the lidar.

[0083] Step 2: When the target object moves away from the lidar, determine f bd1 and f bd2 Is it a positive value, where

[0084] 2.1 If f bd1 and f bd2 are all positive, then we can use the above formula 5 and formula 6 and adopt the beat frequency f of the first upscaling stage bu1 and the beat frequency f of the first frequency reduction stage bd1 Or use the beat frequency f of the second upscaling stage bu2 and the beat frequency f of the second frequency reduction stage bd2 , calculate the speed v and distance D of the target object;

[0085] 2.2 If f bd1 is a positive value, f bd2is a negative value, then the beat frequency f of the second frequency reduction stage can be determined bd2 When entering the blind spot of the laser radar, the beat frequency f of the first frequency upscaling stage can be used bu1 and the beat frequency f of the first frequency reduction stage bd1 Calculate the speed v and distance D of the target object using Formula 5 and Formula 6 above;

[0086] 2.3 If f bd2 is a positive value, f bd1 is a negative value, then the beat frequency f of the first frequency reduction stage can be determined bd1 When entering the blind spot of the laser radar, the beat frequency f of the second frequency upscaling stage can be used bu2 and the beat frequency f of the second frequency reduction stage bd2 And the above formula 5 and formula 6, calculate the speed and distance of the target object;

[0087] 2.4 If f bd1 and f bd2 are all negative values, then the beat frequency f in the first frequency reduction stage can be determined bd1 and the beat frequency f of the second frequency reduction stage bd2 If both of them enter the blind area of ​​laser radar, the beat frequency f in the first frequency upscaling stage can be used. bu1 and the beat frequency f of the second up-conversion stage bu2 And the above formula 10-12, calculate the speed v and distance D of the target object.

[0088] Step 3: When the target object moves toward the lidar, determine f bu1 and f bu2 Is it a positive value, where

[0089] 3.1 If f bu1 and f bu2 are all positive, then we can use the above formula 3 and formula 4 and adopt the beat frequency f of the first upscaling stage bu1 and the beat frequency f of the first frequency reduction stage bd1 Or use the beat frequency f of the second upscaling stage bu2 and the beat frequency f of the second frequency reduction stage bd2 , calculate the speed v and distance D of the target object;

[0090] 3.2 If f bu1 is a positive value, f bu2 is a negative value, then the beat frequency f of the second frequency-upgrading stage can be determined bu2 When entering the blind spot of the laser radar, the beat frequency f of the first frequency upscaling stage can be used bu1 and the beat frequency f of the first frequency reduction stage bd1 Calculate the speed v and distance D of the target object using Formula 3 and Formula 4 above;

[0091] 3.3 If f bu2 is a positive value, f bu1 is a negative value, then the beat frequency f in the first frequency-upgrading stage can be determined bu1 When entering the blind spot of the laser radar, the beat frequency f of the second frequency upscaling stage can be used bu2 and the beat frequency f of the second frequency reduction stage bd2 Calculate the speed v and distance D of the target object using Formula 3 and Formula 4 above;

[0092] 3.4 If f bu1 and f bu2 are all negative values, then the beat frequency f in the first frequency-upgrading stage can be determined bu1 and the beat frequency f of the second up-conversion stage bu2 All of them enter the ranging blind area of ​​the laser radar, and the beat frequency f of the first frequency reduction stage can be used bd1 and the beat frequency f of the second frequency reduction stage bd1 And the above formula 7-9, calculate the speed v and distance D of the target object.

[0093] By adopting the two triangular wave waveforms with different sweep frequency bandwidths and different slopes provided in the present application, it can be ensured that in any case, at least two beat frequencies can be used to calculate the distance and speed of the target object, thereby avoiding the ranging blind spot of the laser radar.

[0094] Figure 8 The schematic diagram of the structure of the laser radar ranging system provided by the present application is shown. The laser radar ranging system can be applied to frequency modulated continuous wave laser radar (Frequency-Modulated Continuous Wave, FMCW). Figure 8 The present application provides a distance measurement system for a laser radar, which includes: a laser source 81 , a beam splitter 82 , an optical transceiver 83 , a mixer 84 , a balanced detector 85 , a detector 86 and a measurer 87 .

[0095] The laser source 81 is configured to generate a swept frequency beam. The laser light source 81 can be driven by a chirp signal of an optical signal for direct modulation. For example, a driving signal for controlling the laser source 81 can be input to the laser source 81 with an intensity that varies with time, so that the laser source 81 generates and outputs a swept frequency beam, i.e., a beam whose frequency varies within a predetermined range. The laser source 81 may also include a modulator that receives a modulation signal. The modulator may be configured to modulate the light beam based on the modulation signal to generate and output a swept frequency beam, the frequency of which varies within a predetermined range. The laser light source 81 may be a laser source commonly used in FMCW laser radars, and in order to save space, this application will not be described in detail.

[0096] The beam splitter 82 is configured to split the swept frequency beam into a signal beam and a local oscillator beam. The signal beam and the local oscillator beam have the same frequency at any point in time, that is, the frequency modulation waveforms of the signal beam and the local oscillator beam are exactly the same. In some examples, the beam splitter 82 may specifically be a specific wavelength coupler (beam splitter) for wavelengths of 445 to 2100 nm, such as an SMC series of beam splitters. In other examples, other beam splitters known to those skilled in the art that can split the swept frequency beam into a signal beam and a local oscillator beam may also be used. Each of the signal beam and the local oscillator beam includes a first up-conversion stage, a second up-conversion stage, a first down-conversion stage, and a second down-conversion stage, the slope of the first up-conversion stage is different from the slope of the second up-conversion stage, and the slope of the first down-conversion stage is different from the slope of the second down-conversion stage, such as Figures 4A-4D shown.

[0097] The signal light beam is incident on the light incident port of the optical transceiver 83. The optical transceiver 83 is configured to direct the signal light toward the target object. The signal light beam is incident on the target object to generate a reflected light beam, and the optical transceiver 83 is also configured to receive the reflected light beam. The optical transceiver 83 inputs the reflected light beam to the mixer 84. The mixer 84 is also configured to receive the local oscillator light beam, and optically mix the local oscillator light beam and the reflected light beam. The mixing signal is, for example, a coherent signal generated by the interference between the local oscillator light beam and the corresponding reflected light beam. The mixed signals are respectively sent to the balanced detector 85 for detection. The mixer 84 can be a 2×2 optical coupler. The balanced detector 85 can, for example, include a photodetector 851 and a photodetector 852. The photodetector can obtain a beat frequency electrical signal between the local oscillator light beam and the reflected light beam. The detector 86 is configured to obtain the beat frequency electrical signal from the balanced detector 85, and detect the beat frequency f of the first up-conversion stage between the local oscillator light beam and the reflected light beam according to the beat frequency electrical signal. bu1 , the beat frequency f of the second frequency-upgrading stage bu2 , the beat frequency f of the first frequency reduction stage bd1 and the beat frequency f of the second frequency reduction stage bd2 The measurer 87 is configured to use the beat frequency f of the first up-conversion stage bu1 and the beat frequency f of the second up-conversion stage bu2 , determine the speed v of the target object and / or the distance D between the target object and the laser radar; or use the beat frequency f of the first frequency reduction stage bd1 and the beat frequency f of the second frequency reduction stage bd2 , determine the speed v of the target object and / or the distance D between the target object and the laser radar.

[0098] In some embodiments, the measurement device 87 is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k0 ×(f bu2 -f bu1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage.

[0099] Optionally, the measuring device 87 is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k 0 ×(f bd2 -f bd1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage.

[0100] Optionally, the measuring device 87 is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0101] (k f ×f bu1 -f bu2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage.

[0102] Optionally, the measuring device 87 is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0103] (k f ×f bd1 -f bd2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency increase stage.

[0104] Optionally, the laser radar also includes: a polarization beam splitter (e.g., a polarization splitter-rotator (PSR)): arranged between the optical transceiver 83 and the target object, configured to change the polarization direction of the light beam or merge multiple light beams into a polarized light beam; a lens assembly, configured to collimate the signal light beam and focus the reflected light beam to couple it into the optical transceiver; and a beam scanning guide device, configured to achieve light deflection and scanning.

[0105] By adopting the two triangular wave waveforms with different sweep frequency bandwidths and different slopes provided in the present application, it can be ensured that in any case, at least two beat frequencies can be used to calculate the distance and speed of the target object, thereby avoiding the ranging blind spot of the laser radar.

[0106] Fig. 9 Another schematic diagram of the structure of the laser radar ranging system provided by the present application is shown. Fig. 9 The laser radar ranging system provided in this application includes: a signal source transmitting module 91, a beat frequency signal acquiring module 92 and a measuring module 93.

[0107] The signal source transmitting module 91 is used to transmit a periodic frequency modulated continuous wave to the target object, wherein the time-frequency waveform of the frequency modulated continuous wave of a frequency sweep cycle includes a first frequency increase stage, a second frequency increase stage, a first frequency reduction stage, and a second frequency reduction stage, the slope of the first frequency increase stage is different from the slope of the second frequency increase stage, and the slope of the first frequency reduction stage is different from the slope of the second frequency reduction stage, such as Figures 4A-4D shown.

[0108] The beat frequency signal acquisition module 92 is used to obtain the beat frequency f of the first frequency reduction stage based on the reflected signal returned by the target object. bd1 , the beat frequency f of the second frequency reduction stage bd2 , the beat frequency f of the first frequency-upgrading stage bu1 and the beat frequency f of the second up-conversion stage bu2 .

[0109] The measurement module 93 is configured to use the beat frequency f of the first up-conversion stage bu1 and the beat frequency f of the second up-conversion stage bu2 , determine the speed v of the target object and / or the distance D between the target object and the laser radar; or use the beat frequency f of the first frequency reduction stage bd1 and the beat frequency f of the second frequency reduction stage bd2 , determine the speed v of the target object and / or the distance D between the target object and the laser radar.

[0110] In some embodiments, the measurement module 93 is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k 0 ×(f bu2 -f bu1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage.

[0111] Optionally, the measurement module 93 is specifically configured to obtain the distance D between the target object and the laser radar using the following formula: D=k 0 ×(f bd2 -f bd1 ) / (k f -1), where k 0 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage.

[0112] Optionally, the measurement module 93 is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0113] (k f ×f bu1 -f bu2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage.

[0114] Optionally, the measurement module 93 is specifically configured to obtain the velocity V of the target object using the following formula: V=k 1 ×

[0115] (k f ×f bd1 -f bd2 ) / (k f -1), where k 1 is the preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency increase stage.

[0116] Fig. 10A and Fig. 10B An example autonomous vehicle 1000 according to an embodiment of the present application is illustrated, which may include the present application Figure 8 Or any component of the measurement system of the lidar shown in 9. The autonomous vehicle 1000 shown includes a sensor array, which is configured to capture one or more target objects of the external environment of the autonomous vehicle and generate sensor data related to the captured one or more target objects for controlling the operation of the autonomous vehicle 1000. Fig. 10A Sensors 1001 , 1002 , 1003 , 1004 , and 1005 are shown. Fig. 10B Sensors 1001 , 1002 , 1003 , 1004 , 1005 , 1006 , 1007 , 1008 , and 1009 are illustrated. Fig. 10B Shown is a top view of autonomous vehicle 1000. Any of sensors 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, and 1009 may include the Figure 8 Or the measurement system for lidar in 9. The autonomous vehicle may include a powertrain including a prime mover powered by an energy source and capable of powering a transmission system. The autonomous vehicle may also include a control system including direction control, powertrain control, and braking control. The autonomous vehicle may be implemented as any number of different vehicles, including vehicles capable of transporting people and / or cargo and capable of traveling in a variety of different environments. It should be understood that the above-mentioned components can vary widely based on the type of vehicle utilizing the components.

[0117] It can be understood that the functions of each module in the system of this embodiment correspond to the method steps of the above embodiment, and the optional items in the above embodiment are also applicable to this embodiment, so they will not be described repeatedly here.

[0118] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A ranging method for laser radar, characterized in that: The method comprises: generating a swept beam; Splitting the frequency sweeping beam into a signal beam and a local oscillator beam, wherein each of the signal beam and the local oscillator beam comprises a first frequency up-conversion stage, a second frequency up-conversion stage, a first frequency down-conversion stage, and a second frequency down-conversion stage, the slope of the first frequency up-conversion stage is different from the slope of the second frequency up-conversion stage, and the slope of the first frequency down-conversion stage is different from the slope of the second frequency down-conversion stage; emitting the signal light beam; Receiving a reflected light beam generated when the signal light beam is reflected from a target object; Detecting a beat frequency of the first up-conversion stage, a beat frequency of the second up-conversion stage, a beat frequency of the first down-conversion stage, and a beat frequency of the second down-conversion stage between the local oscillator light beam and the reflected light beam; and The beat frequency of the first up-frequency stage and the beat frequency of the second up-frequency stage are used to measure the speed of the target object and / or the distance between the target object and the laser radar; or the beat frequency of the first down-frequency stage and the beat frequency of the second down-frequency stage are used to measure the speed of the target object and / or the distance between the target object and the laser radar.

2. The distance measurement method according to claim 1, characterized in that: Using the beat frequency of the first frequency up-conversion stage and the beat frequency of the second frequency up-conversion stage, determining the distance between the target object and the laser radar includes: The distance D between the target object and the laser radar is obtained using the following formula: D=k0×(f bu2 -f bu1 ) / (k f -1), where k0 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

3. The distance measurement method according to claim 1, characterized in that: Using the beat frequency of the first frequency reduction stage and the beat frequency of the second frequency reduction stage, determining the distance between the target object and the laser radar includes: The distance D between the target object and the laser radar is obtained using the following formula: D=k0×(f bd2 -f bd1 ) / (k f -1), where k0 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, f bd1 is the beat frequency of the first frequency reduction stage, f bd2 is the beat frequency of the second frequency reduction stage.

4. The distance measurement method according to claim 1, characterized in that: Using the beat frequency of the first frequency-upgrading stage and the beat frequency of the second frequency-upgrading stage, determining the speed of the target object includes: Use the following formula to obtain the velocity V of the target object: V=k1×(k f ×f bu1 -f bu2 ) / (k f -1), where k1 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

5. The distance measurement method according to claim 1, characterized in that: Using the beat frequency of the first frequency reduction stage and the beat frequency of the second frequency reduction stage, determining the speed of the target object includes: Use the following formula to obtain the velocity V of the target object: V=k1×(k f ×f bd1 -f bd2 ) / (k f -1), where k1 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, f bd1 is the beat frequency of the first frequency reduction stage, f bd2 is the beat frequency of the second frequency reduction stage.

6. A ranging system for laser radar, characterized in that: The system comprises: a laser source configured to generate a swept beam; A beam splitter configured to split the frequency-sweeping beam into a signal beam and a local oscillator beam, wherein each of the signal beam and the local oscillator beam comprises a first up-conversion stage, a second up-conversion stage, a first down-conversion stage, and a second down-conversion stage, the slope of the first up-conversion stage is different from the slope of the second up-conversion stage, and the slope of the first down-conversion stage is different from the slope of the second down-conversion stage; an optical transceiver configured to transmit the signal light beam and receive a reflected light beam generated when the signal light beam is reflected from a target object; A mixer configured to perform optical mixing between the local oscillator light beam and the reflected light beam; A balanced detector configured to obtain a beat frequency electrical signal between the local oscillator light beam and the reflected light beam; a detector configured to obtain the beat frequency electrical signal from the balanced detector, and detect the beat frequency of the first up-conversion stage, the beat frequency of the second up-conversion stage, the beat frequency of the first down-conversion stage, and the beat frequency of the second down-conversion stage between the local oscillator light beam and the reflected light beam according to the beat frequency electrical signal; and A measuring device uses the beat frequency of the first up-conversion stage and the beat frequency of the second up-conversion stage to measure the speed of the target object and / or the distance between the target object and the laser radar; or uses the beat frequency of the first down-conversion stage and the beat frequency of the second down-conversion stage to measure the speed of the target object and / or the distance between the target object and the laser radar.

7. The distance measurement system according to claim 6, characterized in that: The measuring device is specifically configured as follows: The distance D between the target object and the laser radar is obtained using the following formula: D=k0×(f bu2 -f bu1 ) / (k f -1), where k0 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

8. The distance measurement system according to claim 6, characterized in that: The measuring device is specifically configured as follows: The distance D between the target object and the laser radar is obtained using the following formula: D=k0×(f bd2 -f bd1 ) / (k f -1), where k0 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, f bd1 is the beat frequency of the first frequency reduction stage, f bd2 is the beat frequency of the second frequency reduction stage.

9. The distance measurement system according to claim 6, characterized in that: The measuring device is specifically configured as follows: Use the following formula to obtain the velocity V of the target object: V=k1×(k f ×f bu1 -f bu2 ) / (k f -1), where k1 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency up-conversion stage to the slope of the second frequency up-conversion stage, f bu1 is the beat frequency of the first upscaling stage, f bu2 is the beat frequency of the second up-conversion stage.

10. The distance measurement system according to claim 6, characterized in that: The measuring device is specifically configured as follows: Use the following formula to obtain the velocity V of the target object: V=k1×(k f ×f bd1 -f bd2 ) / (k f -10, where k1 is a preset value related to the laser radar, k f is a parameter related to the ratio of the slope of the first frequency reduction stage to the slope of the second frequency reduction stage, f bd1 is the beat frequency of the first frequency reduction stage, f bd2 is the beat frequency of the second frequency reduction stage.

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