WO2022206293A1 - 一种激光雷达测距方法及探测系统 - Google Patents
一种激光雷达测距方法及探测系统 Download PDFInfo
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- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
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- G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
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- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
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- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
- G01S17/14—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
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- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
- G01S17/26—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals
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Definitions
- the present application relates to the field of detection technology, and in particular, to a lidar ranging method and a detection system.
- the distance detection system is based on the principle of actively emitting emitted light for detection through the light source, such as near-infrared type detection light, whose wavelength can be selected in the range of 800-1200nm, It is not limited to this here.
- the use of near-infrared detection waves can also ensure safety when there is a human object in the field of view. Therefore, active detection systems of near-infrared type are more and more widely used in various scenarios, such as autonomous driving, smart doors Locks, security cameras, mobile phone 3D cameras, etc.
- Time of Flight (TOF) Light Detection and Ranging is a technology for long-range distance measurement.
- TOF LIDAR sensors determine the distance between an instrument including the sensor and an object by measuring the time it takes for a laser pulse to travel between the instrument and the object.
- ITOF Indirect Time of Flight
- DTOF Direct Time of Flight
- Most of the indirect time-of-flight measurement schemes use the method of measuring phase offset, that is, measuring the phase difference between the transmitted wave and the received wave.
- the abscissa of the transmitted wave and the received wave is the time, and the ordinate is the light intensity.
- the direct flight time measurement scheme generally uses a measurement system with picosecond resolution (mostly SPAD+TDC) to directly obtain the time difference triggered by the transmitter and the corresponding receiver, which is the flight time t, so as to calculate the distance of the detected object.
- a type of detection method which is called coherent detection.
- the specific working principle is as follows: the coherent laser signal and the local laser oscillation signal satisfy the wavefront matching condition (that is, on the photosensitive surface of the entire laser detector). While maintaining the same phase relationship), they are incident on the photosensitive surface of the detector together, resulting in beat frequency or coherent superposition.
- the output electrical signal of the detector is proportional to the square of the sum of the laser signal wave to be measured and the local laser oscillation wave. Detection methods, of course, the above detection methods have their own advantages, but they still have great deficiencies in terms of pixel-level, fast processing and efficient use of emitted energy.
- LiDAR principles for direct time-of-flight detection have also been developed, gradually becoming a detection technology that is more widely understood.
- the patent application number CN202010604232.3 is named as a new type of laser ranging method and lidar system, and a new type of detection mechanism is proposed.
- the principle of coherent light is not used on the optical path, but the correlation operation is performed in the electrical signal stage, and further through The correlation operation of the electrical signal obtains the final distance or other information of the detected object.
- the above methods have the following limitations: (1) According to the principle of incoherent chirped signal AM continuous wave laser 3D imaging, the difference frequency signal is generated by multiplying the delayed chirp signal and the local oscillator signal.
- the energy of the difference frequency signal within the sampling interval of the A/D conversion is not used, and the energy of the delayed chirp signal and the energy emitted by the continuous wave laser are not used. Therefore, the average laser emission power of the existing technology (incoherent chirped signal amplitude-modulated continuous wave laser 3D imaging) is relatively high, and the ranging range is relatively small; (2) broadband amplifiers, mixers and A/D The dynamic range of these devices limits the dynamic range of the received laser signal, thus limiting the dynamic receiving range; (3) The performance of the formed laser 3D imaging system is more affected by the chirp signal FM linearity and FM flatness. big.
- the present application provides a detection method and a detection system for obtaining distance information, so as to accurately and stably output stable and accurate distance results of the detected objects within each distance range in the field of view.
- the present application provides a lidar ranging method, including:
- the driving signal is generated by the driving signal generating part and acts on the laser source through the laser modulation driving circuit, and the laser source receives the driving signal to emit a pulse laser sequence;
- a modulation signal is generated by a processing module according to the driving signal generated by the driving signal generating unit, the processing module obtains a distance-related signal based on the modulation signal according to a preset rule, and the processing module is based on the distance-related signal Output the distance information of the detected object.
- the present application provides a detection system for distance detection, comprising: a driving signal generating part, the driving signal generating part is configured to generate a driving signal and act on a laser source through a laser modulation driving circuit, the The laser source receives the driving signal and drives to emit a pulsed laser sequence; the array type return light receiving module is configured to receive the return light signal reflected by the detected object in the field of view, and generate the return signal; and the processing module, the processing module The module is configured to generate a modulation signal according to the driving signal generated by the driving signal generating part, obtain a distance-related signal based on the demodulated signal according to a preset rule, and output the received signal according to the distance-related signal. The distance information of the detected object.
- Embodiments of the present application provide a lidar ranging method and a detection system.
- the method includes: generating a driving signal by a driving signal generating part and acting on a laser source through a laser modulation driving circuit, the laser source receiving the driving signal to emit a pulsed laser sequence;
- the returned light signal reflected by the detected object in the field generates the return signal;
- the processing module generates a modulation signal according to the driving signal generated by the driving signal generating part, and the processing module obtains the modulation signal according to a preset rule A distance-related signal, the processing module outputs the distance information of the detected object according to the distance-related signal.
- the present application uses the driving signal to drive the light source to emit a pulsed laser sequence.
- the emitted energy can be greatly reduced, and on the other hand, the distance correlation signal is obtained by calculating the signal generated by the returned light according to preset rules, which ensures the accuracy of the detection result.
- the present application performs preset operations with the modulation sequence through more than one photon triggering statistical results of single-photon avalanche diode arrays or similar APD array detectors, which can reduce the actual number of operations, and make the entire statistics and operations The complexity is greatly reduced, which ensures the high efficiency of the entire detection system and ranging method.
- the counting sequence generation module generates an adaptive counting sequence according to the return signal, and the processing module obtains the distance-related signal based on the adaptive counting sequence and the modulation signal to finally obtain the distance information of the detected object, which is designed in this way , which can enhance the anti-jamming capability of the radar detection system.
- the counting sequence splicing module obtains the replica splicing signal according to the return signal, and the processing module obtains the distance-related signal based on the replica splicing signal and the modulation signal to finally obtain the distance information of the detected object, so designed, Smaller ranging deviations can be achieved by using smaller laser energy.
- FIG. 1 is a schematic diagram of a modularized working principle of a detection system provided by an embodiment of the present application
- FIG. 2 is a schematic diagram of a detection scheme provided by the prior art
- FIG. 3 is a schematic diagram of implementing a pulsed detection scheme provided by an embodiment of the present application.
- FIG. 4 is a schematic diagram of an array-type receiving module provided by an embodiment of the present application.
- FIG. 5 is a schematic diagram of a preset rule computing module provided by an embodiment of the present application.
- FIG. 6 is a schematic diagram of a counting sequence result of returning light statistics of a laser sequence that emits L times according to an embodiment of the present application
- Fig. 7 is a kind of schematic diagram that utilizes the drive signal to generate discrete modulation sequence
- FIG. 8 is a schematic diagram of obtaining a distance-related signal by using a preset rule computing module according to an embodiment of the present application
- FIG. 9 is another schematic diagram of obtaining a distance-related signal by using a preset rule computing module according to an embodiment of the present application.
- FIG. 10 is a schematic diagram of obtaining a distance-related signal according to an embodiment of the present application.
- FIG. 11 is a schematic diagram of a three-dimensional imaging system according to an embodiment of the present application.
- FIG. 13 is a flow chart of generating an adaptive accumulating count sequence provided by an embodiment of the present application.
- FIG. 15 is a flowchart of generating an adaptive accumulating count sequence according to a pre-generated adaptive correction sequence according to an embodiment of the present application.
- Figure 16a to Figure 16c provide the spectrum of the distance-related signal when the adaptive counting sequence or the adaptive cumulative counting sequence is not added according to the embodiment of the present application;
- FIG. 17 is a spectrum of distance-related signals obtained when an adaptive counting sequence or an adaptive cumulative counting sequence is added according to an embodiment of the present application.
- FIG. 18 is a schematic diagram of a detection system provided by an embodiment of the present application.
- FIG. 19 is a schematic diagram of a detection system provided by an embodiment of the present application.
- Figure 20 is a schematic diagram of obtaining a replication splicing sequence provided by the embodiment of the application.
- Figure 21 is another schematic diagram of obtaining a replication splicing sequence provided by the embodiment of the application.
- FIG. 22 is a schematic diagram of waveforms during three-dimensional imaging according to an embodiment of the present application.
- the currently used detection system basically includes: a light source module 110 , a processing module 120 , and a light receiving module 130 .
- the light source module 110 includes, but is not limited to, semiconductor lasers, solid-state lasers, and other types of lasers.
- a semiconductor laser As a light source, a vertical cavity surface emitting laser VCSEL (Vertical-cavity surface-emitting laser) or an edge-emitting semiconductor laser EEL (edge-emitting laser) can be used, which is only illustrative and not specifically limited here.
- the light source module 110 emits a sine wave, a square wave, a triangle wave, or a pulse wave, etc., most of which are lasers with a certain wavelength in ranging applications, such as infrared lasers of 950 nm and the like (preferably near-infrared lasers).
- the emitted light is projected into the field of view, and the detected object 140 existing in the field of view can reflect the projected laser light to form return light, which enters the detection system and is captured by the light receiving module 130 .
- the light receiving module 130 may include a photoelectric conversion part, wherein in the ITOF ranging, it may receive the most commonly used four-phase scheme to obtain delayed received signals of 0°, 90°, 180° and 270°.
- the four-phase distance calculation scheme is described here by taking the sine wave method as an example.
- the amplitude of the received signal is measured at four equally spaced points (such as 90° or 1/4 ⁇ interval).
- the distance to the target is determined by the following formula:
- the pixel unit of the array sensor is a SPAD (Single Photon Avalanche Diode, single-photon avalanche photodiode) device, it is an avalanche photodiode working in Geiger mode.
- SPAD Single Photon Avalanche Diode, single-photon avalanche photodiode
- the absorption of photons by avalanche photodiodes will generate electron-hole pairs, which are accelerated by the strong electric field generated by the high reverse bias voltage, so as to obtain sufficient energy, and then interact with the lattice. Collision, a chain effect is formed, resulting in the formation of a large number of electron-hole pairs, causing an avalanche phenomenon, and the current increases exponentially.
- the light source emits a pulsed laser with a certain pulse width, for example, several nanoseconds, and the pulsed laser is reflected by the detection target and returns to the array-type receiving module containing the SPAD in the avalanche state.
- the detection unit in the avalanche state can receive the returned signal, and after processing by the processing module, the distance between the detection system and the detection target can be output to complete the detection.
- FIG. 2 is a solution disclosed in the prior art for obtaining information such as the distance of a detected object by using a non-coherent (direct detection solution) method.
- the driving signal generating part generates a driving signal
- the driving signal here can be a driving signal with an identification function.
- the period of the signal gradually increases or decreases gradually.
- a driving signal with certain characteristics and identification functions, a chirp signal is used as an example here, but the actual implementation is not limited to this.
- the driving signal acts on the laser transmitter, which is a continuous wave laser here, through a laser modulation driving circuit, thereby emitting a detection laser with a law similar to that of the driving signal.
- a returned laser signal is formed. Due to the difference in distance between the detected objects in the field of view, different areas of the light receiving module can obtain delayed return light signals.
- Correlation processing is performed with the drive signal inside the mixer to obtain the output signal after mixing.
- the signal processor processes the mixed output signal to obtain a beat frequency signal, wherein the signal processor may include a low-pass filter circuit to filter out clutter interference to obtain a real useful beat frequency signal.
- the amplifier can amplify the difference frequency signal after filtering, and then obtain the to-be-processed difference frequency signal with strong anti-interference ability and more real signal, and finally convert the A/D converter to obtain a digital signal.
- the converted digital type difference frequency signal is passed to the time-frequency domain conversion module, which can obtain the frequency spectrum of the difference frequency signal through time-frequency domain conversion, and finally identify the final spectral characteristics through the characteristics of the spectrum, such as peak characteristics.
- the detection results of information such as the speed and distance of the detected object.
- the time-frequency domain conversion module may further include a threshold detection unit, an information calculation unit, and the like.
- the chirp signal generator generates two chirp signals, one is used as the local oscillator signal of the mixer, and the other is sent to the laser modulation drive circuit, so that the laser power emitted by the continuous wave laser changes according to the following rules:
- P t0 is the average laser emission power
- m t is the emission modulation depth
- f 0 is the starting frequency of the chirp signal
- t is the time
- the receiving optical system focuses the laser signal reflected by the target to the photodetector, and obtains the delayed chirp signal through photoelectric conversion.
- the signal is amplified and mixed with the local oscillator signal, and the difference frequency signal is obtained after low-pass filtering.
- the delayed chirp signal is:
- a r (t) A r0 [1+m t cos(2 ⁇ f 0 (t- ⁇ )+ ⁇ k(t- ⁇ ) 2 + ⁇ 0 + ⁇ 0 )], t ⁇ [ ⁇ ,T+ ⁇ ] (4 )
- the local oscillator signal is:
- a LO (t) A LO0 [1+m LO cos(2 ⁇ f 0 t+ ⁇ kt 2 + ⁇ LO )], t ⁇ [0,T] (5)
- a LO0 is the average amplitude of the local oscillator signal
- m LO is the modulation depth of the local oscillator signal
- ⁇ LO is the initial phase of the local oscillator signal.
- the difference frequency signal is:
- AIF is the amplitude of the difference frequency signal, is the phase difference signal.
- the relative distance of the target is obtained as:
- the difference frequency signal is generated by multiplying the delayed chirp signal and the local oscillator signal. From the perspective of energy utilization, due to the A/D conversion of the difference frequency signal, the energy of the difference frequency signal within the sampling interval of the A/D conversion is not used, and because the energy of the delayed chirp signal is positive with the emission energy of the continuous wave laser Therefore, the average laser emission power of the prior art (incoherent chirped signal AM continuous wave laser 3D imaging) is higher, and the ranging range is smaller;
- the inventor of the present application proposes an improved detection method and detection method.
- the system uses a pulsed laser, so the active detection laser emitted is a pulsed laser sequence segment composed of a pulse sequence.
- the drive signal generator in the system generates a drive signal.
- the drive signal here can be similar to The chirp signal in the previous example can also adopt other types of driving signals.
- the essential feature of the driving signal here is to modulate the emitted laser light of the device to obtain an emitted light signal with identifiable characteristics.
- the driving signal acts on the pulsed laser through the laser modulation driving circuit, and the laser can utilize at least part of the characteristics of the driving signal, such as the total period of the driving signal as the period of the pulse sequence segment, and the individual pulses in the pulse segment can be selected to have the same or similar peak value , the peak duration is the same or similar, or the amplitude information of the driving signal is used as the basis for the peak value of the pulse sequence.
- the peak values contained in the pulse sequence can be different, and even the small period of the driving signal segment can be decreased or increased.
- the law is used as the basis for the trigger probability of the pulses in the emitted laser segments to generate pulsed laser segments with non-equidistant spacing, etc.
- the specific implementation scheme of the pulsed laser segments emitted by the pulsed laser source is not limited here.
- the emitted pulsed laser sequence is regarded as The reflection of the detected object in the field generates a return light signal, and the return light signal is received by the photodetector to form a photon counting sequence.
- the preset rule operation module included in the processing module uses the drive signal to generate a discontinuous modulation sequence Y on the one hand, On the other hand, the distance correlation signal can be obtained by calculating the photon counting sequence and the modulation sequence Y according to the preset rules.
- the output includes the distance information of the detected object, and can also include speed information, etc., which are not specifically limited here, similar to
- the time-frequency domain conversion module includes a unit that can perform time-frequency domain conversion processing, which can perform, for example, wavelet operation, segmented FFT, FFT, chirp-Z operation, DFT, etc.,
- time-frequency domain conversion module may also include a threshold detection unit and/or an information calculation unit, which is not limited here.
- the light receiving module may adopt an array type receiving module as shown in FIG. 4 .
- the array-type receiving module includes a pixel unit 410 composed of diodes.
- M*N pixel units can be used to form the active area of the array-type receiving module, and the number of pixel units can be tens of thousands or even tens of thousands. The magnitude of 10,000, etc., is not limited here.
- the array-type receiving module may include a lens portion 4301 and a detection unit base portion 4302 .
- the lens portion 4301 includes a plurality of lens units, and the lens units may be composed of micro-lens units having a predetermined curvature.
- the lens portion may also include a structure with more than one layer, and the specific implementation scheme is not limited here.
- the base portion 4302 can be disposed at the position of the focal plane corresponding to the lens portion 4301, so as to ensure that the detection pixel unit can obtain accurate return light information to the greatest extent.
- the lens of the lens part 4301 can construct an optical channel, so that the signal received by the photosensitive part of the detection unit is near the corresponding focal position.
- the detection unit base portion 4302 includes a photosensitive pixel array arranged in an array type.
- the diode of the photosensitive pixel unit here can be a single photon avalanche diode array (SPAD) with single photon sensitivity.
- a Geiger-mode detector unit array APD or an array-type detector composed of photon-counting-type detection pixel units with a linear amplification factor, etc., can also be used, which is not limited here.
- the signal directly output in the detector array of the present application is a photon counting sequence
- the direct output and transmission of digital signals is realized, and the preset rule operation module takes the driving signal as the mother, and obtains the modulation sequence Y, which is also discontinuous
- the sequence type signal of , or even directly obtain the digitized modulation sequence Y, both are not analog signals similar to those in the prior art, so do not need to go through A/D analog-to-digital conversion and directly perform correlation operation in the preset rule operation module.
- the chirp signal generator is still taken as an example for exemplary description.
- the chirp signal generator generates a chirp signal as the modulation sequence Y, and the modulation sequence here can be the discretization of the continuous signal in the previous example, and finally converted into a digital type modulation sequence signal, here the laser emitted
- the period is chosen to be the chirped signal period T (ie the total duration within the lasing segment is chosen to be the periodic characteristic of the chirped signal).
- the chirp signal generator controls the laser modulation drive circuit to generate the pulse laser drive signal
- the pulse laser drive signal controls the pulse laser to emit the laser pulse sequence
- the emission optical system projects the laser pulse sequence to the target area;
- the pulse energies are equal, and this is just an example.
- the receiving system includes a receiving optical system, a photodetector, a digital correlator, a digital integrating accumulator, etc., wherein the receiving optical system reflects the laser pulse sequence back from the target. Focusing on the photodetector, the photodetector starts to detect when the laser pulse sequence is emitted, and the photon counting result in the emission period of the laser pulse sequence is obtained.
- the scene in the field of view is firstly illuminated by using the pulse sequence emitted for L times (wherein L is an integer greater than or equal to 1). More optimally, in order to obtain more accurate detection results, L can be selected to be in the order of hundreds of thousands, etc., which is not limited here. Of course, in order to ensure the accuracy of data or the effect of accurate and fast operation, etc., this is not limited to performing statistics on all the detection results of the L times to obtain statistical values.
- a statistical photon counting sequence X can be generated for the statistical results obtained by using the excitation information of the returned light less than or equal to L times.
- the following scenario is an exemplary solution for illustrating the generation and construction of the statistical photon sequence X.
- Perform L L is a positive integer and L ⁇ 1) cumulative detection on the laser pulse sequence reflected back by the target, each cumulative detection includes M (M is a positive integer and M ⁇ 1) detection pulses, and the d (d is positive)
- the photon count result obtained by the i-th (i is a positive integer and 1 ⁇ i ⁇ M) detection pulse in the cumulative detection is an integer and 1 ⁇ d ⁇ L) is x di , which is composed of M detection pulse counting results.
- the basic count sequence X is:
- the above steps can in principle be represented as the scheme in Fig. 5, where the laser sequence emitted by a single shot is the case shown at the top, the laser sequence emitted each time contains M detection pulses, and the laser source outputs L in the form of L times. and then obtain the trigger information of the return light of the probe light emitted no more than L times through the detection module to obtain the statistical photon counting sequence, as shown in Equation (9), the final constructed statistical photon counting sequence is as follows The results are shown at the bottom of Figure 5.
- the specific structure of the preset rule operation module is shown in FIG. 6 , which includes a digital multiplier unit and a digital integral accumulator unit.
- the digital multiplier unit and digital integral accumulator unit in the preset rule operation module can be realized, and the maximum detection distance can be adaptively adjusted with the change of the scene to realize the self-adjustment of detection accuracy, etc. , and can also realize the correlation operation between the signals through the digital multiplier unit to improve the anti-interference ability of the system. That is to say, it can be obtained according to the solution of the following example, the aforementioned statistical photon counting sequence X of the returned light is obtained from L times of pulsed light emission. Fig.
- the functional expression of the driving signal is f(x), and a discrete modulation sequence Y similar to the driving emission laser pulse is obtained by using a discretization scheme, wherein the The single-shot laser sequence includes M pulsed laser excitation high-value units, and the modulation sequence also includes N pulsed high-value units.
- the modulation signal is a discontinuous modulation sequence generated by the driving signal generated by the driving signal generating unit according to the similar rule of the emission light pulse sequence, and the result is shown in the following formula (10).
- the preset rule operation module can perform a correlation operation on the two sets of sequences according to the units in the module, so as to obtain the correlation operation results of the two sets of sequences.
- Figures 8 and 9 illustrate two different schemes, respectively. According to the operation scheme of FIG. 8 , the multiplication operation can be performed on the statistical photon counting sequence and the modulation sequence, that is, the modulation counting sequence Z d can be obtained by using a digital multiplier:
- the digital integral accumulator can perform segmented accumulation on the modulation count sequence, where the accumulation interval is the interval segment where the accumulation operation is performed, and the processing module can set the actual size of the accumulation interval according to certain rules. Performing the segmental accumulation of the multiplication result sequence in the effective superposition area in the interval can obtain the enhancement effect of the signal and at the same time ensure the accuracy of detection.
- the number of superimposition units in the effective superposition area is K, so the segmental accumulation operation is performed. After that, the segmented cumulative count sequence S d is finally obtained:
- FIG. 9 is another implementation idea.
- Each unit in this module first performs a segmented accumulation operation for the sequence, that is, the aforementioned statistical photon counting sequence X and modulation sequence Y are firstly divided into the effective superposition interval within the accumulation interval to perform segmental accumulation operation respectively, after completion Then perform the multiplication operation on the two, the operation results generated by the two sequences may be different, which is not limited here, but both can contain the result-related information associated with the physical characteristics such as the distance and speed of the detected object.
- the signal processing system includes time-frequency domain conversion, threshold detection and information calculation, etc.
- the time-frequency domain conversion realizes the conversion of the spectrum of the accumulated count sequence S according to, for example, wavelet operation, segmented FFT, FFT, chirp-Z operation, DFT, etc.
- threshold detection realizes the detection of the spectral peak characteristics of the cumulative counting sequence S, including the highest peak information, the second highest peak information or the peak information in the area of interest, etc.
- the information calculation is based on the spectral information of the cumulative counting sequence S to obtain the target relative Information such as distance, relative velocity, and 3D imagery.
- Fig. 10 can also be interpreted as a description of another detailed solution for realizing the solution of the present invention. It is explained in conjunction with Fig. 10.
- the laser source emits L times of pulse sequence output, and the reflected detection laser of the detected object in the field of view forms a return at the receiving end.
- the photon statistical result X of light which can be the return result of L times
- the modulation sequence can perform multiplication operation with each output modulation sequence and each returned photon statistical sequence to obtain the modulated statistical sequence Z, and finally execute the segmented cumulative result Thereby, the final counting sequence S is obtained.
- This scheme is also a scheme protected by the present application.
- the execution step is to first obtain X d by using a pulse sequence
- the photon counting sequence or the cumulative photon counting sequence in the above embodiment can not only be generated by the laser pulse sequence received by the photodetector array, but also the ambient background light received by the photodetector array can also generate the photon counting sequence or the cumulative photon counting sequence,
- the ambient background light includes natural background light and unnatural background light.
- the detector array does not receive photons, it is only caused by the detector array itself. For example, the dark count of the Geiger mode APD photodetector array, the count caused by the noise of the readout circuit, etc., will also generate a photon counting sequence or accumulation. Photon counting sequence. Among them, the photon counting results generated by ambient background light and the detector array itself will reduce the signal-to-noise ratio of the detection system, resulting in the deterioration of detection performance.
- the above statistical law can be determined according to the photon counting sequence or the cumulative photon counting sequence; on the other hand, due to the laser pulse
- the sequence generation rules and the photon counting rules generated by them are known, so the photon counting statistical rules caused by unnatural background light interference, such as interference light from other detection equipment, can be distinguished from the photon counting sequence or the cumulative photon counting sequence; According to the ambient background light and the statistical law of photon counting generated by the detector array itself, the photon counting sequence (or cumulative photon counting sequence) generated by the photodetector array can be corrected, thereby improving the signal-to-noise ratio and detection performance of the detection system.
- a counting sequence generation module is added to the receiving system, the function of which is to acquire the photon counting sequence, or accumulate the statistical characteristics of the photon counting sequence, and generate an adaptive counting sequence or accumulate self-adaptive counting sequences according to preset rules. Adapt to counting sequences.
- FIG. 11 is a schematic diagram of a three-dimensional imaging system according to an embodiment of the present application. Compared with FIG. 3, FIG. 11 adds a counting sequence generation module, and the functions of other modules are the same as those shown in FIG. 3, and will not be repeated here.
- the counting sequence generation module generates an adaptive counting sequence according to the statistical characteristics of the photon counting sequence and preset rules.
- FIG. 12 is a flowchart of generating an adaptive counting sequence according to an embodiment of the present application.
- the counting sequence generation module obtains natural background light, such as sunlight, etc., and counting results generated by the detector array itself according to the photon counting sequence, and generates an adaptive counting sequence accordingly.
- the specific way is that the adaptive counting sequence module according to the photon counting sequence
- formula (17) and formula (18) The function of formula (17) and formula (18) is to obtain the characteristics of the photon counting sequence.
- the summation operation in formula (17) and the mean value calculation in formula (18) are only for illustration, and no specific limitation is made here. .
- construct an adaptive correction sequence that conforms to a certain distribution for example, construct an adaptive correction sequence X dm with mathematical distribution such as Poisson distribution with binomial distribution or Gaussian distribution. limit.
- the sum of the variance and mean of the adaptive correction sequence X dm and the photon counting sequence X d A d or the arithmetic mean and other characteristics are in certain specific relationships, such as positive correlation or negative correlation, or some specific values, which are not specifically limited here.
- the preset rule of formula (19) is equivalent to inserting the adaptive correction sequence X dm into the photon counting sequence X d to obtain the adaptive counting sequence X da .
- the subsequent signal processing process performed after X da is obtained is the same as that in the foregoing embodiment, and will not be repeated here.
- FIG. 13 is a flowchart of generating an adaptive accumulating count sequence according to an embodiment of the present application.
- the counting sequence generation module generates an adaptive cumulative counting sequence according to the statistical characteristics and preset rules of the cumulative photon counting sequence.
- the counting sequence generation module obtains the natural background light such as sunlight and the counting results generated by the detector array itself according to the photon counting sequence, and generates an adaptive counting sequence accordingly.
- the specific way is that the adaptive counting sequence module according to the accumulated photon counting sequence
- formula (21) and formula (22) The function of formula (21) and formula (22) is to obtain the characteristics of the accumulated photon counting sequence.
- the summation operation in formula (21) and the mean value calculation in formula (22) are only for illustration, and are not detailed here. limit.
- construct an adaptive correction sequence that conforms to a certain distribution for example, construct an adaptive correction sequence X m with a mathematical distribution such as a Poisson distribution with a binomial distribution or a Gaussian distribution. make restrictions.
- the variance and mean of the adaptive correction sequence X m and the sum A of the accumulated photon count sequence X or the arithmetic mean and other characteristics are in certain specific relationships, such as positive correlation or negative correlation, or some specific values, which are not specifically limited here.
- the preset rule of formula (23) is equivalent to adding the adaptive correction sequence X m and the accumulated photon counting sequence X to obtain the adaptive accumulated counting sequence X a .
- the threshold can be Among them: ⁇ is a certain positive integer, which is not specifically limited here. Screen out the high-value elements in the cumulative photon counting sequence X whose value is greater than the threshold XH , by analyzing the distribution characteristics of the above-mentioned high-value elements and combining the known emission frequency characteristics of the laser pulse sequence, distinguish and eliminate the interference caused by unnatural background light. The high-value elements of , get the adaptive cumulative count sequence X a .
- the adaptive accumulation count sequence X a can be obtained by performing operations according to the preset rules in the following formula (25):
- the real-time generation of the adaptive counting sequence in the above-mentioned embodiment will enhance the anti-interference effect, but at the same time, it also increases the difficulty of implementing the imaging system.
- FIG. 14 is another flowchart of generating an adaptive counting sequence provided by an embodiment of the present application.
- the counting sequence generation module can also be based on the interference of natural background light (such as sunlight, etc.) obtained in advance, the cause of the detector array itself, unnatural background light (such as interference light from other detection devices, etc.) interference, etc.
- the a priori information of the counting statistical law generated by the factor is used to generate an adaptive correction sequence in advance.
- the pre-generated adaptive correction sequence is stored in the counting sequence generation module, and the adaptive correction sequence is not generated in real time and dynamically according to the photon counting sequence or the accumulated photon counting sequence.
- the process is shown in FIG. 14
- the process of generating the adaptive cumulative count sequence is shown in FIG.
- the preset rules described in FIG. 14 and FIG. 15 may be the same as the preset rules in the above-mentioned embodiment, and are not described here. Repeat. The subsequent signal processing process is the same as that in the foregoing embodiment, and will not be repeated here.
- Figures 16a to 16c schematically show the spectrum of the distance-related signal provided by the embodiment of the present application when the adaptive counting sequence or the adaptive cumulative counting sequence is not added, which are natural background light of a certain intensity (such as sunlight, etc.) and The spectrum of the distance-related signal obtained when the detector array itself generates counts without adding the adaptive counting sequence or the adaptive cumulative counting sequence.
- the distance-related signal spectrum shown in Figure 16(a) which has a high signal-to-noise ratio, and the maximum value of its spectrum amplitude reflects the target distance; there is a greater probability to obtain Figure 16 (
- the signal-to-noise ratio of the distance-related signal spectrum shown in b) is lower than that of Fig. 16(a).
- the maximum value of the spectrum amplitude can still reflect the target distance, because the second maximum value of the spectrum amplitude is more than the maximum value of the spectrum amplitude. close, the average noise power of the spectrum is higher, thus increasing the difficulty of extracting the target distance; there is a small probability to obtain the distance-related signal spectrum shown in Figure 16(c), the signal-to-noise ratio of which is further reduced, and the second largest value of the spectrum amplitude is the same as The maximum value of the spectrum amplitude is closer, and the difficulty of extracting the target distance is further increased.
- FIG. 17 schematically shows a spectrum of a distance-related signal obtained when an adaptive counting sequence or an adaptive cumulative counting sequence is added according to an embodiment of the present application. At this time, the distribution of high-value elements in the adaptive counting sequence or the adaptive cumulative counting sequence is more uniform, so that the spectrum of the distance-related signal shown in Figure 17 can be obtained. target distance.
- FIG. 18 is a schematic diagram of a detection system provided by an embodiment of the present application. As shown in FIG. 18 , the difference between it and the embodiment shown in FIG. 3 is that a counting sequence duplication and splicing module is added between the photodetector and the digital multiplier in the detection system, and other modules are the same as the embodiment shown in FIG. 3 . , and will not be repeated here.
- FIG. 19 is a schematic diagram of another detection system provided by an embodiment of the present application. As shown in FIG. 19 , the difference from the embodiment shown in FIG. 11 is that a counting sequence duplication and splicing module is added between the photodetector and the counting sequence generation module in the detection system, and the other modules are the same as the embodiment shown in FIG. 11 . are the same, and will not be repeated here.
- the counting sequence replication splicing module converts the photon counting sequence X d into the replication splicing sequence X c :
- the digital multiplier obtains the modulation count sequence Zd:
- the preset rule operation module performs segment accumulation on the modulation count sequence Z d to obtain the segment accumulation count sequence S d :
- N 0 is an integer whose value is closest to N/M
- K is an integer
- R max is the maximum detectable distance
- the preset rule operation module accumulates the L subsection accumulative counting sequences obtained in the process of transmitting the L laser pulse sequences, and obtains the accumulative counting sequence S:
- the counting sequence replication and splicing module obtains the replication splicing sequence X by replicating one or more elements in the photon counting sequence X d and splicing it with the photon counting sequence X d c .
- FIG. 20 is a schematic diagram of obtaining a replicating splicing sequence provided by the embodiment of the present application.
- the emission period of the laser pulse train is equal to the chirp signal period T, but each laser pulse train consists of (M is a positive integer) laser pulses (each laser pulse sequence in Fig.
- all elements in the photon counting sequence X d are taken as the first N/2 items in the replication splicing sequence X c , and all elements in the photon counting sequence X d are replicated as the last N/2 items in the replication splicing sequence X c term, so as to obtain the replication splicing sequence X c represented by formula (26), the number of elements of which is N.
- the embodiment shown in FIG. 20 is for illustrative purposes only, and is not limited to only emitting laser pulses in half a cycle, and can emit laser pulses in 1/3 cycle, 1/4 cycle . . .
- the method of the embodiment obtains the replica splicing signal.
- FIG. 21 is another schematic diagram of obtaining a replicating splicing sequence provided in the embodiment of the present application.
- the counting sequence replication splicing module can obtain the replication splicing sequence through the embodiment shown in FIG. 21 .
- an accumulated count sequence S including M elements can be obtained.
- the cumulative count sequence S obtained by using a laser pulse sequence including M pulses may have more than M elements. Since the target information is obtained by analyzing the spectral characteristics of the cumulative count sequence S, if the target information obtained by using the cumulative count sequence S obtained by the methods in the embodiments shown in FIG. 3 and FIG.
- the target information obtained by the calculation of the cumulative count sequence S obtained by the method in the embodiment shown in 19 is basically the same, then using the methods in the embodiments shown in FIG. 18 and FIG. 19 , the total required laser emission energy will be smaller, The detection efficiency will be higher.
- the method in the embodiment shown in FIG. 21 can be repeatedly executed. Based on the last execution result, some elements in the last result are superimposed and spliced again to obtain a new sequence, which can further improve the ranging accuracy.
- the embodiment shown in 21 is only for schematic illustration, and does not make specific limitations.
- FIG. 22 is a schematic diagram of waveforms during three-dimensional imaging according to an embodiment of the present application, which is a schematic diagram of waveforms during three-dimensional imaging in the embodiment shown in FIG. 18 .
- the principle of the three-dimensional imaging schematic diagram of the embodiment shown in FIG. 19 is similar to that in FIG. 18 , and details are not repeated here.
- the driving signal generator generates two signals, one of which controls the laser modulation driving circuit, and then controls the pulsed laser to emit laser light. After the beam is shaped and expanded by the transmitting optical system, the laser pulse sequence is projected to the target area. . The laser pulse sequence reflected back by the target is filtered and shaped by the receiving optical system, and then focused on the photodetector. Fig.
- the photodetector performs the first detection within the TR time after the laser pulse sequence starts to emit the first pulse, that is, within the time period of 0 ⁇ t ⁇ TR , and the first detection is obtained.
- the photon counting sequence X d1 of the second detection its element number is K, if the maximum detectable distance of the three-dimensional laser imaging is R max , then T R ⁇ 2R max /c (c is the speed of light in vacuum), in the first detection , the number of elements of the modulation sequence Y 1 in the first detection is also K, and the corresponding elements in X d1 and Y 1 are multiplied to obtain the modulation count sequence Z d1 in the first detection.
- the summation can obtain S d1 , which is regarded as the first element of the segmented accumulative count sequence S d in the emission period of a certain laser pulse sequence.
- the second detection is performed within the time period of T/M ⁇ t ⁇ T/M+ TR . Although there is no pulse emission during the second detection, the photodetector can still detect the photon counting sequence of the second detection.
- X d2 the number of elements is K
- the number of elements of the modulation sequence Y 2 is also K
- X d2' can be obtained by adding the corresponding elements of X d1 and X d2
- S d2 can be obtained by summing the elements in Z d2 , which is taken as the second element of the segmented accumulative counting sequence S d in the emission period of a certain laser pulse
- the steps of the first detection are correspondingly executed; in the fourth, sixth, and eighth detections, the corresponding executions are performed according to the steps of the second detection, which will not be repeated here.
- a total of L subsection accumulative counting sequences can be added to obtain the accumulative counting sequence S, which can be solved by analyzing the spectral characteristics of the accumulative counting sequence S. target information, and then realize 3D imaging.
- the existing technology mainly includes incoherent sinusoidal/pulse amplitude modulated laser 3D imaging technology (itof, hereinafter referred to as technology 1).
- the present application uses pulsed laser for detection, which avoids the problem of wasting laser emission energy within the sampling interval of A/D conversion in technique 1, thus greatly improving the energy utilization rate and reducing the average laser emission power ;
- the application does not use devices such as broadband amplifiers, mixers, and A/Ds in the receiving system, which avoids the problem that the above-mentioned devices limit the dynamic range of the received laser signal, thereby making the receiving system of the present application more efficient.
- the system has a larger dynamic receiving range;
- a digitized chirp signal is used as a modulation sequence, and a digital multiplier is used to realize sequence multiplication, which reduces the chirp signal FM linearity and FM flatness on ranging performance impact;
- the present application has range resolution because the chirped signal is used for correlation reception, which can effectively avoid the influence of multipath effects;
- the present application improves the anti-light interference ability due to the use of correlation reception, Fourier analysis and spectrum detection, so the ranging performance is less affected by light interference, and the required laser energy under the same detection situation is smaller. ;
- the present application extracts target distance information from the frequency spectrum, thereby reducing the influence of pulse shape distortion on the ranging performance;
- the present application improves the anti-light interference capability by adopting correlation reception, Fourier analysis, and spectrum detection, so the ranging performance is less affected by light interference.
- multiple direct receptions are used to form a distance-amplitude spectrum (frequency domain), and the time-of-flight is determined by threshold detection in the frequency domain and the spectrum peak value.
- the spectrum amplitude threshold value can be set adaptively; the spectrum peak value can also be Accurately determine that the scheme as a whole is a digital frame structure type, and more FFT points can be used to ensure the accuracy; under the premise of a large amount of calculation, the quasi-accuracy and accuracy of detection can be guaranteed, and the exposure time is in the form of accumulated charges.
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Abstract
提供了一种激光雷达测距方法及探测系统,该探测系统包括:驱动信号发生部,所述驱动信号发生部用于产生驱动信号作用于激光源,所述激光源接收所述驱动信号以发射出脉冲激光序列;阵列型返回光接收模块,所述阵列型返回光接收模块用于接收经由视场内被探测物反射的返回光信号,并产生返回信号;以及处理模块,所述处理模块依据所述驱动信号发生部产生的所述驱动信号产生调制信号,并按照预设规则基于所述调制信号获得距离相关的信号,所述处理模块依照所述距离相关的信号输出所述被探测物的距离信息。
Description
相关申请的交叉引用
本申请要求于2021年3月30日提交中国专利局的申请号为202110334626.6、发明名称为“一种激光雷达测距方法及探测系统”,于2021年9月23日提交中国专利局的申请号为202111112299.6、发明名称为“一种激光雷达探测系统”,以及于2022年2月14日提交中国专利局的申请号为202210132268.5、发明名称为“一种激光雷达探测系统以及探测方法”的专利申请的优先权,其全部内容通过引用结合在本申请中。
本申请涉及探测技术领域,特别涉及一种激光雷达测距方法及探测系统。
距离探测系统,尤其是利用激光源实现的主动型探测系统,其原理为通过光源主动发射用于进行探测的发射光,例如近红外类型的探测光,其波长可以选择为800-1200nm范围内,此处并不限定于此。采用近红外类型的探测波,还能够保证在视场内存在以人为对象时的安全性,因此近红外类型的主动探测系统越来越普遍地应用于各种场景中,例如自动驾驶、智能门锁、安防摄像、手机三维摄像等等。
飞行时间(Time of Flight,TOF)光检测和测距(Light Detection and Ranging,LIDAR)是一种用于远程距离测量的技术。TOF LIDAR传感器通过测量激光脉冲在仪器和物体之间传播所需的时间来确定包括传感器的仪器与物体之间的距离。
目前应用较广泛的探测方法包含间接飞行时间(Indirect Time of Flight,ITOF)测量方案和直接飞行时间(Direct Time of Flight,DTOF)测量方案。大部分的间接飞行时间测量方案都是采用了测相位偏移的方法,即测量发射波与接收波之间的相位差。发射波和接收波的横坐标是时间,纵坐标是光强,根据二者的相位差便可获得飞行时间t,从而根据公式D=ct/2计算获得探测物体的距离。直接飞行时间测量方案一般通过皮秒级分辨率的测量系统(多采用SPAD+TDC),直接获得发射端与对应的接收端触发的时间差,即为飞行时间t,从而计算探测物体的距离。另外,还有一种类型的探测方法,其被称为相干探测,具体的工作原理为:相干的激光信号和本机激光振荡信号在满足波前匹配的条件(即在整个激光探测器的光敏表面上保持相同的相位关系)下,一起入射到探测器的光敏表面上,产生拍频或相干叠加,探测器输出电信号大小正比于待测激光信号波和本机激光振荡波之和的平方的探测方式,当然上述的探测方式有其自身优势,但是对于像素级、快速处理和发射能量的高效利用方面还是具有很大的不足。
近年来,一些直接飞行时间探测(非相干)的激光雷达原理也被开发出来,逐渐变成了一种为更多人所了解的探测技术。专利申请号CN202010604232.3名称为一种新型激光测距方法及激光雷达系统,提出了一种新类型的探测机理,在光路上不采用相干光原理,而在电信号阶段进 行相关运算,进一步通过电信号的相关运算获得最终的被探测物的距离或者其他信息。然而,上述方法存在如下的局限性特点:(1)由非相干啁啾信号调幅连续波激光三维成像原理可知,差频信号由延迟的啁啾信号与本振信号相乘产生。从能量利用角度看,由于对差频信号进行了A/D转换,因此A/D转换的采样间隔内的差频信号能量未被利用,又由于延迟的啁啾信号能量与连续波激光器发射能量呈正比,因此造成现有技术(非相干啁啾信号调幅连续波激光三维成像)的激光平均发射功率较高,测距范围较小;(2)采用了宽带放大器、混频器和A/D转换器等器件,这些器件的动态范围限制了接收激光信号的动态范围,从而限制了动态接收范围;(3)所形成的激光三维成像系统性能受啁啾信号调频线性度和调频平坦度影响较大。
因此,为了克服前述的技术问题,亟需开发一种更高效的探测方法和探测系统,使得在能效方面能够更大限度地利用发射激光的回波能量,在抗干扰方面能够适应更多探测系统存在于视场内的状况下高效地识别出被探测物并且获得准确的距离信息。
发明内容
有鉴于此,本申请提供一种获取距离信息的探测方法及探测系统,以准确稳定地输出视场内各个距离范围内被探测物的稳定且准确的距离结果。
本申请实施例采用的技术方案如下:
第一方面,本申请提供了一种激光雷达测距方法,包括:
由驱动信号发生部产生驱动信号并通过激光调制驱动电路作用于激光源,所述激光源接收所述驱动信号以发射出脉冲激光序列;
由阵列型返回光接收模块接收经由视场内被探测物反射的返回光信号并产生返回信号;以及
由处理模块依据所述驱动信号发生部产生的所述驱动信号产生调制信号,所述处理模块按照预设规则基于所述调制信号获得距离相关的信号,所述处理模块依照所述距离相关的信号输出所述被探测物的距离信息。
第二方面,本申请提供一种用于进行距离探测的探测系统,包括:驱动信号发生部,所述驱动信号发生部被配置成产生驱动信号并通过激光调制驱动电路作用于激光源,所述激光源接收所述驱动信号驱动发射出脉冲激光序列;阵列型返回光接收模块,被配置成接收经由视场内被探测物反射的返回光信号,并产生返回信号;以及处理模块,所述处理模块被配置成依据所述驱动信号发生部产生的所述驱动信号产生调制信号,并按照预设规则基于所述解调信号获得距离相关的信号,以及依照所述距离相关的信号输出所述被探测物的距离信息。
本申请的有益效果是:
本申请实施例提供的一种激光雷达测距方法及探测系统。所述方法包括:由驱动信号发生部产生驱动信号并通过激光调制驱动电路作用于激光源,所述激光源接收所述驱动信号以发射出脉冲激光序列;由阵列型返回光接收模块接收经由视场内被探测物反射的返回光信号并产生返回信号;以及由处理模块依据所述驱动信号发生部产生的所述驱动信号产生调制信号,所述处理模块按照预设规则基于所述调制信号获得距离相关的信号, 所述处理模块依照所述距离相关的信号输出所述被探测物的距离信息。本申请利用驱动信号驱动光源发射脉冲激光序列,一方面使得发射的能量能够被大幅减小,另一方面通过与返回光产生的信号按照预设规则运算得到距离相关信号保证了探测结果的准确性,进一步本申请通过单光子雪崩二极管阵列或者类似的APD阵列型探测器的多于一次的光子触发统计结果,与调制序列进行预设的运算,可以减少实际的运算次数,使得整个统计和运算的复杂度大大降低,保证了整个探测系统和测距方法的高效性。此外,计数序列生成模块依据所述返回信号生成自适应计数序列,处理模块基于所述自适应计数序列和所述调制信号获得所述距离相关的信号以最终得到被探测物的距离信息,如此设计,可以增强雷达探测系统的抗干扰能力。进一步地,计数序列拼接模块根据所述返回信号得到复制拼接信号,处理模块基于所述复制拼接信号和所述调制信号获得所述距离相关的信号以最终得到被探测物的距离信息,如此设计,可以用更小的激光发射能量,实现较小的测距偏差。
为了更清楚地说明本申请实施例的技术方案,下面将对实施例中所需要使用的附图作简单地介绍,应当理解,以下附图仅示出了本申请的某些实施例,因此不应被看作是对范围的限定,对于本领域普通技术人员来讲,在不付出创造性劳动的前提下,还可以根据这些附图获得其他相关的附图。
图1为本申请实施例提供的一种探测系统模块化工作原理的示意图;
图2为现有技术提供的一种探测方案的示意图;
图3为本申请实施例提供的一种脉冲化探测方案实现示意图;
图4为本申请实施例提供的一种阵列型接收模块示意图;
图5为本申请实施例提供的一种预设规则运算模块示意图;
图6为本申请实施例提供的一种发射L次激光序列的返回光统计的计数序列结果示意图;
图7为一种利用驱动信号产生离散型调制序列的示意图;
图8为本申请实施例提供的一种利用预设规则运算模块获取距离相关信号的示意图;
图9为本申请实施例提供的另一种利用预设规则运算模块获取距离相关信号的示意图;
图10为本申请实施例提供的一种获得距离相关信号的示意图;
图11为本申请实施例提供的一种三维成像系统示意图;
图12为本申请实施例提供的生成自适应计数序列流程图;
图13为本申请实施例提供的生成自适应累加计数序列流程图;
图14为本申请实施例提供的又一生成自适应计数序列流程图;
图15为本申请实施例提供的根据预先生成的自适应修正序列产生自适应累加计数序列流程图。
图16a至图16c为本申请实施例提供的未加入自适应计数序列或自适应累加计数序列时的距离相关信号频谱;
图17为本申请实施例提供的加入自适应计数序列或自适应累加计数序列时得到的距离相关信号频谱;
图18为本申请实施例提供的一种探测系统示意图;
图19为本申请实施例提供的一种探测系统示意图;
图20为本申请实施例提供的得到复制拼接序列的示意图;
图21为本申请实施例提供的另一得到复制拼接序列的示意图;
图22为本申请实施例提供的一种三维成像时的波形示意图。
为使本申请实施例的目的、技术方案和优点更加清楚,下面将结合本申请实施例中的附图,对本申请实施例中的技术方案进行清楚、完整地描述,显然,所描述的实施例是本申请一部分实施例,而不是全部的实施例。通常在此处附图中描述和示出的本申请实施例的组件可以以各种不同的配置来布置和设计。
因此,以下对在附图中提供的本申请的实施例的详细描述并非旨在限制要求保护的本申请的范围,而是仅仅表示本申请的选定实施例。基于本申请中的实施例,本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例,都属于本申请保护的范围。
应注意到:相似的标号和字母在下面的附图中表示类似项,因此,一旦某一项在一个附图中被定义,则在随后的附图中不需要对其进行进一步定义和解释。
目前采用的探测系统基本包括:光源模块110、处理模块120、以及光接收模块130。光源模块110包括但不仅限于半导体激光器、固体激光器、 也可包括其他类型的激光器。当采用半导体激光器作为光源时,可以采用垂直腔面发射激光器VCSEL(Vertical-cavity surface-emitting laser)或者边发射半导体激光器EEL(edge-emitting laser),此处仅为示例性说明并不作具体限定。光源模块110发射出正弦波或者方波或者三角波,或者脉冲波等等,在测距应用中多为具有一定波长的激光,例如950nm等等的红外激光(最优地为近红外激光)。发射光被投射向视场内,视场内存在的被探测物140可以反射投射的激光进而形成返回光,返回光进入探测系统中被光接收模块130捕获。所述光接收模块130可以包含光电转化部,其中ITOF测距中,其可以最常用的四相位方案进行接收而获得0°、90°、180°和270°的延时接收信号。利用四相位的距离计算方案此处以正弦波的方法为示例进行说明,在四个等距点(例如90°或1/4λ的间隔)测量接收信号的幅度,如下是四相位测距的距离计算公式:
A1和A3的差值与A2和A4的差值的比等于相位角的正切值。ArcTan实际上是双变量反正切函数,可映射至适当的象限,当A2=A4并且A1>A3或A3>A1时,分别定义为0°或180°。
到目标物的距离由以下公式确定:
至此,还需要确定发射激光的频率即可来进行距离测算,其中c是光速,
是相位角(以弧度来度量),f是调制频率。通过上述的方案可以实现对于视场内被探测物的距离探测的效果,这一方案被称为四相位延时方案 获得探测结果。当然光接收模块光电转化生成不同的信息,在某些情况下也使用0°和180°两相位方案实现被探测物的信息获取,也有文献公开了0°、120°和240°三相位获得目标信息,甚至有文献也公开了五相位差延时方案,本申请并不具体限定。
在DTOF测距中由于阵列传感器的像素单元为SPAD(Single Photon Avalanche Diode,单光子雪崩光电二极管)器件,其为工作在盖革模式下的雪崩光电二极管。在盖革模式下,雪崩光电二极管吸收光子会产生电子-空穴对,在高反偏电压产生的强电场作用下,电子-空穴对被加速,从而获得足够的能量,然后与晶格发生碰撞,形成连锁效应,结果形成大量的电子-空穴对,引发雪崩现象,电流成指数增长。此时SPAD的增益理论上是无穷的,单个光子就能够使SPAD的光电流达到饱和,因此SPAD成为高性能单光子探测系统的首选。下面具体介绍测距原理。光源发射具有一定脉宽的脉冲激光例如几纳秒级别,脉冲激光经过探测目标反射返回至处于包含雪崩状态SPAD的阵列型接收模块。其中处于雪崩状态的探测单元可以接收返回的信号,经过处理模块的处理可以输出探测系统至探测目标之间的距离,从而完成探测。其中为了获得高可信度的结果,可以发射数万次的激光脉冲,探测单元获得一个统计结果,这样通过对于统计结果的处理可以获得更精确的距离。本申请的申请人对应用较多的两种比较典型的测距方法ITOF测距方法和DTOF测距方法进行了对比,如下表1所示。通过表1的比较可以看到,这两种应用较多的飞行时间测距方案具有一定的局限性,也需要开发一种新型的探测方法来获得更准确和抗干扰能力更强的结果。
表1.ITOF与DTOF测距方法对比
图2为现有技术公开的一种利用非相干(直接探测方案)实现对于被探测物距离等信息进行获取的方案。如图2所示,驱动信号发生部产生驱动信号,此处的驱动信号可以为具有标识功能的驱动信号,例如信号的周期逐渐增加或者逐渐递减,当然也可以通过一些特定的函数或者内部算法获得具有一定特征和标识作用的驱动信号,此处以啁啾信号为示例,但是实际实现不限于此。驱动信号通过激光调制驱动电路作用于激光发射器, 此处为连续波激光器,从而发射出具有与驱动信号相类似规律的探测激光。探测激光在视场内经过被探测物的反射之后形成返回的激光信号。由于视场内的被探测物存在距离上的差异,因而光接收模块的不同区域可以获得延时的返回光信号,在光接收模块通过光电转化而获得的延时启动信号,经过带宽放大器之后,在混频器内部与驱动信号进行相关处理获得混频之后的输出信号。信号处理器对于所述混频后的输出信号进行处理可以获得差频信号,其中信号处理器可以包含低通的滤波电路,对于杂波干扰进行滤除获得真正的有用的差频信号,差频放大器可以对滤波之后的差频信号进行放大,进而获得传输抗干扰能力强且信号更真实的待处理差频信号,最后经过A/D转换器转换得到数字信号。转化后的数字类型差频信号,被传递至时频域转换模块,其可以通过时频域转换获得差频信号的频谱,最终通过频谱的特征,例如峰值特征,识别出最终的与频谱特征相关的例如被探测物的速度、距离等信息的探测结果。此外,为了保证频域转化的信号满足探测需求,时频域转换模块还可以包含阈值检测单元和信息解算单元等等。在图2中,以驱动信号发生器为啁啾信号发生器为例进行进一步的说明。啁啾信号发生器产生两路啁啾信号,一路作为混频器的本振信号,另一路送入激光调制驱动电路,使得连续波激光器发射的激光功率按照如下规律变化:
P
t(t)=P
t0[1+m
tcos(2πf
0t+πkt
2+θ
0)],t∈[0,T] (3)
式中,P
t0为激光平均发射功率;m
t为发射调制深度;f
0为啁啾信号起始频率;t为时间;k为调频斜率且k=B/T(B为啁啾信号带宽,T为啁啾信号周期),θ
0为初始相位。
接收光学系统将由目标反射回的激光信号聚焦到光电探测器,经光电转换得到延迟的啁啾信号,该信号经过放大后与本振信号混频,经过低通滤波后得到差频信号。其中,延迟的啁啾信号为:
A
r(t)=A
r0[1+m
tcos(2πf
0(t-τ)+πk(t-τ)
2+θ
0+φ
0)],t∈[τ,T+τ] (4)
式中,A
r0为延迟的啁啾信号的平均幅度;φ
0为目标反射引入的附加相位;τ=2R/c(R为目标相对距离,c为真空中光速)为激光往返于目标和测距仪的时间。
本振信号为:
A
LO(t)=A
LO0[1+m
LOcos(2πf
0t+πkt
2+θ
LO)],t∈[0,T] (5)
式中,A
LO0为本振信号平均幅度,m
LO为本振信号调制深度,θ
LO为本振信号初始相位。
差频信号为:
将差频信号放大后进行A/D转换,并通过快速傅里叶变换(FFT)得到其频谱,对其频谱进行阈值检测,得到差频信号频率为:
根据差频信号频率与目标相对距离间的关系,得到目标相对距离为:
虽然这种非相干类型的探测技术可以在一定程度上补充ITOF与DTOF甚至是相干探测方法所存在的一些缺陷,但是上述的现有技术在探测中仍 然具有如下的局限性:
(1)由非相干啁啾信号调幅连续波激光三维成像原理可知,差频信号由延迟的啁啾信号与本振信号相乘产生。从能量利用角度看,由于对差频信号进行了A/D转换,因此A/D转换采样间隔内的差频信号能量未被利用,又由于延迟的啁啾信号能量与连续波激光器发射能量呈正比,因此造成现有技术(非相干啁啾信号调幅连续波激光三维成像)的激光平均发射功率较高,测距范围较小;
(2)由图2和系统工作原理描述可知,现有技术采用了宽带放大器、混频器和A/D等器件,这些器件的动态范围限制了接收激光信号的动态范围,从而限制了现有技术的动态接收范围;
(3)利用现有技术实现的激光三维成像系统性能受啁啾信号调频线性度和调频平坦度影响较大。
正是由于现有的非相干类型的探测方法所存在的技术问题和数据处理上所存在的复杂性数据量巨大等等的问题,本申请的发明人提出了一种改进类型的探测方法和探测系统。如图3所示,系统采用脉冲型激光器,从而发射的主动型探测激光为由脉冲序列所组成的脉冲激光序列片段,系统中的驱动信号发生部产生驱动信号,此处的驱动信号可以采用类似之前示例的啁啾信号,也可以采用其他类型的驱动信号,此处的驱动信号的本质特征在于对于设备发射激光进行调制以获得具有可识别特征的发射光信号。驱动信号通过激光调制驱动电路作用于脉冲型激光器上,激光器可以利用驱动信号的至少部分特征,例如驱动信号的总周期作为脉冲序列片段的周期,脉冲片段内的单个脉冲可以选择为峰值相同或者相近,峰值持续 时间相同或者相近的方案,或者驱动信号的幅度信息作为脉冲序列的峰值依据,此时被包含于脉冲序列中的峰值可以不同,甚至可以将驱动信号的片段内小周期的递减或递增规律作为发射的激光片段内脉冲触发概率的依据从而产生非等间距配置的脉冲型激光片段等等,此处并不限定脉冲激光源发射的脉冲激光片段具体实现方案,发射的脉冲激光序列被视场内被探测物的反射产生返回光信号,返回光信号被光电探测器接收形成光子计数序列,此时处理模块内部包含的预设规则运算模块一方面利用驱动信号产生非连续的调制序列Y,另一方面可以通过对于光子计数序列与调制序列Y按照预设规则运算得到距离相关信号,所述的距离相关信号再经过时频域转换模块得到距离相关信号转换的频谱信号,再利用该频谱信号的特征,例如峰值特征(包含最高峰值信息、次高峰值信息或者关心区域内的峰值信息等等)输出包含被探测物距离信息,还可以包含速度信息等等,此处不进行具体限定,类似地对于脉冲类型的非连续性探测方案,时频域转换模块内包含可以进行时频域转化处理的单元,其可以执行例如小波运算、分段FFT、FFT、chirp-Z运算、DFT等等,当然此处对于具体的算法实现不再详细赘述,此处也只是进行示例性地列举,当然时频域转换模块还可以包含阈值检测单元和/或信息解算单元,此处也不限定。
光接收模块可以采用如图4所示的阵列型接收模块。阵列型接收模块中包含二极管组成的像素单元410,在实际的实现中可以采用M*N个像素单元组成阵列型接收模块的有源区,其组成的像素单元可以为上万数万乃至数十万等等的量级,此处并不限定。阵列型接收模块可以包含透镜部4301和探测单元基体部4302。透镜部4301包含多个透镜单元,透镜单元可以为 具有预定曲率的微透镜单元组成。为了保证对于返回光的最大限度的利用,透镜部也可以包含多于1层的结构,此处并不限定具体的实现方案。在更优的情况下基体部4302可以设置于透镜部4301对应的焦平面位置,这样可以保证探测像素单元能够最大限度地获取准确的返回光信息。在此情况下,透镜部4301的透镜能构建一个光通道,使得探测单元的光敏部接收的信号处于相应的焦点位置附近。探测单元基体部4302中包含阵列型布置的光敏像素阵列,此处为了配合非连续型的探测需求,此处的光敏像素单元的二极管可以为具有单光子敏感度的单光子雪崩二极管阵列(SPAD),也可以采用盖革模式的探测器单元阵列APD,或者具有线性放大系数的光子计数型的探测像素单元组成的阵列型探测器等等,此处并不限定。由于本申请的探测器阵列中直接输出的信号为光子计数序列,实现了数字信号的直接输出和传递,预设规则运算模块以驱动信号为母本,获得调制序列Y,其也为非连续性的序列型信号,甚至直接获得数字化的调制序列Y,两者均不是现有技术中类似的模拟信号,因此不需要经过A/D模数转换而直接在预设规则运算模块中进行相关运算。
此处仍以啁啾信号发生器为例进行示例性的说明。一方面,啁啾信号发生器产生一路啁啾信号作为调制序列Y,此处的调制序列可以为前述示例中连续信号的离散化,并最终转换为数字类型的调制序列信号,此处激光发射的周期选择为啁啾信号周期T(也就是发射激光的片段内总持续时间选择为啁啾信号的周期特征)。另一方面,啁啾信号发生器控制激光调制驱动电路产生脉冲激光器驱动信号,脉冲激光器驱动信号控制脉冲激光器发射激光脉冲序列,发射光学系统将激光脉冲序列投射到目标区域;激光脉 冲序列中各激光脉冲能量相等,此处也只是示例性地列举了一种情况,接收系统包括接收光学系统、光电探测器、数字相关器、数字积分累加器等,其中接收光学系统将目标反射回的激光脉冲序列聚焦到光电探测器,光电探测器在发射激光脉冲序列时开始探测,得到激光脉冲序列发射周期内的光子计数结果。为了保证后续的计算结果运算量较小,首先利用L次发射的脉冲序列对于视场内场景进行照射(其中L为大于等于1的整数)。更优化地,为了获得更为准确的探测结果,可以选择L为数百数千等等的量级此处并不进行限定。当然为了保证数据的准确性或者运算精确快速等等的效果,此处也不限定为对于这L次的所有探测结果进行统计获得统计值。此处可以为利用小于等于L次返回光的激发信息获得的统计结果产生统计后的光子计数序列X,例如下述场景为一种示例性地说明统计后的光子序列X产生和构造方案。对目标反射回的激光脉冲序列进行L(L为正整数且L≥1)次累积探测,每次累积探测包括M(M为正整数且M≥1)个探测脉冲,第d(d为正整数且1≤d≤L)次累积探测中的第i(i为正整数且1≤i≤M)个探测脉冲得到的光子计数结果为x
di,由此得到由M个探测脉冲计数结果组成的基本计数序列X为:
先进行L次累积探测,得到L次累积探测后得到的基本计数序列X(X为L个X
d的累加),然后让X与Y相乘得到Z(Z为L个Z
d的累加),然后 对Z进行分段累加得到S。
上述的步骤在原理上可以表示为图5的方案,其中单次发射的激光序列为最顶部示意的情况,每次发射的激光序列中包含M个探测脉冲,激光源以L次的形式输出L次的脉冲激光序列,再通过探测模块获得不超过L次发射的探测光的返回光的触发信息获得统计的光子计数序列,如式(9)所示,最终构造出的统计的光子计数序列如图5最下部所示意的结果。
预设规则运算模块的具体结构如图6所示,其包括数字乘法器单元和数字积分累加器单元。通过预设规则运算模块中的数字乘法器单元和数字积分累加器单元,可以实现对于探测视场内场景的自适应,并且随场景的变化可以自适应调整探测最大距离实现探测精度等的自调整,也能够通过数字乘法器单元实现信号之间的相关运算进而提升系统的抗干扰能力。也就是可以按照如下示例的方案得到,前述由L次的脉冲光发射获得了返回光的统计光子计数序列X。图7为一种利用驱动信号产生离散型的调制序列Y的示意图,驱动信号的函数表达式为f(x),利用离散化方案获得与驱动发射激光脉冲类似的离散型调制序列Y,其中所述单次发射的激光序列包含M个脉冲激光激发高值单元,所述调制序列也包含N个脉冲高值单元。所述调制信号为由所述驱动信号发生部所产生的驱动信号按照所述发射光脉冲序列类似规则生成的非连续型的调制序列,结果如下式(10)所示。
Y={y
i|y
i=f(i)i=1,2,...,N} (10)
获得了发射光返回所激发的统计光子计数序列与调制序列之后,预设规则运算模块可以按照模块内的单元对两组序列进行相关运算,从而获得两组序列的相关运算结果。图8和图9分别示意了两种不同的方案。按照 图8的运算方案,可以对于统计的光子计数序列与调制序列执行乘法运算,也就是可以利用数字乘法器得到调制计数序列Z
d:
Z
d={z
di|z
di=x
di·y
i,i=1,2,...,N} (11)
完成乘法运算单元的计算之后,数字积分累加器可以对调制计数序列执行分段累加,其中累加区间为执行累加操作的区间片段,处理模块可以依照一定的规则设置出累加区间的实际大小,在累加区间内执行有效叠加区域内的乘法结果序列的分段累加,可以获得信号的增强效果,同时也能保证探测的准确性,其中有效叠加区域内的叠加单元数量为K,因此执行分段累加操作之后的最终得到分段累加计数序列S
d:
最后利用数字积分累加器,将在L(L为正整数且L≥d)个激光脉冲序列发射周期内得到L个分段累加计数序列累加,得到累加计数序列S:
图9为另一种实现思路,参照附图9,我们可以得到相关运算模块实现的另一种方案。该模块内的各个单元首先对于序列执行分段累加操作,也就是之前所述的统计光子计数序列X和调制序列Y首先分为累加区间内的有效叠加区间内分别执行分段累加操作,完成之后再对两者执行相乘运算,两种顺序所产生的运算结果可以不相同,此处并不限定,但是两者均可以包含与被探测物距离、速度等等物理特征相关联的结果相关信息,信号处理系统包括时频域转换、阈值检测和信息解算等,时频域转换实现对累加计数序列S的频谱按照例如小波运算、分段FFT、FFT、chirp-Z运算、DFT 等等转化计算,阈值检测实现对累加计数序列S的频谱峰值特征的检测,包含最高峰值信息、次高峰值信息或者关心区域内的峰值信息等等,信息解算根据累加计数序列S的频谱信息得到目标相对距离、相对速度和三维图像等信息。
图10也可以解释为实现本发明方案的又一种详细方案描述,结合图10来进行阐述,激光源发射L次的脉冲序列输出,视场内被探测物的反射探测激光再接收端形成返回光的光子统计结果X,其可以为L次的返回结果,调制序列可以按照每次输出调制序列并与每次的返回光子统计序列执行乘法运算获得调制的统计序列Z,最终执行分段累计结果从而获得最终的计数序列S,此种方案也是本申请所进行保护的一种方案,执行步骤为先利用一次脉冲序列得到X
d,
X
d={x
di|i=1,2,...,N} (14)
与前述方案类似获得非连续的调制序列Y,然后让X
d与Y相乘得到Z
d,
Z
d={z
di|z
di=x
di·y
i,i=1,2,...,N} (15)
然后对Z
d进行分段累加得到S
d,类似于式13所示的分段累加方案,当然此处也只是示意性地阐述图示的一种情况,实际实现不限于此种方式。与之前不同在于该方案可能需要更大的计算量,在快速输出的要求下需要采用更优化的方案来实现探测,此处并不限定。
上述实施例中的光子计数序列或累加光子计数序列不仅可以通过光电探测器阵列接收到的激光脉冲序列产生,光电探测器阵列接收到的环境背景光也会产生光子计数序列或累加光子计数序列,其中环境背景光包括自然背景光和非自然背景光。此外,在探测器阵列未接收到光子时,仅由探 测器阵列自身原因产生,例如盖革模式APD光电探测器阵列的暗计数、读出电路噪声引起的计数等也会产生光子计数序列或累加光子计数序列。其中,环境背景光、探测器阵列自身原因等产生的光子计数结果会降低探测系统信噪比,造成探测性能恶化。
由于自然背景光,如太阳光等以及由探测器阵列自身原因产生的计数结果通常服从一定的统计规律,因此可以根据光子计数序列或累加光子计数序列确定上述统计规律;另一方面,由于激光脉冲序列产生规则及由其产生的光子计数规律已知,因此可以从光子计数序列或累加光子计数序列中分辨出由非自然背景光干扰,如其他探测设备的干扰光等产生的光子计数统计规律;根据环境背景光以及由探测器阵列自身原因产生的光子计数统计规律,可以对光电探测器阵列产生的光子计数序列(或累加光子计数序列)进行修正,从而提高探测系统信噪比和探测性能。
为抑制上述问题,在一些实施例中接收系统中增加了计数序列生成模块,其作用是获取光子计数序列,或累加光子计数序列的统计特性,并按照预设规则产生自适应计数序列或累加自适应计数序列。
图11为本申请实施例提供的一种三维成像系统示意图。图11相对于图3,增加了一个计数序列生成模块,其他模块功能和图3所示相同,这里就不再赘述。在图11中,计数序列生成模块根据光子计数序列统计特性和预设规则产生自适应计数序列。
图12为本申请实施例提供的生成自适应计数序列的流程图。在一些实施例中,计数序列生成模块根据光子计数序列,得到自然背景光,如太阳光等以及由探测器阵列自身原因产生的计数结果,并据此生成自适应计数 序列。具体方式为,自适应计数序列模块根据光子计数序列
X
d={x
di|i=1,2,...,N} (16)
对公式(16)所述的X
d求和得到:
或者对公式(16)所示的X
d求平均值得到:
公式(17)和公式(18)的作用在于得到光子计数序列的特性,公式(17)中的求和运算以及公式(18)的求均值运算仅是为了示意说明,在这里并不做具体限制。根据光子计数序列的特性,构建符合一定分布的自适应修正序列,例如构建具有二项式分布的泊松分布或者高斯分布等数学分布的自适应修正序列X
dm,这里对具体的数学分布不做限制。自适应修正序列X
dm的方差和均值与光子计数序列X
d之和A
d或算数平均值
等特性呈某些特定关系,如呈正相关或负相关,或为某些特定值,这里不做具体限定。将光子计数序列X
d与自适应修正序列X
dm={x
dmi|i=1,2,...,N}按照规定的预设规则进行运算,从而改变光子计数序列X
d中的高值元素数量,得到自适应计数序列X
da。例如可以根据公式(19)的预设规则进行运算:
公式(19)的预设规则相当于将自适应修正序列X
dm插入到光子计数序列X
d,得到自适应计数序列X
da。得到X
da之后进行的后续信号处理过程与前述实施例中相同,这里就不再赘述。
图13为本申请实施例提供的生成自适应累加计数序列的流程图。在图13中,计数序列生成模块根据累加光子计数序列统计特性和预设规则产生自适应累加计数序列。
在一些实施例中,计数序列生成模块根据光子计数序列,得到自然背景光如太阳光等以及由探测器阵列自身原因产生的计数结果,并据此生成自适应计数序列。具体方式为,自适应计数序列模块根据累加光子计数序列
对公式(20)中的序列进行求和得到:
或者对公式(20)中的序列求平均值得到:
公式(21)和公式(22)的作用在于得到累加光子计数序列的特性,公式(21)中的求和运算以及公式(22)的求均值运算仅是为了示意说明,在这里并不做具体限制。根据累加光子计数序列的特性,构建符合一定分布的自适应修正序列,例如构建具有二项式分布的泊松分布或者高斯分布等数学分布的自适应修正序列X
m,这里对具体的数学分布不做限制。自适应修正序列X
m的方差和均值与累加光子计数序列X之和A或算数平均值
等特性呈某些特定关系,如呈正相关或负相关,或为某些特定值,这里不做具体限定。将累加光子计数序列X与自适应修正序列X
m={x
mi|i=1,2,...,N}按照规定的预设规则进行运算,从而改变累加光子计数序列X中的高值元 素数量,得到自适应累加计数序列X
a。例如可以根据公式(23)的预设规则进行运算:
X
a={x
ai|x
ai=x
i+x
mi,i=1,2,...,N} (23)
公式(23)的预设规则相当于将自适应修正序列X
m与累加光子计数序列X相加,得到自适应累加计数序列X
a。
在另外的一些实施例中,可以从公式(20)~公式(22)以及公式(20)的所示数列的方差:
等特性得到阈值X
H,例如,可令阈值
其中:λ为某一正整数,这里不做具体限定。筛选出累加光子计数序列X中的数值大于阈值X
H的高值元素,通过分析上述高值元素的分布特性并结合已知的激光脉冲序列发射频率特性,分辨并剔除由非自然背景光干扰产生的高值元素,得到自适应累加计数序列X
a。
可以按照下式(25)中的预设规则进行运算得到自适应累加计数序列X
a:
得到自适累加计数序列X
a之后进行的后续处理和前面所述的实施例中相同,这里就不再赘述。
上述实施例中实时生成自适应计数序列会增强抗干扰效果,但同时也参加了成像系统的实现难度。
图14为本申请实施例提供的又一生成自适应计数序列流程图。在其他 一些实施例中,计数序列生成模块也可以根据事先获得的自然背景光(如太阳光等)干扰、探测器阵列自身原因、非自然背景光(如其他探测设备的干扰光等)干扰等因素产生的计数统计规律的先验信息,预先生成自适应修正序列。在这种实现方式中,计数序列生成模块中存储有预先生成的自适应修正序列,而不再根据光子计数序列或累加光子计数序列实时、动态地生成自适应修正序列,生成自适应计数序列的流程如图14所示,生成自适应累加计数序列的流程如图15所示,在图14与图15中所述的预设规则可以是和上述实施例的预设规则相同的,这里就不再赘述。其后续对于信号的处理过程与前述实施例相同这里就不再赘述。
图16a至图16c示意性地示出本申请实施例提供的未加入自适应计数序列或自适应累加计数序列时的距离相关信号频谱,其为一定强度的自然背景光(如太阳光等)以及探测器阵列自身原因产生计数时,未加入自适应计数序列或自适应累加计数序列时得到的距离相关信号频谱。此时,有较大的概率得到图16(a)所示的距离相关信号频谱,它具有较高的信噪比,其频谱幅度最大值反映了目标距离;有较大的概率得到图16(b)所示的距离相关信号频谱,其信噪比相比图16(a)有所下降,虽然其频谱幅度最大值仍然可以反映目标距离,但是由于频谱幅度次大值与频谱幅度最大值更加接近,频谱平均噪声功率更高,因此增加了目标距离提取难度;还有较小的概率得到图16(c)所示的距离相关信号频谱,其信噪比进一步下降,频谱幅度次大值与频谱幅度最大值更加接近,目标距离提取难度进一步增大。
图17示意性地示出本申请实施例提供的加入自适应计数序列或自适应累加计数序列时得到的距离相关信号频谱。此时,自适应计数序列或自适 应累加计数序列中的高值元素分布更加均匀,从而可以得到图17所示的距离相关信号频谱,它具有较高的信噪比,其频谱幅度最大值反映了目标距离。
图18为本申请实施例提供的一种探测系统示意图。如图18所示,其与图3所示实施例的差别在于,该探测系统中在光电探测器与数字乘法器之间增加了计数序列复制拼接模块,其他模块与图3所示实施例相同,这里就不再赘述。
图19为本申请实施例提供的另一种探测系统示意图。如图19所示,其与图11所示实施例的差别在于,该探测系统中在光电探测器与计数序列生成模块之间增加了计数序列复制拼接模块,其他模块与图11所示实施例相同,这里就不再赘述。
在图18与图19所示的实施例中,计数序列复制拼接模块将光子计数序列X
d转化为复制拼接序列X
c:
X
c={x
ci|i=1,2,...,N} (26)
数字乘法器得到调制计数序列Zd:
Z
d={z
di|z
di=x
ci·y
i,i=1,2,...,N} (27)
预设规则运算模块对调制计数序列Z
d进行分段累加,得到分段累加计数序列S
d:
预设规则运算模块对在L次激光脉冲序列发射过程中得到的L个分段累加计数序列进行累加,得到累加计数序列S:
在图18与图19所示的实施例中,所述计数序列复制拼接模块通过复制光子计数序列X
d中的一个或多个元素,并将其与光子计数序列X
d拼接得到复制拼接序列X
c。图20为本申请实施例提供的得到复制拼接序列的示意图。在图20所示的实施例中,激光脉冲序列的发射周期等于啁啾信号周期T,但每个激光脉冲序列由
(M为正整数)个激光脉冲组成(图7中每个激光脉冲序列由M
0=M/2=4个激光脉冲组成),也就是只有在啁啾信号的前半个周期内发射激光脉冲,因此在啁啾信号的前半个周期内,光电探测器在探测第d(d为正整数且d≤L)次激光脉冲序列时得到的光子计数序列为X
d,其元素数为N
0=N/2:
此时,将光子计数序列X
d中的全部元素作为复制拼接序列X
c中的前N/2项,并复制光子计数序列X
d中的全部元素作为复制拼接序列X
c中的后N/2项,从而得到公式(26)所表示的复制拼接序列X
c,其元素数为N。图20所示的实施例只是为了示意性说明,并不局限于只在半个周期内发射激光脉冲,可以在1/3周期,1/4周期…..发射激光脉冲,通过图20所示实施例的方法得到复制拼接信号。
图21为本申请实施例提供的另一得到复制拼接序列的示意图。图18与图19所示的实施例中所述计数序列复制拼接模块,可以通过图21所示 的实施例得到复制拼接序列。在图21所示的实施例中激光脉冲序列的发射周期等于啁啾信号周期T,每个激光脉冲序列由M=f
s·T(M为正整数)个激光脉冲组成(图21中每个激光脉冲序列由M=4个激光脉冲组成),光电探测器在探测第d(d为正整数且d≤L)次激光脉冲序列时得到的光子计数序列为X
d,其元素数为N。复制光子计数序列X
d中的全部元素,将其中的前N-N/2M(假设N可被2M=8整除,图21中所示N=64)个元素与X
d中的后N-N/2M个元素叠加;将其中的后N/2M个元素与X
d中的前N/2M个元素叠加,从而得到复制拼接序列X
c,其元素数同样为N,即:
作为对比,按照图3所示实施例与图11所示实施例中的方法,利用包含有M个脉冲的激光脉冲序列,可以得到包含有M个元素的累加计数序列S,而采用图18与图19所示实施例的方法,利用包含有M个脉冲的激光脉冲序列所得到的累加计数序列S,其元素数可以大于M个。由于通过分析累加计数序列S的频谱特性得到目标信息,因此,如果利用图3与图18所示实施例中的所述方法得到的累加计数序列S解算得到的目标信息与利用图18与图19所示实施例中所述方法得到的累加计数序列S解算得到的目标信息基本相同,那么采用图18与图19所示实施例中的方法,所需的激光发射总能量将更小,探测效率将更高。
可以重复执行图21所示的实施例中方法,基于上次的执行结果,再次对上次的结果中的部分元素进行叠加和拼接,再次得到新的序列,这样可以进一步提高测距精度,图21所示实施例只是为了示意性的说明,并不做 具体限制。
图22为本申请实施例提供的一种三维成像时的波形示意图,其为图18所示实施例中三维成像时的波形示意图。图19所示实施例的三维成像示意图原理与图18类似,这里就不再赘述。在图18所示实施例中,驱动信号发生部产生两路信号,其中一路控制激光调制驱动电路,进而控制脉冲激光器发射激光,经过发射光学系统整形扩束后,激光脉冲序列被投射到目标区域。目标反射回的激光脉冲序列经过接收光学系统滤波、整形后,被聚焦到光电探测器,图22示出了可能的一种实现方式对应的部分波形示意图。其中,激光脉冲发序列的发射周期为T,每个周期内包含有M=4个脉冲。在第d个激光脉冲序列发射周期内,光电探测器在激光脉冲序列开始发射第一个脉冲后的T
R时间内,即0≤t≤T
R时间段内进行第一次探测,得到第一次探测的光子计数序列X
d1,其元素数为K,如果设激光三维成像的最大可探测距离为R
max,则T
R≥2R
max/c(c为真空中光速),在第一次探测中,第一次探测的调制序列Y
1的元素数也为K,将X
d1和Y
1中的对应元素相乘可得到第一次探测中的调制计数序列Z
d1,将Z
d1中的元素求和可得到S
d1,将其作为某个激光脉冲序列发射周期内的分段累加计数序列S
d的第一个元素。
在T/M≤t≤T/M+T
R时间段内进行第二次探测,在第二次探测过程中虽然没有脉冲发射,但光电探测器仍然可探测得到第二次探测的光子计数序列X
d2,其元素数为K,在第二次探测中,调制序列Y
2的元素数也为K,可将X
d1与X
d2对应元素相加后得到X
d2’,将X
d2’与Y
2中的对应元素相乘得到第二次探测中的调制计数序列Z
d2,也可令X
d2=X
d1,将X
d2与Y
2中的 对应元素相乘得到第二次探测中的调制计数序列Z
d2,将Z
d2中的元素求和可得到S
d2,将其作为某个激光脉冲序列发射周期内的分段累加计数序列S
d的第二个元素。
以此类推,在第三、五、七次探测中,按照第一次探测的步骤对应执行;在第四、六、八次探测中,按照第二次探测的步骤对应执行,这里不再赘述,分别得到S
d的其余元素,在第d个激光脉冲序列周期得到的分段累加计数序列S
d如图22最下一行所示。最后,将L个激光脉冲序列周期得到的S1,S2,…,SL共计L个分段累加计数序列对应单元相加,可得到累加计数序列S,通过分析累加计数序列S的频谱特性能够解算目标信息,进而实现三维成像。
综合来看,现有技术除上文所述非相干啁啾信号调幅连续波激光三维成像技术(下文简称技术1)外,主要还包括非相干正弦/脉冲调幅激光三维成像技术(itof,下文简称技术2)和脉冲光子计数激光三维成像技术(dtof,下文简称技术3),与上述技术相比,本申请有如下优点:
(1)相比技术1,本申请使用脉冲激光进行探测,避免了技术1在A/D转换采样间隔内激光发射能量浪费的问题,因此大幅提高了能量利用率,减小了激光平均发射功率;
(2)相比技术1,本申请在接收系统中,不再采用宽带放大器、混频器和A/D等器件,避免了上述器件限制接收激光信号动态范围的问题,从而使得本申请的接收系统具有更大的动态接收范围;
(3)相比技术1,本申请在接收系统中,使用数字化的啁啾信号作为调制序列,使用数字乘法器实现序列相乘,减小了啁啾信号调频线性度和 调频平坦度对测距性能的影响;
(4)相比技术2,本申请由于采用啁啾信号进行相关接收,因此具有距离分辨力,可有效避免多径效应影响;
(5)相比技术2,本申请由于采用相关接收、傅里叶分析、频谱检测提高了抗光干扰能力,因此测距性能受光干扰影响更小,相同探测情况下所需的激光能量更小;
(6)相比技术2,本申请不再采用A/D,具有更大的动态接收范围;
(7)相比技术3,本申请需要传输处理的是累加计数序列,而非光子计数序列,因此大幅减少了数据传输量;
(8)相比技术3,本申请从频谱上提取目标距离信息,减小了脉冲形状畸变对测距性能的影响;
(9)相比技术3,本申请由于采用相关接收、傅里叶分析、频谱检测提高了抗光干扰能力,因此测距性能受光干扰影响更小。
本申请利用多次直接接收,形成距离-幅度谱(频域),以频域过阈值检测,频谱峰值来确定飞行时间,在具体实现中频谱幅度阈值可以自适应设定;频谱峰值也可以被准确判定,方案整体上为数字框架结构类型,可以通过较多的FFT点数以保证精度;在较大的运算量的前提下能够保证探测的准精确性和精确性,曝光时间内以累积电荷形式引入,通过FFT和相关接收(零均值的FMCW相关信号)从算法层面抑制了背景光干扰的问题,在能量利用方面发射功率完全被接收,实现了最高效率的能量利用整个系统和方法解决了现有的方案中所存在的一些方法本身问题,具有广泛的应用前景和推广价值。
需要说明的是,术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含,从而使得包括一系列要素的过程、方法、物品或者设备不仅包括那些要素,而且还包括没有明确列出的其他要素,或者是还包括为这种过程、方法、物品或者设备所固有的要素。在没有更多限制的情况下,由语句“包括一个……”限定的要素,并不排除在包括所述要素的过程、方法、物品或者设备中还存在另外的相同要素。
以上所述仅为本申请的优选实施例而已,并不用于限制本申请,对于本领域的技术人员来说,本申请可以有各种更改和变化。凡在本申请的精神和原则之内,所作的任何修改、等同替换、改进等,均应包含在本申请的保护范围之内。应注意到:相似的标号和字母在下面的附图中表示类似项,因此,一旦某一项在一个附图中被定义,则在随后的附图中不需要对其进行进一步定义和解释。以上所述仅为本申请的优选实施例而已,并不用于限制本申请,对于本领域的技术人员来说,本申请可以有各种更改和变化。凡在本申请的精神和原则之内,所作的任何修改、等同替换、改进等,均应包含在本申请的保护范围之内。
Claims (40)
- 一种激光雷达测距方法,包括:由驱动信号发生部产生驱动信号并通过激光调制驱动电路作用于激光源,所述激光源接收所述驱动信号以发射出脉冲激光序列;由阵列型返回光接收模块接收经由视场内被探测物反射的返回光信号并产生返回信号;以及由处理模块依据所述驱动信号发生部产生的所述驱动信号产生调制信号,并由所述处理模块按照预设规则基于所述调制信号获得距离相关的信号,所述处理模块依照所述距离相关的信号输出所述被探测物的距离信息。
- 根据权利要求1所述的激光雷达测距方法,所述返回信号为所述返回的脉冲激光序列激发产生的光子计数序列。
- 根据权利要求2所述的激光雷达测距方法,所述驱动信号以L次驱动所述激光源发射L次激光序列,所述阵列型返回光接收模块接收所述L次激光序列的返回光信号,所述处理模块依据全部或部分所述L次激光序列的返回光信号的统计结果产生统计的光子计数序列,其中L为大于等于1的整数。
- 根据权利要求3所述的激光雷达测距方法,所述处理模块依据全部所述L次激光序列的返回光信号的统计结果产生统计的光子计数序列。
- 根据权利要求3所述的激光雷达测距方法,所述调制信号为由所述驱动信号发生部所产生的所述驱动信号按照所述发射光脉冲序列类似规则生成的非连续型的调制序列。
- 根据权利要求4或5所述的激光雷达测距方法,所述单次发射的激 光序列包含M个脉冲激光激发高值单元,或者脉冲序列在接收模块所激发的光子计数序列的计数单元数为M个,其中M为大于等于1的整数。
- 根据权利要求6所述的激光雷达测距方法,所述预设规则包含所述统计的光子计数序列与所述调制序列按照相乘的运算得到运算计数序列。
- 根据权利要求7所述的激光雷达测距方法,所述预设规则还包含所述运算计数序列执行分段累加获得所述距离相关信号。
- 根据权利要求6所述的激光雷达测距方法,所述预设规则包含所述统计的光子计数序列与所述调制序列分别执行相同的分段累加获得中间值序列,所述两个中间值序列按照相乘的运算获得所述距离相关信号。
- 根据权利要求8或9所述的激光雷达测距方法,所述距离相关信号在所述处理模块中执行时频域转换运算获得距离相关的信号频谱,所述处理模块依据所述信号频谱的特征输出视场内所述被探测物的距离信息。
- 根据权利要求10所述的激光雷达测距方法,所述距离相关信号在所述处理模块中执行的信号处理还包含阈值检测和信息解算。
- 根据权利要求1至6中任一项所述的激光雷达测距方法,还包括:在由所述处理模块按照所述预设规则基于所述调制信号获得所述距离相关的信号之前,计数序列生成模块依据所述返回信号生成自适应计数序列,其中由所述处理模块按照所述预设规则基于所述调制信号获得所述距离相关的信号包括:由所述处理模块按照所述预设规则基于所述调制信号和所述自适应计数序列获得所述距离相关的信号。
- 根据权利要求12所述的激光雷达测距方法,其中依据所述返回信 号生成所述自适应计数序列包括:按照所述返回信号的均值和/或所述返回信号的和生成自适应修正序列,并基于所述返回信号和所述自适应修正序列生成所述自适应计数序列。
- 根据权利要求13所述的激光雷达测距方法,所述预设规则包含将所述自适应修正序列插入所述返回信号得到的光子计数序列中。
- 根据权利要求13所述的激光雷达测距方法,所述预设规则包含所述返回信号得到的光子计数序列与所述自适应修正序列按照相加的运算得到所述自适应计数序列。
- 根据权利要求13所述的激光雷达测距方法,所述预设规则包含根据所述返回信号得到的光子计数序列的特性得到阈值,根据所述阈值分辨并剔除由非自然背景光干扰产生的高值元素,得到所述自适应计数序列。
- 根据权利要求1至6以及12、13中任一项所述的激光雷达测距方法,还包括:在由所述处理模块按照所述预设规则基于所述调制信号获得所述距离相关的信号之前,计数序列拼接模块根据所述返回信号获得复制拼接信号;其中由所述处理模块按照所述预设规则基于所述调制信号获得所述距离相关的信号包括:由所述处理模块按照所述预设规则基于所述调制信号和所述复制拼接信号获得所述距离相关的信号。
- 根据权利要求17所述的激光雷达测距方法,所述激光光源在小于一个探测周期内发射探测激光序列,得到返回信号,所述计数序列拼接模块复制在所述小于一个探测周期内发射的探测激光序列的返回信号,将返回信号进行拼接,得到所述复制拼接信号。
- 根据权利要求17所述的激光雷达测距方法,所述激光光源在一个探测周期内发射探测激光序列,得到返回信号,所述计数序列拼接模块复制在所述一个探测周期内发射的探测激光序列的返回信号的部分元素,并将其与所述返回信号进行运算,得到所述复制拼接信号。
- 根据权利要求17所述的激光雷达测距方法,基于最近一次的复制拼接信号,所述计数序列拼接模块复制所述最近一次的复制拼接信号的部分元素,并将其与所述最近一次的复制拼接信号运算,得到所述复制拼接信号。
- 一种用于进行距离探测的探测系统,包括:驱动信号发生部,被配置成产生驱动信号并通过激光调制驱动电路作用于激光源,其中所述激光源接收所述驱动信号以发射出脉冲激光序列;阵列型返回光接收模块,被配置成接收经由视场内被探测物反射的返回光信号,并产生返回信号;以及处理模块,被配置成依据所述驱动信号发生部产生的所述驱动信号产生调制信号,按照预设规则基于所述调制信号获得距离相关的信号,以及依照所述距离相关的信号输出所述被探测物的距离信息。
- 根据权利要求21所述的探测系统,所述返回信号为所述返回的脉冲激光序列激发产生的光子计数序列。
- 根据权利要求22所述的探测系统,所述驱动信号以L次驱动所述激光源发射L次激光序列,所述阵列型返回光接收模块接收所述L次激光序列的返回光信号,所述处理模块依据全部或部分所述L次激光序列的返回光信号的统计结果产生统计的光子计数序列,其中L为大于等于1的整 数。
- 根据权利要求23所述的探测系统,所述处理模块依据全部所述L次激光序列的返回光信号的统计结果产生统计的光子计数序列。
- 根据权利要求23所述的探测系统,所述调制信号为由所述驱动信号发生部所产生的所述驱动信号按照所述发射光脉冲序列类似规则生成的非连续型的调制序列。
- 根据权利要求24或25所述的探测系统,所述单次发射的激光序列包含M个脉冲激光激发高值单元,或者脉冲序列在接收模块所激发的光子计数序列的计数单元数为M个,其中M为大于等于1的整数。
- 根据权利要求26所述的探测系统,所述预设规则包含所述统计的光子计数序列与所述调制序列按照相乘的运算得到运算计数序列。
- 根据权利要求27所述的探测系统,所述预设规则还包含所述运算计数序列执行分段累加获得所述距离相关信号。
- 根据权利要求26所述的探测系统,所述预设规则包含所述统计的光子计数序列与所述调制序列分别执行相同的分段累加获得中间值序列,所述两个中间值序列按照相乘的运算获得所述距离相关信号。
- 根据权利要求28或29所述的探测系统,所述距离相关信号在所述处理模块中执行时频域转换运算获得距离相关的信号频谱,所述处理模块依据所述信号频谱的特征输出视场内所述被探测物的距离信息。
- 根据权利要求30所述的探测系统,所述距离相关信号在所述处理模块中执行的信号处理还包含阈值检测和信息解算。
- 根据权利要求21至26中任一项所述的探测系统,还包括:计数序列生成模块,被配置成依据所述返回信号生成自适应计数序列,其中所述处理模块还被配置成按照所述预设规则基于所述调制信号和所述自适应计数序列获得所述距离相关的信号。
- 根据权利要求32所述的探测系统,所述计数序列生成模块被配置成:按照所述返回信号的均值和/或所述返回信号的和生成自适应修正序列,并基于所述返回信号和所述自适应修正序列生成所述自适应计数序列。
- 根据权利要求33所述的探测系统,所述预设规则包含将所述自适应修正序列插入所述返回信号得到的光子计数序列中。
- 根据权利要求33所述的探测系统,所述预设规则包含所述返回信号得到的光子计数序列与所述自适应修正序列按照相加的运算得到所述自适应计数序列。
- 根据权利要求33所述的探测系统,所述预设规则包含根据所述返回信号得到的光子计数序列的特性得到阈值,根据所述阈值分辨并剔除由非自然背景光干扰产生的高值元素,得到所述自适应计数序列。
- 根据权利要求21至26以及32、33中任一项所述的探测系统,还包括:计数序列拼接模块,被配置成根据所述返回信号获得复制拼接信号;其中所述处理模块还被配置成按照所述预设规则基于所述调制信号和所述复制拼接信号获得所述距离相关的信号。
- 根据权利要求37所述的激光雷达测距方法,所述激光光源在小于一个探测周期内发射探测激光序列,得到返回信号,所述计数序列拼接模块复制在所述小于一个探测周期内发射的探测激光序列的返回信号,将返 回信号进行拼接,得到所述复制拼接信号。
- 根据权利要求37所述的激光雷达测距方法,所述激光光源在一个探测周期内发射探测激光序列,得到返回信号,所述计数序列拼接模块复制在所述一个探测周期内发射的探测激光序列的返回信号的部分元素,并将其与所述返回信号进行运算,得到所述复制拼接信号。
- 根据权利要求37所述的激光雷达测距方法,基于最近一次的复制拼接信号,所述计数序列拼接模块复制所述最近一次的复制拼接信号的部分元素,并将其与所述最近一次的复制拼接信号运算,得到所述复制拼接信号。
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