CN112346069A - Echo processing method and device of laser radar, distance measuring method and device and laser radar system - Google Patents

The invention discloses an echo processing method and device, a distance measuring method and device and a laser radar system of a laser radar. The echo processing method comprises the steps of conducting derivation on a transmitting signal, conducting cross-correlation operation on the derived transmitting signal and an echo signal, and searching a zero crossing point for an obtained cross-correlation pulse signal. The invention can maximally improve the detection and ranging signal-to-noise ratio of the laser radar, improve the accuracy and the robustness of echo processing and ranging of the conventional laser radar, and can realize the maximized utilization of pulse information quantity and the reduction of ranging jitter errors.

Echo processing method and device of laser radar, distance measuring method and device and laser radar system

Technical Field

The invention relates to the technical field of laser detection, in particular to an echo processing method and device, a distance measuring method and device and a laser radar system of a laser radar.

Background

The laser radar is a device which can realize the distance measurement and the gray scale measurement of a target object by sending a laser to the surface of the object and then measuring the arrival time of a reflected light beam, and is an advanced detection mode combining a laser technology and a photoelectric detection technology. Laser radar is widely applied to the fields of automatic driving, traffic communication, unmanned aerial vehicles, intelligent robots, energy safety detection, resource exploration and the like due to the advantages of high resolution, good concealment, strong active interference resistance, good low-altitude detection performance, small volume, light weight and the like.

The stronger the range finding ability of laser radar, the richer road surface information that obtains, just also can prevent getting into the bud more, guarantee vehicle and personal safety. The laser radar based on Time of Flight (TOF) ranging obtains the distance to a detection target by measuring the Time interval between the emission and the reception of light pulses, which is a prerequisite for the measurement method, in which the laser radar needs to detect light pulses from a waveform Time series received by a photodetector.

The common pulse ranging method comprises a rising edge measuring method, a peak value measuring method, a gravity center method and the like, but the rising edge measuring method introduces walking errors, compensation needs to be carried out according to different pulse amplitudes, the peak value measuring method is limited by the stability of signals, conventional ADC sampling needs interpolation and fitting to calculate accurate distance information, the gravity center method is the most stable ranging algorithm at present, the gravity center of a waveform is calculated by taking all points of the waveform, the largest amount of information is applied, and the algorithm is also the algorithm with higher precision at present. But the range finding precision divergence of the gravity center method under the condition of low signal-to-noise ratio is serious, and the jitter is large.

Disclosure of Invention

The invention aims to solve the technical problems of improving the detection and ranging signal-to-noise ratio of the laser radar and improving the precision and the robustness of the pulse ranging method.

The technical scheme provided by the invention is as follows:

an echo processing method of a laser radar includes: carrying out derivation operation on a transmitting pulse signal f (t) transmitted by a transmitting device of the laser radar to obtain a derivative signal f' (t) of the transmitting pulse signal; performing threshold judgment detection on a first echo pulse signal received by a receiving device of a laser radar to obtain a second echo pulse signal g (t) meeting a threshold condition, wherein the second echo pulse signal g (t) is positioned in a first time interval; performing cross-correlation operation on the derivative signal f' (t) and the second echo pulse signal g (t) to obtain a cross-correlation pulse signal r (t); searching the cross-correlation pulse signal r (t) for the position of the zero crossing point in the first time interval, thereby obtaining the arrival time of the second echo pulse signal according to the position of the zero crossing point.

Optionally, searching for the position of the zero crossing comprises: obtaining the maximum value r (t) of the pulse signal of the cross-correlation pulse signal r (t) in a first time interval_max) Corresponding maximum time t_maxAnd minimum value r (t) of pulse signal_min) Corresponding minimum time t_min(ii) a The maximum time t_maxAnd the minimum time t_minA second time interval in between; obtaining the value r (t) with the minimum modulus value of the second time interval_amin) Corresponding time t_amin，t_aminIs the zero crossing τ.

Optionally, the searching for the position of the zero crossing point collects the first echo pulse signal through an analog-to-digital converter ADC, and when the zero crossing point τ is not an integer sampling point, the searching for the position of the zero crossing point includes: obtaining two sampling points n just crossing the zero point₁,n₂Corresponding cross-correlation pulse signals r [ n ]₁]And r [ n ]₂]And satisfies the following equation

where Δ t is the sampling period of the ADC.

Optionally, before performing the cross-correlation operation, the derivative signal f' (t) or the second echo pulse signal g (t) is multiplied by a compensation function c (t), the compensation function c (t) being at least related to the transmit signal amplitude and/or the noise floor energy.

The invention also provides an echo processing device of the laser radar, which comprises: the derivation unit is used for carrying out derivation operation on a transmitting pulse signal f (t) transmitted by a transmitting device of the laser radar to obtain a derivative signal f' (t) of the transmitting pulse signal; the threshold decision detection unit is used for carrying out threshold decision detection on the first echo pulse signal received by the receiving device of the laser radar to obtain a second echo pulse signal g (t) meeting a threshold condition, and the second echo pulse signal g (t) is positioned in a first time interval; the cross-correlation operation unit is used for performing cross-correlation operation on the derivative signal f' (t) and the second echo pulse signal g (t) to obtain a cross-correlation pulse signal r (t); and the time operation unit is used for searching the position of a zero crossing point of the cross-correlation pulse signal r (t) in a first time interval and obtaining the arrival time of the second echo pulse signal according to the position of the zero crossing point.

Optionally, the time operation unit further includes a zero crossing searching subunit, configured to obtain a maximum value r (t) of the pulse signal of the cross-correlation pulse signal r (t) in a first time interval_max) Corresponding maximum time t_maxAnd minimum value r (t) of pulse signal_min) Corresponding minimum time t_minSaid maximum time t_maxAnd the minimum time t_minThe zero crossing searching subunit is further configured to obtain a value r (t) with a minimum modulus value of the second time interval_amin) Corresponding time t_amin，t_aminIs the zero crossing τ.

Optionally, the echo processing device further includes: an analog-to-digital converter (ADC) for collecting the first echo pulse signal, a zero crossing point searching subunit in the time operation unit for acquiring two sampling points n just crossing the zero point when the zero crossing point tau is not an integer sampling point₁,n₂Corresponding cross-correlation pulse signals r [ n ]₁]And r [ n ]₂]And satisfies the following equation

where Δ t is the sampling period of the ADC.

Optionally, the cross-correlation operation unit further comprises a compensation subunit, wherein the compensation subunit is configured to multiply the derivative signal f' (t) or the second echo pulse signal g (t) by a compensation function c (t), and the compensation function c (t) is at least related to the amplitude of the transmit signal and/or the energy of the bottom noise.

The invention also provides a ranging method of the laser radar, which comprises the following steps: emitting a laser beam toward a target object with an emitting device; receiving with a receiving device echoes reflected from the target object; processing the echo by using the echo processing method of the laser radar to obtain the position of a zero crossing point tau of an echo signal; obtaining the arrival time of a second echo pulse signal according to the position of the zero crossing point; according to the arrival time of the second echo pulse signal and the corresponding emission time t of the laser beam₀The distance between the lidar and the target object is calculated.

The present invention also provides a laser radar system, comprising: a transmitting device for transmitting a laser beam to a target object; wherein the emitting device comprises a light source; a scanning device configured to reflect light from the light source at a controllable deflection angle to scan a target object; receiving means for receiving an echo signal reflected from a target object; wherein the receiving means comprises a photosensor means; the processing device is used for processing the echo signal received by the receiving device by adopting the echo processing device of the laser radar; according to the arrival time of the second echo pulse signal and the corresponding emission time t of the laser beam₀The distance between the lidar and the target object is calculated.

Optionally, the lidar system further comprises a control device for communicative coupling with the transmitting device and the receiving device, wherein the control device is configured to control the transmitting device and to control a deflection angle of the scanning unit. The present invention also provides an echo processing device, including: a processor; a memory for storing processor-executable instructions; wherein the processor is configured to: carrying out derivation operation on a transmitting pulse signal f (t) transmitted by a transmitting device of the laser radar to obtain a derivative signal f' (t) of the transmitting pulse signal; carrying out threshold judgment detection on a first echo pulse signal received by a receiving device of a laser radar to obtain a second echo pulse signal g (t) meeting a threshold condition, wherein the second echo pulse signal is positioned in a first time interval; performing cross-correlation operation on the derivative signal f' (t) and the second echo pulse signal g (t) to obtain a cross-correlation pulse signal r (t); for the cross-correlation pulse signal r (t), searching the position of a zero-crossing point τ in the first time interval, and obtaining the arrival time of the second echo pulse signal according to the position of the zero-crossing point.

The invention also provides a computer readable storage medium having stored thereon computer instructions which, when executed by a processor, carry out the steps of the echo processing method described above.

The present invention also provides a ranging apparatus for a laser radar, comprising: a processor; a memory for storing processor-executable instructions; wherein the processor is configured to: carrying out derivation operation on a transmitting pulse signal f (t) transmitted by a transmitting device of the laser radar to obtain a derivative signal f' (t) of the transmitting pulse signal; performing threshold judgment detection on a first echo pulse signal received by a receiving device of a laser radar to obtain a second echo pulse signal g (t) meeting a threshold condition, wherein the second echo pulse signal g (t) is positioned in a first time interval; performing cross-correlation operation on the derivative signal f' (t) and the second echo pulse signal g (t) to obtain a cross-correlation pulse signal r (t); searching the cross-correlation pulse signal r (t) for the position of a zero-crossing point tau in the first time interval, and obtaining the arrival time of an echo pulse signal according to the position of the zero-crossing point; according to the arrival time of the second echo pulse signal and the corresponding emission time t of the laser beam₀The distance between the lidar and the target object is calculated.

The present invention also provides a computer readable storage medium having stored thereon computer instructions which, when executed by a processor, implement the steps of the echo ranging method described above.

The technical scheme of the invention has the beneficial effects that: the detection and ranging signal-to-noise ratio of the laser radar is improved to the maximum degree, the accuracy and the robustness of echo processing and ranging of the existing laser radar are improved, and the pulse information quantity can be utilized to the maximum degree and the ranging jitter error can be reduced.

Drawings

Fig. 1 is a flowchart of an echo processing method of a laser radar according to an embodiment of the present invention.

Figure 2 is a schematic illustration of a transmit pulse signal and a received echo pulse signal of one embodiment of the present invention.

FIG. 3 is a schematic illustration of the derivative of the transmit pulse signal of one embodiment of the present invention.

Fig. 4 is a schematic diagram of a cross-correlated pulse signal of one embodiment of the present invention.

Fig. 5 is a schematic structural diagram of an echo processing device of a laser radar according to an embodiment of the present invention.

Fig. 6 is a flowchart of a ranging method of a lidar according to an embodiment of the present invention.

Fig. 7 is a schematic diagram of a lidar system according to an embodiment of the present invention, which is a coaxial lidar system.

Fig. 8 is a schematic diagram of a lidar system according to another embodiment of the invention, the lidar system being a non-coaxial lidar system.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of systems consistent with certain aspects of the invention, as detailed in the appended claims.

Lidar based on time-of-flight measurement (TOF) ranging, where the range to a target is obtained by measuring the time interval between transmitted and received laser pulses, a measurement method that requires the lidar to detect a pulse signal from a waveform time sequence received by a photodetector. Generally, the farther away the distance, the darker the target, and the weaker the pulse signal returned. At present, a voltage threshold is mostly set for the detection pulse, and once a signal in the waveform exceeds the threshold, a pulse signal is considered to be received once. The threshold value must be higher than the ambient light noise and the electronics noise of the waveform, otherwise false triggering may occur resulting in detection noise. Therefore, the waveform signal-to-noise ratio determines the detection capability of the laser radar, and the higher the signal-to-noise ratio is, the stronger the detection capability is. When the electronic noise of the system is optimized to the limit, the improvement of the distance measurement capability only depends on the improvement of the transmitting light power, and the increase of the aperture of the receiving lens is used for improving the signal-to-noise ratio of the signal, however, the problems of the increase of the power consumption of the system, the improvement of the safety risk of human eyes, the reduction of the reliability of a laser, the increase of the cost, the increase of the volume and the like are obviously caused.

Therefore, the embodiment of the invention provides an echo processing method and device, a distance measuring method and device and a laser radar system of a laser radar, which can maximally improve the signal-to-noise ratio of detection and distance measurement on the premise of not increasing the transmitting light power, and improve the accuracy and robustness of echo processing and distance measurement of the existing laser radar.

In order to make the present invention better understood and implemented by those skilled in the art, the echo processing method, the distance measuring method and apparatus, and the lidar system according to the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Fig. 1 is a flowchart of an echo processing method of a laser radar according to an embodiment of the present invention.

As shown in fig. 1, according to an embodiment of the present invention, an echo processing method for a lidar includes the following steps:

step S101: carrying out derivation operation on a transmitting pulse signal f (t) transmitted by a transmitting device of the laser radar to obtain a derivative signal f' (t) of the transmitting pulse signal; the specific operation is shown in formula (1):

in a specific implementation process, the derivation step is equivalent to a differential operation of discrete signals, and the signal at the next time and the amplitude of the signal at the current time are directly subtracted in sequence to obtain the difference. According to one embodiment of the invention, this differential operation may optionally be implemented by a differentiator.

Figure 2 is a schematic illustration of a transmit pulse signal and a received echo pulse signal of one embodiment of the present invention. The upper diagram of fig. 2 shows the transmit pulse signal f (t), when the echo pulse signal has not yet been received. Fig. 3 is a schematic diagram of a derivative of the transmission pulse signal according to an embodiment of the present invention, showing a pulse shape of a derivative signal f' (t) of the transmission pulse signal after a derivation operation.

Step S102: and carrying out threshold judgment detection on the first echo pulse signal received by the receiving device of the laser radar to obtain a second echo pulse signal g (t) meeting the threshold condition, wherein the second echo pulse signal g (t) is positioned in a first time interval.

Alternatively, the threshold condition may be set according to the ambient light noise and the electronics system noise of the waveform. For example, the threshold may be multiplied by a detection coefficient at the background noise level, which may be obtained in advance by assuming the noise distribution and the false alarm probability, and may be obtained by table lookup. Of course, the threshold condition may be set according to other conditions, and is not limited in this embodiment. The opening and closing of the first time interval are different depending on the set threshold conditions, and the opening and closing of the first time interval is not specifically limited in this embodiment.

In FIG. 2, the first time interval is (t)₁,t₂) For illustration, fig. 2 shows the transmission pulse signal f (t) and the signal in the first time interval (t)₁,t₂) A certain time interval exists between the first echo pulse signal g (t), and the time position corresponding to the maximum amplitude value of the first echo pulse signal g (t) is the position of the zero crossing point τ.

Alternatively, the implementation sequence of step S101 and step S102 may be that S101 precedes S102, that S102 precedes S101, that S101 and S102 are performed simultaneously, and the sequence of step S101 and step S102 is not limited in this embodiment.

Step S103: and performing cross-correlation operation on the derivative signal f' (t) and the second echo pulse signal g (t) to obtain a cross-correlation pulse signal r (t).

Fig. 4 is a schematic diagram of the cross-correlation pulse signal r (t) according to an embodiment of the present invention.

Alternatively, the cross-correlation operation may be obtained by translating the transmitted differentiated signal, multiplying the translated signal by the echo signal, and then accumulating the multiplied signal, which reflects the matching similarity between the echo signal and the transmitted signal, thereby improving the calculation accuracy of the pulse position.

Step S104: searching the position of a zero-crossing point tau in a first time interval for the cross-correlation pulse signal r (t), thereby obtaining the arrival time of the second echo pulse signal according to the position of the zero-crossing point tau.

The time at which the pulse peak is located maps the time at which the cross-correlation result is zero, i.e. the pulse position that is sought. By derivative cross-correlation, the amount of cross-correlation with the echo signal at the pulse peak instant will have a zero crossing because the derivative of the pulse signal will have a zero value at the peak instant of the original pulse. By derivative cross-correlation, the estimation of the maximum is converted into the estimation of the zero crossing point, and the estimation of the zero crossing point is better than that of the maximum by the traditional algorithm. Therefore, the technical scheme provided by the invention can realize the maximized improvement of the detection signal-to-noise ratio and the improvement of the zero crossing point detection precision.

Through the technical scheme, the signal-to-noise ratio of detection and ranging can be improved to the maximum degree, the accuracy and the robustness of echo processing and ranging of the existing laser radar are improved, and the pulse information quantity can be utilized to the maximum degree and the ranging jitter error can be reduced.

According to an alternative embodiment of the present invention, the formula of the cross-correlation operation in step S103 is as follows:

according to an alternative embodiment of the present invention, the derivative signal f '(t) may be multiplied by a compensation function c (t), and then cross-correlation may be performed on f' (t) c (t) and g (t). Or multiplying the second echo pulse signal g (t) by a compensation function c (t), and performing cross-correlation operation on f' (t) and g (t) c (t). The compensation function c (t) is a function that varies with time, the compensation function c (t) being related to at least the amplitude of the transmitted signal and/or the energy of the noise floor. The Avalanche Photodiode (APD) dark current and the receiving circuit in the actual circuit can form bottom noise, and the influence of the bottom noise on the zero crossing point can be eliminated through the compensation function, so that the more accurate arrival time of the echo pulse signal can be obtained.

The formula for multiplying the derivative signal f' (t) by the compensation function c (t) and then performing the cross-correlation operation is as follows:

the formula of the second echo pulse signal g (t) multiplied by the compensation function c (t) and then performing the cross-correlation operation is as follows:

according to an alternative implementation of the embodiment of the present invention, when r (t) is a continuous function, the step of searching for the position of the zero-crossing point in step S104 includes:

step S1041, obtaining the maximum value r (t) of the pulse signal of the cross-correlation pulse signal r (t) in the first time interval_max) Corresponding maximum time t_maxAnd minimum value r (t) of pulse signal_min) Corresponding minimum time t_minThe calculation formula is as follows:

maximum time t_maxAnd a minimum time t_minWith a second time interval in between.

Step S1042: obtaining a second time interval (t)_max,t_min) Value r (t) at which the modulus is minimum_amin) Corresponding time t_aminThe following formula is satisfied:

r(t_amin)＝min(|r(t)|),t∈(t_max,t_min) (6)

t_aminis the zero crossing τ.

According to an alternative implementation of an embodiment of the invention, the further processing is performed by an analog-to-digital converter (ADC)

Collecting echo pulse signals, wherein the collected echo pulse signals are discrete signals, and if a zero crossing point tau is not an integer sampling point, obtaining two sampling points n just crossing the zero point₁,n₂Corresponding cross-correlation pulse signals r [ n ]₁]And r [ n ]₂]And satisfies the following equation

where Δ t is the sampling period of the ADC.

where Δ t is the sampling period of the ADC.

The echo processing device shown in fig. 5 corresponds to the echo processing method shown in fig. 1, and reference may be made to the description of the method embodiment for parts not described in detail in the device embodiment.

As shown in FIG. 6, according to an embodiment of the present invention, the present invention further provides a ranging method of a lidar including the steps S301 of transmitting a laser beam to a target object by a transmitting device of the lidar; s302, receiving an echo reflected from a target object by a receiving device of the laser radar; s303, processing the echo by adopting the echo processing method of the laser radar to obtain the position of a zero crossing point tau of the second echo pulse signal, and obtaining the arrival time of the second echo pulse signal according to the position of the zero crossing point; s304, according to the arrival time of the second echo pulse signal and the corresponding transmitting time t of the laser beam₀The distance between the laser radar and the target object is calculated according to the time interval.

Fig. 7 shows a schematic diagram of a coaxial lidar system, and fig. 8 shows a schematic diagram of a non-coaxial lidar system.

According to an embodiment of the present invention, there is also provided an echo processing apparatus including: a processor;

a memory for storing processor-executable instructions; wherein the processor is configured to: carrying out derivation operation on a transmitting pulse signal f (t) transmitted by a transmitting device of the laser radar to obtain a derivative signal f' (t) of the transmitting pulse signal; carrying out threshold judgment detection on a first echo pulse signal received by a receiving device of the laser radar to obtain a second echo pulse signal g (t) meeting a threshold condition, wherein the second echo pulse signal is positioned in a first time interval; performing cross-correlation operation on the derivative signal f' (t) and the second echo pulse signal g (t) to obtain a cross-correlation pulse signal r (t); searching the position of a zero-crossing point tau in a first time interval for the cross-correlation pulse signal r (t), and obtaining the arrival time of the second echo pulse signal according to the position of the zero-crossing point.

In this embodiment, the at least one processor may constitute any physical device having circuitry to perform logical operations on one or more inputs. For example, at least one processor may include one or more Integrated Circuits (ICs) including an Application Specific Integrated Circuit (ASIC), a microchip, a microcontroller, a microprocessor, all or a portion of a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA), or other circuitry suitable for executing instructions or performing logical operations. The instructions executed by the at least one processor may be preloaded into a memory integrated with or embedded in the controller, for example, or may be stored in a separate memory. The memory may include Random Access Memory (RAM), Read Only Memory (ROM), hard disk, optical disk, magnetic media, flash memory, other permanent, fixed, or volatile memory, or any other mechanism capable of storing instructions. In some embodiments, the at least one processor may comprise more than one processor. Each processor may have a similar structure, or the processors may have different configurations that are electrically connected or disconnected from each other. For example, the processor may be a separate circuit or integrated in a single circuit. When more than one processor is used, the processors may be configured to operate independently or cooperatively. The processors may be coupled electrically, magnetically, optically, acoustically, mechanically or by other means allowing them to interact. According to an embodiment of the present invention, the present invention further provides a computer readable storage medium having stored thereon computer instructions for executing the steps of the echo processing method described above by a processor.

In the present embodiment, the non-transitory computer readable storage medium may be a ROM, a Random Access Memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like.

According to an embodiment of the present invention, there is also provided a ranging apparatus for a laser radar, including: a processor; a memory for storing processor-executable instructions; the processor is configured to: carrying out derivation operation on a transmitting pulse signal f (t) transmitted by a transmitting device of the laser radar to obtain a derivative signal f' (t) of the transmitting pulse signal; carrying out threshold judgment detection on a first echo pulse signal received by a receiving device of the laser radar to obtain a second echo pulse signal g (t) meeting a threshold condition, wherein the second echo pulse signal is positioned in a first time interval; performing cross-correlation operation on the derivative signal f' (t) and the second echo pulse signal g (t) to obtain a cross-correlation pulse signal r (t); searching the position of a zero crossing point tau in a first time interval for the cross-correlation pulse signal r (t), and obtaining the arrival time of the echo pulse signal according to the position of the zero crossing point; according to the arrival time of the second echo pulse signal and the corresponding emission time t of the laser beam₀The distance between the laser radar and the target object is calculated according to the time interval.

The invention also provides a computer readable storage medium having stored thereon computer instructions which, when executed by a processor, implement the steps of the echo ranging method described above.

Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the embodiments of the present invention, and they should be construed as being included therein. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.