CN114252866A - Laser radar detection method and laser radar - Google Patents

Laser radar detection method and laser radar Download PDF

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Publication number
CN114252866A
CN114252866A CN202010999876.7A CN202010999876A CN114252866A CN 114252866 A CN114252866 A CN 114252866A CN 202010999876 A CN202010999876 A CN 202010999876A CN 114252866 A CN114252866 A CN 114252866A
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Prior art keywords
laser
detection
detection unit
pulse control
control parameter
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CN202010999876.7A
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Chinese (zh)
Inventor
孙恺
向少卿
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Hesai Technology Co Ltd
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Hesai Technology Co Ltd
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Priority to CN202010999876.7A priority Critical patent/CN114252866A/en
Priority to PCT/CN2021/089527 priority patent/WO2022062382A1/en
Publication of CN114252866A publication Critical patent/CN114252866A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/484—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/4865—Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/487—Extracting wanted echo signals, e.g. pulse detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers
    • G01S7/487—Extracting wanted echo signals, e.g. pulse detection
    • G01S7/4873—Extracting wanted echo signals, e.g. pulse detection by deriving and controlling a threshold value

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

The invention provides a method for detecting by utilizing a laser radar, wherein the laser radar comprises a laser and a detection unit corresponding to the laser, and the method comprises the following steps: within a time window, driving the laser to emit laser pulses to detect a target object according to a pulse control parameter, wherein the pulse control parameter is determined based on an echo signal and a corresponding decision threshold; and/or controlling the laser and/or the detection unit to be switched on or off according to the pulse control parameter.

Description

Laser radar detection method and laser radar
Technical Field
The present invention generally relates to the field of laser radar technology, and more particularly, to a detection method for laser radar and a laser radar using the detection method.
Background
Laser radar is a range finding sensor commonly used, has characteristics such as detection range is far away, resolution ratio is high, receive environmental disturbance little, and the wide application is in fields such as intelligent robot, unmanned aerial vehicle, unmanned driving. The principle of operation of lidar is to use the time taken for a light wave to travel to and from the lidar and a target to assess the magnitude of the range. The original lidar was a single line lidar, i.e. only one laser and detector, which scanned a limited range of targets, easily causing the loss of the detected targets. To compensate for the shortcomings of the single line lidar, the multiline lidar is becoming the focus of research and commercial use. The multi-line laser radar adopts a plurality of lasers and corresponding detectors to be arranged in the vertical direction, so that the detection range in the vertical direction is enlarged. However, such a lidar has the disadvantage of high cost, and the power of the lidar cannot be adjusted, which may cause waste. In addition, as a laser light source system, the laser radar needs to emit laser power meeting the requirements of human eye safety in order to avoid injury to human bodies.
Some mechanical radars can realize the reduction of the power consumption of the laser radar and avoid waste by distributing the power proportion according to the radar detection area, but the modeling and power distribution algorithm in such a mode is complex, and once the model is determined, the distribution algorithm is fixed and cannot be adaptively adjusted.
The single photon detection technology has the advantages of ultrahigh sensitivity, ultra-fast response speed and the like, can detect the minimum energy particles of light, and is an important detection method at present. The energy of a single photon is extremely small, and a special photoelectric device is required to be adopted for detecting the single photon. The Single Photon Avalanche Diode is an Avalanche Photodiode (APD) with an operating voltage higher than a breakdown voltage, and the Avalanche photodiode operating in the geiger mode is also called a Single Photon Avalanche photodiode (SPAD). The SPAD has the advantages of high avalanche gain, high response speed, low power consumption and the like, and becomes the best device for single photon detection. The SPAD amplifies the photocurrent based on the physical mechanism of impact ionization and avalanche multiplication, thereby improving the sensitivity of detection. In the Geiger mode, the operating voltage of the SPAD is greater than the avalanche breakdown voltage thereof, so that the avalanche effect can be ensured to be caused even if a single photon enters a carrier excited by the incident excitation. For a photo detector using Silicon photomultiplier (SiPM), the photo detector is usually implemented by using a plurality of SiPM units (or may be called as a pixel), and each SiPM unit uses a plurality of SPADs connected in parallel. And outputs a pulse according to the photon total amount received by the whole array at one time and the superposed current. However, the single photon detection technology is not fully utilized at present, and the advantage of high sensitivity is not fully embodied.
The statements in this background section merely represent techniques known to the public and are not, of course, representative of the prior art.
Disclosure of Invention
In view of at least one of the drawbacks of the prior art, the present invention provides a lidar solution that may conserve power consumption.
The invention provides a method for detecting by utilizing a laser radar, wherein the laser radar comprises a laser and a detection unit corresponding to the laser, and the method comprises the following steps:
within a time window, driving the laser to emit laser pulses to detect a target object according to a pulse control parameter, wherein the pulse control parameter is determined based on an echo signal and a corresponding decision threshold; and/or
And controlling the laser and/or the detection unit to be switched on or off according to the pulse control parameter.
According to an aspect of the invention, wherein the method further comprises:
driving the laser to emit laser pulses for detection according to the pulse control parameters;
acquiring an echo signal reflected by the laser pulse on a detection target through the detection unit;
and updating pulse control parameters according to the echo signals so as to control the laser and/or the detection unit to be switched off or switched on.
According to an aspect of the invention, wherein the step of updating the pulse control parameter according to the echo signal further comprises:
a, when a detection target is changed, updating the pulse control parameter according to the target information of the new detection target;
b, controlling the emission of the laser according to the updated pulse control parameter so as to measure the changed detection target.
According to an aspect of the present invention, wherein the object information includes a reflectivity, the step a further includes:
a11 updates the pulse control parameter based on the new reflectivity and the current decision threshold.
According to an aspect of the invention, wherein the target information includes a time of flight, the step a further includes:
a21 updating the emission time of the pulse control parameter based on the new time of flight and the current decision threshold.
According to an aspect of the present invention, wherein the step a further comprises:
determining whether the detection target is changed according to at least one of the following parameters:
-the number of received echo pulses within the same time window;
-time of flight of the echo pulse;
-detecting the reflectivity of the object.
According to one aspect of the invention, the method further comprises the steps of:
-acquiring an intensity of ambient light;
-setting the decision threshold in dependence of the intensity of the ambient light.
According to an aspect of the invention, wherein the detection unit comprises one or more single photon avalanche diodes, wherein the step of setting the decision threshold value according to the intensity of the ambient light further comprises:
-measuring the number of avalanches corresponding to ambient light onto said detection unit per unit time;
-setting/updating said quantity decision threshold in dependence of the number of avalanches of ambient light within said unit of time.
According to an aspect of the invention, wherein the method further comprises:
-performing measurements based on the probing information obtained by the probing unit.
According to one aspect of the invention, the method further comprises: in the next time window, the laser and/or the detection unit are activated.
According to an aspect of the invention, wherein the laser is a vertical cavity surface emitting laser.
The present invention also provides a laser radar comprising:
a laser configured to emit laser pulses for detecting a target object;
the detection unit corresponds to the laser and is configured to receive an echo reflected by the laser pulse on a target object and output an echo signal;
a control unit coupled to the laser and the detection unit and receiving the echo signal, the control unit configured to: within a time window, driving the laser to emit laser pulses to detect a target object according to a pulse control parameter, wherein the pulse control parameter is determined based on an echo signal and a corresponding decision threshold; controlling the laser and/or the detection unit to be turned on or off.
According to an aspect of the invention, wherein the control unit is further configured to:
driving the laser to emit laser pulses for detection according to the pulse control parameters;
acquiring an echo signal reflected by the laser pulse on a detection target through the detection unit;
updating pulse control parameters according to the echo signal to control the laser and/or the detection unit to be switched off or on.
According to an aspect of the invention, wherein the control unit further comprises:
an updating module configured to update the pulse control parameter according to target information of a detection target when the detection target is changed;
and the transmitting module is used for controlling the transmission of the laser according to the updated pulse control parameter so as to measure the changed detection target.
According to an aspect of the invention, wherein the target information comprises reflectivity, the update module is further configured to:
-updating the transmission power of the pulse control parameter in dependence of the new reflectivity and the current decision threshold.
According to an aspect of the invention, wherein the target information comprises time of flight, the update module is further configured to:
-updating the time of transmission of the pulse control parameter according to the new time of flight and the current decision threshold.
According to an aspect of the invention, wherein the control unit is further configured to:
determining whether the detection target is changed according to at least one of the following parameters:
-the number of received echo pulses within the same time window;
-time of flight of the echo pulse;
-detecting the reflectivity of the object.
According to an aspect of the invention, wherein the control unit is further configured to:
-acquiring an intensity of ambient light;
-setting the decision threshold in dependence of the intensity of the ambient light.
According to an aspect of the invention, wherein the detection unit comprises one or more single photon avalanche diodes, wherein the control unit is further configured to:
measuring the avalanche times corresponding to the ambient light on the detection unit in unit time;
the number determination threshold is set/updated according to the number of avalanches of the ambient light in the unit time.
According to an aspect of the invention, wherein the control unit is further configured to:
-performing measurements based on the probing information obtained by the probing unit.
According to an aspect of the invention, wherein the control unit is further configured to:
in the next time window, the laser and/or the detection unit are activated.
According to an aspect of the invention, wherein the laser is a vertical cavity surface emitting laser.
The preferred embodiment of the present invention provides a scheme for setting the decision threshold according to the ambient light, and further continuously updating the pulse control parameter during the detection process, so as to control the emitting time of the laser and/or the receiving time of the detection unit in each time window. Through the scheme, the power consumption of the whole scheme can be effectively reduced. In the scheme of the invention, the environmental light information at the current moment can be easily obtained by utilizing the highly sensitive characteristic of SPADs or SiPMs, and because the environmental light and the signal light are detected by the same detector and the measuring standard is uniform, the intensity of the signal light and the environmental light, the avalanche times and the like can be conveniently compared. And, through reducing the pulse quantity of launching in every fixed time window, can greatly practice thrift the energy of laser emitter when guaranteeing the detection quality, reduce the power consumption. Meanwhile, the protection to the eye safety can be increased, and the eye safety risk caused by long-time laser pulse emission is reduced.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 schematically illustrates a detection method of a lidar according to a preferred embodiment of the present invention;
FIG. 2a schematically illustrates a laser according to a preferred embodiment of the present invention;
fig. 2b schematically shows a detection unit according to a preferred embodiment of the invention.
FIG. 3 schematically illustrates a pulse signal waveform diagram according to a preferred embodiment of the present invention;
figure 4a shows schematically a histogram of the number of photons output from a single photon avalanche diode;
FIG. 4b schematically shows a waveform diagram of a silicon photomultiplier output pulse;
fig. 5 schematically shows a block diagram of the structure of a lidar according to a preferred embodiment of the invention.
Detailed Description
In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection, either mechanically, electrically, or in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.
The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.
The embodiments of the present invention will be described in conjunction with the accompanying drawings, and it should be understood that the embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.
According to a preferred embodiment of the present invention, the present invention provides a method 100 for object detection using a lidar 10, the lidar 10 including a laser 11 and a detection unit 12 (shown in fig. 5) corresponding to the laser 11. The laser 11 corresponds to the detection unit 12, which means that when a laser pulse emitted by the laser 11 irradiates on a target object at infinity and is diffusely reflected, a reflected echo is received by the detection unit 12. Each laser 11 and its corresponding detection unit 12 form a detection channel, and the lidar 10 may include a plurality of detection channels, for example, 8, 16, 32, 40, 64, or 128, etc.
The Laser 11 according to the present invention can be implemented by a Vertical Cavity Surface Emitting Laser (VCSEL) or an edge-Emitting Laser (EEL).
Preferably, the laser 11 according to the present invention can be implemented using a VCSEL.
More preferably, the lidar according to the present invention is an area Array FLASH (FLASH) type lidar implemented using a VCSEL area Array (Array).
More preferably, the transmitting end of the FLASH type laser radar is realized by a VCSEL area array, and the receiving end is realized by a SPADs array or a SiPM array.
The detection method according to an embodiment of the present invention includes step S100.
In step S100, within a time window, driving the laser to emit laser pulses according to a pulse control parameter to detect a target object, wherein the pulse control parameter is determined based on the echo signal and a corresponding decision threshold; and/or controlling the laser and/or the detection unit to be switched on or off according to the pulse control parameter.
Wherein the time window may be determined based on at least any one of:
1) scanning frequency; for example, a single frame scan time is a time window.
2) A predetermined scan interval, etc.
Wherein the pulse control parameter is used for indicating the number of pulses emitted by the laser in the time window; alternatively, the pulse control parameter is used to indicate the on-time of the laser and/or the detection unit within a time window.
In particular, the pulse control parameter is determined based on the echo signal and a corresponding decision threshold. Such as the time of flight of the echo signal, and for example, the light intensity information of the echo signal.
Preferably, the decision threshold may be determined according to the intensity of the echo signal.
Refer to fig. 1 to 3. According to a preferred embodiment of the present invention, as shown in fig. 1, the method for determining the pulse control parameter comprises step S101, step S102 and step S103.
With continued reference to fig. 2a and 2 b. An area array of lasers is illustrated in fig. 2 a. Each cell shown in fig. 2a corresponds to a laser, such as laser 11-1, laser 11-2, etc. Preferably, the laser may be a VCSEL light emitting channel or EEL laser. When the laser is implemented using VCSEL light emitting channels, one VCSEL light emitting channel may include an array of one or more photovoltaic cells therein. Each photocell is realized by structures such as a quantum well capable of emitting laser beams and a resonant cavity thereof. One light emitting channel may be excited simultaneously and emit a probe pulse.
Figure 2b illustrates an area array of detection units. Each cell in fig. 2b corresponds to an individually addressable detection unit 12, wherein the detection unit 12 may comprise an array of at least one SPAD; alternatively, the detection unit 12 may correspond to a SiPM unit.
Fig. 3 schematically shows a pulse diagram of a detection signal, which is continuously emitted with pulses at certain pulse intervals to detect as shown in fig. 3.
Specifically, the method 100 according to the present invention includes steps S101, S102, and S103:
in step S101, the laser radar drives the laser 11 to emit laser pulses to detect the target object.
Specifically, at the beginning of a time window, the laser 11 is driven to emit laser pulses at normal power for detection. The laser radar 10 generally has a transmitting lens, and the laser 11 is located on a focal plane of the transmitting lens, so that laser pulses emitted by the laser 11 are collimated by the transmitting lens and then emitted to the surrounding environment as parallel light for detecting a target object.
In step S102, the lidar acquires an echo signal of the laser pulse reflected by the target object through the detection unit 12.
The laser pulse is diffusely reflected at the target, and a part of the reflected echo returns to the laser radar and is received by a detection unit 12 corresponding to the laser 11, and the detection unit 12 usually includes a photodiode, and can convert an optical signal into an electrical signal for subsequent signal processing.
In step S103, the laser radar updates the pulse control parameter according to the echo signal to control the laser 11 and/or the detection unit 12 to be turned off or on.
Specifically, the laser radar updates the pulse control parameter according to the light intensity information and/or the flight time of the echo signal.
Preferably, the laser radar obtains the pulse control parameter according to a decision threshold. Wherein the decision threshold comprises a quantity decision threshold. The number decision threshold is used to indicate the number of received echo signals. Preferably, the decision threshold further comprises a light intensity decision threshold for determining the available echo signal.
Wherein the pulse control parameter comprises a pulse transmission duration. More preferably, the pulse control parameter further comprises a pulse transmission power.
Wherein the light intensity information may take different forms of characterization depending on the device used by the actual detection unit 12. Preferably, in an embodiment according to the invention, the detection unit 12 is implemented using single photon avalanche diodes.
More preferably, the detection unit according to an embodiment of the invention is a SPAD array or a SiPM unit. When the detecting unit 12 is implemented by different devices, the corresponding light intensity determination threshold may have different expressions.
For example, when the detection unit 12 is implemented using an SPAD array, the light intensity determination threshold may be expressed as a photon number. Counting the SPAD array every time when the echo signal is detected, and determining that the light intensity information of the current echo signal is greater than the light intensity judgment threshold when the counting result is greater than the light intensity judgment threshold.
For another example, when the detection unit 12 is implemented using an SiPM unit, the light intensity determination threshold may be represented as a peak voltage. And measuring the peak voltage of the SiPM unit each time the echo signal is detected, and determining that the current light intensity information of the echo signal is greater than the light intensity judgment threshold when the peak voltage of the echo pulse is greater than the light intensity judgment threshold.
According to a preferred embodiment of the present invention, wherein the lidar performs said steps S101 to S103 in at least one time window. More preferably, the laser radar performs the steps S101 to S103 every time window.
In addition, in the context of the present invention, it is within the scope of the present invention to "turn off" the laser 11 and/or the detection unit 12, including but not limited to turning off the driving circuit of the laser 11 and/or the detection unit 12, and so on, only to actually put the laser 11 and/or the detection unit 12 into a mode in which it cannot normally operate, thereby saving power consumption.
According to an embodiment of the present invention, the step S103 further includes a step S1031 and a step S1032.
In step S1031, when the detection target is changed, the laser radar updates the pulse control parameter according to the target information of the detection target.
Specifically, the laser radar may update the transmission duration of the pulse control parameter according to the flight time so as to satisfy a number determination threshold in the determination threshold; or, the laser radar may update the transmitted light intensity information of the pulse control parameter according to the reflectivity and/or the light intensity information of the echo signal, so that the transmitted light intensity information meets the light intensity determination threshold in the determination threshold.
Wherein the target information of the detection target at least comprises any one of the following information:
1) detecting the ranging information corresponding to the target: the ranging information includes any information that can indicate the relative distance to the laser radar, for example, the distance information to the laser radar; for example, time-of-flight information of the probe target, and the like.
2) And detecting the reflectivity information corresponding to the target.
Wherein the target information of the detection target can be determined by detecting the obtained echo signal at least once.
Wherein whether the detection target is changed is determined according to at least one of the following parameters:
1) the number of received echo pulses within the same time window;
2) time of flight of the echo signal;
3) the reflectivity of the target is detected.
According to a preferred embodiment, when the target information includes a time of flight, the step S1031 further includes: updating the pulse control parameter based on the new time of flight and the current decision threshold.
According to the first example of the present invention, the pulse interval is 20ns, the time window is 1 μ s, the flight time TOF1 corresponding to the current detection target is 60ns, the pulse control parameter includes the emission time length 120ns, and the determination threshold includes the number determination threshold 4 times/cycle. That is, in a time window, the pulse is continuously transmitted only in the first 120ns, and then the laser 11 is turned off, and at the same time, the detecting unit 12 is required to obtain at least 4 echo signal pulses in each time window period.
In this embodiment, since the dead time of the device, which typically uses SiPM or SPAD arrays, is in the order of a few nanoseconds, such as 5ns, each reflected echo signal can be received with a pulse interval of 20ns without the effect of the reception.
When the detected target changes, the time of flight TOF2 of the new detected target is 80ns according to the time of the detecting unit 12 obtaining the echo signal pulse in the time window, and at this time, only 3 echo signal pulses can be obtained in the current time window according to the current control pulse parameters. Then at this point a new transmit duration is obtained based on the number decision threshold of 4/cycle, in combination with a new time of flight of 80 ns.
Wherein the transmission duration may be obtained based on the following formula:
the transmission duration is the time of flight + the pulse interval time (quantity decision threshold-1);
the new transmission duration is 80ns +20ns 3 ns 140 ns.
That is, in subsequent time windows, pulses are emitted continuously for the first 140ns of each window, followed by turning off the laser 11.
Similarly, when the distance of the detected target is close and the flight time is short, the transmission time can be shortened in consideration of saving power, and only the time for acquiring 4 echo pulses is reserved.
According to a preferred embodiment, when the target information includes a reflectivity, the step S1031 further includes: updating the pulse control parameter based on the new reflectivity.
According to the second example of the present invention, the pulse interval is 15ns, the time window is 1 μ s, the detection unit 12 employs SiPM, the light intensity determination threshold thereof is 30mv, the reflectivity of the current detection target is 90%, and the peak value of the echo signal is 45 mv; when the detected object is changed to a new detected object having a reflectivity of 50%, the peak value of the obtained echo signal is 25mv, which is smaller than the light intensity determination threshold value. At this time, the transmission power can be increased by updating the power control parameter of the pulse control parameter, so that the echo signal intensity can still be kept in the optimal detection interval with the peak value of about 45 mv.
It should be understood by those skilled in the art that, since the ranging information and the reflectivity are often changed simultaneously when the detection target is changed, the transmission duration and the transmission power information may need to be adjusted simultaneously, and such a manner is also included in the scope of the present invention and will not be described herein again.
Next, in step S1032, the laser radar controls the emission of the laser according to the updated pulse control parameter, so as to measure the changed detection target.
According to a preferred embodiment of the present invention, the method 100 further comprises the following step S104 (not shown): the number determination threshold (Nth) of the determination thresholds is set/updated according to the ambient light.
The ambient light can be obtained from the detection result of the detection unit 12, or can be obtained from an external sensor.
Preferably, the determination threshold value further includes a light intensity determination threshold value for determining whether or not the signal light is appropriate. Wherein the light intensity can be characterized in different ways based on different detection units 12, rather than directly in lux units and the like.
For example, when the detection unit 12 is a Single Photon Avalanche Diode (SPAD), the number of photons received by each SPAD array can be used to characterize the light intensity; for another example, when the detection unit 12 is a silicon photomultiplier (SiPM), the output voltage of the SiPM unit is used to characterize the light intensity and the like.
Specifically, the detection unit determines the intensity of the ambient light from the number of photons obtained within a predetermined initial detection period, and determines/updates the determination threshold of the signal light based on the determined ambient light.
Preferably, the processor may set/update the number determination threshold Nth of the signal light according to the number of unit avalanches of the ambient light according to a predetermined rule.
For example, the predetermined rule may be set as the following formula (1)
Nth＝n*S； (1)
Where Nth is a threshold for determining the number of signal lights, S is the number of avalanches per unit time of the average detected ambient light, and n is a preset multiple. That is, the number determination threshold of the signal light may be set to n times the number of the ambient light average avalanches.
More preferably, n is adjustable according to the magnitude of the average intensity of the ambient light.
Specifically, when the average intensity of the ambient light is small, n may be set to a small value; and when the average intensity of the ambient light is larger, n may be set to a larger value. Therefore, when the ambient light is weak, the measurement can be completed by using a few pulses, and when the ambient light is strong, the measurement accuracy is ensured by increasing the number of pulses.
According to a preferred embodiment of the present invention, the predetermined detection period is set to be 100 μ S before the laser pulse is emitted after the laser radar is activated, and the predetermined rule is Nth 5 × S. The time window is 1 mus, one cycle of which is one time window. If the detection unit 12 detects 70 avalanches within the 100 μ s, the lidar processor determines that the number of avalanches of the ambient light within one period is 0.7. Then, the processor determines the intensity threshold of the signal light according to a predetermined rule as follows:
nth is 5S 0.7 (pieces/period) is 3.5 (pieces/period).
It should be noted that the foregoing formula (1) is only an example, and is not the only way to determine the threshold value, as will be understood by those skilled in the art. Any manner of obtaining the determination threshold of the signal light based on the average light intensity should be included in the predetermined rule of the present invention, for example, other formula relationships, such as multiplication by a multiple and then rounding, and other corresponding relationships between the light intensity and the threshold, etc.
For example, a corresponding relationship between the light intensity of the ambient light and the determination threshold is preset, and a manner of obtaining the corresponding determination threshold by searching according to the currently obtained light intensity of the ambient light is also included in the solution of the present invention.
Fig. 4a shows a waveform diagram of the output of the detection unit during a predetermined detection period when a Single Photon Avalanche Diode (SPAD) is used as the detection unit, the output of the SPAD is a photon count, i.e. a digital signal, and fig. 4b shows an output waveform when a silicon photomultiplier (SiPM) is used as the detection unit and receives photons.
It should be noted that, for sipms, the actual output is a voltage obtained by adding the outputs of a plurality of SPADs, that is, an analog signal. Even at the level of weak optical signals, the output photocurrent of the SiPM is proportional to the incident optical power, and the SiPM presents linear response; as the incident optical power increases, its output photocurrent begins to deviate from the linear response region due to the limit of the number of SiPM pixels, and saturation eventually occurs. Thus, when a large number of photons are received by the SiPM, its output waveform exhibits a pulse waveform with a linear response similar to that of an APD over a certain period.
The number determination threshold Nth may be obtained based on previous measurement of the ambient light or the ambient noise, and may be set by, for example, performing a single measurement on the ambient light or performing multiple measurements on the ambient light.
The setting of the number determination threshold Nth by performing a single measurement of the ambient light includes, for example:
measuring the photon count of the ambient light incident on the detection unit 12 per unit time;
the number determination threshold Nth is set so that the number determination threshold Nth is larger than the photon number of the ambient light incident on the detection unit 12 in the unit time.
For the laser radar, for example, the intensity of the ambient light may be measured at a preset cycle, and the set number determination threshold Nth may be updated based on the result of the measurement. In addition, for each detection unit 12 having its fixed detection time slot within which the echo should return to the detection unit 12, it is possible to measure the ambient light with a time period outside the detection time slot of that detection unit 12, since the photons received by the detection unit 12 at this time should belong to the ambient light.
The setting of the number determination threshold Nth by measuring the ambient light a plurality of times includes, for example:
measuring the photon count of the ambient light incident on the detection unit 12 per unit time;
measuring for multiple times to obtain the avalanche times of the environment light in average unit time;
the number determination threshold Nth is set so that the number determination threshold Nth is larger than the average avalanche number of times of the ambient light.
As described above, the ambient light may be measured at a predetermined cycle, or may be measured in a time period other than the sounding time slot of the sounding unit 12.
According to a preferred embodiment of the present invention, in the method 100, only the detecting unit 12 may be turned off to reduce the photon detection efficiency of the detecting unit 12, and preferably, the detecting unit 12 is a single photon avalanche diode, so that the number of devices for avalanche of the detecting unit 12 is reduced, thereby avoiding the waste of receiving end power. And the laser 11 can be turned off only, because the currently detected optical signal is enough to calculate the target distance, the laser 11 is turned off temporarily in the pulse period, so that the transmitting power of the transmitting end is saved, and the threat to the safety of human eyes is avoided. It will be readily understood by those skilled in the art that it is fully feasible to switch off both the laser 11 and the detection unit 12 corresponding thereto when the number of received echo pulses is greater than the number decision threshold Nth, all of which are within the scope of the present invention.
According to a preferred embodiment of the present invention, the method 100 further comprises: in the next time window, the laser 11 and/or the detection unit 12 are activated such that the laser 11 and/or the detection unit 12 are in a normal operating state.
According to the scheme, the laser is turned off for a period of time in one time window, so that the energy emitted outwards by the laser in each time window is reduced, the energy of the laser is saved, the power consumption is reduced, and the eye safety performance of the laser radar can be improved.
It will be appreciated by those skilled in the art that the above examples are merely illustrative of how to compare the decision threshold and turn off the laser and/or detection unit, and not actual values.
According to a preferred embodiment of the present invention, the lidar 10 includes a plurality of lasers 11 and a plurality of detection units 12 corresponding to the plurality of lasers 11, and the method 100 further includes:
when the number of pulses of the echo signal received by the detection unit 12 exceeds the number determination threshold Nth, the laser 11 corresponding thereto is turned off.
It will be readily understood by those skilled in the art that the detection unit 12 may be selectively turned off, the laser 11 may be turned off, or both, when the number of photons received by the detection unit 12 exceeds the threshold Nth. In the next time window, it can be determined whether to turn on the laser 11, depending on whether the detection unit 12 has been turned on (the last time window has been turned off or is within the dead time of the photodiode). It is also possible to determine whether or not the adjacent laser 11 of the laser 11 is on, and to ensure that an obstacle is not missed, the emission of all the lasers 11 cannot be stopped within a certain range. The determination may also be performed according to a map drawn by the sensor module or a current detection result of the lidar, when the surrounding environment is complex (for example, on a noisy road surface, there are various objects, such as vehicles, pedestrians, buildings, etc., in the surrounding environment), the detection unit 12 is turned on, and when the surrounding environment is simple, for example, in a field with fewer obstacles, the laser 11 may not be turned on temporarily.
According to a preferred embodiment of the present invention, wherein the laser 11 is a Vertical Cavity Surface Emitting Laser (VCSEL). The lidar 10 may calculate the range of the obstacle from the time of flight of the transmitted pulse and the echo signal, or the reflectivity of the target spatial obstacle from the power of the transmitted pulse and the echo signal.
As shown in fig. 5, according to a preferred embodiment of the present invention, there is provided a laser radar 10 including: a laser 11, a detection unit 12 and a control unit 13. Wherein the laser 11 is configured to emit laser pulses for detecting the object. The detection unit 12 corresponds to the laser 11, and as shown in fig. 2a and 2b, the detection unit 12 and the laser 11 form a one-to-one correspondence relationship. Only one laser 11 and one detection unit 12 are schematically shown in fig. 5, and it will be readily understood by a person skilled in the art that the lidar 10 may comprise any number of pairs of lasers 11 and detection units 12. The detection unit 12 is configured to receive an echo reflected by the laser pulse on the target object and output an echo signal. A control unit 13 is coupled to the laser 11 and the detection unit 12 and receives the echo signals, the control unit 13 being configured to function as: driving the laser to emit laser pulses to detect a target object according to a pulse control parameter within a time window, wherein the pulse control parameter is determined based on an echo signal and a corresponding decision threshold; and/or controlling the switching on or off of the laser and/or the detection unit.
Wherein the time window may be determined based on at least any one of:
1) scanning frequency; for example, a single frame scan time is a time window.
2) A predetermined scan interval, etc.
Wherein the pulse control parameter is used to indicate the number/power of pulses emitted by the laser within the time window; alternatively, the pulse control parameter is used to indicate the on-time of the laser and/or the detection unit within a time window.
In particular, the pulse control parameter is determined based on the echo signal and a corresponding decision threshold.
Preferably, the decision threshold may be determined according to the intensity of the echo signal.
According to a preferred embodiment of the invention, the control unit 13 is further configured to have the following functions:
1. and driving the laser 11 to emit laser pulses according to the pulse control parameters so as to detect the target object.
Specifically, at the beginning of a time window, the laser 11 is driven to emit laser pulses at normal power for detection. The laser radar 10 generally has a transmitting lens, and the laser 11 is located on a focal plane of the transmitting lens, so that laser pulses emitted by the laser 11 are collimated by the transmitting lens and then emitted to the surrounding environment as parallel light for detecting a target object.
2. The echo signal of the laser pulse reflected by the target object is acquired by the detection unit 12.
The laser pulse is diffusely reflected at the target, and a part of the reflected echo returns to the laser radar 10 and is received by a detection unit 12 corresponding to the laser 11, and the detection unit 12 usually includes a photodiode, and can convert an optical signal into an electrical signal for subsequent signal processing.
3. The pulse control parameters are updated in dependence of the echo signal to control the laser 11 and/or the detection unit 12 to be switched off or on.
Specifically, the laser radar updates the pulse control parameter according to the light intensity information and/or the flight time of the echo signal.
Preferably, the laser radar obtains the pulse control parameter according to a decision threshold. Wherein the decision threshold comprises a quantity decision threshold. The number decision threshold is used to indicate the number of received echo signals. Preferably, the decision threshold further comprises a light intensity decision threshold for determining the available echo signal.
Wherein the pulse control parameter comprises a pulse transmission duration. More preferably, the pulse control parameter further comprises a pulse transmission power.
According to a preferred embodiment of the invention, the control unit 13 is further configured with the following modules:
and the updating module is configured to update the pulse control parameter according to the target information of the detection target when the detection target is changed.
And the transmitting module is used for controlling the transmission of the laser according to the updated pulse control parameter so as to measure the changed detection target.
Specifically, the updating module may update the transmission duration of the pulse control parameter according to the flight time so as to satisfy the number determination threshold of the determination threshold; or the transmitted light intensity information of the pulse control parameter can be updated according to the reflectivity and/or the light intensity information of the echo signal, so that the transmitted light intensity information meets the light intensity judgment threshold of the judgment threshold.
Wherein the target information of the detection target at least comprises any one of the following information:
detecting the ranging information corresponding to the target:
the ranging information includes any information that can indicate the relative distance to the laser radar, for example, the distance information to the laser radar; for example, time-of-flight information of the probe target, and the like.
Reflectivity information corresponding to the detection target:
wherein the object information of the detection object can be determined by at least one detection.
Wherein whether the detection target is changed is determined according to at least one of the following parameters:
1) the number of received echo pulses within the same time window;
2) time of flight of the echo signal;
3) the reflectivity of the target is detected.
According to a preferred embodiment of the invention, the control unit 13 is further configured with the following functions:
acquiring the intensity of ambient light;
the determination threshold is set according to the intensity of the ambient light.
According to a preferred embodiment of the invention, wherein the detection unit 12 comprises one or more single photon avalanche diodes, the control unit 13 is further configured to:
measuring the avalanche times corresponding to the ambient light on the detection unit in unit time;
the number determination threshold is set/updated according to the number of avalanches of the ambient light in the unit time.
According to a preferred embodiment of the invention, the control unit 13 is further configured to:
and measuring according to the detection information obtained by the detection unit.
According to a preferred embodiment of the invention, the control unit 13 is further configured to:
in the next time window, the laser and/or the detection unit are activated.
The preferred embodiment of the invention provides a method for setting a judgment threshold value of signal light according to ambient light, further setting pulse control parameters, and adjusting the on/off of a laser and/or a detection unit (preferably also comprising the transmitting power of the laser) according to the pulse control parameters in each time window, and a laser radar for detecting by using the method, thereby saving the transmitting/receiving power consumption of the laser radar, avoiding waste and simultaneously reducing the threat of transmitting laser pulses to the safety of human eyes.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that various changes, modifications and substitutions can be made without departing from the spirit and scope of the invention as defined by the appended claims. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (22)

1. A method of detection with a lidar comprising a laser and a detection unit corresponding to the laser, wherein the method comprises the steps of:
within a time window, driving the laser to emit laser pulses to detect a target object according to a pulse control parameter, wherein the pulse control parameter is determined based on an echo signal and a corresponding decision threshold; and/or
And controlling the laser and/or the detection unit to be switched on or off according to the pulse control parameter.
2. The method of claim 1, wherein the method further comprises:
driving the laser to emit laser pulses for detection according to the pulse control parameters;
acquiring an echo signal reflected by the laser pulse on a detection target through the detection unit;
and updating pulse control parameters according to the echo signals so as to control the laser and/or the detection unit to be switched off or switched on.
3. The method of claim 1 or 2, wherein the step of updating the pulse control parameter in dependence on the echo signal further comprises:
a, when a detection target is changed, updating the pulse control parameter according to the target information of the new detection target;
b, controlling the emission of the laser according to the updated pulse control parameter so as to measure the changed detection target.
4. The method of claim 3, wherein the target information comprises reflectivity, the step a further comprising:
a11 updates the pulse control parameter based on the new reflectivity and the current decision threshold.
5. The method of claim 3, wherein the target information comprises time of flight, the step a further comprising:
a21 updating the emission time of the pulse control parameter based on the new time of flight and the current decision threshold.
6. The method of claim 4 or 5, wherein the step a further comprises:
determining whether the detection target is changed according to at least one of the following parameters:
-the number of received echo pulses within the same time window;
-time of flight of the echo pulse;
-detecting the reflectivity of the object.
7. The method of claim 1 or 2, further comprising the steps of:
-acquiring an intensity of ambient light;
-setting the decision threshold in dependence of the intensity of the ambient light.
8. The method of claim 7, wherein the detection unit comprises one or more single photon avalanche diodes, wherein the step of setting the decision threshold as a function of the intensity of ambient light further comprises:
-measuring the number of avalanches corresponding to ambient light onto said detection unit per unit time;
-setting/updating said quantity decision threshold in dependence of the number of avalanches of ambient light within said unit of time.
9. The method of claim 1 or 2, wherein the method further comprises:
-performing measurements based on the probing information obtained by the probing unit.
10. The method of claim 1 or 2, further comprising: in the next time window, the laser and/or the detection unit are activated.
11. The method of claim 1 or 2, wherein the laser is a vertical cavity surface emitting laser.
12. A lidar comprising:
a laser configured to emit laser pulses for detecting a target object;
the detection unit corresponds to the laser and is configured to receive an echo reflected by the laser pulse on a target object and output an echo signal;
a control unit coupled to the laser and the detection unit and receiving the echo signal, the control unit configured to: within a time window, driving the laser to emit laser pulses to detect a target object according to a pulse control parameter, wherein the pulse control parameter is determined based on an echo signal and a corresponding decision threshold; controlling the laser and/or the detection unit to be turned on or off.
13. The lidar of claim 12, wherein the control unit is further configured to:
driving the laser to emit laser pulses for detection according to the pulse control parameters;
acquiring an echo signal reflected by the laser pulse on a detection target through the detection unit;
updating pulse control parameters according to the echo signal to control the laser and/or the detection unit to be switched off or on.
14. The lidar according to claim 12 or 13, wherein the control unit further comprises:
an updating module configured to update the pulse control parameter according to target information of a detection target when the detection target is changed;
and the transmitting module is used for controlling the transmission of the laser according to the updated pulse control parameter so as to measure the changed detection target.
15. The lidar of claim 14, wherein the target information comprises reflectivity, the update module further configured to:
-updating the transmission power of the pulse control parameter in dependence of the new reflectivity and the current decision threshold.
16. The lidar of claim 14, wherein the target information comprises a time of flight, the update module further configured to:
-updating the time of transmission of the pulse control parameter according to the new time of flight and the current decision threshold.
17. The lidar according to claim 15 or 16, wherein the control unit is further configured to:
determining whether the detection target is changed according to at least one of the following parameters:
-the number of received echo pulses within the same time window;
-time of flight of the echo pulse;
-detecting the reflectivity of the object.
18. The lidar of claim 12 or 13, wherein the control unit is further configured to:
-acquiring an intensity of ambient light;
-setting the decision threshold in dependence of the intensity of the ambient light.
19. The lidar of claim 18, wherein the detection unit comprises one or more single photon avalanche diodes, wherein the control unit is further configured to:
measuring the avalanche times corresponding to the ambient light on the detection unit in unit time;
the number determination threshold is set/updated according to the number of avalanches of the ambient light in the unit time.
20. The lidar of claim 12 or 13, wherein the control unit is further configured to:
-performing measurements based on the probing information obtained by the probing unit.
21. The lidar of claim 12 or 13, wherein the control unit is further configured to:
in the next time window, the laser and/or the detection unit are activated.
22. The lidar of claim 12 or 13, wherein the laser is a vertical cavity surface emitting laser.
CN202010999876.7A 2020-09-22 2020-09-22 Laser radar detection method and laser radar Pending CN114252866A (en)

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