WO2022095247A1

WO2022095247A1 - Distance measurement error calibration system and calibration method for laser radar

Info

Publication number: WO2022095247A1
Application number: PCT/CN2020/138471
Authority: WO
Inventors: 苏健; 何燃; 李国花; 朱亮; 闫敏
Original assignee: 深圳奥锐达科技有限公司
Priority date: 2020-11-06
Filing date: 2020-12-23
Publication date: 2022-05-12
Also published as: CN112363149A; CN112363149B

Abstract

A distance measurement error calibration system and calibration method for laser radar (300). The distance measurement error calibration system for the laser radar (300) comprises a calibration assembly (10) and a processing unit. The calibration assembly (10) is arranged at a position which is a preset distance away from the laser radar (300), the laser radar (300) emits laser beams to the calibration assembly (10), the laser beams are reflected by the calibration assembly (10), the calibration assembly (10) can change the reflection intensities of the reflected beams multiple times, and the laser radar (300) receives the reflected beams reflected by the calibration assembly (10), and measures the corresponding measurement distances when reflected beams of different reflection intensities are received. The processing unit calculates a distance measurement error according to the measurement distance and the preset distance, and constructs a relationship function between the distance measurement error and the reflection intensities. The two parameters, i.e. the distance measurement error and the reflection intensities, can be measured and calculated by means of the laser radar (300), the reflection intensities can intuitively and accurately reflect the impact thereof on the distance measurement error, and the constructed relationship function between the distance measurement error and the reflection intensities can be used for correcting the actual measurement result and improving the measurement accuracy of the laser radar (300).

Description

Lidar ranging error calibration system and calibration method

technical field

The present application belongs to the technical field of sensor calibration, and more specifically, relates to a ranging error calibration system and calibration method for laser radar.

Background technique

Lidar is a radar system that detects the position, speed and other characteristics of a target by emitting a laser beam. It has the advantages of high accuracy, fast operation speed and high efficiency. It can be used as automatic driving of cars, robot positioning and navigation, space environment mapping, security, etc The essential core sensor in the field. At present, lidar is mainly based on the time-of-flight principle for ranging. Lidar generally includes a transmitter and a collector. The transmitter is used to emit a beam to the target space, and the collector collects the beam reflected by the target, and then calculates the beam from the target. The time taken from transmit to receive to calculate the distance of the object. However, in the actual ranging process, affected by factors such as the distance of the object, the reflectivity of the object, and the ambient light, the light intensity of the reflected beam collected by the collector usually changes, resulting in a ranging error.

SUMMARY OF THE INVENTION

The purpose of the embodiments of the present application is to provide a ranging error calibration system and calibration method for lidar, so as to solve the problem in the prior art that the reflected light beams collected by the collector due to factors such as object distance, object reflectivity, and ambient light exist in the prior art. The technical problem of ranging error caused by the change of light intensity.

In order to achieve the above purpose, the technical solution adopted in the present application is to provide a ranging error calibration system for lidar, which includes a calibration component and a processing unit. The calibration component is set at a preset distance from the lidar, the lidar emits a laser beam to the calibration component, and the laser beam is reflected by the calibration component, and the calibration component can change the reflection intensity of the reflected beam multiple times, and the laser radar receives and passes through the calibration component. and measure the corresponding measurement distance when receiving reflected beams with different reflection intensities. The processing unit calculates the ranging error according to the measured distance and the preset distance, and constructs an error correction curve of the ranging error and reflection intensity.

Optionally, the calibration component includes an attenuator and a calibration plate, the attenuator includes a plurality of attenuation regions with different attenuation rates for the laser beam, and the light intensity of the laser beam is attenuated to different degrees after passing through the different attenuation regions of the attenuator. to reflect the laser beam.

Optionally, the attenuator is a rotatable dimming dial.

Optionally, the attenuating element is located on the emission light path or the reflection light path of the laser beam.

Optionally, the calibration assembly includes a plurality of calibration plates having different reflectivities.

Optionally, all calibration plates are distributed around the lidar.

Optionally, all the calibration boards are sequentially connected as one.

Optionally, the top or bottom edge of the calibration plate forms an inclined straight line or a curve of predetermined curvature.

According to another aspect of the present invention, the present invention further provides a method for calibrating ranging error of laser radar, comprising the following steps:

Setting steps: Set the calibration component at a preset distance from the lidar;

Measurement steps: control the lidar to emit a laser beam toward the calibration component and receive the reflected beam reflected by the calibration component. The calibration component can change the reflection intensity of the reflected beam multiple times. When the lidar measures the reflected beam with different reflection intensities, the corresponding the measurement distance;

Steps of constructing a relation function: Calculate the ranging error between the measured distance and the preset distance, and construct a relation function between the ranging error and the reflection intensity of the reflected beam.

Optionally, in the measurement step, a pulse signal is transmitted to the calibration component by the transmitter of the lidar, and at least part of the pulse signal is collected and received by the collector of the lidar, and the TDC circuit built in the collector calculates the time of flight of the photon from emission to collection. And form a measurement signal representing the flight time, address the storage location in the built-in histogram memory of the collector according to the measurement signal, use the location of the histogram memory as the time histogram to form a histogram, and the processing circuit of the lidar processes the histogram to obtain a The peak position in the histogram is determined to calculate the measurement distance according to the flight distance corresponding to the peak position, and the processing circuit characterizes the reflection intensity of the reflected beam according to the photon count value in the time histogram corresponding to the peak position.

The beneficial effects of the laser radar ranging error calibration system and the laser radar ranging error calibration method provided by the present application are: compared with the prior art, by setting the calibration component at a position away from the laser radar preset distance in the present application, The laser beam emitted by the lidar is reflected by the calibration component and then received by the lidar again. The calibration component can repeatedly change the light intensity of the reflected beam (ie, the reflection intensity), so that the lidar can measure the corresponding measurement of the reflected beam with different reflection intensities. distance. After collecting multiple sets of data in this way, the processing unit calculates the difference between the measured distance and the preset distance (ie, the actual distance), obtains the measurement error, and constructs a relationship function and an error correction curve between the measurement error and the reflected intensity. . It is understandable that the two parameters of ranging error and reflection intensity can be measured and calculated by lidar, and the data is accurate and reliable; compared with constructing the relationship function between ranging error and object distance, reflection intensity can be more intuitive. And accurately reflect its influence on ranging error, so it can improve the accuracy of lidar calibration and correction. In addition, since the calibration component can repeatedly change the reflection intensity of the reflected beam, the variable is the reflection intensity rather than the distance, so the calibration component is fixed, and the calibration plate does not need to be moved frequently during the lidar calibration process. Obtaining multiple sets of measurement data, the operation is simple and efficient, and the calibration efficiency is greatly improved.

Description of drawings

In order to illustrate the technical solutions in the embodiments of the present application more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only for the present application. In some embodiments, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

FIG. 1 is a schematic structural diagram of a ranging error calibration system for a lidar according to a first embodiment of the present application;

FIG. 2 is a schematic structural diagram of a ranging error calibration system for a lidar according to a second embodiment of the present application;

Fig. 3 is a schematic structural diagram of the calibration component of the ranging error calibration system of the lidar in Fig. 2 under an assumed flattened state.

Among them, each reference sign in the figure:

10-calibration component; 11-attenuator; 12-calibration board; 300-lidar; 310-transmitter; 320-collector; 330-control circuit.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

It is to be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top" , "bottom", "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, only for the convenience of describing the application and simplifying the description, rather than indicating or implying the indicated A device or element must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as a limitation of the present application.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present application, "plurality" means two or more, unless otherwise expressly and specifically defined.

Referring to FIG. 1 , the structure of the laser radar ranging error calibration system provided by the first embodiment of the present application and its working process of calibrating the laser radar 300 will now be described. The ranging error calibration system of the lidar includes a calibration component 10 and a processing unit (not shown in the figure).

The calibration component 10 is set at a position at a predetermined distance D from the lidar 300 . The lidar 300 includes a transmitter 310 , a collector 320 and a processing circuit 330 . The transmitter 310 includes a light source composed of one or more lasers. The transmitter 310 emits a laser pulse beam to the calibration assembly 10 , and at least part of the pulse beam is reflected by the calibration assembly 10 back to the lidar 300 and received by the collector 320 . The collector 320 includes a pixel composed of one or more sensing elements for collecting photons in the reflected light beam and outputting photon signals, wherein the sensing elements can be an avalanche photodiode (Avalanche Photo Diode, APD), a single photon avalanche diode ( Single Photon Avalanche Diode, SPAD), silicon photomultiplier (Silicon photomultiplier, SiPM) and other single photon devices. The collector 320 further includes a TDC (Time-to-Digital Converter, time-to-digital converter) circuit and a histogram memory connected to each other. The processing circuit 330 of the lidar 300 synchronizes the trigger signals of the transmitter 310 and the collector 320 and calculates the time-of-flight required by the photons in the light beam from being emitted to being collected and received. It will be appreciated that the TDC circuit and histogram memory may also be provided as part of the processing circuit 330 in some embodiments.

The calibration assembly 10 can change the reflected intensity of the reflected beam multiple times. Specifically, the calibration assembly 10 includes an attenuator 11 and a calibration plate 12, and the attenuator 11 and the calibration plate 12 are arranged at intervals. The attenuating element 11 includes a plurality of attenuating regions with different attenuation rates for the laser beam, so that the light intensity of the laser beam is attenuated to different degrees after passing through the different attenuation regions of the attenuating element 11 . The calibration plate 12 is used to reflect the laser beam, and the calibration plate 12 can be a common reflection plate. The attenuating element 11 is disposed on the emitting optical path of the laser beam. The laser beam emitted by the transmitter 310 of the lidar 300 first passes through the attenuating element 11 so that the light intensity is attenuated and then is reflected by the calibration plate 12 back to the collector 320 of the lidar 300 . Or the attenuating element 11 is arranged on the reflected light path of the laser beam, and the laser beam emitted by the transmitter 310 of the lidar 300 is first reflected by the calibration plate 12 and then passes through the attenuating element 11 so that the light intensity is attenuated and returned to the collector of the lidar 300 320. In the actual calibration process, the laser radar 300 or the attenuating element 11 can be selectively adjusted so that the laser beam is projected to different attenuation regions of the attenuating element 11, so that the reflection intensity of the reflected beam can be adjusted.

Optionally, the attenuator 11 is a rotatable dimming turntable and is disposed on the emission light path of the laser beam. By rotating the dimming dial, attenuation regions with different attenuation rates can be placed on the optical path of the laser beam, thereby adjusting the light intensity of the emitted beam projected on the calibration plate 12, that is, changing the reflection intensity of the reflected beam. The dimming dial is circular, square, triangular or any other reasonable shape. The attenuation area divided on the dimming dial is fan-shaped or any other reasonable shape, the number of attenuation areas can be any reasonable value, such as six or ten, and the shape and area size of different attenuation areas can be the same or different.

After the collector 320 of the lidar 300 receives the reflected beam, the built-in TDC circuit of the collector 320 calculates the time-of-flight of photons from emission to collection and forms a measurement signal representing the time-of-flight, and converts the measurement signal into a time code (binary code, temperature code, etc.). Then the histogram memory will count according to the measurement signal in the corresponding internal time unit, for example, increment by 1, so as to realize the addressing of the storage location in the histogram memory built in the collector 320 . After a number of measurements, a histogram can be plotted using the histogram memory locations as time bins and counting photon counts in all time bins. Then the processing circuit 330 in the lidar 300 processes the histogram to determine the peak position in the histogram, thereby calculating the measurement distance Dn according to the flight time corresponding to the peak position, n=1, 2, 3..., n, and processes The circuit 330 characterizes the reflection intensity In of the reflected light beam according to the photon count value in the time bin corresponding to the peak position, n=1, 2, 3 . . . n. The reflection intensity In (n=1, 2, 3..., n) corresponds to the measurement distance Dn (n=1, 2, 3..., n) one-to-one, and n represents the number of times the calibration component 10 changes the reflection intensity of the reflected beam (for example, , the attenuating element 11 has n attenuation regions with different attenuation rates, then the attenuating element 11 can change the reflection intensity of the reflected beam n times, correspondingly, n reflection intensities can be obtained). For the working principle of the TDC circuit and the histogram memory, please refer to the content in the patent application number 201910889452.2. In this way, the lidar receives the reflected light beam reflected by the calibration component 10 and measures the corresponding measurement distances when receiving the reflected light beam with different reflected intensities.

The preset distance D between the calibration component 10 and the lidar 300 is the actual distance between the two, and the difference between the measurement distance Dn measured by the lidar 300 and the preset distance D is the ranging error ΔDn, ΔDn =Dn-D, n=1, 2, 3, ..., n. The processing unit calculates the ranging error ΔDn according to the measured distance Dn and the preset distance D, and analyzes and fits the relationship function between the ranging error ΔDn and the reflection intensity In through multiple sets of calibration data, so as to construct the ranging error and reflection Relationship function between intensity and error correction curve. The relationship function and error correction curve can adopt various existing styles, for example, a polynomial function y=aI ² +bI+c can be fitted, where y is the ranging error, I is the reflection intensity, and a, b, and c are the fitting coefficient.

In practical applications, the measurement distance of the target object is first measured by the lidar 300 and the reflection intensity of the beam is calculated, and the measurement distance can be corrected according to the reflection intensity and the ranging error determined by the error correction curve to obtain a more accurate measurement distance result.

As shown in FIG. 2 , the structure of the laser radar ranging error calibration system provided by the second embodiment of the present application is basically the same as that of the first embodiment, and the difference lies in the calibration component 10 . The calibration assembly 10 includes a plurality of calibration plates 12 with different reflectivities and omits the attenuation member 11 in the first embodiment. The difference in reflectivity of the calibration plate 12 can be achieved by using the calibration plate 12 of different materials or coating the calibration plate 12 with different coatings. In one embodiment, the laser radar can be adjusted so that the laser beam is projected on the calibration plate 12 with different reflectivity, so that the reflection intensity of the reflected beam can be adjusted. In another embodiment, all the calibration plates 12 can also be distributed around the lidar 300, and the lidar 300 adopts a rotating lidar. In this way, when the laser radar 300 is regulated to rotate and scan, a laser beam can be emitted to any calibration plate 12. After the laser beam is reflected by different calibration plates 12, the laser radar 300 receives reflected beams with different reflection intensities, so as to further calculate and measure the corresponding a number of different measured distance values.

Further, as a specific implementation manner, all the calibration plates 12 are sequentially connected as a whole, so that all the calibration plates 12 form a cylinder, the lidar 300 is located at the center axis of the cylinder, and the radius of the cylinder is the calibration component. 10 Preset distances from Lidar 300. The radius of the cylinder can be set to any value within the range that can be measured by the lidar. In other embodiments, the calibration plate 12 may not be connected as a whole, but distributed around the lidar 300 at intervals. In other embodiments, all the calibration plates 12 may not be connected to form a cylinder with a complete 360° circumference, but a half cylinder or any segment of arc surface. The division between regions with different reflectivity can be divided equally according to the central angle or divided in any shape and size.

As a specific embodiment, the top edges of all the calibration plates 12 connected as a whole form an inclined straight line or a curve with a predetermined curvature, and the top edge of the calibration plate 12 with relatively high reflectivity is higher than that of the calibration plate 12 with relatively low reflectivity The top edge of the plate 12. In this way, when the laser radar 300 rotates onto the calibration plate 12 with low reflectivity, only part of the light spot formed by the laser beam is reflected and echoed by the calibration plate 12, and the rest is projected from the top edge of the calibration plate 12, which can further The reflection intensity of the reflected beam reflected by the calibration plate 12 with low reflectivity is reduced, that is, the echo signal intensity is reduced, thereby increasing the intensity discrimination of the reflected beam.

According to another aspect of the present application, the present application further provides a method for calibrating a ranging error of a lidar, comprising the following steps:

Setting step: set the calibration component 10 at a preset distance D from the lidar 300;

Measurement step: control the laser radar 300 to emit a laser beam to the calibration component 10 and receive the reflected beam reflected by the calibration component 10, wherein the calibration component 10 can change the reflection intensity of the reflected beam multiple times, and the laser radar 300 measures the received beam with different reflection intensities The corresponding measurement distance when the reflected beam is reflected;

In the measurement step, a pulse signal is transmitted to the calibration component through the transmitter 310 of the laser radar, and at least part of the pulse signal is collected and received by the collector 320 of the laser radar. The built-in TDC circuit of the collector 320 calculates the photon from emission to collection. The time of flight is generated and a measurement signal representing the time of flight is formed, which is converted into a time code (coded by binary code, temperature code, etc.).

The histogram memory includes an address decoder, a memory matrix, a read/write circuit, and a histogram drawing circuit. The TDC circuit inputs the acquired time code (binary code, temperature code, etc.) reflecting the flight time into the address decoder, and converts it into address information through the address decoder, and the address information will be stored in the storage matrix. Specifically, the storage matrix includes a plurality of storage units, that is, time units, and each storage unit is pre-configured with a certain address (or address range). The histogram memory will address the storage location in the histogram memory according to the time code converted from the measurement signal and count, such as adding 1, in the corresponding storage unit inside. Specifically, when the time code address received by the address decoder is consistent with the address of a certain storage unit or is within the address range of the storage unit, the read/write circuit will execute + 1 operation, that is, one photon count is completed. After multiple measurements, the data in each storage unit reflects the number of photons received in the time interval.

After multiple measurements, the data of all storage cells in the storage matrix of the histogram memory are read out to the histogram drawing circuit, and the position of the histogram memory is taken as the time histogram (bin) and the photons in all the time histogram (bin) The counts are counted and plotted to form a histogram.

The processing circuit 330 of the lidar processes the histogram to determine the peak position in the histogram to calculate the measurement distance according to the flight distance corresponding to the peak position, and the processing circuit 330 represents the photon count value in the time histogram corresponding to the peak position. The reflected intensity of the reflected beam. For the working principle of the TDC circuit and the histogram memory, please refer to the content in the patent application number 201910889452.2.

In the step of constructing the relationship function, the preset distance D between the calibration component 10 and the lidar 300 is the actual distance between the two, and the difference between the measured distance Dn measured by the lidar 300 and the preset distance D is the measured distance Distance error ΔDn, ΔDn=Dn-D, n=1, 2, 3, ..., n. The processing unit calculates the ranging error ΔDn according to the measured distance Dn and the preset distance D, and analyzes and fits the relationship function between the ranging error ΔDn and the reflection intensity In through multiple sets of calibration data, so as to construct the ranging error and reflection Relationship function between intensity and error correction curve. The relationship function and error correction curve can adopt various existing styles, for example, a polynomial function y=aI ² +bI+c can be fitted, where y is the ranging error, I is the reflection intensity, and a, b, and c are the fitting coefficient.

The laser radar transmitter ranging error calibration system and calibration method provided by this application, through the calibration, the relationship function between the ranging error and the reflection intensity is constructed. Compared with the relationship function between the ranging error and the object distance, the reflection intensity can more intuitively and accurately reflect its influence on the ranging error, so it can be It is used to correct the actual measurement results of lidar and improve the accuracy of lidar ranging. In addition, since the calibration component can repeatedly change the reflection intensity of the reflected beam, the variable is the reflection intensity rather than the distance, so the calibration component is fixed, and the calibration plate does not need to be moved frequently during the lidar calibration process. Obtaining multiple sets of measurement data, the operation is simple and efficient, and the calibration efficiency is greatly improved.

The above descriptions are only preferred embodiments of the present application, and are not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application shall be included in the protection of the present application. within the range.

Claims

A ranging error calibration system for lidar, characterized in that it includes:

A calibration component, the calibration component is arranged at a preset distance from the lidar, the lidar emits a laser beam to the calibration component, the laser beam is reflected by the calibration component, and the calibration component can change the reflection of the reflected beam multiple times Intensity, the laser radar receives the reflected beam reflected by the calibration component and measures the corresponding measurement distance when receiving the reflected beam with different reflected intensities;

and a processing unit, the processing unit calculates the ranging error according to the measured distance and the preset distance, and constructs a relationship function between the ranging error and the reflection intensity.
The ranging error calibration system for lidar according to claim 1, wherein the calibration component includes an attenuator and a calibration plate, the attenuator includes a plurality of attenuating regions with different attenuation rates for the laser beam, and the laser After the light beam passes through different attenuation regions of the attenuating element, the light intensity is attenuated to different degrees, and the calibration plate is used to reflect the laser beam.
The ranging error calibration system for lidar according to claim 2, wherein the attenuator is a rotatable dimming turntable.
The ranging error calibration system for lidar according to claim 2, wherein the attenuator is located on the emission optical path or the reflected optical path of the laser beam.
The ranging error calibration system for lidar according to claim 1, wherein the calibration component comprises a plurality of calibration plates with different reflectivities.
The ranging error calibration system for lidar according to claim 5, wherein all calibration plates are distributed around the lidar.
The ranging error calibration system for lidar according to claim 5, wherein all the calibration boards are connected in sequence as a whole.
The ranging error calibration system for lidar according to claim 7, wherein the top edge of the calibration plate forms an inclined straight line or a curve with a predetermined curvature.
A method for calibrating ranging error of laser radar, characterized in that it includes the following steps:

Setting steps: Set the calibration component at a preset distance from the lidar;

Measurement step: control the laser radar to emit a laser beam to the calibration component and receive the reflected beam reflected by the calibration component, wherein the calibration component can change the reflection intensity of the reflected beam multiple times, and the laser radar measures the received beam with Corresponding measurement distances when reflecting beams with different reflection intensities;

The step of constructing a relationship function: calculating the ranging error between the measured distance and the preset distance, and constructing a relationship function between the ranging error and the reflected intensity of the reflected beam.
The method for calibrating ranging error of lidar according to claim 9, characterized in that, in the measuring step, a pulse signal is transmitted to the calibration component through the transmitter of the lidar, and at least part of the pulse signal is transmitted by the lidar's transmitter. The collector collects and receives. The built-in TDC circuit of the collector calculates the flight time of photons from emission to collection and forms a measurement signal representing the flight time. According to the measurement signal, the storage location in the built-in histogram memory of the collector is addressed, and the histogram memory is stored. The position of the laser radar is used as a time histogram to form a histogram, and the processing circuit of the lidar processes the histogram to determine the peak position in the histogram to calculate the measurement distance according to the flight distance corresponding to the peak position, and the processing circuit calculates the measurement distance according to the time corresponding to the peak position. The photon count value within the histogram characterizes the reflected intensity of the reflected beam.