CN113848558A - Flight time distance measuring system and method - Google Patents

Flight time distance measuring system and method Download PDF

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Publication number
CN113848558A
CN113848558A CN202010599501.1A CN202010599501A CN113848558A CN 113848558 A CN113848558 A CN 113848558A CN 202010599501 A CN202010599501 A CN 202010599501A CN 113848558 A CN113848558 A CN 113848558A
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histogram
time
peak
distance measurement
trigger
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雷述宇
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Ningbo Abax Sensing Electronic Technology Co Ltd
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Ningbo Abax Sensing Electronic Technology Co Ltd
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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
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
    • 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
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
    • G01S17/894—3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
    • 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
    • G01S7/497—Means for monitoring or calibrating

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

Abstract

The invention provides a system and a method for calibrating flight time distance measurement, wherein the flight time distance measurement system comprises the following components: the histogram statistic module, the histogram calibration module and the detection distance calculation module; the histogram statistics module generates a histogram based on a trigger time; the histogram calibration module is used for calibrating the histogram peak value; the detection distance calculation module obtains a detection distance based on the calibrated histogram.

Description

Flight time distance measuring system and method
Technical Field
The present application relates to the field of detection technology, and more particularly to the field of calibrating time-of-flight distance measurement systems.
Background
Time of flight (TOF) is a method of finding a distance to an object by continuously transmitting light pulses to the object, receiving light returning from the object with a sensor, and detecting the Time of flight (round trip) of the light pulses.
Direct Time of flight (DTOF) is one of TOF, and the DTOF technology directly obtains the target distance by calculating the transmitting and receiving Time of an optical pulse, and has the advantages of simple principle, good signal-to-noise ratio, high sensitivity, high accuracy and the like, and receives more and more attention.
At present, the laser radar based on the flight time method mainly has two types, namely a mechanical type and a non-mechanical type, the distance measurement of a 360-degree large view field is realized through a rotating base in the mechanical type, and the laser radar has the advantages of large measurement range, but the problems of high power consumption, low resolution ratio, low frame rate and the like. The non-mechanical medium-area array laser radar can solve the problem of the mechanical laser radar to a certain extent, transmits an area light beam with a certain view field in space once, and receives the light beam through the area array receiver, so that the resolution and the frame rate of the non-mechanical medium-area array laser radar are improved, and in addition, the non-mechanical medium-area array laser radar is easier to install because a rotating part is not needed. Nevertheless, area-array lidar still faces some challenges.
However, as the demand for the detection distance increases, the existing DTOF technology has a problem of low detection distance accuracy. For example, in the DTOF ranging process, due to the different energy of the emitted light beam, the light receiving module may be triggered by the echo of the rising edge of the emitted light beam, and may also be triggered by the echo of the peak of the emitted light beam, and when determining the detection distance, it is unknown whose echo triggers the light receiving module, which may result in the accuracy of the distance measurement being reduced.
Disclosure of Invention
The present application aims to provide a system and a method for measuring a flight time distance, aiming at the above-mentioned deficiencies in the prior art, so as to solve the technical problem that the detection distance of the existing detection device is not far enough.
In order to achieve the above purpose, the technical solutions adopted in the embodiments of the present application are as follows:
in a first aspect, an embodiment of the present application provides a measurement system, including:
the histogram statistic module, the histogram calibration module and the detection distance calculation module;
the histogram statistics module generates a histogram based on a trigger time;
the histogram calibration module is used for calibrating the histogram peak value;
the detection distance calculation module obtains a detection distance based on the calibrated histogram.
Optionally, the peak of the histogram may be calibrated with a fixed value when the triggering time of the peak of the histogram is greater than a threshold.
Optionally, the histogram calibration function may be used to calibrate the peak of the histogram when the triggering time of the peak of the histogram is less than a threshold.
Optionally, the histogram calibration function may represent a correspondence between the deviation and the peak trigger rate, or may be an interpolation function.
Optionally, the peak trigger rate is a ratio of a peak trigger number and an effective trigger number in the histogram.
Optionally, the number of valid triggers refers to the number of observations or the number of valid SPADs that can be used by a valid signal.
Optionally, the effective triggering times may be obtained according to the background light energy estimation result and the system parameter.
In a second aspect, an embodiment of the present application provides a time-of-flight distance measurement method, which is characterized by including the following steps:
obtaining a histogram based on the trigger time;
calibrating the peak value of the histogram;
the detection distance is obtained from the calibrated histogram.
Optionally, the peak of the histogram may be calibrated with a fixed value when the triggering time of the peak of the histogram is greater than a threshold.
Optionally, the histogram calibration function may be used to calibrate the peak of the histogram when the triggering time of the peak of the histogram is less than a threshold.
Optionally, the histogram calibration function may represent a correspondence between the deviation and the peak trigger rate, or may be an interpolation function.
The beneficial effect of this application is:
the embodiment of the application provides a system and a method for measuring flight time distance, and the system for measuring flight time distance comprises: the histogram statistic module, the histogram calibration module and the detection distance calculation module;
the histogram statistics module generates a histogram based on a trigger time;
the histogram calibration module is used for calibrating the histogram peak value;
the detection distance calculation module obtains a detection distance based on the calibrated histogram. Therefore, the calibration of the triggering time error is realized, and more accurate detection distance can be obtained according to the propagation speed of light and the echo time.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained from the drawings without inventive effort.
Fig. 1 is a schematic functional block diagram of a time-of-flight distance measurement system according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram of a statistical histogram according to an embodiment of the present disclosure;
FIG. 3 is a graph illustrating the deviation of TOF estimates from the true TOF at different distances according to an embodiment of the present disclosure;
figure 4 provides a background light of 300lux for this embodiment,
Figure BDA0002558083290000041
a schematic of the relationship to distance; fig. 5 is a corresponding relationship between the deviation and the peak trigger rate when the background light provided by the present embodiment is 300 lux;
fig. 6 is a schematic flowchart of a time-of-flight distance measurement method according to an embodiment of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, generally described and illustrated in the figures herein, can be arranged and designed in a wide variety of different configurations.
Thus, the following detailed description of the embodiments of the present application, presented in the accompanying drawings, is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
Fig. 1 is a functional block diagram of a time-of-flight distance measurement system according to an embodiment of the present disclosure. As shown in fig. 1, the time-of-flight distance measurement system includes: a light emitting module 110, a light receiving module 120, a histogram statistic module 130, a histogram calibration module 140, and a detection distance calculation module 150.
The light emitting module 110 provides a light beam to the target space to illuminate the object in the space, at least a portion of the light beam is reflected by the object to form a reflected light beam, and at least a portion of the light signal (photons) of the reflected light beam is received by the light receiving module 120. The light receiving module 120 may include a single photon avalanche photodiode (SPAD) in this embodiment.
The light emitting module 110 emits a pulse laser with extremely short duration, the pulse laser is reflected by a target object after passing through the distance L to be measured, a pulse laser signal is emitted and received by the photoelectric detector of the pixel, and the distance L between the target object and the emitting position is obtained by calculating the time t between laser emission and the arrival of an echo signal.
The Geiger ranging method of DTOF adopts SPAD to carry out single photon detection, namely measuring the arrival time t _ TOF of the first returned photon after the pulse is sent out, and the measuring distance is
Figure BDA0002558083290000061
Considering the influence of background light and light detection efficiency, histogram statistics is usually performed by performing multiple measurements, and the value of t _ TOF is determined according to the histogram. The histogram statistics module 130 counts the time when SPAD is triggered and draws a histogram. The histogram calibration module 140 calibrates the histogram obtained by the histogram statistics module 130 because the emission energy and the influence of the background light have an error in the histogram obtained by the histogram statistics module 130. And determining the value of t _ TOF according to the calibrated histogram. The detection distance calculation module 150 calculates the detection distance according to formula (1), wherein the value of t _ TOF is obtained from the calibrated histogram.
Fig. 2 is a schematic diagram of a statistical histogram according to an embodiment of the present disclosure. As shown in FIG. 2, the estimated time-of-flight values t1 and t1 may be trigger times corresponding to peaks in the histogram or may be a time average value around the peaks, for example, the number of triggers of the peaks in the histogram is N as shown in FIG. 2, and t1 may be determined according to the average value of the trigger times corresponding to the number of triggers of N, N-1, N-2.
Fig. 3 is a schematic diagram of the deviation of the TOF estimation value obtained from the peak value from the true TOF at different distances according to the embodiment of the present application. As shown in fig. 3, under the background light of 300lux, the deviation of the TOF estimation values obtained from the peak value at different distances from the real TOF is not large after 1m distance, so that the statistically obtained histogram can be calibrated by using a fixed value in this embodiment when the distance is greater than 1 m. Assuming that the pulse width γ of the emission signal and t0 is the trigger time at a distance of 1m in this embodiment, the histogram calibration module 140 can calibrate the peak value of the histogram with a fixed value γ/2 when t1> t0 in this embodiment. The detection distance calculation module 150 may obtain the detection distance according to equation 2.
Figure BDA0002558083290000071
As shown in fig. 3, when t1< t0, it can be seen that the deviation of the TOF estimation value from the true TOF is relatively large, and cannot be calibrated with a fixed value. The statistically derived histogram peaks may be calibrated using a calibration function. Setting the background light energy estimation as e _ bg and the peak triggering frequency as N _ max, obtaining the average number of photons N _ B of the background light before t1 according to the background light energy estimation result and the system parameters, thereby obtaining the estimation value of the effective observation frequency as
Figure BDA0002558083290000072
Where PDE is the trigger probability for each photon, the number of detections is N, and the number of valid observations, N _ s, refers to the number of observations (or SPADs) that a valid signal can use. Of course Ns can also be derived from histogram statistics, the total number of observations minus the total number of triggers before the active trigger period (i.e., before t1- γ). A peak trigger rate of
Figure BDA0002558083290000073
The detection distance calculation module 150 may obtain the detection distance calculated from the calibrated histogram according to formula (4), where F is a calibration function:
Figure BDA0002558083290000081
where the value of t0 and the numerical expression of function F represent the correspondence between the deviation and the peak trigger rate, which can be obtained in advance from simulation.
Figure 4 provides a background light of 300lux for this embodiment,
Figure BDA0002558083290000082
schematic of the relationship with distance. When t1 is less than 1m corresponding to a time of flight, i.e. 1 x 2/c, as shown in fig. 4, it can be seen that the peak firing rate is
Figure BDA0002558083290000083
Has a one-to-one correspondence with the distance, so that it can be used
Figure BDA0002558083290000084
The F function of the histogram to obtain a more accurate measurement distance according to the calibrated histogramAnd (5) separating.
Fig. 5 shows the corresponding relationship between the deviation and the peak trigger rate when the background light provided by the present embodiment is 300 lux. As can be seen from FIG. 5, the peak trigger rate is when t1 is less than 1m corresponding to a time of flight
Figure BDA0002558083290000085
Has a one-to-one correspondence with the deviation, so that it can be used
Figure BDA0002558083290000086
The peak value of the histogram is calibrated, and more accurate measurement distance is obtained according to the calibrated histogram.
In summary, based on the calibration of the peak value of the histogram, a more accurate detection distance can be obtained, in the above embodiment, the detection distance is obtained by using the triggering time of the peak value of the histogram, and a certain time width of the histogram is known in advance, so that even if the triggering rising edge of the peak value of the histogram is not included, other positions of the peak value can be used to obtain the detection distance, and the present application is not limited thereto.
The above embodiment t0 is set to the trigger time of 1m, which may be different in practical situations, and is not limited in this application. In addition, in embodiments of the present application the calibration function is an
Figure BDA0002558083290000091
The function concerned, in other embodiments, does not limit the necessary sum of the F function
Figure BDA0002558083290000092
It is related.
Fig. 6 is a schematic flowchart of a time-of-flight distance measurement method according to an embodiment of the present application. The method can be applied to the flight time distance measurement system, the basic principle and the generated technical effect of the method are the same as those of the corresponding system embodiment, for the sake of brief description, the parts which are not mentioned in the embodiment can refer to the corresponding parts in the system embodiment
And (4) carrying out the following steps. As shown in fig. 6, the time-of-flight distance measurement method includes:
s101, emitting a light beam by the light emitting module.
S102, the light receiving module receives the light beam reflected by the space object.
And S103, obtaining a histogram based on the triggering time of the emitted back light beam to the receiving module.
S104, calibrating the peak value of the histogram
Optionally, the histogram is calibrated with a fixed value when the peak trigger time of the histogram is greater than a given threshold.
Optionally, the histogram is calibrated with a calibration function when the peak trigger time of the histogram is less than a given threshold.
And S105, acquiring the detection distance according to the calibrated histogram.
The method is applied to the system for measuring the flight time distance provided by the foregoing embodiment, and the implementation principle and technical effect are similar, which are not described herein again.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application. It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures. The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims (12)

1. A time-of-flight distance measurement system, comprising: the histogram statistic module, the histogram calibration module and the detection distance calculation module;
the histogram statistics module generates a histogram based on a trigger time;
the histogram calibration module is used for calibrating the histogram peak value;
the detection distance calculation module obtains a detection distance based on the calibrated histogram.
2. The time-of-flight distance measurement system of claim 1, wherein a peak of the histogram may be calibrated with a fixed value when a peak trigger time of the histogram is greater than a threshold value.
3. The time-of-flight distance measurement system of claim 1, wherein a peak of the histogram may be calibrated with a histogram calibration function when a peak trigger time of the histogram is less than a threshold.
4. A time-of-flight distance measurement system according to claim 3, wherein the histogram calibration function may be representative of a correspondence between deviation and peak trigger rate or may be an interpolation function.
5. The time-of-flight distance measurement system of claim 4, wherein the peak trigger rate is a ratio of a peak trigger count and a valid trigger count in the histogram.
6. A time-of-flight distance measurement system according to claim 5, in which the number of active triggers is the number of observations or the number of active SPADs available for use by the active signal.
7. The time-of-flight distance measurement system of claim 6, wherein the effective number of triggers is derived from the background light energy estimate and system parameters.
8. The time-of-flight distance measurement system of claim 1, wherein the probe distance may be calculated from a peak value of the histogram after calibration.
9. A method of time-of-flight distance measurement, comprising the steps of:
obtaining a histogram based on the trigger time;
calibrating the peak value of the histogram;
the detection distance is obtained from the calibrated histogram.
10. The method of time-of-flight distance measurement according to claim 9, wherein the peak of the histogram may be calibrated with a fixed value when the peak trigger time of the histogram is greater than a threshold value.
11. The method of time-of-flight distance measurement according to claim 9, wherein the histogram peak may be calibrated with the histogram calibration function when a peak trigger time of the histogram is less than a threshold.
12. The method of claim 9, wherein the histogram calibration function is a function representing the relationship between deviation and peak trigger rate or an interpolation function.
CN202010599501.1A 2020-06-28 2020-06-28 Flight time distance measuring system and method Pending CN113848558A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114509740A (en) * 2022-04-18 2022-05-17 深圳阜时科技有限公司 Time-of-flight offset correction method, ToF device, electronic apparatus, and storage medium

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114509740A (en) * 2022-04-18 2022-05-17 深圳阜时科技有限公司 Time-of-flight offset correction method, ToF device, electronic apparatus, and storage medium
CN114509740B (en) * 2022-04-18 2022-08-09 深圳阜时科技有限公司 Time-of-flight offset correction method, ToF device, electronic apparatus, and storage medium

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