CN111443361A

CN111443361A - Time-of-flight ranging method and related system

Info

Publication number: CN111443361A
Application number: CN202010558785.XA
Authority: CN
Inventors: 王浩任; 李宗德; 杨孟达
Original assignee: Shenzhen Goodix Technology Co Ltd
Current assignee: Shenzhen Goodix Technology Co Ltd
Priority date: 2020-06-18
Filing date: 2020-06-18
Publication date: 2020-07-24
Anticipated expiration: 2040-06-18
Also published as: CN111443361B

Abstract

The application discloses a time-of-flight distance measurement method and a time-of-flight distance measurement system, which are used for measuring the distance between a target object and the time-of-flight distance measurement system. The time-of-flight ranging method comprises the following steps: sensing a reflected light signal reflected by the target object through an optical sensor, and obtaining a phase shift between the reflected light signal and an incident light signal, wherein the phase shift is less than 2 pi; obtaining a plurality of first depth information according to the phase shift, wherein the plurality of first depth information are phase-mixed depth information; obtaining, by a processing unit, an aberration of the reflected light signal corresponding to the incident light signal; obtaining second depth information according to the aberration; and obtaining the distance from the plurality of first depth information according to the second depth information.

Description

Time-of-flight ranging method and related system

Technical Field

The present disclosure relates to a method and system for measuring a distance between a target object and a target object, and more particularly, to a method and system for measuring a distance between a target object and a target object.

Background

The time-of-flight ranging is implemented by measuring the phase difference between incident light and reflected light through a sensor, and has high calculation complexity, large power consumption and long calculation time. In order to increase the accuracy, the prior art raises the frequency of the optical signal. However, increasing the frequency of the optical signal causes a wavelength drop, so that the problem of phase ambiguity becomes severe because the wavelength becomes shorter at the same measurement distance. Therefore, the prior art senses a plurality of optical signals with different frequencies to ensure the phase accuracy, and accordingly, the power consumption and the operation time are increased. How to solve the above problems without affecting accuracy has become an important work item in the art.

Disclosure of Invention

One objective of the present application is to disclose a time-of-flight ranging method and a related system, so as to solve the technical problem of time and power consumption of the time-of-flight ranging method in the prior art.

An embodiment of the application discloses a time-of-flight distance measurement method for measuring a distance to a target object. The time-of-flight ranging method comprises the following steps: sensing a reflected light signal reflected by the target object through an optical sensor, and obtaining a phase shift between the reflected light signal and an incident light signal, wherein the phase shift is less than 2 pi; obtaining a plurality of first depth information according to the phase shift; obtaining, by a processing unit, an aberration (disparity) of the reflected light signal corresponding to the incident light signal; obtaining second depth information according to the aberration; and obtaining the distance from the plurality of first depth information according to the second depth information.

An embodiment of the present application discloses a time-of-flight ranging system for measuring a distance to a target object. The time-of-flight ranging device comprises an optical sensor and a processing unit. The optical sensor is used for sensing a reflected light signal reflected by a target object. The processing unit is used for obtaining a phase shift between the reflected light signal and the incident light signal and an aberration of the reflected light signal corresponding to the incident light signal according to the sensed reflected light signal, obtaining a plurality of first depth information according to the phase shift, and obtaining second depth information according to the aberration, wherein the phase shift is smaller than 2 pi. The processing unit is further used for obtaining the distance from the plurality of first depth information according to the second depth information.

Specifically, the time-of-flight ranging method disclosed by the present application solves the problem of phase ambiguity (phase ambiguity) of the time-of-flight distance in a novel manner, thereby reducing power consumption and processing time.

Drawings

Fig. 1 is a block diagram of an embodiment of a time-of-flight ranging system of the present application.

Fig. 2 is a waveform diagram of an optical signal in a sensing operation.

Fig. 3 is a schematic operational diagram of an embodiment of a time-of-flight ranging system of the present application.

Fig. 4 is a geometric simulation of the time-of-flight ranging system of the present application.

Fig. 5 is a flowchart of a time-of-flight ranging method according to the present application.

Detailed Description

The following disclosure provides various embodiments or illustrations that can be used to implement various features of the disclosure. The embodiments of components and arrangements described below serve to simplify the present disclosure. It is to be understood that such descriptions are merely illustrative and are not intended to limit the present disclosure. For example, in the description that follows, forming a first feature on or over a second feature may include certain embodiments in which the first and second features are in direct contact with each other; and may also include embodiments in which additional elements are formed between the first and second features described above, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or characters in the various embodiments. This 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.

The existing three-dimensional image sensor has three main implementation modes: stereoscopic binocular, structured light and time of flight ranging (ToF). Generally, in the implementation of time-of-flight ranging, a sensor is used to measure the time of flight of an optical signal, and then the time-of-flight distance, i.e. the distance between the sensor and the measured object, is calculated by combining the speed of light, wherein the time of flight of the optical signal is obtained by the inverse derivation of the phase delay between the emitted laser and the returned laser.

However, the distance between the target object (i.e., the object to be measured) may delay the phase by more than one period (i.e., 2 π), which is a phase ambiguity caused by phase aliasing.

Therefore, it is necessary to use the aberration of the optical signal to help determine that the phase delay overlaps several cycles to obtain the distance to the target. The details thereof are explained below.

Fig. 1 is a block diagram of an embodiment of a time-of-flight ranging system 100 according to the present disclosure, referring to fig. 1, the time-of-flight ranging system 100 is configured to sense a phase shift θ of an incident light signal L T and a reflected light signal L R, and calculate a distance to a target 101 according to a frequency of the incident light signal L T and the phase shift θ, wherein the incident light signal L T and the reflected light signal L R are laser signals, generally, the phase shift θ is less than 2 π, but as described above, if the frequency of the incident light signal L T is higher or the measured distance is too large, the actual phase delay may be greater than 2 π, i.e., the phase delay is equal to θ +2n (n is an integer), for example, when the phase delay is equal to θ +2n π, the depth information Z1 is calculated from the target 101, and when the phase delay is equal to [ θ +2 (n + 1) π ], the depth information Z Z2. is calculated from the depth information Z2 and the depth information Z1 is different by a wavelength of the incident light signal L T, and the length of the calculated for each time frame length of the time-of the calculated by the time-of the flight ranging system 100 is reduced.

The flight ranging system 100 includes a light emitting device 120, an optical sensor 140, and a processing unit 160, the light emitting device 120 is configured to emit an incident light signal L T to a target 101, the optical sensor 140 is configured to receive a reflected light signal L R reflected from the target 101 and generate an electronic signal according to the received reflected light signal L R, the processing unit 160 is coupled to the light emitting device 120 and the optical sensor 140 and configured to control operations of the light emitting device 120 and the optical sensor 140, such as controlling the light emitting device 120 and the optical sensor 140 to be turned on and off by a clock signal, the processing unit 160 is further configured to process the electronic signal generated by the optical sensor 140, in some embodiments, the processing unit 160 includes a Micro Control Unit (MCU), a Central Processing Unit (CPU), or a Graphics Processing Unit (GPU).

Since the phase of the incident light signal L T emitted by the light emitting device 120 is known, the phase shift θ can be obtained when the optical sensor 140 receives the reflected light signal L R, for clarity, the incident light signal L T and the reflected light signal L R are represented by the following signal equations 1-2.

(equation 1)

(equation 2)

Where A and A 'are amplitudes, f is frequency, T is time, and B is noise generated in the time-of-flight ranging system 100, specifically, when the light emitting device 120 generates the incident light signal L T, system noise B is generated along with the system noise B, which becomes B' after being reflected by the target, and is reflected back to the optical sensor 140 along with the reflected light signal L R.

Referring to fig. 2, when measuring the phase shift θ, the light emitting device 120 generates an incident light signal L T to irradiate the target 101, and the optical sensor 140 respectively senses light intensities Q1, Q2, Q3, and Q4 of the reflected light signal L R varying with the phase at four different time points T1, T2, T3, and T4. in some embodiments, the light emitting device 120 generates the incident light signal L T to irradiate the target 101 four times, and the optical sensor 140 senses only one of the light intensities Q1, Q2, Q3, and Q4 (i.e., four images are obtained) in each irradiation, since the frequency f of the incident light signal L T is known and the frequency of the reflected light signal L R is not changed, the amplitude a ', the phase shift θ, and the system noise B' can be obtained by substituting the reflected light intensities Q1, Q2, Q3, and Q4 into the equation 2 of the incident light signal L R at the time points T1, T2, T3, and T4, wherein the phase shift θ is smaller than pi.

For ease of calculation, time t1 is chosen half a cycle from t3, converted to a phase change, from time t1 to t3, and a phase change of π, such as from 0 to 180, and correspondingly, time t2 and t4 are also chosen half a cycle, such as from 90 to 270, under which conditions reflected light signal L R equation 2 can be solved as follows.

(equation 3)

(equation 4)

(equation 5)

Where k is the phase change between time t2 and t1, the parameters A1-A4 are expressed by the following equations.

(equation 6)

(equation 7)

(equation 8)

(equation 9)

In some embodiments, k may be set to 0.5 π to further simplify the parameters of the reflected light signal L R equation as follows.

(equation 10)

(equation 11)

The phase shift θ can be calculated from the light intensities Q1-Q4, so that multiple (multiple different n) possible values of the phase delay θ +2n π can be known. The processing unit 160 obtains a plurality of possible depth information z (n) by phase delaying θ +2n pi. The depth information z (n) is represented by the following equation.

(equation 12)

Where c is the speed of light.

However, the time-of-flight ranging system 100 cannot determine how much n is in the true phase delay θ +2n pi based on the incident light signal L T and the reflected light signal L R alone, and therefore the time-of-flight ranging system 100 needs to obtain the true distance z from a plurality of possible depth information through the aberration d between the incident light signal L T and the reflected light signal L R.

Referring to fig. 3, to obtain the aberration d between the incident light signal L T and the reflected light signal L R, the light emitting device 120 generates light with a predetermined pattern (pattern), such as structured light (structured light), as the incident light signal L T, and the optical sensor 140 senses the reflected light signal L R, so that the processing unit 160 obtains the aberration d according to the pattern on the reflected light signal L R and the pattern on the incident light signal L T.

The light emitting device 120 includes a light source 122 and an optical microstructure 124. the light source 122 generates a laser signal L S to irradiate the optical microstructure 124. the optical microstructure 124 changes a traveling path of the laser signal L S to generate an incident light signal L T. the incident light signal L T has a predetermined pattern, so that energy is concentrated in the predetermined pattern. in the embodiment of FIG. 3, the incident light signal L T is projected on the target 101 to form a spot pattern of a plurality of spots S1-S5 separated from each other.

By way of example, and not limitation, the optical microstructures 124 may include Diffractive Optical Elements (DOE) or Refractive Optical Elements (ROE) for cone-diffracting (or cone-refracting) the laser signal L S to generate the incident optical signal L T, such that the incident optical signal L T may form a plurality of spots separated from each other when projected on the target 101. in some embodiments, a collimating lens may be disposed between the light source 122 and the optical microstructures 124 for shaping the laser signal L S into parallel light.

For example, in some embodiments, the laser signal L S generated by the light source 122 includes a laser array composed of M lasers, as the laser array passes through the optical microstructure 124, the optical microstructure 124 replicates each laser in the laser array into n spots, M and n being positive integers, to form M spots on the target 101.

After the optical sensor 140 receives the reflected light signal L R having the plurality of patterns of spots S1-S5, the processing unit 160 calculates the aberration d of each of the patterns of spots S1-S5 using epipolar geometry (epipolar geometry), and then calculates the depth information Z' using the aberration, which is expressed by the following equation.

(equation 13)

Where b is the baseline distance in the epipolar geometry and F is the focal length of the optical sensor 140. For example, referring to fig. 4, the offset distance between the coordinates of the light spot S1 on the optical microstructure 124 (the first imaging plane) S1a and the coordinates on the optical sensor 140 (the second imaging plane) S1b is an aberration d, wherein the position of the optical sensor 140 corresponding to S1a is S1a ', and the aberration d is the difference between S1a' and S1 b. The distance Z' of the light spot S1 from the distance measuring system 100 in flight on the target 101 is known from the baseline distance b and the focal length F, where the baseline distance b is the distance from the light source 122 to the virtual focus VF behind the optical sensor 140.

Since the epipolar geometry is used to calculate the aberration d on the basis of geometric optics, the calculated aberration d is independent of the phase of the optical signal, and thus the depth information Z' does not have the problem of phase ambiguity. However, since geometric optics itself has errors at all times, the calculation of the depth information Z' has a certain degree of error. In this case, the processing unit 160 can determine which of the depth information Z (n) is the real distance Z according to the depth information Z'.

In the process of obtaining the real distance Z, the processing unit 160 compares the depth information Z 'with a plurality of depth information Z (n) with different values of n, selects one of the depth information Z (n) that is closest to the depth information Z', and finally determines the selected depth information Z (n) as the real distance Z. In some embodiments, the processing unit 160 subtracts the depth information Z ' (n) from the depth information Z ' to obtain absolute values, selects the smallest one of the absolute values, and determines the depth information Z ' (n) corresponding to the selected absolute value as the real distance Z.

For the same incident light signal L T and the target 101, the aberration d is larger when the distance Z is close and the aberration d is smaller when the distance Z is far, for the example of FIG. 1, the aberration d reflected by the spots S1-S5 at the depth of Z1 is larger than the aberration d reflected by the spots S1-S5 projected on Z2. to avoid the interference of the spots S1-S5 reflected back to the optical sensor 140, the illuminator 120 must control the intervals between the spots S1-S5 not to be too close, the spots S1-S5 reflected back to the optical sensor 140 can be identified with certainty, in particular, because the aberration d is in inverse proportion to the distance Z, the illuminator 120 determines the intervals between the spots S1-S638 according to the shortest measured distance Zmin of the distance measuring system 100 when flying, and ensures that the maximum spot S1-S9/S5 is not affected by the adjacent spots S636 (S3527/S5).

In some embodiments, light emitting device 120 controls incident light signal L T to have a pattern of regularly arranged spots in some embodiments, light emitting device 120 controls incident light signal L T to have a pattern of irregularly arranged spots in which all spots are spaced from adjacent spots by the limit of the shortest measured distance Zmin of time-of-flight ranging system 100.

In summary, compared to the prior art, the time-of-flight ranging system 100 does not need to additionally emit an optical signal with a frequency f different from the frequency f to assist in determining the value n, thereby reducing the number of times of irradiation of the incident optical signal L T, and utilizes the aberration d to assist in solving the problem of phase ambiguity, so that the time-of-flight ranging system 100 obtains the true distance z from the target without reducing the sensing accuracy because the number of times of irradiation of the incident optical signal L T is reduced, thereby reducing the system power consumption without reducing the frame rate.

As can be seen from the above description, the time-of-flight ranging system 100 of the present application may use the time-of-flight ranging method 500 of fig. 5 to sense the distance Z from the target 101, first, the light emitting device 120 generates the incident light signal L T, irradiates the target 101 and generates the reflected light signal L R (S510), the optical sensor 140 then senses the reflected light signal L R, so that the processing unit 160 obtains the phase shift θ between the reflected light signal L R and the incident light signal L T according to the sensed reflected light signal L R (S520), and obtains a plurality of depth information Z ' (S550) according to the phase shift θ (S530), the processing unit 160 further obtains the aberration d between the reflected light signal L R and the incident light signal L T by using the antipode geometry (S540), and obtains the depth information Z ' (S550) according to the aberration d, and finally, obtains the distance Z from the plurality of depth information Z ' (Z) (S101) according to the depth information Z560).

Claims

1. A time-of-flight ranging method for measuring a distance to a target object, comprising:

sensing, by an optical sensor, a reflected light signal reflected by the target object and obtaining a phase shift between the reflected light signal and an incident light signal, wherein the phase shift is less than 2 pi;

obtaining a plurality of first depth information according to the phase shift, wherein the plurality of first depth information are phase-aliasing depth information;

obtaining, by a processing unit, an aberration of the reflected light signal corresponding to the incident light signal;

obtaining second depth information according to the aberration; and

and acquiring the distance from the plurality of pieces of first depth information according to the second depth information.

2. The time-of-flight ranging method of claim 1, wherein the incident optical signal is a structured optical signal.

3. The time-of-flight ranging method of claim 1, wherein obtaining the distance from the plurality of first depth information comprises:

comparing the plurality of first depth information with the second depth information;

selecting a first depth information of the plurality of first depth information that is closest to the second depth information; and

determining the selected first depth information as the distance.

4. The time-of-flight ranging method of claim 1, further comprising:

illuminating, by a light emitting device, the incident light signal to the target object and generating the reflected light signal, wherein the incident light signal has a plurality of light spots, wherein the plurality of light spots have a minimum interval therebetween, wherein the minimum interval is associated with a shortest measurement distance of the time-of-flight ranging method, and wherein the plurality of light spots of the incident light signal do not overlap each other after being reflected by the optical sensor after the shortest measurement distance is reflected by the optical sensor.

5. The time-of-flight ranging method of claim 4, wherein obtaining, by the processing unit, the aberration of the reflected light signal corresponding to the incident light signal comprises:

and obtaining the aberration of the plurality of light spots by utilizing the epipolar geometry according to the distance between the light-emitting device and the optical sensor.

6. The time-of-flight ranging method of claim 4, wherein illuminating the incident light signal to the target object and generating the reflected light signal further comprises:

generating a laser signal by a light source, wherein the laser signal comprises a laser array consisting of M lasers; and

changing the traveling route of the laser signal through an optical microstructure to generate the incident light signal, wherein the plurality of light spots are converted into M x n light spots by the laser array through the optical microstructure,

wherein M and n are positive integers.

7. The time-of-flight ranging method of any one of claims 4-6, wherein the plurality of light spots are regularly arranged.

8. The time-of-flight ranging method of claim 1, further comprising:

irradiating the incident light signal to the target 4 times by a light emitting device,

wherein sensing the reflected light signal reflected by the target object further comprises:

in each illumination, the reflected light signal is sensed in a first phase, a second phase, a third phase and a fourth phase, respectively, wherein the third phase is different from the first phase by pi, and the fourth phase is different from the second phase by pi.

9. The time-of-flight ranging method of claim 8, wherein the second phase differs from the first phase by 0.5 pi.

10. A time-of-flight ranging system for measuring a distance to a target object, comprising:

an optical sensor to sense a reflected light signal reflected by the target object;

a processing unit for obtaining a phase shift between the reflected light signal and an incident light signal and an aberration of the reflected light signal corresponding to the incident light signal according to the sensed reflected light signal, obtaining a plurality of first depth information according to the phase shift, and obtaining a second depth information according to the aberration, wherein the phase shift is less than 2 pi, and the plurality of first depth information are phase-mixed depth information,

the processing unit is further configured to obtain the distance from the plurality of first depth information according to the second depth information.

11. The time-of-flight ranging system of claim 10, wherein the incident optical signal is a structured optical signal.

12. The time-of-flight ranging system of claim 10, wherein the processing unit is further configured to compare the plurality of first depth information with the second depth information, select a first depth information from the plurality of first depth information that is closest to the second depth information, and determine the selected first depth information as the distance.

13. The time-of-flight ranging system of claim 10, further comprising:

a light emitting device for illuminating the incident light signal to the target object to generate the reflected light signal, wherein the incident light signal has a plurality of light spots, wherein the light spots have a minimum interval therebetween, wherein the minimum interval is associated with a shortest measurement distance of the time-of-flight ranging method, and wherein the light spots of the incident light signal do not overlap with each other after being reflected by the optical sensor after the shortest measurement distance is reflected by the optical sensor.

14. The time-of-flight ranging system of claim 13, wherein the processing unit further derives the aberrations of the plurality of light points using epipolar geometry based on a distance between the light emitting device and the optical sensor.

15. The time-of-flight ranging system of claim 13, wherein the light emitting device comprises:

a light source to generate a laser signal, wherein the laser signal comprises a laser array consisting of M lasers; and

an optical microstructure for changing the traveling path of the laser signal to generate the incident light signal, wherein the plurality of light spots are converted into M x n light spots by the laser array through the optical microstructure,

wherein M and n are positive integers.

16. The time-of-flight ranging system of any one of claims 13-15, wherein the plurality of light points are regularly arranged.

17. The time-of-flight ranging system of claim 11, further comprising:

a light emitting device for irradiating the incident light signal to the target 4 times,

the optical sensor is further configured to sense the reflected light signals in a first phase, a second phase, a third phase and a fourth phase during each illumination, wherein the third phase is different from the first phase by pi, and the fourth phase is different from the second phase by pi.

18. The time-of-flight ranging system of claim 17, wherein the second phase differs from the first phase by 0.5 pi.