WO2022160611A1 - 一种基于时间融合的距离测量方法、系统和设备 - Google Patents

一种基于时间融合的距离测量方法、系统和设备 Download PDF

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WO2022160611A1
WO2022160611A1 PCT/CN2021/106027 CN2021106027W WO2022160611A1 WO 2022160611 A1 WO2022160611 A1 WO 2022160611A1 CN 2021106027 W CN2021106027 W CN 2021106027W WO 2022160611 A1 WO2022160611 A1 WO 2022160611A1
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distance
error
time
photon
photons
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PCT/CN2021/106027
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English (en)
French (fr)
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刘浏
闫敏
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深圳奥锐达科技有限公司
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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
    • 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
    • G01S7/495—Counter-measures or counter-counter-measures using electronic or electro-optical means

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  • the present application relates to the technical field of ranging, and in particular, to a distance measurement method, system and device based on time fusion.
  • the time of flight principle can be used to measure the distance of the target to obtain a depth image containing the depth value of the target, and the distance measurement system based on the time of flight principle has been widely used in consumer electronics, unmanned aerial vehicles, AR/VR and other fields.
  • the distance measurement system based on the time-of-flight principle usually includes an emitter and a collector.
  • the emitter is used to emit a pulsed beam to illuminate the target field of view, and the collector is used to collect photons in the reflected beam, and calculate the flight time of the photon from the emission to the reflection to calculate the object. the distance.
  • the time-to-digital converter is used to record the flight time of photons from emission to collection and generate photon signals, and use the photon signals to find the corresponding time bin (time interval) in the histogram circuit, so that the The photon count value is increased by 1.
  • the histogram of the photon count corresponding to the time signal can be obtained statistically, and the flight time of the photon from the emission to the reception can be calculated according to the histogram to further calculate the distance of the object.
  • the advantage is that it has high sensitivity, and even echoes of the order of single photons can respond to cause avalanches, but when the echo signals are of the order of single photons, due to the quantum nature of photons, The signal photons in the echo are randomly distributed in the signal pulse, resulting in the randomness of the time distribution of single photon detection, so it is necessary to reduce the random error (measurement error) by photon counting (TCSPC).
  • the Poisson noise jitter of the signal photons becomes the main factor affecting the ranging accuracy; when the ambient light is strong, the Poisson noise of a large number of ambient photons caused by the ambient light Jitter also affects ranging accuracy.
  • the difference between Poisson noise and common Gaussian noise is that the commonly used filtering algorithms have limited effect.
  • the methods to reduce the Poisson noise jitter include increasing the number of repeated detections and averaging the distances of multiple measurements, so as to reduce the measurement error and improve the ranging accuracy. However, these current methods will affect the frame rate of the system.
  • the present application proposes a distance measurement method, system and device based on time fusion to solve at least one technical problem existing in the above-mentioned prior art.
  • a distance measurement method based on time fusion comprising: calculating the time of flight of photons from being emitted to being received according to a histogram, and calculating the distance of a target according to the time of flight; wherein the histogram includes continuous time intervals, and the The time interval includes the count value of photons in the pulse beam collected by the collector after the pulse beam emitted by the transmitter is reflected by the target; the measurement error generated when measuring the distance of the target is calculated and set according to the measurement error Error threshold; calculate the distance difference between the measured distance of the current frame and the measured distance of the historical frame; compare the distance difference with the error threshold, and output the final target distance according to the comparison result.
  • the measurement error is calculated according to the jitter error of the single photon distribution and the number of detected signal photons, and the specific formula is:
  • ⁇ t is the standard deviation of ranging, which is used to characterize the measurement error; ⁇ each is the jitter error of single photon distribution; N s characterizes the number of detected signal photons, according to the echo interval corresponding to the pulse beam in the histogram The sum of photon counts within is determined.
  • the number of signal photons is equal to the sum of photon counts in the echo interval minus the total number of noise photons in the echo interval; wherein the total number of noise photons in the echo interval is equal to the histogram The number of noise photons contained in each time interval in multiplied by the number of time intervals contained in the echo interval.
  • the noise photon count is calculated by: selecting a local area away from the pulse peak position from the histogram; calculating the total photon count in the local area according to the number of time intervals in the local area Calculate the mean value, and denote the number of noise photons; or, calculate the number of noise photons by the following method: select an area other than the pulse position in the histogram, and calculate the total photon count value in this area according to the time in this area. The number of intervals is averaged and recorded as the number of noise photons.
  • the jitter error of the single photon distribution is calculated by:
  • T pulse represents the pulse duration, that is, the pulse width;
  • K represents the quantization parameter;
  • the jitter error of the single-photon distribution is calculated by the method of error superposition; wherein, the error term for error superposition includes the jitter error of the signal photon distribution, the jitter error of the transmitted pulse waveform, the single-photon response jitter error, and the noise photon count. error, avalanche pulse waveform jitter error, TDC timing jitter error, or quantization error accumulated in the histogram.
  • the calculating the distance difference between the measured distance of the current frame and the measured distance of the historical frame includes:
  • ⁇ D represents the distance difference
  • D current is the measured distance of the current frame
  • D previous is the measured distance of the historical frame; preferably, the historical frame is the previous frame of the current frame.
  • the comparing the distance difference with an error threshold, and outputting the final target distance according to the comparison result includes: when the distance difference is less than or equal to the error threshold, measuring the current frame The distance and the measured distance of the historical frame are weighted and fused to output the final target distance; when the distance difference is greater than the error threshold, the measured distance of the current frame is directly output as the final target distance, and the measured distance of the historical frame is used. Updates to the measured distance for the current frame.
  • a distance measurement system based on time fusion comprising: a transmitter for emitting a pulsed beam towards a target; a collector for collecting photons in the pulsed beam reflected back by the target and forming a photon signal; a processing circuit, and The transmitter and the collector are connected to process the photon signal to form a histogram, and perform the steps of the aforementioned distance measurement method based on time fusion.
  • a distance measurement device based on time fusion comprising a memory, a processor, and a computer program stored in the memory and running on the processor, the processor implementing the aforementioned time-based program when the processor executes the computer program A fused distance measurement method.
  • An embodiment of the present application provides a distance measurement method based on time fusion, including: calculating the time of flight of photons from emission to being received according to a histogram, and calculating the distance of a target according to the time of flight; wherein the histogram includes a continuous Time interval, the time interval includes the count value of photons in the pulse beam collected by the collector after the pulse beam emitted by the transmitter is reflected by the target; Set an error threshold for the measurement error; calculate the distance difference between the measurement distance of the current frame and the measurement distance of the historical frame; compare the distance difference and the error threshold, and output the final target distance according to the comparison result.
  • the application flexibly outputs the final target distance according to the comparison between the distance difference and the error threshold, which effectively reduces the measurement error caused by photon Poisson noise jitter in the continuous frame measurement process, and improves the ranging accuracy without affecting the system. affect the frame rate.
  • FIG. 1 is a schematic diagram of a distance measurement system according to an embodiment of the present application.
  • FIG. 2 is a flowchart of a distance measurement method according to an embodiment of the present application.
  • FIG. 3 is an exemplary histogram of an embodiment of the present application.
  • FIG. 1 is a schematic diagram of a distance measurement system based on time fusion according to an embodiment of the present application.
  • the distance measurement system 10 includes a transmitter 11, a collector 12 and a processing circuit 13.
  • the transmitter 11 includes a light source 111 composed of one or more lasers, and is used to emit a pulsed beam 30 to the target 20, and at least part of the pulsed beam is reflected by the target 20 to form a reflected beam 40 back to the collector 12;
  • the collector 12 includes a A pixel array 121 composed of a plurality of pixels is used to collect photons in the reflected beam 40 and output photon signals, and the processing circuit 13 synchronizes the trigger signals of the transmitter 11 and the collector 12 to calculate the required photons in the beam from emission to reception. flight duration.
  • the transmitter 11 includes a light source 111, an emission optical element 112, a driver 113, and the like.
  • the light source 111 is a VCSEL array light source chip formed by growing multiple VCSEL light sources on a single semiconductor substrate.
  • the light source 111 can emit a pulse beam at a certain frequency (pulse period) under the driving control of the driver 113, and the pulse beam is projected onto the target scene through the emission optical element 112 to form an illumination spot, wherein the emission frequency is set according to the measurement distance.
  • the collector 12 includes a pixel array 121, a filter unit 122, a receiving optical element 123, and the like.
  • the receiving optical element 123 images the spot beam reflected by the target onto the pixel array 121
  • the pixel array 121 includes a plurality of pixels for collecting photons, and the pixels can be one of APD, SPAD, SiPM and other single-photon devices for collecting photons,
  • the pixel array 121 collects photons, it is regarded as a photon detection event occurs and a photon signal is output.
  • the pixel array 121 comprises a plurality of SPADs that can respond to an incident single photon and output a photon signal indicative of the corresponding arrival time of the received photon at each SPAD.
  • a readout circuit (not shown in the figure) composed of one or more of a signal amplifier, a time-to-digital converter (TDC), a digital-to-analog converter (ADC) and other devices connected to the pixel array.
  • TDC time-to-digital converter
  • ADC digital-to-analog converter
  • These circuits can be integrated with the pixels as a part of the collector or as a part of the processing circuit 13 . For the convenience of description later, they will be regarded as a part of the processing circuit 13 .
  • the processing circuit 13 is used for receiving the photon signal and processing to calculate the flight time of the photon from emission to reception, and further calculates the distance information of the target.
  • the processing circuit 13 includes a TDC circuit and a histogram memory, the TDC circuit receives the photon signal for determining the time of flight of the photon from emission to acquisition, and generates a time code representing the time of flight information, and uses the time code to find the histogram
  • the corresponding position in the memory is added, and the value stored in the corresponding position of the histogram memory is increased by "1", and the histogram is constructed according to the position of the histogram memory as a time bin (time interval).
  • FIG. 2 is a flowchart of a distance measurement method based on time fusion according to an embodiment of the present application.
  • the distance measurement method includes the following steps:
  • the processing circuit 13 controls the transmitter 11 to emit a pulse beam toward the target area, and part of the pulse beam reflected by the target is incident on the collector 12 , and the collector 12 collects photons in the reflected pulse beam. and generate a photon signal including the time of flight of the photon; the processing circuit 13 receives the photon signal and processes it to form a histogram, the histogram includes continuous time intervals, and each time interval is used to represent the count of photons collected by the collector during the detection period value.
  • the processing circuit 13 calculates the time-of-flight of photons from emission to reception according to the histogram, wherein the calculation methods used include a peak finding method, a centroid method, a template matching method, and the like.
  • the method for calculating the photon flight time according to the histogram is not specifically limited.
  • FIG. 3 is a schematic diagram of a histogram of an embodiment of the present application.
  • the histogram can be referred to as detection data and is used to represent the temporal distribution of photons collected by the collector during the detection period.
  • the time interval 301 is in the range of ten to several tens of picoseconds, and the photon signal of a pulsed beam is correspondingly distributed in an echo interval in the histogram, and the echo interval includes a plurality of time intervals.
  • the number is determined according to the pulse duration (pulse width) of the pulse beam.
  • the pulse position corresponding to a pulse beam in the histogram is the echo interval 302 .
  • the time of the time interval where the pulse peak position is located can be selected as the flight time of the pulse beam, and the middle amount of the time interval is generally selected as the time of the time interval.
  • the pulse width of the pulse beam is 2ns
  • the size of a time interval 301 in the histogram is 100ps
  • the photon signal of one pulse is correspondingly distributed in 20 consecutive time intervals in the histogram, that is, The number of time intervals at the pulse positions in the histogram is 20.
  • the measurement errors When the distance measurement system measures the target distance, measurement errors will occur, and the measurement errors are mainly affected by the jitter error of the single-photon distribution. Since different photons are independent of each other in the distance measurement process, the use of TCSPC (Time Correlated Single Photon Counting) technology can reduce the jitter error. Therefore, when calculating the measurement error, the jitter error of the single photon distribution can be calculated first, and then The measurement error is calculated from the jitter error of the single-photon distribution. Among them, the jitter error of single photon distribution is affected by many factors, including system parameters, ambient light, and signal light intensity.
  • TCSPC Time Correlated Single Photon Counting
  • the jitter error of the single-photon distribution is mainly affected by the jitter error of the signal photon distribution, and the jitter error of the signal photon distribution is calculated according to the width of the emitted pulse beam (abbreviated as the pulse width, that is, the pulse duration), then the signal photon
  • the pulse width that is, the pulse duration
  • the jitter error of the distribution is recorded as the jitter error of the single-photon distribution, and the specific formula is:
  • ⁇ each is the jitter standard deviation of the single-photon distribution, which is used to characterize the jitter error of the single-photon distribution;
  • T pulse characterizes the pulse duration.
  • the pulse duration is determined according to the pulse half-peak width, and K represents a quantitative parameter, which can be determined through theoretical analysis or experimental measurement and calculation.
  • the measurement error is calculated according to the jitter error of the single photon distribution, and the calculation formula is:
  • ⁇ t is the standard deviation of ranging, which is used to characterize the measurement error
  • N s characterizes the number of detected signal photons, which can be determined according to the sum of photon counts in all time intervals in the echo interval corresponding to the pulse beam in the histogram; preferably The number of signal photons is equal to the sum of photon counts in the echo interval minus the total number of noise photons in the echo interval.
  • the total number of noise photons in the echo interval is determined according to the number of noise photons contained in each time interval in the histogram. Specifically, the total number of noise photons in the echo interval is equal to the number of noise photons contained in each time interval in the histogram Multiply by the number of time intervals contained within the echo interval. In one embodiment, the number of noise photons is calculated from a local area intercepted from the histogram. Specifically, a local area away from the position of the pulse peak is selected according to the position of the pulse peak in the histogram to calculate the number of noise photons.
  • the pulse peak position is in the second half of the histogram, select a local area in the first half of the histogram to calculate the number of noise photons.
  • the total number of photon counts in the area is averaged according to the number of time intervals in the local area, and recorded as the number of noise photons; similarly, if it is located in the first half, select a local area from the second half to calculate the number of noise photons.
  • the number of noise photons is calculated according to the entire time interval of the initial histogram, that is, an area other than the pulse position in the histogram is selected, and the total photon count value in this area is calculated according to the number of time intervals in this area.
  • the mean value is calculated and recorded as the number of noise photons.
  • the influencing factors affecting the jitter error of the single photon further include the jitter error of the transmitted pulse waveform, the single-photon response jitter error, the noise photon count error, the avalanche pulse waveform jitter error, the TDC timing jitter error, the histogram accumulated Therefore, the jitter error of a single photon is calculated by the error superposition method.
  • the specific calculation formula is:
  • the jitter error of a single photon is calculated by using the square sum root of multiple errors.
  • the error superposition formula at least two kinds of errors are included, one of which is the jitter error of the signal photon distribution.
  • the above-mentioned various error values may be determined according to actual measurement conditions or may be determined according to system parameters.
  • the jitter error of the transmitted pulse waveform is affected by the performance of the light source and the driver, and the jitter error of the transmitted pulse waveform can be directly determined according to the parameters of the light source and the driver in the system.
  • the single-photon response jitter error is affected by the rising edge rate of the photon response and the Schmitt trigger threshold, and is related to the design parameters of the collector.
  • the noise photon counting error is affected by the noise intensity of ambient light.
  • the number of noise photons is calculated according to the histogram, and the corresponding noise photon counting error is calculated according to the number of noise photons.
  • the TDC timing jitter error is mainly affected by the performance parameters of the TDC circuit itself, the timing accuracy of the TDC and other characteristics.
  • the TDC timing jitter error can be determined through theoretical analysis or experimental testing according to the specific design of the TDC circuit.
  • the quantization error accumulated in the histogram is related to the width of the time bin in the histogram. When the width of the time bin is greater than the time resolution of the TDC, the result of quantizing each photon count into each specific time bin will produce non-conformity. Linear error, the quantization error accumulated in the histogram can be calculated according to the width of the time bin in the histogram.
  • a distance value can be obtained for each frame measured, but due to the existence of measurement errors, it may lead to measurement errors between the distance values of multiple frames, so based on the continuity of the measurement time, the time fusion method is used to correct Measurement error.
  • the calculation formula is:
  • D current is the measurement distance of the current frame
  • D previous is the measurement distance of the historical frame
  • the historical frame is the previous frame of the current frame.
  • the distance difference ⁇ D calculated in step S3 is compared with the error threshold Th , and the target distance is output according to the comparison result.
  • the distance difference ⁇ D is less than or equal to the error threshold Th , it can be considered that the distance measurement system and the target are relatively static, there is no obvious spatial movement, and the deviation mainly comes from the measurement error.
  • the final target distance D output is output :
  • D output represents the target distance
  • ⁇ is the weight for fusion.
  • the measured distance of the historical frame is updated to D output , which is used as a reference for data fusion of the next frame.
  • the distance difference ⁇ D is greater than the error threshold Th .
  • the target has undergone significant spatial movement, including movement along the depth direction or moving out of the field of view.
  • the distance difference is no longer mainly affected by the measurement error.
  • the measurement distance D current of the current frame is directly output as the target distance, and the measurement distance of the historical frame is updated to D current .
  • a distance measurement device based on time fusion including: a memory, a processor, and a computer program stored in the memory and executable on the processor; wherein the When the processor executes the computer program, the distance measurement method described in the foregoing embodiments is implemented.
  • Embodiments of the present application may include or utilize a special purpose or general purpose computer including computer hardware, as discussed in more detail below. Embodiments within the scope of the present application also include physical and other computer-readable media for carrying or storing computer-executable instructions and/or data structures. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer system. Computer-readable media that store computer-executable instructions are physical storage media. Computer-readable media carrying computer-executable instructions are transmission media. Thus, by way of example and not limitation, embodiments of the present application may include at least two distinct computer-readable media: physical computer-readable storage media and transmission computer-readable media.
  • An embodiment of the present application further provides a computer device, the computer device includes a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor executes the computer During the program, at least the distance measurement method described in the foregoing embodiments is implemented.

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Abstract

本申请公开了一种基于时间融合的距离测量方法、系统和设备，方法包括：根据直方图计算光子从发射到被接收的飞行时间，并根据飞行时间计算目标的距离；其中，所述直方图包括有连续的时间间隔，所述时间间隔内包含由发射器发出的脉冲光束被目标反射后、经由采集器采集的脉冲光束中光子的计数值；计算测量目标距离时产生的测量误差，并根据所述测量误差设定误差阈值；计算当前帧的测量距离与历史帧的测量距离的距离差值；对比所述距离差值与误差阈值，并根据对比结果输出最终的目标距离。

Description

一种基于时间融合的距离测量方法、系统和设备
本申请要求于2021年1月28日提交中国专利局，申请号为202110120017.0，发明名称为“一种基于时间融合的距离测量方法、系统和设备”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及测距技术领域，具体涉及一种基于时间融合的距离测量方法、系统和设备。
背景技术
利用飞行时间原理(TOF，Time of Flight)可以对目标进行距离测量以获取包含目标的深度值的深度图像，而基于飞行时间原理的距离测量系统已被广泛应用于消费电子、无人架驶、AR/VR等领域。基于飞行时间原理的距离测量系统通常包括发射器和采集器，利用发射器发射脉冲光束照射目标视场并利用采集器采集反射光束中的光子，计算光子由发射到反射接收的飞行时间来计算物体的距离。其中，时间数字转换器(TDC)用于记录光子从发射到被采集的飞行时间并生成光子信号，利用该光子信号寻找直方图电路中相应的时间bin(时间间隔)，使得该时间间隔内的光子计数值加1，当进行大量重复脉冲探测后，可以统计得到时间信号对应的光子计数的直方图，根据直方图计算出光子从发射到接收的飞行时间进一步计算出物体的距离。
对于基于光子计数飞行时间的距离测量系统，其优点是具有高灵敏度，即使单光子量级的回波也能响应引起雪崩，但是当回波信号为单光子量级时，由于光子的量子性，回波中的信号光子随机地分布在信号脉冲内，导致单次光子探测的时刻分布具有随机性，因此需要通过光子计数(TCSPC)来减少随机误差 (测量误差)。
当回波信号较弱时，实际接收到的光子数有限，信号光子的泊松噪声抖动成为影响测距精度的主要因素；当环境光较强时，环境光造成的大量环境光子的泊松噪声抖动也会影响测距精度。而泊松噪声区别与常见的高斯噪声，常用的滤波算法效果有限，降低泊松噪声抖动的方法包括增加重复探测次数、多次测量距离求均值等，以实现降低测量误差从而提高测距精度，但是目前的这些方法均会对系统的帧频会造成影响。
发明内容
有鉴于此，本申请提出一种基于时间融合的距离测量方法、系统和设备，以解决上述现有技术所存在的至少一种技术问题。
为了解决上述技术问题，本申请的一种技术方案为：
一种基于时间融合的距离测量方法，包括：根据直方图计算光子从发射到被接收的飞行时间，并根据飞行时间计算目标的距离；其中，所述直方图包括有连续的时间间隔，所述时间间隔内包含由发射器发出的脉冲光束被目标反射后、经由采集器采集的脉冲光束中光子的计数值；计算测量所述目标的距离时产生的测量误差，并根据所述测量误差设定误差阈值；计算当前帧的测量距离与历史帧的测量距离的距离差值；对比所述距离差值与误差阈值，并根据对比结果输出最终的目标距离。
在一些实施例中，所述测量误差根据单光子分布的抖动误差和探测到的信号光子数计算得到，具体公式为：
Figure PCTCN2021106027-appb-000001
其中，σ t为测距标准差，用于表征所述测量误差；σ each为单光子分布的抖动误差；N s表征探测到的信号光子数，根据直方图中与脉冲光束对应的回波区间内的光子计数总和确定。
在一些实施例中，所述信号光子数等于所述回波区间内的光子计数总和减去所述回波区间内的噪声光子总数；其中，所述回波区间内的噪声光子总数等于直方图中每个时间间隔内包含的噪声光子数乘以所述回波区间内包含的时间间隔数量。
在一些实施例中，所述噪声光子数通过如下方式计算：从直方图中选取远离脉冲峰值位置的一局部区域；将所述局部区域内的光子计数总值按照该局部区域内时间间隔的数量求均值，记为所述噪声光子数；或，所述噪声光子数通过如下方式计算：选取直方图中除脉冲位置处以外的区域，并将该区域内的光子计数总值按照该区域内时间间隔的数量求均值，记为所述噪声光子数。
在一些实施例中，所述单光子分布的抖动误差通过如下方式计算：
Figure PCTCN2021106027-appb-000002
其中，T pulse表示脉冲持续时间，即脉宽；K表示量化参数；
或者，所述单光子分布的抖动误差通过误差叠加的方法计算得到；其中，进行误差叠加的误差项包括信号光子分布的抖动误差、发射脉冲波形的抖动误差、单光子响应抖动误差、噪声光子计数误差、雪崩脉冲波形抖动误差、TDC计时抖动误差或直方图累计的量化误差。
在一些实施例中，根据所述测量误差设定误差阈值T h，令T h＝εσ t；其中，σ t表示测量误差，ε为预先设定的线性控制参数。
在一些实施例中，所述计算当前帧的测量距离与历史帧的测量距离的距离差值，包括：
ΔD＝D current-D previous
其中，ΔD表示所述距离差值，D current为当前帧的测量距离，D previous为历史帧的测量距离；优选地，历史帧即为当前帧的前一帧。
在一些实施例中，所述对比所述距离差值与误差阈值，并根据对比结果输出最终的目标距离，包括：当所述距离差值小于或等于所述误差阈值时，对当 前帧的测量距离与历史帧的测量距离进行加权融合后输出最终的目标距离；当所述距离差值大于所述误差阈值时，直接输出当前帧的测量距离作为最终的目标距离，并将历史帧的测量距离更新为当前帧的测量距离。
本申请的另一技术方案为：
一种基于时间融合的距离测量系统，包括：发射器，用于朝向目标发射脉冲光束；采集器，用于采集被目标反射回的所述脉冲光束中的光子并形成光子信号；处理电路，与所述发射器以及所述采集器连接，用于对所述光子信号进行处理以形成直方图，并执行前述的基于时间融合的距离测量方法的步骤。
本申请的另一技术方案为：
一种基于时间融合的距离测量设备，包括存储器、处理器以及存储在所述存储器中并可在所述处理器上运行的计算机程序，所述处理器执行所述计算机程序时实现前述的基于时间融合的距离测量方法。
本申请实施例提供一种基于时间融合的距离测量方法，包括：根据直方图计算光子从发射到被接收的飞行时间，并根据飞行时间计算目标的距离；其中，所述直方图包括有连续的时间间隔，所述时间间隔内包含由发射器发出的脉冲光束被目标反射后、经由采集器采集的脉冲光束中光子的计数值；计算测量所述目标的距离时产生的测量误差，并根据所述测量误差设定误差阈值；计算当前帧的测量距离与历史帧的测量距离的距离差值；对比所述距离差值与误差阈值，并根据对比结果输出最终的目标距离。本申请根据距离差值与误差阈值的对比来灵活输出最终的目标距离，有效的减少了在连续帧测量过程中由光子泊松噪声抖动产生的测量误差，提升测距精度的同时不会对系统的帧频产生影响。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付 出创造性劳动性的前提下，还可以根据这些附图获得其他的附图。
图1是本申请实施例的距离测量系统的示意图；
图2是本申请实施例的距离测量方法的流程图；
图3是本申请实施例的一种示例性的直方图。
具体实施方式
为了使本技术领域的人员更好地理解本申请方案，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分的实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都应当属于本申请保护的范围。
需要说明的是，本申请的说明书和权利要求书及上述附图中的术语“第一”、“第二”等是用于区别类似的对象，而不必用于描述特定的顺序或先后次序。应该理解这样使用的数据在适当情况下可以互换，以便这里描述的本申请的实施例能够以除了在这里图示或描述的那些以外的顺序实施。此外，除非另有明确的规定和限定，术语“安装”、“相连”、“连接”、“固定”等术语应做广义理解，例如，可以是固定连接，也可以是可拆卸连接，或成一体；可以是机械连接，也可以是电连接；可以是直接相连，也可以通过中间媒介间接相连，可以是两个元件内部的连通或两个元件的相互作用关系。对于本领域的普通技术人员而言，可以根据具体情况理解上述术语在本申请中的具体含义。
另需要理解的是，术语“长度”、“宽度”、“上”、“下”、“前”、“后”、“左”、“右”、“竖直”、“水平”、“顶”、“底”“内”和“外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本申请和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本申请的限制。
图1所示为本申请一个实施例基于时间融合的距离测量系统的示意图。距 离测量系统10包括发射器11、采集器12以及处理电路13。其中，发射器11包括由一个或多个激光器组成的光源111，用于向目标20发射脉冲光束30，至少部分脉冲光束经过目标20反射形成反射光束40回到采集器12；采集器12包括由多个像素组成的像素阵列121，用于采集反射光束40中的光子并输出光子信号，处理电路13同步发射器11与采集器12的触发信号以计算光束中的光子从发射到接收所需要的飞行时间。
发射器11包括光源111、发射光学元件112以及驱动器113等。在一个实施例中，光源111是在单块半导体基底上生成多个VCSEL光源以形成的VCSEL阵列光源芯片。其中，光源111可以在驱动器113的驱动控制下以一定频率(脉冲周期)向外发射脉冲光束，脉冲光束经过发射光学元件112投射到目标场景上形成照明斑点，其中，发射频率根据测量距离进行设定。
采集器12包括像素阵列121、过滤单元122和接收光学元件123等。接收光学元件123将目标反射的斑点光束成像到像素阵列121上，像素阵列121包括多个采集光子的像素，所述像素可以是APD、SPAD、SiPM等采集光子的单光子器件中的一种，像素阵列121采集到光子的情况被视为光子检测事件发生并输出光子信号。在一个实施例中，像素阵列121包括由多个SPAD组成，SPAD可以对入射的单个光子进行响应并输出指示所接收光子在每个SPAD处相应到达时间的光子信号。一般地，还包括有与像素阵列连接的信号放大器、时数转换器(TDC)、数模转换器(ADC)等器件中的一种或多种组成的读出电路(图中未示出)。这些电路既可以与像素整合在一起，作为采集器的一部分，也可以作为处理电路13的一部分，后面为便于描述，将统一视作处理电路13的一部分。
处理电路13用于接收光子信号并进行处理计算出光子从发射到接收的飞行时间，并进一步计算出目标的距离信息。在一个实施例中，处理电路13包括TDC电路以及直方图存储器，TDC电路接收光子信号用于确定光子从发射到采集的飞行时间，并生成表征飞行时间信息的时间码，利用时间码寻找直方图存储器 中的对应位置，并使得直方图存储器的对应位置处存储的数值加“1”，根据直方图存储器的位置作为时间bin(时间间隔)构造直方图。
图2所示是本申请一个实施例一种基于时间融合的距离测量方法的流程图。该距离测量方法包括如下步骤：
S1、根据直方图计算光子从发射到接收的飞行时间，并根据飞行时间计算目标距离；其中，所述直方图包括连续的时间间隔，所述时间间隔内包含由发射器发出的脉冲光束被目标反射后、经由采集器采集的所述脉冲光束中光子的计数值。
结合图1所示，在距离测量系统中，处理电路13控制发射器11朝向目标区域发射脉冲光束，被目标反射的部分脉冲光束入射到采集器12，采集器12采集反射的脉冲光束中的光子并生成包含光子的飞行时间的光子信号；处理电路13接收光子信号并进行处理形成直方图，直方图包括连续的时间间隔，每个时间间隔用于表示在检测时段内采集器采集到光子的计数值。处理电路13对直方图进行处理后，根据直方图计算出光子从发射到被接收的飞行时间，其中采用的计算方法包括寻峰法、质心法、模板匹配法等。在本申请的实施例中，根据直方图计算光子飞行时间的方法不做具体限制。
图3所示是本申请一个实施例的直方图的示意图。直方图可以被称为检测数据，用于表示在检测时段内采集器采集到光子的时间分布。一般地，时间间隔301的大小为十几到几十皮秒，则一个脉冲光束的光子信号在直方图中对应分布在一个回波区间内，该回波区间包括多个时间间隔，时间间隔的数量根据脉冲光束的脉冲持续时间(脉宽)确定，比如一个脉冲光束在直方图中对应的脉冲位置为回波区间302。则可以选取脉冲峰值位置所处时间间隔的时间作为脉冲光束的飞行时间，一般选择时间间隔的中间量为该时间间隔的时间。在本申请实施例中，假设脉冲光束的脉宽为2ns，直方图中一个时间间隔301的大小为100ps，则一个脉冲的光子信号在直方图中对应分布在连续的20个时间间隔内，即在直方图中脉冲位置处的时间间隔的数量为20。
S2、计算测量目标距离时产生的测量误差，并根据所述测量误差设定误差阈值。
在距离测量系统进行目标距离测量时会产生测量误差，测量误差主要受到单光子分布的抖动误差影响。由于距离测量过程中不同光子之间是相互独立，则采用TCSPC(时间相关单光子计数)技术能够使得抖动误差减小，因此在计算测量误差时，可以先计算出单光子分布的抖动误差，再根据单光子分布的抖动误差计算出测量误差。其中，单光子分布的抖动误差受到多种因素的影响，包括系统参数、环境光以及信号光强度等等。
在一个实施例中，单光子分布的抖动误差主要受到信号光子分布的抖动误差影响，信号光子分布的抖动误差根据发射脉冲光束的宽度(简称脉宽，即脉冲持续时间)计算，则将信号光子分布的抖动误差记为单光子分布的抖动误差，具体公式为：
Figure PCTCN2021106027-appb-000003
其中，σ each为单光子分布的抖动标准差，用于表征单光子分布的抖动误差；T pulse表征脉冲持续时间。在一个实施例中，根据脉冲半峰宽确定脉冲持续时间，K表征量化参数，可通过理论分析或者实验测量计算确定。
进一步的，再根据单光子分布的抖动误差计算测量误差，计算公式为：
Figure PCTCN2021106027-appb-000004
其中，σ t为测距标准差，用于表征测量误差；N s表征探测到的信号光子数，可以根据直方图中与脉冲光束对应的回波区间内全部时间间隔内光子计数总和确定；优选地，所述信号光子数等于该回波区间内的光子计数总和减去该回波区间内的噪声光子总数。
回波区间内的噪声光子总数根据直方图中每个时间间隔内包含的噪声光子数确定，具体而言，回波区间内的噪声光子总数等于直方图中每个时间间隔内包含的噪声光子数乘以所述回波区间内包含的时间间隔数量。在一个实施例中， 从直方图中截取局部区域计算噪声光子数，具体的，根据直方图中脉冲峰值位置选择远离脉冲峰值位置的局部区域用于计算噪声光子数。比如以直方图中间位置的时间间隔为分界线，若脉冲峰值位置处于直方图的后半部分，则在直方图的前半部分选择局部区域计算噪声光子数，即选定局部区域后，将该局部区域内的光子计数总值按照该局部区域内时间间隔的数量求均值，记为所述噪声光子数；同理，若位于前半部分，则从后半部分选择局部区域计算噪声光子数。在一个实施例中，根据初始直方图全部的时间间隔计算噪声光子数，即选取直方图中除脉冲位置处以外的区域，并将该区域内的光子计数总值按照该区域内时间间隔的数量求均值，记为所述噪声光子数。
在一个实施例中，影响单光子的抖动误差的影响因素还包括发射脉冲波形的抖动误差、单光子响应抖动误差、噪声光子计数误差、雪崩脉冲波形抖动误差、TDC计时抖动误差、直方图累计的量化误差等等，因此，采用误差叠加方法计算出单个光子的抖动误差，具体计算公式为：
Figure PCTCN2021106027-appb-000005
其中，
Figure PCTCN2021106027-appb-000006
对应一种存在的误差情况，即利用多个误差的平方和开根号计算出单个光子的抖动误差。在误差叠加公式中，至少包括两种误差，其中一种误差为信号光子分布的抖动误差。在距离测量系统中，上述的多种误差值可以根据实际测量的情况确定或者可以根据系统参数确定。
具体的，发射脉冲波形的抖动误差受到光源及驱动器性能的影响，可根据系统中光源及驱动器的参数直接确定出发射脉冲波形的抖动误差。单光子响应抖动误差受到光子响应上升沿速率以及斯密特触发器阈值的影响，与采集器的设计参数相关。噪声光子计数误差受到环境光噪声强度的影响，根据直方图计算噪声光子数，并根据噪声光子数计算出对应的噪声光子计数误差。TDC计时抖动误差主要受到TDC电路本身的性能参数、TDC的计时精度等特性的影响， 可根据TDC电路的具体设计通过理论分析或者实验测试确定TDC计时抖动误差。直方图累计的量化误差与直方图中时间bin的宽度有关，当时间bin的宽度大于TDC的时间分辨率时，在将每个光子的计数结果量化到每个具体的时间bin内时会产生非线性误差，可以根据直方图中时间bin的宽度计算出直方图累计的量化误差。
根据计算出的测量误差σ t设定误差阈值T h，令T h＝εσ t，其中，σ t用于表征测量误差；ε为线性控制参数，可以根据不同场景进行设定。
S3、计算当前帧的测量距离与历史帧的测量距离的距离差值；
在距离测量过程中，每测量一帧都可以得到一个距离值，但由于测量误差的存在，则可能导致多帧距离值之间存在测量误差，因此基于测量时间的连续性采用时间融合的方法修正测量误差。
具体的，计算当前帧的测量距离与历史帧的测量距离的距离差值ΔD，计算公式为：
ΔD＝D current-D previous
其中，D current为当前帧的测量距离，D previous为历史帧的测量距离，优选地，历史帧即为当前帧的前一帧。
S4：对比所述距离差值与误差阈值，并根据对比结果输出目标距离。
根据步骤S3中计算出来的距离差值ΔD与误差阈值T h进行对比，并根据对比结果输出目标距离。当距离差值ΔD小于或等于误差阈值T h时，则可以认为距离测量系统与目标间相对静止，没有产生明显的空间移动，偏差主要来自于测量误差，则对当前帧测量距离与历史帧测量距离进行加权融合后输出最终的目标距离D output：
D output＝α*D current+(1-α)*D previous
其中，D output表征目标距离，α为进行融合的权重。并且将历史帧的测量距离更新为D output，用于作为下一帧数据融合的参考。
在实际应用中，也会存在距离差值ΔD大于误差阈值T h的情况，此时则可以 认为目标产生了明显的空间移动，包括沿着深度方向或者移出视场范围的方向移动，则此时距离差值不再主要受到测量误差的影响，此时直接输出当前帧的测量距离D current作为目标距离，并将历史帧的测量距离更新为D current。
作为本申请另一实施例，还提供一种基于时间融合的距离测量设备，包括：存储器、处理器以及存储在所述存储器中并可在所述处理器上运行的计算机程序；其中，所述处理器执行所述计算机程序时实现前述实施例所述的距离测量方法。
本申请的实施例可以包括或利用包括计算机硬件的专用或通用计算机，如下面更详细讨论的。在本申请的范围内的实施例还包括用于携带或存储计算机可执行指令和/或数据结构的物理和其他计算机可读介质。这样的计算机可读介质可以是可以被通用或专用计算机系统访问的任何可用介质。存储计算机可执行指令的计算机可读介质是物理存储介质。携带计算机可执行指令的计算机可读介质是传输介质。因此，作为示例而非限制，本申请的实施例可以包括至少两种截然不同的计算机可读介质：物理计算机可读存储介质和传输计算机可读介质。
本申请实施例还提供一种计算机设备，所述计算机设备包括存储器、处理器以及存储在所述存储器上并可在所述处理器上运行的计算机程序，其中，所述处理器执行所述计算机程序时至少实现前述实施例方案中所述的距离测量方法。
在上述实施例中，对各个实施例的描述都各有侧重，某个实施例中没有详述或记载的部分，可以参见其它实施例的相关描述。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本申请的保护范围之内。

Claims (10)

  1. 一种基于时间融合的距离测量方法，其特征在于，包括：
    根据直方图计算光子从发射到被接收的飞行时间，并根据飞行时间计算目标的距离；其中，所述直方图包括有连续的时间间隔，所述时间间隔内包含由发射器发出的脉冲光束被目标反射后、经由采集器采集的脉冲光束中光子的计数值；
    计算测量所述目标的距离时产生的测量误差，并根据所述测量误差设定误差阈值；
    计算当前帧的测量距离与历史帧的测量距离的距离差值；
    对比所述距离差值与所述误差阈值，并根据对比结果输出最终的目标距离。
  2. 如权利要求1所述的基于时间融合的距离测量方法，其特征在于，所述测量误差根据单光子分布的抖动误差和探测到的信号光子数计算得到，具体公式为：
    Figure PCTCN2021106027-appb-100001
    其中，σ t为测距标准差，用于表征所述测量误差；σ each为单光子分布的抖动误差；N s表征探测到的信号光子数，根据直方图中与脉冲光束对应的回波区间内的光子计数总和确定。
  3. 如权利要求2所述的基于时间融合的距离测量方法，其特征在于，所述信号光子数等于所述回波区间内的光子计数总和减去所述回波区间内的噪声光子总数；其中，所述回波区间内的噪声光子总数等于直方图中每个时间间隔内包含的噪声光子数乘以所述回波区间内包含的时间间隔数量。
  4. 如权利要求3所述的基于时间融合的距离测量方法，其特征在于，所述噪声光子数通过如下方式计算：
    从直方图中选取远离脉冲峰值位置的一局部区域；
    将所述局部区域内的光子计数总值按照该局部区域内时间间隔的数量求均 值，记为所述噪声光子数；
    或，所述噪声光子数通过如下方式计算：
    选取直方图中除脉冲位置处以外的区域，并将该区域内的光子计数总值按照该区域内时间间隔的数量求均值，记为所述噪声光子数。
  5. 如权利要求2所述的基于时间融合的距离测量方法，其特征在于，所述单光子分布的抖动误差通过如下方式计算：
    Figure PCTCN2021106027-appb-100002
    其中，T pulse表示脉冲持续时间，即脉宽；K表示量化参数；
    或者，
    所述单光子分布的抖动误差通过误差叠加的方法计算得到；其中，进行误差叠加的误差项包括信号光子分布的抖动误差、发射脉冲波形的抖动误差、单光子响应抖动误差、噪声光子计数误差、雪崩脉冲波形抖动误差、TDC计时抖动误差或直方图累计的量化误差。
  6. 如权利要求1所述的基于时间融合的距离测量方法，其特征在于，根据所述测量误差设定误差阈值T h，令T h＝εσ t；其中，σ t表示测量误差，ε为预先设定的线性控制参数。
  7. 如权利要求1所述的基于时间融合的距离测量方法，其特征在于，所述计算当前帧的测量距离与历史帧的测量距离的距离差值，包括：
    ΔD＝D current-D previous
    其中，ΔD表示所述距离差值，D current为当前帧的测量距离，D previous为历史帧的测量距离；优选地，历史帧即为当前帧的前一帧。
  8. 如权利要求1所述的基于时间融合的距离测量方法，其特征在于，所述对比所述距离差值与误差阈值，并根据对比结果输出最终的目标距离，包括：
    当所述距离差值小于或等于所述误差阈值时，对当前帧的测量距离与历史帧的测量距离进行加权融合后输出最终的目标距离；
    当所述距离差值大于所述误差阈值时，直接输出当前帧的测量距离作为最终的目标距离，并将历史帧的测量距离更新为当前帧的测量距离。
  9. 一种基于时间融合的距离测量系统，其特征在于，包括：
    发射器，用于朝向目标发射脉冲光束；
    采集器，用于采集被目标反射回的所述脉冲光束中的光子并形成光子信号；
    处理电路，与所述发射器以及所述采集器连接，用于对所述光子信号进行处理以形成直方图，并执行权利要求1所述的基于时间融合的距离测量方法的步骤。
  10. 一种基于时间融合的距离测量设备，包括存储器、处理器以及存储在所述存储器中并可在所述处理器上运行的计算机程序，其特征在于：所述处理器执行所述计算机程序时实现权利要求1所述的基于时间融合的距离测量方法。
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