WO2020223982A1 - 时间飞行深度相机及抗干扰的距离测量方法 - Google Patents

时间飞行深度相机及抗干扰的距离测量方法 Download PDF

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WO2020223982A1
WO2020223982A1 PCT/CN2019/086295 CN2019086295W WO2020223982A1 WO 2020223982 A1 WO2020223982 A1 WO 2020223982A1 CN 2019086295 W CN2019086295 W CN 2019086295W WO 2020223982 A1 WO2020223982 A1 WO 2020223982A1
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pulse
time
signal
taps
flight
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PCT/CN2019/086295
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English (en)
French (fr)
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朱亮
胡小龙
王飞
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深圳奥比中光科技有限公司
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Priority to PCT/CN2019/086295 priority Critical patent/WO2020223982A1/zh
Publication of WO2020223982A1 publication Critical patent/WO2020223982A1/zh

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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
    • G01S7/483—Details of pulse systems
    • G01S7/486—Receivers

Definitions

  • the invention relates to the technical field of optical measurement, in particular to a time-of-flight depth camera and an anti-interference distance measurement method.
  • ToF ranging method is a technology that achieves precise ranging by measuring the round-trip flight time of light pulses between the transmitting/receiving device and the target object.
  • dToF directly measuring the optical time of flight
  • the emitted light signal is periodically modulated, and the phase delay of the reflected light signal relative to the emitted light signal is measured.
  • the measurement technique that calculates the time of flight phase delay is called iToF (Indirect-TOF) technique.
  • CW continuous wave
  • PM Pulse Modulated
  • the optical signal is used for optical flight time after being reflected by the measured target (TOF) measurement image sensor (such as CMOS, complementary metal oxide semiconductor) and so on.
  • the image sensor used for time-of-flight (TOF) measurement usually contains two or more taps.
  • the electrons generated by the sensor excited by the signal light are collected at different times and the collected electrons are converted into The digital signal is output, and finally through the analysis and calculation of the phase relationship between each tap and the output light pulse and the output digital signal, the time delay between the reflected light signal and the output light signal received by the sensor is obtained, and then combined with the optical parameters of the imaging system Calculate the target distance.
  • the receiving unit of the device will not only receive the light signal reflected by the object from the light-emitting unit of the device, but also Will receive the emitted light or reflected light from other devices. These light signals from other devices will interfere with the amount of electrons collected between the taps, and will adversely affect the accuracy and precision of the final target distance measurement .
  • the present invention provides a time-of-flight depth camera and an anti-interference distance measurement method.
  • a time-of-flight depth camera comprising: a processing circuit for providing a modulation signal and a demodulation signal; a light source, under the control of the modulation signal provided by the processing circuit, emitting a pulse beam to an object to be measured, the pulse beam It includes at least one pulse group, the pulse group includes at least one pulse, and different time intervals are set between the pulse groups; an image sensor composed of at least one pixel, the pixel includes at least 3 taps, and the taps are Under the control of the demodulation signal provided by the processing circuit, the charge signal generated by the beam containing the reflected pulse beam reflected by the object to be measured is collected; the processing circuit is also used for receiving the at least 3 taps The charge signal data is used to calculate the flight time of the pulse beam and/or the distance of the object to be measured based on the charge signal data.
  • the pulse group contains different numbers of pulse times.
  • the time interval between the pulse groups is randomly set or pseudo-randomly set.
  • the demodulation signal is also used to control the at least three taps to sequentially collect the charge signals generated in the time interval.
  • the pixel includes four of the taps, and one of the taps is used to collect or discharge the charge signals generated in each of the time intervals under the control of the demodulation signal.
  • the present invention also provides a distance measurement method, including: providing a modulation signal and controlling the light source to emit a pulse beam to the object to be measured, the pulse beam includes at least one pulse group, the pulse group includes at least one pulse, and the pulse group There are different time intervals between them; it provides demodulation signals and controls the image sensor composed of at least one pixel to collect the charge signal generated by the beam containing the reflected pulse beam reflected by the object to be measured, and the pixel includes at least 3 Taps, the taps are used to collect the charge signal; receive the charge signal data of the at least 3 taps and calculate the flight time of the pulse beam and/or the distance of the object to be measured according to the charge signal data .
  • the pulse group contains different numbers of pulse times.
  • the time interval between the pulse groups is set randomly or pseudo-randomly.
  • the demodulation signal is also used to control the at least three taps to sequentially collect the charge signals generated in the time interval.
  • the pixel includes 4 taps, and one of the taps is used to collect or discharge the charge signals generated in each of the time intervals under the control of the demodulation signal.
  • the beneficial effect of the present invention is to provide a time-of-flight depth camera and an anti-interference distance measurement method, which can effectively reduce the interference problem between multiple cameras by grouping the emitted light signals and setting different time intervals between the groups , So as to ensure that the single camera can be applied to more occasions.
  • this method is not only more suitable for implementation but also more effective.
  • Fig. 1 is a schematic diagram of the principle of a time-of-flight camera according to an embodiment of the present invention.
  • Fig. 2 is a schematic diagram of a first time-of-flight camera optical signal emission and collection method according to an embodiment of the present invention.
  • Fig. 3 is a schematic diagram of light signal emission and collection of a second time-of-flight camera according to an embodiment of the present invention.
  • Fig. 4 is a schematic diagram of a third time-of-flight camera optical signal emission and collection method according to an embodiment of the present invention.
  • Fig. 5 is a schematic diagram of light signal emission and collection of a fourth time-of-flight camera according to an embodiment of the present invention.
  • connection can be used for fixing or circuit connection.
  • first and second are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with “first” and “second” may explicitly or implicitly include one or more of these features.
  • a plurality of means two or more than two, unless otherwise specifically defined.
  • Fig. 1 is a schematic diagram of a time-of-flight camera according to an embodiment of the present invention.
  • the time-of-flight camera 10 includes a transmitting module 11, a collecting module 12, and a processing circuit 13.
  • the transmitting module 11 provides a transmitted light beam 30 to the target space to illuminate an object 20 in the space, and at least part of the transmitted light beam 30 is reflected by the object 20 Afterwards, a reflected light beam 40 is formed. At least part of the reflected light beam 40 is collected by the collection module 12.
  • the processing circuit 13 is respectively connected with the transmission module 11 and the collection module 12 to synchronize the trigger signals of the transmission module 11 and the collection module 12 to calculate The time required for the light beam to be emitted by the transmitter module 11 and received by the collection module 12, that is, the flight time t between the transmitted light beam 30 and the reflected light beam 40, further, the total light flight distance D of the corresponding point on the object can be determined by Calculate:
  • c is the speed of light.
  • the transmitting module 11 includes a light source 111, a beam modulator 112, a light source driver (not shown in the figure), and the like.
  • the light source 111 can be a light source such as a light emitting diode (LED), an edge emitting laser (EEL), a vertical cavity surface emitting laser (VCSEL), or a light source array composed of multiple light sources.
  • the light beam emitted by the light source can be visible light or infrared light. , UV light, etc.
  • the light source 111 emits light beams outward under the control of the light source driver (which can be further controlled by the processing circuit 13). For example, in one embodiment, the light source 111 emits a pulsed light beam at a certain frequency under control, which can be used in the direct time flight method.
  • the frequency is set according to the measurement distance, for example, it can be set to 1MHz ⁇ 100MHz, and the measurement distance is from several meters to several hundred meters; in one embodiment, the light source 111 is controlled to modulate the beam amplitude. It can be used in indirect time-of-flight (Indirect TOF) measurement by emitting pulsed beam, square wave beam, sine wave beam and other beams. It is understandable that a part of the processing circuit 13 or a sub-circuit independent of the processing circuit 13 can be used to control the light source 111 to emit related light beams, such as a pulse signal generator.
  • the beam modulator 112 receives the light beam from the light source 111 and emits a spatially modulated beam, such as a flood beam with uniform intensity distribution or a patterned beam with uneven intensity distribution. It is understandable that the uniform distribution here is a relative concept, not absolute uniformity. Generally, a slightly lower beam intensity at the edge of the field of view is allowed, and the intensity of the imaging area in the middle can also be within a certain threshold. Changes, for example, can allow for intensity changes not exceeding 15% or 10%. In some embodiments, the beam modulator 112 is also used to expand the received beam to expand the angle of view.
  • the acquisition module 12 includes an image sensor 121, a lens unit 122, and may also include a filter (not shown in the figure).
  • the lens unit 122 receives and reflects at least part of the spatially modulated light beams reflected by the object and images at least part of the image.
  • the filter needs to select a narrow-band filter that matches the wavelength of the light source to suppress the background light noise in the other wavelength bands.
  • the image sensor 121 may be an image sensor composed of charge coupled device (CCD), complementary metal oxide semiconductor (CMOS), avalanche diode (AD), single photon avalanche diode (SPAD), etc.
  • the size of the array represents the resolution of the depth camera , Such as 320x240, etc.
  • connected to the image sensor 121 also includes a readout circuit composed of one or more of a signal amplifier, a time-to-digital converter (TDC), an analog-to-digital converter (ADC) and other devices (not shown in the figure). ).
  • a readout circuit composed of one or more of a signal amplifier, a time-to-digital converter (TDC), an analog-to-digital converter (ADC) and other devices (not shown in the figure).
  • the image sensor 121 includes at least one pixel, and each pixel includes multiple taps (tap, used to store and read or discharge the charge signal generated by incident photons under the control of the corresponding electrode), for example, including 3 taps , To read the charge signal data.
  • tap used to store and read or discharge the charge signal generated by incident photons under the control of the corresponding electrode
  • the time-of-flight depth camera 10 may also include a drive circuit, a power supply, a color camera, an infrared camera, an IMU and other devices, which are not shown in the figure.
  • the combination with these devices can achieve richer functions, such as 3D texture modeling, infrared face recognition, SLAM and other functions.
  • the time-of-flight depth camera 10 can be embedded in electronic products such as mobile phones, tablet computers, and computers.
  • the processing circuit 13 can be an independent dedicated circuit, such as a dedicated SOC chip, FPGA chip, ASIC chip, etc. composed of CPU, memory, bus, etc., or a general processing circuit, such as when the depth camera is integrated into a mobile phone, In smart terminals such as televisions and computers, the processing circuit in the terminal can be used as at least a part of the processing circuit 13.
  • the processing circuit 13 is used to provide a modulation signal (transmission signal) required when the light source 111 emits laser light, and the light source emits a pulse beam to the object under test under the control of the modulation signal; in addition, the processing circuit 13 also provides an image sensor 121 The demodulated signal (collection signal) of the tap in each pixel.
  • the tap collects the charge signal generated by the beam containing the reflected pulse beam reflected by the object under the control of the demodulated signal.
  • the processing circuit 13 can also provide auxiliary monitoring signals, such as temperature sensing, overcurrent, overvoltage protection, fall protection, etc.; the processing circuit 13 can also It is used to save the raw data collected by each tap in the image sensor 121 and perform corresponding processing to obtain the specific location information of the object to be measured.
  • the modulation and demodulation method, control, processing and other functions performed by the processing circuit 13 will be described in detail in the embodiments of FIG. 2 to FIG. 5.
  • the PM-iTOF modulation and demodulation method is used as an example for description.
  • FIG. 2 is a schematic diagram of a method for transmitting and collecting optical signals of a time-of-flight camera according to the first embodiment of the present invention.
  • Figure 2 exemplarily shows the timing diagram of the laser emission signal (modulation signal), the received signal and the acquisition signal (demodulation signal) within a single frame period T.
  • the meaning of each signal is: Sp represents the pulse emission signal of the light source , Each pulse emission signal represents a pulse beam; Sr represents the reflected light signal of the pulsed light reflected back by the object, and each reflected light signal represents the corresponding pulse beam reflected back by the object under test, which is in the time line (horizontal in the figure).
  • the axis) has a certain delay relative to the pulse emission signal.
  • the delay time t is the flight time of the pulse beam to be calculated;
  • S1 represents the pulse acquisition signal of the first tap of the pixel,
  • S2 represents the pulse acquisition signal of the second tap of the pixel,
  • S3 represents the pulse collection signal of the third tap of the pixel, each pulse collection signal represents that the tap has collected the charge signal (electrons) generated by the pixel in the time period corresponding to the signal; pulse emission signal, reflected light signal, and pulse collection of each tap
  • the period of the signal is Tp
  • the pulse width is Th
  • the entire frame period T is divided into two time periods Ta and Tb, where Ta represents the time period during which each tap of the pixel performs charge collection and storage, and Tb represents the time period during which the charge signal is read out.
  • Ta represents the time period during which each tap of the pixel performs charge collection and storage
  • Tb represents the time period during which the charge signal is read out.
  • the charge collection and storage period Ta there is a phase delay time (n-1) ⁇ Th between the collected signal pulse of the n-th tap and the laser emission signal pulse.
  • each The tap collects the electrons generated on the pixel during its pulse period.
  • the collection signal of the first tap is triggered synchronously with the laser emission signal.
  • the first tap, the second tap, and the third tap respectively perform charge collection and storage in sequence.
  • the charges q1, q2, and q3 are obtained respectively, and a pulse period Tp is thus completed.
  • Tp 3Th.
  • Multiple pulses are emitted in a single frame period T, and these pulses are divided into multiple (X) pulse groups.
  • the period Ts of each pulse group contains multiple (Y) pulses.
  • the period Ts of the pulse group Y ⁇ Tp.
  • the specific number of pulses can be set arbitrarily according to actual needs. In addition, the number of pulses in different frame periods can also vary.
  • the total amount of charge collected and read out by each tap in the Tb period is the sum of the corresponding charges of the optical signal collected by each tap multiple times (9 times in Figure 2) within the entire frame period T.
  • Each tap in a single frame period The total charge of can be expressed as follows:
  • the total charge in the single frame period of the first tap, second tap, and third tap is Q1, Q2, and Q3.
  • the processing circuit can calculate the distance of the object according to the following formula:
  • modulation and demodulation method and the distance calculation method described in formula (3) are only an example, and any other modulation and demodulation method and distance calculation method can be used in this application.
  • the number of pulses in each pulse group may be the same or set to be different.
  • the influence of external optical signals on the collection of each tap can be further reduced, so as to better reduce the influence of interference.
  • the time interval Tg between pulse groups is randomly set.
  • the time interval Tg between the pulse groups is set pseudo-randomly.
  • an array composed of all the time intervals Tg can be set in advance, and each value in the array is set to a fixed value to form a pseudo-random array .
  • the pulse period in each pulse group may be the same or set to be different.
  • the influence of external optical signals on the collection of each tap can be further reduced, so as to better reduce the influence of interference.
  • Fig. 3 is a schematic diagram of a method for transmitting and collecting optical signals of a time-of-flight camera according to a second embodiment of the present invention.
  • the demodulation signal is set in this embodiment so that each tap collects the generated charge signal in each time interval Tg, so as to avoid entering a single tap. Bring greater error.
  • the electrons generated in these time intervals should be divided into different taps as much as possible.
  • each tap can be turned on in turn to collect each time interval separately, as shown in FIG. 3. It is understandable that due to the difference of each time interval, when the number of pulse intervals is large enough, turning on sequentially can achieve better results, but if the time interval difference is large and/or the number of pulse intervals is small, the effect of turning on sequentially will also be effective. It cannot be guaranteed that the number of electrons in each tap is divided as much as possible. For this, all time intervals in the frame period can be pre-processed, and the taps that should be turned on at each time interval are calculated and allocated in advance to ensure the acquisition time of each tap Same as possible.
  • the acquisition signal time of the first tap in the cycle is broadened to acquire the optical signal in the time interval and the optical signal in a pulse period Th.
  • the third tap since the time interval is connected to the time of the acquisition signal in the previous pulse period, if the third tap turns on the acquisition signal in the time interval, it can also be considered as the third tap in the previous pulse period.
  • the acquisition signal time of the tap is broadened to acquire the optical signal within a pulse period Th and the time interval.
  • Fig. 4 is a schematic diagram of a method for transmitting and collecting optical signals of a time-of-flight camera according to a third embodiment of the present invention. It can be seen from Fig. 4 that this embodiment can be regarded as a further improvement of the embodiment shown in Fig. 3. The difference lies in that when each tap collects signals within a time interval, the width of the collected signal is smaller than the time interval. The two acquisitions can be distinguished in time, thereby avoiding the problem of increasing the difficulty of processing circuit modulation caused by the superposition of the two acquisition signals.
  • Fig. 5 is a schematic diagram of a method for transmitting and collecting optical signals of a time-of-flight camera according to a fourth embodiment of the present invention.
  • this embodiment further includes a fourth tap, and the fourth tap may be a tap used to store electrons or a tap used to drain electrons.
  • the fourth tap is turned on in each time interval. If it is a storage electronic tap, it is used to store the electrons generated in each time interval, and if it is a discharge electron tap, it is used to discharge the electrons generated in each time interval. Since the fourth tap collects or discharges the electrons generated in this period of time within the time interval, these electrons are prevented from entering the tap in the next frame period, and the measurement accuracy is improved. It can be understood that the time that the fourth tap is turned on in the time interval may be the same as the time interval, or may be less than the time interval.
  • Figures 2 to 4 describe the anti-interference modulation and demodulation method based on 3-tap
  • Figure 5 adds 1 tap to the 3-tap basis to realize the optimized anti-interference modulation and demodulation method based on 4-tap. It is understandable that, in some embodiments, for pixels with 4 or more taps, the anti-interference modulation and demodulation method shown in Figure 2 to Figure 4 is also applicable, and only one or more of the taps are not involved. Just work.
  • the anti-interference by grouping pulses and setting different time intervals between groups is equally applicable.
  • the optimized anti-interference modulation and demodulation method similar to that shown in Figure 5 by adding a tap on this basis is also applicable.
  • the indirect time-of-flight method (PM-iTOF) based on pulsed light signals is taken as an example for description. It is understandable that the above method is also applicable to the indirect time of flight method (CW-iTOF) based on continuous wave signals (such as square waves or sine waves), or the direct time of flight method (PM-dTOF) based on pulse signals or continuous wave signals. Or CW-dTOF).
  • CW-iTOF indirect time of flight method
  • continuous wave signals such as square waves or sine waves
  • PM-dTOF direct time of flight method
  • Tp the continuous signal of a single period Tp can be equivalent to the single pulse signal in the above embodiments.
  • the beneficial effect achieved by the present invention is to effectively reduce the interference problem between multiple cameras by grouping the emitted light signals and setting different time intervals between the groups, thereby ensuring that a single camera can be applied to more occasions.
  • this method is not only easier to implement but also more effective.

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Abstract

一种时间飞行深度相机(10)及抗干扰的距离测量方法，时间飞行深度相机(10)包括用于提供调制信号及解调信号的处理电路(13)、光源(111)和由至少一个像素组成的图像传感器(121)，光源(111)在调制信号的控制下向待测物(20)发射包含至少一个脉冲组的脉冲光束，包含至少一个脉冲的脉冲组之间设置不同的时间间隔，像素包括至少3个抽头，抽头在解调信号的控制下采集由包含待测物(20)反射回的反射脉冲光束的光束所产生的电荷信号，处理电路(13)接收电荷信号数据并根据电荷信号数据计算脉冲光束的飞行时间和/或待测物(20)的距离。时间飞行深度相机(10)及抗干扰的距离测量方法能有效降低多相机之间的干扰问题，确保单相机可适用于更多的场合，易实现且有效。

Description

时间飞行深度相机及抗干扰的距离测量方法 技术领域
本发明涉及光学测量技术领域，尤其涉及一种时间飞行深度相机及抗干扰的距离测量方法。
背景技术
ToF的全称是Time-of-Flight，即飞行时间，ToF测距法是一种通过测量光脉冲在发射/接收装置和目标物体间的往返飞行时间来实现精确测距的技术。在ToF技术中直接对光飞行时间进行测量的技术被称为dToF(direct-TOF)；对发射光信号进行周期性调制，通过对反射光信号相对于发射光信号的相位延迟进行测量，再由相位延迟对飞行时间进行计算的测量技术被成为iToF(Indirect-TOF)技术。按照调制解调类型方式的不同可以分为连续波(Continuous Wave，CW)调制解调方法和脉冲调制(Pulse Modulated，PM)调制解调方法。
无论是PM-iToF技术还是CW-iToF技术或者其他iToF的调制解调方法，其均是通过激光器等发射单元发射经调制的光信号，待光信号被被测目标反射后被用于光飞时间(TOF)测量的图像传感器(如CMOS，互补金属氧化物半导体)等接收。用于光飞时间(TOF)测量的图像传感器通常含有两个及以上的抽头，接受解调信号的控制在不同的时刻对传感器受信号光激发产生的电子进行收集并将收集的电子量转换为数字信号进行输出，最终通过对各抽头与出射光脉冲之间的相位关系及输出数字信号的分析计算，获取传感器接收到的反射光信号与出射光信号的时间延迟，进而结合成像***的光学参数对目标距离进行计算。
由于基于iToF技术的测量设备需要进行主动发光，因而当多个iToF设备在较近的距离上同时工作时，设备的接收单元不仅会接受到物体反射的来自于设备自身发光单元的光信号，还会接收到来自于其他设备的发射光或者反射光，这些来自于其他设备的光信号会对各抽头间收集的电子量产生干扰，并进而对最终的目标距离测量的准确度和精度产生不利影响。
发明内容
本发明为了解决现有iToF相机之间的多机干扰的问题，提供一种时间飞行深度相机及抗干扰的距离测量方法。
为了解决上述问题，本发明采用的技术方案如下所述：
一种时间飞行深度相机，包括：处理电路，用于提供调制信号以及解调信号；光源，在所述处理电路提供的所述调制信号的控制下向待测物发射脉冲光束，所述脉冲光束包含至少一个脉冲组，所述脉冲组包含至少一个脉冲，所述脉冲组之间设置不同的时间间隔；由至少一个像素组成的图像传感器，所述像素包括至少3个抽头，所述抽头在所述处理电路提供的所述解调信号的控制下采集由包含所述待测物反射回的反射脉冲光束的光束所产生的电荷信号；所述处理电路还用于接收所述至少3个抽头的电荷信号数据并根据所述电荷信号数据计算所述脉冲光束的飞行时间和/或所述待测物的距离。
在本发明的一种实施例中，所述脉冲组中包含不同数量的脉冲次数。所述脉冲组之间的所述时间间隔是随机设置或伪随机设置。所述解调信号还用于控制所述至少3个抽头依次分别采集所述时间间隔内产生的电荷信号。所述像素包含4个所述抽头，其中一个所述抽头用于在所述解调信号的控制下采集或排出各个所述时间间隔内产生的电荷信号。
本发明还提供一种距离测量方法，包括：提供调制信号并控制光源向待测物发射脉冲光束，所述脉冲光束包含至少一个脉冲组，所述脉冲组包含至少一个脉冲，所述脉冲组之间具有不同的时间间隔；提供解调信号并控制包括由至少一个像素组成的图像传感器采集由包含所述待测物反射回的反射脉冲光束的光束所产生的电荷信号，所述像素包括至少3个抽头，所述抽头用于采集所述电荷信号；接收所述至少3个抽头的电荷信号数据并根据所述电荷信号数据计算所述脉冲光束的飞行时间和/或所述待测物的距离。
在本发明的一种实施例中，所述脉冲组中包含不同数量的脉冲次数。所述脉冲组之间的时间间隔是随机设置或伪随机设置。所述解调信号还用于控制所述至少3个抽头依次分别采集所述时间间隔内产生的电荷信号。所述像素包含4个抽头，其中一个所述抽头用于在所述解调信号的控制下采集或排出各个所述时间间隔内产生的电荷信号。
本发明的有益效果为：提供一种时间飞行深度相机及抗干扰的距离测量方法，通过对发射光信号进行分组并在各个组间设置不同时间间隔的方式以有效降低多相机之间的干扰问题，从而确保单相机可以适用于更多的场合。相比于传统的设置不同频率、变频或者扫频等抗干扰方法，本方法不仅更宜实现且更加有效。
附图说明
图1是根据本发明实施例的一种时间飞行深度相机原理示意图。
图2是根据本发明实施例的第一个时间飞行深度相机光信号发射与采集方法示意图。
图3是根据本发明实施例的第二个时间飞行深度相机的光信号发射与采集示意图。
图4是根据本发明实施例的第三个时间飞行深度相机光信号发射与采集方法示意图。
图5是根据本发明实施例的第四个时间飞行深度相机的光信号发射与采集示意图。
具体实施方式
为了使本发明实施例所要解决的技术问题、技术方案及有益效果更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
需要说明的是，当元件被称为“固定于”或“设置于”另一个元件，它可以直接在另一个元件上或者间接在该另一个元件上。当一个元件被称为是“连接于”另一个元件，它可以是直接连接到另一个元件或间接连接至该另一个元件上。另外，连接即可以是用于固定作用也可以是用于电路连通作用。
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”、“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发明实施例和简化描述，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发明的限制。
此外，术语“第一”、“第二”仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”的特征可以明示或者隐含地包括一个或者更多该特征。在本发明实施例的描述中，“多个”的含义是两个或两个以上，除非另有明确具体的限定。
图1是根据本发明一个实施例的时间飞行深度相机示意图。时间飞行深度相机10包括发射模组11、采集模组12以及处理电路13，其中发射模组11提供 发射光束30至目标空间中以照明空间中的物体20，至少部分发射光束30经物体20反射后形成反射光束40，反射光束40的至少部分被采集模组12采集，处理电路13分别与发射模组11以及采集模组12连接，同步发射模组11以及采集模组12的触发信号以计算光束由发射模组11发出并被采集模组12接收所需要的时间，即发射光束30与反射光束40之间的飞行时间t，进一步的，物体上对应点的总光飞行距离D可由下式计算出：
D＝c·t  (1)
其中，c为光速。
发射模组11包括光源111、光束调制器112以及光源驱动器(图中未示出)等。光源111可以是发光二极管(LED)、边发射激光器(EEL)、垂直腔面发射激光器(VCSEL)等光源，也可以是多个光源组成的光源阵列，光源所发射的光束可以是可见光、红外光、紫外光等。光源111在光源驱动器(其可以进一步被处理电路13控制)的控制下向外发射光束，比如在一个实施例中，光源111在控制下以一定的频率发射脉冲光束，可以用于直接时间飞行法(Direct TOF)测量中，频率根据测量距离进行设定，比如可以设置成1MHz～100MHz，测量距离在几米至几百米；在一个实施例中，光源111在控制下其发射的光束振幅被调制以发射脉冲光束、方波光束、正弦波光束等光束，可以用于间接飞行时间法(Indirect TOF)测量中。可以理解的是，可以利用处理电路13中的一部分或者独立于处理电路13存在的子电路来控制光源111发射相关的光束，比如脉冲信号发生器。
光束调制器112接收来自光源111的光束，并向外发射空间调制光束，比如强度分布均匀的泛光光束或者强度分布不均匀的图案化光束等。可以理解的是，这里的分布均匀是一个相对的概念，并非绝对的均匀，一般地视场边缘的光束强度稍低是被允许的，另外在中间用于成像区域的强度也可以一定的阈值内变化，比如可以允许有不超过15％或者10％等数值的强度变化。在一些实施例中，光束调制器112还用于将接收到的光束进行扩束，以扩大视场角。
采集模组12包括图像传感器121、透镜单元122，还可以包含滤光片(图中未示出)，透镜单元122接收并将由物体反射回的至少部分空间调制光束并成像在至少部分所述图像传感器121上，滤光片需选择与光源波长相匹配的窄带滤光片，用于抑制其余波段的背景光噪声。图像传感器121可以是电荷耦合元件 (CCD)、互补金属氧化物半导体(CMOS)、雪崩二极管(AD)、单光子雪崩二极管(SPAD)等组成的图像传感器，阵列大小代表着该深度相机的分辨率，比如320x240等。一般地，与图像传感器121连接的还包括由信号放大器、时数转换器(TDC)、模数转换器(ADC)等器件中的一种或多种组成的读出电路(图中未示出)。
一般地，图像传感器121包括至少一个像素，每个像素则包含多个抽头(tap，用于在相应电极的控制下存储并读取或者排出由入射光子产生的电荷信号)，比如包括3个抽头，以用于读取电荷信号数据。
在一些实施例中，时间飞行深度相机10还可以包括驱动电路、电源、彩色相机、红外相机、IMU等器件，在图中并未示出，与这些器件的组合可以实现更加丰富的功能，比如3D纹理建模、红外人脸识别、SLAM等功能。时间飞行深度相机10可以被嵌入到手机、平板电脑、计算机等电子产品中。
处理电路13可以是独立的专用电路，比如包含CPU、存储器、总线等组成的专用SOC芯片、FPGA芯片、ASIC芯片等等，也可以包含通用处理电路，比如当该深度相机被集成到如手机、电视、电脑等智能终端中去，终端中的处理电路可以作为该处理电路13的至少一部分。在一些实施例中，处理电路13用于提供光源111发射激光时所需的调制信号(发射信号)，光源在调制信号的控制下向待测物发射脉冲光束；此外处理电路13还提供图像传感器121各像素中抽头的解调信号(采集信号)，抽头在解调信号的控制下采集由包含待测物反射回的反射脉冲光束的光束所产生的电荷信号，一般地，除了待测物反射回的反射脉冲光束之外还有一些背景光、干扰光等光束；处理电路13还可以提供辅助的监测信号，如温度传感、过电流、过压保护、脱落保护等；处理电路13还可以用于将图像传感器121中各个抽头采集到的原始数据保存并作相应处理，得到待测物的具***置信息。处理电路13所执行的调制解调方法、控制、处理等功能将在图2-图5的实施例中进行详细介绍，为了便于阐述均以PM-iTOF调制解调方法为例进行说明。
图2是根据本发明第一实施例的一种时间飞行深度相机光信号发射与采集方法示意图。图2中示例性给出了单个帧周期T内的激光发射信号(调制信号)、接收信号以及采集信号(解调信号)的时序示意图，其中各个信号的含义为：Sp表 示光源的脉冲发射信号，每个脉冲发射信号表示一次脉冲光束；Sr表示脉冲光被物体反射回的反射光信号，每个反射光信号表示被待测物反射回的相应的脉冲光束，其在时间线(图中横轴)上相对于脉冲发射信号有一定的延迟，延迟的时间t即是需要计算的脉冲光束的飞行时间；S1表示像素第一抽头的脉冲采集信号、S2表示像素第二抽头的脉冲采集信号、S3表示像素第三抽头的脉冲采集信号，每个脉冲采集信号表示抽头采集了该信号对应的时间段内像素所产生的电荷信号(电子)；脉冲发射信号、反射光信号、各抽头的脉冲采集信号的周期为Tp，脉冲宽度为Th，Tp＝N×Th，其中N为参与像素电子收集的抽头数量。
整个帧周期T被分成两个时间段Ta以及Tb，其中Ta表示像素各抽头进行电荷采集与存储的时间段、Tb表示电荷信号被读出的时间段。在电荷采集与存储时间段Ta中，第n抽头的采集信号脉冲相对与激光发射信号脉冲分别存在一个(n-1)×Th的相位延迟时间，在反射光信号被物体反射回像素时，各抽头在其脉冲时间段内对像素上产生的电子进行收集。在本实施例中，第一抽头的采集信号与激光发射信号同步被触发，在反射光信号被物体反射回像素时，第一抽头、第二抽头、第三抽头分别依次进行电荷采集与存储，分别获取电荷量q1、q2以及q3，如此完成一个脉冲周期Tp，对于3抽头的情形，Tp＝3Th。在单个帧周期T内发射了多个脉冲，且这些脉冲被分成了多个(X个)脉冲组，每个脉冲组的周期Ts中含有多个(Y个)脉冲，脉冲组的周期Ts＝Y·Tp。图2所示实施例中，单个帧周期T内发射了9次脉冲，脉冲被分成了3个脉冲组，且每个脉冲组中有3个脉冲周期Tp，即Y＝3，可以理解的是，这里仅作为示意，实际上单个帧周期内可以发射几百、甚至几万次的脉冲，具体的脉冲数量根据实际需要可以进行随意设置，另外，不同帧周期内的脉冲次数也可以不等。
在Tb时间段各个抽头共收集及读出的总电荷量为各个抽头在整个帧周期T内多次(图2中为9次)采集的光信号对应电荷量的和，单帧周期内各个抽头的总电荷量可以表示如下：
Figure PCTCN2019086295-appb-000001
根据公式(2)可得第一抽头、第二抽头、第三抽头单帧周期内总电荷量为Q1、Q2和Q3。
若反射光信号被第一抽头以及第二抽头采集(第一抽头及第二抽头同时也会 采集到环境光信号)，第三抽头则用于采集环境光信号，这样基于各个抽头所采集到的总电荷量，处理电路根据下式可以计算出物体的距离：
Figure PCTCN2019086295-appb-000002
可以理解的是，公式(3)所描述的是调制解调方法以及距离计算方法仅是一种示例，其他任意调制解调方法以及距离计算方法均可以用于本申请中。
当多台时间飞行深度相机共同工作时，当其中一台中发射出的光信号通过待测物反射或者直接入射到另一台深度相机中的图像传感器中时，将会对测量产生干扰，影响测量精度。为了降低干扰，本实施例中在各个脉冲组之间设置多个不同的时间间隔Tg。由于时间间隔Tg的加入，会使得外界干扰信号难以持续对各抽头收集到的电子数量产生持续固定的影响，当分组X足够大时，可以认为外界干扰信号对各抽头的影响几乎一致，类似背景信号(如环境光，暗电流噪声对iToF设备的影响)，此时可以通过一些背景信号消除手段(如抽头信号间的相减)即可有效消除其他深度相机中的光信号对测量精度的影响。
在一个实施例中，各个脉冲组中的脉冲次数可以相同也可以设置成不同。对于设置成不同的情形，可以进一步降低外部光信号对各抽头采集产生的影响，从而更好的降低干扰影响。
在一个实施例中，脉冲组之间的时间间隔Tg被随机设置。
在一个实施例中，脉冲组之间的时间间隔Tg被伪随机设置，比如由所有时间间隔Tg组成的数组可以被提前设定好，数组中的各个数值被设置成固定的数值形成伪随机数组。
在一个实施例中，各个脉冲组中的脉冲周期可以相同也可以设置成不同。对于设置成不同的情形，可以进一步降低外部光信号对各抽头采集产生的影响，从而更好的降低干扰影响。
在***的时间间隔Tg内外界光信号(包括干扰光、环境光)以及其他噪声源会持续激发像素产生电子，所产生的电子中的大部分将会进入间隔时间结束后首先开启的抽头，比如图2所示实施例中将会进入第一抽头中，会导致第一抽头的信号偏高从而造成测量误差。为了降低这一影响，本发明提供了几种解决方案，详见图3-图5。
图3是根据本发明第二实施例的一种时间飞行深度相机光信号发射与采集方法示意图。为了不让每个时间间隔内产生的电荷信号都进入第一抽头，本实施例中通过设置解调信号使得在各个时间间隔Tg内让各个抽头分别对产生的电荷信号进行采集，避免进入单一抽头带来较大的误差。为了降低误差，应尽可能让这些时间间隔内产生的电子均分到各个不同的抽头中去。
在一个实施例中，可以依次开启每个抽头分别对各个时间间隔进行采集，如图3所示。可以理解的是，由于各个时间间隔的差异性，当脉冲间隔数量足够多时，依次开启可以取得较好的效果，但若时间间隔差异性较大和/或脉冲间隔数量不多时，依次开启的效果也将无法保证各个抽头内的电子数尽可能均分，对此可以对帧周期内的所有时间间隔进行预先的处理，提前计算并分配好各个时间间隔上应开启的抽头以保证各个抽头的采集时间尽可能相同。
可以理解的是，对于第一抽头而言，由于时间间隔与下一脉冲周期内的采集信号的时间连接，所以若是第一抽头在时间间隔内开启采集信号的话，也可以认为是将下一脉冲周期内的第一抽头的采集信号时间进行拓宽以采集时间间隔内的光信号以及一个脉冲周期Th内的光信号。对于第三抽头而言，由于时间间隔与上一脉冲周期内的采集信号的时间连接，所以若是第三抽头在时间间隔内开启采集信号的话，也可以认为是将上一脉冲周期内的第三抽头的采集信号时间进行拓宽以采集一个脉冲周期Th以及时间间隔内的光信号。
图4是根据本发明第三实施例的一种时间飞行深度相机光信号发射与采集方法示意图。从图4中可以看出，该实施例可以看成是图3所示实施例的进一步改进，不同之外在于各个抽头在时间间隔内进行采集信号时，采集信号的宽度小于时间间隔，由此可以将这两次采集从时间上区别开，从而避免两个采集信号的叠加而带来的处理电路调制难度提升问题。
图3、4所示实施例中所采用的是均分思想，难以从根本上解决时间间隔内产生的电子所引起的误差问题。本申请将提供另一种解决方案。
图5是根据本发明第四实施例的一种时间飞行深度相机光信号发射与采集方法示意图。与前文各实施例相比，不同的是本实施例中还包含有第四抽头，第四抽头可以是用于存储电子的抽头也可以是用于排出(drain)电子的抽头。第四抽头在各个时间间隔内被开启，若其是存储电子抽头则用于存储在各个时间间隔内 产生的电子，若其是排出电子抽头则用于排出在各个时间间隔内产生的电子。由于第四抽头在时间间隔内将该段时间内产生的电子收集或排出，从而避免了这些电子进入下一帧周期内的抽头内，提升了测量精度。可以理解的是，第四抽头在时间间隔内开启的时间可以与时间间隔相同，也可以小于时间间隔。
图2-图4中所描述的是基于3抽头的抗干扰调制解调方法，图5是在3抽头的基础上增加1个抽头实现了基于4抽头的优化抗干扰调制解调方法。可以理解的是，在一些实施例中，对于4个或以上抽头的像素而言，图2-图4所示的抗干扰调制解调方法同样适用，只需将其中一个或多个抽头不参与工作即可。
在一些实施例中，对于基于4个或以上抽头的调制解调方法而言(默认四个抽头均参与工作)，上述各实施例中通过对脉冲进行分组以及组间设置不同时间间隔的抗干扰方法同样适用。另外，在此基础上增加一个抽头所实现的类似图5所示的优化抗干扰调制解调方法也同样适用。
在以上各实施例中，以基于脉冲光信号的间接时间飞行法(PM-iTOF)为例进行说明。可以理解的是，上述方法同样适用于基于连续波信号(比如方波或者正弦波)的间接时间飞行法(CW-iTOF)，或者基于脉冲信号或者连续波信号的直接时间飞行法(PM-dTOF或者CW-dTOF)。对于连续波信号而言，可以将单个周期Tp的连续信号等效成上述各实施例中的单个脉冲信号，因此本申请中所提及的脉冲信号应理解为广义上的脉冲信号，其可以是指脉宽极短的高频脉冲信号(图2中Tp＝3Th，占空比33％)，也可以指脉宽较长的方波连续信号(Tp＝2Th，占空比50％)，也可以指在周期与脉冲周期Tp相同的正弦波信号等。
本发明达到的有益效果为，通过对发射光信号进行分组并在各个组间设置不同时间间隔的方式以有效降低多相机之间的干扰问题，从而确保单相机可以适用于更多的场合。相比于传统的设置不同频率、变频或者扫频等抗干扰方法，本方法不仅更易实现且更加有效。
以上内容是结合具体的优选实施方式对本发明所作的进一步详细说明，不能认定本发明的具体实施只局限于这些说明。对于本发明所属技术领域的技术人员来说，在不脱离本发明构思的前提下，还可以做出若干等同替代或明显变型，而且性能或用途相同，都应当视为属于本发明的保护范围。

Claims (10)

  1. 一种时间飞行深度相机，其特征在于，包括：
    处理电路，用于提供调制信号以及解调信号；
    光源，在所述处理电路提供的所述调制信号的控制下向待测物发射脉冲光束，所述脉冲光束包含至少一个脉冲组，所述脉冲组包含至少一个脉冲，所述脉冲组之间设置不同的时间间隔；
    由至少一个像素组成的图像传感器，所述像素包括至少3个抽头，所述抽头在所述处理电路提供的所述解调信号的控制下采集由包含所述待测物反射回的反射脉冲光束的光束所产生的电荷信号；
    所述处理电路还用于接收所述至少3个抽头的电荷信号数据并根据所述电荷信号数据计算所述脉冲光束的飞行时间和/或所述待测物的距离。
  2. 如权利要求1所述的时间飞行深度相机，其特征在于，所述脉冲组中包含不同数量的脉冲次数。
  3. 如权利要求1所述的时间飞行深度相机，其特征在于，所述脉冲组之间的所述时间间隔是随机设置或伪随机设置。
  4. 如权利要求1所述的时间飞行深度相机，其特征在于，所述解调信号还用于控制所述至少3个抽头依次分别采集所述时间间隔内产生的电荷信号。
  5. 如权利要求1所述的时间飞行深度相机，其特征在于，所述像素包含4个所述抽头，其中一个所述抽头用于在所述解调信号的控制下采集或排出各个所述时间间隔内产生的电荷信号。
  6. 一种距离测量方法，其特征在于，包括：
    提供调制信号并控制光源向待测物发射脉冲光束，所述脉冲光束包含至少一个脉冲组，所述脉冲组包含至少一个脉冲，所述脉冲组之间具有不同的时间间隔；
    提供解调信号并控制包括由至少一个像素组成的图像传感器采集由包含所述待测物反射回的反射脉冲光束的光束所产生的电荷信号，所述像素包括至少3个抽头，所述抽头用于采集所述电荷信号；
    接收所述至少3个抽头的电荷信号数据并根据所述电荷信号数据计算所述脉冲光束的飞行时间和/或所述待测物的距离。
  7. 如权利要求6所述的距离测量方法，其特征在于，所述脉冲组中包含不同数量的脉冲次数。
  8. 如权利要求6所述的距离测量方法，其特征在于，所述脉冲组之间的时间间隔是随机设置或伪随机设置。
  9. 如权利要求6所述的距离测量方法，其特征在于，所述解调信号还用于控制所述至少3个抽头依次分别采集所述时间间隔内产生的电荷信号。
  10. 如权利要求6所述的距离测量方法，其特征在于，所述像素包含4个抽头，其中一个所述抽头用于在所述解调信号的控制下采集或排出各个所述时间间隔内产生的电荷信号。
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